VARIABLE-VOLUME INTERNAL GEAR PUMP

Abstract

The invention relates to a variable-volume internal gear pump, in particular for use as an engine lubrication pump for automobiles. The internal gear pump comprises a housing (7, 10) and a rotor set chamber (40) formed therein comprising a low pressure chamber (17) and a high pressure chamber (18) for a fluid. Inside the rotor set chamber (40) are an inner rotor (2) that can be rotatably driven by a shaft (1) about an axis of rotation (Di) and a rotatable outer rotor (3) with an outer rotor axis of rotation (Da) that is arranged eccentric with respect to the axis of rotation (Di). When a rotational force is applied, conveyance cells (30, 31) form between the inner rotor (2) and the outer rotor (3) in which the fluid is conveyed from the low pressure chamber (17) to the high pressure chamber (18). An adjusting member (5) upon which axial springs (8) act and which is guided in the internal gears (34) of the outer rotor (3) in axial motion causes a pressure-related axial movement of the inner rotor (2). The outer rotor (3) comprises radial channels (41) in the gaps between the teeth of the internal gears (34) thereof proximate to the low pressure chamber (17) and the high pressure chamber (18). The axial position of the inner rotor (2) relative to the outer rotor (3) can be adjusted by the axial motion of the adjusting member (5), whereupon the volume of the conveyance cells (30, 31) changes depending on the pressure.

Description

The invention relates to an internal gear pump, in particular for use as an engine lubrication pump for automobiles, according to the precharacterizing clause of claim 1.

Owing to the requirement for power losses which are as small as possible over the total speed and power range of the engine, engine designers are increasingly being faced with the requirement that the oil transport of the pump should no longer increase with the engine speed, as in the past. The lubricating oil requirement curve of the engine has a digressive characteristic over the variation of the engine speed. This means that the engine does not have a lubricating oil requirement which is proportional to the speed. Thus, this is substantially smaller at high speed.

In the case of pumps which cannot be controlled, the lubricating oil flows via a bypass valve back into the suction side of the pump from a certain maximum oil pressure. This gives rise to a considerable loss of hydrostatic power, which is substantially avoidable in a demand-oriented manner by an automatically controlled pump. In fact, this loss develops exponentially with constant specific delivery of the pump since, in addition to the delivery, the oil pressure too simultaneously increases over the speed. This state of affairs has yet another aspect: when the engine is cold and hence the lubricating oil is extremely viscous, the oil pressure assumes inadmissibly high values in spite of the bypass valve, so that especially the main flow filter of the engine is endangered. Moreover, the ageing of the oil increases if it is subjected to extreme stress for a long time by the narrow gaps of the system and with a high pressure difference at high sheer rate. Engine lubricating pumps controllable in their specific delivery, with more or less undesired secondary phenomena, are already known.

A known variable-volume internal gear pump controls the specific delivery by rotating the centre distance line of the gear set relative to the suction and pressure chambers in the pump housing in an oil pressure-dependent manner. However, this has two substantial disadvantages, namely that, in the case of a controlled pump, unavoidable squeezing losses arise through this so-called differential control and the pump therefore develops considerable noises at high speed. Moreover, the squeezing losses reduce the mechanical efficiency of the pump in this operating range. In addition, the squeezing losses give rise to considerable pressure peaks between the teeth, with the result that the components are additionally loaded and the lifetime is reduced.

Another solution is known as a type of vane pump or “oscillating vane pump”, in which the eccentricity of the rotor occupied by vanes is changed relative to the housing ring in a known manner. This has a relatively large number of very fine components which are fracture-sensitive and expensive to produce.

Finally, an external gear pump is also known in which the effective tooth width of the pump is reduced with increasing pressure by axial displacement of the two gears relative to one another. Since these gears must be relatively broad, the pump housing with its spectacle-like inner contour must also have a corresponding length. This leads to high manufacturing costs for machining of the housing cavern. In addition, external gear pumps are sensitive to cavitation and hence noise owing to their high delivery pulsation and owing to their radial filling on the suction side.

