Published by: O Robert Bosch GmbH, 1995 Postfach 30 02 20 D-70442 Stuttgart Automotive Equipment Business Sector. Department for Technical Information (KHNDT). Management: Dipl.-lng. (FH) Ulrich Adler.

Editor-in-Chief: Dipl.-lng. (FH) Horst Bauer.

Editors: Dipl.-lng. (FH) Anton Beer, Ing. (grad.) Arne Cypra.

Presentation: Dipl.-lng. (FH) Ulrich Adler, Joachim Kaiser, Helmut Flaig (Zweckwerbung Kirchheim).

Translation: Peter Girling.

Technical graphics: Bauer & Partner, Stuttgart.

Unless otherwise specified, the above persons are employees of Robert Bosch GmbH, Stuttgart.

Reproduction, copying, or translation of this pub- lication, wholly or in part, only with our previous written permission and with source credit. Illustrations, descriptions, schematic drawings, and other particulars only serve to explain and illustrate the text. They are not to be used as the basis for design, installation, or delivery conditions. We assume no responsibility for agreement of the contents with local laws and regulations. Robert Bosch is exempt from liability, and reserves the right to make changes at any time.

Printed in Germany. lmprime en Allemagne. 2nd Edition, March 1995 English translation of the German edition dated: April 1994

in the I C0mbustion inxthe spark-ignition ..gine spark-ignition engine

The spark-ignition or the actual work energy (power). After each combustion the spent gases Otto-cycle engine are expelled from the and a fresh air-fuel mixture is drawn in. In automotive engines this exchange of gases is gene- Principles rally regulated according to the four- The spark-ignition or Otto-cycle') engine stroke principle, with two is a combustion engine with externally revolutions being required for each com- supplied ignition which converts the plete cycle. energy contained in the fuel into kinetic energy. The four-stroke principle The spark-ignition engine employs a mix- The four-stroke spark-ignition engine ture-formation apparatus located outside employs gas-exchange valves to control the to form an air- the gas flow. These valves open and fuel mixture (based on gasoline or a gas). close the cylinder's intake and exhaust As the descends, the mixture is tracts: drawn into the combustion chamber, where it is then compressed as the piston Ist stroke: Induction moves upward. An external ignition 2nd stroke: Compression and ignition source, triggered at specific intervals, 3rd stroke: Combustion and work uses a to initiate combustion 4th stroke: Exhaust. in the mixture. The heat released in the combustion process raises the pressure Induction stroke within the cylinder, and the piston pushes Intake valve: open, down against the crankshaft, providing Exhaust valve: closed, Piston travel: downward, Fig, 1: Design concept of the reciprocating pi- Combustion: none. ston engine TDC Top Dead Center, BDC Bottom Dead Center, Vh Stroke volume, Vc Compression volume, The piston's downward motion increases s Piston stroke. the cylinder's effective volume and pulls OT in fresh air-fuel mixture through the open intake valve.

"h Compression stroke UT Intake valve: closed, Exhaust valve: closed, Piston travel: upward, Combustion: initial ignition phase.

1) After Nikolaus August Otto (1832 - 1891), who unveiled the first four-stroke gas-compression engine at the Paris World Exhibition in 1878. As the piston travels upward, it reduces When thg spark at the spark plug ignites The the cylinder's effective volume and com- the air-fuel mixture, the gas mixture com- spark-ignition presses the air-fuel mixture. Just before busts and the temperature increases. or Otto-cycle the piston reaches top dead center The pressure level in the cylinder also in- engine (TDC), the spark plug ignites the com- creases, pushing the piston downward. pressed air-fuel mixture to initiate com- The force from the moving piston is bustion. transferred through the The is calculated with and to the crankshaft in the form of work; the stroke volume Vh this is the actual source of the engine's and compression volume Vc: power. & = (Vh+VC)/VC. Output rises as a function of increas- Compression ratios E range between ed engine speed and higher torque 7 and 13 to one, depending upon engine (P = Mew). design. Increasing the compression ratio A transmission incorporating various in a combustion engine enhances its conversion ratios is required to adapt the thermal efficiency and provides more ef- combustion engine's power and torque fective use of the fuel. For instance, rais- curves to the demands of actual vehi- ing the compression ratio from 6: 1 to cular operation. 8: 1 produces a 12 % improvement in thermal efficiency. The latitude for such Exhaust stroke increases is restricted by the knock (or Intake valve: closed, preignition) limit. Knock refers to uncon- Exhaust valve: open, trolled mixture combustion characterized Piston travel: upward, by a radical increase in pressure. Com- Combustion: none. bustion knock leads to engine damage. Appropriate fuels and combustion-cham- As the piston travels upward, it pushes ber configurations can be employed to the spent gases (exhaust gases) out shift the knock limit toward higher com- through the open exhaust valve. The pression ratios. cycle is then repeated. The periods when the valves are open overlap by a certain Power stroke degree; this improves the gas-flow and Intake valve: closed, oscillation patterns for enhanced cylinder Exhaust valve: closed, filling and scavenging. Piston travel: upward, Combustion: combustion completed.

