Turbocharger bearing system

A bearing system for a turbocharger shaft comprising a rotatable elongated cylinder with axially spaced journal bearing surfaces on the inside diameter and a thrust face on each end. A sleeve on the shaft incorporates a flange on one end that transmits thrust force to one thrust face on the elongated cylinder. A flanged collar on the opposite end of the shaft transmits thrust force to the thrust face on the opposite end of the elongated cylinder. A radially extending flange on one end of the elongated cylinder transmits thrust forces to stationary housings.

FIELD OF THE INVENTION

This invention relates to bearing systems for turbochargers used on internal combustion engines that have rotor assemblies that rotate at very high speed and have shafts that are exposed at one end to very high temperatures.

BACKGROUND OF THE INVENTION

Nearly all vehicular diesel engines have used turbochargers for many years and, more recently, are becoming more prevalent on gasoline engines due to their ability to improve fuel consumption. The more stringent miles-per-gallon regulations imposed by the federal government standards will be the motivation for more vehicle engines to be turbocharged.

Small turbochargers have become a viable commercial product, primarily due to the development of satisfactory bearing systems that have allowed them to operate successfully at very high rotational speeds. A very great amount of time and effort has been expended over the years to develop bearing systems that damp destructive shaft vibrations, insulate the rotor from external shock loads, and withstand the heat transferred into the shaft from the hot turbine wheels that are exposed to engine exhaust gas.

The most prevalent of these successful bearing systems utilize floating sleeve bearings to support the shaft and have an inner and outer oil film where the outer oil film provides a damping cushion that permits the turbocharger rotor to pass through its critical speed without destroying the bearing system. The floating sleeve bearings also permit the rotor to find and rotate about its mass center, thereby eliminating radial forces that would be imposed on the bearings if the rotor were constrained to rotate about its geometric center.

Dynamic balancing of the rotor components and the rotor assembly results in making the mass center and geometric centers coincidental, however, there is almost always a small difference left between these centers in practice, and that causes an orbital motion of the rotor. This orbital motion is permitted to occur within the oil film thicknesses of the floating sleeve bearings and contributes to the long-term durability of the floating sleeve bearing systems.

The early floating sleeve journal bearing systems required a separate thrust bearing, capable of carrying the axial thrust forces generated in turbocharger operation that can occur in both axial directions. Since the friction loss in radial thrust bearings that are perpendicular to the shaft axis is proportional to the fourth power of the radius, any collar attached to the shaft that bears axially against the stationary thrust bearing surface will generate a relatively high friction loss. Accordingly, the radius of the thrust bearing should be kept as small as possible in designing a complete turbocharger bearing system.

An early attempt to minimize thrust bearing losses is illustrated in U.S. Pat. No. 3,390,926, dated Jul. 2, 1968, where a large shoulder on the turbine wheel hub bore against the end of a tubular one piece bearing, the other end of which was forced against a stationary plate to carry thrust in one axial direction. The tubular bearing was rotatably carried on a film of oil in the stationary bearing housing and had two axially spaced journal bearing surfaces on its inside diameter. When rotor conditions caused thrust in the opposite direction, a collar attached to the shaft was forced against the said stationary plate to carry the thrust load.

This bearing system worked satisfactorily as long as exhaust gas temperatures were moderate. However, when exhaust gas temperatures became high as with highly rated engines, the heat carried from the turbine wheel to the hub that bore against the end of the tubular bearing could cause distress on the bearing surface.

Sleeve bearing systems are particularly desirable in turbochargers which employ wide usage because they are less expensive to manufacture and can be easily assembled. However, there is a need for improved sleeve bearing systems which are more efficient and reliable when operating at very high speeds in the presence of very high temperatures, such as those experienced by turbochargers for highly rated internal combustion engines.

SUMMARY OF THE INVENTION

This invention provides an improvement on previously known turbocharger sleeve bearing systems for very high speed rotating shafts operating in the presence of very high temperatures. The invention includes a one-piece sleeve bearing element that contains both journal and thrust bearing surfaces and where the rotating turbocharger shaft transmits thrust forces to the thrust bearing surfaces on the one-piece sleeve bearing ends by radially extending flanges that are cooled by bearing lubricant. The invention can further include a sleeve bearing system where a radially extending bearing surface at the hot turbine end of the turbocharger shaft is provided by a separate collar which minimally interfaces with the turbocharger shaft and the adjacent thrust bearing surface of the one-piece sleeve bearing to both reduce heat transfer from the hot turbine end of the turbocharger to the remainder of the bearing system and to reduce thrust bearing losses. The lubrication and cooling of the thrust bearing at the turbine end of the turbocharger can be enhanced by one or more lubricant passageways formed in at least one of its adjacent thrust bearing surfaces. In addition, the one-piece sleeve bearing element provides rotatable thrust bearing surfaces that reduce the relative speed differential between the adjacent thrust bearing surfaces of the rotating shaft and the one-piece sleeve bearing element.

