Piston motors are available in axial and radial types. Also available are fixed and variable displacement axial piston motors that operate at a high, medium, or low speed with a bent axis or swash plate. The axial piston motor has a higher volumetric efficiency than other types of motors. Radial piston motors generally operate with a high torque at a low speed.
(1) Bent axis fixed displacement piston motor: This motor is based on the same structural principles as the bent axis fixed displacement piston pump. Variable displacement type is also available. The motor can have a bent-axis angle of up to 40 degrees and is generally suitable for high-speed operation.
(2) Swash plate type piston motor: The high-speed type of this piston motor is based on a structure similar to that of the fixed displacement swash plate type pump. Fig. 10.7 shows an example of the low- /medium-speed type. Its cylinder block has two pistons and swash plates facing each other. It provides good low-speed performance at a time of the motor starts.
(3) Eccentric radial piston motor: This motor is widely known as the star-shaped motor. It has several fixed cylinders perpendicularly placed on the output shaft in a radial pattern. The flow is fed or discharged to/from the cylinders through a distributor valve connected to the shaft with a swivel joint. When a hydraulic pressure is applied to the piston, it reciprocates and pushes the eccentric cam on the shaft to produce torque. This motor is designed for low-speed high-torque applications.
(4) Multi stroke radial piston motor: This motor has a piston placed in the direction of the radius of the shaft with a cam roller. The piston moves on the patterned cam ring to produce torque. This motor can offer a larger displacement capacity than that of any other hydraulic motors. It is often used in winches and crushing machines.
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