Analysis of the phenomenon of low speed and high torque hydraulic motor running weakly

In the late 1950s, the original low-speed high torque Hydraulic Motor was developed from a stator and rotor component of the oil pump, which was composed of an internal gear ring and a matching gear or rotor.

1、 Low speed high torque hydraulic motor has weak rotation

The hydraulic motor is an actuator, which is located at the end of the hydraulic transmission. It converts hydraulic energy into mechanical energy to make the platform rotate. This motor is a hydraulic motor with medium speed in point contact with the axial plunger.

1. Phenomenon

During operation, the rotating speed of the platform is lower than 6R / min

2. Cause analysis

The structure and working principle of hydraulic motor and axial piston pump are basically the same. Axial piston pump generates power through oil suction and oil pressure, i.e. converts mechanical energy into liquid pressure energy. The hydraulic motor enters the high pressure oil and discharges the low pressure oil, that is, the liquid pressure energy is converted into mechanical energy. Therefore, the hydraulic motor is essentially equivalent to the combination of multiple single cylinder plunger cylinders, that is, the multiple one-way cylinders are evenly distributed circumferentially, and the outer end of the plunger is against the swash plate. When the oil pump supplies pressure oil to the oil cylinder, the plunger extends under the action of pressure oil and slides down on the swash plate, thus generating a torque. The oil pump continuously supplies pressure oil to the hydraulic motor, and the hydraulic motor rotates continuously. The final drive gear is meshed with the internal gear ring fixed on the frame through the gear transmission box to drive the platform to rotate.

It can be seen from the above that the structure and working principle of the hydraulic motor are basically the same as the working principle of the aforementioned Hydraulic Cylinder. If the hydraulic motor has a fault of slow rotation speed, the analysis, diagnosis and troubleshooting methods are similar to those of the hydraulic cylinder and axial piston pump of the working device, so they will not be repeated here. Please refer to the above contents when analyzing, diagnosing and troubleshooting hydraulic motor faults.

2、 "Crawling" state of low-speed high torque hydraulic motor

1. Phenomenon

When the platform rotates, it stops and moves, that is, the rotation is discontinuous. Slow speed and insufficient strength.

2. Cause analysis

The low-speed high torque 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 is not considered, the input of energy should be equal to the output. From this, it can be seen that the lack of 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 rotation resistance of the platform, the rotation will stop.

According to the principle of hydraulic transmission, the hydraulic motor rotates by hydraulic pressure. When the hydraulic motor is stopped when the control valve is connected to the pressure oil circuit, it must be stopped because the oil working pressure input to the hydraulic motor plunger cylinder is insufficient to overcome the platform running resistance. When the accumulated energy is enough to overcome the resistance, the hydraulic motor will make the hydraulic motor jump and rotate to overcome the resistance. The oil pressure in the system will drop sharply and the motor will stop again. In this way, the platform will "crawl" or the resistance to prevent the hydraulic motor from rotating is too large, which will lead to "crawl". As for the decrease in the flow rate and working pressure of the input hydraulic fluid, please refer to the cause analysis and diagnosis of slow lifting of the boom cylinder.

In short, the "crawling" of the hydraulic motor makes the oil pressure in the system unstable. Most of the unstable oil pressure is caused by the air in the system. The reason for the air entering the system is the same as the first part.

The reason why the rotation resistance of the hydraulic motor is too large leads to the low mechanical efficiency of the motor itself. For example, 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 caused by the poor bearing is too large, or the mechanical transmission efficiency of the transmission case is low. Or the mechanical friction resistance of the turntable of the platform is too large.

3、 Diagnosis and troubleshooting

If the oil cylinder of the hydraulic working device also has the phenomenon of "crawling", the fault is in the general oil circuit of the Hydraulic System, the diagnosis shall be carried out according to the diagnosis method described in the first part of the boom oil cylinder lifting slowly, with emphasis on checking the cavitation, finding out the cause and troubleshooting.

If the boom hydraulic cylinder of the working device works normally, the failure of "crawling" of the hydraulic motor should be at the end of the hydraulic motor and transmission, i.e. the mechanical transmission box and the platform turntable.

(1) Inspection of hydraulic motor relief valve

Try to adjust the safety valve at the lower part of the hydraulic motor control valve. Unscrew the nut of the safety valve, rotate the adjusting screw plug with an Allen wrench, and change the pressure by 2.345mpa per turn. Therefore, the pressure gauge test shall be 9.8MPa. If it is lower than 9.8MPa, it indicates that the "creeping" fault is mostly caused by the low set pressure of the hydraulic motor.

(2) Check the hydraulic motor and mechanical transmission part. If the set pressure of the safety valve of the hydraulic motor is 9.8mps, it indicates that "crawling" is due to excessive mechanical friction resistance between the hydraulic motor and the slewing platform.

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

If the temperature of the hydraulic motor is normal, the temperature of the hand mold transmission box and the rotary table can be reused, or the lubrication can be observed. If there are parts with high temperature and poor lubrication, it indicates that most of the "crawling" faults are caused by excessive friction resistance, which should be eliminated.