Polyphase hydraulic drive system

The present invention comprises an input drive system, which provides a plurality of phases of oscillating fluid flow, and an output drive system connected directly to the input drive system that is powered by the plurality of phases of oscillating fluid flow. The input drive system comprises a plurality of pistons that are caused to move in a reciprocating fashion by a power source. The power source may be a rotating power source, such as that provided by an electric motor, a diesel or petrol engine, or a turbine system. The input drive system comprises a cam ring attached to a rotating power source, a plurality of cam rollers in contact with the cam ring; and a plurality of pistons attached to the cam rings. The output drive system comprises one or more pistons that are attached to move in a reciprocating fashion by the oscillating fluid flow provided by the input drive system. The output drive system comprises a cam ring attached to a load, a plurality of cam rollers in contact with the cam ring, and a plurality of pistons attached to the cam rings.

BACKGROUND OF THE INVENTION

The present invention relates to hydraulic drive systems for gear-less inter-conversion of rotational energy and gear-less conversion of rotational energy to linear kinetic energy.

Henricson (U.S. Pat. No. 5,657,681) discloses a hydraulic drive system comprising a plurality of hydraulically driven piston units with cam rollers, which are disposed to act against a wave-shaped cam profile of a cam curve element, so that linear movement of the cam rollers against the cam profile produces a relative driving movement between the cam element and the piston units. The characterizing feature of the invention is that the drive system is composed of separate, assembled cam curve element modules and separate assembled piston units.

Reboredo (U.S. Pat. No. 5,689,956) discloses a hydraulic variable speed drive assembly including a hydraulic pump having a cylinder with an associated end cover, a hydraulic motor having a cylinder with an associated end cover, and an intermediate plate with ports or passages for enabling a flow of fluid from the hydraulic pump to the hydraulic motor at a high pressure and from the hydraulic motor to the hydraulic pump at a low pressure, in order to close the circuit. The shafts of the rotors of the hydraulic pump and the hydraulic motor have a common geometric axis, static with respect to the outside, about which they can rotate independently, this rotation being their only possible movement. The variable drive assembly has as its only possible movement, the rotation about a geometric axis fixed with respect to the outside and is different from the geometric axis of the hydraulic pump cylinder, from the geometric axis of the hydraulic motor cylinder, and from the common geometric axis of the rotors. The rotation of the variable drive assembly is effected from the outside and results in that the hydraulic pump cylinder and the hydraulic motor cylinder approach or withdraw their geometric axes with respect to those of their corresponding rotors, thus causing variation of the ratio between the rotation speeds of the hydraulic pump rotor and of the hydraulic motor rotor.

Folsom and Tucker (U.S. Pat. No. 5,956,953) disclose an infinitely variable hydrostatic transmission that includes a radial piston pump having outwardly opening pump cylinders containing radial pump pistons, and a radial piston motor, arranged concentrically around the pump, having inwardly opening motor cylinders containing radial motor pistons. Fluid passages in the transmission intermittently connect the pump cylinders and the motor cylinders in a closed fluid flow circuit. A flexible cam ring is radially interposed between the pump and the motor in load bearing relation to the pump pistons on an inside surface of the cam ring, and in load bearing relation to the motor pistons on an outside surface of the cam ring. An input shaft is coupled in torque driving relation to the pump, and an output shaft is coupled in torque driven relation through a commutator plate to the cam ring. An adjustment mechanism is provided for adjusting the cam ring to a desired radial profile to set the transmission to a desired transmission ratio. A fluid distribution system has passages, including kidney shaped slots through the commutator plate, for fluid flow of fluid pressurized in the pump cylinders to the motor cylinders during a power stroke of the pump and motor pistons, and for fluid flow of spent fluid from the motor cylinders to the pump cylinders during a suction phase of the stroke of the pump and motor pistons. A control system adjusts the profile of the cam ring to control the transmission ratio, and a pressure compensator automatically reduces the transmission ratio when the resistance torque on the output shaft exceeds a predetermined value, as when the vehicle is ascending a steep hill.

These systems use a hydraulic pump and a system of valves to apply hydraulic power to the cam ring. Such valve systems add extra complexity to the design of these systems, and they require associated controlling mechanisms. In addition valve systems introduce some inefficiency into the device, and require maintenance.

