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Whereas the call for higher engine output was the foremost consideration at the start of the development work on gasoline injection, today the target is to achieve higher fuel economy an

Gasoline Fuel-Injection System K-Jetronic

Gasoline-engine management

Technical Instruction

Published by:

© Robert Bosch GmbH, 2000

Postfach 30 02 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) Jürgen Crepin.

Bauer & Partner, Stuttgart.

Unless otherwise stated, the above are all

employees of Robert Bosch GmbH, Stuttgart.

Reproduction, copying, or translation of this publication, including excerpts therefrom, is only to ensue with our previous written consent and with source credit.

Illustrations, descriptions, schematic diagrams, and other data only serve for explanatory purposes and for presentation of the text They cannot be used as the basis for design, installation, or scope

of delivery We assume no liability for conformity of the 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.

Imprimé en Allemagne.

4th Edition, February 2000.

English translation of the German edition dated: September 1998.

Combustion in the gasoline engine

Since its introduction, the K-Jetronic

gasoline-injection system has

pro-ved itself in millions of vehicles

This development was a direct result

of the advantages which are inherent

in the injection of gasoline with

regard to demands for economy of

operation, high output power, and

last but not least improvements to

the quality of the exhaust gases

emitted by the vehicle Whereas the

call for higher engine output was the

foremost consideration at the start of

the development work on gasoline

injection, today the target is to

achieve higher fuel economy and

lower toxic emissions

Between the years 1973 and 1995,

the highly reliable, mechanical

multi-point injection system K-Jetronic

was installed as Original Equipment

in series-production vehicles Today,

it has been superseded by gasoline

injection systems which thanks to

electronics have been vastly

im-proved and expanded in their

func-tions Since this point, the K-Jetronic

has now become particularly

impor-tant with regard to maintenance and

repair

This manual will describe the

K-Jetronic’s function and its

particu-lar features

The spark-ignition

or Otto-cycle engine Operating concept

The 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

Today’s 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 of

a 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 principle

The four-stroke engine employs control valves to govern gas transfer(charge control) These valves open andclose the intake and exhaust tractsleading to and from the cylinder:

flow-1st stroke: Induction,2nd stroke: Compression and ignition,3rd stroke: Combustion and work,4th stroke: Exhaust

Induction stroke

Intake valve: open,Exhaust valve: closed,Piston travel: downward,Combustion: none

The piston’s downward motion increasesthe cylinder’s effective volume to drawfresh air/fuel mixture through the passageexposed by the open intake valve

Compression stroke

Intake valve: closed,Exhaust valve: closed,Piston travel: upward,Combustion: initial ignition phase

Reciprocating piston-engine design concept

OT = TDC (Top Dead Center); UT = BDC (Bottom Dead Center), Vh Swept volume, VC Compressed volume, sPiston stroke.

Fig 1

OT

UT OT

As the piston travels upward it reduces

the cylinder’s effective volume to

compress the air/fuel mixture Just before

the piston reaches top dead center (TDC)

the spark plug ignites the concentrated

air/fuel mixture to initiate combustion

Stroke volume Vh

and compression volume VC

provide the basis for calculating the

compression ratio

ε= (Vh+VC)/VC

Compression ratios ε range from 7 13,

depending upon specific engine design

Raising an IC engine’s compression ratio

increases its thermal efficiency, allowing

more efficient use of the fuel As an

example, increasing the compression ratio

from 6:1 to 8:1 enhances thermal

efficiency by a factor of 12 % The latitude

for increasing compression ratio is

restricted by knock This term refers to

uncontrolled mixture inflammation

charac-terized by radical pressure peaks

Combustion knock leads to engine

damage Suitable fuels and favorable

combustion-chamber configurations can

be applied to shift the knock threshold into

higher compression ranges

Power stroke

Intake 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 engine’spower

Power rises as a function of engine speedand torque (P= M⋅ω)

A transmission incorporating variousconversion ratios is required to adapt thecombustion engine’s power and torquecurves to the demands of automotiveoperation under real-world conditions

