GB2503029A

GB2503029A - Variable geometry turbine

Info

Publication number: GB2503029A
Application number: GB1210669.6A
Authority: GB
Inventors: Tim Denholm
Original assignee: Cummins Ltd
Current assignee: Cummins Ltd
Priority date: 2012-06-15
Filing date: 2012-06-15
Publication date: 2013-12-18
Anticipated expiration: 2032-06-15
Also published as: GB201210669D0; GB2503029B

Abstract

A variable geometry turbine has an annular inlet 9 to a turbine wheel 5, the inlet includes first and second axially spaced passages which extend from an outer diameter to an inner diameter. A generally cylindrical sleeve 30 is moveable for varying the size of the annular inlet. The sleeve is movable in a first direction from a first position to an opening position of the second inlet passage, during which movement the second inlet passage is closed. When the sleeve is in the opening position, the cross-sectional area of an opening to the first inlet passage defined between a free, first end of the sleeve and the first inlet passage sidewall is substantially equal to the minimum cross-sectional area of the first inlet passage. Movement of the sleeve in the first direction beyond the opening position of the second inlet passage serves to initiate opening of the second inlet passage.

Description

Turbine The present invention relates to a variable geometry turbine. The variable geometry turbine may, for example, form a part of a turbocharger.

Turbochargers are well known devices for supplying air to an intake of an internal combustion engine at pressures above atmospheric pressure (boost pressures). A conventional turbocharger essentially comprises an exhaust gas driven turbine wheel mounted on a rotatable shaft within a turbine housing connected downstream of an engine outlet manifold. Rotation of the turbine wheel rotates a compressor wheel mounted on the other end of the shaft within a compressor housing.

The compressor wheel delivers compressed air to an engine intake manifold. The turbocharger shaft is conventionally supported by journal and thrust bearings, including appropriate lubricating systems, located within a central bearing housing connected between the turbine and compressor wheel housings.

The turbine stage of a typical turbocharger comprises: a turbine chamber within which the turbine wheel is mounted; an annular inlet defined between facing radial walls arranged around the turbine chamber; an inlet volute arranged around the annular inlet; and an outlet passageway extending from the turbine chamber. The passageways and chamber communicate such that pressurised exhaust gas admitted to the inlet volute flows through the inlet to the outlet passageway via the turbine and rotates the turbine wheel. It is also known to improve turbine performance by providing vanes, referred to as nozzle vanes, in the inlet so as to deflect gas flowing through the inlet. That is, gas flowing through the annular inlet flows through inlet passages (defined between adjacent vanes) which induce swirl in the gas flow, turning the flow direction towards the direction of rotation of the turbine wheel.

Turbines may be of a fixed or variable geometry type. Variable geometry turbines differ from fixed geometry turbines in that the size of the inlet can be varied to optimise gas flow velocities over a range of mass flow rates so that the power output of the turbine can be varied to suit varying engine demands. For instance, when the volume of exhaust gas being delivered to the turbine is relatively low, the velocity of the gas reaching the turbine wheel is maintained at a level which ensures efficient turbine operation by reducing the size of the inlet using a variable geometry mechanism.

Turbochargers provided with a variable geometry turbine may be referred to as variable geometry turbochargers.

Nozzle vane arrangements in variable geometry turbochargers can take different forms. In one type, known as a sliding nozzle ring", the vanes are fixed to an axially movable wall that slides across the inlet passageway. The axially movable wall moves towards a facing shroud plate in order to close down the inlet passageway and in so doing the vanes pass through apertures in the shroud plate. Alternatively, the nozzle ring is fixed to a wall of the turbine and a shroud plate is moved over the vanes to vary the size of the inlet passageway.

The moving component of the variable geometry mechanism, whether it is the nozzle ring or the shroud plate, is supported for axial movement in a cavity in a part of the turbocharger housing (usually either the turbine housing or the turbocharger bearing housing). It may be sealed with respect to the cavity walls to reduce or prevent leakage flow around the back of the nozzle ring.

The moveable wall of the variable geometry mechanism is axially displaced by a suitable actuator assembly comprising an actuator and a linkage. An example of such a known actuator assembly is for instance disclosed in US 5,868,552. The linkage comprises a yoke pivotally supported within the bearing housing and having two arms, each of which extends into engagement with an end of a respective push rod on which the moving component (in this instance the nozzle ring) is mounted. The yoke is mounted on a shaft journaled in the bearing housing and supporting a crank external to the bearing housing which may be connected to the actuator in any appropriate manner. The actuator which moves the yoke can take a variety of forms, including pneumatic, hydraulic and electric forms, and can be linked to the yoke in a variety of ways. The actuator will generally adjust the position of the moving wall under the control of an engine control unit (ECU) in order to modify the airflow through the turbine to meet performance requirements.

In use, axial forces are imparted on the moveable wall by the air flow through the inlet, which must be accommodated by the actuator assembly. In addition, a torque is imparted to the nozzle ring as a result of gas flow vane passages being deflected towards the direction of rotation of the turbine wheel. If the nozzle ring is the moving wall of the variable geometry mechanism this torque also has to be reacted or otherwise accommodated by the actuator assembly such as by parts of the linkage.

It is one object of the present invention to obviate or mitigate the aforesaid disadvantages. It is also an object of the present invention to provide an improved or alternative variable geometry mechanism and turbine.

According to a first aspect of the invention there is provided a variable geometry turbine comprising a turbine wheel mounted for rotation about a turbine axis within a turbine chamber defined by a housing, the chamber having an annular inlet, the annular inlet including: a first inlet passage which extends from an outer diameter to an inner diameter and which is defined between first and second inlet passage sidewalls; and a second inlet passage which extends from an outer diameter to an inner diameter; wherein the second inlet passage is axially displaced from the first inlet passage; and wherein the turbine further comprises a generally cylindrical sleeve for varying the size of the annular inlet, the sleeve being movable in a first direction to increase the size of the annular inlet; wherein the inner diameter of the sleeve is greater than the inner diameter of at least one of the first and second inlet passages; wherein the sleeve is movable in the first direction from a first position to an opening position of the second inlet passage, during which movement the second inlet passage is closed; wherein, when the sleeve is in the opening position, a cross-sectional area of an opening to the first inlet passage defined between a free, first end of the sleeve and the first inlet passage sidewall is substantially equal to the minimum cross-sectional area of the first inlet passage; and wherein movement of the sleeve in the first direction beyond the opening position of the second inlet passage serves to initiate opening of the second inlet passage.

The first direction may be an opening direction. The opening position of the second inlet passage may be described as the position of the sleeve beyond which movement of the sleeve in the first direction will cause the second inlet passage to become open from being closed.

When the sleeve is located at the opening position of the second inlet passage, the first end of the sleeve may be substantially axially aligned with an inlet passage sidewall which, at least in part, defines the second inlet passage.

The first and second inlet passage sidewalls may be axially spaced.

The first direction may be a direction which is substantially parallel to the turbine axis.

The first and second inlet passages may both have a cross-sectional shape which is substantially the same.

The first and second inlet passages may both form part of an array of inlet passages.

The inner diameter of the sleeve may be greater than the outer diameter of at least one of the first and second inlet passages.

The minimum cross-sectional area of the first inlet passage may be the cross-sectional area of the first inlet passage at the inner diameter of the first inlet passage.

The first and second inlet passage sidewalls may be substantially parallel to one another.

The first and second inlet passage sidewalls may diverge as they extend towards the turbine axis.

The cross-sectional area of the opening when the sleeve is at a fully open position, in which the first end of the sleeve is axially aligned with the second inlet passage sidewall, may be substantially equal to the minimum cross-sectional area of the first inlet passage.

The first and second inlet passage sidewalls may converge as they extend towards the turbine axis.

The outside diameter of the second inlet passage may be axially displaced from the outside diameter of the first inlet passage by a distance which is substantially equal to the minimum cross-sectional area of the first inlet passage multiplied by an axial height of the first inlet passage and divided by the cross sectional area of the first inlet passage at the outside diameter, wherein the axial height is the axial distance between the first inlet passage sidewall and the second inlet passage sidewall at the outside diameter of the first inlet passage.

The first inlet passage may form part of a first axial array of inlet passages, wherein there are a plurality of inlet passages in the first axial array of inlet passages and wherein all the inlet passages which are part of the first axial array of inlet passages have substantially the same shape.

The second inlet passage may form part of a second axial array of inlet passages, wherein there are a plurality of inlet passages in the second axial array of inlet passages and wherein all the inlet passages which are part of the second axial array of inlet passages have substantially the same shape.

The turbine may further comprise an inlet sidewall away from which the sleeve moves in the first direction in order to increase the size of the annular inlet, and wherein the turbine further comprises a third inlet passage which extends radially inboard from an outer diameter to an inner diameter and which is adjacent the inlet sidewall; wherein the third inlet passage has a height at its outside diameter in a direction parallel to the first direction which is greater than the height of the first inlet passage at its outside diameter in a direction parallel to the first direction; and wherein the height of the third inlet passage at its outside diameter in a direction parallel to the first direction is greater than the height of the third inlet passage at its inside diameter in a direction parallel to the first direction.

According to a second aspect of the invention there is provided a method of designing a variable geometry turbine according to any preceding claim, the method including determining a desired axial displacement between the outside diameters of the first and second inlet passages; and determining a cross-sectional shape and relative positioning of both the first and second inlet passages such that the opening position of the sleeve is displaced from a third position of the sleeve in which the sleeve substantially fully closes the first inlet passage by a distance which is substantially equal to the desired axial displacement between the outside diameters of the first and second inlet passages.

Specific embodiments of the present invention will now be described, with reference to the accompanying drawings.

Figure 1 is an axial cross-section through a known turbocharger including a variable geometry turbine; Figure 2 is a schematic representation of a radial view around a portion of the circumference of an annular inlet of the turbine illustrated in Figure 1; Figure 3 is an axial cross-section through part of a turbocharger including a variable geometry turbine in accordance with a known embodiment of a variable geometry turbocharger; Figures 4a and 4b illustrate detail of the nozzle assembly of the turbine of Figure 3; Figure 5 is a schematic representation of a radial view around a portion of the circumference of the annular inlet of the nozzle assembly of Figures 4a and 4b; Figure 6 shows the schematic illustration of Figure 5 modified to show a sleeve forming part of the nozzle assembly of Figures 4a and 4b; Figure 7 shows a schematic axial cross-section through a portion of the inlet of the turbine of Figure 3; Figure 8 is a schematic graph of flow through an inlet passageway of the inlet of the turbine of Figure 3; Figure 9 is a schematic graph of total flow through the inlet of the turbine of Figure 3; Figure 10 shows several inlet passage configurations which may form part of inlets according to known embodiments of variable geometry turbochargers; Figure 11 shows a schematic graph of flow through an inlet passageway of the inlet of several turbines, each turbine having a different inlet passageway configuration according to those shown in figure 10; Figure 12 shows a schematic graph of total flow through a turbine inlet having one of the inlet passage configurations shown in figure 10; Figures 1 3a and 1 3b show two separate schematic representations of a radial view around a portion of the circumference of an annular inlet which forms part of a turbine according to the present invention; Figure 14 shows a schematic graph of flow through an inlet passageway of an inlet having an inlet passage configuration as shown in either Figure 1 3a or Figure 1 3b; Figure 15 shows a schematic graph of total flow through the inlet of a turbine having an inlet passage configuration as shown in either Figure 13a or Figure 13b; Figure 16 shows a schematic representation of a further inlet passage configuration which may form part of an inlet of a turbine according to an embodiment of the present invention.

