THEORETICAL ANALYSIS OF AN ACTIVE SUSPENSION FITTED TO A LONDON TRANSPORT BUS

For the past decade, the automotive products group have been developing an active suspension system for road vehicles. Early in 1974 this system will be fitted to a London transport route master bus for evaluation. This paper presents a theoretical analysis of the active suspension system and the results of tests on the bus. The suspension system consists of gas springs in which a fluid may be pumped in or out. The movement of the fluid is controlled by a model whose purpose is to identify inertia forces acting on the vehicle. The suspension system thus has two modes of operation (a) a passive mode-in which no fluid is pumped in or out of the system; (b) an active mode-in which pumping does take place. In the passive mode, the model does not come into play, and the system acts in a manner similar to a conventional suspension system. The passive mode governs the response of the system to variations in road surface. When inertia forces are acting on the vehicle (e.g. In cornering), they are identified by the model and bring into operation the active mode. In the active mode, hydraulic fluid can be pumped in or out of the gas springs leading to a form of integral control. The model simulates the passive response of the vehicle and discriminates between road surface variations and inertia forces acting on the vehicle. This paper deals principally with the theoretical design and response of the active suspension system and the advantages of partial or total decoupling of the six degrees of freedom of the main vehicle body. Decoupling simplifies the task of predicting the vehicle response and hence the selection of suspension parameters. The main advantage of the active suspension system over conventional systems lies in its superior anti-roll behaviour. /Author/TRRL/