Fig. 2: Operating cycle of the four-stroke spark-ignition engine

Stroke 1: Induction Stroke 2: Compression Stroke 3: Combustion Stroke 4: Exhaust Mixture formation Mixture formation

Overview Excess-air factor The excess-air factor (or air ratio) d has been chosen to indicate how far the actual air-fuel mixture deviates from the theoretical optimum (14.7: 1). Parameters Air-fuel mixture d = Induction air masslair requirement for The spark-ignition engine requires a stoichiometeric combustion specific airlfuel ratio (A/F ratio) in order to operate. The theoretical ideal for com- il = 1: The induction air mass corre- plete combustion is 14.7:1, and is re- sponds to the theoretical requirement. ferred to as the stoichiometric ratio. d < 1: Air deficiency, rich mixture. In- Mixture corrections are required to creased output is available at d = satisfy the special engine demands 0.85.. .0.95. encountered under particular operating d > 1: Excess air (lean mixture) in the conditions. range d = 1.05.. .1.3. Excess-air factors The specific fuel consumption of the in this range result in lower fuel con- spark-ignition engine is largely a function sumption accompanied by reduced per- of the A/F ratio. In theory, excess air is formance. required to achieve the minimum fuel d > 1.3: The mixture ceases to be ignit- consumption that would result from com- able. Ignition miss occurs, accompanied plete combustion. In practice, however, by pronounced loss of operating smooth- latitude is restricted by factors such as ness. mixture flammability and limits on the time available for combustion. On contemporary engines, minimum fuel consumption is encountered at an A/F Fig. 1: A/F ratio for combustion with ratio corresponding to approximately minimum specific fuel consumption 15... 18 kg air for each kg of fuel. In other words, about 10,000 litres of air are re- 10,000 litre quired to support combustion in one litre air of fuel (Figure 1). Because automotive powerplants spend most of their time operating at part- , engines are designed for mini- mum fuel consumption in this range. Mix- tures containing a higher proportion of fuel provide better performance under other conditions such as idle and full- throttle operation. The mixture-formation system must be capable of satisfying these variegated requirements. 1- litre fuel Spark-ignition engines achieve their Adapting to specific maximum output at air-deficiency levels operating conditions of 5...15% (d = 0.95...0.85), while minimum fuel consumption is achieved Certain operating states will cause the with an air excess of 10...20% (d = fuel requirement to deviate considerably 1 .I . . .I.2). d = 1 provides optimum from that required by a stationary engine idling characteristics. at normal operating temperature; the Figures 2 and 3 illustrate the effect of the mixture must be corrected accordingly. excess-air factor d on output, specific fuel consumption and exhaust emissi- Cold starts ons. It will be noted that no single excess- During cold starts, the relative amount of air factor can simultaneously generate fuel in the mixture decreases; the mixture optimal response in all areas. Air factors "goes lean." Inadequate blending of fuel ranging from d 0.9.. .1.1 provide the and air in the intake mixture, low fuel best results in actual practice. vaporization and condensation on the Once the engine has reached its normal walls of the intake tract due to the operating temperature, it is essential that low temperatures, all contribute to this d = 1 be maintained to support subse- phenomenon. To compensate, and to quent exhaust treatment with a three- assist the cold engine in "getting started," way . The precon- supplementary fuel must be made avail- ditions for satisfying this requirement are able for starting. precise determination of the induction-air quantity accompanied by an arrange- Post-start phase ment capable of providing exact fuel After starts at low temperatures, supple- metering. mentary fuel must be provided to enrich To ensure a satisfactory combustion the mixture until the combustion chamber process, precise fuel metering must be heats up and the mixture formation within accompanied by homogeneous mixture the cylinder improves. The richer mixture formation. The fuel must be thoroughly also increases torque to provide a atomized. If this condition is not satisfied, smoother transition to the desired idle large fuel droplets will form along the speed. walls of the inlet tract, leading to higher HC emisssions.

Fig. 2: Effect of excessair factor il Fig. 3: Effect of excess-air factoril on output P and specific fuel consumption be on exhaust emissions a) Rich mixture (a~rdeficiency) b) Lean mixture (excess air).

