PC200-7 hydraulic excavator fault repair explanation

- Nov 24, 2018-

The PC200-7 hydraulic excavator is a new product of Komatsu Corporation of Japan. The excavator's slewing mechanism uses a tilt-shaft type plunger motor to generate torque by reacting a high-pressure hydraulic oil on a reciprocating plunger. The drive shaft outputs power, and after being decelerated by the rotary reducer, the output power is applied to the swing support, so that the upper body of the excavator realizes the left turn and the right turn.

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1 swing lock function


When the operator puts the swing lock switch in the "ON" position, the brake piston of the swing motor and the friction plate are pressed by the spring force, and the upper body cannot be rotated.


1.1 Swing lock status


When the swing lock switch is placed in the "ON" position, the swing lock solenoid valve is de-energized, the spool is moved to the left by the spring force, and the oil of the swing motor MB port is returned to the hydraulic tank brake spring by the swing lock solenoid valve. The brake piston is pushed down and pressed against the friction lining to brake the motor.


When the swing lock switch is placed in the "OFF" position, the swing lock solenoid valve is energized, the spool moves to the right against the spring force, and the pressure oil from the self-pressure pressure reducing valve enters the swing motor MB port through the swing lock solenoid valve to overcome the system. The spring force of the spring pushes the brake piston upward, so that the friction plate is separated from the brake piston, and the brake is eliminated.


1.2 Swing operation


By manipulating the rotary handle, the pilot oil pressure reaches the two ends of the rotary main valve core through the rotary operation handle, and overcomes the force of the spring to move the main spool. The high-pressure oil formed by the main pump reaches the MA port of the motor through the main spool, and the pressure of the MA port rises, pushing the motor to start rotating. The low-pressure oil coming out of the motor returns from the MB port to the hydraulic tank through the main spool.


1.3 slewing stop


When the rotary operation handle is placed in the neutral position, the main spool of the rotary body returns to the neutral position under the action of the spring force, and the high-pressure oil coming out of the main pump cannot reach the MA port of the swing motor, and the hydraulic oil from the outlet of the swing motor MB is hydraulically rotated. The main spool is cut off. The slewing motor continues to rotate under the action of the inertial force, and the pressure at the MB port rises and is lower than the set pressure of the safety valve by 29 MPa, which produces a braking effect on the slewing motor. If the motor continues to rotate, the pressure exceeds 29 MPa and the high pressure oil pushes the shuttle valve 5, then opens the safety valve and simultaneously opens the suction valve 2, and the oil enters the MA port to prevent cavitation.


Author: digging machine House

Link: https://www.jianshu.com/p/35312f04130e

Source: Short book

The copyright of the book is owned by the author. Any form of reprint should be contacted by the author for authorization and the source.

2 Typical failure analysis


2.1 Excavator upper body can not be rotated


(1) Fault phenomenon:


When the excavator is working, other working devices are working normally, and only the upper body of the excavator cannot be rotated.


(2) Failure analysis:


According to the working principle of the excavator's swing motor, the fault of the excavator's ground rotation and the main pump, the self-pressure reducing valve, the rotary operating handle, the swing lock switch, the swing lock solenoid valve, the swing motor, the swing reducer, and the return bearing In accordance with the principle of simple to complex, in order to avoid unnecessary disassembly, causing unnecessary losses, the relevant components should be analyzed and eliminated one by one.


1Because the other working devices are working normally, the main pump and the self-pressure reducing valve share the components of the hydraulic part of the excavator, indicating that the main pump and the self-pressure reducing valve have not failed.


2 Ask the operator that there is no abnormal noise or vibration before the failure. According to experience, if the rotary reducer or the slewing bearing fails, abnormal noise or vibration will occur, thus eliminating the possibility of failure of the rotary reducer and the slewing bearing.


3 Measure the swing operating pressure. The pressure is 3.3 MPa, which is within the normal range. Check the main spool of the rotary, the main spool is flexible in the valve body, no stuck phenomenon, indicating that the main oil circuit can reach the swing motor smoothly.


4 Check the swing lock switch (in the OFF position), use the universal meter to measure the voltage across the switch is 24V, measure the resistance of the rotary lock solenoid valve coil, the resistance is the normal range, indicating that the coil has no open circuit or short circuit, and the work is normal. Connect the tee joint at the outlet of the rotary solenoid valve control oil line and connect a 4MPa pressure gauge to operate the excavator to rotate. The pressure is only 0.1MPa, which means that the oil pressure in the flow direction is too low to be used. Exclude the brakes so that the excavator cannot turn.


Author: digging machine House

Link: https://www.jianshu.com/p/35312f04130e

Source: Short book

The copyright of the book is owned by the author. Any form of reprint should be contacted by the author for authorization and the source.

(3) Troubleshooting:


When the swing lock solenoid valve was removed, it was found that the spool was stuck and could not move. After removing the spool, it was found that there was a small piece of broken O-ring inside. After cleaning each component, re-installing and testing the vehicle, and operating the rotary operation handle, the rotation operation is normal, and the fault is eliminated.


2.2 Upper body rotation angle is too large


(1) Fault phenomenon:


When the turning operation is finished and the operating handle is in the neutral position, the excavator is often too large under the action of the inertial force, and cannot be in the position that the operator wants to reach.


(2) Failure analysis:


According to the working principle of the swing motor, this fault phenomenon is caused by the lack of timely braking or insufficient braking force. It can be seen from the figure that it is related to the release of the brake oil pressure, the rotary lock solenoid valve, the rotary brake pad, the rotary brake seal and the like.


1 rotary lock valve circuit part. The line connection is reliable, there is no short (broken) way, the solenoid valve measuring coil and the spool work normally, indicating that the circuit part is not faulty.


2Measure the release brake oil pressure. The pressure measurement is 3 MPa, indicating that the pressure is normal, so the fault should be in the swing motor.


(3) Troubleshooting:


Remove the swing motor and check that the spring force is normal and there is no break; the seal ring on the brake platen is also intact; when checking the brake return line, it is found that there is a colloidal particle at the orifice of the return line, and the orifice It is not completely blocked, resulting in too slow oil return, prolonged time, and the time when the braking part acts accordingly, so that the slip amount (ie, the deflection angle) is too large when the turning motion stops. Clean the components, paying special attention to the orifice and the small oil passage. After each component is installed, the test is carried out, and the amount of slippage is within the specified range, so that the fault can be eliminated.


Author: digging machine House

Link: https://www.jianshu.com/p/35312f04130e

Source: Short book

The copyright of the book is owned by the author. Any form of reprint should be contacted by the author for authorization and the source.