The present invention relates to a turbine, particularly but not exclusively, a turbine for use in a turbocharger.

Turbochargers are well known devices for supplying air to the intake of an internal combustion engine at pressures above atmospheric pressure (boost pressures). A conventional turbocharger essentially comprises a housing in which is provided an exhaust gas driven turbine wheel mounted on a rotatable shaft connected downstream of an engine outlet manifold. A compressor impeller wheel is mounted on the opposite end of the shaft such that rotation of the turbine wheel drives rotation of the impeller wheel. In this application of a compressor, the impeller wheel delivers compressed air to the engine intake manifold. The turbocharger shaft is conventionally supported by journal and thrust bearings, including appropriate lubricating systems.

In known turbochargers, the turbine stage comprises a turbine chamber within which the turbine wheel is mounted; an annular inlet passage defined between facing radial walls arranged around the turbine chamber; an inlet arranged around the inlet passage; and an outlet passage extending from the turbine chamber. The passages and chambers communicate such that pressurised exhaust emissions, including gaseous and particulate species, admitted to the inlet chamber flow through the inlet passage to the outlet passage via the turbine and rotate the turbine wheel. It is also known to improve turbine performance by providing vanes, referred to as nozzle vanes, in the inlet passage so as to deflect gas flowing through the inlet passage 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 passage 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 suite 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 annular inlet passage.

As the level of performance required from turbochargers has increased, so too have the technical requirements placed on turbocharger components. An important property of the turbine housing within which the turbine wheel is mounted is that it is sufficiently strong to contain debris generated as a result of turbine wheel failure. As turbine wheels have become heavier, stronger and operated at higher speeds it has therefore become necessary to increase the strength of the turbine housing. To date, this increased strength has been achieved by using stronger, heavier materials which require stronger means of attachment to the adjacent bearing housing, and consequently, more robust means for attachment to the engine exhaust manifold. As a result the cost and complexity of turbocharger manufacture has increased to provide the desired increases in performance.

It is an object of the present invention to obviate or mitigate one or more of the problems set out above.

According to a first aspect of the present invention there is provided a turbine comprising: a turbine housing; a turbine wheel supported within said turbine housing for rotation about a turbine axis; and a turbine inlet passageway within said turbine housing upstream of said turbine wheel; wherein a frangible element is located in a generally annular region defined around the periphery of the turbine wheel within the outer diameter of the turbine housing.

In this way, the kinetic energy of high velocity material ejected by a failed turbine wheel is absorbed by the frangible element, which significantly reduces the risk of turbine housing failure. As well as affording significant safety benefits, the use of frangible elements of this kind enables the remainder of the turbine housing to be less strong and therefore potentially lighter and/or cheaper. This reduction in weight is also beneficial since it reduces the loading requirements on the means of attachment of the turbine housing to the bearing housing, and the engine exhaust manifold when the turbine is employed in a turbocharger, thereby reducing the cost and complexity of manufacturing a turbocharger and exhaust manifold incorporating such a turbine.

The generally annular region around the periphery of the turbine wheel is the region through which high velocity fragments from the turbine wheel are thrown outwardly following a wheel failure. While the path of such fragments is generally radial, this is not the case in all circumstances and some fragments may deviate from a perfectly radial path due to collisions with other fragments or due to the nature of the incident giving rise to the failure. It is preferable for the frangible element to reside in the predicted 'line-of- sight' of such fragments. Accordingly, the generally annular region defined above in the first aspect of the present invention should not be construed as necessarily being limited to a classical annulus around the periphery of the turbine wheel whose axial width and position coincide exactly with the axial extent of the turbine wheel. The generally annular region may extend axially beyond one or both sides of the turbine wheel. Moreover, the generally annular region may define a regular annulus having parallel sides or may define a flared or conical annulus having sides which converge or diverge in an outward radial direction.

In a first preferred embodiment, the frangible element extends from the turbine housing into the turbine inlet passageway. As a result of providing a frangible element in the turbine inlet passageway, in the event of a turbine wheel failure, material ejected from the turbine wheel impinges on the frangible element before the turbine housing, fracturing the frangible element in preference to the turbine housing.

The frangible element may be provided in the turbine inlet passageway at a location which is radially outboard of the turbine wheel and which axially overlies a section of the turbine wheel. This affords protection against turbine wheel failure in the region or regions of the turbine housing which are most likely to be impinged by debris flung radially outwards from the turbine wheel upon failure during use.

The turbine inlet passageway may comprise an inlet volute and an annular inlet passage, the annular inlet located in between the inlet volute and the turbine wheel. In this case, the frangible element may extend from the turbine housing into the inlet volute, and optionally not the annular inlet passage.

The frangible element may have a root at the point at which the frangible element connects to the turbine housing and a tip which is located in the inlet volute and which is spaced from the root. The root and tip may be connected by an intermediate section which includes a fracturable region.

The fracturable region may be pre-formed so as to be weaker than the section of the housing connected to the root of the frangible element to ensure that the fracturable region breaks or shears rather than the turbine housing when hit by debris from the turbine wheel immediately after failure.

