GB2028428A

GB2028428A - Rotary Positive-displacement Fluid-machines

Info

Publication number: GB2028428A
Application number: GB7919713A
Authority: GB
Original assignee: Nichols Co W H
Current assignee: Nichols Co W H
Priority date: 1978-06-07
Filing date: 1979-06-07
Publication date: 1980-03-05
Also published as: DE2922921A1; GB2028428B

Abstract

A gerotor machine, which may be a pump, has an inner member (20) rotatable about its axis and an outer internally-toothed member (30) rotatable about its axis, which is parallel to the first-mentioned axis. The inner member has roller teeth (26), which are movable radially outwardly and held against the outer member by both centrifugal force and the pressure of the working fluid thereunder, Fig. 3 (not shown). <IMAGE>

Description

SPECIFICATION Improvements in or Relating to a Gerotor This invention relates to an internally generated roller gerotor (IGR) and more particularly to an IGR having an improved means for sealing between adjacent teeth as well as an improved method of operation.

As is known, an IGR is a gerotor device for supplying fluid under pressure (e.g. a pump) having an inner rotor which is rotatable within the inner periphery of a rotatable outer rotor. The axis of rotation of the inner rotor is eccentric with respect to the axis of rotation of the outer rotor.

The inner rotor has gear-teeth-like elements which consist of cylindrical rollers equally circumferentially spaced around the periphery of and received in radial pockets of the inner rotor.

The outer rotor has corresponding gear-teeth-like elements which are of a generated nature so as to provide continuous conjugate interaction with the gear teeth elements of the inner rotor in a manner that a plurality of alternately expanding and contracting chambers are effected upon rotation of the rotors with respect to each other.

The conjugate interaction of the gear teeth serve effectively to isolate or seal adjacent expanding and contracting chambers from communication with one another. This isolation or sealing occurs to a certain degree throughout the.

operation of the IGR, however, it is not of operational significance during those portions of operating cycle when the pressure within adjacent chambers are equal or substantially equal. Equality of pressure within adjacent chambers occurs throughout the major portion of the IGR cycle on both the low pressure tank or supply side and on the high pressure load discharge side, however, the seal between adjacent volume chambers is of significant importance at "cross-over" conditions. "Crossover" is at those locations of the operating cycle where the mating teeth of the inner and outer rotor are located intermediate high pressure and tank sides of the IGR.Thus a chamber on one side of the mating teeth at cross over is at low pressure and the chamber on the other side of such mating teeth is at high pressure with the resulting potential of decreased operational efficiency being caused by the back flow of the hydraulic pressure fluid from the high pressure to the low pressure chamber.

Some IGR's utilized heretofore had the roller teeth of the inner rotor captively maintained within the said respective pockets. In such instances, if the clearance between adjacent "mating" teeth were to great, a flow path between adjacent chambers is created which will result in a back flow of fluid at cross over locations from the high pressure to the low pressure chamber thus substantially decreasing the potential volumetric efficiency of the IGR.

Manufacturers of IGR's have attempted to overcome this volumetric inefficiency problem resulting from such a clearance space by manufacturing an interference fit between the mating teeth of the inner and outer rotors. An example of an interference fit IGR is illustrated in U.S.A. Patent Specification No. 3,623,829. While interference fit roller gerotors have proved successful in overcoming or alleviating such volumetric inefficiences, problems generally associated with interference fits of relatively rotating members are readily apparent, for example, reduction in mechanical efficiency, increased wear, close tolerance control of interface hardware and the like.

An effort to overcome the problems of interference fits with gerotor devices while still maintaining volumetric efficiency at cross over is described in an EGR illustrated in U.S.A. Patent Specification No. 3,930,766. EGR's are also fluid pressure devices of the gerotor type and in general are similar in construction to the IGR's discussed above with the primary distinction therebetween being that rollers are circumferentially positioned as the gear teeth on the outer rotor and the gear teeth of the inner rotor are of a generated nature so as to provide continuous conjugate interaction with the roller gear teeth of the outer rotor.