I

CO 2 C .-0 -Q C 0 5 V) V) .-a, .-- x -E F 0 a, s = <2 a b 0- .- 3 !Eo s - .-+ Y a o $ 6- 2 g KO IIIIIIII, 0.8 1.O 1.2 0.6 0.8 1.0 1.2 1.4 Excess-air factor h Excess-air factor h Mixture Warm-up phase that no harmful exhaust emissions are formation The starting and post-start phases are generated in this operating mode. followed by the engine's warm-up phase. In this phase the engine still requires a High-altitude adjustment richer mixture, as the cylinder walls are Increases in altitude (as encountered still cool, and a portion of the fuel con- during alpine operation) are accompa- tinues to condense on them. Since the nied by a reduction in air density. This quality of mixture formation drops along means that the intake air being drawn with failing temperatures (due to less ef- into the engine at high altitudes displays fective mixing of air and fuel, and large a lower mass per unit of volume. A fuel droplets), condensation forms in the system which fails to adjust the mixture intake manifold, where it remains until it accordingly will supply an excessively is vaporized as temperatures increase. rich mixture, and the ultimate result will These factors make it necessary to pro- be higher fuel consumption and in- vide progressive mixture enrichment in creased exhaust emissions. response to decreasing temperatures.

Part-throttle operation During part-throttle operation priority is Mixture-formation systems assigned to adjusting the mixture for The function of the or fuel- minimum fuel consumption. The three- injection system is to supply the engine way catalytic converters required to meet with the optimum air-fuel mixture for stringent emissions limits are making instantaneous operating conditions. For it increasingly important to control the some years now, has re- systems ford = 1. presented the preferred method, a devel- opment accelerated by the advantages Full-throttle operation that injecting the fuel provides in the When the throttle valve has opened to areas of economy, performance, drive- its maximum aperture, the engine should ability and low exhaust emissions. Fuel respond by providing its maximum injection can be applied for extremely torqueloutput. As Figure 2 indicates, this precise metering, supplying exactly the necessitates enrichening the air-fuel correct amount of fuel for given operating mixture to 1 = 0.85.. .0.90. and load conditions while simultaneously ensuring minimum levels of exhaust Acceleration emissions. The composition of the mix- When the throttle valve opens suddenly, ture is controlled to maintain low emis- the air-fuel mixture responds by leaning sions. out briefly. This is due to the fuel's restricted vaporization potential at higher Multipoint fuel injection levels (increased Multipoint injection supplies the ideal tendency to form fuel layers on intake- starting point for meeting these objec- tract walls). tives. The multipoint injection system To obtain good transition response, the uses a separate injector to inject the fuel mixture must be enriched by an amount directly through the intake valve at each which varies according to engine tempe- individual cylinder. Examples of this type rature. This enrichment provides good of design are the KE- and L-Jetronic in acceleration response. their various individual configurations (Figure 4). Trailing-throttle (overrun) operation The fuel-metering process can be inter- rupted on trailing throttle to reduce fuel consumption during descents and under 6 braking. Another advantage is the fact Mechanical iniection svstem Single-point (throttle-body, central) K-Jetronic is a mechanical injection fuel injection system in widespread use. This driveless Single-point fuel injection describes an system injects the fuel in a continuous electronically-controlled injection unit process. featuring an electromagnetic injector lo- cated directly above the throttle valve. Combined mechanical and This injector sprays fuel into the intake electronic injection system manifold in an intermittent pattern. KE-Jetronic is an expanded version of Mono-Jetronic is the brand name of the the basic K-Jetronic system. It monitors Bosch single-point injection system (Fig- an extended range of operating data for ure 5). electronic open-loop control of auxiliary functions to provide more precise fuel Advantages of fuel injection metering under varying engine operating conditions. Reduced fuel consumption This system monitors all essential engine Electronic injection systems operating data (e.g., engine speed, load, Electronically-controlled injection sys- temperature, throttle-valve aperture) for tems use electro-magnetic injectors to precise adaptation to stationary and dy- inject the fuel intermittently. namic operating conditions, thereby en- Examples: suring that the engine receives only the L-Jetronic, LH-Jetronic, and the Motronic amount of fuel that it actually requires un- integrated fuel-injection and ignition der any given circumstances. system. Improved performance K- and L-Jetronic allow greater latitude in intake-tract design for better cylinder- back to cover a period of almost one controlled D-Jetronic! In 1973 the air-flow-controlled L-Jetro- The Gasmotorenfabik Deutz was nic appeared on the market, at the manufacturing plunger pumps for In- same time as the K-Jetronlc, which jecting fuel in a limited production featured mechanical-hydraulic control series as early as 1898. as well as an air-flow sensor. A short time later the uses of the ven- 1979 marked the introduction of a new turi-effect for carburetor design were system: Motronic, featuring digital pro- discovered, and fuel-injection systems cessing for numerous engine func- based on the technology of the time tlons. This system combined L-Jetro- ceased to be competitive. nic with electronic program-map con- Bosch started research on gasoline- trol for the ignition. The first automo- injection pumps in 1912. The first tive microprocessor! aircraft engine featuring Bosch fuel in- In 1982, the K-Jetronic model became jection, a 1200-hp unit, entered series available in an expanded configura- production in 1937; problems with - tion including an electronic closed- buretor icing and fire hazards had lent loop control circult and a Lambda oxy- special impetus to fuel-injection devel- gen sensor the KE-Jetronic. opment work for the aeronautics field. These were joined by Bosch Mono- This development marks the begin- Jetronic in 1983: This particularly ning of the era of fuel injection at cost-efficient single-point injection unit Bosch, but there was still a long path made it feasible to equip small ve- to travel on the way to fuel injection for hicles with Jetronic. passenger . 1991 saw Bosch fuel-injection units 1951 saw a Bosch direct-injection unit performing in more than 37 million ve- being featured as standard equipment hicles throughout the world. on a small car for the first time. Sev- 5.6 million engine-management sys- era1 years later a unit was installed in tems were delivered in 1992. Of this the 300 SL, the legendary production number, 2.5 million were Mono-Jetro- sports car from Daimler-Benz. nic and Mono-Motronic systems, with In the years that followed, develop- 2 million Motronic systems being sup- ment on mechanical injection pumps plied with~nthe same period. Today continued, and ... fuel-injection systems have become In 1967 fuel injection took another an essential automotive component.