The fracturable region may have a smaller dimension than the corresponding dimension of a section of the turbine housing connected to the root of the frangible element. Said dimension may be the thickness of the respective component, i.e. the thickness of the fracturable region of the frangible element and the thickness of the section of the housing connected to the root of the frangible element. Alternatively, said dimension may be the cross sectional area of the respective component.

Said dimension may be determined with reference to a plane parallel to the plane of the turbine wheel, the plane of the turbine wheel being orthogonal to any plane containing the turbine axis of course. Alternatively, said dimension in respect of the fracturable region of the frangible element may be determined with reference to a plane parallel to the plane of the turbine wheel and said dimension in respect of the section of the turbine housing may be determined with reference to a plane transverse to the plane of the turbine wheel. The angle between the plane of the turbine wheel and said transverse plane may be from around 10 ° to around 80 °, from around 25 ° to around 65 °, or from around 35 ° to around 55 °.

The frangible element may take any convenient form, i.e. size and/or shape, provided it is appropriately dimensioned to afford the required degree of impact protection for debris generated by a turbine wheel failure.

The intermediate section of the frangible element may include an axially extending portion that incorporates said fracturable region. The axially extending portion may be connected to the root of the frangible element by a radially extending portion of said intermediate section.

The tip of the frangible element may have an enlarged dimension compared to said intermediate section or said fracturable region. For example, the frangible element may have a tip that is of greater radial cross sectional area than the intermediate section of the frangible element or the fracturable region. In this embodiment, the fracturable region may be thought of as a wasted region as compared to the tip of the frangible element.

The frangible element may extend continuously or discontinuously around at least a portion of the circumference of the turbine wheel. That is, the frangible element may have a uniform shape and dimension throughout its circumferential extent, or its shape and/or dimension may vary throughout its circumferential extent. The frangible element may define an arcuate member of constant radial thickness and axial length. The arcuate member may define a constant radius, or a radius which varies, such as a radius which approximately matches the varying radius of the turbine inlet volute (or 'scroll' as it is sometimes referred).

The frangible element may incorporate a single fracturable region or it may comprise a plurality of fracturable regions. Where multiple fracturable regions are provided, they may all take the same general form, i.e. may all have the same size, shape, thickness etc, or they may take a different form. For example, in a frangible element including four fracturable regions, a first pair may have a first radial thickness while a second pair may have a second, greater radial thickness. Additionally, the first pair of fracturable regions may be provided radially inboard of the second pair so that the second pair, which may be closer to the turbine housing, are more robust and therefore less likely to shear all of the way through their radial thickness than the first pair and expose the turbine housing to the flying debris from the failed turbine wheel. Alternatively, it may be preferable to form the radially inboard pair so that they are more robust than the radially outboard pair so that the radially inboard pair, which will be impinged upon first by flying debris, are capable of absorbing more energy from the debris than the radially outboard pair, which are in effect, a 'back-up' to the radially inboard pair and so their weight should be kept to a minimum since they may not always be needed in the event of a turbine wheel failure.

It will be appreciated that the turbine may include a single frangible element or the turbine may comprise a plurality of frangible elements. Where two or more frangible elements are provided, they may be of the same form, i.e. size, shape, etc, or each frangible element may take a different form; or where three or more frangible elements are provided, any two or more may take the same general form and one or more others take a different form.

The turbine housing may incorporate a single turbine inlet passageway defining a single flow path for gas to flow to the turbine wheel, or the turbine housing may incorporate two or more turbine inlet passageways defining a corresponding number of flow paths for gas to flow to the turbine.

A turbine incorporating multiple turbine inlet passageways may be what is commonly referred to as a 'twin entry turbine' or a 'double entry turbine'. In a twin entry turbine the two turbine inlet passageways are arranged to feed gas to the same circumferential region of the turbine wheel, whereas in a double entry turbine the two turbine inlet passageways are arranged to feed gas to different, circumferentially offset regions of the turbine wheel.

The two turbine inlet passageways in a twin entry turbine are typically axially offset and separated by a dividing wall. In this arrangement, the frangible element may extend from the dividing wall or from another section of the turbine housing. A twin entry turbine incorporating a frangible element according to the invention may have one or more frangible elements in each turbine inlet passageway. Where two or more frangible elements are provided, one or more frangible elements may extend from each side of the dividing wall into each turbine inlet passageway.

In a double entry turbine where the two turbine inlet passageways open onto the turbine wheel at a first circumferential location and a second, circumferentially offset location respectively, the two turbine inlet passageways are typically radially offset with respect to one another up until the location at which the first of the turbine inlet passageways opens onto the turbine wheel at the first circumferential location. A dividing wall separates the two radially offset turbine inlet passageways. The frangible element may extend from the dividing wall or from another section of the turbine housing. A double entry turbine incorporating a frangible element according to the invention may have one or more frangible elements in each turbine inlet passageway. For example, one or more frangible elements may extend from the dividing wall in the radially inner turbine inlet passageway and one or more frangible elements may extend from the turbine housing in the section in between the first and second circumferentially offset locations over which only a terminal section of the former radially outer turbine inlet passageway extends so that frangible elements are only provided in regions of the two turbine inlet passageways that are likely to be exposed to debris flying from a failed turbine wheel.

