2. Description of the Prior Art Turbochargers are used to increase the performance of engines, such as diesel engines used in locomotive and marine applications. Referring to Fig. 1, a typical turbocharged engine cycle 10 is illustrated schematically. The turbocharged engine cycle 10 includes a turbocharger 11 connected to an engine 12. The turbocharger 11 generally includes a turbine 16 connected to a work output 17 of the engine 12, and a compressor 18 connected to an air input 20 to the engine 12. The turbine 16 has a rotating turbine wheel (not shown) and the compressor 18 has a rotating compressor wheel (not shown).

A shaft 22 connects the turbine wheel to the compressor wheel, and operatively connects the turbine 16 to the compressor 18. The turbine 16 provides mechanical power through the shaft 22 to operate the compressor 18. The compressor 18 increases the air pressure of the air entering the engine 12. Fig. 1 shows an optional intercooler 24 between the compressor 18 and the engine 12, which cools the air entering the engine 12 from the compressor 18. Air input to the compressor 18 is represented by arrow 25 in Fig. 1.

Turbochargers typically include a rotating assembly generally defined by a turbine wheel, a compressor wheel, and a shaft interconnecting these elements. Figs.

2-4 schematically show several prior art embodiments of a rotating assembly 26 used in turbochargers. In each of the embodiments shown in Figs. 2-4, the rotating assembly 26 includes a turbine wheel 27, a compressor wheel 28, and a shaft 29 operatively connecting the turbine wheel 27 and the compressor wheel 28. A pair of journal bearings 30 rotatably supports the rotating assembly 26. The journal bearings 30 are located, respectively, at opposite ends of the shaft 29. In particular, one of the journal bearings 30 is located at a turbine end 32 of the rotating assembly 26, and the second journal bearing 30 is located at a compressor end 34 of the rotating assembly 26.

Referring to Fig. 2, a first prior art configuration of the rotating assembly 26 locates a thrust bearing 36 and a thrust collar 38 at both the turbine end 32 and the compressor end 34 of the rotating assembly 26. At the turbine end 32 of the rotating

assembly 26, the thrust bearing 36 and the thrust collar 38 are located between the turbine wheel 27 and the journal bearing 30. At the compressor end 34 of the rotating assembly 26, the thrust bearing 36 and the thrust collar 38 are located between the compressor wheel 28 and the journal bearing 30. The thrust bearings 36 are integral to (i. e., part of) the journal bearings 30. Thus, the thrust bearing 36 and journal bearing 30 at the turbine end 32 of the rotating assembly 26 are an integral unit, as are the thrust bearing 36 and journal bearing 30 at the compressor end 34 of the rotating assembly 26.

Referring to Fig. 3, a second prior art configuration of the rotating assembly 26 locates two thrust bearings 36 at the compressor end 34 of the rotating assembly 26, with the thrust bearings 36 located on either side of the journal bearing 30.

In this prior art configuration of the rotating assembly 26, the thrust bearings 36 are integral to (i. e., part of) the journal bearing 30 at the compressor end 34 of the rotating assembly 26. Two thrust collars 38 are located at the compressor end 34 of the rotating assembly 26, with the thrust collars 38 positioned on either side of the integral thrust bearing 36 and journal bearing 30 at the compressor end 34 of the rotating assembly 26.

Referring to Fig. 4, a third prior art configuration of the rotating assembly 26 also locates two thrust bearings 36 at the compressor end 34 of the rotating assembly 26. However, the thrust bearings 36 are now located between the journal bearing 30 at the compressor end 34 of the rotating assembly 26 and the compressor wheel 28. In the prior art rotating assembly 26 shown in Fig. 4, the thrust bearings 36 are separated by a single thrust collar 38. The thrust bearing 36, which is immediately adjacent and in contact with the journal bearing 30 at the compressor end 34 of the rotating assembly, is integral to (i. e., part of) the journal bearing 30.

The thrust bearings 36 in each of the above-discussed embodiments of the rotating assembly 26 generally operate to accommodate axial forces generated by the turbine wheel 27 and compressor wheel 28 during operation of the rotating assembly 26.

These axial forces are generally directed from the turbine wheel 27 toward the compressor wheel 28 of the rotating assembly 26.

