# Hydraulic Motor

#### 2023-08-16

We mentioned the displacement of the motor earlier, and this issue of Hanjiu will talk to you about the minimum stable speed. The definition of the minimum stable speed is based on the minimum speed at which the hydraulic motor does not crawl under rated load. What is the phenomenon of crawling? That is, when the working speed of the hydraulic motor is too low, it cannot maintain a uniform speed, thus entering an unstable state of moving and stopping.

One of the reasons for the crawling motion is that the magnitude of the friction force is unstable. We all know that the frictional force increases with the increase of the speed, but for the motor working in the static and low-speed region, the frictional resistance will not increase when the working speed increases, but will decrease, forming the so-called "negative characteristic". resistance. When the object is still or the speed is very low, the resistance is high, and the spring is continuously compressed to increase the thrust. Only when the spring is compressed to the point where its thrust is greater than the static friction does it begin to move. Once the object starts to move, the resistance suddenly decreases, and the object suddenly accelerates and jumps. As a result, the compression of the spring is reduced, and the thrust is reduced. When the thrust increases, the object jumps again, forming a state of moving and stopping as shown in the figure. For hydraulic motors, this is the phenomenon of crawling.

The second is that the leakage volume is unstable. The leakage of the hydraulic motor is not the same every moment, it fluctuates periodically with the change of the phase angle of the rotor rotation. Since the flow rate entering the motor is small at low speed, the proportion of leakage will increase, and the instability of the leakage will obviously affect the flow value participating in the motor work, resulting in fluctuations in the speed. When the motor is running at a low speed, the inertia of the rotating part and the load it carries is small, and the above-mentioned effects are more obvious, so the phenomenon of crawling occurs. The maximum operating speed of the hydraulic motor is mainly limited by the service life and mechanical efficiency. After the speed is increased, the wear of each kinematic pair will be intensified, and the service life will be reduced. If the speed is high, the flow that the hydraulic motor needs to input will be large, so the flow of each overcurrent part With a corresponding increase in flow rate, pressure loss also increases, resulting in a decrease in mechanical efficiency. For some hydraulic motors, the speed increase is also limited by the back pressure. For example, the crankshaft connecting rod hydraulic motor, when the speed increases, the oil return back pressure must be significantly increased to ensure that the connecting rod will not hit the surface of the crankshaft, thereby avoiding the impact phenomenon. As the rotational speed increases, the back pressure value required for the oil return chamber should also increase accordingly. However, excessively increasing the back pressure will significantly reduce the efficiency of the hydraulic motor. In order for the efficiency of the motor not to be too low, the rotational speed of the motor should not be too high.

Hanjiu Hydraulic Company Shijiazhuang Hanjiu Technology Co., Ltd. is a professional manufacturer of series cycloidal hydraulic motors and BZZ steering gears. The factory has dozens of high-quality professional engineering and technical personnel, and introduced a number of advanced machines in 2010. The production facility is a large factory in northern China, producing more than 300,000 units per year. Our factory specializes in designing and producing any type of motor and steering gear required by customers, from large to small, from low to high displacement, which can replace Danfoss, Eaton, M+S series models. Products are widely used in construction machinery, mining machinery, metallurgical machinery, petroleum machinery, agricultural machinery, injection molding machinery, fishery machinery and other fields.

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