Gasoline Fuel-Injection System K-Jetronic

Gasoline Fuel-Injection System K-Jetronic
Gasoline-engine management

Gasoline Fuel-Injection
System K-Jetronic

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).

Dipl.-Ing. (FH) Horst Bauer.

Editorial staff:
Dipl.-Ing. Karl-Heinz Dietsche,
Dipl.-Ing. (BA) Jürgen Crepin.

Dipl.-Ing. (FH) Ulrich Adler,
Joachim Kaiser,
Berthold Gauder, Leinfelden-Echterdingen.

Peter Girling.

Technical graphics:
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.

Since its introduction, the K-Jetronic    Combustion in the gasoline engine
gasoline-injection system has pro-        The spark-ignition or
ved itself in millions of vehicles.       Otto-cycle engine                  2
This development was a direct result      Gasoline-engine management
of the advantages which are inherent      Technical requirements             4
in the injection of gasoline with         Cylinder charge                    5
regard to demands for economy of          Mixture formation                  7
operation, high output power, and         Gasoline-injection systems
last but not least improvements to        Overview                          10
the quality of the exhaust gases          K-Jetronic
emitted by the vehicle. Whereas the       System overview                   13
call for higher engine output was the     Fuel supply                       14
foremost consideration at the start of    Fuel metering                     18
the development work on gasoline          Adapting to operating conditions  24
injection, today the target is to         Supplementary functions           30
achieve higher fuel economy and           Exhaust-gas treatment             32
lower toxic emissions.                    Electrical circuitry              36
Between the years 1973 and 1995,          Workshop testing techniques       38
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

This manual will describe the
K-Jetronic’s function and its particu-
lar features.
Combustion in
  the gasoline
                 Combustion in
                 the gasoline engine

                                                                          combustion process pressurizes the
                 The spark-ignition                                       cylinder, propelling the piston back down,
                 or Otto-cycle engine                                     exerting force against the crankshaft and
                                                                          performing work. After each combustion
                                                                          stroke the spent gases are expelled from
                 Operating concept                                        the cylinder in preparation for ingestion of
                 The spark-ignition or Otto-cycle1)                       a fresh charge of air/fuel mixture. The
                 powerplant is an internal-combustion (IC)                primary design concept used to govern
                 engine that relies on an externally-                     this gas transfer in powerplants for
                 generated ignition spark to transform the                automotive applications is the four-stroke
                 chemical energy contained in fuel into                   principle, with two crankshaft revolutions
                 kinetic energy.                                          being required for each complete cycle.
                 Today’s standard spark-ignition engines
                 employ manifold injection for mixture
                 formation outside the combustion
                                                                          The four-stroke principle
                 chamber. The mixture formation system                    The four-stroke engine employs flow-
                 produces an air/fuel mixture (based on                   control valves to govern gas transfer
                 gasoline or a gaseous fuel), which is                    (charge control). These valves open and
                 then drawn into the engine by the suction                close the intake and exhaust tracts
                 generated as the pistons descend. The                    leading to and from the cylinder:
                 future will see increasing application of
                 systems that inject the fuel directly into the           1st stroke:    Induction,
                 combustion chamber as an alternate                       2nd stroke:    Compression and ignition,
                 concept. As the piston rises, it compresses              3rd stroke:    Combustion and work,
                 the mixture in preparation for the timed                 4th stroke:    Exhaust.
                 ignition process, in which externally-
                 generated energy initiates combustion via                Induction stroke
                 the spark plug. The heat released in the                 Intake valve: open,
                 Fig. 1                                                   Exhaust valve: closed,
                  Reciprocating piston-engine design concept              Piston travel: downward,
                  OT = TDC (Top Dead Center); UT = BDC (Bottom            Combustion: none.
                  Dead Center), Vh Swept volume, VC Compressed
                  volume, s Piston stroke.                                The piston’s downward motion increases
                            OT                                            the cylinder’s effective volume to draw
                                                                          fresh air/fuel mixture through the passage
                                                s                         exposed by the open intake valve.
                           UT                                             Compression stroke
                                                                          Intake valve: closed,
                                                                          Exhaust valve: closed,
                                       OT                                 Piston travel: upward,
                                                                          Combustion: initial ignition phase.

                                                                          1)  After Nikolaus August Otto (1832 –1891), who
                                       UT                                 unveiled the first four-stroke gas-compression engine
            2                                                             at the Paris World Exhibition in 1876.
As the piston travels upward it reduces                The ignition spark at the spark plug                   Otto cycle
the cylinder’s effective volume to                     ignites the compressed air/fuel mixture,
compress the air/fuel mixture. Just before             thus initiating combustion and the
the piston reaches top dead center (TDC)               attendant temperature rise.
the spark plug ignites the concentrated                This raises pressure levels within the
air/fuel mixture to initiate combustion.               cylinder to propel the piston downward.
Stroke volume Vh                                       The piston, in turn, exerts force against
and compression volume VC                              the crankshaft to perform work; this
provide the basis for calculating the                  process is the source of the engine’s
compression ratio                                      power.
ε = (Vh+VC)/VC.                                        Power rises as a function of engine speed
Compression ratios ε range from 7...13,                and torque (P = M⋅ω).
depending upon specific engine design.                 A transmission incorporating various
Raising an IC engine’s compression ratio               conversion ratios is required to adapt the
increases its thermal efficiency, allowing             combustion engine’s power and torque
more efficient use of the fuel. As an                  curves to the demands of automotive
example, increasing the compression ratio              operation under real-world conditions.
from 6:1 to 8:1 enhances thermal
efficiency by a factor of 12 %. The latitude           Exhaust stroke
for increasing compression ratio is                    Intake valve: closed,
restricted by knock. This term refers to               Exhaust valve: open,
uncontrolled mixture inflammation charac-              Piston travel: upward,
terized by radical pressure peaks.                     Combustion: none.
Combustion knock leads to engine
damage. Suitable fuels and favorable                   As the piston travels upward it forces the
combustion-chamber configurations can                  spent gases (exhaust) out through the
be applied to shift the knock threshold into           passage exposed by the open exhaust
higher compression ranges.                             valve. The entire cycle then recommences
                                                       with a new intake stroke. The intake and
Power stroke                                           exhaust valves are open simultaneously
Intake valve: closed,                                  during part of the cycle. This overlap
Exhaust valve: closed,                                 exploits gas-flow and resonance patterns
Piston travel: upward,                                 to promote cylinder charging and
Combustion: combustion/post-combus-                    scavenging.
tion phase.

