(1) The hydraulic motor needs to be positive and negative, and must have symmetry in the internal structure, and the hydraulic pump often rotates in one direction. In order to improve efficiency, most of them are asymmetrical. For example, gear pumps often use an asymmetrical unloading groove structure, while gear motors must use symmetrical; the vane groove of the vane pump often has an inclination angle on the rotor, and the vane groove of the vane motor must be arranged radially. Arrangement, the blade will be broken when reversed; the valve plate of the axial piston pump often adopts an asymmetric structure to reduce cavitation and noise, while the axial piston motor must adopt a symmetric structure.
(2) When determining the structure of the bearing and its lubrication method, the hydraulic motor should ensure that it can work normally in a wide speed range. When the motor speed is very low, if a dynamic pressure bearing is used, it is not easy to form a lubricant film , In this case, rolling bearings or hydrostatic bearings should be used. The hydraulic pump often runs in a certain high-speed area, and the speed hardly changes, so there is no such demanding requirement.
(3) In order to increase the starting torque of the hydraulic motor, the required torque pulsation is small, and the internal friction of the structure is small. Therefore, the number of teeth of a gear motor cannot be as small as that of a gear pump; the pre-tightening force during axial clearance compensation is also much smaller than that of the pump to reduce frictional resistance and increase starting torque.
(4) The hydraulic motor has no requirement for self-priming, but the pump must ensure this basic function. Therefore, it is impossible to use a point-contact axial plunger hydraulic motor (with no spring at the bottom of the plunger) as a pump.
(5) When the vane pump relies on the rotor to rotate, the centrifugal force thrown by the vanes makes the vanes close to the stator to seal the oil and form a working cavity. If it is used as a hydraulic motor, because there is no force to make the blades close to the stator when starting, and the working cavity cannot be closed, it cannot be started. Therefore, the vane motor must have a leaf pressing mechanism such as a swallow-shaped swing spring or a coil spring, which is exactly what the vane pump does not need.