Pitch plane analysis of a twin-gas-chamber strut suspension

Abstract

A twin-gas-chamber hydropneumatic suspension strut concept is proposed to achieve enhanced bounce and pitch ride, and pitch attitude control. The response characteristics of the twin-gas-chamber strut suspension are compared with those of a single-gas-chamber strut suspension to demonstrate not only superior performance potentials but also the added design flexibility offered by the twin-gas-chamber struts. The relative responses of both strut suspensions are evaluated through analysis of a pitch plane vehicle model, subject to straight-line braking inputs and excitations arising from randomly distributed road elevations. A generalized formulation for the strut forces is presented to derive the bounce and pitch rates of the proposed strut suspensions. The results reveal that the twin-gas-chamber strut suspension exhibits a slightly lower pitch stiffness in the vicinity of design ride height, but progressively hardening effects with increasing pitch deflections. Moreover, the twin-gas-chamber strut suspension exhibits considerably fewer hardening—softening effects in suspension rate compared with the suspension involving the single-gas-chamber struts. The results attained from the parametric studies are also discussed to demonstrate superior design flexibility of the twin-gas-chamber struts for tuning of the suspension bounce and pitch stiffness properties. The dynamic responses of the vehicle model with different suspensions are assessed subject to random road roughness excitations as well as braking torque inputs. The results demonstrate that the twin-gas-chamber strut suspension offers considerable potential for enhancing bounce and pitch ride, pitch attitude control, and suspension travel responses under braking, while the influence on the ride and road-holding responses under random road inputs is insignificant. The results also suggest that a relatively soft front suspension design could provide further enhancement of pitch ride and pitch deflection responses under random road roughness excitations.