Exhaust stroke

Intake 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 patterns

to promote cylinder charging andscavenging

Technical requirements

Spark-ignition (SI) engine torque

The power P furnished by the ignition engine is determined by theavailable net flywheel torque and theengine speed

spark-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 required

to 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 forcombustion 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 management functions

engine-The engine-management system’s firstand foremost task is to regulate theengine’s torque generation by controllingall of those functions and factors in thevarious engine-management subsystemsthat determine how much torque isgenerated

Cylinder-charge control

In 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 opening

on conventional injection systems via thephysical link with the accelerator pedal

Mixture formation

The “mixture formation” subsystem culates the instantaneous mass fuelrequirement as the basis for determiningthe correct injection duration and optimalinjection timing

Gasoline-Driveline torque factors

1 Ancillary equipment

(alternator, a/c compressor, etc.),

Engine output torque

Flywheel torque

Drive force

5

Ignition

Finally, the “ignition” subsystem

de-termines the crankshaft angle that

corresponds to precisely the ideal instant

for the spark to ignite the mixture

The purpose of this closed-loop control

system is to provide the torque

demanded by the driver while at the

same time satisfying strict criteria in the

The gas mixture found in the cylinder

once the intake valve closes is referred to

as the cylinder charge, and consists of

the inducted fresh air-fuel mixture along

with residual gases

Fresh gas

The fresh mixture drawn into the cylinder

is a combination of fresh air and the fuel

entrained with it While most of the fresh

air enters through the throttle valve,

supplementary fresh gas can also be

drawn 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

– The mass of recirculated exhaust gas(on systems with exhaust-gas recircu-lation, Figure 2)

The proportion of residual gas is termined by the gas-exchange process

de-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 pensate for reductions in fresh-gas filling

com-Cylinder charge in the spark-ignition engine

1 Air and fuel vapor,

9

α

are needed to meet higher torquedemand These higher angles reduce theengine’s 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).

Control elements

Throttle valve

The power produced by the ignition engine is directly proportional tothe mass airflow entering it Control ofengine output and the correspondingtorque at each engine speed is regulated

spark-by 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 valve’s 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 function

of throttle-valve aperture

Gas exchange

The 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

Dynamic pressure charging

A supercharging (or boost) effect can beobtained by exploiting dynamics withinthe intake manifold The actual degree ofboost will depend upon the manifold’sconfiguration as well as the engine’sinstantaneous operating point(essentially a function of the engine’sspeed, 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 through

a wide operational range

Mechanical superchargingFurther increases in air mass areavailable through the agency of

Gasoline-engine

management

6

Throttle-valve map for spark-ignition engine

Throttle valve at intermediate aperture

Throttle valve completely closed

Idle

7

mechanically driven compressors

pow-ered by the engine’s crankshaft, with the

two elements usually rotating at an

in-variable relative ratio Clutches are often

used to control compressor activation

Exhaust-gas turbochargers

Here the energy employed to power the

compressor is extracted from the exhaust

gas This process uses the energy that

naturally-aspirated engines cannot

exploit directly owing to the inherent

restrictions imposed by the gas

ex-pansion characteristics resulting from the

crankshaft concept One disadvantage is

the higher back-pressure in the exhaust

gas exiting the engine This

back-pressure stems from the force needed to

maintain compressor output

The exhaust turbine converts the

exhaust-gas energy into mechanical

energy, making it possible to employ an

impeller to precompress the incoming

fresh air The turbocharger is thus a

combination of the turbine in the

exhaust-fas flow and the impeller that compresses

the intake air

Figure 4 illustrates the differences in the

torque curves of a naturally-aspirated

engine and a turbocharged engine

is a mass ratio of 14.7:1, referred to asthe stoichiometric ratio In concrete termsthis translates into a mass relationship of14.7 kg of air to burn 1 kg of fuel, whilethe corresponding volumetric ratio isroughly 9,500 litres of air for completecombustion of 1 litre of fuel

The air-fuel mixture is a major factor indetermining the spark-ignition engine’srate of specific fuel consumption

Genuine complete combustion andabsolutely minimal fuel consumptionwould be possible only with excess air,but here limits are imposed by suchconsiderations as mixture flammabilityand the time available for combustion