Since the frangible element(s) of the present invention extend into the turbine inlet passageway it is preferable that they are sized and shaped so as not to unacceptably reduce the efficiency of the turbine inlet passageway in conditioning the flow of gas towards the turbine wheel. That is, it is preferred that the aerodynamic properties of the frangible element(s) are tailored to suit the location at which they are provided in the turbine inlet passageway, and the extent to which they extend into the turbine inlet passageway since frangible elements which project a greater distance from the turbine housing into the turbine inlet passageway have the potential to present a more significant obstacle to gas flowing through the turbine inlet passageway than frangible elements that extend a shorter distance from the turbine housing.

The frangible element(s) may be cast with the turbine housing, or they may be manufactured separately and then connected to the turbine housing using a suitable method, such as welding or brazing.

The frangible element(s) may be formed from the same material as the turbine housing, or they may be formed from or include one or more subsections formed from a different material. By way of example, the fracturable region(s) may be formed of a weaker or more brittle material than the adjacent regions of the frangible element(s) so as to use the relative properties of the materials making up the various regions of the frangible element(s) to ensure that the frangible element(s) breaks or cracks at the fracturable region(s) in preference to the other regions of the frangible element(s). The use of different materials in this way may be used instead of defining the fracturable region(s) by way of the size, shape and/or dimension of the fracturable region(s), or they may be used in combination.

In addition, or by way of an alternative to the above use of differing material properties to define the fracturable region(s), the frangible element(s) may comprise a deformable, energy absorbing material, such as a cellular material, to further enhance the energy absorbing properties of the frangible element(s). The cellular material may comprise an open or closed pore material, and may be, for example, a metal foam and/or metal mesh. The deformable, energy absorbing material may comprise at least one metal or metal alloy or a composite of two or more metals and/or metal alloys, for example steel reinforced aluminium. Optionally, the deformable, energy absorbing material may incorporate one or more polymeric and/or ceramic materials.

Furthermore, the turbine housing may incorporate one or more sections which incorporate a deformable, energy absorbing material as described above.

A second preferred embodiment provides a turbine according to the first aspect of the present invention wherein the frangible element is a section of the turbine housing arranged to break or shear in a predetermined, controlled manner upon impact by a component of the turbine wheel following failure of the turbine wheel during use. In this embodiment, said section of the turbine housing may define one or more areas of weakness relative to the turbine housing adjacent to said one or more areas. Said one or more areas of weakness may be defined by one or more cavities, grooves, slots or the like defined by the turbine housing.

The turbine inlet passageway may comprise an inlet volute positioned upstream of an annular inlet passage, said section of the turbine housing located in between said inlet volute and said turbine wheel. Said section of the turbine housing may, wholly or in part, define said annular inlet passage. Said annular inlet passage is defined between opposing side walls of the housing, one or both of said side walls being defined, at least in part, by said section of the turbine housing.

The turbine according to the second preferred embodiment may, where technically compatible, incorporate any of the features defined above in respect of the first preferred embodiment. For example, the second preferred embodiment may be applied to a single or twin entry turbine.

According to a second aspect of the present invention there is provided a turbocharger comprising a turbine according to the first aspect of the present invention.

A third aspect of the present invention provides a turbocharger comprising: a turbocharger shaft rotatable about an axis; a compressor comprising an impeller wheel mounted to one end of the shaft for rotation about said axis within a compressor housing; a turbine comprising a turbine wheel provided at the other end of the shaft for rotation about said axis within a turbine housing; a turbine inlet passageway within said turbine housing upstream of said turbine wheel; wherein a frangible element is located in a generally annular region defined around the periphery of the turbine wheel within the outer diameter of the turbine housing, the frangible element arranged to break, e.g. shear, crack or fragment, and thereby absorb energy generated as a result of the failure of the turbine wheel during use.

Any of the optional features described above in relation to the turbine according to the first aspect of the present invention may be applied to the turbine forming part of turbocharger of the third aspect of the present invention. The turbocharger of the second and/or third aspects of the present invention may be a fixed geometry turbocharger or a variable geometry turbocharger.

Other advantageous and preferred features of the invention will be apparent from the following description.

Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is an axial cross-section through a known variable geometry turbocharger;

Figure 2 is a longitudinal cross sectional view of a portion of a turbine housing incorporating a frangible element for use in a turbine according to a first embodiment of the present invention;

Figure 3 is a longitudinal cross sectional view of a portion of a turbine housing incorporating a frangible element for use in a turbine according to a second embodiment of the present invention;

Figure 4 is a longitudinal cross sectional view of a portion of a turbine housing incorporating a frangible element for use in a turbine according to a third embodiment of the present invention;

Figure 5 is a radial cross sectional view of a portion of a turbine housing incorporating a frangible element for use in a turbine according to a fourth embodiment of the present invention;

Figure 6 is a radial cross sectional view of a portion of a turbine housing incorporating a frangible element for use in a turbine according to a fifth embodiment of the present invention;

Figure 7 is a longitudinal cross sectional view of a portion of a turbine housing incorporating a frangible element for use in a turbine according to a sixth embodiment of the present invention; Figure 8 is a longitudinal cross sectional view of a portion of a turbine housing incorporating a frangible element for use in a turbine according to a seventh embodiment of the present invention;

Figure 9 is a longitudinal cross sectional view of a portion of a turbine housing incorporating a frangible element for use in a turbine according to an eighth embodiment of the present invention;

