Theoretical Research on Hydraulic Control of Electronically Controlled Hydraulic Actuator

Theoretical study on hydraulic control of electronically controlled hydraulic actuators Zhang Lin Coal Research Institute Tangshan Branch, Tangshan City, Hebei Province, 063012, qualitative impact and response characteristics.

1 Overview For most hydraulic control systems, the dynamic characteristics of the hydraulic power mechanism largely determine the performance of the entire system. The power mechanism can be divided into a basic type of valve-controlled motor valve-controlled hydraulic cylinder pump-controlled motor pump-controlled hydraulic cylinder according to different combinations of control elements and actuators. The 02 series electronically controlled hydraulic actuator developed by the Tangshan Branch of the Coal Research Institute is an automatic actuator for opening and closing and adjusting various valves. It adopts a pump-controlled hydraulic cylinder mechanism. This paper analyzes the control theory of the pump-controlled hydraulic cylinder of the product.

Control Theory Analysis of Pump-Controlled Hydraulic Cylinder 2.1 Basic Equation The above formula can obtain the total mass of the load after Laplace transformation, kg; 5 is the viscous damping coefficient of the piston and the load, N, Sm; is the spring stiffness of the load, Nm; F is any external load force acting on the piston. It is assumed that the internal and external leakage of the pump and the hydraulic cylinder are laminar flow; the connecting pipe is short, the pressure loss in the pipe, the mass effect of the fluid and the dynamics of the pipe are neglected; The pipes are identical, the total volume of the two chambers consisting of the pump cylinder and the pipe is equal, the temperature and volume elastic modulus of the oil in each chamber are constant, the pressure is evenly equal; the stiffness of the connecting member between the hydraulic cylinder and the load Very large, ignoring the effects of structural compliance. Bay 1 1 applies the continuity equation nvDv claw 3 to the high pressure chamber to the pressure of the oil chamber as the load pressure, the heart is the pressure of the return chamber, 3; the effective area of ​​the piston, 12; the displacement of the piston, 1; the hydraulic pressure Cylinder inlet chamber volume, 13; where the effective volume elastic modulus includes the air mixed into the oil and the mechanical flexibility of the working chamber, Nm2Pa; Clp is the internal leakage coefficient of the pump, 5 叩 is the external leakage coefficient of the pump, 13,3 is the internal leakage coefficient of the cylinder, 3,3; 06. For the external leakage of the cylinder is the Laplace transform, the block and transfer function of the 2.2 pump-controlled hydraulic cylinder are usually obtained, considering the return pressure. In the case where the corpse 2 is a constant, the item including the corpse 2 in the linearization analysis can be omitted. In addition, assuming that the total leakage coefficient is 6 =, +, then Equation 12 can be simplified as the block of the pump-controlled hydraulic cylinder can be listed by Equation 3 or 4. In general, the load spring stiffness is zero = 0, and the damping coefficient 0 is much larger than the decision, that is, the price 0 is far less than the equation 5 can be simplified to 4 for the power mechanism damping ratio, and the following two transfer functions can be derived from Equation 6. The transfer function with the displacement of the pump as the input is the dynamic compliance of the power mechanism. The transfer function of the pump-controlled hydraulic cylinder is composed of the integral link oscillation link and the amplification link, and its Bode 2. changes in the shape of the sex. Your changes move the amplitude-frequency characteristics up and down and change the crossing frequency, but the phase-frequency characteristics do not change. Gainable changes have a direct impact on system stability and accuracy.

2.3 Analysis of main performance parameters The transfer function of Equation 7 can determine the main performance parameters of the dynamic mechanism characteristics, such as gain natural frequency damping ratio. The following is an analysis of the 1 gain step, which is applied to the pump-controlled hydraulic cylinder system of the electronically controlled hydraulic actuator. The piston cylinder area of ​​the motor speed hydraulic cylinder is relatively fixed. In the design process, the selection of these two parameters is subject to The influence of other factors, after the system is determined, the gain is a relatively constant amount... The natural frequency of the natural frequency is caused by the interaction between the load mass and the hydraulic spring. The size determines the response speed of the system. The larger the response, the higher the response speed. Fast, therefore, measures should be taken to increase the natural frequency of the system. The main factor affecting the influence is that the effective volume elastic modulus of a liquid is proportional to a few. There are many factors affecting the 10,000. Among them, the air mixed into the oil has a large influence, which will greatly reduce the number. Generally speaking, the 10,000 e of the pure oil is 1 380 MPa, and the oil of the air mixed with 10 is about 690 MPa. The pressure is 4 MPa. Yes, it is necessary to take various measures to reduce the incorporation of air. The working chamber volume and the working area of ​​the hydraulic cylinder are inversely proportional to 71%, and proportional to 4%. Then, increasing the piston area can increase the value, but at the same time, 6 is also increased, and the increase of the piston area also leads to the overall Disadvantages such as increased weight and increased flow. Therefore, the design should be considered comprehensively. It should be noted that it is very advantageous to minimize the ineffective volume under the condition of ensuring the effective stroke of the hydraulic cylinder.

In addition to the price, the remaining parameters have been determined by other factors, so the value is mainly determined by 0 and the value. The total leakage coefficient is the sum of the internal and external leakage coefficient of the pump and the internal and external leakage coefficient of the hydraulic cylinder. After the design is completed, the coefficient is basically constant. This value is as small as the increase in leakage is not allowed. At the same time, the viscous damping coefficient of the hydraulic cylinder can not be very large, and the large value will cause the cylinder to generate a considerable amount of heat at high speed operation, thereby increasing the required power. Yes, the damping ratio of the pump-controlled hydraulic cylinder is substantially small and constant. This makes the system more susceptible to oscillations and affects the performance of the entire control system. It is often necessary to sacrifice part of the power to set the bypass discharge channel and the viscous damper to improve the response characteristics of the system.

3 Conclusion Compared with other power mechanisms, the hydraulic frequency of the pump-controlled hydraulic cylinder is lower, the damping is smaller but more constant, and the gain value is also constant. Therefore, the pump-controlled hydraulic cylinder is a relatively linear component and is not easily affected by the operating point. The impact is easy to achieve control. However, its dynamic stiffness characteristics and overall response characteristics are not as good as valve control systems, which determines that pump-controlled hydraulic cylinders can only be used in applications where accuracy and rapidity are not critical.

Like other power mechanisms, the selection of various parameters of the pump-controlled hydraulic cylinder should take into account the constraints of various factors, and consider the specific working conditions applied by the mechanism. In the design process, the load speed of the actual working conditions should be required. Determine the overall system control characteristics.

Drawn down. After the system is designed, the performance of the system is determined according to the parameters of the actual mechanism, and the design of the mechanism is revised according to the experiment. 2,314 responsible editor Zhao Hongxin