It is the object of the invention to provide a pump which is controllable in its specific delivery, in particular an engine lubricating pump, which avoids these disadvantages in a comprehensive manner.

This object is achieved by realizing the features of the independent claim. Features which further develop the invention in an alternative or advantageous manner are described in the dependent patent claims.

The invention comprises a variable-volume internal gear pump. The advantage of an internal gear pump over other engine lubricating pumps controllable in their specific delivery is in particular that firstly an internal gear pump is superior to the external gear pump with regard to the noise, owing to its low instantaneous delivery pulsation over the angle of rotation of the gears. Moreover, it can be designed with small numbers of teeth and simultaneously an extremely centric design. Both lead to low tooth engagement frequency and to low hydraulic pressure pulsations. Possible large eccentricity of the rotor set gives rise to very large-volume delivery cells which, at the required displacement volume, lead to small radial dimensions of the pump. At the same time, the exact internal machining of the pump housing is very simple because in principle only circular manufacturing operations easily implementable on the lathe are required.

The variable-volume internal gear pump according to the invention comprises a housing and a rotor set chamber which is formed in the housing and which has a low pressure chamber with an inlet opening and a high pressure chamber with an outlet opening for a fluid. An inner rotor held in the rotor chamber is rotatable about an axis of rotation and can be driven by a shaft. In the rotor set chamber, an outer rotor having an outer rotor axis of rotation arranged eccentrically relative to the axis of rotation is held in a rotatable manner. The inner rotor has outer teeth and the outer rotor has inner teeth such that the outer rotor can rotate with the inner rotor by means of the outer-inner teeth in a constant rotational ratio to one another and, in the case of a rotary drive, forms delivery cells in which the fluid is transported from the low pressure chamber to the high pressure chamber.

According to the invention, an adjusting member which produces an axial movement of the inner rotor is provided. The adjusting member is guided in an axially moveable manner in the inner teeth of the outer rotor. The outer rotor has radial channels in the tooth spaces between the teeth of its inner teeth in the region of the low pressure chamber and of the high pressure chamber. The axial position of the inner rotor relative to the outer rotor is variable by the axial movement of the adjusting member so that the volume of the delivery cells can be adjusted thereby and an internal gear pump controllable in its specific delivery is provided.

In particular, the displacement volume and the specific delivery of the internal gear pump are pressure-dependent, the volume of the delivery cells and hence also the specific delivery decreasing with increasing pressure at the outlet opening and hence with increasing pressure in the high pressure chamber.

The outer teeth of the inner rotor have a shape such that axially effective springs, in particular coil springs, can be installed between the shaft driving the inner rotor and the tooth contour of the outer teeth and are arranged there.

Preferably, the springs which act axially on the adjusting member are arranged in the inner rotor between the shaft driving the inner rotor and the tooth contour of the outer teeth. An adjustment space which is connected to the high pressure chamber and axially bounded by the adjusting member is formed within the inner teeth of the outer rotor so that a pressure of the fluid within the adjustment space acts axially on the adjusting member against the spring force of the springs. The opposite arrangement of the adjustment space, which is connected to the high pressure chamber and hence also to the outlet opening and whose fluid pressure acts from one side on the adjusting member, and the spring force which presses from the other side onto the adjusting member, the delivery cells being present in between, have the result that, with increasing pressure in the high pressure chamber, the adjusting member is displaced against the spring force of the springs and the volume of the delivery cells decreases.

These springs are supported in the axial direction on the shaft, for example via a pot-like intermediate member and a securing ring. In particular, three springs, in particular coil springs, are arranged uniformly distributed on the circumference on the inner rotor.

