The Research Of A New Load Sensitive Brake Valve

Hydraulic drive is based on oil as a medium for energy transfer and conversion and control. The hydraulic cylinder is the main actuators in hydraulic drive. However,when hydraulic cylinder with overloaded and high-speed need braking in an emergency situation, there are a big hydraulic impact with vibration and noise in the buffer cavity and vacuum causing cavitation in the oil cavity. In order to make hydraulic cylinder brake smoothly, there need to be setting buffer-brake system. So how to design brake-buffer system is important for this paper.The traditional buffer-brake device is divided into two kinds:in the cylinder and outside the cylinder. Buffer-brake in the cylinder is mainly for the end of cylinder; but emergency-brake at any position of entire stroke is achieved only outside thecylinder. So buffer-brake device is needed. In this paper, by understanding brake circuit of hydraulic press in all fields, six basic brake circuit were analyzed such as buffer-brake of reversing valve, buffer-brake of relief valve, buffer-brake of sequence valve, buffer-brake of proportional valve, buffer-brake of brake components. Analysis shows that buffer-brake of reversing valve can’t avoid the hydraulic impact, only for situation of low speed and light load; because of overshoot performance of overflow valve, impact is still very serious; due to the leakage of sequence valve itself,hydraulic cylinder can’t brake smoothly; using the brake, which rely on friction, isn’t satisfied for hydraulic cylinder; although using proportional valve can achieve ideal brake, it is too expensive to unfavorable to use; using brake components is equivalent to using overflow valve. Integrated the advantages and disadvantages of various braking ways, then the new load sensitive brake valve is put forward.The working conditions of a new type of hydraulic brake valve is divided into five stages:firstly, when the pressure in the buffer cavity do not reach its spring compression force, valve core keeps stationary; secondly, when pressure in the buffer cavity reaches spring force, as the pressure rises, the throttle valve core moves so that it can provide enough back pressure by increasing the effective length of throttle hole; thirdly, when reaching to the biggest displacement, the throttle valve cannot continue to move,and throttle hole length keep the maximum; fourthly, as the pressure in the buffer cavity drops, the throttle valve core move to the initial position to make back pressure falling; fifthly, because the throttle valve core goes back to the original position, oil pressure in the buffer cavity drop by fixed throttle opening.Through the analysis of working principle of the new type brake valve, the structure of the valve is designed. It consists of five parts: electromagnetic directional valve, shuttle valve, two check valves, load sensitive throttle valve, which load sensitive throttle valve core is the key part. By simulation to the buffer-brake process of new valve with MATLAB software, the structural parameters were optimized. The results show that no impact in the process of braking produce and the practical range is obtained.New load sensitive brake valve meet the requirements of brake system in a wide range, which can eliminate hard impact and reduce soft impact...