Some Common Faults of Hydraulic Motors

The hydraulic motor is an executive element that converts the hydraulic energy output by the hydraulic pump into mechanical energy. Theoretically speaking, the hydraulic motor and the hydraulic pump are reversible, and their structure is basically the same. The fault diagnosis and elimination can refer to the method of the hydraulic pump. However, in practice, hydraulic motors and hydraulic pumps of the same type have different structures due to their different use purposes. In order to understand the cause of the failure, it is necessary to understand the difference between the two.

The speed range of the hydraulic motor is very wide, requiring low-speed stability and large starting torque. The hydraulic pump generally has a high speed, and the structure of the hydraulic pump must ensure the self-priming capacity, while the hydraulic motor does not have such a requirement. The point-contact axial piston hydraulic motor has no spring at the bottom of the piston and cannot be used as a hydraulic pump because it has no self-priming ability.

For the above reasons, in fact, many types of hydraulic pumps and hydraulic motors cannot be used in reverse, so their failure causes and diagnosis are not the same.

The special problems of hydraulic motors are the problems of starting torque and starting efficiency, which is also related to the failure of the hydraulic system.

The common fault analysis of hydraulic motor is as follows.

1. The Hydraulic Motor is Weak in Rotation or Slow in Speed

This kind of failure is often related to the output power of the hydraulic pump. Once the hydraulic pump fails, it will directly affect the hydraulic motor. The reasons are:

(1) The outlet pressure of the hydraulic pump is too low. Except for the insufficient adjustment pressure of the relief valve or the failure of the relief valve, the reasons are all on the hydraulic pump. Due to the insufficient outlet pressure of the hydraulic pump, the hydraulic motor is weak in rotation, so the starting torque is very small, and there is even no torque output. The solution is to eliminate the cause of insufficient pressure generated by the hydraulic pump.

(2) Insufficient flow rate The insufficient oil supply of the hydraulic pump and the low outlet pressure lead to the insufficient output power of the hydraulic motor, so the output torque is small. At this time, the oil supply of the hydraulic pump should be checked to find the cause of insufficient oil supply and eliminate it.

2. Hydraulic Motor Leakage

(1) The leakage of the hydraulic motor is too large, and the volumetric efficiency is greatly reduced. The leakage is unstable, causing the hydraulic motor to vibrate or stop when turning (that is, crawling). The size of the leakage is related to the working pressure difference, the viscosity of the oil, the structure of the hydraulic motor, the size of the displacement and the quality of processing and assembly. This phenomenon is more obvious at low speed because the flow into the hydraulic motor at low speed is small and the leakage is large, which is easy to cause speed fluctuations.

(2) External leakage will cause the braking performance of the hydraulic motor to decrease. When the hydraulic motor is used to lift heavy objects or drive the wheels, in order to prevent the heavy objects from automatically falling or the wheels automatically sliding down on the slope, there must be certain braking requirements. After the oil inlet and outlet of the hydraulic motor are cut off, in theory, the motor should not rotate at all, but in fact it is still rotating slowly (that is, there is external leakage). The slow falling of heavy objects or the sliding of the vehicle on the slope will cause an accident. The solution is to check the sealing performance, select hydraulic oil with appropriate viscosity, and set up a special braking device if necessary.

3. Hydraulic Motor Crawling

Hydraulic motor crawling is one of the faults that are prone to occur at low speeds. The minimum stable rotational speed of the hydraulic motor refers to the lowest rotational speed at which the creeping phenomenon does not occur under the rated load. The reasons why the hydraulic motor crawls at low speed are:

(1) The size of frictional resistance is uneven or unstable The change of frictional resistance is related to the assembly quality of the hydraulic motor, the wear of the sliding surface of the parts, the lubrication condition, the viscosity of the hydraulic oil and the degree of pollution.

(2) The leakage is unstable, which leads to the creeping phenomenon of the hydraulic motor. At high speed, because of its large rotational inertia, crawling is not obvious; while at low speed, the inertia is small, and the phenomenon of uneven rotation, jitter, or crawling when moving and stopping will obviously occur.

In order to avoid or reduce the creeping phenomenon of the hydraulic motor, the maintenance personnel should timely judge the friction and wear of the hydraulic motor according to the abnormal changes in temperature and noise, so as to ensure that the relative moving surface has sufficient lubrication; select the appropriate oil and keep it clean; Keep a good seal, check the leaking parts in time, and take leak-proof measures.

4. Hydraulic Motor Void and Impact

For some hydraulic motors, such as crank-link hydraulic motors, due to the increase of the rotational speed, the connecting rod will sometimes be close to the surface of the crankshaft and sometimes be separated from the surface of the crankshaft. Another example is when the multi-action inner curve hydraulic motor performs the return movement, the plunger and the roller will be separated from the surface of the guide rail (ie, empty) due to the inertial force. In order to avoid collision and voiding, the back pressure of the oil return chamber must be guaranteed.