INTERNAL GEAR PUMP

Abstract

An internal gear pump for delivering a fluid, in particular one of the gerotor pump type, having a driven gear wheel, a rotatable annular gear interacting with the gear wheel, and a substantially cylindrical housing, in which the gear wheel and the annular gear are arranged. The housing has a base portion, an annular portion and a cover portion, the base portion having a pressure port, which forms a delivery chamber of the pump or opens into the latter. A thrust ring is arranged between the gear wheel and the annular gear on the one hand and the cover portion of the housing on the other. At least one connecting passage on or in the housing of the pump extends from the delivery chamber of the pump up to a gap between the thrust ring and the cover portion of the housing, in order to carry fluid from the delivery chamber into the gap.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119 to German Patent Application No. 10 2011 017 374 (filed on Apr. 1, 2011), which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The invention relates to an internal gear pump for delivering a fluid, in particular one of the gerotor pump type.

BACKGROUND OF THE INVENTION

Such an internal gear pump has a driven gear wheel (also referred to as an inner rotor) and an annular gear (also referred to as an external rotor) interacting with the gear wheel, the annular gear having at least one tooth more than the gear wheel.

FIG. 7 illustrates a cross-sectional view of a conventional gerotor pump 101 (also referred to as an annular gear pump). The pump 101 has a substantially cylindrical housing having an annular portion 103. An annular gear 105 is supported on the circular inner circumference of the annular portion 103 so that it is free to rotate about an axis A1. A gear wheel 107, which is driven by way of a drive shaft (not shown) to rotate clockwise about an axis A2, for example, is arranged radially inside the annular gear 105 and eccentrically in relation to the annular gear 105. The gear wheel 107 has an external toothing, and the annular gear 105 has an internal toothing with a greater number of teeth than that of the gear wheel 107. The gear wheel 107 meshes with the annular gear 105 and thereby drives the annular gear 105 to rotate. Owing to the greater number of teeth, however, the annular gear 105 rotates more slowly than the gear wheel 107.

Also illustrates in FIG. 7 are a suction port 109 and a pressure port 111, which are formed on a base portion 113 of the pump housing, on which the annular gear 105 and the gear wheel 107 rest. Axially offset from the base portion 113 relative to the axes A1, A2, the annular gear 105 and the gear wheel 107 are covered by a cover portion of the housing (not shown). Due to the rotation of the gear wheel 107 relative to the housing (annular portion 103, base portion 113 and cover portion), rotating pump chambers of variable volume, into which a fluid is drawn from the suction port 109, are formed between the gear wheel 107 and the annular gear 105. The fluid is finally expelled into a pressure chamber 115 of the pump 101, into which the pressure port 111 opens or which is formed by the pressure port 111 itself.

One particular problem of such an internal gear pump is the friction between the gear wheel 107 and the annular gear 105 on the one hand and the surrounding portions of the housing on the other. This friction causes an unwanted loss of power, which is accompanied by a heating and impairment of the fluid.

German Patent Publication DE 43 15 432 A1, therefore, discloses the arrangement of a thrust ring, which is rotationally fixed to the rotating annular gear, between the gear wheel and the annular gear on the one hand and the cover portion of the housing on the other. The thrust ring reduces the power loss by virtue of a reduction in the differential speed and hence a reduction in the friction. In particular, the thrust ring may be composed of a material having a low coefficient of friction, or it may be provided with a coating of a material having a low coefficient of friction. This is comparatively costly, however, and even then still does not bring about the feasible reduction of the friction losses consistent with cost-effective manufacturing.

SUMMARY OF THE INVENTION

An object of the invention is to create an internal gear pump of said type, which being of simple construction exhibits a low degree of friction between the gear wheel and the annular gear on the one hand and the housing on the other.

A further object of the invention is to stabilize the alignment of the gear wheel.

At least these objects are achieved by an internal gear pump that includes at least the following: a thrust ring arranged between a gear wheel and an annular gear on the one hand and a cover portion of the housing on the other, at least one connecting passage on or in the housing of the pump extending from the delivery chamber of the pump up to a gap between the thrust ring and the cover portion of the housing, in order to carry fluid from the delivery chamber into the gap.

