Page 31
Acceleration response
The good acceleration response is a result of “overswing” of the air-flow sensor
plate (Figure 29).
Transitions from one operating condition
to another produce changes in the mixture ratio which are utilized to improve
driveability.
If, at constant engine speed, the throttle
valve is suddenly opened, the amount
of air which enters the combustion
chamber, plus the amount of air which is
needed to bring the manifold pressure
up to the new level, flow through the
airflow sensor. This causes the sensor
plate to briefly “overswing” past the fully
opened throttle point. This “overswing”
results in more fuel being metered to the
engine (acceleration enrichment) and
ensures good acceleration response.
K-Jetronic
Fig. 30
1
a During idle and part
load,
b During full load.
1 Electrical heating,
2 Bimetal spring,
3 Vacuum connection
(from intake manifold),
4 Valve diaphragm,
5 Return to fuel tank,
6 Control pressure
(from fuel distributor),
7 Valve springs,
8 Upper stop,
9 To atmospheric pressure,
10 Diaphragm,
11 Lower stop.
a
2
3
4
5
,,,,,,,
,
,,,,,,,
,
,,,,,,,
,
,,,,,,,
,
,,,,,,,,,,,,,,,,,,,,
, ,,,,,,,
,
,,,,,,,
,,,,,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,,,,,
,,
,,,,,,,,,,,,,,,,,,,,
,,
,,,,,,,,,,,,,,,,,,,,
11
b
6
7
8
9
10
,,,,,,,
,
,,,,,,,
,
, ,,,,,,,
,,,,,,,
,
,,,,,,,,,,,,,,,,,,,,
, ,,,,,,,
,,,,,,,
,,,,,,,,,,,,,,,,,,,,
,,,,,,,
,,,,,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,,,,,
,,,,,,,,,,,,,,,,,,,,
,,
,,,,,,,,,,,,,,,,,,,,
,,
,,,,,,,,,,,,,,,,,,,,
UMK1660Y
Warm-up regulator
with full-load
diaphragm
29
Page 32
Supplementary functions
Engine speed limiting
The fuel supply can be cut off to limit the
maximum permissible engine speed.
Overrun fuel cutoff
Smooth fuel cutoff effective during overrun responds as a function of the engine
speed. The engine-speed information is
provided by the ignition system. Intervention is via an air bypass around the
sensor plate. A solenoid valve controlled
by an electronic speed switch opens the
bypass at a specific engine speed. The
sensor plate then reverts to zero position
and interrupts fuel metering. Cutoff of the
fuel supply during overrun operation
permits the fuel consumption to be
reduced considerably not only when
driving downhill but also in town traffic.
Lambda closed-loop control
Open-loop control of the air-fuel ratio is
not adequate for observing extremely
low exhaust-gas limit values. The lambda
closed-loop control system required for
operation of a three-way catalytic converter necessitates the use of an electronic control unit on the K-Jetronic. The
important input variable for this control
unit is the signal supplied by the lambda
sensor.
In order to adapt the injected fuel quantity
to the required air-fuel ratio with λ = 1, the
Fig. 31
Additional components for lambda closed-loop control
1 Lambda sensor,
2 Lambda closed-loop controller,
3 Frequency valve (variable restrictor),
4 Fuel distributor,
5 Lower chambers of the differentialpressure valves,
6 Metering slits,
7 Decoupling restrictor
(fixed restrictor),
8 Fuel inlet,
9 Fuel return line.
2
1
3
4
10
6
5
30
,,
,,,,,,
,,
,,,,,,,
,,,,
,,,,,
,,,,,
,,,,,
7
10
8
9
7
UMK1507Y
Gasolineinjection
systems
Page 33
pressure in the lower chambers of the
fuel distributor is varied. If, for instance,
the pressure in the lower chambers is
reduced, the differential pressure at the
metering slits increases, whereby the
injected fuel quantity is increased. In
order to permit the pressure in the lower
chambers to be varied, these chambers
are decoupled from the primary pressure
via a fixed restrictor, by comparison with
the standard K-Jetronic fuel distributor.
