Turbocharger with predetermined breaking point for an internal combustion engine

Abstract

Disclosed is a turbocharger for an internal combustion engine, having a bearing housing. A turbocharger rotor is mounted to be rotatable in the bearing housing about the rotor axis of rotation of its rotor shaft, wherein a turbine wheel is arranged for conjoint rotation on the rotor shaft and in a turbine housing fixed on the bearing housing. Between the rotor shaft and the bearing housing, an oil seal for sealing the bearing housing with respect to the turbine housing is arranged between the turbine wheel and a radial bearing associated with the turbine wheel in order to seal the bearing housing with respect to the turbine housing. A predetermined breaking point is formed for the turbocharger rotor of the turbocharger which lies in a breaking point region and extends axially between the turbine wheel back and an axial end, facing the turbine wheel back, of the rotor-shaft oil seal.

Claims

1. A turbocharger for an internal combustion engine, comprising: a bearing housing having a compressor side and a turbine side and a bearing housing interior, a turbine housing, which is fixed mechanically on the bearing housing on the turbine side; a turbocharger rotor, which has a rotor shaft and a turbine wheel, wherein the rotor shaft of the turbocharger rotor is rotatably mounted in the bearing housing by means of at least two radial bearings, and the turbine wheel is arranged for conjoint rotation on a turbine end of the rotor shaft and in the turbine housing, and at least one turbine-side rotor-shaft oil seal for sealing the bearing housing interior with respect to the turbine housing, the seal being arranged on the rotor shaft and between the rotor shaft and the bearing housing, wherein, axially in relation to a rotor axis of rotation, the turbine-side rotor-shaft oil seal is arranged on the rotor shaft between a turbine wheel back, which faces the bearing housing, and a radial bearing closest to the turbine wheel, wherein a predetermined breaking point is formed for the turbocharger rotor, the breaking point lying in a breaking point region which, in relation to the rotor axis of rotation, extends axially between the turbine wheel back and an axial end, facing the turbine wheel back, of the turbine-side rotor-shaft oil seal which is arranged furthest away from the turbine wheel, the rotor shaft breaks at the predetermined breaking point in the event of a failure.

2. The turbocharger as claimed in claim 1, wherein there is a weld seam in the region of the predetermined breaking point, by means of which weld seam the turbine wheel is connected to the rotor shaft.

3. The turbocharger as claimed in claim 1, wherein, axially in relation to the rotor axis of rotation, the predetermined breaking point is arranged at that point of the breaking point region of the rotor shaft which is subject to a highest stress during operation of the turbocharger.

4. The turbocharger as claimed in claim 3, wherein there is a weld seam in the region of the predetermined breaking point, by means of which weld seam the turbine wheel is connected to the rotor shaft.

5. The turbocharger as claimed in claim 3, wherein a predetermined rubbing contact point between the rotor shaft and the bearing housing is provided in the region of the predetermined breaking point, wherein a smallest radial spacing between the rotor shaft and a rotor shaft opening of the bearing housing is provided in a region of the rubbing contact point, with the result that, during normal operation, the rotor shaft runs without contact within the rotor shaft opening and, in the event of failure of the radial bearings, initially rubs against the bearing housing in the region of the rubbing contact point.

6. The turbocharger as claimed in claim 1, wherein, axially in relation to the rotor axis of rotation, the predetermined breaking point is arranged between the turbine wheel back and the axial end, facing the turbine wheel back, of the turbine-side rotor-shaft oil seal which is closest to the turbine wheel back.

7. The turbocharger as claimed in claim 6, wherein there is a weld seam in the region of the predetermined breaking point, by means of which weld seam the turbine wheel is connected to the rotor shaft.

8. The turbocharger as claimed in claim 6, wherein a predetermined rubbing contact point between the rotor shaft and the bearing housing is provided in the region of the predetermined breaking point, wherein a smallest radial spacing between the rotor shaft and a rotor shaft opening of the bearing housing is provided in a region of the rubbing contact point, with the result that, during normal operation, the rotor shaft runs without contact within the rotor shaft opening and, in the event of failure of the radial bearings, initially rubs against the bearing housing in the region of the rubbing contact point.

9. The turbocharger as claimed in claim 1, wherein, axially in relation to the rotor axis of rotation, the predetermined breaking point is arranged in an immediate vicinity of the turbine wheel back of the turbine wheel.

10. The turbocharger as claimed in claim 9, wherein there is a weld seam in the region of the predetermined breaking point, by means of which weld seam the turbine wheel is connected to the rotor shaft.

