GB2412695A

GB2412695A - Centrifugal compressor with multiple diffuser passages

Info

Publication number: GB2412695A
Application number: GB0407625A
Authority: GB
Inventors: Michael Atkinson
Original assignee: TRIVISTA ENGINEERING Ltd
Current assignee: TRIVISTA ENGINEERING Ltd
Priority date: 2004-04-02
Filing date: 2004-04-02
Publication date: 2005-10-05
Also published as: GB0407625D0

Abstract

A centrifugal compressor 1, suitable for use in a turbo charger, comprises an impeller 3, a housing 4 and at least two diffuser passages 5, 6. Valve means are provided downstream of the diffuser passages 5, 6 which control fluid flow though at least one of them. The diffuser passages 5, 6 are also arranged to have different flow characteristics, such that a range of operating flow rates can be accommodated without suffering problems associated with surge or choke. Diffuser vanes 8, 9 having different flow characteristics may be used in each diffuser passage 5, 6. A two-way valve may be applied to a first and second outlet, such that flow though each diffuser passage 5, 6 may be controlled independently.

Description

24 1 2695 Variable Flow Diffuser Centrifugal Compressor This invention

relates to a variable flow diffuser mechanism for a centrifugal compressor, for use particularly, but not exclusively to compress air.

Centrifugal compressors increase the pressure of a fluid by means of an impeller enclosed in a housing. The fluid enters the compressor axially and is pressurised by the rotation of the impeller blades. In some centrifugal compressors the fluid is driven radially through diffuser vanes or passages around the impeller which slows down the fluid, before it exits the device and is used.

However, centrifugal compressors as described above have a limited flow range which can be determined by the shape and angle of the diffuser vanes or of the diffuser passages. The compressors are inhibited at low flow rate by surge, and at high flow rate by choke, and are only useful between these limits.

It is known to provide complex variable rotation diffuser vane mechanisms to overcome this problem. An actuator can rotate each vane about an axis point, such that the diffuser flow area can be reduced for low flow, and increased for high flow, which therefore increases the useful range of the device.

However, providing means inside the device to rotate each separate vane, significantly increases the number of internal working parts in what it a relatively simple device, and therefore increases costs to an inhibitive level and can also endanger reliability.

In addition, a clearance is required between the sides of the vanes and the housing to allow the vanes to rotate. This clearance is known to reduce the efficiency of the diffuser vanes.

Centrifugal compressors with variable geometry are used in industrial air conditioning systems. However, despite the clear improvement in performance they are not used with smaller mechanical devices where cost and reliability are paramount, for example automotive turbochargers.

The present invention is intended to overcome some of the above problems.

Therefore, according to the present invention a centrifugal compressor comprises an inlet, an impeller, a housing, at least two diffuser passages, and valve means downstream of the diffuser passages which is adapted to control a flow through at least one of said diffuser passages, in which each of said diffuser passages is provided with different flow characteristics.

It will be appreciated that any number of diffuser passages can be provided, but in a preferred construction two diffuser passages can be provided.

It will also be appreciated that there are various ways to create a desired flow characteristic through a diffuser passage. For example, the passage can be dimensioned in a particular way, it can have a certain shape, and it can be located at a certain position in relation to the impeller blades. However, in a preferred embodiment a first diffuser passage may be provided with a first set of diffuser vanes and a second diffuser passage can be provided with a second set of diffuser vanes.

In a preferred construction the first diffuser passage can be set for high flow rates, and the second diffuser passage can be set for low flow rates. In particular, the first set of diffuser vanes can provide a larger flow area than the second set of diffuser vanes. Further the flow characteristics of the two diffuser passages can overlap. That is, the area of surge of the flow characteristics of the first diffuser passage can be within the effective operating area of the flow characteristics of the second diffuser passage. This allows the first and the second diffuser passages to be used simultaneously, and one at a time, depending on the desired arrangement and the flow rate.

With this arrangement the compressor can operate at a wider range of flow rates than with a single static set of diffuser vanes, and there are no complex moving parts inside the housing.

In addition, as the first set of diffuser vanes and the second set of diffuser vanes are static, there are no undesirable clearances between the sides of the vanes and the housing, which is the cause of problems in known variable geometry compressors.

It will be appreciated that centrifugal compressors can be provided with a regular collector space around the diffuser passage, or a volute which increases in area around its circumference. The invention is intended to cover both arrangements, but in one embodiment a first volute can extend from the first diffuser passage, and a second volute can extend from the second diffuser passage. The first volute can be of greater dimensions than the second volute. me first volute can be provided with a first outlet and the second volute can be provided with a second outlet.