The EGR described in U.S.A. Patent Specification No. 3,930,766 is an arrangement wherein the roller teeth are biased inwardly by fluid pressure. This arrangement while overcoming the problems of interference fit does not provide optimal operational efficiency.

Specifically the design shown in U.S.A. Patent Specification No. 3,930,766 is an EGR wherein the rollers are received in the pockets of the outer member in a manner to permit radial movement of the roller. With this arrangement there are no forces tending to bias the rollers into engagement with the inner rotor until a pressure differential is created at cross over. Indeed, the operational forces on the rollers act adversely to the objective of sealing engagement with the inner rotor regardless of whether or not the outer rotor is utilized in a stationary or rotating mode. During non-active portions of each cycle (i.e. when there is no pressure differential on adjacent sides of mating teeth) the rollers tend to migrate radially outwardly from the inner rotor.Thus at cross over when pressure differential exists, the rollers must be forced to move inward into sealing engagement with the inner rotor. This inward movement of the rollers is resisted by outwardly directed operational forces caused by centrifugal action and/or contact forces intermediate the roller and the adjacent surfaces of the inner rotor.

At typical operating speeds the response time required to move the sealing roller into sealing engagement with the inner rotor significantly decreases volumetric efficiency. The total time during which sealing is required is only a matter of a few milliseconds, accordingly, it is readily apparent that only a small response time can significantly effect operational efficiency.

According to one aspect of this invention there is provided a gerotor comprising, a gerotor set having an inner member coaxially rotatable about an axis and an outer internally toothed member coaxial about an axis which is parallel to said first mentioned axis, said inner member supporting a plurality of circumferentially spaced roller teeth means, said roller means being radially movable outwardly with respect to said inner member to provide sealing conjugate interaction with the adjacent inner peripheral surface of said outer member, and said inner and outer members, in conjunction with said roller means, defining a plurality of circumferentially spaced chamber portions therebetween.

According to a second aspect of this invention there is provided a method of operating a fluid pressure gerotor assembly having a gerotor set with an inner member having roller teeth supported thereby and an internally toothed outer member having sealing conjugate interaction with the roller teeth, comprising continuously maintaining said conjugate interaction by moving said roller teeth radially outwardly by providing a continously outwardly directed centrifugal biasing force to said roller teeth and additionally providing an outwardly directed fluid pressure force to said roller teeth.

The preferred embodiment of the present invention comprises an IGR wherein the rollers of the inner rotor are received in circumferentially spaced pockets therefore to permit a controlled radial movement. The radii of the rollers and the respective pockets are proportional such that upon rotation of the inner rotor an outwardly directed centrifugal force will bias the rollers radially outwardly into engagement with the outer rotor while the roller will simultaneously be supported by an adjacent arcuate portion of the pocket. Furthermore, at cross over, the pressure fluid already present radially intermediate the roller and the portion of the pocket radially spaced therefrom will act to further bias the roller radially outwardly into sealing engagement with adjacent peripheral portions of the outer rotor.In this instance the gear teeth of the outer rotor will be generated to provide a conjugate interaction with the radially outwardly biased rollers. Thus it is believed that the preferred embodiment of the invention described herein will overcome the deficiences noted hereinabove with respect to interference fits while still providing an adequate seal between adjacent gear teeth to provide operational efficiency of the IGR during cross over conditions.

In order that the invention may be more readily understood, and so that further features thereof may be appreciated the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is transverse cross sectional view, partially schematic, of an IGR in accordance with the present invention; Figure 2 is a longitudinal cross sectional view, partially schematic, taken on lines 2-2 of Figure 1; and Figure 3 is an enlarged end view of a portion of the IGR of Figure 1 and illustrating a roller applied with a pocket.

The drawings illustrate an IGR 10 in accordance with the present invention which comprises an IGR displacement or gear set 12 driven by a shaft 14 which is rotatably supported within a formed opening 1 6 of a suitable housing 18.

