GB2551450A

GB2551450A - Turbocharger arrangement

Info

Publication number: GB2551450A
Application number: GB1711631.0A
Authority: GB
Inventors: Michael Bywater John
Original assignee: Cummins Ltd
Current assignee: Cummins Ltd
Priority date: 2012-01-14
Filing date: 2012-01-14
Publication date: 2017-12-20
Anticipated expiration: 2032-01-14
Also published as: GB201711631D0; GB2551450B

Abstract

A turbocharger arrangement (50, figure 4) comprises a turbocharger (52), a generator (54), a turbine wheel (4) and a compressor wheel (58) mounted to a turbocharger shaft 71. The turbocharger shaft is supported by a bearing assembly 13a, located between the turbine wheel and the compressor wheel, and the compressor wheel is provided between the generator and the bearing assembly wherein the generator comprises a rotor portion (55) and a stator portion (57). The rotor portion is associated with a generator shaft 72 that defines a feature 76 that is adapted to engage an end region of the turbocharger shaft. The feature may matingly engage the end region of the turbocharger shaft and / or be a female formation configured to receive a complimentary male formation, preferable with respective screw threads, which may be complimentary. An exducer portion (58b) of the compressor wheel may be located between an inducer portion (58a) and the bearing assembly or the inducer portion may be located between the exducer portion and the bearing assembly.

Description

Turbocharger Arrangement

The present invention relates to a turbocharger arrangement. In particular, the present invention relates to a turbocharger arrangement having a turbocharger and a generator.

Turbochargers are well known devices for supplying air to an inlet 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 inlet 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 of a conventional 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 characteristics of the inlet (such as the inlet’s size) 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 are referred to as variable geometry turbochargers.

Nozzle vane arrangements in variable geometry turbochargers can take different forms. Two known types of variable geometry turbine are swing vane turbochargers and sliding nozzle turbochargers.

Generally, in swing vane turbochargers the inlet size (or flow size) of a turbocharger turbine is controlled by an array of movable vanes in the turbine inlet. Each vane can pivot about an axis extending across the inlet parallel to the turbocharger shaft and aligned with a point approximately half way along the vane length. A vane actuating mechanism is provided which is linked to each of the vanes and is displaceable in a manner which causes each of the vanes to move in unison, such a movement enabling the cross sectional area available for the incoming gas and the angle of approach of the gas to the turbine wheel to be controlled.

Generally, in sliding nozzle turbochargers the vanes are fixed to an axially movable wall that slides across the inlet. The axially movable wall moves towards a facing shroud plate in order to close down the inlet 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.

The compressor of a conventional turbocharger comprises a compressor housing defining compressor chamber within which the compressor wheel is mounted such that it may rotate about an axis. The compressor also has a substantially axial inlet passageway defined by the compressor housing and a substantially annular outlet passageway defined by the compressor housing between facing radially extending walls arranged around the compressor chamber. A volute is arranged around the outlet passageway and an outlet is in flow communication with the volute. The passageways and compressor chamber communicate such that gas (for example, air) at a relatively low pressure is admitted to the inlet and is pumped, via the compressor chamber, outlet passageway and volute, to the outlet by rotation of the compressor wheel. The gas at the outlet is generally at a greater pressure (also referred to as boost pressure) than the relatively low pressure of the gas which is admitted to the inlet. The gas at the outlet may then be pumped downstream of the compressor outlet by the action of the compressor wheel.

Some known turbochargers are fitted with a generator such that rotation of the turbocharger rotor (turbine wheel, compressor wheel and shaft) when the turbocharger is in use can be used to generate electrical power. Under certain operational conditions the generator can also be used as a motor to drive the turbocharger, such as during an increase in engine speed from idle and after gear changes to reduce turbo-lag and particulate emissions. References to generators and motors are often used interchangeably in this field of application and so all references to a ‘generator’ hereinafter should be understood as relating to a motor capable of driving the turbocharger as well as a generator capable of generating electrical power from the turbocharger.

Known turbochargers fitted with a generator suffer from significant thermal issues as a result of the high operating temperatures at the turbine stage of the turbocharger causing heat to be conducted along the turbocharger shaft to the generator. Heat transmission may be reduced to some extent by improved cooling of the bearing assembly in between the turbine and compressor stages but this increases the overall cost and complexity of the turbocharger.

