Active Stabilizer Bar

Active Stabilizer Bar (one assembly per axle): The active stabilizer bar consists an oscillating motor and two stabilizer bar halves with press fit roller bearings to mount the assembly to the axle carrier.




The oscillating motor and the oscillating motor housing joins the two halves of the stabilizer bar.

The rear axle Active Stabilizer Bar is shown on the right.

The Active Stabilizer Bar assembly has three tasks:

- The oscillating motor decouples the two halves of the stabilizer bar.
- The oscillating motor guides the torque into the two halves of the stabilizer bar.
- In the event of system failure (Failsafe mode), the front axle stabilizer bar creates sufficient damping from the oscillating motor hydraulic fluid (hydraulic locking) to work like a conventional stabilizer bar.

Exception: If the oscillating motor chambers do not contain any fluid as a result of a leak, the front axle stabilizer bar will not dampen and rely on the spring strut assemblies.

Oscillating Motors: The oscillating motors are split chamber hydraulically controlled rotary actuators. This motor contains a total of four chambers, opposing chambers are connected with one another and receive the same hydraulic pressure.




Two chambers are supplied with high pressure through an internal connection and the other two chambers are connected to the reservoir return line.

The pressure and drain (return) is switched between the two pairs for right or left hand torsional twists.

The different pressures result in the high and low forces that apply torque. One halt of the stabilizer bar is connected to the shaft and the other half is connected to the housing.




The two halves will turn in opposite directions. As a result, the shaft will turn in an opposite direction of the housing.

The stabilizer bar is mounted to the axle carrier. The torque generated while cornering will force the body upwards on the outside of the curve and pull it down on the inside of the curve.




The maximum torque influence on the front and rear axle occurs when there is a high degree of lateral acceleration (producing body roll). During this situation, the system pressure is 180 bar at the front axle and 170 bar at the rear axle. The front oscillating motor is smaller than the rear one and builds up a force of 600 Nm at 180 bar. The rear oscillating motor builds up a force of 800 Nm at 170 bar. The oscillating motors also act as torsional vibration dampers (hydraulic cushion).

During torsional twists, the fluid is displaced from two chambers returning through the lines and the valve block to the reservoir. The return path has a slight hydraulic resistance which creates damping. With failsafe (hydraulic blocking), the oscillating motor will turn as a unit because of the closed circuit hydraulic locking occurring internally (like a conventional stabilizer bar).

Tandem Pump: The tandem pump mounted on the engine and is driven by the ribbed V belt. The pump assembly consists of a radial piston pump for Dynamic Drive and a vane pump for the power steering.




When the engine is idling, the pump speed is approx. 750 rpm providing a minimum flow rate of 4.5 1/min at 0 - 5 bar and 3.3 1/min at 180 bar.

This volume and pressure provides sufficient system dynamics when the engine is idling. At a pump speed of approx. 1165 rpm, the flow rate is limited to 7 1/min. Dynamic Drive and power steering share the fluid reservoir and fluid cooler.

Fluid Reservoir: The fluid reservoir is identical on all E65/E66 vehicles, whether equipped with Dynamic Drive or not. The fluid reservoir also supplies the power steering hydraulic circuit.




The reservoir contains a fluid filter (as on models in current use) and a fluid level sensor to detect when the fluid level drops below the minimum amount.

Fluid Cooler: The cooler ensures a long term fluid temperature of < 120 °C and a short term fluid temperature of < 135 °C in all hydromechanical components under all operating conditions.