GB2064656A

GB2064656A - A Turbo-supercharger

Info

Publication number: GB2064656A
Application number: GB8038017A
Authority: GB
Original assignee: SKF Kugellagerfabriken GmbH
Current assignee: SKF GmbH
Priority date: 1979-12-01
Filing date: 1980-11-27
Publication date: 1981-06-17
Also published as: IT1134439B; FR2470860A1; FR2470860B1; JPS5685524A; GB2064656B; DE2948398A1; IT8026202A0

Abstract

A turbo-supercharger has a compressor wheel (13) and a turbine wheel (11) mounted on a common shaft (15). A partition (19) extends radially to the shaft (15) between the turbine and compressor wheels (11, 13). An air bearing having bearing surfaces (21, 22, 23, 24) is formed between the partition (19) and the hubs of the turbine and compressor wheels (11, 13) supporting the wheels axially and radially for rotation relative to the partition (19). <IMAGE>

Description

SPECIFICATION A Turbo-supercharger The invention relates to a turbo-supercharger comprising a compressor wheel and a turbine wheel mounted on a common shaft and bearings disposed between them in a housing.

Some known turbo-superchargers have an externally mounted shaft, i.e. the shaft bearing the turbine wheel and the impeller wheel is mounted in bearings axially outside the wheels at the ends of the shaft. Other known turbo-superchargers have "internal suspension", i.e. the turbine wheel and the compressor wheel are mounted on a common shaft and a suspension in an intermediate housing connected to the turbine housing and the compressor housing is disposed between the two wheels. The last-mentioned suspension comprises two bearings (or even three if there is a separate axial bearing), e.g. rolling or sliding (plain) bearings which, to ensure rigidity, usually have to be spaced a relatively long distance apart.

Ducts or the like connected to the engine oil circuit are formed in the intermediate housing for lubricating the bearing surfaces of the suspensions, which are usually hydrodynamic plain bearings.

These known embodiments are usually very long, particularly in the axial direction, and thus take up considerable space and contain a considerable amount of material and therefore are heavy and have high inertia. In addition, the known bearings have a number of parts, which are difficult to manufacture and put together.

In one aspect the invention provides a turbosupercharger comprising a compressor wheel and a turbine wheel mounted on a common shaft and bearings disposed between them in a housing, characterised in that the turbine wheel and the compressor wheel are disposed on the shaft so as to leave only a small intermediate axial space in between, a partition is disposed in the intermediate space and the bearing is a doubleacting air suspension bearing having one bearing surface disposed immediately at the hub of the turbine wheel and the compressor wheel, whereas the complementary bearing surfaces are disposed at the partition between the turbine housing and the compressor housing.

In another aspect the invention provides a turbo-supercharger having a rotor structure and a stator structure, the rotor structure comprising a compressor rotor, a turbine rotor and a shaft all connected to rotate as one; the stator structure comprising a partition extending radially towards the shaft between the compressor rotor and the turbine rotor; and a bearing supporting the rotor structure for rotation relative to the stator structure, the only bearing surfaces serving to locate the rotor structure radially and axially with respect to the stator structure cooperating with bearing surfaces formed on or fixed with respect to the partition, wherein the bearing surfaces are air lubricated.

In a further aspect the invention provides a turbo-supercharger comprising a compressor and a turbine for driving the compressor, the turbosupercharger including a housing, a shaft disposed within the housing, a turbine wheel and a compressor wheel mounted in the housing on and for rotation with the shaft and being axially spaced from each other, an annular partition connected to the housing and extending radially towards the shaft and between the turbine wheel and the compressor wheel, and an air bearing for axially and radially supporting the shaft and turbine and compressor wheels in rotation relative to the partition and housing, the air bearing having bearing surfaces formed on or fixed with respect to the partition and complementary bearing surfaces at the hubs of the turbine and compressor wheels and formed on or fixed with respect to the shaft and turbine and compressor wheels.

A turbo-supercharger according to the invention has important advantages over the known embodiments. The compressor wheel and the turbine wheel can be disposed very close to one another so that the shaft can be much shorter; this reduces the axial space required and also reduces the weight, the material needed and the masses in rotation. The shaft and the wheels thereon are mounted substantially at the mass centre, thus reducing the out-of-balance forces and vibration. Finally, the thermal expansion is also reduced, with the result that the gaps between the turbine and compressor wheels and the associated housing surfaces can be kept narrower, thus substantially improving efficiency.

The relatively complicated housing required in the known embodiments is reduced to a partition which, again, needs less material and is therefore lighter. The partition is cheaper to produce than the bearing housings used in the known embodiments.

