223 Introduction

ENGINES FOR PETROL COMMERCIAL VEHICLES. 223

ENGINES FOR PETROL COMMERCIAL VEHICLES.

By W. D. WILLIAYSON

INTRODUCTION.

THE purpose of the first portion of the paper is to put formd for consideration certain factors governing the sizes of engines suitable for use in commercial vehicles, and by promoting discussion upon the points raised to endeavour to direct effort towards greater uniformity and possibly a closer co-operation among commercial vehicle manufacturers and engine builders, to the general advantage of the industry. Secondly, by an examination of well known successful types of engines, an endeavour is made to outline modern practice, and to arrive at simple. formulae covering those parts where commercial vehicle engines may be said to depart from current pleasure car design on account of the different conditions of service. In a paper to be kept within reasonable limits, it is impossible to go deeply into all the points worthy of attention-a volume might be written on the possibilities of the split pin-but if only some of the points touched upon prove of interest, or serve to bring forward helpful discussion, the author’s purpose will be served. In the present paper it is proposed to deal only with enginea for vehicles having a useful capacity of two tons and upwards, EO that artificial restrictions imposed by a tax based on the bore of the cylinders do not apply. The problem presented in the design syld construction of engines for commercial vehicles differ very considerably from those involved in engines for pleasure car work. The pleasure car designer has constantly befom him the question of horse-power output for cylinder capacity, and having done all

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 224 THE INSTITUTION OF AUTOMOHILE ENGINEPHS. he can to obtain the maximum torque from a given oylinder, devotes his energies to the pursuit of “revolutions.” With him, and even more so with the aeronautical engineer, horse-power for weight is a serious consideration. The designer of engines for use solely in commercial vehicles has more scope, in that, unhampered by considerations other than those of strict utility and manufacturing cost, he can set out to design an engine to give the best possible results in the hands o€ the average user, and under the conditions in which it is intended to operate. Within reasonable limits, the question of weight in other than the reciprocating pa&i is not of great moment provided always that additional weight is serving a useful purpose in increasing the wearing qualities of the engine or presenting other advantages in the way of accessibility or fuel efficiency. The user demands an engine capable of propelling his vehicle at a reasonable speed with a high fuel efficiency as expressed in ton-miles per gallon. This engine must be of robust design to give long life and freedom from breakdown under severe conditions, and all parts must be rn accessible as possible for djust- ment or replacement. Here, again, the questions of bore and weight are not involved. Other things being satisfactory, the user is often favourably impressed by the fact that an engine is, say, Bin. larger in bore than a competitor, and few users would object to mrrying quite an appreciable extra weight if it would emure the absence of breakdown, or decrease the cost of running. From this it must not be understood that the ideal engine from the user’s point of view is of huge proportions and terrific weight, but rather that bore and weight are of secondary importance and should not be allowed to have consideration at the expense of other more material requirements. Silence of operation, which; is of the greatest importance for engines for pleasure vehicles, has not been an outstanding feature of commercial vehicles in the past, and some of the most successful types have not been notable for quietness. Comparatively few owners drive their own lorries, consequently this feature has given way to other claims. In the past, too, the engine noise has been drowned by the general uproar, but in these days of live axle drives, enclosed chains and quiet gear boxes, considerably more attention is being paid io silencing the engine. Many heavy vehicles of to-day leave little to be desired in this respect. Motor buses and char-a-bancs set the fashion; fare-paying passengers quite naturally select the

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vehicle of greatest general comfort, and when once it occurred to the manufacturer of commercial vehicles that it was possible and even desirable for heavy vehicles to run more quietly, it did not take long to effect considerable1 improvement. The silencing of one portion of the chassis threw the noise from another into prominence; this in turn was given attention, and a remedy found, when a third became apparent, and so on. To-day, on reasonably good roads, high class motor lorries are operating with a lack of noise and fussiness undreamt of only a few years ago. From the manufacturer’s standpoint the engine must first satisfy the user in the points covered above; secondly, that engine must be capable of being produced at a competitive price. These two considerations are related to each other mope closely than io apparent at first sight. In spite of the fact that commercial vehicles are strictly utilitarian, there is undoubtedly a fashion in them, or a preference shown in some districts for one make over another. In many instances this may be due to the fact that one make is particularly suitable for a certain district; on the other hand, there is little doubt that where certain vehicles are working in a district and are known to be giving entire satisfaction they are purchased again and again to the exclusion of other and possibly equally good vehicles. A purchaser in one district will insist on having, say, “A” vehicles even if they do cost him a little more than “B.” The manufacturer of “A” vehicles can therefore consolidate his position by putting that extra price or a portion of it into the vehicle in the way of little improvements or extra good workmanship, and so endeavour to make his satisfied customer even more satisfied. Although the policy may appear strange to American manufacturers with large outputs of one model, few British builders of commercial chassis devote themselves exclusively to one size or type of vehicle, but build a range of chassis having useful carrying capacities of perhaps from two to five tons with possibly one or two sizes specially adapted for passenger work. This means the provision of a suitable range of engines, and, from a manufacturing point of view, it is highly desirable to obtain this range or series of engines with the fewest possible changes. The engines may be grouped so that one sine is made suitable for two or three different types of vehicles, and provision can be made in some case5 for larger cylinders and pistons to be used in conjunction with standard crankcases where additional power is required. 15‘1 I, L 1A MSON . P

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Further, standardisation can be carried out with respect to the method of attaching the engines to the frame, so that it is possible to fit, say, either a 30 h.p. engine or a 40 h.p. engine in the same frame without a lot of alterations. The manufacturer is then in a position to make combinations of engines with the remainder of the chassis, also suitably altered, to meet special requirements, at little extra cost. Where a manufacturer is building vehicles for general purposes and not to suit one particular set of requirements, a little forethought in this direction may me&n both advantage Q himself and increased satisfaction to the user.

ENGINESIZE. In fixing the size of the engine, the first and most important consideration is the most satisfactory ratio between engine speed and road speed. For this it is necessary to examine the various factors governing the actual speeds of engine and vehicle, and discover the most economical speed at which to run the engine, and the road speed at which the best results are obtained from the vehicle. The determination of the road speed, as presenting fewer diffi- cultiw, may be taken first. The commercial vehicle user is obvi- ously interested in getting loads from one point to another as quickly as possible. High road speed reduces the charges per mile or per ton-mile, due to proportion of driver's wages, interest on capital and garage expenses, and, further, by affording a greater mileage per vehicle per day, makm fewer vehicles necessary for any given amount of work, and so decreases capital expenditure. On the other hand, tyre costs, petrol consumption and upkeep generally are increased by high speeds. In ordinary delivery work for loads of two to four tom, a very satisfactory maximum speed is 15 miles an hour. On reasonably good roads the chassis should take no great amount of harm at this speed, but if it is exceeded to any great extent, particularly on a bad road and when the vehicle is running light, the effect is not conducive to long life of the mechanism. For loads of four and five tons the maximum should be reduced to 10 or 12 miles an hour. In the case of passenger vehicles, particularly for long journeys, greater speed is in many cases demanded,.and the larger returns from this traffic allow of a concession to the passengers in the way of increased running costs.

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For loads up to four tom it is proposed to assume 15 miles an hour as being the best maximum speed, and for heavier loads 12 miles an hour. For char-a-bancs a larger engine will be found necessary, as not only is a higher average speed called for. but passengers also like hill-climbing power considerably in excess of what is reasonable for lorry or van work. To find the best speed at which to run the engine for this road speed, the conditions peculiar to the commercial vehicle must be studied. Considered broadly, it will be found that the high speed, high compression engine which has so large a field for pleasure car work does not suit the purpose. Such an engine in a pleasure car is rarely required to run at low speeds with full throttle opening, and then as a rule only for short periods. In other words, the volumetric efficiency is low, and both its average compression due to throttle restriction, and its average rate of revolutions, are considerably below the maximum. Engines of this type, too, are apt to require more attention to minor points than the commerEial vehicle engke obtains. While it is desirable to fit an engine no larger than the work requires, at the same time, as previously stated, weight is not of the first importance and should certainly give place to length of life and reliability. One of the principal points for consideration is the engine speed at which the best results are obtained for the petrol consumed. Having decided upon the speed at which the vehicle is to be propelled along the road, the engine speed which will do this work for the least possible expenditure in petrol must then be determined unless other factors cause a modification. For any particular engine, torque and consumption curves must be taken and consideration given to the bearing these curves have on the desirable engine speed.

TORQUECURVES. For the purpose of illustration the author proposes to use the diagram shown in Fig. 1 taken from a Dorman engine after it had been in use some little time. In examining this torque curve it will be seen that from the lowest speed at which regular torque is obtained, say, 300 revolutions, there is a rise showing increased load on the piston. The offective torque of the engine depends upon volumetric efficiency, cooling, carburation, internal mechanical loss, and on the relative P2

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 228 THE INSTITUTION OF AUTOMOHILE ENGINEERS. gains and lomw due to thwe governing factors at various speeds. The volumetric efficiency should be greatest at the lowest speed at which the engine will run steadily, tw under such conditions the cylinder should receive a full charge of mixture. At this

CU'BVSS EROWINQ Toaam AND ~ONSOXPTION. 110 XX. x 140 rat. DOESUNENGINE.

FIG. 1. speed, however, the cooling effect is most pronounced. The working temperature of the whole engine is lower, the heat losses during the cycle are considerably greater than at high speeds, and the thermal efficiency, of the engine suffers. Carburation at

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 ENGINES FOR PETROL COMMERCIAL VEHICLES. 229 this speed with the usual carburettor setting would probably not be as perfect as at higher speeds. Mechanical loss per stroke or per cycle where lubrication is thorough, might be expected to decrease with increased speed, if the actual loss due to friction alone is taken into account. In addition to this, however, the engine is called upon to overcome the valve spring pressure and valve inertia, and to drive the fan, water pump and magneto. The loss due to these increases more rapidly than the gain due to decreased friction, so that there is a probability of a greater total mechanical loss at high speeds. It might be suggwted that by suitable carburettor setting and by modification of the cooling arrangement the thermal lossw at low speeds could be reduced, and the engine made to give an excellent torque at this speed. This is, no doubt, quite true, but the object is not to endeavour to alter the conditions to make the engine produce good results at any particular speed, but rather to find out at what speed the engine gives the best all round results for our purpose. Tracing the torque curve through its rising speed the maximum is approached at about 700 revs. per minute, and the curve remains fairly flat from there to 1,000 revolutions, where it com- mences to fall. Up to 700 revs. per minute the power of the engine per cycle is evidently increasing. The volumetric efficiency may be decreas- ing and the mechanical losses probably increasing, but these are evidently more than balanced by the increase in thermal efficiency and the more perfect mixing of the charge. From 700 to 1,100 revs. per minute the gains and losses are evidently almost balanced, as there is little variation in torque between those speeds, but as the speed increases, restrictions due to the valves and pipes begin to have their effect. Volumetric efficiency probably falk off and mechanical loses increase; the net rasult is a decreased torque.

