HSA - Hill Start Assist [2013-2018]: Function
HSA is integrated in Brake control module (BCM) that uses the acceleration and angle sensor in the Body sensor cluster stability sensor (BSC), the gear position signal from Transmission Control Module (TCM), as well as the speed signal from the wheel sensors.
The following conditions must be fulfilled to activate HSA:
- ignition is on (key in pos. 2)
- engine is running
- driver is braking
- the vehicle is at a standstill
- the start attempt takes place on a hill with a grade of at least approx. 4%.
HSA is activated if the driver brakes and stops on a hill with a grade of at least 4%, the vehicle is at a standstill (signal from wheel sensors should be "0" for at least 0.4 seconds). The angle sensor in the Body sensor cluster stability sensor (BSC) calculates the grade of the hill. When the driver releases the brake pedal to press down the accelerator pedal, the valves in the hydraulic unit close so that the brake pressure in the brake system is maintained for 1.5 - 2 seconds to prevent an unwanted backwards or forwards movement.
The reason for maintaining the brake pressure only for 1.5 - 2 seconds is that the driver should not have time to leave the vehicle before it starts to roll.
The HSA-function can be divided into the following phases:
- Phase 1 "activation"
- Phase 2 "hold"
- Phase 3 "start"
Phase 1 "activation"
The driver stops the vehicle on an uphill with a grade of at least 4%. The vehicle is kept at a standstill by pressing the brake.
Phase 2 "hold"
The brake pressure is maintained for approx. 1.5 - 2 seconds after the driver has released the brake pedal.
Phase 3 "start"
When the driver presses down the accelerator to drive off, HSA controls the brake pressure to prevent the vehicle from rolling backwards.
HSA also prevents the vehicle from driving off with applied brakes by Brake control module (BCM) receiving information about engine torque and drive axle torque from Engine control module (ECM) and Transmission control module (TCM).
HSA is not activated if the driver brakes and releases the brake or presses on the accelerator before the vehicle is at a complete standstill.