The air-fuel mixture is also vital indetermining the efficiency of exhaust-gastreatment system The current state-of-the-art features a 3-way catalyticconverter, a device which relies on astoichiometric A/F ratio to operate atmaximum efficiency and reduce un-desirable exhaust-gas components bymore than 98 %

Current engines therefore operate with astoichiometric A/F ratio as soon as theengine’s operating status permits

Certain engine operating conditionsmake mixture adjustments to non-stoichiometric ratios essential With acold engine for instance, where specificadjustments to the A/F ratio are required

As this implies, the mixture-formationsystem must be capable of responding to

a range of variable requirements

Torque curves for turbocharged

and atmospheric-induction engines

with equal power outputs

1 Engine with turbocharger,

Excess-air factor

The designation l (lambda) has beenselected to identify the excess-air factor(or air ratio) used to quantify the spreadbetween the actual current mass A/F ratioand the theoretical optimum (14.7:1):

λ = Ratio of induction air mass to airrequirement for stoichiometric com-bustion

λ= 1: The inducted air mass corresponds

to the theoretical requirement

λ < 1: Indicates an air deficiency,producing a corresponding rich mixture

Maximum power is derived from λ =0.85 0.95

λ > 1: This range is characterized byexcess air and lean mixture, leading tolower fuel consumption and reducedpower The potential maximum value for λ– called the “lean-burn limit (LML)” – isessentially defined by the design of theengine and of its mixture for-mation/induction system Beyond thelean-burn limit the mixture ceases to beignitable and combustion miss sets in,accompanied by substantial degener-ation of operating smoothness

In engines featuring systems to inject fueldirectly into the chamber, these operatewith substantially higher excess-airfactors (extending to λ = 4) since com-bustion proceeds according to differentlaws

Spark-ignition engines with manifoldinjection produce maximum power at air

deficiencies of 5 15 % (λ = 0.95 0.85),but maximum fuel economy comes in at10 20 % excess air (λ= 1.1 1.2).Figures 1 and 2 illustrate the effect of theexcess-air factor on power, specific fuelconsumption and generation of toxicemissions As can be seen, there is nosingle excess-air factor which cansimultaneously generate the mostfavorable levels for all three factors Airfactors of λ = 0.9 1.1 produce

“conditionally optimal” fuel economy with

“conditionally optimal” power generation

in actual practice

Once the engine warms to its normaloperating temperature, precise andconsistent maintenance of λ = 1 is vitalfor the 3-way catalytic treatment ofexhaust gases Satisfying this re-quirement entails exact monitoring ofinduction-air mass and precise metering

of fuel mass

Optimal combustion from current gines equipped with manifold injectionrelies on formation of a homogenousmixture as well as precise metering of theinjected fuel quantity This makeseffective atomization essential Failure tosatisfy this requirement will foster theformation of large droplets of condensedfuel on the walls of the intake tract and inthe combustion chamber These dropletswill fail to combust completely and theultimate result will be higher HCemissions

a Rich mixture (air deficiency),

b Lean mixture (excess air).

9

Adapting to specific

operating conditions

Certain operating states cause fuel

requirements to deviate substantially from

the steady-state requirements of an engine

warmed to its normal temperature, thus

necessitating corrective adaptations in the

mixture-formation apparatus The

follow-ing descriptions apply to the conditions

found in engines with manifold injection

Cold starting

During cold starts the relative quantity of

fuel in the inducted mixture decreases: the

mixture “goes lean.” This lean-mixture

phenomenon stems from inadequate

blending of air and fuel, low rates of fuel

vaporization, and condensation on the

walls of the inlet tract, all of which are

promoted by low temperatures To

com-pensate for these negative factors, and to

facilitate cold starting, supplementary fuel

must be injected into the engine

Post-start phase

Following low-temperature starts,

supplementary fuel is required for a brief

period, until the combustion chamber

heats up and improves the internal

mixture formation This richer mixture

also increases torque to furnish a

smoother transition to the desired idle

speed

Warm-up phase

The warm-up phase follows on the heels

of the starting and immediate post-start

phases At this point the engine still

requires an enriched mixture to offset the

fuel condensation on the intake-manifold

walls Lower temperatures are

synony-mous with less efficient fuel

proces-sing (owing to factors such as poor

mix-ing of air and fuel and reduced fuel

va-porization) This promotes fuel

precip-itation within the intake manifold, with

the formation of condensate fuel that will

only vaporize later, once temperatures

have increased These factors make it

necessary to provide progressive mixture

enrichment in response to decreasing

temperatures

Idle and part-load

Idle is defined as the operating status inwhich the torque generated by the engine

