From the concept of energy conversion, the hydraulic oil pump and Hydraulic motor It is a reversible hydraulic component, which can be transformed into the working condition of hydraulic motor by feeding running fluid to any hydraulic oil pump; Conversely, when the main shaft of the hydraulic motor rotates from the external torque, it can also become the working condition of the hydraulic oil pump. The reason is that they have the same essential structural factors - closed capacity that can be changed by cycle time and corresponding oil distribution mechanism. However, because the operating environment of the hydraulic motor and the hydraulic oil pump is different, and the basic functional requirements of the two are also different, there are still many differences between the hydraulic motor and the hydraulic oil pump of the same type. First of all, the hydraulic motor should be able to rotate forward and backward, so the structure inside should be symmetrical in center; The rotation speed range of the hydraulic motor is very large, especially for its lower standard stable rotation speed, so it generally uses rolling bearings or hydrostatic sliding bearings; In addition, because the hydraulic motor operates under the premise of input pressure oil, it does not need to have self-priming ability, but requires a certain degree of original tightness to supply the essential starting torque. Because of this kind of difference, the hydraulic motor and hydraulic oil pump are similar in structure, but cannot operate reversibly.

According to its structure, hydraulic motors can be divided into gear type, vane type, plunger type and so on. According to the rotation speed, hydraulic motors can be divided into high speed and low speed. In addition, if the rotation speed exceeds 500r/min, it belongs to High speed hydraulic motor In addition, those with rotation speed less than 500r/min belong to low speed hydraulic motors. The essential types of high-speed hydraulic motors are gear type, screw type, vane type and axial plunger type. The first characteristics of both are high rotation speed, small moment of inertia, convenient starting and braking, and high adjustment (speed regulation and reversing) sensitivity. Generally, the output torque of high-speed hydraulic motor is not large, so it is also called high-speed small torque hydraulic motor. The essential type of low speed hydraulic motor is radial plunger type. In addition, there are also low speed structural types in axial plunger type, vane type and gear type. The first feature of low speed hydraulic motor is large displacement, large volume and low rotation speed (sometimes it can reach a few revolutions per minute or even a few revolutions per minute), so it can be directly connected with the operating mechanism without requiring a reducer, The transmission mechanism is greatly simplified. Generally, the output torque of low speed hydraulic motor is relatively large, so it is also called low speed high torque hydraulic motor.