At least these objects are further achieved by an internal gear pump that includes at least the following: a driven gear wheel; a rotatable annular gear operatively communicating with the driven gear wheel; a housing in which the driven gear wheel and the rotatable annular gear are arranged, the housing comprising a base portion, an annular portion and a cover portion, the base portion having a pressure port which forms a fluid delivery chamber; a thrust ring arranged between the driven gear wheel and the rotatable annular gear and also the driven gear wheel and the cover portion; a gap formed between the thrust ring and the cover portion; and at least one fluid connecting passage extending from the fluid delivery chamber up to the gap in order to carry fluid from the delivery chamber into the gap.

At least these objects are also achieved by an internal gear pump that includes at least the following: a gear wheel which is rotatable about a first axis; an annular gear which is rotatable about a second axis; a thrust ring rotationally fixed to the annular gear; a housing which houses the gear wheel, the annular gear and the thrust ring, the housing having a fluid delivery chamber and a cover portion; a gap formed between the thrust ring and the cover portion; and a fluid connecting passage in the housing through which fluid flows from the fluid delivery chamber to the gap to thereby form a hydrodynamic lubricating film in the gap which reduces operational friction between the thrust ring and the cover portion.

At least these objects are further achieved by an internal gear pump that includes at least the following: a gear wheel; an annular gear; a thrust ring; a housing having a fluid delivery chamber and a cover portion configured for placement such that a gap is formed between the thrust ring and the cover portion; and a fluid connecting passage through a fluid flows from the fluid delivery chamber to the gap to thereby form a hydrodynamic lubricating film in the gap which reduces operational friction between the thrust ring and the cover portion. The fluid connecting passage has a first connecting groove in communication with the fluid delivery chamber, a second connecting groove in communication with the first connecting groove, and a third connecting groove in communication with the second connecting groove and the gap. The thrust ring has a plurality of distribution grooves on a surface thereof which faces the gap and which are configured to distribute the fluid into the gap.

Between the thrust ring and the inside of the cover portion of the housing facing the thrust ring a gap is formed, which may extend over the entire surface of the thrust ring or merely a part thereof. A connecting passage on or in the housing of the pump leads from the delivery chamber of the pump up to the gap, in particular right behind the thrust ring, when viewed from the base portion of the housing. The pressurized fluid can therefore flow from the delivery chamber up to the gap, in order to build up a hydraulic pressure between the thrust ring and the cover portion of the housing and to form a hydrodynamically effective lubricating film as the thrust ring rotates.

It is possible here that the gap will only actually be formed by the pressurized fluid flowing in between the thrust ring and the cover portion of the housing. In other words, although the thrust ring may rest directly on the cover portion of the housing when the pump is at a standstill, when the pump is in operation it is important that a minimum clearance be provided between the thrust ring and the cover portion of the housing, in order to allow the formation of a fluid cushion or a lubricating film. For this purpose the fluid delivered by the pump is specifically carried along the connecting passage up to the gap between the rotor disc and the cover portion of the housing, the pressurized fluid, when necessary, being structurally configured to lift the thrust ring off slightly from the cover portion of the housing.

This results in a hydrodynamic lubrication, which serves to reduce the power loss still further. The additional design cost is minimal, since the connecting passage can be formed on or in the pump housing through simple production operations. A further advantage consists in that feeding the pressurized fluid to the rear side of the thrust ring exerts a force, which serves to reduce or even avoid any tilting or wobbling of the gear wheel. Furthermore, the specifically diverted fluid serves for hydraulically centring the annular gear, thereby increasing the service life of the pump still further.

The thrust ring is preferably rotationally fixed to the annular gear. In particular, the annular gear and the thrust ring may be integrally formed. Alternatively, however, the thrust ring may also be rotatably coupled to the gear wheel, or the thrust ring is “floating,” that is to say, supported so that it is free to rotate.