A further restrictor connects the lower
chambers and the fuel return line.
This restrictor is variable: if it is open, the
pressure in the lower chambers can drop.
If it is closed, the primary pressure builds
up in the lower chambers. If this restrictor
is opened and closed in a fast rhythmic
succession, the pressure in the lower
chambers can be varied dependent upon
the ratio of closing time to opening time.
An electromagnetic valve, the frequency
valve, is used as the variable restrictor. It
is controlled by electrical pulses from the
lambda closed-loop controller.
K-Jetronic
Fig. 32
Components of the K-Jetronic system
1
2
3
4
5
6
9
7
10
1 Fuel accumulator, 2 Electric fuel pump, 3 Fuel filter, 4 Warm-up regulator, 5 Mixture-control unit with
air-flow sensor and fuel distributor, 6 Cold-start valve, 7 Thermo-time switch, 8 Injection valves,
9 Auxiliary-air device, 10 Electronic control relay.
UMK0040Y
8
31
Page 34
Lambda sensor
The Lambda sensor inputs a voltage
signal to the ECU which represents
theinstantaneous composition of the airfuel mixture.
The Lambda sensor is installed in the
engine exhaust manifold at a point which
maintains the necessary temperature for
the correct functioning of the sensor over
the complete operating range of the
engine.
Operation
The sensor protrudes into the exhaustgas stream and is designed so that the
outer electrode is surrounded by exhaust
gas, and the inner electrode is connected
to the atmospheric air.
Basically, the sensor is constructed from
an element of special ceramic, the surface of which is coated with microporous
platinum electrodes. The operation of the
sensor is based upon the fact that
ceramic material is porous and permits
diffusion of the oxygen present in the air
(solid electrolyte). At higher temperatures, it becomes conductive, and if the
oxygen concentration on one side of the
electrode is different to that on the other,
then a voltage is generated between the
electrodes. In the area of stoichiometric
airfuel mixture (λ = 1.00), a jump takes
place in the sensor voltage output curve.
This voltage represents the measured
signal.
32
Construction
The ceramic sensor body is held in a
threaded mounting and provided with a
protective tube and electrical connections. The surface of the sensor ceramic
body has a microporous platinum layer
which on the one side decisively influences the sensor characteristic while on
the other serving as an electrical contact.
A highly adhesive and highly porous
ceramic coating has been applied over
the platinum layer at the end of the
ceramic body that is exposed to the exhaust gas. This protective layer prevents
the solid particles in the exhaust gas from
eroding the platinum layer. A protective
metal sleeve is fitted over the sensor
on the electrical connection end and
crimped to the sensor housing. This
sleeve is provided with a bore to ensure
pressure compensation in the sensor interior, and also serves as the support for
the disc spring. The connection lead is
crimped to the contact element and is led
through an insulating sleeve to the outside of the sensor. In order to keep
combustin deposits in the exhaust gas
away from the ceramic body, the end of
the exhaust sensor which protrudes into
the exhaust-gas flow is protected by a
special tube having slots so designed
that the exhaust gas and the solid particles entrained in it do not come into
direct contact with the ceramic body.
In addition to the mechanical protection
thus provided, the changes in sensor
temperature during transition from one
operating mode to the other are effectively reduced.
The voltage output of the λ sensor, and
its internal resistance, are dependent
upon temperature. Reliable functioning
of the sensor is only possible with
exhaust-gas temperatures above 360 °C
(unheated version), and above 200 °C
(heated version).
Fig. 33
Control range of the lambda sensor and
reduction of pollutant concentrations in
exhaust
Without catalytic aftertreatment
With catalytic aftertreatment
λ-control range
HC
NOx
NOx
CO
CO
HC
0.9
Voltage curve
of λ sensor
0.95 1.0 1.05 1.1
Excess-air factor λ
UMK0004-2E
Exhaust-gas treatment
Exhaust emissions, sensor voltage
Gasolineinjection
systems
Page 35
Heated Lambda oxygen sensor
To a large extent, the design principle of
the heated Lambda sensor is identical to
that of the unheated sensor.