CONSUMPTIONCURVES. Considerations of torque alone would lead to the conclusion that unless the valve and pipe diameters are increased the engine is likely to give the best resulh if ita range of revolutions is kept between 700 and 1,100 revs. per minute. Before any definite conclusion can be arrived at, however, it is necessary to go into

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 280 THE INSTITUTION OF AUTOMORlLE ENGINEERS. the cost of this torque. The object in a commercial vehicle engine is to obtain torque for the least possible expenditure of petrol, the ideal being attained when the range of maximum torque coincides with the speeds for minimum consumption-a result which is rarely obtained. While the consumption curve must depend on the carburettor setting for its actual value and rela- tionship to the torque curve, it is generally found that the range of minimum consumption is at a higher rate of revolutions than that of maximum torque. For the purpose of explanation, this range is confined to within 15 per cent of the best consumption. In the curve shown this would give from about 700 to 1,300 revs. per minute as the correct range of speeds. At 1,300 revs. per minute the torque is falling, and although the torque per foot-lb. is costing no more since the consumption is at its best, yet the best range of mechanical efficiency is being departed from. If the maximum engine speed is taken at a point far down on the descent of the torque curve, the resulting torque is only equivalent to what might be obtained from a smaller engine at a lower speed. There appears to be no objection to allowing the maximum speed to be located some little distance down the curve, as on meeting increased tractive resistance the reduction in engine speed to come within the range of maximum torque would not be great. This maximum speed might then be taken at 1,300 revs. per minute. An examination of the curves on these lines would lead to the conclusion that the maximum engine speed would be governed by the torque curve, and the minimum speed by the consumption curve. If the left-hand end of the curves be considered, it is found that from 700 to 500 revs. per minute the torque value is mode- rately high, but the consumption curve shows that this torque is only obtained at a very expensive rate. Take the case of a vehicle under load ascending a hill which eventually causes a change to a lowef gear. As the tractive effort increases the engine speed falla from its maximum to a speed at which a higher torque value is obtained, and this continues until with the driver’s well-known persistence in hanging on to the top gear as long as possible, the engine speed has fallen back to below 700 revs. per minute, and the engine is running outside its range of emnomica1 working. High torque at this low speed end of the torque curve is there-

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 ENGINES FOR PETROL COMMERCIAL VEHICLES. 23 1 fore not an advantage unless it is accompanied by reasonable fuel efficiency.

NUMBEROF CYLINDERS. The four cylinder engine appears to have become firmly established for oommercial work, and can be taken as standard for the vehicles under consideration. There is a decided tendency in America to multiply the number of cylinders for pleasure car purposes, but even there it has not affected heavy vehicles, and as far as this country is concerned the only heavy vehicles having engines of more than four cylinders are for fire engine or other special purposes.

CALCULATIONSFOR ENGINESIZE. The usual ratio of engine to road speed in modern vehicles is for 1,000 revs. per minute to oorrespond to about 15 miles per hour, but for any engine with curves corresponding to Fig. 1 there is a 'decided advantage in increasing the engine speed It0 1,300 revs. per minute. Not only is the consumption improved, but the increased speed allows a decrease in engine size for any given weight of vehicle, with a corresponding lightening of transmission parts up to but not including the final drive. For the engine under consideration it is proposed to assume 1,300 engine revs. per minute for 15 miles per hour. The next step is to arrive at some formula to give the actual figures for engine sizes to meet particular requirementa. In the following method the author has aimed at obtaining a formula that is easy 'to handle rather than one which will give muracy to a large number of decimal places. The useful work obtained from the engine per minute is represented in foot-lb. by:- Mean effective brake preesure x area of cylinder in sq. in. x stroke in feetxnumber of working strokes. Let V represent volume of one cylinder in cu.in. D the diameter of cylinder in in. S the stroke in in., and N the revolutions per minute. stroke and if T is taken -, then stroke = r D and the useful work as bore obtained per mipub b:-

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130

120

110

100

4 5 6 7 8 9 10 11 12 13 14 15 ROADSPEED M.P.H. 345 430 520 605 690 780 865 950 1040 1125 1210 1300 ENQINESPIED R.P.Y. Curve R is from Mr. WIYPERIB’formula Resistance = 40 + 14 (G) lb. per ton where V is speed in M.P.H. FIG.2.

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rrr D3 or rip x ~ x foot-lb. 4 rrD3 but ___-- Volume of one cylinder, 4 N and therefore rip x x V = foot-lb. per minute. The work this engine has to perform is to propel the vehicle against the internal friction of the vehiols itself, the external resistance due to the road and the wind pressure. Let S represent the speed of vehicle in miles per hour. W the gross weight of vehicle in tons. R the total resistance on the level in lb. per ton. Then the total foot-lb. of work per minute required by the vehicle on the level is:- 1760 x 3 WX.EtXSX 6o Hence, for an engine just large enough to drive any vehicle on a level road:- N 1760 X 3 ~p X XXV= W x R x S x Taking rip at 80 lb. from Fig. 1, and R at 71’5 from Fig. 2, with 15 miles per hour at 1,300 revs. per minute we get:- 1300 1760 x 3 80 X __ X V = W X 71.5 X 15 X ___- 6 60 71.5 X 15 X 1760 % 3 x 6 or v = W x 60 X 80 X 1300 or V = 5.5 W approximately. That is to say, the cubic capacity of one cylinder of the engine is found by multiplying the gross weight of the vehicle in tons by 5.5. This factor the author has called “Q.” In dealing with “Q,” it must be remembered that the factor assumes a definite ratio between engine and road speed-in this case 1,300 revs. per minute and 15 miles per hour. An engine designed with a “Q” of 5.5 would not be a commercial success. As long a.~ the vehicle remained on a level road and had a total resistance of 71.5 lb. per ton the engine would be equal to the work required, and would be doing that wo& under most economical conditions. The drawback is that it has practically no reserve for hill climbing. Curve 1, on Fig. 2, shows the engine torque taken from Fig. 1,

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 234 THE INSTITUTION OF AUTOMOBILE ENGINEERS. and is plotted to correspond with the figures for road resistance. This show6 the engine torque and road resistance cutting each other at 15 miles per hour. On an increasing gradient, as the engine speed falls the torque increases to a maximum at about 1,000 revs. per minute and the road resistance decreases. The ability of this vehicle to climb is represented by the distance between the Curve R and Curve No. 1 (Fig. 2), but at its maximum

Per cent *

SPEEDIN M.P.H. FIG.3. is less than 30 lb. per ton which is the increase in resistance dbe to a gradient of only 1 in 74. The maximum gradient up which the engine would drive the vehicle on top gear is represented by Curve 1 in Fig. 3.

ENGINESIZES FOR HILL CLIMBING. The modern lorry is expected to be able to climb gradients. of about 1 in 30 on top sped with full load, and w0 may take this to be a reasonable figure. From Fig. 1 it is found that t!he

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 ENGINES FOR PETROL COMMERCIAL VEHICLES. 235 engine has its range of highest torque at about 1,000 revs. per minute or 114 miles an hour, and this is taken a,y the climbing speed. np is 87 lb. and R is 58.5. The total resistanae due to R and the gradient is

1755 + 2240 ( -- 30 ) 3995 (approximate total resistance=133 lb. per ton) =w--30 and the equation becomes:- 1000 3995 x 11.5 x 1760 x 3 87 x x 11 =W x -- -___-- 30 X 60 3995 x 11.5 x 1760 x 3 x 6 orV= W x ______30 X 6U X 1000 X 87 V = 9.3 W approximately, Q = 9.3. The curve showing the relation of torque to road rssistance is Curve 2 in Fig. 2, and the gradients the vehicle is capable of climbing on top gear at various speeds are shown in Curve 2, Fig. 3. PETROLCONSUMPTION. Having found the engine size for the gradient desired, the cost of this climbing power in petrol consumption should be examined. Taking the original engine with " Q " = 5-5, and assuming the vehicle is on the level with a total resistance of 71.5 Ib. per ton and a consumption of 0.58 pints per b.h.p. per hour, then for 0'58 pints the work done = 33000 x 60 = 1980000 foot-lb., and for one gallon the work done= 1980000 x 13.8 = 27324000 foot-lb. One ton of gross weight absorbs, per mile, on the leve1:- 71.5 x 1760 x 3 = 377000 foot-lb. The consumption would therefore be

27324000~ -. = 72.5 ton-miles per gallon. 377000

In the case of the engine with " Q " = 9.3 it is capable of giving out at full load a torque to overcome a road resistance at 15 m.p.h.

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 236 THE INSTITUTIOX OF AUTOMOBILE ENGINEERS. of 121 lb. per ton, but is only using 71'5 lb. per ton or abouzl 59 per cent. Reference to Curve 1, Fig. 4, shows that this means an increase

Chart showing effect of Light Loads upon Petrol Consumption with Governed Engine.

FIG. 4. in consumption of 33 per cent. The consumption per b.h.p. per hour risas to 0.77 pints, and the ton-milea per gallon falls to 54.5. Probably 75 or 80 per cent of the distance travelled is on level, or almost level, roads, and this increase in consumption

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 ENGINES FOR PETROL COMMERCIAL VEHICLES. 237 serves to show the cost of the reserve power considered newsmy for hill climbing. As far as current practice is concarned, this would be looked upon as quite a reasonable result. Curve 2 on Fig. 4 shows the improvement that can be obtained at decreased loads by increased comprassion. This curve was taken from the same engine as Curve 1. The increased compression made the engine very prone to knock at low speeds with full throttle opening. This knocking commenced at about 700 revs. per minute, or, in other words, at about the speed at which a change of gear should be made to keep the engine within it9 range of minimum consumption. It would appear that engine builders do not give sufficient, attention to the fact that the normal condition of working is at about 60 per cent of full load. Consumption curves are usually taken under full load, and the carburettor adjusted to give the best result under these conditions. Probably better consumption on the road would be obtained if the carburettor were set to meet these conditions of light load at which the engine is running for the greater portion of its time. Even though this lead to slightly decreased maximum torque and a slightly increased consumption at full load, the net result would be a decided gain.

ENGINESIZES FOR VARIOUSVEHICLES. Taking “Q” =9’3 for 1,300 revs. per minute and 15 miles per hour, Table A. gives the engine sizes for various vehicles.

TABLEA. (Q =9’3).

Bore aud atroke of Engines, Gross Weight of Cylinder capacity, in inches, with Vehicle. cubic inches. approximately 1.3 ratio.

41.85 3+ x 4+ 46.5 3% x 4Q 55.8 3;-: x 5 65.1 4 x 5f 74.4 4& x 5* 56.25 3tQ x 5 62.5 3f4 x 5&

I * Twelve miles per hour. NOTE.-For 9 and 10 tons gross weight the Table is corrected

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 238 THE INSTITUTION OF AUTOMOBILE ENQINEERS. for road speed and resistance, and “Q” therefore becomes 6’25 for these cases The conclusions arrived at with regard to engine speed to suit maximum road speed are borne out by the curves shown in Fig. 5 taken from a 5 in. by 6 in. Tylor engine fitted to Karrier Subsidy ”ype vehicles.

CURVESSEEWING TORQUE AND Coiisuaaprro~. FIG. 5.

PART2.

CURRENTPRACTICE IN ENGINESIZES. An examination of the engines in a number of successful types of commercial vehicles shows that the average ratio of engine speed to road speed is 1,000 revs. per minute for 15 miles per hour, and that “Q” has a value of 12’5. (This agrees quite well with the 9’3 obtained for 1,300 revs. per minute if the necessary correction be made for engine speed 12.5 x 1000 = 9.64.) 1300

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RATIOOF STROKETO BORE. There does not appear to be any tendency to fix a definite ratio of stroke to bore. Examination of a large number of engines showed an average of 1.3, but this figure would appear to be of little value since no maker appears to have two engines of different sizes with the same ratio. Curioqsly enough more than 50 per cent of the engines examined had strokes of 53in., and the tendency appears to be to have a range of engines to suit the various sizes of vehicles all having the same stroke. No doubt this arrangement materially decreases the number of jigs and allows for interchangeability of a number of parts, so cutting down cost of production. Taking "Q" at 12.5, and allowing 15 miles an hour at 1,000 revs. per minute for vehicles up to and including four-tonners, and 12 miles an hour, with the necessary correction, for five and six-tonners, Tables B. and C. give the engine sizes.

TABLEB. (Q = 12'5).

Engine size Gross Cylinder Engine size Engine size with constant weight of capacity, suggested, with 1.3 ratio, inches. stroke (54 in.), Vehicle. cubic inches. inches. inohes.

56 25 4 x 49

62.5 4) x 44

75 4) x 58

87.5 45 x 58

100 42 x 59

75 4* x 54

83.3 4$ x 54

* Twelve miles per hour.

The following table relates to the approximate weights of actual vehicles, and is based on the same lines as Table B.

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TABLEC. (Q = 12'5

Cylinder Engine size Gross weight. capacity, Engine size Useful load. 1.3 ratio. with 5+ in. :ubic inches. stroke.

