Gasoline Fuel-InjectionSystem K-Jetronic
Robert Bosch GmbH, 2000Postfach 3002 20,D-70442 Stuttgart.Automotive Equipment Business Sector,Department for Automotive Services,Technical Publications (KH/PDI2).
Editor-in-Chief:Dipl.-Ing. (FH) Horst Bauer.
Editorial staff:Dipl.-Ing. Karl-Heinz Dietsche,Dipl.-Ing. (BA) Jrgen Crepin.
Presentation:Dipl.-Ing. (FH) Ulrich Adler,Joachim Kaiser,Berthold Gauder, Leinfelden-Echterdingen.
Technical graphics:Bauer & Partner, Stuttgart.
Unless otherwise stated, the above are allemployees of Robert Bosch GmbH, Stuttgart.
Reproduction, copying, or translation of thispublication, including excerpts therefrom, is only toensue with our previous written consent and withsource credit.Illustrations, descriptions, schematic diagrams, and other data only serve for explanatory purposesand for presentation of the text. They cannot beused as the basis for design, installation, or scopeof delivery. We assume no liability for conformity ofthe contents with national or local legal regulations.We are exempt from liability. We reserve the right to make changes at any time.
Printed in Germany.Imprim en Allemagne.
4th Edition, February 2000.English translation of the German edition dated: September 1998.
Combustion in the gasoline engineThe spark-ignition or Otto-cycle engine 2Gasoline-engine managementTechnical requirements 4Cylinder charge 5Mixture formation 7Gasoline-injection systemsOverview 10K-JetronicSystem overview 13Fuel supply 14Fuel metering 18 Adapting to operating conditions 24Supplementary functions 30Exhaust-gas treatment 32Electrical circuitry 36Workshop testing techniques 38
Since its introduction, the K-Jetronicgasoline-injection system has pro-ved itself in millions of vehicles.This development was a direct resultof the advantages which are inherentin the injection of gasoline with regard to demands for economy ofoperation, high output power, andlast but not least improvements tothe quality of the exhaust gasesemitted by the vehicle. Whereas thecall for higher engine output was theforemost consideration at the start ofthe development work on gasolineinjection, today the target is toachieve higher fuel economy andlower toxic emissions. Between the years 1973 and 1995,the highly reliable, mechanical multi-point injection system K-Jetronicwas installed as Original Equipmentin series-production vehicles. Today,it has been superseded by gasolineinjection systems which thanks to electronics have been vastly im-proved and expanded in their func-tions. Since this point, the K-Jetronichas now become particularly impor-tant with regard to maintenance andrepair.
This manual will describe the K-Jetronics function and its particu-lar features.
The spark-ignition or Otto-cycle engine
Operating conceptThe spark-ignition or Otto-cycle1)powerplant is an internal-combustion (IC)engine that relies on an externally-generated ignition spark to transform thechemical energy contained in fuel intokinetic energy. Todays standard spark-ignition enginesemploy manifold injection for mixtureformation outside the combustionchamber. The mixture formation systemproduces an air/fuel mixture (based ongasoline or a gaseous fuel), which is then drawn into the engine by the suctiongenerated as the pistons descend. Thefuture will see increasing application ofsystems that inject the fuel directly into thecombustion chamber as an alternateconcept. As the piston rises, it compressesthe mixture in preparation for the timedignition process, in which externally-generated energy initiates combustion viathe spark plug. The heat released in the
combustion process pressurizes thecylinder, propelling the piston back down,exerting force against the crankshaft andperforming work. After each combustionstroke the spent gases are expelled fromthe cylinder in preparation for ingestion ofa fresh charge of air/fuel mixture. Theprimary design concept used to governthis gas transfer in powerplants forautomotive applications is the four-strokeprinciple, with two crankshaft revolutionsbeing required for each complete cycle.
The four-stroke principleThe four-stroke engine employs flow-control valves to govern gas transfer(charge control). These valves open andclose the intake and exhaust tractsleading to and from the cylinder:
1st stroke: Induction,2nd stroke: Compression and ignition,3rd stroke: Combustion and work,4th stroke: Exhaust.
Induction strokeIntake valve: open,Exhaust valve: closed,Piston travel: downward,Combustion: none.
The pistons downward motion increasesthe cylinders effective volume to drawfresh air/fuel mixture through the passageexposed by the open intake valve.
Compression strokeIntake valve: closed,Exhaust valve: closed,Piston travel: upward,Combustion: initial ignition phase.
