Overview
This document contains information on:
General
Function requirements
Function
General
The standstill control causes the vehicle to assume a safe standstill state. For this purpose, the standstill control monitors the braking driver assistance systems until the vehicle is at a safe standstill.
Function requirements
Engine in operation
Drive train operational
Brake and traction system functional
Vehicle speed < 10 km/h
Function
Standstill check
When the vehicle is at a safe standstill, the rolling monitoring function of the standstill control is requested by the driver assistance systems. If vehicle rolling is detected, the brake pressure is increased until the vehicle is stationary again. If the brake pressure measured by means of the circuit pressure sensors drops relative to the specified pressure request of the standstill control, the specified pressure of the standstill control is restored by means of an active pressure buildup.
Securing in the event of a fault
If one of the following events occurs, the standstill control secures the vehicle:
Driver's door open and driver's seat belt buckle not inserted (driver is detected as absent)
Engine OFF, unless the engine has been switched off by the ECO start/stop function
Undervoltage or overvoltage in on-board electrical system (except undervoltage during a warm start)
Request to secure the vehicle by a driver assistance system
ESP® and vehicle bus faults that result in temporary deactivation
Standstill control monitoring events that result in temporary or permanent deactivation
Expiry of the defined hydraulic holding period of 10 min
Checking door contact switch for plausibility
The plausibility test is used to detect a fault along the signal path from the left front door safety catch microswitch or right front door safety catch microswitch (depending on the global country coding for right-hand or left-hand drive vehicles).
If, as a result of an electrical or mechanical fault, "driver's door closed" is detected although the driver's door is open, this is detected by the door contact plausibility test in the standstill control. The ESP® control unit stores the corresponding fault.
Standstill control deactivation
The standstill control is deactivated in the ESP® control unit. Activation of the driver assistance systems is no longer possible. In addition, securing of the vehicle is requested immediately if the standstill control is deactivated and a driver assistance system is active.
Secure vehicle
The standstill control requests the electric parking brake to secure the vehicle. The vehicle is secured as soon as the request to close the vehicle is implemented. The existing brake pressure at the wheels is then reduced and the standstill control becomes inactive.
The electric parking brake is detected as defective and the securing strategy becomes active if one of the following events occurs:
Close request is not implemented within a defined time
The electric parking brake detects a system malfunction
Safety strategy, request engage "P" or Emergency-P path (on vehicles with automatic transmission)
The securing strategy is performed via the fully integrated transmission control unit. The ESP® control unit sends a request to engage drive range "P". The vehicle is secured after drive range "P" has been engaged by the fully integrated transmission control unit and following feedback to the ESP® control unit. The brake pressure applied at the wheels is reduced and the standstill control is switched to inactive.
If the fully integrated transmission control unit does not signal engagement of gear range "P" within a defined time, the Emergency-P function of the electronic ignition lock control unit forces gear range "P" to be engaged.
For this purpose, the electronic ignition lock control unit also receives the request to engage drive range "P" from the ESP® control unit and itself sends a request to the fully integrated transmission control unit. If the electronic ignition lock control unit does not receive any feedback from the fully integrated transmission control unit within a defined time, the following occurs:
After enabling by the fully integrated transmission control unit, the Emergency-P path is actuated by the electronic ignition lock control unit
Drive range "P" is engaged in the fully integrated transmission control unit (forcibly by a spring mechanism)
Securing strategy (on vehicles with manual transmission)
The securing strategy on vehicles with manual transmission is divided into three stages:
Stage 1
In the event of incorrect operation or a system error, the warning message "Brake Immediately!" is displayed on the instrument cluster.
Stage 2
The 2nd stage additionally warns the driver by means of an acoustic signal (beep).
Stage 3
This beeping becomes louder in stage 3.
The beeping is stopped immediately as soon as the driver deactivates the active driver assistance system.