Axial Piston Motors

Axial piston motors are often used as hydrostatic drive units on off-highway equipment. The operation of this pump is described by referencing Figure 13–30.

The endcap contains ports A and B, each of which can act as either an inlet or outlet port depending on the desired direction of rotation. The pistons reciprocate in bores machined into the cylinder block rotor. As fluid enters port A, the piston bore is charged with high-pressure oil that forces the piston against a fixedangle swashplate. This allows the piston to slide down the swashplate face, turning the cylinder block that in turn rotates the output shaft. As the cylinder block continues to turn, other piston bores align with the inlet port A, allowing each to be similarly actuated in sequence. Oil is discharged at lower pressure through the outlet port B as it comes into register at the end of each piston stroke.

Most axial piston motors are fixed displacement and not reversible. In variable-displacement applications of axial piston motors, the swashplate angle can be adjusted using an arm and lever assembly. The greater the swashplate angle to the shaft, the larger the amount of oil that has to be displaced, resulting in a decrease in motor output speed. In other words, swashplate angle determines motor displacement per cycle.

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