Co-ordinated Intervention by the Dynamic Handling Systems

The possibilities for intervention available in the past (and, of course, still available now) in order to generate the required yaw force calculated by the central dynamic handling controller are listed below. In brackets in each case are the dynamic handling systems concerned.

• Modulation of individual brakes (DSC)
• Adjustment of engine torque (ASC+T, DSC, MSR)
• Adjustment of front-wheel steering angle independently of driver input (Active Steering).

Subordinate to the centralized dynamic handling control system is an "actuator coordination" function. It decides which dynamic handling system can be used to produce the yaw force in the particular situation concerned.

For example, if the vehicle is exhibiting significant understeer, it can be counteracted by controlled braking of the rear wheel on the inside of the bend. If the vehicle has Integrated Active Steering, the same effect can be brought about even more harmoniously by steering the rear wheels to an appropriate degree.

As both means of intervention are limited in their degree, it can also be useful to use them both simultaneously. Avoidance of understeer is noticeable to the driver in the shape of a significant gain in agility.

The F01/F02 is also the first model on which there is true functional networking between the Integrated Chassis Management and vertical dynamics management functions. But that doesn't simply mean that the ICM registers the ride height data, processes it and passes to the VDM.

An integral component of the dynamic handling control system is that the ICM also actively initiates the Dynamic Drive function in order to affect the self-steering characteristics. As is familiar from conventional suspension and steering designs, a stiffer anti-roll bar results in a lower achievable overall lateral friction force at the pair of wheels concerned. The actuator motors in the Dynamic Drive anti-roll bars can be used to simulate the effect of stiffer and more flexible anti-roll bars.

Thus the ICM centralized dynamic handling control system can use the Dynamic Drive's active anti-roll bars to selectively control the available lateral friction force at a pair of wheels. If the vehicle is oversteering, that means there is too little lateral friction force on the rear wheels. In that case, it is better to reduce the roll limiting force on the rear suspension. In return, there is a gain in lateral friction force on the rear wheels which helps to stabilize the vehicle.

The input/output diagram on the following page summarizes the effect of the centralized dynamic handling control functions on the ICM control unit.

Fig 1: Input/Output Signal Diagram - Centralized Dynamic Handling Control On ICM

Courtesy of BMW OF NORTH AMERICA, INC.