Figure 17 shows a schematic graph of flow through an inlet passageway of an inlet having an inlet passage configuration as shown in Figure 16; Figure 18 shows a schematic graph of total flow through the inlet of a turbine having an inlet passage configuration as shown in Figure 16; Figure 19 shows a schematic axial cross-section through a portion of an inlet according to a further embodiment of the present invention; Figure 20 shows four separate schematic representations of radial views around a portion of the circumference of several annular inlets having the structure shown in Figure 19 and which may form part of an embodiment of the present invention; Figure 21 shows a schematic graph of total flow through the inlet of a turbine according to an embodiment of the present invention and having a configuration as shown in Figure 19; Figure 22 shows a schematic axial cross-section through a portion of an inlet according to a further embodiment of the present invention; Figure 23 shows two separate schematic representations of radial views around a portion of the circumference of several annular inlets having the structure shown in Figure 22 and which may form part of an embodiment of the present invention; Figure 24 shows a graph of flow through several portions of an inlet of a turbine as shown in figures 22 and 23; Figure 25 shows two further separate schematic representations of radial views around a portion of the circumference of two annular inlets having the structure shown in Figure 22 and which may form part of an further embodiments of the present invention; Figure 26 shows a graph of flow through several portions of an inlet of a turbine as shown in 25; Figure 27a and 27b show schematic representations of radial views around a portion of the circumference of an annular inlet (at an outside diameter and an inside diameter of the inlet respectively) which may form part of a further embodiment of the present invention; Figure 28 shows a schematic axial cross-section through a portion of an annular inlet as shown in Figures 27a and 27b; Figure 29 shows a schematic graph of flow through several portions of an inlet of a turbine as shown in Figure 28; Figure 30 shows an alternative inlet passage configuration which may form part of an inlet of a turbine according to a further embodiment of the present invention; Figure 31 shows a schematic axial cross-section through a portion of an annular inlet according to a further embodiment of the present invention; Figure 32 shows a schematic representation of radial view around a portion of the circumference of an annular inlet having the structure shown in Figure 31; Figure 33 shows a schematic graph of flow through several inlet passageways of an inlet having an inlet passage configuration as shown in Figure 32; Figure 34 shows a schematic graph of flow through several portions of an inlet of a turbine as shown in Figures 31 and 32; Figure 35 shows a schematic representation of radial view around a portion of the circumference of a further annular inlet having the structure shown in Figure 31; and Figure 36 shows a schematic graph of flow through several portions of an inlet of a turbine having the structure shown in Figure 35.

Referring to Figure 1, this illustrates a known turbocharger comprising a variable geometry turbine housing 1 and a compressor housing 2 interconnected by a central bearing housing 3. A turbocharger shaft 4 extends from the turbine housing 1 to the compressor housing 2 through the bearing housing 3. A turbine wheel 5 is mounted on one end of the shaft 4 for rotation within the turbine housing 1, and a compressor wheel 6 is mounted on the other end of the shaft 4 for rotation within the compressor housing 2. The shaft 4 rotates about turbocharger axis 4a on bearing assemblies located in the bearing housing.

The turbine housing 1 defines a volute 7 to which gas from an internal combustion engine (not shown) is delivered. The exhaust gas flows from the volute 7 to an axial outlet passageway 8 via an annular inlet 9 and turbine wheel 5. The inlet 9 is defined between sides walls, one sidewall being surface 10 of a radial wall of a movable annular nozzle ring wall member 11 and on the opposite sidewall being an annular shroud plate 12. The shroud 12 covers the opening of an annular recess 13 in the turbine housing 1.

The nozzle ring 11 supports an array of circumferentially and equally spaced nozzle vanes 14 each of which extends across the full axial width of the inlet 9. The nozzle vanes 14 are orientated to deflect gas flowing through the inlet 9 towards the direction of rotation of the turbine wheel 5. When the nozzle ring 11 is proximate to the annular shroud 12, the vanes 14 project through suitably configured slots in the shroud 12, into the recess 13.

An actuator (not shown) is operable to control the position of the nozzle ring 11 via an actuator output shaft (not shown), which is linked to a stirrup member 15. The stirrup member 15 in turn engages axially extending guide rods 16 that support the nozzle ring 11. Accordingly, by appropriate control of the actuator (which may for instance be pneumatic or electric or any other suitable type), the axial position of the guide rods 16 and thus of the nozzle ring 11 can be controlled. It will be appreciated that details of the nozzle ring mounting and guide arrangements may differ from those illustrated.

The nozzle ring 11 has axially extending radially inner and outer annular flanges 17 and 18 that extend into an annular cavity 19 provided in the turbine housing 1. Inner and outer sealing rings 20 and 21 are provided to seal the nozzle ring 11 with respect to inner and outer annular surfaces of the annular cavity 19 respectively, whilst allowing the nozzle ring 11 to slide within the annular cavity 19. The inner sealing ring 20 is supported within an annular groove formed in the radially inner annular surface of the cavity 19 and bears against the inner annular flange 17 of the nozzle ring 11. The outer sealing ring 20 is supported within an annular groove formed in the radially outer annular surface of the cavity 19 and bears against the outer annular flange 18 of the nozzle ring 11.

Gas flowing from the inlet volute 7 to the outlet passageway 8 passes over the turbine wheel 5 and as a result torque is applied to the shaft 4 to drive the compressor wheel 6. The turbine wheel 5, shaft 4 and compressor wheel hence rotate about the turbocharger axis 4a, which may also be referred to as the turbine axis. Rotation of the compressor wheel 6 within the compressor housing 2 pressurises ambient air present in an air inlet 22 and delivers the pressurised air to an air outlet volute 23 from which it is fed to an internal combustion engine (not shown). The speed of the turbine wheel 5 is dependent upon the velocity of the gas passing through the annular inlet 9. For a fixed rate of mass of gas flowing into the inlet 9, the gas velocity is a function of the width of the inlet 9, the width being adjustable by controlling the axial position of the nozzle ring 11. (As the width of the inlet 9 is reduced, the velocity of the gas passing through it increases.) Figure 1 shows the annular inlet 9 fully open. The inlet passageway 9 may be closed to a minimum by moving the nozzle ring 11 towards the shroud 12.

Referring to Figure 2, this is a schematic representation of a radial view around a portion of the circumference of the annular inlet 9 of the turbine of Figure 1, un-rolled and laid flat in the plane of the paper. In this representation the nozzle ring 11 is in a fully open position such that parallel lines 11 and 12 represent the nozzle ring 11 and shroud plate 12 respectively, and parallel lines 14 represent the leading edges of the nozzle vanes 14 which extend across the inlet 9. The dimension c is a portion of the circumference of the inlet 9, and the dimension w is the maximum width of the annular inlet 9. Arrow A indicates the direction of the turbine axis. From Figure 2 it can be seen that the vanes 14 divide the annular inlet 9 into an annular array of circumferentially adjacent inlet passages 14a. Each inlet passage 14a extends generally radially, but with a forward sweep (with decreasing radius) resulting from the configuration of the vanes 14 which as mentioned above is designed to deflect the gas flow passing through the inlet 9 towards the direction of rotation of the turbine wheel.

The geometry of each of the inlet passages 14a, which extend across the full width w of the inlet 9, is defined by the configuration and spacing of the vanes 14, but as shown have a generally rectangular cross-section.

Figure 3 is a cross-section through part of a further known turbocharger including a variable geometry turbine. Where appropriate corresponding features of the turbochargers of Figure 1 and Figure 3 are identified with the same reference numbers. References to axial' and axially" are to be understood as referring to the axis of rotation of the turbine wheel. Figure 3 shows the bearing housing 3 and turbine housing 4 of the turbocharger, with the compressor (not shown) removed. As with the known turbocharger of Figure 1, a turbocharger shaft 4 extends through the bearing housing 3 to the turbine housing 1 and a turbine wheel 5 is mounted on one end of the shaft 4 within the turbine housing 1. The turbine housing 1 defines a volute 7 from which exhaust gas flow is delivered to an annular inlet 9 which surrounds the turbine wheel 5.

The size of the inlet 9 is variable by controlling the position of an axially sliding cylindrical sleeve 30 which is supported on guide rods 31 which are slidably mounted within a cavity 19 defined by the bearing housing 3. The guide rods 31 may have a configuration substantially the same as that of the guide rods 16 illustrated in Figure 1, and be actuated in the same way via a yoke (not shown) linked to inboard ends 31 a of the guide rods 31. Outboard ends 31a of the guide rods 31 are connected to radially extended flanges 30a of the sleeve 30. Respective separate flanges 30a maybe provided for connection to the guide rods 31 as illustrated, or the sleeve 30 may comprise a single annular radially extending flange which is connected to the guide rods 31. The sleeve 30 has a free end which projects into the inlet 9 so that the width of the inlet can be varied in a controlled manner by appropriate movement and positioning of the sleeve 30 via the guide rods 31.

The inlet 9 is, at least in part, defined between facing sidewalls of the turbine housing which in this embodiment comprise nozzle rings 32 and 33 of a nozzle assembly 34. The nozzle assembly 34 is shown in greater detail in Figures 4a and 4b (together with a section of the sleeve 31, and a guide rod 31). The first nozzle ring 32 of the nozzle assembly 34 extends radially across the opening of the cavity 19 of the turbine housing to the sleeve 30. Seal ring 35 seals the nozzle ring 32 with respect to the sleeve 30 to prevent gas leakage between the inlet 9 and the cavity 19. Similarly, a seal ring 36 seals the nozzle ring 32 with respect to the turbine housing adjacent a radial inner periphery of the nozzle ring 32. The second nozzle ring 33 of the nozzle ring assembly 34 is fixed to a radial wall of the turbine housing, within a shallow annual recess defined by the turbine housing and is sealed with respect thereto by seal ring 36 to prevent gas leakage between the nozzle ring 33 and the turbine housing.

An annular array of circumferentially equispaced nozzle vanes 37 extend between the first and second nozzle rings 32 and 33. The nozzle vanes 37 divide the annular inlet into circumferentially spaced inlet portions. Radially extending annular inlet baffles 38a, 38b and 38c are axially equispaced between the nozzle rings 32 and 33 and further divide the annular inlet 9 into axially spaced inlet portions. The baffles 38 are relatively thin rings coaxial with the turbine axis and orientated parallel to the nozzle rings 32 and 33 so that they have radially extending laces. Accordingly, the vanes 37 together with the inlet baffles 38a-38c divide the annular inlet 9 into a plurality of discrete inlet passages 39 (not all of which are individually referenced in the drawings) which is best illustrated in Figure 5 which is a schematic representation of a radial view of an un-rolled portion of the circumference of the nozzle assembly 34 corresponding to the representation of the known inlet structure shown in Figure 2.

The vanes 37 and/or inlet baffles 38a-38c may be referred to as inlet passage sidewalls. Again the dimension w is the full width of the inlet 9 and the dimension c is a portion of the circumference of the inlet.

Referring to Figure 5, the vanes 37, and inlet baffles 38a-38c, divide the inlet 9 into four axially spaced annular arrays of circumferentially spaced inlet passages 39a, 39b, 39c and 39d respectively. In contrast, the known arrangement of Figure 2 has a single annular array of circumferentially spaced inlet passages, each of which extends across the full width of the inlet 9. The exact configuration of the inlet passages 39a to 39d is defined by the configuration of the vanes 37 and baffles 38a to 38c, but as illustrated it can be seen that the passages have a generally rectangular (in this case nearly square) cross section. Each of the inlet passages 39a -39d directs gas flow to the turbine wheel, and due to the sweep of the vanes 37 turns the gas flow in a direction towards to the direction of the rotation of the turbine wheel 5. In this embodiment the inlet passages 39 in each annular array are circumferentially adjacent and each annular array 39a to 39d is axially adjacent to the next. It is also the case that inlet passages from each of the annular arrays of inlet passages 39a, 39b, 39c and 39d which are aligned with one another in the axial direction A form axial arrays of inlet passages (for example 39e).

As described above, the size of the inlet 9 is controlled by adjustment of the axial position of the sleeve 30 which slides over the outside diameter of the vanes and baffles. Depending upon the positioning of the sleeve 30, one or more of the axially spaced annular arrays of inlet passages 39a-39d may therefore be blocked or partially blocked to gas flow through the inlet 9. For instance, Figure 4a illustrates the sleeve 30 in an almost fully open position in which the first annular array of gas flow passages 39a is partially blocked to gas flow, and the second to fourth annular arrays of inlet passages 39b-39d are fully open to gas flow. Figure 4b (and Figure 3), show the sleeve 30 in a fully closed position in which the end of the sleeve 30 bears against the nozzle ring 33 and all four of the axially adjacent annular arrays of inlet passages 39a- 39d are closed (subject to the potential for a minimum amount of leakage into the inlet passages 39d between the sleeve 30 and the nozzle ring 33).

By controlling the position of the sleeve 30 between the open and closed positions, a selected number of the axially adjacent annular arrays of inlet passages 39a-39d may be opened or blocked, or partially opened/blocked. For instance, by positioning the sleeve 30 so that the free end of the sleeve is axially aligned with the first inlet baffle 38a, the first annular array of inlet passages 39a is closed and the second to fourth annular arrays of inlet passages 39b-39d are fully opened to gas flow.

