LIVE AXLES FOR COMMERClAL VEHICLES. 161

LIVE AXLES FOR COMMERCIAL VEHICLES.

BY GEO. W. WATSON (MEMBEROF COUNCIL).

INTRODUCTION. THE purpose of this paper is to present a rhm8 of up-to-date practice relating to the design of live back axles for commercid vehicles for load capacities of two tons and upwards. The paper admittedly does not go so fully into certain details as it might, but this has been chiefly due to unforeseen circumstances which have left the author all too little time to complete its preparation in the manner he had at first intended; he trusts, however, that it may suffice as a basis for discussion with a view to the improvement of so vital a unit in the anatomy of a commeroial vehicle. Any information that is obtainable in regard to experience with the thousands of vehicles with the Expeditionary Force would appear to show that no small percentage of the troubles experi- enced has related to back axles. British designers and con- structors will be pleased to learn that comparatively few failures have occurred with axles entirely of home design and manufacture. Before proceeding with details it should be made clear that in this paper it is not intended to deal with road wheels, bearing springs, cardan shafts and joints or gear-shaft brakes. The first-named, so far as forged stelel wheels are concerned, were ably dealt with by Mr. T. Clarkson, in a paper read last session,* while bearing springs have been dealt with in a paper which Mr. G. H. Baillie read in May, 1913.t The other points, it is hoped, may be fully discussed at a later date. The author has divided his subject into a number of headings, and it8 far as possible has avoided the overlapping of subject-

* See Proo. I. A. E., Vol. IX.,p. 105. t See Proo. I. A. E., Vol. VII., p. 451. WATSON. L

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 162 THE 1KS 1 ITUTION OF AUTOMOI5ILE ESGIXHERS. mattcr, but this has not been possible in every case. The designer of a live axle ha4 to be guided very largely by proved practice. This may seoin ail unscientific method of treatment €or so im- portant a piece of machinery, but apart from the calculation of known loads, which is straightforward work, it is not possible to tbeorise with any degree of certainty, or even probability, con- cerning the momentary stresses due to road shocks of unknown intensity. In all calculations for axles the author takes as a basis the limit of adhesion between plain solid tyres and the surface of the road. He accepts this limit as 0’4 of the imposed weight on tho back tyres (including the wheels themselves), and as this is about the worst condition to be met with on any macadamised road, it has been found to meet the case better than working either from the power end of the transmission, or from the braking effort. A factor of safety of not lem than sevcn on thle yield point of the material should be allowed for the load-bearing parts, and not less than four on the transmission shafts and gears. It is, of course, desirable to keep down the unsprung weight as much as possible, but on no account should this consideration be allowed to outweigh others, as it has still to be proved that unsprung weight, as weight, has any real effect upon the wear of either tyre or road. Col. Crompton has stated tkat it is speed which counts most in these respects.

L)UTIES OF A LIVE AXLE. A live axle has four important duties to perform: firstly, it has to carry a large part of the chassis load, plus a still larger part of the weight of the body and tho useful load; secondly, it has to transmit the engine power to the wheel rims and tyres; thirdly, it lias to transmit the tractive eBort, or push the vehicle along the road; and fourthly, the containing casing, or forging, has to resist the torquc due to the drive, in some axlos this casing has also to resist the braking load. The simplest form of live axle is, of course, that used on the majority of steam wagons. This consists, primarily, of a straight shaft of steel running in axle boxes which carry the rear bearing springs; one of the road wheels is keyed, or otherwise secured to one end of the shaft whilst the other wheel, freely mounted on tlic end of the shaft, is driven through a sleeve from a differential gearing. A greatly improved form of such an axle is shown in Fig. 1. .This siniple form of live axle, hmver, has its limitations;

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COMMEHCTAL VEHICLES. 163 whikt being the cheapest to sonstruct, it does not easily lend itself to my but a single-hain or spur-gear type of drive, and w the main shaft must perform all the three duties named, it follows that the direction of stress in the material will be con- tinually changing ,dlthe time the vehide is running. Conse- quently, it is neither practicable nor convenient to employ thi8 form of axle for other than oomparatively slow moving vehicles. On the majority of petrol vehicles the type of live axle is such that for the purpose of detailed oonsid,eration the complete unit can be divided into two dishct parts: (a) the outer casing, or forging, which carries the imposed load, and may be likened to a beam supported in the hubs of the road whleels {andloaded at the two

FIQ.1 .-Live Axle used on Allchin Steam Wagons. spring flats; (b) the driving shafts, through whioh the power is transmitted to the wheels. There is another type used on certain vehicles which are partly or wholly of Amrioan origin, of which tho Sheldon axle may be taken as an oxample. In this the casing acts as B housing for all the bearings and gears, while the differ- ential shafts aarry the bending stresses due to the lodand tmtive effort, in addition to the torsional stmesses due to the drive, but &Q the differential gear oage is mounted in bearings within the main casing, the differential shafts are not called upon to take the bendiag load due to the worm drive. British builders of live axle commercial vehicles gen,erally have adopted the first named type of axle. L2

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COMMERCIAL VEHICLES. 165

FLOATINGAXLES. There appeaxs to be much diversity of opinion as to the meaning of the term ‘’ floating,” ‘‘ semi-floating,” and ‘‘ non-floating,” as applied to live axles. Them terms, which the author believea me of American origin, axe much used in impressive tones by many mleamen and others who have obviously no concaption of their meaning; they often couple them with varying arrangements of spring mounting, torque and thrust rods, etc., in a most perplexing manner. The interpretations which the author proposes to use throughout this paper, are as follows:- Floating Axle.-An axle in which the wheel-driving, or dif- ferential, shafts transmit only torsional effort. (Fig. 2.) Semi-Floating Axle.-An axle in which the wheel-driping sbafta

I

FIG.3.-An American-built Axle : The Sheldon.

partly, or whlolly,snxpport the bending stresses due to the gear drive plus the torsional stresses, but which are relieved oP all bending stresses due to the imposed lload and the tradve resistanoe. (Fig. lo.) Non-Floating Axle.-An axle in which the differential shafts wholly or partly take the combined bending stresses due to the hposed load and the tnactive reaistanoe, plus the torsional stresses due to the transmission of power to the wheels. (Fig. 3.)

TYPESOF AXLES. For the purpose of further identification it is also proposed to describe the preeent two standard methods of construction of the load-bearing axle proper as the solid-forging ” and the “ built-

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 166 THE INSTITUTION OF AUTOMOBILE ENGINEERS. up ” types. By ‘‘ solid-forging ” type is meant that class of axle in which the road wheels are jourdled upon the two ends of a solid forging mhich carries the imposed load, and on which the driving gearing and shafts are mounted. The “ built-up ” type includes all axleis which are built up of steel castings, tubes, eta., which not only take the imposed loads, but also act as housings for +he drking gears and shafts.

The ‘‘ Solid-Forging ” Axle -The author will not venture to make any assertion as to who was the first to use an axle of tkis type. The Leyland Company, however, have long used one form on their petrol vehicles. In their early ales the road wheels were journalled upon hollowed, or tubular, extensions from a cradled forging, in the dip of which the housing for the driving and differential gearing was mounted. The wheel-driving shafts, projecting from each side of the housing passed through the tubu- lar extensions of the forging, to couplings on the wheel hubs. There were oertain objections to this form, arising from the dip, as any deflection of the axle was acoompmied by a corresponding end load on the wheel-driving shafts, with consequent momentary excessive side loads upon the ball bearings within the driving gear housing. This difficulty was partly overcome by adding a separate compression, or arched, member above the casing, of somewhat similar dimensions to the dip below. A better form of this axle, in the author’s opinion, is the Pagefield, shown in Fig. 4, which is also noteworthy for the amessibility of its working parts. In machining this axle from a stamping both outside and inside the centre enlargement can be finished on a profiling mill, with a special fixture, or, if made from a steam-hammer forging, the inside could be machined on a dotter, after drilling holes of suitable size at the corners. The former method, of course, is the cheaper where quantity production is concerned, but British stampers are not easily persuaded to undertake the production of stampings of this size. For a.xlels in which the axis of the differential gear is coincident with that of the road wheels, as in Fig. 2, it is cronveinient to make the axle forging in the shape of a double-shafted banjo, in the manner long used by tb Maudslay Company. The general impreasion is that this company mas the first to use this form of axle, but the author lreaalls that in 1906, or 1907, Thornyarofts showed shch a worm-driven axle at Olympia; that axle was then scoffed at because the lotad-carrying member, having originally

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COMMERCIAL VEHICLES. 167 been made for a bevel-driven axle, had been laid on its side and adapted for a worm-drive. What was ridiculed then has now become the standard practice with some of our foremost builders of commercial vehicles. This kind of axle when laid upon its side, as shown in Fig. 2, is not in its best position for taking imposed loads and is liable to excessive deflection under such loads. A few makers have tried to overcome this by deepening the ring-shaped enlargement, but that does not help matters, as the modulus of section through the centre of the axle is already generally much greater than at. any other point. The allowanm of more metal at the junction of the tubular extensions with the ring is of much greater import than depth of section of the ring, as it is at the junctions, or “ throats,” that deflection, and sometimes fracture, occurs. In the axle shown in Fig. 2 this weakness has been overcome by making the throats start at a tangent from the periphery of the ring, and die out into the extension8 with easy curves. The extensions, also, are made free from sudden changes of diameter on the outside, and the bore is simply a rough drilled clearance hole, free from expensive counterbores. The little extra metal at the “ throats ” does not add much to the weight of the finished axle, but greatly increases the resistanoe to deflection. Comparative tests upon this axle and one in which the extensions ran into the ring at a radius of 4 in showed that, for the same diameter of extension and depth of ring, and the same wheel and spring oentres, the former defleoted only one-sixth as much as the latter. Although the horizontal disposition of the banjo is not the most favourable so far as imposed vertical loads are concerned, it is not necessarily the worst having regard to all the conditions which have to be met. For instance, the horizontal thrust from a central torque-thrust member, due to the tractive resistance, may conceivably impose a greater bending moment on the axle than that due to the vertical loads. Such conditions would arise when- ever the vehicle be driven, with full load, up gradients steeper than 1 in 7. In the axle of their Subsidy Vehicle, the Wolseley Company have adopted an original variant of the banjo type; they have tilted the forging so that the ring is inclined at 25 degrees from the vertical. Probably better results would have been obtained had the forging been inclined at 25 degrees from the horizontal, because at or about this angle the axle is practiaally equally strong to resist

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 168 THE INSTITUTION OF AUTOMOHILE ENGINEERS.

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COMMERCIAL VEHICLES. 169

fl

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 170 THE INSTITUTION OF AUTOMOBILE ENGINEERS. both imposed vertiml load and horizontal thrust due to the oentral torque-thrust member when driving on low gear. The arrange- ment is shown in Figs. 5 and 18, an examination of which will also show that the Wolseley Company have made the wheel journal portions of the axle separate from thfeoentral forging; this permits the use of a me-hardening steel, ground and polished to take the wheel bu&es, whilst the axle body is made of medium-carbon steel, oil-hardened and tempered. Wriigley’s axle, &own in Fig. 6, also has separate journal portions for the same reason, and in this axle the banjo forging is arranged vertically.

