Development history and application fields of hydraulic motors

The original model of hydraulic motor can be traced back to the Chinese water wheel (also known as "water wheel") in 100 BC. The water wheel is a power device that rotates with the power of running water; in ancient China, it was very common to use water wheels to drive irrigation machinery and spinning wheels. Before the 19th century, the development of hydraulic motor technology was relatively slow. With the rapid development of hydraulic transmission and control technology and hydraulic pumps in the 19th and 20th centuries, especially in the 20th century, the need for a rotary output mechanism with specific performance requirements in the hydraulic system has become more and more urgent, which has promoted the rapid development of hydraulic motors. Now, hydraulic motors have become one of the two major output actuators in hydraulic transmission systems. They are widely used in industry, engineering machinery, agriculture, forestry, fishery, military, aerospace and other fields.

It is generally believed that hydraulic motors are nothing more than hydraulic pumps that perform reverse energy conversion, but this is only a superficial and one-sided understanding. Hydraulic pumps and hydraulic motors are reversible in principle, that is, any type of positive displacement pump can be used as a positive displacement hydraulic motor, and vice versa. However, pumps and motors have many differences in working requirements. For some hydraulic pumps or hydraulic motors, in order to improve their respective performance (such as efficiency, rated speed, rated torque, low-speed stability, etc.) to adapt to different applications, the corresponding types of hydraulic pumps and hydraulic motors are still different in their specific structures. The main differences in their structures are:

Hydraulic motors need to rotate forward and reverse, and must have symmetry in their internal structure, while hydraulic pumps usually rotate in one direction and are mostly asymmetric to improve efficiency. For example, gear pumps often use asymmetric unloading groove structures, while gear motors must use symmetric ones; the vane grooves of vane pumps often have an angle of placement on the rotor, while the vane grooves of vane motors must be arranged radially. If they are arranged at an angle, the blades will break when reversing; the distribution plate of axial piston pumps often uses an asymmetric structure to reduce cavitation and noise, while axial piston motors must use a symmetric structure, etc.

2) When determining the bearing structure and lubrication method of the hydraulic motor, it should be ensured that it can work normally within a wide speed range. When the motor speed is very low, it is not easy to form a lubricating oil film if a hydrodynamic bearing is used. In this case, rolling bearings or hydrostatic bearings should be used. Hydraulic pumps often run in a high-speed area, and the speed has almost no change, so there is no such harsh requirement.

3) In order to increase the starting torque, the hydraulic motor requires small torque pulsation and small internal friction. Therefore, the number of teeth of the gear motor cannot be as small as that of the gear pump, and the pre-load force during axial clearance compensation is much smaller than that of the pump, so as to reduce friction resistance and increase the starting torque.

4) Hydraulic motors do not require self-priming ability, but pumps must ensure this basic function. Therefore, point-contact axial piston hydraulic motors cannot be used as pumps.

5) Vane pumps rely on the centrifugal force of the rotor rotating to throw the blades so that the blades are close to the stator to seal the oil and form a working container. If used as a hydraulic motor, there is no force to make the blades close to the stator when starting, and the working chamber cannot be sealed, so the motor cannot start. Therefore, the vane motor must have a blade clamping mechanism such as a swallow-shaped swing spring or a spiral spring, which is not available in vane pumps.