Electrically Adjustable Seats

Electrically Adjustable Seats

Electrically adjustable seats
The following seat versions are used:
- Basic seat
- Sports seat
- Comfort seat

Depending on the seat version and the optional equipment, the following seat functions are possible:
- Forward/back seat adjustment
- Seat height adjustment
- Seat-tilt adjustment
- Seat depth adjustment
- Backrest angle adjustment
- Seat backrest width adjustment
- Backrest upper section adjustment
- Headrest restraint height adjustment
- Lumbar-support adjustment







The following optional equipment is available for the various seat versions:







Brief component description
The following components are described for the electric seats:

Switch block for seat adjustment on driver's side or front passenger side
Depending on the equipment fitted, the switch block contains the following buttons:
- Lumbar support switch
- Button for backrest angle and headrest height adjustment
- Buttons for backrest upper section adjustment
- Buttons for backrest width adjustment
- Switch for forward/back, height and seat angle adjustment
- Button for seat depth adjustment
- Button for active seat
- Memory switch with two position buttons

The following components of the switch block for seat adjustment on the driver's side and/or front passenger side are described:
- Lumbar support switch
Pressing the corresponding side of the button enables the lumbar support to be adjusted as follows:
- Press front of button: The curvature of the lumbar support is reinforced (adjustment of lower lumbar support).
- Press rear of button: The curvature of the lumbar support is weakened (adjustment of lower lumbar support).
- Press top of button: The curvature of the lumbar support is shifted upwards (adjustment of upper lumbar support).
- Press bottom of button: The curvature of the lumbar support is shifted downwards (adjustment of upper lumbar support).

- Button for backrest angle and headrest height adjustment
- Press button upwards: The head restraint extends.
- Press button downwards: The head restraint retracts.
- Turn button to the front: The backrest adjusts towards the front.
- Turn button to the rear: The backrest adjusts towards the rear.

- Buttons for backrest upper section adjustment
The buttons for the backrest upper section adjustment are integrated in the button for the backrest angle and headrest height adjustment.
- Press the front button: The backrest upper section adjusts forwards.
- Press the rear button: The backrest upper section adjusts backwards.

During adjustment, the complete backrest upper section including the head restraint does not move (as in F01, F02), but only the top section of the backrest.

- Buttons for backrest width adjustment
For the backrest width adjustment, the backrest side sections are adjusted mechanically.
- Press the front button: The backrest width is reduced.
- Press the rear button: The backrest width is increased.

- Switch for forward/back, height and seat angle adjustment
To adjust the desired seat position, operate the button as follows:
- Press button to the front: The seat is adjusted forwards in longitudinal direction (forward/back seat adjustment).
- Press button to the rear: The seat is adjusted backwards in longitudinal direction (forward/back seat adjustment).
- Press button upwards: The seat is adjusted upwards (seat height adjustment).
- Press button downwards: The seat is adjusted downwards (seat height adjustment).
- Turn button upwards: The seat is tilted upwards (seat angle adjustment).
- Turn button downwards: The seat is tilted downwards (seat angle adjustment).

- Button for seat depth adjustment
The seat depth adjustment varies the position of the thigh support: The further the thigh support is extended, the lower the seat.
- Press button to the front: The thigh support extends.
- Press button to the rear: The thigh support retracts.

- Button for active seat
The massage function is switched on or off by pressing the button with integrated function indicator light.

- Memory switch
The memory switch consists of a button pad with 3 buttons: the memory button with integrated function indicator light and 2 position buttons. The position buttons can be used to store and retrieve 2 seat positions.
- Storing a seat position
- Switch the ignition on.
- Adjust the seat to the desired seat position.
- Press button M. The function indicator light lights up.
- Press position button 1 or 2. The function indicator light goes out.

The stored seat position can be retrieved via a convenience function or via a safety function.
- To call up a stored seat position via convenience function:
- Open driver's door or front passenger door.
- Switch off ignition.
- Briefly press the position button for the stored seat position on the switch block for the driver's side seat adjustment or the switch block for the front passenger side seat adjustment.

The corresponding seat position is automatically made.

