Main parameters and commonalities of hydraulic motors

创建于05.17

1.7.6 low speed stability and creeping phenomenon

The low speed stability of hydraulic motor is usually measured by the lowest stable speed.

(1) Minimum stable speed and speed pulsation rate the minimum stable speed refers to the minimum speed at which the speed pulsation rate of the hydraulic motor does not exceed the allowable value under the rated load after excluding the pulsation factors of the external input motor.

Speed fluctuation rate δ n (%) is the ratio of speed change amplitude ±△ n to average speed NAV, i.e

δn=±△n/nav                      (1-37)

For various hydraulic motors in different applications, the requirements of speed pulsation rate are different. However, the speed with angular velocity pulsation rate less than ± 10% under rated load is generally regarded as the lowest stable speed of the hydraulic motor. In engineering practice, the lowest speed of the hydraulic motor before crawling phenomenon (shaking or turning and stopping) observed by naked eyes is often regarded as the lowest stable speed of the motor.

(2) When the speed of the motor is low, the friction coefficient of the hydraulic parts increases gradually, and the friction coefficient of the hydraulic parts increases. The material and technological quality of sliding surface, structural form and viscosity of oil will play an important role in the occurrence of this instability.

The causes of low-speed crawling of hydraulic motor are: the leakage is unstable; the theoretical torque pulsation of hydraulic motor; the friction is unstable. The internal and external leakage of each friction pair of hydraulic motor is different at every moment. The leakage is related to the structure of motor, the clearance of friction pair, working pressure difference, liquid viscosity and other factors. With the decrease of the flow rate of the input hydraulic motor, the influence of the leakage flow pulsation on the output speed pulsation of the motor increases gradually. That is to say, when the motor speed decreases to the low speed state, the speed pulsation rate increases rapidly, and the motor appears unstable crawling.

Figure a shows the speed pulsation rate curve of the hydraulic motor. It can be seen that when the speed is less than 3R / min, the speed pulsation rate increases rapidly, so it can be determined that the minimum stable speed of the motor is 3R / min.

When the hydraulic motor with load works at a speed lower than the minimum stable speed, the friction increases and is unstable, and the system pressure fluctuates. At this time, the sliding surface of the force transmission parts of the hydraulic motor is easy to damage, which reduces the service life of the motor and directly affects the working quality of the host machine. Therefore, it is generally not allowed for the hydraulic motor to run in the crawling state for a long time.

(3) The minimum stable speed range of different types of hydraulic motors from the perspective of engineering practice, in order to expand the speed range of the motor, the smaller the minimum stable speed of the hydraulic motor, the better.

For hydraulic motors with different structures, the minimum stable speed ranges are as follows: gear motor is generally 200-300r / min, individual can be 50-150r / min; high speed vane motor is about 50-100r / min; low speed high torque vane motor is about 5R / min; multi action inner curve motor is about 0.1-lr / min; crankshaft connecting rod motor is about 2-3r / min; hydrostatic balance motor is about 2-3r / min; axial balance motor is about 2-3r / min The piston motor is about 30 ~ 50R / min, some can reach 1.2 ~ 5R / min, some can reach 0.5 ~ 1.5r/min.

In the design of hydraulic system, in order to reduce the minimum stable speed, it should be carefully considered. For example, by using the low speed control system of the hydraulic motor, the lowest stable speed of the inner curve motor can be reduced to 0. OLR / min.

1.7.7 vibration, noise and control

Hydraulic motor is also the main noise source of hydraulic system. Vibration and noise are also important indexes to measure the performance of hydraulic motor. Similar to hydraulic pump, the noise of hydraulic motor mainly includes mechanical noise and fluid noise.

The allowable noise value of hydraulic motor in China is specified in JB / T 8728-1998 low speed high torque hydraulic motor: for example, under rated conditions, the noise value of radial piston hydraulic motor with inner curve whose displacement is > 0.16-0.56l/r should be ≤ 82 dB (a); the noise value of axial piston hydraulic motor with double swash plate whose displacement is > 1.25-280l/r should be ≤ 80 dB (a).

From the perspective of selection, use and maintenance, the main ways to control the vibration and noise of hydraulic motor are as follows: give priority to low noise hydraulic motor; try to improve the processing and installation accuracy of hydraulic motor and its connecting parts to reduce the mechanical vibration and noise; make the high and low pressure oil switching process as mild as possible to avoid sudden hydraulic shock; reasonably configure the system pipeline, such as as as far as possible The larger diameter pipe is used to reduce the flow rate of oil in the pipeline, avoid sharp local resistance, and reduce the torque ripple of hydraulic motor; the leakage oil port of the motor is placed on the upper end of the shell, so that the rotating part is immersed in the liquid, so as to increase the anti vibration damping and reduce the vibration and noise of the motor.

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