Typically, the generator rotor will be mounted on the turbocharger shaft and the generator stator provided at a suitable location around the area swept by the rotor during operation. In some arrangements the rotor is mounted in between the turbine and compressor wheels, while in other arrangements the rotor is mounted outboard of the compressor such that the compressor wheel is located in between the generator and turbine wheel. Locating the rotor and associated stator in between the turbine and compressor wheels does not increase the axial length of the turbocharger but can result in significant heat transfer from the turbine stage of the turbocharger to the generator which may harm its performance. Provision of the generator rotor and associated stator outboard of the compressor wheel reduces problems associated with heat transfer from the turbine stage but it does increase the axial length of the turbocharger shaft and, as a result, the overall size of the turbocharger. A longer turbocharger shaft is also more difficult and costly to manufacture and balance than a turbocharger shaft of conventional length.

It is an object of the present invention to provide a turbocharger arrangement which obviates or mitigates at least one of the above described disadvantages or other disadvantages present in the prior art.

According to the present invention there is provided a turbocharger arrangement comprising a turbocharger and a generator, the turbocharger comprising a turbine wheel and a compressor wheel mounted to a turbocharger shaft; the turbocharger shaft being supported by a bearing assembly located between the turbine wheel and the compressor wheel such that the turbocharger shaft may rotate about an axis; and the compressor wheel being provided between the generator and the bearing assembly; wherein the generator comprises a rotor portion and a stator portion, the rotor portion being associated with a generator shaft that defines a feature that is adapted to engage an end region of the turbocharger shaft.

By adopting an arrangement whereby the generator and turbocharger have dedicated shafts which are connected together the length of the turbocharger shaft can be reduced as compared to a conventional turbocharger / generator assembly with a generator outboard of the compressor which employs a single long shaft supporting both the turbocharger and the generator rotor. This enables the turbocharger and generator shafts to be balanced independently which is easier than balancing a single longer shaft. Moreover, the design of the generator shaft can be optimised for supporting the rotor and connecting to the turbocharger shaft rather than a single shaft having to accommodate the significantly varying operating conditions at the turbine stage, compressor stage and generator stage of the turbocharger arrangement. For example, in a specific preferred embodiment described below the generator rotor is formed integrally with the generator shaft, which would not previously have been possible when a single shaft was used. In this way it may be possible to improve the performance of the generator as compared to generators in conventional combined turbocharger/generator arrangements and/or produce such combined arrangements at lower cost than before.

The feature defined by the generator shaft may be of any suitable size and/or shape provided it can engage the end region of the turbocharger shaft. The ability for the two shafts to be connected together via the engagement of the end region of the turbocharger shaft with the feature defined by the generator shaft may be at least partly dependent upon both of the components that engage together have complementary or co-operating shapes and/or sizes.

It is preferred that said feature defined by the generator shaft is adapted to matingly engage the end region of the turbocharger shaft. In one preferred embodiment, the feature defined by the generator shaft is a female formation configured to receive a complementary male formation defined by the end region of the turbocharger shaft. In a further preferred embodiment the feature on the generator shaft may be a male formation and the end region of the turbocharger shaft may define a complementary female formation, In a still further preferred embodiment, the feature defined by the generator shaft may incorporate a plurality of female formations, male formations or a mixture of female and males formations adapted to matingly engage complementary male, female or a mixture of male and female formations respectively.

The feature defined by the generator shaft preferably defines a screw thread of complementary profile to a screw thread defined by the end region of the turbocharger shaft. Screw threads are relatively simple to incorporate into the structure of each shaft and provide a quick and easy way to assemble the generator shaft and the turbocharger shaft together. The orientation of the screw thread (i.e. whether it is a left-handed screw thread or a right-handed screw thread) should be chosen to ensure that there is no tendency for the screw connection between the two shafts to loosen and for the shafts to move apart during use of the turbocharger arrangement.

An end region of the generator shaft may be configured to abut a hub of the compressor wheel mounted on the turbocharger shaft. In this way, the generator shaft can function as a ‘nut’ or the like to help to secure the compressor wheel to the turbocharger shaft.

