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The Comparison of Guided Resistive Half-bridge in Two 2D Servo Valves

Author: FangYingGuo
Tutor: RuanJian
School: Zhejiang University of Technology
Course: Mechanical Engineering
Keywords: round pass 2D servo valve full arch 2D servo valve guided resistive half bridge dynamic response
CLC: TH137.52
Type: Master's thesis
Year: 2011
Downloads: 15
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Abstract

As a key component in an electro hydraulic servo system, electro hydraulic servo valve is a bridge between electrical components and hydraulic component. Its performances impact the system’s performance greatly. With the increasing demand of industrial development, an electro hydraulic servo valve which is of large flow, fast response, wide band width, high precision, strong anti pollution and low cost, is highly desired. It can be easily controlled by computer without D/A converter. 2D servo valve has a good linear repeatability, fast response, strong anti pollution, low zero leakage, and high precision. It is therefore widely used in electro hydraulic servo system.This thesis focus on two 2D servo valves, namely round pass and full arch types. The relationship between dynamic response and the change of resistive half bridge in these two servo valves are analyzed. Two non linear models are proposed based on the analysis, followed by the linearization of the model for round pass 2D servo valve. Simulations of the two valves are carried out based on the proposed non linear models. Simulations show: In full arch 2D servo valve, several factors such as the length of the sensitive cavity, the radius of the spool, system operating pressure has less compact on settling time compared with round pass one. The spiral pitch angle even has no impact on response time. However, the weight of spool and radius of small hole has more important impact in 2D full arch type. At a spool weight of 21.58g, the valve achieves the highest response time of 0.7ms, which is 30% less than round pass type. Finally, experimental results show round pass valve has a low zero leakage and the dynamic results (step response and frequency response) which agree well with simulations.The thesis is organized as follows:In chapter one, the organization and principle of 2D servo valve is reviewed, followed by the analysis of digital control components in electro hydraulic system. It is proposed that stepper motor is used in 2D valve as the component to do electric mechanic transfer, as well as the usage of continuous tracking algorithm.In chapter two, basic equations of the movement of 2D servo valve are derived. Based on the small hole flow equation in round pass 2D valve, several nonlinear models such as high pressure, low pressure small hole continuous equations and force balance equation of spool, are proposed. Similar work about full arch type is carried out as well. Finally, linearization is done for the model in round pass type servo valve to derive transfer function.In chapter three, simulations of the two valves are carried out to compare their different responses such as step response and frequency response at different input parameters. Full arch type usually has a faster response. For example, it reaches a settling time of 0.7ms when the weight of spool is 21.58g, compared with 1ms in round pass type.Chapter four presents the experimental results. Critical performances, such as zero leakage, static and dynamic response of round pass 2D servo valve are measured. It shows a good static repeatability (an accuracy of repeatability and precision within 1%), zero leakage (0.6L/min under a working pressure of 21MPa) and low step response time (about 8ms).

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CLC: > Industrial Technology > Machinery and Instrument Industry > Mechanical parts and gear > Hydraulic transmission > Hydraulic components > Hydraulic control valves
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