The active sensor ceramic is heated internally by a ceramic heating element
with the result that the temperature of the
ceramic body always remains above the
function limit of 350 °C.
The heated sensor is equipped with a
protective tube having a smaller opening.
Amongst other things, this prevents the
sensor ceramic from cooling down when
the exhaust gas is cold. Among the advantages of the heated Lambda sensor
are the reliable and efficient control at low
exhaust-gas temperatures (e.g. at idle),
the minimum effect of exhaust-gas temperature variations, the rapid coming into
effect of the Lambda control following
engine start, short sensor-reaction time
which avoids extreme deviations from the
ideal exhaust-gas composition, versatility
regarding installation because the sensor
is now independent of heating from its
surroundings.
Lambda closed-loop control circuit
By means of the Lambda closed-loop
control, the air-fuel ratio can be maintained precisely at λ= 1.00.
The Lambda closed-loop control is an
add-on function which, in principle, can
supplement every controllable fuelmanagement system. It is particularly
suitable for use with Jetronic gasolineinjection systems or Motronic. Using the
closed-loop control circuit formed with
the aid of the Lambda sensor, deviations from a specified air-fuel ratio can be
detected and corrected. This control
principle is based upon the measurement
of the exhaust-gas oxygen by the
Lambda sensor. The exhaust-gas oxygen is a measure for the composition of
the air-fuel mixture supplied to the engine. The Lambda sensor acts as a probe
in the exhaust pipe and delivers the
information as to whether the mixture is
richer or leaner than λ = 1.00.
In case of a deviation from this λ = 1.00
figure, the voltage of the sensor output
signal changes abruptly. This pronounced
change is evaluated by the ECU which is
provided with a closed-loop control circuit
for this purpose. The injection of fuel to
the engine is controlled by the fuelmanagement system in accordance with
the information on the composition of the
air-fuel mixture received from the Lambda
sensor. This control is such that an airfuel
ratio of λ = 1 is achieved. The sensor
voltage is a measure for the correction of
the fuel quantity in the air-fuel mixture.
Fig. 34
Fig. 35
Positioning of the lambda sensor
in a dual exhaust system
Location of the lambda sensor in the exhaust
pipe (schematic)
K-Jetronic
1 Sensor ceramic, 2 Electrodes, 3 Contact,
4 Electrical contacting to the housing,
5 Exhaust pipe, 6 Protective ceramic coating
(porous), 7 Exhaust gas, 8 Air. U voltage.
1
2
7
8
4
3
6
UMK1684Y
U
UMK 0151Y
,,,,,,,
,
,,,,,,,,,,,,,,
, ,,
,,,,,,,,,,,,,,
,,,
,
,
,,,,
,
,
,
,
, , , ,,,,
,,,,
5
33
Page 36
Gasolineinjection
systems
means of an open-loop control. Starting
enrichment is by means of appropriate
components similar to the Jetronic
installations not equipped with Lambda
control.
The signal which is processed in the
closed-loop control circuit is used to
control the actuators of the Jetronic installation. In the fuel-management system
of the K-Jetronic (or carburetor system),
the closed-loop control of the mixture
takes place by means of an additional
control unit and an electromechanical
actuator (frequency valve). In this manner,
the fuel can be metered so precisely that
depending upon load and engine speed,
the air-fuel ratio is an optimum in all
operating modes. Tolerances and the
ageing of the engine have no effect whatsoever. At values above λ = 1.00, more
fuel is metered to the engine, and at
values below λ = 1.00, less. This continuous, almost lag-free adjustment of the
air-fuel mixture to λ = 1.00, is one of the
prerequisites for the efficient aftertreatment of the exhaust gases by the
downstream catalytic converter.
Acceleration and full load (WOT)
The enrichment during acceleration can
take place by way of the closed-loop
control unit. At full load, it may be necessary for temperature and power reasons
to operate the engine with an air-fuel ratio
which deviates from the λ = 1 figure.