Figure 10 is a longitudinal cross sectional view of a portion of a turbine housing incorporating a frangible element for use in a turbine according to a ninth embodiment of the present invention;

Figure 1 1 is a longitudinal cross sectional view of a portion of a turbine housing incorporating a frangible element for use in a turbine according to a tenth embodiment of the present invention;

Figure 12 is a radial cross sectional view of a portion of a turbine housing incorporating a frangible element for use in a turbine according to a eleventh embodiment of the present invention;

Figure 13 is a longitudinal cross sectional view of a portion of a turbine housing incorporating a frangible element for use in a turbine according to a twelfth embodiment of the present invention;

Figure 14 is a longitudinal cross sectional view of a portion of a turbine housing incorporating a frangible element for use in a turbine according to a thirteenth embodiment of the present invention;

Figure 15 is a longitudinal cross sectional view of a portion of a turbine housing incorporating a frangible element for use in a turbine according to a fourteenth embodiment of the present invention;

Figure 16 is a longitudinal cross sectional view of a portion of a turbine housing incorporating a frangible element for use in a turbine according to a fifteenth embodiment of the present invention; and Figure 17 is a radial cross sectional view of a portion of a turbine housing incorporating a frangible element for use in a turbine according to a sixteenth embodiment of the present invention.

Referring to Figure 1 , this illustrates a known variable geometry turbocharger comprising a housing comprised of 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 3.

The turbine housing 1 defines an inlet volute 7 to which gas from an internal combustion engine (not shown) is delivered. The exhaust gas flows from the inlet volute 7 to an axial outlet passage 8 via an annular inlet passage 9 and the turbine wheel 5. The inlet passage 9 is defined on one side by a face 10 of a radial wall of a movable annular wall member 1 1 , commonly referred to as a "nozzle ring", and on the opposite side by an annular shroud 12 which forms the wall of the inlet passage 9 facing the nozzle ring 1 1 . The shroud 12 covers the opening of an annular recess 13 in the turbine housing 1 .

The nozzle ring 1 1 supports an array of circumferentially and equally spaced inlet vanes 14 each of which extends across the inlet passage 9. The vanes 14 are orientated to deflect gas flowing through the inlet passage 9 towards the direction of rotation of the turbine wheel 5. When the nozzle ring 1 1 is proximate to the annular shroud 12, the vanes 14 project through suitably configured slots in the shroud 12, into the recess 13.

The position of the nozzle ring 1 1 is controlled by an actuator assembly of the type disclosed in US 5,868,552. An actuator (not shown) is operable to adjust the position of the nozzle ring 1 1 via an actuator output shaft (not shown), which is linked to a yoke 15. The yoke 15 in turn engages axially extending actuating rods 16 that support the nozzle ring 1 1 . Accordingly, by appropriate control of the actuator (which may for instance be pneumatic or electric), the axial position of the rods 16 and thus of the nozzle ring 1 1 can be controlled. The speed of the turbine wheel 5 is dependent upon the velocity of the gas passing through the annular inlet passage 9. For a fixed rate of mass of gas flowing into the inlet passage 9, the gas velocity is a function of the width of the inlet passage 9, the width being adjustable by controlling the axial position of the nozzle ring 1 1 . Figure 1 shows the annular inlet passage 9 fully open. The inlet passage 9 may be closed to a minimum by moving the face 10 of the nozzle ring 1 1 towards the shroud 12.

The nozzle ring 1 1 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 1 1 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 1 1 . 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 1 1 .

Gas flowing from the inlet volute 7 to the outlet passage 8 passes over the turbine wheel 5 and as a result torque is applied to the shaft 4 to drive the compressor wheel 6. 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).

A conventional fixed geometry turbocharger typically incorporates all of the components of the variable geometry turbocharger shown in Figure 1 except for the components which enable the annular wall member 1 1 ("nozzle ring") to be moved across the inlet passage 9, and the shroud 12 and annular recess 13 in the turbine housing 1 , since there is no requirement to accommodate sliding movement of the vanes 14.

In Figures 2 to 10, there are illustrated nine embodiments of turbines according to the first aspect of the present invention that can be substituted for the turbine described above in the context of the turbocharger shown Figure 1 . That is, modification of the turbine housing 1 of the turbocharger shown in Figure 1 to incorporate frangible elements according to any one or more of the nine embodiments shown in Figures 2 to 10 provides a turbocharger according to the second and third aspects of the present invention.

Referring now to Figure 2 there is shown a section of a turbine housing according to a first embodiment of the present invention. Components shown in Figure 2 which correspond to those described above in relation to Figure 1 take the same reference numerals but increased by 100. In Figure 2 there is shown a turbine housing 101 which defines a single inlet volute 107 opening into an annular inlet passage 109. The turbine housing 101 has been cast so as to incorporate an integral frangible element 124, which is designed to shear at the plane x-x in preference to the turbine housing 101 cracking in the plane z-z upon failure of the turbine wheel (not shown) during use.