BRIEF SUMMARY OF THE INVENTION

Thus a need has arisen for a valve-less hydraulic drive system.

The present invention comprises an input drive system, which provides a plurality of phases of oscillating fluid flow, and an output drive system connected directly to the input drive system that is powered by the plurality of phases of oscillating fluid flow.

In one embodiment, the input drive system comprises a plurality of pistons that are caused to move in a reciprocating fashion by a power source. In a preferred embodiment, the power source may be a rotating power source, such as that provided by an electric motor, a diesel or petrol engine, or a turbine system.

In a further embodiment, the input drive system comprises a cam element having a wave-shaped profile attached to a power source; a plurality of cam rollers in contact with the cam element; and a plurality of pistons attached to one or more hydraulic fluid lines and to the cam rollers, so that a movement of the wave-shaped profile against the cam rollers produces a plurality of phases of oscillating fluid flow in the hydraulic fluid lines, and the relative position of the cam rollers against the cam element determines a relative phase angle for the oscillating fluid flows.

In a further embodiment, the output drive system comprises one or more pistons that are caused to move in a reciprocating fashion by the oscillating fluid flow provided by the input drive system.

In a further embodiment, the output drive system comprises a cam element attached to a load; a plurality of cam rollers in contact with the cam element; and a plurality of pistons attached to one or more hydraulic fluid lines and to the cam rollers, so that a movement of the cam rollers caused by said oscillating fluid flow against the wave-shaped profile produces a movement of the cam element.

A technical advantage of the present invention is that the input drive system is connected directly to the output drive system, thereby eliminating the need for valves.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention and its advantages are best understood by referring in more detail toFIGS. 1 through 3, in which like numerals refer to like parts throughout.

Referring now toFIG. 1a, which shows a simple schematic of the present invention, an input drive system102and output drive system104are directly connected by hydraulic lines106. In this example, the input drive system produces three phases of oscillating fluid output, and these are fed independently and directly to the output drive system by three fluid lines. The connection between the hydraulic elements on the input drive side and the output drive side may be achieved in a number of ways known to the art. For example, the hydraulic elements may be two piston units108with cam-followers110directly connected as shown inFIG. 1b. The pistons are very simple single port pistons, with drive and driven pistons directly connected. The piston pair can be connected via a check valve114to a fluid reservoir112, in order to compensate for leaks. If the pressure in the piston pair ever falls below the supply level, then hydraulic fluid is added to the system, as shown inFIG. 1c.

Referring now toFIGS. 1dand1e, which shows in diagrammatic form how the piston units may be actuated by a cam ring, three piston units108are arranged as shown so that their cam-followers110are in contact with a cam ring114. In this example, one cam ring has 3 lobes and the other has 10 lobes.

The height and number of the lobes on the cam ring govern the displacement of the piston in the piston units. Referring again toFIGS. 1dand1e, the height of the cam ring, h, relative to the dashed line116(which is a circle) is proportional to the sine of the number of lobes multiplied by the relative angle;
h á sin(number of lobes×angle)

In one embodiment, each cam ring is mounted on a load-bearing axle, the axle of one cam ring forming an input shaft, and the axle of the other cam ring forming an output shaft. Each cam ring is in contact with a plurality of cam rollers, or cam followers, and each cam roller is attached to a hydraulic piston. The cam rollers of one set of piston may be arranged radially with respect to the cam ring attached to the input shaft so that as the cam ring turns, the cam rollers follow the cam ring and transmit a reciprocating motion into the corresponding pistons. The cam rollers of the other set of pistons are arranged radially with respect to the cam ring attached to the output shaft so that as the pistons move in a reciprocating fashion in response to the reciprocating motion transmitted from the other set of pistons, the cam rollers cause the cam ring to turn. The drive system does not rely on the use of valves. Hydraulic pistons from the input drive and the output drive are connected to each other by means of a sealed connection. In one embodiment, the input shaft is connected to an electric motor, and the output shaft is connected to a load. In another embodiment, the input shaft is connected to a source of rotational energy, and the output shaft is connected to a generator.