Fro. B.-Wrigley’s Proprietary Axle for %ton Vehicles.

Built-up Axles.-Figs. 3, 7, 8 and 9 show four forms of built- up axles, only one of which oan safely be used without a tie bar or truss. The design shown in Fig. 7, in the author’s opinion, leaves very much to be desired, both 011 the soore of rigidity of the complete axle and accuracy of assembly of the worm gem and differential. The axle shown in Fig. 9 is better from the wsemb- ling point of view, but undoubtedly weak as a load carrier for use over bumpy roads as the oming is so irregular in contour that rigidity can only be obtained by the use of a tie bar; what might happen in the not improbable event of the breakage of the tie bar

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXT.ES FOR COMMERClAL VEHICLES. 171

better be imagined than d,wcribed. Fig. 8 shows Wrigley’s axle for two-ton chassis; although a tie bar is here shown, it k I-11

FIG.7.-An Axle which does not conform to the generally-accepted ideas of Commercial Motor Builders.

not nearly so neoessary as in the two for,egoing instanoes, but the need for this independent reinforoement oould have been eliminated

w FIG.8.-Wrigley’s 2-ton Axle.

by enlarging the flanged connections between tha main weand the sleeved extensions, and joining them up with a couple of ribs below

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 172 THE INYTlTUTION OF AUTOMOBILE ENGINEERS. the axle, in the manner shown in Fig. 10. The last-named view depicts the Dennis Subsidy Vehicle axle, probably the beat of the built-up type, although the author feels that it could be im- proved by giving independent bearings for the differential wheels, instead of relying upon their fit on the differential shafts, whiah are thus not entirely free from beding stresfies. The same remark applie to the axle shown in Fig. 11. With the exmption of bhat shown in Fig. 7, all these ,axlesdepend

FIG.10.-Dennis %ton Axle. to a certain extent for strength land rigidity upon steel tubes which are forced into one part under hydraulic prassure and spigot into the central wing, in this way stiffening up the connection between the respective parts. The desiher of the American axle shown in Fig. 9 appears to have ignored this point. The wessity for the careful fitting of this tube was long ago impressed upon designers in this country, who have also found that solid-drawn or extruded steel tubes for this purpose cannot be relid upon. The author understands that the London General Omnibus Co., in the “ B” type axles, make these tubes from solid bmof nickel-steel. This axle was illustrated and described in Mr. T. B. Browne’s paper ou

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 Fro. 9.-A well-known American Axle for %to11Vehicles. [ To face page 1 72.

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COMMERCIAL VEHICLES. 173

“ The London Motor Omnibus Service,” red at the Summer Meet- ing, in th0 U.S.A.,in 1913.*

AXLECOLLARS. No matter whether the axle body be of solid or of built-up type, provision must be made for keeping the wheels on the journds. Most makers provide mmed collaxs, but for these the most positive of locking devices should be employed, such as that shown at A in Fig. 4. The screwed oollas allows of adjustment for weax of the thrust faces, but in view of many instances of wheel seizure

HALF PLAN

FIG.11 .-As fitted on ‘‘ Karrier ” Subsidy Vehicles. due to these collars being scmwed up too tightly by unskilled men, the author prefm the method shown in Fig. 2, where a split 00lla.r takes the plaoe of the screwed collar. This split collar is held in place by an outer collar, or muff, which, in turn, is held by B circular spring clip. GEARHOUSINGS. The modern method of mounting the whole of the driving gears upon one base plate, or casing cover, has much to recommend it. * SeeProc. I. A. E., Vol. VII., p. 566.

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 174 THE INSTITUTION OF AUTOMOBILE ENGINEERS.

The gears are thus more easily assembled and adjusted for depth of mesh, thrust clearance, etc., and if the differential shafts can be withdrawn from the wheel end there is the further advantage of easy dismounting for impection and repairs. This construction, however, lowers the power of resistance of the axle aaaing to bending under vertiml load by retamn of the removal of so much " compression " material. It is not advisable to rely entirely upon the top over to replace the necessary compraision material, and a better plan appeam to be that adopted by Dennis Bros., cia shown in Fig. 10, whioh provides a wide and continuous flange towhich

FIG.12.-Showing positive adjustment for thrust bearing by aid of ground washer A. the top casing may be secured by bolts, which at all times axe preferable to studs. The class of housing shown in Fig. 7 is no,t to be reoommended, as, although it may bfecheaper to produce, it is not emy to assemble the gears and bearings with any &ah degree of accuracy. AXLEGEARING. Worm-driven axles appear to be incneasing in favour, md probably at least two builders of Subsidy Vehicles who now employ double-reduction axles would also be using worm-drive had the original W.D. Specifimtion permitted. It haa proved to be both

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COMMERCIAL VEHICLES. 175

a highly efficient and constantly efficient means of power transmis- sion, it is silent in operation, lends itself to a symmetrical design of wing, and, a point whiclh is of great importance, makes for a cheaper axle than one produoed with double-reduction gears. For vehicle8 intended for use on paved, or good macadam, roads. the author advooates the worm drive for all axles up to six tons limit of axle weight, but for heavier and slower-moving vehiolles he considers the double-reduction type to be the better, particu- larly if the differential ge'ar be mounted on the mown-wheel shaft and the final drive taken through two pairs of spur gears, ias shown in Fig. 4. Attention is directed to the m,ethod of mounting

i FIG. 13. -Showing adjustment for thrust bearing by grinding the sleeve B.

the differential cage on independent bearings on this axle, instead of passing a solid shaft through the gears and oage, and then carry- ing that shaft on one pair of ball bearings, as has been the practice of one maker. The arrangement of gearing shown in Fig. 4 is probably the best possible as far as awssibility is concerned, as the whole of the working parts may be dismantled without using a jack, or even removing the body or load. The type of drive shown in Fig. 11 is both lighter in weight and cheaper in cost of production than that last described, and although it does mot possess equal facility for removal of thS parts without first taking off the bdy or l'oed, it is none the less practioial, and has

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 176 THE INSTITUTION OF AUTOMOBILE ENGINEERS. proved to be reliable, efficient, and reasonably quiet. Thorny- croft’s original Subsidy Vehicle axle was a variation of this type, the drive being first taken through spur gearing to a find bevel gear drive. This axle bad two distinct advantages: firstly, th,e pitch speed of the bevels was bw, with a resulting quietness of running, land secondly, the arrangement allowed the use of a double banjo axle, with the banjo set in the vertical direction, and this allowed all pararts to be remomd without disturbing the body or load. The laxge diameter bevels, however, were expensive to pduce, and as soon as the W.D. permitted the change, a worm- driven axle was substituted.

FIG.14.-The Daimler method of mounting the Worm Shaft.

If any future specifidion issued by the W.D. calls for increased ground clearance the worm drive may not be acceptable, bemuse it is not prachable to make a worm (wheel as small in diameter, for a given gear ratio and load, aa the final gear wheel of a double- reduction axle. The selection of m&erials for axle gears is one on which various opinions are held, but it may be intepesting to know that in one of the most successful of double-reduction axles all the gems are made of K.E. 805. The Wolseley Company use case-hardened nickel-steel, and Messrs. Wrigley uee an oil-hardening ohrome- nickel steel for the bevel pinions, case-hardened nickel-steel for

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXI.ER WOK COMMERCIAL VEHICLES. 177 t.he crown wheel and spur pinion, and a good tyre steel for the spur wheel. With regard to the pitch of the gear teeth for an axle of the three-ton Subsidy Vehicle type, excellent results have been obtained with No. 5 diametral pitch for the bevels and No. 4 for the spur gem, all of involute shape with the standard angle of preesure. In the erne of' worm drive it is usual to make the worm of nickel-steel, me-hardened, ground and polished, and the wheel of a high-grade phosphor bronze, the pitch being as large as possible, consktent with the strength of the worm shaft. It is not here propoised to enter into questions relating to the

.-

FIQ.15.-Both thrust and journal loads are taken by tapered roller bearings. proportions, shape of tooth, etc., as such questions have previously been discussed before this Institution." The general practice as applied to worm driven vehicles is to mount the worm above the wheel in order to obtain a practically straight line drive from the gear-box. If the worm shaft is placed below the worm-wheel there is the double disadvantage of great angularity for the caxdan shaft, and low ground clearance. So far as lubrication is aoncerned, it does not matter for all practid

*! See Proc. I. A. E., Vol. VII., p. 215. WATSOS . M

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 178 THE INS'1'ITU'l'ION OF AUTOMOBILE ENGlNEERS. purposes whether the worm is plmed above or below its mating wheel. Figs: 12 to 15 show examples of worm mounting. The worm shaft is usually located by a double-thrust bearing at one end of the worm shaft, the idea being-to avoid overloading the thrust- bearings by reason of any expansion of the worm shaft when it. warms up to its work. The Daimler Company, it should be noted, use a double-thrust bearing at one end, in spite of the fact that a Lanohester type of worm gem is employed, as may be seen in Fig. 14. The arrangement shown in Fig. 15 employs Timken taper roller bearings, and it would appear that any undue heating of the worm might cause these bearing8 to wedge. It might be an improvement to reverse the bearings so that they would slacken instead of tighten by expansion of the shaft.

DIFFERENTIALGEARING. The type of differential gear employed is largely a matter of cost of production and oonvenienoe of design. In the spur-gear type it is not always possible to give the planetary pinions the necessary number of teeth of suitable size to avoid undercutting, unless the angle of pressure be made very much larger than the 20 degrees now most generally uwd for this class of gear. If that angle is exceeded the load on the pinion spindles leads to rapid wear. Another objection is that in this type there is double the amount of backlash present in the bevel type, due to the aggregate clearances between bearings and gear teeth, and this in time is liable to become serious. With the bevel type it is quite possible to allow a large pitch of tooth and an ample number of teeth in the pinions, oombined with a low angle of pressure. End-thrust is always present with the bevel type of gear, but it is not difficult to cope with it. Fig. 2 includes a differential gear which has given very satisfactory service on lqe numbers of four-ton vehicles. The wheels have each 28, and the four pinions 14, teeth in. circular pit&, liin. face width, and 20 degrees angle of pressure; these gears are made of Ubas or Sanderson's we- hardened steel, with the bearing surfaoes ground and polished. For vehicles up to 50cwt. capacity th6 same differential gear ha been used very suwssfully with two planetary pinions instead of four. For vehicles intended for loads of over four tom, the differential gear preferably should not be mounted on the find-

