Internal gear fluid machine and method for producing an internal gear fluid machine

Description

[0001] The invention relates to an internal gear fluid machine, comprising a first gear having an external toothing and mounted rotatably about a first axis of rotation, and a second gear having an internal toothing that meshes with the external toothing in an engagement region and is mounted rotatably about a second axis of rotation different from the first axis of rotation, wherein a filler piece is arranged between the first gear and the second gear away from the engagement region, which filler piece rests on the one hand on the external toothing and on the other hand on the internal toothing in order to divide a fluid space present between the first gear and the second gear into a first fluid chamber and a second fluid chamber,and wherein, in the axial direction with respect to the first axis of rotation, housing walls of a machine housing of the internal gear fluid machine are arranged on both sides of the first gear and the second gear, and the filler piece is mounted on the machine housing by means of at least one retaining pin engaging at least one of the housing walls.

[0002] For example, the prior art document DE 199 30 911 C1 is known. This describes an internal gear fluid machine for reversing operation in a closed circuit; with an externally toothed pinion, with an internally toothed ring gear that meshes with the pinion, with a housing, with a filling that fills the crescent-shaped space between the pinion and the ring gear. The filling comprises two identical filling pieces; a stop pin is provided, which is mounted in the housing and against which the filling pieces rest with their end faces. Axial discs are provided on both sides of the pinion. An axial pressure field is provided between the outer side of each axial disc and the corresponding housing wall, and a control field is provided between the inner side of each axial disc and the pinion. At least one control slot is connected to each control field, which tapers towards its free end.

[0003] Furthermore, the document DE 10 2008 053 ​​318 A1 discloses a reversibly operable gear machine comprising a housing in which two gears are arranged. A first bearing chamber and a second bearing chamber are provided, wherein in a first operating direction of the gear machine, the first bearing chamber and, in an opposite second operating direction, the second bearing chamber are subjected to hydraulic fluid pressure, forming a hydrostatic bearing for a gear. Furthermore, a vehicle steering system is described, comprising a hydraulic circuit, a hydraulic cylinder, and a gear machine that operates as a pump and applies hydraulic pressure to a first working chamber in its first operating direction and to a second working chamber of the hydraulic cylinder in its second operating direction.

[0004] An internal gear fluid machine having the features of the preamble of claim 1 is known from the document DE 30 47 609 A1.

[0005] The object of the invention is to propose an internal gear fluid machine which has advantages over known internal gear fluid machines, in particular has a longer service life or higher fatigue strength and can also be manufactured cost-effectively.

[0006] This is achieved according to the invention with an internal gear fluid machine having the features of claim 1. It is provided that the retaining pin is rotatably mounted on the housing wall via at least one intermediate piece, wherein the housing wall consists of a housing wall material and the intermediate piece consists of an intermediate piece material different from the housing wall material, wherein the intermediate piece material has a greater value of a material characteristic than the housing wall material, and wherein the material characteristic is the modulus of elasticity, the tensile strength, the yield strength, the 0.2% yield strength or the elastic limit.

[0007] Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims.

[0008] The internal gear fluid machine is in particular a fluid conveying device and is used to convey a fluid, for example a liquid or a gas. For this purpose, the internal gear fluid machine has two gears, namely the first gear and the second gear. The first gear can also be referred to as a pinion and the second gear as a ring gear. The pinion has the external toothing and the ring gear has the internal toothing. Viewed in the circumferential direction, the external toothing and the internal toothing engage with each other in some areas, i.e. they mesh with each other in some areas, namely in the engagement region. The two gears are intended for fluid conveyance and are therefore designed such that they interact during a rotary movement to convey the fluid and in doing so engage or mesh with each other.

[0009] The first gear is preferably coupled to a machine shaft or drive shaft of the internal gear fluid machine, preferably either rigidly and / or detachably or permanently. The coupling can thus be rigid on the one hand. On the other hand, it can be designed either detachably or permanently. In the case of detachable coupling, for example, there is a plug-in pinion that is plugged onto the drive shaft and can be removed from it without damage. The plug-in pinion preferably has internal teeth that interact with external teeth of the machine shaft to drive-couple the plug-in pinion to the machine shaft. For example, the first gear is rotatably mounted in a machine housing of the internal gear fluid machine by means of the machine shaft. The first gear is preferably arranged on the machine shaft so that it always has the same speed as the machine shaft during operation of the internal gear fluid machine.

[0010] Both the first gear and the second gear are arranged in the machine housing and are rotatably mounted therein. The first gear is rotatably mounted about the first axis of rotation, whereas the second gear is rotatably mounted about the second axis of rotation. The first axis of rotation can also be referred to as the pinion axis of rotation and the second axis of rotation as the ring gear axis of rotation. Viewed in cross-section, i.e. in a sectional plane perpendicular to the axes of rotation, the first gear is arranged in the second gear in such a way that the external teeth of the first gear mesh with or are in engagement with the internal teeth of the second gear in the engagement region. This means that a rotational movement of the first gear is transmitted directly to the second gear and conversely a rotational movement of the second gear is transmitted directly to the first gear.

[0011] The engagement region is, for example, fixed to the housing, meaning it does not rotate with the first gear or the second gear. In the engagement region, a tooth of one of the gears engages with a tooth space of the other of the gears. The tooth space is circumferentially delimited by teeth of the respective gear. For example, a tooth of the internal gear engages with a tooth space of the external gear, or conversely, a tooth of the external gear engages with a tooth space of the internal gear. In the engagement region, the internal and external gears interact to form a seal.

[0012] The filler piece is arranged on the other side of the engagement region, i.e., preferably on the side diametrically opposite the engagement region with respect to the first axis of rotation and / or the second axis of rotation. The filler piece is located between the first gear and the second gear, or in other words, between the external toothing of the first gear and the internal toothing of the second gear. The filler piece is thus arranged in a fluid space that is bounded radially inward by the first gear and radially outward by the second gear, respectively with respect to the first axis of rotation and the second axis of rotation.

[0013] The filler piece rests on the outer toothing on one side and the inner toothing on the other. More precisely, the filler piece rests sealingly on the tooth tips of the outer toothing and sealingly on the tooth tips of the inner toothing to divide the fluid space into the first fluid chamber and the second fluid chamber. Thus, viewed in the circumferential direction, each of the two fluid chambers is bounded on the one hand by the filler piece and on the other hand by the tight meshing of the outer toothing and the inner toothing in the engagement area.

[0014] Depending on the direction of rotation of the internal gear fluid machine, one of the fluid chambers serves as the suction chamber and the other as the pressure chamber. If the internal gear fluid machine is designed as a pump or is operated as a pump, fluid is supplied to the respective suction chamber, which the internal gear fluid machine pumps towards the pressure chamber or into the pressure chamber. The suction chamber can accordingly also be referred to as the inlet chamber and the pressure chamber as the outlet chamber; what is crucial is that the fluid is always pumped from the inlet chamber towards the outlet chamber during operation of the internal gear fluid machine. When operated as a pump, the pressure in the inlet chamber is always lower than the pressure in the outlet chamber. Of course, however, the pressure in the inlet chamber can already be (significantly) greater than ambient pressure.For example, with the help of the internal gear fluid machine, pressurized fluid is pumped from the inlet chamber towards the outlet chamber.