Where, in connection with the pump in accordance with the invention, reference is made to a “base portion” of the housing, this relates to the portion of the housing on which the pressure port is provided, which opens into the delivery chamber of the pump or which forms the delivery chamber. Where reference is made to a “cover portion” of the housing, this relates to the portion of the housing on which the thrust ring rests. In other words, the terms “base portion” and “cover portion” of the housing are used irrespective of whether the “base portion” in the pump installation position is arranged on an underside or an upper side of the pump, for example.

The connecting passage may be formed by one or more bores in the housing of the pump, for example, in particular by a bore in the base portion of the housing and/or by a bore in the annular portion of the housing.

In accordance with a preferred embodiment, however, the connecting passage includes at least one connecting groove, which extends along the inner circumference of the annular portion of the housing. It is therefore only necessary to apply a groove to the inside of the pump housing, for example by machining or by moulding, in order to carry the pressurized fluid up to the gap. The connecting groove in the annular portion of the housing may extend, for example, up to the transition between the annular portion and the cover portion of the housing. The connecting groove along the inner circumference of the annular portion of the housing preferably extends parallel to the axis of rotation of the annular gear. Alternatively, the connecting groove may also be slanted at an angle conducive to the flow and need not necessarily have a rectilinear course.

Such an “axial” connecting groove may emerge directly from the delivery chamber of the pump. Alternatively, a further connecting groove may be provided, which extends from the delivery chamber of the pump along the inside of the base portion of the housing up to the connecting groove in the annular portion of the housing, in particular radially outwards, in order to form a duct of L-shaped longitudinal section for the fluid.

In accordance with an advantageous embodiment the connecting passage (in particular the connecting groove in the annular portion of the housing) opens into an annular groove, which extends circumferentially along the transition between the annular portion and the cover portion of the housing and/or along the thrust ring. This allows the pressurized fluid to be distributed along the circumference of the thrust ring and/or the cover portion of the housing, in order to penetrate into the gap between the thrust ring and the cover portion of the housing in multiple different angular positions, and therefore, to form a lubricating film that is as uniform as possible.

It is particularly advantageous if the cover portion of the housing includes at least one distribution groove, which extends radially inwards on the inside of the cover portion facing the thrust ring. This is particularly effective in conducting the fluid into the gap between the thrust ring and the cover portion of the housing, in order to form the desired lubricating film. To do this the respective distribution groove need not extend radially inwards in an exact straight line, other courses and alignments also being possible (for example, a slanting alignment, a laterally offset arrangement or a curved path with a component directed radially inwards). The distribution groove preferably extends radially inwards starting from the transition between the annular portion and the cover portion of the housing and/or from the annular groove. A plurality of such distribution grooves are preferably provided.

With regard to the distribution groove in the cover portion of the housing it is preferred, in order to avoid additional leakage losses, if this groove has only a limited length, that is to say if the distribution groove does not extend radially inwards all the way through. In other words, the distribution groove is in this case to be formed as a stepped groove. This is particularly important if the thrust ring and/or the cover portion of the housing has a central through-hole for a drive shaft. If additional leakage is required, however, it is alternatively advantageous if the distribution groove of the cover portion is continuous, that is to say if the distribution groove extends radially all the way inwards.

Alternatively, or in addition to the distribution groove in the cover portion of the housing, on the side facing the cover portion (that is to say on its rear side) the thrust ring may also have at least one distribution groove, which extends radially inwards from the outer circumference of the thrust ring. Such a distribution groove on the thrust ring also serves to enhance the distribution of the pressurized fluid inside the gap between the thrust ring and the cover portion of the housing, so that a more uniform build-up of pressure and a more efficient hydrodynamic lubrication is obtained. The distribution groove in the thrust ring also need not be aligned radially inwards in an exact straight line, other courses and alignments being feasible.

With regard to the distribution groove in the thrust ring it is likewise possible for this to have a limited length, in order to reduce leakage losses in the radially inner area of the pump. Alternatively, the distribution groove in the thrust ring may extend radially inwards all the way through, in order to bring about a specific leakage, as explained above in connection with the distribution groove in the cover portion of the housing.