2 tons 5 tons 62.5

26 9) 5 ,, 12 cwts. 71 3 6 7, 10 77 81.25 Sublidy 7 9, 10 ,, 93.76 4 tons 8 7, 5 79 103.125 5 9, 10 ,, (12m.p.h.) 83.3 93-75 6 >, 11+ l> 9)

By grouping, three sizes of engines can be used for the swen vehicles in Table C., any small discrepancy being easily regulated by adjustmenk in gear ratio; the arrangement might be as folI0w~:- TABLED.

Engine size . . . . 4in. x 54in. 49in. x 54in. 43in. x 53in. Useful load of 2 and 24-ton %ton and 5-ton" Subsidytype 4-ton vehicle vehicles vehicles and 6-ton."

* Twelve miles per hour.

For motor char-a-banes, which are expected to have greater climbing ability on top gear, the gradient may be taken as 1 in 24, to be climbed at 12 miles per hour, with the engine running at 800 revs. per minute. 800 2240 Then 87 x Volume 7= W (60 + 124) X 12 X 88, 800 1440 W + 2240 W 12 88, or 87 x Volume X - = 6 24 3680 --- W X 12 X 88, 24 3680 12 X 88 X 6 6072 and Volume = W __ 24 x --soO-x~ = w-435 Or Volume = 14 W approximately.

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Taking as an example a 30-seated vehicle weighing, when loaded, 6 tons, we get:- Cylinder volume Gross weight. in cu. in. Cylinder size. 6 tons...... 84 ...... 4T76in. )< 5&in. In the last named case one of the three standard sizes suggested might be used, namely, 43in. by 5iin. with suitable gear correction.

0 1 2 3 5 6 RATEDLOAD CAPACITY IN TONS. Chart showing relation between total Cylinder capacity and useful Load, FIG.6.

The curve in Fig. 6 shows current American practice, and is based on the average of 160 vehicles.

CQMPRESSIONPRESSURE. An examination of a number of engines shows the average ratio of total volume to swept volume to be 4'4, and if the compression is calculated on PV1*S=Constant, with 13 Ib. initial WILLIAMSON. Q

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 242 THE INSTITUTION OF AUTOMOBILE ENGINEERS. pressure, this gives us a gauge pressure on compression of about 75 lb., and an explosive pressure which, under ordinary conditions of cylinder shape and cooling, might be taken at 280 lb. per square inch.

CONNECTINGROD BEARINGS. Coming to the bearing surface usually allowed for the big end of the connecting rod, the practice of manufacturers shows an average of 765 lb. per sq. in. on the projected area. The highest pressure observed was about 950 and the lowest about 620 lb. per sq. in. Neglecting the pressure and taking into amount only the respective areas of cylinder and bearing, an average of 1 sq. in. of big end area for 2.73 sq. Sn. of piston area is obtained. In the limits of the engines under consideration, say from 33 in. bore to 5 in. bore, the average diameter of the crank pin in use corresponds very closely with 0'4 bore + 3 in. Gudgeon pin pressure may be taken at 2100 Ib. per sq. in., D2 or the area of the pin is given by in sq. in., D being the 796 diameter of the cylinder. Gudgeon pin diameters show a close approximation to big end diameter - 1& in. for the sizes of engines under consideration.

CRANKSHAFTBEARINGS. In comaercial vehicle engine design, the three-bearing crankshaft is usually used, and there would appear to be no particular reason for fitting five bearings. At the same time there are two or three very successful engines having five-bearing crankshafts, and one at least with only two main bearings. In several engines of the three-bearing type the middle bearing 'is the same size as &hebig ends, and as this may offer manufacturing advantages and seems to be satisfactory in service it is no doubt to be recom- mended. In the way of standardisation and reduction of spare parts, some makers also have the front bearing of the same dimensions. The average lengths, however, for the three bearings, taking the length of the connecting rod big end bearing as 1, are 1'21 for the front, 1.17 for the middle, and 1-48 for the rear. Setting down the average surfaces as found from the engine examined, where D =cylinder diameter, we have:- Big end :-Average pressure, 765 Ib. ;

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piston area area, _. 2.73 ’ diameter of pin, 0.4D + tin. Gudgeon pin :-Average pressure, 2100 lb. ; area, DZ-- 9.6 ’ diameter of pin = big-end diameter - I& in. Main bearings have the same diameters as the crank piq, and the lengths are respectively 1.21, 1.17 and 1.48 times the crank pin length. These dimensions may seem to savour too much of the “rule of thumb,” but they have been arrived at after a close examindion of a number of engines running successfully in ordinary service, and if they do not appear to take all the factors into &ccoun~,i+ is because an attempt has been made to simplify the formula m, !much as possible. They are put forward, not aa being the ideal, but as representing aa closely as possible current practice as shown by the engines of which the requisite data were available.

BALL BEARINGSFOR CRANKSHAFTS. Only two prominent builders of commercial vehicle engines in ;this country use ball journal bearin@ for the crankshaft. The arrangement is clearly shown in Fig. 13. The fact that these are retained shows that the makers are satisfied with the results.

VALVES. With the exception of the Daimler vehicles, all British commercial vehicles have engines of the poppet valve type. These valves are usually of 3 per cent or 3.5 per cent nickel steel with seats at 45 degrees. The London General Omnibus Company, after experimenting with other materials, standardised mild steel valves suitably case-hardened and ground to overcome the difficulty of wear in the stems. Where trouble has arisen due to excessive wear or pitting of the face, nickel chrome steel has been used with advantage, while one maker has found a remedy in a return to cast iron heads. Examination of a number of engines showed an average valve seat bore of 0’46 of the cylinkr boseiwith a lifi ’of clykz!der borellg. Taking into account the angle of the seat, this gives a clear Q2

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 244 THE INSTITUTION OF AUTOMOBILE ENGINEERS. vdve opening area of 0'108 of the cylinder area, or approximately we have:- Opening in valve seat = 0'46 cylinder diameter. - cylinder diameter Vdve - lift 12 cylinder area Effective area of valve opening= Vdve tappets adjustable by set screws at the upper end and fitted with rollers at the lower end are standard. In the case of the Albion, Napier, !Cilling Stevens and White and Poppe engines cornendable cam has been taken to ensure ample wearing 6ur- face in the tappet guides with tappets as light as possible (Figs. 7 to 10). VALVE SETTING. The average taken over a number of settings is shown as a diagram in Fig. 11. This is intended to illustrate current ideaa and is not put forward &s an ideal setting.

PISTONS. Except in one or two cases it cannot be said that any great effort has been made in the way of obtaining very light pistons, and this appears to be a point to which more attention might be paid. General practice favours three rings above the gudgeon pin. The Donaan engine is a notable exception, being fitted with a special type of compound ring which gives excellent results. The usual method of securing the gudgeon pin is by one set screw, which must be securely locked. Some difficulty has arisen where two set screws have been used for this purpose, as it is extremely difficult, even by the use of jigs, to ensure that the holes in the gudgeon pin and bosses are drilled exactly the medistance apart, and even the smallest error may cause piston distortion. A single set scqew seems to give the necessary secu- rity, and there appears to 'be no reason for duplication. Two or three makers use a ring for retaining the gudgeon pin, and strangely enough these are the engines in which it is usual to find a fifth ring acting as a scraper. The author is very strongly impressed by the claims of the Zephyr patent piston shown in Fig. 12. Until recently pistons of this design were turned from solid

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Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 248 THE INSTITUTION OF AUTOMOBILE ENGINEERS. steel blanks, which prevented their use except in cases where cost was of little moment. Now, however, they are being made in cast iron at no greater met than ordinary pistons. Pistons of this design are usually about half the weight of the ordinary type, while the shape obviates the need for a scraper ring and allows of a very simple method of securing the gudgeon pin. The author understands that arrangements are being made

FIQ.11 .-Average Valve Setting. to produce these pistons in aluminium alloy and so effect a still greater saving in weight.

LUBRICATION. Prmtically all commercial vehicle engines are fitted with some form of pump for oil circulation. The type most in favour is the gear pump, which seems to answer the purpose extremely well for oil, although not so successful when, as in the past, it ie

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.used for circulating jacket water. Oil is usually fed under pres- 5ure to the m'&n bearings and through the crankshaft to the connecting rod bearings. Cylinder walls and gudgeon pins are lubricated by splash. Forced lubrication is, no doubt, theoretically the correct practice, but even with the best systems the unforeseen may happen. Where the system does not admit of any splash when the pressure

FIQ.12.-Zephyr Patent Piston. system is out of order, there is little reserve measured in lorry mila. In other words, excellent as the forced system is, if it should fail for any reason it means that the lorry must stop at once or bearing trouble Will follow. Again, a forced system supply is regulated according to the speed of the engine and not according to the load on the bearings. This means that the required oil pressure must be developed at a low speed and the exce-ss oil driven through at high speed^ should be released from the circulation by a valve set at the predetermined pressure. This excess oil may with advantage be directed t~ the timing gears as in the case of the Dorman, Fig. 14.

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The ideal would appear to be some combination of a forced system with the trough system as used in Daimler engines, the two systems being independent, so that in case the forced system fails the bearings are not endangered. Even if each system is capable of taking care of the engine, there should be no ill results due to the increased supply of oil, so long as efficient means are provided to prevent over-lubrication of the piston. In any forced system the greatest care should be taken to protect the pump on both intake and pressure sides by efficient, filters, and these filters should be accessible for cleaning. The Wolseley and Albion engines (Figs. 15 and 7) are specially

CLi FIG.14.--Lubrication System of Dorman Engines. worthy of attention, the first for the arrangem\ent of oil col- lecting galleries, and the second for the manner in which the thrower rings are arranged on the crank webs for the lubrication of the big ends. More consideration might be given in many cases to the position of the crank chamber filling orifice. This should be so placed as to allow of a large tin being up-ended over it without fouling other pa& and without wasting a lot of oil, In addition, this orifice should be provided with a filter. In the Wolseley (Fig. 15) and Leyland (Pig. 16) engines this point has evidently received attention. The Dorman engine (Fig. 17), where the oil is introduced through the top of the fan

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 252 THE IKSTITUTION Or’ AUTOMOBILE ENGINEERS. bracket, offers a very ingenious solution which is to be improved by moving the filling orifice a little to one side 80 as not to be, immediately beneath the water outlet pipe.

DRIVE FOR TIMING GEARS.

With a few exceptions, notably the London General “ B ” type engine (Fig. 18) and the White and Poppe engine (Fig. 10) fitted

Fig. 15.--Wolseley Engine 4g in. by 54 in. to Dennis lorries, poppet valves are arranged on one side of th.e engine. Like every other engineering compromise, this system has both advantages and disadvantages. The chief disadvantage. would appear to be that it neoessitatw somewhat small valves or givm greater overall length to the engines. Considering the speed at which commercial vehicle engines are called upon to work, the restriction of valve diameter dow not appear to be very material, and the advantages in other directions have no doubt Idto this arrangement being generally adopted. For the camshaft drive the usual practice is to have two helical gears of steel, the pinion being hardened and the wheel, to ensure quiet running, being of a steel giving the requisite m-enring properties without hardening.

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In the larger engines these gears are usually helical, with teeth 8 diametrical pitch by 14in. wide. Silent chains are used in the Daimler (Fig. 19), Wolseley (Fig. 15), and Tilling Stevens (Fig. 9); Daimler and Wolseley chains axe +in. pitch. Belsize engines (Fig. 20) have gin. pitch roller chain drive,

c--l FIQ.17.-Dorman Subsidy Type Engine. which appears to be quite satisfactory as regards both silence. and life.

DRIVESFOR PUMPAND MAGNETO. When deciding upon the positiom for pump and magneto, two main points should be kept to the fore. These are that the pump should be easily acoeissible for re-packing the glands, and the contact breaker should be in such a position that it is nut

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 254 THE INSTITUTION OF AIJTOMOBILE ENBINXRRS. only accessible to the hands, but also so placed that the mechanism can be seen when the cover is removed. These conditions are obtainable most readily by the fitting of: a cross-shaft over the timing case.