Fig. 2
 Operating cycle of the 4-stroke spark-ignition engine

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

              engine management
              Technical requirements                                            Primary engine-
                                                                                management functions
                                                                                The engine-management system’s first
              Spark-ignition (SI)                                               and foremost task is to regulate the
              engine torque                                                     engine’s torque generation by controlling
                                                                                all of those functions and factors in the
              The power P furnished by the spark-                               various engine-management subsystems
              ignition engine is determined by the                              that determine how much torque is
              available net flywheel torque and the                             generated.
              engine speed.
              The net flywheel torque consists of the                           Cylinder-charge control
              force generated in the combustion                                 In Bosch engine-management systems
              process minus frictional losses (internal                         featuring electronic throttle control (ETC),
              friction within the engine), the gas-                             the “cylinder-charge control” subsystem
              exchange losses and the torque required                           determines the required induction-air
              to drive the engine ancillaries (Figure 1).                       mass and adjusts the throttle-valve
              The combustion force is generated                                 opening accordingly. The driver exercises
              during the power stroke and is defined by                         direct control over throttle-valve opening
              the following factors:                                            on conventional injection systems via the
              – The mass of the air available for                               physical link with the accelerator pedal.
                 combustion once the intake valves
                 have closed,                                                   Mixture formation
              – The mass of the simultaneously                                  The “mixture formation” subsystem cal-
                 available fuel, and                                            culates the instantaneous mass fuel
              – The point at which the ignition spark                           requirement as the basis for determining
                 initiates combustion of the air/fuel                           the correct injection duration and optimal
                 mixture.                                                       injection timing.
              Fig. 1
               Driveline torque factors
               1 Ancillary equipment                    1      1       2        3           4
                 a/c compressor, etc.),
               2 Engine,
               3 Clutch,
               4 Transmission.

                Air mass (fresh induction charge)
                                                             Combustion      Engine        Flywheel                    Drive
                Fuel mass                                    output torque   output torque torque              Trans- force
                                                    Engine                                            Clutch
                                                                              –             –              –   mission
                Ignition angle (firing point)
                                                                                                           –        –

                Gas-transfer and friction

                Clutch/converter losses and conversion ratios
                Transmission losses and conversion ratios
Ignition                                            emissions control system (Figure 2). The              Cylinder
Finally, the “ignition” subsystem de-               air entering through the throttle-valve and           charge
termines the crankshaft angle that                  remaining in the cylinder after intake-
corresponds to precisely the ideal instant          valve closure is the decisive factor
for the spark to ignite the mixture.                defining the amount of work transferred
                                                    through the piston during combustion,
The purpose of this closed-loop control             and thus the prime determinant for the
system is to provide the torque                     amount of torque generated by the
demanded by the driver while at the                 engine. In consequence, modifications to
same time satisfying strict criteria in the         enhance maximum engine power and
areas of                                            torque almost always entail increasing
– Exhaust emissions,                                the maximum possible cylinder charge.
– Fuel consumption,                                 The theoretical maximum charge is
– Power,                                            defined by the volumetric capacity.
– Comfort and convenience, and
– Safety.                                           Residual gases
                                                    The portion of the charge consisting of
                                                    residual gases is composed of
                                                    – The exhaust-gas mass that is not
Cylinder charge                                        discharged while the exhaust valve is
                                                       open and thus remains in the cylinder,
Elements                                               and
The gas mixture found in the cylinder               – The mass of recirculated exhaust gas
once the intake valve closes is referred to            (on systems with exhaust-gas recircu-
as the cylinder charge, and consists of                lation, Figure 2).
the inducted fresh air-fuel mixture along           The proportion of residual gas is de-
with residual gases.                                termined by the gas-exchange process.
                                                    Although the residual gas does not
Fresh gas                                           participate directly in combustion, it does
The fresh mixture drawn into the cylinder           influence ignition patterns and the actual
is a combination of fresh air and the fuel          combustion sequence. The effects of this
entrained with it. While most of the fresh          residual-gas component may be thoroughly
air enters through the throttle valve,              desirable under part-throttle operation.
supplementary fresh gas can also be                 Larger throttle-valve openings to com-
drawn in through the evaporative-                   pensate for reductions in fresh-gas filling
Fig. 2
 Cylinder charge in the spark-ignition engine
  1 Air and fuel vapor,
  2 Purge valve
    with variable aperture,                                                 2         3
  3 Link to evaporative-emissions
    control system,                                        1
  4 Exhaust gas,
  5 EGR valve with                                     α           4        5
    variable aperture,
  6 Mass airflow (barometric pressure pU),                             11       12
  7 Mass airflow
    (intake-manifold pressure ps),              6              7                     10
  8 Fresh air charge                                                        8
    (combustion-chamber pressure pB),
  9 Residual gas charge                                                     9
    (combustion-chamber pressure pB),
 10 Exhaust gas (back-pressure pA),

 11 Intake valve,
 12 Exhaust valve,
 α Throttle-valve angle.
Gasoline-   are needed to meet higher torque                on a supplementary EGR valve linking
     engine   demand. These higher angles reduce the          the intake and exhaust manifolds. The
management    engine’s pumping losses, leading to             engine ingests a mixture of fresh air and
              lower fuel consumption. Precisely reg-          exhaust gas when this valve is open.
              ulated injection of residual gases can
              also modify the combustion process to           Pressure charging
              reduce emissions of nitrous oxides (NOx)        Because maximum possible torque is
              and unburned hydrocarbons (HC).                 proportional to fresh-air charge density, it
                                                              is possible to raise power output by
                                                              compressing the air before it enters the
              Control elements                                cylinder.

              Throttle valve                                  Dynamic pressure charging
              The power produced by the spark-                A supercharging (or boost) effect can be
              ignition engine is directly proportional to     obtained by exploiting dynamics within
              the mass airflow entering it. Control of        the intake manifold. The actual degree of
              engine output and the corresponding             boost will depend upon the manifold’s
              torque at each engine speed is regulated        configuration as well as the engine’s
              by governing the amount of air being            instantaneous        operating       point
              inducted via the throttle valve. Leaving        (essentially a function of the engine’s
              the throttle valve partially closed restricts   speed, but also affected by load factor).
              the amount of air being drawn into the          The option of varying intake-manifold
              engine and reduces torque generation.           geometry while the vehicle is actually
              The extent of this throttling effect            being driven, makes it possible to employ
              depends on the throttle valve’s position        dynamic precharging to increase the
              and the size of the resulting aperture.         maximum available charge mass through
              The engine produces maximum power               a wide operational range.
              when the throttle valve is fully open
              (WOT, or wide open throttle).                   Mechanical supercharging
              Figure 3 illustrates the conceptual             Further increases in air mass are
              correlation between fresh-air charge            available through the agency of
              density and engine speed as a function          Fig. 3
              of throttle-valve aperture.                      Throttle-valve map for spark-ignition engine
                                                                                   Throttle valve at intermediate aperture
              Gas exchange
              The intake and exhaust valves open and
              close at specific points to control the
              transfer of fresh and residual gases. The                                       Throttle valve
              ramps on the camshaft lobes determine                                           completely open
              both the points and the rates at which the
              valves open and close (valve timing) to
              define the gas-exchange process, and
                                                                Fresh gas charge