[0015] If, however, the internal gear fluid machine is designed as a motor or is operated as a motor, fluid is supplied to the pressure chamber, which enters the suction chamber, causing the gears to rotate. In this case, the pressure chamber acts as the inlet chamber and the suction chamber as the outlet chamber; the pressure in the inlet chamber is higher than the pressure in the outlet chamber. This description does not explicitly address the operation of the internal gear fluid machine as a motor; instead, the internal gear fluid machine and its function are explained for operation as a pump. Of course, use as a motor is also possible, and the explanations are analogously applicable to such a design of the internal gear fluid machine or such a use.

[0016] It should be noted that, for the purposes of this description, the suction chamber can also be referred to as the low-pressure chamber, and the pressure chamber as the high-pressure chamber. Analogously, the suction side of the internal gear fluid machine corresponds to a low-pressure side, and the pressure side to a high-pressure side. The terms "low pressure" and "high pressure" do not imply a restriction to a specific pressure level; rather, the pressure in the high-pressure chamber, or on the high-pressure side, is simply relatively higher than the pressure in the low-pressure chamber, or on the low-pressure side.

[0017] Preferably, the filler piece is designed in several parts and thus has several segments. The segments of the filler piece are arranged next to one another in the radial direction, so that a first segment is arranged on the side of a second segment facing the first gear, and conversely, the second segment is arranged on the side of the first segment facing the second gear. The first segment bears sealingly against the first gear or its external toothing, and the second segment bears sealingly against the second gear or the internal toothing of the second gear.

[0018] The two segments are preferably displaceable relative to one another in the radial direction. Particularly preferably, a gap existing between them is subjected to fluid pressure during operation of the internal gear fluid machine in such a way that the first segment is forced towards the first gear and the second segment towards the second gear, so that the segments bear sealingly against the respective gear or the tooth tips of the corresponding gearing. The internal gear fluid machine is thus radially compensated or gap-compensated in the radial direction. Each of the segments can be further subdivided into segments. For example, the first segment is one-piece or consists of at least two sub-segments and / or the second segment is one-piece and consists of at least two segments. These segments of the filler piece are also preferably mounted so that they can be displaced relative to one another, i.e., they can be displaced independently of one another.This achieves particularly effective gap compensation.

[0019] If the segments are further subdivided into further segments, these additional segments are preferably arranged next to one another in the circumferential direction. For example, the additional segments have the same extent in the circumferential direction and / or are symmetrical to one another. Such a configuration enables bidirectional operation of the internal gear fluid machine, i.e., any direction of rotation. The internal gear fluid machine is not limited to a specific direction of rotation; rather, the direction of rotation can be changed during operation of the internal gear fluid machine. Such an internal gear fluid machine can also be referred to as a four-segment internal gear fluid machine due to the four segments that are then preferably present. Of course, bidirectional operation of the internal gear fluid machine can also be implemented without radial gap compensation.In this case, the two segments are preferably arranged side by side in the circumferential direction and are each constructed as a single piece. It is also possible for the entire filler piece to be constructed as a single piece.

[0020] The internal gear fluid machine has the machine housing. The two gears of the internal gear fluid machine are arranged between housing walls of the machine housing, specifically as viewed in the axial direction relative to one of the axes of rotation. One of the housing walls is therefore located on a first side of the gears, and a second of the housing walls is located on a second side of the gears, opposite the first side in the axial direction, so that the housing walls accommodate the gears between them as viewed in the axial direction. In particular, a gap remaining between the housing walls and the gears is dimensioned so small that the housing walls ensure sufficient sealing of the fluid space or fluid chambers. For example, the gears are mounted on and / or in the machine housing.

[0021] The housing walls are connected to one another, for example, via a base body of the machine housing, wherein the base body at least partially, but preferably completely, encompasses the two gears in the circumferential direction. It can be provided that at least one of the housing walls and the base body are constructed as a single piece and made of the same material. In this case, the base body and the respective housing wall together form a pot-shaped element, the interior of which is sealed by the other housing wall.

[0022] Preferably, at least one of the housing walls has an opening for the machine shaft of the internal gear fluid machine, to which the first gear and / or the second gear are drive-coupled. If such a recess is provided in only one of the housing walls, the other of the housing walls is designed to be continuous and uninterrupted, thus sealing the interior in a fluid-tight manner. Alternatively, however, it can also be provided that the machine shaft passes through both housing walls, so that a corresponding recess is formed in each of the housing walls.

[0023] Such a design of the internal gear fluid machine allows, for example, a drive motor to be coupled to the machine shaft of the machine housing, on the one hand, and a further device, in particular a further internal gear fluid machine, to be connected to the machine shaft, on the other hand. In this case, the further device can be driven by the drive device via the internal gear fluid machine or its machine shaft, so that ultimately the internal gear fluid machine and the further device are jointly driven by the drive device.

[0024] The filler piece is also arranged in the machine housing and is preferably located largely in the base element. It is mounted on both sides of the machine housing, viewed in the axial direction, in particular, movably or rotatably. The rotatable mounting allows the position of the filler piece to be adjusted to the current operating state of the internal gear fluid machine and also to compensate for wear that occurs over time during operation of the internal gear fluid machine. The at least one retaining pin, which engages at least one of the housing walls, serves to mount the filler piece.

[0025] It can be provided that the filler piece is only supported on the retaining pin, in particular in the circumferential direction, i.e. fundamentally not rigidly attached to the retaining pin, but is movable relative to it. For example, the retaining pin has a support surface for this purpose, in particular a continuously flat support surface, on which the filler piece is supported via a counter-support surface of the filler piece. The support is in particular provided over the entire surface. This means that the entire support surface rests against the counter-support surface, particularly preferably continuously against the entire counter-support surface. Alternatively, however, the filler piece can also be rigidly attached to the retaining pin, in particular in a form-fitting and / or material-fitting manner or can be designed as a single piece and / or made of the same material as it.

[0026] For example, the retaining pin engages directly in a retaining pin receptacle of the machine housing, which is formed in one of the housing walls, or engages directly on the housing wall. Preferably, the retaining pin is rotatably mounted in the retaining pin receptacle, thus ensuring the relocatability of the filler piece. The fundamental goal is to use the internal gear fluid machine for higher speeds, higher pressures, and higher speed and pressure gradients, or generally for higher performance, and to upgrade it accordingly. However, when using the internal gear fluid machine at high power levels - if the machine housing is not designed accordingly - the retaining pin can overload the machine housing, resulting in damage to the internal gear fluid machine.For this reason, the machine housing is sometimes made of a material with sufficiently high strength. However, this leads to high costs in the production of the internal gear fluid machine.

