BMW 740iL Reparaturanleitung PDF herunterladen (Seite 53)

Level Control Systems

Operating Principle

Initialization/Reset Performance

When the control unit is powered up after a reset (such as an undervoltage < 4.5 V or by a

load cutoff), different tests and initializations are performed. This system is only enabled

after the tests have been successfully completed and starts to execute the control pro-

grams on a cyclical basis.

Occurring faults are stored and displayed.

Control Sequence

In an ongoing control operation, the high pass filter (fast filter) is always used to prevent the

controlled height from overshooting the nominal value. If a low pass filter (slow filter) were

used to calculate the ride height, brief changes of ride height would be consumed. The

low-pass filter is used while the vehicle is driven. This type of filtering filters out vibrations

which are excited by the road surface.

The high pass filter is used to respond quickly to ride level deviations from setpoint. These

take place while the vehicle is stationary in the event of large load changes.

Both sides of the vehicle are controlled individually, i.e. even the setpoint/actual value com-

parison for both sides is carried out individually. Exception: check for undershooting of the

minimum height in Pre-mode and Kerf mode: consideration of the left and right mean val-

ues in each case.

The following stipulations are applicable here:

• Raising before lowering

• Activation of all valves with control in the same direction

• Individual wheel deactivation

To ensure safe closing of the non-return valve in the air drier, the drain valve is actuated

briefly for 200ms after the control operation has ended.

The permissible ON period of the components is monitored while control up operation are

executed.

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BMW 740iL Reparaturanleitung Seite 53