Optimum design and control of hydraulic systems driven by swash plate pumps using vibration based diagnosis

摘要

Swash plate pumps are widely used to drive hydraulic systems, especially because they offer high specific power. In order to improve their performance and make them more reliable, it is necessary to reduce the flow fluctuations, incorporate a control system that is more responsive, and minimize vibration levels. Furthermore, the flow should be controlled according to load requirements and pipe response at the design level. Moreover, there is a need to monitor the health of the system by analysing its vibration signatures. A novel port plate design is used with a pair of deep silencing grooves on the edges of delivery and suction ports, which reduces the flow fluctuations and improves the pump output. In addition to the load information, the pipe dynamics are also used as a control input. Hence, pipe instabilities with different boundary conditions are studied, where simple, accurate and comprehensive expressions to describe the pipe instabilities are produced, solved, and plotted. In swash plate pumps, the control unit changes the pump output according to the load requirements. The current pump design is equipped with a double negative feedback strategy. The inner loop controls the spool position, and the outer loop controls the swash plate angle. Since this design has a high rise time, it was suggested to equip the pump with a single feedback PD controller. Although this reduced the rise time, it introduced high levels of vibration. The present research proposes a new control strategy with a single feedback PID controller that minimizes vibration levels. Results are obtained experimentally. The control strategy is generalized to control the pump flow according to load requirements and pipe vibration levels. A compensation factor is introduced to moderate the negative impact of the pipe vibrations, and to generate a new set value for the inclination angle. For timely detection of faults, the application of wavelet analysis to detect different defects is examined. Some defects are produced, such as pipe flutter, pump dynamic instability, and voltage unbalance in the driving electric motor. Continuous wavelet and discrete wavelet analyses are used to analyze the vibration signature by using Debauches' mother wavelet. The data is collected experimentally. The results show that wavelet analysis is very efficient at identifying defects in the pipe or pump. The results are discussed and appropriate conclusions are drawn based on the present research. Suggestions for future extensions of the research are proposed