A rotary fluid pressure device, such as a low-speed, high-torque gerotor motor, is provided with a valve drive shaft that is partially inserted into and engaged with a main drive shaft as the main drive shaft engages a rotating output shaft and engages a rotating and orbiting star member of a positive displacement device. The device is also provided with a drive retainer configured to retain the engagement of the main drive shaft and the valve drive shaft.

Downhole tools for earth-boring applications may include a component of a steel material and including a bore. An inner surface defining the bore may be treated with a surface treatment. The surface treatment may include a nitrided region having nitrogen diffused into the steel material and a ceramic material adjacent to the nitrided region; the ceramic material defining the inner surface. Methods of making downhole tools for earth-boring applications may involve exposing a component of the downhole tool to an elevated temperature to heat the component in a nitrogen-rich environment. Nitrogen may be diffused into a steel material of the component and a nitrided region may be formed at one or more surfaces of the component. A ceramic material may be coated on the nitrided region of the component.

Downhole tools for earth-boring applications may include a component of a steel material and including a bore. An inner surface defining the bore may be treated with a surface treatment. The surface treatment may include a nitrided region having nitrogen diffused into the steel material and a ceramic material adjacent to the nitrided region; the ceramic material defining the inner surface. Methods of making downhole tools for earth-boring applications may involve exposing a component of the downhole tool to an elevated temperature to heat the component in a nitrogen-rich environment. Nitrogen may be diffused into a steel material of the component and a nitrided region may be formed at one or more surfaces of the component. A ceramic material may be coated on the nitrided region of the component.

A hydrostatic transmission system includes a hydraulic motor and at least one proportional control valve and at least one pump connected to the hydraulic motor to provide fluid to operate the hydraulic motor. The at least one pump includes at least one fluid driver having a prime mover and a fluid displacement assembly to be driven by the prime mover such that fluid is transferred from the pump inlet to the pump outlet. The hydrostatic transmission system also includes a controller that establishes at least one of a speed and a torque of the at least one prime mover and concurrently establishes an opening of the at least one proportional control valve to adjust at least one of a flow and a pressure in the hydrostatic transmission system to an operational set point.

A hydrostatic transmission system includes a hydraulic motor and at least one proportional control valve and at least one pump connected to the hydraulic motor to provide fluid to operate the hydraulic motor. The at least one pump includes at least one fluid driver having a prime mover and a fluid displacement assembly to be driven by the prime mover such that fluid is transferred from the pump inlet to the pump outlet. The hydrostatic transmission system also includes a controller that establishes at least one of a speed and a torque of the at least one prime mover and concurrently establishes an opening of the at least one proportional control valve to adjust at least one of a flow and a pressure in the hydrostatic transmission system to an operational set point.

A gear pump or a gear motor includes a casing, a helical drive gear, a helical driven gear, a drive-side space, and an idler-side space. The drive and driven gears mesh with each other in the casing to partition inside of the casing so as to include high and low pressure spaces. The drive-side and idler-side spaces are each configured to allow pressure therein to become higher than a pressure in the low-pressure space. The drive-side space faces an end portion of a drive shaft rotatably supporting the drive gear. The idler-side space faces an end portion of an idler shaft rotatably supporting the driven gear. The end portion of the drive shaft is pushed in a predetermined direction by working fluid supplied to the drive-side space. The end portion of the idler shaft is pushed in the predetermined direction by working fluid supplied to the idler-side space.

A gear pump or a gear motor includes a casing, a helical drive gear, a helical driven gear, a drive-side space, and an idler-side space. The drive and driven gears mesh with each other in the casing to partition inside of the casing so as to include high and low pressure spaces. The drive-side and idler-side spaces are each configured to allow pressure therein to become higher than a pressure in the low-pressure space. The drive-side space faces an end portion of a drive shaft rotatably supporting the drive gear. The idler-side space faces an end portion of an idler shaft rotatably supporting the driven gear. The end portion of the drive shaft is pushed in a predetermined direction by working fluid supplied to the drive-side space. The end portion of the idler shaft is pushed in the predetermined direction by working fluid supplied to the idler-side space.

A hydraulic geroller (gerotor) motor, wherein an inner rotor of a revolving group has a plurality of lobes circumferentially spaced along an outer periphery of the inner rotor, and an orbiter of the revolving group includes an orbiting ring and rounded vane portions preferably formed by roller vanes contained in inner recesses of the orbiting ring for common orbiting with the orbiting ring about the fixed longitudinal axis. The orbiter also has fixed for orbiting therewith, fluid windows for directing fluid from the fluid ports to the revolving group. The windows may be formed in an integral portion of the orbiter or in a valve plate mounted for common orbiting with the orbiting orbiter. The valve plate cooperates with a stationary commutator plate or assembly to provide an efficient arrangement for the delivery and exhaust of hydraulic pressure fluid to and from the hydraulic motor.

A hydraulic geroller (gerotor) motor, wherein an inner rotor of a revolving group has a plurality of lobes circumferentially spaced along an outer periphery of the inner rotor, and an orbiter of the revolving group includes an orbiting ring and rounded vane portions preferably formed by roller vanes contained in inner recesses of the orbiting ring for common orbiting with the orbiting ring about the fixed longitudinal axis. The orbiter also has fixed for orbiting therewith, fluid windows for directing fluid from the fluid ports to the revolving group. The windows may be formed in an integral portion of the orbiter or in a valve plate mounted for common orbiting with the orbiting orbiter. The valve plate cooperates with a stationary commutator plate or assembly to provide an efficient arrangement for the delivery and exhaust of hydraulic pressure fluid to and from the hydraulic motor.

A gear pump for power generation comprises a first rotor and a second rotor in a case. The first rotor comprises a first plurality of radially spaced teeth, wherein the first plurality of radially spaced teeth wrap around the first rotor helically in a clockwise direction, and wherein at a first position the first plurality of radially spaced teeth have a helix angle different than the helix angle of the first plurality of radially spaced teeth at a second position. The second rotor comprises a second plurality of radially spaced teeth, wherein the second plurality of radially spaced teeth wrap around the second rotor helically in a counter-clockwise direction, and wherein at a first position the second plurality of radially spaced teeth have a helix angle different than the helix angle of the second plurality of radially spaced teeth at a second position.