Bosch gasoline fuel injection from the year 1954 Mixture be registered and converted into electri- forma tion cal signals by sensors. These signals are then passed on to the control unit of the fuel-injection system which pro- Outline of system cesses them and calculates the exact The L-Jetronic is an electronically con- amount of fuel to be injected. This is in- trolled fuel-injection system which in- fluenced via the duration of injection. jects fuel intermittently into the intake ports. It does not require any form of Function drive. It combines the advantages of A pump supplies the fuel to the engine direct air-flow sensing and the special and creates the pressure necessary for capabilities afforded by electronics. injection. Injection valves inject the fuel into the individual intake ports and onto As is the case with the K-Jetronic the intake valves. An electronic control system, this system detects all changes unit controls the injection valves. resulting from the engine (wear, depo- The L-Jetronic consists principally of the sits in the combustion chamber and following function blocks: changes in valve settings), thus guaran- - fuel supply system, teeing a uniformly good exhaust gas - operating-data sensing system and quality. - fuel-metering system. The task of the gasoline injection system is to supply to each cylinder Fuel-supply system precisely the correct amount of fuel The fuel system supplies fuel from the as is necessary for the operation of the to the injection valves, creates engine at that particular moment. A pre- the pressure necessary for injection and requisite for this, however, is the maintains it at a constant level. processing of as many influencing fac- tors as possible relevant to the supply of Operating-data sensing system fuel. Since, however, the operating con- The sensors register the measured vari- dition of the engine often changes quite ables which characterize the operating rapidly, a speedy adaptation of the fuel mode of the engine. delivery to the driving situation at any The most important measured variable is given moment is of prime importance. the amount of air drawn in by the engine Electronically controlled gasoline in- and registered by the air-flow sensor. jection is particularly suitable here. It en- Other sensors register the position of the ables a variety of operational data at throttle, the engine speed, the air tempe- any particular location of the vehicle to rature and the engine temperature.

Fig. 1: Principle of the L-Jetronic (simplified) Fuel-metering system The signals delivered by the sensors Fuel Sensors Air are evaluated in the electronic control unit (ECU) where they are used to generate the appropriate control pulses for the injection valves.