The gear set 12 includes an inner rotor 20 having external tooth supporting portion 22 includes a radially inwardly directed outwardly open pocket 24 formed therewithin for respectively supporting solid metal cylindrical tooth members or rollers 26. The gear set 12 additionally includes an outer rotor 30 having internal teeth 23 which are of a generated nature so as to provide continuous conjugate action with the rollers 26 of the inner rotor 20. As will be discussed hereinafter, the rollers 26 are movable radially outwardly during operation of the IGR 10.

Accordingly, the generated configuration of the teeth 28 and the conjugate interaction of the teeth 28 with the rollers 26 is determined as during operation of the IGR 10 when the rollers 26 are moved radially outwardly from their respective pockets 24. Further rollers 26 are cooperable with the internal teeth 28 of the outer rotor 30 in a manner to define inlet andoutlet pumping chambers 32 and 34, respectively, therebetween. As is known, chambers 32 and 34 are formed by a plurality of adjacent chamber portions which are defined between rotors 20 and 30. Pumping chambers 32 and 34 are respectively in communication with kidney shaped inlet and outlet ports 36 and 38 to provide for a known flow and pumping pattern for fluid flowing through IGR 10.As this invention is directed primarily to the gear set 1 2 and the method of operation of IGR 10, the concepts of the invention may be employed wherever such gear sets find utility and is not limited to particular end uses. However, for the purposes of the description herein, the drawings illustrate a typical application of an IGR 10 in a pump such as a lubricating oil pump. Further, in devices of the type shown, the inner and outer rotors rotate on fixed, mutually spaced axes. However, the invention herein may be employed in other types of devices wherein one of the members is held fixed and the other rotates about its own axis which in turn orbits about the axis of the fixed gear, for example as illustrated in U.S.A. Patent Applications Serial Nos. 846,693 and 846,886 which were both filed on 31st October 1977 and are assigned to the same assignee as is this invention. Also, such devices may be pumps, motors or transmissions of various kinds, all as is well known in the art. Furthermore, in as much as the basic structure and operation of IGR's are well known in the art, further detailed description thereof will not be set forth hereinafter except as is necessary in the description of this invention.

For a detailed description of the structure and operation of an IGR reference is hereby made to U.S.A. Specification No. 3,623,829 which is assigned to the same assignee as is this invention .and which is incorporated herein for purposes of this description.

As best seen in Figure 3 pockets 24 are of a generally semi-circular configuration and are struck from a radius slightly larger than the radius of the cylindrical rollers 26 thereby providing a seating surface whereby rollers 26 are rotatably disposed and are radially movable. Thus when inner rotor 20 is being driven by shaft 14, the rollers 26 will move radially outwardly under the influence of two independent forces, namely a radial outwardly directed centrifugal force, generally indicated at X and an intermittently applied radially outwardly directed resultant hydraulic force which is represented as a pressure gradient Y on a peripheral portion of roller 26.

This radially outward movement of roller 26 creates a clearance 40 intermediate pocket 24 and an adjacent spaced portion of rollers 26, however, pockets 24 are proportioned such that they will provide a seating and sealing surface for the respective rollers 24 throughout the radial movements thereof.

At this point it is important to note that there has been found to be an optimum radial clearance of the roller 26 with respect to the pocket 24 at which an IGR 10 constructed in accordance with the present invention will perform most efficiently. This optimum clearance can best be stated as primarily a function of the diameter of roller 26 where R is radius of the pocket 24 and D is the diameter of the roller 26 as follows: RmaxD/2+0.005D Rmin.=D/2+0.003D Furthermore, in as much as it is of primary importance that the roller 26 be relatively freely movable radially outwardly into rolling engagement with the outer rotor 30, in no instance is the arc length of pocket 24 taken in conjunction with D and R, to be of such a length as to inhibit this outward movement of roller 26.

The centrifugal force X is dependent upon rotation of the inner rotor 20 and no such centrifugal or inertia force exists under static conditions. Accordingly, it is understood that for proper operation of an IGR constructed in accordance with this invention the inner rotor thereof is necessarily subject to rotation about a transverse axis, including but not limited to, the central axis thereof.