Since the bearing surfaces can be formed on the wheel hubs and the partition, and can easily be machined or worked in, the number of parts is reduced, thus simplifying manufacture and assembly.

Air for the bearing can be supplied directly from atmosphere or from the compressor intake pipe or the compressor space. There is thus no need to connect the bearing to the engine oil circuit, i.e. expensive connecting pipes can be omitted. There is also no additional heating of the engine oil.

The advantage of an air bearing is that the bearing associated with the relatively hot turbine wheel has an intrinsically higher load carrying capacity, because the inflowing air there is hotter, and therefore at a higher pressure than the air in the bearing associated with the compressor wheel. This is a great advantage in practice, because the bearing associated with the turbine wheel is also more heavily loaded in operation.

Another advantage of an air bearing is that the turbo-supercharger according to the invention can be oriented in any position, e.g. with the shaft vertical.

Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, of which: Figures 1 to 4 are longitudinal sections through various embodiments of a turbo-supercharger.

Like parts are denoted by like reference numbers.

Figure 1 shows a turbo-supercharger comprising a double-flow turbine (turbine wheel 11 and turbine housing 12) and a compressor (compressor wheel 13 and compressor housing 14). Wheels 11 and 13 are mounted on a common shaft 15 and separated only by a short axial spacer sleeve 1 6. In order axially to secure the parts, shaft 1 5 has an annular collar 1 7 at one end and a threaded projection at the other end, on which a retaining nut 1 8 is screwed. Nut 1 8 presses wheel 11, sleeve 16 and wheel 13 against collar 17, thus providing a non-positive connection between the parts.

A partition 19 is disposed between housing 12 and housing 14 in the interior of housing 12 and is secured thereto and extends radially towards the shaft into the space between wheels 11 and 1 3, up to very near the outer surface 20 of sleeve 16. The hubs of wheels 11 and 13, which are formed e.g. with annular recesses 41 have spherical convex annular surfaces 21, 22 facing one another at the facing side surfaces and having centres of curvature disposed at a distance "x" from one another along the axis of shaft 1 5.

Surfaces 21 and 22 co-operate with corresponding spherical concave annular surfaces 23 and 24 of partition 19, which face away from one another and are formed with a number of peripheral bearing pockets 25 and 26, to form two bearings, which support shaft 1 5 and wheels 11 and 13 both axially and radially. In order to supply air to the bearing from the intake space 27 for the compressor, shaft 1 5 has a central bore 28 connected radially via one or more radial bores 29, 30 in shaft 15 and sleeve 16 respectively to the bore space 31 inside partition 1 9. From there, the air is guided into pockets 25, 26 and builds up pressure so as to hold the bearing surfaces apart and thus support shaft 1 5 and wheels 11 and 13.

The resulting air suspension bearing has much iess friction than an oil-lubricated bearing. It thus has a shorter starting time and a higher speed can be reached, and has the further advantage that the bearing space need not be so hermetically sealed from the turbine and compressor space as in oil-lubricated bearings, where there is a risk that oil will penetrate into the two last-mentioned spaces and thus e.g. increase the proportion of unburnt hydrocarbons in the exhaust gas. In many cases an adequate seal is obtained if the turbine wheel 11, at the disc bearing the blades above the hub, is provided with an annular axial projection 32 which engages in a corresponding annular recess 33 in partition 19 and thus forms a multi-stage labyrinth seal against the turbine exhaust-gas space 34.

Since the convex spherical or concave spherical surfaces 21,22 and 23, 24 are disposed so that their centres are at a distance "x" from one another, the resulting suspension is spherical and can receive both radial and axial forces and moments.

The resulting "0" system, in spite of its shortness, has a relatively large bearing width, i.e.

has high bearing rigidity.

In addition, the length of sleeve 1 6 can be chosen so as to adjust the axial and radial clearance in the two spherical bearings, thus improving efficiency and accuracy. The diameter of the spherical bearing surfaces the angle of contact and the distance "x" can be chosen so as to compensate for thermal changes in length.

In addition, the material for wheels 11 and 13 and/or partition 1 9 can be chosen to obtain a suitable pair of low friction surfaces for starting, before pressure has built up in the spherical bearings.

Cooling water, via connections (not shown), can be supplied to and removed from the space 35 formed by partition 19 and housing 12, thus preventing heat from being transfered from the turbine to the compressor.