The frangible element 124 incorporates a root 125, a tip 126 and an intermediate section 127 which connects the root 125 to the tip 126. The intermediate section 127 extends axially from an inner surface 128 of the axially outboard side 129 of the turbine housing 101 . As a result, the intermediate section 127 and tip 126 of the frangible element 124 reside in the inlet volute 107 upstream of the annular inlet passage 109. The tip 126 of the frangible element 124 extends over a greater radial extent than the intermediate section 127 of the frangible element 124. Thus, the frangible element 124 may be considered as incorporating an enlarged tip 126 as compared to the form of intermediate section 127. In this way, the thickness of the intermediate section 127 at the plane x-x is narrower than that of the tip 126, and is also narrower than the thickness of the turbine housing 101 in the plane z-z as shown in Figure 2. Consequently, when the frangible element 124 is impinged upon by high velocity debris emanating radially from a failed turbine wheel (not shown) the frangible element 124 will tend to shear at or adjacent to the plane x-x in preference to the housing 101 cracking or fragmenting at the plane z-z, or indeed, at any other location. In this way, the frangible element 124 absorbs a significant proportion of the kinetic energy of the high velocity debris and ensures that any such debris striking the turbine housing 101 does so with much less kinetic energy and is therefore much less likely to damage the turbine housing 101 .

In the embodiment shown in Figure 2, the frangible element 124 incorporates an intermediate section 127 of significant axial length such that the frangible element 124 as a whole (i.e. incorporating the root and tip, as well as the intermediate section) extends across around 70 to 80% of the distance separating the portion of the turbine housing 101 connected to the root 125 of the frangible element 124 and the opposite inner surface of the turbine housing 101 . It will be appreciated that the frangible element 124 may extend across any appropriate proportion of the axial separation between opposing side walls of the inlet volute 107 provided the frangible element 124 is positioned so as to be contactable by debris flying from a failed turbine wheel and fragment in preference to the turbine housing 101 . Figure 3 shows a generally similar arrangement to that shown in Figure 2, but which is now applied in a turbine housing 201 which defines twin inlet volutes 207A, 207B. In this embodiment, each inlet volute 207A, 207B is provided with a frangible element 124A, 124B respectively, which has the same general form as the frangible element 124 described above in respect of the embodiment shown in Figure 2. That is, each frangible element 124A, 124B shown in Figure 3 includes a root 125A, 125B which is connected to a corresponding tip 126A, 126B by an intermediate section 127A, 127B.

In the Figure 3 embodiment, each root 125A, 125B of the frangible element 124A, 124B is connected to the turbine housing 201 via a dividing wall 230 which is cast integrally with the turbine housing 201 and extends radially inwardly from a radially outboard side of 231 of the turbine housing 201 . The dividing wall 230 is essentially conventional in construction, save for its connection to the frangible elements 124A, 124B.

The radial thickness along each plane x-x of each respective frangible element 124A, 124B is less than the axial width of the dividing wall in plane y-y. The axial thickness x-x of each frangible element 124A, 124B is also less than the thickness of the turbine housing 201 in a plane z-z which passes through the plane of the turbine wheel (not shown). In this way, if the turbine wheel fails, the high velocity debris emanating from the turbine wheel will strike each frangible element 124A, 124B and shear each frangible element 124A, 124B across plane x-x. The kinetic energy of the flying debris is thereby used to shear each frangible element 124A, 124B rather than being passed to the turbine housing 201 . In this way the frangible elements 124A, 124B protect the turbine housing 201 from damage due to the failed turbine wheel.

Also shown in Figure 3 is a second pair of axially extending frangible elements 124AA, 124BB, which lie radially inboard of the other pair of frangible elements 124A, 124B described above. The radially inboard pair of frangible elements 124AA, 124BB take the same general form as the other pair 124A, 124B, but can be designed so as to be more or less resistant to shearing upon impact by debris emanating from a failed turbine wheel than the radially outboard pair 124A, 12B. Provision of a second pair of frangible elements 124AA, 124BB, may add to the weight of the turbine housing 201 and the complexity of its manufacture, however, this may be more than offset by the improvement they provide in respect of containment of turbine wheel debris as a result of a turbine wheel failure. It will be appreciated that, although two pairs of frangible elements 124A, 124B; 124AA, 124BB, are shown in Figure 3, any desirable number of pairs of frangible elements may be employed. Moreover, the number and form of frangible elements provided in each inlet volute may not be the same, and may vary from one inlet volute to the other.

Figure 4 shows a further embodiment of a turbine housing 301 incorporating a frangible element 324. The frangible element 324 again has a root 325 and a tip 326 connected by an intermediate section 327. In this embodiment, the intermediate section 327 incorporates a radially extending section 332 and an axially extending section 333, the radially and axially extending sections 332, 333 being of approximately equal length.

As can be seen from Figure 4, the axially extending region 333 of the frangible element 324 incorporates a waisted region adjacent to the plane x-x which is of narrower radial thickness than the neighbouring regions of the axially extending portion 333 of the frangible element 324. In this way, this waisted region along plane x-x is more susceptible to shearing upon impact of debris flying from a failed turbine wheel than the remainder of the frangible element 324. In this way, any debris hitting the frangible element 324 will cause the frangible element 324 to shear along the plane x-x, absorbing a significant proportion of the kinetic energy of the debris and lessening the chance of it damaging the turbine housing 301 .