For the interconversion of rotational energy, assuming the drive cam element has x lobes and rotates at and angular velocity of y, and the output cam element has a lobes and rotates at and angular velocity of b, then:
y/b=a/x

Referring now toFIG. 2a, which shows two cam rings for a 10:1 speed reducer, cam ring202is part of the input drive system and has one lobe, and cam ring204has 10 lobes and is part of the output drive system. In this embodiment, the output drive system cam ring204has thirty piston/cam followers206arranged evenly around the cam as shown at angles of 0, 12, 24, 36 . . . etc (only 9 are shown for simplicity). The height of the cam ring relative to the dashed line116is again shown. The relative phase angle of each piston in the output drive side is thus the angle multiplied by the number of lobes on the cam ring, and is therefore 10×angle, or 0, 120, 240, 360, 0 . . . degrees. Since there are thus only three phases, just three piston/cam followers are placed around the input drive cam ring, and 3 sets of hydraulic pipes106connect the input drive system and the output drive system. In general terms, the phase angle φ between each phase is given by:
φ=360×(number of lobes)/(number of cams)

If 360 divided by φ, which is the same as the number of cams divided by the number of lobes, is an integer, then this value is the number of phases. So in the example above, the number of phases=30/10=3. If it is not an integer number, then the number of phases is the lowest integer multiple of this ratio. For example, if there are 24 cams and 10 lobes, then the number of cams divided by the number of lobes=24/10=2.4. The lowest integer multiple of this ratio is 12, and thus the number of phases would be 12. In the example given below, the number of cams divided by the number of lobes=31/10=3.1. The lowest integer multiple of this ratio is 31, and thus the number of phases is 31.

The relative size of the pistons on the drive side and the driven side are selected so that the piston displacement (piston bore×stroke×number of pistons) is equal.

In a further embodiment, shown inFIG. 2b, cam ring202is part of the input drive system and has one lobe, and cam ring204has 3 lobes and is part of the output drive system. The output drive system cam ring204has nine piston/cam followers206arranged evenly around the cam as shown at angles of 0, 40, 80, 120 . . . degrees, etc. The phase angle of each piston in the output drive side is thus the angle multiplied by the number of lobes on the cam ring, and is therefore 3×angle, or 0, 120, 240, 360, 0 . . . degrees. Since there are thus only three phases, just three piston/cam followers are placed around the input drive cam ring, and 3 sets of hydraulic pipes106connect the input drive system and the output drive system. The embodiment shown inFIG. 2bis thus a 3:1 speed reducer.

Referring again toFIG. 2a, if 31 piston/cam followers are positioned equally around the output drive system cam ring (not shown), then the physical angle of each piston is 11.6, 23.2, 34.8, 46.5 . . . and the phase angle is 0, 116, 232, 348, 105 . . . which gives 31 different phases. This means that now 31 piston/cam followers can be used on the output drive system cam ring, which are connected to the 31 pistons surrounding the input drive system cam ring by 31 independent hydraulic pipes. For a drive cam ring having one lobe, as shown inFIGS. 2aand2b, then this embodiment would be a direct drive (1:1) connection.

Referring now toFIG. 3, in a further embodiment, a linear cam302replaces the cam ring connected to the output shaft, and the corresponding pistons are arranged linearly; in this embodiment a linear rather than a rotational output is achieved. Thus the hydraulic drive system of the present invention may be used for the gear-less and valve-less interconversion of rotational energy, for the conversion of rotational energy to linear kinetic energy, and for the conversion of linear kinetic energy to rotational energy.

In the foregoing, the pistons are shown in the diagrams schematically and all have similar dimensions; however, the stroke of the pistons need not be the same. The only things that must match between the drive and the driven side are: (a) The number of phases must be the same, and (b) within each phase, the volume displaced by the driven and the drive side must be the same. In the foregoing, the diameter of the cams rings are shown to be roughly equal; however it is not outside the scope of the present invention for the diameter of the cam rings, and the amplitude of the wave-shaped profile, can be different.

In the foregoing, the cam rings and pistons are shown to be radial to the drive or output shafts, but they could also be axial, with pistons parallel to the axis of rotation and a cam ring of constant radius but changing thickness (not shown). As shown inFIG. 3, the cam element need not be a ring; it could be a wavy surface (elevator linear actuator, for example)

The drive system of the present invention may be used in a number of applications where hydraulic transmission systems are currently used, for example in hoists and generators. Advantageously, the present invention does not use valves and thus is simpler to operate and maintain.