The commutation of the change of oil flow from the low pressure chamber—also referred to as suction chamber—to the high pressure chamber—also referred to as pressure chamber—and back from the pressure chamber to the suction chamber is effected in a gentle manner via the outer rotor with its radial channels communicating with the housing, so that any squeezing of the fluid here, in particular of the oil, in the delivery cells is substantially avoided. The possibility of the exactly circular bore in the pump housing for the mounting of the outer rotor and the separation webs between the suction chamber and pressure chamber, which are preferably to be complied with as accurately as possible, permit this precise commutation.

In a further development of the invention, the adjusting member has outer teeth which fit the inner teeth of the outer rotor with sufficient but small play and are therefore axially displaceable therein while providing a seal.

The geometrical shape of the inner-outer teeth, i.e. of the outer teeth of the inner rotor and of the inner teeth of the outer rotor which are coordinated with them, is, for example, in the form of epicycloidal or arc-like outer teeth on the inner rotor, which are produced by a self-generating milling movement of the inner teeth of the outer rotor with one tooth more. Here, the outer teeth of the inner rotor therefore have one tooth less than the inner teeth of the outer rotor. This self-generating principle, also referred to as self-generating milling, in which a master profile is milled in a counter-wheel, the eccentricity and the rotational ratio being retained, is known from the teaching on tooth systems and need not be explained in more detail here. The person skilled in the art is aware that other geometrical configurations, as are known from the prior art in the case of gear pumps, in particular epicycloidal outer teeth, are possible. For example, the geometrical shape of the outer-inner teeth can be determined by epi- and hypocycloids.

The outer teeth of the inner rotor have, for example, between 5 and 8 teeth, in particular 6 teeth.

In one embodiment of the invention, the inner rotor is arranged in an axially displaceable and nonrotatable manner substantially runout-free on the shaft driving it. The arrangement in a nonrotable and axially displaceable manner is effected, for example, by means of a feather key.

The delivery cells are preferably closed in the axial direction and in a position opposite to the adjusting member by a pinion plate whose inner teeth fit the outer teeth of the inner rotor with sufficient but little play in such a way that the inner rotor is axially moveable within the inner teeth of the pinion plate. Blading corresponding to a centrifugal pump is preferably arranged or formed on the pinion plate. This blading corresponding to a centrifugal pump is in particular axial blading. As a result of this blading, the pump is so to speak pitched on the suction side so that, with increasing speed, the liquid pressure in the suction chamber increases approximately with the square of the speed. According to the invention, this pump is therefore suitable for extremely high speeds, owing to the avoidance of cavitation bubbles in the oil. This too leads to small space requirement of the pump in the engine.

A compensating pressure region which is subjected to high pressure, compensates the axial forces and acts as a compensating surface can be provided on the drive side between the housing and a drive wheel arranged outside the housing on the shaft. Alternatively, this compensating pressure region subjected to high pressure and compensating the axial forces is provided on the side opposite the drive side, between the housing or a cover of the housing and the pot-like intermediate member. In both cases, the compensating pressure region, which is connected to the high pressure region or the high pressure chamber, ensures that a hydraulic compressive force in the compensating pressure region counteracts the hydraulic compressive force in the adjustment space which is likewise subjected to high pressure.

In the drawings, the subject matter of the invention is shown schematically, purely by way of example, with reference to specific working examples.

FIG. 1 shows an embodiment of the internal gear pump in a longitudinal section through the middle of the shaft and the middle of the inner rotor of the pump at maximum specific delivery;

FIG. 2 shows an identical longitudinal section at minimum specific delivery;

FIG. 3 shows a cross-section through the pump along the section line A-A of FIG. 1;

FIG. 4 shows a longitudinal section through the middle of the shaft and the middle of the inner rotor along the section line B-B of FIG. 3 at maximum specific delivery;

FIG. 5 shows an identical longitudinal section at minimum specific delivery;

FIG. 6 shows a cross-section along the section line C-C of FIG. 1;

FIG. 7 shows a diagram of the pinion plate with the axial blading for the axial centrifugal pump, which blading is fixed on said pinion plate;

FIG. 8 shows a diagram of the adjusting member;

FIG. 9 shows an alternative embodiment of the internal gear pump with an alternative compensating pressure region in a longitudinal section at maximum specific delivery;

FIG. 10 shows an identical longitudinal section at minimum specific delivery; and

FIG. 11 shows a diagram of the outer rotor of the alternative embodiment, in the form of a crown gear.