- To call up a stored seat position via safety function:
- Close driver's door or front passenger door or switch on the ignition.
- Hold the position button for the stored seat position on the switch block for the driver's side seat adjustment or the switch block for the front passenger side seat adjustment pressed until the.adjustment procedure has been completed.







SMFA and SMBF: driver's seat module and front passenger seat module
The driver seat module and front passenger seat module are identical components. Identification of the driver's seat or front passenger seat is implemented via pin coding.
Depending on the seat version and optional equipment, the driver's seat module or front passenger seat module controls and monitors the following functions:
- Seat adjustment
- Seat heating
- Active seat ventilation
- Active seat lumbar drive
- Pressure distributor, active seat and pressure distributor 2, active seat
- Valve block, lumbar support (only with active seat equipment)

The seat module evaluates the button signals and activates the required functions. The seat module is a bus user on the K-CAN (body controller area network).
Depending on the seat version and the optional equipment, the seat module is either connected with the switch block (switch block, driver's side or front passenger side seat adjustment) via a line connection or via a bus connection (local interconnect network bus) .







Lumbar support drive and lumbar support valve block without active seat
The lumbar support in the backrest comprises 2 inflatable lumbar support cushions. The lumbar supports overlap in some areas.
A pneumatic pump (lumbar support drive, driver or front passenger) supplies the lumbar supports with compressed air.
The desired setting for the lumbar support is controlled using the button for the lumbar-support adjustment.
The button signals are not evaluated in the seat module, but by the evaluation electronics in the valve block for the lumbar support. The evaluation electronics activate the electrically powered air pump and the solenoid valves in the valve block for the lumbar support (valve block, lumbar support, driver or front passenger).
The individual lumbar support cushions are filled or emptied via the valve block for the lumbar support. This means that the lumbar support can vary its height and strength (adjustment of upper lumbar support and adjustment of lower lumbar support). A pressure relief valve in the valve block for the lumbar support protects the system against excessive system pressure.







Lumbar active-seat drive with lumbar support valve block and pressure distributor, active seat and pressure distributor 2, active seat
Depending on the requirements, the seat module controls 2 power stages via the control electronics on the lumbar active-seat drive:
- Active seat function selected:
the pump motor runs with reduced power output.

- Lumbar support function selected:
the pump motor runs with full power output.

The lumbar active-seat drive (lumbar active-seat drive, driver and/or front passenger) supplies the air cushions in the active seat and the lumbar supports with compressed air.
- Lumbar support valve block (valve block, lumbar support, driver and/or front passenger)
The lumbar support in the backrest comprises 2 inflatable lumbar support cushions. The lumbar supports overlap in some areas.
The desired setting for the lumbar support is controlled using the button for the lumbar-support adjustment. The button signals are transferred across a LIN bus to the seat module on the driver's side (SMFA) and/or seat module on the front passenger's side (SMBF). The seat module activates the valve block for the lumbar support.
The individual lumbar support cushions are filled or emptied via the valve block for the lumbar support. This means that the lumbar support can vary its height and strength (adjustment of upper lumbar support and adjustment of lower lumbar support).
A pressure relief valve in the valve block for the lumbar support protects the system against excessive system pressure.







- Pressure distributor, active seat and pressure distributor 2, active seat
The 2 pressure distributors distribute the air flow generated by the pneumatic pump (lumbar active-seat drive) to the 4 air cushions in the active seat. Two air cushions are arranged one above the other on the left-hand and right-hand seat cushions.
The 2 pressure distributors automatically regulate the inflation and deflation of the air cushions. The 2 pressure distributors are divided into master and slave.
Pressing the active seat button activates the system. The button signals are transferred across a LIN bus to the seat module on the driver's side (SMFA) and/or seat module on the front passenger's side (SMBF). The seat module activates the pneumatic pump and the master pressure distributor.







The valve technology used in the valve block and the pressure distributors is based on a wire made of shape memory alloy. As of a certain temperature, this wire changes its grid structure and contracts. The wire always attempts to reassume its original shape.
There is a valve with 2 wires for each air cushion. One wire opens or closes the air duct for deflation. The other wire opens or closes the air duct for inflation. Without current, the valves are closed.