Similarly, by positioning the free end of the sleeve 30 part way between inlet baffles 38b and 38c the first and second annular arrays of inlet passages 39a and 39b will be fully closed, the fourth annular array of inlet passage 39d will be fully open and the third annular array of inlet passages 39c will be partially open. This is schematically illustrated in Figure 6 which superimposes the sleeve 30 on the view shown in Figure 5.

The sleeve 30 can fully close the inlet, i.e. block the inlet 9 completely. In other embodiments the sleeve need not necessarily be capable of closing the inlet fully, but might have a "closed' or "fully closed" position in which at least one annular array of inlet passages 39 is at least partially open. For instance, the free end of the sleeve could be provided with axially extending lands which provide a hard stop for the closed position of the sleeve, with flow gaps defined between lands around the circumference of the sleeve.

In this embodiment, the increased acceleration of the gas flow is achieved by reducing the size of the inlet 9 upstream of the inlet passages 39. In the absence of inlet baffles 38, gas accelerating past the end of the sleeve 30 will expand axially across the full width of the inlet 9 before it reaches the turbine wheel 5. This would result in substantial loss of energy in the gas flow as it passes through the inlet which may largely negate the desired effect of constricting the inlet. Accordingly, such a variable geometry turbine could be expect to be very inefficient and thus impractical for many applications, such as for instance for use in a turbocharger turbine. With the present invention, as the sleeve 30 moves beyond the first and subsequent inlet baffles, the volume of the inlet 9 within which the gas can expand is reduced which similarly reduces the potential for loss in energy by expansion of the gas flow within the inlet 9 upstream of the turbine wheel. This in turn significantly improves the efficiency of the inlet. As the free end of the sleeve aligns with a given inlet baffle it is effectively equivalent to a moving radial wall member. Between these locations it is possible there may be a drop off in efficiency but this will not be to the same extent as would be experienced in the absence of any inlet baffles. Surprisingly, simulations suggest that the inlet structure of the present invention has even better efficiency than some known moving wall inlet structures, particularly at smaller inlet widths.

The turbine according to the embodiment illustrated in Figures 3 to 6 also has a number of other advantages over the known moving nozzle ring turbine shown in Figure 1. With the present invention there are considerably reduced pressure and aerodynamic forces on the sleeve compared to those acting on a radial wall. For instance, the axial force imposed on the sleeve 30 by air flow through the inlet is much less than that imposed on a moveable radial wall. This allows the use of a smaller, less robust actuator, and also a less robust linkage between the actuator and the sleeve, as the axial force required to move the sleeve and hold it in position is much less than that required to control the position of a radial wall. Smaller, less robust actuators/linkages may weigh less and cost less than more heavy or robust actuators/linkages. The reduction in axial forces on the sleeve compared to those experienced by a radial wall also simplifies accurate control of the size of the inlet.

Employing a cylindrical sleeve as the moving component for varying the inlet size, instead of a moving radial wall, also avoids the need to provide slots to receive the vanes as the inlet width is reduced, which is a requirement of known inlet structures comprising a moving nozzle ring (as illustrated for instance in Figure 1) and also of alternative known structures in which the vanes are fixed and a slotted shroud is moved axially over the vanes to vary the inlet width. The embodiment illustrated in Figures 3 to 6 thus eliminates many of the interface requirements between the moving component and the vane array which in turn increases manufacturing tolerances.

Absence of such slots also reduces the possibility of gas leakage around the vane array and simplifies sealing requirements.

Known devices comprising a moveable nozzle ring in which the moving wall member includes the vanes, for instance as shown in Figure 1, also experience significant torque as the gas flow is deflected by the vanes. With the present invention there is no such torque on the moving component which further reduces the force on the actuator and actuator linkages.

Figure 7 shows an axial schematic cross-section of a portion of the turbine of the turbocharger shown in Figure 3. In common with the positioning of the sleeve within Figure 6, the sleeve 30 within Figure 7 is positioned such that the free end of the sleeve is partway between inlet baffles 38b and 38c. In this position of the sleeve 30, the first and second annular arrays of inlet passages 38a and 39b will be fully closed, the fourth annular array of inlet passages 39b will be fully open and the third annular array of inlet passages 39c will be partially open. As previously discussed, when a inlet passage 39 is open or partially open, gas flows from the volute of the turbine through the said inlet passage to a turbine chamber 40 which contains the turbine wheel (not shown in Figure 7). It can be seen within Figure 7 that the inlet baffles 38a, 38b, 38c which define the annular arrays of inlet passages 39a, 39b, 39c and 39d are substantially parallel to one another. Consequently, the inlet passages of the annular arrays of inlet passages 39a, 39b, 39c and 39d are also substantially parallel to one another. Each inlet passage 39, as shown most clearly in Figure 5, has a generally square-shaped cross-section.

Due to the fact that the diameter (defined relative to the turbine axis) of the inlet at its outer diameter (adjacent the sleeve 30) indicated generally by 41 is greater than the diameter of the inner diameter 42 of the inlet, each inlet passage 39 tapers inwards (in a plane perpendicular to the turbine axis) as the inlet passage moves from the outside diameter 41 to the inside diameter 42. That is to say that the circumferential width (i.e., the width along a circumferential path around the turbocharger axis) of each inlet passage decreases from a maximum at the outside diameter of the inlet to a minimum at the inside diameter 42 of the inlet. For an individual inlet passage, the portion of the inlet passage which is located at the outside diameter of the inlet may be referred to as the outside diameter of the inlet passage; and the portion of the inlet passage which is located at the inside diameter of the inlet may be referred to as the inside diameter of the inlet passage.

Figure 8 shows a graph of flow (F) through a single first inlet passage 39 against sleeve position (P). At the left hand side of the graph the sleeve position P is equal to 0. In this sleeve position P the free end of the sleeve 30 is axially aligned with a first inlet baffle 38 (which may also be referred to as an inlet passage sidewall of the first inlet passage) such that the first inlet passage 39 is substantially blocked by the sleeve 30. Consequently, when the sleeve position P is equal to 0 the flow F of gas through the first inlet passage 39 is also substantially 0. Moving across the graph shown in Figure 8 from left to right the sleeve position P increases. That is to say, that as the sleeve position P is increased, this represents a movement of the sleeve such that the axial distance between the free end of the sleeve and the previously mentioned first inlet baffle 38 increases. A movement of the sleeve 30 such that the sleeve position P increases is an axial movement of the sleeve 30 in a direction indicated by arrow I within Figure 7. It may also be said that increasing the sleeve position P (i.e., moving from the left to the right in the graph of Figure 8) is equivalent to moving the sleeve 30 such that the first inlet passage 39 is opened or further opened.

It can be seen within the graph of Figure 8 that, as the sleeve position P is increased, the flow through the first inlet passage 39 also increases up until a sleeve position P indicated by PG. PG may be referred to as the critical position of the sleeve.

The sleeve position P which is indicated in the graph as PF is the position of the sleeve in which the free end of the sleeve 30 is axially aligned with a second inlet baffle which is axially adjacent to the first inlet baffle. The second inlet baffle is a second inlet passage sidewall of the first inlet passage. It can be seen that as the sleeve position P increases between P0 and Pthere is substantially no change in the amount of gas flow F through the inlet passage 39. The reason for this is discussed below.

As previously discussed, the circumferential width of each inlet passage decreases from the outside diameter 41 of the inlet passage to the inside diameter 42 of the inlet passage 39. As a consequence of this, the cross-sectional area of the inlet passage 39 (i.e., the area of the inlet passage 39 perpendicular to the direction of flow of gas through the inlet in use) is a minimum at the inside diameter of the inlet passage 39. For the sake of clarity, within the current description, the flow of gas through the turbine inlet (and consequently through the inlet passages) is assumed to be substantially radial with respect of the turbocharger axis, although as previously discussed, the flow of gas through the inlet may be generally spiral shaped in a direction towards the turbine axis. The minimum cross-sectional area of the inlet passage 39 which is at the inside diameter 42 of the inlet passage 39 may be referred to as the throat area of the inlet passage.

The throat area of the inlet is the minimum cross-sectional area of the inlet.

That is to say, the throat area of the inlet is the minimum cross-sectional area of the inlet through which gas will pass as it moves from the volute, through the inlet and into the turbine chamber. Similarly, the throat area of an inlet passage is the minimum cross-sectional area of the inlet passage through which gas will pass as it travels from the volute, through the inlet passage, and into the turbine chamber.

As the sleeve 30 moves such that the sleeve position P increases (i.e., so that the axial distance between the free end of the sleeve 30 and the first inlet baffle increases), the cross-sectional area of the inlet passage at its outside diameter 41, defined between the free end of the sleeve 30 and the first inlet baffle, increases. The cross-sectional area of the inlet passage which is defined between the free end of the sleeve 30 and the first inlet baffle will henceforth be referred to as the sleeve-defined cross-sectional area of the inlet passage. As the sleeve-defined cross-sectional area of the inlet passage increases there is a greater area through which gas can flow as it moves from the volute of the turbine into the inlet passage. Increasing the cross-sectional area through which gas can enter the inlet passage from the volute increases the flow F of gas through the inlet passage. There is a linear relationship between the position of the sleeve P and the flow F of gas through the inlet passage due to the fact that the inlet passage is shaped such that at its outside diameter 41 the inlet passage has a constant circumferential width which does not vary in the axial direction (i.e., in the direction of movement of the sleeve).

When the sleeve (and hence the free end of the sleeve) is at sleeve position P0 the sleeve-defined cross-sectional area of the inlet passage is equal to the throat area of the inlet passage. If the sleeve position P is increased past Pc towards PF then the sleeve-defined cross-sectional area of the inlet passage will increase. However, due to the fact that the throat area of the inlet passage is fixed, increasing the outside cross-sectional area of the inlet passage will not have any effect on the amount of gas which flows through the inlet from the inlet volute to the turbine chamber. Consequently, the flow F of gas through the inlet passage remains substantial constant as the sleeve position P increases past P3.

Figure 9 shows a graph of total flow FT through the inlet having a structure as shown in Figures 3 to 7 against sleeve position P. The total flow F1 through the inlet is the total of the flow through all of the individual inlet passages at any given moment. In the current embodiment, due to the fact that the inlet has annular arrays of axially aligned inlet passages and due to the fact that the sleeve moves in an axial direction, at any given moment the outside cross-sectional area of each inlet passage within a particular annular array of (axially aligned) inlet passages will be substantially the same.

The graph in Figure 9 shows that as the sleeve position P increases from 0 (i.e., when the sleeve is in a fully closed position), the total flow through the inlet F1 increases in a substantially linear manner until the sleeve position is P3. As previously discussed, when the sleeve is at the position P0 (i.e., the critical position of the sleeve) the sleeve-defined cross-sectional area of each of the inlet passages in the fourth annular array 39d of inlet passages is substantially equal to the throat area of each of the respective inlet passages 39. As the sleeve position P increases from P to PE (in which the free end of the sleeve is axially aligned with the third baffle 38c), there is no increase in flow through each of the inlet passages 39 of the array of inlet passages 39d as previously discussed. Consequently there is no increase in total flow F1 through the inlet. As the sleeve position increases from PF there is a linear increase in total flow F1 through the inlet due to the fact that the sleeve-defined cross-sectional area of each of the inlet passages 39 of the third annular array of inlet passages 39c increases as the sleeve 30 moves in an opening direction (I). Again, once the sleeve position P reaches a critical position P31 (i.e. the critical position in relation to flow through the third annular array of inlet passages), there is no further increase in flow through any of the inlet passages of the third annular array of inlet passages 39c, and hence no further increase in total flow FT through the inlet. There is no further increase in total flow F-1-through the inlet until the sleeve 30 moves past the fully open position PF1 relating to the third annular array of inlet passages 39c in which the free end of the sleeve 30 is axially aligned with the second baffle 38b. As previously discussed, the reason that there is no increase in total flow F1 as the sleeve is moved between the second critical position P01 of the sleeve 30 and the second fully open position PF1 is because when the sleeve is in the second critical position P01, the outside cross-sectional area of each of the inlet passages of the third annular array of inlet passages 39c is substantially equal to the throat area of each of the respective inlet passages of the third annular array of inlet passages.

