Turbocharger bearing arrangement

Abstract: A turbocharger includes a main housing (1) for housing a turbine rotor (2) and a compressor impeller (4). An independent bearing box (23) is provided in the main housing (1). The main housing (1) is comprised of a turbine housing (3) and a compressor housing (5). A rotating shaft (7) connecting the turbine rotor (2) with the compressor impeller (4) is supported by a semi-float bearing metal (24) placed in the bearing box (23). An oil passage (26) is formed in the main housing (1) for feeding an oil to inside and outside of the semi-float bearing metal (24) in the bearing box (23). Oil grooves (37) are formed in end faces of the bearing metal (24) and another grooves (34) are formed at end faces of the bearing box (23) for discharging the oil from the semi-float bearing metal (24). Oil flow in the turbocharger housing (1) is controlled by the oil grooves (34, 37).

Description: The present invention generally relates to a turbocharger according to the first part of claim 1 and more particularly to an improvement of a structure for feeding an oil to a bearing unit supporting a rotating shaft in a turbocharger housing and an improvement of a structure for supporting a semi-float bearing of the bearing unit in the turbocharger housing. A turbocharger of this type is known from FR-A-2 449 820. Generally, a turbocharger housing is comprised of three major parts, i.e., a turbine housing, a compressor housing and a bearing housing. A typical example of such a turbocharger housing is illustrated in Figure 6 of the accompanying drawings. As depicted, the turbocharger housing y includes a turbine housing b for housing a turbine rotor a , a compressor housing d for housing a compressor impeller c and a bearing housing g for housing a set of bearings f supporting a rotating shaft e . The shaft e connects the turbine rotor a with the compressor impeller c . The turbine housing b and the bearing housing g are fixedly aligned by a pin h provided at their interface k . An outer periphery of the interface k is firmly held by a clamp i . The bearing housing g and the compressor housing d are joined with each other by a bolt j . The bearing set f includes a plurality of journal bearings f1 and a thrust bearing f2 . The journal bearings f1 are rotatably fitted in a shaft bore formed in the bearing housing g . The shaft e extends through the shaft bore. The thrust bearing unit f2 is provided at the right end of the shaft bore. Each of the journal bearings f1 is a cylindrically shaped full float bearing which is rotatable in the rotating shaft bore of the bearing housing g . The journal bearings f1 support a radial force. The thrust bearing f2 includes a first ring-shaped bearing member fa secured to the rotating shaft e and a second bearing member fb engaged over the first bearing member fa and fixed to the bearing housing g . The thrust bearing f2 supports a thrust force. In the illustrated turbocharger housing y , the journal bearings f1 and the thrust bearing f2 should be respectively assembled in the bearing housing g so that the number of necessary parts is large and an assembling process is troublesome and time consuming. In addition, a degree of freedom in designing oil feeding and discharging passages and spaces for the bearings f1 and f2 is quite limited due to accuracy and shape of a core used in a molding process and structure and locations of the bearings f1 and f2 . Particularly in case of a small turbocharger, it is impossible to design oil passages and spaces which can optimally control flow of a lubrication oil in the bearing housing g . To simplify the assembling process, reduce the number of necessary parts and to provide a controlled flow of oil in the turbocharger housing y , it has been proposed to separate the bearing housing from the turbocharger housing y and to employ a semi-float bearing unit (bearing metal) which functions as both the journal and thrust bearings instead of the full float bearing. This simplifies the assembling process, reduces the number of necessary parts and provides a larger freedom in designing the oil passages and spaces in the turbocharger housing. Specifically, an independent bearing box is prepared separately, and a semi-float bearing metal is provided in the bearing box in such a manner that it can move in a radial direction and is fixed in axial and peripheral directions relative to the bearing box. This one-piece semi-float bearing supports the rotating shaft in a full float manner and bears a thrust load. However, this semi-float bearing has the following drawbacks. The semi-float bearing supports thrust loads at its ends so that the oil flow is more unstable than conventional structures on both the turbine and compressor sides. Accordingly, the lubrication oil tends to flow to sealing members provided between the turbine rotor and the rotating shaft (or bearing box) and between the compressor impeller and the rotating shaft (or bearing box), i.e., the desired oil discharge flow is not realized. Furthermore, the