1. Vane hydraulic motor

Due to the action of the pressure oil, the unbalanced force causes the rotor to generate torque. The output torque of the vane hydraulic motor is related to the displacement of the hydraulic motor and the pressure difference between the inlet and outlet of the hydraulic motor, and its speed is determined by the flow rate input to the hydraulic motor. Since the hydraulic motor is generally required to be able to rotate forward and reverse, the vanes of the vane hydraulic motor should be placed radially. In order to keep the pressure oil flowing at the root of the blade, a one-way valve should be set on the passage between the return and pressure oil chambers leading to the root of the blade. The inner surface of the stator is in close contact to ensure a good seal, so a preload spring should be set at the root of the blade. The vane type hydraulic motor is small in size, small in moment of inertia, and sensitive in action. Therefore, vane hydraulic motors are generally used in occasions with high rotational speed, small torque and sensitive action requirements.

2. Radial piston hydraulic motor

The working principle of radial plunger hydraulic motor, when the pressure oil enters the bottom of the plunger in the cylinder through the window of the fixed oil distribution shaft 4, the plunger protrudes outward and tightly supports the inner wall of the stator. There is an eccentricity in the cylinder. At the point where the plunger contacts the stator, the reaction force of the stator to the plunger is . The force can be decomposed into two components and . When the oil pressure acting on the bottom of the plunger is p, the diameter of the plunger is d, and the angle between the force and the force is X, the force produces a torque on the cylinder body, causing the cylinder body to rotate. The cylinder block then outputs torque and rotational speed through the transmission shaft connected at the end face.

In the case of a plunger generating torque analyzed above, since there are several plungers acting in the oil pressure area, the torque generated on these plungers all make the cylinder rotate and output torque. Radial piston hydraulic motors are mostly used in the case of low speed and high torque.

3. Axial piston motor

In addition to valve distribution, other forms of axial piston pumps can be used as hydraulic motors in principle, that is, axial piston pumps and axial piston motors are reversible. The working principle of the axial piston motor is that the oil distribution plate and the swash plate are fixed, and the motor shaft is connected with the cylinder to rotate together. When the pressure oil enters the plunger hole of the cylinder block through the window of the oil distribution plate, the plunger stretches out under the action of the pressure oil, and a normal reaction force p is generated on the plunger against the swash plate and the swash plate, which can be decomposed into Axial force component and vertical force component Q. Q balances the hydraulic pressure on the plunger, and Q causes the plunger to generate a torque to the center of the cylinder, driving the motor shaft to rotate counterclockwise. The instantaneous total torque produced by the axial piston motor is pulsating. If the input direction of the motor pressure oil is changed, the motor shaft will rotate clockwise. The change of the swash plate inclination angle a, that is, the change of the displacement, not only affects the torque of the motor, but also affects its rotational speed and steering. The greater the swash plate inclination angle, the greater the torque and the lower the rotational speed.

4. Gear hydraulic motor

In order to meet the requirements of forward and reverse rotation in the structure of the gear motor, the oil inlet and outlet are equal and symmetrical, and there is a separate oil leakage port to lead the leakage oil of the bearing part out of the casing; in order to reduce the starting friction torque, rolling bearings are used; in order to reduce the torque A pulsating gear hydraulic motor has more teeth than a pump.

The gear hydraulic motor has poor dry sealing, low capacity and rental efficiency, and the input oil pressure cannot be too high and cannot generate large torque. And the instantaneous speed and torque change with the position of the meshing point, so the gear hydraulic motor is only suitable for occasions with high speed and small torque. Generally used in construction machinery, agricultural machinery and machinery and equipment that do not require high torque uniformity.