1991-09-01

Use of a Flapper-Nozzle Valve for Axial Piston Pump Control 911817

A mathematical model of an axial piston pump with a flapper-nozzle valve was developed. The first stage was dynamically stable, and calculated values of first-stage gain and dynamic response agreed well with experimental values. Linearized relations were produced for each component part and were combined to form the total state-variable representation of the model. The open loop system, the combined axial piston pump and flapper-nozzle valve, exhibited dynamic instability. However, when the feedback loop was augmented by the output pressure differential, stability was achieved.
From the time responses of the augmented optimal control system, we observed that an increase of input current had little effect on the system response. Doubling the discharge flow rate doubled the overshoot, and an increase in the discharge volume slowed down the system responses. Increasing rotational speed of the pump produced a higher overshoot and a slower response.
The performance of an axial piston pump with a flapper-nozzle valve used as a controller was compared to the performances of such a pump with a four-way hydraulic valve, a single-stage electrohydraulic servovalve, and a two-stage electrohydraulic servovalve used as controllers. We found the combination of a flapper-nozzle valve and an axial piston pump to be superior to other combinations in terms of the balance between pressure-time response and maximum pressure overshoot.

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