GB2187797A

GB2187797A - Turbocharger

Info

Publication number: GB2187797A
Application number: GB08705609A
Authority: GB
Inventors: Steven D Arnold
Original assignee: Household Manufacturing Inc
Current assignee: Household Manufacturing Inc
Priority date: 1987-03-10
Filing date: 1987-03-10
Publication date: 1987-09-16
Also published as: GB8705609D0

Abstract

A turbocharger comprises a turbine rotor 20 and a compressor rotor 24 mounted on a shaft 30 and a housing 12, 14 defining a volute about each impeller. The housing includes a wall 25 between the impellers which comprises a ceramic portion 26 adjacent the turbine and a metal portion 28 adjacent the compressor and contiguous with the ceramic portion. A ball bearing 32 is mounted in the metal portion of the wall and supports the shaft, and a ball bearing is mounted in the housing 14 and supports the compressor. The bearings are lubricated by oil from sump 40 via delivery line 42 and 44. <IMAGE>

Description

SPECIFICATION Turbocharger The present invention relates generally to turbochargers and, more particularly, to turbochargers of a compact design having an improved bearing support and lubrication system.

Turbochargers are well known devices which utilize the energy of exhaust gases from an internal combustion engine to compress air to be supplied to the combustion chambers of the engine. A conventional turbocharger comprises two impellers mounted on opposite ends of a common shaft, each impeller capable of rotating within its own cavity within the turbocharger housing. One impeller functions as a fluid motor, the exhaust gases from the engine causing rotation of this impeller. The other impeller, commonly termed the pump or compressor impeller, functions to draw in ambient air and to compress the air to higher pressure which can be used, for example, to increase the flow of combustion air into the engine for greater engine power.

A common construction for a turbocharger is to rotatably support the impeller shaft with a bearing assembly located between the two impellers. Such a bearing assembly typically is a housing having journal type bearings about the shaft. Several inherent problems are associated with this type of construction for the bearing assembly. For example, journal bearings tend to make the turbocharger inefficient, particularly at low speeds, at least partly because these bearings require considerable inner and outer diameter clearances which necessitate excessive compressor and turbine impeller clearances. Journal bearings also have relatively high frictional losses.In addition, by having the impellers in essence cantilevered from the ends of the shaft, the inefficiency caused by journal bearings is further multiplied by tilting of the impellers which necessitates even larger impeller clearances.

In order to minimize the inefficiencies associated with the use of journal bearings, it has been common practice to make the diameter of the shaft as small as possible to reduce friction losses and to make the span between bearings as large as possible to minimize impeller tilt. As a consequence, the shaft tends to be quite flexible. With the impellers cantilevered off the ends of such a flexible shaft, high speed rotation of the impeller group produces an unstable dynamic system which passes through or even operates at the first bending critical or higher order criticals. Even with some type of damping means associated with the impeller groups, only a marginally stable dynamic system is achieved.

Journal bearings also require high oil pressure in order to support the impeller group in a hydrodynamic oil film as well as large quantities of oil to remove the heat generated in the journal bearings due to viscous friction and the heat gained from the turbine portion.

Oil is generally supplied through inconvenient connections from the engine oil system. Since it takes the engine some time to develop sufficient oil pressure and supply it to the turbocharger, on startup the conventional turbocharger sometimes runs with little or no oil or only with residual oil such that the journal bearings function for a time as bushings.

Proposals to replace journal bearings in turbochargers with other types of bearings to reduce these problems have met with limited success. For example, the use of ball bearings in turbochargers to support the impeller shaft produces other problems. since ball bearings have no damping capability, some sort of fluid film damper must be provided since conventional designs have bending criticals in the operating range. In addition, exposure to high temperatures tends to reduce the hardness of bearings thereby lowering the useful life of the bearing. The bearings can encounter extremely high temperatures after a hot turbocharger is shut down in what is commonly termed "soakback" where the residual heat in the turbine portion elevates the temperature of the entire turbocharger since the cooling effect provided by air flow through the compressor portion has ceased.

The present invention therefore seeks to provide a turbocharger having a bearing assembly wherein a relatively short, thick shaft is supported by a ball bearing and a ball bearing supporting the nose of the compressor impeller.

The present invention also seeks to provide a turbocharger with a housing having a ceramic portion and an associated metal heat sink portion to help prevent bearing damage caused by ''soakback'.

The present invention also seeks to provide a turbocharger with a reduced number of parts which is relatively simple to assemble.

