Hill START ASSIST (HSA) FUNCTION
System configuration
When the vehicle has completely stopped on a steep uphill by the service brake, ASC-ECU judges whether or not start the HSA function control in accordance with the signals (ETACS-ECU, CVT-ECU, G & yaw rate sensor, brake fluid pressure sensor, engine-ECU, wheel speed sensor).
HSA function state transition diagram (Overview)
Note:
- ASC-ECU judges the inclination angle of the slope according to the G and yaw rate sensor output.
- When either of the following conditions is satisfied, the mode is shifted to the forcible termination mode, and HSA function control is terminated.
- The parking brake operation is detected.
- The shift lever operation to the shift or selector position other than the uphill direction driving is detected (Forward uphill driving: shift or selector position other than "D"*, Reverse uphill driving: shift or selector position other than "R").
- The accelerator pedal and brake pedal are depressed at the same time.
- The wheel speed sensor pulse is generated (When the vehicle moved)
- The engine is stopped by engine stall, etc.
*: When uphill driving, if shift position is "N" position, HSA function is operated
HSA function control activated
ASC-ECU judges that the HSA operation condition is satisfied. When the driver releases the brake pedal, ASC-ECU maintains the brake wheel cylinder pressure and waits.
FLUID PRESSURE HOLD MODE
By closing the cut valve, ASC-ECU maintains the brake wheel cylinder pressure of the time when the brake pedal is depressed, to prevent the vehicle from moving backward.
START MODE
ASC-ECU releases the brake wheel cylinder pressure maintained by the cut valve, depending on the engine torque generated by depressing the accelerator pedal.
FORCIBLE TERMINATION MODE
ASC-ECU immediately releases the brake wheel cylinder pressure maintained by the cut valve and terminates HSA function control.