In an accordance with another embodiment of an advantageously simple design, the side of the thrust ring facing the cover portion of the housing may be of plane design. It is also advantageous, however, if the side of the thrust ring facing the cover portion of the housing is of tapered design, truncated cone-shaped design or convexly curved. Such a shaping of the thrust ring is a simple way of ensuring that along the entire circumference a minimum gap always exists between the thrust ring and the cover portion of the housing, at least in a radially outer area, in order to ensure an efficient hydrodynamic lubrication.

Alternatively, or in addition to this, the inside of the cover portion of the housing facing the thrust ring may also be of tapered design, truncated cone-shaped design or convexly curved. In these embodiments distribution grooves may additionally be provided on the cover portion of the housing and/or on the thrust ring, in particular without or with specific leakage, as explained above.

Where a specific leakage of the fluid carried into the gap between the thrust ring and the cover portion of the housing is brought about (for example, by a distribution groove in the cover portion or the thrust ring extending radially inwards all the way through), an advantage may lie, for example, in a reduced pressure level at higher rotational speeds (lower mechanical losses). Furthermore, such a specific leakage creates an additional facility for cooling the pump and/or the fluid. Such a specific leakage can furthermore serve to provide an interim storage of fluid not needed in certain operating states.

As an alternative or addition, in the case of such a specific leakage the fluid (particularly if the fluid is a lubricating oil) may be used for the lubrication of components close to the pump (for example through the use of a slinger ring). For example, the fluid may be carried out of the gap or directly out of the distribution groove to another component, which is arranged on or adjacent to the pump. In particular, the housing of the pump may have an outlet port, in order to conduct a proportion of the fluid, carried out of the delivery chamber towards the gap, to another component and thereby to lubricate the latter. The outlet port may, in particular, be provided in a radially inner area of the pump housing, for example, in the area of a central through-hole in the cover portion of the housing intended for a drive shaft. However, such a through-hole in the cover portion intended for a drive shaft need not be present in all embodiments of a pump in accordance with the invention.

It is furthermore preferred if the thrust ring extends in one piece in a radial direction between the gear wheel and the annular gear. In other words, the thrust ring in accordance with this embodiment should at least partially cover not only the annular gear, but also the gear wheel in a radial direction, there being no possibility for direct communication of the gap (hydrodynamic lubrication gap between the thrust ring and the cover portion of the housing) with the pump chambers, which are formed between the gear wheel and the annular gear. For a simple construction, the thrust ring therefore ensures that no significant leakage losses occur in an axial direction (relative to the axis of rotation of the gear wheel and of the annular gear).

BRIEF DESCRIPTION OF THE DRAWINGS

Advantageous refinements of the invention will emerge from the dependent claims. An exemplary embodiment of the invention will be discussed in principle below on the basis of the drawing, in which:

FIG. 1 illustrates a view in longitudinal section through an internal gear pump.

FIG. 2 illustrates a cross-sectional view of an internal gear pump.

FIGS. 3 a and 3b illustrates a top view and a side view respectively of a thrust ring in accordance with embodiments.

FIG. 4 illustrates a top view of a thrust ring in accordance with embodiments.

FIG. 5 illustrates a view in longitudinal section through a thrust ring in accordance with embodiments.

FIG. 6 illustrates a view in longitudinal section through a thrust ring in accordance with embodiments.

FIG. 7 illustrates a cross-sectional view of a conventional internal gear pump.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 illustrates an internal gear pump 1 in accordance with the invention of the gerotor pump type. The pump 1 includes a gear wheel 7, which is driven to rotate about an axis A2 by a shaft 17 passing through the pump. The pump 1 further includes a freely rotatable annular gear 5, that is to say an internal gear, the internal toothing of which meshes with the external toothing of the gear wheel 7. The axis of rotation A1 of the annular gear 5 is eccentric to the axis of rotation A2 of the gear wheel 7. A thrust ring 19 is rotationally fixed to the annular gear 5, for example, via weld or bond. Alternatively, the thrust ring 19 is integrally formed with the annular gear 5. The thrust ring 19 may be composed, for example, of steel. Apart from a central through-hole for the shaft 17, the thrust ring 19 is closed (that is to say it is without apertures) and is formed in one piece. The outside diameter of the thrust ring 19 corresponds to or is otherwise substantially equal to that of the annular gear 5.

