Hydrostatic power transmission system

Claim 2

A hydrostatic power transmission system for delivering a driving torque from an input shaft to an output shaft which is in line with the input shaft comprising, in combination, first, second and third fluid displacement units each comprising a rotatable cylinder bLock coaxial with the input and output shafts and a cam ring positioned around said cylinder block, the cylinder blocks of the first and second fluid displacement units being rotatable with said input shaft, the cam ring of the second fluid displacement unit and the cylinder block of the third fluid displacement unit being in driving engagement with said output shaft, each of said cylinder blocks having a plurality of cylinders which are directed toward an axis of rotation of the cylinder block and a plurality of piston elements which are respectively received within said cylinders and movable toward and away from said axis, said piston elements being in frictional engagement with said cam surface of the associated cam ring, the cam ring of the first fluid displacement unit being movable over the associated cylinder block in a plane substantially transverse to the axis of rotation of the cylinder block for providing controlled degrees of eccentricity between the cam surface of the particular cam ring and the axis of rotation of the associated cylinder block, actuating means for moving the cam ring of said first fluid displacement unit in said plane for varying the displacement of the first fluid displacement unit, the cam ring of the second fluid displacement unit being held stationary for keeping constant the displacement of the second fluid displacement unit, and fluid pressure distribution passage means providing controlled fluid communication between the cylinders of said first, second and third fluid displacement units for radially outwardly biasing said piston elements within each of the cylinders, said first fluid displacement unit being operable to displace the fluid in either direction from zero to maximum.

Claim 3

A hydrostatic power transmission system according to claim 1, in which the maximum displacement per turn of the cylinder block of the first displacement unit being smaller than the displacement per turn of the cylinder block of said second fluid displacement unit, said third fluid displacement unit being operable to displace the fluid in a fixed direction.

Claim 4

A hydrostatic power transmission system according to claim 1, in which the cam ring of said first fluid displacement unit is moved relative to the associated cylinder block to a position in which the displacement of the first fluid displacement unit is smaller than the displacement of the second fluid displacement unit for causing said output shaft to be driven at a speed relatively lower than and in the same direction as said input shaft to provide an underdrive condition.

Claim 5

A hydrostatic power transmission system according to claim 1, in which the cam ring of the first fluid displacement unit is moved relative to the associated cylinder block to a position in which the displacement thereof equals the displacement of the second fluid displacement unit for causing said output shaft to stop to provide a neutral condition.

Claim 6

A hydrostatic power transmission system according to claim 1, in which the cam ring of said third fluid displacement unit is movable over the associated cylinder block in a plane substantially transverse to an axis of rotation of the cylinder block for providing controlled degrees of eccentricity between the cam surface of the cam ring and the axis of rotation of the cylinder block, said system further comprising actuating means for displacing the cam ring of said third fluid displacement unit in said plane for varying the displacement of the third fluid displacement unit, said cam ring of the third fluid displacement unit being moved relative to the associated cylinder block to a position providing a maximum displacement of the third fluid displacement unit during neutral, underdrive and reverse drive conditions.

Claim 7

A hydrostatic power transmission system according to claim 5, in which the cam ring of said first fluid displacement unit is adjusted to be in concentric alignment with the associated cylinder block to interrupt the displacement of the first fluid diSplacement unit to cause said output shaft to be driven at a speed lower than said input speed but higher than the speed of rotation of the output speed during the underdrive condition, wherein the cam ring of said third fluid displacement unit is moved relative to the associated cylinder block to a position in which the displacement of the third fluid displacement unit is decreased for establishing a low-speed condition.

Claim 8

A hydrostatic power transmission system according to claim 5, in which the cam rings of the first and third fluid displacement units are moved relative to the associated cylinder blocks to be in concentric alignment with these cylinder blocks to interrupt the displacements of the two units concurrently for causing said output shaft to be driven at the same speed and in the same direction as said input shaft to establish a direct drive condition.

Claim 9

A hydrostatic power transmission system according to claim 5, in which the cam ring of the first fluid displacement unit is moved relative to the associated cylinder block to a position in which the direction of the displacement thereof is reversed and concurrently the cam ring of the third fluid displacement unit is moved relative to the associated cylinder block to be in concentric alignment with the cylinder block to cause said output shaft to be driven at a higher speed than said input shaft to establish an overdrive condition.

Claim 10

A hydrostatic power transmission system according to claim 5, further comprising valve means operable to block entry of pressurized fluid into said first and third fluid displacement units during a direct drive condition.

Claim 11

A hydrostatic power transmission system according to claim 1, in which the cam ring of the third fluid displacement unit is held stationary.

Claim 12

A hydrostatic power transmission system according to claim 10, in which the cam ring of the first fluid displacement unit is moved relative to the associated cylinder block to a position in which the displacement of the first fluid displacement unit is smaller than the displacement of the second fluid displacement unit for causing said output shaft to be driven in the same direction as said input shaft.

Claim 13

A hydrostatic power transmission system according to claim 10, in which the cam ring of said first fluid displacement unit is moved relative to the associated cylinder block to a position in which the displacement of the first fluid displacement unit is larger than the displacement of the second fluid displacement unit for causing said output shaft to be driven in a reverse direction to said input shaft.