Turbochargers typically rotate at extremely high speeds. Typical turbochargers for locomotive and marine applications have maximum rotation speeds ranging from 10,000 rpm to 30,000 rpm. The resultant axial forces generated by the turbine and compressor of the turbocharger are generally directed from the turbine toward

the compressor of the turbocharger. As discussed previously, one prior art rotating assembly configuration for turbochargers generally has a thrust bearing located at both the turbine end and at the compressor end of the rotating assembly. Other prior art rotating assembly configurations, as discussed previously, have two thrust bearings located at the compressor end of the rotating assembly, with at least one of the thrust bearings located between the journal bearing at the compressor end of the rotating assembly and the compressor wheel of the compressor. Each of these prior art rotating assembly configurations for turbochargers has certain disadvantages.

Locating thrust bearings at the turbine end of the rotating assembly exposes the thrust bearings to the high temperatures generally present at the turbine end during operation of the turbocharger. The high temperatures at the turbine end generally cause lubricants, such as oil, used in the thrust bearings to degrade quickly. The thermal degradation of the bearing lubricant oil is generally known in the art as"coking", and is evidenced by the buildup of carbonaceous deposits on the rotating assembly. These deposits can cause an imbalance in the rotating assembly and reduce the clearance and life of the thrust bearings and journal bearings. High temperatures also generally reduce the load carrying capacity of bearings by thinning the lubricant oil and causing accelerated wear. Consequently, locating the thrust bearings at the turbine end of the rotating assembly causes turbochargers with this type of rotating assembly configuration to require frequent overhauls to recondition the bearings at the turbine end, both thrust and journal bearings, and generally recondition the rotating assembly.

Locating thrust bearings at the compressor end of the rotating assembly also has certain disadvantages. The most important disadvantage of locating the thrust bearings at the compressor end is that the"overhang"or"cantilever"of the compressor increases. Due to the high speeds at which turbochargers operate, turbochargers necessarily become more dynamically unstable the longer the compressor overhang becomes. In particular, locating the thrust bearings at the compressor end of the rotating assembly causes the compressor to be moved longitudinally farther away from a vertical centerline of the turbocharger, which makes the turbocharger more unstable and increases vibration of the turbocharger.

Locating the thrust bearings at the compressor end has additional disadvantages. By grouping both the thrust bearings and the compressor end journal

bearing in close proximity, the available space for feeding lubricant oil to these bearings is restricted. As a result, the amount of lubricant oil to the thrust and journal bearings can be inadequate and result in increased failures at these bearings. Also. the thrust bearings are typically fed with"used"lubricant oil passing from the compressor end journal bearing to the thrust bearing rather than from a"fresh"supply of lubricant oil. This results in additional heating of the lubricant oil and high lubricant oil temperature, which generally reduces the load carrying capacity of bearings by thinning the lubricant oil and causing accelerated wear. Furthermore, distribution of lubricant oil to each bearing is difficult to meter and optimize. Likewise, the available space for draining lubricant oil from these bearings is restricted. Restricting the drainage from the thrust bearings and the compressor end journal bearing can lead to foaming, vibration. and increased wear at these bearings.

Turbochargers are known in the art which locate thrust bearings at the center of the turbocharger, such as the configuration disclosed by U. S. Patent No.

5,857,332 to Johnson et al. Such"center"thrust bearing configurations have certain disadvantages. The thrust bearings in such"center"thrust bearing configurations are cantilevered radially from a stationary housing. Therefore, the thrust load generated by the turbocharger will create a significant moment force on the radially cantilevered thrust bearings thus causing deformation of the bearing surface, and further causing an inability to operate under high load conditions. Additionally, in such"center"thrust bearing configurations, the thrust bearings are not supplied with lubricant oil independently. The "loaded"thrust bearing will be choked of lubricant oil which causes the lubricant oil flow to favor the"unloaded"thrust bearing, thus starving the loaded thrust bearing of lubricant oil. Further, this type of configuration requires the housing to be vertically split at the center to allow insertion of the thrust bearings. The vertical split of the housing precludes the use of water cooling, or severely limits the effectiveness of water cooling thereby risking thermal cracking of the housing.

Furthermore, all prior art turbochargers which incorporate a thrust collar inboard of a thrust bearing, such as the prior art rotating assembly 26 configurations shown in Figs. 2-4, require the journal bearing immediately adjacent the thrust bearing to operate against a sleeve. The sleeve slides over the shaft of the rotating assembly with

some required looseness between the sleeve and the shaft. This resulting looseness may lead to increased vibration and wear.

