GB2349427A

GB2349427A - Multi-stage turbocharger having coaxial shafts

Info

Publication number: GB2349427A
Application number: GB9908979A
Authority: GB
Inventors: Francis Heyes
Original assignee: Alstom Gas Turbines Ltd
Current assignee: Alstom Power UK Holdings Ltd
Priority date: 1999-04-21
Filing date: 1999-04-21
Publication date: 2000-11-01
Also published as: GB9908979D0

Abstract

A multi-stage turbocharger comprises at least first 8, and second 11, exhaust gas driven turbines, each linked by a respective drive shaft 10,13 to a respective compressor 9,12, means to conduct exhaust gases from the first turbine to the second turbine, and means to conduct compressed air from the outlet of a first of the compressors to the inlet of the second compressor, wherein one drive shaft 13, is tubular and is mounted coaxially around the other shaft 10. The high-pressure turbine 8, may be reversed (fig. 3) so that it exhausts towards the low-pressure turbine 11, and means may be provided for selectively controlling flow between the turbines and between the compressors. The flow control means may allow for synchronous control of the turbines and compressors.

Description

TURBOCHARGER Field of the Invention This invention relates to a turbocharger for an internal combustion piston engine, and in particular to a multi-stage turbocharger.

Background to the Invention Multi-stage turbochargers are commonly used to increase the compression of the air fed to an internal combustion engine. Typically, these consist of two or more single-stage turbochargers operating in series, with appropriate ducting to carry the exhaust gases and compressed air from one turbocharger to the other. A disadvantage with such arrangements is that the resultant package can be unduly heavy and occupy a relatively large amount of room which, regardless of the size of the engine-which may be for a ship, a railway engine, or even a motor vehicle, for example-will reduce both payload and available space. This problem is exacerbated by the need for ducting to connect the turbochargers together. It is also possible for lengthy ducting to reduce efficiency, both by pressure losses and in the excessive cooling of the exhaust gases between the stages.

In the design of turbocompressors it has been proposed to increase compactness by linking stages together with a common shaft or with gearing driving the compressors with a single power source. Examples of such arrangements are disclosed in GB-A-2 018 893, US-A-5 154 571 and GB-A-992 651. In addition, it is known in turbojet engines to provide independently-driven high and low pressure compressor stages with c-axial shafts linked to respective turbine stages.

Summary of the Invention According to the invention, there is provided a multi-stage turbocharger, comprising at least first and second exhaust gas driven turbines, each linked by a respective drive shaft to a respective compressor, means to conduct exhaust gases from the first turbine to the second turbine, and means to conduct compressed air from the outlet of a first of the compressors to the inlet of the second compressor, wherein one drive shaft is tubular and is mounted coaxially around the other shaft.

Preferably, the inner shaft carries a higher pressure turbine and a higher pressure compressor, and the outer shaft carries a lower pressure turbine and a lower pressure compressor.

Control means may be provided for selectively directing the exhaust gas flow between the turbines, so that all or part of the exhaust gas flow may be directed to the higher and lower pressure turbines separately. Thus, it might be possible to operate the higher and lower pressure turbines in parallel instead of the exhaust gas flowing sequentially through the two stages, should operating conditions make this desirable.

Provision might also be made for simply diverting a proportion of the gas flow back to the exhaust system without passing through one or other of the turbines. Similar control means may be provided between the lower and higher pressure compressor stages to control air flow into and between them. The turbine control means may be linked to the compressor control means to permit synchronised operation of these.

The tubular drive shaft is preferably carried on bearings located on the other shaft. In this way, the relative speed of rotation at these bearings is reduced, reducing bearing losses and wear.

The turbines may be the same or different, and may be radial, axial or mixed flow turbines. The turbines may be mounted in such a way that the exhaust gases leaving one turbine flow directly into the other turbine without first passing into a separate manifold or the like.

Cooling means may be provided between the compressors to cool the compressed air, thereby increasing compression efficiency. Similarly, exhaust gas heating means may be provided to heat the exhaust gas between turbine stages to increase the turbine power output. Both these measures are known in turbocharger design.

It will be seen that if, for example, both compressors operate with a pressure ratio of 4: 1, a combined pressure ratio of 16: 1 can be achieved. This can be done with a relatively simple structure not requiring the use of exotic materials such as titanium in the compressor stages.

The turbocharger of the invention can be made considerably more compact than conventional multi-stage turbochargers, offering advantages in engines of all types from large marine engines down to small automotive engines.