Claim 14

A hydrostatic power transmission system according to claim 10, in which the cam ring of said first fluid displacement unit is moved relative to the associated cylinder block to a position in which the displacement in a reversed direction of the first fluid displacement unit equals the displacement of the third fluid displacement unit.

Claim 15

A hydrostatic power transmission system according to claim 10, in which the cam ring of the first fluid displacement unit is moved relative to the associated cylinder block to a position in which the displacement in either direction of the first fluid displacement unit is greater than the displacement of the third fluid displacement unit.

Claim 16

A hydrostatic power transmission system according to claim 1, further comprising a first stationary sleeve which is interposed between said input shaft and the cylinder block of said first fluid displacement unit and a second stationary sleeve which is interposed between said output shaft and the cylinder block of said third fluid displacement unit, said fluid pressure distribution passage being formed by radial ports formed in inner peripheral walls of the cylinder blocks of said first, second and third fluid displacement units and communicating with said cylinders therein, a pair of diametrically spaced semi-circumferential grooves formed in an outer peripheral wall of said stationary sleeve and alignEd with said radial ports in the cylinders of said first fluid displacement unit, a pair of elongated grooves formed in the outer peripheral wall of said first stationary sleeve and communicating with said semi-circumferential grooves respectively, a pair of radial ports formed in an inner peripheral wall of said first stationary sleeve communicating with said elongated grooves respectively, a pair of spaced annular grooves formed in an outer peripheral wall of said input shaft and constantly communicating with said radial ports in said first stationary sleeve, an axial bore formed in said input shaft and opened at its terminal end, a radial passage formed in said input shaft providing communication between one of said annular grooves, an elongated groove formed in the outer peripheral wall of said input shaft and terminating at said terminal end of the input shaft, said elongated groove in said inner shaft communicating with the other of said annular grooves, an annular groove formed between conjoined ends of the input and output shafts, an axial bore formed in said output shaft and opened at its starting end, the axial bores in said input and output shafts being in communication with each other and substantially coextensive with said first, second and third fluid displacement units, a first radial passage formed in said output shaft and communicating with said axial bore in the output shaft, a pair of diametrically spaced semi-circumferential ports formed in an outer peripheral wall of said output shaft and aligned with said radial ports in the cylinders of said second fluid displacement unit, one of which semi-circumferential ports communicates with said first radial passage and the other of which semi-circumferential ports communicates with said annular groove between said joined ends of the input and output shafts, an elongated groove formed in the outer peripheral wall of said output shaft and communicating with said other of said semi-circumferential ports in the input shaft, a second radial passage formed in said output shaft and communicating with said axial bore in the output shaft, said radial bore in said input shaft and the first and second radial passages in said output shaft being aligned with each other and diametrically opposed to the elongated grooves in the outer peripheral walls of the input and output shafts, a pair of spaced annular grooves formed in the outer peripheral wall of said output shaft and communicating respectively with said second radial passage and said elongated groove in said output shaft, a pair of radial ports formed in an inner peripheral wall of said second stationary sleeve and constantly communicating respectively with said annular grooves in said output shaft, a pair of elongated grooves formed in an outer peripheral wall of said second stationary sleeve and communicating respectively with said radial ports therein, a pair of diametrically spaced semi-circumferential ports formed in the outer peripheral wall of said second stationary sleeve and communicating respectively with said elongated grooves therein, said semi-circumferential ports in the second stationary sleeve being aligned with said radial ports in the cylinders of said third fluid displacement unit, and a pair of valved fluid supply passages communicating with said radial ports in said second stationary sleeve and with a source of pressurized fluid.

Claim 17

A hydrostatic power transmission system according to claim 15, further comprising valve means for closing said radial passage in said input shaft and said second radial passage in said output shaft when the cam rings of the first and third fluid displacement units are moved relative to the associated cylinder blocks to be in concentric alignment with the cylinder blocks for interrupting the displacements of the two fluid displacement units to establish a direct drive condition.

Claim 18

A hydrostatic power transmission system according to claim 16, in which said valve means comprises a pair of piston valves axially movAbly accommodated within first and second larger-diameter bores extending from opposed ends of said axial bores in said input and output shafts respectively, said larger-diameter bores being closed at their outer ends by closure plugs respectively, said valve pistons projecting at their leading ends into said axial bores in said input and output shafts respectively, each of said valve pistons having a flange by which the larger-diameter bore receiving the piston therewithin is divided into constant-pressure and variable-pressure chambers and a passage formed therein for providing communication between the constant-pressure chambers of the two larger-diameter bores and said axial bores in said input and output shafts, and a pair of spring means each mounted within said variable-pressure chambers and biasing each of said pistons toward each of said closure plugs, the variable-pressure chambers being respectively in communication with said fluid supply passages through respective drain passages which are provided with control valves for usually providing communication between said fluid supply and drain passages for causing said valve pistons be moved toward said closure plugs by a fluid pressure passed to the variable-pressure chambers and for opening said drain passages during said direct drive condition to cause said valve pistons to move to positions to close said radial passage in said input shaft and said first radial passage in said output shaft.