Likewise to that discussed above, the total flow F1 through the inlet increases between the second fully open position FF1 and a third critical position P02. Similarly, the total flow F-1-through the inlet increases as the position P of the sleeve moves from a third fully open position PF2 of the sleeve and a fourth critical position P03 of the sleeve. In common with the total flow F1 through the inlet in relation to a change in the position of the sleeve between the critical position P0 and the fully open position PF, and between the second critical position P01 and the second fully open position PF1; there is no change in total flow FT through the inlet as the sleeve position P moves from the third critical position P32 and the third fully open position P2, and from the fourth critical position P03 to the fourth fully open position PF3. The third critical position P02 is the position at which the sleeve-defined cross-sectional area of each of the inlet passages of the second annular array of inlet passages 39b is substantially equal to the throat area of each of said inlet passages of the second annular array of inlet passages. At the third fully open position PF2 of the sleeve, the free end of the sleeve is substantially aligned with the first inlet baffle 38a. In the fourth critical position P03 of the sleeve, the sleeve-defined cross-sectional area of each of the inlet passages of the first annular array of inlet passages 39a is substantially equal to the throat area of each of said inlet passages of the first annular array of inlet passages. At the fourth fully open position PF3 of the sleeve 30 is substantially aligned with the inlet sidewall 32.

The trend shown in the graph of Figure 9 which relates sleeve position P to total flow F1 through the inlet may be referred to as a step-wise trend whereby between some sleeve positions there is no change in the total flow F1 through the inlet, and between other sleeve positions there is an increase in total flow F1 through the inlet with increasing sleeve position P. This step-wise trend may be disadvantageous in certain applications of the turbine. For example, if a turbine controller is linked to an actuator controlling the sleeve position, and if it is desired to actuate the sleeve to a position which will result in a specific total flow through the inlet of the turbine, the turbine controller will have to hunt so as to find the required sleeve position. Hunting for the desired sleeve position may involve the turbine controller actuating the sleeve actuator so that the position of the sleeve moves through at least one of the portions of the trend (relating total flow through the inlet to sleeve position) in which there is substantially no change in total flow through the inlet with a change in sleeve position.

This may lead to the actuator requiring additional time and/or power in order to move the sleeve to the desired position (i.e., the time and/or power which is required to enable the actuator to move through the at least one portion of the trend in which the total flow through the inlet is substantially constant with changing sleeve position).

Furthermore, the step-wise trend relating total flow through the inlet to sleeve position may reduce the accuracy with which the sleeve can be positioned by the actuator so as to achieve a desired total flow through the inlet. The present invention may seek to obviate or mitigate one of these disadvantages.

The gas passages 39 of the embodiment discussed in relation to Figures 3 to 9 are generally rectangular. In addition, the inlet passages 39 are arranged such that there is no axial overlap between each of the arrays of inlet passages. Figure 10 shows three alternative inlet passage configurations which may replace the inlet passage configuration (as seen most clearly in Figure 5) of the previously described embodiment. As before, the inlet passage configurations 50, 52 and 54 are shown as schematic representations of a radial view around a portion of the circumference of a respective annular inlet of the turbine. It will be appreciated that, in order to aid simplicity, the inlet passage configuration of only a small portion of a respective inlet is shown within the configurations 50, 52 and 54 as shown in Figure 10. The type of inlet passage configuration shown in each of the inlet passage configurations 50, 52 and 54 shown in Figure 10 may be referred to generically as a honeycomb inlet passage configuration.

It can be seen that each of the inlet passages 50a of the inlet passage configuration 50 is generally diamond-shaped (i.e has a generally diamond shaped cross-section). Furthermore, the inlet passages 52a and 54a of respective inlet passage configurations 52 and 54 are generally hexagonal.

Common to each of these honeycomb inlet passage configurations 50, 52 and 54, there is axial overlap between adjacent annular arrays of inlet passages. This is explained in more detail below. The axial direction when any of the inlet passage configurations is located within the inlet of a turbine is indicated by the arrow A. The inlet passage configurations 50 and 52 may be considered to show inlet passages (SOa and 52a respectively) which form part of three axially spaced annular arrays of inlet passages. Turning first to the inlet passage configuration 50, inlet passage 501 forms part of a first annular array of inlet passages. Inlet passages 502 and 503 form part of a second annular array of inlet passages. Inlet passage 504 forms part of a third annular array of inlet passages. It can be seen that the first, second and third annular arrays of inlet passages are axially displaced from one another.

Turning now to the inlet passage configuration 52, as previously discussed, the substantially diamond-shaped cross-section of the inlet passages in the inlet passage configuration 50 has been replaced by substantially hexagonally-shaped cross-section inlet passages. For the sake of completeness, inlet passage 521 forms part of a first annular array of inlet passages; inlet passages 522 and 523 form part of a second annular array of inlet passages; and inlet passage 524 forms part of a third annular array of inlet passages. As before, the first, second and third annular arrays of inlet passages are axially displaced from one another.

Finally, in relation to inlet passage configuration 54, inlet passages which form part of two axially spaced annular arrays of inlet passages are shown. Specifically, inlet passages 541 and 542 form part of a first annular array of inlet passages and inlet passages 543 and 544 form part of a second annular array of inlet passages. Again, the first and second annular arrays of inlet passages are axially spaced.

As previously mentioned, each of the inlet passage configurations 50, 52 and 54 contain inlet passages which axially overlap. In other words, in each of the inlet passage configurations 50, 52 and 54, the respective inlet passages of each inlet passage configuration overlap in the axial direction A with at least one other inlet passage of the respective inlet passage configuration. Due to the fact that the inlet passages of the inlet passage configurations 50, 52 and 54 axially overlap, and due to the fact that the sleeve moves in an axial direction, when the sleeve moves in a direction so as to open the inlet (for example direction A within the Figure 10 and/or direction I in Figure 7), then before the sleeve reaches a position in which one annular array of inlet passages is fully opened by the sleeve, the sleeve will have moved past an opening position in which the inlet passages of the adjacent annular array of inlet passages are opened by the sleeve.

Figure 10 shows that in each of the inlet passage configurations 50 and 52 each annular array of inlet passages is displaced from the axially adjacent annular array of inlet passages by a distance HA/2, where HA is the axial height (i.e. the height in the axial direction A) of each of the respective inlet passages 50a, 52a. That is to say, in each of the inlet passage configurations 50, 52 each inlet passage axially overlaps with an inlet passage in an axially adjacent array of inlet passages by a distance which is half the axial height HA of the inlet passages. Within the inlet passage configuration 54, each annular array of inlet passages is displaced from the axially adjacent annular array of inlet passages by a distance H, where H is a fraction of the axial height of each of the inlet passages 54a.

Figure 11 shows a graph showing the relationship between the flow F through a single inlet passage against sleeve position P for flow passages according to each of the flow passage configurations 50, 52 and 54 shown in Figure 10. Line 56 corresponds to an inlet passage 50a of inlet passage configuration 50; line 58 corresponds to an inlet passage 52a of inlet passage configuration 52; and line 60 corresponds to an inlet passage 54a of inlet passage configuration 54.

When the sleeve position P is equal to 0, the free end of the sleeve is aligned with the inlet passage such that the inlet passage is fully closed. When the sleeve position P is at PF, the free end of the sleeve is aligned with the inlet passage such that the inlet passage is fully open. The distance between P=0 and P=P is the axial height HA of the inlet passage. When the sleeve position P is equal to PA the free end of the sleeve is halfway between the position of the free end of the sleeve when the sleeve position is 0 and when the sleeve position is PF. At sleeve position PA, not only is a given inlet passage substantially half (or 50%) open, but also, in the case of inlet passage configurations 50 and 52, due to the fact that each annular array of inlet passages is displaced from the axially adjacent annular array of inlet passages by a distance HA/2, the inlet passages in an annular array of inlet passages adjacent to the annular array of inlet passages of which the given inlet passage forms part is opened by the sleeve. That is to say, at sleeve position PA, the free end of the sleeve is aligned with an open position of the inlet passages of the adjacent annular array of inlet passages. The reason that the free end of the sleeve, when the sleeve is at position PA (in this case half the distance between the position of the sleeve when P=0 and the position of the sleeve when P=P), is aligned with an opening position of the inlet passages of the adjacent annular array of inlet passages is because the inlet passages of each annular array of inlet passages of each configuration of inlet passages 50, 52 axially overlaps with the inlet passages of the adjacent annular array of inlet passages by half the axial height HA of the inlet passages (i.e. because each annular array of inlet passages is displaced from the axially adjacent annular array of inlet passages by a distance HA/2).

Figure 12 shows a graph of total flow F1 through an inlet having the inlet passage configuration 54 shown in Figure 10, against sleeve position P. Again, it can be seen that there is a non-linear relationship between the total flow through the inlet F1 and the position P of the sleeve. In particular, there are steep portions 62 of the relationship in which a small change in sleeve position results in a large change in total flow F1 through the inlet. Furthermore, there are shallow portions 64 of the relationship in which, compared to the steep portion 62, a relatively small change in sleeve position P results in a relatively small change in the total flow F1 through the inlet.

The non-linear relationship between the sleeve position P and the total flow F1 through the inlet means that it is difficult for a turbine controller, which controls an actuator so as to select a desired sleeve position, to accurately select said desired sleeve position. In particular, very fine adjustments to the sleeve position P may be required in order to select a desired total flow FT within a steep portion 62 of the relationship between sleeve position and total flow. Such fine positioning of the sleeve may not be achievable by a particular actuator/turbine controller. Alternatively, an actuator/turbine controller which is capable of the required fine control of the sleeve position may be prohibitively expensive. As before, the step-like relationship between the sleeve position P and the total flow FT through the inlet may result in the turbine controller and actuator hunting for a desired total flow F1 through the inlet. This may be disadvantageous as previously discussed.

Figures 13a and 13b show schematic representations of a radial view around portions of the circumference of two separate annular inlets which form part of two respective turbines in accordance with two respective embodiments of the present invention. Figures 13a and 13b show schematic representations of inlet passage configurations 70 and 72 un-rolled and laid flat in the plane of the paper.

Within Figure 13a the inlet passages 70a have a cross-section which is substantially rectangular-shaped. In Figure 13b the inlet passages 72a have a cross-section which is substantially parallelogram-shaped. Within the inlet passage configurations 70, 72 shown in Figures 13a and 13b, there is a first annular array of inlet passages which comprises inlet passages 74a in Figure 13a and 76a in Figure 1 3b. It can be seen that inlet passages which form part of the first annular array of inlet passages (74a in Figure 13a and 76a in Figure 13b) are axially aligned. That is to say that each inlet passage which forms part of the first annular array of inlet passages is substantially the same distance from an inlet sidewall of the turbine.

The inlet passage configurations 70 and 72 of Figures 13a and 13b respectively also have a second annular array of inlet passages which includes inlet passages 74b (in the case of Figure 13a) and inlet passages 76b (in the case of Figure 13b). Again, the inlet passages 74b, 76b in each of the second annular array of inlet passages are axially aligned.

In contrast to the annular arrays of inlet passages discussed in relation to figure in which the inlet passages of an annular array of inlet passages are contiguous with one another, the inlet passages of the annular arrays of inlet passages in the inlet passage configurations 70 and 72 of Figures 13a and 13b respectively are circumferentially spaced from one another.

Figure 14 is a schematic graph showing the shape of the relationship between sleeve position P and the flow through an inlet passage as shown in either Figure 13a or Figure 13b. If the graph of Figure 14 is compared to the graph shown in Figure 8, it can be seen that the general shape of the two graphs is the same. That is to say that there is a linear increase in flow through the inlet passage as the sleeve position P increases from P=0 to P=P0, where P3 is the critical sleeve position. As the position of the sleeve increases beyond P=P3, the flow F through the inlet passage remains substantially constant until the sleeve position reaches the fully open position PF. As previously discussed in relation to Figure 8, the reason that the flow through the inlet does not increase with increasing sleeve position beyond the critical sleeve position P0 is because beyond the sleeve position P0 the sleeve-defined cross-sectional area of the inlet passage exceeds that of the throat area of the inlet passage. Increasing the sleeve-defined cross-sectional area of the inlet passage beyond that at the critical sleeve position P3 (in which the sleeve-defined cross-sectional area of the inlet passage is substantially equal to the throat area of the inlet passage) will not increase the flow F through the inlet passage because the flow through the inlet passage is limited by the throat area of the inlet passage.

