Range Rover P38
BMW DIESEL
7
DESCRIPTION AND OPERATION
Vehicle speed signal
Vehicle speed is monitored by the ECM from the ABS
ECU.
The ECM uses vehicle speed data when adjusting idle
stabilisation, cruise control and fuel delivery.
Throttle position sensor (TP sensor)
The position, selected by the driver, of the accelerator
pedal is signalled to the ECM by the TP sensor. This
is linked, mechanically to the pedal and electrically to
the ECM.
The sender consists of a thick film TP sensor together
with a sender switch (9 degree switch). With the
accelerator pedal at rest the switch is open. When the
pedal is moved past the 9 degree position the switch
closes.
When the ignition is switched ON, pedal position is
signalled to the ECM. Pedal movement causes
voltage through the TP sensor to vary and the ECM
uses this to measure:
- Required engine speed
- Rate of acceleration
- Rate of deceleration
The ECM calculates the rate of change of the voltage
signal in a positive (accelerate) or negative
(decelerate) direction. From this, acceleration
enrichment, deceleration fuel metering or overrun fuel
cut-off can be carried out by the system.
The sender switch is used together with the voltage
from the TP sensor to check the operation of the
circuit. When the pedal is moved, the switch signals a
logic input to the ECM. The ECM then checks the
voltage signal from the TP sensor. This voltage is
compared with a pre-programmed value to check that
the TP sensor is working correctly.
Servo unit potentiometer (drive potentiometer) on
quantity servo control unit
This potentiometer signals a voltage to the ECM. The
voltage value is used to calculate the position of the
control spool in the injection pump quantity servo
control unit - See description of this item.
Clutch switch
A switch fitted at the clutch pedal position is
connected to the ECM.
The switch detects when the clutch is depressed. This
input is used to deactivate the cruise control and
various driveability strategies.
Brake switch
The brake pedal is fitted with a twin contact switch
which provides two outputs. Both outputs send signals
to the ECM. Both signals are used by the system to
test the operation of the brake circuit, and to
deactivate the cruise control.
Output devices
Output devices of the DDE system comprise the
following:
Quantity servo control unit
Stop solenoid
Injection timing device
Heater time relay
Diagnosis and preheater lamps
Fuel consumption indicator in instrument pack
Quantity servo control unit
The servo is used to accurately control the amount of
fuel delivered to the injectors. It is housed within the
fuel injection pump.
See Injection pump.
The unit consists of a rotary magnet mounted on an
eccentric shaft; the shaft engages with the control
spool of the pump. The rotary magnet is fitted with a
return spring and moves under the influence of a
control coil. The magnet rotates through an arc of
about 60 degrees which moves the control spool from
zero to maximum fuel delivery position. The eccentric
shaft engages with the control spool at one end, while
the opposite end operates a rotary potentiometer.