The present invention also seeks to provide a turbocharger having an improved self-contained lubrication system.

Briefly, in its broader aspects, the present invention comprehends a turbocharger comprising a turbine impeller and a compressor impeller mounted on the ends of a shaft, a housing defining a volute about each impeller and including a wall between said impellers through which the shaft extends, said wall comprising a ceramic portion adjacent the turbine impeller and a metal portion adjacent the compressor impeller and contiguous with the ceramic portion, a ball bearing mounted in the metal portion of the wall and supporting the shaft, and a ball bearing in the housing and supporting the compressor impeller.

The present invention further comprehends a turbocharger comprising a turbine impeller and a compressor impeller mounted on the ends of the shaft, a housing defining a volute about each impeller and including a wall between said impellers through which said shaft extends, a bearing mounted in the wall and sup porting the shaft, and a bearing mounted in said housing and supporting the compressor impeller, and a lubrication system comprising a central bore in the compressor impeller and a connecting central bore in the shaft and radial holes in the shaft extending to the bearing supporting the shaft.

Further advantages and features of the present invention will become more fully apparent from a detailed consideration of the arrangement and construction of the constituent parts as set forth in the following description taken together with the accompanying drawings, wherein Figure 1 is a cross-sectional view of one embodiment of a turbocharger according to the present invention; Figure 2 is a detailed view of a portion of the lubrication system of the turbocharger shown in Fig. 1; Figure 3 is a detailed view of another portion of the lubrication system for the turbocharger of Fig. 1; Figure 4 is a plan view of a preferred embodiment of a metal heatsink portion of the housing wall located between the turbine portion and compressor portion of the turbocharger shown in Fig. 1; and Figure 5 is a cross-sectional view taken along line 5-5 of Fig. 4.

Referring now to the drawings, shown in Fig. 1 is a cross-sectional view of one embodiment of a turbocharger 10 according to the present invention, the turbocharger including housing 11 comprising turbine housing portion 12 and compressor housing portion 14, each portion forming a volute-shaped toroid. Turbine housing portion 12 includes exhaust gas inlet 16 and gas outlet 18 and encloses bladed turbine impeller 20. Compressor housing portion 14 has air inlet 22 and encloses bladed compressor impeller 24. Between turbine impeller 20 and compressor impeller 24 is wall 25 forming a portion of turbocharger housing 11, the wall comprising ceramic portion 26 adjacent turbine impeller 20 and contiguous metal portion 28 adjacent compressor impeller 24. Shaft 30 affixed to turbine impeller 20 extends through a bore in ceramic portion 26 and in metal portion 28.

Shaft 30 is attached to compressor impeller 24 such that the two impellers 20 and 24 rotate in unison. Preferably, shaft 30 is welded to turbine impeller 20 or is cast integrally with the impeller. and compressor impeller 24 is threaded on the end of the shaft.

The composition of ceramic portion 26 of wall 25 can vary considerably but a presently preferred material is a composite material of synthetic mica in a silicon dioxide matrix. A preferred material for metal portion 28 is cast iron since its coefficient of thermal expansion approximates to that of the preferred ceramic material.

Impellers 20 and 24 interconnected by shaft 30 are rotatably supported by ball bearings 32 and 34. Bearing 32 is located within metal portion 28 of wall 25 and supports shaft 30 extending between turbine impeller 20 and compressor impeller 24. Bearing 34 is mounted within bearing housing 35 positioned in the center of air inlet 22 by a plurality of struts 36, the bearing supporting the nose or distal end of compressor impeller 24. Struts 36 may be of a configuration and orientation such that they function as preswirl devices or the struts can be provided with articulated trailing edges to function as movable inlet guide vanes to improve the air flow within the compressor portion of turbocharger 10. Located on the compressor side of bearing 32 and on the turbine side of bearing 34 are rotatable spacers 37 and 38, respectively, each spacer having an associated piston ring 39.

Bearings 32 and 34 are lubricated by oil contained in oil sump 40 located within compressor housing portion 14, the oil being pumped up through delivery line 42 and hollow nipple 43 to central bore 44 in compressor impeller 24 which leads to coaxial central bore 46 in shaft 30. Although delivery line 42 may extend into oil sump 40, preferably the delivery line terminates above the oil level and wick 41 extends from the delivery line into the oil sump so that an air and oil mixture is used to lubricate bearings 32 and 34. With the use of various types of wicks 41, the oil flow to the bearings can be regulated and is generally less than that provided by a delivery line 42 alone. As is best shown in Fig. 2, the portion of compressor impeller 24 adjacent to bearing 34 is provided with a plurality of radial holes 48 which extend outwardly from central bore 44 to the area of the bearing.In a like fashion, shaft 30 includes a plurality of radial holes 50 extending from bore 46 to the area of bearing 32 as is illustrated in Fig. 3.