is just sufficient to compensate for frictionlosses The engine does not providepower to the flywheel at idle Part-load (orpart-throttle) operation refers to therange of running conditions between idleand generation of maximum possibletorque Today’s standard concepts relyexclusively on stoichiometric mixtures forthe operation of engines running at idleand part-throttle once they have warmed

to their normal operating temperatures

Full load (WOT)

At WOT (wide-open throttle) mentary enrichment may be required AsFigure 1 indicates, this enrichmentfurnishes maximum torque and/or power

supple-Acceleration and deceleration

The fuel’s vaporization potential is stronglyaffected by pressure levels inside theintake manifold Sudden variations inmanifold pressure of the kind encountered

in response to rapid changes in valve aperture cause fluctuations in thefuel layer on the walls of the intake tract

throttle-Spirited acceleration leads to highermanifold pressures The fuel respondswith lower vaporization rates and the fuellayer within the manifold runners expands

A portion of the injected fuel is thus lost inwall condensation, and the engine goeslean for a brief period, until the fuel layerrestabilizes In an analogous, but inverted,response pattern, sudden decelerationleads to rich mixtures A temperature-sensitive correction function (transitioncompensation) adapts the mixture tomaintain optimal operational responseand ensure that the engine receives theconsistent air/fuel mixture needed forefficient catalytic-converter performance

Trailing throttle (overrun)

Fuel metering is interrupted during trailingthrottle Although this expedient savesfuel on downhill stretches, its primarypurpose is to guard the catalytic converteragainst overheating stemming from poorand incomplete combustion (misfiring)

Carburetors and gasoline-injection tems are designed for a single purpose:

sys-To supply the engine with the optimal fuel mixture for any given operatingconditions Gasoline injection systems,and electronic systems in particular, arebetter at maintaining air-fuel mixtureswithin precisely defined limits, whichtranslates into superior performance inthe areas of fuel economy, comfort andconvenience, and power Increasinglystringent mandates governing exhaustemissions have led to a total eclipse of thecarburetor in favor of fuel injection

air-Although current systems rely almostexclusively on mixture formation outsidethe combustion chamber, concepts based

on internal mixture formation – with fuelbeing injected directly into the combustionchamber – were actually the foundationfor the first gasoline-injection systems Asthese systems are superb instruments forachieving further reductions in fuelconsumption, they are now becoming anincreasingly significant factor

Overview

Systems with external mixture formation

The salient characteristic of this type ofsystem is the fact that it forms the air-fuelmixture outside the combustion chamber,inside the intake manifold

Multipoint fuel injection

Multipoint fuel injection forms the idealbasis for complying with the mixture-formation criteria described above In thistype of system each cylinder has its owninjector discharging fuel into the areadirectly in front of the intake valve

Representative examples are the variousversions of the KE and L-Jetronic systems(Figure 1)

Mechanical injection systemsThe K-Jetronic system operates byinjecting continually, without an exter-nal drive being necessary Instead ofbeing determined by the injection valve,fuel mass is regulated by the fueldistributor

Combined mechanical-electronicfuel injection

Although the K-Jetronic layout served asthe mechanical basis for the KE-Jetronicsystem, the latter employs expandeddata-monitoring functions for moreprecise adaptation of injected fuelquantity to specific engine operatingconditions

Electronic injection systemsInjection systems featuring electroniccontrol rely on solenoid-operated injection

Multipoint fuel injection (MPI)

valves for intermittent fuel discharge The

actual injected fuel quantity is regulated

by controlling the injector's opening time

(with the pressure-loss gradient through

the valve being taken into account in

calculations as a known quantity)