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COMMERCIAL VEHICLES. 179 drive axis, but amanged as in the double-redudion axle shown in Fig. 4. DRIVINGSHAFTS. Since the adoption of splined shafts, with broached gears and couplings, many old weak spots in axles hlave disappeared, but many new difficulties,chieflyin connection with the fit of the splinw,andthe necessary corrections due to distortion during heat-treatment, have taken their place. There is great need for a very close interchange of views on these points, and a paper on the subject would no doubt prove of considerable value, and be greatly appreciated by members. Much has been done since the reading of Mr. Larard's paper before this Institution.* Tha materials used for driving shafts vary oonsiderably, and often depend upon what can be obtained more than upon questions of peatest suitability. Shafts made of 3 per cent nickel-stwl have proved very satkfiactory in hard servicre with one maker who has the material heat-treated by the steel maker to give an ultimate tensfie strength of 54 tons and an elastic limit of 47 tons per sq. in., with an elongation of 25 per cent on 2in., and a BrineJl hardness test of 248. Thus treated before maahining the di5- culty in rqard to the warping of the splines has been o'crermme. The author does not favour making the axle shafts and driving flanges in one piece, aa shown in Fig. 9, because the flangw are liable to get bent by the camless handling which commercial vehicles usually receive in repair shops. If B flange becomes bent and is subsequently bolted up tightly to a wheel, the shaft is liable to be badly stressed, especially at the junction between the shaft and the flange, and many serious fractures have been caused in this way. AXLEBEARINGS. The use of ball or roller bearings on live axles has now become very general, exoept for the road wheels and differential bearings. For these tw~purposes theae appears to be ample justification for the retention of plain bearings; especially does this apply to road wheels, in the hubs of which floating bushes havse proved that they are much better suited to the rough usage of commercial service than any tried form of roller or ball bearing. A wheel with float- ing bushes is easily and quickly replaced in be event of tyre

* See Proc. I. A. E., Vol. V., p. 133. M2

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 180 THE IKSTITUTION OF AUTOMOBILE ENGINEERS. damage, and if properly made and fitted such a bush offers very little more friction than a ball-bearing hub of equal load capacity, except when starting from rest. Floating Bushes.-To ensure satisfactory results with floating buahes, it is necessary that certain conditions should prevail. In the first place both internal and external clearance should be greater than would be ,allowed for my ordinary bearing; ‘the W.D. Specification allows between 6 and 13’6 thousandths of an inch for both inside and outaide fits, the normal diamebers of the bush to which these limits refer being 3#in. and 4in. With too little d-ce the distribution of lubrication is uncertain. At least one maker of Subsidy Vhicles has been persuaded by transport officers to reduoe the clearance to not less than plus 0‘004in. ot more than plus 0’006in., in order to overoome the apparent play in the wheels when the axle is jacked up. So far, no ill effeat has resulted from the reduction, but it is doubtful whether so little olearance is dasinable, either from the point of view of lubrication or the easy removal of the wheels, and it would not surprise the author if the old allowance is again requested. The play to whioh objection was ’made is much more apparent than real. Another point that requires watching is the spacing of the dis- tribution holes in floating bushes; these are best drilled around the bush along a helioal line, and they should be so spaced as to caxry grease over every bit of the axle and hub surfaces. Then, again, the rubbing surfaces of both axle and hub should be cam- fully ground and polished if the beat results are to be obtained, and for this reason, unless thO hub of the wheel is a forging, or a very clebn and hesat treated mild steel casting, a steel liner should be forced into the hub under hydraulic pressure, the bore being subsequently ground. Good results have been obtained by reamering thwe lbem, but this method was only adopted beoause of the difficulty of getting rid of. the mehl particles left in the oil paemges after grinding. These reamered liners have given very satisfactory results, but they are not to be recommended in all cases on mount of the greater cost of production, due to the wear of the reamers. The author has not found it necessary to harden the wheel journals on an axle, provided that the resultant load, due to the imposed weight and the tractive resistanm, does not set up a greater prwure than 400 lb. per sq. in. between axle and floating bush. Such cases of excessive wear on the axles and the bushes

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COMMERCIAL VEHICLES. 181 which have come to his notioe have been due either to a much higher unit of pressure being allowed, to failure of lubriaation owing to the grease paseages being too small, or to the use of greases heavily loaded with nesinous matter. It might here be noted that the floating type of wheel betaring permits of far greater latitude in the quality of lubricant used than is the case with ball or roller bearings; with the latter it is highly important that the grease should not be a water-oarrier, whereas grease oontaining vegetable fats is by no means so injurious to a plain bearing. Plain Bearings for Differential Gear.-Some makers habitually omit to fit bronze or white-metal bushes between the differential wheels and the age, or between the pinions and their spindles. Suoh makers insist that there is no need to do so, and the author's experience leads him to agree with them so long as the contacting surfaces are hardened, ground and polished. Where this is im- practioable it is highly desirable that bushes should be provided, although the relatiye movement of the parts is admittedly small. The differential cage ihlf, m may be seen in several of the illustrations, is most frequently mounted upon ball or roller bear- ings housed in extensions from the top casing, but in two wes, namely the axles of the Subsidy Vehicles built by the Wolseley Com- pany and Messrs. Wrigley, plain bearings are fitted. The former favour fixed bronze shells lined with white metal, whilst thelatter make 'use of floating bushes. In each case these plain bushes have been adopted because, at the time the drawings were prepared, it vaa' not found practicable to fit any of the standard sizes of ball bear- ings specified in the War Office list, which goes to show the foolish policy of setting out arbitrary specifications at so early a stage in design that every requirement cannot be foreseen. The Specifica- tion left no loophole for designers; they had either to use one of the listed ball bearings or resort to plain bearings. After severe trials with the Wolseley axle, the Mechanical Transport Committee relaxed their view on this matter and gave permission to fit ball bearings of oonvenient size if desired, but it was then too late to make alterations except of a very costly nature. Furthermore, the results so far obtained with the plain bearings were such as to justify their continued use. Ball and Roller Journal Bearings.-In all cases it is advisable to select bearings of such sizes that the makers' recommended safe loads are not exceeded, and to base all odculations on the assump- tion that ball bearings can be used instead of those of the Hoffmann roller type, which are interchangeable with stock sizes of ball

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 182 THE INSTITUTION OF AUTOMOBILE ENGINEERS. bearings. The day my not be far distant when theimproved form of roller bearing may entirely displam ball bearings for journals, but until then it will be well to keep in mind the proba- bility of a ball bearing being fitted by a repairer in places where rollers were originally provided, and unless the contingency is provided for by the designers trouble may result. The arrange- ment of bearings shown in Fig. 4, although expensive, is far the best among the examples given, as in that axle all the journal loads are carried by ball or roller bearings except in the oase of the differential pinions. Tihe mthor does not here propose to deal with the relative merik of various makes and typea of ball bearings. The subject has been dealt with exhaustively in a previous paper before this Institu- tion.* He would, however, here like to express his conviction that it is not always necessary to nut up either the inner or outer race3 of a ball bearing so long a.9 the shafts lare ground to a suitable fit. Ball bearing makers always advocate suoh nutting up, but that is probably because of tihe liberal view th'ey take of limit sizes. The author also takes this opportunity of again expressing an old designer's grumble conaerning the small radius which beaxing makers grudgingly give their bearings, the amount of which can never be relied upon. Many a shaft is converted into a notched bar, and an otherwise excellent design spoiled, in order to accommodate a ball baaring with almost square edges. If roller bearings are fitted it is of course necessary to locate the outer race against sideways movement in both directions, a precaution which is not always neoessary or even desirable, with ball bearings. It is further advisable, with both ball and roller bearings, to fit side guard rings, or plates, to prevent small chipped piecea of prteeth getting into the raws, or allowing broken pieces of balls or rollem to fall out and get caught in the gear teeth. Thrust Bearings.-In no part of an axle should end thrust be left to take weof itself. Wherever possible a single- or double- thrust ball bearing should be fitted; if that is not possible, a floating washer of phosphor bronze should be provided, located between ground steel surfms, preferably, but not necessarily, hardened. C'ase-hardened thrust washers, particularly if used in conjunction with floating bushes in wheel hubs, have an unfortunate habit of cracking, with disastrous results. Very heavy side blows may be transmitted to the thrust washers when n wheel

* See Proc. I. A. E., Vol. VI., p. 195.

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COMMERCIAL VEHICLES. 183 strikes a kerb, and for that reason alom they should be made of ample dimensions, certainly not less than 5/16 in. thick. The W.D. Specification, in its application to thrust bearings, affords another instance of the folly of limiting the number of sizes and types before the actual requirements can possibly be known. That specifimtion allows only two sizes of double-thrust ball bearings, namely 2 in. and 22in. Hoffmann medium type; even the larger of the, if left to take the thrust on the worm shaft of a three-tonner, would not long survive the effort. Of course, worm drive was not oonsidered by the Committee when they drew up the specification, but even for the bevel gearing of other forms of axles a 2frin. medium double thrust is by no means large enough in every instance. The worm shaft shown in Fig. 12 has a No. 15 heavy-type double-thrust bearing on the worm spindle, and although in this axle, and many others where it is similarly loaded, it has given no trouble whatever, the load on the thrust bearing is far too much according to the makers' specified safe loads; these, presumably, are the safe continuous loads, which may be exceeded for dhort periods. American constructors are now making great use of Timken taper roller bearings, which are designed to allow of adjustment. me author has bad no personal experience of such bearings, and has been unable to obtain any independent information aoneerning them. It is hoped that any member who aan speak from personal experience extending over not less than two years without replace- ments, will not fail to give his views on this matter.

LATERALADJUSTMENTS. No matter how carefully each part of an axle may be machined, some form of end-wise adjustment will b'e found necessary when an axle is being erected. This arises chiefly from the fact that all dimensions must be taken from the pitch line of the bevel, or worm, gears. A draughtsman can work to this line without diffi- culty because it (3an be shown on his drawihgs, but as it does not exist upon the finished gears the men in the assembling shop axe not so favourably plmed. Many forms of adjustment have been mggested from time to time, but the author is of the opinion that there is but one praetioal form; that is, the plain mild steel washer of suitable thickness. Such washers may be stocked in about half- a-dozen sizes, so far @ thickness is concerned, the assembler making a suitable w1,ection after ascertaining by mmns of feeler gauges

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 184 THE INS'I'ITUTIOPI' Olr AU'I'OMOBILE ENGINEERS. which thickness is required. An alternative is to stock the washers of full thickness and thin them down by grinding to the desired dimension, the washer meanwhile being held on a magnetic face- plate or chuck. All forms of screw adjustment, whilst perfectly effective and sound in the hands of a skilled mechanic if properly locked, are liable to abuse by inquisitive drivers and inexpert repairers, with the result that gears are often left too shkor LOO deeply in mesh- neither condition being oonducive to silent and efficient worlcing,'or long life for the gears and shafts. Once an adjustment has been correctly made there is no need for further tinkering, as it is im- possible in this way to oompensate for weear of the gem teeth. Another objection to the screwed form of adjustment lies in the fact that it is so very elasy to put a permanent load of a ton or more on the balls, quite apmt from the working load, without being able to detect any tightnass. The author prefers the positive form of adjustment shown at A in Fig. 12, the washers being ground to a thickness which will allow a 1%thousandths feeleT to be inserted between the thrust washer and the packing washer; a two-thousandths feeler should not go in. Fig. 13 shows another positive, but not equally convenient, method of adjustment by grinding. the sleeve B being the grinding portion instead of a washer.

