Shift Control

To provide the different driving characteristics for each mode of operation, the Electronic Automatic Transmission Electronic Control Unit (EAT ECU) incorporates different shift maps of throttle position/engine speed. Base shift points are derived from the appropriate shift map. When a shift is required, the EAT ECU sends a request to the Engine Control Module (ECM) for a reduction in engine torque (by reducing ignition timing), 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 EAT ECU 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 EAT ECU 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 effect on the brake clutches. To counteract this, the EAT ECU applies a pressure adaptation to each shift. To calculate the adaptations, the EAT ECU 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 EAT ECU 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.