1999 JAGUAR S TYPE cruise control

V6 EngineAJ-V6/AJ28
25
Throttle Control System
D.303.1219
Introduction
A fully electronically controlled throttle is fitted,
requiring no mechanical connection between the
accelerator pedal and throttle body. The driver
operates a normal foot pedal and a transducer on
the pedal shaft converts the mechanical rotation
to electrical signals which are sent to the
powertrain control module (PCM) to indicate
driver demand. Signals requesting the desired
throttle plate angle are sent from the PCM to an
electronic module on the throttle assembly, the
throttle actuator control (TAC) module, which
provides closed loop control of the motorised
throttle plate. The actual angle of the throttle
plate is indicated to the PCM by the throttle
position (TP) sensor.
The throttle assembly is mechanically simpler
than those used on previous Jaguar vehicles,
consisting essentially of a motor driven throttle
plate with no other actuators or vacuum devices
(eg cruise control).
Operation is designed to be transparent to the
driver with a total delay of less than 70ms
between pedal actuation and throttle movement.
THROTTLE BODY
Control Components
Throttle Assembly
The electronic throttle assembly consists of four
component sub-assemblies:
¥ throttle body
¥ drive motor unit
¥ throttle actuator control (TAC) module
¥ throttle position (TP) sensor
The throttle body is an aluminium casting with a
70mm air intake bore, housing a shaft with brass
throttle plate, rotating in ball bearings, and with a
spur gear and return spring fitted to the drive
end. A stop screw against the spur gear is pre-
adjusted and sealed on assembly to set the
throttle mechanical closed position and a second
stop prevents the throttle plate from being driven
beyond the full throttle position. The internal
tooth spur gear is driven directly from the motor
shaft which is offset to the throttle shaft. The
motor drive unit is an integral assembly
containing the motor, an inductive position
encoder and the mating connector to the TAC
module. Should the motor fail, the return spring
will move the throttle plate to the closed position.
The TAC module consists of a printed circuit
board enclosed within an aluminium module with
D.303.1219

V6 Engine AJ-V6/AJ28
28¥ Limp home mode in which a high idle speed
is set, with no accelerator pedal response, to
allow the vehicle to creep: the RED warning
light and FAIL SAFE ENGINE MODE message
are activated: this mode is set by, eg the loss
of two or more sensors.
¥ Engine shutdown due to serious throttle
malfunction.
J.303.1363
THROTTLE CONTROL SYSTEM
System Monitoring
Within the PCM, operation of the overall throttle
control system (main processor logic and
software) is itself monitored by a separate,
independent microprocessor, the electronic
throttle monitor. Communication is maintained
between the two processors but if it is lost or if
faults are detected by the monitor (eg throttle
angle greater than demanded), the monitor
processor may call for a restricted operating mode
such as cruise cancellation or a forced idle
condition or engine shutdown.
Failure Modes
There are four failure modes:
¥ Loss of redundancy eg a failure of one sensor
output: this type of fault causes the AMBER
warning light to illuminate and FAIL SAFE
ENGINE MODE to be displayed on the
message centre (the engine remains fully
functional).
¥ Cruise inhibit.
J.303.1363
PCM
Electronic
Throttle
Monitor
Main
Processor
SystemTAC
Module
Motor
Electronic Throttle
TP Sensor
Command 1
Command 2
SCP
APP
Sensor
Motor Winding 1
Motor Winding 2
To the TP Sensor
APP1
APP2
APP3
5V
5V
5V
5V
5V
12V
12V
TP1
TP2
TP3
Inductive
Position
Encoder

Automatic TransmissionAJ-V6/AJ28
63 controlled solenoid are mounted on an
integral, replaceable, control module
¥ three speed sensors mounted on the external
casing: turbine speed sensor, intermediate
speed sensor and output speed sensor
¥ an oil temperature sensor is fitted inside the
transmission.
The gear select lever is connected via a Bowden
cable to an operating lever on the left side of the
transmission casing. A digital rotary switch, the
transmission range switch, fits over the shaft of
the operating lever and is fixed by two bolts to
the transmission casing. Selection of a particular
drive function generates a 4 bit binary coded
signal which is transmitted directly to the PCM
over a four wire parallel interface. As on the XK
and XJ Series, lateral movement of the gear select
lever across the gate, D to 4 or 4 to D, operates a
switch which indicates the selected function to
the PCM (the Bowden cable is not actuated
laterally).
The PCM directly controls the transmission
actuators as a response to driver demand, engine
requirements and according to the selected shift
mode. Gear selection is controlled by commands
to the four shift solenoids. If, during gear
selection, the relative speeds monitored by the
speed sensors are not as expected, the PCM
varies the analogue signal to the variable force
solenoids to increase/decrease the clutch pressure
(closed loop control). Increased engagement times
due to ageing are also controlled by adaptive shiftpressure.
Apart from the sports mode and traction mode
selected by the driver, there are pre-programmed
modes selected by the PCM in response to sensed
driving conditions :
¥ increased load such as gradients and trailer
towing
¥ cruise control
¥ hot mode: strategies including clutch lock up
are applied to reduce heat.
Transmission Oil Cooler
The transmission fluid is cooled externally by a
dedicated oil to air radiator which is mounted in
the integral cooling pack between the engine
radiator and A/C condenser and below the PAS
cooler.
D.307.320
TRANSMISSION OIL COOLING
Transmission
Oil Cooler
D.307.320

Manual Transmission AJ-V6/AJ28
68
Clutch Pedal Assembly
The clutch pedal is mounted on a combined
assembly with the brake pedal. The clutch master
cylinder is directly actuated by the pedal and
shares a common reservoir with the brake system.
An assistor spring is fitted to the clutch pedal to
reduce the actuation load.
Operation of the pedal when in cruise control
mode activates a switch which cancels this mode.
D.307.316
CLUTCH PEDAL ASSEMBLY
D.307.316
Cruise Deactivate
Switch
Slave Cylinder
Hydraulic
Connection
Fluid from Brake
Reservoir
Clutch Master
Cylinder