Automatic gearbox – circuit operation rev: 11/2000

AUTOMATIC GEARBOX – CIRCUIT OPERATION REV: 11/2000

CIRCUIT OPERATION

Economy, Sport and Manual Modes

The Auto Gearbox 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 gear changes more sensitive to throttle movement, thereby shifting down earlier and holding lower gears longer than the Economy mode. If the vehicle is in Low range, Manual mode can be selected. This will make the gearbox change into the selected gear as quickly as possible and hold on to that gear at all speeds.

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

The Auto Gearbox Control Unit (Z255) uses engine torque, engine speed and throttle angle signals from the ECM (Z132) to calculate which gear is required. The Auto Box Control Unit supplies gear selection information to the solenoid valves which will then engage the correct gear. A torque reduction signal is sent from the Auto Gearbox Control Unit to the ECM which will retard the ignition point on each cylinder. This reduces engine power during gear changes. The combination of retarded ignition and reduced engine power delivers a smoother gear change. Information about engine speed, engine torque, throttle angle and torque reduction is received from the ECM (Z132) by the Auto Gear Box Control Unit (Z255) via CAN bus ‘high’ and ‘low’ line on pins 16 and 44.

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

Engine speed is received by the Auto Gearbox Control Unit (Z255) on pin 3, the throttle angle on pin 47. The torque reduction signal is sent to the ECM from the Auto Gearbox Control Unit (Z255) via pin 32.

Interface to Auto Gear Box Control Unit (Z255) Gear Box Position Switch - pins 14, 33, 50, Diesel (pins 8, 36, 37 Petrol)

The Gearbox Position Switch (X294) is mounted on the side of the gearbox and contains 3 internal switches. The switches are connected to the Auto

Gearbox Control Unit (Z255) via pins 50, 14 and 33 for diesel (pins 8, 36, 37 for petrol). By analysing the status of these 3 switches, the Auto Gearbox Control Unit (Z255) calculates which gear the vehicle is in. If a fault occurs with the switch, the Auto Gearbox Control Unit (Z255) may try to override driver requests and select a different gear.

Solenoid Valves - pins 5, 6, 19, 24, 42 Diesel (pins 5, 30, 32, 33, 53 Petrol)

The Auto Gearbox 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 diesel (pin 53 petrol), which is activated via a relay in the Auto Gearbox Control Unit (Z255) itself.

MV1 - pin 5 Diesel (pin 30 Petrol), MV2 - pin 24 Diesel (pin 33 Petrol)

When the driver selects ”D” (drive), the Auto Gearbox Control Unit (Z255) controls gear selection via two solenoid valves. If a fault occurs with one or both of the valves, a different gear than the one selected will result. If the Auto Gear Box Control Unit (Z255) defaults the gearbox, 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. MV2 is also used to prevent the driver from selecting reverse gear when the vehicle is moving forward at speeds greater than 8 km/h and from disengaging reverse gear at speeds greater than 6 km/h. This function is known as ”Reverse Safety” and will not be available if MV2 is non-operational and/or the gearbox is in default mode.

Torque Converter Lock-Up Solenoid - pin 42 Diesel (pin 32 Petrol)

The torque converter slips to allow smooth operation of the gearbox. Lock-Up occurs when the vehicle reaches a speed of 45 mph or above in either third or fourth gears.

Pressure Regulator Solenoid - pin 6 Diesel (pin 5 Petrol)

Gearshift quality is controlled by modulating the pressure regulator which is controlled by the Auto Gearbox Control Unit (Z255). When energised the solenoid is in the closed position. If a failure occurs, then the regulator only allows mechanical gear change between third and fourth gears.