Currently, some of the most efficient hydraulic pump/motors cannot go 'over-center'. An experimental test setup and an analytical model investigate the dynamics, advantages, and disadvantages of using poppet valves to switch operation between pump and motor, leading to development of optimal switching methods. This is of particular interest in hydraulic drive vehicles that use regenerative braking. Three major areas of concern are pressure spikes during the transition, event time span, and energy loss. The analytical model uses a bond graph to help construct the system state equations for numerical integration. Experiments measured pressure, speed, and torque using a Volvo V11-60 variable displacement hydraulic pump/motor and a modular valve block. Experimental results show that transition occurs within 150 ms, pressure spikes are within acceptable limits, while energy loss is quite large. The reason for large losses and lower than expected pressure spikes is an open valve overlap, a period of time when a direct flow path exists from high to low pressure. Valves were given a simultaneous electronic signal. However, actual valve opening and closing times are very different. Thus for a fraction of second, two valves are open simultaneously. A possible solution investigated with the analytical model is to activate valves sequentially. The challenge is balancing energy storage loss with higher pressure spikes.
Investigation of the dynamics of switching from pump to motor using external valving
Untersuchung der Dynamik der Umschaltung von der Pumpe zum Motor mit Hilfe externer Tellerventile
1995
8 Seiten, 9 Bilder, 7 Quellen
Aufsatz (Konferenz)
Englisch
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