[0027] For this reason, it is now provided that the retaining pin does not engage the housing wall directly, but is rotatably mounted thereon via the at least one intermediate piece. In other words, the retaining pin does not engage the housing wall directly - at least partially or alternatively completely - but only indirectly via the intermediate piece. To ensure cost-effective production while simultaneously ensuring high operational reliability of the internal gear fluid machine, the housing wall is made of the housing wall material and the intermediate piece is made of the intermediate piece material that is different from the housing wall material. The intermediate piece material is selected such that it can withstand the loads exerted on the intermediate piece by the retaining pin permanently or over the entire intended service life of the internal gear fluid machine.For example, the retaining pin consists of a retaining pin material, the housing wall consists of the housing wall material, and the intermediate piece consists of the intermediate piece material. It may be provided that the intermediate piece material is the same as the retaining pin material. In any case, however, the housing wall material is different from the intermediate piece material.

[0028] The spacer is also arranged on the housing wall in such a way that the forces exerted by the retaining pin on the spacer are reliably transmitted into the housing wall without damaging the housing wall. The spacer distributes the forces exerted by the retaining pin and transmits them more evenly into the housing wall than would be possible with a retaining pin acting directly on the housing wall. The provision of the spacer enables the use of a cost-effective housing wall material while still allowing the internal gear fluid machine to operate at high performance.

[0029] A further development of the invention provides that, in addition to the retaining pin, there is a further retaining pin by means of which the filler piece is mounted on a further housing wall opposite the housing wall, wherein the further retaining pin is rotatably mounted on the further housing wall via at least one further intermediate piece. The filler piece is therefore rotatably mounted on the machine housing not only by means of the retaining pin, but by means of several retaining pins. The statements made for the retaining pin preferably apply to the further retaining pin; the statements for the intermediate piece more preferably apply analogously to the further intermediate piece. The retaining pin and the further retaining pin are located on opposite sides of the filler piece in the axial direction with respect to one of the axes of rotation or engage on opposite sides thereof.The filler piece is rotatably mounted on the housing wall via the retaining pin, and on the other housing wall via the additional retaining pin, preferably around a common axis of rotation. This design enables a cost-effective and compact design of the internal gear fluid machine.

[0030] A further development of the invention provides that the retaining pin is rotatably mounted on both the housing wall and the further housing wall by means of the intermediate piece and the further intermediate piece. With such a configuration, the retaining pin extends from the intermediate piece to the further intermediate piece and is rotatably mounted on opposite sides on the housing wall and the further housing wall. It is provided that the retaining pin extends from the intermediate piece to the further intermediate piece. Such a configuration enables operation of the internal gear fluid machine with particularly high performance, since a very robust mounting of the filler piece on the machine housing or the intermediate walls of the machine housing is realized, which reliably connects the filler piece to the machine housing.

[0031] A further development of the invention provides that a retaining pin material of the retaining pin has a larger or at least the same value of a material parameter as the intermediate piece material. According to the invention, it is provided that the intermediate piece material has a larger value of the material parameter than the housing wall material. Examples of material parameters used include the modulus of elasticity, the tensile strength, the yield strength, the 0.2% proof stress or the elastic limit. The value of the material parameter is to be understood as the value for the respective material. It is therefore provided, for example, that the retaining pin material has a larger or at least the same modulus of elasticity as the intermediate piece material, although one of the other material parameters can of course also be used instead of the modulus of elasticity.Additionally or alternatively, the elastic modulus of the spacer material is greater than the elastic modulus of the housing wall material, although any of the other material parameters can be used instead of the elastic modulus. This enables particularly high fatigue strength of the internal gear fluid machine, especially at high power.

[0032] A further development of the invention provides that the housing wall material is aluminum or an aluminum alloy and / or the intermediate piece material is tempered steel, in particular nitrided steel, and / or the retaining pin material is steel. In order to realize a particularly cost-effective and lightweight embodiment of the internal gear fluid machine, a light metal, namely aluminum or an aluminum alloy, is to be used as the housing wall material. However, this housing wall material usually has a material characteristic value that is insufficient to enable reliable operation of the internal gear fluid machine at high power if the retaining pin engages directly with the housing wall. For this reason, the intermediate piece is used, as described. This is preferably made of a high-strength material, namely tempered steel.Nitriding steel is particularly preferred as a heat-treatable steel, for example nitrided or unnitrided nitriding steel.

[0033] A further development of the invention provides that the retaining pin engages in a retaining pin receptacle of the intermediate piece and the intermediate piece engages in an intermediate piece receptacle of the housing wall. The intermediate piece receptacle is formed as a recess in the housing wall. The intermediate piece receptacle only partially penetrates the housing wall and is delimited by a base in the direction facing away from the gears in the axial direction. The intermediate piece is arranged in the intermediate piece receptacle. The intermediate piece, in turn, has the retaining pin receptacle in which the retaining pin is partially arranged. For example, it is provided that the retaining pin projects in the axial direction into the intermediate piece receptacle and is thus partially arranged in it.

[0034] In such a configuration, the intermediate piece is preferably completely accommodated in the intermediate piece receptacle, i.e., it does not protrude from the intermediate piece receptacle. Alternatively, the intermediate piece projects beyond the intermediate piece receptacle in order to realize particularly reliable protection of the housing wall against the forces acting on the retaining pin. However, it can also be provided that the intermediate piece projects beyond the intermediate piece receptacle and the retaining pin receptacle is arranged or configured on or in the intermediate piece in such a way that the retaining pin is completely outside the intermediate piece receptacle. In such a configuration, the intermediate piece holds the retaining pin outside the intermediate piece receptacle and at a corresponding distance from the housing wall. Each of the described embodiments enables the realization of the advantages already described.

[0035] A further development of the invention provides that a retaining pin radial play existing between the retaining pin and an inner wall of the intermediate piece defining the retaining pin receptacle is different from an intermediate piece radial play existing between an outer wall of the intermediate piece and the housing wall defining the intermediate piece receptacle. The retaining pin radial play and the intermediate piece radial play exist when the retaining pin is arranged in the retaining pin receptacle and when the intermediate piece is arranged in the intermediate piece receptacle. The retaining pin radial play describes a play of the retaining pin in the retaining pin receptacle in the radial direction; the intermediate piece radial play describes a play of the intermediate piece in the intermediate piece receptacle, likewise in the radial direction. The retaining pin radial play and the intermediate piece radial play are different from one another.It can be provided that one of the radial clearances is zero, so that the respective element is held rigidly in the corresponding holder.