In the “ Pagefield ” arrangement (Fig. 21) this cross-shaft is set at an angle so that the pump is thrown down in line with the outlet from the radiator, and the contact breaker is lifted up to become quite the most accessible part when the bonnet is lifted. In this arrangement the angle of the helical gears is modified ta

FIG.18.-Engine fitted to London General (( B ” Type Omnibuses. allow of the spiral gear on the cross-shaft engaging with the wheel on the cam shaft. The Halley, Leyland, Tilling Stevens, Tylor and White and Poppe are other engines where the cross-shaft is adopted, and only one gland is required for the pump. The Tylor arranp- ment, showing also the half compression device, is illustrated in Figs. 22 and 23, the White and Poppe arrangement in Fig. 24. The Napier (Fig. 8) and the Dorman (Fig. 25) are typical

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 ENGINES FOR PETROL COMMERCIAL VEHICLES. 255 examples of the arrangement where pump and magneto are placed in line alongside the engine.

The Wolseley arrangement (Fig. 26) shows that the designer appreciated the advantage of keeping the magneto as far forward of the dashboard as possible. In this case, regard for the magneto

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FIG.21 .-Arrangement of Pagefield Cross-shaft Drive for Pump and Magneto.

FIG.22.-Arrangement of Tylor Croes-shaft.

WlLLIAMSON. R

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Pro. 24.-Arrangement of Cross-shaft, White and Poppe Engines.

FIG.25.-Dorman Pump and Magneto Drive.

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has caused the front gland of the pump to be somewhat inaccas- sible. The Albion arrangement of pump drive (Fig. 7), where the cylinder jacket serves as the pump casing, is an entb departure from common practice, and posaesses distinct advantages in the way of simplicity. GOVERNORS. The question of the advisability or otherwise of fitting a governor on a commercial vehicle engine is one that has not been settled satisfactorily. For some purposes there appears to be no doubt that a governor is of advantage. The War Department scheme calk for this fitting, and it is quite easy to understand that for night driving in convoy, without lights, it simplifies

Fro. 26,-wolseley Pump and Magneto Drive. the driver’s work to know that all the lorries must travel at approximately the same pace. The usual method of driving appears to be to give the engine full throttle and leave the rest to the governor. In ordinary commercial service the fitting of a governor should provide a means of ensuring that the vehicle is not over-driven when light. On the other hand, a vehicle with a governed engine is not as nice to drive, the power of accele- rating beyond normal speed in an emergency is absent, and gear changing is, perhaps, not quite so easy. The most popular type of governor, as far as the ordinary driver is concerned, seems to be the one that is most easily put out of action. It is a matter of considerable difficulty to arrange for the governor to have that accessibility combined with simplicity expected of all parts of commercial vehicle engines. The Daimler a2

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(Fig. 19) and the Pagefield (Fig. 27) are worthy of note in this respect. The latter has the advantage that it is entirely enclosed. The practice followed in some cases of arranging the governor to act on the carburettor throttle valve is not calculated to give the best results in petrol consumption. In the case of a carburettor with a throttle valve shaped to give a rich mixture at, very small openings, for easy starting, the throttle may assume this position on a favourable gradient at high engine revolutions, and the mixture taken into the cylinders may consequently be much too rich. In such a case a separate valve under the control of the governor affords a distinct saving in petrol.

HALFCOMPRESSION AND STARTINGDEVICES. The author is of the opinion that for the larger engines, say 44in. bore and upwards, a simple arrangement for releasing compression for starting purposes is a decided advantage in many cases. For vehicles running regular services with only very short stops, or for motor buses having relatively few engine stops, this fitting is not necessary. But for lorries that axe paxked in the open or for vehicles such as furniture remo~ers’vans, that may have to stand for some hours in the coldest weather, the small complication of, say, a sliding cam shaft does appear to be WOJ%I while. If it becomes necessary to have female drivers for the heaviest vehicles, anything that helps to ease matters for them will find favour, and it may be that the self-starier proper will find advocates. For the present, the fitting of self-starters to commercial vehicle engines has not been attended with succws. They have been tried with the idea of saving petrol by en- couraging the driver to stop his engine when the vehicle is making only a momentary halt for the delivery of perhaps a single package, but the saving effected has not been all that was expected.

CYLINDERDESIGN. Cylinder design calls for little comment. Cylinders cast in pairs axe the rule. The most notable exceptions are the Austin engine, and the Albion engine shown in Fig. 7. Austin cylinders are separate castings, and the Albion is a mono-block. Ample water jackets with carefully considered arrangement round the valve pockets and stems are required, and are found in

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 262 THE INdTITUTION OF AUTOMOBILE ENGINEERS. most modern engines. The author is of the opinion that the water jacket should extend down the cylinders to the level of the top ring or at least the top of the piston when the crank is on the bottom dead centre, although some designs appear to operate successfully with jackets shorter than thk. The plan adopted in the Napier and Pagefield engines of having the cylinders cast with large openings in the jacket at top and sides has much to recommend it, as it simplifies moulding and ensures the jacket cores being thoroughly cleared. With 'the ordinary small core plugs it is often almost impossible to clear the jackets about the valve pockets.

CRANKCASE. Crank cases differ very little in general from those in pleasure cars, although naturally they are more robust in design. The usual practice is to split the case horizontally on the centre of the crank shaft, carrying the bearings in the upper half, and to we the lower half principally as an oil retainer and dust excluder. External ribs on the lower half, although they may be of distinct advantage for oil cooling, are not general. Perhaps the most noteworthy departure from the usual design is that adopted in London General " B" type engines, where the lower half is little more than an oil tray (Fig. 18). The plan adopted in this engine of scraping the face to form an oil-tight joint between the two halves without the necessity of packing is one that is to be recom- mended. The'oiled paper joint is not an unmixed blessing. It does not always prevent leakage, and usually requires renewing if the engine is dismantled. The fitting of inspection doors to the crank case as required by the Subsidy scheme is coming into general favour. It is not suggested that it is advisable or even possible in most engines to attempt to carry out repairs through these doors, but for inspection of the internal mechanism, location of trouble, and in some oases the doming or mmovd of the oil flter, they are very useful. Any tendency they may have to weaken the case is usuaU.y overcome without special provision by the extra metal required for the facing and to carry 'the studs.

OIL INDICATOR. All lubrication systems should embody some form of indicator on the dashboard. This indicator is best arranged in series with

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 ENGINES FOR PETROL COMMERCIAL VEHICLES. 263 the oil leads to the bearings. The plunger type indicator, arranged so that it can be seen in daylight and to be.within easy reach of the driver’s hand for night driving, is probably the most convenient. There appears to be room for a reliable indicator of somewhat stronger construction than the usual patterns for use bn commercial vehicles.

ENGINESUSPENSION. As long as a vehicle is intended for ordinary commercial pur- pows and is not built with the idea of crossing broken ground, there does not appear to be any neoessity to make special provision against frame distortion. The ordinary underframe method of construction has much to recommend it, and experiments the author has made show that for any distortion that might occur under normal conditions this arrangement is quite sound, and would appear to be more satisfactory than extending the crank case arms to the main frame. In one experiment made with a four ton chassis having the engine on a sub-frame, the engine was started and throttled down so that it just continued to run. The near side front wheel was then gradually raised. When the wheel was 12 in. clear of the ground, no difference ww discernible in the running of the engine. From 12 in. to 15 in. the twisting of the frame did have an effect, and at the latter height the engine showed signs of stopping. The ignition was switched off, and when tested at the starting handle the engine was found to be stiff with the clutch either in or out. The chmsis was gradually allowed to fall back again, and at 12 in. the whole of the stiffness had disappeared. Standing at the back of the chassis, the shape and twist baken by the near side long member of the frame made it appear that three point suspension is more important for the gear box than for the engine. The front of the chassis was tilted on to the off side front wheel, and no doubt helped by the fact that the front spring acted in some measure to restrain the bending of the side member in front, very little distortion was apparent in front of the dashboard. The greatest change of shape was encountered between the dashboard and the front bracket of the rear spring, where the frame was both bent and twisted. Many three point suspensions are three point in name only and not in effect, and while they may do no harm, at the same

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 264 THE TNSTITUTION OF AUTOMOBILE ENGINEERS. time, unless they make for simplicity, as for instance in the Daimler, they are not worth while. Where conditions are such that great frame distortion may be expected, the best method would appear to be to have an underframe supported at three points arranged in such a way that these points allow flexibility. Any tendency to whip, even the small amount caused by overcoming the necessary friction in the suspension points, is thus prevented from reaching the aluminium casting. In any engine having a tendency to vibrate at certain critical speeds flexible suspension may be a decided disadvantage.

COOLING. The problem of cooling a commercial vehicle engine, which appeared to present considerable difficulty only a few years ago, has now been satisfactorily solved. Extended running under full load at low road speeds when climbing stiff gradients threw excessive work upon the cooling system. Ample water jackets and pipes of larger bore have helped to overcome the original troubles, and a better grasp of the conditions and of the amount of heat to ba dissipated has enabled the necessary provision to be made, so that lorries now work under the most severe conditions without showing signs of boiling. Practically all cooling systems for commercial vehicle engines embody a circulating pump, and this pump is invariably of the centrifugal type. Other types of pump have been tried, but the centrifugal, as having the fewest wearing parts, is now firmly established. Cooling fans are of robust design, and in most cases mounted on standard type ball bearings. A fan with arms and boss cast in aluminium in one piece, secured to a malleable iron centre shaped to serve as the fan pulley, appeare to be the most satisfactory type. In many engines the fan driving belts are much too light and weak for the work they have to perform. At maximum engine speed these belts have 'to transmit quite an appreciable power, and in addition are subject to shocks due to fan inertia and fan momentum when the engine speed is altered quickly. The positive drive for the fan in the Hallford engine (Fig. 28) is specially worthy of attention. Turning to the radiator proper, the type in most general use, and the one that appears to meet most of the requiirements, is

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the tubular type formed of vertical water tubes soldered to tube plates, and having top and bottom boxes of cast aluminium. Honeycomb radiators are, as a rule, too delicate for heavy vehicle work. They are apt to leak through vibration when used in a vehicle having solid tyres, and are not as easy to repair with the limited facilities often at hand, as are those of tubular $Pe. Opinion seems to be divided as to whether the tubes should or should not have gills, although the general practice favours gills. The usual tube is of 26 gauge brass or copper & in. external diameter with gills +# in. diameter or Q$ in. square, soldered in position at about + in. pitch. Experiments carried out by a large maker of radiators showed the most useful ratio of gill diameter to tube diameter to be three to one. In these experiments where +in. tube was used with gin. gills for appearance instead of 15 in., the efficiency fell approximately 10 per cent. Where plain copper tubes lare used they are usually + in. external diameter by 28 or 30 gauge. Further experiments went to show that the relative efficiency of gilled to plain tubes is about three to one by reason of the much increased suxface of the gills exposed to the air current. In other words, three times as many tubes are required in a tube stack having plain tubes as in a stack having gilled tubes. Trouble with tubular radiators usually occurs where the tubes join the tube plates, and the reduction of the number of joints, and consequently of the poslsibility of leaks, is a strong recommen- dation for the gilled tube type. The gills, in addition, help to stiffen the tubes and afford some measure of protection against damage by impact. It might be suggeeted that in order to further stiffen the tubes and increase the surface area, the tubes might be threaded through a number of plates instead of being fitted with gills. 'This method would make the isolation and repair or replacement of a single tube much more difficult. While it is not con,- tended that commercial vehicle radiator design has reached per- fection, at least a type hm been evolved that gives satisfactory servicle . When makers of vehiclm commenced to deal with the trouble of insufficient cooling, the tendency at first was to err on the other side. In some cases very large radiators wem fitted, having more cooling surface than is now found necessary. Current prac-

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 ENGINES FOR PETROL COMMERClAL VEHICLES. 267 tice is very well repreEcented by the following formula, for a four cylinder engine:-- Bore inin. Xstroke in in. x 8 = feet of & in. tube with % in. gills. Objection may be taken to this formula in that it does not take into account variations in cylinder design, disposition of valves, and other factors, but it has the advantage that it is easy to handle

a P u 8- FIQ.29. and gives a result which can be relied upon for satisfiadory cooling. There are engines in commercial vehicles with cooling surface considerably less than that given by the formula. In one wethe cooling surface was carefully cut down, starting from bore x stroke X 7, and at bore X stroke x 6'2 the limit appeared to be reached beyond which it was unsafe to go. It is probable that in enginas

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where other conditions were not as favourable, the cutting down process would have been forced to stop before this.