Advantages of the L-Jetronic system

Low fuel consumption injection Eng~ne valves In carburetor systems, due to segrega- (tnjectors) tion processes in the intake manifold, the individual cylinders of the engine do

Mixture Fuel supply system housing is fitted with metal rollers in forma tion notches around its circumference which The fuel supply system comprises the ,are pressed against the pump housing following components: by centrifugal force and act as seals. - electric , The fuel is carried in the cavities which - fine filter, form between the rollers. The pumping - fuel rail, action takes place when the rollers, - pressure regulator and after having closed the inlet port, force - fuel-injection valves. the trapped fuel around in front of them until it can escape from the pump An electrically driven roller-cell pump through the outlet port (Figure 5). The pumps the fuel from the fuel tank at a fuel flows directly around the electric pressure of approximately 2.5 bar motor. There is no danger of explosion, through a filter into the fuel rail. From the however, because there is never an fuel rail, fuel lines diverge to the in- ignitable mixture in the pump housing. jection valves. At the end of the fuel rail is a pressure regulator which maintains The electric fuel pump delivers more the injection pressure at a constant level fuel than the maximum requirement of (Figure 3). More fuel circulates in the the engine so that the pressure in the fuel system than is needed by the en- fuel system can be maintained under all gine even under the most extreme operating conditions. A check valve in conditions. The excess fuel is returned the pump disconnects the fuel system to the fuel tank by the pressure regula- from the fuel tank by preventing return tor but not under pressure. The constant flow of fuel to the fuel tank. flushing through of the fuel system en- The electric fuel pump starts immedia- ables it to be continually supplied with tely when the ignition and starting cool fuel. This helps to avoid the forma- switch is operated and remains switch- tion of fuel vapour bubbles and guaran- ed on continously after the engine has tees good hot-starting characteristics. started. A safety circuit prevents fuel from being delivered when the ignition Electric fuel pump is switched on, but when the engine is The electric fuel pump is a roller-cell stationary (e.g. after an accident). The pump driven by a permanent-magnet fuel pump is located in the direct vicinity electric motor. The rotor plate which is of the fuel tank and requires no main- eccentrically mounted in the pump tenance.

Fig. 3: Fuel supply system 1 Fuel tank 2 Electric fuel Pump 3 4 Fuel rail 5 Fuel-pressure regulator 6 Fuel-injection valve (injector) 7 Cold-start valve I

12 Fuel filter The fuel filter filters off impurities in the 3 Roller-cell pump, fuel which could impair the function of 5 Check vahre, 6 Outlet port. the injection system. The filter contains a paper element with an average pore size of 10 pm, which is backed up by a fluff strainer (Figure 6). This combina- tion ensures a high degree of filtration. A support plate secures the filter in its metal housing. The filter is installed in the fuel line downstream of the fuel accumulator. When the filter is changed, it is impera- tive that the throughflow direction as indicated by the arrow on the housing 4 Roller race plate, 5 Outlet port. be observed.

Fuel rail The fuel rail supplies all injection valves with an equal quantity of fuel and ensu- res the same fuel pressure at all in- jection valves. The fuel rail has a storage function. Its volume, compared with the amount of fuel injected during each working cycle of the engine, is large enough to pre- vent variations in pressure. The injec- tion valves connected to the fuel rail are therefore subjected to the same fuel pressure. The fuel rail also facilitates easy fitting of the injection valves.

Pressure regulator The pressure regulator keeps the pres- sure differential between the fuel pres- sure and manifold pressure constant. not under pressure, to the fuel tank. Thus, the fuel delivered by the electro- The spring chamber is connected by magnetic injection valve is determined a tube with the intake manifold down- solely by the valve opening time. stream of the throttle valve. This has The pressure regulator is a diaphragm- the effect that the pressure in the fuel controlled overflow pressure regulator system is dependent upon the absolute which controls pressure at 2.5 or 3 bar, manifold pressure; therefore, the pres- dependent upon the system in question. sure drop across the fuel-injection val- It is located at the end of the fuel rail and ves is the same for any throttle position. consists of a metal housing, divided into two spaces by a flanged diaphragm: a chamber for the spring that preloads the diaphragm, and a chamber for the fuel (Figure 7). When the preset pres- sure is exceeded, a valve operated by the diaphragm opens the return line for the excess fuel to flow back,