              with it the amount of fresh gas available
              for combustion.
              Valve overlap defines the phase in which
              the intake and exhaust valves are open
              simultaneously, and is the prime factor in
              determining the amount of residual gas
              remaining in the cylinder. This process is
              known      as    "internal"  exhaust-gas                                        Throttle valve

              recirculation. The mass of residual gas                                         completely closed

              can also be increased using "external"                               min.                                max.
         6    exhaust-gas recirculation, which relies                                 Idle             RPM
mechanically driven compressors pow-
ered by the engine’s crankshaft, with the
                                                                              Mixture formation                             Mixture
two elements usually rotating at an in-
variable relative ratio. Clutches are often
used to control compressor activation.
Exhaust-gas turbochargers                                                     Air-fuel mixture
Here the energy employed to power the                                         Operation of the spark-ignition engine is
compressor is extracted from the exhaust                                      contingent upon availability of a mixture
gas. This process uses the energy that                                        with a specific air/fuel (A/F) ratio. The
naturally-aspirated     engines     cannot                                    theoretical ideal for complete combustion
exploit directly owing to the inherent                                        is a mass ratio of 14.7:1, referred to as
restrictions imposed by the gas ex-                                           the stoichiometric ratio. In concrete terms
pansion characteristics resulting from the                                    this translates into a mass relationship of
crankshaft concept. One disadvantage is                                       14.7 kg of air to burn 1 kg of fuel, while
the higher back-pressure in the exhaust                                       the corresponding volumetric ratio is
gas exiting the engine. This back-                                            roughly 9,500 litres of air for complete
pressure stems from the force needed to                                       combustion of 1 litre of fuel.
maintain compressor output.
The exhaust turbine converts the                                              The air-fuel mixture is a major factor in
exhaust-gas energy into mechanical                                            determining the spark-ignition engine’s
energy, making it possible to employ an                                       rate of specific fuel consumption.
impeller to precompress the incoming                                          Genuine complete combustion and
fresh air. The turbocharger is thus a                                         absolutely minimal fuel consumption
combination of the turbine in the exhaust-                                    would be possible only with excess air,
fas flow and the impeller that compresses                                     but here limits are imposed by such
the intake air.                                                               considerations as mixture flammability
Figure 4 illustrates the differences in the                                   and the time available for combustion.
torque curves of a naturally-aspirated
engine and a turbocharged engine.                                             The air-fuel mixture is also vital in
                                                                              determining the efficiency of exhaust-gas
Fig. 4                                                                        treatment system. The current state-of-
 Torque curves for turbocharged                                               the-art features a 3-way catalytic
 and atmospheric-induction engines                                            converter, a device which relies on a
 with equal power outputs                                                     stoichiometric A/F ratio to operate at
 1 Engine with turbocharger,                                                  maximum efficiency and reduce un-
 2 Atmospheric-induction engine.
                                                                              desirable exhaust-gas components by
                                                                              more than 98 %.

                                                                              Current engines therefore operate with a
                                                                              stoichiometric A/F ratio as soon as the
                                      1                                       engine’s operating status permits
  Engine torque Md

                                                                              Certain engine operating conditions
                                             2                                make mixture adjustments to non-
                                                                              stoichiometric ratios essential. With a
                                                                              cold engine for instance, where specific
                                                                              adjustments to the A/F ratio are required.
                                                                              As this implies, the mixture-formation
                                                                              system must be capable of responding to

                     1            1              3       1
                         4            2              4       1                a range of variable requirements.
                             Engine rpm nn
Gasoline-   Excess-air factor                                                          deficiencies of 5...15 % (λ = 0.95...0.85),
     engine   The designation l (lambda) has been                                        but maximum fuel economy comes in at
management    selected to identify the excess-air factor                                 10...20 % excess air (λ = 1.1...1.2).
              (or air ratio) used to quantify the spread                                 Figures 1 and 2 illustrate the effect of the
              between the actual current mass A/F ratio                                  excess-air factor on power, specific fuel
              and the theoretical optimum (14.7:1):                                      consumption and generation of toxic
              λ = Ratio of induction air mass to air                                     emissions. As can be seen, there is no
              requirement for stoichiometric com-                                        single excess-air factor which can
              bustion.                                                                   simultaneously generate the most
              λ = 1: The inducted air mass corresponds                                   favorable levels for all three factors. Air
              to the theoretical requirement.                                            factors of λ = 0.9...1.1 produce
              λ < 1: Indicates an air deficiency,                                        “conditionally optimal” fuel economy with
              producing a corresponding rich mixture.                                    “conditionally optimal” power generation
              Maximum power is derived from λ =                                          in actual practice.
              0.85...0.95.                                                               Once the engine warms to its normal
              λ > 1: This range is characterized by                                      operating temperature, precise and
              excess air and lean mixture, leading to                                    consistent maintenance of λ = 1 is vital
              lower fuel consumption and reduced                                         for the 3-way catalytic treatment of
              power. The potential maximum value for λ                                   exhaust gases. Satisfying this re-
              – called the “lean-burn limit (LML)” – is                                  quirement entails exact monitoring of
              essentially defined by the design of the                                   induction-air mass and precise metering
              engine and of its mixture for-                                             of fuel mass.
              mation/induction system. Beyond the                                        Optimal combustion from current en-
              lean-burn limit the mixture ceases to be                                   gines equipped with manifold injection
              ignitable and combustion miss sets in,                                     relies on formation of a homogenous
              accompanied by substantial degener-                                        mixture as well as precise metering of the
              ation of operating smoothness.                                             injected fuel quantity. This makes
              In engines featuring systems to inject fuel                                effective atomization essential. Failure to
              directly into the chamber, these operate                                   satisfy this requirement will foster the
              with substantially higher excess-air                                       formation of large droplets of condensed
              factors (extending to λ = 4) since com-                                    fuel on the walls of the intake tract and in
              bustion proceeds according to different                                    the combustion chamber. These droplets
              laws.                                                                      will fail to combust completely and the
              Spark-ignition engines with manifold                                       ultimate result will be higher HC
              injection produce maximum power at air                                     emissions.
              Fig. 1                                                                     Fig. 2
               Effects of excess-air factor λ on power P and                              Effect of excess-air factor λ on untreated
               specific fuel consumption be.                                              exhaust emissions
               a Rich mixture (air deficiency),
               b Lean mixture (excess air).