THE TIE BAROR TRUSS. The author has a rooted objection to the use of tie bars on any structure which is subjected to great variations of load, and that objection is particularly strong in relation to axle tie bars. A tie bar is a source of weakness in a commercial vehicle axle, for the simple reason that it oannot be adjusted to bahnce the bending moment set up in the axle by the imposed load at more than one point. The resulting bending-moment diagram of an axle, due to a tie bar anchored at its two ends and bearing under the centre of the axle, is represented by a triangle, whereas that due to the imposed load on the bearing springs is represented by a trapezoid. The forces are opposite, but not equal in value; hence, the careless adjustment of a tie bar, so as to take qll sag out of the ,ale when the vehicle is under full load, may lead to excessive bend- ing stresses in the axle casing in the opposite direotion when the load is removed. It is only necessary to picture a vehicle travel- ling over a very bumpy road, when the axle may momentarily be

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES PO& COMMEKCIAJ, VEHICLES. 185

relieved of the imposed load, to realise what may happen; the casing may be dangerously stressed in a reverse direction by the tension of the tie rod, or, when the l'oad again rwts on the ale, the tie rod itself may suffer as a result of the suddenly-increased tension. Generally, and as the present conditions in France have shown, it is the tie rod that gives out first, but injury to the ade frequently follows. An axle should be so designed and made that its strength jS sufficient without the doubtful and extraneous aid of a tie rod; that this can be done has been demonstrated by several makers of repute. Considerations of weight, how'ever, as in the case of a London omnibus, more or less foroe the designer to the use of tie bars, but vehiclm with such axles a'e by no means suitable for country or provincial service, where road surfaces ma% not be so good as in London, unless they carry greatly reduced loads and axe run at lower speeds.

TORQUEAND THRUST. The neoessity for some means of transmitting the tractive effort from the axle to the main chassis: frame, and for msisting the reaction of the gear drive upon thle axle body, or wing, is obvious. There is, however, great diversity of opinion as to the best meam of attaining the+se results. Some of the tried methods are as follows :- (1) A combined torque and thrust member of tubular section, enclosing the cardm shaft, and anchored at its iiorward end by means of a suitable forked, or ball and socket, connection to one of the cross members. (Fig. 17). (2) A torque member.of tubular section as above, the traotive effort being taken through the top leaves of the beaxing springs. (3) A combined triangular torque and thrust member forming the two side of m isosoeles triangle, the apex of which terminates in a ball that is socketed in a cross member. (Figs. 6 and 26.) (4) Two separate thrust, or radius, rods parallel with the frame, leaving the torque to be taken through the springs. (Fig. 29.) (5) One or two parallel torque bars, leaving the thrust to be taken by .the springs. (Fig. 2.) (6) Both torque and thrust taken by the springs. (7) Both torque and thrust taken through two perch bars, or radius rods, which also oarry a differential countershaft whence tihe road wheels are driven through pinions and racks, as on the

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 186 THE INSTITUTION OF AUTOMOBILE ENGINEERS.

Milnes-Daimler and Bema chassis; theee, however, are not strictly live ales. (8) Variants of methods 1, 2, 3, 5, and 7, in some of which the braking effort is taken by the springs, and others in which the braking effort is resisted by the axle owing and torque bars. It (38n. be argued as an objection to methods Nos. 1 and 2 that they permit of only one unhersal joint flor the cardan shaft, unless the one fitted at the mar end be left most ~naccessible. Further, the whole tractive effort, or thrust, being taken at the oentre of the axle in a more or less horizontal plane, imposes stresses on the axle which may be avoimded by the use of other methods. On

i FIG.16.-The Torque and Thrust Member on Dennis Three-tonner.

the other hand, these mangements give a clean and simple appear- moe to a chmis, and it is doubtful whether the two foregoing objections are really S~F~QUS,within oertain limits-say, up to the capacity of a Subsidy type of chassis. The first system is used by Dennis Bros. (Fig. IS), Karrier Cars (Fig. 17), Leyland Motors, and Thornycroft, among others, whilst method No. 2 is employed in the Wells chassis. A modification of the first system is fitted to the Pagefield Subsidy Vehicle, which, in the author's opinion, is an improvement on the tubular member, although it is not so neat in appearance. This, as shown in the middle view of Fig. 4, consists of an open cast member which permits of two accessible universal joints being fitted to the cardan shaft.

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COMMERCIAL VEHICLES. 187

The triangular member of system No. 3 is probably the best arrangement which can be fitted, at any rate for loads of three tons and upwards, as it leaves the joints mssible and the axle takeis the thrust load near the spring seats, thus minimising the

Cf

!A FIG.17.-Torque and Thrust Member, with ball-socket cross member, as fitted on the Karrier Subsidy Wagon. bending moment on the axle or casing. Wrigley’s axle (Figs. 6 land 26) is one of this type, and, to a lesser extent, so also is the Wolseley (Fig. 18). A further advantage of this form of construotion is that the torque and thrust member can be disposed so as to take

FIG.18.-The Wolseley Axle, showing inclination of banjo forging. the thrust in a practidly horizontal direction from the axis aP the road wheels, instead of obliqnely, or in a line above the axis of the wheels, as in the first system. The system most favoured by the author is No. 5 (Fig. 2), his

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 188 THE 1NSTITI!'L'LON OF AUTOMOBILE ENGINEERS.

reasons for this preperenoe being that it is simple and practical, and ensureis a minimum bending moment on the axle; further, it does not ask too much of the springs. The latter only take the thrust in addition to the usual imposed load, and the twisting effort due to the two wheels passing mer uneven ground; this they me well able to do if properly proportioned and if the top plate be made of extra thickness, with all the plates properly located to prevent lateral movemlent. The bar, or bars, can &o be arranged to relieve the springs of braking loads by mring the brake anchorage braicket to the axle fosing. The author has found this arrangement very satisfadory for passenger vehicle work, a8 it tends to reduoed vibration, whilst the upward kick to the frame, resulting horn the starting or mbrating effort each time the clutch is engaged, may be reduced to a negligible amount if the torque bars are anchored at a point about 4 ft. forward of the axle centre, as shown in Fig. 2. The author dom not favour the use of spring cushioning for the forward end of the torqw bars, as such springs invariably break, or cbse up, and leave an objec- tionabb amount of backlash. No. 4 method strikes the author as a clumsy and costly one, becauBe unless provision be made for movement in every possible direction the radius rods will be subjected to torsional stresses. Another objection to this method is that when one wheel strikes a road obstruction the radius rod on that side is called upon to take an exceptional load in a reverse direction, tending to produoe backlaah in the connections. System No. 6 is certainly the simplest of all, and flor a vehicle that is primarily intended for use on roads with good surface, and for moderate load variations over the back axl,e, as on a London omnibus, it may be recommended on the score of cheapness and light weight. It is, however, nlot very mitable for rough roads and big load variations, as on s goods lorry.

BRAKES. The practice of fitting both sets of brakes on the back axle, acting directly within drums fitted to the road wheels, has found may advocates sinoe this arrangement was adopted for London motor- bus service. There appears to be no objection to the system pro- vided the general design of thle complete vehicle will permit of the extra width which the two brakes should occupy when arranged

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COMMERCTAL VEHICLES. 189 side by side. It is not always possible so to arrange them without increasing the distance from the centre of the wheel trdto the centre of 'the spring seating, which involves an increased bending moment on the axle tubes, or forging, because so much depends upon the design of the road wheel. If, however, C-M. (Claxkson), or a similar type of wheels be used, which do not need so large a spoke width as is the case for cast-stoel wheels with cruciforin

FIU.lg.-Straker-Squire arrangement of twin brakes on the Road Wheels. spokes, it is possible to accommodate a pair of brake drums of wsidezable width, side by side, without greatly exceeding the distance between centres of tread and spring. These centres should allow from 1+ in. to 2 in. clearance between wheel and spring to allow of the fitting of anti-skid chains or cross bars to enable a vehicle to travel over snow-bound roads. When arranged side by side it is possible to make the brake shoes, liners and springs interchangeable, a condition which cannot

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 190 THE INSTITUTION OF AUTOMOBILE ENGINEERS. be fuElled if the drums are concentric, the inner one being of the expanding, and the outer one of the contracting, type. Concen- trically arrqed, the two sets of brakes can be made more compact, but it is doubtful if they are so effective for hilly roads on account of the difficulty of cooling the inner drums. The author does not agree with the use of two sets of brake shoes acting side by side in a single dnun, as shown in Fig. 19. Such an arrange- ment does not permit of the effective alternate we of the two sets of shoes when travelling down a long gradient, aa the drum never gets a chance to cool, and there is oonsiderable risk of firing. The axrangement shown in Fig. 20 is even wowe in this respect; this view shows an American idea of an economia

1 FIG.20.-Economizing space ; an American design. arrangement which comprises two pairs of brake shoes, each shoe bearing for less than 90 degrees of the circumference and so arranged that all four show contact within one drum of practi- cally the same width as ahshoe. The author does not agree that it is either economical or practical. For public service work, which involves many stops, or for use on good roads with no very steep gradients, it is probably pre- ferable to mount both sets of brakes on the back axle, at any rate for vehicles up to three tons load capacity. None of the braking load is imposed on the driving shafts or universal joints with this arrangement, and it has much to recommend it on the score of interchangeability of parts, if the design be carried out with that idea in view. For vehicles exceeding three tons load capacity it

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COMMERCIAL VEHICLES. 191 is not easy to provide enough braking surface without increasing the width of axle beyond the legal limit; further, the weight of the axle would become prohibitive. For these reasons the fitting of one brake on a geax shaft and the other set on the wle is probably the correct solution. With regard to the diameters and widths of brake drums, makers appear to study convenience of design far more than actual re- quirements. For vehicles exceeding six tons back axle weight, which may not legally run at more than eight miles an hour, the drums should not be less than 21 in. in diameter, with a 3 in. faae, whilst for a vehicle just under the six-ton limit drums about 18 in. in diameter, with a 2frin. fme, have proved quite satisfactory.

FIQ.21 .-Brake-actuating mechanism with positive release.

Large diameter drums, on fast-moving vehicles, appear to have a tendency to fire, especially if they are completely enclosed. The type of actuating mechanism doeis not seem to have much influence on the braking effect, and a simple but properly designed cam has been shown to be just as effective as a more elaborate system of toggle levers or links. Figs. 21, 22, and 23 show three very practical methods, two of them being entirely dependent on springs for releasing the brakes, the other having a positive release. In Fig. 23 the cam is made very long, and has well curved bearing surfaces, consequently it is not so prone to bind, or jam, as the shorter cam shown in Fig. 22. The shoes of this brake, it should be noted, are designed to allow of the maximum wear being got out of them before they are scrapped,

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 192 THE INBI'ITUTION OF AUTOMOHI1.E ENGINEERS. which procedure, in the author's view, is to be preferred to lined brakes except where users employ a skilled man for repairs. The average garage fitter usually makes 4 mess of fitting liners, and is not always particular about using copper rivets, with the result that brake drums are sometimes ruined. Cast-iron shoes do not need much machining, and can often be replaced more cheaply than liners, especially if the fitter's time be taken into account. If unlined cast-iron shoes be used, there is no need to provide hmdened faces where the cams bear. The brake-cam spindle should always be well supported, and in this respect the Straker mrangement of twin brakes (Fig. 19) shows that the matter has received careful consideration.