Accordingly, an object of the present invention is to provide a turbocharger for use with engines which minimizes bearing lubricant coking and lengthens the time between overhaul periods for the turbocharger. It is a further object of the present invention to provide a turbocharger which generally overcomes the disadvantages known with prior art turbocharger rotating assembly configurations, such as those discussed previously. Furthermore, it is an object of the present invention to provide a turbocharger in which bearing metal temperatures are maintained within acceptable predefined values by optimizing bearing lubricant flow, such that maximum bearing metal temperatures under load conditions would be substantially equalized.

SUMMARY OF THE INVENTION The above objects are accomplished with a turbocharger made in accordance with the present invention. The turbocharger includes a turbine having a turbine wheel and a compressor having a compressor wheel. The turbocharger further includes a mechanical assembly interconnecting the turbine and the compressor. The mechanical assembly has a turbine end facing the turbine and a compressor end facing the compressor. The mechanical assembly further includes a shaft operatively connecting the turbine wheel and the compressor wheel. An annular housing is positioned about the shaft and may include a water cavity for water cooling of the housing. A first journal bearing is connected to the annular housing and positioned directly about the shaft at the turbine end of the mechanical assembly. A second journal bearing is connected to the annular housing and positioned directly about the shaft at the compressor end of the mechanical assembly. The first and second journal bearings rotatably support the shaft within the annular housing. The mechanical assembly further includes a thrust bearing assembly positioned directly about the shaft and located axially between the first and second journal bearings. The thrust bearing assembly is configured to absorb axial forces acting on the mechanical assembly directed from the turbine wheel toward the compressor wheel generated by rotation of the turbine wheel and compressor wheel during operation of the turbocharger.

The thrust bearing assembly preferably further includes an active thrust bearing positioned immediately adjacent and connected to the second journal bearing, a

thrust collar positioned immediately adjacent and in hydrodynamic contact with the active thrust bearing, and an inactive thrust bearing positioned immediately adjacent and in hydrodynamic contact with the thrust collar. The active thrust bearing and the thrust collar are preferably configured to absorb the axial forces acting on the mechanical assembly directed from the turbine wheel toward the compressor wheel generated by rotation of the turbine wheel and compressor wheel during operation of the turbocharger.

The thrust collar may be removably connected to the shaft. The active thrust bearing may be removably connected to the second journal bearing by mechanical fasteners. The inactive thrust bearing may be removably connected to the annular housing. The active thrust bearing may be annular-shaped and include an inner surface, an outer surface, and a plurality of radially extending conduits extending from the inner surface to the outer surface of the active thrust bearing. The conduits may each define an opening for receiving lubricant oil into the active thrust bearing.

The first journal bearing may be connected to the annular housing by a first journal bearing retainer positioned coaxially about the first journal bearing and carrying the first journal bearing. The second journal bearing may be connected to the annular housing by a second journal bearing retainer positioned coaxially about the second journal bearing and carrying the second journal bearing. A first lubricant seal may be located at the turbine end of the mechanical assembly and positioned radially between the shaft and the first journal bearing retainer for providing a fluid seal between the first journal bearing and the turbine wheel. The second journal bearing and second journal bearing retainer may define a recess adjacent the compressor wheel. The mechanical assembly may further include a sleeve positioned directly about the shaft and located in the recess. A second lubricant seal may be located at the compressor end of the mechanical assembly and positioned radially between the sleeve and the second journal bearing retainer for providing a fluid seal between the second journal bearing and the compressor wheel.

The annular housing and first and second journal bearing retainers may define lubricant oil passages for feeding lubricant oil to the first and second journal bearings and to the active and inactive thrust bearings. The lubricant oil passages at the turbine end of the mechanical assembly may be formed such that lubricant oil feeds the inactive thrust bearing without passing through the first journal bearing during operation

of the turbocharger. The lubricant oil passages at the compressor end of the mechanical assembly may be formed such that lubricant oil feeds the active thrust bearing without passing through the second journal bearing during operation of the turbocharger.

