Bearing bushing for a turbocharger shaft

Abstract

Bearing bushing (6) with a central axis (12) for receiving a shaft (4) of a turbocharger (1) rotating about this axis (12), having at least one axial bearing surface (15) and at least one radial bearing surface (14), which has several helical lubricant grooves (16) for conveying lubricant, wherein the axial bearing surface (15) has a number of detent surfaces (18) in a plane perpendicular to the axis (12) and an equal number of wedge surfaces (19) each between the detent surfaces (18), wherein a keyway (17) extending from radially inside to radially outside is formed at each transition of the wedge surfaces (19) into one of the adjacent detent surfaces (18), and wherein each of the wedge grooves (17) is in contact with at least one of the lubricant grooves (16), characterized in thatthat the wedge surfaces (19) adjacent to one of the detent surfaces (18) are set back by a step in the axial direction and then rise in the circumferential direction to the other adjacent detent surface (18), wherein the wedge grooves (17) rise from radially inside to radially outside and extend in the radial direction only over a part of the radial width of the axial bearing surface (15).

Description

[0001] The invention relates to a bearing bushing for a shaft with a central axis of the type defined in more detail in the preamble of claim 1. The invention also relates to a turbocharger with such a bearing bushing.

[0002] Turbochargers are known from the general state of the art. They typically have a continuous shaft with a turbine mounted on one end and at least one compressor wheel mounted on the other. Bearing bushings, which have axial and radial bearing surfaces, have long been established for supporting the shaft in the turbocharger housing. An example of such a bearing bushing can be found in US disclosure 4,240,678 A.

[0003] A crucial aspect of such bearing bushings is their function as both a thrust bearing and, in particular, a radial bearing for the turbocharger shaft, which typically rotates at tens of thousands of rpm. These bushings can be manufactured as a single piece. For example, the design described in US 6,017,184 A can be cited. EP 1 998 009 B1, for instance, shows a design in which a split bushing is used. This bushing, divided into two parts, has essentially a similar design for both the radial bearing surfaces inside the two bushings and the thrust bearing surfaces on each end face of the bushing.

[0004] International patent application WO 2014 / 055255 A1 discloses a plain bearing with an axial bearing surface. The axial bearing surface consists of a flat surface with pressure-generating means at the inner diameter of the annular surface. These pressure-generating means do not extend to the outer diameter of the surface. They are used to supply oil as a lubricant to the flat surface. The problem with this design is the relatively large flat surface, which increases friction. Furthermore, no means are provided to distribute the lubricant across the flat surface. While this results in a minimal amount of lubricant being required, it also further increases friction.

[0005] From DE 11 2013 003 184 T5, a translation of international application WO 2014 / 003057 A1, a bearing bushing with axial and radial bearings for a turbocharger is also known. The axial bearings have continuous, outwardly extending grooves which have a curved profile and widen accordingly to ensure the most uniform possible supply of lubricant to the axial bearing surfaces and to allow accumulated dirt to drain away. Furthermore, this document discloses two radial bearings in the bearing bushing. These radial bearings have outwardly deepening grooves which are designed to create a pumping effect for lubricant outwards when the shaft rotates relative to the bearing bushing.

[0006] A similar design with spiral grooves running through the radial bearing surfaces is known from WO 2015 / 167844 A1. According to the international patent application, however, these grooves are not intended for lubrication but for the acoustic optimization of the turbocharger's design. They do, however, exhibit opposing helical configurations within the two radial bearing surfaces of the bearing bushing described therein. A pumping effect on the lubricant is therefore to be expected.

[0007] The CN 1 01 550 864 A shows a bearing bushing with crescent-shaped oil distribution grooves in the axial bearing surface.

[0008] DE 203 17 497 U1 shows a combination of wedge surfaces and detent surfaces, wherein intermediate lubricating oil grooves are radially outwardly terminated in an outer ring with a small groove as a throttling point.

[0009] For further information on the state of the art, reference can also be made to JP 2011-153 668 A, DE 11 2015 002 059 T5 and JP 2007-46 642 A.

[0010] The object of the invention is to provide an improved bearing bushing for the shaft of a turbocharger, which allows for good load-bearing capacity together with minimal friction and acceptable lubricant consumption. It is also an object of the invention to provide a turbocharger with such a bearing bushing.

