The open center six-port valve hydraulic system must solve the problems of double pump confluence, linearity of simultaneous operation and operation, and meet the requirements of various operating conditions of the hydraulic excavator. It is difficult to achieve the ideal compound action. To this end, the designer used a lot of brains, thought about many measures, added various control valves, and also used various control methods, such as: linkage operation of the hydraulic system, setting the working conditions to be controlled by solenoid valves, of course It can also be controlled by a microcomputer. However, due to the characteristics of the hydraulic system of the open center six-way valve, it is difficult and undesirable to realize the compound action to meet the requirements of various operating conditions.To better meet the compound action requirements of various operating conditions, it is best to use the neutral position. Closed load sensing pressure compensation system, and make full use of electronic control technology. The characteristics of the hydraulic system for opening the center multi-way valve are summarized as follows.
1) The valve block of the multi-way valve and the fuel supply of the sub-pump, each valve group has two oil supply passages, a direct oil supply passage and a parallel oil supply passage. Straight through the oil supply channel can achieve priority oil supply, parallel oil supply channel can achieve parallel oil supply. When designing a multi-way valve, it can be flexibly applied to form a priority relationship or a parallel relationship between the valves.
2) In order to meet the complex operation requirements of multiple 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 often use single The check valve prevents oil from flowing back and forms a one-way channel. With this measure, the design freedom is greatly increased, and a more complicated oil supply relationship can be realized to meet the needs of the working conditions. There are three ways to operate the on-off valve:
①The pilot control oil of the control valve is operated in conjunction with the control. The pilot control oil controls the on-off valve while controlling the movement of the control valve stem.
②Adopt an oil passage in the control valve as an oil passage to control the on-off valve. In this way, the opening and closing of the on-off valve are also controlled while manipulating the operating valve.
③ Use solenoid valve to operate. In order to realize the complex fuel supply relationship, it is sometimes necessary to apply the above several on-off valve operation methods simultaneously.
3) When the central multi-way valve system supplies oil to multiple hydraulically acting components in parallel, it is necessary to solve the problem of who should give priority to oil supply, such as: boom priority, swing priority, etc.The solution in this system is to give priority to non-priority The oil supply oil channel plus a throttle device uses a fixed orifice or variable orifice. The fixed orifice has a simple structure, but the adjustment performance is poor, and it cannot adapt to the requirements of changing working conditions.The variable orifice has good adjustment performance and can adapt to the requirements of changing working conditions, but the structure is complicated. Generally, electro-hydraulic proportional control is required. Manual electric operation or microcomputer automatic operation.
4) Open center multi-way valves generally use double or triple pumps, and some hydraulically acting components (booms, sticks, and buckets) require large power to confluence and supply oil.The system uses two confluence methods:
①In-valve confluence: For example, the dual-pump confluence supplies a valve stem, and the valve stem controls the oil supply to the hydraulic confluence element required for confluence.The dual-pump confluence oil is supplied through a valve stem, and the diameter design of the valve stem needs to be considered The flow area required for multi-pump oil supply.
② Confluence outside the valve: For example, the double pumps respectively pass through a valve stem and confluently supply oil to the required hydraulically acting components outside the valve stem. In this way, a valve stem must be added to the control valve. And these two valve stems must be operated in conjunction. Obviously the control valve structure is more complicated 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) The linearity problem of walking when the working device operates at the same time, there are the following three ways in the open center multi-way valve system:
①Three pump system:
The left and right running motors are supplied with oil by a single pump, and the remaining one is for the working device.
②The two-position two-way valve is used to make the left and right walking motors form a parallel oil circuit. The structure of this method is very simple. The disadvantage is that walking and working are operated at the same time. Walking and operation are in parallel oil supply relationship, so the operation of the operating device will cause the walking speed fluctuation.
③ The straight-moving valve is used, and one pump is used for walking (parallel oil supply), and the other pump is used for operation. The two are independent of each other, so the movement of the operating device will not cause fluctuations in walking speed. When some straight-line valves operate at the straight-line position and move at the same time, the working oil path can supply oil to the walking through the one-way valve and the orifice, so that the excess oil in the oil path of the working device can be supplied to the walking motor to increase the walking speed.