Combustion in the gasoline
Combustion in the gasoline engine
Reciprocating piston-engine design concept
OT = TDC (Top Dead Center); UT = BDC (BottomDead Center), Vh Swept volume, VC Compressedvolume, s Piston stroke.
1) After Nikolaus August Otto (18321891), whounveiled the first four-stroke gas-compression engineat the Paris World Exhibition in 1876.
As the piston travels upward it reducesthe cylinders effective volume tocompress the air/fuel mixture. Just beforethe piston reaches top dead center (TDC)the spark plug ignites the concentratedair/fuel mixture to initiate combustion.Stroke volume Vhand compression volume VCprovide the basis for calculating thecompression ratio = (Vh+VC)/VC.Compression ratios range from 7...13,depending upon specific engine design.Raising an IC engines compression ratioincreases its thermal efficiency, allowingmore efficient use of the fuel. As anexample, increasing the compression ratiofrom 6:1 to 8:1 enhances thermalefficiency by a factor of 12%. The latitudefor increasing compression ratio isrestricted by knock. This term refers touncontrolled mixture inflammation charac-terized by radical pressure peaks.Combustion knock leads to enginedamage. Suitable fuels and favorablecombustion-chamber configurations canbe applied to shift the knock threshold intohigher compression ranges.
Power strokeIntake valve: closed,Exhaust valve: closed,Piston travel: upward,Combustion: combustion/post-combus-tion phase.
The ignition spark at the spark plugignites the compressed air/fuel mixture,thus initiating combustion and theattendant temperature rise.This raises pressure levels within thecylinder to propel the piston downward.The piston, in turn, exerts force againstthe crankshaft to perform work; thisprocess is the source of the enginespower.Power rises as a function of engine speedand torque (P = M).A transmission incorporating variousconversion ratios is required to adapt thecombustion engines power and torquecurves to the demands of automotiveoperation under real-world conditions.
Exhaust strokeIntake valve: closed,Exhaust valve: open,Piston travel: upward,Combustion: none.
As the piston travels upward it forces thespent gases (exhaust) out through thepassage exposed by the open exhaustvalve. The entire cycle then recommenceswith a new intake stroke. The intake andexhaust valves are open simultaneouslyduring part of the cycle. This overlapexploits gas-flow and resonance patternsto promote cylinder charging andscavenging.
Operating cycle of the 4-stroke spark-ignition engine
Stroke 1: Induction Stroke 2: Compression Stroke 3: Combustion Stroke 4: Exhaust
Spark-ignition (SI)engine torque
The power P furnished by the spark-ignition engine is determined by theavailable net flywheel torque and theengine speed.The net flywheel torque consists of theforce generated in the combustionprocess minus frictional losses (internalfriction within the engine), the gas-exchange losses and the torque requiredto drive the engine ancillaries (Figure 1). The combustion force is generatedduring the power stroke and is defined bythe following factors: The mass of the air available for
combustion once the intake valveshave closed,
The mass of the simultaneouslyavailable fuel, and
The point at which the ignition sparkinitiates combustion of the air/fuelmixture.
Primary engine-management functions
The engine-management systems firstand foremost task is to regulate theengines torque generation by controllingall of those functions and factors in thevarious engine-management subsystemsthat determine how much torque isgenerated.
Cylinder-charge controlIn Bosch engine-management systemsfeaturing electronic throttle control (ETC),the cylinder-charge control subsystemdetermines the required induction-airmass and adjusts the throttle-valveopening accordingly. The driver exercisesdirect control over throttle-valve openingon conventional injection systems via thephysical link with the accelerator pedal.
Mixture formationThe mixture formation subsystem cal-culates the instantaneous mass fuelrequirement as the basis for determiningthe correct injection duration and optimalinjection timing.
Driveline torque factors
1 Ancillary equipment(alternator,a/c compressor, etc.),
2 Engine,3 Clutch,4 Transmission.
Air mass (fresh induction charge)
Ignition angle (firing point)Engine
Gas-transfer and frictionAncillaries
Clutch/converter losses and conversion ratiosTransmission losses and conversion ratios
Combustion output torque
1 1 2 3 4
IgnitionFinally, the ignition subsystem de-termines the crankshaft angle thatcorresponds to precisely the ideal instantfor the spark to ignite the mixture.
The purpose of this closed-loop controlsystem is to provide the torquedemanded by the driver while at thesame time satisfying strict criteria in theareas of Exhaust emissions, Fuel consumption, Power, Comfort and convenience, and Safety.