                                                                                                                          HC               NOX
               Specific fuel consumption be

                                                                                           Relative quantities of

                                                                                           CO; HC; NOX
               Power P ,

                                                      a           b


                                              0.8          1.0          1.2                                         0.6   0.8       1.0        1.2    1.4
                                                    Excess-air factor λ                                                         Excess-air factor λ
Adapting to specific                           Idle and part-load                               Mixture
operating conditions                           Idle is defined as the operating status in       formation
                                               which the torque generated by the engine
Certain operating states cause fuel            is just sufficient to compensate for friction
requirements to deviate substantially from     losses. The engine does not provide
the steady-state requirements of an engine     power to the flywheel at idle. Part-load (or
warmed to its normal temperature, thus         part-throttle) operation refers to the
necessitating corrective adaptations in the    range of running conditions between idle
mixture-formation apparatus. The follow-       and generation of maximum possible
ing descriptions apply to the conditions       torque. Today’s standard concepts rely
found in engines with manifold injection.      exclusively on stoichiometric mixtures for
                                               the operation of engines running at idle
Cold starting                                  and part-throttle once they have warmed
During cold starts the relative quantity of    to their normal operating temperatures.
fuel in the inducted mixture decreases: the
mixture “goes lean.” This lean-mixture         Full load (WOT)
phenomenon stems from inadequate               At WOT (wide-open throttle) supple-
blending of air and fuel, low rates of fuel    mentary enrichment may be required. As
vaporization, and condensation on the          Figure 1 indicates, this enrichment
walls of the inlet tract, all of which are     furnishes maximum torque and/or power.
promoted by low temperatures. To com-
pensate for these negative factors, and to     Acceleration and deceleration
facilitate cold starting, supplementary fuel   The fuel’s vaporization potential is strongly
must be injected into the engine.              affected by pressure levels inside the
                                               intake manifold. Sudden variations in
Post-start phase                               manifold pressure of the kind encountered
Following     low-temperature      starts,     in response to rapid changes in throttle-
supplementary fuel is required for a brief     valve aperture cause fluctuations in the
period, until the combustion chamber           fuel layer on the walls of the intake tract.
heats up and improves the internal             Spirited acceleration leads to higher
mixture formation. This richer mixture         manifold pressures. The fuel responds
also increases torque to furnish a             with lower vaporization rates and the fuel
smoother transition to the desired idle        layer within the manifold runners expands.
speed.                                         A portion of the injected fuel is thus lost in
                                               wall condensation, and the engine goes
Warm-up phase                                  lean for a brief period, until the fuel layer
The warm-up phase follows on the heels         restabilizes. In an analogous, but inverted,
of the starting and immediate post-start       response pattern, sudden deceleration
phases. At this point the engine still         leads to rich mixtures. A temperature-
requires an enriched mixture to offset the     sensitive correction function (transition
fuel condensation on the intake-manifold       compensation) adapts the mixture to
walls. Lower temperatures are synony-          maintain optimal operational response
mous with less efficient fuel proces-          and ensure that the engine receives the
sing (owing to factors such as poor mix-       consistent air/fuel mixture needed for
ing of air and fuel and reduced fuel va-       efficient catalytic-converter performance.
porization). This promotes fuel precip-
itation within the intake manifold, with       Trailing throttle (overrun)
the formation of condensate fuel that will     Fuel metering is interrupted during trailing
only vaporize later, once temperatures         throttle. Although this expedient saves
have increased. These factors make it          fuel on downhill stretches, its primary
necessary to provide progressive mixture       purpose is to guard the catalytic converter
enrichment in response to decreasing           against overheating stemming from poor
temperatures.                                  and incomplete combustion (misfiring).           9
             Gasoline-injection systems

             Carburetors and gasoline-injection sys-         Representative examples are the various
             tems are designed for a single purpose:         versions of the KE and L-Jetronic systems
             To supply the engine with the optimal air-      (Figure 1).
             fuel mixture for any given operating
             conditions. Gasoline injection systems,         Mechanical injection systems
             and electronic systems in particular, are       The K-Jetronic system operates by
             better at maintaining air-fuel mixtures         injecting continually, without an exter-
             within precisely defined limits, which          nal drive being necessary. Instead of
             translates into superior performance in         being determined by the injection valve,
             the areas of fuel economy, comfort and          fuel mass is regulated by the fuel
             convenience, and power. Increasingly            distributor.
             stringent mandates governing exhaust
             emissions have led to a total eclipse of the    Combined mechanical-electronic
             carburetor in favor of fuel injection.          fuel injection
             Although current systems rely almost            Although the K-Jetronic layout served as
             exclusively on mixture formation outside        the mechanical basis for the KE-Jetronic
             the combustion chamber, concepts based          system, the latter employs expanded
             on internal mixture formation – with fuel       data-monitoring functions for more
             being injected directly into the combustion     precise adaptation of injected fuel
             chamber – were actually the foundation          quantity to specific engine operating
             for the first gasoline-injection systems. As    conditions.
             these systems are superb instruments for
             achieving further reductions in fuel            Electronic injection systems
             consumption, they are now becoming an           Injection systems featuring electronic
             increasingly significant factor.                control rely on solenoid-operated injection
                                                             Fig. 1
                                                              Multipoint fuel injection (MPI)
             Overview                                         1 Fuel,                 2
                                                              2 Air,
                                                              3 Throttle valve,
             Systems with                                     4 Intake manifold,                3
                                                              5 Injectors,
             external mixture formation                       6 Engine.     4
             The salient characteristic of this type of
             system is the fact that it forms the air-fuel
             mixture outside the combustion chamber,                  1
             inside the intake manifold.
             Multipoint fuel injection
             Multipoint fuel injection forms the ideal
             basis for complying with the mixture-
             formation criteria described above. In this

