1017 Active suspension

An ideal suspension system should be able to perform numerous functions that are listed below:

1 To absorb the bumps and rebounds imposed on the suspension from the road.

2 To control the degree of body roll when cornering.

3 To maintain the body height and to keep it on an even keel between light and full load conditions.

4 To prevent body dive and squat when the car is rapidly accelerated or is braked.

5 To provide a comfortable ride over rough roads yet maintain suspension firmness for good steering response.

6 To isolate small and large round irregularities from the body at both low and high vehicle speeds.

These demands on a conventional suspension are only partially achieved as to satisfy one or more of the listed requirements may be contrary to the fulfilment of some of the other desired suspension properties. For example, providing a soft springing for light loads will excessively reduce the body height when the vehicle is fully laden, or conversely, stiffening the springing to cope with heavy loads will produce a harsh suspension under light load conditions. Accordingly, most conventional suspensions may only satisfy the essential requirements and will compromise on some of the possibly less important considerations. An active suspension will have built into its design means to satisfy all of the listed demands; however, even then it may not be possible due to the limitations of a design and cost to meet and overcome all of the inherent problems experienced with vehicle suspension. Thus it would be justified to classify most suspensions which have some form of height levelling and anti-body roll features as only semi-active suspensions.

For an active suspension to operate effectively various sensors are installed around the vehicle to monitor changing driving conditions; the electrical signals provided by these sensors are continuously fed to the input of an electronic control unit microprocessor. The microprocessor evaluates and processes the data supplied by the sensors on the changing speed, loads, and driving conditions imposed on the suspension system. On the basis of these data and with the aid of a programmed map memory, calculations are made as to what adjustments should be made to the suspension variables. These instructions are then converted into electrical output signals and are then directed to the various levelling and stiffening solenoid control valves. The purpose of these control valves is to deliver or exit fluid to or from the various parts of a hydraulic controlled self-levelling suspension system.

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