Page 11
Adapting to specific
operating conditions
Certain operating states cause fuel
requirements to deviate substantially from
the steady-state requirements of an engine
warmed to its normal temperature, thus
necessitating corrective adaptations in the
mixture-formation apparatus. The following descriptions apply to the conditions
found in engines with manifold injection.
Cold starting
During cold starts the relative quantity of
fuel in the inducted mixture decreases: the
mixture “goes lean.” This lean-mixture
phenomenon stems from inadequate
blending of air and fuel, low rates of fuel
vaporization, and condensation on the
walls of the inlet tract, all of which are
promoted by low temperatures. To compensate for these negative factors, and to
facilitate cold starting, supplementary fuel
must be injected into the engine.
Post-start phase
Following
low-temperature
starts,
supplementary fuel is required for a brief
period, until the combustion chamber
heats up and improves the internal
mixture formation. This richer mixture
also increases torque to furnish a
smoother transition to the desired idle
speed.
Warm-up phase
The warm-up phase follows on the heels
of the starting and immediate post-start
phases. At this point the engine still
requires an enriched mixture to offset the
fuel condensation on the intake-manifold
walls. Lower temperatures are synonymous with less efficient fuel processing (owing to factors such as poor mixing of air and fuel and reduced fuel vaporization). This promotes fuel precipitation within the intake manifold, with
the formation of condensate fuel that will
only vaporize later, once temperatures
have increased. These factors make it
necessary to provide progressive mixture
enrichment in response to decreasing
temperatures.
Idle and part-load
Idle is defined as the operating status in
which the torque generated by the engine
is just sufficient to compensate for friction
losses. The engine does not provide
power to the flywheel at idle. Part-load (or
part-throttle) operation refers to the
range of running conditions between idle
and generation of maximum possible
torque. Today’s standard concepts rely
exclusively on stoichiometric mixtures for
the operation of engines running at idle
and part-throttle once they have warmed
to their normal operating temperatures.
Mixture
formation
Full load (WOT)
At WOT (wide-open throttle) supplementary enrichment may be required. As
Figure 1 indicates, this enrichment
furnishes maximum torque and/or power.
Acceleration and deceleration
The fuel’s vaporization potential is strongly
affected by pressure levels inside the
intake manifold. Sudden variations in
manifold pressure of the kind encountered
in response to rapid changes in throttlevalve aperture cause fluctuations in the
fuel layer on the walls of the intake tract.
Spirited acceleration leads to higher
manifold pressures. The fuel responds
with lower vaporization rates and the fuel
layer within the manifold runners expands.
A portion of the injected fuel is thus lost in
wall condensation, and the engine goes
lean for a brief period, until the fuel layer
restabilizes. In an analogous, but inverted,
response pattern, sudden deceleration
leads to rich mixtures. A temperaturesensitive correction function (transition
compensation) adapts the mixture to
maintain optimal operational response
and ensure that the engine receives the
consistent air/fuel mixture needed for
efficient catalytic-converter performance.
Trailing throttle (overrun)
Fuel metering is interrupted during trailing
throttle. Although this expedient saves
fuel on downhill stretches, its primary
purpose is to guard the catalytic converter
against overheating stemming from poor
and incomplete combustion (misfiring).
9
Page 12
Gasolineinjection
systems
Gasoline-injection systems
Carburetors and gasoline-injection systems are designed for a single purpose:
To supply the engine with the optimal airfuel mixture for any given operating
conditions. Gasoline injection systems,
and electronic systems in particular, are
better at maintaining air-fuel mixtures
within precisely defined limits, which
translates into superior performance in
the areas of fuel economy, comfort and
convenience, and power. Increasingly
stringent mandates governing exhaust
emissions have led to a total eclipse of the
carburetor in favor of fuel injection.
Although current systems rely almost
exclusively on mixture formation outside
the combustion chamber, concepts based
on internal mixture formation – with fuel
being injected directly into the combustion
chamber – were actually the foundation
for the first gasoline-injection systems. As
these systems are superb instruments for
achieving further reductions in fuel
consumption, they are now becoming an
increasingly significant factor.
Representative examples are the various
versions of the KE and L-Jetronic systems
(Figure 1).
Mechanical injection systems
The K-Jetronic system operates by
injecting continually, without an external drive being necessary. Instead of
being determined by the injection valve,
fuel mass is regulated by the fuel
distributor.