A PETROLCONSUMPTION GAUGE. The apparatus used by Mr. Pentony in making the consumption tests of the Dorman engines while not entirely new is of sulEcient interest to merit a description. The apparatus, Fig. 29, conskts of a float chamber “A” arranged 80 that at rest there is a constant level of petrol in an open-ended glass tube “B.” When petrol is drawn away to the carburettor, the velocity of the flow past the lower end of the pipe ‘‘ B ” causes the level in this pipe to fall. This fall is oonstant for any given velocity in the horizontal pipe, but variea with this velocity, consequently, on a suitably calibrated scale, it is possible to read 08 the flow of petrol in any units. The scale is graduated to show pints per hour, so that the consumption can be obtained instantly. The advantage of thus being able to ascertain the effect of even the most minute alteration to the carburettor setting will be readily understood. IN CONCLUSION. The manner in which information and assistance have been given by practically all the firms approached is undoubtedly a sign of the excellent feeling existing among the members of the industry. The author wishes to tender his sincere thanks not only for the help, but also for the generous way it waa afforded. In particular, he desirw to exprws his thanks to Mr. Geo. W. Watson for his valuable advice, and to Mr. Pentony, of Massrs. W. H. Dorman & Co., Ltd., for the data placed at his disposal.

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FIQ.31 .-Daimler Engine.

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PARTICULARS OF SOME MODERN

I No. 1. No. 2. No. 3. No. 4. Bore ...... 3?&. 3Pin. Sfin. Sfin. Stroked ...... 4Min. 5in. 51iu. 51iu. Number of cyliiders ' .... 4 4 4 4 How cast (single, pairs br'block) ..... Pairs Single Block Pairs Total volume/clearance volume ...... 4.16 4.5 4.33. 4.7 PISTON- Length ...... 4grin . 4iu. 4th. 4:gin. Number of&gs' ...... 3 3 3 Width of rmgs ...... 3Gn. tin. &in. ,%in. Disposition of rings...... Three gas, OM All at top All at top All at top] scraper, oni gudgeon CONNECTING-ROD- Centres .... 9%n. loin., . loin. lliu. Diameter aid lingth'of gudgeon $n de'ariig Bin. by 1Biu. pin. by Ir%m. Bin. by lfin. %in..by lRin Material of bearing ...... Phos. bronze Phos. bronze Phos. bronze Special bromc Diameter and length of big-end bearing . . Itin. by 2fin. Ifin. by 3in. lfin. by 2)in. Zhin. by 2ibin Material of bearing ...... Gun-metal anc White metal Die cast white White metal white metal metal Number of bolts in big-end bearing . . .. 4 4 4 4 CRANK SHAET- Diameter and length of front bearing . . .. ltin. by3in. Ifin. by 3in. lfin. by 3tin. 2hin. by Sfin: middle bearing . . Ifin. by 32in Ifin. by 3in. lfin. by 2)in. 2Ain. by 2fin. rear bearing .. Ifin. by 4in. lfin. by Stin. %in. by Stin. Materizl of bea)hgs ...... White metal Die cast white White metal metal Crank shaft drilled for lubrication .. NO Yes Yes NO VAWES- Disposition of valves ...... Opposite side One side Diameter of head ...... 231in. Isin. ,, stem ...... fin. 1 Gin. bore of valve Bead ...... Itin. p.ln. lain. Matezal of valve ...... 3 per cent. nick, Nickel steel 3.5 per cent. steel nickel steel Lift of inlet valve ...... &in. &p. )in. Lift of exhaust valve .. .. &in. &1n. *in. Position of crank for inlkd op;;?ing' . . .. + 12" + 0" + 100 + 15' cl0slng .. + 30" + 26" + 48" + 36' :: ehust opening: : .. - 46" - 40° - 450 - 540 ,, ClOSlng . . .. + 90 + 6O + 4O + 5O C&iK CAg- Inspection doors ...... None One side One side One side TIHING GEAR& Type of gears or chain ...... Helical spm spur Silent chain Silent chain Material of gears ...... Nickel chrome tee1 and bronze Steel and C.I. - Width of gears...... lain. Ifin. 1)in. 1. liu. Pitch of teeth ...... 10 D.P. 12 D.P. tin. tin. cross shaft for pump'anh'miinetb' .. .. Yes NO No NO LlJBEICA!PION- Lubricating system ...... Splash Force Force 'umu to trough Type of pump ...... Gear Vane Gear Iultiple plunge Working pressure ...... 2 lb. to 5 lb. LO lb. to 15 lb. - Method of indicating leiei . . .. Gauge Eloat and rod Top of filler How are main bearings lubricated i Pressure Pressure Pump fed ,, big-end bearings lubricated ?' ' Chrough crank Trough ,, gudgeon pins lubricated ? .. .. :: Splash Spcsh Splash ,, timin gears lubricated ::j ?ump overtlow ?ump overtlow Pump fed ,, cam-&aft beanngs lubncatei? Splash Splash 'ront by pumr others splash CAEBUE&P!L'OR- Type...... Solex Claude1 Zenith Zenith FLY-WHEEL Diameter ...... 16Pin. 18in. 2oin. Width ...... 3fin. 5in. 4th. 4in. Approximate weight ...... : :I 100 lb. - 84 lb. 113 lb. pression device ...... No No NO NO NO Optional Yes 1000 1200 1240 12) 18 18 i tons 10 cwt. 5 tons 10 cwt.

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COMMERCIAL VEHICLE ENGINES.

I No. 5. No. 6. NO. 7. No. 8. No. 9. No. 10. 4in. 4in. 4fin. 4Ain. 4Ain. 4&in. 5in. 5Bin. 5tin. %in. 5ain. 5gin. 4 4 4 4 4 4 Pairs Pairs Pairs Pairs Pairs Pairs 1 4.8 4.1 4.75 4.5 - - 4kin. 58in. 5in. 5ikin. 61iu. 4in. 3 3 3 4 4 4 fin. tin. fin. &in. .- tin. All at top All at top All at top All at top !hree above pin rwo above pin, one round pin, one scraper llin. llin. 12in. Ilin. - 12iu. lin. by l3in. lin. by 2Qin. lin. by 2iu. IAin. by Ztin. lin. by &tin. Phos. bronze Phos. bronze Special bronze steel Itin. by 2tin. Itin. by ZBin. 2in. by Ztin. :&in. by Ztlin. Isin. by ZBin. 28in. by 2 ,%in. Die cast white White metal White metal White metal - Gun-metal and metal white metal 2 2 4 4 4 - ltin. by %in. Ifin. by Sfin. 2in. by 4in. !fain. by Stin. 1Bin. by %in. ZBin. by 28in. Itin. by %in. Itin. by 2)in. 2in. by Skin. $&in. by 3#n. Itin. by 3Qin. 2Hn. by 2 &in. lain. by 4Bin. lain. by 3in. 2in. by 3fiu. !&in. by Stgin. Itin. by 3fin. 2Bin. by 3iin. Die cast white White metal White metal White metal - Gun-metal and metal white metal Yes NO Yes NO No One side One side Opposite sides Opposite sides Opposite sides ltin. lein. 2hin. 2bin. 26in. tin. gin. &in. tin. &!n. IQin. lein. %in. Ifm. 2&m. Nickel steel - Chrome nickel &in. gin. &in. - tin. Bin. &in. - + 3" + 9" + 15' + 15" + 11" + 31" + 23" + 36" - 56' - 43" - 40" - 530 + 00 + 79 + 8' + 5" One side One side One side One side Both sides Both sides Silent chain Silent chain Helical spur Silent chain Silent chain Spur Steel and C.I. Steel Steel - - - 1.353in. lgin. lin. 1. lin. lin. liu. tin. tin. 8 D.P. tin. - - Yes NO NO NO NO Yes Force Automatic ?orce and splas: 'nmp to trough! Trough feed Trough feed Gear Gear Gear lnltiple plunge] Gear - 5 Ib. to 10 lb. - 5 lb. to 10 lb. - - - Top of filler Level top Gauge line Top of filler - - Pressure Troughs Pressure Pump fed Splash - Through crank Through crank Troughs Troughs Troughs Splash Sp&h Splash Splash Splash Splash Jet Jet Pump fed Splash Troughs Front by pump, others splash Claude1 S.U. Zenith Solex Solex Win. 20tin. 19in. elfin. 21in. 4in. 38in. 4in. 4Bin. 5in. 70 lb. 93 lb. 105 lb. 123 lb. No No NO No No NO Yes NO Yes Yes No 1150 1000 1130 - 17) 15 16 - 6 tons 7 cwt. 4 tons 15 cwt. 7 tons 10 cwt.

WILLIAMSON. S

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No. 11. No. 12. No. 13. Bore ...... atin. 4fin. atin. Stroke ...... 6in. 5in. Blin. Number'df c&hd&s...... 4 4 4 HOW cast (single, pairs or biock'j? ...... Single Block Pairs Total volume/clearance volume ...... 4.3 - 4.34 PISTON- Length ...... 5in. 5th. 7in. Number of ri'n'gs ...... 3 3 3 Width of rings ...... tin. - Kin. Disposition of ring$ ...... All at top All above pin All above pin

CONNEOTINQ-ROD- Centres .... 12in. llin. 15in. Diameter'axidiengih digudgeoripii bearing. ... )in. by 2tbin. ltin. by 2tin. bin. by 2in. Xaterial of bearing ...... Phos. bronze Gun-metal Diameter and length of big-end bearing ...... 2tin. by 2tin. 2in. by 25in. 2in. by 3in. Material of bearing ...... White metal - Gun-metal Number of bolts in big-end- bearing. - ...... 4 4 4 CRANK SHAF- Diameter and length of front bearing .... 2fin. by 3)in. 2in. by 2m. 2in. by 3in. ,, middle bearing 2fin. by 2Qin. :Three) 2in. by 2in. by 4th. l%h. rear bearing ...... I 2iin. by 4iin. 2in. by atin. 2in. by 4th MateJal of bearfgs ...... White metal - White metal Crank shaft drilled for lubrication ...... Crank pin only Yes VALVES- Disposition of valves Opposite sides One side One side Diameter of head 2in. 2fln. ,, stem ...... tin. &in. Tin. bore of vaive seat ...... :I 2tin. lf%iIl. an. Matezal of valve ...... Nickel steel Nickel steel Lift of inlet valve ...... ,%in. sin. Lift of exhaust valve ...... -%In. tin. Position of crank for inlet opening ...... + 50 + 8.50 closing ...... + 200 t 16.5' :: eihanst opening ...... - 40' - 54.50 ,, closing ...... + 10" + 3.5" &ANK CESE- Inspection doors ...... One side One side TIMING GEARS- Type of gears or chain ...... Holler chain YateriaI of gears ...... (he-hardened steel Width of gears ...... 1 tin. lain. ,355iO. Pitch of teeth ...... ::I 1OD.P. -- gin. Cross shaft for pimp and magneto ...... No NO Yes* LUBRICATION-- Lubricating system ...... Force Type of pump ...... Vane Working pressure' ' ...... 21b. to51b. . Method of indicating iivel' ...... Gauge How are main bearings lubricaied ?' ...... Pressure Splash Force ,, .big-end bearings lubricated? ...... Through crank kntrifugal forcf Force thro' cran ,, gudgeon pins lubricated ? ...... Splash Splash Splash ,, timing gears lubricated ? ...... Pumpoverffow ,, cam-shaft bearings lubricated ?' ..... Splash F&e CARBURETTOR- TypeFLY-WHii...... - Zenith Diameter ...... 18in. 20in. 22in. Width ...... Itin. 4fin. 4tin. Approximate weight ...... - - 147 Ib. Half-compression device ...... Yes Yes No Governor ...... No Yes No Normal governed speed, revs. per min...... 900 - 1000 Equivalent road speed in miles per hour .... 9.2 - 14 Approximate weight of loaded vehicle ...... 8 tons 10cwt. - 6 tons 16 cwt. * Cross-ehatt drive for pump

