1. Blade type
Due to the effect of 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 hydraulic motors generally require forward and reverse rotation, the blades of vane hydraulic motors must be placed radially. In order to ensure that pressure oil always flows through the root of the blade, a one-way valve should be installed on the passage from the return and pressure oil chambers to the root of the blade. In order to ensure that the vane hydraulic motor can start normally after the pressure oil is introduced, the top of the blade and The inner surface of the stator is in close contact to ensure good sealing, so a preload spring should be set at the root of the blade. Vane hydraulic motors have small size, small moment of inertia, sensitive movement, and can be used in situations with high commutation frequency; however, they have large leakage and are unstable when working at low speeds. Therefore, vane hydraulic motors are generally used in situations with high speed, small torque and sensitive action requirements.
2. Radial plunger type
The working principle of the radial piston hydraulic motor is that 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 extends outward and tightly resists the inner wall of the stator. There is an eccentricity in the cylinder. At the contact point between the plunger and the stator, the reaction force of the stator on the plunger is . 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, causing the cylinder to rotate. The cylinder block then outputs torque and rotational speed through the transmission shaft connected at the end face. In the case of one plunger generating torque analyzed above, since there are several plungers acting in the oil pressure area, the torque generated on these plungers causes the cylinder to 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 principle, in addition to valve-type flow distribution, other forms of axial piston pumps can be used as hydraulic motors, 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 swash plate are fixed, and the motor shaft is connected to the cylinder and rotates together. When the pressure oil enters the plunger hole of the cylinder through the window of the oil distribution plate, the plunger stretches out under the action of the pressure oil and is close to the swash plate. The swash plate generates a normal reaction force p on the plunger. This force can be decomposed are the axial component and vertical component Q. Q is balanced with the hydraulic pressure on the plunger, and Q causes the plunger to generate a torque against the center of the cylinder, driving the motor shaft to rotate counterclockwise. The total instantaneous torque produced by an 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 speed and steering. The greater the inclination angle of the swash plate, the greater the torque generated and the lower the speed.
4. Gear motor
In order to adapt to the forward and reverse rotation requirements, the structure of the gear motor has equal and symmetrical oil inlet and outlet ports and a separate external oil drain port to lead the leakage oil in the bearing part out of the housing; in order to reduce the starting friction torque, rolling bearings are used; in order to reduce the rotation Torque pulsation, the gear hydraulic motor has more teeth than the pump. Gear hydraulic motors have poor dry sealing, low volumetric efficiency, input oil pressure cannot be too high, and cannot produce 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 high-speed and small-torque situations. Generally used in construction machinery, agricultural machinery and mechanical equipment that do not require high torque uniformity.
5. High speed motor
Motors with a rated speed higher than 500r/min are high-speed motors. The basic forms of high-speed motors are gear type, vane type and axial piston type. Their main features are high rotation speed and small moment of inertia, which are convenient for starting, braking, speed regulation and reversing.
6. Low speed motor
Hydraulic motors with a speed lower than 500r/min are low-speed hydraulic motors. Its basic form is the radial plunger type. The main characteristics of low-speed hydraulic motors are: large displacement, large volume, low speed, and can be directly connected to the working mechanism without the need for a reduction device, which greatly simplifies the transmission mechanism. The output torque of the low-speed hydraulic motor is large, up to several thousand to Tens of thousands of Nm, so it is also called a low-speed high-torque hydraulic motor.