[0011] This problem is solved by a bearing bushing with the features of claim 1. The problem is also solved by a turbocharger with such a bearing bushing.

[0012] The bearing bushing according to the invention is constructed around a central axis about which the shaft of a turbocharger, which is housed in the bearing bushing, rotates. The shaft, together with a compressor and a turbine, forms the so-called rotor of the turbocharger, i.e., the part that rotates in the bearing bushing at the aforementioned speeds. Similar to bearing bushings in the prior art, the bearing bushing has at least one axial bearing surface and at least one radial bearing surface. For example, two separate bearing bushings can be provided, each with one radial bearing surface and one axial bearing surface, or a common bearing bushing can be provided with two radial bearing surfaces and two axial bearing surfaces.

[0013] In at least one radial bearing surface, several helical lubricant grooves are provided for conveying lubricant in one axial direction or the other, depending on the direction of rotation. The axial bearing surface of the bearing bushing according to the invention has a number of so-called detent surfaces in a plane perpendicular to the axis and an equal number of wedge surfaces between each of the detent surfaces. At each transition of the wedge surface into one of the adjacent detent surfaces, a wedge groove extending from radially inward to radially outward is formed, with each of the wedge grooves being connected to at least one of the lubricant grooves. The wedge grooves, which according to an advantageous embodiment of the idea are formed rising from radially inward to radially outward and preferably extending in the radial direction only over a portion of the radial width of the axial bearing surface, are thus each connected to at least one of the lubricant grooves.With the appropriate direction of rotation of the shaft in the bearing bushing, or of the shaft and bearing bushing relative to each other, lubricant is pumped from the side of the radial bearing surface facing away from the axial bearing surface, through the lubricant grooves, towards the keyways of the axial bearing surface. The lubricant is thus reliably pumped in this area and simultaneously lubricates the radial bearing surface. The lubricant pumped into the axial bearing surface reaches the essentially annular area of ​​the axial bearing via the keyway, specifically at the lowest point of the keyway surface, offset from the plane of the indexing surfaces in the direction of the radial bearings.The lubricant can then accumulate in this area of ​​the wedge surface and is increasingly compressed along the wedge surface by the rotational movement of the mating element relative to the axial bearing surface of the bearing bushing. This pressure builds up until the wedge surface reaches the detent surface, and the components rotate not directly against each other, but with a pressure cushion of lubricant between them. This enables a very efficient, low-wear bearing arrangement that, due to the special design, is also very economical in terms of lubricant consumption.

[0014] Furthermore, the wedge surfaces adjacent to one of the detent surfaces are set back by a step in the circumferential direction, i.e., offset from the plane of the detent surface in the direction of the radial bearing. They then rise again in the circumferential direction until they reach the plane of the other adjacent detent surface. This design enables ideal pressure build-up in the lubricant by forming a lubricant wedge.

[0015] The keyways rise from radially inside to radially outside and are only formed over a part of the radial width of the axial bearing surface in the radial direction.

[0016] According to an advantageous embodiment of the idea, the number of lubricant grooves in the at least one radial bearing surface is greater than or preferably equal to the number of keyways in the at least one axial bearing surface. Each of the helically extending lubricant grooves thus supplies one of the keyways and therefore one of the key surfaces of the axial bearing. If the axial bearing is, for example, constructed with four indexing surfaces, it accordingly has four key surfaces and four keyways. Each of the keyways is supplied with lubricant via one of the helical lubricant grooves, so that the lubricant grooves in the radial bearing surface are practically arranged in the manner of a four-start thread.The lubricant grooves do not necessarily have to extend around the entire circumference of the radial bearing surface, so a design corresponding to a four-start thread with a correspondingly high pitch is also conceivable, so that the lubricant grooves only extend around a part of the circumference.

[0017] Alternative forms of lubricant grooves, which in the state rolled onto a projection plane show, for example, linear profiles, a parabolic function, an exponential function, a curve, an S-shaped line, a zigzag line or the like, also fall under the term of helical lubricant grooves in the sense of the invention, as long as they cause a resulting conveying effect of lubricant from one axial side of the radial bearing surface to the other with a constant direction of rotation.

