Page 1
Gasoline-engine management
Gasoline Fuel-Injection
System K-Jetronic
Technical Instruction
Page 2
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.
Presentation:
Dipl.-Ing. (FH) Ulrich Adler,
Joachim Kaiser,
Berthold Gauder, Leinfelden-Echterdingen.
Translation:
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.
Page 3
K-Jetronic
Since its introduction, the K-Jetronic
gasoline-injection system has proved 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 multipoint 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it has been superseded by gasoline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 improved and expanded in their functions. Since this point, the K-Jetronic
has now become particularly important with regard to maintenance and
repair.
This manual will describe the
K-Jetronic’s function and its particular features.
Combustion in the gasoline engine
The spark-ignition or
Otto-cycle engine
2
Gasoline-engine management
Technical requirements
4
Cylinder charge
5
Mixture formation
7
Gasoline-injection systems
Overview
10
K-Jetronic
System overview
13
Fuel supply
14
Fuel metering
18
Adapting to operating conditions
24
Supplementary functions
30
Exhaust-gas treatment
32
Electrical circuitry
36
Workshop testing techniques
38
Page 4
Combustion in
the gasoline
engine
Combustion in
the gasoline engine
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 externallygenerated ignition spark to transform the
chemical energy contained in fuel into
kinetic energy.
Today’s standard spark-ignition engines
employ manifold injection for mixture
formation outside the combustion
chamber. The mixture formation system
produces an air/fuel mixture (based on
gasoline or a gaseous fuel), which is
then drawn into the engine by the suction
generated as the pistons descend. The
future will see increasing application of
systems that inject the fuel directly into the
combustion chamber as an alternate
concept. As the piston rises, it compresses
the mixture in preparation for the timed
ignition process, in which externallygenerated energy initiates combustion via
the spark plug. The heat released in the
Fig. 1
Reciprocating piston-engine design concept
OT = TDC (Top Dead Center); UT = BDC (Bottom
Dead Center), Vh Swept volume, VC Compressed
volume, s Piston stroke.
VC
OT
s
combustion process pressurizes the
cylinder, propelling the piston back down,
exerting force against the crankshaft and
performing work. After each combustion
stroke the spent gases are expelled from
the cylinder in preparation for ingestion of
a fresh charge of air/fuel mixture. The
primary design concept used to govern
this gas transfer in powerplants for
automotive applications is the four-stroke
principle, with two crankshaft revolutions
being required for each complete cycle.
The four-stroke principle
The four-stroke engine employs flowcontrol valves to govern gas transfer
(charge control). These valves open and
close the intake and exhaust tracts
leading to and from the cylinder:
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 increases
the cylinder’s effective volume to draw
fresh air/fuel mixture through the passage
exposed by the open intake valve.
Vh
UT
UT
2
UMM0001E
OT
Compression stroke
Intake valve: closed,
Exhaust valve: closed,
Piston travel: upward,
Combustion: initial ignition phase.
1)
After Nikolaus August Otto (1832 –1891), who
unveiled the first four-stroke gas-compression engine
at the Paris World Exhibition in 1876.
Page 5
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 characterized 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-combustion phase.
The ignition spark at the spark plug
ignites the compressed air/fuel mixture,
thus initiating combustion and the
attendant temperature rise.
This raises pressure levels within the
cylinder to propel the piston downward.
The piston, in turn, exerts force against
the crankshaft to perform work; this
process is the source of the engine’s
power.
Power rises as a function of engine speed
and torque (P = M⋅ω).
A transmission incorporating various
conversion ratios is required to adapt the
combustion engine’s power and torque
curves to the demands of automotive
operation under real-world conditions.
Otto cycle
Exhaust stroke
Intake valve: closed,
Exhaust valve: open,
Piston travel: upward,
Combustion: none.
As the piston travels upward it forces the
spent gases (exhaust) out through the
passage exposed by the open exhaust
valve. The entire cycle then recommences
with a new intake stroke. The intake and
exhaust valves are open simultaneously
during part of the cycle. This overlap
exploits gas-flow and resonance patterns
to promote cylinder charging and
scavenging.
Fig. 2
Operating cycle of the 4-stroke spark-ignition engine
Stroke 2: Compression
Stroke 3: Combustion
Stroke 4: Exhaust
UMM0011E
Stroke 1: Induction
3
Page 6
Gasolineengine
management
Gasolineengine management
Technical requirements
Spark-ignition (SI)
engine torque
The power P furnished by the sparkignition engine is determined by the
available net flywheel torque and the
engine speed.
The net flywheel torque consists of the
force generated in the combustion
process minus frictional losses (internal
friction within the engine), the gasexchange losses and the torque required
to drive the engine ancillaries (Figure 1).
The combustion force is generated
during the power stroke and is defined by
the following factors:
– The mass of the air available for
combustion once the intake valves
have closed,
– The mass of the simultaneously
available fuel, and
– The point at which the ignition spark
initiates combustion of the air/fuel
mixture.
