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Semi-active suspension control deals principally with high bandwidth modulation of passively generated damper forces. When a properly designed semi-active damper is used in an otherwise conventional suspension there is much evidence that a superior overall system results. Large off-road vehicles, such as military transport vehicles, traveling at high speeds over rough terrain, possess suspension control requirements which are different from a road going vehicle. This paper develops these control requirements.

Ride evaluations of prototype semi-active suspensions have demonstrated that acceleration alone is not sufficient in determining acceptable ride quality. The problem involves transient force behavior that is inherent to a semi-active suspension. This transient behavior can be present in both on-off and continuously variable semi-active suspensions. Force discontinuities created by semi-active suspensions can create jerk (the derivative of acceleration) and unwanted audible noise. This paper proposes simple solutions for eliminating unwanted jerk and noise. These solutions involve modifications to the basic control algorithms or system hardware.

This paper describes the fundamental concepts of semi-active control, and the development and testing of a semi-active suspension on an M551 tank. The single degree-of-freedom (SDOF) model of a vehicle suspension is used in explaining the basic concepts. Background information is presented on conventional, fully active, and optimal suspension systems. One goal of this paper is to give the reader an intuitive “feel” for semi-active control. Primary vehicle suspension systems are a natural application for semi-active control, but the concepts apply equally well to general vibration isolation problems.