semi-float bearing is generally secured onto the turbocharger housing by a thrust pin. However, the semi-float bearing is made from a soft material such as copper which provides an excellent bearing property so that the semi-float bearing is easy to wear at point or linear contact between the thrust pin and the semi-float bearing. Another known turbocharger housing is disclosed, for example, in Japanese Patent Application, Laid-Open Publication Nos. 7-139363 and 7-150962. One object of the present invention is to provide a turbocharger housing which does not have the above described problems and in particular to provide a turbocharger housing of a type having a semi-float bearing to support a rotating shaft, which has a sealing structure with an improved oil discharge property. This problem is solved by a turbocharger according to claim 1. The main housing may include a turbine housing for housing the turbine rotor, a compressor housing for housing the compressor impeller and a sealing plate provided between the turbine housing and the compressor housing. The bearing box may be supported by the sealing plate and the turbine housing. The bearing box may have a generally cylindrical shape as well as the semi-float bearing metal having larger diameter portions at its longitudinal ends, which larger diameter portions are joumaly supported by the bearing box. Figure 1 illustrates a sectional view of a major part of a turbocharger according to the present invention; Figure 2a is a left side cross sectional view of a bearing unit shown in Figure 1; Figure 2b is a front sectional view of the bearing unit, which is extracted from Figure 1 and illustrated in an enlarged scale; Figure 3 is an enlarged cross section of the most important part of the turbocharger shown in Figure 1; Figure 4a is an enlarged view of a semi-float bearing shown in Figure 1; Figure 4b illustrates a partial transversal cross section of the semi-float bearing shown in Figure 4a; Figure 5 illustrates an over all cross sectional view of the turbocharger according to the present invention; and Figure 6 depicts a cross section of a conventional turbocharger. Now, preferred embodiments of the present invention will be described with reference to Figures 1 to 5 of the accompanying drawings. Referring first to Figure 5, a fundamental construction of a turbocharger according to the present invention will be described. A turbocharger housing 1 includes a turbine housing 3 for housing a turbine rotor 2 and a compressor housing 5 for housing a compressor impeller 4. A sealing plate 6 is interposed between the turbine housing 3 and the compressor housing 5. The turbine rotor 2 is coupled with the compressor impeller 4 by a rotating shaft 7. The rotating shaft 7 is supported by a bearing unit 9. The bearing unit 9 includes a bearing box 23 having a radial flange-like member 8 which is clamped between the turbine housing 3 and the sealing plate 6. The turbine housing 3 for the turbine rotor 2 includes a scroll chamber 10 formed around the turbine rotor 2, a bearing chamber 11 for housing the bearing unit 9, an exhaust gas inlet 12 for introducing an exhaust gas to the scroll chamber 10, an exhaust gas outlet 13 for discharging the exhaust gas which is fed to the turbine rotor 2 from the scroll chamber 10, a cooling water passage 10a for heat insulation of the back of the scroll chamber 10, an oil inlet 14 for introducing an oil into the bearing chamber 11 and an oil outlet 15 for discharging the oil from the bearing chamber 11. In the compressor housing 5, a second scroll chamber 16 is formed around the compressor impeller 4. An air inlet 17 opens in an axial direction of the impeller 4 and an air outlet 18 extends from the second scroll chamber 16. The bearing box 23 is fitted in a stepwise recess 19 formed in the back of the turbine housing 3. A positioning pin 20 is inserted into the bearing box 23 to fix the position of the bearing box 23. Then, the sealing plate 6 is placed over the bearing box 23 and secured to the turbine housing 3 by bolts 21. The compressor housing 5 is bolted onto the sealing plate 6 using screws 22. The bearing unit 9 includes a generally cylindrical bearing box 23 and a semi-float bearing metal 24 housed in the bearing box 23 for supporting the rotating shaft 7. A thrust pin 25 provided in the bearing box 23 allows the semi-float bearing metal 24 to move in a radial direction. Axial and rotational movements of the semi-float bearing metal 24 are prohibited by the thrust pin 25. The bearing box 23 has an oil feed passage 26 for introduction of an oil into the bearing box 23 from the oil inlet 14 of the turbine housing 5. The semi-float bearing metal 24 has a through hole 27 for leading the oil to the rotating shaft 7 from the oil passage 26. The shaft 7 is assembled in the bearing unit 9 in the following manner. A thrust supporting member 30 is fitted over the shaft 7 from the right until it contacts a stepwise portion 29 of the shaft 7. Then, the shaft 7 integrally having the turbine rotor 2 at its left end is