The end region of the turbocharger shaft that is engaged, preferably matingly engaged, by the feature defined by the generator shaft preferably extends along a proportion of the axial length of the generator shaft. The proportion may be less than about 50 % of the axial length of the generator shaft, less than about 30 % of the axial length of the generator shaft or even less, say less than about 20 % of the axial length of the generator shaft. Is it preferred that the end region of the turbocharger shaft extends at least 5 or 10 % along the axial length of the generator shaft, more preferably along at least around 15 or 20 % of the axial length of the generator shaft.

The rotor portion and the generator shaft may be integrally formed, as in the embodiment depicted in Figures 5 to 8 below, or they may be formed as separate components which are subsequently connected together, i.e. with the rotor portion being mounted on the generator shaft.

In a first preferred embodiment an exducer portion of the compressor wheel is located between an inducer portion of the compressor wheel and the bearing assembly. In this embodiment the compressor wheel is preferably provided in a compressor housing which defines an inlet and an outlet, the inlet being located axially outboard of the compressor wheel.

In a second preferred embodiment an inducer portion of the compressor wheel is located between an exducer portion of the compressor wheel and the bearing assembly. This is therefore the reverse arrangement of the compressor wheel as compared to the first preferred embodiment. In the second preferred embodiment it is preferable for the compressor wheel to be provided in a compressor housing which defines an inlet and an outlet, the inlet being located axially inboard of the compressor wheel. A portion of the generator may be attached directly to a portion of the compressor wheel, preferably a back face of the compressor wheel.

The inlet of the compressor housing may have a first end adjacent the compressor wheel and a second end remote from the compressor wheel. The inlet may be defined by a wall, a portion of the wall defining the first end of the inlet preferably being generally parallel to the axis, such that, in use, gas flowing through the first end of the inlet flows in a direction generally parallel to the axis. A portion of the wall may define the second end of the inlet which is generally radial with respect to the axis, such that, in use, gas flowing through the second end of the inlet flows in a generally radial direction with respect to the axis.

The outlet of the compressor housing may comprise a substantially annular outlet passageway and a volute arranged around the outlet passageway.

The turbocharger shaft may be of unitary construction or may comprise a plurality of discrete shaft portions connected together.

The compressor wheel and the generator may be provided in a one-piece housing. The compressor wheel and the bearing assembly may be provided in a one-piece housing.

The compressor wheel and the generator may be provided in dedicated compressor and generator housings respectively which are produced separately and then assembled into the turbocharger arrangement, or the compressor wheel and the generator may be provided in a one-piece housing which essentially combines a compressor housing and a generator housing.

The compressor wheel and the bearing assembly may be provided in dedicated compressor and bearing housings respectively which are produced separately and then assembled into the turbocharger arrangement, or the compressor wheel and the bearing assembly may be provided in a one-piece housing which essentially combines a compressor housing and a bearing housing. A specific embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a cross-sectional view of a turbocharger;

Figure 2 shows a schematic cross-sectional view of a first known turbocharger arrangement having a turbocharger and a generator;

Figure 3 shows a schematic cross-sectional view of a second known turbocharger arrangement having a turbocharger and a generator which may be modified to incorporate a split turbocharger / generator shaft arrangement according to the present invention;

Figure 4 shows a schematic cross-sectional view of a turbocharger arrangement incorporating a turbocharger and a generator which may be modified to incorporate a split turbocharger / generator shaft arrangement according to the present invention;

Figure 5 shows a schematic cross-sectional view of a turbocharger arrangement according to an embodiment of the present invention in which the turbocharger arrangement is generally similar to that shown in Figure 3 but which incorporates a split turbocharger / generator shaft arrangement according to the present invention;

Figure 6 is a detailed view of the circled section of the Figure 5;

Figure 7 shows a schematic perspective view of subcomponents of the turbocharger arrangement shown in Figure 5 in which the turbocharger and generator shafts have been separated to expose their means of connection; and

Figure 8 is a detailed view of the circled section of Figure 7.

Referring to Figure 1, the turbocharger comprises a turbine 1 joined to a compressor 2 via a central bearing housing 3. The turbine 1 comprises a turbine wheel 4 for rotation within a turbine housing 5. Similarly, the compressor 2 comprises a compressor wheel 6 which can rotate within a compressor housing 7. The compressor housing 7 defines compressor chamber within which the compressor wheel 6 can rotate. The turbine wheel 4 and compressor wheel 6 are mounted on opposite ends of a common turbocharger shaft 8 which extends through the central bearing housing 3.