Combined mechanical-electronic
fuel injection
Although the K-Jetronic layout served as
the mechanical basis for the KE-Jetronic
system, the latter employs expanded
data-monitoring functions for more
precise adaptation of injected fuel
quantity to specific engine operating
conditions.
Electronic injection systems
Injection systems featuring electronic
control rely on solenoid-operated injection
Fig. 1
Overview
Systems with
external mixture formation
The salient characteristic of this type of
system is the fact that it forms the air-fuel
mixture outside the combustion chamber,
inside the intake manifold.
Multipoint fuel injection (MPI)
1 Fuel,
2 Air,
3 Throttle valve,
4 Intake manifold,
5 Injectors,
6 Engine.
4
2
3
1
10
6
UMK0662-2Y
5
Multipoint fuel injection
Multipoint fuel injection forms the ideal
basis for complying with the mixtureformation criteria described above. In this
type of system each cylinder has its own
injector discharging fuel into the area
directly in front of the intake valve.
Page 13
valves for intermittent fuel discharge. The
actual injected fuel quantity is regulated
by controlling the injector's opening time
(with the pressure-loss gradient through
the valve being taken into account in
calculations as a known quantity).
Examples: L-Jetronic, LH-Jetronic, and
Motronic as an integrated engine-management system.
Single-point fuel injection
Single-point (throttle-body injection (TBI))
fuel injection is the concept behind this
electronically-controlled injection system
in which a centrally located solenoidoperated injection valve mounted
upstream from the throttle valve sprays
fuel intermittently into the manifold. MonoJetronic and Mono-Motronic are the
Bosch systems in this category (Figure 2).
Systems for internal
mixture formation
Direct-injection (DI) systems rely on
solenoid-operated injection valves to spray
fuel directly into the combustion chamber;
the actual mixture-formation process takes
place within the cylinders, each of which
has its own injector (Figure 3). Perfect
atomization of the fuel emerging from the
injectors is vital for efficient combustion.
Under normal operating conditions, DI
engines draw in only air instead of the
combination of air and fuel common to
conventional injection systems. This is one
of the new system's prime advantages: It
banishes all potential for fuel condensation
within the runners of the intake manifold.
External mixture formation usually
provides a homogenous, stoichiometric airfuel mixture throughout the entire
combustion chamber. In contrast, shifting
the mixture-preparation process into the
combustion chamber provides for two
distinctive operating modes:
With stratified-charge operation, only the
mixture directly adjacent to the spark plug
needs to be ignitable. The remainder of the
air-fuel charge in the combustion chamber
can consist solely of fresh and residual
gases, without unburned fuel. This strategy
furnishes an extremely lean overall mixture
for idling and part-throttle operation, with
commensurate
reductions
in
fuel
consumption.
Homogenous operation reflects the
conditions encountered in external mixture
formation
by
employing
uniform
consistency for the entire air-fuel charge
throughout the combustion chamber.
Under these conditions all of the fresh air
within the chamber participates in the
combustion process. This operational
mode is employed for WOT operation.
MED-Motronic is used for closed-loop
control of DI gasoline engines.
Fig. 2
Fig. 3
Throttle-body fuel injection (TBI)
Direct fuel injection (DI)
1 Fuel,
2 Air,
3 Throttle valve,
4 Intake manifold,
5 Injector,
6 Engine.
4
1 Fuel,
2 Air,
3 Throttle valve
(ETC),
4 Intake manifold,
5 Injectors,
6 Engine.
4
2
3
Overview
2
3
1
1
UMK0663-2Y
6
6
UMK1687-2Y
5
5
11
Page 14
The story of
fuel injection
The story of fuel injection
The story of fuel injection extends
back to cover a period of almost one
hundred years.
The Gasmotorenfabik Deutz was
manufacturing plunger pumps for injecting fuel in a limited production
series as early as 1898.
A short time later the uses of the venturi-effect for carburetor design were
discovered, and fuel-injection systems
based on the technology of the time
ceased to be competitive.
Bosch started research on gasolineinjection pumps in 1912. The first
aircraft engine featuring Bosch fuel injection, a 1,200-hp unit, entered series
production in 1937; problems with carburetor icing and fire hazards had lent
special impetus to fuel-injection development work for the aeronautics field.