[0036] Preferably, the intermediate piece is arranged immovably, i.e., without intermediate piece radial play, in the intermediate piece receptacle and is accordingly held against the housing wall. The retaining pin radial play is greater than zero, so that the retaining pin is present with play in the retaining pin receptacle. The retaining pin radial play is selected, for example, such that it allows a rotational movement of the retaining pin in the retaining pin receptacle about a retaining pin rotation axis. Preferably, the retaining pin radial play corresponds to an arrangement of the retaining pin in the intermediate piece with an H7 fit.

[0037] Alternatively, it is of course also possible for the retaining pin to be rigidly connected to the intermediate piece, i.e., immovably arranged in the retaining pin receptacle. In this case, the retaining pin radial play is zero, whereas the intermediate piece radial play is greater than zero, so that the intermediate piece is movably, in particular rotatably, arranged in the intermediate piece receptacle. It is of course also possible for both the retaining pin material play and the intermediate piece radial play to be greater than zero, so that both the retaining pin in the retaining pin receptacle and the intermediate piece in the intermediate piece receptacle are arranged with play. In any case, the advantages already mentioned can be easily achieved.

[0038] A further development of the invention provides that the retaining pin radial play is at least 0.02 mm and / or at most 0.06 mm, and / or that the intermediate piece is attached to the housing wall without play. The retaining pin radial play is therefore at least 0.02 mm, preferably more than 0.02 mm. In this respect, the retaining pin radial play can in particular be at least 0.03 mm or at least 0.04 mm. Additionally or alternatively, the retaining pin radial play is at most 0.06 mm or less than 0.06 mm. Preferably, the retaining pin radial play is at most 0.05 mm or at most 0.04 mm. Such dimensions of the retaining pin radial play enable reliable, movable mounting of the filler piece on the machine housing.

[0039] A further development of the invention provides that the intermediate piece is a hollow cylindrical bearing bush or a rolled sheet metal part. In principle, the intermediate piece is preferably hollow cylindrical, particularly preferably hollow circular cylindrical. A conventional bearing bush, such as can also be used in a plain bearing, is used as the intermediate piece. This is particularly the case if the internal gear fluid machine is designed for only low loads. The bearing bush can, for example, be made entirely and continuously from bronze, sintered bronze, steel, or plastic, or comprise at least one of these materials. Of course, the bearing bush can also be made from a composite material.

[0040] Alternatively or additionally, the intermediate piece is in the form of a rolled sheet metal part, i.e., it is produced by rolling. For example, an initially flat sheet metal is processed in such a way that two end edges of the sheet metal that previously faced away from each other now lie opposite each other and thus enclose a gap between them. The gap is preferably as small as possible; in particular, it is dimensioned such that the end edges are spaced apart by no more than 0.05 mm or less. Particularly preferably, the end edges lie directly against each other, so that there is no gap or the gap has dimensions of zero. Preferably, the two end edges of the sheet metal are aligned with each other after rolling. The end edges are therefore arranged abutting against each other after rolling. The described embodiments of the intermediate piece enable cost-effective production of the internal gear fluid machine.

[0041] A further development of the invention provides that the intermediate piece is multi-part, in particular in the form of a split bearing bush. The intermediate piece is therefore composed of several elements which are initially separate from one another and are subsequently fastened to one another, for example, in a force-fitting, form-fitting and / or material-fitting manner. However, it can also be provided that the several parts of the intermediate piece are fixed relative to one another solely by the arrangement of the intermediate piece in the intermediate piece receptacle and / or the arrangement of the retaining pin in the retaining pin receptacle, i.e. are initially inserted loosely and separately from one another into the intermediate piece receptacle. This is particularly the case if the intermediate piece is in the form of a split bearing bush. For example, the intermediate piece is evenly divided, i.e. is composed of two parts of the same size which have the same extents, in particular in the circumferential direction.Such a design of the intermediate piece also serves primarily to ensure cost-effective production of the internal gear fluid machine.

[0042] A further development of the invention provides that the intermediate piece is fastened to the housing wall in a rotationally fixed manner, in particular in a force-fitting and / or form-fitting manner. The rotationally fixed fastening of the intermediate piece to the housing wall prevents the intermediate piece from wandering in the intermediate piece receptacle and thus ensures a constant load on the intermediate piece by the retaining pin. The fastening is particularly preferably carried out in a force-fitting manner, for example by pressing the intermediate piece into the intermediate piece receptacle, and / or in a form-fitting manner. In the latter case, the intermediate piece in particular has a form-fitting device which interacts in a form-fitting manner with a form-fitting counter-device of the housing wall in order to hold the intermediate piece rotationally fixed to the housing wall. The form-fitting device is, for example, in the form of a form-fitting projection and the form-fitting counter-device as a form-fitting receptacle receiving the form-fitting projection, or vice versa.The non-rotatable fastening of the intermediate piece to the housing wall is particularly useful if the intermediate piece is made of multiple parts or is a rolled sheet metal part. In these cases, the fastening prevents the retaining pin from exerting force on the gap between the parts of the bearing bush or the gap remaining after rolling. This effectively prevents damage to the intermediate piece and thus to the internal gear fluid machine.

[0043] A further development of the invention provides that the retaining pin completely penetrates the intermediate piece and rests on a base of the intermediate piece receptacle on its side facing away from the filler piece. In other words, the retaining pin completely penetrates the intermediate piece in the axial direction. It has the projection which is smaller in the radial direction than a region of the retaining pin adjoining the projection. This means that the retaining pin tapers in the direction facing the base. Preferably, the dimensions of the projection in the radial direction on its side facing the base amount to at most 60%, at most 50% or at most 40% of the dimensions of a main body of the retaining pin directly adjoining the projection on its side facing the projection or of the largest dimensions of the main body in the radial direction over its entire extension in the axial direction.

[0044] The retaining pin rests on the base via the projection. This ensures reliable support of the filler piece and also allows for slight tilting of the retaining pin relative to the intermediate piece within the scope of the retaining pin's radial play. In this respect, the described design allows for compensating movement of the retaining pin and, accordingly, the filler piece supported by the retaining pin, thus ensuring reliable operation of the internal gear fluid machine.

[0045] A further development of the invention provides that an opening is formed in the housing wall adjacent to the intermediate piece receptacle, wherein a web is formed between the intermediate piece receptacle and the opening, which web has a wall thickness of at least 50%, at least 75%, at least 100%, or at least 150% of a wall thickness of the intermediate piece. The opening is in the form of a recess, for example, and is therefore delimited by a base on its side facing the gears, and accordingly only partially penetrates the housing wall in the axial direction. In this case, the opening represents, for example, a pressure field which is at least partially, but preferably completely, covered by an axial disk of the internal gear fluid machine.During operation of the internal gear fluid machine, the pressure field is subjected to fluid pressure at least temporarily, so that the axial disc is pushed toward the gears and, in particular, forms a sealing contact with them. In this case, axial gap compensation of the internal gear fluid machine occurs.