As can be seen from Figure 4, the radial thickness of the frangible element 324 in the plane x-x is around 50% of the radial thickness of the turbine housing 301 in the plane z-z which lies radially outboard of the plane x-x and, indeed, planes z-z and x-x are coincident and contain one another. In this way, debris impacting the frangible element 324 will cause it to fragment in the manner described above rather than transmitting a shear force to the housing 301 which could crack or even breach the turbine housing 301 . It will be appreciated that frangible elements 324 of the kind shown in Figure 4 could be employed in a single entry turbine as shown in Figure 4 or in a twin entry turbine (or multiple entry turbine) as shown in Figure 3. That is, one or more of the frangible elements 124A, 124B; 124AA, 124BB from the Figure 3 arrangement could be substituted for a frangible element 324 of the kind shown in Figure 4.

Figure 5 is a radial, rather than longitudinal, cross-section through a turbine housing 401 according to a further embodiment of the present invention. In the design shown in Figure 5, the radial cross-section of the frangible element 424 is shown as shaded. The frangible element 424 extends around an arcuate path that matches that of the inlet volute 407 and in doing so surrounds a significant proportion of the circumference of the turbine wheel (not shown). The frangible element 424 has a longitudinal cross-sectional form that is the same as that shown in Figure 2. When viewed in radial cross-section, it can be seen that the frangible element 424 has a continuous, uniform profile, in that its radial thickness when viewed in radial cross-section is the same throughout the circumferential length of the frangible element 424. The radius of the frangible element 424, however, reduces from its upstream end 434 to its downstream end 435 nearest to the turbine wheel (not shown), in accordance with the reducing radius of the inlet volute 407.

Referring now to Figure 6 there is shown an alternative embodiment of a turbine to that shown in Figure 5. The turbine shown in Figure 6 incorporates a housing 501 into which has been cast a plurality of discontinuous circumferentially extending arcuate members 524, each of which, is an individual frangible element 524. When each frangible element 524 is viewed in longitudinal cross-section it takes the same general form as the frangible element 124 shown in Figure 2, but as will be appreciated, the turbine shown in Figure 6 incorporates a total of 10 separate formations, each of which represents a frangible element 524. Each frangible element 524 takes a generally arcuate form with some frangible elements 524 lying radially inboard of neighbouring frangible elements 524. Thus, while each frangible element 524 defines an arc of generally similar radius, they are oriented so as to follow a general path of decreasing radius from the most upstream frangible element 524A to the most downstream frangible element 524B. Providing a discontinuous frangible element 524 of this kind may afford advantages in terms of aerodynamics, weight, cost and/or complexity in certain applications as compared to a continuous frangible element 424 as shown in Figure 5.

Figure 7 shows another embodiment of a turbine according to the present invention. In this embodiment, the turbine housing 601 incorporates two frangible elements 624A, 624B in the form of elongate members which extend from an inner wall 636 of the section of the turbine housing 601 that defines the turbine inlet volute 607 towards the annular inlet 609. The two frangible elements 624A, 624B extend towards each other in a direction that is inclined to the radius of the turbine wheel (not shown) so as to converge within the turbine inlet volute 607. The combined axial extent, A, of the two frangible elements 624A, 624B is greater than the axial extent of the turbine wheel (not shown), which corresponds broadly with the axial width, B, of the annular inlet 609, to ensure that they are contacted by any fragments of a failed turbine wheel that are ejected outwards towards the turbine inlet volute 607, including those fragments that follow a path that is not perfectly radial.

Figure 8 shows a yet further embodiment in which a turbine housing 701 defines an axially extending frangible element 724 located in the turbine inlet volute 707. The frangible element 724 may be cast integrally with the turbine housing 701 . The frangible element 724 may be cast or machined to define one or more points of weakness 737 at which the frangible element 724 is designed to crack or shear to absorb energy from fragments of a failed turbine wheel (not shown). For the same reasons as described above in relation to the embodiment shown in Figure 7, the frangible element 724 shown in Figure 8 is axially wider than the axial width of the turbine wheel (not shown) or the annular inlet 709.

In Figure 9 there is shown a different embodiment in which a frangible element 824 extends from a side wall 838 of a section of a turbine housing 801 that defines an annular inlet 809. Thus, in this embodiment, the frangible element 824 resides in the annular inlet 809 rather than the turbine inlet volute 807 as in previous embodiments. As a result of being located radially closer to the turbine wheel (not shown), the frangible element 824 may be able to absorb more kinetic energy than if positioned further away from the turbine wheel. In the embodiment shown in Figure 9, a side wall 839 of the annular inlet 809 opposite to the side wall 838 from which the frangible element 824 extends defines a curved profile so as to form a recess 840 shaped to accommodate an end 841 of the frangible element 824 furthest from the side wall 838 from which the frangible element 824 extends. In this way, the frangible element 824 can extend across an axial length that is greater than the axial width of the turbine wheel (not shown) or the annular inlet 809 and thereby ensure that any fragments of a failed turbine wheel impinge upon it rather than striking the turbine housing 801 .