The gear wheel 7, the annular gear 5 and the thrust ring 19 are accommodated in a housing of the pump 1, which includes a hollow cylindrical annular portion 3. The annular gear 5 is rotatably supported on the inner circumference of the annular portion 3.

The housing of the pump 1 further includes a base portion 13, on which the gear wheel 7 and the annular gear 5 rest and which in the exemplary embodiment illustrated in FIG. 1 is integrally formed with the annular portion 3. A delivery chamber 15 of the pump 1 is formed in the base portion 13 of the housing The housing of the pump 1 further includes a cover portion 21, which in the exemplary embodiment illustrated in FIG. 1 takes the form of a separate cover.

The thrust ring 19 is arranged spatially between the gear wheel 7 and the annular gear 5 on the one hand and the cover portion 21 of the housing on the other. A gap 23 of very narrow size is formed between the thrust ring 19 and the cover portion 21. Inside the housing the gear wheel 7, the annular gear 5 and/or the thrust ring 19 may be pre-tensioned in an axial direction relative to the axes of rotation A1, A2 (not illustrated).

When the pump 1 is in operation, the annular gear 5, together with the thrust ring 19 coupled thereto, rotates more slowly than the gear wheel 7. The thrust ring 19 therefore contributes to a certain reduction of the friction losses, since the differential speed between the gear wheel 7 and the cover portion 21 is effectively reduced owing to the arrangement of the thrust ring 19 between the gear wheel 7 and the cover portion 21 of the housing.

A further reduction of the friction losses is achieved in the internal gear pump 1 in accordance with the embodiment illustrated in FIG. 1 in that a connecting passage on the housing of the pump 1 extends from the delivery chamber 15 up to the gap 23 between the thrust ring 19 and the cover portion 21 of the housing. Pressurized fluid is carried from the delivery chamber 15 along the connecting passage into the gap 23, the fluid in the gap 23 forming a hydrodynamically effective lubricating film.

For this purpose the connecting passage comprises a connecting groove 25, which on the inside of the base portion 13 of the housing facing the annular gear 5 extends in a radial direction from the delivery chamber 15 up to the inner circumference of the annular portion 3 of the housing. The radial connecting groove 25 is circumferentially closed by the underside of the annular gear 5. The radial connecting groove 25 opens into and is in communication with an axial connecting groove 27 of the connecting passage, and extends along the inner circumference of the annular portion 3 of the housing parallel to the axis of rotation A1 of the annular gear 5. The axial connecting groove 27 is circumferentially closed by the outer circumference of the annular gear 5. The radial connecting groove 25 and the axial connecting groove 27, therefore, form a duct of L-shaped longitudinal cross-section as illustrated in FIG. 1 for the fluid of the pump 1. The connecting grooves 25, 27 may form a cross-sectional aperture of between 1 to 5 mm², for example, apertures of a different cross section naturally also being possible. The suitable cross section generally depends on the output of the pump, the viscosity of the fluid and the pressure range of the pump.

The axial connecting groove 27 opens at the transition between the annular portion 3 and the cover portion 21 of the housing into a radial distribution groove 29. The radial distribution groove 29 is formed on the inside, that is to say, on the side of the cover portion 21 of the housing facing the thrust ring 19, and which, extending radially inward, is of limited length. Through the connecting passage comprising connecting grooves 25, 27 and distribution groove 29, a proportion of the fluid delivered by the pump 1 can pass or otherwise flow from the delivery chamber 15 into the gap 23 between the thrust ring 19 and the cover portion 21 of the housing, in order to form a hydrodynamically effective lubricating film in the gap 23. The lubricating film acts between the rotating thrust ring 19 and the fixed cover portion 21 of the housing. The friction between the thrust ring 19 and the cover portion 21 of the housing is thereby considerably reduced. This contributes to a reduced wear and reduced heating and impairment of the fluid.