As previously discussed, the cross-sectional area of an inlet passage as shown in Figures 13a and 13b is greater at the outside diameter of the inlet passage compared to that at the inside diameter of the inlet passage. More specifically, the cross-sectional area of an inlet passage as shown in Figure 13a or Figure 13b decreases from a maximum cross-sectional area at the outside diameter to a minimum cross-sectional area at the inside diameter of the inlet passage.

Within the inlet configuration 70, 72 shown in Figures 13a and 13b, the first annular array of inlet passages is axially displaced from the second annular array of inlet passages such that the inlet passages of the first and second annular arrays of inlet passages axially overlap such that they are axially spaced from one another by a distance which is the same proportion of the axial height AH of one of the inlet passages as the ratio between the cross-sectional area of an inlet passage at the outside diameter and the cross-sectional area of the inlet passage at its inside diameter (also referred to as the throat area). That is to say, the inlet passages of the first annular array of inlet passages and the inlet passages of the second annular array of inlet passages are axially spaced from one another such that when the sleeve is at position P equal to P0 (i.e. the position of the sleeve in which the sleeve-defined cross-sectional is equal to the throat area of the inlet passage) the free end of the sleeve is substantially axially aligned with an opening position of the inlet passages of the second annular array of inlet passages. The opening position of an inlet passage may be described as the position beyond which movement of the sleeve in the opening direction will open the inlet passage. In other words, movement of the sleeve in the opening direction beyond the opening position serves to initiate opening of the inlet passage. The axial spacing between the inlet passages of the first annular array of inlet passages is the distance between sleeve position P=O and sleeve position P=P0. In other words, the spacing between the inlet passages of the first annular array of inlet passages and the inlet passages of the second annular array of inlet passages is substantially given by the product of the axial height HA and the cross-sectional area of said inlet passage at the inside diameter (i.e., the throat area) divided by the cross-sectional area of an inlet passage at the outside diameter.

For example if an inlet having an inlet passage configuration as shown in either Figure 13a or 13b had inlet passages which have an inner diameter of 80mm and an outer diameter of 100mm then, assuming that the inlet passages have substantially the same cross-sectional shape at the inside diameter and the outside diameter, the cross- sectional area of the inlet passage at the inside diameter will be 80% of the cross-sectional area of the inlet passage at the outside diameter. Consequently, if a configuration of inlet passages as shown in Figures 1 3a or 1 3b were to be used in conjunction with an inlet having these properties, the inlet passages would be configured such that the inlet passages of a particular annular array of inlet passages are spaced from the inlet passages of the axially adjacent annular array of inlet passages by a distance which is 80% of the axial height of the inlet passages. In this way, the critical position P0 of the sleeve in relation to a given inlet passage (which in this case is when the free end of the sleeve opens 80% of the cross-sectional area of the inlet passage at the outside diameter) is aligned with an opening position of an inlet passage which is axially adjacent the given inlet passage.

Figure 15 shows a schematic graph of total flow F1 through an inlet having an inlet passage configuration as shown in either Figure 13a or 13b, against sleeve position P. It can be seen that the relationship between total flow F1 through the inlet and the sleeve position P is a substantially linear one as the sleeve position P changes such that the free end of the sleeve moves across the axial extent of the inlet. The linear relationship between total flow FT through the inlet and sleeve position P may be advantageous for several reasons. Firstly, due to the fact that the relationship between total flow F1 through the inlet and sleeve position is not step-wise it will be relatively easy for a turbine controller controlling the sleeve position P using an actuator to obtain a desired total flow F-1-without requiring the turbine controller and actuator to hunt for the desired total flow FT through the inlet. Furthermore, due to the fact that the relationship between total flow through the inlet and the sleeve position is substantially linear across substantially the entire range of obtainable total flow through the inlet, it will be relatively easy for the turbine controller and actuator to accurately obtain any desired total flow F1 through the inlet.

It can be seen that, in common with any inlet passage configuration according to the present invention, the inlet passage configurations shown in Figures 13a and 1 3b show an annular inlet which includes a first inlet passage (for example an inlet passage which forms part of a first annular array of inlet passages). The first inlet passage is defined between first and second inlet passage sidewalls (75 and 77 respectively). The inlet also includes a second inlet passage (for example an inlet passage which is part of a second annular array of inlet passages). The second inlet passage (which in this case forms part of the second annular array of inlet passages) is axially displaced from the first inlet passage (which in this case forms part of the first annular array of inlet passages). The turbine of which the inlet forms part further comprises a generally cylindrical sleeve for varying the size of the annular inlet. The sleeve is moveable in a first direction (in this case a substantially axial movement A away from an inlet sidewall) so as to increase the size of the annular inlet.

Increasing the size of the annular inlet will permit more gas to flow through the inlet to the turbine chamber within which the turbine wheel is mounted. The inner diameter of the sleeve is greater than the inner diameter of at least one of the first and second inlet passages (and, in this case, the inner diameter of the sleeve is greater than the outer diameter of both the first and second inlet passages). The sleeve is moveable in the first direction A (i.e., in the direction of increasing sleeve position F) from a first position in which the second inlet passage is closed. For example, referring to Figure 14 the first position of the sleeve may be a sleeve position P which is between 0 and P3 such that the free end of the sleeve is axially aligned such that it is partway across the opening to the first inlet passage at the outside diameter of the inlet passage. In this position, the sleeve extends across the second inlet passage such that the second inlet passage is blocked (and therefore closed) by the sleeve. The sleeve is moveable in the first direction A (i.e., in a direction which is substantially axial and away from an inlet sidewall) from the first position to an opening position. In the opening position of the sleeve, the free end of the sleeve is substantially axially aligned with an inlet passage sidewall of the second inlet passage (in this case, the free end of the sleeve is substantially axially aligned with the inlet passage sidewall which at least in part defines the second inlet passage, and which is the closest of the inlet passage sidewalls defining the second inlet passage to the inlet sidewall away from which the sleeve moves in the first direction A in order to open the inlet). The opening position of the sleeve with respect to the second inlet passage (which may be referred to as the opening position of the second inlet passage) may be described as the position of the sleeve beyond which movement of the sleeve in the opening direction (i.e. first direction A) will open the second inlet passage.

Referring again to Figure 14 the opening position of the sleeve may be said to be when the sleeve is at position P0. In this position, the free end of the sleeve is substantially aligned with an opening position of the second inlet passage. In the opening position of the sleeve the cross-sectional area of the opening to the first inlet passage at the outside diameter of the first inlet passage, the opening being defined between a first end (the free end) of the sleeve and the first inlet passage sidewall, is substantially equal to the minimum cross-sectional area of the first inlet passage. In this case, the minimum cross-sectional area of the first inlet passage is the cross-sectional area of the inlet passage at the inside diameter of the inlet passage (also referred to as the throat area of the inlet passage).

Figure 16 shows an alternative inlet passage configuration 80 which may form part of an inlet of a turbine according to an embodiment of the present invention.

Within the inlet passage configurations shown in Figures 13a and 13b each of the inlet passages has a substantially constant width perpendicular to the axial direction A. Furthermore, the inlet passages are arranged such that an inlet passage and an axially adjacent inlet passage are spaced by a proportion of the axial height of the inlet passages which corresponds to the proportion of cross-sectional area of the inlet passage at the outside diameter which is the cross-sectional area of the inlet passage at the inside diameter. The configuration 80 of the inlet passages shown in Figure 16 is somewhat different and is explained further below.

Contrary to the inlet passage configuration shown in Figures 13a and 13b, the shape of the inlet passages 80a is not such that the width of each inlet passage perpendicular to the axial direction A is substantially constant. Instead, the shape of each of the inlet passages BOa is configured such that when the free end of the sleeve is aligned with a given axial position across the opening of the inlet passage, the sleeve-defined cross-sectional area when the sleeve is at said given axial position is substantially equal to the cross-sectional area of the inlet passage at the inside diameter. In the case shown in Figure 16, the axial position of the sleeve in relation to one of the inlet passages 80a at which the sleeve-defined cross-sectional area is substantially equal to the throat area of the inlet passage is when the free end of the sleeve is aligned with a position that is approximately halfway across the opening of the inlet passage in the axial direction. That is to say, each opening to the inlet passages BOa has a height HA in the axial direction and, in the embodiment shown in Figure 16, the position at which the open end of the sleeve is aligned with an inlet passage such that the sleeve-defined cross-sectional area is substantially equal to the throat area of the inlet passage is a position which is approximately halfway along the axial height HA of the inlet passage (i.e. a distance of HA/2 from the opening position of the inlet passageway).

For example, if the outside diameter of an inlet passage is 100 mm and the inner diameter of the inlet passage is 75 mm, then it will be clear that when 75% of the cross-sectional area of the inlet passage at its outer diameter is open, this is equivalent to the throat area of the inlet passage (in this case, due to the fact that the cross-sectional shape of the inlet passage is substantially the same at the inner diameter of the inlet passage and the outer diameter of the inlet passage. In fact, the cross-sectional shape of the inlet passage in this case is substantially constant along the entire length of the inlet passage). As previously discussed, the inlet passage is shaped so that when the free end of the sleeve is at a position aligned with halfway across the axial height HA of the inlet passage, the sleeve-defined cross-sectional area (i.e., the area of the inlet passage which is not blocked by the sleeve) is substantially equal to the throat area of the inlet passage.

Furthermore, the inlet passages BOa are shaped an configured such that when the sleeve is positioned such that the free end of the sleeve is axially aligned with the axial position across the opening of a given inlet passage at which the sleeve-defined cross-sectional area is substantially equal to the throat area of the inlet passage, the free end of the sleeve is also axially aligned with an opening position of an inlet passage which is axially adjacent the given inlet passage. When the free end of the sleeve is axially aligned with an opening position of an inlet passage which is axially adjacent the given inlet passage, the sleeve may be said to be in an opening position.

In the case shown in Figure 16, the inlet passages are configured such that the opening position of an axially adjacent inlet passage is substantially halfway along the axial height HA of the inlet passage to which the axially adjacent inlet passage is axially adjacent.

It will be appreciated that in other embodiments of the present invention, the shape of the inlet passages may be chosen such that the axial distance between an opening position of a given inlet passage and the position at which the sleeve-defined cross-sectional area is equal to the throat area of the inlet passage may be any appropriate distance. In this case, the shape and configuration of the inlet passages will also be chosen so that the axial displacement between the given inlet passage and an axially adjacent inlet passage is also substantially equal to the axial distance between the opening position of the given inlet passage and the position at which the sleeve-defined cross-sectional area is equal to the throat area of the inlet passage.

Figure 17 shows a schematic graph of flow F through a single inlet passage 80a as shown in Figure 16 against sleeve position P (and hence the position of the free end of the sleeve across the inlet passage). The flow F through the inlet passage increases from when the sleeve position P equals 0 (corresponding to a position of the sleeve at which the inlet passage is just fully closed) to the critical position of the sleeve P3. As previously discussed, the critical position P3 of the sleeve (i.e., the position of the sleeve at which the sleeve defined cross-sectional area is substantially equal to the throat area of the inlet passage) is located substantially halfway along the axial height HA of the inlet passage. This means that the critical position P is substantially 50% of the fully open position PF of the sleeve. The opening position of an inlet passage which is axially adjacent to the inlet passage is substantially axially aligned with the inlet passage such that it is axially aligned with the open end of the sleeve when the sleeve is at the critical position P3 of the inlet passage.

Figure 18 shows a graph of total flow FT through an inlet having the inlet passage configuration 80 as shown in Figure 16 against sleeve position P. It can be seen that the relationship between sleeve position P and total flow through the inlet FT is substantially linear (especially when compared to the relationship exhibited by the prior art shown in figures 9 and 12). The benefits of this substantially linear relationship are discussed in relation to Figure 15. It will be appreciated that although the relationship shown in Figure 18 is not completely linear, it is substantially linear to the extent that the benefits discussed in relation to the linear relationship shown in Figure 15 are still applicable. Furthermore, the inlet passage configuration 80 shown in Figure 16 may be cheaper to manufacture than either of the inlet passage configurations shown in Figures 1 3a and 1 3b.