Further details and advantages of the present invention will become apparent from the following detailed description, in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view of a typical turbocharged engine cycle; Fig. 2 is a schematic view of a prior art turbocharger rotating assembly with two thrust bearings located, respectively, at a turbine end and at a compressor end of the rotating assembly; Fig. 3 is a schematic view of a prior art turbocharger rotating assembly with two thrust bearings located at the compressor end of the rotating assembly, and with the thrust bearings located on either side of a compressor end journal bearing; Fig. 4 is a schematic view of a prior art turbocharger rotating assembly with two thrust bearings located at the compressor end of the rotating assembly, and with the thrust bearings located between the compressor end journal bearing and a compressor wheel of the rotating assembly; Fig. 5 is a cross-sectional view of a turbocharger made in accordance with the present invention; Fig. 6 is a cross-sectional view of a mechanical assembly of the turbocharger of Fig. 5; Fig. 7 is a schematic view of the mechanical assembly of the turbocharger of Fig. 5 showing a thrust bearing assembly in accordance with the present invention located between the compressor end journal bearing and a turbine end journal bearing; Fig. 8 is a cross-sectional view of the turbine end journal bearing of the turbocharger of Fig. 5; Fig. 9 is a cross-sectional view of the compressor end journal bearing of the turbocharger of Fig. 5; Fig. 10 is a schematic cross-sectional view of a prior art active thrust bearing; Fig. 11 is a schematic cross-sectional view of an active thrust bearing in accordance with the present invention and used in the turbocharger of Fig. 5;

Fig. 12 is a cross-sectional view of the mechanical assembly of the present invention showing lubricant oil flow within the mechanical assembly; and Fig. 13 is an enlarged cross-sectional view of the mechanical assembly of Fig. 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Fig. 5, a turbocharger 40 for use in a diesel engine (not shown) and made in accordance with the present invention is shown. The turbocharger 40 is generally defined by a turbine 42, a compressor 44, and a center mechanical assembly 46 linking the turbine 42 to the compressor 44. The turbine 42 includes a turbine housing 48 enclosing a turbine wheel 50. Similarly, the compressor 44 includes a compressor housing 52 enclosing a compressor wheel 54. The mechanical assembly 46 provides the mechanical linkage between the turbine 42 and the compressor 44. The mechanical assembly 46 includes a first or turbine end 56 facing the turbine 42 and a second or compressor end 58 facing the compressor 44. The mechanical assembly 46 further includes an annular housing 60 located between the turbine housing 48 and the compressor housing 52. The annular housing 60 may further define a water cavity 61 for water cooling the annular housing 60. The water cavity 61 preferably extends about 80- 85% around the circumference of the annular housing 60. The remaining portion of the circumference of the annular housing 60 is an oil drainage cavity 63 which is utilized to collect and drain lubricant oil from the annular housing 60. The oil drainage cavity 63 may span about 10-15% of the circumference of the annular housing 60, with the annular housing 60 spanning the remaining 5-10% of the circumference to separate the water cavity 61 from the oil drainage cavity 63.

Referring now to Figs. 5 and 6, the mechanical assembly 46 will be discussed in further detail. In Fig. 6, the mechanical assembly 46 is shown separate from the turbine and compressor housings 48,52. Fig. 6 thus shows the resultant mechanical assembly 46, the turbine wheel 50, and the compressor wheel 54. The mechanical assembly 46 connects the turbine wheel 50 to the compressor wheel 54. In particular, the mechanical assembly 46 includes a shaft 62 operatively connecting the turbine wheel 50 to the compressor wheel 54. The shaft 62 extends from the turbine wheel 50 axially through the annular housing 60 and terminates at the compressor wheel 54. The turbine wheel 50 provides the mechanical power necessary to turn the compressor wheel 54 via

the shaft 62. A sleeve 64 is positioned about a portion of the shaft 62 immediately adjacent the compressor wheel 54. The turbine wheel 50, compressor wheel 54, shaft 62, and sleeve 64 are compressed together by a center stud 66 and nut 68, or another suitable mechanical fastener combination. The turbine wheel 50, compressor wheel 54, shaft 62, and thrust collar with associated fasteners, which is discussed hereinafter, may collectively be referred to as the rotating assembly of the turbocharger 40.

A first journal bearing 70 is located radially between the annular housing 60 and the shaft 62 at the turbine end 56 of the mechanical assembly 46. The annular housing 60 is positioned about the rotating assembly of the turbocharger 40 and, more particularly, the shaft 62. The first or turbine end journal bearing 70 is held in place by a first journal bearing retainer 71, which is connected to the annular housing 60 at the turbine end 56 of the mechanical assembly 46 by mechanical fasteners 72 such as cap screws. The first journal bearing 70 is generally annular-shaped and positioned about the shaft 62. A first or turbine end lubricant seal 74 is located radially between the first journal bearing retainer 71 and the shaft 62 to provide a fluid seal between the first journal bearing 70 and the turbine wheel 50. The first lubricant seal 74 is preferably threaded on an inner surface, with the threads spiraled against the rotation direction of the rotating assembly and, hence, the rotation direction of the shaft 62 to restrict lubricant oil leakage into the turbine 42.