Since FIGS. 1 to 8 show a common embodiment of the invention in different views, sections and degrees of detail, FIGS. 1 to 8 are described substantially together.

FIG. 1 shows the variable-volume internal gear pump in a longitudinal section through the middle of the shaft and the middle of the inner rotor of the pump at maximum specific delivery. The internal gear pump has a two-part housing which is composed of the actual housing 7 and a cover 10 of the housing which are connected to one another by means of screws 19. A rotor set chamber 40 which has a low pressure chamber 17 with an inlet opening 15 and a high pressure chamber 18 with an outlet opening 16 for a fluid is formed in the housing 7. The rotor set chamber 40 holds an inner rotor 2 which is rotatable about an axis of rotation Di within the rotor set chamber of the housing 7 and can be driven by a shaft 1 which is passed through the housing 7 and the cover 10. The inner rotor 2 is axially moveable on the shaft 1 driving it but is arranged in a nonrotatable manner only by means of a feather key 11, substantially runout-free. The rotor set chamber 40 also holds a rotatable outer rotor 3 having an outer rotor axis of rotation Da arranged eccentrically relative to the axis of rotation Di, as shown in FIGS. 3, 4 and 6. The inner rotor 2 has outer teeth 33—namely comprising six teeth—and the outer rotor 3 has inner teeth 34, namely comprising seven teeth (FIGS. 1 and 3)—such that the outer rotor 3 rotates with the inner rotor 2 by means of the outer-inner teeth 33, 34 in a constant rotational ratio and, in the case of a rotary drive, forms delivery cells 30, 31 (FIGS. 1 and 3) in which the fluid is transported from the low pressure chamber 17 to the high pressure chamber 18 (FIGS. 1 and 3). The outer rotor 3 has radial channels 41 arranged in the seven tooth spaces between the teeth of the inner teeth 34 in the region of the low pressure chamber 17 and of the high pressure chamber 18 (FIGS. 2, 3 and 5).

FIGS. 1, 2 and 5 show an adjusting member 5 according to the invention which produces an axial movement of the inner rotor 2. The adjusting member 5 is guided in an axially moveable manner in the inner teeth 34 of the outer rotor 3, the adjusting member 5 having outer teeth 34a which fit the inner teeth 34 of the outer rotor 3 with sufficient but little play and are therefore axially moveable therein while providing a seal. FIG. 8 shows the adjusting member 5 with its outer teeth 34a in a detailed view. The axial position of the inner rotor 2 relative to the outer rotor 3 is adjustable by the axial movement of the adjusting member 5, with the result that the volume of the delivery cells 30, 31 is variable.

Distributed uniformly in the inner rotor 2, three axially acting coil springs 8 are installed between the shaft 1 driving the inner rotor 2 and the tooth contour of the outer teeth 33, as shown in FIGS. 1, 3 and 6. For this purpose, the outer teeth 33 of the inner rotor 2 have a corresponding shape. The three coil springs 8 are supported via a pot-like intermediate member 6 (FIGS. 1 and 5) and a securing ring 12 (FIG. 1) in the axial direction on the shaft 1.

The delivery cells 30, 31 are closed in the axial direction and in a position opposite to the adjusting member 5 by a pinion plate 4 and 46, which is evident in FIG. 1 and shown in detail in FIG. 7. The inner teeth 32 of the pinion plate 4 and 46 fit the outer teeth 33 of the inner rotor 2 with sufficient but little play, in such a way that the inner rotor 2 is axially moveable within the inner teeth 32 of the pinion plate 4 and 46. Blading 42 (FIGS. 5 and 7) corresponding to a centrifugal pump 21 (FIG. 1) is arranged on the pinion plate 4 and 46.