The cover portion 21 of the housing may obviously comprise a plurality distribution grooves 29, particularly in a regular angular arrangement, in order to achieve a more uniform distribution of the fluid along the circumference of the thrust ring 19. For this purpose a separate connecting passage, emerging from the delivery chamber 15, may be provided for each distribution groove 29 in the cover portion 21. Alternatively, an annular groove (not illustrated), which distributes the fluid delivered from the delivery chamber 15 along the connecting grooves 25, 27 along the circumference of the thrust ring 19 or the cover portion 21 of the housing, may be provided on the annular portion 3 of the housing, on the cover portion 21 of the housing and/or along the outer circumference of the thrust ring 19.

FIG. 2 illustrates a cross-sectional view of an internal gear pump in accordance with the invention. FIG. 2 illustrates the radial connecting groove 25 in the base portion 13 and the axial connecting groove 27 in the annular portion 3 of the housing, which form the connecting passage described, extending from the delivery chamber 15 to the thrust ring 19 and the cover portion 21 of the housing.

As illustrated in FIGS. 3a and 3b, alternatively or in addition to the formation of a distribution groove 29 along the cover portion 21 of the housing illustrated in FIG. 1, one or more distribution grooves 31 may be provided on a surface of the rear side 33 of the thrust ring 19 facing the gap 23 (that is to say, on the upper side of the thrust ring 19 in the representation illustrated in FIG. 1). As illustrated in FIGS. 3a and 3b, a plurality if of radial distribution grooves 31 are provided, asymmetrically formed and arranged with a slight lateral offset.

In the embodiment illustrated in FIGS. 3a and 3b the distribution grooves 31 in the thrust ring 19 are formed all the way through, that is to say they extend from the outer circumference up to the inner circumference (central through-hole for the shaft 17). In this way specifically desired leakage effects can be produced, for example, for a build-up of pressure, additional cooling or the lubrication of further components by leakage oil.

As illustrated in FIG. 4, alternatively, the distribution grooves 31 are formed as stepped grooves, which extend radially inwards only along a limited length from the outer circumference of the thrust ring 19, for example, up to approximately 1 mm from the inner circumference of the thrust ring 19. This serves to minimize leakage losses.

In the embodiments illustrated in FIGS. 1, 3a, 3b and 4, the rear side 33 of the respective thrust ring 19 is of plane design.

As illustrated in FIG. 5, alternatively, the rear side 33 of the thrust ring 19 facing the cover portion 21 of the housing may be of tapered design. This serves, as an alternative or addition to the provision of distribution grooves 31, to bring about an enhanced distribution of the fluid delivered via the connecting passage.

As illustrated in FIG. 6, alternatively, the rear side 33 of the thrust ring 19 may have a bowed or arcuate design, that is to say, of convexly curved design. This serves, as an alternative or addition to the provision of distribution grooves 31, to bring about an enhanced distribution of the fluid delivered via the connecting passage.

Alternatively or in addition to such a tapered, truncated cone-shaped or convexly curved design of the rear side 33 of the thrust ring 19, the inside surface of the cover portion 21 of the housing (FIG. 1) facing the thrust ring 19 may be of tapered, truncated cone-shaped or convexly curved design. In both cases, the gap 23 between the thrust ring 19 and the cover portion 21 of the housing (FIG. 1) has, at least in portions, an overall height diminishing radially inwards.

Although embodiments have been described herein, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.

Claims

1. A gear pump for delivering a fluid, comprising: a driven gear wheel;a rotatable annular gear operatively communicating with the driven gear wheel;a housing in which the driven gear wheel and the rotatable annular gear are arranged, the housing comprising a base portion, an annular portion and a cover portion, the base portion having a pressure port which forms a fluid delivery chamber;a thrust ring arranged between the driven gear wheel and the rotatable annular gear and also the driven gear wheel and the cover portion;a gap formed between the thrust ring and the cover portion; andat least one fluid connecting passage extending from the fluid delivery chamber up to the gap in order to carry fluid from the delivery chamber into the gap.