             type of system each cylinder has its own
             injector discharging fuel into the area                                      6
       10    directly in front of the intake valve.
valves for intermittent fuel discharge. The            combination of air and fuel common to                   Overview
actual injected fuel quantity is regulated             conventional injection systems. This is one
by controlling the injector's opening time             of the new system's prime advantages: It
(with the pressure-loss gradient through               banishes all potential for fuel condensation
the valve being taken into account in                  within the runners of the intake manifold.
calculations as a known quantity).                     External mixture formation usually
Examples: L-Jetronic, LH-Jetronic, and                 provides a homogenous, stoichiometric air-
Motronic as an integrated engine-manage-               fuel mixture throughout the entire
ment system.                                           combustion chamber. In contrast, shifting
                                                       the mixture-preparation process into the
Single-point fuel injection                            combustion chamber provides for two
Single-point (throttle-body injection (TBI))           distinctive operating modes:
fuel injection is the concept behind this              With stratified-charge operation, only the
electronically-controlled injection system             mixture directly adjacent to the spark plug
in which a centrally located solenoid-                 needs to be ignitable. The remainder of the
operated injection valve mounted                       air-fuel charge in the combustion chamber
upstream from the throttle valve sprays                can consist solely of fresh and residual
fuel intermittently into the manifold. Mono-           gases, without unburned fuel. This strategy
Jetronic and Mono-Motronic are the                     furnishes an extremely lean overall mixture
Bosch systems in this category (Figure 2).             for idling and part-throttle operation, with
                                                       commensurate         reductions    in    fuel
Systems for internal                                   Homogenous operation reflects the
mixture formation                                      conditions encountered in external mixture
Direct-injection (DI) systems rely on                  formation      by      employing     uniform
solenoid-operated injection valves to spray            consistency for the entire air-fuel charge
fuel directly into the combustion chamber;             throughout the combustion chamber.
the actual mixture-formation process takes             Under these conditions all of the fresh air
place within the cylinders, each of which              within the chamber participates in the
has its own injector (Figure 3). Perfect               combustion process. This operational
atomization of the fuel emerging from the              mode is employed for WOT operation.
injectors is vital for efficient combustion.           MED-Motronic is used for closed-loop
Under normal operating conditions, DI                  control of DI gasoline engines.
engines draw in only air instead of the
Fig. 2                                                 Fig. 3
 Throttle-body fuel injection (TBI)                     Direct fuel injection (DI)
 1 Fuel,                 2                              1 Fuel,
 2 Air,                                                 2 Air,
 3 Throttle valve,                                      3 Throttle valve        2
 4 Intake manifold,              3                        (ETC),
 5 Injector,                                            4 Intake manifold,
 6 Engine.                                              5 Injectors,                     3
                                                        6 Engine.

                                      5                                                       5


                             6                                                       6
The story of
fuel injection   The story of fuel injection                  injection system: the intake-pressure-
                 The story of fuel injection extends          controlled D-Jetronic!
                 back to cover a period of almost one         In 1973 the air-flow-controlled L-Jetro-
                 hundred years.                               nic appeared on the market, at the
                 The Gasmotorenfabik Deutz was                same time as the K-Jetronic, which fea-
                 manufacturing plunger pumps for in-          tured mechanical-hydraulic control and
                 jecting fuel in a limited production         was also an air-flow-controlled system.
                 series as early as 1898.                     In 1976, the K-Jetronic was the first
                 A short time later the uses of the ven-      automotive system to incorporate a
                 turi-effect for carburetor design were       Lambda closed-loop control.
                 discovered, and fuel-injection systems       1979 marked the introduction of a new
                 based on the technology of the time          system: Motronic, featuring digital pro-
                 ceased to be competitive.                    cessing for numerous engine func-
                 Bosch started research on gasoline-          tions. This system combined L-Jetro-
                 injection pumps in 1912. The first           nic with electronic program-map con-
                 aircraft engine featuring Bosch fuel in-     trol for the ignition. The first automo-
                 jection, a 1,200-hp unit, entered series     tive microprocessor!
                 production in 1937; problems with car-       In 1982, the K-Jetronic model became
                 buretor icing and fire hazards had lent      available in an expanded configura-
                 special impetus to fuel-injection devel-     tion, the KE-Jetronic, including an
                 opment work for the aeronautics field.       electronic closed-loop control circuit
                 This development marks the begin-            and a Lambda oxygen sensor.
                 ning of the era of fuel injection at         These were joined by Bosch Mono-
                 Bosch, but there was still a long path       Jetronic in 1987: This particularly cost-
                 to travel on the way to fuel injection for   efficient single-point injection unit
                 passenger cars.                              made it feasible to equip small vehicles
                 1951 saw a Bosch direct-injection unit       with Jetronic, and once and for all made
                 being featured as standard equipment         the carburetor absolutely superfluous.
                 on a small car for the first time. Sev-      By the end of 1997, around 64 million
                 eral years later a unit was installed in     Bosch engine-management systems
                 the 300 SL, the legendary production         had been installed in countless types of
                 sports car from Daimler-Benz.                vehicles since the introduction of the
                 In the years that followed, develop-         D-Jetronic in 1967. In 1997 alone, the
                 ment on mechanical injection pumps           figure was 4.2 million, comprised of
                 continued, and ...                           1 million throttle-body injection (TBI)
                 In 1967 fuel injection took another          systems and 3.2 million multipoint fuel-
                 giant step forward: The first electronic     injection (MPI) systems.
                 Bosch gasoline fuel injection
                 from the year 1954

K-Jetronic                                           Fuel supply
                                                     An electrically driven fuel pump delivers

                                                     the fuel to the fuel distributor via a fuel
System overview                                      accumulator and a filter. The fuel distribu-
                                                     tor allocates this fuel to the injection
The K-Jetronic is a mechanically and                 valves of the individual cylinders.
hydraulically controlled fuel-injection sys-
tem which needs no form of drive and                 Air-flow measurement
which meters the fuel as a function of the           The amount of air drawn in by the engine
intake air quantity and injects it contin-           is controlled by a throttle valve and
uously onto the engine intake valves.                measured by an air-flow sensor.
Specific operating conditions of the
engine require corrective intervention in            Fuel metering
mixture formation and this is carried out            The amount of air, corresponding to the
by the K-Jetronic in order to optimize               position of the throttle plate, drawn in by
starting and driving performance, power              the engine serves as the criterion for
output and exhaust composition. Owing                metering of the fuel to the individual
to the direct air-flow sensing, the K-Je-            cylinders. The amount of air drawn in by
tronic system also allows for engine                 the engine is measured by the air-flow
variations and permits the use of facilities         sensor which, in turn, controls the fuel
for exhaust-gas aftertreatment for which             distributor. The air-flow sensor and the
precise metering of the intake air quantity          fuel distributor are assemblies which
is a prerequisite.                                   form part of the mixture control unit.
The K-Jetronic was originally designed               Injection occurs continuously, i.e. without
as a purely mechanical injection system.             regard to the position of the intake valve.
Today, using auxiliary electronic equip-             During the intake-valve closed phase, the
ment, the system also permits the use of             fuel is “stored”. Mixture enrichment is
lambda closed-loop control.                          controlled in order to adapt to various
The K-Jetronic fuel-injection system                 operating conditions such as start, warm-
covers the following functional areas:               up, idle and full load. In addition, supple-
– Fuel supply,                                       mentary functions such as overrun fuel
– Air-flow measurement and                           cutoff, engine-speed limiting and closed-
– Fuel metering.                                     loop lambda control are possible.