A second journal bearing 80 is located radially between the annular housing 60 and the shaft 62 at the compressor end 58 of the mechanical assembly 46.

The second journal bearing 80 is held in place by a second journal bearing retainer 81, which is connected to the annular housing 60 at the compressor end 58 of the mechanical assembly 46 by mechanical fasteners 82 such as cap screws. The second journal bearing 80 is generally annular-shaped and positioned about the shaft 62. The second journal bearing 80 and second journal bearing retainer 81 define a recess 84 adjacent the compressor wheel 54 for receiving the sleeve 64. A second or compressor end lubricant seal 86 is located radially between the sleeve 64 and the second journal bearing retainer 81 to provide a fluid seal between the second journal bearing 80 and the compressor wheel 54. The second lubricant seal 86 is preferably threaded on an inner surface, with the threads spiraled against the rotation direction of the rotating assembly and, hence, the rotation direction of the shaft 62 to restrict lubricant oil leakage into the compressor 44.

In contrast to the prior art rotating assemblies discussed previously, the first and second journal bearings 70,80 of the present invention coact directly with the shaft 62 and do not operate against a sleeve as is necessary in the prior art turbochargers discussed previously.

Referring now to Figs. 5-7, the mechanical assembly 46 further includes a thrust bearing assembly 90 generally located radially between the annular housing 60 and the shaft 62, and axially between the first and second journal bearings 70,80. The thrust bearing assembly 90 includes an active thrust bearing 92, an inactive thrust bearing 94, and a thrust collar 96 which is positioned between the active thrust bearing 92 and the inactive thrust bearing 94. Within the thrust bearing assembly 90, the active thrust bearing 92 is positioned immediately adjacent and in contact with the second or compressor end journal bearing retainer 81. The active thrust bearing 92 is preferably connected directly to the second journal bearing retainer 81 by mechanical fasteners 93, such as cap screws, which extend through the second journal bearing retainer 81 and engage with the active thrust bearing 92. While the active thrust bearing 92 is connected to the second journal bearing 80 via the second journal bearing retainer 81, it is nonetheless physically separate from the second journal bearing 80 (i. e., not integral to the second journal bearing 80). Thus, the active thrust bearing 92 may be removed from the second journal bearing retainer 81, and thus from the second journal bearing 80 by removing the mechanical fasteners 93. The thrust collar 96 is positioned adjacent and in hydrodynamic contact with the active thrust bearing 92. The thrust collar 96 may be fixed to the shaft 62 with a screw (not shown), a lockwasher 98, and a nut 100, or other similar mechanical fasteners. The thrust collar 96 and any connecting mechanical fasteners may thus form a part of the rotating assembly of the turbocharger 40. The inactive thrust bearing 94 is positioned adjacent and in hydrodynamic contact with the thrust collar 96. The inactive thrust bearing 94 may be fixed to the annular housing 60 by mechanical fasteners 101 such as cap screws. Fig. 7 schematically illustrates the relative positioning of the first and second journal bearings 70,80 and the thrust bearing assembly 90 for clarity. As can be seen in Fig. 7, the thrust bearing assembly 90 lies entirely between the first and second journal bearings 70,80.

The term"hydrodynamic contact"as used herein generally describes that the active and inactive thrust bearings 92,94 do not physically contact the thrust collar

96. The thrust collar 96 is rotatably supported by the active and inactive thrust bearings 92,94, but the distance between these bearings is greater than the thickness of the thrust collar 96. Thus, a small gap exists between the active thrust bearing 92 and the thrust collar 96, and between the inactive thrust bearing 94 and the thrust collar 96. Lubricant oil fills these small gaps during operation of the turbocharger 40 such that the thrust collar 96 is"hydrodynamically"supported on a film of oil, which is circulated across the surfaces of the active and inactive thrust bearings 92,94, and reduces or eliminates wear between the active and inactive thrust bearings 92,94 and the thrust collar 96. Thus, the thrust collar 96 is separated from direct contact with the active and inactive thrust bearings 92,94 by respective thin films of bearing lubricant oil. An analogous situation exists between the shaft 62 and the first and second journal bearings 70,80, with the shaft 62"hydrodynamically"supported on a film of oil, which is circulated across the first and second journal bearings 70,80 during rotation of the shaft 62. A"hydrodynamic"state between the shaft 62 and the first and second journal bearings 70,80 is established shortly after start-up of the turbocharger 40, and is typically fully established when the shaft 62 reaches 100 rpm. In this operational state, the shaft 62 is separated from the first and second journal bearings 70,80 by a thin film of lubricant oil. At rest, the shaft 62 is in physical contact with the first and second journal bearings 70,80, while the active and inactive thrust bearings 92,94 do not typically physically contact the thrust collar 96 at rest.

