Research On Digital Valve Control Axial Piston Pump

Digital pump has anti pollution ability, high repeatability, hysteresis is small, flexible adjustment, low energy consumption, can be combined with other hydraulic equipment to realize the mechanical electrical hydraulic integration, then digital control mode of hydraulic pump has step digital control, inverter control, combination of cylinder control and high speed on-off valve control. The most representative is Rexroth SYDFEC system which adopts high frequency response of electrohydraulic proportional valve as a pilot valve for axial plunger pump pressure and swash plate angle closed loop control system of digital electro-hydraulic. Compared with proportional valve, servo valve and digital valve serve as a pilot valve to control hydraulic pump is advantageous, its degree of pollution standards is low, and easy to realize direct digital control with microcomputer, also getting the ideal constant power hyperbolic characteristics.The First time, introduces the application of digital valve, PWM high speed on-off valve(referred to as digital valve) structure, established the mathematical model of the digital valve. The simulation model of dynamic digital valve under the environment of AMESim, got the static characteristics(no-load), completed control with the duty ratio of linear interval moderate; step response,is on the basis of less than the critical frequency, with the pulse width modulation frequency increases, the linear range is reduced, according to the actual situation, selected the appropriate modulation frequency.The Second time, Based on the PWM digital valve control variable axial piston pump, build digital mathematical model of valve controlled cylinder, the pump output flow and enter the duty ratio of the relationship between the transfer function, can achieve the digital control of valve controlled cylinder closed loop, design of digital pump pressure, flow and power of the double closed loop control strategy, combined with the double closed loop control strategy, build the dynamic simulation model of digital pump pressure on power, flow, power under the environment of AMESim, build digital pump controller-fuzzy adaptive PID controller in the Matlab/Simulink environment, combined with the dynamic simulation of the hydraulic system is established with AMESim, get the constant power stage static curve is relative ideal hyperbola, constant pressure control stage, compared with the machine hydraulic control constant pressure control, the elimination of certain pressure difference. The characteristics of fuzzy PID control is better than PID control, the adjustment time is reduced and the response speed is improved to a certain extent. The linear relationship between the swash plate angle and pump outlet flow is effected by the amount of pressure changes caused leakage of flow, by adding duty ratio of compensation, further optimization of the compensation control.In a word, compared with a single closed loop control, the double closed loop can get the steady-state response of the dynamic balance at the set value fluctuates of near relative reduced, reducing the abrasion caused by ripple, improve stability and the difficulty of input and output analysis. Adding duty ratio of compensation, the average flow of output value fluctuation range decreased and the response speed is improved, compensating the value of flow, further optimization of the compensation control, improve the response of speed.