Figure 19 shows an alternative embodiment of the present invention. The previously discussed embodiments of the present invention have had inlet passage walls which are substantially parallel to one another and, in particular, which are all substantially radial having regard to the axis of the turbine. This type of structure is illustrated schematically in Figure 7 where it can be seen that the inlet baffles 38a, 38b and 38c which define the inlet passages 39a, 39b, 39c and 39d are substantially parallel to one another and are substantially radial. The structure shown in Figure 19 differs from the structure of the previously described embodiments in that the turbine inlet has inlet passage sidewalls 82a and 82b which define inlet passages 84a, 84b and 84c such that the inlet passage sidewalls 82a and 82b and the inlet passages 84a, 84b and 84c diverge (or taper outwards) as they extend radially inwards (i.e., towards the turbine axis). The tapering of the inlet passages Ma, 84b and 84c may be chosen such that the cross-sectional area of each of the inlet passages 84a, 84b and 84c at the outside diameter 86 of the inlet (and hence of each respective inlet passage) is substantially the same as the cross-sectional area of each respective inlet passage at the inside diameter 88 of the inlet (and hence of each respective inlet passage). In some embodiments, the cross-sectional area of each inlet passage may be constant along the length of the inlet passage.

Due to the fact that the cross-sectional area of each inlet passage at the outside diameter of the inlet passage is substantially equal to the cross-sectional area of the inlet passage at the inside diameter of the inlet passage (which may be referred to as the throat area of the inlet passage) the flow through each inlet passage as a function of the position of the sleeve 30 is different to that which has previously been discussed.

In particular, due to the fact that it is not possible to position the sleeve such that the sleeve-defined cross-sectional area is greater than the cross-sectional area of the inlet passage at its inside diameter, there is no position of the sleeve at which movement of the sleeve (for example in an axial direction to open the inlet) will not produce a change in flow through the inlet passage.

Figure 20 shows a schematic representation of a radial view around a portion of the circumference of an annular inlet (at its outside diameter) of a turbine which may have a structure as shown in Figure 19. The radial views shown in Figure 20 are unrolled and laid flat in the plane of the paper. Figure 20 shows that it is possible for embodiments of the invention having the structure shown in Figure 19 to have a variety of cross-sectional shapes of inlet passage.

Figure 21 shows a schematic graph of total flow FT through a turbine inlet having a configuration as discussed in relation to Figures 19 and 20, against sleeve position P. It can be seen that the relationship between total flow through the inlet F1 and sleeve position P is substantially linear. This is because there is no position of the sleeve in which sleeve-defined cross-sectional area is greater than the throat area of the inlet passage. The linear relationship between total flow F1 through the inlet and sleeve position P may be beneficial for several reasons. These reasons have already been discussed in relation to Figure 15.

Within the embodiment of the invention discussed in relation to Figures 19 to 21, due to the fact that the cross-sectional area of the inlet passages 84a, 84b and 84c at the outside diameter of the inlet passages is substantially equal to the cross-sectional area of the respective inlet passage at the inside diameter, the arrangement may be referred to as a 1:1 ratio inlet structure.

Figure 22 shows a schematic cross-sectional view through an inlet which forms part of a turbine in accordance with another embodiment of the present invention. In the same manner as previously described embodiments, the turbine inlet comprises first and second inlet sidewalls 90 and 92 and first and second inlet passage sidewalls 94a, 94b which define inlet passages 96a, 96b and 96c. The inlet sidewalls 90, 92, inlet passage sidewalls 94a, 94b and inlet passages 96a, 96b and 96c may be said to generally converge (or taper inwards) as they extend radially inwards (i.e. towards the turbine axis).

In the present embodiment the inlet passages 96a to 96c converge in a radially inward direction (i.e., in a direction which is radially towards the turbine axis) such that the cross-sectional area of each of the inlet passages 96a, 96b and 96c at the outside diameter 98 of the inlet passages is a desired multiple of the cross-sectional area of each inlet passage 96a, 96b, 96c at the inside diameter 100 of the inlet passages 96a, 96b, 96c. In the present case, the area of each inlet passage at the inside diameter of the inlet passage is the throat area. In the embodiment shown in Figure 22, the desired multiple of the cross-sectional area of each inlet passage at the inside diameter of the inlet passage which is equal to the cross-sectional area of the inlet passage at the outside diameter of the inlet passage is 2. Due to the fact that the cross-sectional area of each inlet passage at its outside diameter is twice the cross-sectional area of the inlet passage at its inside diameter, the inlet may be said to have a 2:1 ratio inlet structure. In some embodiments of a turbine which have a 2:1 ratio inlet structure, the outside diameter of an inlet passage which forms part of the inlet multiplied by the axial height of the inlet passage at the outside diameter of the inlet passage may be equal to twice the inside diameter of the inlet passage multiplied by the axial height of the inlet passage at the inside diameter of the inlet passage.

Figure 23 shows schematic representations of radial views around a portion of the circumference of two annular inlets having the structure shown in Figure 22. The radial views are unrolled and laid flat in the plane of the paper. It will be appreciated that any other appropriate shape of inlet passage other than those shown in Figure 23 may also be used.

Figure 24 shows a schematic graph of flow through various portions of the inlet as a function of sleeve position P. Line 102 within the graph shows the total flow through a first axial array of inlet passages. Referring back to Figure 23, the first axial array of inlet passages includes inlet passages 104a (in the upper portion of the figure) or passages 104b (in the lower portion of the figure). Both the inlet passages 104a and inlet passages 104b which form pad of the respective first axial array of inlet passages have in common that at the inlet sidewall 92 (away from which the sleeve 30 moves so as to open the inlet), the inlet passage 104a, 104b which is adjacent the inlet sidewall 92 and which forms part of the first axial array of inlet passages is an inlet passage which has a cross-sectional shape that is complete (i.e., substantially the same as the shape of an inlet passage near the axial centre of the inlet, and not divided by the inlet sidewall 92 such that the inlet sidewall 92 truncates the inlet passage).

Line 106 within the graph of Figure 24 shows the flow through a second axial array of inlet passages. Referring again to Figure 23, inlet passages which form part of a second axial array of inlet passages are indicated by 1 08a and 1 08b. The second axial array of inlet passages differs from the first axial array of inlet passages in that the inlet passage 108a, 108b of the second axial array of inlet passages which is adjacent the inlet sidewall 92 is truncated (so that it is substantially halved) the inlet sidewall 92 such that the cross-sectional area of the inlet passage of the second axial array of inlet passages which is adjacent the inlet sidewall 92 is approximately half that of the cross-sectional area of other inlet passages of the second axial array of inlet passages.

In Figure 24, line 110 represents the total flow through an inlet having an inlet passage configuration as shown in either part of Figure 23. It will be appreciated that within the graph the vertical scale used for lines 102, 106 and 110 may be different for lines 102 and 106 compared to that used for 110.

The line 110 has two separate substantially linear portions: a first relatively steep substantially linear portion 112 and a second relatively shallow substantially linear portion 114. The first portion 112 is at relatively (compared to the second portion) low values of sleeve position P. As such, the portion 112 relates to positions of the sleeve whereby the free end of the sleeve is relatively close to the inlet sidewall which opposes the free end of the moveable sleeve. That is to say, portion 112 relates to positions of the sleeve at which the sleeve has just opened the inlet by moving away from the opposing inlet sidewall. The portion 114 of line 110 relates to sleeve positions P which are greater in value than those described by portion 112. It follows that the portion 114 relates to positions P of the sleeve whereby the free end of the sleeve is located further away from the inlet sidewall opposing the free end of the sleeve than when the sleeve is at a position in the region 112. Consequently portion 114 represents positions of the sleeve where the inlet is more open than when the sleeve is in a position within portion 112.

It can be seen that when the gradient of portion 112 is greater than the gradient of portion 114. This means that within portion 112 a given change in sleeve position P results in a relatively large change in total flow through the inlet, whereas in portion 114, said given change in sleeve position P results in a relatively smaller change in total flow through the inlet. This has the result that it is harder for a turbine controller (which controls an actuator so as to move the sleeve and hence change the sleeve position) to accurately control the total flow through the inlet within portion 112 than it is within portion 114. This is because, for a desired change in total flow thought the inlet a smaller (and hence more accurate) change in the sleeve position is required in region 112 compared to region 114. That is to say it is harder for the turbine controller and actuator to control the total flow through the inlet when the sleeve is located at a position such that the inlet is fully closed or near a closed position compared to that when the sleeve is located at a position in which the inlet is relatively open. This may be disadvantageous in certain applications because it may be desired to have a greater degree of control over the total flow through the inlet at positions of the sleeve close to the fully closed position of the sleeve. Figure 25 shows a pair of radial views of portions of modified inlets which correspond to the views of inlet portions shown in figure 23. These modified inlets aim to mitigate the previously mentioned disadvantage relating to control of flow through the inlet at positions of the sleeve which are close to the fully closed position (or a closed position) of the sleeve.

It can be seen that within the inlet passage configurations shown in the views of inlets in Figure 25, compared to the inlet passage configurations shown in Figure 23, inlet passages 116a and 116b adjacent the inlet sidewall 92 and which have a smaller cross-sectional area than other inlet passages within the same inlet passage configuration have been filled in or blocked so that no gas can flow through them.

Figure 26 shows schematic graphs of gas flow through various portions of an inlet having a structure as shown in either of the inlet passage configurations of Figure against sleeve position P. Line 118 shows total flow through a first axial array of inlet passages 124a, 124b. Line 120 shows the total flow through a second axial array of inlet passages 126a, 126b. Line 122 shows the total flow through the inlet. As previously discussed in relation to Figure 24, line 112 and lines 118 and 120 may have different vertical scales within the graph.

It can be seen that the total flow through the inlet which is indicated by line 122 is split into first and second linear regions 124, 126 which have different gradients. The first region 124 which occurs at lower values of P compared to the second region 126 has a smaller gradient than that of the second region 126. As previously discussed, positions of the sleeve corresponding to lower values of P represent those positions of the sleeve in which the free end of the sleeve is relatively close (compared to larger values of F) to the inlet sidewall which opposes the moveable sleeve. When the sleeve position P is equal to 0 the sleeve is in a fully closed position such that the inlet is fully closed.

Due to the fact that the gradient of the region 124 close to the fully closed position of the sleeve is smaller than the gradient of the region 126, a given change in sleeve position P in the first region 124 will result in a smaller change in total flow through the inlet compared to the same given change in sleeve position P in the second legion 126. Due to the fact that there is more control over the total flow through the inlet in the first region 124 where the sleeve is close to the fully closed position, this may be advantageous in applications where it is desirable to have more control over total flow through the inlet at sleeve positions close to the position of the sleeve (fully closed position) in which the inlet is fully closed by the sleeve.

Figure 27a and 27b show a further inlet passage configuration according to the present invention. Figure 27a shows a radial view of the outside diameter of the inlet passages, whereas Figure 27b shows a radial view of the inside diameter of the inlet passages. It can be seen that a set of inlet passages 128 at their outside diameter have a shape which is elongated in a generally axial direction compared to the other inlet passages 130 which form part of the inlet passage configuration. The set of inlet passages 128 is located adjacent to an inlet sidewall 134. The inlet passages 128 at their inner diameter (as shown in Figure 27b) have a standard shape and configuration (as previously discussed in relation to the lower portion of Figure 23). That is to say, the inlet passages 128, at their inner diameter, do not have a shape which is extended in the axial direction in a similar manner to their shape at their outer diameter.

Figure 28 shows an axial cross-section through a portion of a turbine according to the present invention which has an inlet passage configuration as illustrated in Figures 27a and 27b. In particular it can be seen that the inlet passage 128 which has an axially elongated shape at its outside diameter 132 is located such that it is adjacent to the inlet sidewall 134 which opposes the moveable sleeve 30. The inlet sidewall 134 is the inlet sidewall away from which the sleeve 30 moves so as to open the inlet. The portions of the inlet passages 128 which are axially extended (in this case such that they each extend axially to an apex 136) are gradually flattened down as the inlet passages extend from the outside diameter of the inlet passage to the inside diameter of the inlet passage. That is to say that the axial height HA of the inlet passages 128 decreases from the outside diameter 132 of the inlet passages 128 to the inside diameter 138 of the inlet passages 128. Consequently, the inlet sidewall 134 (which may define the apexes 136 of the inlet passages 128 at the outside diameter 132) tapers inwardly (i.e., converges) with the opposing inlet sidewall 140 as it extends radially inwards (i.e. towards the turbine axis). In other words, the axial width of the inlet defined between the inlet sidewalls 134 and 140 decreases in the generally radial inward direction towards the turbine axis.