Referring to Figs. 8 and 9, the first and second journal bearings 70,80 are shown, respectively. The first journal bearing 70 is preferably provided as a three lobe journal bearing, with each lobe designated with reference numeral 102. Each of the three lobes 102 is relieved slightly at the leading and trailing edges thereof as represented by shaded areas 104 in Fig. 8, which are exaggerated for clarity. The first journal bearing 70 further defines a plurality of lubricant oil inlet orifices 105, with one of the inlet orifices 105 located in each of the lobes 102. The second journal bearing 80 is similar in structure to the first journal bearing 70 and is formed in the three lobe configuration with each lobe designated with reference numeral 106. Each of the lobes 106 is relieved slightly at the leading and trailing edges as represented by shaded areas 108 in Fig. 9, again exaggerated for clarity. The second journal bearing 80 further defines a plurality

of lubricant oil inlet orifices 109 similar to the first journal bearing 70 discussed hereinabove. One inlet orifice 109 is formed in each of the lobes 106.

Fig. 10 shows a prior art active thrust bearing 110 and is compared to the active thrust bearing 92 of the present invention shown in Fig. 11. As discussed previously, the active thrust bearing 92 is provided as part of the thrust bearing assembly 90, which is shown in Figs. 6 and 7. The prior art active thrust bearing 110 shown in Fig.

10 has lubricants, such as oil, fed from an inner diameter 112 thereof through conduits 114 to an outer diameter 116 thereof. In contrast, in the active thrust bearing 92 shown in Fig. 11, lubricants are fed into conduits 118, which extend from an inner diameter or surface 120 of the active thrust bearing 92 to an outer diameter or surface 122 of the active thrust bearing 92, through openings or inlet orifices 124 in each of the conduits 118. The active thrust bearing 92 is tapered by providing a slight relief cut against shaft rotation for each land 126 of the active thrust bearing 92, as will be appreciated by those skilled in the art.

Referring now to Figs. 1 and 5-7, the operation of the turbocharger 40 made in accordance with the present invention will now be discussed. The turbocharger 40 made in accordance with the present invention will operate with the turbine 42 and compressor 44 operatively connected to an engine (not shown) in a similar manner to which the turbocharger 11 is connected to the engine 12 in Fig. 1. Referring initially to Figs. 5 and 6, the turbine wheel 50 is located within the turbine housing 48. The turbine wheel 50 through the shaft 62 rotates the compressor wheel 54, which is located within the compressor housing 52. The turbine wheel 50, compressor wheel 54, shaft 62, and thrust collar 96 with associated mechanical fasteners rotate at high speed as part of the rotating assembly of the turbocharger 40. During rotation, the turbine wheel 50 and compressor wheel 54 interact with engine exhaust and inlet gases such that axial forces act upon the turbine wheel 50 and compressor wheel 54. The turbine wheel 50 and compressor wheel 54 cause axial forces to act on the rotating assembly of the turbocharger 40 directed from the turbine end 56 of the mechanical assembly 46 toward the compressor end 58 of the mechanical assembly 46. These forces are transmitted through the shaft 62 and act on the thrust collar 96 and the active thrust bearing 92. The active thrust bearing 92 accommodates and absorbs the axial forces directed from the turbine wheel 50 toward the compressor wheel 54. The active thrust bearing 92 and

inactive thrust bearings 94 further act to position the rotating assembly of the turbocharger 40 and thereby the turbine wheel 50 and compressor wheel 54 within the turbine housing 48 and compressor housing 52. The first and second journal bearings 70, 80 rotatably support the shaft 62 and provide for the"hydrodynamic"support of the rotating assembly within the mechanical assembly 46.

As discussed previously in connection with Figs. 2-4, prior art turbochargers generally provide the thrust bearings, both active and inactive, at either the compressor end, the turbine end, or at both the compressor end and turbine end of the rotating assembly. In addition, at least one of the thrust bearings in the prior art rotating assemblies discussed previously is typically provided as an integral journal bearing/thrust bearing. In contrast, as shown in Figs. 5-7, the active thrust bearing 92 of the present invention is not integral to the first or second journal bearings 70,80 and can be physically separated therefrom. In addition, the thrust bearing assembly 90 is located entirely between the first and second journal bearings 70,80, in contrast to the prior art rotating assemblies discussed previously. The active thrust bearing 92 may be replaced independently of the first and second journal bearings 70,80.

