Steering Column: Description and Operation
Steering Column Switch Cluster
Steering column switch cluster
The steering column switch cluster (SZL) is a mechanical and electrical interface from the steering wheel to the vehicle. The steering column switch cluster has a fixed mechanical connection to the steering column. Over and above this purely mechanical connection, the steering column switch cluster is electrically connected via local interconnect network bus systems or directly to components.
The steering column switch cluster is no longer a control unit. The steering column switch cluster is connected to the junction box electronics (JBE) or the front electronic module (FEM) via 2 local interconnect network buses.
The multifunction steering wheel is equipment-dependent: e.g. steering wheel heating telephone or speech input system.
Interfaces to steering-column switch cluster
The steering column switch cluster has a drop arm switch on the left and right. The right-hand steering column stalk is for operation of the functions of the wash/wipe system. The left-hand steering column stalk is for operation of the high-beam headlight or turn indicators as well as the functions of the onboard computer.
A steering angle sensor is no longer installed in the steering column switch cluster. The steering angle is determined by the rotor position sensor of the electromechanical power steering (EPS). Using this signal the Integrated Chassis Management (ICM) calculates the actual steering angle.
The steering column switch cluster receives the signals of the steering wheel via the local interconnect network bus. These signals are forwarded by the steering column switch cluster to each control units.
The steering-column switch cluster forwards the trigger signal for the drivers airbag directly to the airbag's ignition capsules.
The steering-column switch cluster evaluates the button for the steering wheel heating. The steering column switch cluster sends this signal across the LIN bus to the steering wheel module.
Brief component description
The following components are described for the steering column switching centre:
Steering column lever, turn indicator / high-beam switch
The steering-column lever on the left of the steering column has the following functions:
- High beam assistant button
- On-board computer button
- Direction indicator lights
- Headlight flasher
The steering column switch cluster generates the switching signals based on the drop arm's respective position.
The switching signals are made available by the steering column switch cluster via the local interconnect network bus.
The footwell module receives the requests of the turn indicator / high-beam switch as well as the button for the high-beam assistant.
Pressing the onboard computer button in an axial direction triggers the requests for the onboard computer. The steering column switch cluster transmits the commands to display the on-board computer functions via the local interconnect network bus.
In the case of vehicle equipment without the high-beam assistant, the button on the steering column stalk turn indicator / high-beam switch is not required. A large button is used instead.
Steering column lever, wiper switch
The steering-column lever on the right of the steering column has the following functions:
- Windscreen washer system, windscreen
- Windscreen wipers
- Rain-light-solar-condensation sensor button
The steering column stalk is exclusively for the wipe-wash system. All requests for the wipe wash system are picked up in the steering column switch cluster. The steering column switch cluster transmits the commands to the junction box electronics (JBE) via the local interconnect network bus. The junction box electronics execute the requests.
Redundant signal
The signals from the steering column stalk turn indicator / high-beam switch for direction indicator lights as well as headlight flasher are transferred across the FlexRay. To enhance system availability, a direct wire connects the steering column switch cluster (SZL) to the footwell module (FRM). The signals - e.g. for the headlight flasher or turn indicators - are transferred redundantly across this cable.
Vibration actuator (optional equipment)
The control unit for camera-based driver assistance systems (KAFAS) requests activation of the vibration actuator via the PT-CAN. The central gateway module (ZGM) implements the signal on the FlexRay. In this way, the Integrated Chassis Management (ICM) receives the request for activation. The ICM coordinates activation of the vibration actuator.
The steering wheel electronics evaluate the request. The steering wheel electronics activate the vibration actuator and monitor its function. The steering-column switch cluster provides notification of a defect in the vibration actuator or steering wheel electronics across the FlexRay.
Multifunction steering wheel
The left-hand button pad in the multifunction steering wheel has the following functions:
- Setting the desired driving speed
- Cruise control with brake function or active cruise control
The right-hand button pad in the multifunction steering wheel has the following functions:
- Scan audio functions
- Telephone
- Voice input
Steering wheel heating
The button for the steering wheel heating is installed on the left of the steering column shroud.
The button for steering wheel heating is evaluated by the electronics of the steering-column switch cluster. The electronics in the steering column switch cluster transmit the command to the steering wheel electronics to switch the steering wheel heating on or off via the LIN bus. The steering wheel module switches the steering wheel heating on and monitors its function. The steering wheel heating has an NTC resistor. The purpose of this resistor is to control the temperature of the steering wheel heating.
Functional networking
The steering column switch cluster is no longer a control unit. The steering column switch cluster is connected via 2 local interconnect network bus systems to the junction box electronics (JBE). The fault entries for the steering column switch cluster are managed solely in the junction box electronics (JBE).
After being recorded and processed, the data from the steering column switch cluster is relayed to the appropriate control units via the local interconnect network bus.
Notes for Service department
General notes
Care should be taken when replacing the steering-column switch cluster or working on the steering column and the repair instructions should be followed.
Diagnosis instructions
A steering angle sensor is no longer installed in the steering column switch cluster. After replacement of the steering column switch cluster no adjustment must be made to the steering angle sensor.
We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.