Abstract
Hydraulic accumulators are widely used in industry due to their ability to store energy and absorb fluid shock. Researchers have designed kinds of novel accumulators with better performance in these specific areas. However, the pressure in these accumulators decreases significantly when the fluid oil is continuously supplied from the accumulator to the hydraulic system. This limitation leads to a transient large pressure drop, especially in a small hydraulic system with varied working frequency. In this research, a combined piston type accumulator is proposed with a relatively steady pressure property. The gas chamber and the fluid chamber are separated by a cam mechanism. By using the nonlinear property of the cam mechanism, the nonlinear relationship between the pressure and the volume of the gas can be offset. Hence, the fluid pressure can be maintained in a relatively steady range. The defect of the traditional accumulator in the frequency varied system is analyzed in detail. Then, the structure of the new accumulator is proposed and modeled based on the traditional piston type accumulator. The mathematical equation of the cam mechanism is built under the assumption that the nitrogen gas works in an adiabatic process. A simulation system based on the Amesim platform is constructed, and mathematic equations of the system are given. Preliminary experiments are conducted to evaluate the performance of the new accumulator. The comparison results show that the adaptability of the new accumulator is obviously larger than that of the traditional accumulator in a frequency varied system.
Highlights
A hydraulic accumulator is a rigid tank separated into two regions, one filled with nitrogen gas and the other filled with hydraulic fluid
Where P g and P f are the pressures of the gas chamber and the fluid chamber, A and f are the section area and the friction of the piston in the new accumulator, m gp and m f p are the piston masses in the gas chamber and the fluid chamber, J and ω are the moment of inertia and the angular acceleration of the cam mechanism, a gp and a f p are the accelerates of the two pistons in the gas chamber and the fluid chamber, v f p is the piston velocity in the fluid chamber where the velocity is positive when the gas expands, and sgn(x) is the step function as Equation (15):
Due to the friction between the piston and the cylinder, there exists energy loss at the new accumulator, efficiency new accumulator is lower than the traditional accumulator
Summary
A hydraulic accumulator is a rigid tank separated into two regions, one filled with nitrogen gas and the other filled with hydraulic fluid. Henderson designed a novel hydraulic power take-off system with a high pressure accumulator to convert the wave energy [3]. Van de Ven JD proposed a new hydraulic accumulator concept that could keep a constant pressure when it worked. By using a variable area piston and a rolling diaphragm, the accumulator could vary the equivalent section area of the gas chamber and keep the fluid pressure constant [17]. A combined piston type hydraulic accumulator working with low pressure drop is designed. The fluid pressures of the new accumulator with different pre-charge gas pressures are tested at a fixed flow rate.
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