Fig. 1
 Functional schematic of the K-Jetronic

                        Electric                        Fuel
                      fuel pump                      accumulator                 Fuel filter

                   Air filter             Air-flow             Mixture             Fuel
     Air                                  sensor             control unit       distributor

                                    Throttle valve                            Injection valves

                                                             Intake ports


Gasoline-    Fuel supply                                              available. This avoids the formation of
 injection                                                            fuel-vapor bubbles and achieves good
 systems     The fuel supply system comprises                         hot starting behavior.
             – Electric fuel pump,
             – Fuel accumulator,                                      Electric fuel pump
             – Fine filter,                                           The electric fuel pump is a roller-cell
             – Primary-pressure regulator and                         pump driven by a permanent-magnet
             – Injection valves.                                      electric motor.
             An electrically driven roller-cell pump                  The rotor plate which is eccentrically
             pumps the fuel from the fuel tank at a                   mounted in the pump housing is fitted
             pressure of over 5 bar to a fuel accu-                   with metal rollers in notches around its
             mulator and through a filter to the fuel                 circumference which are pressed against
             distributor. From the fuel distributor the               the pump housing by centrifugal force
             fuel flows to the injection valves. The                  and act as rolling seals. The fuel is car-
             injection valves inject the fuel con-                    ried in the cavities which form between
             tinuously into the intake ports of the                   the rollers. The pumping action takes
             engine. Thus the system designation K                    place when the rollers, after having
             (taken from the German for continuous).                  closed the inlet bore, force the trapped
             When the intake valves open, the mixture                 fuel in front of them until it can escape
             is drawn into the cylinder.                              from the pump through the outlet bore
             The fuel primary-pressure regulator                      (Figure 4). The fuel flows directly around
             maintains the supply pressure in the                     the electric motor. There is no danger of
             system constant and reroutes the excess                  explosion, however, because there is
             fuel back to the fuel tank.                              never an ignitable mixture in the pump
             Owing to continual scavenging of the fuel                housing.
             supply system, there is always cool fuel
             Fig. 2
              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.

                                2                                                   4

                                         6            8

                                                  7                                                 9

                                    13       14
                      12                                                           10
                                                           15       16

                                                                         18                      19

The electric fuel pump delivers more fuel        Electric fuel pump                                                   K-Jetronic
than the maximum requirement of the              1 Suction side, 2 Pressure limiter, 3 Roller-cell
engine so that compression in the fuel           pump, 4 Motor armature, 5 Check valve,
system can be maintained under all oper-         6 Pressure side.
ating conditions. A check valve in the                        2 3         4             5
pump decouples the fuel system from
the fuel tank by preventing reverse flow of
fuel to the fuel tank.                            1                                                  6
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
                                                                                                 Fig. 3
has started. A safety circuit is incorpor-      Fig. 4
ated to stop the pump running and, thus,         Operation of roller-cell pump
to prevent fuel being delivered if the ig-       1 Suction side, 2 Rotor plate, 3 Roller,
nition is switched on but the engine has         4 Roller race plate, 5 Pressure side.
stopped turning (for instance in the case                               2 3     4
of an accident).
The fuel pump is located in the imme-
diate vicinity of the fuel tank and requires              1                                 5
no maintenance.

Fuel accumulator
The fuel accumulator maintains the
pressure in the fuel system for a certain       Fig. 5
time after the engine has been switched          Fuel accumulator
off in order to facilitate restarting, parti-    a Empty, b Full.
cularly when the engine is hot. The spe-         1 Spring chamber, 2 Spring, 3 Stop, 4 Diaphragm,
cial design of the accumulator housing           5 Accumulator volume, 6 Fuel inlet or outlet,
                                                 7 Connection to the atmosphere.
(Figure 5) deadens the sound of the fuel
pump when the engine is running.
                                                   a          1     2     3 4       5
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                 7                                                 6
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

Gasoline-    Fuel filter                                              Fuel filter
 injection   The fuel filter retains particles of dirt                1 Paper element,
 systems     which are present in the fuel and which                  2 Strainer,
                                                                      3 Support        1             2   3
             would otherwise have an adverse effect
             on the functioning of the injection system.
             The fuel filter contains a paper element
             with 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 in
             the fuel line downstream from the fuel                                                          Fig. 6
             accumulator and its service life depends                delivery drops slightly, the plunger is
             upon the amount of dirt in the fuel. It is              shifted by the spring to a corresponding
             imperative that the arrow on the filter                 new position and in doing so closes off
             housing showing the direction of fuel flow              the port slightly through which the excess
             through the filter is observed when the                 fuel returns to the tank. This means that
             filter is replaced.                                     less fuel is diverted off at this point and
                                                                     the system pressure is controlled to its
             Primary-pressure regulator                              specified level.
             The primary-pressure regulator main-                    When the engine is switched off, the fuel
             tains the pressure in the fuel system                   pump also switches off and the primary
             constant.                                               pressure drops below the opening pres-
             It is incorporated in the fuel distributor              sure of the injection valves. The pressure
             and holds the delivery pressure (system                 regulator then closes the return-flow port
             pressure) at about 5 bar. The fuel pump                 and thus prevents the pressure in the fuel
             always delivers more fuel than is required              system from sinking any further (Fig. 8).
             by the vehicle engine, and this causes a
             plunger to shift in the pressure regulator              Fuel-injection valves
             and open a port through which excess                    The injection valves open at a given pres-
             fuel can return to the tank.                            sure and atomize the fuel through oscilla-
             The pressure in the fuel system and the                 tion of the valve needle. The injection
             force exerted by the spring on the                      valves inject the fuel metered to them into
             pressure-regulator plunger balance each                 the intake passages and onto the intake
             other out. If, for instance, fuel-pump                  valves. They are secured in special
             Fig. 7
              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.