[0018] In a further advantageous embodiment of the idea, an intermediate surface, arranged parallel to the plane of the locking surfaces, can be provided between the detent surface and the wedge surface, extending from the step. The wedge grooves are arranged in this intermediate surface. The wedge grooves can therefore be located in the wedge surfaces themselves or in intermediate surfaces running parallel to the detent surfaces between the wedge surfaces and the detent surfaces. This can be advantageous for manufacturing, as one side edge of the wedge groove can then simultaneously form the radial boundary between the wedge groove and the wedge surface.

[0019] A particularly advantageous further development provides that the wedge surfaces are planar in the radial direction. The detent surfaces and – if present – ​​the intermediate surfaces, which lie in a plane perpendicular to the axis, are already planar in both the circumferential and radial directions. According to this advantageous further development of the idea, the wedge surfaces can now also be planar in the radial direction. This means that the entire step between one of the detent surfaces and the adjacent wedge surface, or the transition from the intermediate surface, if present, to the wedge surface, is such that the height of the step is the same radially inside and radially outside the axial bearing surface.This is a crucial advantage in terms of manufacturing, as the wedge surface only changes in the circumferential direction and does not also need to be changed in the radial direction in addition to the circumferential direction, which would represent a significant additional effort in terms of manufacturing.

[0020] To ensure an ideal oil supply to the keyways, and thus to the key surfaces and ultimately the axial bearing surface, an advantageous further development of the idea allows each of the lubricant grooves connected to a keyway to open into the keyway on the side facing the circumferential direction of the detent surface. This ensures that the keyway is supplied with lubricant on the side furthest from the center of motion of a counter element on the axial bearing surface, allowing the lubricant conveyed into the keyway area on this side to ideally flow out on the other side of the keyway and radially towards the key surface, contributing to pressure build-up there.

[0021] Ideally, each of the keyways can be assigned to exactly one of the lubrication grooves. This prevents unnecessary lubricant buildup in the radial bearing surfaces caused by additional lubrication grooves, which would, in principle, also be conceivable. If present, these additional lubrication grooves could, for example, terminate in a circumferential groove running along the radial bearing surface. However, assigning exactly one lubrication groove to each keyway results in a well-functioning design that ensures minimal lubricant consumption.

[0022] A very advantageous further development of the idea provides that, in this particularly favorable embodiment of the invention, the bearing bushing has a supply opening for lubricant on the side of the radial bearing surface facing away from the axial bearing surface, so that this lubricant can be conveyed to the axial bearing surface via the conveying action of the spiral lubricant grooves in the radial bearing surface, thereby lubricating both the radial bearings and the axial bearings accordingly.

[0023] According to a further advantageous embodiment, an opening for receiving a locking pin can be provided in the bearing bushing. In principle, both of these openings can be present. For example, if a hollow locking pin is used, one opening would suffice, which would fulfill both the technical function of rotationally fixing the bearing bushing and, through the hollow locking pin, the supply of lubricant.

[0024] According to a particularly advantageous embodiment of the idea, the bushing, as already mentioned above as an option, is designed such that a radial bearing surface and a thrust bearing surface are provided at each of the opposite axial ends of the bearing bushing. The shaft of the turbocharger rotor can thus be supported in a single bushing. In this advantageous embodiment of the idea, the helical lubricant grooves in the two radial bearing surfaces are arranged in opposite directions, so that, with the corresponding direction of rotation of the shaft in the bearing bushing, they both enable a pumping action outwards towards the thrust bearing surfaces.

[0025] A turbocharger according to the invention comprises at least one compressor and one turbine on a common shaft. The turbocharger further comprises a housing with a central opening for receiving the shaft in at least one bearing bushing. According to one of the embodiments described above, the bearing bushing is designed with at least one axial bearing surface comprising wedge surfaces, keyways, and detent surfaces. The bearing bushing also has at least one radial bearing surface with helical lubrication grooves according to the embodiments described above. Such a turbocharger allows for minimal friction in its radial and axial bearings and enables good load-bearing capacity with low lubricant or oil consumption.