Primary enginemanagement functions
The engine-management system’s first
and foremost task is to regulate the
engine’s torque generation by controlling
all of those functions and factors in the
various engine-management subsystems
that determine how much torque is
generated.
Cylinder-charge control
In Bosch engine-management systems
featuring electronic throttle control (ETC),
the “cylinder-charge control” subsystem
determines the required induction-air
mass and adjusts the throttle-valve
opening accordingly. The driver exercises
direct control over throttle-valve opening
on conventional injection systems via the
physical link with the accelerator pedal.
Mixture formation
The “mixture formation” subsystem calculates the instantaneous mass fuel
requirement as the basis for determining
the correct injection duration and optimal
injection timing.
Fig. 1
Driveline torque factors
1
Air mass (fresh induction charge)
Fuel mass
Engine
1
Combustion
output torque
Ignition angle (firing point)
Gas-transfer and friction
Ancillaries
Clutch/converter losses and conversion ratios
Transmission losses and conversion ratios
4
2
3
4
Flywheel
Engine
output torque torque
–
–
Clutch
–
–
Drive
Trans- force
mission
–
–
UMM0545-1E
1 Ancillary equipment
(alternator,
a/c compressor, etc.),
2 Engine,
3 Clutch,
4 Transmission.
Page 7
emissions control system (Figure 2). The
air entering through the throttle-valve and
remaining in the cylinder after intakevalve closure is the decisive factor
defining the amount of work transferred
through the piston during combustion,
and thus the prime determinant for the
amount of torque generated by the
engine. In consequence, modifications to
enhance maximum engine power and
torque almost always entail increasing
the maximum possible cylinder charge.
The theoretical maximum charge is
defined by the volumetric capacity.
Ignition
Finally, the “ignition” subsystem determines 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
areas of
– Exhaust emissions,
– Fuel consumption,
– Power,
– Comfort and convenience, and
– Safety.
Cylinder
charge
Residual gases
The portion of the charge consisting of
residual gases is composed of
– The exhaust-gas mass that is not
discharged while the exhaust valve is
open and thus remains in the cylinder,
and
– The mass of recirculated exhaust gas
(on systems with exhaust-gas recirculation, Figure 2).
The proportion of residual gas is determined by the gas-exchange process.
Although the residual gas does not
participate directly in combustion, it does
influence ignition patterns and the actual
combustion sequence. The effects of this
residual-gas component may be thoroughly
desirable under part-throttle operation.
Larger throttle-valve openings to compensate for reductions in fresh-gas filling
Cylinder charge
Elements
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 evaporativeFig. 2
Cylinder charge in the spark-ignition engine
2
3
1
α
4
5
11
6
12
7
10
8
9
UMM0544-1Y
1 Air and fuel vapor,
2 Purge valve
with variable aperture,
3 Link to evaporative-emissions
control system,
4 Exhaust gas,
5 EGR valve with
variable aperture,
6 Mass airflow (barometric pressure pU),
7 Mass airflow
(intake-manifold pressure ps),
8 Fresh air charge
(combustion-chamber pressure pB),
9 Residual gas charge
(combustion-chamber pressure pB),
10 Exhaust gas (back-pressure pA),
11 Intake valve,
12 Exhaust valve,
α Throttle-valve angle.
5
Page 8
Control elements
Throttle valve
The power produced by the sparkignition engine is directly proportional to
the mass airflow entering it. Control of
engine output and the corresponding
torque at each engine speed is regulated
by governing the amount of air being
inducted via the throttle valve. Leaving
the throttle valve partially closed restricts
the amount of air being drawn into the
engine and reduces torque generation.
The extent of this throttling effect
depends on the throttle valve’s position
and the size of the resulting aperture.
The engine produces maximum power
when the throttle valve is fully open
(WOT, or wide open throttle).
Figure 3 illustrates the conceptual
correlation between fresh-air charge
density and engine speed as a function
of throttle-valve aperture.
6
Gas exchange
The intake and exhaust valves open and
close at specific points to control the
transfer of fresh and residual gases. The
ramps on the camshaft lobes determine
both the points and the rates at which the
valves open and close (valve timing) to
define the gas-exchange process, and
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
recirculation. The mass of residual gas
can also be increased using "external"
exhaust-gas recirculation, which relies
on a supplementary EGR valve linking
the intake and exhaust manifolds. The
engine ingests a mixture of fresh air and
exhaust gas when this valve is open.
Pressure charging
Because maximum possible torque is
proportional to fresh-air charge density, it
is possible to raise power output by
compressing the air before it enters the
cylinder.
Dynamic pressure charging
A supercharging (or boost) effect can be
obtained by exploiting dynamics within
the intake manifold. The actual degree of
boost will depend upon the manifold’s
configuration as well as the engine’s
instantaneous
operating
point
(essentially a function of the engine’s
speed, but also affected by load factor).
The option of varying intake-manifold
geometry while the vehicle is actually
being driven, makes it possible to employ
dynamic precharging to increase the
maximum available charge mass through
a wide operational range.