Button for seat heating and button for active seat ventilation
The seat heating and active seat ventilation are operated using buttons in the control panel of the IHKA.
- Button for seat heating left and button for seat heating right
The button can be used to switch 3 heating stages. The first press of the button for the seat heating switches on the highest heating stage. Further button pressures switch on the next-lowest heating stage or switch off the seat heating.
The selected heating stage is indicated by the function indicator light as follows:
- Heating stage 3 (high heat output): All LEDs (3x) of the function indicator light light up.
- Heating stage 2 (medium heat output): 2 light-emitting diodes light up
- Heating stage 1 (low heat output): 1 light-emitting diode lights up

- Button for active seat ventilation left and button for active seat ventilation right
The button can be used to switch 3 ventilation stages. The first push of the button for active seat ventilation will switch on the highest ventilation stage . Pressing the button repeatedly switches on the next-lowest ventilation stage or switches off the active seat ventilation.
The selected ventilation stage is indicated by the function indicator light as follows:
- Ventilation stage 3 (high fan speed): All LEDs (3x) of the function indicator light light up.
- Ventilation stage 2 (medium fan speed): 2 light-emitting diodes light up
- Ventilation stage 1 (low fan speed): 1 light-emitting diode lights up

The seat module activates the function indicator light for the seat heating and for the active seat ventilation in the control panel of the IHKA.







Switch for the easy entry driver and/or passenger
The rear easy-entry facility is switched using the switch for easy entry, driver and/or front passenger.
The switch for easy entry can be used to automatically move the applicable front seat forward and back again to provide easy entry and exit for rear seat passengers.







Backrest lock switch for driver and backrest lock switch for front passenger
The backrest lock switch for driver and/or passenger monitors the proper locking of the front seat backrest on the driver's and front passenger's side.
Seats with 3-point automatic-reel belt integrated in the front seat backrest are fitted on the convertible. If the backrest is not locked correctly, there is the danger that in the event of a crash occupants could move forward with the backrests and the belt is thereby without restraining effect.







Integrated automatic heating / air conditioning system: Integrated automatic heating / air conditioning system
The buttons for seat heating and active seat ventilation are installed in control panel of the integrated heating / air conditioning system (IHKA). The IHKA control unit processes the respective button signal. The IHKA control unit transmits the button signal as a message via the K CAN to the driver's seat module (SMFA) and/or front passenger seat module (SMBF). The seat module activates the function indicator light for the seat heating and for the active seat ventilation in the control panel of the IHKA.

ZGM: Central gateway module
The Central Gateway Module (ZGM) links all main buses to one another. Examples of 'main buses' include FlexRay, MOST or K-CAN. This enables the Gateway function on the Central Gateway Module to exchange data between the various different bus systems.

System functions
The following graphic shows the system network of the electric seat using the example of a sports seat without the equipment specification active seat (schematic diagram bears no relation to installation space).












The following graphic shows the system network for the electric seat using the Comfort seat as an example (this schematic diagram bears no relation to installation space). In order to show both equipment specifications (with or without active seat) in one system wiring diagram, the system wiring diagram has the following special features:
- Equipment specification with active seat
This equipment specification is illustrated using the example of the driver's seat module (SMFA).
All button signals are transmitted by the switch block for seat adjustment, driver's side, via the bus connection, to the seat module. The seat module activates the valve block for the lumbar support and the lumbar active-seat drive.

- Equipment specification without active seat
This equipment specification is illustrated using the example of the front passenger seat module (SMBF).
The button signals for the lumbar-support adjustment are not evaluated in the seat module, but by the evaluation electronics in the valve block for the lumbar support. All other button signals are transmitted to the seat module. The evaluation electronics in the valve block activate the lumbar support drive and the valve block for the lumbar support.













