The open center six way valve hydraulic system should solve the problems of double pump confluence, linearity of simultaneous operation and walking, meet the requirements of various operating conditions of hydraulic excavator, and it is difficult to realize the ideal compound action. For this reason, the designer has used a lot of brains and thought of a lot of measures, added various control valves, and also adopted various control methods, such as linkage operation of hydraulic system, setting operating conditions and controlling with solenoid valve. Of course, microcomputer can also be used to control. However, due to the characteristics of the open center six-way valve hydraulic system, it is difficult and unsatisfactory to realize the compound action to meet the requirements of various operating conditions. In order to better meet the compound action requirements of various operating conditions, it is best to adopt the medium closed load sensing pressure compensation system and make full use of electronic control technology. The characteristics of open center multi-channel valve hydraulic system are summarized as follows.
1) The valve group of the multi-way valve supplies oil to the block and sub pump. Each valve group has 2 oil supply channels, direct oil supply channels and parallel oil supply channels. The direct oil supply channel can realize priority oil supply, and the parallel oil supply channel can realize parallel oil supply. When designing multi-channel valve, it can be flexibly used to form a priority relationship or parallel relationship between valves.
2) In order to meet the compound action requirements of various operating conditions, simple on-off two position two-way valves and cartridge valves are also required to direct oil from one oil circuit to another, and check valves are often used to prevent oil backflow and form a one-way channel. With this measure, the design freedom is greatly increased, and more complex oil supply relationship can be realized to meet the needs of working conditions. The on-off valve can be operated in the following three ways:
① The pilot control oil of the control valve is used for linkage operation. The pilot control oil controls the on-off valve while controlling the movement of the control valve rod.
② An oil passage is added in the control valve as the oil passage to control the on-off valve, so that the on-off valve can be opened and closed while operating the control valve.
③ It is operated by solenoid valve. In order to realize the complex oil supply relationship, it is sometimes necessary to apply the above-mentioned on-off valve operation modes at the same time.
3) When the open center multi-way valve system supplies oil to multiple hydraulic acting elements in parallel, it is necessary to solve the problem of who gives priority to oil supply, such as boom priority, rotation priority, etc. in this system, the solution is to add a throttling device to the oil circuit with non priority oil supply, and adopt a fixed orifice or variable throttling orifice. The fixed orifice has simple structure, but poor regulation performance, which can not meet the requirements of working condition change. The variable orifice has good regulation performance and can meet the requirements of working condition change, but the structure is complex. Generally, electro-hydraulic proportional control needs to be adopted, which can be operated manually or automatically by microcomputer.
4) Two or three pumps are generally used to open the center multi-way valve. Some hydraulic acting elements (boom, stick and bucket) require large power and need combined oil supply. The system adopts two combined modes:
① Confluence in the valve: for example, the confluence of two pumps supplies a valve rod, which controls the oil supply to the hydraulic action elements required to confluence. The oil confluence of two pumps supplies oil through a valve rod. The pore diameter design of the valve rod needs to consider the flow area required for multi pump oil supply.
② Confluence outside the valve: for example, the two pumps flow through a valve stem respectively, and the confluence oil supply outside the valve stem is supplied to the required confluence hydraulic action elements. In this way, a valve stem must be added to operate the valve. And the two valve rods shall be operated in linkage. Obviously, the structure of the control valve is more complex and the volume is larger, but because the flow through the valve stem is a single pump flow, the valve stem aperture can be small, and it may be common with other valve stems
5) There are three ways to open the center multi-channel valve system:
① Three pump system:
The left and right traveling motors are supplied by a single pump, and the remaining pump is supplied to the operation device.
② The two position two-way valve is used to make the left and right traveling motors form a parallel oil circuit. This method has a very simple structure. The disadvantage is that the traveling and operation act at the same time, and the traveling and operation are in parallel oil supply relationship. Therefore, the action of the operation device will cause the traveling speed fluctuation.
③ The straight travel valve is adopted. One pump is used for traveling (parallel oil supply) and the other pump is used for operation. They are independent of each other. Therefore, the action of the operation device will not cause the fluctuation of traveling speed. When some straight travel valves operate and travel in the straight travel position at the same time, the operation oil circuit can supply oil to the travel through the one-way valve and orifice, so that the excess oil in the oil circuit of the operation device can be supplied to the travel motor to increase the travel speed.