The hydrostatic pressure gradient Y is caused by high pressure fluid within outlet pumping chamber 24 entering the clearance 40 and exerting a gradient hydrostatic pressure between the pocket 24 and roller 26. The resultant of the hydrostatic pressure gradient Y will also be outwardly thereby tending further to bias the roller 26 outwardly into sealing conjugate engagement with the outer rotor 30. It is to be noted that the hydrostatic pressure gradient Y is only germane to positions of rollers 26 at the cross over or open and full mesh relative positions of rotors 20 and 30 which are respectively indicated at the top of Figure 1 at "A" and at the bottom of Figure 1 at points "B".In such positions the hydrostatic pressure gradient, in conjunction with the contour of pockets 24, result in a seating and sealing relationship being established between roller 26 and an upper arcuately extending portion of pocket 24 which is trailing the direction of rotation of rotor 20 (See Figure 3).

Simultaneously, the pressure fluid fills clearance 40, and pressure gradient Y, in conjunction with the centrifugal forces acting on roller 26, result in roller 26 having conjugate interaction with adjacent peripheral portion of rotor 30. In the positions of rollers 26 other than at point A and B the pressure gradients do not exist because the respective volume portions of chambers 32 and 34 on each side of such rollers 26 are both at either high or low pressure and thus sealing in these areas is not a problem. However, it is to be noted that when rollers 26 are biased by centrifugal force in the position illustrated in Figure 3 at points A and B, fluid is always present behind the rollers 26 during this time.When the rollers 26 thereafter pass through the balanced positions to the open and full mesh positions, the fluid within the clearance 40 behind rollers 26 is instantly pressurized to achieve the requisite sealing so as not to lose efficiency of operation of IGR 10.

As discussed hereinbefore, the effectiveness of the prior art EGR's is reduced by the response time required to effect sealing conjugate interaction of the sealing rollers and that although this response time for roller movement is only a few milliseconds, this represents a significant portion of the total time that sealing is required.

However, through the utilization of the present invention which includes an IGR 10 which is operated with a constantly outwardly directed centrifugal force X, the rollers 26 are constantly being biassed outwardly. Hence the clearance 40 is constantly being maintained full of hydraulic fluid which will be instantaneously pressurized when the particular roller 26 is subject to change over conditions. Thus, with the invention herein, the rotation of the inner rotor 20 creates a centrifugal force of a magnitude to aid in the continuous interaction of the rollers 26 with the outer rotor 30, but which magnitude is not so great as to impair the mechanical efficiency of the IGR 10.

The embodiment described herein is the presently preferred embodiment of an IGR constructed in accordance with the invention; however, it is understood that various modifications may be made to the embodiment described herein by those knowledgeable in the art without departing from the scope of the invention as defined by the claims set forth hereinafter. For example, the invention herein is equally applicable to IGR's other than the application to a pump as described herein, the number of teeth may be changed so long as the outer rotor 30 has one more tooth than the inner rotor 20, the configuration of inlet and outlet ports 36 and 38 may be varied, and the like.

From the foregoing it will be appreciated that this invention provides an IGR having rollers disposed in respective pockets of the inner gear for controlled radial movement. The rollers are responsive to both centrifugal and pressure biasing forces to insure intimate contact or sealing conjugate interaction between adjacent teeth at cross over. Also this invention provides a method of operating an IGR which includes providing radially outwardly directed centrifugal and fluid pressure forces and moving the rollers radially outwardly in response to these forces to maintain continuous conjugate interaction between the teeth of the inner and outer rotors.

Claims

1. A gerotor comprising a gerotor set having an inner member coaxially rotatable about an axis and an outer internally toothed member coaxial about an axis which is parallel to said first mentioned axis, said inner member supporting a plurality of circumferentially spaced roller teeth means, said roller means being radially movable outwardly with respect to said inner member to provide sealing conjugate interaction with the adjacent inner peripheral surface of said outer member, and said inner and outer members in conjunction with said roller means, defining a plurality of circumferentially spaced chamber portions therebetween.