              a                                                  b


                                                                             2               3   4       5

holders to insulate them against the heat                          Pressure curve after engine switchoff                             K-Jetronic
radiated from the engine. The injection                            Firstly pressure falls from the normal system
valves have no metering function them-                             pressure (1) to the pressure-regulator closing
selves, and open of their own accord                               pressure (2). The fuel accumulator then causes
                                                                   it to increase to the level (3) which is below the
when the opening pressure of e.g. 3.5                              opening pressure (4) of the injection valves.
bar is exceeded. They are fitted with a
valve needle (Fig. 9) which oscillates                                                 1
(“chatters”) audibly at high frequency
when fuel is injected. This results in ex-
cellent atomization of the fuel even with                                                                   4

                                                                      Pressure p
the smallest of injection quantities. When
the engine is switched off, the injection                                                  2
valves close tightly when the pressure in

the fuel-supply system drops below their
opening pressure. This means that no                                                                            ms
more fuel can enter the intake passages                                                        Time t

once the engine has stopped.                                                                                        Fig. 8
                                                                  Fig. 9
                                                                   Fuel-injection valve
Air-shrouded fuel-injection valves                                 a In rest position,
Air-shrouded injection valves improve the                          b In actuated position.
mixture formation particularly at idle.                            1 Valve housing,
                                                                   2 Filter,
Using the pressure drop across the                                 3 Valve needle,
throttle valve, a portion of the air inducted                      4 Valve seat.                                1
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                                                                        2
and toxic emission constituents.


                                                                                   a             b
Fig. 10
Spray pattern of an injection valve without
air-shrouding (left) and with air-shrouding (right).


Gasoline-    Fuel metering                                    Principle of the air-flow sensor
 injection                                                    a Small amount of air drawn in: sensor plate only
 systems     The task of the fuel-management system           lifted slightly, b Large amount of air drawn in:
             is to meter a quantity of fuel corre-            sensor plate is lifted considerably further.
             sponding to the intake air quantity.
             Basically, fuel metering is carried out                   a
             by the mixture control unit. This com-
             prises the air-flow sensor and the fuel
             In a number of operating modes however,                                    h
             the amount of fuel required deviates
             greatly from the “standard” quantity and it
             becomes necessary to intervene in the                     b
             mixture 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 operating
                                                             Fig. 11
             load. The air-flow sensor operates ac-
             cording to the suspended-body principle,        air-fuel mixture. Since the air drawn in by
             and measures the amount of air drawn in         the engine must pass through the air-flow
             by the engine.                                  sensor before it reaches the engine, this
             The intake air quantity serves as the           means that it has been measured and
             main actuating variable for determining         the control signal generated before it
             the basic injection quantity. It is the         actually enters the engine cylinders. The
             appropriate physical quantity for deriving      result is that, in addition to other
             the fuel requirement, and changes in the        measures described below, the correct
             induction characteristics of the engine         mixture adaptation takes place at all
             have no effect upon the formation of the        times.
             Fig. 12
              Updraft                            1       2         3          4              5
              air-flow sensor
              a Sensor plate in its
                zero position,            a
              b Sensor plate in its
                operating position.

              1 Air funnel,
              2 Sensor plate,
              3 Relief cross-section,
              4 Idle-mixture
                adjusting screw,
              5 Pivot,
              6 Lever,
              7 Leaf spring.                         7                                       6


The air-flow sensor is located upstream                    Barrel with metering slits                                     K-Jetronic
of the throttle valve so that it measures all              1 Intake air, 2 Control pressure, 3 Fuel inlet,
the air which enters the engine cylinders.                 4 Metered quantity of fuel, 5 Control plunger,
It comprises an air funnel in which the                    6 Barrel with metering slits, 7 Fuel distributor.
sensor plate (suspended body) is free to                                             7
pivot. The air flowing through the funnel                                                        2
deflects the sensor plate by a given                                                         ,,,,,
amount out of its zero position, and this                                            5       ,,,,,       6
                                                                                     4     ,,,, ,,,,     4

movement is transmitted by a lever sys-                                                    ,,,,
                                                                                           ,,,, ,,,,
                                                                                           ,,,, ,,,,
                                                                                           ,,,, ,

tem to a control plunger which deter-                                                3
                                                                                           ,,,, , ,,,

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                    1

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               Fig. 13
cross-section in the funnel. A rubber
buffer limits the downward stroke (the                    Fuel distributor
upwards stroke on the downdraft air-flow                  Depending upon the position of the plate
sensor). A counterweight compensates                      in the air-flow sensor, the fuel distributor
for the weight of the sensor plate and                    meters the basic injection quantity to the
lever system (this is carried out by an                   individual engine cylinders. The position
extension spring on the downdraft air-                    of the sensor plate is a measure of the
flow sensor). A leaf spring ensures the                   amount of air drawn in by the engine. The
correct zero position in the switched-off                 position of the plate is transmitted to the
phase.                                                    control plunger by a lever.

Fig. 14
 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.

                  ,,,,,,                             ,,,,,,                          ,,,,,,
            a     ,,,,,,                       b     ,,,,,,                      c   ,,,,,,
                  ,,,,,,                 1
                                                     ,,,,,,                          ,,,,,,
                  ,,,,,,                             ,,,,,,                          ,,,,,,
                  ,,,,,,                             ,,,,,,
                                                     ,,,,,,                          ,,,,,,

          ,,,,,                                                    , ,
                  ,,,,,,,                    ,,,,,    ,,,,, , , ,
                                                    ,,,,,, ,,,,,, ,,  ,,,,
          ,,,,,,,,, ,,,,,
                     ,,,,                4   ,
                                             , ,
                                               , ,
                                                 , ,
                                                   ,, ,,,,, , , , ,  ,,,,,
           ,,,,,    ,                        ,,,,,    ,            , ,
                     ,,,,                    , , , ,
                                                       ,,,, , ,
                                                    ,,,,,, ,,,,,, ,
                  , ,
                 , ,,,,                             , ,
                                             ,,,, ,,,, ,,,, ,,,,