inserted into the gas outlet 13 of the turbine housing 3 until a right end enlarged portion 28 of the turbine rotor 2 (Figure 1) abuts a left end face of the thrust semi-float bearing metal 24. The thrust supporting member 30 naturally fits in a thrust supporting face 31 of the sealing plate 6. Alternatively, the thrust supporting member 30 may be fitted over the shaft 7 after the shaft 7 is inserted to bearing unit 9 and when the sealing plate 6 is attached to the turbine housing 3. The semi-float bearing metal 24 joins the turbine rotor 2 with the compressor impeller 4 since its left end abuts the enlarged portion 28 of the turbine rotor 2 and its right end abuts the thrust supporting member 30. The semi-float bearing metal 24 journally supports the rotating shaft 7 and bears a thrust load at the same time since it is supported by the bearing box 23 via the thrust pin 25. In the illustrated embodiment, the bearing box 23 is provided inside the turbocharger housing 1, the bearing box 23 has a fan-shaped flange 8 (Figure 2a), the semi-float bearing metal 24 is housed in the bearing box 23 and the rotating shaft 7 is supported by the bearing metal 24. Now referring to Figures 1, 2a and 2b, oil discharge grooves 34 are formed at both lower ends of the bearing box 23. These grooves 34 are made by, for example, cutting away the end faces of the bearing metal 24 in an arch shape respectively. The semi-float bearing metal 24 is made from a relatively soft material such as copper or its alloy. This bearing metal 24 has a plurality of oil grooves 37 at both ends as illustrated in Figures 2a and 4a. In the illustrated embodiment, four radial grooves 37 are formed in each end face of the bearing metal 24. The rotating shaft 7 has journal portions 38 at longitudinal ends thereof. These journal portions 38 have a larger diameter than other part of the shaft 7 and contact the end portions of the bearing metal 24 as shown in Figure 1. The oil fed inside the bearing metal 24 creates oil films at the journal portions 38 to journally support the rotating shaft 7. The oil then flows into the oil grooves 37 and in turn to the oil discharge grooves 34. Therefore, the oil lubricates the contact between the enlarged portion 28 of the turbine rotor 2, the right journal portion 38 of the shaft 7, the bearing metal 24 and the bearing box 23 and between the thrust supporting member 30, the left journal portion 38 of the shaft 7, the bearing metal 24 and the bearing box 23, thereby bearing thrust loads of the rotating shaft 7. Ultimately, the oil drops into the bearing chamber 11 below the bearing unit 9. Accordingly, control of the oil flow is realized. As a result, oil sealing on both the rotor and compressor sides is appropriately insured. One of the oil discharge grooves 34 formed at both ends of the bearing box 23 is illustrated in Figure 2a. It should be noted that the illustrated oil discharge groove 34 has an arc shape of about 110 degrees, but it may have a 180-degree expansion at most as viewed from the center of the end face of the bearing box 23. Numeral 46 in Figure 2a designates an opening formed in the flange 8 of the bearing box 23 for receiving the positioning pin 20. The upper end of the oil passage 26 opens in the bearing box flange 8 as illustrated in Figure 2a. It is communicated with a lower end of the oil inlet 14 as understood from Figures 1 and 2b. Referring to Figure 2b, a bore 36 is formed in the bearing box 23. As understood from Figure 3, the thrust pin 25 is inserted in this bore 36 formed in the bearing box 23 and secured therein such that an approximately upper half of the thrust pin 25 projects from the bore 36. The bearing metal 24 has a larger opening 40 at a corresponding position, which is coaxial to the bore 36, and a hard ring 42 having an inner diameter slightly larger than the bore 36 is fitted in the opening 40 so that the projecting upper half of the thrust pin 25 is loosely received in the ring member 42. The bearing metal 24 has larger diameter portions 41 at its longitudinal ends as best seen in Figure 4a. These portions 41 are journally supported in the bearing box 23. The ring member 42 fitted in the bore 40 of the bearing metal 24 is made from a hard material such as stainless steel or iron alloy. Although not shown, the ring member 42 has a slit so that it can shrink in a peripheral direction and reduce its diameter upon grasping. This allows a manual insertion of the ring member 42 into the mating bore 40. Alternatively, the ring member 42 may have a complete ring shape having no slit and it may be press-fitted in the bore 40 or the ring member 42 may be provided in the bore 40 during a molding process of the bearing metal 24 (i.e., insert molding). The thrust pin 25 is a solid member in this particular embodiment. However, it may be a spring pin. Further, the thrust pin 25 may have a shape other than the illustrated one. For example, a groove may be formed in an inner surface of the bearing box 23 and a first ring adapted to fit in the groove may be used instead of the