PIG.22.-A simple cam-operated brake with renewable shoes.

The lubrication of cam spindles is often badly neglected by drivers, sometimes for the reason that makers fit such puny greasers that they are easily broken off and are rarely replaced. Designers should pay more attention than in the past to this point. Dennis Bros. have kept this matter in view to a certain extent in their Subsidy Vehicle axle by leading oil which leaks from the wheel bearings on to the cam spindle, as shown in Fig. 10. The other short bearings on these spindles, however, are not so well provided. Before passing from the last-named illustration atten- tion might be drawn to the fact that the oil-catching ring is cast integral with the brake anchorage bracket, instead of forming part o€ the wheel hub, from which it could qot escape until the channel is full to overflowing.

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COMMERCIAL VEHICLES. 193

L'UBRICATION The axle is one ,of the parts which n,ever receives attention in the way of lubrication at the hands of some drivers, to which may be added the springs. Men will tinker about for hours with an engine in the endeavour to obtain greater pulling power, whereas the engine most likely is not in the least at fault. Bent axle casings due to slack tie rods, nearly dry bearings, binding brakes, etc., are frequent causes of the failure of a vehicle to take its full load up a given gradient on the usual gear. The general design of an axle allows of sufficient oil being carried to keep the gears and centre bearings well lubricated for about 1,000 miles of running, but slack joints and badly faced covers may often

Pig. 23.--I)ennis Bros.' latest brake shoes, designed for cheapness of renewal. allow of enough leakage to necessitate more frequent renewals of BUPPlY. Many makers go to a lot of trouble to prevent the oil passing from the central casing to the wheel bearings, and rely entirely upon grease lubrication for those parts. This may have been a necessary precaution with old forms of axles, but it has been the experience of many makers that better results can be obtained Ky allowing leakage to occur, provided that steps are taken to catch such leakage and drain it away from the brakes and wheels as shown in Figs. 2 and 10. This may not appear to be an economical method, but it must be admitted that a little waste oil costs less than a pair of new wheel bushes, not to mention the WATSON. x

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 194 THE INSTITUTION OF AUTOMOBILE ENGINEERS. possible loss of service and inconvenience to the user in the cwe of a wheel seizure when the vehicle is miles away from home. There appears to be no reason why leaking oil should not be led to other working parts, such as brake cams, etc., and thus dispense with a number of small greasers. An axle is more likely to receive proper attention in the way of lubrication if it gives the driver no more trouble than putting an occasional pint or so of oil into the central casing. Where it is not desirable to allow leakage in this manner, substantial independent lubricators should be fitted on the wheels. This is, at best, a poor method, and the caps are in constant danger of being knocked off by contact with passing vehicles or road obstructions, or by working loose as a result of centrifugal force, and once a cap is lost a driver rarely thinks of fitting a new one until a seized bearing draws his attention to the lack of lubrica- tion. If lubricators are fitted, they should be kept filled with a very thin grease, which is the next best lubricant to heavy gear oil for the purpose. The author, however, prefers to allow of the free passage of oil from the central case to the wheel journals, as shown in Fig. 2. He has also found it to be good practice to mill a broad flat on the top side of the wheel journals, when plain or floating bushes are fitted, as this flat greatly facilibates the distri- bution of lubricant over the whole length of the bearing. Substantial greasers, fitted in convenient but safe positions, should be provided for all other working parts, such as brake cams, etc. All passages to these bearings should be as large &s possible and free from sharp turns, as in cold weather grease is liable to congeal into such a solid mass that it is impossible to force it along the passages. Greasers, too, should have screwed necks not less than half an inch in diameter, otherwise they are easily broken off. All thrust washers should be provided with distribution paths, preferably in the form of eccentric grooves with the throw of the eccentrics on the two sides arranged dia- metrically opposite, otherwise the washer will be so weakened that it may split along the groove. Gross, or radial, grooves are a source of danger because they invariably lead to breaktage of. the washer.

REPRESENTATIVEMAKERS OF AXLES. There is no question, in the author’s mind, but that the best of the double-reduction axles here dealt with is that built by Walker

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COMMERCIAL VEHICLES. 195

Bros., of Wigan, and fitted to their Pagefield chassis. This is shown in Fig. 4. Admittedly it is a more expensive form than some of the others shown, but it must be borne in mind thait it was designed with a view to being used on vehicles carrying useful loads of five tons, and yet its weight' does not greatly exceed that of other Subsidy Vehicle axlee. For non-Subsidy Vehicles carrying a total load not exceeding 33 tons, this maker also builds a lighter form of axle, with a forging of the double-banjo type arranged horizontally, but the same' arrangement of gearing, first through a pair of bevels and finally through two pairs of spur gears, is incorporated. The Wrigley Subsidy Vehicle axle is one of the double-reduction class, the first reduction being obtained by a pair of bevel gems,

FIG.24.-Wrigley's Concentric Brakes. and the final reduction by a single pair of spur gears. The first reduction shaft is mounted on Hoffmann roller bearings, and is provided with ball thrust bearings. The final reduction gears and the road wheels are mounted on floating bronze bushes, the latter being in accordance with the War Department Subsidy Specifica- tion. The structure of the axle is formed by a double-banjo steel member, which carries the gear casings and brake anchorage, the road-bearing portion of the axle being renewable. Each piece can be lifted by one man. The standard total gear ratio is 8.4 : 1, but other reductions mn be accommodated; tbe makers have already tried out gears having ratios of 7'77: 1, 7.19 : 1, and 6'68 : 1. The standard track is 66 in., measured from centre to centre of the road wheels. This axle, it must be remembered, is N2

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 196 THE INSTITUTION OF AUTOMOBILE ENGINEERS.

a proprietary unit, and for that reason it is designed to allow of variation in the spring centres from 44 in. to 46 in., if springs 3in. wide axe used, but with 4in. springs the centres are fixed at 45 in. It is suitable for a solid rubber tyred wanmeroo'd vehicle of 74 tons gross load, of which not more than two-thirds is taken on the rear tyres. The gearing and shafts are calculated to take the torque of an engine giving 40 b.h.p. at 1,000 revs. per minute, provided that no lower ratio than 5-2 : 1 is used on the first speed in the gearbox. The method of fixing the renewable ends of the axle body is as follows. The ends of the double-banjo forgings are splined, a8 may be seen by Fig, 6. The brake anchorage casting is then forced on to the centre forging under considerable pressure by hydraulic power and further secured by tapered screws. The renewable ends axe then forced into the double-banjo axm, md bolted up to the brake anchorage; the internal portion of the journal ends has a tendency to swell out the double-banjo arms and make still tighter the fit of the brake anchorage castings on the castellations of the banjo forgkg. The brake anchorage also carries the oonnectiom for the torque triangle, thus transmitting the drive to the frame as near as possible to the point of power application to the road. The Woheley Subsidy Vehicle axle, shown in Figs. 5 and 18, like that built by Meesrs. Wrigley, has renewable ends, but in this cam the ends are not a foroed fit in the ends of the main axle forging, and mmequently they may more easily be removed for replacement den necawary. Further, the connection by bolts and flanged faces makes a more atisfactory job than is presented by a forced fit and tapered screws. The bed of the Karrieir rear ,axle (we Figs. 11 apd 17) is a double- banjo forging of high tensile steel, and carries the whole of the imposed load. The reduction gear consists of one pair of beveJ and one pair of spur gears. The cardan shaft drives the bevel pinion and transmits power to the crown wheel mounted on a short cross-shaft which also carries a broad spur pinion; this pi.nion gears into a spur ring surmunding the differential cage. The top casing of the axle carrias the bearings for the differential cage, and also forms one-half of the housing for the cross-shaft bearings, the other half of the housing forming a separate cover. This cover can easily be disconnected for examination of the gearing, or removal of the cross-shaft and bevel pinion, and by

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COMMERCIAL VEHICLES. 197

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 198 THE INBTITUTION OF AUTOMOBILE ENGINEERS. withdrawing the axle shafts the entire top casing can be lifted off, carrying with it the whole of the final-drive geaxing iand differential. Alternatively, the spur wheel and differential can be dropped by removing the bottom casing and undoing the four cap bolts which hold it in position, either of the operations being performed without jacking up the vehicle or removing the road wheels. The bottom casing of the axle is simply an oil well, and is not subjected to either driving or loading strains. Power is transmitted from the differential to the road wheels through axle shafts with splined ends, the outer extremities of which are fitted with ‘‘ dogged ” axle caps engaging in corresponding slots on the rear road wheels. These axle shafts are subjected to driving strains only. Another axle of unusual design is that shown in Fig. 25, and fitted to the Burford two-ton chassis. In this axle the load carrier is a solid forging having a comparatively small circular enlarge- ment in the centre, through which the bevel pinion housing of the driving gear case protrudes forwards. The driving gear case is thus relieved of all load-bearing stresses excepting those due to the drive. Spur pinions on the outer ends of the differential shafts transmit the final drive to internally-toothed racks on the road wheels. These spur gears, together with the wheel brake mechanism, are completely enclosed. The footbrake drum is mounted at the forward end of the bevel pinion shaft, the cast shoes being anchored to members projecting from the axle forging.

CONCLUSION. In conclusion, the author wishes to acknowledge his indebted- ness to the various manufacturers who have assisted him by supplying blue prints, photographs, etc., as well as supplying information of considerable value. He particularly appreciates the help given by Mr. A. A. Remington (and the Wolseley Corn- pany), to Mr. F. W. Wmllarcl, of Mwrs. E. G. Wrigley & Co., and to Mr. W. D. Willimon, of Messrs. Walker Bros.

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COXMERCIAL VEHICLES. 199

APPENDIX.

ACCORDINGto the regulations governing the use and construction of motor vehicles, every motor vehicle must be fitted with two independent brakes in good working order, and of such efficiency that the application of either shall cause two wheels on the same axle to be effectually prevented from revolving. If this is to be taken literally, then the total frictional force applied tco any set of brake drums, multiplied by the diameter of the drum, must be equal in value to the resistance of the tyres to skidding multiplied by the diameter of the wheels on which the drums act. It is not practicable to meet this condition to the letter under all circumstances with any ordinary form of brake which is directly applied to the road wheels. To do so, hydraulically-operated brakes must be resorted to, a system of levers of such gear ratio as to make it objectionable be introduoed, or a brake lining material be found which possesses a coefficient of friction of about 1.0. Brakes applied to gear shafts running at from four to eight times the speed of the road wheels can be designed to meet the conditions, but their regular use does not conduce to long life of the transmission parts. Any well-designed wheel brake of suitable proportions will effectually prevent the road wheels from rotating under normal conditions. In practice, the work which is expected of a brake is to offer su6cient retarding force to the rotation of the road wheels to bring the vehicle to rest within a reasonably short distance under the most difficult conditions. In this Appendix it is only pro- posed to deal with brakes which are applied directly to the road wheels, but the same methods also apply to gear shaft brakes, with the single difference that the gear ratio between the gear shaft and the road wheels should be taken into account. The author knows of no puljlished data upon the subject, but the following shows the methods of treatment he ha;r evolved and has long used with success.