This development marks the beginning of the era of fuel injection at
Bosch, but there was still a long path
to travel on the way to fuel injection for
passenger cars.
1951 saw a Bosch direct-injection unit
being featured as standard equipment
on a small car for the first time. Several years later a unit was installed in
the 300 SL, the legendary production
sports car from Daimler-Benz.
In the years that followed, development on mechanical injection pumps
continued, and ...
In 1967 fuel injection took another
giant step forward: The first electronic
Bosch gasoline fuel injection
from the year 1954
12
injection system: the intake-pressurecontrolled D-Jetronic!
In 1973 the air-flow-controlled L-Jetronic appeared on the market, at the
same time as the K-Jetronic, which featured mechanical-hydraulic control and
was also an air-flow-controlled system.
In 1976, the K-Jetronic was the first
automotive system to incorporate a
Lambda closed-loop control.
1979 marked the introduction of a new
system: Motronic, featuring digital processing for numerous engine functions. This system combined L-Jetronic with electronic program-map control for the ignition. The first automotive microprocessor!
In 1982, the K-Jetronic model became
available in an expanded configuration, the KE-Jetronic, including an
electronic closed-loop control circuit
and a Lambda oxygen sensor.
These were joined by Bosch MonoJetronic in 1987: This particularly costefficient single-point injection unit
made it feasible to equip small vehicles
with Jetronic, and once and for all made
the carburetor absolutely superfluous.
By the end of 1997, around 64 million
Bosch engine-management systems
had been installed in countless types of
vehicles since the introduction of the
D-Jetronic in 1967. In 1997 alone, the
figure was 4.2 million, comprised of
1 million throttle-body injection (TBI)
systems and 3.2 million multipoint fuelinjection (MPI) systems.
Page 15
K-Jetronic
System overview
The K-Jetronic is a mechanically and
hydraulically controlled fuel-injection system which needs no form of drive and
which meters the fuel as a function of the
intake air quantity and injects it continuously onto the engine intake valves.
Specific operating conditions of the
engine require corrective intervention in
mixture formation and this is carried out
by the K-Jetronic in order to optimize
starting and driving performance, power
output and exhaust composition. Owing
to the direct air-flow sensing, the K-Jetronic system also allows for engine
variations and permits the use of facilities
for exhaust-gas aftertreatment for which
precise metering of the intake air quantity
is a prerequisite.
The K-Jetronic was originally designed
as a purely mechanical injection system.
Today, using auxiliary electronic equipment, the system also permits the use of
lambda closed-loop control.
The K-Jetronic fuel-injection system
covers the following functional areas:
– Fuel supply,
– Air-flow measurement and
– Fuel metering.
Fuel supply
An electrically driven fuel pump delivers
the fuel to the fuel distributor via a fuel
accumulator and a filter. The fuel distributor allocates this fuel to the injection
valves of the individual cylinders.
K-Jetronic
Air-flow measurement
The amount of air drawn in by the engine
is controlled by a throttle valve and
measured by an air-flow sensor.
Fuel metering
The amount of air, corresponding to the
position of the throttle plate, drawn in by
the engine serves as the criterion for
metering of the fuel to the individual
cylinders. The amount of air drawn in by
the engine is measured by the air-flow
sensor which, in turn, controls the fuel
distributor. The air-flow sensor and the
fuel distributor are assemblies which
form part of the mixture control unit.
Injection occurs continuously, i.e. without
regard to the position of the intake valve.
During the intake-valve closed phase, the
fuel is “stored”. Mixture enrichment is
controlled in order to adapt to various
operating conditions such as start, warmup, idle and full load. In addition, supplementary functions such as overrun fuel
cutoff, engine-speed limiting and closedloop lambda control are possible.
Fig. 1
Functional schematic of the K-Jetronic
Electric
fuel pump
Air filter
Air
Fuel
accumulator
Air-flow
sensor
Mixture
control unit
Fuel filter
Fuel
distributor
Injection valves
Throttle valve
Mixture
Intake ports
Combustion
chamber
UMK0009E
Fuel
13
Page 16
Gasolineinjection
systems
Fuel supply
The fuel supply system comprises
– Electric fuel pump,
– Fuel accumulator,
– Fine filter,
– Primary-pressure regulator and
– Injection valves.