Examples: L-Jetronic, LH-Jetronic, and

Motronic as an integrated

engine-manage-ment system

Single-point fuel injection

Single-point (throttle-body injection (TBI))

fuel injection is the concept behind this

electronically-controlled injection system

in which a centrally located

solenoid-operated injection valve mounted

upstream from the throttle valve sprays

fuel intermittently into the manifold

Mono-Jetronic and Mono-Motronic are the

Bosch systems in this category (Figure 2)

Systems for internal

mixture formation

Direct-injection (DI) systems rely on

solenoid-operated injection valves to spray

fuel directly into the combustion chamber;

the actual mixture-formation process takes

place within the cylinders, each of which

has its own injector (Figure 3) Perfect

atomization of the fuel emerging from the

injectors is vital for efficient combustion

Under normal operating conditions, DI

engines draw in only air instead of the

combination of air and fuel common toconventional injection systems This is one

of the new system's prime advantages: Itbanishes all potential for fuel condensationwithin the runners of the intake manifold

External mixture formation usuallyprovides a homogenous, stoichiometric air-fuel mixture throughout the entirecombustion chamber In contrast, shiftingthe mixture-preparation process into thecombustion chamber provides for twodistinctive operating modes:

With stratified-charge operation, only themixture directly adjacent to the spark plugneeds to be ignitable The remainder of theair-fuel charge in the combustion chambercan consist solely of fresh and residualgases, without unburned fuel This strategyfurnishes an extremely lean overall mixturefor idling and part-throttle operation, withcommensurate reductions in fuelconsumption

Homogenous operation reflects theconditions encountered in external mixtureformation by employing uniformconsistency for the entire air-fuel chargethroughout the combustion chamber

Under these conditions all of the fresh airwithin the chamber participates in thecombustion process This operationalmode is employed for WOT operation

MED-Motronic is used for closed-loopcontrol of DI gasoline engines

The story of

fuel injection

12

The story of fuel injection

The story of fuel injection extendsback to cover a period of almost onehundred years

The Gasmotorenfabik Deutz wasmanufacturing plunger pumps for in-jecting fuel in a limited productionseries as early as 1898

A short time later the uses of the turi-effect for carburetor design werediscovered, and fuel-injection systemsbased on the technology of the timeceased to be competitive

ven-Bosch started research on injection pumps in 1912 The firstaircraft engine featuring Bosch fuel in-jection, a 1,200-hp unit, entered seriesproduction in 1937; problems with car-buretor icing and fire hazards had lentspecial impetus to fuel-injection devel-opment work for the aeronautics field

gasoline-This development marks the ning of the era of fuel injection atBosch, but there was still a long path

begin-to travel on the way begin-to fuel injection forpassenger cars

1951 saw a Bosch direct-injection unitbeing featured as standard equipment

on a small car for the first time eral years later a unit was installed inthe 300 SL, the legendary productionsports car from Daimler-Benz

Sev-In the years that followed, ment on mechanical injection pumpscontinued, and

develop-In 1967 fuel injection took anothergiant step forward: The first electronic

injection system: the controlled D-Jetronic!

intake-pressure-In 1973 the air-flow-controlled nic appeared on the market, at thesame time as the K-Jetronic, which fea-tured mechanical-hydraulic control andwas also an air-flow-controlled system

L-Jetro-In 1976, the K-Jetronic was the firstautomotive system to incorporate aLambda closed-loop control

1979 marked the introduction of a newsystem: Motronic, featuring digital pro-cessing for numerous engine func-tions This system combined L-Jetro-nic with electronic program-map con-trol for the ignition The first automo-tive microprocessor!

