As a novel alternative of internal combustion engine (ICE), the free piston engine (FPE) eliminates the mechanical crankshaft and the associated constraints on its piston motion. Due to this extra degree of freedom and reduced inertia, the FPE is able to generate variable output power with higher efficiency and less emissions, while possessing a short response time. Hence, a hydraulic FPE (HFPE), which combines the FPE with a linear hydraulic pump, is a promising candidate as a fluid power source, especially for mobile applications. In this paper, such potential is investigated. The working principle of a prototype HFPE as a fluid power source is described and a comprehensive HFPE model is developed. Two novel control methods are proposed to regulate the output flow rate at any given load pressure so as to realize throttle-less fluid power control. Effectiveness of these two methods are demonstrated through simulation, where results clearly show the effectiveness of both methods in providing different output flow rates at given load pressure, thus demonstrating the HFPE’s capability as an efficient and flexible mobile fluid power source.

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