Other features and advantages of the invention will be apparent from the more detailed description and claims that follow and from the drawings.

BEST MODE FOR CARRYING OUT THIS INVENTION

The bearing system of this invention is adapted to support, within stationary elements of a turbocharger, a high-speed rotating shaft that is subject to heat conduction on one end axially from a hot turbine wheel.FIG. 1, for example, illustrates the components of a turbocharger10, comprising a bearing housing11, a seal plate12enclosing a rotating shaft13carrying a turbine wheel14at one end and a compressor wheel15at the other end. A combination one-piece journal and thrust bearing19of this invention carries the rotating shaft13and is rotatably carried in the bearing housing11. The turbine wheel14is driven by exhaust gas from an internal combustion engine exhaust manifold; consequently, the turbocharger shaft13must withstand high temperatures conducted into it from the hot turbine wheel14.

Where, in this application, we use the term “outer”, it means in the direction of the bearing housing11, and where we use the term “inner”, it means in the direction of the turbocharger shaft.

FIGS. 2-4illustrate the combination bearing19which includes an outer cylindrical bearing surface32, which is rotatably carried in the inner cylindrical surface11aof the bearing housing11. The combination bearing19comprises an elongated cylinder rotatably mounted in bearing housing11with two inwardly projecting portions19aand19bproviding two axially spaced journal bearing surfaces29and30on its inside diameter. The two axially spaced inwardly projecting portions19aand19bform, with a separate turbocharger shaft sleeve portion20, an oil reservoir28interposed there between. A flange33extends radially from the compressor end of the outer bearing element19and transmits thrust loads to seal plate12and bearing housing11. The outside surface32of combination bearing element19is fed lubricating oil from oil inlet16and the oil flows axially in both directions over the entire outer bearing surface32of combination bearing element19and between the thrust bearing surface11bof the bearing housing11, exiting into the oil drain area17. As can be discerned in the drawings, oil from oil inlet16also flows inward through the lubricant Passageway24, into the oil reservoir28from which it flows axially in both directions through bearing clearances29and30. From bearing clearance30, the lube oil flows outwardly over thrust bearing surface11cand enters the oil drain area17. From bearing clearance29, the lube oil flows outwardly over thrust bearing surface26, entering the oil drain area17. Circumferential groove23in the outer cylindrical bearing surface provides a continuous supply of lube oil from oil inlet16through lubricant passageway24into the oil reservoir28as the combination bearing element19rotates during operation. The diametrical clearance between the outside cylindrical bearing surface32of combination bearing element19and the inner cylindrical surface11aof the bearing housing11is of the order of 0.003″ to 0.005″ and cushions the turbocharger rotating assembly against shock and vibration. In addition, the combination bearing element19comprises a pair of thrust bearing surfaces, one26on the outer side of the inwardly projecting portion19aat the turbine end of the combination bearing element19, and the other21on an inwardly projecting portion19bat the compressor end of the combination bearing element19. The combination bearing element19is a unique construction comprising both thrust bearing surfaces26and21, and axially spaced journal bearings29and30in one member and rotates in the bearing housing bore11aat a fraction of the speed of the turbocharger shaft13. This reduces the relative speed between the shaft13and all bearing surfaces and contributes to minimizing both journal and thrust bearing losses.

To reduce the heat transfer from the hot turbocharger shaft13through the shaft shoulder25into the turbine end thrust bearing surface26of the outer bearing element19, a thrust flange27, located at the turbine end of a cylindrical shaft sleeve20, is interposed between shaft shoulder25and thrust bearing surface26. The shaft shoulder25is shallow in depth with a minimal cross-sectional area that serves to minimize heat flow into the thrust flange27. For example, the shoulder25can extend outwardly less than about ⅛ inch from the cylindrical outer surface of the turbocharger shaft, significantly less than about 40% of the outward extent of flange27. This feature of this invention serves to protect the thrust bearing surface26of outer bearing element19and the thrust bearing surface27aof thrust flange27from deterioration when carrying high thrust loads imposed by the rotating turbocharger shaft13. The thrust bearing surfaces26and27aare also cooled by lubricating oil coming from the oil reservoir28, through the turbine end journal bearing29, and flowing radially outward between the thrust bearing surfaces26and27aand on into the oil drain area17. As illustrated inFIGS. 3 and 4, the outer side thrust bearing surface26of the outer bearing element19adjacent thrust flange27can be provided with one or more lubricant passageways, preferably with a plurality of space lubricant passageways. In a preferred provision of lubricant passageways26a-26f, the plurality of lubricant passageways are formed by grooves uniformly angularly spaced around the outer side thrust bearing surface26and extending radially outwardly from the inner cylindrical bearing surface29. As illustrated by26ainFIG. 4, the plurality of grooved lubricant passageways26a-26fcan preferably have a shallow V-shaped cross section. For example, the lubricant passageways can be formed by side surfaces that intersect with an included angle of 150 degrees at a depth of about 0.012 inches.

