The factors to be considered in the selection of hydraulic motor are working pressure, rotating speed range, operating torque, total efficiency, volume efficiency, slip characteristics, life and other mechanical properties and installation conditions, appearance, etc..

Many types of hydraulic motors, characteristics are not the same, should be selected for the specific purpose of the hydraulic motor, the table lists the characteristics of the typical hydraulic motor. Low speed motor can be used in low speed, and it can be used with a high speed motor with a speed reducer. Two in the structure layout, occupancy space, cost, efficiency and other aspects of the advantages, must be carefully demonstrated.

Comparison of typical hydraulic motor

 

 

 

Type high speed motor

Gear type vane piston type radial piston type

Rated pressure Mpa 2117.53535

4-300 25-300 10-1000 125-38000 ml/r

Speed 300-5000 400-3000 10-5000 1-500 r/min

Total efficiency% 75-90 85-95 80-92 75-90

70-80 80-90 75-85 50-85

Large and small size of the leakage

Pollution sensitive small and small

Variable ability can not be difficult

 

After determining the type of the hydraulic motor, according to the required speed and torque from the product line to meet the needs of several kinds of specifications, and then use the characteristics of various specifications to find out (or calculate) the corresponding pressure drop, flow and total efficiency. The following is a comprehensive technical and economic evaluation to determine the specifications. If the original cost is the most important, it should choose the smallest flow, such as pump, valve, pipeline, etc., if the most important operation costs, the total efficiency should be the highest, if the working life of the most important, the choice should be chosen to minimize the pressure drop; perhaps the best choice is the solution of the above.

A motor running at low speed is required to check the minimum stable speed. If there is no data, it should be in the relevant system of the required conditions of the actual test and then decide. In order to smooth running at very low speed, the motor leakage must be constant and load to a constant, to a certain return oil pressure (such as 0.3 - 0.5 MPa) and at least 35mm2/s oil liquid viscosity.

The bearing life is related to the speed and load:

 

Type Lnew - bearing actual life (H);

Lref - bearing B10 life (H) under rated conditions;

Nnew -- actual speed (r/min);

Nref - rated speed (r/min);

Pnew - the actual shaft load (N);

PREF - rated shaft load ($).

According to these relations, if the speed of half the bearing life is extended to 2 times the original. On the shaft, the bearing life is lengthened by 40% while the load is reduced.

When starting with the motor, the torque is required to be checked.

When braking with a hydraulic motor, such as a crane, a heavy load or a hydrostatic transmission system, the motor operates in a pump condition.

At this time, the relationship between the brake torque and the torque of the motor is as follows:

 

Type:

Mbr - Brake torque;

Eff Mmot - effective torque of motor;

HM -- hydraulic mechanical efficiency.

The brake torque calculated by the formula must not exceed the maximum operating torque of the motor.

In order to prevent the occurrence of cavitation or loss of braking ability of the brake motor, the motor should ensure that the motor's "oil absorbing mouth" has enough oil pressure. This can be achieved by the closed circuit in the oil pump or open circuit in the back pressure valve to achieve. When the hydraulic motor drives the large inertia load, in order to prevent the motor from the inertia of the parking process, the motor is short of oil, and the parallel connection of the motor with the motor is set up.

When it is needed to prevent the load movement, the hydraulic release mechanism should be used on the motor shaft.