[0046] Alternatively, the opening can also be designed as a through-opening and thus extend completely through the housing wall in the axial direction. For example, in this case the opening is in the form of a fluid line via which one of the fluid chambers of the internal gear fluid machine is fluidly connected to a fluid connection of the internal gear fluid machine. The intermediate piece receptacle and the opening are separated from the web. The web is designed such that it is resistant to forces introduced into the housing wall by the retaining pin. For this purpose, it has a wall thickness which is at least 50% of the wall thickness of the intermediate piece, but is preferably greater. The wall thickness of the web particularly preferably has at least one of the aforementioned values. This results in a high fatigue strength of the internal gear fluid machine.

[0047] A further development of the invention provides that a ratio between dimensions of the intermediate piece in the radial direction and dimensions of the retaining pin in the same direction is at least 110%, at least 120%, or at least 125%. The dimensions are to be understood as the largest dimensions in the radial direction of the respective element over the entire element, in particular in the axial direction. Since the retaining pin at least substantially rests on the inner circumferential surface of the intermediate piece, the ratio between the outer dimensions of the intermediate piece and the inner dimensions of the intermediate piece is additionally or alternatively at least 110%, at least 120%, or at least 125%. This also determines the wall thickness of the intermediate piece, which is selected depending on the dimensions of the retaining pin in the radial direction.This means that the wall thickness of the spacer is increased the larger the internal gear fluid machine is. This also helps achieve high fatigue strength for the internal gear fluid machine.

[0048] A further development of the invention provides that the intermediate piece has a coating, in particular a polymer coating, on its inner wall which at least partially and / or at least temporarily rests against the retaining pin, and / or that the intermediate piece is heat-treated at least partially. The coating is a component of the inner wall, wherein the coating is present on the side of the inner wall facing the retaining pin. The coating is preferably a polymer coating, in particular a polytetrafluoroethylene coating. This can ensure particularly low-friction displacement of the filler piece. Additionally or alternatively, the intermediate piece is heat-treated at least partially. Particularly preferably, the heat treatment is carried out for the inner wall in any case.The heat treatment is aimed at hardening the intermediate piece, and in particular the inner wall, so that the forces exerted by the retaining pin on the intermediate piece cannot cause damage to the intermediate piece. In any case, the aforementioned designs achieve a particularly high fatigue strength of the internal gear fluid machine.

[0049] A further development of the invention provides that the inner wall of the intermediate piece has a surface structure, formed in particular by honing or long-stroke honing. The surface structure serves to produce improved sliding properties of the retaining pin with respect to the intermediate piece. The surface structure is designed, for example, in the manner of the surface structure of a cylinder liner. The surface structure is preferably implemented such that a rotational movement of the retaining pin with respect to the intermediate piece exerts a conveying effect on a fluid, in particular conveys the fluid present in the internal gear fluid machine between the inner wall and the retaining pin in order to achieve a particularly good lubricating effect. The surface structure is preferably produced by honing or long-stroke honing in a fundamentally known manner.

[0050] A further development of the invention provides that the intermediate piece has at least one fluid guide groove, in particular a fluid guide groove designed with an open edge in the inner wall. The fluid guide groove enables a fluid to flow between the intermediate piece and the retaining pin arranged in the intermediate piece. The fluid guide groove preferably extends over the entire extent of the intermediate piece in the axial direction. For example, contaminants that have accumulated between the intermediate piece and the retaining pin can be removed through the fluid guide groove toward other areas of the internal gear fluid machine. This improves the fatigue strength of the internal gear fluid machine.

[0051] A further development of the invention provides that the retaining pin is rotatably mounted in the intermediate piece by means of a hydrostatic bearing, in particular by means of a hydrostatic bearing that is fluidly connected to a pressure field of the internal gear fluid machine. The hydrostatic bearing is formed by fluid pressure being applied to a fluid chamber located radially between the retaining pin and the inner wall of the intermediate piece. For this purpose, the fluid chamber is preferably fluidically connected to a fluid source. The pressure field of the internal gear fluid machine or, alternatively, one of the fluid chambers serves as the fluid source, for example. The bearing by means of the hydrostatic bearing significantly reduces the frictional force acting between the retaining pin and the intermediate piece, which in turn improves the bearing of the retaining pin and thus also the fatigue strength of the internal gear fluid machine.

[0052] The invention further relates to a method for producing an internal gear fluid machine, in particular an internal gear fluid machine according to the embodiments within the scope of this description, wherein the internal gear fluid machine has a first gear having an external toothing and mounted rotatably about a first axis of rotation, and a second gear having an internal toothing that meshes with the external toothing in an engagement region and is mounted rotatably about a second axis of rotation different from the first axis of rotation, wherein a filler piece is arranged between the first gear and the second gear, away from the engagement region, which filler piece rests on the external toothing on the one hand and on the internal toothing on the other hand, in order to divide a fluid space present between the first gear and the second gear into a first fluid chamber and a second fluid chamber,and wherein, in the axial direction relative to the first rotational axis, housing walls of a machine housing of the internal gear fluid machine are arranged on both sides of the first gear and the second gear, and the filler piece is mounted on the machine housing by means of at least one retaining pin engaging at least one of the housing walls. It is provided that the retaining pin is rotatably mounted on the housing wall via at least one intermediate piece, wherein the housing wall is made of one housing wall material and the intermediate piece is made of an intermediate piece material different from the housing wall material.

[0053] The advantages of such a procedure or such a design of the internal gear fluid machine have already been pointed out. Both the internal gear fluid machine and the method for its manufacture can be further developed according to the explanations in this description, so reference is made to these in this regard.

[0054] The features and feature combinations described in the description, in particular the features and feature combinations described in the following description of the figures and / or shown in the figures, can be used not only in the respective combination specified, but also in other combinations or on their own, without departing from the scope of the invention. Thus, embodiments are also considered to be encompassed by the invention that are not explicitly shown or explained in the description and / or the figures, but which follow from or can be derived from the explained embodiments.

[0055] The invention will be explained in more detail below with reference to the exemplary embodiments shown in the drawings, without limiting the invention. In the drawings: Figure 1 shows a schematic cross-sectional view of an internal gear fluid machine, Figure 2 shows a schematic plan view of a region of a machine housing of the internal gear fluid machine in an alternative embodiment, and Figure 3 shows a schematic longitudinal section through the region of the machine housing.

[0056] The Figure 1shows a schematic cross-sectional view of an internal gear fluid machine 1, which has a machine housing 2, in which a first gear 3 and a second gear 4 are rotatably mounted. The first gear 3 can also be referred to as a pinion and the second gear 4 as a ring gear. The first gear 3 is rotatably mounted in the machine housing 2 about a first axis of rotation 5 and the second gear 4 about a second axis of rotation 6. It can be seen that the first axis of rotation 5 and the second axis of rotation 6 are arranged parallel and spaced from one another, so that the first gear 3 and the second gear 4 have different axes of rotation. The first gear 3 has an external toothing 7 and the second gear 4 has an internal toothing 8, which mesh with one another in an engagement region 9, i.e. are in engagement with one another.

