GF42.45-D-2020H Start-Off Assist (AAS), Function

GF42.45-D-2020H Start-off Assist (AAS), Function


The start-off assist (AAS) prevents the vehicle from rolling away unintentionally (opposite the desired direction of travel) when starting off on inclines. The AAS only becomes active as of inclines of approx. 4 %.

The brake pressure specified by the driver during the stopping procedure is maintained in the brake system when vehicle standstill is detected. Standstill detection is performed within the limits of the active rpm sensors and the brake pressure sensor.

Activation or retention of the function is contingent on the brake being actuated. If the brake is released (brake light switch (S9/1) no longer actuated), the brake pressure is released after a pressure holding time of t = 2 s. This gives the driver enough time to actuate the accelerator pedal module (B37/3) and to start off.

If the brake is released but the accelerator pedal module is not actuated within the specified time, the function is canceled and the vehicle can roll away. If the vehicle threatens to roll away, while the start-off assist (AAS) is active, then the driver can increase the brake pressure at any given time.

The start-off assist (AAS) function remains active after the stop lamp switch has been active for any period of time.

AAS is activated when the vehicle speed remains below the minimum speed for a certain period of time (standstill detection). The following operating conditions must also exist at the same time:

^ Stop lamp switch activated (brake pressed)
^ Engaged gear and a gradient that exceeds a specified threshold value
^ Parking brake not operated

AAS remains active when the brake is actuated (stop lamp switch activated) and when the following operating conditions exist:

^ Gear engaged
^ Parking brake not engaged and brake pressure greater than specified minimum pressure

The AAS remains activated if the brake is not actuated (brake light switch deactivated) and the accelerator pedal module is actuated (pedal value > 4 %).

The AAS is deactivated if one of the following combinations of operating conditions exists:

^ Brake not actuated (stop lamp switch deactivated) and time interval of t = 2 s exceeded
^ Brake not actuated (brake light switch deactivated), accelerator pedal module actuated and engine torque > required starting torque
^ Brake not engaged (stop lamp switch deactivated) and parking brake engaged
^ Brake not engaged (stop lamp switch deactivated) and gear not engaged
^ Brake not engaged (stop lamp switch deactivated) and engine off
^ Brake not actuated (stop lamp switch deactivated) and vehicle speed > minimum speed

The transmission neutral position switch (S164) informs the AAS when a gear has been engaged.

The transmission neutral position switch is read in by the ESP control unit (N30/4) via a discrete line.