For an explanation of the function in the individual figures, the direction of rotation of the rotor set of the pump may be in the given direction of the arrows 43 (FIG. 3), 44 (FIG. 6) and 45 (FIGS. 5 and 7), so that the respective suction side and pressure side corresponding to the expanding and compressing delivery cells of the teeth are clearly shown. The intake connection on the inlet opening 15 which forms the suction opening is arranged in the cover 10. A suction space 20 surrounds the pot-like intermediate member 6 and is at the same time the suction side of the blading 42 of the axial centrifugal pump 21. The pressure side of this axial centrifugal pump 21 is at the same time the low pressure chamber 17 of the internal gear pump, which low pressure chamber acts as a suction chamber. The oil is sucked into the expanding delivery cells 30 against the centrifugal force via the radial channels 41 of the outer rotor 3. In the pump shown in the drawing, the axial impeller of the centrifugal pump 21 runs in relation to the number of teeth of the rotor set by a factor of 7:6 faster than the outer rotor 3, so that the centrifugal pressure in the radial channels 41 of the outer rotor 3 is more than compensated by the pump pressure of the impeller of the centrifugal pump 21. With increasing speed of the axial centrifugal pump 21 on the pinion plate 4 and 46 according to FIG. 7, the pressure in the suction chamber 17 becomes constantly greater so that vapor and air bubble formation in the oil and the associated danger of cavitation are ruled out there, even at the highest speeds. The same applies to the delivery cells 30 on the suction side.

The compressing delivery cells 31 (cf. FIG. 3) displace the oil into the high pressure chamber 18 towards the outlet opening 16.

In FIG. 1, the rotor set has the maximum tooth width when the coil springs 8 are able to push the inner rotor 2 and hence the adjusting member 5 completely to the left, almost up to impact on the housing 7. This is the case when a very low pressure prevails in the adjustment space 25, clearly shown in FIG. 2. It is expedient if the coil springs 8 are prevented by a snap ring 13 from pressing the adjusting member 5 axially onto the housing 7, so that no unnecessary frictional loss occurs at zero pressure, i.e. when idling. The distance between this snap ring 13 and the securing ring 12 in the form of a Seeger circlip ring, both fixed on the shaft 1, should be chosen so that, between the packet consisting of, in particular, the adjusting member 5, the inner rotor 2, the coil springs 8, the pot-like intermediate member 6 and the pinion 4, 46, there is still sufficient axial play between the adjusting member 5 and the housing 7.

If this internal gear pump is now connected on the high pressure side at the outlet opening 16 to the lubricating oil circulation, for example of an internal combustion engine, the oil pressure in the high pressure chamber 18 increases according to the absorption curve of the motor with increasing motor speed and hence (in the case of a rigid drive) pump speed. Via channels 23 and 24, which are clearly shown in FIG. 2, this high pressure also prevails in the adjustment space 25 and, depending on the speed level and hence the high pressure level, pushes the adjusting member 5 and with it the inner rotor 2 to the right against the spring force. However, the outer rotor 3 maintains its axial position, owing to the small axial play between the housing 7 and the pinion plate 4 and 46. The effective tooth width of the rotor set is reduced thereby and the specific delivery is reduced, as illustrated in FIG. 2.

The hydraulic compressive force in the adjustment space 25 on the adjusting member 5 and hence, via the inner rotor 2, on the coil springs 8 and the pot-like intermediate member 6 and also on the axial surface of the outer rotor 3 via the pinion plate 46, 4 is supported via the securing ring 12 on the shaft 1. To prevent the securing ring 12 or the pot-like intermediate member 6 from running against the cover 10 at the shaft bearing 27 with great force, a compensating pressure region 22 which is subjected to high pressure via the channel 23 (FIG. 2) is provided on the drive side between a drive wheel 9 (FIG. 1), arranged outside the housing 7 on the shaft 1, and the housing 7. This compensating pressure region 22 is dimensioned so that the axial force it exerts on the shaft 1 via a central screw 14 to the left in FIG. 1 is somewhat smaller than the total hydrostatic axial force of the rotor system to the right. As a result, the lubrication and the cooling of an annular sealing surface 47 between the drive wheel 9 and the housing 7, which sealing surface seals the compensating pressure region 22 from the outside, can be optimized.