Operating-data sensing fluences .can be considered: the sen- L-Jetronic system sors mentioned above detect the data for trans'ition response when accelerat- Sensors detect the operating mode of ing, for maximum engine-speed limi- the engine and signal this condition tation and during overrun. The sensor electrically to the control unit. The sen- signals have a particular relationship to sors and ECU form the control system. each other in these operating ranges. The sensors are described in conjunc- The control unit recognizes these rela- tion with the relevant main function or tionships and influences the control compensation function. signals of the injection valves accord- ingly. Measured variables The measured variables characterizing Calculating engine speed the operating mode of the engine are as Information on engine speed and the follows: start of injection is passed on to the - main measured variables L-Jetronic ECU in breaker-triggered - measured variables for compensa- ignition systems by the contact-breaker tion points in the ignition , and, in - measured variables for precise com- breakerless ignition systems, by termi- pensation. nal 1 of the . The ECU evaluates all measured vari- ables together so that the engine is al- Measuring the air flow ways supplied with exactly the amount The amount of air drawn in by the en- of fuel required for the instantaneous gine is a measure of its loading condi- operating mode. This achieves optimum tion. The air-flow measurement system driveability. allows for all changes which may take place in the engine during the service Main measured variables life of the vehicle, e.g. wear, combu- The main measured variables are the stion-chamber deposits and changes to engine speed and the amount of air the valve setting. drawn in by the engine. These deter- Since the quantity of air drawn in must mine the amount of air per stroke which first pass through the air-flow sensor be- then serves as a direct measure for the fore entering the engine, this means loading condition of the engine. that, during acceleration, the signal leaves the sensor before the air is Measured variables for compensation actually drawn into the cylinder. This For operating conditions such as cold start and warm-up and the various load Fig. 9: Calculating engine speed conditions which deviate from normal with a breaker-triggered 1 Ignition distributor, 2 ECU. operation, the mixture must be adapted n Engine speed. to the modified conditions. Starting and warm-up conditions are detected by sensors which transmit the engine tem- perature to the control unit. For com- pensating various load conditions, the load range (idle, part-load, full-load) is transmitted to the control unit via the throttle-valve switch.

Measured variables for precision compensation In order to achieve optimum driving be- havior, further operating ranges and in- 15

mpabllWea to be implemented as pared wtth the previous analog techni- SpedClc -ma for spedflc mad@@ qua uwd. hmin Ihe moantime bsen devebm The LS-Jetronlc systsrn LB avaiedle on the basis cd the L~~ Them both wtth and wlthout lambda elwxb mrnr indude ths LE-Jetrmric without Imp mntrol. Ooth vcdono haw whd Is lambda clossdSsop amtrd for Euqx died a Yirnphome" fumnwhich en- end& LU4ehnicsyetemwW MWa &lee the drivfar b drlw the vshlele to clwoontrol tor mumwlth the near& workshop If ths miem- Wct ahaust gas emklm l~a10on puter faib. In dknthe input algnak (e.g. the USA). The rrrost maatd&p of eue cheeload for plaudblri, is. rn In devdcpmsnt Is the LSJarc~~icwhlch plausible Inm elgnal (e.0.snglns taw dbrsfrom it8 prsdefwsars in mpsct perarturn lower Win -40°C) Ir Lgnomd of the following c!fakillg: and a default value &xrad in ths control - the mntrol unk whlch te su&blo tor unlt b uwd In it8 @me. IMallatim in the engine wmparbnsnt, Is amto ths alr-flow manmr-and FUrupPlY thug no lon~rwgl~ e~glcs in the On this oys4arn, the fuel is suppllsd to peseengw-, the Injection vaks In the wmm way ~e - the mmbinsd wrl of contrcl unit and on the Wetranle mrn via an slsctrlc dr-low wnmrwlth Internal connections fuel pump, fuel illbar, fuel rail and pa& elrnplnies the &Is hamem an3 re sure rsgulator. dminstallatJon expime, - the uw of digM techniques permb new fundbns whh impmad mhptatlon Operating-data sensing system sions of the potentiometer chamber in L -Jetronic The ignition system supplies the infor- the air-flow sensor and of the control unit mation on engine speed to the control have beep reduced to such an extent that unit. A temperature sensor in the cool- the overall height of the entire unit does ant circuit measures the engine tempe- not exceed that of the previous air-flow rature and converts it to an electrical sensor alone. Other features of the new signal for the control unit. The throttle- air-flow sensor include the reduced valve switch signals the throttle-valve weight due to the aluminum used in place positions "idle" and "full load" to the con- of the zinc material for the housing, the trol unit for controlling the engine in or- extended measuring range and the der to allow for the different optimization improved damping behavior in the event criteria in the various operating conditi- of abrupt changes in the intake air quan- ons. The control unit senses the fluctua- tity. Thus, the L3-Jetronic incorporates tions in the electrical vehicle supply and clear improvements both in respect of compensates for the resultant response electronic components and in respect of delays of the fuel-injection valves by mechanical components whilst requiring correcting the duration of injection. less space (Figs. 32 and 33).

