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Ningbo ShuoLi hydraulic takes you to know how the hydraulic motor should choose its parameters!


Hydraulic motors, also known as oil motors, are mainly used in injection molding machinery, ships, hoists, engineering machinery, construction machinery, coal mining machinery, mining machinery, metallurgical machinery, marine machinery, petrochemical industry, port machinery, etc.


High speed motor gear motor has the advantages of small volume, light weight, simple structure, good manufacturability, insensitive to oil pollution, impact resistance and small inertia. Disadvantages include large torque pulsation, low efficiency, small starting torque (only 60% - 70% of rated torque) and poor low-speed stability.

From the point of view of energy conversion, hydraulic pump and hydraulic motor are reversible hydraulic components. Inputting working fluid to any kind of hydraulic pump can turn it into the working condition of hydraulic motor; Conversely, when the main shaft of the hydraulic motor rotates driven by external torque, it can also be changed to the working condition of the hydraulic pump. Because they have the same basic structural elements - closed and periodically variable volume and corresponding oil distribution mechanism. 

However, due to the different working conditions of hydraulic motor and hydraulic pump, there are still many differences between the same type of hydraulic motor and hydraulic pump. The hydraulic motor shall be able to forward and reverse, so its internal structure is required to be symmetrical; The speed range of hydraulic motor needs to be large enough, and there are some requirements for its stable speed. 

Therefore, it usually adopts rolling bearing or hydrostatic sliding bearing; Secondly, because the hydraulic motor works under the condition of input pressure oil, it does not need to have self-priming capacity, but it needs some initial tightness to provide starting torque. Due to these differences, the hydraulic motor and hydraulic pump are similar in structure, but they can not work reversibly.


For the hydraulic motor, there are several important parameters during operation. Shuoli hydraulic will show you the following:

1. Working pressure and rated pressure

Working pressure: the actual pressure of the input motor oil, which depends on the load of the motor. The difference between the inlet pressure and the outlet pressure of the motor is called the differential pressure of the motor. Rated pressure: the pressure that enables the motor to work continuously and normally according to the test standard.

2. Displacement and flow

Displacement: the volume of liquid input required for each revolution of the hydraulic motor without considering leakage. VM (m3 / RAD) flow: the flow without leakage is called theoretical flow qmt, and the leakage flow is considered as actual flow QM.

3. Volumetric efficiency and speed

Volumetric efficiency η MV: ratio of actual input flow to theoretical input flow.

4. Torque and mechanical efficiency

Regardless of the loss of the motor, its output power is equal to the input power. Actual torque T: torque loss due to actual mechanical loss of motor Δ T. Make it smaller than the theoretical torque TT, that is, the mechanical efficiency of the motor η Mm: equal to the ratio of the actual output torque of the motor to the theoretical output torque

5. Power and overall efficiency

The actual input power of the motor is PQM and the actual output power is t ω。 Total motor efficiency η M: The ratio of actual output power to actual input power The hydraulic motor has two circuits: the hydraulic motor series circuit and the hydraulic motor braking circuit, and these two circuits can be classified at the next level. One of the hydraulic motor series circuits: connect the three hydraulic motors in series with each other, and use a directional valve to control their start, stop and steering. 

The flow of the three motors is basically the same. When their displacement is the same, the speed of each motor is basically the same. It is required that the oil supply pressure of the hydraulic pump is high, and the flow of the pump can be small. It is generally used in the occasion of light load and high speed. Hydraulic motor series circuit 2: each directional valve in this circuit controls a motor. Each motor can act alone or at the same time, and the steering of each motor is also arbitrary. The oil supply pressure of the hydraulic pump is the sum of the working pressure difference of each motor, which is suitable for high-speed and small torque occasions. One of the parallel circuits of hydraulic motors: two hydraulic motors are controlled by their respective directional valves and speed regulating valves, which can operate simultaneously and independently, regulate speed respectively, and keep the speed basically unchanged. However, with throttling speed regulation, the power loss is large. 

The two motors have their own working pressure difference, and their speed depends on the flow they pass through. Hydraulic motor parallel circuit 2: the shafts of the two hydraulic motors are rigidly connected together. When the change-over valve 3 is in the left position, motor 2 can only idle with motor 1, and only motor 1 outputs torque. If the output torque of motor 1 cannot meet the load requirements, place valve 3 in the right position. At this time, although the torque increases, the speed should be reduced accordingly. 

Hydraulic motor series parallel circuit: when solenoid valve 1 is energized, hydraulic motors 2 and 3 are connected in series. When solenoid valve 1 is powered off, motors 2 and 3 are connected in parallel. When the two motors are connected in series through the same flow, the speed is higher than that when they are connected in parallel. When they are connected in parallel, the working pressure difference of the two motors is the same, but the speed is lower.

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