The alternative embodiment of the internal gear pump, shown in FIGS. 9 to 11, corresponds in substantial parts to the embodiments of the internal gear pump which are illustrated in FIGS. 1 to 8, and it is for this reason that in some cases only the substantial differences are discussed below.

The alternative embodiment of the internal gear pump has the housing 7 with the cover 10 belonging to the housing. The housing is provided with the rotor set chamber 40, which has the low pressure chamber 17 with the inlet opening 15 and the high pressure chamber 18 with the outlet opening 16 for a fluid. The rotor set chamber 40 holds the inner rotor 2 which is rotatable about the axis of rotation D_i and can be driven by the shaft 1. The outer rotor 3a rotatably held in the rotor set chamber 40 has an outer rotor axis of rotation arranged eccentrically relative to the axis of rotation D_i. The inner rotor 2 has outer teeth 33, and the outer rotor 3a has inner teeth 34, such that the outer rotor 3a rotates with the inner rotor 2 by the outer-inner teeth 33, 34 in a constant rotational ratio and, in the case of a rotary drive, forms the delivery cells 30, 31 in which the fluid is transported from the low pressure chamber 17 to the high pressure chamber 18. By means of the adjusting member 5 guided in an axially moveable manner in the inner teeth 34 of the outer rotor 3, an axial movement of the inner rotor 2 can be produced. The axial position of the inner rotor 2 relative to the outer rotor 3a is variable by the axial movement of the adjusting member 5 so that the volume of the delivery cells 30, 31 can be varied. Here, FIG. 9 shows the internal gear pump at maximum specific delivery and FIG. 10 shows said pump at minimum specific delivery. The outer teeth 33 of the inner rotor 2 have a shape such that the axially effective springs 8 are located between the shaft 1 driving the inner rotor 2 and the tooth contour of the outer teeth 33. Regarding these features, the alternative embodiment of the internal gear pump of FIGS. 9 and 10 corresponds to the embodiment of FIGS. 1 to 8.

The outer rotor 3a likewise has radial channels 41a in the tooth spaces between its inner teeth 34 in the region of the low pressure chamber 17 and of the high pressure chamber 18, but these radial channels 41a are not formed as radial bores in the middle of the outer rotor 3a, as can be seen in the first embodiment and as can be seen in FIG. 1, but the radial channels 41a are present as slot-like radial recesses at the edge of the outer rotor 3a. In other words, the outer rotor 3a is in the form of a crown gear, as shown in FIG. 11 in an individual front view and an individual side view. An advantage of this arrangement consists in the easier producability of the radial channels 41a.

In addition, an annular intermediate plate 50 is provided between the cover 10 and the remaining housing 7, which intermediate plate has passages for the channels, the pattern of holes corresponding substantially to the pattern of holes of the housing 7.

The springs 8 are likewise supported via a pot-like intermediate member 6a and a securing ring 12 in the axial direction on the shaft 1, but the pot-like intermediate member 6a has an outer shape—in particular cylindrical outer shape—such that the intermediate member 6a touches the cover 10 of the housing 7 while providing a radial seal. In this context, a piston ring 48 is provided for sealing. Thus, a compensating pressure region 22a subjected to high pressure between the housing 10 and the pot-like intermediate member 6a and compensating the axial forces is formed between the pot-like intermediate member 6a and the cover 10 of the housing 10. In order to subject the compensating pressure region 22a to high pressure, a channel 49 which connects the compensating pressure region 22a to the high pressure chamber 18 is provided. This compensating pressure region 22a, too, is dimensioned so that hydraulic pressure in the compensating pressure region 22a counteracts the hydraulic pressure in the adjustment space 25 likewise subjected to high pressure. In other words, in this embodiment, the compensating pressure region 22a was moved from the side of the drive wheel 9, FIG. 1, to the opposite side. This has in particular the advantage that the drive wheel 9 in the embodiment of FIGS. 9 to 11 no longer has a sealing function and can be easily replaced by another drive wheel 9 on the shaft 1.

Claims

1. Variable-volume internal gear pump which comprises a housing,a rotor set chamber which is formed in the housing and which has a low pressure chamber with an inlet opening and high pressure chamber with an outlet opening for a fluid,an inner rotor which is held in the rotor set chamber and is rotatable about an axis of rotation and is drivable by a shaft, andan outer rotor rotatably held in the rotor set chamber and having an outer rotor axis of rotation arranged eccentrically relative to the axis of rotation, the inner rotor having outer teeth, and the outer rotor having inner teeth, such that the outer rotor rotates with the inner rotor by the outer-inner teeth in a constant rotational ratio and, in the case of a rotary drive, forms delivery cells in which the fluid is transported from the low pressure chamber to the high pressure chamber,

2. Internal gear pump according to claim 1, wherein in the inner rotor, the springs which act axially on the adjusting member are arranged between the shaft driving the inner rotor and the tooth contour of the outer teeth andan adjustment space which is connected to the high pressure chamber and is axially bounded by the adjusting member is formed within the inner teeth of the outer rotor, a pressure within the adjustment space acting axially on the adjusting member against the spring force of the springs with delivery cells located in between, in such a way that, with increasing pressure in the high pressure chamber and the adjustment space, the adjusting member 5 moves against the spring force of the springs and the volume of the delivery cells decreases.

3. Internal gear pump according to claim 1, wherein the springs are supported via a pot-like intermediate member and a securing ring in the axial direction on the shaft.

4. Internal gear pump according to claim 1, wherein the adjusting member has outer teeth which fit with sufficient but little play in the inner teeth of the outer rotor and are therefore axially moveable therein by providing a seal.

5. Internal gear pump according to claim 1, wherein the geometrical shape of the outer-inner teeth is formed as epicycloid or arc-like outer teeth on the inner rotor, which produces the inner teeth of the outer rotor with one tooth more by a self-generating milling movement.

6. Internal gear pump according to claim 1, wherein the geometrical shape of the outer-inner teeth is determined by epi- and hypocycloids.

7. Internal gear pump according to claim 1, wherein the inner rotor is arranged on the shaft driving it, in an axially moveable manner but nonrotatably—in particular secured by a feather key—substantially runout-free.

8. Internal gear pump according to claim 1, wherein the delivery cells are closed in the axial direction and in a position opposite to the adjusting member by a pinion plate whose inner teeth fit with sufficient but little play in the outer teeth of the inner rotor in such a way that the inner rotor is axially moveable within the inner teeth of the pinion plate.

9. Internal gear pump according to claim 8, wherein blading corresponding to a centrifugal pump is arranged or formed on the pinion plate.

10. Internal gear pump according to claim 9, wherein the blading corresponding to the centrifugal pump is axial blading.

11. Internal gear pump according to claim 1, wherein a compensating pressure region subjected to high pressure and acting to compensate the axial forces is provided between the housing and a drive wheel arranged outside the housing on the shaft.

12. Internal gear pump according to claim 3, wherein a compensating pressure region subjected to high pressure and acting to compensate the axial forces is provided between the housing and the pot-like intermediate member.

13. Internal gear pump according to claim 1, wherein the outer teeth of the inner rotor have between 5 and 8 teeth.

14. Internal gear pump according to 1, wherein the outer teeth of the inner rotor have six teeth.

15. Internal gear pump according to claim 14, three springs are arranged uniformly distributed over the circumference in the inner rotor.

16. Internal gear pump according to claim 1, wherein the springs are in the form of coil springs.