The system for self-leveling suspension runs the following functions:
The control module activates all the valves, the compressor and the LEDs. Moreover, the control module also generates fault messages on the instrument cluster and stores faults. The control functions use information from: the height sensors, the button and the K-CAN bus as well as the accumulator pressure and temperature sensor. Exchange of information is by means of data telegrams on the data buses.
The button can be used to select two vehicle levels. To display the current vehicle level, an LED is located above the button.
The suspension travel at the individual wheels is determined using angle of rotation sensors (Hall sensors) to measure the relative movement between the wheel and the body.
The air supply unit contains a pneumatic drain valve, an electric relay valve, a high-pressure ventilation valve, an air dryer, a compressor, a sinter filter and a temperature sensor.
The air supply unit is fitted beneath a sound-insulating cover in the luggage compartment.
The air accumulator/valve unit contains air lines, the pressure accumulator, a pressure sensor and the valve unit. The valve unit contains four bellows valves and the pressure accumulator valve. When de-energized, these valves are closed by spring force.
The accumulator/valve unit is located beneath the fuel tank between the luggage compartment and the rear seat.
The automatic self-leveling suspension is controlled by the control module by evaluation of the following signals and K-CAN telegrams:
The signals are compared with the nominal values stored in the control module. The differential value is the adjusting value for the control system. The control module decides in each individual case whether a control procedure is to be carried out.
To run the self-leveling suspension (lifting and lowering), the air bellows are enlarged and reduced by supplying and drawing off air through pressure accumulator valve unit.
The automatic self-leveling suspension works at every vehicle level.
The button can be used to select the following vehicle levels:
The selected vehicle level is indicated by an LED.
All regulating operations are run without moving to intermediate heights. The vehicle is raised and lowered in all load situations virtually in parallel. Depending on the load, the movement can be slightly faster on one axle than on the other. If a threshold value is exceeded, the faster axle is halted briefly. The movement operations in different situations are described below.
Upward movement functions are enabled by activation of a compressor and various valves in the air supply system and the accumulator unit. Under certain circumstances, an upward movement is possible from the pressure accumulator or the compressor.
Sleep mode: A vehicle is placed in the sleep mode 16 minutes after turning off the engine. In the Sleep mode, no regulating operations take place.
Wake-up mode: The control module is woken every six hours to compensate for any inclination. To keep the power consumption low, the vehicle is only lowered. During lowering, the wheels with the higher level are lowered to the level of the lowest wheel.
Pre-/after-run mode: The vehicle wakes from the sleep mode as a result of bus activity on the K-CAN data bus in the pre-/after-run mode. As the engine is off in this mode, the tolerance range is extended to ± 25 mm. Control is from the memory provided the pressure is sufficient. In the case of an empty memory, the control is directly from the compressor. A level change using the button and filling the pressure accumulator are not possible.
Terminal 15: When the ignition is switched on (terminal 15 On), the vehicle level can be moved downwards using the button. Moving the vehicle level upwards, however, is only possible with the engine running, as this requires the compressor to fill the pressure accumulator. Level compensation is 10 mm upwards and 10 mm downwards.
Engine on: With the engine running, vehicle level compensation, raising and lowering the vehicle level, and filling the pressure accumulator are possible. The compressor starts up for each control procedure. In the case of a deviation, level compensation is 10 mm upwards and 10 mm downwards.
When the vehicle is stationary, the system can react immediately to changes in the load using the corresponding signals. As soon as the vehicle moves, there is a switch to slower vehicle level changes. The system then regulates with a mean value and no longer reacts to strokes of the shock absorbers due to irregularities in the road surface. Only when the vehicle is stationary and a lid (trunk or hood) is opened (loading or unloading) is a switch made to faster control.
Detection of lifting platform: If the control module detects when the vehicle is stationary that the defined height threshold is simultaneously exceeded on all four wheels, it detects ”lifting platform”.
For ”detection of lifting platform”, there are the following reset options:
Car jack detection: If the control module detects that a lowering speed below the stored threshold value occurs on one wheel when the vehicle is being lowered, it detects ”car jack”. The height on the detected wheel is stored.
For ”car jack detection”, there are the following reset options:
Imbalance control: If an imbalance occurs, e.g. by driving with one wheel onto a curb, the control is not permitted to attempt a height compensation. An imbalance (inclination mode) is detected when the vehicle is stationary and the difference between the front axle heights plus the opposing difference between the rear axle heights is greater than a specified threshold value. The inclination mode is discontinued when the imbalance falls below the stored threshold value or if the vehicle is moved. In the case of very large imbalances, no control procedure is permitted.
Note: The system also regulates in the diagnostic mode. Prior to work on the system and in the case of height settings, activate the end-of-line mode.
End-of-line mode: In the end-of-line mode, the heights are stored as fixed values. No height compensation can take place. The function LED is deactivated. The text message ”self-leveling suspension inactive” is displayed on the instrument cluster.
Transport mode: In the transport mode, the heights are regulated differently depending on the position of the ignition key. When the ignition is switched on, the text message ”self-leveling suspension inactive” is displayed on the instrument cluster. Stored for the transport mode:
Height setting offset: Under certain conditions, e.g. after replacement of a height setting sensor, a height setting offset must be carried out. On the front and rear axle, the right-hand and left-hand heights are set separately. The activations for the self-leveling suspension are run using the diagnostic program (height setting values, see TIS). After the setting, the heights are stored via the offset function.
Note: Before entering the offset command, check the heights once again.