11. The turbocharger as claimed in claim 9, wherein a predetermined rubbing contact point between the rotor shaft and the bearing housing is provided in the region of the predetermined breaking point, wherein a smallest radial spacing between the rotor shaft and a rotor shaft opening of the bearing housing is provided in a region of the rubbing contact point, with the result that, during normal operation, the rotor shaft runs without contact within the rotor shaft opening and, in the event of failure of the radial bearings, initially rubs against the bearing housing in the region of the rubbing contact point.

12. The turbocharger as claimed in claim 9, wherein the turbine wheel has a cylindrical hub connection piece on the side of the turbine wheel facing the rotor shaft, the connection piece having a transitional region, embodied as a fillet, to the turbine wheel back, wherein the predetermined breaking point is arranged in the transitional region.

13. The turbocharger as claimed in claim 1, wherein a predetermined rubbing contact point between the rotor shaft and the bearing housing is provided in the region of the predetermined breaking point, wherein a smallest radial spacing between the rotor shaft and a rotor shaft opening of the bearing housing is provided in a region of the rubbing contact point, with the result that, during normal operation, the rotor shaft runs without contact within the rotor shaft opening and, in the event of failure of the radial bearings, initially rubs against the bearing housing in the region of the rubbing contact point.

14. The turbocharger as claimed in claim 13, wherein the turbine-side rotor-shaft oil seal is formed by at least one piston ring arranged in an encircling piston ring groove between two piston ring lands, wherein, in relation to the rotor axis of rotation, the piston ring land which is closer to the turbine wheel back has a smallest radial gap relative to the rotor shaft opening of the bearing housing in order to form the rubbing contact point.

15. A turbocharger for an internal combustion engine, comprising: a bearing housing having a compressor side, a turbine side and a bearing housing interior, a turbine housing fixed mechanically on the bearing housing on the turbine side thereof; a turbocharger rotor comprising a rotor shaft and a turbine wheel, wherein the rotor shaft is rotatably mounted in the bearing housing by at least two radial bearings, and the turbine wheel is arranged for conjoint rotation with the rotor shaft on a turbine end of the rotor shaft and in the turbine housing, and at least one turbine-side rotor-shaft oil seal configured to seal the bearing housing interior with respect to the turbine housing, the seal being arranged on the rotor shaft and between the rotor shaft and the bearing housing, wherein, axially in relation to a rotor axis of rotation, the turbine-side rotor-shaft oil seal is arranged on the rotor shaft between a turbine wheel back, which faces the bearing housing, and a radial bearing of the at least two radial bearings that is closest to the turbine wheel, wherein a predetermined breaking point is formed for the turbocharger rotor, the breaking point lying in a breaking point region which, in relation to the rotor axis of rotation, extends axially between the turbine wheel back and an axial end, facing the turbine wheel back, of the turbine-side rotor-shaft oil seal which is arranged furthest away from the turbine wheel, the rotor shaft breaks at the predetermined breaking point in the event of a failure.

16. The turbocharger as claimed in claim 15 wherein, axially in relation to the rotor axis of rotation, the predetermined breaking point is arranged in one of at that point of the breaking point region of the rotor shaft which is subject to a highest stress during operation of the turbocharger, between the turbine wheel back and the axial end, facing the turbine wheel back, of the turbine-side rotor-shaft oil seal which is closest to the turbine wheel back, and in an immediate vicinity of the turbine wheel back of the turbine wheel.

17. The turbocharger as claimed in claim 15, wherein the region of the predetermined breaking point includes a weld seam which connects the turbine wheel to the rotor shaft.

18. The turbocharger as claimed in claim 15, wherein the turbine wheel includes a cylindrical hub connection piece on the side of the turbine wheel facing the rotor shaft, the cylindrical hub connection piece having a transitional region, formed as a fillet, to the turbine wheel back, wherein the predetermined breaking point is arranged in the transitional region.

19. The turbocharger as claimed in claim 15, wherein a predetermined rubbing contact point between the rotor shaft and the bearing housing is provided in the region of the predetermined breaking point, wherein a smallest radial spacing between the rotor shaft and a rotor shaft opening of the bearing housing is provided in a region of the rubbing contact point such that during normal operation, the rotor shaft runs without contact within the rotor shaft opening and, in the event of failure of the radial bearings, initially rubs against the bearing housing in the region of the rubbing contact point.