Oil return aperture 52 extends from bearing 34 back to oil sump 40 and oil return bore 54 extends from bearing 32 through metal portion 28 of wall 25 to the oil sump. For simplicity of construction, radial holes 48 in compressor impeller 24 can sometimes be eliminated, the oil flow path to bearing 34 being provided by the clearance between the end of the compressor impeller and nipple 43.

On the side of bearing 32 opposite from radial holes 50, spacer 37 is provided with a plurality of small radial blades 56 which together act as a centrifugal pump to draw oil through the bearing. In a like manner, spacer 38 on the opposite side of bearing 34 from radial holes 40 is provided with a plurality of radial blades 58 which also collectively function as a centrifugal pump to draw oil through the bearing.

A particularly preferred construction for metal portion 28 of housing wall 25 is illustrated in the plan view of Fig. 4. The surface of metal portion 28 which is adjacent to ceramic portion 26 is provided with a plurality of radially extending fins 60. The number of fins 60 and their configuration may vary considerably but the general purpose of the fins is to provide good contact between metal portion 28 and the ceramic material of portion 26, particularly when the ceramic portion is formed by casing fluid ceramic containing material on the metal portion and then solidifying the material. Fins 60 thus promote good anchoring between metal portion 28 and ceramic portion 26.It should be noted that, in this embodiment, the lowermost of fins 60 is significantly thicker than the remainder of the fins so that oil return bore 54 can be easily formed within metal portion 28 of wall 25 by means such as drilling and the like. Fig. 5 illustrates a presently preferred configuration and height for fins 60.

In operation of turbocharger 10, exhaust gases from an internal combustion engine (not shown) enter turbine inlet 16, pass about about turbine impeller 20 thereby causing the impeller to rotate, and then exit via outlet 18.

The rotation of turbine impeller 20 is imparted to compressor impeller 24 which draws air in through inlet 22, compresses the air, and then feeds the air to the engine.

The rotating compressor impeller 24 and shaft 30 act as centrifugal pumps and cause oil to be drawn from sump 40 into delivery line 42, through nipple 43 and into central bore 44 in compressor impeller 24 and bore 46 in shaft 30. Centrifugal force from the rotation of impeller 24 and shaft 30 causes oil to be forced outwardly through the radial holes 48 and 50 and then drawn through lubricating bearings 32 and 34 by blades 56 and 58 of spacers 37 and 38 respectively.

The oil is cooled as it flows through delivery tube 42 which is in the flow path of the air passing through compressor inlet 22.

When the operation of turbocharger 10 is terminated, thermal damage to bearings 32 and 34 is effectively prevented by the heat barrier provided by the thermal resistance of ceramic portion 26 and by metal portion 28 of wall 25 acting as a heat sink. As a consequence, damage to turbocharger 10, particularly to bearings 32 and 34, due to "soakback" tends to be eliminated.

As is apparent from the foregoing, turbocharger 10 in accordance with the invention requires little or no damping since shaft 30 is of very short length and has a relatively large diameter such that the shaft is of sufficient stiffness that the first bending critical will be cut out of the operating range of the turbocharger. Furthermore, by having the nose of compressor impeller 24 supported by ball bearing 34, one cantilever impeller has been eliminated, a long span between bearings can be achieved in a compact volume, and the compressor impeller functions as an extremely stiff shaft. Consequently, impeller tilt is drastically reduced and thus the clearances of compressor and turbine impellers 20 and 24 relative to housing 11 can be made extremely small thereby improving turbocharger efficiency.The use of ball bearings 32 and 34 significantly reduces bearing friction as compared with journal type bearings thus further contributing to turbocharger efficiency.

It should also be appreciated that wall 25 between impellers 20 and 24, by being partially of ceramic material, tends to reduce heat loss from the turbine portion which also increases turbine efficiency. Similarly, wall 25 with ceramic portion 26 and associated metal portion 28 acting as a heat sink tends to reduce heat gain in the compressor portion of the turbocharger thereby improving compressor efficiency. The ceramic portion 26 of wall 25 also reduces the heat load on bearings 32 and 34 which increases the life of the bearings, reduces the amount of oil flow necessary for cooling the bearings and enables the bearings to be fabricated of lower temperature resistant materials.