Figure 2 shows an embodiment differing from Figure 1 in that the air supply for the bearing surfaces 21,23 and 22, 24 comes from the external atmosphere, radially through bores 42 in the partition 19 and bores 43 in the housing 12 to space 31. In Figure 2, instead of plain bearing surfaces in the bearing pockets 25, 26 in partition 19, the surfaces 21, 22 of the hubs of wheels 11 and 13 are formed with spiral grooves 36 which build up a pressure in the gap between surfaces 21,22 and 23, 24 and hold the bearing surfaces apart.

In the embodiment of Figure 3, in contrast to Figures 1 and 2, the disc of turbine wheel 11 bearing the blades is given a smooth side surface 37, and does not have a labyrinth seal. This is advantageous in cases where the exhaust-gas pressure in the turbine-wheel gap is smaller than the bearing air outflow pressure, allowing for the effect of the gap and suction at wheel 11. In the present case the suspension bearing is in the form of an aerostatic bearing; compressed air is supplied from compressor chamber 38 to the bearing pockets 40 via bores 39 in partition 19. In addition, shaft 1 5 is much shorter than in the embodiments in Figures 1 and 2.

In the previously-described embodiments, partition 1 9 is disposed radially inside the turbine housing 12, whereas Figure 4 shows an embodiment in which the partition 1 9 is made of ceramics and is extended radially outwards and forms a partition between the compressor housing 14 and the turbine housing 12 along itsentire radial length. This ensures that the hot exhaust gases in the turbine do not heat the compressed air in the compressor. This increases the efficiency of the turbo-supercharger. As in the embodiments in Figures 2 and 3, cooling water can be sent through the space 35 between partition 19 and housing 12. In Figure 4, shaft 15 is a differentially-threaded screw.

The spherical bearings used in the previouslydescribed embodiments have the advantage of not being sensitive to changes in the shape of the mounted parts or the manner in which they bear against one another. Instead of having convex spherical annular surfaces 21, 22 at the hubs of wheels 11 and 13 and concave spherical annular surfaces 23, 24 at the partition, the opposite system can be adopted, i.e. the convex spherical surfaces can be formed on the partition and the concave spherical surfaces on the hubs of wheels 11 and 13. Of course it is also possible and in some cases advantageous to replace the aforementioned spherical bearings by bearings having conical surfaces.In that case, the conical bearing surfaces will advantageously be inclined in opposite directions towards one another to receive axial forces in both directions and thus provide accurate axial guidance of the shaft bearing the turbine wheel and compressor wheel.

Partition 19 can be made of ceramics and so more particularly can the parts exposed to the heat of the exhaust gases, e.g. the turbine wheel and turbine housing or the other parts of the turbo-supercharger.

The invention can also be varied with regard to the air supply to the bearing surfaces. In the embodiment of Figure 1, for example, air can be supplied from the central axial bore 28 through radial bores into the recesses 41 in the hubs of wheels 11 and 1 3 and thence through corresponding bores to the bearing surfaces 21 or 22. Similarly, in the embodiment of Figure 2, the air sucked from atmosphere can be supplied through suitable bores directly to the annular surfaces 23 and 24 on partition 1 9.

Claims

1. A turbo-supercharger comprising a compressor wheel and a turbine wheel mounted on a common shaft and bearings disposed between them in a housing, characterised in that the turbine wheel (11) and the compressor wheel (13) are disposed on the shaft (15) so as to leave only a small intermediate axial space in between, a partition (19) is disposed in the intermediate space and the bearing is a double-acting air suspension bearing having one bearing surface (21, 22) disposed immediately at the hub of the turbine wheel (11) and the compressor wheel (13), whereas the complementary bearing surfaces (23, 24) are disposed at the partition between the turbine housing (12) and the compressor housing (14).

2. A turbo-supercharger according to claim 1, characterised in that the air suspension bearing comprises two conical bearings having conical surfaces inclined in opposite directions.

3. A turbo-supercharger according to claim 1, characterised in that the air suspension comprises two spherical bearings having spherical annular surfaces (21, 22) directed towards one another and corresponding hollow spherical annular surfaces (23, 24) facing away from one another.

4. A turbo-supercharger according to claim 1, characterised in that the air suspension comprises two spherical bearings having spherical annular surfaces facing away from one another and corresponding hollow spherical annular surfaces facing towards one another.

5. A turbo-supercharger according to any of claims 1 to 4, characterised in that the air suspension is an aerostatic bearing.

6. A turbo-supercharger according to any of claims 1 to 4, characterised in that the air suspension is an aerodynamic bearing.

7. A turbo-supercharger according to claim 6, characterised in that at least one of the annular surfaces (21, 22 and/or 23, 24) is formed with spiral grooves (36) for building up pressure.