In 1982, the K-Jetronic model becameavailable in an expanded configura-tion, the KE-Jetronic, including anelectronic closed-loop control circuitand a Lambda oxygen sensor

These were joined by Bosch Jetronic in 1987: This particularly cost-efficient single-point injection unitmade it feasible to equip small vehicleswith Jetronic, and once and for all madethe carburetor absolutely superfluous

Mono-By the end of 1997, around 64 millionBosch engine-management systemshad been installed in countless types ofvehicles since the introduction of the D-Jetronic in 1967 In 1997 alone, thefigure was 4.2 million, comprised of

1 million throttle-body injection (TBI)systems and 3.2 million multipoint fuel-injection (MPI) systems

Bosch gasoline fuel injection from the year 1954

System overview

The K-Jetronic is a mechanically and

hydraulically controlled fuel-injection

sys-tem which needs no form of drive and

which meters the fuel as a function of the

intake air quantity and injects it

contin-uously onto the engine intake valves

Specific operating conditions of the

engine require corrective intervention in

mixture formation and this is carried out

by the K-Jetronic in order to optimize

starting and driving performance, power

output and exhaust composition Owing

to the direct air-flow sensing, the

K-Je-tronic system also allows for engine

variations and permits the use of facilities

for exhaust-gas aftertreatment for which

precise metering of the intake air quantity

is a prerequisite

The K-Jetronic was originally designed

as a purely mechanical injection system

Today, using auxiliary electronic

equip-ment, the system also permits the use of

lambda closed-loop control

The K-Jetronic fuel-injection system

covers the following functional areas:

Air-flow measurement

The amount of air drawn in by the engine

is controlled by a throttle valve and measured by an air-flow sensor

Fuel metering

The amount of air, corresponding to theposition of the throttle plate, drawn in bythe engine serves as the criterion for metering of the fuel to the individual cylinders The amount of air drawn in bythe engine is measured by the air-flowsensor which, in turn, controls the fueldistributor The air-flow sensor and thefuel distributor are assemblies whichform part of the mixture control unit

Injection occurs continuously, i.e withoutregard to the position of the intake valve

During the intake-valve closed phase, thefuel is “stored” Mixture enrichment iscontrolled in order to adapt to variousoperating conditions such as start, warm-

up, idle and full load In addition, mentary functions such as overrun fuelcutoff, engine-speed limiting and closed-loop lambda control are possible

Fuel accumulator

Air-flow sensor

Fuel distributor

Fuel

Air

Injection valves

Mixture control unit

Fuel supply

The fuel supply system comprises – Electric fuel pump,

– Fuel accumulator,– Fine filter,

– Primary-pressure regulator and – Injection valves

An electrically driven roller-cell pumppumps the fuel from the fuel tank at apressure of over 5 bar to a fuel accu-mulator and through a filter to the fuel distributor From the fuel distributor thefuel flows to the injection valves Theinjection valves inject the fuel con-tinuously into the intake ports of theengine Thus the system designation K(taken from the German for continuous)

When the intake valves open, the mixture

is drawn into the cylinder

The fuel primary-pressure regulatormaintains the supply pressure in the system constant and reroutes the excessfuel back to the fuel tank

Owing to continual scavenging of the fuelsupply system, there is always cool fuel

available This avoids the formation offuel-vapor bubbles and achieves goodhot starting behavior

Electric fuel pump

The electric fuel pump is a roller-cellpump driven by a permanent-magnet electric motor

The rotor plate which is eccentrically mounted in the pump housing is fittedwith metal rollers in notches around itscircumference which are pressed againstthe pump housing by centrifugal forceand act as rolling seals The fuel is car-ried in the cavities which form betweenthe rollers The pumping action takesplace when the rollers, after havingclosed the inlet bore, force the trappedfuel in front of them until it can escapefrom the pump through the outlet bore(Figure 4) The fuel flows directly aroundthe electric motor There is no danger ofexplosion, however, because there is never an ignitable mixture in the pumphousing

Schematic diagram of the K-Jetronic system with closed-loop lambda control

1 Fuel tank, 2 Electric fuel pump, 3 Fuel accumulator, 4 Fuel filter, 5 Warm-up regulator, 6 Injection valve,

7 Intake manifold, 8 Cold-start valve, 9 Fuel distributor, 10 Air-flow sensor, 11 Timing valve, 12 Lambda sensor, 13 Thermo-time switch, 14 Ignition distributor, 15 Auxiliary-air device, 16 Throttle-valve switch,

