Active suspension

Active suspension is a type of automotive suspension that controls the vertical movement of the wheels relative to the chassis or vehicle body with an onboard system, rather than in passive suspensions where the movement is being determined entirely by the road surface; see Skyhook theory. Active suspensions can be generally divided into two three classes: pure active suspensions, and adaptive and semi-active suspensions. While adaptive suspensions only vary shock absorber firmness to match changing road or dynamic conditions, active suspensions use some type of actuator to literally raise and lower the chassis independently at each wheel.

These technologies allow car manufacturers to achieve a greater degree of ride quality and car handling by keeping the tires perpendicular to the road in corners, allowing better traction and control. An onboard computer detects body movement from sensors throughout the vehicle and, using data calculated by opportune control techniques, controls the action of the active and semi-active suspensions. The system virtually eliminates body roll and pitch variation in many driving situations including cornering, accelerating, and braking.

Active suspensions, the first to be introduced, use separate actuators which can exert an independent force on the suspension to improve the riding characteristics. The drawbacks of this design are high cost, added complication and mass of the apparatus, and the need for frequent maintenance on some implementations. Maintenance can require specialised tools, and some problems can be difficult to diagnose.

Michelin's Active Wheel incorporates an in-wheel electrical suspension motor that controls torque distribution, traction, turning maneuvers, pitch, roll and suspension damping for that wheel, in addition to an in-wheel electric traction motor.

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