Steering Torque Specification, Basic Function - GF54.71-P-9903A

Model all (CAR) 

with code 23P (Driving Assistance package) 

Model all (CAR) 

with code P20 (Driving Assistance package Plus) 

Overview 

This document contains the following information:

• General 
• Function requirements 
• Active track guidance 
• Lane change 
• Steer and touch recognition 
• Active Emergency Stop Assist 
• Functional restrictions 

General 

The steering torque function specification assists the driver in keeping the vehicle in a straight path and in the center of a lane when in slight corners. Up to a speed of 210 km/h the system is orientated on the lane markings and up to 130 km/h on vehicles driving in front. This means that active track guidance is also still available when lane markings are not visible or not clearly visible or when a structured traffic situation is given (clustering characteristic). To evaluate the lane markings, the system uses a multifunction camera behind the windshield close to the inside rearview mirror.

If the driver indicates that he wishes to change lane by turn signaling and the system does not detect another vehicle in the adjacent lane, the system assist the lane change with the aid of steering torques. An emergency stop assistant is activated if the driver ignores prompts from the intelligent hands-off warning to place the hands onto the steering wheel. It brakes the vehicle in the lane until it comes to a standstill, if the driver is obviously distracted or if the driver has lost control of the vehicle.

In stop-and-go traffic (traffic jam) on freeways, the vehicle is routed off-center in the lane (as of market launch of model 167). This enables a rescue lane/corridor to be formed when required.

The system relieves the driver through active track guidance on freeways and highways thereby improving safety and comfort. The system is active in a vehicle speed range of 0 to 210 km/h, and it can be switched on and off manually.

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The system decides whether the vehicle driving in front is to be pursued or if it should follow the lane markings instead.

Torque-assisted traffic jam driving is still possible even where lane markings are not visible or not clearly visible or where structured traffic situations are given (cluster characteristic).

Function requirements 

• Engine running or drive train operational
• ESP® functional
• Distance control switched on
• Active track guidance switched on
• No trailer operation (vehicles with trailer hitch)
• Tire pressure of all wheels within the tolerance range (no run-flat mode active)
• Standstill comparison successfully completed

Active track guidance 

The system evaluates the traffic area monitoring data to calculate any necessary reactions. To do so, the front and rear radar sensors and multifunction camera provide the corresponding information. The system also evaluates the following function-relevant parameters:

• Vehicle speed/direction of travel/acceleration
• Electric power steering, status
• Multifunction camera lane data
• Location information (position finding) for traffic assessment (map data)
• Intention to change lane (flashing)
• Steering torque from the driver and wheel angle (Hands-Off Detection status)
• Steering wheel angle
• Driving stage engaged

The system evaluates all relevant influencing parameters and calculates the required steering torque, which is then implemented by the electric power steering.

For longitudinal control the system controls engine output, the transmission and the brakes, and for lateral control it actuates the electric power steering as required. The driver receives noticeable feedback through the steering wheel. The system status is indicated to the driver by a steering wheel symbol.

The system is intended to assist the driver only. The driver must always be aware that at any given time the system may make a track-aligning intervention. The responsibility for maintaining a safe distance, for speed, timely braking and for staying within the lane remains with the driver.

Lane change 

The system supports the driver when changing lane through appropriate steering-wheel torque. Lane changing is assisted between 80 and 180 km/h.

The following conditions must be fulfilled for this:

• The function is activated/switched on.
• The journey is on a freeway or a road with several lanes (roads with multiple lanes are referenced from the map data of the navigation system).
• The driver starts to change lane by switching on the turn signal.
• The turn signal indicator is switched on.
• The adjacent lane is marked with a broken limiting line.
• No other vehicle is detected in the relevant lane into which the change is to be made. The traffic area is monitored by the front and rear radar sensor system and the multifunction camera.

The lane changing maneuver is interrupted under the following conditions:

• The driver steers too much in the direction of the lane change.
• The driver switches on the turn signal indicator in the opposite direction.
• The driver steers in the opposite direction.
• Distance control or active track guidance is canceled by depressing the brake.
• The traffic area monitoring detects objects on the lane into which the change is to be made.
• Traffic area monitoring detects a critical situation such as, for example the tail-end of a traffic jam.
• The system is not able to carry out lane changes due to surrounding influences, such as bending roadway.

If a lane change is not immediately possible, then the green steering wheel symbol is shown with a green arrow for several seconds.

Courtesy of MERCEDES-BENZ USA

With the activation conditions are met, the status display changes to green.

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If the system detects within a brief period that the lane is free, the turn signal indicator is automatically activated and the lane change is then initiated. The driver can cancel the lane changing maneuver at any given time.

