How to troubleshoot the faults of the rotary motor of an excavator

Cause analysis

A hydraulic motor is an energy conversion device, that is, the input liquid pressure energy is converted into mechanical energy output. If the efficiency of the hydraulic motor itself is not taken into account, the input energy should be equal to the output. From this perspective, the weak rotation of the hydraulic motor must be due to the reduction of the energy input to the hydraulic motor. When the energy is difficult to overcome the resistance of the platform's rotation, the motor stops rotating.

According to the principle of hydraulic transmission, it is known that the hydraulic motor rotates by the pressure of the liquid. When the hydraulic motor stops rotating when the control valve is connected to the pressure oil circuit, it must be because the working pressure of the oil input into the plunger cylinder of the hydraulic motor is insufficient to overcome the resistance of the platform operation. When the accumulated energy is sufficient to overcome the resistance, the hydraulic motor jumps and rotates to overcome the resistance. The oil pressure in the system drops sharply again, and the motor stops. This process repeats itself, causing the platform to "crawl", or the resistance that prevents the hydraulic motor from rotating is too large, resulting in "crawling".

The excessive rotational resistance of the hydraulic motor leads to low mechanical efficiency of the motor itself. If the friction resistance between the plunger and the mating friction pair is too large, the friction resistance between the swash plate and the plunger is too large, the friction resistance is too large due to poor bearing, or the mechanical transmission efficiency of the transmission box is low. It could be caused by excessive mechanical frictional resistance of the platform's turntable.

Diagnosis and exclusion

If the large arm hydraulic cylinder of the working device is operating normally, the "crawling" fault of the hydraulic motor should occur at the end of the hydraulic motor and transmission, that is, the mechanical transmission box and the platform turntable part.

(1) Inspection of the safety valve of the hydraulic motor: Test and adjust the safety valve at the lower part of the hydraulic motor control valve. Unscrew the safety valve nut and use an internal hexagonal wrench to rotate and adjust the plug. Each full rotation changes the pressure by 2.345MPa. Therefore, the pressure gauge test should be 9.8MPa. If the pressure is lower than 9.8MPa, it indicates that the "crawling" fault is mostly caused by the set pressure of the hydraulic motor being too low.

(2) Check the hydraulic motor and mechanical transmission parts. If the set pressure of the safety valve of the hydraulic motor is 9.8MPs, it indicates that the "crawling" is due to excessive mechanical frictional resistance from the hydraulic motor to the rotary platform.

If you touch the housing of the hydraulic motor with your hand and feel it is hot, it indicates that the friction force of the hydraulic motor is too large, which proves that it is the cause of the "crawling" fault and should be eliminated.

If the temperature of the hydraulic motor is normal, you can check the temperature conditions of the transmission box and the turntable by hand, or observe the lubrication situation. If there are parts with a relatively high temperature and poor lubrication, it indicates that the main cause of the "crawling" fault is excessive frictional resistance and should be eliminated.