Created on:2021-08-28 09:59

Fault diagnosis and maintenance of marine hydraulic equipment_ Fault protection module of electro-hydraulic servo control system

Fault diagnosis and maintenance of marine hydraulic equipment_ Fault protection module of electro-hydraulic servo control system

(1) Application of fault protection module

① Multipoint coordinated loading fault protection module the obstacle protection module based on the principle shown in Figure L has been used in the mining structure multipoint coordinated loading system. The functions of this module are as follows.

a. Overload and load limiting protection. The two load limiting relief valves 5 and 6 on the module correspond to the two load chambers of the hydraulic cylinder respectively. Before the test, check and set each overflow valve according to the maximum load in the tension and pressure direction of each loading point. In order to improve the unloading accuracy of the system, the relief valve in this module adopts the similarity principle, that is, the pressure of the two load chambers of the hydraulic cylinder corresponds to the front and rear chambers of the relief valve respectively, and the effective area ratio of the two is similar.

b. Power off protection. When the system works normally, the solenoid valve 1 is energized, the two position six way valve 2 works in the left position, and the system oil pressure controls the hydraulic cylinder through the electro-hydraulic servo valve. If solenoid valve 1 is powered off, the spring force pushes the spool of valve 2 to the left, and each valve in the module is in the state shown in Figure L. As can be seen from figure L, the two load chambers of the hydraulic cylinder are connected with the oil return circuit through two position six-way valve 2 and one-way throttle valves 3 and 4, that is, the hydraulic cylinder is in the unloading state.

c. Unloading speed control. The load form of the system is generally elastic load or inertial load. In normal operation, the load can be reduced to zero as instructed. However, in case of failure state unloading or artificial emergency unloading, the unloading speed needs to be controlled in order to avoid load impact. Therefore, two one-way adjustable flow valves 3 and 4 are symmetrically arranged in the unloading circuit shown in Figure l to control the unloading speed by adjusting the flow rate in the load chamber of the hydraulic cylinder.

② 6-DOF motion platform hydraulic system protection module 6-DOF motion platform is composed of 6 hydrostatic supported high-precision electro-hydraulic servo cylinders. It is widely used in simulation training equipment such as ships and boats, as well as the moving parts of amusement facilities such as dynamic movies. As such equipment involves personal safety, hydraulic protection must be set to ensure that the moving platform can return to the initial state safely and smoothly.

Figure m shows a schematic diagram of non working state of fault protection module for electro-hydraulic servo cylinder of 6-DOF motion platform. During normal operation, solenoid valve 1 is energized, and the left control chamber of valve 2 is connected with low-pressure oil circuit through orifice 6. Since the right control chamber communicates directly with the pressure oil circuit, the pressure oil pushes the valve core to move left, and the valve 2 works in the right position to communicate the oil port of the two load chambers of the servo valve and the oil circuit of the load chamber of the hydraulic cylinder, and the hydraulic cylinder works according to the input command of the servo valve. The orifice 6 of the left control chamber of valve 2 and the low-pressure oil circuit plays a role in slowing down the left movement speed of the valve core, so as to reduce the pressure impact when the valve core is opened, which is very necessary for the servo system of the training simulator with high requirements for force interference. In case of power failure or emergency stop, even if solenoid valve 1 is in the power-off state (the pressure oil reaches the left control chamber of valve 2 through solenoid valve 1), since the two control chambers of valve 2 are designed to be differential, the area of the left chamber is large and the area of the right chamber is small, the oil pressure pushes the valve core to move to the right, makes valve 2 work in the left position, and cuts off the oil circuit between the servo valve and the hydraulic cylinder, At the same time, the high-pressure oil reaches the rod cavity of the hydraulic cylinder to force the piston rod of the hydraulic cylinder to retract. At this time, the rodless chamber of the hydraulic cylinder passes through the low-pressure oil circuit of throttle valve 3, and the retraction speed of the piston rod of the hydraulic cylinder is set by throttle valve 3. The purpose of differential design of switching valve 2 is to ensure reliable switching of valve core, that is, to ensure reliable retraction of platform.

③ Anti cavitation function module figure n shows the schematic diagram of a fault protection module of an electro-hydraulic servo steering system with anti cavitation function. The module can enable the steering gear to select servo valve control or manual valve control, and the conversion between them is realized through the on-off and power-off of hydraulic control valve 2 and solenoid valve 1. Similarly, in case of power failure, the steering gear can be automatically turned into manual operation through solenoid valve 1. Another function of this module is to have a good anti cavitation effect. In the general valve controlled cylinder system, installing a check valve with low opening pressure in both chambers of the hydraulic cylinder can play the role of anti cavitation. For the hydraulic steering system such as ship, the rudder surface is subject to large and frequent wave interference load, long hydraulic pipeline, large pressure fluctuation and other factors are the direct causes of cavitation in the system. Before effective anti cavitation measures were taken for the steering system, the cavitation was very serious, resulting in the scrapping of the steering gear and servo valve and great pipeline noise. According to the cavitation causes of the system, the anti cavitation Function Module shown in Figure n is designed. Its feature is that in addition to normal oil supplement to the steering gear, it can effectively prevent cavitation in the steering gear in case of pressure impact and negative pressure in the pipeline.

(2) Structural features of protection module

The hydraulic fault protection module is specially designed according to the requirements of the control object. Integrated structure is usually adopted in design. The oil circuit of the main manifold block shall have reasonable layout, appropriate diameter, small volume and good manufacturability. Each functional valve shall first be installed in threaded plug-in or plate type. Generally, the function valves with special requirements shall be designed by themselves, such as load limiting valves 5 and 6 in Figure L, anti cavitation unit 3 in Figure n, etc. The servo control system generally has bandwidth requirements, so the protection module should be installed directly on the hydraulic cylinder or as close to the hydraulic cylinder as possible. The oil circuit between the module and the load chamber of the hydraulic cylinder shall use a hard pipe. For power-off fault protection, small diameter two position solenoid valve shall be used as the monitoring element of system electrical signal. When the system works normally, the electromagnet shall be energized. For overload protection, a threaded plug-in overflow valve is generally installed on the oil circuit of the two load chambers of the hydraulic cylinder.

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