An electrically driven roller-cell pump
pumps the fuel from the fuel tank at a
pressure of over 5 bar to a fuel accumulator and through a filter to the fuel
distributor. From the fuel distributor the
fuel flows to the injection valves. The
injection valves inject the fuel continuously into the intake ports of the
engine. Thus the system designation K
(taken from the German for continuous).
When the intake valves open, the mixture
is drawn into the cylinder.
The fuel primary-pressure regulator
maintains the supply pressure in the
system constant and reroutes the excess
fuel back to the fuel tank.
Owing to continual scavenging of the fuel
supply system, there is always cool fuel
available. This avoids the formation of
fuel-vapor bubbles and achieves good
hot starting behavior.
Electric fuel pump
The electric fuel pump is a roller-cell
pump driven by a permanent-magnet
electric motor.
The rotor plate which is eccentrically
mounted in the pump housing is fitted
with metal rollers in notches around its
circumference which are pressed against
the pump housing by centrifugal force
and act as rolling seals. The fuel is carried in the cavities which form between
the rollers. The pumping action takes
place when the rollers, after having
closed the inlet bore, force the trapped
fuel in front of them until it can escape
from the pump through the outlet bore
(Figure 4). The fuel flows directly around
the electric motor. There is no danger of
explosion, however, because there is
never an ignitable mixture in the pump
housing.
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.
1
3
5
2
4
11
8
9
7
12
13
14
10
15
16
17
18
14
19
BOSCH
UMK0077Y
6
Page 17
1 Suction side, 2 Pressure limiter, 3 Roller-cell
pump, 4 Motor armature, 5 Check valve,
6 Pressure side.
2 3
4
5
6
UMK0121-2Y
1
Fig. 3
Fig. 4
Operation of roller-cell pump
1 Suction side, 2 Rotor plate, 3 Roller,
4 Roller race plate, 5 Pressure side.
2 3
4
1
5
UMK0120-2Y
Fuel accumulator
The fuel accumulator maintains the
pressure in the fuel system for a certain
time after the engine has been switched
off in order to facilitate restarting, particularly when the engine is hot. The special design of the accumulator housing
(Figure 5) deadens the sound of the fuel
pump when the engine is running.
The interior of the fuel accumulator is
divided into two chambers by means of a
diaphragm. One chamber serves as the
accumulator for the fuel whilst the other
represents the compensation volume
and is connected to the atmosphere or to
the fuel tank by means of a vent fitting.
During operation, the accumulator
chamber is filled with fuel and the diaphragm 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 accumulator volume, as long as the engine is
running.
K-Jetronic
Electric fuel pump
Fig. 5
Fuel accumulator
a Empty, b Full.
1 Spring chamber, 2 Spring, 3 Stop, 4 Diaphragm,
5 Accumulator volume, 6 Fuel inlet or outlet,
7 Connection to the atmosphere.
a
7
1
2
3 4
5
6
b
UMK1653Y
The electric fuel pump delivers more fuel
than the maximum requirement of the
engine so that compression in the fuel
system can be maintained under all operating conditions. A check valve in the
pump decouples the fuel system from
the fuel tank by preventing reverse flow of
fuel to the fuel tank.
The electric fuel pump starts to operate
immediately when the ignition and starting switches are operated and remains
switched on continuously after the engine
has started. A safety circuit is incorporated to stop the pump running and, thus,
to prevent fuel being delivered if the ignition is switched on but the engine has
stopped turning (for instance in the case
of an accident).
The fuel pump is located in the immediate vicinity of the fuel tank and requires
no maintenance.
15
Page 18
Fuel filter
The fuel filter retains particles of dirt
which are present in the fuel and which
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
accumulator and its service life depends
upon the amount of dirt in the fuel. It is
imperative that the arrow on the filter
housing showing the direction of fuel flow
through the filter is observed when the
filter is replaced.
Fuel filter
1 Paper element,
2 Strainer,
1
3 Support
plate.
2
3
UMK0119Y
Gasolineinjection
systems
Fig. 6
delivery drops slightly, the plunger is
shifted by the spring to a corresponding
new position and in doing so closes off
the port slightly through which the excess
fuel returns to the tank. This means that
less fuel is diverted off at this point and
the system pressure is controlled to its
specified level.
When the engine is switched off, the fuel
pump also switches off and the primary
pressure drops below the opening pressure of the injection valves. The pressure
regulator then closes the return-flow port
and thus prevents the pressure in the fuel
system from sinking any further (Fig. 8).