[0026] A further advantageous development of the turbocharger involves the housing incorporating a lubricant channel to supply lubricant to the inlet. Ideally, this channel runs radially within the housing. This significantly reduces the housing's complexity compared to designs with multiple, sometimes angled, lubricant supply lines.

[0027] Further advantageous designs and developments of the bearing bushing and the turbocharger also result from the exemplary embodiment, which is described in more detail below with reference to the figures.

[0028] This shows: Fig. 1 a section through a part of a turbocharger according to the invention in one possible embodiment; Fig. 2 a section through a part of a turbocharger according to the invention in an alternative embodiment; Fig. 3 a three-dimensional view of a bearing bushing in an embodiment according to the invention; Fig. 4 a sectional view through the bearing bushing; Fig. 5 a top view of a design of the axial bearing surface in a design of the bearing bushing according to the invention; Fig. 6 a part of the axial bearing surface viewed radially inside with a counter element running on the axial bearing surface; Fig. 7 a view analogous to the one in Fig. 6, from radial outside; Fig. 8 a three-dimensional view of a bearing bushing in a further embodiment according to the invention; and Fig. 9 a top view of the axial bearing surface in the further embodiment of the bearing bushing according to the invention.

[0029] In the presentation of the Fig. Figure 1 shows a section of a turbocharger 1, particularly suitable for use as an exhaust gas turbocharger. The core of the turbocharger 1 consists of a turbine 2 and, mounted on a common shaft 4 with the turbine 2, a compressor 3 at the other end of the shaft 4. The turbocharger 1 itself comprises a central housing 5 in which a bearing bushing 6 is arranged for supporting the shaft 4. The central housing 5 is laterally completed in the area of ​​the compressor 3 by an attached compressor housing and in the area of ​​the turbine 2 by a turbine housing (both not shown). For the following invention, the central area of ​​the housing 5 and the bearing bushing 6 for the axial and radial support of the so-called rotor, consisting of the shaft 4, turbine 2, and compressor 3, are of particular importance.

[0030] The housing 5 has a radial lubricant channel 7 for supplying lubricant to a supply opening 8 located in the bearing bushing 6. The lubricant thus preferably enters the interior of the bearing bushing 6 centrally to supply both sides of the bearing bushing 6 evenly. It then flows from the bearing bushing 6, via its radial bearing surfaces 14 (which will be described in detail below), to the axial bearing surfaces 15 located on both end faces of the bearing bushing 6. From there, the lubricant flows to the discharge channels 9, through which it is collected and removed. This is well known to those skilled in the art of turbochargers.

[0031] Furthermore, the bearing bushing 6 has an opening 10 for receiving a locking pin 11, which secures the bearing bushing 6, in particular preventing it from rotating. The opening 10 can be correspondingly larger than the diameter of the locking pin 11, so that the bearing bushing 6 can be fixed both circumferentially and axially around a central axis 12, as shown in the illustration of the Fig. 1 can be seen to be movable.

[0032] In the presentation of the Fig. Figure 2 shows the same setup again. The only difference is that the opening 10 and the supply opening 8 are combined by inserting a locking pin 11' which has a central bore 13, so that it can perform both the function of fixing and the function of supplying lubricant. All other elements are analogous to the elements described above. Fig. 1 is designated and to be understood.

[0033] In the presentation of the Fig. Figure 3 is now a first embodiment of the bearing bushing 6 in a three-dimensional view and below in the Fig. 4 and Fig. Figure 5 shows a cross-sectional view and a top view of one of the axial bearing surfaces 15 of the bearing bushing 6. The design is such that the bearing bushing 6 has radial bearing surfaces 14 and axial bearing surfaces 15 at both axial ends. In the three-dimensional view of the Fig. Figure 3 shows one of the axial bearing surfaces 15 and one of the radial bearing surfaces 14. The view of the Fig. Figure 5 shows a top view of the axial bearing surface 15. Lubricant enters the interior of the bearing bushing 6 through the supply opening 8. The two radial bearing surfaces 14 have several, in the embodiment shown here four, lubricant grooves 16 extending helically through the radial bearing surfaces 14. With the appropriate direction of rotation of the shaft 4 in the bearing bushing 6, these lubricant grooves 16 ensure that the lubricant supplied to the interior of the bearing bushing 6 through the supply opening 8 is conveyed outwards through the lubricant grooves 16 towards the axial bearing surfaces 15. The lubricant flowing through the lubricant grooves 16 in the radial bearing surfaces 14 is sufficient for adequate lubrication of the radial bearing surfaces 14 themselves.