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 200 THE 1NS’III UTlOS OF AUTOMOBILE ENGINEERS.

Fig. 30 shows, in diagrammatic form, the method of ascertaining the braking pressure on each of a pair of cam-operated brake shoes. This method, whilst not strictly correct except for shoes which bear against the drum at exactly diametrically opposite points, gives sufficiently accurate results for all practical purposes. Referring to the diagram, it will be seen that the pressure on the two shoes of an ordinary cam-operated brake is unequal, whereas in a brake such as that shown in Fig. 21, each shoe acts equally upon the drum.

FIG.10.-Diagrammatic Arrangement of Brake Shoes.

Taking the two forces in the cam-operated brake.as PI and P,

BpR x A x B2 and Pz = axC and the total braking force for the two drums = p =.f(P1 + P2) x 2 where p, R and f are as given in the accompanying Table.

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LlVE AXLES FOR COMMERCIAL VEHICLES. 20 1

The kinetic energy of a moving vehicle is represented by E=-w vz 29 where the weight must be taken in lb., and the velocity in feet per second. As the speed in miles per hour may be converted into feet par second by multiplying by the constant 1'4666, we can simplify the above formula as follows:- W X 2240 X 1.4666 8' = 75 E= s2 2 x 32.2 which is near enough for all practical purposes. The brakes, therefore, must be designed to absorb the energy represented by E, and their effectiveness may be expressed as followl3 :- 75 W x Sz x D For a level road, L ~ Pd 75WxS2xD For an upward gradient, L = Pd + W Sine? 75WxS2xD and for IL downward gradient, L = --___~~-- Pd - W Sine6 Sine 8,however, in this case may more conveniently be expressed as -2240, and the equation for downward gradient therefore assumes 0 the following form:- 75W x x D L= Sz Pd - w ("") GI Let us take, for example, the case of a vehicle under the following conditions :- w = 8 tons w = 5 tons S = 15 m.p.h. R =1O p = 45 lb. A = 10 in. a = 1 in. B, = 17.5 in. B, = 15.5 in. C = 8.25 in. D = 40 in. d = 21 in.

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 202 THE INSTITUTlON OF AUTOMOBILE ENGINEERS.

Then pR = 450 lb. and the total load on all the cam faces = pRA =4500 lb. One half of this form is applied to the two forward shoes (PI), and one half applied to the other shoes (Pz). 2250 x 17.5 Then €'I = = 4772 lb. 8.25 2250 x 15.5 and P2 = = 4227 lb. 8.25 and total pressure = 8999 lb. When using a brake lining having a coefficient of friction of 0'3, the value of P = 8999 x 0.3 =say, 2700 lb. Utilising this value for P to find the distance required to bring the vehicle to rest on a level road, if running at 15 m.p.h. at the instant the brakes are applied- and similarly, on a downward gradient of 1 in 10,

If the above distances are considered excessive under the con- ditions named, we can improve upon them in one or more of the following ways:- (1) By increasing the value of R. (2) By increasing the value of A. (3) By decreasing the value of a. (4) By decreasing the value of (3 whilst keeping the values of B1 and B, the same. (5) By increasing the value of d. (6) By using a brake lining having a greater coefficient of friction. The foregoing example relates to an actual vehicle of the War- Office Subsidy type, which has proved to be perfectly safe with regard to its brakes even under the most difficult conditions ever likely to be met. The brake shoes on this vehicle are 3in. wide, and each shoe makes contact for approximately a quarter of the circumference of the drum. The value of E for this vehicle under the conditions named is:- E = 75 X 8 X 15 X 15 = 135,000 ft. Ib.

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COMMERCIAL VEHICLES. 203 and as the shoes present a total of 198 sq. in. of wearing surface, the “ intensity ” of energy absorption = 135000 198 = (nearly) 700 ft. lb. per sq. in. of surface in contact. Experience with colliery winding drums has shown that if there are rewon- able facilities for dissipating the heat, a drum can safely absorb 10,000 ft. Ib. of energy per sq. in. of shoe in contact. The low rate of 700 ft. Ib. per sq. in., therefore, shows that the brakes on the vehicle in question are well within safe limits, even allowing, for the masking effect of the road wheels and wings, which to a large extent hinder the free dissipation of heat from t,he drums to the air. The foregoing calculations refer to the loads and braking sur- faces. The proportions and sizes of the link pins, etc., may eeaisily be calculated, from the data given. The diagram (Fig. 30) shows only a simple forin of expanding brake, but a similar method of treatment may be employed in getting out the propor- tions of most known modifications of the expanding principle. It should be noted, however, that unless the anchor pins are at least as long as the width of the shoe, which width should be not lw than one-seventh the diameter of the drum, slackness will soon develop, and the brakes will become noisy. Chattering may be avoided by keeping the distance (a) small, so as to equalise, as much as possible, the total braking pressures upon the two shoes, and by fitting very strong springs to hold the ghoes out of engagement with the drum. These springs need tb be very much stronger than is generally supposed; service in France has shown that they must be at least twice as strong as usually fitted by well-known makers. W = total weight of vehicle (in tons). w = total weight on driving wheel tyres (in tons). S = velocity in miles an hour. V = velocity in feet per second = 1.4666 8. S. v.

5 10 14.70 22.05 20*’ 1 29.40

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 204 THE INSTITUTION OF AUTOMOBILE ENGINEERS.

D = diameter of driving wheel tyres (in inches). d = diameter of brake drum (in inches). F = coefficient of adhesion between smooth rubber tyre and road taken at (0.4 W) 896 lb. ton. (Wimperis, on page 297, Proceedings I.A.E., 1913-14, gives this as 700 Ib. per ton, but the author prefers to take the higher figure.) f = coefficient of friction of brake surfaces :- Cast iron on cast steel = 0.20 Steel on steel = 0.18 Bronze on steel = 0.16 Cork inserts on steel = 0.35 Compressed fabric on steel = 0.30-0.40. E = kinetic energy of moving vehicle (in ft. lb.). g = 32.2. P = total frictional braking force (in lb.). p = force applied at pedal or hand lever :- For pedal = 75 Ib. For hand lever (push on) = 45 lb. For hand lever (pull on) = 60 lb. R = total ratio of leverage between pedal or hand lever and cam lever. L = distance required to stop vehicle with wheels locked (in feet). 8 = inclination of road surface in degrees. Q = gradient expressed as 1 in x ; thus, for 1 in 30, Q = 30.

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COMMERCIAL VEHICLES. 205

THE DISCUSSION. Colonel R. E. CROMPTON,in opening the discussion, said: I accept the author's facts as indisputable, but I take leave to challenge some of his opinions; he says, for instance, that we know little of the effect of unsprung weight on the roads. In January of this year, a very interesting paper on the heavier claw of electric locomotives was read before the Institution of Civil Engineers by Mr. Carter, in which the author called atten- tion to various methods of construction, some of which involved p0at unsprung weight; in the course of the 'discussion, Mr. Aspinall, of the Lancashire and Yorkshire Railway, pointed out the terrible effecte of this very point on the rails, their joints and all parts of the railway track which suffer from impact. It is also stated in the paper that I have said th& it is speed which counts most in this respect; I think this is a case where some of my remarks are quoted apart from the context, which quite alters my meaning. What I have said, and still maintain, is that the damage to roads known as deformation, generally wave-like in form, is always due to impact, and that in the past and even to-day the excessive impact has been generally due to vehicles being driven at much higher speeds than was in- tended or is allowed, and not so much to their excessive weight. I think, therefore, that when we are comparing designs for live axlee, we ought to give the fullest consideration to those such as Burford's and others, which reduce this unsprung weight. I think the author deals too easily with the question of the leakage of lubricating oil; such leakage as he mentions may be a meam by which the driver can feel confident that sufficient lubrication gets to certain points, but if it involves pools of oil or grease on the roadway whenever the vehicle is at rest I am strongly against this practice, as the damage caused, not only to the more expensive forms of roads but to all vehicles which have rubber tyres, is far greater than the author appears to appreciate. The practice of the London General Omnibus Co. of providing catch-trays which are only emptied at the garages is an excellent one, and obviates the diffioulty in sucrh an ewy manner that I

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 206 THE INSTITUTION OF AUTOMOBILE ENGINEERS. (Cal. R. E. Grompton.) wonder their example is not followed by the majority of con- structors. Mr. W. D. WILLIAMSON:The question of the effect of unsprung weight is one which I have always had in mind, and I have attmked it from the point of view of tyre wear and its influence on running cost. I was at one time interested in chain driven vehiclm exclusively, and I though+ that if I coultd get the tyre makers to tell me that live ,axle vehiclw were heavier on tyres than chain driven vehicles I shoultd have a very good selling point. I made enquiriels, but the replies indicated on the contrary that some of the ohain driven vehicles were notoriously heavy on tyres. In those days, too, no tyre manufacturer would make any difference in price between live axle and chain driven vehicles of equal capacity when quoting for tyres on a mileage basis. Theae points rather go to prove that unsprung weight is not quite as injurious m Colonel Crompton would have us believe. Given perfect roads,

FXQ.31. it is difficult to see that any harm would result from having alz weight unsptung. I agree very strongly with the author with regard to the advis- ability of having a good long radius where the tubular extensions join the banjo. In certain axles with which I had to deal, the central portion of the axle was lightened very much, by putting the joint bolts inside the banjo instead of drilling the holes through the axle (Fig. 31). Tests were made with the axle, and it was found that as long as the radii from the tubular part: to the banjo were long, it was quite safe to make this latter portion very light indeed. Bearing on the same point, it is extremely important that the tubular portion of built up axles should extend well to the centre of the axle and get a good hold on the central portion of it, so as to take the load from the flanges where the tubes bolt up to the cmting.