20. The turbocharger as claimed in claim 19, wherein the turbine-side rotor-shaft oil seal is formed by at least one piston ring arranged in an encircling piston ring groove between two piston ring lands, wherein, in relation to the rotor axis of rotation, the piston ring land which is closer to the turbine wheel back has a smallest radial gap relative to the rotor shaft opening of the bearing housing in order to form the rubbing contact point, the smallest radial gap comprising the smallest radial spacing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Of the figures:

(2) FIG. 1 shows a schematic sectional view of a turbocharger according to the prior art in order to explain a conventional illustrative embodiment of a turbocharger;

(3) FIG. 2 shows a schematic sectional view of a turbocharger rotor according to the prior art in order to illustrate a conventional illustrative embodiment of a turbocharger rotor;

(4) FIG. 3 shows a schematic partial sectional view of a turbocharger rotor (turbine impeller and rotor shaft part) of a turbocharger according to a first illustrative embodiment; and

(5) FIG. 4 shows a schematic partial sectional view of a rotor shaft, of the turbine impeller and of the bearing housing of a turbocharger according to a second illustrative embodiment.

DETAILED DESCRIPTION

(6) Items of identical function and designation are denoted by the same reference signs throughout the figures.

(7) FIGS. 1 and 2 relate to the known prior art and have already been described in the introduction in order to explain the construction of a respective illustrative embodiment of a conventional turbocharger and of an associated turbocharger rotor.

(8) Two illustrative embodiments of turbochargers 1 are described with reference to FIGS. 3 and 4, in which a predetermined breaking point 61 is provided on the turbocharger rotor 10, said predetermined breaking point allowing selective breaking of the rotor shaft 14 at this predetermined breaking point 61 in the event of failure of the radial bearings 42 of the turbocharger 1 or in the case of any other overloading of the turbocharger rotor 10.

(9) FIG. 3 relates to a first illustrative embodiment of a turbocharger 1, which basically corresponds to a turbocharger 1 with a turbocharger rotor 10 as per FIGS. 1 and 2, for example. FIG. 3 shows only a segment of the turbocharger rotor 10 schematically in section, this section emphasizing on an enlarged scale the turbine impeller 12, that part of the rotor shaft 14 which adjoins said impeller and is relevant here, and the transitional region between them.

(10) As in FIG. 4, the turbine wheel 12 with its turbine wheel back 67 and the rotor shaft 14 with the turbine-side rotor-shaft oil seal 51 for sealing the bearing housing interior with respect to the turbine housing 21 can be seen in FIG. 3, said seal extending over a certain axial extent 51a in relation to the rotor axis of rotation 15 and having two piston rings 52a, which are each arranged in piston ring grooves 64 between two piston ring lands 52. When viewed as a whole, the turbine-side rotor-shaft oil seal 51 accordingly has a first axial end, which faces away from the turbine wheel back 67, i.e., is further away from the turbine wheel back 67, and a second axial end, which faces the turbine wheel back 67, i.e., is closer to the turbine wheel back 67. However, since each of the two piston rings 52a, when considered per se, can be regarded as an individual rotor-shaft oil seal, there is accordingly a rotor-shaft oil seal 51b which is arranged closest to the turbine wheel 12 and a rotor-shaft oil seal 51c which is arranged furthest away from the turbine wheel.

(11) In this case, according to an embodiment, the breaking point region 62 extends axially, that is to say, in relation to the rotor axis of rotation (15), between the turbine wheel back (67) and an axial end, facing the turbine wheel back, of the turbine-side rotor-shaft oil seal (51c) which is arranged furthest away from the turbine wheel (12). That is to say, when viewed in the drawing, from the turbine wheel back to the right-hand axial end, i.e., the end facing the turbine wheel back, of the piston ring 52a which is arranged furthest away from the turbine wheel 12, i.e., of the piston ring on the left.

(12) The turbine wheel 12 has a first axial end, which faces the rotor shaft 14, and a second axial end, which faces away from the rotor shaft 14. The turbine wheel 12 has a turbine wheel back 67, which is defined substantially as a disk, faces the rotor shaft 14 and thus also the motor-shaft oil seal 51 and extends substantially perpendicularly to the rotor axis of rotation 15. The largest diameter of the turbine wheel 12 is in the region of the turbine wheel back 67. A transitional region 59 in the form of a fillet is formed between the rotor shaft 14 and the turbine wheel 12. In the transitional region 59, therefore, the outer contour of the turbine wheel 12 has a concave curvature, e.g., a radius or an arc-shaped contour.

(13) In an alternative embodiment, it is also possible for a further section, e.g. a step or a tapered section (not illustrated) to be formed in the transitional region 59 between the turbine wheel 12 and the rotor shaft 14.

(14) In general, the turbine impeller 12 and the rotor shaft 14 are connected securely in a materially integral manner to form a single component, that is to say are welded by means of and along at least one encircling weld seam 60, as illustrated in FIGS. 3 and 4.