Cylinder chargeElementsThe gas mixture found in the cylinderonce the intake valve closes is referred toas the cylinder charge, and consists ofthe inducted fresh air-fuel mixture alongwith residual gases.
Fresh gasThe fresh mixture drawn into the cylinderis a combination of fresh air and the fuelentrained with it. While most of the freshair enters through the throttle valve,supplementary fresh gas can also bedrawn in through the evaporative-
emissions control system (Figure 2). Theair entering through the throttle-valve andremaining in the cylinder after intake-valve closure is the decisive factordefining the amount of work transferredthrough the piston during combustion,and thus the prime determinant for theamount of torque generated by theengine. In consequence, modifications toenhance maximum engine power andtorque almost always entail increasingthe maximum possible cylinder charge.The theoretical maximum charge isdefined by the volumetric capacity.
Residual gasesThe portion of the charge consisting ofresidual gases is composed of The exhaust-gas mass that is not
discharged while the exhaust valve isopen and thus remains in the cylinder,and
The mass of recirculated exhaust gas(on systems with exhaust-gas recircu-lation, Figure 2).
The proportion of residual gas is de-termined by the gas-exchange process.Although the residual gas does notparticipate directly in combustion, it doesinfluence ignition patterns and the actualcombustion sequence. The effects of thisresidual-gas component may be thoroughlydesirable under part-throttle operation.Larger throttle-valve openings to com-pensate for reductions in fresh-gas filling
Cylinder charge in the spark-ignition engine
1 Air and fuel vapor,2 Purge valve
with variable aperture,3 Link to evaporative-emissions
control system,4 Exhaust gas,5 EGR valve with
variable aperture,6 Mass airflow (barometric pressure pU),7 Mass airflow
(intake-manifold pressure ps),8 Fresh air charge
(combustion-chamber pressure pB),9 Residual gas charge
(combustion-chamber pressure pB),10 Exhaust gas (back-pressure pA),11 Intake valve,12 Exhaust valve, Throttle-valve angle.
6 7 108
are needed to meet higher torquedemand. These higher angles reduce theengines pumping losses, leading tolower fuel consumption. Precisely reg-ulated injection of residual gases canalso modify the combustion process toreduce emissions of nitrous oxides (NOx)and unburned hydrocarbons (HC).
Throttle valveThe power produced by the spark-ignition engine is directly proportional tothe mass airflow entering it. Control ofengine output and the correspondingtorque at each engine speed is regulatedby governing the amount of air beinginducted via the throttle valve. Leavingthe throttle valve partially closed restrictsthe amount of air being drawn into theengine and reduces torque generation.The extent of this throttling effectdepends on the throttle valves positionand the size of the resulting aperture.The engine produces maximum powerwhen the throttle valve is fully open(WOT, or wide open throttle).Figure 3 illustrates the conceptualcorrelation between fresh-air chargedensity and engine speed as a functionof throttle-valve aperture.
Gas exchangeThe intake and exhaust valves open andclose at specific points to control thetransfer of fresh and residual gases. Theramps on the camshaft lobes determineboth the points and the rates at which thevalves open and close (valve timing) todefine the gas-exchange process, andwith it the amount of fresh gas availablefor combustion.Valve overlap defines the phase in whichthe intake and exhaust valves are opensimultaneously, and is the prime factor indetermining the amount of residual gasremaining in the cylinder. This process isknown as "internal" exhaust-gasrecirculation. The mass of residual gascan also be increased using "external"exhaust-gas recirculation, which relies
on a supplementary EGR valve linkingthe intake and exhaust manifolds. Theengine ingests a mixture of fresh air andexhaust gas when this valve is open.
Pressure chargingBecause maximum possible torque isproportional to fresh-air charge density, itis possible to raise power output bycompressing the air before it enters thecylinder.
Dynamic pressure chargingA supercharging (or boost) effect can beobtained by exploiting dynamics withinthe intake manifold. The actual degree ofboost will depend upon the manifoldsconfiguration as well as the enginesinstantaneous operating point(essentially a function of the enginesspeed, but also affected by load factor).The option of varying intake-manifoldgeometry while the vehicle is actuallybeing driven, makes it possible to employdynamic precharging to increase themaximum available charge mass througha wide operational range.
Mechanical superchargingFurther increases in air mass areavailable through the agency of
Throttle-valve map for spark-ignition engine