17 ECU, 18 Ignition and starting switch, 19 Battery.

BOSCH

The electric fuel pump delivers more fuel

than the maximum requirement of the

engine so that compression in the fuel

system can be maintained under all

oper-ating conditions A check valve in the

pump decouples the fuel system from

the fuel tank by preventing reverse flow of

fuel to the fuel tank

The electric fuel pump starts to operate

immediately when the ignition and

start-ing switches are operated and remains

switched on continuously after the engine

has started A safety circuit is

incorpor-ated to stop the pump running and, thus,

to prevent fuel being delivered if the

ig-nition is switched on but the engine has

stopped turning (for instance in the case

of an accident)

The fuel pump is located in the

imme-diate vicinity of the fuel tank and requires

no maintenance

Fuel accumulator

The fuel accumulator maintains the

pressure in the fuel system for a certain

time after the engine has been switched

off in order to facilitate restarting,

parti-cularly when the engine is hot The

spe-cial design of the accumulator housing

(Figure 5) deadens the sound of the fuel

pump when the engine is running

The interior of the fuel accumulator is

divided into two chambers by means of a

diaphragm One chamber serves as the

accumulator for the fuel whilst the other

represents the compensation volume

and is connected to the atmosphere or to

the fuel tank by means of a vent fitting

During operation, the accumulator

chamber is filled with fuel and the

dia-phragm is caused to bend back against

the force of the spring until it is halted by

the stops in the spring chamber The

diaphragm remains in this position, which

corresponds to the maximum

accumu-lator volume, as long as the engine is

1 Spring chamber, 2 Spring, 3 Stop, 4 Diaphragm,

5 Accumulator volume, 6 Fuel inlet or outlet,

7 Connection to the atmosphere.

Operation of roller-cell pump

1 Suction side, 2 Rotor plate, 3 Roller,

4 Roller race plate, 5 Pressure side.

Electric fuel pump

1 Suction side, 2 Pressure limiter, 3 Roller-cell pump, 4 Motor armature, 5 Check valve,

6 Pressure side.

4

6 1

a

b

Fig 3 Fig 4

Fig 5

Fuel filter

The fuel filter retains particles of dirtwhich are present in the fuel and whichwould otherwise have an adverse effect

on the functioning of the injection system

The fuel filter contains a paper elementwith a mean pore size of 10 µm backed

up by a fluff trap This combination ensures a high degree of cleaning

The filter is held in place in the housing

by means of a support plate It is fitted inthe fuel line downstream from the fuel accumulator and its service life dependsupon the amount of dirt in the fuel It isimperative that the arrow on the filterhousing showing the direction of fuel flowthrough the filter is observed when the filter is replaced

Primary-pressure regulator

The primary-pressure regulator tains the pressure in the fuel system constant

main-It is incorporated in the fuel distributorand holds the delivery pressure (systempressure) at about 5 bar The fuel pumpalways delivers more fuel than is required

by the vehicle engine, and this causes aplunger to shift in the pressure regulatorand open a port through which excessfuel can return to the tank

The pressure in the fuel system and theforce exerted by the spring on the pressure-regulator plunger balance eachother out If, for instance, fuel-pump

delivery drops slightly, the plunger is shifted by the spring to a correspondingnew position and in doing so closes offthe port slightly through which the excessfuel returns to the tank This means thatless fuel is diverted off at this point andthe system pressure is controlled to itsspecified level

When the engine is switched off, the fuelpump also switches off and the primarypressure drops below the opening pres-sure of the injection valves The pressureregulator then closes the return-flow portand thus prevents the pressure in the fuelsystem from sinking any further (Fig 8)

Fuel-injection valves

The injection valves open at a given sure and atomize the fuel through oscilla-tion of the valve needle The injectionvalves inject the fuel metered to them intothe intake passages and onto the intakevalves They are secured in special