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No. 14. No. 15. No. 16. No. 17. No. 18. NO. 19. 4fin. 4liin. 4tin. 42in. 4tin. 5in. 5th. 5fin. 5tin. 5tin. 6in. 4 4 4 4 4 Pairs Pairs Pairs Pairs Pairs Pairs 4.1 4.35 4.03 4.75 5 5fin. 5t4in. 5 I-gin. - 5,bin. 5th. 3 5 4 3 3 tin. tin. tin. fin. fin. All above pin All at top Three gas, one All at top All at top All at top scraper one gudgeoh Wi?, . 12in. llfin. 12&in. 15in. tin. by lin. by 2&in. ldin. by 2din. lin. by 2fin. ltin. by 2Jin. Phos. bronze Phos. bronze Phos. bronze Phos. bronze Phos. bronze 2tin. by 2fin. Itin. by 2Bin. Isin. by 3in. 2tin. by 3in. White metal White metal lie cast white White metal metal 4 4 4 4 4 2in. by 3fin. 1Bin. by sin. 2in. by 3in. 2fin. by 54in. 2fin. by 3in. 2in. by 3Hn. liin. by 4fin. 2in. by 3in. 2tin. by 4in. 2fin. by 3in. 2in. by 3iin. lfin. by 5in. 2in. by 4fin. &$in.by 5th. 2fin. by 4th. White metal Wbit.e metal Xe cast white White metal White metal metal I- Ho NO Yes Yes Yes One side One side One side One side One side One side Btin. 2iin. 2Ain. 2.22in. Ziain. 2fin. &in. tin. gin. &in. din. +in. !?$in. 2in. ?in 2in. 2ikin. 2tin. - -

only. magneto drive parallel. s2

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THE DISCUSSION. Mr. BLACKWOODMURRAY, in opening the disaussion, said: On page 229 the author shtes that the valve spring pmwure and valve inertia awount for part of the mechanical losses in an engine; it should be remembered, however, that a certain portion of this energy is meturned as the valve comw back to its seat and the spring is relaxed. I disagree with the author a9 to the value of high torque at low speed unless accompanied by reasonable fuel efficiency, and I think that he is losing sight of the fact that high torque at this low speed is a neoessity to enable the vehicle to get over the lmt portion of a hill without change of speed and to pi& up rapidly when changing to a higher speed. The proportion of time during which the engine is running at this low sped under full load is so small that even a relatively poor fuel economy under these conditions is unimportant. In my opinion, the author has suggested too high a speed for commercial vehicle engines, the present normal of about 1,000 being more nearly right, bearing in mind the high speed reduction factor between the crankshaft and the road wheels which neoessarily obtains in commercial vehicles, and also in view of the fact that the inertia stresses on reciprocating parts increase as the square of the speed; to my mind the supreme importance of reducing wear and tear to a minimum makes the lower speed preferable for commercial vehicle work. I should be inclined to put the normal working conditions a little lower than the 60 per cent of full load given by the author. I think, however, that engineers are fully alive to this point, but it is not easy to get a sakisflactory solution of the difliculty. Ten years ago, having this point in view, I fiW to an ordinary 4-cylinder engine a devioe, controlled from a small lever below the steering wheel, and consisting of a three-way cock fitted in the inlet mani- fold connections of the first and fourth cylinders. By throwing over this lever the driver oould cut out cylinders 1 and 4, leaving them to draw pwe fresh air, and cylinders 2 and 3 took up the whole work, thereby insuring that for the greater part of the time these two cylinders wene working under practically full load conditions. The devioe was a very pleasant one to drive with, and

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 ENQINES FOR PETROL COMMERCIAL VEHIC1,ES. 277 the running of the engine was perfectly sweet on the two middle cylinders, as the explosions were equally spaced, and the moment the load became too great for the engine the power could be immediately doubled by throwing over the lever. The improvement in petrol comumption, however, was very disappointing, amounting to something less than 8 per cent, which was not sufficient to warrant the adoption of the device. Other designers have tried variable compression spaces, but so far as I am aware not one of theise has proved itself a practicable device. In my opinion the ford lubrication circulation system, which is perhaps the most popular to-day, is anything but a perfeot one. Where care is exercised in seeing that the oil is thoroughly drained off and replaced at regular intervals, the system works fairly well, but in careless hands it is very frequently found that the oil in the circulation system deteriorates to such m extent that it largely loses its lubricating properties, while the liquid and solid impurities which it collects cause rapid weiar in the journals and bushes. I am firmly convinced, after extended experience of both systems, that by far the most satisfactory method is to pump a definite quantity of pure fresh oil to each main bearing. I think it must be admitted that in tfhe interests of the owner a governor should form an essential past of the commercial vehicle engine, otherwise the average driver will, and does, take a pleasure in racing home when running light, to the serious detriment of the vehicle ultimately and the disadvantage of the unfortunate commercial vehicle builder, upon whose innocent head all the blame is visited. Mr. T. CLARKSON:One question which the author has not referred to is that of the materials for cylinder construction. A great deal of differenoe of opinion exists as to the nature of the cast iron to be employed in the manufacture of cylinders, and I should be very glad if some standard specification for materid could be arrived at. We hear of the employment of aluminium for pistons, and even aluminium cylinders are being used, but so far as my experience of aluminium goes, I should consider it a most unsuitable material for the latter purpose. Still, the metal- lqy of aluminium is in its infancy, and we must be ready to expect very considerable developmenk, even to the point of render- ing aluminium suitable for cylinder construction. The author referred to indicators for the lubricating system, but these were only pressure indicators, which are essential in connection with a

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 278 THE INSTITUTIOK OF AUTOMOBILE ENGINEERS. (Mr. T. Glarbn.) pressure feed, although when I used them on buses I found they were the only things that gave trouble. We finally had to cut them out to eliminate the possibility of the whole of the oil in the sump leaking out from a broken connection to the indicator. !Phere is, however, another indicator which it is desirable to have, and that is an indicator of the amount of oil in the crank me. Neither test cocks or a glass in the form of a gauge are satisfactory. Thce latter is easily broken, and if this happens when the connection is open the oil is lost. The Cadillac car is fitted with a very nioe indicator ahowing the amount of oil in the crank chamber, con- sie.ting of a twisted strip with a %oat which shows the level at a glance without opening a cock or running the risk of the glass being broken. I find there is quite a fmovement now in the United States against the Ramsbottom ring, and they are adopting a type of ring which is known here a8 the Willans ring, land which has been used a good deal on steam engines. It consists of two narrow rings in the same groove as, and on top of, a third ring, sprung in. This, although a more di5cult ring to construct, is much more efficient. We have used both types of rings on our engines, and I think the three ring type is the most e5cient. The trouble of over lubrication in the Ford car can be overcome by drilling a few holes 1/16in. dia. through the piston at the bottom of the groove in which the scraper ring lies. Mr. 0. D. NORTH:This is the first time we have had the question of engine size in commercial vehicles really thrashed out. I can understand the point of view of the road surveyor who naturally thinks that a 6-ton lorry should not be driven so fast as a +-ton lorry, but I do not believe that any salesman will find it at all easy to sell a 6-ton 'lorry with an engine smaller than that in a 4-ton lorry. Customexs will have a big engine, though then they grumble about petrol consumption. The question of engine size is, of course, bound up with that of engine speed, and I presume the author would not claim that 1,300 revs. per minute is the best speed for all sizes of engines; other things being equal, the scale speed of a small engine is higher than that of a large engine. There is no unanimity on the subject of govemors. I believe that at the Front lorrias had at first to be run on occasions at fairly high speeds and that the governors were disconnected very extensively, and a good many cast iron flywheels burst. My experience is that 1,000 revs. per minute is a great den1 too slow for work

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in ordinary undulating country; it takes all life out of the chassis. I made a test with a governor set to 1,000, 1,200, and 1,300 revs. per minute over undulating country, and I think it would be quite fair to say that nobody would buy the lorry with the governor set at 1,000 revolutions. Directly a rise wm reached the engine started to knock and gear had to be changed, and it also made changing up very difficult. At 1,300 revolutions the lorry wm all right. The hill-climbing powers were almost as good as without the governor at all, and it saved the engine a good deal because this particular engine, when not governed, was often run at 2,000 revs. per minute for miles on end. I have taken the running times on some of the char-a-bane trips in Wales, and, working out the gear ratio, I have found that the engine must have been running at 2,000 revs. per minute for miles. It is hardly to be wondered at that the centre bearings will not stand UP. The author has given us a unit Q in addition to the existing one called K in the Automobile Engineer handbook. My only objection to Q is that it apparently alters when the gear ratio alters. What I think we want is something which I believe that K did give, that is, an expreasion which gives the displacement of the engine pistons for every foot or yard or mile traversed by the vehicle on the road, and I would suggest another figure which I call the “propelling area.” I know it is empirical; it is obtained by working out on top gear the area of a piston which, acted on by a pressure equal to the brake mean effective pressure, would give the same driving thrust as the engine at any given speed, allowing for transmission losses. I should like to point out that the author does not seem to have allowed for these losses in his consumption figures. On page 235 he assumes that an engine with a Q of 5.5, which is an engine just capable of taking the lorry along the level, gives 72 ton miles per gallon. In that I do not detect any allowance for transmission efficiency, but if this is taken at 85 per cent it would bring the ton miles down to 62 or 60, assuming an engine taking 0’58 pints of petrol per b.h.p. Many engine makers claim that figure, I know, but most of us are pleased to get 0’65 pints per b.h.p. hour. In any case 0’58 is a figure only obtained at one point on the curve. To sum up, tu far as I can see, according to the author’s figures, the best consumption likely to be obtained with a lorry is about 47 to 48 tonmiles per gallon, though 65 ton miles is often claimd, an’d 60 ton mile..

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 280 THE INSTITUTION OF AUTOMOBILE ENGINEERS. (Mr. 0. D. North.) c@nbe obtained in practice with care. There are some causes of high consumption not mentioned; running down hill, for instance, The ordinary carburettor is for the sake of simplicity fitted with a slow running stop to keep the engine running, but I estimate that if the petrol were shut off entirely at the top of a hill, the average petrol consumption would be reduced by quite 10 per cent in undulating country with gradienb of, say, 1 in 30. Another point which has an important bearing on petrol consumption is the temperature of the engine. For instance, in some recent tests with a lorry, at the start when all .wm cold, we got only 4+ miles per gallon for the first mile or two and then about 6 miles per gallon for the next five or six miles. Though there was a strong head wind blowing at the time, I am perfectly convinced that the extra consumption was not due to wind reeistanoe but to the fact that the engine was not properly warmed up. Coming back after 82 miles, the engine was very much hotter and the petrol consumption was less. It would really seem worth while to fit a thermostat to keep the water as hot as possible. My objection to the Zephyr piston is that it seems to be excel- lently designed for roasting gudgeon pins, sincre the heat from the crown of the piston is conducted straight to the gudgeon pin bosses which do not touch the walls of the cylinder, and are in fact insu- lated by an air blanket. Thie piston has been successful chiefly on small bore engines, but on a 5 in. bore engine I think it would lead to trouble by over-heating of the gudgeon pin. Mr. R. PENTONY:One of the most valuable features of the paper is that it draws attention to the question of the relation of cylinder capacity to total load. I think this is a subject that has been rather neglected in the pat, but it has a very special bearing on consumption. I should like to refer first of all to Fig. 4 on page 236, where a mrve is given showing the pementqe increase in consumption as the load decreases. I find that the author has not given an engine speed for this curve, but I suppose it is about 1,300 revs. per minute, equivalent to his Q. Now I find that the petrol consumption varies very considenably with engine speed, and if the engine is running at 1,000 revs. per minute and at only 60 per cent of full load, instead of getting an increased petrol consumption of 33 per cent, we shall get 27 per cent, and as the speed decreases we shall

