Steering column switch cluster (SZL) and multifunction steering wheel (MFL)

The functions of the steering column switch cluster can be subdivided into three main blocks:

• Steering column switch cluster as satellite with connection to the data buses BYTEFLIGHT and chassis CAN
  
• Steering column switch cluster as switching centre for the control functions at the steering column
  
• Steering column switch cluster as steering-angle sensor.
  

The multifunction steering wheel provides the means by which the driver can easily and ergonomically perform the following functions:

• audio, telephone, fanfare horn and a definable button -> via the function buttons of the multifunction steering wheel
  
• direction indicators / high beam headlights, windscreen wiper, cruise control, -> via the control levers on the steering column
  

Brief description of components

The multifunction steering wheel consists of

• Steering-column levers: All steering-column levers are one-touch levers and do not lock in the operated position
  
• Fanfare horn
  
• 2 blocks with function buttons
  
• Airbag system.
  

Located below the multifunction steering wheel are

• a button for the steering column setting
  
• the steering column switch cluster module with integral steering angle sensor
  

The electronic control system for the steering column switch cluster and the multifunction steering wheel is divided into two electronic modules:

• Steering column electronics (= steering column switch cluster)
  
• Steering wheel electronics.
  

Signal transmission from the steering wheel module to the steering column module is effected by means of a coil-spring conductor.

Steering column stalk, top left: Turn indicator-low beam switch

The turn indicator-low beam switch consists of

• a steering-column lever
  
• two one-touch buttons.
  

The turn signal/dip switch also incorporates two axial touch switches.

• The top button activates the Info display on the right of instrument cluster below the rev counter.
  
• The bottom button activates the Info Display on the left of instrument cluster below the speedometer.
  

Transfer concept: steering column stalks and axial touch buttons have differing signal transmission routes:

Steering column stalk signal transmission route: When the driver operates the steering column lever, a message is sent to the light module. Signal path: from steering column switch cluster -> data bus BYTEFLIGHT -> Safety and Gateway Module -> data bus K-CAN -> light module.

For safety reasons, there is an additional serial cable from the steering column switch cluster to the light module. An analogue coded signal is applied to that cable and is analysed by the light module. Each switch position is allocated a voltage range. The serial cable enables transmission of all positions of the turn signal/dip switch in the event of a bus fault, though with some limitations to the possible functions:

• Main beam and headlamp flasher only function if the steering column stalk is held in position.
  
• The direction indicators only function while the steering column stalk is held in position, no continuous flashing, no automatic reset
  
• No hazard-warning lights in the event of a crash and when arming the antitheft alarm.
  

Touch button signal transmission path: When the driver operates one of the axial touch buttons, a message is sent to the instrument cluster.

Signal path: from steering column switch cluster -> data bus BYTEFLIGHT -> Safety and Gateway Module -> data bus K-CAN -> instrument cluster.

Steering-column lever, bottom left: vehicle speed control

The lever for the cruise-control system consists of

• a steering-column lever
  
• a one-touch button
  
• a knurled wheel.
  

Transfer concept: When the driver operates the steering-column lever or the axial one-touch button, a message is sent to the digital engine electronics.

Signal path: from steering column switch cluster -> data bus BYTEFLIGHT -> Safety and Gateway Module -> data bus PT-CAN -> Digital Engine Electronics.

Transfer concept: When the driver operates the knurled wheel, a message is sent to the Active Cruise Control (ACC) control unit.

Signal path: from steering column switch cluster -> data bus BYTEFLIGHT -> Safety and Gateway Module -> data bus PT-CAN -> Active Cruise Control (ACC).

Steering column stalk, bottom right: Wiper switch

The wiper switch consists of:

• a steering-column lever
  
• a one-touch button
  
• a knurled wheel.
  

Transfer concept: When the driver operates the steering column lever, a message is sent to the body base module.

When the driver operates the axial button or the adjuster wheel,

• on a vehicle without rain/light sensor, a message is sent to the body base module.
  
• on a vehicle with rain/light sensor, a message is sent to the rain/light control unit.
  

Signal path: from steering column switch cluster -> data bus BYTEFLIGHT -> Safety and Gateway Module -> data bus K-CAN -> body base module and/or rain/driving light sensor.

Function button block on the left and right of the multifunction steering wheel

The function buttons enable selection of

• Voice input
  
• Search
  
• Audio functions (radio, telephone, etc.)
  

Steering wheel adjuster button

The steering wheel is adjusted by means of the button on the side of the steering column trim.

• Semi-electric steering column adjustment: Press the steering column adjustment button. An electric motor releases the steering column lock for five seconds.
  Within that period, the driver can adjust the position of the steering wheel manually as required.
  After five seconds, the steering column is automatically locked in position again.
  If the period of five seconds is too long for the driver, the steering column can be locked immediately by pressing the button again.
  
• Fully electric steering column adjustment: The steering wheel position is adjusted electrically by means of a button. The adjuster button has four possible directions of movement. These enable the steering wheel to be moved up, down, forwards or backwards.
  

Fanfare horns

The fanfare horns serve both as a warning signal and as redundant-system audible alarms of the vehicle.

The directly read horn switch signal is sent as a valid status via the steering wheel module and the coil spring conductor to the steering column module (steering column switch cluster control module). The steering column module can control the high-tone and low-tone horns separately.

Steering wheel heater

The steering wheel heating system consists of

• a button for switching the steering wheel heater on and off
  
• a function indicator in the steering wheel heater switch which lights up when the steering wheel heater is on.
  
• the heater coil in the steering wheel rim which heats up the steering wheel
  
• a temperature sensor in the steering wheel rim which sends the temperature signal back to the steering column switch cluster.
  

The steering column switch cluster activates the heater coil as required in order to ensure even heating of the steering wheel.

Service functions

Notes on safety

All work on the airbags must be carried out with the battery disconnected!

Connect and disconnect all BYTEFLIGHT control units, sensors and generators only with the battery disconnected!

If a fibre-optic cable on the BYTEFLIGHT bus has to be repaired, it must be borne in mind that there may only be one join between the Safety and Gateway Module and a satellite. For this reason, no repairs may be performed on the fibre-optic cable between the Safety and Gateway Module and the door satellites, as there is already a join with the door connector. In the case of a defect, the fibre-optic cable must be replaced!