Air-flow sensor Fuel metering The air-flow sensor of the L3-Jetronic Fuel is injected onto the intake valves system measures the amount of air of the engine by means of solenoid- drawn in by the engine using the same operated injection valves. One solenoid measuring principle as the air-flow sen- valve is assigned to each cylinder and is sor of the conventional L-Jetronic sy- operated once per crankshaft revolu- stem. Integrating the control unit with the tion. In order to reduce the circuit com- air-flow sensor to form a single mea- plexity, all valves are connected electri- suring and control unit requires a modi- cally in parallel. The differential pres- fied configuration however. The dimen- sure between the fuel pressure and

Fig, 32: Integration of ECU and air-flow sensor of the L34etronic to form a single measuring and control unit 1 ECU, 2 Alr-flow sensor wlth potentlometer.

b 3 1 Mixture intake-manifold pressure is maintained* Fig. 33: Air-flow sensor of the L3-Jetronic i formation constant at 2.5 or 3 bar so that the quan- 1 Sensor flap, 2 Compensation flap, 3 Damping volume. tity of fuel injected depends solely upon, the opening time of the injection valves. 1 For this purpose, the control unit sup- plies control pulses, the duration of which depends upon the inducted air quantity, the engine speed and other actuating variables which are detected by sensors and processed in the control unit.

Electronic control unit (ECU) By contrast with the L-Jetronic system, the digital control unit of this system adapts the air-fuel ratio by means of a 3 2 loadlengine-speed map. On the basis of the input signals from the sensors, the control unit computes the injection dura- switch issues a switching signal to the tion as a measure of the amount of fuel control unit. to be injected. The microcomputer sy- stem of the control unit permits the re- Auxiliary-air device quired functions to be influenced. The A plate which is moved by a bimetallic control unit for attachment to the air-flow spring or expansion element supplies sensor must be very compact and must extra air to the engine during the warm- have very few plug connections in addi- up phase. This results in the higher idle tion to being resistant to heat, vibration speed which is required during the and moisture. These conditions are met warm-up phase for smooth running of by the use of a special-purpose hybrid the engine. circuit and a small PC board in the cont- A closed-loop idle-speed control sy- rol unit. In addition to accommodating stem, in the form of a separate system, the microcomputer, the hybrid circuit al- can be used instead of the auxiliary-air so accommodates 5 other integrated device to control the idle speed. circuits, 88 film resistors and 23 capaci- tors. The connections from the ICs to Engine-temperature sensor the thick-film board comprise thin gold The engine-temperature sensor, a tem- wires which are a mere 33 thousandths perature-dependent resistor, controls of a millimeter in thickness. warm-up enrichment. The overrun fuel cutoff function, and the speed limiting Adaptation to operating conditions function at maximum permissible en- During certain operating conditions gine speed, permit fuel economy and a (cold start, warm-up, acceleration, idle reduction in pollutant emission. and full load), the fuel requirement dif- fers greatly from the normal value so Lambda closed-loop control that it is necessary to intervene in mix- In the control unit, the signal from the ture formation. lambda sensor is compared with an ideal value (setpoint), thus controlling a Throttle-valve switch two-position controller. Dependent upon This switch is operated by the throttle- the result of the comparison, either an valve shaft and has a switching contact excessively lean air-fuel mixture is en- for each of the two end positions of the riched or an excessively rich mixture is throttle valve. When the throttle valve is leaned. Fuel metering is influenced via 32 closed (idle) or fully open (full load), the the opening time of the injection valves.

Mixture temperature-dependent resistances. A I cally in parallel. The differential pres- formation voltage signal which is proportional to the sure between the fuel pressure and in- air-mass flow is transmitted to the ECU ., take-manifold pressure is maintained (Figs. 35 and 36). constant at 2.5 or 3 bar so that the quan- tity of fuel injected depends solely upon Hot-film air-mass meter the opening time of the injection valves. With the hot-film air-mass meter, the For this purpose, the control unit sup- electrically heated element is in the form plies control pulses, the duration of of a platinum film resistance (heater). which are dependent upon the inducted The heater's temperature is registered air quantity, the engine speed and other by a temperature-dependent resistor actuating variables which are detected (throughflow sensor). The voltage ac- by sensors and processed in the control ross the heater is a measure for the air- unit. mass flow. It is converted by the hot-film air-mass meter's electronic-circuitry into Electronic control unit (ECU) a voltage which is suitable for the ECU By comparison with the L-Jetronic sy- (Fig. 37). stem, the digital control unit of this sy- stem adapts the air-fuel ratio by means of Fuel metering a loadlengine-speed map. On the basis Fuel is injected by means of solenoid- of the input signals from the sensors, the operated injection valves onto the in- control unit computes the injection dura- take valves of the engine. A solenoid tion as a measure of the quantity of fuel to valve is assigned to each cylinder and is be injected. The microcomputer system operated once per crankshaft revolu- of the control unit permits the required tion. In order to reduce the circuit com- functions to be influenced. plexity, all valves are connected electri-