Brief Description of the Drawings In the drawings, which illustrate diagrammatically an exemplary embodiment of the invention: Figure 1 is a view of the external casing of the turbocharger; Figure 2 is a schematic representation of the rotating parts and gas flows in the turbocharger of Figure 1; and Figure 3 is a schematic representation of an alternative arrangement to that shown in Figure 2.

Detailed Description of the Illustrated Embodiment Referring to Figure 1, engine exhaust gases from an internal combustion piston engine, for example a diesel engine, enter a higher pressure turbine (HPT) 8 (Figure 2) in the direction of arrow A through a casing inlet 1. After passing through the HPT 8, the gases are directed through ducting 2 to the lower pressure turbine (LPT) 11 (Figure 2) from where they are directed to an exhaust gas discharge system via the casing outlet 3 in the direction of arrow B. At the opposite end of the casing 7, ambient air is drawn in the direction of arrow C through a casing inlet 4 into a lower pressure compressor (LPC) 12 (Figure 2), passing from there to a higher pressure compressor (HPC) 9 (Figure 2) through ducting 5. The compressed air leaving the HPC passes through the casing outlet 6 in the direction of arrow D to supply the engine with combustion air.

Referring now to Figure 2, a main shaft 10 carries at one end the HPT 8 and at the other end the HPC 9. Exhaust gases are introduced to the HPT 8 as illustrated diagrammatically by arrow A. The gases give up some energy in producing rotation of the turbine, which drives the HPC 9. The gases leaving the HPT 8 pass to the LPT 11, where further energy is extracted. The gases are then discharged to the exhaust system as illustrated by arrow B.

The LPT 11 is mounted on one end of a tubular shaft 13 which is located coaxially around the first shaft 10 by way of bearings 14 between the shafts and by external bearings 15. The other end of the shaft 13 carries the LPC 12 which draws in ambient air as illustrated diagrammatically by arrow C and compresses the air, for example in a pressure ratio of 4: 1. The air then passes HPC 9, where it is further compressed, for example again at a pressure ratio of 4: 1, giving an overali pressure ratio of 16: 1. The compressed air leaving the high pressure compressor is represented by arrow D and passes to the inlet manifold of the associated engine in conventional manner.

Figure 3 shows an alternative arrangement in which the HPT 8 is mounted so that the gas flow therethrough is reversed with respect to that shown in Figure 2, so that the exhaust gases leaving the HPT 8 pass axially towards the LPT 11, thereby eliminating the need for the ducting 2 shown in Figure 1.

Various other modifications to the basic system described are possible. For example, an intercooler may be provided between the two stages of compression and exhaust gas heating means may be incorporated between the turbines, as are conventional in the art. Variable compression may be effected by providing gas flow deflecting means in either or both of the turbine and compressor gas flow paths, and such means may be controlled to give synchronous operation between the turbine and compressor stages. For example a portion of the gas emerging from the HPT may be diverted to the exhaust system, thus bypassing the LPT.

It will be understood that, while the invention has been described in relation to two stages of compression, it is possible for more than two stages to be accommodated in the same manner.

Claims

1. A multi-stage turbocharger, comprising at least first and second exhaust gas driven turbines, each linked by a respective drive shaft to a respective compressor, means to conduct exhaust gases from the first turbine to the second turbine, and means to conduct compressed air from the outlet of a first of the compressors to the inlet of the second compressor, wherein one drive shaft is tubular and is mounted coaxially around the other shaft.

2. A turbocharger according to Claim 1, wherein the inner shaft carries a higher pressure turbine and a higher pressure compressor, and the outer shaft carries a lower pressure turbine and a lower pressure compressor.

3. A turbocharger according to Claim 1 or 2, comprising exhaust gas control means for selectively directing the exhaust gas flow between the higher pressure and lower pressure turbines.

4. A turbocharger according to Claim 1,2 or 3, comprising air control means for selectively controlling the flow of air into and between the lower pressure and higher pressure compressors.

5. A turbocharger according to Claim 4, wherein the air control means is linked to the exhaust gas control means to allow synchronous control of the turbines and compressors.

6. A turbocharger according to any preceding claim, wherein the tubular drive shaft is carried on bearings located on the other shaft.

7. A turbocharger according to any preceding claim, wherein at least one of the turbines is an axial flow turbine.

8. A turbocharger according to any preceding claim, wherein at least one of the turbines is a radial flow compressor.

9. A turbocharger according to any preceding claim, wherein at least one of the turbines is a mixed flow compressor.

10. A turbocharger according to any preceding claim, wherein the exhaust gases flow directly from the first turbine to the second turbine.

11. A turbocharger, substantially as described with reference to, or as shown in the drawings.