Steering Column Switch Cluster
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 bus systems or directly to components.
The version of the steering-column switch cluster depends on the options fitted.
The following optional equipment expands the version:
- Cruise control with brake function or active cruise control
- Vibration actuator for lane departure warning or lane change warning
- Steering wheel heating
Interfaces to steering-column switch cluster
The steering-column switch centre (SZL) features column-mounted stalks on the left and right sides. The righthand 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.
An optical steering-angle sensor is installed in the steering-column switch cluster. The steering angle sensor uses a non-contact optical measuring system for steering-angle detection.
The steering column switch cluster receives the button signals of the steering wheel directly or via the LIN bus.
These signals are forwarded by the steering column switch cluster to each control units.
The signals (e.g. of the buttons for volume adjustment of the radio) are sent by the steering-column switch cluster across the FlexRay. The steering-column switch cluster receives the signal to activate the vibration actuator, for example, across the FlexRay.
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 assesses the button status for the electrical steering column adjustment. The requests are output across the FlexRay. The steering-column switch cluster also 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 (SZL):
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
- Headlamp flasher
The steering column switch cluster (SZL) generates the switching signals based on the status of the column stalk's current position. The switch signals are made available by the steering-column switch cluster across the FlexRay. 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 sends the requests to display the onboard computer functions via FlexRay. 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 commands being transmitted to the wash/wipe system are registered in the steering column switch cluster (SZL). The steering column switch cluster transmits the commands to the junction box electronics (JBE) via Flex-Ray. 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.
Steering angle sensor
The steering angle as well as the steering-angle speed are picked up by a non-contact optical measuring system, the optical steering-angle sensor.
The data of the optical steering-angle sensor are processed by the electronics in the steering column switch cluster. These data are sent across the FlexRay to the integrated chassis management (ICM).
The steering-angle sensor picks up the following variables:
- Steering angle
- Steering wheel angular velocity (calculated in steering column switch cluster)
- Steering-wheel turns
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
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.
Steering column adjustment and steering wheel heating
The button for the steering column adjustment can be moved in four directions. It can be used to raise or lower the steering column or to set the distance to the driver.
The steering column switch cluster (SZL) evaluates the status of the switch. The steering column switch cluster relays this status to the footwell module (FRM). The signal is sent across the FlexRay to the central gateway module (ZGM). The signal then proceeds from the central gateway module to the footwell module (FRM) on the KCAN2. The footwell module activates the drive of the steering column adjustment accordingly. The activation and function are monitored by the footwell module.
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
After being recorded and processed, the data from the steering column switch cluster (SZL) are relayed to the appropriate control units via FlexRay. The steering column switch cluster can be assessed with the diagnosis system via the central gateway module (ZGM). Information on the diagnosis can be called up via the FlexRay.
Notes for Service department
General notes
The shape of the steering-angle sensor retains it in the steering column switch cluster (SZL).
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
The diagnosis system includes a service function for calibrating the steering-angle sensor.
The steering-column switch cluster (SZL) can only be ordered as a complete new component. After replacement, the steering-angle sensor must be calibrated.
Use the following path: Service functions -> Chassis -> Steering-angle sensor
Place the steering wheel straight ahead from a visual point of view. The front wheels must be in the straight-ahead position.
We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.