Created on:2021-06-09 13:38

Working principle of gear motor

Gear motor

2.2.1 type characteristics

(l) Classified gear motor is a hydraulic motor based on meshing principle, which belongs to high-speed hydraulic motor. It is the simplest structure of various hydraulic motors. Its detailed classification is shown in Figure y. Among them, the two gear type involute external gear motor is most widely used.


(2) The characteristics are shown in the table below.


Characteristics of gear motor




















2.2.2 working principle

(l) Working principle of two gear type involute external gear motor and some problems needing attention

① The working principle diagram Z shows the working principle of two gear type involute external meshing gear motor. The centers of two meshing gears I and II are O1 and O2 respectively, and the radius of meshing point is R1 and R2 respectively. Gear I is an output shaft with a load. When the high pressure oil P1 (P2 is the return oil pressure) enters the oil inlet chamber of the gear motor, which is composed of the surfaces of teeth 1 ', 2', 3 'and 1', 2 ', 3', 4 'and the relevant inner surfaces of the shell and the end cover, because the radius of the meshing point is less than the radius of the addendum circle, the unbalanced oil pressure as shown by the arrow will be generated on the tooth surfaces of teeth 1' and 2 '. The hydraulic pressure generates torque for axes 01 and 02. Under the action of the torque, the gear motor rotates continuously in the direction shown in the figure. With the rotation of the gear, the oil is taken to the oil return chamber and discharged. As long as the pressure oil is continuously supplied to the gear motor, the motor will rotate continuously and output torque and speed. In the process of gear motor rotation, the output torque of the motor is pulsating because the meshing point constantly changes position.


② Compared with gear pump, gear motor has the following problems.

a. The gear motor has the requirement of forward and reverse rotation, so the internal structure and oil passage are symmetrical.

b. The oil in the low-pressure cavity of the motor is squeezed out by the gear, so the pressure in the low-pressure cavity is slightly higher than the atmospheric pressure, so the motor will not produce cavitation phenomenon because of the high suction flow rate like the gear pump.

c. Due to the back pressure of the oil return from the motor, in order to prevent the shaft end seal from being damaged during the forward and reverse rotation of the motor, a separate oil leakage port is set on the gear motor housing, so as to lead the leakage oil of the bearing part to the oil tank outside the housing, instead of leading the leakage oil to the low pressure chamber as the gear pump does.

d. Gear pump provides pressure and flow, emphasizing the volumetric efficiency, while gear motor produces output torque, emphasizing the mechanical efficiency, and trying to have good starting performance and low minimum stable speed. In order to improve the starting performance, it is necessary to reduce the friction torque, the starting pressure and the dead zone (see figure a). To reduce the minimum stable speed is to make the motor run stably at a very low speed without crawling. Therefore, the following measures are usually taken.


i. Needle bearings are often used to reduce the starting friction torque of the motor.

II. Improve the lubrication and cooling conditions of bearings, especially ensure good lubrication at the moment of starting.

III. reduce the radial force to reduce the load on the bearing, so as to reduce the friction torque.

IV. the compression coefficient of the clearance compensation device should be reduced as far as possible, so that the compensation device only slightly contacts with the gear with a weak tightening force, so as to reduce the friction torque.

5. The number of teeth of gear motor is generally more than that of gear pump, so as to reduce the fluctuation of torque, reduce the minimum stable speed, improve the low-speed stability and improve the starting performance. In addition, increasing the number of teeth is also beneficial to reduce vibration and noise. The number of teeth Z1 of the gear connected with the output shaft of the motor is greater than or equal to 14. The number of teeth of high pressure gear pump is generally z = 6 ~ 14 (in order to prevent undercutting and weaken the root strength, the tooth profile should be modified).

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