Gasoline-    Depending upon its position in the barrel        Barrel with metering slits
 injection   with metering slits, the control plunger         The slits are shown enlarged (the actual slit is
 systems     opens or closes the slits to a greater or        about 0.2 mm wide).
             lesser extent. The fuel flows through the
             open section of the slits to the differential
             pressure valves and then to the fuel
             injection valves. If sensor-plate travel is
             only small, then the control plunger is
             lifted only slightly and, as a result, only a
             small section of the slit is opened for the
             passage of fuel. With larger plunger
             travel, the plunger opens a larger section
             of the slits and more fuel can flow. There
             is a linear relationship between sensor-
             plate travel and the slit section in the
             barrel which is opened for fuel flow.
             A hydraulic force generated by the so-
             called control pressure is applied to the
             control plunger. It opposes the movement

             resulting from sensor-plate deflection.
             One of its functions is to ensure that the
             control plunger follows the sensor-plate
                                                             Fig. 15
             movement immediately and does not, for
             instance, stick in the upper end position       the air drawn in by the engine can deflect
             when the sensor plate moves down again.         the sensor plate further. This results in
             Further functions of the control pressure       the control plunger opening the metering
             are discussed in the sections “Warm-up          slits further and the engine being allo-
             enrichment” and “Full-load enrichment”.         cated more fuel. On the other hand, if the
                                                             control pressure is high, the air drawn in
             Control pressure                                by the engine cannot deflect the sensor
             The control pressure is tapped from the         plate so far and, as a result, the engine
             primary pressure through a restriction          receives less fuel. In order to fully seal off
             bore (Figure 16). This restriction bore         the control-pressure circuit with absolute
             serves to decouple the control-pressure         certainty when the engine has been
             circuit and the primary-pressure circuit        switched off, and at the same time to
             from one another. A connection line joins       maintain the pressure in the fuel circuit,
             the fuel distributor and the warm-up            the return line of the warm-up regulator is
             regulator (control-pressure regulator).         fitted with a check valve. This (push-up)
             When starting the cold engine, the              valve is attached to the primary-pressure
             control pressure is about 0.5 bar. As the       regulator and is held open during oper-
             engine warms up, the warm-up regulator          ation by the pressure-regulator plunger.
             increases the control pressure to about         When the engine is switched off and the
             3.7 bar (Figure 26).                            plunger of the primary-pressure regulator
             The control pressure acts through a             returns to its zero position, the check
             damping restriction on the control              valve is closed by a spring (Figure 17).
             plunger and thereby develops the force
             which opposes the force of the air in the       Differential-pressure valves
             air-flow sensor. In doing so, the restric-      The differential-pressure valves in the
             tion dampens a possible oscillation of the      fuel distributor result in a specific pres-
             sensor plate which could result due to          sure drop at the metering slits.
             pulsating air-intake flow.                      The air-flow sensor has a linear charac-
             The control pressure influences the fuel        teristic. This means that if double the
       20    distribution. If the control pressure is low,   quantity of air is drawn in, the sensor-
Primary pressure
 and control pressure           3    ,,,,,,,,,,,,,,,,,,,,,

 1 Control-pressure             2    ,,,,,,,,,,,,,,,,,,,,,
   effect (hydraulic

 2 Damping restriction,

 3 Line to warm-up regulator,

 4 Decoupling restric-

   tion bore,

 5 Primary pressure
   (delivery pressure),
 6 Effect of air pressure.           ,,,,,,,,,,,,,,,,,,,,,
                                     ,,,,,,,,,  , , , , ,
                                                          , , , , ,
                                      ,,,,,,,,, , , , , , , , , , ,

                                                  6                          5
                                                                                            Fig. 16
Fig. 17
 regulator with push-
 up valve in the                a
 a In zero (inoperated)
 b In operating position.
 1 Primary pressure
 2 Return (to fuel tank),
 3 Plunger of the
 4 Push-up valve,
 5 Control-pressure             b
   intake (from warm-
   up regulator).               1                                                           5


                                                      2          3               4

plate travel is also doubled. If this travel is       The differential-pressure valves main-
to result in a change of delivered fuel in            tain the differential pressure between the
the same relationship, in this case double            upper and lower chamber constant re-
the travel equals double the quantity,                gardless of fuel throughflow. The differ-
then a constant drop in pressure must                 ential pressure is 0.1 bar.
be guaranteed at the metering slits                   The differential-pressure valves achieve
(Figure 14), regardless of the amount of              a high metering accuracy and are of the
fuel flowing through them.                            flat-seat type. They are fitted in the fuel          21

              Differential-pressure valve

              a Diaphragm

                position with a
                low injected
                fuel quantity

                                            ,,,,,,,, ,,
                                            ,,,,,,,, ,
                                            ,,,,,,,,  ,

              b Diaphragm
                position with a
                large injected
                fuel quantity
                                            ,,,,,,,, ,
                                            ,,,,,,,, ,,
                                            ,,,,,,,,  ,

                                                                                              Fig. 18
             distributor and one such valve is allo-     is located in the upper chamber. Each
             cated to each metering slit. A diaphragm    upper chamber is connected to a
             separates the upper and lower chambers      metering slit and its corresponding con-
             of the valve (Figures 18 and 19). The       nection to the fuel-injection line. The
             lower chambers of all the valves are con-   upper chambers are completely sealed
             nected with one another by a ring main      off from each other. The diaphragms are
             and are subjected to the primary pres-      spring-loaded and it is this helical spring
       22    sure (delivery pressure). The valve seat    that produces the pressure differential.
Fuel distributor with differential-pressure valves                                                                     K-Jetronic
 1 Fuel intake
   (primary                          2      3                    4          5                    6
 2 Upper chamber of
   the differential-

   pressure valve,

 3 Line to the fuel-
   injection valve
 4 Control plunger,
 5 Control edge and
   metering slit,
 6 Valve spring,                ,,,,,,,,,,
 7 Valve diaphragm,

 8 Lower chamber of
   the differential-
   pressure valve.         1

                                           8                                             7

                                                                                                         Fig. 19
                                                      Fig. 20
If a large basic fuel quantity flows into the          Mixture formation with air-shrouded fuel-
upper chamber through the metering slit,               injection valve
the diaphragm is bent downwards and                    1 Fuel-injection valve, 2 Air-supply line,
enlarges the valve cross-section at the                3 Intake manifold, 4 Throttle valve.
outlet leading to the injection valve until
the set differential pressure once again
                                                                           1         2       3       4
If the fuel quantity drops, the valve cross-
section is reduced owing to the equilib-
rium of forces at the diaphragm until the
differential pressure of 0.1 bar is again
present.                                                   ÀÀÀ
This causes an equilibrium of forces to                    ,,,
prevail at the diaphragm which can be                        ,,
maintained for every basic fuel quantity
by controlling the valve cross-section.                      ,,

Mixture formation
The formation of the air-fuel mixture                        ,,
takes place in the intake ports and                          ,,
cylinders of the engine.
The continually injected fuel coming from             Air-shrouded fuel-injection valves favor
the injection valves is “stored” in front of          mixture formation since they atomize
the intake valves. When the intake valve              the fuel very well at the outlet point
is opened, the air drawn in by the engine             (Figures 10, 20).
carries the waiting “cloud” of fuel with it
into the cylinder. An ignitable air-fuel
mixture is formed during the induction
stroke due to the swirl effect.                                                                                         23
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