Shift Control

To provide the different driving characteristics for each mode of operation, the auto gear box control unit incorporates different shift maps of throttle position/road speed. Base shift points are derived from the appropriate shift map. When a shift is required, the auto gear box control unit sends a request to the ECM for a reduction in engine torque, in order to produce a smoother shift. The percentage of torque reduction requested varies according to the operating conditions at the time of the request.

When the auto gear box control unit receives confirmation of the torque reduction from the ECM, it then signals the shift solenoid valves in the automatic transmission to produce the shift. To further improve shift quality, the auto gear box control unit also signals the pressure regulating solenoid valve to modulate the hydraulic pressure and so control the rate of engagement and disengagement of the brake clutches.

With time, the components in a automatic transmission wear and the duration of the gear shifts tends to increase, which has an adverse affect on the brake clutches. To counteract this, the auto gear box control unit applies a pressure adaptation to each shift. To calculate the adaptations, the auto gear box control unit monitors the pressure modulation used, and time taken, for each shift. If a subsequent shift of the same type, in terms of throttle position and engine speed, has a longer duration, the auto gear box control unit stores an adaptation for that type of shift in a volatile memory. The adaptation is then included in future pressure calculations for that type of shift, to restore shift duration to the nominal.