2. A gerotor as claimed in claim 1 wherein the teeth of said outer member are of a generated nature with respect to the outer rotational path of said roller means.

3. A gerotor as claimed in claim 1 or 2 wherein said inner member includes a plurality of circumferentially spaced radially outwardly open supporting pockets and with each of said pockets supporting a respective one of said roller means therewithin.

4. A gerotor as claimed in claim 3, wherein said pockets provide a supporting surface for said roller means throughout the radial movement thereof and when each of said roller means is in the radially outermost location thereof, and said supporting surface is an arcuately extending portion of a respective one of said pockets, which portion is trailing the direction of rotation of said inner member.

5. A gerotor as claimed in claim 4 wherein said roller means each comprise elongated rigid cylindrical member and the longitudinal axis of said cylindrical member is parallel to said first and second mentioned axes.

6. A gerotor substantially as herein described with reference to and as shown in the accompanying drawings.

6. A gerotor as claimed in claim 5 wherein said pockets are arcuate and are struck from a radius being substantially within the range of D/2+0.005D for a maximum and D/2+0.003D for a minimum and where D is equal to the diameter of said cylindrical member.

7. A method of operating a fluid pressure gerotor assembly having a gerotor set with an inner member having roller teeth supported thereby and an internally toothed outer member having sealing conjugate interaction with the roller teeth, comprising continuously maintaining said conjugate interaction by moving said roller teeth radially outwardly by providing a continuously outwardly directed centrifugal biasing force to said roller teeth and additionally providing an outwardly directed fluid pressure force to said roller teeth.

8. A method of operating a fluid pressure gerotor assembly as claimed in claim 7 wherein said step of additionally providing an outwardly directed fluid pressure force is performed at least during those periods when said roller teeth are passing from the low pressure side of said gerotor assembly to the high pressure side thereof.

9 A method of operating a fluid pressure gerotor assembly as claimed in claim 8 comprising the further step during said period of supporting the ones of said roller teeth intermediate said low and high pressure sides at a location on said inner member which is trailing the direction of rotation of said inner member.

10. A gerotor substantially as herein described with reference to and as shown in the accompanying drawings.

11. A method of operating a gerotor substantially as herein described with reference to the accompanying drawings.

12. Any novel feature or combination of features disclosed herein.

New Claims or Amendments to Claims filed on 1 November 1979.

Superseded Claims 1 to 12.

New or Amended Claims

1. A gerotor comprising a gerotor set adapted to be connected to hydraulic fluid inlet and outlet means and having an inner member coaxially rotatable about an axis and an outer member coaxially rotatable about an axis which is parallel to said first mentioned axis, said outer member including a plurality of inwardly extending circumferentially spaced gear teeth, said inner member supporting a plurality of circumferentially spaced roller teeth means for conjoint rotation therewith said roller means being movable radially outwardly during rotation of said inner member to provide conjugate, interaction with the adjacent inner peripheral surface of said outer member, said inner and outer members, in conjunction with said roller means, defining a plurality of circumferentially spaced chamber portions therebetween, the said gear teeth being of a generated nature with respect to the outer path of said roller means.

2. A gerotor as claimed in claim 1 wherein said inner member includes a plurality of circumferentially spaced radially outwardly open supporting pockets, each of said pockets supporting a respective one of said roller means therewithin.

3. A gerotor as claimed in claim 2, wherein each of said pockets provide a supporting surface for the respective said roller means throughout the radial movement thereof and when each of said roller means is in the radially outermost location thereof, said supporting surface being an arcuately extending portion of the pocket, which portion is trailing the direction of rotation of said inner member.

4. A gerotor as claimed in claim 2 or claim 3 wherein said roller means each comprise an elongated rigid cylindrical member and the longitudinal axis of said cylindrical member is parallel to said first and second mentioned axes.

5. A gerotor as claimed in claim 4 wherein said pockets are arcuate and are struck from a radius being substantially within the range of D/2+0.005D for a maximum and D/2+0.003D for a minimum and wherein D is equal to the diameter of said cylindrical member.