Variable displacement hydraulic motor

1. A variable displacement hydraulic motor, comprising:

a swash plate with a tilt angle; and

a plurality of piston assemblies configured to rotate about a drive shaft;

wherein each of the plurality of piston assemblies includes:

an inner piston slideably coupled to an outer piston that mates with a cylinder in a cylinder block; and

a retainer device positioned within the cylinder block and configured to inhibit axial movement of the outer piston in a first position and permit axial movement of the outer piston in a second position;

wherein the cylinder block rotates about the drive shaft;

wherein each of the retainer devices includes a pin that is radially aligned with regard to a rotational axis of the drive shaft; and

wherein each of the retainer devices includes an actuation chamber that is hydraulically coupled to a hydraulic line.

2. The variable displacement hydraulic motor of claim 1 , wherein the tilt angle is fixed.

3. The variable displacement hydraulic motor of claim 1 , wherein each of the retainer devices includes a spring that mates with the pin.

4. The variable displacement hydraulic motor of claim 1 , wherein the hydraulic line is internally routed through the cylinder block.

5. The variable displacement hydraulic motor of claim 1 , wherein the hydraulic line is routed through a housing that encloses the cylinder block.

6. The variable displacement hydraulic motor of claim 5 , wherein the hydraulic line extends through a housing.

7. The variable displacement hydraulic motor of claim 5 , wherein the hydraulic line extends through a valve plate.

8. The variable displacement hydraulic motor of claim 1 , wherein the retainer device includes an axially displaceable body that includes a radial extension that axially delimits the outer piston in a retracted position.

9. The variable displacement hydraulic motor of claim 1 , wherein the inner and outer pistons are constructed out of nitride steel.

10. The variable displacement hydraulic motor of claim 1 , further comprising a controller including instructions that when executed cause the controller to:

transition the retainer device between the first position and the second position.

11. The variable displacement hydraulic motor of claim 10 , wherein the controller is a transmission control unit in a hydromechanical transmission.

12. A method for operation of a variable displacement hydraulic motor, comprising:

selectively adjusting a displacement of the variable displacement hydraulic motor via adjustment of multiple hydraulic retainer devices;

wherein each of the multiple hydraulic retainer devices are configured to:

in a first position, delimits axial movement of an outer piston in a piston assembly that includes an inner piston, wherein the inner piston and the outer piston are included in a cylinder block; and

in a second position, permit concurrent axial movement of the outer piston and the inner piston;

wherein the multiple hydraulic retainer devices are positioned within the cylinder block;

wherein the multiple piston assemblies rotate about a drive shaft;

wherein the cylinder block rotates about the drive shaft;

wherein each of the multiple hydraulic retainer devices includes a pin that is radially aligned with regard to a rotational axis of the drive shaft; and

wherein each of the hydraulic retainer devices include an actuation chamber that is hydraulically coupled to a hydraulic line.

13. The method of claim 12 , wherein selectively adjusting the displacement of the variable displacement hydraulic motor includes:

during a first operating condition, moving or sustaining the multiple hydraulic retainer devices into the first position.

14. The method of claim 12 , wherein selectively adjusting the displacement of the variable displacement hydraulic motor includes:

during a second operating condition, moving or sustaining the multiple hydraulic retainer devices into the second position.

15. The method of claim 12 , wherein adjustment of the multiple hydraulic retainer devices includes augmenting a pressure of a hydraulic fluid in a hydraulic line coupled to the hydraulic retainer device to transition the hydraulic retainer device between the first and second positions.

16. A multi-speed hydraulic motor, comprising:

a swash plate with a fixed tilt angle;

a plurality of piston assemblies configured to rotate about a drive shaft;

wherein each of the plurality of piston assemblies includes:

an inner piston slideably coupled to an outer piston that mates with a cylinder in a cylinder block; and

a hydraulic retainer device delimiting the axial displacement of the outer piston in a reduced displacement configuration and permitting full axial displacement of the outer piston in a full displacement configuration;

wherein each of the hydraulic retainer devices are positioned within the cylinder block;

wherein the cylinder block rotates about the drive shaft;

wherein each of the retainer devices includes a pin that is radially aligned with regard to a rotational axis of the drive shaft; and

wherein each of the retainer devices includes an actuation chamber that is hydraulically coupled to a hydraulic line.

17. The multi-speed hydraulic motor of claim 16 , wherein the hydraulic line is internally routed through the cylinder block.

18. The multi-speed hydraulic motor of claim 16 , wherein the inner piston is coupled to a slipper that is in face sharing contact with the swash plate.

19. The multi-speed hydraulic motor of claim 16 , wherein the hydraulic line is routed through a housing that encloses the cylinder block.

20. The multi-speed hydraulic motor of claim 16 , wherein the multi-speed hydraulic motor is a two-speed hydraulic motor.