The article describes a new type of high-speed hydraulic switch valve, using giant magnetostrictive actuator and cone-spool structure. The valve has a high switching speed and frequency, can be used as a large flow speed switch valve of the pilot control valve can also be used directly as a control valve in the small flow loop.
Digital PWM pulse modulation control in the hydraulic system has a number of significant advantages, such as easy connection with the computer system is inexpensive, anti-pollution and anti-interference ability. But this control system requires a high-speed switching valves. The current domestic and development of some of the high-speed switch valve, mostly using the electromagnet as the drive, and therefore slow the switching speed of the valve; piezoelectric crystal type although the drive to improve the switching speed and frequency, but the required voltage is high, large power consumption. Therefore it is necessary to develop new types of high-speed switching valve.
In recent years, domestic and foreign giant magnetostrictive effect for rare earth iron compounds applied research attention. A magnetostrictive effect refers to the phenomenon of ferromagnetic material and the ferrimagnetic material will cause the volume and length of the small changes in the magnetic field effect. Ni and Co, Fe, rare earth compounds and amorphous alloys, magnetostrictive coefficient called giant magnetostrictive (giant magnetostrictive material short GMM), more representative for the Terfenol-D. The linear actuator made of this material has a variety of uses, wherein the electro - mechanical conversion means as a hydraulic control valve having a fast switching speed and high frequency, energy consumption, etc. characteristics.
Structure and working principle of the switch valve
Giant magnetostrictive actuator
Center of magnetostrictive material rod produced by the Beijing University of Science and Technology TbDYFe (φ12 × 110), its lower end clamped together, the upper end pass through the telescopic shaft and spring to the magnetostrictive material with prestressed. The magnetostrictive material around is generated driving field excitation coil and cooling coil with copper pipes. Peripheral yoke (carbon steel), it constitutes a closed magnetic circuit together with the magnetostrictive material, to leakproof magnetic. Telescopic transmission shaft and other parts are made of non-magnetic stainless steel. Super-magnetostrictive material internal strain and motivate the magnetic field strength, material properties constant state of stress is directly related to its external displacement, force output in fact the result of mutual coupling of the magnetic field - flexible field. Therefore, the appropriate configuration of the structural parameters of the mechanical and electrical (mostly pre-compressive stress, and the bias magnetic field), the super magnetostrictive material can be in the optimal electromechanical coupling state, to improve the energy conversion efficiency. When using alternating current excitation, the super magnetostrictive material in the positive and negative magnetic field under the action of an elongated, which generates the mechanical movement of the frequency is twice the frequency of the applied current, and this is the so-called "frequency doubling phenomenon. To enable the mechanical motion of the drive line for the interval, usually plus a bias magnetic field to eliminate this phenomenon. However, when the driver uses a the PWM pulse voltage excitation, since no negative magnetic field, does not appear multiplier phenomenon, it is not necessary to the bias magnetic field. The purpose of applying a suitable prestressed to the giant magnetostrictive material, avoid magnetostrictive material in a state of tension; can increase the amount of magnetostrictive. According to the ferromagnetic theory, this is to improve the saturation magnetization of the material due to an applied stress, and its saturation magnetic Rev. coefficient increased's sake.
The structure of the switching valve
Usually required as a hydraulic pilot valve spool smallest displacement of not less than 0.5mm. Giant magnetostrictive actuator output displacement amplification via a lever mechanism. Displacement amplification at the same time, the driving force of the spool are reduced. Giant magnetostrictive actuator without spring return spool driving force simply to overcome the friction can be the driving force does not require much. The switch valve is adapted from existing a two-way solenoid valve. The action of the spring to eliminate displacement enlarged gap between the lever and the other with the Department, so do not need a lot of stiffness coefficient.
The characteristic test of the switching valve
The characteristic test of the switching valve mainly includes the magneto the quiescent current of the drive - the output displacement, the output force and switching valve is turned on and off time test, the test is conducted under the conditions of the thermostat isolator.
Static magnetic drive current - output displacement, output force test
The magnetostrictive rod, the pre-pressure of 820N, i.e., when the input current is zero, due to the equivalence relation of action and reaction, the magnetically induced drive output force also for 820N. When the input current of 1550mA, the output force of 980N, the displacement output of 40 μm. The curve of the hysteresis, displacement and force output exists due to the material in the exciting current is positive and negative when not coincident. For the switching valve is controlled by the PWM signal, which itself is not a linear element, and therefore does not require the drive has a linear, require that when only the excitation current decreases inversely to 0:00, and the output displacement of the drive is also equal to zero. For the hysteresis, can also be in the end of each of the PWM control signal of a positive reverse through the program and a negative voltage to eliminate the remanence.
Switch valve opening and closing time
The opening and closing time of the switch valve measured by the test to have a major impact of the valve of static and dynamic performance, the opening and closing time of the switch valve is determined by measuring the strain step response. Signal generator to the switch valve the input square wave signal, and then obtaining the response curve of by strain test device measuring. The strain response of the rise time and fall time are substantially equal, and only about 0.5ms, but this time is the opening and closing time of the switch valve.
Summary
The hydraulic speed switching valve can be obtained by the test results above, the use of the super-magnetostrictive actuator to a shorter switching time and a higher switching frequency, and the power consumption is very low. PWM control for hydraulic systems able to obtain a higher level of control precision and economic efficiency. This article is only a preliminary study for further application there are a number of issues need to be addressed, such as: the hysteresis of magnetostrictive material output displacement amplification and temperature effects. It should be noted that this is a promising high-speed switch valve hydraulic.
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