Figure 10 shows a further alternative embodiment of a turbine according to the present invention. A fundamental different between this embodiment and those shown in Figures 2 to 9 is that this embodiment does not include an elongate member extending into the turbine inlet passageway, i.e. either the turbine inlet volute or the annular inlet. Instead, in this embodiment, the turbine housing 901 is shaped so as to define a side wall 939 to a annular inlet 909 that has a curved profile when viewed in cross section as shown in Figure 10. To ensure satisfactory exhaust gas flow through the annular inlet 909 the opposite side wall 938 of the annular inlet 909 has a profile that is curved in a broadly similar fashion to the opposite side wall 939. The curvature results in an upstream part 942 of one of the side walls 939 residing in a generally annular region defined around the periphery of the turbine wheel (not shown). Consequently, if the turbine wheel fails, fragments of the turbine wheel flung generally radially outwards will impinge upon the part 942 of the side wall 939 since it axially overlies the turbine wheel. A region 943 of the turbine housing 901 adjacent the part 942 of the side wall 939 defines a groove 944 which extends outwards from an inboard end 945 within the annular inlet 909 to an outboard end 946 within the turbine inlet volute 907. This groove 944 defines a region 943 of the housing 901 that is thinner and therefore less strong than the surrounding regions of the housing 901 . Consequently, when the axially overlying part 942 of the side wall 939 is impacted by fragments of a failed turbine wheel, the housing 901 preferentially breaks or fractures at that thinned area, i.e. in the vicinity of the groove 944. This has the effect of absorbing a significant amount of the kinetic energy of the turbine wheel fragments, thereby allowing the remainder of the turbine housing to be thinner and therefore lighter. It will be appreciated that the groove 944 may be replaced or supplemented with additional grooves, slots and/or a suitably shaped cavity cast or machined into the housing 901 . A groove 944 may be provided just to one side of the annular inlet 909, as shown in Figure 10, or a groove, slot, cavity or the like may be provided to both sides of the annular inlet 909, or may circumscribe the majority or all of the circumference of the annular inlet 909.

Figure 1 1 shows a yet further embodiment of a turbine according to the present invention where the turbine housing 1001 has been manufactured, for example by casting, so as to define one or more cavities or voids 1047 in a section of the turbine housing 1001 which lies radially outboard of the turbine wheel (not shown) and the turbine inlet 1007. One or more of the cavities 1047 can be filed with any desirable material, such as sand or the like, or it can be left empty. Region 1048 of the turbine housing 1001 radially inboard of the or each cavity 1047 is therefore thinner than adjacent sections of the turbine housing 1001 axially either side of the or each cavity 1047. As a result, the region 1048 of the turbine housing 1001 which radially underlies the or each cavity 1047 is more likely to fracture upon impingement by a fragment of a failed turbine wheel (not shown) than adjacent sections of the turbine housing 1001 . Additionally, where one or more of the cavities 1047 is filled with a material, such as sand, the material in the one or more cavities 1047 can also contribute to absorbing kinetic energy from the fragments of the turbine wheel that impinge upon region 1048 of the turbine housing 1001 . In this way, as well fracturing, the region of the turbine housing 1048 may also crumple to some extent to absorb energy. It will be appreciated that a number of different materials could be provided in one or more of the cavities 1047, such as an energy absorbing foam, mesh or the like. Moreover, where multiple cavities 1047 are provided, some may contain material, while others may not, and, the cavities 1047 containing material may contain the same or different types and/or amounts of material.

Figure 12 shows a further embodiment of a turbine according to the present invention which includes a plurality of circumferentially spaced cavities 1 147 similar to the cavities 1047 described above in relation to Figure 1 1 . In the embodiment shown in Figure 12, a plurality of cavities 1 147 extend in a series circumferentially circumscribing the turbine wheel 1 105, in a broadly similar fashion to the embodiment described above in relation to Figure 6, noting, however, that in the Figure 6 embodiment the frangible elements are positioned in the turbine inlet, whereas in the Figure 12 embodiment, they form part of the turbine housing 1 101 itself. Further in relation to the Figure 12 embodiment, it is not necessary to define cavities 1 147 in the region 1 149 of the turbine housing 1 101 which lies radially outboard of the turbine wheel but which also lies radially outboard of the tongue 1 150 of the turbine housing 1 101 . That is, tongue 1 150 shields the section 1 149 of the turbine housing 1 101 from the dotted line 1 151 shown in Figure 12 to the outlet of the turbine housing 1 152.

Turning to Figure 13, this shows a further embodiment of a turbine according to the present invention. In the embodiment shown in Figure 13, the turbine housing 1201 has been cast so as to define a pair of opposed arms 1253 which extend axially from opposite sides of the turbine housing 1201 to define an annular gap 1254 between the arms 1253 and, radially outboard, one or more cavities 1255 which, contrary to the Figure 1 1 embodiment, are now open to the turbine volute 1207. As in previous embodiments, the arms 1253 lie in a generally annular region around the periphery of the turbine wheel (not shown) but within the outer diameter of the turbine housing 1201 . The arms 1253 are designed to fracture upon impact by parts of a failed turbine wheel so as to extract energy therefrom and prevent such fragments escaping from the turbine housing 1201 .