Primary-pressure regulator
The primary-pressure regulator maintains the pressure in the fuel system
constant.
It is incorporated in the fuel distributor
and holds the delivery pressure (system
pressure) at about 5 bar. The fuel pump
always delivers more fuel than is required
by the vehicle engine, and this causes a
plunger to shift in the pressure regulator
and open a port through which excess
fuel can return to the tank.
The pressure in the fuel system and the
force exerted by the spring on the
pressure-regulator plunger balance each
other out. If, for instance, fuel-pump
Fuel-injection valves
The injection valves open at a given pressure and atomize the fuel through oscillation of the valve needle. The injection
valves inject the fuel metered to them into
the intake passages and onto the intake
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
16
3
4
5
UMK1495Y
1
Page 19
K-Jetronic
Pressure curve after engine switchoff
Firstly pressure falls from the normal system
pressure (1) to the pressure-regulator closing
pressure (2). The fuel accumulator then causes
it to increase to the level (3) which is below the
opening pressure (4) of the injection valves.
bar
1
4
3
Pressure p
2
Time t
ms
UMK0018E
holders to insulate them against the heat
radiated from the engine. The injection
valves have no metering function themselves, and open of their own accord
when the opening pressure of e.g. 3.5
bar is exceeded. They are fitted with a
valve needle (Fig. 9) which oscillates
(“chatters”) audibly at high frequency
when fuel is injected. This results in excellent atomization of the fuel even with
the smallest of injection quantities. When
the engine is switched off, the injection
valves close tightly when the pressure in
the fuel-supply system drops below their
opening pressure. This means that no
more fuel can enter the intake passages
once the engine has stopped.
Fig. 8
Fig. 9
Fuel-injection valve
a In rest position,
b In actuated position.
1 Valve housing,
2 Filter,
3 Valve needle,
4 Valve seat.
UMK0042Y
b
3
4
UMK0069-2Y
2
a
Fig. 10
Spray pattern of an injection valve without
air-shrouding (left) and with air-shrouding (right).
1
UMK0041Y
Air-shrouded fuel-injection valves
Air-shrouded injection valves improve the
mixture formation particularly at idle.
Using the pressure drop across the
throttle valve, a portion of the air inducted
by the engine is drawn into the cylinder
through the injection valve (Fig. 20): The
result is excellent atomization of the fuel
at the point of exit (Fig. 10). Air-shrouded
injection valves reduce fuel consumption
and toxic emission constituents.
17
Page 20
Gasolineinjection
systems
Fuel metering
Principle of the air-flow sensor
The task of the fuel-management system
is to meter a quantity of fuel corresponding to the intake air quantity.
Basically, fuel metering is carried out
by the mixture control unit. This comprises the air-flow sensor and the fuel
distributor.
In a number of operating modes however,
the amount of fuel required deviates
greatly from the “standard” quantity and it
becomes necessary to intervene in the
mixture formation system (see section
“Adaptation to operating conditions”).
a Small amount of air drawn in: sensor plate only
lifted slightly, b Large amount of air drawn in:
sensor plate is lifted considerably further.
a
h
b
Air-flow sensor
The quantity of air drawn in by the engine
is a precise measure of its operating
load. The air-flow sensor operates according to the suspended-body principle,
and measures the amount of air drawn in
by the engine.
The intake air quantity serves as the
main actuating variable for determining
the basic injection quantity. It is the
appropriate physical quantity for deriving
the fuel requirement, and changes in the
induction characteristics of the engine
have no effect upon the formation of the
UMK0072Y
h
Fig. 11
air-fuel mixture. Since the air drawn in by
the engine must pass through the air-flow
sensor before it reaches the engine, this
means that it has been measured and
the control signal generated before it
actually enters the engine cylinders. The
result is that, in addition to other
measures described below, the correct
mixture adaptation takes place at all
times.
Fig. 12
Updraft
air-flow sensor
a Sensor plate in its
zero position,
b Sensor plate in its
operating position.
1
2
3
4
5
a
1 Air funnel,
2 Sensor plate,
3 Relief cross-section,
4 Idle-mixture
adjusting screw,
5 Pivot,
6 Lever,
7 Leaf spring.
7
6
18
UMK1654Y
b