Composite shock absorbers consisting of hydraulic dampers and coiled springs or air springs form compact damping units. However, the telescoping, hydraulic dampers react independently of loading. Consequently, if shock absorption is designed for full-load operation, the vehicle is over-damped at partial loads. The paper presents a new shock absorber design to overcome this problem: a unidirectional, hydraulic shock absorber is centrally installed in and attached parallel to conventional air spring bellows. An auxiliary membrane is mounted between the air spring fitting and the hydraulic cylinder; air spring pressure acting upon it assures that damping force does not exceed the vehicle loading. The operation of this hybrid shock absorber is explained in detail.
An experimental model of this proposed design was produced and tested. Results for various operating conditions and frequency ranges are compared to test results of conventional shock absorbers. As hoped, the hybrid design provided relatively flat damping characteristics throughout the loading range whereas the conventional design characteristics proved strongly load-dependent.