thrust pin 25. In this case, a second ring having a mating groove may be provided on an outer surface of the bearing metal 24 instead of the ring 42 such that the second ring may engage with the first ring. Combination of such first and second rings allow the bearing metal 24 to rotate, and the bearing metal 24 only bears a thrust load. The contact between the turbine rotor 2 and the turbocharger housing 1 is sealed by a first seal ring 44 as illustrated in Figure 1. The contact between the thrust supporting member 30 and the sealing plate 6 is sealed by a second seal ring 45. Unlike the conventional turbocharger, the oil fed from the oil inlet 14 does not flow to these seal rings 44 and 45 excessively since the oil discharge passages are determined by the grooves 37 and 34 or the oil discharge route is controlled in this invention. The rotating shaft 7 is journally supported by the bearing metal 24 and the thrust load exerted by the rotating shaft 7 is also born by the bearing metal 24 by way of the large diameter portion 28 of the turbine rotor 2 and the thrust supporting member 30. The thrust load is in turn supported by the bearing box 23 via the ring member 42 and the thrust pin 25. It should be noted that the thrust pin 25 is loosely fitted in the ring member 42 so that a small amount of radial movement of the bearing metal 24 is permitted. The ring member 42 and the thrust pin 25 are both made from a hard material so that the duration of the bearing unit 9 is extended. Particularly, even if the semi-float bearing moves in an undesired or unexpected manner due to the thrust load or the like, the hard ring 42 contacts the thrust pin 25 so that the longevity of the bearing unit 9 is insured. As mentioned earlier, the oil fed from the inlet 14 of the turbocharger housing 1 flows in the oil passage 26 of the bearing box 23 and reaches the inside and outside of the bearing metal 24 supported in the bearing box 23. The oil prevailing over the outer surface of the bearing metal 24 and the oil flowing in the bearing metal 24 from the oil bore 27 form in combination oil films over the journally supported portions 38 of the rotating shaft 7. Then, the oil proceeds to the oil feeding grooves 37 formed in the end faces of the bearing metal 24 so that it lubricates the contact between the large diameter portion 28, the left end face of the shaft 7, the bearing box 23 and the bearing metal 24 and between the thrust supporting member 30, the right end face of the shaft 7, the bearing box 23 and the bearing metal 24. It is possible to select an optimal material for the bearing metal 24 without taking into account hardness and strength of the bearing metal 24.

Claims: A turbocharger including: a main housing (1) for housing a turbine rotor (2) and a compressor impeller (4), a rotating shaft (7) connecting the turbine rotor (2) with the compressor impeller (4), a bearing (24) for supporting the rotating shaft (7), a bearing box (23) is provided in the main housing (1), the bearing is a semi-float bearing metal (24) placed in the bearing box, and a thrust load supporting member (30) provided at back of the compressor impeller (4), an oil passage (14) is formed in the main housing (1) for feeding an oil to inside and outside of the semi-float bearing metal (24) in the bearing box (23), oil discharge means (34) is formed at ends of the bearing box (23) for discharging the oil from the semi-float bearing metal (24), the semi-float bearing metal (24) has a first end face which is in contact with an enlarged portion (28) of the turbine rotor (2) formed at a back of the turbine rotor (2) and a second end face which is in contact with the thrust load supporting member (30), and characterized in that a plurality of oil grooves (37) is formed in the first and second end faces of the semi-float bearing metal (24) for introducing the oil flowing between the rotating shaft (7) and the bearing metal (24) into the oil discharge means (34) which is a pair of grooves (34) formed in end faces of the cylindrical bearing box (23) in an arch shape respectively. The turbocharger of claim 1, characterized in that the main housing (1) includes a turbine housing (3) for housing the turbine rotor (2), a compressor housing (5) for housing the compressor impeller (4) and a sealing plate (6) provided between the turbine housing (3) and the compressor housing (5), and the bearing box (23) is supported by the sealing plate (6) and the turbine housing (3). The turbocharger of claim 1 or 2, characterized in that the bearing box (23) has a generally cylindrical shape, the semi-float bearing metal (24) has a generally cylindrical shape having larger diameter portions (41) at its longitudinal ends and the larger diameter portions (41) of the bearing metal (24) are journaly supported by the bearing box (23).

Inventors: KOIKE TAKAAKI, TAKAHASHI YUKIO, KOIKE, TAKAAKI, TAKAHASHI, YUKIO
Applicants: ISHIKAWAJIMA HARIMA HEAVY IND, ISHIKAWAJIMA-HARIMA HEAVY INDUSTRIES CO., LTD.
Application year: 1997
Main classification: F01D25
IPC codes: F01D25