Fig. 35: Hot-wire air-mass meter. The 70pm thin platinum wire is suspended inside the measuring venturi. Adaptation to operating conditions Enaine-tem~eraturesensor During certain operating conditions The engine-temperature sensor, a tem- (cold start, warm-up, acceleration, idle peratuydependent resistor, controls and full load), the fuel requirement dif- warm-up enrichment. fers greatly from the normal value, thus necessitating an intervention in mixture Supplementary functions formation. The overrun fuel cutoff function, and the speed limiting function at maximum Throttle-valve switch permissible engine speed, permit fuel This switch has a switching contact for economy and a reduction in pollutant each of the two end positions of the emission. throttle valve. It issues a switching signal to the control unit when the throttle valve Lambda closed-loop control is closed (idle) or fully open (full load). The lambda sensor supplies a signal which represents the instantaneous mix- Rotary idle actuator ture composition. In the control unit, the The idle speed can be reduced and signal of the lambda sensor is compared stabilized with the idle-speed control with an ideal value (setpoint), thus con- function. For this purpose, the rotary trolling a two-position controller. Depen- idle actuator opens a bypass line to the dent upon the result of comparison, throttle valve and supplies the engine either an excessively lean air-fuel mix- with more or less air. Since the hot-wire ture is enriched or an excessively rich air-mass meter senses the extra air, the mixture is leaned. Fuel metering is in- injected fuel quantity also changes as fluenced via the opening time of the in- required. jection valves.

Fig. 36: Hot-wire air-mass meter Fig. 37: Hot-film air-mass meter 1Hybrid circuit, 2 Cover, 3 Metal insert, a) Housing, b) Hot-film sensor (fitted in the middle 4 Venturi with hot wire, 5 Housing, 6 Screen, of the housing). 7 Retaining ring. 1 Heat sink, 2 Intermediate module, 3 Power module, 4 Hybrid circuit, 5 Sensor element. a

5

b

1 3

4 2

5

Fig. 2: Catalytic converter for reducing harmful emissions of CO, HC and Nq( Exhaust-gas 1 Ceramic material coated with catalytically active substances, 2 Steel-wool retainer, 3 Housing. composition

Main components substance by inhibiting the blood's ability to absorb oxygen. For this reason an en- The main exhaust-gas components are gine should never be run in an enclosed nitrogen, carbon dioxide and water space unless an exhaust-gas extraction vapor. These substances are non-toxic. system has been connected and Nitrogen (N2) is the element most abun- switched on. dant in the atmosphere. Although it is not The hydrocarbons assume the form of directly involved in the combustion pro- unburned fuel components as well as cess, at approx. 71 % it represents the new hydrocarbons formed during com- major exhaust-gas component. Small bustion. Aliphatic hydrocarbons are odor- amounts of nitrogen react with oxygen to less and have a low boiling point. The form nitrous oxides. closed-chain aromatic hydrocarbons Complete combustion converts the hy- (benzol, toluol, polycyclic hydrocarbons) drocarbons contained in the fuel's chemi- emit a distinct odor, and are considered cal bonds into carbon dioxide (C02) carcinogenic with continuous exposure. which makes up about 14% of the ex- Partially-oxidated hydrocarbons (alde- haust gas. The hydrogen contained in hydes, cetones, etc.) emit a disagreable the fuel's chemical structure combusts to odor. When exposed to sunlight they de- form water vapor (H20), most of which cay to form substances that are con- condenses as it cools (producing the sidered to act as carcinogens in people vapor cloud which can be seen emerging continually exposed to high concen- from the exhaust on cold days). trations. The term NOx is employed to identify the various oxides of nitrogen (mostly NO and NO2) that result as oxy- Secondary components gen combines with atmospheric nitrogen The secondary components carbon mon- during high-temperature combustion. oxide, hydrocarbons and incompletely- NO is colorless and odorless and is oxidized hydrocarbons are the result of gradually converted to NO2 in the atmos- incomplete combustion, while nitrous ox- phere. Pure NO2 is a toxic reddish-brown ides form in response to secondary reac- gas with a pungent odor. At the levels tions that accompany all air combustion found in air with high pollutant concen- processes. Carbon monoxide (CO) is a trations, NO2 can irritate the mucous colorless, odorless gas. It acts as a toxic membranes in the respiratory system.