The annular housing 60 in accordance with the present invention preferably defines a plurality of lubricant oil passages for lubricant oil flow to the active thrust bearing 92, the inactive thrust bearing 94, and the first and second journal bearings 70,80. The lubricant oil flow within the annular housing 60 generally serves two purposes. First, the lubricant oil removes heat caused by the high rotation speeds of the turbocharger 40 (i. e., the rotating assembly) and second lubricates the aforementioned bearings. The novel lubricant oil flow configuration of the present invention will now be discussed with reference to Figs. 12 and 13.

The annular housing 60 defines a main inlet conduit 200. The main inlet conduit 200 intersects with an axial branch conduit 202 defined by the annular housing 60. The annular housing 60 further defines a turbine end inlet arc groove 204, which connects to a turbine end annular distribution groove 206. The first journal bearing 70 is preferably connected by the first journal bearing retainer 71 to the annular housing 60.

The first journal bearing retainer 71 defines apertures 208, which extend radially through the first journal bearing retainer 71. The apertures 208 connect the turbine end annular distribution groove 206 to an annular journal bearing distribution groove 210, which

supplies lubricant oil to the surface of the first journal bearing 70 through the inlet orifices 105 defined in the first journal bearing 70. The apertures 208 in the first journal bearing retainer 71 are in fluid communication with the inactive thrust bearing 94 through axial connecting openings 212 and an annular inactive thrust bearing distribution groove 214. The annular inactive thrust bearing distribution groove 214 is connected to inlet orifices 216 defined in the inactive thrust bearing 94 for supplying lubricant oil to the surface of the inactive thrust bearing 94. A similar arrangement to the foregoing is used to supply lubricant oil to the second journal bearing 80 and the active thrust bearing 92.

The axial branch conduit 202 is connected to a compressor end annular distribution groove 218 defined by the annular housing 60. The second journal bearing 80 is preferably connected by the second journal bearing retainer 81 to the annular housing 60.

The compressor end annular distribution groove 218 connects to distribution openings 219. The second journal bearing retainer 81 defines axial inlet holes 222, which intersect with radial inlet holes 224 defined through the second journal bearing retainer 81. The axial inlet holes 222 connect to the distribution openings 219 for passing lubricant oil to the second journal bearing 80. The radial inlet holes 224 connect to an annular journal bearing distribution groove 226 defined within the second journal bearing retainer 220.

The annular journal bearing distribution groove 226 connects to the inlet orifices 109 defined in the second journal bearing 80 for supplying lubricant oil to the surface of the second journal bearing 80. At the active thrust bearing 92, the compressor end annular distribution groove 218 is further connected through the distribution openings 219 to radial inlet holes 228 defined in the active thrust bearing 92. The radial inlet holes 228 connect to the openings or inlet orifices 124 formed in the conduits 118 (shown in Fig.

11) defined in the active thrust bearing 92 to supply lubricant oil to the surface of the active thrust bearing 92.

Figs. 12 and 13 show with arrows the lubricant oil flow path in the annular housing 60 of the present invention. Lubricant oil generally enters the annular housing 60 through the main inlet conduit 200. The lubricant oil then flows into the axial branch conduit 202 and divides, with a portion of the lubricant oil flowing toward the first journal bearing 70, and a portion of the lubricant oil flowing toward the second journal bearing 80. The lubricant oil flowing toward the first journal bearing 70 feeds into the turbine end inlet arc groove 204, the turbine end annular distribution groove 206,

and then into the apertures 208 in the first journal bearing retainer 71. At this point, the lubricant oil flow again divides with a portion of the flow passing into the annular journal bearing distribution groove 210 and lubricating the surface of the first journal bearing 70 through inlet orifices 105 defined in the first journal bearing 70. Another portion of the lubricant oil flow flows toward the inactive thrust bearing 94 through the axial connecting openings 212. The lubricant oil flow enters the inactive thrust bearing distribution groove 214 from the axial connecting openings 212 and flows through the inlet orifices 216 defined in the inactive thrust bearing 94. The lubricant oil flow passing through the inlet orifices 216 then lubricates the surface of the inactive thrust bearing 94.