[0057] The first gear 3 and the second gear 4 jointly define a fluid chamber 10. The first gear 3 defines the fluid chamber 10 radially inward, and the second gear 4 defines the fluid chamber 10 radially outward. The fluid chamber 10 is circumferentially divided into a first fluid chamber 12 and a second fluid chamber 13 by the meshing of the gears 3 and 4 on the one hand and a filler piece 11 on the other. Depending on the direction of rotation of the internal gear fluid machine 1, one of the fluid chambers 12 and 13 serves as a suction chamber and another of the fluid chambers 12 and 13 serves as a pressure chamber.

[0058] In the exemplary embodiment shown here, the filler piece 11 is designed symmetrically to enable reversing operation of the internal gear fluid machine 1. The internal gear fluid machine 1 can therefore be operated in both directions of rotation. Additionally or alternatively, the filler piece 11 is designed in several parts and has a plurality of segments 14 and 15 or 16 and 17. The segments 14 and 15 or 16 and 17 are divided in the radial direction. Accordingly, the first segment 14 or 16 rests on the first gear 3 and the second segment or 17 rests on the second gear 4. For example, a first filler piece part is formed by the segments 14 and 15 and a second filler piece part is formed by the segments 16 and 17. The internal gear fluid machine 1 can, for example, have only the first filler piece part, only the second filler piece part, or both filler pieces.In the first two cases, the internal gear fluid machine is fixed to a specific direction of rotation; in the latter embodiment, the aforementioned reversing operation is possible.

[0059] According to the exemplary embodiment illustrated here, a gap 18 or 19 exists between segments 14 and 15, or 16 and 17, which can be pressurized with fluid or is at least temporarily pressurized. This fluid application forces segments 14 and 15, or 16 and 17, apart in the radial direction and thus toward the respective gear 3 or 4, so that the respective segment 14, 15, 16, or 17 bears sealingly against the respective gear 3 or 5. This realizes radial compensation of the internal gear fluid machine 1, which can also be referred to as radial gap compensation.

[0060] It can also be seen that the second gear 4 is encompassed in the circumferential direction at least in regions, in particular only in regions, by one or more bearing recesses 20. The bearing recesses 20 are fluidically connected to fluid connections (not shown here) of the internal gear fluid machine 1, preferably each via a fluid channel 21. The flow connections between the respective bearing recess 20 and the fluid connections can be established via a respective connecting channel 22 or 23. For this purpose, the bearing recesses 20 are connected to the connecting channels 22 and 23 via the fluid channels 21. The bearing recesses 20 are designed such that they are at least temporarily subjected to pressurized fluid, for example from the fluid connections, so that they form a hydrostatic bearing for the second gear 4.

[0061] It can be provided that one of the bearing recesses 20 is fluidly connected only to that one of the fluid connections that is assigned to a pressure side of the internal gear fluid machine 1. This is particularly the case if the internal gear fluid machine 1 is not designed to be reversible or is only operated in one preferred direction of rotation. However, if the internal gear fluid machine 1 is intended for reversing operation and is operated with temporarily alternating directions of rotation, the bearing recesses 20 are preferably fluidly connected to both fluid connections, namely one of the bearing recesses 20 to a first of the fluid connections and another of the bearing recesses 20 to another of the fluid connections.Thus, one of the bearing recesses 20 is always subjected to the pressure present on the pressure side of the internal gear fluid machine 1, whereas the other of the bearing recesses 20 is subjected to any pressure, for example to the pressure present on the suction side, which is lower.

[0062] Also shown is a return line 24, via which fluid, in particular leakage fluid, can be discharged from the internal gear fluid machine 1 and / or fed back to the internal gear fluid machine 1 or the respective suction pressure chamber. For example, the return line 24 is fluidly connected directly to the suction side or the suction chamber. However, it can also be provided that the return line 24 is fluidly connected to a fluid tank. This fluid tank can be a component of the internal gear fluid machine 1, but can also be located separate from it. For example, it is fluidly connected to the suction side of the internal gear fluid machine 1. Viewed in the direction of flow, the return line 24 is arranged between the bearing recesses 20, in the exemplary embodiment shown here, centrally or at least approximately centrally with respect to the filler piece 11, preferably exactly centrally.Particularly preferably, the return 24 is symmetrical with respect to an imaginary plane which includes both the first axis of rotation 5 and the second axis of rotation 6.

[0063] The return 24 has a return recess 25 which passes through an inner circumferential surface of the machine housing 2 facing the second gear 3, such that the return recess 25 is open in the direction of the gears 3 and 4. In addition, the return 24 has return pockets (not shown here), which are preferably in flow connection with the return recess 25. While the return recess 25 overlaps with the gears 3 and 4 in the axial direction, the return pockets are located on both sides of the gears 3 and 4 in the axial direction, in particular they are formed on the sides of the sealing disks in the machine housing 2 facing away from the gears 3 and 4.

[0064] The fluid can be discharged via the return line 24, i.e., via the return recess 25 and / or the return pockets, and preferably fed back into the respective suction chamber. For example, the bearing recess 20 opens into the return recess 25. It can be provided that bearing webs that delimit the bearing recess 20 in the axial direction also delimit the return recess 25 in the axial direction. However, the bearing recesses 20 are preferably arranged at a distance from the return recess 25 in the circumferential direction. The bearing recesses 20 are preferably designed symmetrically with respect to the return recess 25, in particular, they are at the same distance from it.

[0065] The filler piece 11 is mounted on the machine housing 2 by means of at least one retaining pin 26. For example, the filler piece 11 is supported on the retaining pin 26 in the circumferential direction. However, it can also be provided that the filler piece 11 is rigidly connected to the retaining pin 26. In any case, the filler piece 11 is rotatably mounted on the machine housing 2 via the retaining pin 26, in particular about an axis of rotation running parallel to the axes of rotation 5 and 6. This axis of rotation corresponds, for example, to a longitudinal center axis of the retaining pin 26 or at least runs parallel to such an axis.

[0066] The Figure 2shows a schematic representation of an area of ​​the internal gear fluid machine 1 in an alternative embodiment, namely a housing wall 27 of the machine housing 2. The internal gear fluid machine 1 in the embodiment shown has only one of the filler pieces, in particular the filler piece comprising the segments 14 and 15, and is therefore not designed for reversing operation, but rather with a preferred direction of rotation. The housing wall 27 delimits the internal gear fluid machine 1 in the axial direction or closes off the machine housing 2 in this direction. The machine housing typically has several such housing walls 27, namely on opposite sides in the axial direction.

