Overview
This document contains information on:
General
Function requirements
Function
General
Brake force boosting comprises the following tasks:
Brake force boosting reduces the control force that the driver must apply in order to reach the desired vehicle braking effect.
The BAS brake assistance system assists the driver in emergency braking situations in order to shorten the stopping distance. In order to achieve the maximum possible deceleration, the function detects emergency braking situations and increases the brake pressure up to the ABS controlled range.
Function requirements
Drive train operational
Engine in operation
Brake and traction system functional
Vehicle deceleration > 3 m/s2
Function
Brake force boosting
The driver is supported during braking so that they do not have to use so much pedal force. Brake force boosting occurs pneumatically using vacuum. The vacuum acts in the brake booster.
Brake assistance system (BAS)
The ESP® control unit evaluates the increase in pressure in the brake system and initiates an emergency stop if a certain activation threshold is exceeded. To do so, the system monitors the driver's response. The driver's response is defined by the actuation speed and actuation strength with which the brake pedal is pressed.
Amplification of the brake force is also possible from an unbraked state and during partial braking. The function also triggers even during brake interventions by other systems, e.g. by the ESP®.
If the driver clearly releases the brake pedal during the function intervention, brake force boosting is ended.
On vehicles with environment sensor system: With the help of the sensors, the deceleration necessary to prevent a collision is calculated. The following information is used for this:
Distance to vehicle immediately ahead
Vehicle's own speed and acceleration
Vehicle speed and acceleration of the vehicle driving in front
Fail boost
The fail boost function ensures brake force boosting in the event of a system error. It is activated if the pneumatic brake booster cannot adequately support driver braking because of a system error in the vacuum supply.
The system error in the vacuum supply is displayed in the instrument cluster. The failure of the pneumatic brake booster is read out directly by the ESP® control unit.
The fail boost function implements hydraulic brake force boosting using a suitable boost factor. The function actuates the solenoid valves and the traction system hydraulic unit.