At present, the loader steering and working devices are controlled by the hydraulic system to complete the majority of the loader uses a dual-pump confluence system that does not turn when the loader steering hydraulic steering pump output hydraulic control system forced by the hydraulic valve All of the confluence to work hydraulic control system go. The system requires a high pressure and low flow when the loader bucket excavation material, while the current loader hydraulic control system provided by the quantitative pump is a high pressure and high flow, so a lot of hydraulic oil overflow pressure relief valve Back to the tank. As a result, the working hydraulic control system has low power utilization rate, large energy consumption and large pollution, meanwhile the heating of the hydraulic system causes the heat balance temperature of the hydraulic system to be too high, which affects the reliability of the hydraulic system and reduces the traction during operation of the loader performance. XCMG LW820G wheel loader steering system uses a dual-pump shunt pilot pressure unloading hydraulic system, which includes hydraulic steering gear, priority flow control valve, the pilot control unloading valve, limit valve and other components, the system The application greatly improves the performance of the whole machine and improves the reliability of the whole machine.
one. System Features:
1. The use of smaller flow of pilot oil to promote the flow of the main valve spool movement to control the steering pump over a large flow of pressure oil into the steering cylinder to achieve low pressure small flow control of high pressure flow purposes and reduce the operator's labor strength.
2. In addition to preferentially supplying the steering system, the steering excess oil can be merged into the work system to achieve double-pump confluence, reducing the displacement of the working pump, improving the reliability, saving energy and improving three items and performance.
3. Pilot oil-controlled unloader valve enables the steering pump to direct low-pressure unloading oil back to the loader excavator to improve the traction of the loader, and at the same time can satisfy the requirement of rapid raising of boom Request.
4. By unloading valve directly to the oil, reducing the system heat, improve the thermal balance of the system and improve system reliability.
two. System composition and working principle:
1. System composition
Under different working conditions, the basic structure of the control system is different.
2. Hydraulic system works:
The working unit control system is supplied by two oil pumps, the main pump P7600-F100 for controlling the movement of the boom and bucket cylinder, the pilot pump P124-G16 for controlling the proportional pilot valve and thus the main reversing valve Core displacement, to control the boom, bucket cylinder working speed. Pilot pump oil first into the brake valve, to ensure that the brake oil, the pilot system to provide control of oil, the oil through the pressure reducing valve to pilot control system required control pressure into the control circuit, Control the completion of the work of the device.
Pull the handle to move backward, the pilot oil into the proportional pilot valve, the pilot oil from the proportional pilot valve to control the main valve spool movement, the work of the pump into the boom cylinder oil boom boom . Proportional pilot pressure relief valve the greater the output pressure, the control of the main valve spool displacement greater the main valve flow through the greater the boom up faster. When the operating handle is pulled to the limit position, the limit electromagnet in the handle is energized and the handle is pulled in the limit position. When the boom is raised to the position limited by the boom upper limit switch, the handle limit electromagnet is de-energized, the handle automatically returns to the neutral position, and the boom is held in the defined position. If the boom needs to stay in a certain position during boom-up, the operator must be returned to the neutral position.
In the promotion and other operations, the pilot control valve unloading valve is closed, the steering pump to open the one-way valve to the work of the oil flow system, the working unit hydraulic oil increased to meet the needs of the operation of low-pressure high flow requirements, The boom lift and other operations to improve speed, shortening the cycle of operations, is an extremely efficient high-performance hydraulic system is extremely significant.
2.2 Bucket loading
Move the bucket control handle to the right, control pressure output from the proportional relief valve Pilot oil controls the bucket control spool in the main reversing valve to move the bucket cylinder to complete the loading action. In the excavation, loading operations, the pilot control oil to promote unloading valve spool movement, steering pump to the oil through the opening of the unloading valve spool directly unloaded back to the oil. So that the work flow to the hydraulic equipment to reduce, reduce the hydraulic load, this part of the power is assigned to the drive wheel.
At this moment, it meets the requirements of high pressure and small flow rate and large tractive force required by the operation, thus reducing the heat balance temperature and power loss of the system, improving the working efficiency of the machine, improving the traction force, and enabling the digging and loading capacity to be stronger.
Pilot-controlled unloading valve can automatically achieve double-pump confluence according to the operating conditions, direct unloading oil, reducing system temperature and power loss, improve the traction when the loader shoveling; When working, boom boom requirements.
Pilot control unloading valve in the solenoid valve is an option, the optional control signal can be used to achieve automatic unloading, the operator can send an electrical signal to the solenoid valve according to the actual conditions, the unloading valve spool open Unloading oil. This machine no use of electrical signals, but the direct use of pilot oil as the control signal also achieved good results.
XCMG LW820G Wheel Loader is a self-developed product. The dual-pump combined flow diversion and pilot pressure unloading technology has been successfully applied to the aircraft. It won acclaim for its outstanding performance, high work efficiency and good appearance.
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