Mechanical supercharging
Further increases in air mass are
available through the agency of
Fig. 3
Throttle-valve map for spark-ignition engine
Throttle valve at intermediate aperture
Throttle valve
completely open
Throttle valve
completely closed
min.
Idle
max.
RPM
UMM0543-1E
are needed to meet higher torque
demand. These higher angles reduce the
engine’s pumping losses, leading to
lower fuel consumption. Precisely regulated injection of residual gases can
also modify the combustion process to
reduce emissions of nitrous oxides (NOx)
and unburned hydrocarbons (HC).
Fresh gas charge
Gasolineengine
management
Page 9
mechanically driven compressors powered by the engine’s crankshaft, with the
two elements usually rotating at an invariable relative ratio. Clutches are often
used to control compressor activation.
Mixture formation
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 expansion characteristics resulting from the
crankshaft concept. One disadvantage is
the higher back-pressure in the exhaust
gas exiting the engine. This backpressure 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 exhaustfas 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.
Air-fuel mixture
Operation of the spark-ignition engine is
contingent upon availability of a mixture
with a specific air/fuel (A/F) ratio. The
theoretical ideal for complete combustion
is a mass ratio of 14.7:1, referred to as
the stoichiometric ratio. In concrete terms
this translates into a mass relationship of
14.7 kg of air to burn 1 kg of fuel, while
the corresponding volumetric ratio is
roughly 9,500 litres of air for complete
combustion of 1 litre of fuel.
Fig. 4
Torque curves for turbocharged
and atmospheric-induction engines
with equal power outputs
1 Engine with turbocharger,
2 Atmospheric-induction engine.
Engine torque Md
1
2
Engine rpm nn
3
4
1
1
UMM0459-1E
2
4
Parameters
The air-fuel mixture is a major factor in
determining the spark-ignition engine’s
rate of specific fuel consumption.
Genuine complete combustion and
absolutely minimal fuel consumption
would be possible only with excess air,
but here limits are imposed by such
considerations as mixture flammability
and the time available for combustion.
The air-fuel mixture is also vital in
determining the efficiency of exhaust-gas
treatment system. The current state-ofthe-art features a 3-way catalytic
converter, a device which relies on a
stoichiometric A/F ratio to operate at
maximum efficiency and reduce undesirable exhaust-gas components by
more than 98 %.
Current engines therefore operate with a
stoichiometric A/F ratio as soon as the
engine’s operating status permits
1
1
Mixture
formation
Certain engine operating conditions
make mixture adjustments to nonstoichiometric 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
a range of variable requirements.
7
Page 10
Gasolineengine
management
Excess-air factor
The designation l (lambda) has been
selected to identify the excess-air factor
(or air ratio) used to quantify the spread
between the actual current mass A/F ratio
and the theoretical optimum (14.7:1):
λ = Ratio of induction air mass to air
requirement for stoichiometric combustion.
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 by
excess air and lean mixture, leading to
lower fuel consumption and reduced
power. The potential maximum value for λ
– called the “lean-burn limit (LML)” – is
essentially defined by the design of the
engine and of its mixture formation/induction system. Beyond the
lean-burn limit the mixture ceases to be
ignitable and combustion miss sets in,
accompanied by substantial degeneration of operating smoothness.
In engines featuring systems to inject fuel
directly into the chamber, these operate
with substantially higher excess-air
factors (extending to λ = 4) since combustion proceeds according to different
laws.
Spark-ignition engines with manifold
injection produce maximum power at air
deficiencies of 5...15 % (λ = 0.95...0.85),
but maximum fuel economy comes in at
10...20 % excess air (λ = 1.1...1.2).
Figures 1 and 2 illustrate the effect of the
excess-air factor on power, specific fuel
consumption and generation of toxic
emissions. As can be seen, there is no
single excess-air factor which can
simultaneously generate the most
favorable levels for all three factors. Air
factors 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 normal
operating temperature, precise and
consistent maintenance of λ = 1 is vital
for the 3-way catalytic treatment of
exhaust gases. Satisfying this requirement entails exact monitoring of
induction-air mass and precise metering
of fuel mass.
Optimal combustion from current engines equipped with manifold injection
relies on formation of a homogenous
mixture as well as precise metering of the
injected fuel quantity. This makes
effective atomization essential. Failure to
satisfy this requirement will foster the
formation of large droplets of condensed
fuel on the walls of the intake tract and in
the combustion chamber. These droplets
will fail to combust completely and the
ultimate result will be higher HC
emissions.
Fig. 1
Fig. 2
Effects of excess-air factor λ on power P and
specific fuel consumption be.
Effect of excess-air factor λ on untreated
exhaust emissions
a Rich mixture (air deficiency),
b Lean mixture (excess air).
HC
NOX
Power P ,
Specific fuel consumption be
CO
0.8
8
b
1.0
1.2
Excess-air factor λ
UMK0033E
a
0.6
0.8
1.0
1.2
Excess-air factor λ
1.4
UMK0032E
be
Relative quantities of
CO; HC; NOX
P