Land Rover Defender: Operation

POWER FLOWS

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

• Vehicle speed
• Throttle position
• Engine load
• 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 PANEL CLUSTER

The virtual display Instrument Panel Cluster (IPC) is connected to the Body Control Module (BCM)/ Gateway Control Module (GWM) on the High Speed (HS) Controller Area Network (CAN) Human Machine Interface (HMI) systems bus.

The TCM is connected to the BCM/ GWM on the FlexRay systems bus.

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

Transmission status is indicated to the driver by a message in the message center or illumination of a warning indicator. Transmission status is transmitted by the TCM and displayed to the driver in 1 of 2 displays on the IPC.

Malfunction Indicator Lamp

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

The MIL is illuminated by the PCM on receipt of a relevant fault message from the TCM on the FlexRay system bus.

The nature of the fault can be diagnosed using the Jaguar Land Rover (JLR) approved diagnostic equipment which reads the DTC, stored in the TCM memory.

Transmission Status Display

The transmission status display is located in the virtual display IPC. The display shows the TCS or the selected gear when in manual and sport modes.

The following table shows the displays and their descriptions.

P - PARK (P) selected
R - REVERSE (R) selected
N - NEUTRAL (N) selected
D* - DRIVE(D) and temporary manual mode selected ( * = current gear)
S* - SPORT (S) 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 IPC. 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 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 Valves (EPRS).

The TCM processes signals from the transmission speed and temperature sensors, the TCS, the PCM and other vehicle systems.

From the received signal inputs and pre-programed 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 Control Module (ABS) 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 is controlling braking or traction control.

The 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 Underbody (UN) 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 IPC.

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 RPM, the transmission switches to NEUTRAL (N) and 'D' illumination flashes in the IPC. The driver needs to select NEUTRAL (N) or PARK (P) and then press the brake pedal to restart the engine.

If the start/stop 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 start/stop 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

NOTE: The Cold Start Neutral (CSN) function has been introduced on 8HP70 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 (D) or SPORT (S) 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 (D) or SPORT (S). 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 1,600 RPM) but this is normal with CSN.

CONTROL DIAGRAM

A = HARDWIRED:
AX = FLEXRAY BUS:
BA = HS CAN HMI SYSTEMS BUS:
BL = HS CAN UNDERBODY (UN) SYSTEMS BUS.

1. TCM
2. IPC
3. BCM/ GWM
4. TCS
5. PCM
6. ABS
7. Mechatronic valve block
8. TCS
9. Ground
10. Power supply

READ NEXT: