Gerotor Motor or Pump Having Sealing Rings in Commutator Members

The present invention relates to rotary valves designed for use with Gerotor rotary machines which are used as fluid pumps or motors in which the fluid introduced is contracted and expanded by a meshing gear system generally known as a Gerotor, and more particularly the invention relates to a rotary valve including sealing means designed to prevent leakage of fluid between the high pressure side and the low pressure side of the commutator.

With a fluid motor or pump of the Gerotor type in which a rotor formed with one less external teeth than the number of internal teeth of a stator, is rotated in eccentric mesh with the stator and a plurality of expanding and contracting cavities are defined by the teeth of the stator and the rotor in response to the eccentric rotation kf the rotor, it has been the practice to use a rotary valve so as to selectively communicate the fluid passages with the Gerotor cavities so that a hydraulic oil is supplied to impart a turning force to the rotor in the case of a fluid motor, while a hydraulic oil is discharged from the contracting Gerotor cavities in the case of a fluid pump.

With a known rotary valve of this type, due to the fact that the commutator is rotated within the valve chamber, a clearance which is as small so as not to impede the rotation of the commutator is provided at each side of the commutator, and consequently there is a disadvantage that the oil tends to leak from the high pressure side to the low pressure side within the valve chamber, thus deteriorating the volumetric efficiency of a motor or pump. As a result, the width of the clearance on each side of the commutator has been made very small so far as the rotation of the commutator is not impeded, thus requiring a high degree of finishing accuracy for the component parts of the rotary valve. However, there is a disadvantage that even if the component parts with a high degree of finishing accuracy are used, the clamping force of bolts or the like used in assembling the valve tends to distort the component parts of the valve chamber and moreover the existence of the high oil pressure portion and the low oil pressure portion within the valve chamber tends to similarly distort the component parts of the valve chamber by the pressure difference between the two portions, thus increasing the width of the clearance at each side of the commutator. This condition may be aggravated when thermal expansion occurs in use causing mechanical seizure of the parts.

It has been further found that upon continued operation of the Gerotor unit, and resultant thermal gradients will cause dimensional expansion which will cause binding, seizure and surface scoring of the commutator.

In U.S. Pat. No. 3,452,680, it has been proposed that a sealing element be interposed between the casing or housing and the commutator. Although such an arrangement provides a seal, it has the disadvantage in that the continuous movement of the seal element relative to the casing causes wear on the sealing element requiring maintenance, repair and replacement.

In U.S. Pat. No. 4,449,898, a solution to the aforementioned problems was proposed wherein the commutator comprised two spaced members movable in unison with a sealing element interposed between the two members.

In practice, it has been found that such a fluid motor operates satisfactorily for unidirectional operation. However, when input flow was reversed, it has been found that there is improper axial pressure balance and may result in insufficient sealing.

Accordingly, among the objectives of the present invention are to provide a rotary valve for a Gerotor type fluid rotary machine wherein the axial sealing forces are pressure balanced or biased to minimize the slippage volume and improve the volumetric efficiency, minimize the coulomb friction and improve the mechanical efficiency, provide proper break-away torque characteristics for rotation in either direction, which will make the axial separating force less dependent on the compression of an elastomeric seal; which will permit the application of the fluid motor in hydraulic systems with overrunning loads; and which will make the rotating/orbiting disc more tolerant to thermal shock; which can be manufactured readily by the utilization of conventional manufacturing techniques.

In accordance with the invention, the commutator comprises circumferentially spaced pairs of sealing rings adjacent the outer and inner periphery of the two spaced members.

FIG. 1 is a longitudinal sectional view showing the construction of a motor embodying the invention.

FIG. 2 is a fragmentary sectional view on an enlarged scale of a portion of the motor shown in FIG. 1.

FIG. 3 is a fragmentary sectional view on an enlarged scale of a portion of the motor shown in FIGS. 1 and 2.

FIG. 4 is a fragmentary exploded perspective view of the motor.

FIG. 5 is a sectional view on an enlarged scale of a portion of a motor.

FIG. 6 is a sectional view taken along the line 6-6 in FIG. 5.

FIGS. 7 and 8 are schematic diagrams of the hydrostatic pressure fields in a motor embodying the invention.

FIGS. 9 and 10 are schematics of the hydrostatic pressure fields in a motor of the prior art.

A rotary valve provided in accordance with this invention is designed for use with fluid rotary machines of the Gerotor type. Irrespective of whether the rotary machine is used as a fluid motor or pump, the Gerotor unit of the identical construction is used in either cases and the machine is usable either as a motor or pump. In the embodiments described hereunder, the rotary valve of this invention is used with a fluid motor of the Gerotor type.

As shown in FIGS. 1 and 4, the rotary valve comprises a commutator 10, a port member 12, a spacer 14, an end cover 16 and an eccentric circular cam 18. The eccentric circular cam 18 is rotatably supported in roller bearings 20 and 22 which are assembled in the end cover 16 and the port member 12, respectively. The spacer 14 is interposed between the end cover 16 and the port member 12 to define a valve chamber, and these component parts and a Gerotor stator 24 are accurately positioned by locating pins 26 and firmly fastened together with bolts 30 with seals 28 interposed therebetween. The commutator 10 is rotatably mounted on the eccentric circular cam 18 within the valve chamber.

A cam portion 32 of the eccentric circular cam 18 has its center offset from an axis of rotation of the eccentric circular cam 18, and the commutator 10 is fitted on the cam portion 32. As a result, when the cam 18 is rotated, the commutator 10 is rotated with the valve chamber eccentrically or in an orbit with respect to the axis of the cam 18. Commutator 10 is provided with annular grooves 38 and 40 which are formed in its sides, and these annular grooves 38 and 40 communicate with each other through a suitable number of holes 42.

The side of the port member 12 which is opposite to the commutator 10, is formed with seven elongated grooves 44 which are arranged at equal spacing along the same circumference around the axis of the eccentric circular cam 18, and these elongated grooves 44 are connected to the other side of the port member 12 through holes 46. An annular groove 48 is similarly formed concentrically with the shaft center on the inner side of the grooves 44, and the groove 48 is also connected to the other side of the port member 12 through a hole 50. An elongated elliptic groove 52, which is circumferentially curved about the center of the shaft on the outer side of the diamondshaped grooves 44, is also connected to the other side of the port member 12 through a hole 54.

The Gerotor unit comprises the stator 24, a rotor 56 and a drive shaft 58, and five round bars 60 and hollow bushings 62 and 64 are fitted in the stator 24 thus forming seven internal teeth thereon. The holes of the hollow bushings 62 and 64 constitute oil inlet and outlet passages and their positions respectively communicate with the hole 54 of the port member 12 and the hole 50 of the port member 12. The rotor 56 is formed with one less teeth than the number of teeth of the stator 24, and meshes with the internal teeth of the stator 24. The rotor 56 which is in mesh with the internal teeth of the stator 24 rotates about the center of the stator 24 while rotating on its axis. The orbiting of a center of the rotor 56 follows a circular path. The center of the stator 24 coincides with the axis of rotation of the eccentric circular cam 18. Drive shaft 58 is coupled by spline grooves to the central portion of the rotor 56, and the rotation of the rotor 56 on its axis is transmitted to the drive shaft 58. In this case, the center of the rotor 56 makes one rotation about the center 36 of the stator 24 or one orbiting rotation for every 1/6 rotation of the rotor 56 on its axis, for example. The cavities or chambers which are separated from one another are defined between the stator 24 and the rotor 56 and each of the cavities is varied in volume as the rotor 56 is rotated. As the rotor 56 is rotated, some of the cavities are increased in volume and the other cavities are decreased in volume. As a result, if the hydraulic oil is introduced into some cavities, and the oil in the other cavities is discharged to the outlet, the rotor 56 is rotated clockwise and the rotation on its axis is transmitted to the drive shaft 58, thus causing the Gerotor to operate as a motor. In this case, since there is the previously mentioned relation between the orbiting and the rotation on its axis for maxing one rotation of the drive shaft 58, the hydraulic oil for 7 cavities.times.6 (rotations)=42 cavities is introduced. Thus, the hydraulic motor of the Gerotor type is capable of providing 1/6 speed reduction with an output torque which is 6 times that of the prior art hydraulic motors. The previously mentioned rotary valve is designed so that hydraulic oil is alternately supplied to and discharged from the Gerotor cavities so as to continuously rotate the Gerotor rotor 56 smoothly. For this purpose, as shown in FIG. 1, the rotation of the drive shaft 58 is transmitted to the eccentric circular cam 18 by way of a pin 66 and the commutator 10 is rotated to change the connections of the oil passages. On the drive shaft 58 side, the pin 66 is fitted in the central portion of the drive shaft 58, and on the cam 18 side the pin 66 is fitted in an elongated hole of the cam 18. The center of the drive shaft 58 moves to describe a circular path in response to the rotation of the rotor 56, and thus the pin 66 is fitted in the hole of the drive shaft at a position so that the center of the pin 66 is deviated from the center of axis of the cam 18 by an amount corresponding to the radius of the circular path, thus transmitting the orbital rotation of the rotor 56 to the eccentric cam 18.

In accordance with well known understanding of the operation of such type motors, as the hydraulic oil is supplied to some of the cavities, the rotary valve and particularly the commutator function to selectively connect the expanding chambers with the fluid input and the contracting with the fluid output. Such an arrangement is well known as shown, for example, U.S. Pat. Nos. 3,316,814, 3,452,680 and 3,558,245, which are incorporated herein by reference for the description of the operation.

While the construction and operation of the Gerotor type motor with the rotary valve have been described briefly, such Gerotor type motor or pump is disadvantageous in that the oil leaks from the high pressure portion to the low pressure portion in the rotary valve thus deteriorating the efficiency of the machine. Consider the case of the Gerotor type motor shown in FIG. 1, when the cavity in the valve chamber is on the inlet side of hydraulic oil with a higher pressure and the annular grooves 38 and 40 of the commutator 10 and the annular groove 48 of the port member 12 are on the outlet side of hydraulic oil with a lower pressure. If the commutator valve 10 is made of a single rigid member with operating clearance, the oil will leak from the inlet side to the outlet side through the gap between the commutator 10 and the end cover 16 or through the gap between the commutator 10 and the port member 12.

Similarly, if the annular groove 48 is pressurized, there will be leakage through the same gaps toward cavity 70. In addition, in a design of the kind shown in FIG. 1, there is a vented area around eccentric cam 18 and leakage will occur from annular grooves 38 and 40 to this vented area.

In the past it has been customary to use a method of improving the finishing accuracy of the spacer 14, the commutator 10 and the end cover 16 so as to make the clearance on each side of the commutator 10 as small as possible and thereby to minimize oil leakage. However, when such a method is used, there is a possibility of increasing the clearance due to the clamping pressure of the clamping bolts, due to distortion caused by internal hydraulic pressures or due to thermal dimensional changes or distortion.

In the aforementioned U.S. Pat. No. 4,449,898, a solution to the aforementioned problems was proposed wherein the commutator comprises two spaced members movable in unison with a sealing element interposed between the two members. The motor heretofore described is substantially identical to that of U.S. Pat. No. 4,449,898 which is incorporated herein by reference.

Referring to FIGS. 2, 3, 5 and 6, in accordance with the invention, the commutator 10 is made of two members 72, 74 having their outer surfaces contacting respectively the port member 12 and the end cover 16. The adjacent surfaces of the members 72, 74 are provided with spaced pairs of annular sealing members 76, 78 and 80, 82 spaced radially from one another about the commutator members 72, 74.

Referring to FIG. 3, the sealing members are positioned in annular grooves 84 in commutator member 72 and 86 in commutator member 74. Each sealing member comprises an annular hole ring 76, 78 and a right angle metal retainer 92, 94. The backing member 92, 94 are positioned such that they abut one another with one leg of each member lying in the same plane as the corresponding radially extending leg of the other member and the other leg of the backing member extending axially. As shown in FIG. 5, the inner sets of seal packs 80, 82 are similarly arranged. However, as shown in FIG. 5, the seal pack 80 on the commutator member 72 is spaced radially inwardly of the seal pack 82 on the commutator member 74. This may be contrasted to the outermost seal pack 76, 78 wherein the seal pack 76 on the commutator member 72 is spaced radially inwardly of the seal pack 78 o the commutator member 74.

By this arrangement, the radially spaced pairs of seal packs permit a design for pressure balancing as well as making the motor capable of operating in both directions.

Referring to FIGS. 5 and 6, the motor further includes a bearing 96 interposed between the cam 18 and the commutator members 72, 74 constituting the commutator 10. Bearing 96 includes an annular rib 88 that extends radially toward the commutator members 72, 74. The commutator members in turn include circumferentially spaced radially inwardly extending arcuate notches 100 that define axial projections 102 on the commutator members 72, 74 on opposite sides of rib 90. Hydraulic fluid can thus flow freely through the associated passages and equalize the pressure on the members 72, 74. The bearing 96 is captured between members 72, 74.

