【正文】 , and the design to achieve the functional requirements, develop the system closedloop control of hydraulic systems, hydraulic systems used to satisfy the synchronization requirements of precision and control to achieve the fourwheeled vehicles in a controlled synchronous lifting height lifting range, to achieve safe and reliable control of the two front, two rear, two revolvers, two rounds of synchronous lifting the right and to ensure the accuracy of synchronous movements. To meet the synchronous lifting hydraulic system, the system needs to have synchronization control device to achieve synchronization. Synchronization of hydraulic system is currently running multiple control methods, mainly mechanical synchronization method, pump or motor parallel method, double rod cylinder in series, control valve, synchronizer, synchronization control valve circuit, servo and so on. According to the design of machinery and equipment requirements for the realization of a better twocar frontwheel, two rear, two revolvers, two synchronous lifting the right wheel, respectively, the flexible control, the design of the four hydraulic cylinders used for its intended to achieve their respective parts of the wheel lift and flexible control. Synchronization to achieve higher accuracy and more flexible control, the design does not use the traditional control valves to control, but intends to adopt more new electrohydraulic proportional control valve to control. Electrohydraulic proportional control valve is between the ordinary hydraulic valve and servo valve between a fluid control valves, servo valves with similar functions, but also has its specific advantages. Proportional solenoid valve is replaced by the proportion of ordinary hydraulic valve adjustment and control devices and form, it can be given input voltage or current signal proportional continuous, remote control of the direction of flow, pressure and flow. Reasonable use of electrohydraulic proportional control valve can improve the automation and accuracy, and simplify the system. Commonly used proportional valve can be divided into: proportional pressure valve, proportional flow valves and proportional directional valve three. The design uses electrohydraulic proportional control system, closedloop feedback control system, the detection by the sensor and fed back through the electrohydraulic proportional plc valve, electrohydraulic proportional control valve opening size corresponding to the achievement of the hydraulic cylinder to achieve synchronous lifting control accuracy. To ensure the hydraulic cylinder to achieve at work to ensure selflocking, hydraulic system should be in each cylinder fuel supply system with check valve to achieve selflock function to ensure the safety of hydraulic lifting platform. Overload protection to ensure the realization of the hydraulic system, hydraulic system relief valve in the hydraulic pump that needs to be installed to ensure the safety of the system to provide a certain pressure. Oil to the system to meet the system requirements to run and quality of hydraulic oil, hydraulic system should be in the inlet and outlet port to install filters. In order to meet the hydraulic system can be fully automated, the system of hydraulic directional control valve solenoid valve are used. In order to better respond to energy problems, you can, where necessary, instead of using the accumulator motordriven pump provides the pressure accumulator to provide the direct use of the hydraulic cylinder pressure to meet the relevant sport. In order to achieve selflocking hydraulic cylinder to the function of the hydraulic system in the bottom of each cylinder are equipped with check valve, check valve can achieve oneway selflocking, twoway munication function of the oil. In order to provide security to meet the hydraulic system pressure, not suddenly as high pressure hydraulic system of the adverse effects or even damage some of the hydraulic ponents, so as a safety valve with pressure relief valve to prevent hydraulic overload protection. In order to achieve automation of the hydraulic system to meet the simultaneous operation of the system is more accurate, and the realization of the system39。 Original Abstract Hydraulic lifting platform is a versatile crane lifting equipment, widely used in factories, docks, construction, transportation, sports, equipment maintenance and other highaltitude operations and maintenance. Existing hydraulic lifting platform there are many, can be roughly divided into: fourwheel mobile lifting platform, pushtype lift platform, car load lifting platform, fixed platform lift, scissor lift platform, fourpost lift The two column lift and so on. In recent years, with the rapid increase in the use of cars, China39。s booming auto industry, especially the car industry. This makes the auto repair industry has grown, demand for automotive maintenance equipment rapid expansion, but also the maintenance requirements in the automotive tools and equipment requirements on the increasingly high lift