Similar to the acceleration range, a sensor signals the full-load operating mode
to the closed-loop control unit which then
switches the fuel-injection to the openloop mode and injects the corresponding
amount of fuel.
Deviations in air-fuel mixture
The Lambda closed-loop control operates in a range between λ = 0.8…1.2 in
which normal disturbances (such as the
effects of altitude) are compensated for
by controlling λ to 1.00 with an accuracy
of ±1 %. The control unit incorporates a
circuit which monitors the Lambda
sensor and prevents prolonged marginal
operation of the closed-loop control. In
such cases, open-loop control is selected
and the engine is operated at a mean
λ-value.
Control functions at various
operating modes
Start
The Lambda sensor must have reached
a temperature of above 350 °C before it
outputs a reliable signal. Until this temperature has been reached, the closedloop mode is suppressed and the air-fuel
mixture is maintained at a mean level by
Fig. 36
Heated lambda sensor
1 Sensor housing, 2 Protective ceramic tube, 3 Connection cable, 4 Protective tube with slots, 5 Active
sensor ceramic, 6 Contact element, 7 Protective sleeve, 8 Heater, 9 Clamp terminals for heater.
4
34
5
2
6
7
3
8
9
10
UMK 0143Y
1
Page 37
K-Jetronic
Lambda closed control-loop
The Lambda closed control-loop is superimposed upon the air-fuel mixture control. The fuel quantity to
be injected, as determined by the air-fuel mixture control, is modified by the Lambda closed-loop control
in order to provide optimum combustion.
Uλ Lambda-sensor signal
Engine (controlled system)
Catalytic
converter
Exhaust-gas oxygen
(controlled
variable)
Air-flow
sensor
Intake
air
Lambda
sensor
Fuel-injection
valves
Sensor-plate
position
(mechanical)
Fuel
Fuel
distributor
Differential pressure
(manipulated variable)
Uλ
Lambda closed-loop control
in the Motronic ECU
Fig. 38
UMK 0307 E
Frequency valve
(final controlling
element)
Fig. 37
UMK0282Y
View of the unheated (front) and heated lambda sensors
35
Page 38
Gasolineinjection
systems
Electrical circuitry
If the engine stops but the ignition remains switched on, the electric fuel
pump is switched off.
The K-Jetronic system is equipped with
a number of electrical components, such
as electric fuel pump, warm-up regulator,
auxiliary-air device, cold-start valve and
thermo-time switch. The electrical supply
to all of these components is controlled by
the control relay which, itself, is switched
by the ignition and starting switch.
Apart from its switching functions, the
control relay also has a safety function.
A commonly used circuit is described
below.
Function
When cold-starting the engine, voltage is
applied to the cold-start valve and the
thermo-time switch through terminal 50
of the ignition and starting switch. If the
cranking process takes longer than
between 8 and 15 seconds, the thermotime switch switches off the cold-start
valve in order that the engine does not
“flood”. In this case, the thermo-time
switch performs a time-switch function.
If the temperature of the engine is above
approximately +35 °C when the starting
process is commenced, the thermo-time
switch will have already open-circuited
the connection to the start valve which,
Fig. 39
1 Ignition and starting
switch,
2 Cold-start valve,
3 Thermo-time switch,
4 Control relay,
5 Electric fuel pump,
6 Warm-up regulator,
7 Auxiliary-air device.
30
30
1
50
50
15
15
W
30
87
G
1
3
2
31
4
5
6
7
5
6
7
1
UMK 0196 Y
Circuit without
voltage applied
Fig. 40
Cold-start valve and
thermo-time switch are
switched on. The engine turns (pulses are
taken from terminal 1 of
the ignition coil). The
control relay, electric
fuel pump, auxiliary-air
device and warm-up
regulator are switched
on.
30
30
1
50
50
15
15
W
30
87
G
1
2
1
36
3
31
4
UMK 0197 Y
Starting (with the
engine cold)
Page 39
consequently, does not inject extra fuel.
In this case, the thermo-time switch
functions as a temperature switch.