When the commutator is moved in an orbital manner, an effective seal is provided without causing wear of the seal thereby insuring long life and minimum maintenance. The contacting surfaces of the commutator 10 with the end cover 16 and port member 12 are suitably treated or made of suitable material to insure long life.

In practice, the resilience of the seal axially will place the contacting faces of the commutator members 72, 74 in initial contact with the end cover 16 and seal member 12. Hydrostatic pressure acting between the members 72, 74 radially inwardly or radially outwardly will hold the faces in contact against the pressure gradients that act across the orbiting faces of the commutator. The resilience of the seal axially will avoid mechanical binding or possible seizure between the commutator and the end cover and port member such as might occur upon thermal expansion.

It has been found that the Gerotor type fluid rotary machine made in accordance with the invention provides an axial pressure balance such that the machine can be operated for rotation in either direction.

The manner in which the commutator made in accordance with the invention functions to achieve the objectives of the invention is believed t be shown by reference to the schematics of hydrostatic pressure fields as shown in FIGS. 7 and 8. These schematics refer to the hydrostatic pressures on the commutator members 72, 74. P.sub.1 comprises tank pressure, P.sub.2 comprises the pressure from the left and right respectively. Referring to FIG. 7, which represents the hydrostatic pressure fields for left hand rotation, it can be seen that the pressures can be substantially balanced. Specifically, constant pressure field A.sub.l may be made equal to or slightly larger than the pressure field A.sub.3 which is a decaying pressure field by controlling the radial position of the seal packs. Thus, the position of the relative areas A.sub.1, A.sub.2 defined by the horizontal legs of the retainer members of each seal pack determine the areas and, in turn, the relative pressures.

When a motor is designed for proper balance in the direction as identified in FIG. 7 and is rotated in the opposite or right hand direction of rotation, the pressure forces remain substantially balanced. As shown in FIG. 8, the pressure force A.sub.2 is substantially equal to or may be made slightly larger than the pressure force A.sub.3.

The aforementioned construction may be contrasted to similar schematics of hydrostatic pressures in commutators of the prior art and specifically of those shown in U.S. Pat. No. 4,449,898 by reference to FIGS. 9 and 10. As shown in FIG. 9, a single seal pack can be designed so that the pressure field A.sub.1 is equal to the pressure field A.sub.3 in one direction of rotation. However, as shown in FIG. 10, when the rotation is reversed, the hydrostatic pressure force of A.sub.l +A.sub.2 exceed that of A.sub.3 and the split disc will be subjected to axial binding.

Among the advantages achieved are the following:

1. The axial sealing forces (separating) of the "split" disc rotating/orbiting flow distributor are pressure balanced or biased to minimize the slippage volume (improved volumetric efficiency);

2. The axial sealing force (separating) of the split disc rotating/orbiting flow distributor are pressure balanced or biased to minimize the coulomb friction (improved mechanical efficiency);

3. The controlled axial balance of the split design disc provides respectable break-away torque characteristic for rotation in either direction;

4. The controlled hydrostatic pressure balance or bias makes the axial separating force less dependent on the compression of the elastomer seal;

5. The controlled axial balance of the split design disc permits the application of the HTLS fluid motor in hydraulic systems with overrunning loads;

6. The controlled axial force and the resiliency of the elastomer seal and the selection of materials makes the rotating/orbiting disc less vulnerable to seizure;

7. The controlled axial force and the resiliency of the elastomer seal and the selection of materials makes the rotating/orbiting disc more tolerant to thermal shock; and

8. The simple design of the split disc flow distributor allows for the utilization of manufacturing techniques to achieve a relatively economical part.

It can thus be seen that there has been provided a rotary valve for a Gerotor type fluid rotary machine wherein the axial sealing forces are pressure balanced or biased to minimize the slippage volume and improve the volumetric efficiency, minimize the coulomb friction and improve the mechanical efficiency, provide proper break-away torque characteristics for rotation in either direction, which will make the axial separating force less dependent on the compression of an elastomeric seal; which will permit the application of the fluid motor in hydraulic systems with over-running loads; and which will make the rotating/orbiting disc more tolerant to thermal shock; which can be manufactured readily by the utilization of conventional manufacturing techniques.