In one construction the first diffuser passage and first volute, and the second diffuser passage and second volute can be axially adjacent one another. The diffuser passages and volutes can be axially arranged in any order, but in one arrangement the first diffuser passage and the first volute can be disposed axially in front of the second diffuser passage and the second volute.

The valve means can be disposed adjacent the first outlet and/or the second outlet.

In the Statement of Invention above the valve means is adapted to control a flow through at least one of said diffuser passages. Therefore, in one embodiment the valve means can be a single one way valve applied to only one or the other of the first outlet or the second outlet, such that in use a flow can pass through one diffuser passage all the time, and the flow through the other diffuser passage can be controlled.

However, in an alternative embodiment the valve means can be a two-way valve which can be applied to the first outlet and the second outlet, such that in use the flow through the first diffuser passage and the flow through the second diffuser passage can be controlled independently. With this arrangement a flow can pass completely through both, only one, or to a controlled degree through one and/or the other diffuser passage independently, as desired.

The invention can be performed in various ways, but one embodiment will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional side view of a section of a centrifugal compressor according to the present invention; Figure 2 is a diagrammatic view of a front cross-section of the centrifugal compressor along hashed line A - A in Figure 1; and, Figure 3 is a second diagrammatic view of a front cross-section of the centrifugal compressor along hashed line B - B in Figure 1.

As shown in the Figures a centrifugal compressor 1 comprises an inlet 2, an impeller 3, a housing 4, at least two diffuser passages (5 and 6), and valve means in the form a two-way flow control valve 7 downstream of the diffuser passages (5 and 6) which is adapted to control a flow through each of said diffuser passages (5 and 6), in which each of said diffuser passages (5 and 6) is provided with different flow characteristics.

A first diffuser passage 5 contains a first set of diffuser vanes 8 and a second diffuser passage 6 contains a second set of diffuser vanes 9. The vanes 8 in the first diffuser passage 5 are arranged at a greater radial angle relative to the impeller 3, and thus provide a greater flow area between them, than the vanes 9 in the second diffuser passage 6. Therefore, generally speaking, the first diffuser passage 5 is for use at higher flow rates than the second diffuser passage 6.

As shown in Figure 1 the first diffuser passage 5 and the second diffuser passage 6 are axially adjacent one another, with the first diffuser passage 5 axially in front of the second diffuser passage 6. A first volute 10 extends from the first diffuser passage 5, and a second volute 11 of smaller dimensions extends from the second diffuser passage 6. The first volute 10 and the second volute 11 are also axially adjacent one another, and the first volute 10 ends at a first outlet 12 and the second volute 11 ends at a second outlet 13.

As is clear from Figure 1 the first set of diffuser vanes 8 and the second set of diffuser vanes 9 are fixed in place inside the diffuser passages 5 and 6, and as such there are no clearances between the sides of the vanes 8 and 9 and the sides of the diffuser passages 5 and 6. Therefore the diffusion passages 5 and 6 can operate at optimum efficiency.

The flow control valve 7 is disposed at the outlets 12 and 13 and comprises a known type of variable two-way valve which will not be further described here. It can control flows through the first diffusion passage 5 and the first volute 10 independently of the second diffusion passage 6 and the second volute 11, by opening and closing the outlets 12 and 13.

The compressor 1 is provided with known inlet and outlet fittings and a drive means for the impeller (not shown), and is adapted for use with an internal combustion engine turbocharging device.

The flow characteristics of the first diffusion passage 5 overlap with the flow characteristics of the second diffusion passage 6, such that the area of surge of the flow characteristics of the first diffusion passage 5 are within the effective operating area of the flow characteristics of the second diffusion passage 6.

In use air enters the inlet 2 and is pressurized by the rotation of the impeller 3 and forced radially towards the first diffusion passage 5 and the second diffusion passage 6. If the compressor 1 is used at a low flow rate the two-way valve 7 closes the first outlet 12, and the air passes through the second diffusion passage 6, over the second set of diffuser vanes 9 and down the second volute 11. The second set of vanes 9 are angled to provide the optimum compressor flow rate for the turbocharger at low flow rates.

If the flow rate increases to a pre-determined flow rate less than the area of choke of the flow characteristics of the second diffuser passage 6, ie to a point at the top of the effective flow rate of the second diffuser passage 6, the two-way valve 7 opens the first outlet 12 and closes the second outlet 13. As a result the air passes through the first diffuser passage 5, over the first set of vanes 8 and down the first volute 10. The compressor 1 can now be used up to the maximum effective flow rate of the first diffuser passage 5, which is higher than the maximum effective flow rate of the second diffuser passage 6.