(15) In the illustrative embodiment shown in FIG. 3, the weld seam 60 is arranged in the transitional region 59 between the first axial end of the turbine impeller 12 and the rotor shaft 14, which is directly adjacent in this case. In the first illustrative embodiment, the weld seam 60 is designed and positioned in such a way that it forms a weak point in the rotor shaft/turbine wheel assembly and thus simultaneously forms the predetermined breaking point 61 for the turbocharger rotor 10.

(16) If the connection point between the turbine wheel 12 and the rotor shaft 14 and thus the weld seam 60 is situated in the transitional region 59, as illustrated in FIG. 3, it is located in the region of the most highly stressed point 62a between the rotor shaft 14 and the turbine wheel 12. Thus, both the weld seam 60 and the predetermined breaking point 61 are situated in the region of the turbine rotor 10 which is subject to the highest centrifugal forces and temperatures and thus forms the most highly stressed point 62a. In this way, the predetermined breaking point 61 is as it were defined in a redundant manner, greatly increasing the probability of breaking at precisely this predetermined breaking point 61 in the event of failure.

(17) FIG. 4 shows another illustrative embodiment of a turbocharger 1. The turbocharger 1 corresponds very largely to the above descriptions, and therefore features in FIG. 4 that are provided with reference signs are not described again. Here too, only a segment of the turbocharger rotor 10 is shown schematically in section, this section emphasizing on an enlarged scale the turbine impeller 12, that part of the rotor shaft 14 which adjoins said impeller and is relevant here, and the transitional region between them. In addition, the segment of the bearing housing 41 in this region, having the bearing shaft opening 47, is also illustrated here.

(18) Axially in relation to the rotor axis of rotation 15, on the side facing the rotor shaft 14, e.g., at the first axial end, the turbine wheel 12 has a cylindrical hub section, which is referred to below as hub connection piece 58. In a transitional region 59, which is in the form of a fillet, the hub connection piece 58 adjoins the turbine wheel back 67. Thus, in this case too, the outer contour of the turbine wheel 12 has a concave curvature, e.g., a radius or an arc-shaped contour, in the transitional region 59.

(19) FIG. 4 once again illustrates the turbine-side rotor-shaft oil seal 51, which is formed by at least two piston rings 52a as already described above.

(20) In this illustrative embodiment, a predetermined breaking point 61 is defined by a predetermined rubbing contact point 63. Here, the rubbing contact point 63 is predetermined by the radially encircling outer surface of the piston ring land 52 situated closest to the turbine wheel 12. The rubbing contact point 63 is surrounded directly by the inner surface of the rotor shaft opening 47 of the bearing housing 41, forming a minimum radial gap 65.

(21) In the region of the abovementioned piston ring land 52 with the rubbing contact point 63, the rotor shaft 14 has the smallest radial clearance with respect to the bearing shaft opening 47 of the surrounding bearing housing 41. By virtue of this fact, the rotor shaft 14 comes into contact initially with the bearing housing 41 at the defined rubbing contact point 63 in the event of failure, e.g., of a radial bearing 42, and the resulting wobbling movement of the turbocharger rotor 10, and therefore the temperature of the rotor shaft 14 increases significantly in this axial region owing to the friction which occurs and it breaks in the breaking point region 62 of the rotor shaft 14. Accordingly, the rubbing contact point 63 can also be referred to as a predetermined rubbing point.

(22) In order to define the predetermined breaking point 61 more clearly in the vicinity of the rubbing contact point 63, additional measures can be taken. In FIG. 4, a breaking point groove 62b is introduced for this purpose at the bottom of the nearest piston ring groove 64, immediately adjoining the piston ring land 52, said groove representing a diminution of the rotor shaft diameter and thus an additional weak point at a defined position, i.e., the predetermined breaking point 61. Of course, it is also possible for a breaking point groove 62b of this kind to be arranged on that side of the piston ring land 52 designed as a rubbing contact point 63 which faces the impeller back 67 and directly adjoining said land in the rotor shaft 14. Thus, in the example shown, both piston rings 52a would maintain their position in the rotor shaft opening 47 of the bearing housing 41 and thus their sealing function between the bearing housing interior 46 and the turbine housing 21 in the event of the rotor shaft breaking.

(23) In another embodiment, the weld seam 60 can also be arranged as a weak point in the immediate vicinity of a rubbing contact point 63, with the result that the predetermined breaking point 61 is additionally defined by the weld seam.

(24) Conversely, it is also possible, as it were combining the embodiments in FIGS. 3 and 4, for the rubbing contact point to be provided at some other position, e.g. in the transitional region 59 and thus at least close to the most highly stressed point 62a of the rotor shaft 14, thereby predetermining the failure of the rotor shaft 14, i.e., the breaking of the shaft, at this point.