piston motors

PISTON MOTORS

1. What are Piston Motors?

• Piston motors are positive displacement motors which can develop an output torque at the shaft by allowing pressurised fluid to act on the pistons.

• The piston motors can be either fixed or variable-displacement devices.

• They are suitable for low speed, high torque traction applications such as earth-moving machinery, agricultural tractors, railway locomotive and other industrial applications. 

• The piston motors are the most efficient and can operate at the highest speeds and pressures, when compared to gear and vane type motors.

• Types: Piston motors can be classified in terms of the piston motion as :

1. Axial-piston motors, and

2. Radial-piston motors.

2. Axial Type Piston Motors

Construction and Operation : The operation of an axial type piston motor is essentially the same as that of an axial piston pump except for the direction of flow (refer Section 4.17, and Fig.4.15)

The pressurised liquid introduced through the motor inlet forces the piston assembly against the thrust cam or swash/wobble plate. The angular application of this force causes the plate to rotate and this rotation is transmitted by the shaft. The displacement can be varied by changing the angle of the thrust cam.

3. Radial Type Piston Motors

Construction and Operation: The operation of a radial type piston is also essentially the same as that of an radial piston pump except for the direction of flow (refer Section 4.19 and Fig.4.21). Fluid enters the piston chamber through a central eccentric cam. The piston is forced radially outward against the thrust ring, thereby producing a force tangent to the piston chamber. The resulting torque causes the shaft to rotate.

4. Advantages of Piston Motors

(i) The piston motors exhibit very high volumetric efficiencies.

(ii) They produce very high torque.

(iii) They are capable of working at very high pressures and speeds.

(iv) They are available in both fixed and variable type displacement units.

5. Disadvantages of Piston Motors

(i) The cost per horse power is relatively high.

(ii) The power-to-weight ratio of piston motors are comparatively less as that of gear and vane motors.

6. Ranges

The piston motors are available at pressure ratings upto 350 bars with rated capacities upto 30 Lps and at operating speeds of 12,000 rpm.