The following system functions are described for the electric seat:
- Seat adjustment
- Easy access in rear compartment
- Monitoring of the backrest lock
- Seat heating
- Active seat ventilation
- Active seat function

Seat adjustment
During seat adjustment, the adjustment travel is registered by the Hall effect sensor in the drive and processed in the seat module. The position value of the mechanical limits stops is detected and saved as end stop the first time it is detected. For subsequent adjustments, the seat stops before this position is reached (soft stop).
For activation of the selected drive, integrated measurement of the control currents takes place in the seat module. This measurement ensures fault recognition (e.g. overload current, short circuit or locking). If certain threshold values are exceeded or undershot, the voltage supply to the drive is switched off.
The seat module has its own overheating protection to prevent the drive from overheating. The heating of the drive is calculated continuously on the basis of the operation time (running time and off-load phase) by means of a thermal model in the seat module. As of a certain temperature threshold, the seat module switches off the drive.







Easy access in rear compartment
The switch for the driver and/or front passenger entry aid can be activated from terminal R ON.
The rear easy-entry facility can be activated under the following conditions:
- Vehicle must be stationary.

and

- The door must be opened

A rocker switch is integrated in the switch for easy entry driver and/or passenger. The rocker switch will return to the initial position after pressing.
The driver's seat module (SMFA) and/or passenger seat module (SMBF) evaluates the button signal. Depending on the request, the seat module activates the drive for the rear easy-entry facility.

Monitoring of the backrest lock
If a front seat backrest is not correctly locked, the assigned seat module will issue a message on the K CAN. The Check-Control message is shown in the instrument panel and in the central information display.
The backrest lock switch (microswitch) is resistance encoded. The microswitch has 2 resistors.
When the front seat backrest is properly locked, the backrest lock switch is mechanically operated via the locking device. The circuit is thereby applied via resistor 2 to the seat module.
When the backrest is mechanically unlocked through the locking lever for the backrest lock, the microswitch is not used. The circuit to the seat module is thereby applied via resistor 1.
The seat module evaluates the signal change.

Seat heating
The seat heating includes backrest heating and seat cushion heating.
The seat heating can be switched on separately for the driver's and front passenger seat as of terminal 15 On using the buttons in the control panel of the integrated automatic heating and air conditioning system (IHKA). The IHKA control unit processes the respective button signal. The IHKA control unit transmits the button signal as a message via the body controller area network (K-CAN) to the following components:
- Driver seat module (SMFA)
- Front passenger seat module (SMBF)

According to the selected heating stage, the seat module generates a pulse-width modulated signal (PWM signal) that is used to activate the seat heating. Depending on the seat version, the seat heating is monitored by one or two temperature sensors (NTC resistors). The temperature sensors are integrated in the seat heating pads and connected with the seat module.







Active seat ventilation
Depending on the button signal, the seat module specifies the fan settings. The fan settings are switched via a transistor in the seat module. Each fan has a control / diagnostic line in addition to the voltage supply and ground connection. The fan settings are activated and the fans are monitored via this control and diagnostic line.
If a fan is not rotating (alarm status), the transistor switches a resistor to terminal 31. The evaluation of this diagnosis feedback is only possible if the interface for the fans is set to fan setting 3.







Active seat function
The active seat function is activated from terminal 15 ON. Pressing the active seat button activates the system. The button signals are transferred across a LIN bus to the seat module on the driver's side (SMFA) and/or seat module on the front passenger's side (SMBF). The seat module activates the pneumatic pump and the master pressure distributor. The master pressure distributor activates the slave pressure distributor. The operating cycle is continuously calculated in the master pressure distributor using a calculation model. Based on the calculation, the master pressure distributor will also specify the pulsing to inflate and deflate the connected air cushions for the slave pressure distributor. The pressure distributors enable the inflation, holding pressure and deflation of air cushions.
If the driving speed and lateral acceleration are above a defined value for approx. 0.25seconds, the active seat function is disabled. The function indicator light remains switched on. If the value is again undershot for approx. 3 seconds, the system resumes the function at the stopped position.

Notes for Service department

General notes
After replacement of a seat module (driver's seat module and/or front passenger seat module), seat standardisation must be carried out. A service function is available for the seat standardisation.
Seat standardisation comprises the following:
- Teaching of the mechanical end stops to define the position of the seat relative to the vehicle environment (normalization)
- Adjustment of stiff movement for force limitation (adaptation)

We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.