System Overview
Block Diagram: Basic seat
Lumbar components are not shown.
Scheme 1
Block Diagram: Comfort seat.
Lumbar, ventilation and active seat components are not shown.
Scheme 2
Operation
The seat heating can be turned on from terminal 15 and the engine running. Stage 3 (maximum temperature) is activated when the button is pressed for the first time. Each subsequent pressing of the button selects the next stage lower or "off". The seat heating is turned off if the button is pressed for longer than 1.2 seconds.
The seat heating remains in stand-by (service station feature) for 15 minutes after terminal 15 is switched off.
The seat ventilation can be turned on from KL 15 "on" and the engine running.
Seat ventilation has 3 stages but only two fan speeds
- Stage 3: High speed backrest, high speed cushion (seat bottom)
- Stage 2: low speed backrest, high speed cushion
- Stage 1: low speed backrest, low speed cushion
Stage 3 is activated when the button is pressed for the first time. Each subsequent pressing of the button selects the next stage lower or "off". The seat ventilation is turned off if the button is pressed for longer than 1.2 seconds.
The system switches down automatically from stage 3 to stage 2 after an running time of 15 minutes. The ventilation remains in stand-by for 15 minutes after KL R off is received.
Lumbar adjustment is performed by 2 inflatable chambers (air bladders) in the backrest. The air chambers are inflated and deflated by 2 solenoid valves. The air pump delivers the required air pressure.
The air pump and the actuators are activated by the seat module based on the commands from the seat switch block.
The signals for operating the lumbar support are transmitted over the buses.
Signal path: Switch block - 12-pin ribbon cable - BZM - K-CAN S - CAS - K-CAN P - SMFA or SMBF.
Functional Description
The system is filled with a glycol fluid. This fluid is pumped alternately into the left and right fluid bags (by reversing the direction of pump rotation).
The following components are required for the active-seat function
- Hydraulic pump: the hydraulic-pump motor is activated with alternating polarity by semi conductors in the seat module.
- Hal sensor: a Hall sensor records the revolutions of the hydraulic-pump motor. The motor function is monitored with this signal.
- Solenoid valve: the solenoid valve is installed between the two fluid bags and opens and closes the delivery to the fluid bags. The valve is activated by semiconductors in the seat module. The solenoid valve is closed when the system is deactivated and in the intervals between the adjustments. In order not to irritate the driver when cornering fast, the operational sequence of the active seat is stopped immediately at high transversal acceleration: the solenoid valve remains closed from a specific transversal vehicle acceleration. The yaw-rate sensor telegrams the transversal-acceleration signal via the bus system.
- Vacuum switch: a vacuum switch is installed in each of the fluid bags. These switches identify the extent to which the fluid bags are drained. In the event of a fault, the system stops or holds in order to avoid further damage.