Study On Servovalve Spool Valve Overlap Value Hydraulic Measuring System And The Key Technics Of The System

Electro-hydraulic servo control system is widely applied in the navigating control field for astronavigation, navigation and aviation, and as the key part of electro-hydraulic servo control system, the performance of electro-hydraulic servovalve takes an important role on the servo control system. Spool valve is composed of valve spool and valve sleeve, and as the power stage of servo valve, it has a high degree of accuracy and is difficult for machining. The mate-grinding for axial mate dimension of valve spool and valve sleeve is the key process during machining, and the axial mate dimension is called as overlap values. Actually, overlap value reflects the opening state of spool's null position, and there are four orifices on a spool valve, so there are four overlap values. The overlap value is 1-2μm, and the tolerance is about±0.5μm. Generally, grinding on valve spool shoulder is the way for getting and adjusting the overlap value, which is ensured by the process of repeatedly measuring and grinding practically. Each valve spool or valve sleeve does not have the capability of interchangeable assembly, spool valve couple is made by so called matching part mate machining, so the spool null cutting and measuring are called as"mate-grinding". According to the above analysis, it is unable to calculate and control the overlap value by individually measuring the axial position dimension of throttling edge for each valve spool. Moreover, the method of measuring axial position dimension of each throttling edge for valve spool and the mate valve sleeve and calculating the overlap value is infeasible, and it is necessary to measure the relative opening state of working edge by assembling the valve spool and valve sleeve, so to measuring overlap value of spool valve is a difficulty in servovalve industry. At present, servovalves are mainly produced for military demands, which belong to small batch production and trial-manufacture, the produce of spool valve is the bottle-neck problem which decreases production efficiency. With the development of navigation and astronavigation industry, the large batch production of servovalves is bringing forward, and spool valve overlap measuring precision and efficiency has became the key point in servovalve machining process, the reaserch on the measuring technology for overlap value of spool valve has an important significance for increasing national defense strength and application foreground.This dissertation researches on the discharge characteristic of spool valve orifice, and analyzes the discharge characteristics of ideal orifice, and actual orifice which has round angle on spool working edge and diametral clearance using CFD numerical simulation method. In order to analyze effect of flow pattern change of fluid's contribution on orifice discharge coefficient, this dissertation develops a mathematic model about discharge coefficient versus Reynolds number, this model can be used to calculate discharge coefficient of spool valve fluid in the different flow patterns. Based on this foundation, obtains a new flow rate formula for orifice, which discards the impact of changing of flow pattern, and has a commonality for describing the discharge characteristic of spool valve orifice. And a verification experiment has been made to ensure the formula is correct.Based on thorough analyzing the disadvantages of the pneumatic measurement for servovalve overlap value, this dissertation proposes a flow measurement method adopted hydraulic oil as the measuring medium, which is called as flow hydraulic measurement method. For measuring the four discharge characteristic lines of spool valve, and then calculates overlap values by regression method. This dissertation develops the error model of overlap measurement, which divides the source of errors into structural errors and flow pattern errors. The structural errors come from the round angle and the diametral clearance of spool valve. The flow pattern errors are affected by fluid flow pattern, and an error compensation method was put forward for calculating overlap values.The present servovalve spool valve overlap value measurements and systems have low degree of precision and inaccuracy data for measuring large flow servovalves. In order to solve this problem, a new measuring system has be developed in this dissertation, which improves measuring precision, insures data accuracy, and can adapt to overlap value measuring for multi types of different flow range servovalve, improves the versatility of measuring equipment and realizes automatic measurement.Constant orifice differential pressure is the premise for high accuracy hydraulic measuring, so thorough analyse of orifice differential pressure control technology has been taken. Differential pressure control system is composed of a constant flow pump-electro hydraulic proportional safety valve system, using PID closed loop control method. On the basis of thorough analysis of pressure drop of flowmeter, in order to improve the controller performance, this dissertation develops a compound PID control strategy based on feedforward control, and a verification experiment is made for approving the validity and merits of this method.Hydraulic oil temperature is one of main influence factors for measuring, so this dissertation researches the hydraulic oil temperature control technology in detail. This dissertation develops a compressor-electric heater temperature control method, and considers the non-linearity time-variation feature in compressor refrigeration control, and a self-adapting fuzzy control algorithm has been utilized in compressor system superheat control. Quantization and proportion factors can be self-adjusted in this algorithm. And an evaporator superheat experiment is made. The control results between normal fuzzy controller and self-adapting fuzzy controller has been compared in this experiment.