Shaft sleeve20rotates with the turbocharger shaft13and is securely held in place by compression exerted by lock nut18through compressor wheel15, flinger sleeve22and end cap31. End cap31includes a radially extending flange portion31awith a thrust bearing inner surface31band carries axial rotor thrust in the direction toward thrust flange27. This thrust face is lubricated by oil coming from oil reservoir28through the compressor end journal bearing30and flowing radially outward between thrust bearing surfaces31band21into the oil drain area17.

If the shaft sleeve20were not employed, the hub diameter of the shaft would need to be increased to the size of the thrust flange27. This would greatly increase the heat transfer from the hot turbine wheel14into the thrust flange27, leading to a deterioration of the thrust surface that could cause eventual failure.

As shown by the description and drawings, the invention provides a bearing system for rotationally carrying a turbocharger shaft13for rotation at very high speeds in the presence of very high exhaust gas temperatures. Such a preferred bearing system can be inserted into and carried by a turbocharger bearing housing11including a cylindrical bearing surface11a, and includes a combination outer bearing element19having an outer cylindrical bearing surface32adapted to be rotatably carried within the cylindrical bearing surface11aof the turbocharger bearing housing11and further having two spaced inwardly projecting portions19a,19b, each inwardly projection portion19a,19bof the outer bearing element19having an inner cylindrical journal bearing surface29,30for carrying a cylindrical turbocharger shaft portion20and an outer side thrust bearing surface26,21, said two spaced inwardly projecting portions19a,19bforming with the turbocharger shaft portion20a centrally located lubricant reservoir28. The turbocharger shaft13of such a preferred bearing system can be provided with thrust bearing surfaces27a,31badjacent each outer side thrust bearing surface26,21of the inwardly projecting portions19a,19bof the outer bearing element19and can be adapted to transfer thrust from the turbocharger shaft13to the outer bearing element19in the two opposing axial directions of the turbocharger shaft13. In such a preferred bearing system10, the turbocharger bearing housing11, outer bearing element19and turbocharger shaft portion20can be adapted to provide a flow of lubricant from outside the turbocharger bearing housing11to between the inner cylindrical bearing surface11aof the turbocharger bearing housing11and the outer cylindrical bearing surface32of the outer bearing element19, through the centrally located lubricant reservoir28, and outwardly between the bearing surfaces of the combination bearing element19, that is, the inner cylindrical journal bearing surfaces29,30and the outer side thrust bearing surfaces26,21of the inwardly projecting portions19a,19bof the outer bearing element19, and the cylindrical turbocharger shaft portions20and thrust bearing surfaces27a,31bof the turbocharger shaft13adjacent each outer side thrust bearing surface26,21of the outer bearing element19to reliably carry the rotating turbocharger shaft13and transfer thrust from the rotating turbocharger shaft13to the outer bearing element19in both axial directions of the turbocharger shaft13. Furthermore, the turbocharger shaft13can include a shallow shoulder25adjacent its turbine end and the thrust flange27and its thrust bearing surface27aat the turbine end of the turbocharger shaft13to reduce heat transfer from the turbine14of the turbocharger into the bearing system. Furthermore, the outer side thrust bearing surface26of the inwardly projecting portion19aof the outer bearing element19at the turbine end of the turbocharger shaft13can include a plurality of grooves forming spaced lubricant passageways in the turbine end thrust bearing. (See, for example, grooves26a-26f.) Preferably, the plurality of grooved lubricant passageways are shallow in depth and extend radially outwardly from the inner cylindrical journal bearing surface29and are uniformly spaced around the outer side thrust bearing surface26.

The illustrated bearing system of this invention comprises a reliable floating elongated cylindrical outer bearing element forming axially spaced journal bearing surfaces and thrust bearing surfaces on both ends. The rotating combination bearing is easily inserted and removed from the bearing housing and acts like a floating sleeve bearing that protects the rotor assembly of the turbocharger from shock and vibration. In addition, the oil film on the outside diameter of the combination bearing allows the rotating assembly of the turbocharger to find and rotate about its center of mass without transmitting excessive radial loads to the stationary housing parts.

The bearing system of this invention further embodies combination thrust and journal bearings, wherein the turbocharger shaft has a separate flange forming a thrust collar on one end that has minimal contact with a small shoulder on the turbine wheel hub, thus minimizing the heat that is conducted from the hot turbine wheel into the bearings. Since the flange on the sleeve is cooled by a flow of lubricating oil, it is capable of functioning as a thrust-carrying surface satisfactorily even when exhaust temperatures are high.

The combination thrust and journal bearing of the present invention rotates in the bearing housing at a fraction of the speed of the shaft. This reduces the speed differential between the two members and minimizes the thrust and journal bearing friction losses.

While this foregoing description describes a preferred embodiment of the invention, other embodiments may be devised without departing from the spirit or scope of the following claims: