Vehicle suspension design can be simplified by using compressible fluid (CF) based struts. One single CF strut can provide both spring and damping force instead of two independent components of spring and shock absorber in a traditional vehicle suspension system. With the application of a digital displacement pump motor (DDPM) to modulate the fluid amount in CF struts, a hydraulic based active suspension can be developed. Each vehicle suspension corner (i.e., CF strut) can be linked to (at least) one cylinder of a multiple cylinder DDPM. Each cylinder has two poppet valves to allow exchanging flow between strut and accumulator. Those valves are actively controlled according to a properly designed control strategy. Thus DDPM can regulate the fluid flow to/from the CF struts to create a desired strut force at each suspension corner. This paper focuses on elaborating this novel active suspension using CFS and DDPM, and then presents a model that can well capture the macro-behavior of this new active suspension.

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