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 EXGINES FOR PETROL COMMERCIAL VEHICLES. 28 1 get a very much smaller incmase in consumption. For instance, at 75 per cent of full load it varies between 12 per cent and 19 per mnt, and at half load between 30 per cent and 43 per cent over a speed range of 500 to 1,500 revs. per minute. These figures refer to an engine with average compression, the clearance volume being 33 per cent of the swept volume. For higher compressions the same thing applies. At 75 per cent of full load and 500 revs. per minute we might expect only 3 per cent increase, and at half load 12 per cent increase, but at 1,500 revs. per minute we should have 20 per cent and 36 per mnt increase respectively. I have only taken speeds between 500 and 1,500 revs. per minute as I think that that is the useful range. The consumption also varies very much with the oarburettor used; it has a very great bearing on the shape of the consumption curve, and with different carburettors the loweet point of consumption does not always come in the same place, although the range is pretty much the same. I believe that the author’s statement that “ consumption curves are usually taken under full load with the carbupettor adjusted to give the best results under these conditions,” very fairly repreqents the case, but I think the general practice in the trade is to put in a very big engine to ensure ample reserve $ofpoqer, and then to out down the power by putting a hot air pipe on to the carburettor. The author has not mentioned hot air pipas, and it would be interesting if he could give us figures showing the effect on power and consumption of heating the inlet gases. I recently oarried out a rough test, the results of which are given in Fig. 32. The engine used had a cylinder capacity of 97.5 cu. in. This is rather a large engine, but it very often goes into a 3-ton chassis; the torque curve is represented by TI. The engine advocated by the author on page 240 is an engine of 81’25 cu. in. cylinaer capacity, which gives a torque curve like T2, whilst the consumption curve with the larger engine is represented by C1. When I closed the throttle to get the rreduced torque T2 the consumption increased to C2, but if we had taken the smaller engine running at full load we should have retained the consumption C1. Then I fitted a hot air pipe to the carburettor and heated up the charge until with fully open throttle the torque was reduced to values corresponding to T3, which started level with T2, but tailed off as would ba expected at the higher speeds. In this case I found that the consumption Cs waa very similar to Ci at the lower speeds, 4 per oent incmase in consumption on the

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 262 THE 1NSTITUTION OW AUTOMOHILE ENGINEERS. (Mr.R. Pentony.) colder charge at 500 revs. per minute, 8 per cent increase at 1,000 revs. per minute, but it went up to 30 per cent inorease at something like 1,500 revs. per minute. It does not, therefore, seem that there is very much advantage in having a hot air pipe,

c3. 8 C! /

ENQINESPEED. FIU.32. but that it is very much better to have smaller engines, espe- cially for speeds in excees of 1,000 revs. per minute. Incidentally, I had to heat the charge up to 60°C. to get the torque cm down, and with 17 per cent drop in torque the compression was reduced 91b. per sq. in.

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Therefore, for ideal conditions it seems that a small engine is best with the gas taken in fairly cold, but with a big engine a hot air pipe inust be fitted as a compromise. I agree with Mr. North about the 5-ton vehicles. I do not think many people can be induced to have smaller engines on {be larger cars, as it is a question of time economy as well as petrol economy. The curve given in Fig. 6 shows that in America they do not consider small engines at all, and I do not think many people in this country will either. Mr. G. W. WATSON:The author takes 15 miles an hour as his basis for road speeds; that, I believe, is quite fast enough, as I have come adross many examples nf serious damage to axles and transmission gear generally due to higher speeds. Many vehicles are over-engined and are capable of very high speeds up to 30 to 35 miles an hour. Referring to mechanicial losses, the author states that “ loss due to this increase8 more rapidly than the gain due to decreased friction, so that tbere is a probability of a greater total mechanical loss at higher speeds.” I would like to know if this statement is deduced froin the curves or how it is arrived at. On page 231 he takes the 4-cylinder engine as being standard; that is so, but I understand that at least one maker has made, or is making, engines with both eight and twelve cylinders, and that the 12-cylinder machine is not intended entirely for fire- engine work, but is to be used for military motors to get over the diffioulty of starting in cold weather. That engine is of comparatively small bore, being a little less than 3 in., with a stroke of about 5in. The author assumes that self-starters were neglected by commercial vehicle builders because they did not show the saving in fuel consumption that had been hoped for. I think the real reason is that most of the starters on the market have not the reserve necessary for dealing with a stubborn engine, though perfectly effective for two or three starts. Still I believe that this device really has a future, if only on the score of wnvenienoe, particularly for smdl vehicles used for house-to-house delivery The author’s method of arriving at engine size may not appeal to designers of high-speed engines, but none the less I believe it is perfectly sound. I do not agree with Mr. North when he says we want a means of comparison between the piston and road speed. I think the way the author has put it is a much more convenient one for handling; we must of necessity take into account the requirements of each particular vehicle. If we want

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 284 THE INSL‘ITUTION OF AUTOMOBILE ENGINEEKS. (&. G. W. Watson.) a vehicle to run under normal conditions in ordinary commercial service, the factor 9.3 which the author gives, is a very suitable one. If we want a vehicle for abnormal conditions, such as for char-a-banc work, where it is expected to take steep gradients at top speed, then we must expect to use the higher constant. On the subject of lubrication, I prefer a combination of feed and the trough. I think the arrangement of the magnetio and water pump shown in Fig. 21 is the best. I do no6 like the pump shaft arranged parallel with the crankshaft, as, if the shaft is placed high enough for the magneto and the pump glanh to be acoessible, the chances are that it interferes with the access to the valves or crank case. The author rather mems to dismiss cylinder design in too few words. He might have added a word of warning as to the advisability of keeping a uniform section of metal around the valve seats, without which it is impossible to keep valves tight on the seatings owing to distortion. Inspection doors in crank cases are now generally being provided, thanks to the Subsidy Specification, but in many cases they lead to very dirty engines and waste of oil, &s they are difficult to keep tight unless carefully faced and provided with an aiiiple number of bolts and nuts. The latter condition involves a good deal of trouble in making an examination of the interior. To obviate this I suggest that the bolts should be made in the form of swing bolts with wing nuts, with the ends of the bolts rivetted over slightly to prevent the nut coming off. I do not like either the “plunger” or the “gauge” type of oil indicator, for the simple reason that it is impossible to be sure whether it is oil pressure or air pressure that is being indicated. I rather favour the type used by Commer-cars and by Thornycrofts, in which the oil is lifted up above the dash and passed through a visible-flow indicator to the bearings, and this can be adapted to both pressure or splash feed. The author reminds us that many people do not appreciate the power absorbed in driving cooling fans. Some time ago I made tests on a 16 in. 4-bladed fan taken from a very well known make of commercial vehicle, and I found that it required 38 h.p. to drive it at 1,000 revs. per minute; yet the makers fitted a thin belt only $ in. wide to do the work. It is not surprising to learn that the user had to put a new belt on every week or ten days, or be content to leave the fan out of action altogether.

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Mr. F. A. WILLCOX:If the bottom curve in Fig. 1 is examined, it will be seen that while the revolutions vary from 900 to 1,300, the petnol consumption varim from 0.6 to 0'62, that is, about 3 per cent. I believe the power developed was measured by means of a fan brake, and I doubt whether power can be measured accurately to within 3 per cent by this means. I believe these brakes are accurate only to about 5 per cent, and unless the instruments for measuring power are accurate to something considerably nearer than 3 per cent it is impossible to dif- ferentiate between measurements such as 0'6 and 0'62, so that the bottom curve becomes a horizontal straight line. I feel that very great care must be taken in deducing formulae to examine thoroughly into the limits of accuracy of the instruments used for measuring the quantities involved. I always use an electric generator for testing; this is the method employed by Professor Hopkinson and other investigators as being the most accurate. With this apparatus I have always found the consumptions per brake horse power higher than with the fan brake. I have obtained seven miles per gallon on a 4-tm vehiclo running over the measured mile. Observations were taken in two directions, one slightly down hill, and the other slightly up hill. I do not, hQwever, consider that this method is sufficiently exhaustive to give an accurate measurement of the petrol consumption. I should like to ask whether in the formula for determining the surface of radiators the fan is taken into consideration. Last year I carried out a mnsidenable number of investigations on the surface of radiators to determine the most important element in the cooling system, and this I found to be th,e fan. The method adopted waa to estimate the amount of heat trans- mitted by the radiator under different oonditions. I started with water at 180"F. which passed through the radiator into a tank, in w'hich it was kept at a constant temperature by means of a steam jet. The water in passing through the radiator experienced a drop in temperature, and knowing the quantity, the amount of heat eliminated could be cdcuhted. The apparatus was stationary, and consequently the effect of the motion of the vehicle could not bfe observed. The water pump was driven at the same speled as it would be driven by the engine. I found that with the water passing through the radiator at its

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 286 THE INSTITUTION OF AUTOMOBILE ENGINEERS. (Mr. F. A. Willcox.) maximum velocity in still air the heat eliminated was only about 2,000 to 3,000 B.Th.U. per hour, whereas with the fan at full ~ped the amount eliminated was approximately 100,000 B.Th.U. per hour, while the radiator of a 30 horse power petrol engine has to eliminate from 100,000 to 120,000 B.Th.U. per hour. By using various types of fans and running them at different velocities, the results obtained showed conclusively that the most important element in the cooling system is the fan. The surFace of the radiator might be reduced considerably without having any appreciable effect upon the results, but a slight reduction in the fan power produced very considerable effects. Mr. A. C. CLIFFORD:I think inspection covers should be very securely bolted up and perhaps mled to prevent drivers having too easy access to the crank chamber, to avoid the risk of their leaving tools inside, and also to prevent that which some of us have to contend with, malicious damage. Such a cover will not stop emery being put into a base chamber, but it will kecep out odds and ends and bits of iron. I also think that a grid might be incorporated in the oil filling pipe. The author suggests that indicators should be arranged in series with oil pipes leading to the bearings, but I prefer no external oil pipes at d,as if they get broken the oil indicator (in some oars) is merely misleading. I would like to suggest that the fan which is bolted on the end of the crankshaft, as in some of the Leyland vehicles, should be more extensively adopted, with a view to eliminating all trouble with belts, belt fastenings, pulleys, etc. I know it is not quite ideal, but if it can be adopted it is a great step in the direction of simplicity. Mr. F. L. MARTINEAU:It would add to the interest of the paper if the compression ratios of the two engines with different compressions compared in Fig. 4 were given so as to assist in future calculations. The use of two bolts for fixing the gudgeon pins in pistons is condemned because of the difficulty of accurately drilling for and fitting both pins; I think that the difference in expansion of the two metals, pin and piston, will distort the piston and bring about exactly the same result as inmcurate drilling. This is particularly noticeable with large diameter pistons and when some alloy pistons are used. Mr. H. J. USHER:Mr. Clifford referred to the practioe of fitting the fan on the main shaft, but I had a Leyland vehicle in which the fan was mounted in this way, and we found that the speed of the fan was not sufficient to keep the water cool enough to prevent

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 ENGINES FOR PETROL COMMERCIAL VEHICLES. 287 it boiling. The Willans piston ring is an interesting proposition, but the rings should be pinned in so that the slots do not allow any steam, or gas, to pass through to cause a loss of compression, and the spring ring should not have so much eccentricity aa to cause any binding or undue pressure on the walls of the cylinder; a piston with the ring fitted should just fall down the cy.linder of it8 own weight. I believe in inspection doors on all engines, but I would not use bolts but studs screwed in and burred on the inside so that they could not come out. With regard to petrol consumption, I have found that the great thing is careful driving, and the man