[0034] The lubricant, conveyed axially outwards towards the axial bearing surfaces 15, then enters a keyway 17 connected to each of the lubricant grooves 16. Next to this keyway 17, on one side, are so-called detent surfaces 18, which lie in a plane perpendicular to the axis 12 and which serve to improve visibility in the illustration of the Fig. The 5 are marked with hatching, even though this is not a section as is usually the case with hatching. These resting surfaces 18 are flat in both the circumferential and radial directions. Wedge surfaces 19 extend between them, into the area of ​​which the wedge grooves 17 open. The transition between the wedge surfaces 19 and the resting surfaces 18 on one side in the circumferential direction, in this case on the side in which the wedge grooves 17 are arranged, is formed in the form of a step. This step has the same height h radially inside and radially outside, so that the wedge surface is flat in the radial direction. It then rises to the resting surface 18 adjacent on the other side in the circumferential direction and transitions into this resting surface 18.

[0035] The keyway 17 is machined into the wedge surface 19 in conjunction with each of the lubricant grooves 16 in the area of ​​this step-like transition from the detent surface 18 to the wedge surface 19 and decreases continuously in depth in the radial outward direction. After approximately two-thirds of the radial width of the axial bearing surface 15, viewed from the radial inside to the outside, the keyway 17 ends at the plane of the wedge surface 19. The keyway 17 itself is radially aligned only at one of its circumferentially oriented side edges or, for example, with its centerline. The other side edge, or both side edges if the centerline is radially oriented, are parallel to it / to each other, so that the keyway 17 can be produced very easily with a milling cutter.The lubricant groove 16 terminates in the wedge groove 17 in the direction of the adjacent detent surface 18, allowing lubricant to be supplied from this direction. The lubricant then spreads ideally across the wedge surface 19 on the bearing bushing 6, which is fixed in the housing 5 of the turbocharger 1, due to the rotation of the counter element 20. The height h of the step can be, for example, on the order of a few tens of micrometers, with an outer diameter of the bearing bushing 6 of, for example, 10 to 30 mm.

[0036] In the presentation of the Fig. Figure 6 shows a rolled-up section of part of the axial bearing surface viewed from the radial inside; in Fig. 7 The same section seen from the radial outside. In Fig. Figure 6 shows the height h of the step; likewise the keyway 17 and the lubricant groove 16 opening into the keyway 17. A counter-element 20 to the axial bearing surface 15 moves relative to the axial bearing surface 15 according to the arrow shown, so that the lubricant arriving via the lubricant groove 16 spreads in the direction from which it flows over the keyway surface 19 and lubricates the components. In the illustration of the Fig. 7 is the same structure from the radial outside, and therefore with the reversed orientation as in the illustration of the Fig. Figure 6 shows that the keyway 17 does not extend into the radially outer region, so that essentially only the key surface 19 is visible. This is essentially the case because, in the embodiment, the Fig. 6 and Fig. 7 and also in the Fig. 8 and Fig. 9, which will be described below, has a slightly different construction than previously described. Instead of the opening of the wedge groove 17 into the wedge surface 19, this embodiment features an intermediate surface marked 21, which runs parallel to the detent surfaces 18 and forms a section between the actual wedge surface 19 and the step. The wedge groove 17 is then machined into this intermediate surface 21, so that the transition of the wedge groove 17 to a flat, non-wedge-shaped rising surface, as in the previously shown embodiment, occurs. The technical effect is essentially the same; however, with regard to manufacturing, one variant or the other may be advantageous depending on the tools used. Both variants can be used in both described embodiments of the bearing bushing 6 and can therefore be interchanged compared to the examples described.It would also be conceivable to construct a bearing bushing 6 with two different axial bearing surfaces 15 according to the exemplary embodiments.

