Research On Characteristics Of Low-Speed-High-torque Hydraulic Motor With Digital Distribution And Speed Adjusting Mechanism

As a hydraulic actuator, the characteristic of the low-speed-high-torque (LSHT) hydraulic motor make this type of hydraulic motor widely used in the engineering machines. To these hydraulic motors, the distribution mechanism is the key component. The shaft distribution and plane distribution mechanisms are the commonly used ones in the LSHT hydraulic motor. However, these two types not only have complex structure and high machining cost, but also have low efficiency. In addition to that, the traditional distribution mechanism can only realize the distribution task. In the case of speed adjusting, the hydraulic motor need extra component such as electro-hydraulic servo valve or electro-hydraulic proportional valve to work together, resulting in high system cost and complexity. Therefore, this paper proposes a solution of hydraulic motor using the high speed on/off solenoid valve (HSV). This hydraulic motor has a digital distribution mechanism which has ten high speed solenoid on/off valves to replace the traditional ones. With computer control technology, this new distribution mechanism can not only overcome the natural disadvantages of the shaft and plane distribution mechanism, but also fulfill the distribution and speed adjusting of bi-direction. For the sake of distinction, the hydraulic motor with the digital distribution and speed adjusting mechanism is named as new type hydraulic motor.Around the new type hydraulic motor, this paper analyzes the operating principle of the new distributor based on the mechanical structure of the plane distribution mechanism on the traditional hydraulic motor. Then the mathematical model is established by analyzing the piston kinematics and torques. The related simulations including distribution characteristics, static and dynamic speed adjusting characteristics, low speed characteristics are conducted. In order to validate the simulation results, the model machine and the measurement & control system are developed. The experimental research including distribution characteristics, speed adjusting characteristics and low speed characteristics are carried out. The main work is listed as follows:1) The operating principle of digital distribution and speed adjusting mechanism for the new type hydraulic motor is studied.The distribution rule of the plane distribution mechanism is obtained through the analysis of the crank shaft and connecting-rod type radical plunger hydraulic motor (JMDG1) which is made in China. Two solutions for the new type hydraulic motor are proposed and their advantages and disadvantages are compared. Then, the distribution tables for the counter-clockwise rotation (CCW) and clockwise (CW) rotation and the working angle sections for each plunger are derived from the selected schematic of the new hydraulic motor. The implementation method of speed adjusting is introduced based on the principle of PWM (Pulse Width Modulation) signal. Therefore, the basis for the model study and the development of the model machine is established.2) The static and the dynamic mathematical models of the new type hydraulic motor are established.The model of the high speed solenoid on/off valve is identified using the RBF (Radical Basis Function) artificial neural network. The input variables are the frequency and duty cycle of PWM signal and the output variable is the flow rate. Then the static mathematical model is obtained through the analysis of the kinematics and the delivery capacity for plunger. The dynamical mathematical model is established by studying the forces on each plunger and analyzing the process of high pressure oil from flowing through the HSV to form the torque. The unknown parameters related to the hydraulic motor are also identified from the experimental results using Laplace method. These mathematical models provide the theory for computer simulations of all characteristics.3) The simulation and analysis for distribution characteristics and its influence factors of the new type hydraulic motor are conducted.The distribution characteristics and its influence factors including initial control volume of plunger, absolute rotary encoder and HSV of the new hydraulic motor for CCW rotation are analyzed based on the dynamic mathematical model. The main influence of initial control volume is the ripple of speed between every distribution process. The resolution of absolute rotary encoder has obvious effect on the switch point during distribution process and the angle error for placement will influence the load capability of new type hydraulic motor. On the side of HSV, the open and close delay time and the different flow rate are studied. Finally, the distributions for CCW and CW rotations are compared and the switch process between these two rotations is analyzed. These simulations provide the guidelines for model machine of new type hydraulic motor.4) The simulation and analysis for speed adjusting characteristics and low speed characteristics of the new type hydraulic motor are carried out.The speed adjusting characteristic of the new type hydraulic motor is demonstrated based on the static mathematical model. The rotary speed under different duty cycle is given. A compensation method named match duty cycle method is proposed for eliminating the mutation of speed. The influence of duty cycle and switch frequency for HSV, damping coefficient, inertia and torque of extern load are simulated for CCW rotation. In addition to that, the low speed characteristics considering the nonlinear friction are also studied. The simulation results show that the new type hydraulic motor not only has convenient speed adjusting method but also lower speed. These results demonstrate that the new hydraulic motor has more merits than the traditional hydraulic motor and provide the guidelines for experiments on model machine.5) The model machine and its measurement & control system based on PC are developed.The HSV is selected after considering the rated flow rate and open and close delay time; the absolute rotary encoder is chosen with considering the resolution and dimension. The digital distributor is designed based on the characteristics of traditional plane distribution on JMDG1 hydraulic motor. Another important component such as distribution connect shaft is designed and finally the model machine is developed. The hardware system includes encoder signal acquisition and conversion module, the digital output drive module. The software system includes angle detection & distribution module, PWM module and other auxiliary module. The model machine provides the platform for the experimental research of the new type hydraulic motor.6) The experimental research and application research about constant speed control of the new type hydraulic motor is conducted.The experimental research including distribution characteristics, speed adjusting characteristics and low speed characteristics are carried out on the model machine. The experiments for distribution characteristics include the influence of angle error for absolute rotary encoder and the distribution switch process. The experiments for speed adjusting characteristics include the duty cycle and frequency of HSV and torque of extern load. The experiments for low speed characteristics focus on the speed of new type and traditional hydraulic motor when working at low speed, especially the lowest speed. Besides, the comparison of efficiency between new and traditional hydraulic motor are also conducted. The experimental results show that the operating principle of the new type hydraulic motor is correct and the basic characteristics of it are superior to the traditional one. Compared to the simulation results, the mathematical model of the new type hydraulic motor is reasonable. Therefore, this model provides the theory tool for develop digital distribution and speed adjusting hydraulic motor of another type.At last, the experiments about constant speed control are conducted and the experimental results shows that the new type hydraulic motor can fulfill constant speed control without extra speed control valve. Therefore, the new type hydraulic motor has the two functions of distribution and speed adjusting is convinced.The works accomplished and the conclusions obtained above can provide the basis for the further study on the digital distribution and speed adjusting hydraulic motor. The techniques of digital distribution and speed adjusting can be applied to more objects with the development of HSV.