System Operation And Component Description (G1779568): Operation

Power Flows 

Operation of the transmission is controlled by the TCM (Transmission Control Module), which electrically activates various solenoids to control the transmission gear selection. The sequence of solenoid activation is based on programmed information in the TCM memory and physical transmission operating conditions such as vehicle speed, throttle position, engine load and TCS (Transmission Control Switch) position.

All gear shifts from 1st to 8th and 8th to 1st are known as 'overlap' shifts. Overlap shifts are during a gear shift and one clutch must remain capable of transmitting torque at a reduced main pressure until the other clutch is ready to accept the torque.

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Engine torque is transferred, via operation of single or combinations of clutches to the 4 planetary gear trains. All gear trains are controlled by reactionary inputs from brake clutches to produce the 8 forward gears and 1 reverse gear. The ratios are as follows:

Shift Elements 

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The shift elements, clutches and brakes are actuated hydraulically. Fluid pressure is applied to the required clutch and/or brake, pressing the plates together and allowing drive to be transmitted through the plates. The purpose of the shift elements is to perform power-on shifts with no interruption to traction and smooth transition between gear ratios.

Instrument Cluster (IC) 

Instrument Cluster in Standard mode 

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The IC (Instrument Cluster) is connected to the TCM via the HS (High Speed) CAN (Controller Area Network) Powertrain bus. Transmission status is transmitted by the TCM and displayed to the driver in the IC. Refer to: INSTRUMENT CLUSTER

Malfunction Indicator Lamp (MIL) 

Transmission related faults that effect the vehicle emissions output will illuminate the MIL (Malfunction Indicator Lamp). The MIL is illuminated by the ECM (Engine Control Module) on receipt of a relevant fault message from the TCM on the HS CAN Powertrain bus. The nature of the fault can be diagnosed using a Jaguar approved diagnostic system, which reads the fault codes stored in the TCM memory.

Transmission Status Display 

The transmission status display is located in the tachometer. The display shows the TCS position. When the transmission is in the sequential shift mode the current gear is displayed in the status display.

Message Center 

The message center is located in the IC. The message center is a Thin Film Transistor display that relays vehicle status and operating information to the driver and can display messages relating to a number of vehicle systems. If a transmission fault occurs, the message 'GEARBOX FAULT'  is displayed in the message center. Refer to: INFORMATION AND MESSAGE CENTER

Transmission Control Module (TCM) 

The TCM outputs signals to control the shift control solenoid valves and the EPRS (Electronic Pressure Regulating Solenoid)'s to control the hydraulic operation of the transmission.

The TCM processes signals from the transmission speed and temperature sensors, the TCS, the ECM and other vehicle systems. From the received signal inputs and pre-programmed data, the TCM calculates the correct gear, torque converter clutch setting and optimum pressure settings for gear shift and lock-up clutch control.

The ECM supplies the engine management data over the HS CAN Powertrain bus. The TCM requires engine data to efficiently control the transmission operation, for example; flywheel torque, engine speed, accelerator pedal position, engine coolant temperature. The ABS (Anti-lock Brake System) control module also supplies data to the TCM on the HS CAN Powertrain bus. The ABS control module receives the steering angle data from the SASM (Steering Angle Sensor Module) via the HS CAN Chassis bus, converts the message and forward it to the TCM via the HS CAN Powertrain bus. The TCM uses data from these systems to suspend gear changes when the vehicle is cornering and/or the ABS is controlling braking or traction control.

The CJB (Central Junction Box) supplies steering wheel paddle data over the HS CAN Powertrain bus. The TCM uses this to schedule driver requested upshifts and downshifts.

Using the signal inputs and the memorized data, the TCM control program computes the correct gear and torque converter lock-up clutch setting and the optimum pressure settings for gear shift and lock-up clutch control. Special output-side modules (power output stages, current regulator circuits), allow the TCM to control the solenoid valves and pressure regulators and consequently precisely control the hydraulics of the automatic transmission. In addition, the amount and duration of engine interventions are supplied to the engine management by way of the HS CAN Powertrain bus.

The TCM determines the position of the TCS using signals from the TCS on the HS CAN Powertrain bus and a hardwired connection for the 'P' (park) position determination.

The TCM transmits the position of the TCS and any manual gear selected on the HS CAN Powertrain bus. This information is shown in the transmission status display in the IC.

Engine Stall 

If the vehicle stalls it will coast down in gear, with the transmission providing drive to the engine. A restart can be attempted at this point and the engine may start and the driver can continue.

If the coast down speed reduces such that the speed of the engine is less than 400 RPM, the transmission will go to neutral, D illumination will flash in the IC. The driver needs to select neutral or park and then press the brake pedal to restart the engine.

If the Stop/start switch is pressed when driving, the message 'ENGINE STOP BUTTON PRESSED'  is displayed in the message center but there will be no change to the ignition state. If the driver requires to switch off the engine, the Stop/start switch must be pressed for a second time. The engine will be stopped and will be back driven by the transmission as the vehicle coasts down.