Furthermore, by having a lubrication system which is self-contained, conventional lines running to the engine lubrication system have been eliminated. The self-contained lubrication system also allows the use of a lubricant which is especially adapted for the demands of the turbocharger environment instead of a conventional engine oil.

While there has been shown and described what is considered to be a preferred embodiment of the present invention, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the invention as defined in the appended claims.

CLAIMS 1. A turbocharger comprising a turbine impeller and a compressor impeller mounted on the ends of a shaft, a housing defining a volute about each impeller and including a wall between said impellers through which said shaft extends, said wall comprising a ceramic portion adjacent said turbine impeller and a metal portion adjacent said compressor impeller and contiguous with said ceramic portion, a ball bearing in said metal portion of the wall and supporting the shaft, and a ball bearing in said housing and supporting the compressor impeller.

2. A turbocharger according to claim 1, wherein the housing includes a bearing housing mounted in an inlet adjacent the compressor impeller, the bearing housing containing the bearing supporting the compressor impeller.

3. A turbocharger according to claim 2,

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Claims

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the bearing.

A particularly preferred construction for metal portion 28 of housing wall 25 is illustrated in the plan view of Fig. 4. The surface of metal portion 28 which is adjacent to ceramic portion 26 is provided with a plurality of radially extending fins 60. The number of fins 60 and their configuration may vary considerably but the general purpose of the fins is to provide good contact between metal portion 28 and the ceramic material of portion 26, particularly when the ceramic portion is formed by casing fluid ceramic containing material on the metal portion and then solidifying the material. Fins 60 thus promote good anchoring between metal portion 28 and ceramic portion 26.It should be noted that, in this embodiment, the lowermost of fins 60 is significantly thicker than the remainder of the fins so that oil return bore 54 can be easily formed within metal portion 28 of wall 25 by means such as drilling and the like. Fig. 5 illustrates a presently preferred configuration and height for fins 60.

In operation of turbocharger 10, exhaust gases from an internal combustion engine (not shown) enter turbine inlet 16, pass about about turbine impeller 20 thereby causing the impeller to rotate, and then exit via outlet 18.

The rotation of turbine impeller 20 is imparted to compressor impeller 24 which draws air in through inlet 22, compresses the air, and then feeds the air to the engine.

The rotating compressor impeller 24 and shaft 30 act as centrifugal pumps and cause oil to be drawn from sump 40 into delivery line 42, through nipple 43 and into central bore 44 in compressor impeller 24 and bore 46 in shaft 30. Centrifugal force from the rotation of impeller 24 and shaft 30 causes oil to be forced outwardly through the radial holes 48 and 50 and then drawn through lubricating bearings 32 and 34 by blades 56 and 58 of spacers 37 and 38 respectively.

The oil is cooled as it flows through delivery tube 42 which is in the flow path of the air passing through compressor inlet 22.

When the operation of turbocharger 10 is terminated, thermal damage to bearings 32 and 34 is effectively prevented by the heat barrier provided by the thermal resistance of ceramic portion 26 and by metal portion 28 of wall 25 acting as a heat sink. As a consequence, damage to turbocharger 10, particularly to bearings 32 and 34, due to "soakback" tends to be eliminated.

As is apparent from the foregoing, turbocharger 10 in accordance with the invention requires little or no damping since shaft 30 is of very short length and has a relatively large diameter such that the shaft is of sufficient stiffness that the first bending critical will be cut out of the operating range of the turbocharger. Furthermore, by having the nose of compressor impeller 24 supported by ball bearing 34, one cantilever impeller has been eliminated, a long span between bearings can be achieved in a compact volume, and the compressor impeller functions as an extremely stiff shaft. Consequently, impeller tilt is drastically reduced and thus the clearances of compressor and turbine impellers 20 and 24 relative to housing 11 can be made extremely small thereby improving turbocharger efficiency.The use of ball bearings 32 and 34 significantly reduces bearing friction as compared with journal type bearings thus further contributing to turbocharger efficiency.