The lubricant oil flow toward the second journal bearing 80 first enters the compressor end annular distribution groove 218. From the compressor end annular distribution groove 218, the flow enters the distribution openings 219 where the flow again splits. A portion of the flow enters the radial inlet holes 228 defined in the active thrust bearing 92, which connect to the openings or inlet orifices 124 formed in the conduits 118 (shown in Fig. 11) in the active thrust bearing 92. This portion of the lubricant oil flow lubricates the surface of the active thrust bearing 92 through the radial inlet holes 228 and the openings or inlet orifices 124. In the lubricant flow arrangement described hereinabove, it will be apparent that the active and inactive thrust bearings 92, 94 each receive"fresh"lubricant oil rather than lubricant oil that has been first circulated through the first and second journal bearings 70,80, which is often the case with prior art turbochargers.

Another portion of the lubricant oil flows into the axial inlet holes 222 formed in the second journal bearing retainer 81 from the distribution openings 219. The lubricant oil flow then passes into the radial inlet holes 224 in the second bearing retainer 81. From the radial inlet holes 224, the flow enters the annular journal bearing distribution groove 226 which connects to the inlet orifices 109 in the second journal bearing 80. The lubricant oil then flows through the inlet orifices 109 to lubricate the surface of the second journal bearing 80.

The total flow rate of all lubricant oil flowing through the various lubricant oil passages discussed hereinabove is preferably between eight and ten gallons per minute. A maximum inlet flow velocity is preferably about seventeen feet per second at ten gallons per minute in any of the various lubricant oil passages discussed hereinabove within the annular housing 60. The lubricant oil flow distributions at the various bearings are preferably distributed in the following proportions: TABLEI Bearing Percentage Turbine End Journal Bearing (70) 40% Compressor End Journal Bearing (80) 16% Active (Compressor End) Thrust Bearing (92) 34% Inactive (Turbine End) Thrust Bearing (94) 10%

Thus, approximately 40% of the lubricant oil flow through the annular housing 60 reaches the turbine end journal bearing, or first journal bearing 70. The foregoing distributions are provided such that, when combined with the centrifugal pumping action of the thrust collar 96, the lubricant flow rate to each bearing is sufficient to provide complete separation of the rotating assembly from each of the bearings.

Furthermore, the distribution of flow to each bearing is provided such that acceptable bearing metal temperatures are maintained throughout the operation of the turbocharger 40, thus providing acceptable bearing and lubricant oil life. An acceptable bearing metal temperature is a temperature which does not cause or accelerate degradation of the bearing surface.

The present invention provides a turbocharger for use with engines, such as diesel engines, that overcomes the disadvantages known in the prior art by placing the thrust bearing assembly 90 between the first and second journal bearings 70,80. The thrust bearing assembly 90 is now advantageously located away from the high temperatures and possible hot gas leakage present at the turbine end 56 of the mechanical assembly 46 thereby minimizing bearing lubricant coking. The time between overhaul periods is substantially increased in turbochargers made in accordance with the present invention. As discussed previously, lubricant coking is not desirable because this necessitates frequent overhauls of turbochargers. Positioning the thrust bearing assembly 90 of the present invention as described hereinabove may be applied to all turbochargers thereby reducing lubricant coking and extending the overhaul period substantially. In addition, by locating the thrust bearing assembly 90 inboard of the second or compressor

end journal bearing 80, the"overhang"of the compressor 44 in the turbocharger 40 is reduced.

The lubricant oil flow in the annular housing 60 may be optimized and distributed as discussed previously so that the maximum bearing metal temperature of the bearings under load conditions is substantially equalized and maintained at acceptable values.

The active and inactive thrust bearings 92,94 of the present invention optimize the load capacity, increase minimum fluid film thickness, and reduce the lubricant oil film temperature in the turbocharger 40. Increasing the minimum oil film thickness and reducing the lubricant oil film temperature result in increasing the life of the turbocharger 40 substantially by increasing the length of time between overhaul periods. The turbocharger 40 of the present invention will cause only minor degradation of the lubricant oil.

Further, the rotordynamic response and stability of the turbocharger 40 is improved over the prior art discussed previously by eliminating subsynchronous vibration and reducing the overall vibration level through improved journal bearing design.

The present invention has been described with reference to a preferred embodiment, which is merely illustrative of the present invention and not restrictive thereof. Obvious modifications and alterations of the present invention may be made without departing from the spirit and scope of the invention. The present invention is defined in the appended claims and equivalents thereto.