The actual lane changing maneuver is shown to the driver. If the maneuver is aborted, a corresponding message is shown.

Steer and touch recognition 

The steer and touch recognition system monitors the torque on the steering wheel or any touching of the steering wheel by the driver's hand (vehicles with capacitive steering wheel). If it does not detect any torque on the steering wheel or torque that is too low or if it determines that the steering wheel is not being touched, it issues a message to the driver.

The steering wheel symbol flashes. A warning message also appears. If the driver fails to respond to these messages, warning tones are then issued as a take-over prompt (hands-off warning).

The system regards active steering or system operations using the buttons on the multifunction steering wheel (as of Driving Assistance Package Generation 5) as reactions to these messages.

If the driver fails to respond to the warnings, the distance control reduces speed first. The vehicle is then braked to a standstill using the Active Emergency Stop Assist if no response is forthcoming.

The volume of active audio sources is reduced during the warnings.

Warnings are also only issued when tangible hazardous situations are detected.

When a gray steering wheel is displayed, the system is switched on, but the lateral control function is in passive mode.

Courtesy of MERCEDES-BENZ USA

A white steering wheel with red hands indicates when the driver is to take over lateral guidance.

A display is issued in the following situations:

• Lateral control is approaching the system limit.
• The maximum duration without driver activity has been exceeded.

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When a green steering wheel is shown, the system is switched on and the lateral control is active.

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Active Emergency Stop Assist 

The Active Emergency Stop Assist enhances level of road traffic safety. It intervenes when the driver is no longer capable of steering and braking the vehicle. The vehicle is braked to a controlled standstill in its own lane and then secured by applying the parking brake. As soon as the vehicle is at a standstill for more than 10 s, an automatic emergency call is issued. After another 10 s, the vehicle is automatically unlocked. The system recognizes a permanently distracted driver or a driver who is no longer capable of intervening in driving events, e.g. in event of unconsciousness. It evaluates steering and contact detection information for this. The hands-off warning is issued during an emergency stop. Distance control remains active. The distances to vehicles in front and the track guidance are still supported. If the system changes because of system impairments (e.g. glare from solar radiation) from an active status to a passive one, the Active Emergency Stop Assist still brakes down to a standstill. Track guidance is not supported here.

Sequence and display 

• After several acoustic hands-off warnings (take-over prompts) the system starts the Active Emergency Stop Assist.
• After further acoustic hands-off warnings, the deceleration procedure is started.
• If the driver fails to respond, an "Emergency stop initiated" message is shown.
• The setting speed is reduced.
• The hazard warning lights are switched on at speeds below 60 km/h.
• Once at vehicle standstill, the vehicle is secured with the electric parking brake.
• After 10 s, an emergency call is sent to the Mercedes-Benz Emergency Call Center.
• After another 10 s, the vehicle is unlocked so that external assistance can render aid.

The Active Emergency Stop Assist activities are ceased when driver reactions are detected.

Functional restrictions 

The steering torque function specification may be impaired by backlighting, darkness, rain or snow. The system permits a limited degree of steering torque only for lateral guidance. Under certain circumstances, the steering torque may no longer be sufficient to keep the vehicle in the lane. If traffic area monitoring is impaired, the system changes to a passive mode and no longer offers any assistance.

	Function schematics
	Function schematic for detection of transmission position	Model 118, 167, 177, 247, 293 with code 23P (Driving Assistance package) Model 167 with code P20 (Driving Assistance package Plus)	PE27.19-P-2500-97A
	Specify steering torque, function schematic	Model 118, 167, 177, 247, 293 with code 23P (Driving Assistance package) Model 167 with code P20 (Driving Assistance package Plus)	PE54.71-P-2504-97A
	Subsystems
	Distance control, basic function		GF30.30-P-9903A
	Driver activity detection, basic function		GF54.30-P-1000A
	Traffic area monitoring, basic function		GF54.71-P-1000A
	Track guidance, basic function	Model all (CAR) with code 23P (Driving Assistance package) Model all (CAR) with code P20 (Driving Assistance package Plus)	GF54.71-P-9900A
	Additional basic functions
	Brakes, basic function		GF42.00-P-9900A
	Emergency call system, basic function	Model all (CAR) with code 23P (Driving Assistance package) with code 362 (HERMES LTE) Model all (CAR) with code 362 (HERMES LTE) with code P20 (Driving Assistance package Plus)	GF82.95-P-9900A
	Control units
	Hand detection system control unit, basic function	Model all (CAR) with code 23P (Driving Assistance package) with code 25U (Capacitive steering wheel) Model all (CAR) with code 25U (Capacitive steering wheel) with code P20 (Driving Assistance package Plus)	GF82.90-P-9891A