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COMMERCIAL VEHICLES. 207

Referring to axle materials, I think that oil-hardening steels for reax axle gears, particularly for those of the double reduction type, certainly result in a more silent axle than when case- hardening steel is used. On page 185 the author &musses the best method of making the necessary provision for thrust and torque. Certainly the cheapest and neatest arrangement is to take both through the springs. The trouble is, that when the vehicle is empty, and there is therefore Little load on the springs, the rear universal joint geb an excessive upward jerk when the drive is applied. This is caused by the torque, and the author is right in Fig. 2, where he takes the thrust through the springs, and the torque

CB FIG.32. through a special member. As drawn, however, this member does not make allowance for the movement which takes place when one of the wheels rises higher than the other in going over an obstruction on the road. There is a joint at the top of the link which may appear .to allow for this movement, but the motion that takes place must twist the whole of the torque member and endeavour to turn the small pin at the b'ottom about its length. Another advantage in taking the thrust and torque through the springs is shown in Fig. 32. With the frame and axle in position for light load, a vertical line from the centre of the axle meets the ground at the point B. When the vehicle is working, the torque member may be assumed to be constantly moving between the position shown in the sketch and the horizontal, due to the

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 208 THE INSTITUTION OF A~JTOMOBILEENGINEERS. (Mr. W. D. Williamson.) load and the uneven nature of the road. When horizontal the point of contact is C, and the relative displacement between wheel and road is the angle A. In the “Horseless Age,” in 1909, figures were given of experiments made as follows. A pointer was attaohed to the shaft, and readings were taken for four different arrangements. With the torque tube hinged to the cross member, as in the sketch, the movement of the pointer was 54 degrees- obviously, the movement of the pointer is multiplied by the gear- ing. In the case of a triangular torque tube, spring supported from the frame, and separate radius rods, the movement ww 31 degrees. Taking thrust and torque through the springs only it was 5 degrees, while with a parallel motion connecting axle to frame, the movement was 1 degree. Taking thrust and torque through the springs, there is only 5 degrees of movement, and the expense of a complicated link arrangement to get the parallel motion only improves matters from 5 degrees to 1 degree. One important point not mentioned by the author is the diffe- rential lock. When the differential proper is locked, the whole of the driving load may be taken through one road wheel and one side of the differential, and thus the differential gears are loaded up to possibly double what they are intended to carry. Fig. 33 shows a differential lock which overcomes this difficulty for a double reduction axle on the Pagefield principle. In this two gems are keyed on a shaft and arranged to slide into mesh with laxge spurs for the lock. The advantage of this arrange- ment is that half the load through the differential and the spur drive must go in the ordinary way, and half through the other side of the spur -drive to the locking pinion aid along the locking pinion shaft to the large spur. The differential ia therefore relieved of anything more than the normal load which it was intended to carry, the left-hand side in Fig. 33 alone driving. A reasonable method of dealing with the question of running clearance on floating bushes would be to allow the minimum, say 4 to 6 one-thousandths, inside the bush, and the maximum, 10 to 12 one-thousandths, outside; the expansion of the bush, due to heat or rolling out under load, would then tend to equalise the clearanceis. I quite agree with the author with regard to the spacing of the holes for distribution of the lubricant, and would like to add that these holes should be countersunk both inside and outside the bush.

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOK COMMERCIAL VEHICLES. 209

Mr. 0. D. NORTH:There is one point which is always a matter of grmt controversy amongst designers, and that is the solid aj against the built up axle, or, in other words, the forged aa against the cast axle. I am very strongly in favour of the forged axle, and I imagine that most of the better English builders take that view. One of the advantages of the forged axle is that it is not so &iff as a cast axle and yields slightly all along its length, particularly in the centre. I believe that a wheel journal of a

FIQ.33. certain diameter and material, with a shoulder where it joins the spring seat, will lead to fewer fractures at this point if the centre is a forged one of ordinary design than if a caet casing is wed. If a casting is to be made so strong that it will not fracture, it must be stiff, and that is a bad point in an axle. Makers of ordinary carts have realised this, and they have for a long time made their axles flexible. One of the disadvantages of the forged axle is the trouble of getting it made, especially in these WATSON. 0

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 210 THE 1NSTlTU‘L’ION OF .4 UTOM( )H 1 I .E ENGIX EEKS. (Mr. 0. D. North.) times. I think the author’s suggestion that these banjoea zliould be made as shallow as the extension is valuable, because the deeper the section is the more likely the die is to fracture. It has occurred to me that instead of drop stamping this part it might be forged in a hydraulic press, and in fact it might be possible to forge the under-pan solid, and I do not think such axles would weigh any more than the ordinary banjo forging with separate under-pan. It gets rid of the objectionable stud holes in the tension side of the member and must give extra strength, and it makes an under-pan which will stand striking a rock which an aluminium end pan will not. If it can be done in a hydraulic press, I believe cast iron dies will be satisfactory. Axle collars have always given trouble, and are still giving trouble. I do not like that shown in Fig. 2, for if a collar seizes or begins to seize the lorry will go on running until the “D” washer bursts, if hardened, or stretches, if soft. Pro- bably nobody realises what has happened, and the lorry is, perhaps, run for 1,000 miles or so with the thrust washer revolv- ing against the split ring until the ring or the edge of the groove in the axle wears away and the wheel comes off. I have seen every conceivable design of thrust washer give trouble one way or another, and I think the only safe plan is a thick hardened nut with a good locking device which will pull a lorry up dead before it will shear. Will the author say if he has found a satisfactory stuffing box for retaining oil in wheel bearings, and also can he give figurcs to show how the efficiency of the worni gearing varies with tho height of the oil level? With regard to springs, I think thekc are perfectly capable of taking the driving thrust and the torque and so getting rid of as many wearing parts as possible. Tlic great thing is to have long springs and to make the point of attachment to the frame as low as possible. The longer tho spring the greater the initial bending moment due to the load, and hence the less the percentage increase in the bending moment due to torque, and if the spring is underslung, the bending moment due to torque is reduced still more. Care must be taken that the car do= not roll badly, but long underslung springs will be perfectly satisfactory for an ordinary lorry. With regard to brake cams, the author shows that used by Messra Dennis, and I hardly think it is generally realised how much better it is than many other designs. There are three sorts

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COMMERC1.41, VlF,HlCI,ES. 211

of cam, the lozenge shape, the parallel caiii with one large radius at each end, and the Dennis design (Fig. 23 in tho paper). All three can be considered as double-ended levers with pins at the centres from which the radii of the operating surfaces are struck. The lozenge cam has a small radius at the working surface causing considerable wear of the thrust pads on the shoes. This form of cam is equivalent to a lever starting work 30 degrees past the vertical position. The next form of cam is better; it has a larger radius of the face and also is equal to a lever starting vertiod. The Dennis design has a larger radius still, and is equal to a, lever starting 30 degrees behind the vertical and having a useful movement of nearly 90 degrees before approaching the dead centre. Has the author any facts or strong opinions relative to increased life of transmission parts due to putting both brakw on the back wheels? For practical purposes, it seems to me that putting both brakes in this position is equivalent to putting a ton on the carrying capacity, i.e., a 4-ton lorry could take 5 tons without having trouble with the transmission. I do not think there can be anything better than the Straker brake drum, in which there are two shoes in one drum, because the whole of the wheel is acting as a radiating surface. Mr. F. G. WOOLLARD:I do not agree with all the definitions on page 165. I agree with that of the full floating type, but the American description of the semi-doating and %-floating axle is much more to the point. The semi-flosting type, according to American definition, is one in which the differential shaft takes both the torsional stresses and the stress due to loading, in fact it is similar to the axle shown in Fig. 3. In the $-floating axle, shown in Fig. 34, the bearing is mounted on an extension of the axle tube, and the centre line of the wheel passes through the centre line of the bearing. When the vehicle is on a level road there is no bending stress on the differentid shaft. On an uneven road or when rounding corners, the driving plate which is attached to the axle shaft transfers the bending stresses to the axle shaft, thus loading the differential case bearing. These definitions are accepted in America, and are, I think, more nearly correct. The Wolseley arrangement in which the hub bearing portion of the axle structure is made separate from the main double banjo member is due partly to manufacturing reasons; it is 02

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 212 THE INSTITUI ION OF AUTOMOHILE ENGINEERS. (Mr. F. G. Woollard.) difficult to harden and grind the ends of the double banjo when it is in one piece. I think the author is quite right in his refer- ence to the use of a tie-bar in Fig. 8, where it was merely a sop to a customer, and the fact that the casting is wall webbed inside renders a tie-bar superfluous. I should not call the type

FIG.34.-Double bearing here shown is for load carrying capacity within the limited space given by bore of a standard wheel. A single bearing would do otherwise.

of axle shown in Fig. 10 a good load carrier. The tubes need to be a forced fit, and should be put in with a suitable lubricant. I quite agree that the gears should be mounted as a unit on the top cover as it allows the gear assembly to be properly adjusted before the axle is finally closed up; proper adjustments cannot

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COMMERCIAL VEHICLES. 213 be made unless the mechanism can be seen open on the bench. If the suggestion that the War Department will call for increased clearance is realised, I think we shall have to adopt the internal gear drive as shown in Fig. 25. It is not desirable to make axle shafts and driving flanges in one piece, but it sometimes has to be done to aave overhang. Very often the rear caps stand out five or six inches beyond the front hub caps, and lamp-posts and walls suffer rather badly through this defect, the driver usually taking his sight from the front hub cap. If the surfaces in contact are hardened and ground the practice of omitting bushings to the differential wheels and pinions is sound; I know of a few thousands running and giving no trouble. Departures can be made (experimentally) from the ball bearing makers’ lists, but if a “no trouble job” is wanted, their figures and instructions must be adhered to, when the bearings will usually outlast the vehicle. On page 183 the author discusses screweld adjustments as againbt positive adjustments. I prefer the screwed adjustment, as I always have a feeling that the small packing washers may be lost. The author also discusses the question of torque and thrust; if the torque tube construction is used, it will be found that it nullifies the ease of dismounting the axle which has been gained by having the mechanism mounted on the top cover. I might remark that such a form of torque connection as that described in Fig. 2 is not permitted by the War Department Specification. I agree with the author that the best position for brakes is on the rear wheels, and for dissipating the heat, as Mr. North said, the wheels make excellent radiators. If a differential brake is to be used, it should be put in the position shown on the Burford axle, as in Fig. 25. This certainly saves the universal joints, although it does not help the differential. I do not think outside band brakes are very desirable. The one shown in Fig. 24, for which I am responsible, has a single casting for the brake drum with air spaces $in. wide between the inside and the outside working surfaces, aee Fig. 35. I think lubrication should be controlled from a central reservoir. Some pleasure cars are leading the way in this direc- tion, and no doubt there is much to be said for that m6thod. I have heen in touch with some American correspondents lately, and I hear that the internal gear form of drive shown in Fig. 25 is in great favour for moderate size commercial vehicles. In this

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 214 THE INSTITUTION OF AUTOMOBILE ENQINEERS. (Mr. F. G. Woollard.) country I think only the Berna, and on the Continent the Meroedea, both heavy vehicles, are fitted with this drive. I have had one laid out recently which appeared very much lighter than the double reduction type. There is a good deal of sameness about these internal gear drive axlm in America, for the reason that 90 per cent of the truck manufacturers there assemble from proprietary axles, of which there are three well-known sources of supply. Mr. H. G. BURFORD:The paper is one of great interest to me especially after the remarks of the last speaker. I have been associated with the heavy vehicle movement for a great many years, and I still have faith in the internal gear drive. The axlw mentioned are assembled in some shops in America, but the axle in the Burford vehicle is made in the works of the H. G. Burford Company, Fremont, Ohio. I am entirely in agreement with Colonel Crompton when he emphasises the question of +---

FIO.35.-Shows air spaces in brake drum. unsprung weight, and that is why I have always favoured this form of transmission. The axle is about one-third of the weight of any other ordinary axle that can be built. I regret that the author, in compiling the paper, did not give some references to the comparative cost of maintenance of the various forms of drives -the bevel, the worm, and the rack and pinion. I believe I was the first to introduce into this country a vehicle having a load carrying capacity of five tons mounted on ball bear- ings, and I believe the ball bearing to be the right bearing for the following reasons. First, it is absolutely interchangeable; second, after the designer has worked out his stresses and sizes, there is no possible chance of their being altered by the repairer through any tendency to reduce the shaft to take out scores, etc. The ball race may break, but it is a standmdked job and can be replaced, and the machine is not altered from its original design or conception.