2. The gear pump of claim 1, wherein the connecting passage comprises at least one connecting groove which extends along the inner circumference of the annular portion of the housing.

3. The gear pump of claim 2, wherein the connecting groove along the inner circumference of the annular portion is aligned parallel to the axis of rotation of the rotatable annular gear.

4. The gear pump of claim 1, wherein the connecting passage comprises a connecting groove which extends from the delivery chamber of the pump along the base portion of the housing.

5. The gear pump of claim 1, wherein the connecting passage opens into an annular groove which extends circumferentially along a transition between the annular portion and the cover portion of the housing and along the thrust ring.

6. The gear pump of claim 1, wherein the cover portion of the housing comprises at least one distribution groove which extends radially inward on the inside surface of the cover portion.

7. The gear pump of claim 6, wherein the distribution groove of the cover portion extends radially inward from the outer circumference of the cover portion to a central aperture of the cover portion.

8. The gear pump of claim 1, wherein the thrust ring comprises at least one distribution groove which on the side of the thrust ring facing the cover portion of the housing extends radially inward from the outer circumference of the thrust ring.

9. The gear pump of claim 8, wherein the distribution groove of the thrust ring extends radially inward from the outer circumference of the thrust ring to a central aperture of the thrust ring.

10. The gear pump of claim 1, wherein the surface of the thrust ring facing the cover portion of the housing is one of tapered, truncated cone shape, and convexly curved.

11. The gear pump of claim 1, wherein the housing comprises an outlet port configured to conduct a proportion of the fluid, carried out of the delivery chamber towards the gap, to another component to thereby lubricate the component.

12. The gear pump of claim 1, wherein the thrust ring extends in one piece in a radial direction between the driven gear wheel and the rotatable annular gear.

13. The gear pump of claim 1, wherein the thrust ring is rotationally fixed to the annular gear.

14. The gear pump of claim 1, wherein the rotatable annular gear and the thrust ring are integrally formed.

15. A gear pump for a gerotor pump, the gear pump comprising: a gear wheel which is rotatable about a first axis;an annular gear which is rotatable about a second axis;a thrust ring rotationally fixed to the annular gear;a housing which houses the gear wheel, the annular gear and the thrust ring, the housing having a fluid delivery chamber and a cover portion;a gap formed between the thrust ring and the cover portion; anda fluid connecting passage in the housing through which fluid flows from the fluid delivery chamber to the gap to thereby form a hydrodynamic lubricating film in the gap which reduces operational friction between the thrust ring and the cover portion.

16. The gear pump of claim 15, wherein the fluid connecting passage comprises: a first connecting groove extending radially and in communication with the fluid delivery chamber;a second connecting groove extending axially and in communication with the first connecting groove; anda third connecting groove extending radially and in communication with the second connecting groove and the gap.

17. The gear pump of claim 15, wherein the thrust ring has a plurality of distribution grooves on a surface thereof which faces the gap and which are configured to distribute the fluid into the gap.

18. The gear pump of claim 17, wherein the plurality of distribution grooves extend from an outer circumference to an inner circumference of the thrust ring portion.

19. The gear pump of claim 17, wherein the plurality of distribution grooves extend from an outer circumference of the thrust ring portion to a predetermined distance from the inner circumference of the thrust ring portion.

20. A gear pump comprising: a gear wheel;an annular gear;a thrust ring;a housing having a fluid delivery chamber and a cover portion configured for placement such that a gap is formed between the thrust ring and the cover portion; anda fluid connecting passage through a fluid flows from the fluid delivery chamber to the gap to thereby form a hydrodynamic lubricating film in the gap which reduces operational friction between the thrust ring and the cover portion,wherein: the fluid connecting passage has a first connecting groove in communication with the fluid delivery chamber, a second connecting groove in communication with the first connecting groove, and a third connecting groove in communication with the second connecting groove and the gap, andthe thrust ring has a plurality of distribution grooves on a surface thereof which faces the gap and which are configured to distribute the fluid into the gap.