It should also be appreciated that wall 25 between impellers 20 and 24, by being partially of ceramic material, tends to reduce heat loss from the turbine portion which also increases turbine efficiency. Similarly, wall 25 with ceramic portion 26 and associated metal portion 28 acting as a heat sink tends to reduce heat gain in the compressor portion of the turbocharger thereby improving compressor efficiency. The ceramic portion 26 of wall 25 also reduces the heat load on bearings 32 and 34 which increases the life of the bearings, reduces the amount of oil flow necessary for cooling the bearings and enables the bearings to be fabricated of lower temperature resistant materials.

Furthermore, by having a lubrication system which is self-contained, conventional lines running to the engine lubrication system have been eliminated. The self-contained lubrication system also allows the use of a lubricant which is especially adapted for the demands of the turbocharger environment instead of a conventional engine oil.

While there has been shown and described what is considered to be a preferred embodiment of the present invention, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the invention as defined in the appended claims.

CLAIMS 1. A turbocharger comprising a turbine impeller and a compressor impeller mounted on the ends of a shaft, a housing defining a volute about each impeller and including a wall between said impellers through which said shaft extends, said wall comprising a ceramic portion adjacent said turbine impeller and a metal portion adjacent said compressor impeller and contiguous with said ceramic portion, a ball bearing in said metal portion of the wall and supporting the shaft, and a ball bearing in said housing and supporting the compressor impeller.
2. A turbocharger according to claim 1, wherein the housing includes a bearing housing mounted in an inlet adjacent the compressor impeller, the bearing housing containing the bearing supporting the compressor impeller.
3. A turbocharger according to claim 2,

wherein the bearing housing is mounted in the inlet by a plurality of struts.
4. A turbocharger according to claim 1, 2 or 3 further including a lubrication system comprising a central bore in the compressor impeller and a connecting central bore in the shaft and radial holes in said compressor impeller extending to the bearing supporting the compressor impeller and radial holes in the shaft extendiing to the bearing supporting the shaft.
5. A turbocharger according to claim 4, wherein the lubrication system further includes a sump contained within the housing and a wick extending from the sump to a delivery line leading to one of the central bores.
6. A turbocharger according to claim 5, wherein the delivery line extends to the central bore within the compressor impeller.
7. A turbocharger according to claim 5 or 6, wherein the lubrication system further includes an oil return aperture extending from the bearing supporting the compressor to the sump and an oil return bore extending from the bearing supporting the shaft to the pump.
8. A turbocharger according to any one of the preceding claims wherein the ball bearing in the housing supports the nose of the compressor impeller.
9. A turbocharger comprising a turbine impeller and a compressor impeller mounted on the ends of a shaft, a housing defining a volute about each impeller and including a wall between said impellers through which said shaft extends, a bearing mounted in the wall and supporting the shaft, and a bearing mounted in said housing and supporting the compressor impeller, and a lubrication system comprising a central bore in the compressor impeller and a connecting central bore in the shaft and radial holes in the shaft extending to the bearing supporting the shaft.
10. A turbocharger according to claim 9, wherein the housing includes a bearing housing mounted in an inlet adjacent the compressor impeller, the bearing housing containing the bearing supporting the compressor impeller.
11. A turbocharger according to claim 10 or 11, wherein the bearing mounted in the housing supports the nose of the compressor impeller and the housing includes a hollow nipple adjacent to the nose of the compressor, the nipple and the nose defining a ciearance.
12. A turbocharger according to claim 9, 10 or 11, wherein the lubrication system further includes a sump contained within the housing and a wick extending from the sump to a delivery line leading to the nipple which communicates with the central bore in the compressor impeller.
13. A turbocharger according to claim 12, wherein the lubrication system further includes an oil return aperture extending from the bearing supporting the compressor to the sump and an oil return bore extending from the bearing supporting the shaft to the sump.
14. A turbocharger according to any one of claims 9 to 13, wherein the lubrication system includes radial holes in the compressor impeller extending adjacent to the bearing supporting the compressor impeller.
15. A turbocharger according to any one of claims 9 to 14, wherein the lubrication system includes a rotatable spacer adjacent to the bearing supporting the compressor impeller, the spacer having a plurality of blades.
16. A turbocharger according to any one of claims 9 to 15, wherein the lubrication system includes a rotatable spacer adjacent to the bearing supporting the shaft, the spacer having a plurality of blades.
17. A turbocharger according to claim 16, wherein the radial holes extending to one side of the bearing and the spacer is located on the other side of the bearing such that the blades of the spacer upon rotation tend to draw lubricant through the bearing.
18. A turbocharger substantially as shown in the accompanying drawings and described herein with reference thereto.