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COMMERCIAL VEHICLES. 215

Further, all the ball bearing makers are very reliable, and I feel to-day, after some sixteen years' experience, that ball bearings on heavy vehicles are quite the right kind of bearing for that class of work. I entirely agree that forged back axles are the best form, and whether the die wmts $100 or 2200 or even $300, when it is once made properly there is very little trouble. Unfortunately, the die from which our axlee are pressed out waa recently broken. The drop forging company told me that my output was so small that they could not afford to make a better die, but as I was going to give them a bigger order they would put in a substantial 'die and it would never happen again. The trouble is, that manufacturers are not in a position to give drop forging companies big enough orders to justify the expense of really good dies. The question of torque tubes has been prominent throughout the discussion. I am strongly of opinion that the best way to take the torque is through the springs. When I was with the Humber Company, one of my fist machines there was the 11 h.p. Humber in which we adopted this plan, with the resulh that we never had any trouble. On the 14 h.p. car, where we had to give way to the views of the agents, we adopted a different axrangement and had nothing but trouble.

Major B. W. SHII.SON:As this is a resume of back axle design, I may mention the Jeffrey Quad, in which the back axle ialso a steering axle and the differential is a spiral gear one,-the first spiral gear differential that I have seen. I am glad see that the author has published, in the form of an Appendix, calculations for rear brakes. There is really very little useful information to the designer on that subject, and I think it will be very helpful. The author is rather severe on the War Office, but I think everyone is rather apt to look at a question from his own point of view. The designer looks at it purely from the question of design. The War Office in this case were looking upon it from the point' of view of interchangeability, store accommodation and handling, and I think that although they may have imposed certain restric-, tions on the designer, they certainly had good cause to do so. Recently, in obtaining particulars of frame dimensions and frame side members, I found that one maker who had supplied 330 vehicles of one type had no less than 150 different frame drawing.,

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 216 THE INSTITUTION OF AUTOMOBILE ENGINEERS. (Major B. W. Shilson.) that is, 150 drawings for 330 frames, so I think the War Offiw were not quite as wide of the mark as it might appear. Mr. A. F. EVANS:There is one form of.oil seal which is used rather sparingly, and I wonder why it cannot be used to a greater extent, that is, a thread is cut on the edges of the flange opposite to the direction of the rotation of the shaft. No oil can leak past the thread, and if oil is poured over that shaft fram the ead bearing it will go into the gear box. It is much more effioient than any form of felt pad, and never wears out. Anything from ten thread9 to the inch to four to the inch, or any angle from 30 degrees, can be employed.

Mr. WATSON,in replying on the discussion, said: My severest critic on the question of unsprung weight has been Colonel Crompton. I quite agree with him that unsprung weight should be limited as much &s possible, but I cannot agree that this ques- tion alone should be allowed to govern design. It may be asked, for instance, why did we ever depart from chain drive, which certainly presented the best possible conditions from this point of view. We probably only departed from that form of drive for convenience of wheel change, and to secure greater silence of running. Mr. Williamson has informed us that, in his en- quiries among tyre makers, he failed to get any definite views as to the effect of unsprung weight upon tyre wear. That also has been my own experience, md I believe I am right in thinking that the new regulations which may ba iwued in the near future by the Local Government lhard will actually allow greater axle weight than hitherto. Roads are being improved, largely due to the closer co-operation of road builders, and I believe Colonel Crompton has advocated that we should have axle weights in- creased to a certain extent, from the point of view of economical transport. I do not see myself that we are going off the right trmk so long as the unsprung weight is kept down to a minimum consistent with safety. Colonel Crompton warns us of the damage to the roads as well w to the tyres of other vehicles by the leakage of oil. The London General Omnibus Company has certainly taught us a practical lesson in this respect, and I .think we might follow it. It is not very costly to add to an axle something in the way of an oil catcher pan in the centre of the casing, with smaller pans

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COMMERCIAL \'EHl( LES. 217 underneath the spring seatings to catch all leakage from the wheels and the brake cam bearings. Mr. Williamson supports my argument that the banjo centre should have a good wide throat, and I believe it is possible, with safety, to cut down the thickness of the ring portion of an axle to about gin. on a depth of about 4: or 4#in., providing the throat is easy, but if the throat has a counter bore, or is made with a sharp radius, then it is positively dangerous. Mr. Williammn gives it as his opinion that gears made of oil- hardening steels tend to greater silence. That has also been my experience, and I prefer gears of oil-hardened steels to those of case-hardened steels. His arguments in connection with the torque being taken through the springs appear to coincide with my own. I believe the form of differential lock advocated by Mr. Williamson is the best, because it frees the differential gear from all stresses due to the lock of the wheels. Mr. North holds the opinion that forged axles are more flexible than the built up cast axles. Most certainly they are, and that is why I believe they are so much better and give so much more aatisfactory results. I think the safety of the forged axle. is in its flexibility, whereas a cast casing has no flexibility, or 60 little that the whole structure of the axle is bound to suffer to a certain extent on account of increased vibration. Mi,. North's suggestion that the under-pan shoulid be stamped in one piece with the axle ie oertainly ingenious, but I think it would interfere with one of the advantages of the built up axle, that is, the removal of the under-pan, which enables all the parts to be examined without lifting the heavy top cover off. The latter can only be removed, in some cases, after lifting the body off and then making use of a crane or tackle. He also spoke of the high cost of deep centred forgings; the high cost, and risk of damage due to twisting of the forging, is due very largely to the great pressure necessary to force the metal into the deep pockets, and that is one reason why I very strongly advocate giving a wide throat: and comparatively shallow centres. Such an axle makes a com- paratively cheap stamping, or even if the quantities do not justify the making of dies, it could be made from a steam hammer forging with the centre part trepanned out on comparatively old-fashioned face plate lathes, the rest being finished on a centre lathe and boring machine. I believe that in that way it is possible to produce axles comparing closely in cost with stampings.

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 218 THE INS'I'ITU'L'ION OF AUTOMOBILE ENGINEERS. (Mr. Wahn.) I think Mr. North must have overlooked the fact that I recommended that the split collars for axles should be enclosed in a muff to prevent them spreading. I have not found agy, stuffing box that is effective as applied to an axle. The best way I know to prevent oil leakage beyond a cover is the method suggested by Mr. Evans, namely, a thread cut on the inside of the cover bush; the oil is then scraped off the rotating shart and carried back in the direction whence it came. Mr. North also advocates long springs, placed well down on to the axle. I agree, and I also think the springs should have ae little camber as possible compatible with the general design of the machine. He also states that underslung springs have a tendency to roll. I well remember an example of this, on one of the early steam buses running from Shepherd's Bush to Marble Arch. I am afraid I was rather severe in condemning the Straker arrangement of brake shown in Fig. k9, and I must admit that in doing so I overlooked the fact that in this particular case the full width of the brake drum itself is in metallic contact with extensions from the wheels. These conditions, however, do not always prevail, and the brake drum is often bolted through a flange to the sides of the spokes, and in such a case if the inner brake shoes heat up their part of the drum, the outer shoes become more or less ineffective, as the heat generated has to escape past an already heated surface. In short, if the whole width of the brake drum is free to dissipate its heat through the spokes, the two seh of shoes in one drum may be acceptable. I quite agree that if both brakes are on the back axle the useful load 011 a machine can generally be increased without increasing the wear and tear on the chassis, because the stresses on the differential gear and all the transmission parts are reduced. Mr. Woollard takes me to task for my definitions, but I only put these forward to make my meaning clear, not as being what should be accepted by everybody. I will adopt any others if they are standardised by any authoritative body. If any new regulations are issued which demand increased clearance as hinted at by Mr. Woollard we may have to use a double reduction type of axle, with rack and pinion drive, such as is used on the Burford vehicles. I like that type of axle very much, and had Mr. Burford used the same type on his new four- tonner I should most certainly have given greater attention to it.

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COMMERCIAL VEHICLES. 2 19

It had gained rather an unfortunate reputation on account of the noise it used to make when the rack and pinion were exposed, but this has entirely been removed by reducing the diameter of the rack as Mr. 'Burford has done, and enclosing it in a well lubricated and dust-proof case. I have had a good deal of experience with Mr. Burford's 2-ton axle and have never found an axle of that capacity that I liked so well, though for larger sizes there are certain difficulties in the way of its adoption, one of which is the great width it occupies between wheel and springs. It3 use entails either very narrow spring centres or extra wide track. With regard to Mr. Woollard's objection to the use of packing washers, which, he says, get lost, I do not think there is much fear of that if the washers are made at least a quarter of an inch thick as I suggest. A man could not very well assemble a worm shaft for instance, and leave a quarter of an inch of slack in it without knowing that something has been left out. If the packing washers are numerous and very thin, then undoubtedly their use is objec- tionable. I prefer to start with a thick washer and grind it down to the required thickness, and then no mistake can possibly be made. I am quite aware that the system of torque bars shown in Fig. 5 would not be permitted by the War Department, but it must be borne in mind that all vehicles are not built to War Office Specification. I suggest Fig. 5, or a modification of it, as being a suitable one for public service vehicles carrying passengers and: to overcome Mr. Williamson's objection, because if the upward kick due to the starting effort can be transferred well to the front, the pitching effect on the vehicle will be reduced and riding will be easier. I quite agree with Mr. Burford that ball bearings eliminate the possibility of a repairer weakening a shaft by reducing it and fitting a thicker bush in order to remove the effects of wear. I regret that I am not in a position to give comparative c0st.s for the maintenance of the various types of axlea mentioned. I have studied the drawings of the Jeffery Quad axle which were handed in by Major Shilson, but as they refer particularly to combined steering and driving axles it is not my intention to discuss them. Apart from the property named, they do not embody any noteworthy features of design. Major Shilson takes me to task for my remarks upon the War Office methods. They

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 220 THE INSTITU1’ZON OF AUTOMOBILE ENGINEERS. (Nr. Watson.) may look upon the matter its a question of stock v. design, but in order to reduce their stock they ask us to use certain sizes of ball bearings which are absolutely unsafe for the work, and we must either use them or adopt a plain bearing which will not give quite euch good results.

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COMMERCIAL VEHICLES. Plate IX

FIG.26.-Wrigley’s Subsidy Axle and Torque-Thrust A1 eniler.

FIG.27.-The I’ngefieltl Axle, showing the differential gear renmvod.

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COMMERCIAL VEHICLES. Plate X

[email protected] and Shafts of Wolseley’s Subsidy Axle.

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016 LIVE AXLES FOR COMMERCIAL VEHICLES. Plate XI

a 1%3

Downloaded from pau.sagepub.com at NANYANG TECH UNIV LIBRARY on June 4, 2016