[0067] A recess 28 is visible in the housing wall 27. The recess 28 serves to accommodate a machine shaft of the internal gear fluid machine 1, which is rotationally fixedly coupled to the first gear 3 and is preferably only drive-connected to the second gear 4 via the first gear 3. Accordingly, the recess 28 is centered with respect to the first axis of rotation 5. A pressure field 29, which is in the form of a depression, is also formed in the housing wall 27. The pressure field 29 is overlapped by an axial disk (not shown here) of the internal gear fluid machine 1, which is urged towards or against the gears 3 and 4 by the application of pressure from the pressure field 29 in order to form a sealing contact with them. A further recess 30 forms a suction bore through which fluid can flow into the fluid space 10, namely in particular the respective suction chamber.

[0068] The retaining pin 26 is rotatably mounted on the housing wall 27 for supporting the filler piece 11 on the machine housing 2. The support is not provided directly, but only indirectly via an intermediate piece 31. The intermediate piece 31 is arranged in an intermediate piece receptacle 32 formed in the housing wall 27. The intermediate piece 31 in turn has a retaining pin receptacle 33 into which the retaining pin 26 engages. In this case, it is provided that the housing wall 27 consists of a housing wall material and the intermediate piece 31 consists of an intermediate piece material different from the housing wall material. Preferably, the housing wall 27, in particular the entire machine housing 2, is made of aluminum or an aluminum alloy, whereas the intermediate piece 31 is made of a stronger material, for example steel, in particular heat-treated steel, particularly preferably nitrided steel.The intermediate piece 31 effectively prevents excessive stress on the housing wall 27 caused by forces introduced into the housing wall 27 by the retaining pin 26. In particular, over-compression of the housing wall 27, especially excessive Hertzian pressure, is prevented. Accordingly, the fatigue strength of the internal gear fluid machine 1 is significantly improved by means of the intermediate piece 31.

[0069] The Figure 3 shows a sectional view through a portion of the machine housing 2, more precisely along the Figure 2shown section line A - A. It can be seen that the intermediate piece 31 is in the form of a hollow cylinder, namely in particular as a right hollow circular cylinder. In addition, the intermediate piece 31 is arranged completely within the intermediate piece receptacle 32 and therefore does not protrude from it. In the exemplary embodiment shown here, the retaining pin 26 extends completely through the intermediate piece 31 in the direction of an axis of rotation 34, about which the retaining pin 26 is rotatably mounted on the housing wall 27 by means of the intermediate piece 31. This means that the retaining pin 26 is supported on a base 35 of the intermediate piece receptacle 32. Accordingly, the retaining pin 26 is supported in the radial direction with respect to the axis of rotation 34 only indirectly via the intermediate piece 31 on the housing wall 27 and in the axial direction directly on the housing wall 27.

[0070] The retaining pin 26 has a projection 36 extending from a base body 37 of the intermediate piece 31. The base body 37 is preferably continuously cylindrical, in particular continuously circularly cylindrical. On the side of the base body 37 facing away from the projection 36, a support part (not further designated) extends from the base body 37. The filler piece 11 is supported on the support part on the retaining pin 26, or the filler piece 11 is fastened to the retaining pin 26 via the support part. The projection 36, like the base body 37, can be cylindrical or circularly cylindrical. In any case, it has smaller dimensions in the radial direction with respect to the axis of rotation 34 than the base body 37. In particular, the projection 36 is arranged centered with respect to the base body 37 and / or the axis of rotation 34. The retaining pin 26 is supported on the base 35 of the intermediate piece receptacle 32 via the projection 36.This allows tilting of the retaining pin 26 within the retaining pin receptacle 33 within a certain retaining pin play.

[0071] Between the intermediate piece receptacle 32 and the pressure field 29 is a web 38, which fluidically separates the intermediate piece receptacle 32 from the pressure field 29. Preferably, the aforementioned axial disc rests against the web 38. This supports the axial disc and prevents excessive fluid from escaping from the pressure field 29. The web 38 has a wall thickness that corresponds to at least 50% of the wall thickness of the intermediate piece 31, but is preferably greater. This ensures that the web 38, and thus the housing wall 27, is not deformed and thus damaged by forces introduced into the housing wall 27 via the retaining pin 26.

[0072] The intermediate piece 31 is preferably pressed into the intermediate piece receptacle 32, i.e., arranged therein with a press fit. Accordingly, the intermediate piece 31 is fixed in a force-locking manner with respect to the housing wall 27, namely in particular in the circumferential direction with respect to the rotation axis 34. Additionally or alternatively, it can be provided that the intermediate piece 31 is fastened to the housing wall 27 in a form-locking manner, in particular again to prevent a rotational movement of the intermediate piece 31 in the intermediate piece receptacle 32 in the circumferential direction.

[0073] It can optionally be provided that a fluid guide groove 39, only indicated here, is formed in the intermediate piece 31 on its side facing the retaining pin 26. This serves to transport dirt particles out of the intermediate piece receptacle 32 by fluid flowing in the fluid guide groove 39. For example, it is provided for this purpose that the intermediate piece receptacle 32 or the retaining pin receptacle 33 is subjected to pressurized fluid so that, on the one hand, a smooth-running bearing of the retaining pin 26 on the housing wall 27 is realized and, on the other hand, any dirt particles that may arise are reliably transported out of the intermediate piece receptacle 32 or the retaining pin receptacle 33. It is particularly preferably provided for the retaining pin 26 to be mounted in the retaining pin receptacle 33 by means of a hydrostatic bearing.For this purpose, pressurized fluid is supplied to the retaining pin receptacle 33 or to a bearing space located in the radial direction between the intermediate piece 31 and the retaining pin 26, for example via a fluid line 40, which is only indicated schematically here and which fluidically connects the bearing space to the pressure field 29.

[0074] Particularly preferably, an inner wall 41 of the intermediate piece 31, against which the retaining pin 26 rests at least temporarily and / or at least in some areas, is provided with a coating and / or a surface structure. The coating is in particular a polymer coating, particularly preferably a polytetrafluoroethylene coating. Such a coating is preferably designed to reduce the friction between the retaining pin 26 and the intermediate piece 31 and accordingly to achieve a low-friction rotary mounting of the retaining pin 26 on the housing wall 27. The surface structure is designed, for example, such that fluid from the fluid chamber 10 is conveyed between the retaining pin 26 and the intermediate piece 31, i.e., into the retaining pin receptacle 33. This likewise improves the mounting of the retaining pin 26 due to reduced friction.The surface structure is preferably characterized by elevations and depressions with a height in the micrometer range, so that the surface structure can also be referred to as a micro-surface structure. The surface structure is formed in particular by honing or long-stroke honing and is designed in a manner similar to the surface structure of a cylinder liner.

