Trouble description: When the excavator is started, it is found that the rotation has no action, and other actions are normal.
When the operating handle is placed in the rotary position, the control oil reaches the control valve, and the rotary valve stem is pushed so that the high-pressure oil provided by the rear working oil pump enters the rotary motor; at the same time, the oil path of the control oil return tank is cut off, so that the brake is released The pressure of the valve increases, pushing its valve stem to make another auxiliary pressure oil into the brake piston, opening the rotary brake device to make the rotary motor operate; the rotary motor outputs power through the pinion of the transmission, and the pinion gear is generated by the meshing of the rotary ring gear Swing action.
1. Failure cause analysis and inspection
Known from the working principle of the slewing mechanism, there are three reasons for the failure, namely the main working oil circuit, mechanical transmission and control oil circuit.
(1) Inspection of main working oil circuit
If the pressure of the main swing oil circuit is low, the swing operation will not occur. Measure the pressure of the main working oil system. There is an internal hexagonal oil plug at the pressure outlet of the rear working oil pump. After removing it, install a pressure gauge and operate the rotary handle to accelerate the diesel engine. The measured pressure reaches 23.5MPa, which is the normal work of the system. Pressure, indicating that the hydraulic components of the main working oil circuit are normal.
(2) Inspection of mechanical transmission part
The rotary motor outputs power through the pinion of the transmission, and the pinion rotates around the rotary ring gear. During this power output, if the meshed gears get stuck, there will be no rotary motion.
Generally, abnormal gear meshing will produce abnormal noise. Now the driver does not hear abnormal noise during rotation, so mechanical transmission failure can be excluded for the time being.
(3) Inspection of control oil circuit
Since the other actions of the excavator are normal, it means that the auxiliary oil pump that provides the control oil pressure works normally. There are three control oil passages for the swing action, namely the oil passages for controlling the rotary valve stem, brake release valve and parking brake piston. The specific analysis is as follows.
When operating the rotary handle, there is a strong oil flu when touching the pressure oil pipe of the rotary motor, indicating that the main working pressure oil has reached the rotary motor, the rotary valve stem of the control valve can be opened normally, and the control oil circuit works normally. Measure the oil pressure to the parking brake piston. Open the pipe joint of the oil path to the rotary motor, install the tee joint and pressure gauge, and the measured pressure reaches 4MPa, indicating that the pressure of the oil path is normal.
Measure the oil pressure to the brake release valve. Open the pipe joint of the oil path to the rotary motor, install the three-way joint and pressure gauge, the measured pressure is 0.4-0.6MPa, obviously this pressure is too low (normal working pressure should be 4MPa), unable to open the brake release When the valve is opened, the control oil of the other path will not flow into the brake piston, and the rotary brake device will not be opened, so the rotary will not move. There are two reasons for the low pressure of the oil circuit. One is the leakage of the control valve, so that the oil pressure of the brake release valve becomes low (connect the pressure gauge to the control oil pipe from the control valve to the brake release valve) On the pipe joint, the actual measured oil pressure is only 0.4-0.6MPa, indicating that the control valve has been judged to be leaking correctly); Second, the brake loosened valve has a large fit clearance due to wear and leakage (after disassembly inspection, the valve stem and The valve hole fits well, and there is no stuck phenomenon).
2. Troubleshooting
According to the analysis and inspection of the cause of the failure, the main cause of the failure is the leakage of the control valve.
Due to the difficulty in repairing, the control valve was replaced. After the repair, the swing movement returned to normal.
