Key points of swing hydraulic motor
Key points of swing hydraulic motor
(1) According to the selection of hydraulic system, only when the load swings, the swing hydraulic motor is selected as the executive component. However, the model, specification and manufacturer of the swing hydraulic motor are not as many as the general hydraulic components such as pumps, valves and continuous rotary motors, so designers often encounter difficulties in the selection.
Since the swing hydraulic motor is only an executive component in the whole hydraulic system, the type and main parameters of the swing motor must be selected according to the working pressure of the system, the available flow rate, the load conditions of the swing motor (actual load torque, maximum and minimum angular velocity, maximum swing angle) and the functional requirements (such as the necessity of holding the middle position to stop) (angle, torque, speed, etc.).
(2) The selection of structure type is mainly based on the angle and installation space. For the load with small swing angle, the vane type swing motor with smooth operation can be selected; when the swing angle is more than 310 degrees, the piston type swing motor can be selected. If the installation space is small and the torque is large, and the hydraulic system allows, the motor with higher working pressure can be selected.
(3) At present, the maximum angle of swing hydraulic motor is not more than 300 ° for vane type and 720 ° for piston type. If the blade type is used in series, a larger swing angle can be obtained. But the axial dimension will be increased, and the installation is complex and the cost is high.
Generally, the angle of swing hydraulic motor can not be adjusted. When the output shaft is directly connected with the load, the maximum angle should be equal to the maximum swing angle required by the load. Under special circumstances, the swing hydraulic motor with large swing angle can be selected, and the external electric travel switch can be installed, and the swing angle required by the load can be set by the positions of the two travel switches; or a carefully calculated limit block can be installed on the internal stop of the motor to limit the swing angle of the swing hydraulic motor. But this kind of method had better let the manufacturer to do, in order to avoid the problems such as leakage when disassembling the swing hydraulic motor.
(4) When the structure size of the swing hydraulic motor is determined, the output torque only depends on the working pressure and the mechanical efficiency of the motor.
The output torque of the swing motor should be slightly greater than the load torque (including the friction torque of the load, the torque caused by the weight of the load and the torque required to make the load obtain the necessary angular acceleration), otherwise, the load may not rotate or the speed may not reach the required speed. Some swing hydraulic motors, due to structural reasons, the output shaft will be subject to lateral force. At this time, measures should be taken in the installation and connection mode, so that the output shaft does not bear additional lateral force as far as possible. In order to improve the service life of the swing hydraulic motor, the rated output torque of the swing hydraulic motor can be about 20% higher than that of the load.
In the selection, if the working pressure of the system is less than the working pressure of the swing hydraulic motor, in addition to reducing part of the output torque of the swing hydraulic motor, it will only have a favorable impact on the use of the swing hydraulic motor. On the contrary, when the working pressure of the system is greater than that of the swing hydraulic motor, the working pressure of the system can be reduced to that of the swing hydraulic motor by installing a pressure reducing valve in front of the swing hydraulic motor. In this way, as long as the output torque can meet the load requirements, the swing hydraulic motor with lower working pressure can still be applied in the medium and high pressure system.
(5) The starting pressure and internal leakage of swing hydraulic motor are closely related to the sealing quality of its moving parts.
Sealing the moving parts tightly can reduce the internal leakage, but increase the starting pressure. High quality swing hydraulic motor, should start low pressure and internal leakage as small as possible. In addition to the strict geometric dimension and form and position tolerance of the working chamber, the surface roughness, sealing form, sealing material and the compression of the sealing parts of the working chamber should also have quite high requirements. When the swing hydraulic motor is used in the general hydraulic system, because the starting pressure is often small compared with the working pressure, it will not have a great impact on the output torque. The system flow loss caused by internal leakage is usually very small compared with the displacement of swing hydraulic motor, so they do not have to be the main consideration in the selection of swing hydraulic motor. But when the swing hydraulic motor is used in the electro-hydraulic servo system with high dynamic quality requirements or the system with high low-speed stability requirements of the load, we must pay attention to its starting pressure and internal leakage index, because they will have a bad impact on the dynamic quality of the servo system, especially the increase of internal leakage will cause the flow to overflow from the oil discharge chamber and reduce the speed of the load . Internal leakage often changes instantaneously and causes pressure change, resulting in undesirable torque change and unnecessary load acceleration. The research shows that the change of internal leakage is the decisive factor affecting the load stability at low speed. Especially when the load is large, even the swing hydraulic cylinder will crawl.
(6) Terminal buffer and stop (limit) measures swing hydraulic motor swing speed is usually low. When the load is small, the cylinder block itself can bear the impact force produced by the blade turning to the terminal position and touching the stop, without setting another buffer or stop (limit) device. But for large load, high speed (angular velocity ≥ 100). /s) In order to avoid the damage of the stop caused by inertia force, it is necessary to take buffer and stop (limit) measures. At this time, the buffer mechanism is generally set inside the cylinder block. When the impact force caused by high pressure and high speed is great, the reduction hydraulic circuit can be used outside the swing hydraulic motor, the flow valve can be installed, the small relief valve or sequence valve can be set at the oil inlet and outlet, and the accumulator can be installed in the pipeline to eliminate the impact of inertial force and hydraulic pressure. If necessary, install another mechanical stop (limit) device to force the load to stop.
(7) The selection and filtration of working medium should be carried out according to the requirements of the product manual. The type and brand of working medium should be selected and filtered. The filtration accuracy is generally 25 μ M. The working oil temperature should be controlled within 20 ~ 50 ℃.
(8) Installation and preservation
① During the transportation and installation of the swing hydraulic motor, the output shaft shall not have any external impact load, so as to avoid the deformation of the output shaft.
② The drain line must be connected to the tank separately.
③ Elastic coupling is recommended between the motor output shaft and its driving mechanism, and its coaxiality error is generally not more than 0.10 mm.
④ If it is not used for a long time, the internal working cavity of the motor should be filled with oil, and the oil inlet, outlet and drain ports should be blocked, and the leakage and dust prevention measures should be taken.