FIG.33. who shuts off completely down a hill obtains the best efficiency. As regards climbing hi&, the best driver is the man who changes at the right moment, but most of them change too late. Mr. G. B. GARRARD:There am two main places where engine noises may mme from, the valve returning to its seat, and the timing wheels. I am of opinion that we have bean putting the timing wheels at th,e wrong end of the crankshaft, and that it is the whip in the crankshaft which gives the kick in the timing wheels which causes the noise. I designed some engines in 1911 with the spur wheels at the same end as the fly wheel, and there

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 288 THE INSTITUTION OF AUTOMOBILE ENGINEERS. (Mr. B. B. Gamard.) was no noise from these wheels; the Daimler Company is now putting the chain drive at the .same end as the fly wheel. The wheels are every bit as wm&ble as at the front, it is just .as easy to unbolt the fly wheel from its flange as to remove the radiator. The noise from the valves can be overcome by putting a little ramp where the cam proper leaves off before joining the circle. With a ramp 5ix one-thousandths of an inch, and the tappets set with a 0‘003 or 0’004 feeler there an infinitesimal period of “wire drawing” before the valve seats itself, which acts as a dash pot. A self-starter added to a chassis is so much more machhery that should not be placed in the bands of an unqualified driver if it can be helped, but I devid a very good compromise for a marine engine. The magneto oontact breaker was fixed in the best position for very slow running, and the magneto drive was fitted with a right and left square thread long pitch nut, in order to vary the advance of the Qsmature relatively to the engine. When starting up, the armature waa retarded about 50 degrees before the running position by means of the thread, the engine was primed, switched off, then pulled just over the first or second oompression, switched on again, and by advancing the lever sihrply, thus turning the armature past the contact break, the engine never failed to st‘irt. I have a sample of a case-hardened valve that has been running for six years, and the turning marks that were Dot taken out by the grinding are not yet worn off. Thie valve was not ground in for two seasons, and I have never replaced a case-hardened valve. I often wonder why one groove is not fitbed in a piston instead of three, the ring being fitted as shown in Fig. 33. The outer rings are machined to size (no spring allowance at all), the inner ring has a suitable spring albwanoe only. With that ring I have had two inches too much oil in the crank chadber and go6 no smoking, though after two inches I began to get smoke.

Mr. WILLIAMSON,in replying on the discusision, said: Mr. Black- wood Murray disagrees with me with regard to the question of torque at low engine speeds. Certainly high torque at low speeds is an advantage if it is accompanied by reasonable petrol consumption, but this is not often the case. If we can impress on. the driver, as Mr. Usher said, that the time to change speed is when the engine falls below a certain number of revolutions for any particular gear, the engine would always be kept in the

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range of economical working, and whether it had high torque or not at low speeds would be a matter of no importance. While it is admitted in agreement with Mr. Blackwood Murray that forced lubrication has drawbacks, surely those drawbacks can be overcome in a very simple manner by fitting efficient filters at both the intake and the foroe side of the pump. The question of materials referred to by Mr. Clarkson is so extensive that it is well worthy of a paper on its own account. Throughout the present paper it has been assumed that current practice for pleasure cars should be accepted as a general basis in materials, and to some extent in design. I quite agree with Mr. Clarkson that the lubrication indicator is an endless source of trouble, and stated that there is room for pomething better than what we have at present. Every lubrication indicator appears to be worse than the last one we tried‘. Also undoubtedly there should be some method of indicating the amount of oil in the crank case, and the method he suggests is quite good. Mr. North suggested that 1,300 revolutions per minute is not the best speed for all engines. With this I agree. The correct proce- dure is to examine the torque and consumption curves for the particular engine with which it is proposed to deal, and from these settle the dwirable speed for that engine. It is impossible to settle off-hand the speed for any or every engine from curves given in this paper. The curves are included to prove a general case, whereas any particular engine may have merits or otherwise of its omTn, which may have an effect on its curves. I quite agree with Mr. North that “Q” alters for different relative engine and road speeds; in fact, this is expressly mentioned in the paper. “&” is taken for 1,300 engine revolutions and a road speed of 15 miles an hour. Again, in reply to Mr. North, the transmission losses are accounted for in curve “R.” I have to thank Mr. Wimperis for this curve, showing road resist- ancea, which was taken from one of his papers read before the Institution. The resistance R is the resistance at the clutch, and includes gear box and rear axle losses. I am sorry Mr. North does not believe his petrol consumption figures when he gets them. I do not know why; possibly the explanation that R includes all the losses may help his case. The question of fitting a thermostat or some other automatic device for regulating the action of the WILLIAMSON. T

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 290 THE INSTITUTION OF AUTOMOBILE ENGINEERS. (Nr. Williamson.) fan or the efficiency of the water pump, may not be out of place in thwe days when petrol is so dear. I am very much obliged to Mr. Pentony for having drawn further attention to figures of petrol consumption at various loads. The matter is most interesting, and is one to which all commercial automobile engineers might well give their very close attention. There is bound up with this, also, the question as to whether tbe engine in a five-ton vehicle need be larger than that in a four- tonner. The sizes obtained by using my formulae do not agree with what is looked upon at present as correct practice, but iff it is reasonable to assume that the speed be 12 miles an hour for five-tonners and 15 miles an hour for four-tonners, the figures I have laid before you prove that the engine does not require to be 'bigger. Mr. Watson agrees that the road speeds I have taken ape high enough; others are convinced I have erred on the low side. I will leave them to argue it out. Mr. Watson has got a good case. The mechanical losses of the engines were deduced. I had arranged to have experiments made by which the engine would be driven electrically with various parts removed in order to t.est the power required at various speeds, and with various parts of the engine in position and not in position, but unfortunately I was not able to carry these experiments through in time. The 12-cylinder engine spoken of is well on its way, if it is not actually in being at the moment. I agree that the inspection doors are inclined to make an engine dirty if very great care is not taken to ensure a good scraped joint. The ventilation of the crank case has considerable effect on the cleanliness of an engine. If the case is not well ventilated there is great difficulty in preventing the escape of oil. With regard to the power for fan driving, I carried out experiments some time ago which bear out what Mr. Watson says. These experiments were for the purpose of settling the type of fan to be fitted in a vehicle. I did not measure the h.p. required to drive the fan, but I measured the h.p. of the air which the fan would propel. I was very much surprised to find what h.p. could be obtained in the air from a small fan such as might be fitted to* a commercial vehicle. In reply to Mr. Willcox's remarks, I may say the curves were obtained by the Heenan and Froude brake, and not by the ordinary fan air brake. The radiator sizes are for radiators working under

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 ENGINES FOR PGTROL COMMERCIAL VEHICLES. 291 normal conditions with the fan included. That it is quite possible to cut down where the fan is highly efficient, or where it is inoro eficient than usual and where other conditions, are favourable, is quite true; that is explained in the same portion of the paper where one engine is spoken of as having figure of 6.2 instead of 8. Inspection doors are thought dangerous by Mr. Clifford. Pos- sibly they are, but if people wish to damage a vehicle maliciously, I suppose they might even take the bottom off the crank case. With regard to not having external oil pipes, I am afraid I did not quite grasp his argument that if the pipes break the damage is done before the indicator shows there is anything wrong. If the indicator is in series with the pipes, the pressure will fall a8t once if there is a leakage such as would be caused by a broken lead. In reply to Mr. Martineau, the pressures in Fig. 4 are respectively 77 lb. and 91 Ib. at 1,000 revis. per minute. Mr. Garrard’s suggestion to place the timing gears at the rear end of the crank case is one that can only be tried out by experiment. No doubt it would have a silencing effect on the engine, but the timing gears would not be as accessible as at present arranged. His suggestion to taper off the end of the cam, where it runs down into the round, is quite sound, and has been done, as Mr. Garrard says, with very satisfactory results.

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COMMUNICATION.

Mr. JOHNYOUNGER wrote: In 1913 Mr. C. T. Myers gave a paper before the Sooiety of Automlobile Engineers of America to establish the following formula for engine capacity:- TF = 28.22 x d2sR DW ’ Where TF is a tractive factor d is diameter of cylinder in in. The 4-cycle engine is s is stroke of cylinder in in. 1 assumed. R is total gear reduction D is diameter of driving tyms in in. W is gross weight of vehicle in lb. For reasons stated in hit3 paper, he gave the value of TF as being 0’04 for god practice, European lorries being slightly less, and American lorrieis being then somewhat more. In another form he stated that ...... d2sRDW should equal 0.0014 (8) The present author’s formula is V Q = ...... (b) Where V is volume of one cylinder in cu. in. W is might of vehicle in long tons (2,2401b.). All his lorrimesare assumed to run at 15 m.p.h. with an engine speed of 1,300 revs. per minube, so that approximately, R=-.?rD 12 Substituting this in (a), we have

Tr - dls l2 = 0.0014 -W- or 2 dls 4 = 0.0014 3 X 2240W

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This is in exceeding close agreement with the present author’s 9.3, and is rather wonderful, considering that the premises and method of attacking the problem are quite different. Thomas’ Formula. The formula is, however, somewhkt involved, and to my mind a simpler formula can be devised. Mr. H. K. Thomas uses the following for the wpaoity of a lorry:- 63000PRe = 1 .. (a) 11 x D- x w [20g + .I 2 2000

Where P is horse-power of engine at TZ revs. per minute R is as before e is mechanical efficiency of transinitting mechanism W is weight of vehicle in lb. g is percentage grade T is road resistance in Ib. per 2,000 lb. By stating what a lorry is definitely expected to do, the value of P can be found, and hence V. My practice, and I find it accept- able, is that a lorry should climb a 3 per cent grade on high gear with a road resi&mm of 50 lb. per ton, with practically no fdling off in a speed of about 15 miles per hour. Its e should be 0‘85. Personally, for many lemons concerning not only the engine but the whole vehicle, I think a governed speed of 1,000 revs. per minute preferable, and I do not limit the speed of fifteen miles per hour to light lorries, but carry it up to those of 5 tons capacity. The gear ratio R then becomes 7rD 15.85 So that we have 63000P x 0.85 x -7rL) 13.85 = 1. 1ooox -D x w [xo-60 + 50] 2

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 294 THE INSTITUTION OF AUTOMOBILE ENQINEERS. (Mr. John Younger.) or 386P -w = 1. Now P at 1,000 revs. per minute with an mp of 95 lb per sq. in. is 0.485V, and W= 2240W so that 38.6 xO.485v - - -1 a24ow or’ ;= 12. This is obtained with an engine speed of 1,000 revs per minute; correcting this to the present author’s 1,300, 12 would reduce in inverse proportion to giving us again the figure also in remarkable accordance with the others In its simplest form we may take it that a motor lorry for use in any country should be just capable of climbing a grade of 3 per cent on high gear at full motor speed against a road resistance of 50 lb. per ton of 2,000 lb. The motor capacity should be such that V 1000 w =12Xy 2240 or Vn -w = 5.36 ...... (e) Where V is volume of one cylinder in cu. in. (a 4-cylinder, 4-cycle engine being assumed), n is normal number of revolutions of engine W is gross weight of vehicle in lb.

In connection with the above, it is somewhat interesting to note that Mr. H. K. Thomas introduced a coefficient “ Q ” in 1913, aa a standard of compariaon between different vehicles, lorries and pleasure cars. This “Q” is really a measure of piston displacement per foot

Downloaded from pau.sagepub.com at Kungl Tekniska Hogskolan / Royal Institute of Technology on June 4, 2016 ENGlNES FOB PETROL COMMERClAL VEHICLES. 295 travelled per 1,000 Ib. gross weight, as will be seen from the formula 7r d2snR Q= L, r- x w 12 R is number of cylinders. TV is gross weight per 1,000 lb. This reduces to the simpler form 3d2snR, Q = -DW- ...... (f)

This coefficient is of great value and has been adopted as a standard of comparison by the combined engineering departmenh of the Pierce-Arrow Motor Car Company. It also gives an indication of the relative petrol consumption of the different vehicles.

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FIG.9.--Tilling-Stevens Engine, 4; x 5;.

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FIG.16.-Leyland Subsidy Type Engine.

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FIG.23.-Tylor Engine 5 in. by 6 in. as fitted to Karrier Subsidy Type Vehicles.

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