[0075] The described design of the internal gear fluid machine 1 enables operation at high power levels, particularly at high pressures and / or at high speeds and / or pressure gradients, without requiring the housing wall 27 to be constructed from a more rigid material. Rather, the retaining pin 26 is reliably mounted on the housing wall 27 by means of the intermediate piece 31, so that even at high power levels, deformation of the housing wall 27 cannot occur. The described measures thus extend the service life of the internal gear fluid machine 1, while simultaneously allowing and maintaining cost-effective manufacturing. LIST OF REFERENCE SYMBOLS

[0076] 1 Internal gear fluid machine 2 Machine housing 31. Gear 42. Gear 51. Rotational axis 62. Rotational axis 7 External gearing 8 Internal gearing 9 Engagement area 10 Fluid chamber 11 Filler piece 121. Fluid chamber 132. Fluid chamber 14 Segment 15 Segment 16 Segment 17 Segment 18 Gap 19 Gap 20 Bearing recess 21 Fluid channel 22 Connecting channel 23 Connecting channel 24 Return 25 Return recess 26 Retaining pin 27 Housing wall 28 Recess 29 Pressure field 30 Recess 31 Intermediate piece 32 Intermediate piece holder 33 Retaining pin holder 34 Rotational axis 35 Base 36 Projection 37 Base body 38 Web 39 Fluid guide groove 40 Fluid line 41Interior wall

Claims

1. Internal gear fluid machine (1), with - a first gearwheel (3) having an outer toothing (7) and mounted for rotation about a first axis of rotation (5) and a second gearwheel (4) having an inner toothing (8) regionally meshing with the outer toothing (7) in an engagement region (9) and mounted for rotation about a second axis of rotation (6) different from the first axis of rotation (5), wherein - a filler piece (11) is arranged between the first gearwheel (3) and the second gearwheel (4) away from the engagement region (9), which filler piece (11) bears on one side against the outer toothing (7) and on the other side against the inner toothing (8) in order to divide a fluid space (10) present between the first gearwheel (3) and the second gearwheel (4) into a first fluid chamber (12) and a second fluid chamber (13), wherein - housing walls (27) of a machine housing (2) of the internal gear fluid machine (1) are arranged on both sides of the first gearwheel (3) and the second gearwheel (4) in the axial direction with respect to the first axis of rotation (5), and the filler piece (11) is mounted on the machine housing (2) by means of at least one retaining pin (26) engaging on at least one of the housing walls (27), wherein the retaining pin (26) is rotatably mounted on the housing wall (27) by means of at least one intermediate piece (31), wherein the housing wall (27) consists of a housing wall material and the intermediate piece (31) consists of an intermediate piece material different from the housing wall material, characterised in that the intermediate piece material has a greater value of a material characteristic than the housing wall material, wherein the material characteristic is the modulus of elasticity, the tensile strength, the yield strength, the 0.2 % proof stress or the elastic limit.

2. Internal gear fluid machine according to claim 1, characterised in that a retaining pin material of the retaining pin (26) has a larger or at least the same value of the material characteristic as the intermediate piece material.

3. Internal gear fluid machine according to one of the preceding claims, characterised in that the retaining pin (26) engages in a retaining pin receptacle (33) of the intermediate piece (31) and the intermediate piece (31) engages in an intermediate piece receptacle (32) of the housing wall (27).

4. Internal gear fluid machine according to one of the preceding claims, characterised in that a retaining pin radial clearance present between the retaining pin (26) and an inner wall (41) of the intermediate piece (31) delimiting the retaining pin receptacle (33) is different from an intermediate piece radial clearance present between an outer wall of the intermediate piece (31) and the housing wall (27) delimiting the intermediate piece receptacle (31).

5. Internal gear fluid machine according to one of the preceding claims, characterised in that the intermediate piece (31) is a hollow cylindrical bearing bush or a sheet metal rolled part.

6. Internal gear fluid machine according to one of the preceding claims, characterised in that the intermediate piece (31) is made of multiple parts.

7. Internal gear fluid machine according to one of the preceding claims, characterised in that the retaining pin (26) engages completely through the intermediate piece (31) and rests against a base (35) of the intermediate piece receptacle (32) on its side facing away from the filler piece (11).

8. Internal gear fluid machine according to one of the preceding claims, characterised in that the retaining pin (26) has a projection (36) on its side facing the base (35) of the intermediate piece receptacle (32), which projection (36) is supported against the base (35).

9. Internal gear fluid machine according to one of the preceding claims, characterised in that an opening is formed in the housing wall (27) adjacent to the intermediate piece receptacle (32), wherein a web (38) is formed between the intermediate piece receptacle (32) and the opening, which web (38) has a wall thickness of at least 50 %, at least 75 %, at least 100 % or at least 150 % of a wall thickness of the intermediate piece (31).

10. Internal gear fluid machine according to one of the preceding claims, characterised in that a ratio between dimensions of the intermediate piece (31) in the radial direction and dimensions of the retaining pin (26) in the same direction is at least 110%, at least 120% or at least 125%.

11. Internal gear fluid machine according to one of the preceding claims, characterised in that the intermediate piece (31) has a coating on its inner wall (41), which bears against the retaining pin (26) at least partially and / or at least temporarily, and / or in that the intermediate piece (31) is heat-treated at least partially.

12. Internal gear fluid machine according to one of the preceding claims, characterised in that the inner wall (41) of the intermediate piece (31) has a surface texture.

13. Internal gear fluid machine according to one of the preceding claims, characterised in that the intermediate piece (31) has at least one fluid guide groove (39).

14. Internal gear fluid machine according to one of the preceding claims, characterised in that the retaining pin (26) is rotatably mounted in the intermediate piece (31) by means of a hydrostatic bearing.

15. Method of manufacturing an internal gear fluid machine (1), in particular an internal gear fluid machine (1) according to one or more of the preceding claims, wherein - the internal gear fluid machine (1) comprises a first gearwheel (3) having an outer toothing (7) and mounted for rotation about a first axis of rotation (5), and a second gearwheel (4) having an inner toothing (8) regionally meshing with the outer toothing (7) in an engagement region (9) and mounted for rotation about a second axis of rotation (6) different from the first axis of rotation (5), wherein - a filler piece (11) is arranged between the first gearwheel (3) and the second gearwheel (4) away from the engagement region (9), which filler piece (11) bears against the outer toothing (7) on the one hand and against the inner toothing (8) on the other hand in order to divide a fluid space (10) present between the first gearwheel (3) and the second gearwheel (4) into a first fluid chamber (12) and a second fluid chamber (13), wherein - housing walls of a machine housing (2) of the internal gear fluid machine (1) are arranged on both sides of the first gearwheel (3) and the second gearwheel (4) in the axial direction with respect to the first axis of rotation (5), and the filler piece is mounted on the machine housing (2) by means of at least one retaining pin (26) engaging on at least one of the housing walls (27), wherein the retaining pin (26) is rotatably mounted on the housing wall (27) by means of at least one intermediate piece (31), wherein the housing wall (27) is made of a housing wall material and the intermediate piece (31) is made of an intermediate piece material different from the housing wall material, characterised in that the intermediate piece material has a greater value of a material characteristic than the housing wall material, wherein the modulus of elasticity, the tensile strength, the yield strength, the 0.2 % proof stress or the elastic limit is used as the material characteristic.