Automatic gearbox – circuit operation

AUTOMATIC GEARBOX – CIRCUIT OPERATION

CIRCUIT OPERATION

Economy, Sport and Manual Modes

The Auto Gear Box Control Unit (Z255) has various different driving modes available, with Economy being selected automatically on start up. When the vehicle is in High range, Sport mode can be selected. This will make the gear change much more sensitive to throttle movement, thereby shifting down earlier and holding onto lower gears longer than the Economy mode equivalent. If the vehicle is in Low range, then Manual mode can be selected. This will make the gear box change into the selected gear as quickly as possible and hold on to that gear at all speeds, i.e. if “3” is selected, then the gear box will not shift down to “2” or “1” as the vehicle slows down. It will only change gear to prevent the vehicle from stalling.

Interface to Petrol Engine Control Module (ECM) (Z132)

The Auto Gear Box Control Unit (Z255) takes the engine torque, engine speed and throttle angle signals from the ECM, calculates which gear is required, outputs to the solenoid valves and sends a torque reduction signal back to the ECM, thereby retarding the ignition point on each of the cylinders and so giving a reduction in engine power during gear changes that result in a smooth change. The engine torque is received by the Auto Gear Box Control Unit (Z255) on its pin 21, the engine speed on pin 3 and the throttle angle on pin 47. The torque reduction signal is sent to the ECM from the Auto Gear Box Control Unit (Z255) via its pin 32.

Interface to Diesel Engine Control Module (ECM) (Z132)

The functionality of the interface is similar to the petrol interface, except for the format of the signal.

Interface to Auto Gear Box Control Unit (Z255) Gear position Switch-pins 14, 33, 50

The gear position switch is mounted on the side of the gearbox and contains five internal switches, although only 3 are connected to the Auto Gear Box Control Unit (Z255)via pins 50, 14, and 33. By analysing the status of these 3 switches, the Auto Gear Box Control Unit (Z255) calculates which gear the vehicle is in.

If a fault occurs with the switch, then the Auto Gear Box Control Unit (Z255) may try to put the gearbox into a different gear than the driver’s request.

Solenoid Valves-pins 5, 6, 19, 24, 42

The Auto Gear Box Control Unit (Z255) has control over 4 solenoid valves: MV1, MV2, torque converter lock up and pressure regulator. These are all supplied via pin 19, which is activated via a relay in the Auto Gear Box Control Unit (Z255) itself. MV1 - pin 5, MV2 - pin 24: When the driver selects “D”rive, then the Auto Gear Box Control Unit (Z255) controls the gear selection by the use of the two solenoid valves. If a fault occurs with one or both of the valves, then a different gear than the one selected will result. If the Auto Gear Box Control Unit (Z255) defaults the gearbox, then the common supply to all the solenoid valves is removed and the gearbox mechanically shifts either to third gear, if the vehicle is stationary, or fourth, if moving.