[0037] In the depictions of the Fig. 8 and Fig. Figure 9 shows the second described structure of the axial bearing surface 15 again, otherwise analogous to the illustrations in Fig. 3 and Fig. 5. Another difference in the structure is that in the Fig. 3 to 5 the bearing bushing 6 has a relatively large outer diameter in the area of ​​the radial bearing surfaces 14, for example to accommodate a corresponding central opening in the housing 5 without having to change the inner diameter, the radial bearing surfaces 14 and the axial bearing surfaces 15. The design in the Fig. 8 and Fig.Figure 9 shows the same construction, without the material ridges on the bearing bushing 6, indicating that this bearing bushing 6 is designed for a correspondingly smaller diameter. Otherwise, the constructions are largely identical. A groove 22 indicated in the bearing bushing 6 has no technical function in the true sense, but serves only to symbolize the direction in which the bearing bushing 6 must be inserted during assembly, since directional assembly is necessary to ensure the conveying effect of the helical lubricant grooves 16 from the center of the bearing bushing 6 towards the axial bearing surfaces 15 in all cases.

Claims

[1] Bearing bushing (6) with a central axis (12) for receiving a shaft (4) of a turbocharger (1) rotating about this axis (12) having at least one axial bearing surface (15) and at least one radial bearing surface (14) which has several helical lubricant grooves (16) for conveying lubricant, wherein the axial bearing surface (15) has a number of detent surfaces (18) in a plane perpendicular to the axis (12) and an equal number of wedge surfaces (19) each between the detent surfaces (18), wherein at each transition of the wedge surfaces (19) into one of the adjacent detent surfaces (18) a keyway (17) extending from radially inside to radially outside is formed, and wherein each of the keyways (17) is in contact with at least one of the lubricant grooves (16), characterized by, that the wedge surfaces (19) adjacent to one detent surface (18) are set back by a step in the axial direction and then rise in the circumferential direction to the other adjacent detent surface (18), wherein the wedge grooves (17) rise from radially inside to radially outside and extend in the radial direction only over a part of the radial width of the axial bearing surface (15). [2] Bearing bushing (6) according to claim 1, characterized by , that the number of helical lubricant grooves (16) in the least one radial bearing surface (14) is greater than or preferably equal to the number of keyways (17) in the at least one axial bearing surface (15). [3] Bearing bushing (6) according to claim 1 or 2, characterized by , that between the resting surface (18) and the adjacent wedge surface (19) starting from the step there is an intermediate surface (21) arranged parallel to the plane of the resting surfaces (18), in which the wedge groove (17) is arranged. [4] Bearing bushing (6) according to one of claims 1 to 3, characterized by , that the wedge surfaces (19) are planar in the radial direction. [5] Bearing bushing (6) according to any one of claims 1 to 4, characterized by , that each of the helical lubricant grooves (16) connected to one of the keyway (17) opens into the keyway (18) on the side of the keyway (17) facing the circumferential direction of the detent surface (18). [6] Bearing bushing (6) according to any one of claims 1 to 5, characterized by , that each of the keyways (17) is assigned to exactly one of the helical lubricant grooves (16). [7] Bearing bushing (6) according to any one of claims 1 to 6, characterized by a supply opening (8) for lubricant on the side of the radial bearing surface (14) facing away from the axial bearing surface (15). [8] Bearing bushing (6) according to any one of claims 1 to 7, characterized by an opening (10) for receiving a fixing pin (11'). [9] Bearing bushing (6) according to any one of claims 1 to 8, characterized by , that the keyways (17) have side edges aligned parallel to each other in the radial direction. [10] Bearing bushing (6) according to any one of claims 1 to 9, characterized by , that a radial bearing surface (14) and an axial bearing surface (15) are provided at opposite axial ends, wherein the helical lubricant grooves (16) in the two radial bearing surfaces (14) are formed in opposite directions. [11] Turbocharger (1) with at least one compressor (3) and one turbine on a common shaft (4) with a housing (5) which has a central opening for receiving the shaft (4) in at least one bearing bushing (6), characterized by the bearing bushing (6) according to one or more of claims 1 to 10. [12] Turbocharger (1) according to claim 11 and with a bearing bushing (6) according to any one of claims 7 to 10, characterized by, that in the housing (5) a lubricant channel (7), in particular radially extending, is provided for supplying lubricant to the supply opening (8) of the bearing bushing (6).

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