In Figure 14, there is shown a further embodiment of a turbine according to the present invention in which a dividing wall 1330 of a split volute turbine, similar to that described above in relation to Figure 3, is shaped so as to shear in a predetermined manner to absorb energy from fragments of a failed turbine wheel. In the embodiment shown in Figure 14, the dividing wall 1330 extends radially from the turbine housing 1301 into the turbine volute 1307 to divide it into twin volutes 1307A and 1307B. Furthermore, the dividing wall 1330 extends from the turbine housing 1301 via a waisted or thinned region 1356 (shown between arrows X in Figure 14), which is defined so as to cleave preferentially to regions of the dividing wall 1330 radially either side of the wasted region 1356. In this way, the dividing wheel will shear preferentially between arrows XX upon impingement by fragments of a failed turbine wheel and thereby absorb energy from those fragments.

Turning to Figure 15, there is shown a further embodiment of a turbine according to the present invention. In Figure 15, the turbine housing 1401 has been cast so as to define a pair of radially offset axially extending arms 1457A and 1457B. The arms 1457A, 1457B are radially offset by the distance shown between the arrows XX in Figure 15. The arms 1457A and 1457B are axially offset by the distance denoted by arrow Y in Figure 15. The radial separation X-X between the arms 1457A, 1457B should be sufficiently large to ensure that the arms 1457A, 1457B do not restrict gas flow through the turbine volute. Furthermore, the axial spacing Y between the arms 1457A, 1457B should not be so large as to enable fragments of a failed turbine wheel likely to breach or significantly weaken the turbine housing 1401 through the gap of width Y, but the axial spacing Y should be sufficiently large to ensure that it does not represent a significant restriction to flow through the turbine volute. The axial dimension Y may also be sufficiently large to enable small fragments of a failed turbine wheel between the arms 1457A, 1457B, provided those fragments are so small that they will not breach or significantly weaken the turbine housing 1401 following a turbine wheel failure. Similar to the embodiments shown in Figures 5 and 6 as described above, the arms 1457A, 1457B may extend circumferentially around the turbine wheel within the turbine volute 1407 either continuously (as shown in Figure 5) or discontinuously (as shown in Figure 6).

In Figure 16 there is shown a further alternative embodiment of a turbine according to the present invention. In this embodiment, the turbine housing 1501 has been cast so as to incorporate a radially inwardly extending arm 1558, which can, itself, act as a frangible element so as to absorb energy from a failed turbine wheel. The embodiment shown in Figure 16 also includes one or more notches 1559 defined in the wall of the turbine housing 1501 so as to define preferential fracture planes which will fracture in preference to the surrounding housing when the arm 1558 is contacted by fragments of a failed turbine wheel. Notches 1559 may be provided in a continuous or discontinuous circumferential arrangement to one side of the turbine housing 1501 as shown in Figure 16, or they may be provided in a continuous or discontinuous arrangement to both sides of the turbine housing 1501 , thus including the additional set of notches shown in dotted lines and denoted 1560 in Figure 16. As further shown in Figure 16, a section of 1561 of the turbine housing 1501 which radially overlies the turbine wheel may be cast so as to curve radially inwards and to define a recess in the outer surface of the turbine housing 1501 extending circumferentially around that portion 1561 of the turbine housing 1501 . Portion 1561 of the turbine housing 1501 could, by virtue of its form, be stronger than a conventionally shaped turbine housing 1501 in that portion 1561 of the turbine housing 1501 but may still fracture to some extend upon impact by a fragment of a failed turbine wheel. The portion 1561 of the turbine housing defining the aforementioned recess is shown in dotted lines in Figure 16. Strengthening this portion 1561 of the turbine housing 1501 can ensure, with a greater degree of certainty, that the housing 1501 fractures at the or each notch 1559/1560. It will be appreciated that in certain alternative embodiments it may be preferred to have one or more notches 1560 but not notches 1559 on the opposite side of the turbine housing.

Figure 17 shows a further alternative embodiment of a turbine according to the present invention which is similar to that described above in relation to Figure 16 but where a discontinuous series of fracture notches 1659 are defined by the housing 1601 in a circumferential array around the turbine wheel (not shown). In certain embodiments, the or each notch 1659 may be connected to each adjacent notch 1659 by a thinned region 1661 of the housing 1601 , or each region 1661 of the housing 1601 in between adjacent notches 1659 may be of conventional thickness, i.e. have a similar thickness to the turbine housing 1601 radially adjacent to each region 1661 .

It will be appreciated that numerous modifications may be made to the preferred embodiments described above without departing from the underlying inventive concepts defined in the various aspects of the present invention. By way of example, in addition to the frangible element(s), any section or sections of the turbine housing may comprise deformable, energy absorbing material to act as a "crumple zone" to absorb energy released as a result of turbine wheel failure during operation. Moreover, any one or more of the above described preferred embodiments could be combined with one or more of the other preferred embodiments to suit a particular application.

The described and illustrated embodiments are to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the scope of the inventions as defined in the claims are desired to be protected. It should be understood that while the use of words such as "preferable", "preferably", "preferred" or "more preferred" in the description suggest that a feature so described may be desirable, it may nevertheless not be necessary and embodiments lacking such a feature may be contemplated as within the scope of the invention as defined in the appended claims. In relation to the claims, it is intended that when words such as "a," "an," "at least one," or "at least one portion" are used to preface a feature there is no intention to limit the claim to only one such feature unless specifically stated to the contrary in the claim. When the language "at least a portion" and/or "a portion" is used the item can include a portion and/or the entire item unless specifically stated to the contrary.