If the flow rate decreases to a pre-determined flow rate greater than the area of surge of the flow characteristics of the first diffuser passage 5, ie to a point at the bottom of the effective flow rate of the first diffuser passage 5, the two-way valve 7 opens the second outlet 13 and closes the first outlet 12. As a result the air flow returns to the second diffuser passage 6.

Therefore, the compressor can operate at a wider range of flow rates than if it had only one diffuser passage. In addition, this wider range of flow rates is achieved without any working parts inside the housing 4 other than the impeller 3, and without the problems of a clearance around any of the vanes.

In use, the two-way valve 7 can open outlet 12 and close outlet 13 at the same time as described above, such that only one diffusion passage is used at a time. However, the two-way valve 7 can also be set to open both of the outlets 12 and 13 between pre-determined flow rates so air can pass through both diffusion passages 5 and 6 simultaneously. mis could be done at a flow rate within the effective range of both the first diffusion passage 5 and the second diffusion passage 6. This allows a smooth transition from first diffusion passage 5 usage to second diffusion passage 6, and visa versa. Therefore, the operation of the two-way valve 7 can be adjusted depending on the desired performance characteristics of the compressor 1.

It will be appreciated that compressor 1 could be changed without departing from the spirit of the invention. In particular, in a further embodiment (not shown) the first diffuser passage 5 or the second diffuser passage 6 can carry no vanes, and provide the diffusion effect simply by virtue of their dimensions or shape.

In another embodiment (not shown) more than two diffusion passages are provided, the effective flow rates of which overlap sequentially, along with an appropriate valve mechanism. mis could provide the compressor with an even greater range of effective use.

In one further alternative embodiment (not shown) the valve means can take the form of a one way valve applied to only one or the other of the first outlet or the second outlet, such that a flow can pass through one diffuser passage all the time, and the flow through the other diffuser passage can be controlled.

Thus, a centrifugal compressor is provided with the significant increase of performance provided by variable diffuser geometry, without any of the significant cost and reliability issues of having working parts inside the housing, nor any of the flow problems associated with clearances around the sides of any of the diffuser vanes.

In addition, most automotive turbochargers are provided with vaneless diffuser passages, because they have a wider operating range. However, vaneless diffuser passages are less efficient than those with vanes. The centrifugal compressor of the present invention may also overcome this problem because it uses vaned diffuser passages for greater efficiency, but still has an operating range broad enough for such applications.

Claims

Claims 1. A centrifugal compressor comprising an inlet, an impeller, a

housing, at least two diffuser passages, and valve means downstream of the diffuser passages which is adapted to control a flow through at least one of said diffuser passages, in which each of said diffuser passages is provided with different flow characteristics.
2. A centrifugal compressor as claimed in Claim 1 in which two diffuser passages are provided.
3. A centrifugal compressor as claimed in Claim 1 or 2 in which a first diffuser passage is provided with a first set of diffuser vanes and a second diffuser passage is provided with a second set of diffuser vanes, and in which the flow characteristics of the first set of diffuser vanes is different to the flow characteristics of the second set of diffuser vanes.
4. A centrifugal compressor as claimed in Claim 3 in which the first diffuser passage is set for higher flow rates than the second diffuser passage, and in which the first set of diffuser vanes provide a larger flow area than the second set of diffuser vanes,
5. A centrifugal compressor as claimed in Claim 4 in which the flow characteristics of the first diffuser passage and the second diffuser passage overlap.
6. A centrifugal compressor as claimed in Claim 5 in which the first diffuser passage and the second diffuser passage are axially adjacent one another.
7. A centrifugal compressor as claimed in Claim 6 in which a first volute extends from the first diffuser passage, and a second volute extends from the second diffuser passage, and in which the first volute and the second volute are axially adjacent one another, in which the first volute is provided with a first outlet and the second volute / is provided with a second outlet, and in which the first volute is of greater dimensions than the second volute.
8. A centrifugal compressor as claimed in Claim 7 in which the first diffuser passage and the first volute are disposed axially in front of the second diffuser passage and the second volute.
9. A centrifugal compressor as claimed in Claim 7 in which the second diffuser passage and the second volute are disposed axially in front of the first diffuser passage and the first volute.
10. A centrifugal compressor as claimed in Claim 8 or 9 in which the valve means is disposed adjacent the first outlet and/or second outlet.
11. A centrifugal compressor as claimed in Claim 10 in which the valve means is a one way valve applied to the first outlet or to the second outlet, such that in use a flow passes through one diffuser passage all the time, and the flow through the other diffuser passage is controlled.
12. A centrifugal compressor as claimed in Claim 10 in which valve means is a two-way valve applied to the first outlet and the second outlet, such that in use a flow through the first diffuser passage and a flow through the second diffuser passage are controlled independently.
13. A centrifugal compressor substantially as described herein and as shown in the accompanying drawings.