8. A turbo-supercharger according to any of claims 1 to 7, characterised in that at least the partition (19) between the turbine housing (12) and the compressor housing (14) is made of ceramics.

9. A turbo-supercharger according to any of claims 1 to 8, characterised in that a spacer sleeve (16) is disposed between the turbine wheel (11) and the compressor wheel (13) in order to adjust the bearing clearance to the optimum value.

10. A turbo-supercharger according to any of claims 1 to 9, characterised in that a cavity (35), which can be supplied with cooling water, is formed in the partition (19).

11. A turbo-supercharger according to any of claims 1 to 10, characterised in that a central bore (28) extending from the compressor inlet is provided in the shaft (15) for supplying air from the compressor to the bearing surfaces (21, 22 and/or 23, 24) and radial bores (29) extending from the central bore are provided in the shaft (15) together with corresponding radial bores (30) in the spacer sleeve (16).

12. A turbo-supercharger according to any of claims 1 to 10, characterised in that, in order to supply air radially from the exterior, the partition (19) is formed with at least one radial bore (42, 43) connected to the space (31) between the turbine wheel (11) and the compressor wheel (13).

13. A turbo-supercharger according to any of claims 1 to 10, characterised in that bores (39) connected to the bearing pockets (40) are formed in the partition (19) for supplying air from the compressor chamber (38).

14. A turbo-supercharger having a rotor structure and a stator structure, the rotor structure comprising a compressor rotor, a turbine rotor and a shaft all connected to rotate as one; the stator structure comprising a partition extending radially towards the shaft between the compressor rotor and the turbine rotor; and a bearing supporting the rotor structure for rotation relative to the stator structure, the only bearing surfaces serving to locate the rotor structure radially ahd axially with respect to the stator structure cooperating with bearing surfaces formed on or fixed with respect to the partition, wherein the bearing surfaces are air lubricated.

1 5. A turbo-supercharger comprising a compressor and a turbine for driving the compressor, the turbo-supercharger including a housing, a shaft disposed within the housing, a turbine wheel and a compressor wheel mounted in the housing on and for rotation with the shaft and being axially spaced from each other, an annular partition connected to the housing and extending radially towards the shaft and between the turbine wheel and the compressor wheel, and an air bearing for axially and radially supporting the shaft and turbine and compressor wheels in rotation relative to the partition and housing, the air bearing having bearing surfaces formed on or fixed with respect to the partition and complementary bearing surfaces at the hubs of the turbine and compressor wheels and formed on or fixed with respect to the shaft and turbine and compressor wheels.

1 6. A turbo-supercharger as claimed in claim 15, wherein the air bearing comprises two air bearings each having conically extending bearing surfaces, the conically extending bearing surfaces of one bearing converging in the opposite axial direction to those of the other bearing.

1 7. A turbo-supercharger as claimed in claim 15, wherein the air bearing comprises two air bearings each having spherically curved bearing surfaces, with a convex bearing surface of one bearing facing a convex bearing surface of the other bearing.

18. A turbosupercharger as claimed in any one of claims 15 to 17, wherein the air bearing is an aerodynamic bearing.

1 9. A turbo-supercharger as claimed in claim 18, wherein one of the bearing surfaces has spirally extending grooves.

20. A turbo-supercharger as claimed in any one of claims 1 5 to 1 9, wherein the annular portion is a ceramic material.

21. A turbo-supercharger as claimed in any one of claims 1 5 to 20, wherein a sleeve is disposed between and axially spaces apart the turbine wheel and the compressor wheel.

22. A turbo-supercharger as claimed in any one of claims 1 5 to 21 wherein the annular partition has an internal cavity to receive a supply of cooling fluid.

23. A turbo-supercharger as claimed in any one of claims 1 5 to 22, wherein the shaft has a duct communicating with the compressor and to between the turbine and compressor wheels for the supply of air to the air bearing.

24. A turbo-supercharger as claimed in claims 21 and 23, wherein the sleeve has at least one aperture for the supply of air to the air bearing.

25. A turbo-supercharger as claimed in any one of claims 1 5 to 22, wherein the annular partition has at least one aperture communicating with the outside of the housing and to between the turbine and compressor wheels for the supply of air from outside of the housing to the air bearing.

26. A turbo-supercharger as claimed in any one of claims 1 5 to 1 7, wherein the annular partition has a duct communicating with a high pressure part of the compressor and opening into one of the surfaces of the air bearing.

27. A turbo-supercharger substantially as herein described with reference to and as shown in Figure 1, or with reference to and as shown in Figure 2, or with reference to and as shown in Figure 3, or with reference to and as shown in Figure 4 of the accompanying drawings.