Voltage from the ignition and starting
switch is still present at the control relay
which switches on as soon as the engine
runs. The engine speed reached when
the starting motor cranks the engine is
high enough to generate the “engine
running” signal which is taken from the
ignition pulses coming from terminal 1 of
the ignition coil. An electronic circuit in
the control relay evaluates these pulses.
After the first pulse, the control relay is
switched on and applies voltage to the
electric fuel pump, the auxiliary-air
device and the warm-up regulator. The
control relay remains switched on as long
as the ignition is switched on and the
ignition is running. If the pulses from
terminal 1 of the ignition coil stop because the engine has stopped turning,
for instance in the case of an accident,
the control relay switches off approximately 1 second after the last pulse is
received.
K-Jetronic
This safety circuit prevents the fuel pump
from pumping fuel when the ignition is
switched on but the engine is not turning.
Fig. 41
Operation
30
30
1
50
50
15
15
W
30
87
G
1
3
2
31
4
5
6
7
5
6
7
1
UMK 0198 Y
Ignition on and engine
running.
Control relay, electric
fuel pump, auxiliary-air
device and warm-up
regulator are switched
on.
Fig. 42
No pulses can be taken
from terminal 1 of the
ignition coil. The control
relay, electric fuel
pump, auxiliary-air
device and warm-up
regulator are switched
off.
30
30
1
50
50
15
15
W
30
87
G
1
2
1
3
31
4
UMK 0199 Y
Ignition on
but engine stopped
37
Page 40
Gasolineinjection
systems
Workshop testing techniques
Bosch customer service
Customer service quality is also a measure for product quality. The car driver has
more than 10,000 Bosch Service Agents
at his disposal in 125 countries all over the
world. These workshops are neutral and
not tied to any particular make of vehicle.
Even in sparsely populated and remote
areas of Africa and South America the
driver can rely on getting help very quickly.
Help which is based upon the same
quality standards as in Germany, and
which is backed of course by the identical
guarantees which apply to customer-service work all over the world. The data and
performance specs for the Bosch systems
and assemblies of equipment are precisely matched to the engine and the vehicle.
In order that these can be checked in the
workshop, Bosch developed the appropriate measurement techniques, test equipment, and special tools and equipped all
its Service Agents accordingly.
Testing techniques for K-Jetronic
Apart from the regular replacement of the
fuel filter as stipulated by the particular
vehicle’s manufacturer, the K-Jetronic
gasoline-injection system requires no
special maintenance work.
In case of malfunctions, the workshop
Fig. 43
38
UMK 1494 Y
Injector tester
expert has the following test equipment,
together with the appropriate test specs,
at his disposal:
– Injector tester
– Injected-quantity comparison tester
– Pressure-measuring device, and
– Lambda closed-loop control tester (only
needed if Lambda control is fitted).
Together with the relevant Test Instructions and Test Specifications in a variety of
different languages, this uniform testing
technology is available throughout the
world at the Bosch Service Agent workshops and at the majority of the workshops belonging to the vehicle manufacturers. Purposeful trouble-shooting and
technically correct repairs cannot be performed at a reasonabe price without this
equipment. It is therefore inadvisable for
the vehicle owner to attempt to carry out
his own repairs.
Injector tester
The injector tester (Fig. 43) was developed specifically for testing the K- and
KE-Jetronic injectors when removed
from the engine. The tester checks all the
functions of the injector which are essential for correct engine running:
– Opening pressure,
– Leakage integrity,
– Spray shape,
– Chatter.
Those injectors whose opening pressure
is outside tolerance are replaced. For the
leak test, the pressure is slowly increased up to 0.5 bar below the opening
pressure and held at this point. Within
60 secs, no droplet of fuel is to form at the
injector. During the chatter test, the
injector must generate a “chattering”
noise without a fuel droplet being formed.
Serviceable injectors generate a fully
atomized spray pattern. “Pencil” jets and
“bundled” jets are not to form.
Injected-quantity comparison tester
Without removing the fuel distributor from
the vehicle, a comparitive measurement is
made to determine the differences in the
delivered quantities from the various fueldistributor outlets (this applies to all engines of up to maximum eight cylinders.