Land Rover Defender: Operation

POWER FLOWS

Operation of the transmission is controlled by the Transmission Control Module (TCM), which electrically activates various solenoids to control the transmission gear selection. The sequence of solenoid activation is based on progamed information in the TCM memory and physical transmission operating conditions such as:

• Vehicle speed
• Throttle position
• Engine load
• Transmission Control Switch (TCS) position.

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

Engine torque is transferred, through 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

1. Brake A
2. Brake B
3. Gear set 1
4. Gear set 2
5. Gear set 3
6. Clutch E
7. Clutch C
8. Clutch D
9. Gear set 4

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

The virtual display Instrument Cluster (IC) is connected to the Body Control Module/Gateway Module (BCM/GWM) on the High Speed (HS) Controller Area Network (CAN) comfort systems bus. The Transmission Control module (TCM) is connected to the BCM/GWM on the FlexRay systems bus.

Automatic transmission status is transmitted from the TCM to the virtual display IC through the BCM/GWM.

Transmission status is indicated to the driver by a message in the message center or illumination of a warning indicator.

The Thin Film Transistor (TFT) display IC is connected to the TCM through the HS CAN Human Machine Interface (HMI) systems, the BCM/GWM and the FlexRay systems bus. Transmission status is transmitted by the TCM and displayed to the driver in 1 of 2 displays in the instrument cluster.

Malfunction Indicator Lamp

The Malfunction Indicator Lamp (MIL) is located in the virtual display Instrument Cluster (IC). Transmission related faults which may affect the vehicle emissions illuminates the MIL.

The MIL is illuminated by the Powertrain Control Module (PCM) on receipt of a relevant fault message from the Transmission Control Module (TCM) on the FlexRay system bus. The nature of the fault can be diagnosed using approved diagnostic equipment which reads the fault codes stored in the TCM memory.

Transmission Status Display

The transmission status display is located in the virtual display Instrument Cluster. The display shows the Transmission Control Switch (TCS) or the selected gear when in manual and sport modes.

The following table shows the displays and their descriptions.

P - Park selected
R - Reverse selected
N - Neutral selected
D* - Drive and temporary manual mode selected ( * = current gear)
S* - Sport mode selected ( * = current gear)

1. 1st gear selected (manual CommandShift mode)
2. 2nd gear selected (manual CommandShift mode)
3. 3rd gear selected (manual CommandShift mode)
4. 4th gear selected (manual CommandShift mode)
5. 5th gear selected (manual CommandShift mode)
6. 6th gear selected (manual CommandShift mode)
7. 7th gear selected (manual CommandShift mode)
8. 8th gear selected (manual CommandShift mode)

Message Center

The message center is located in the virtual display Instrument Cluster (IC). The message center display 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.

TRANSMISSION CONTROL MODULE

The Transmission Control Module (TCM) outputs signals to control the hydraulic operation of the transmission. Signals are sent to the shift control solenoid valves and the Electronic Pressure Regulating Valve's (EPRS).

The TCM processes signals from the transmission speed and temperature sensors, the Transmission Control Switch (TCS), the Powertrain Control Module (PCM) and other vehicle systems. From the received signal inputs and preprogamed data, the TCM calculates the:

• Correct gear
• Torque converter clutch setting
• Optimum pressure settings for gear shift and lock-up clutch control.

The PCM supplies the engine management data over the FlexRay systems bus. The TCM requires engine data to efficiently control the transmission operation, for example:

• Flywheel torque
• Engine speed
• Accelerator pedal angle
• Engine temperature.

The steering angle sensor and the Anti-lock Brake System (ABS) control module also supply data to the TCM on the FlexRay systems bus. The TCM uses data from these systems to suspend gear changes when the vehicle is cornering and/or the ABS control module is controlling braking or traction control.

The Body Control Module/Gateway Module (BCM/GWM) supplies steering wheel paddle data over the FlexRay systems 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
• 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. This allows precise control the hydraulics of the automatic transmission. In addition, the amount and duration of engine interventions are supplied to the engine management through the FlexRay systems bus.

The TCM determines the position of the TCS using signals from the TCS through the HS CAN systems bus.

The TCM transmits the position of the TCS and any manual gear selected on the FlexRay systems bus to the BCM /GWM. This information is shown in the gear selector display in the instrument cluster.

Engine Stall

If the engine stalls it coasts 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 100 Revolutions Per Minute (RPM), the transmission goes to neutral, D illumination flashes in the instrument cluster. The driver needs to select NEUTRAL (N) or PARK (P) and then press the brake pedal to restart the engine.

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

Cold Start Neutral

NOTES:

• The Cold Start Neutral (CSN) function has been introduced on 8HP45 transmissions for the V6 3.0L S/C Petrol engine variants only from 15MY onwards.
• The Cold Start Neutral (CSN) function has been introduced on 8HP45 transmissions for all petrol engine variants from 18MY onwards.

Cold Start Neutral (CSN) is a software function. The software function operates when the engine is cold. When the driver selects drive or sport with their foot on the brake, the transmission delays the engagement of gear. This allows the engine speed to remain high. If the driver releases the brake the engine speed reduces to idle and the transmission engages the gear. The function is also exited and the transmission engages the gear if while the driver has their foot on the brake the engine reaches operating temperature.

Previous transmissions would engage the gear when the driver selected drive or sport. This resulted in a noticeable gear engagement. The introduction of CSN delays gear engagement until either the driver releases the brake or the engine reaches operating temperature. The purpose of the function is to assist in maintaining engine management control during the warm up cycle. Some customers may indicate that there is a delay in gear selection or an elevated engine speed (circa 1600 Revolutions Per Minute (RPM) but this is normal with CSN.

CONTROL DIAGRAM

A = HARDWIRED:
AX = FLEXRAY BUS:
BA = HIGH SPEED (HS) CONTROLLER AREA NETWORK (CAN) HUMAN MACHINE INTERFACE (HMI) SYSTEMS BUS:
BL = HS CAN UNDERBODY SYSTEMS BUS.

1. Transmission Control Module (TCM)
2. Instrument Cluster (IC)
3. Body Control Module/Gateway Module (BCM/GWM)
4. Transmission Control Switch (TCS)
5. Powertrain Control Module (PCM)
6. Anti-lock Brake System (ABS) control module
7. Mechatronic valve block
8. Transmission Control Switch (TCS)
9. Ground
10. Power supply

READ NEXT: