gear motors

GEAR MOTORS

1. What are Gear Motors?

• Like gear pumps, gear motors are fixed displacement devices.

• Also, gear motors can be classified as external or internal gear units.

• External gear motors include the gear-on-gear units such as the spur gear motor.

• Internal gear motors include the crescent seal types and the gerotor type unit.

2. Construction and Operation

Fig.5.11 illustrates the operation of a gear motor. In this type, both the gear wheels are driven and one of the gear wheel has an extended shaft to provide output torque.

In the gear motor, rotary motion is produced by the unbalanced hydraulic forces on the gear teeth. The hydraulic imbalance in a gear motor is caused by gear teeth unmeshing. As gear teeth unmesh, all teeth subjected to system pressure are hydraulically balanced, except for one side of one tooth on one gear. This imbalance of force on gears, as shown in Fig.5.11, develops the torque. It should be noted that the larger the gear tooth or higher the pressure, more is the torque produced.

• These motors provide rotary output motion over a finite angle. That is, the rotation of the shaft of these motors is less than 360°. (Usually 90°, 180°, or 270°).

3. Advantages of Gear Motors

The gear motors are simple in design, and very cheap in cost.

4. Disadvantages of Gear Motors

(i) Gear motors are subjected to relatively high internal leakage. Therefore, they are not suitable for high torque, low speed applications.

(ii) The high pressure at the inlet, coupled with the low pressure at the outlet, generates very high bearing loads.

5. Ranges

The gear motors are available for peak operating pressures upto about 125 bars, with rated capacities upto 10 Lps, and maximum speeds of about 3000 rpm.