The tapering of the inlet in this manner (i.e., such that the axial height of the inlet passages 128 decreases in a direction that is radially inward towards the turbine axis) the nozzle blades do not experience intermittent gas flow and the nozzle blades are not stimulated to vibrate. Vibrations of the nozzle blades (i.e., inlet passage sidewalls) may result in additional stress being experienced by the inlet passage sidewalls, which may cause the inlet sidewalls to deform or in some cases split.

Figure 29 shows a schematic graph of flow through various portions of an inlet having the inlet passage configuration shown in Figure 27a, 27b and 28. Line 142 shows the total flow through a first axial array of inlet passages (indicated as 144 in Figure 27a) as a function of sleeve position P. Line 146 shows the total flow through a second axial array of inlet flow passages 146 as a function of sleeve position P. It can be seen that the second axial array 146 of inlet passages includes an inlet passage 128 which has a greater axial height than the equivalent inlet passage 128 of the first axial array 144 of inlet passages. Line 148 of the schematic graph shown in Figure 29 shows the total flow through the inlet as a function of sleeve position P. Linel48 has first, second and third regions 150, 152 and 154 respectively. As with previous graphs, the vertical scale of the graph for line 148 may be different to the vertical scale for lines 142and146.

The first and second regions 150, 152 of line 148 have a substantially (although not completely) constant gradient, whereas portion 154 of line 148 shows a substantially linear relationship between sleeve position P and total flow through the inlet. The average gradient of the first and second regions 150, 152 is less than the gradient of the third region 154. The first and second regions 150, 152 correspond to low values of the sleeve position. The relatively low values of sleeve position P (compared to the values of P for the third region 154) corresponds to positions of the sleeve in which the free end of the sleeve is relatively close (again compared to sleeve position in the third region 154) to the inlet sidewall 134 which opposes the sleeve 30.

Furthermore, it will be appreciated that when the sleeve position P is in the first or second regions 150, 152 the sleeve is relatively close (compared to the position of the sleeve in the third region 154) to the fully closed position of the sleeve. As previously discussed, it may be advantageous for the gradient of the total flow through the inlet as a function of sleeve position P to be less near the fully closed position of the sleeve compared to the gradient at positions of the sleeve which are relatively far away from the fully closed position of the sleeve. These advantages have already been discussed in relation Figure 26.

Figure 30 shows a radial view of the outside diameter of a plurality of inlet passages in an inlet passage configuration which may form part of an inlet of a turbine in accordance with an embodiment of the present invention. In a similar manner to the inlet passages 128 shown in Figure 27a, the inlet passages 128a within Figure 30 are extended in an axial direction and are located adjacent an inlet sidewall which opposes the moveable sleeve. As with the previously described embodiment, the inlet passages 128a which are axially extended at their outside diameter have an axial height at their inside diameter which is reduced compared to that of the outside diameter. Consequently, an axial cross-section through an inlet having an inlet passage configuration as shown in Figure 30 will look similar to that shown in Figure 28 (albeit with inlet passage 128 within Figure 28 being equivalent to an inlet passage 128a as shown in Figure 30). The total flow through an inlet having an inlet passage configuration as shown in Figure 30 as a function of sleeve position P is substantially similar to that shown by line 148 in Figure 29.

It should be noted that both the embodiment of the invention shown in Figure 30 and the embodiment of the invention shown in Figures 27a, 27b and Figure 28 have an inlet ratio for all the inlet passages which have not been axially extended which is 2:1.

That is to say that all of the inlet passages which have not been axially extended at their outer diameter have a cross-sectional area at their outside diameter which is twice that of their cross-sectional area of their inside diameter.

Figure 31 shows a schematic axial cross-section through an inlet of a turbine in accordance with a further embodiment of the present invention. In a similar manner to the turbine inlet shown in Figure 22, the turbine inlet shown in Figure 31 comprises inlet sidewalls 160, 162 and inlet passage sidewalls 164a, 164b and 164c which define inlet passages lGGa, 166b, lGGc and 166d which converge as they extend radially inwards (i.e. towards the turbine axis). That is to say each of the inlet passages 166a, 166b, 1 66c and 1 66d have a greater axial height at their outside diameter 168 than they do at their inside diameter 170. Due to this fact, each of the inlet passages has a greater cross-sectional area at their outside diameter 168 than they do at their inside diameter 170. In this particular case, the inlet is configured such that the cross-sectional of the inlet passages at their outside diameter 168 is 1.5 times the cross-sectional area of each inlet passage at its inside diameter 170 (the cross-sectional area of each inlet passage at its inside diameter may be referred to as the throat area of the inlet passage). For this reason, the inlet shown in Figure 31 may be said to have a 3:2 ratio inlet structure. In particular, the outside diameter of an inlet passage multiplied by the axial height of said inlet passage may be equal to 1.5 times the inside diameter of said inlet passage multiplied by the axial height of the inlet passage at the inside diameter of the inlet passage.

Figure 32 shows a radial view of the outside diameter of the inlet passages which form part of an inlet having the configuration shown in Figure 31. The inlet passage configuration shown in Figure 32 comprises three different (cross-sectional) shapes of inlet passage indicated by 172, 174 and 176 respectively. It will be appreciated that although the shapes 172, 174 and 176 are shown in black, this is to aid clarity and there is nothing which makes the indicated shapes different from the other similar shapes within the inlet passage configuration. The three different shapes of inlet passage 172, 174 and 176 each form part of an axial array of inlet passages within which the inlet passages have substantially the same cross-sectional shape. For example, a first axial array of inlet passages 178 contains inlet passages which each have the same cross-sectional shape as the first shape 172 (apart from those inlet passages adjacent the inlet sidewalls 160 and 162 which may be shaped such that they are only a portion of the shape 172). Similarly, the second and third axial arrays of inlet passages 180, 182 each contain inlet passages which have the same cross-sectional shape, that shape being shape 174 or 176 respectively. Again, inlet passages adjacent the inlet sidewalls 160 may be shaped such that they are only a portion of shapes 174 or 176 respectively. The inlet passage configuration has a periodic structure in a circumferential direction. In particular the inlet passage configuration is a periodic series of axial arrays of inlet passages. The repeating unit of the periodic series of axial arrays of inlet passages (from left to right in Figure 32) includes an axial array of inlet passages that is of the same configuration as the first axial array of inlet passages 178, an axial array of inlet passages that is of the same configuration as the third axial array of inlet passages 182, an axial array of inlet passages that is of the same configuration as the second axial array of inlet passages 180, and an axial array of inlet passages 184 that includes inlet passages having a shape which is generally a reflection of the third shape 176 in an axis A parallel to the axis of the turbine.

It will be appreciated that in other embodiments of the present invention the inlet passage configuration may be a periodic series of axial arrays of inlet passages having a repeating unit which has any appropriate number of axial arrays of inlet passages.

Figure 33 shows a graph of flow F through each of the inlet passages 172, 174 and 176 in Figure 32 against sleeve position P. Line 184 represents the flow through inlet passage 172. Line 186 relates to the flow through the inlet passage 174 and line 188 relates to the flow through inlet passage 176. In each case, when the sleeve position P equals 0 the sleeve 30 is positioned such that its free end is substantially aligned with an inlet passage sidewall of the respective inlet passage, said inlet passage sidewall being the sidewall of the inlet passage which is closest to the inlet sidewall 162. The inlet sidewall 162 is the inlet sidewall which opposes the free end of the moveable sleeve 30 (i.e. the inlet sidewall 162 is the sidewall away from which the sleeve 30 moves in order to open the inlet). Consequently, when the moveable sleeve is in a fully closed position in which the inlet is closed by the sleeve, the free end of the sleeve 30 may abut or be adjacent to the inlet sidewall 162.

Figure 33 shows that for each of the cross-sectional shapes of inlet passage 172, 174 and 176, the flow through the inlet passage increases as the sleeve position P increases (i.e., the sleeve moves in a direction to open the inlet). The flow through each of the inlet passages having different cross-sectional shapes (indicated by lines 184, 186 and 188 respectively) increases up until a critical sleeve position which is approximated by P0. Beyond the critical sleeve position the flow F through the inlet passages remains substantially constant until the sleeve reaches a sleeve position PF.

The sleeve position PF is the fully open position of the sleeve. The fully open position of the sleeve corresponds to a position of the sleeve in which the free end of the sleeve is substantially aligned with a sidewall of the inlet passage sidewall of a respective inlet passage which is the greatest distance from inlet sidewall 162. As previously stated P0 is only the approximate position of the critical position of each inlet passage at which the maximum flow through each of the different shaped inlet passages is reached. The graph in Figure 33 shows that the maximum flow through the first shape of inlet passage 172 indicated by line 184 is reached at a sleeve position that is slightly less than P0 (i.e. the critical position of the sleeve in relation to the first shape of inlet passage 172 is reached at a sleeve position that is slightly less than F0). The maximum flow through the second shape of inlet passage 174 indicated by line 186 is reached at a sleeve position that is substantially equal to P0 (i.e. the critical position of the sleeve in relation to the second shape of inlet passage 174 is reached at a sleeve position that is substantially equal to F3). The graph also shows that the sleeve position P at which the third shape of inlet passage 176 which is indicated by line 188 reaches maximum flow is slightly greater than the position F0 (i.e. the critical position of the sleeve in relation to the third shape of inlet passage 176 is reached at a sleeve position that is slightly greater than the position F3).

In the embodiment of the invention which relates to Figures 31 to 33, the critical position of each the inlet passages is approximately F0 which is approximately equal to % of FF. That is to say F0 occurs at a position in which the free end of the sleeve is substantially aligned with a position which is approximately % along the axial height HA of an inlet passage at its outside diameter. In other words, P3 approximately occurs at a sleeve position in which the free end of the sleeve is a distance of % of the axial height HA of an inlet passage (or % of FF) from the sidewall of the inlet passage which is closest to the inlet sidewall 162.

Referring again to Figure 32, it can be seen that the inlet passages are arranged such that the opening position of a first inlet passage 190 (i.e., when the sleeve 30 is positioned such that its free end is substantially aligned with inlet passage sidewall 191 of the inlet passage 190, inlet passage sidewall 191 being the inlet passage sidewall of the inlet passage that is closest to the inlet sidewall 162) occurs when the free end of the sleeve is substantially aligned with a position which is an axial distance of approximately % the axial height HA of a second inlet passage 192 from inlet passage sidewall 193 of the second inlet passage 192 (inlet passage sidewall 193 being the inlet passage sidewall of the second inlet passageway 192 that is closest to the inlet sidewall 162).

In this way, when the sleeve reaches a position which is substantially the critical position (approximately P3) of the inlet passage 192, the sleeve will be at an opening position of inlet passage 190 in which the inlet passage 190 will be opened. Similarly, in general, within the inlet passage configuration shown in Figure 32, an inlet passage will have an axially adjacent inlet passage which is located such that when the sleeve reaches a position which is substantially the critical position of the inlet passage, the sleeve will be at the opening position of the axially adjacent inlet passage.

Figure 34 shows a graph of the flow through various portions of an inlet as shown in Figures 31 and 32 against sleeve position P. Line 194 shows the total flow of gas through the first axial array 178 of inlet passages. Line 196 shows the total flow through the third axial array of inlet passages 182. Line 198 shows the total flow through the second axial array 180 of inlet passages. Line 200 shows the total flow of gas through the inlet.

As previously discussed in relation to Figure 24, it can be seen that the line 200 which represents total flow through the inlet shown in Figure 34 has a first region 202 and a second region 204. The first region 202 has a gradient which is greater than that of the second region 204. The potential disadvantages of a turbine having an inlet which has a steeper gradient of total flow through the inlet versus sleeve position at positions close to the fully closed position of the inlet relative to the gradient of positions further away from the fully closed position of the inlet have previously been discussed. Consequently, discussion of this point will not be repeated here. However, it will be appreciated that points made in relation to previous embodiments apply mutatis mutandis.

Figure 35 shows an inlet passage configuration which is similar to that shown in Figure 32. The inlet passage configuration shown in Figure 35 differs from that shown in Figure 32 in that flow passages which were present adjacent inlet sidewall 162 within Figure 32, and which were shaped such that they were only a portion of the shape of other inlet passages within their respective axial array of inlet passages, have been blocked/omitted in Figure 35. That is to say that the black areas 206 represent inlet passages which are present in the inlet passage configuration shown in Figure 32 but which have been blocked/omitted in the inlet passage configuration shown in Figure 35.