pres-

Gasoline-injection

systems

16

Primary-pressure regulator fitted to fuel distributor

a In rest position, b In actuated position

1 System-pressure entry, 2 Seal, 3 Return to fuel tank, 4 Plunger, 5 Spring.

holders to insulate them against the heat

radiated from the engine The injection

valves have no metering function

them-selves, and open of their own accord

when the opening pressure of e.g 3.5

bar is exceeded They are fitted with a

valve needle (Fig 9) which oscillates

(“chatters”) audibly at high frequency

when fuel is injected This results in

ex-cellent atomization of the fuel even with

the smallest of injection quantities When

the engine is switched off, the injection

valves close tightly when the pressure in

the fuel-supply system drops below their

opening pressure This means that no

more fuel can enter the intake passages

once the engine has stopped

Air-shrouded fuel-injection valves

Air-shrouded injection valves improve the

mixture formation particularly at idle

Using the pressure drop across the

throttle valve, a portion of the air inducted

by the engine is drawn into the cylinder

through the injection valve (Fig 20): The

result is excellent atomization of the fuel

at the point of exit (Fig 10) Air-shrouded

injection valves reduce fuel consumption

and toxic emission constituents

K-Jetronic

17

Pressure curve after engine switchoff

Firstly pressure falls from the normal system

pressure (1) to the pressure-regulator closing pressure (2) The fuel accumulator then causes

it to increase to the level (3) which is below the opening pressure (4) of the injection valves.

1

2

3 4 b

a

Fig 8 Fig 9

Fig 10

Spray pattern of an injection valve without

air-shrouding (left) and with air-shrouding (right).

Fuel metering

The task of the fuel-management system

is to meter a quantity of fuel sponding to the intake air quantity

corre-Basically, fuel metering is carried out

by the mixture control unit This prises the air-flow sensor and the fueldistributor

com-In a number of operating modes however,the amount of fuel required deviatesgreatly from the “standard” quantity and itbecomes necessary to intervene in themixture formation system (see section

“Adaptation to operating conditions”)

Air-flow sensor

The quantity of air drawn in by the engine

is a precise measure of its operatingload The air-flow sensor operates ac-cording to the suspended-body principle,and measures the amount of air drawn in

by the engine

The intake air quantity serves as themain actuating variable for determiningthe basic injection quantity It is the appropriate physical quantity for derivingthe fuel requirement, and changes in theinduction characteristics of the enginehave no effect upon the formation of the

air-fuel mixture Since the air drawn in bythe engine must pass through the air-flowsensor before it reaches the engine, thismeans that it has been measured andthe control signal generated before it actually enters the engine cylinders Theresult is that, in addition to other measures described below, the correctmixture adaptation takes place at alltimes

a Sensor plate in its

Principle of the air-flow sensor

a Small amount of air drawn in: sensor plate only lifted slightly, b Large amount of air drawn in:

sensor plate is lifted considerably further.

The air-flow sensor is located upstream

of the throttle valve so that it measures all

the air which enters the engine cylinders

It comprises an air funnel in which the

sensor plate (suspended body) is free to

pivot The air flowing through the funnel

deflects the sensor plate by a given

amount out of its zero position, and this

movement is transmitted by a lever

sys-tem to a control plunger which

deter-mines the basic injection quantity

re-quired for the basic functions

Consider-able pressure shocks can occur in the

intake system if backfiring takes place in

the intake manifold For this reason, the

air-flow sensor is so designed that the

sensor plate can swing back in the

opposite direction in the event of misfire,

and past its zero position to open a relief

cross-section in the funnel A rubber

buffer limits the downward stroke (the

upwards stroke on the downdraft air-flow

sensor) A counterweight compensates

for the weight of the sensor plate and

lever system (this is carried out by an

extension spring on the downdraft

air-flow sensor) A leaf spring ensures the

correct zero position in the switched-off

phase

Fuel distributor

Depending upon the position of the plate

in the air-flow sensor, the fuel distributormeters the basic injection quantity to theindividual engine cylinders The position

of the sensor plate is a measure of theamount of air drawn in by the engine Theposition of the plate is transmitted to thecontrol plunger by a lever

K-Jetronic

19

Barrel with metering slits and control plunger

a Zero (inoperated position), b Part load, c Full load

1 Control pressure, 2 Control plunger, 3 Metering slit in the barrel, 4 Control edge, 5 Fuel inlet,

6 Barrel with metering slits.

Barrel with metering slits

1 Intake air, 2 Control pressure, 3 Fuel inlet,

4 Metered quantity of fuel, 5 Control plunger,

6 Barrel with metering slits, 7 Fuel distributor.

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