As previously discussed in relation to the embodiment of the present invention shown in Figure 25, blocking or omitting inlet passages adjacent the inlet sidewall 162 which opposes the free end of the moveable sleeve modifies the total flow through the inlet at positions of the sleeve which are close to a fully closed position of the sleeve when compared to an inlet passage configuration which does not have blocked/omitted inlet passages. This can be seen by comparing the graph shown in Figure 36 to the graph shown in Figure 34.

Figure 36 shows a schematic graph of the flow through various portions of an inlet having an inlet passage configuration as shown in Figure 35 against sleeve position P. Lines 208, 212 and 216 within the graph of Figure 36 show the total flow through first, second and third axial arrays of inlet passages 210, 214 and 218 respectively. Line 220 shows the total flow through the inlet. As previously discussed in relation to the graph shown in Figure 26, it can be seen that the line 220 which represents total flow through the inlet has a first region 222 and a second region 224.

The gradient of the first region 222 of the line 220 is less than the gradient of the second region 224. The first region 222 is closer to the fully closed position (P=0) of the inlet compared to the second region 224. The benefits of the gradient of a first region of sleeve positions which is relatively close to the fully closed position of the sleeve being less than that of a second region of sleeve positions which is further away from the fully closed position of the sleeve has previously been discussed (in particular in relation to Figure 26). It will be appreciated that the benefits discussed in relation to previously described embodiments apply mutatis mutandis to the present embodiment.

It will be appreciated that although all the described embodiments have the sleeve located at the outside diameter of the inlet passages, the sleeve may be located at any appropriate position. For example, the sleeve may have a diameter such that it is located between the inner and outer diameters of the inlet passages which form part of the inlet. In this case, the portions of the inlet passages which are upstream of the sleeve may be disregarded for the purposes of the invention.

However, it will be appreciated that the inner diameter of the sleeve is greater than the inner diameter of at least one of the inlet passages. This is because if the moveable sleeve were to be located at the inside diameter of the inlet passages then the cross-sectional area of the inlet passage which is opened by the sleeve will automatically be the same as the throat area for the inlet passage. Consequently, one of the problems solved by the invention, whereby there is mismatch in the sleeve-defined cross-sectional area and the throat area of the inlet passage that results in a step-like relationship between flow through the inlet and sleeve position, will no longer exist. This problem is obviated or mitigated by configuring the inlet and the inlet passages of the inlet in a manner according to the present invention.

Within any of the previously described embodiments of the invention, the sleeve is movable in when the sleeve is in the opening position, a cross-sectional area of an opening to the first inlet passage defined between a free, first end of the sleeve and the first inlet passage sidewall is substantially equal to the minimum cross-sectional area of the first inlet passage; and wherein movement of the sleeve in the first direction beyond the opening position of the second inlet passage serves to initiate opening of the second inlet passage.

Although the hereinbefore described embodiments of the invention have inlets which have a specific inlet flow ratio (e.g., 1:1, 2:1 and 3:2) and which have corresponding inlet passage configurations wherein each inlet passage is displaced from an axially adjacent inlet passage by a specific portion of the axial height of the inlet passage at its outside diameter (e.g., 100% of the axial height, 50% of the axial height and approximately 66% of the axial height respectively), it will be appreciated that any appropriate inlet flow ratio and/or corresponding displacement between axially adjacent inlet passages and/or shape of inlet passages may be used provided that the opening position of the axially adjacent inlet passage corresponds to the axial position at which the sleeve-defined cross-sectional area of the inlet passage to which the axially adjacent inlet passage is axially adjacent is substantially equal to the minimum cross-sectional area of the inlet passage.

Furthermore, although specific cross-sectional shapes and inlet passage configurations have been shown in the described embodiments, a turbine according to the present invention may have an inlet having inlet passages with any appropriate cross-sectional shape or configurations.

Although the described embodiments show a turbine which forms part of a turbocharger and which has a sleeve which is actuated by a mechanism which is located, at least in part, in the bearing housing of the turbocharger, a turbine according to the present invention may form part of any appropriate type of turbomachine and the sleeve may be actuated by a mechanism which is located at any appropriate location.

Furthermore, any appropriate sleeve configuration or actuator configuration may be used. For example, the sleeve may not be generally cylindrical and/or may not move in a generally axial direction.

Although the described embodiments are configured such that the inner diameter of the inlet passages is the portion of the inlet passages which has the minimum cross-sectional area of the inlet passages (also referred to as the throat area of the inlet passages), this need not be the case. The throat area of the inlet passages may be located at any appropriate location within the inlet passages. For example, in some embodiments there may be a constriction in the inlet passages at a location between the inside diameter and outside diameter of the inlet passages. In this case, the constriction may be the portion of the inlet passages which has the minimum cross sectional area of the inlet passages and therefore defines the throat area of the inlet passages.

Within the previous description, the term cross-sectional area has been used to refer to a geometric' cross-sectional area. That is to say, the cross-sectional area in the previous description of a portion of an inlet passage is defined only by the dimensions of the portion of the inlet passage. Examples of such cross-sectional areas include the cross-sectional area of an opening to an inlet passage defined between an end of the sleeve and an inlet passage sidewall, and the minimum cross-sectional area of an inlet passage. It will be appreciated that in other embodiments of the invention the cross-sectional area of a portion of an inlet passage may be defined in different manner. For example, the cross-sectional area of a portion of an inlet passage may be an aerodynamic' cross-sectional area.

The geometric cross-sectional area of a portion of an inlet passage contributes to the aerodynamic cross-sectional area of the portion of the inlet passage. In simplistic terms the aerodynamic cross-sectional area is smaller in comparison to the size of the geometric cross-sectional area in order to account for energy loss in the gas flowing through the portion of the inlet passage due to various effects discussed below. In other words, the aerodynamic cross-sectional takes into account energy losses that effectively provide a further blockage' to the geometric cross-sectional area to thereby reduce the size of the geometric cross-sectional area in order to account for the aforementioned energy loss.

As discussed above, the aerodynamic cross-sectional area reduces the geometric cross-sectional area to account for energy loss due to various effects. These effects include friction due to non-laminar flow (e.g. boundary layers and orifice edge effects), non-linear flow and the viscosity of the gas. The aerodynamic cross-sectional area of a portion of the inlet passage may be defined as the cross-sectional area of an orifice perpendicular to the direction of gas flow which would have substantially the same flow rate of gas through it as the portion of the inlet passage under conditions in which there is substantially no energy loss in the gas as it passes through the portion of the inlet passage. Consequently, the aerodynamic cross-sectional area of a portion of an inlet passage assumes that the gas is under the following conditions: that the flow of gas through the orifice is a substantially steady-state, inviscid and laminar, that the gas is substantially incompressible, that there is no change in elevation of the gas and that there are negligible frictional losses as the gas flows through the orifice. It follows that the aerodynamic throat area of the inlet passage may be defined at least by the geometric throat area of the inlet passage, the flow direction of gas which passes through the inlet passage (which may include, for example, the flow direction of gas relative to the orientation of the walls of the gas passage), the viscosity of the gas and frictional losses (for example due to edge effects). In practice, the geometric throat area and the aerodynamic throat area of an inlet passage may be very similar. For example, the aerodynamic cross sectional area may be between about 95% and 100% of the geometric cross-sectional area.

Determining the aerodynamic cross-sectional area from the geometric cross-sectional area is a routine process for a person skilled in the art utilising computational fluid dynamics analysis as is well known in the art.

Claims

CLAIMS: 1. A variable geometry turbine comprising a turbine wheel mounted for rotation about a turbine axis within a turbine chamber defined by a housing, the chamber having an annular inlet, the annular inlet including: a first inlet passage which extends from an outer diameter to an inner diameter and which is defined between first and second inlet passage sidewalls; and a second inlet passage which extends from an outer diameter to an inner diameter; wherein the second inlet passage is axially displaced from the first inlet passage; and wherein the turbine further comprises a generally cylindrical sleeve for varying the size of the annular inlet, the sleeve being movable in a first direction to increase the size of the annular inlet; wherein the inner diameter of the sleeve is greater than the inner diameter of at least one of the first and second inlet passages; and wherein the sleeve is movable in the first direction from a first position to an opening position of the second inlet passage, during which movement the second inlet passage is closed; wherein, when the sleeve is in the opening position of the second inlet passage, a cross-sectional area of an opening to the first inlet passage defined between a free, first end of the sleeve and the first inlet passage sidewall is substantially equal to the minimum cross-sectional area of the first inlet passage; and wherein movement of the sleeve in the first direction beyond the opening position of the second inlet passage serves to initiate opening of the second inlet passage.
2. A variable geometry turbine according to claim 1, wherein the first and second inlet passage sidewalls are axially spaced.
3. A variable geometry turbine according to claim 1 or claim 2, wherein the first direction is a direction which is substantially parallel to the turbine axis.
4. A variable geometry turbine according to any preceding claim, wherein the first and second inlet passages both have a cross-sectional shape which is substantially the same.
5. A variable geometry turbine according to any preceding claim, wherein the first and second inlet passages both form part of an array of inlet passages.
6. A variable geometry turbine according any preceding claim, wherein the inner diameter of the sleeve is greater than the outer diameter of at least one of the first and second inlet passages.
7. A variable geometry turbine according any preceding claim, wherein the minimum cross-sectional area of the first inlet passage is the cross-sectional area of the first inlet passage at the inner diameter of the first inlet passage.
8. A variable geometry turbine according to any preceding claim, wherein the first and second inlet passage sidewalls are substantially parallel to one another.
9. A variable geometry turbine according to any of claims 1 to 7, wherein the first and second inlet passage sidewalls diverge as they extend towards the turbine axis.
10. A variable geometry turbine according to any preceding claim, wherein the cross-sectional area of the opening when the sleeve is at a fully open position, in which the first end of the sleeve is axially aligned with the second inlet passage sidewall, is substantially equal to the minimum cross-sectional area of the first inlet passage.
11. A variable geometry turbine according to any of claims 1 to 7, wherein the first and second inlet passage sidewalls converge as they extend towards the turbine axis.
12. A variable geometry turbine according to any preceding claim, wherein the outside diameter of the second inlet passage is axially displaced from the outside diameter of the first inlet passage by a distance which is substantially equal to the minimum cross-sectional area of the first inlet passage multiplied by an axial height of the first inlet passage and divided by the cross sectional area of the first inlet passage at the outside diameter, wherein the axial height is the axial distance between the first inlet passage sidewall and the second inlet passage sidewall at the outside diameter of the first inlet passage.
13. A variable geometry turbine according to any preceding claim, where in the first inlet passage forms part of a first axial array of inlet passages, wherein there are a plurality of inlet passages in the first axial array of inlet passages and wherein all the inlet passages which are part of the first axial array of inlet passages have substantially the same shape.
14. A variable geometry turbine according to any preceding claim, wherein the second inlet passage forms part of a second axial array of inlet passages, wherein there are a plurality of inlet passages in the second axial array of inlet passages and wherein all the inlet passages which are part of the second axial array of inlet passages have substantially the same shape.
15. A variable geometry turbine according to any preceding claim, wherein the turbine further comprises an inlet sidewall away from which the sleeve moves in the first direction in order to increase the size of the annular inlet, and wherein the turbine further comprises a third inlet passage which extends radially inboard from an outer diameter to an inner diameter and which is adjacent the inlet sidewall; wherein the third inlet passage has a height at its outside diameter in a direction parallel to the first direction which is greater than the height of the first inlet passage at its outside diameter in a direction parallel to the first direction; and wherein the height of the third inlet passage at its outside diameter in a direction parallel to the first direction is greater than the height of the third inlet passage at its inside diameter in a direction parallel to the first direction.
16. A method of designing a variable geometry turbine according to any preceding claim, the method including: determining a desired axial displacement between the outside diameters of the first and second inlet passages; determining a cross-sectional shape and relative positioning of both the first and second inlet passages such that the opening position of the sleeve is displaced from a third position of the sleeve in which the sleeve substantially fully closes the first inlet passage by a distance which is substantially equal to the desired axial displacement between the outside diameters of the first and second inlet passages.