The turbine housing 5 has an exhaust gas inlet volute 9 located annularly around the turbine wheel 4 and an axial exhaust gas outlet 10. The compressor housing 7 has an axial air intake passage 11 and a volute 12 arranged annularly around the compressor chamber. The volute 12 is in gas flow communication with a compressor outlet 25. The turbocharger shaft 8 rotates on journal bearings 13 and 14 housed towards the turbine end and compressor end respectively of the bearing housing 3. The compressor end bearing 14 further includes a thrust bearing 15 which interacts with an oil seal assembly including an oil slinger 16. Oil is supplied to the bearing housing from the oil system of the internal combustion engine via oil inlet 17 and is fed to the bearing assemblies by oil passageways 18. The oil fed to the bearing assemblies may be used to both lubricate the bearing assemblies and to remove heat from the bearing assemblies. The heating of the bearing assemblies may be caused by at least one of the following processes: friction due to rotation of the shaft, heat transferred from the turbine to the bearing assemblies via the bearing housing, and heat transferred to the bearing assemblies via the shaft 8. Other known turbochargers may use other types of bearing to support the turbocharger shaft within the turbocharger. For example, rolling element bearings may be used instead of journal bearings.

In use, the turbine wheel 4 is rotated by the passage of exhaust gas from the annular exhaust gas inlet 9 to the exhaust gas outlet 10. The turbine wheel 4 in turn rotates the compressor wheel 6 which thereby draws intake air through the compressor inlet 11 and delivers boost air to the intake of an internal combustion engine (not shown) via the volute 12 and then the outlet 25.

Some known turbocharger arrangements incorporate a turbocharger and a generator. Figures 2 and 3 each show a schematic representation of a different known turbocharger arrangement having a turbocharger and a generator.

The turbocharger arrangement 30 shown in Figure 2 is very similar to the turbocharger shown in Figure 1.

Features of the turbocharger arrangement 30 shown in Figure 2 which are substantially similar to those shown in the turbocharger of Figure 1 have been numbered with the same reference numerals.

The turbocharger shown in Figure 2 differs from that shown in Figure 1 in that the bearing housing 3 not only houses bearing assemblies 13a which support the shaft 8, but also a generator indicated generally by 32.

The generator 32 comprises a rotor portion 33 which is linked to the shaft 8 so that it rotates therewith, and a stator portion 34 which is fixed with respect to the bearing housing.

The generator 32 is of conventional construction, wherein one of the rotor portion 33 or stator portion 34 comprises the armature portion of the generator, which is the power producing portion of the generator; and the other of the rotor or stator comprises a field portion of the generator, which is the portion of the generator that produces a magnetic field. Rotation of the rotor portion 33 relative to the stator portion 34 due to the rotation of the shaft 8 causes the generator 32 to produce electrical power. It will be appreciated that by appropriate control the generator 32 can also be used as a motor to drive rotation of the shaft 8 under certain operating conditions, such as speed-up from idle and after gear changes to reduce turbo-lag and particulate emissions.

Due to the fact that the generator 32 is mounted in the bearing housing 3, which is adjacent to the turbine 1, the operating performance of the generator 32 can be adversely affected by heat transferred from the relatively high temperature gases which flow through the turbine housing 5 during use. For example, the turbine housing 5 and turbine wheel 4 may be at a temperature of between about 600 degrees Celsius and 900 degrees Celsius during operation of the turbocharger. Heat from the turbine housing 5 and turbine wheel 4 may be transmitted to the generator 32 via the bearing housing 3, the bearing assemblies 13a due to friction, or the shaft 8. This can decrease the operating performance of the generator 32 for various reasons, including an increase in resistance of the armature portion of the generator 32.

Some known turbocharger arrangements similar to that shown in Figure 2 incorporate additional cooling so as to reduce the temperature of the bearing housing and thereby the generator. This additional cooling may be provided by a water cooling system or by increasing the flow of oil to the bearing housing. Although oil is provided to the bearing housing primarily for lubricating the bearing arrangements, the oil also cools components within the bearing housing (including the generator). It will be appreciated however that the provision of additional cooling may add to the cost and/or complexity of the turbocharger arrangement.

Figure 3 shows a further known turbocharger arrangement 40. Again, features of the turbocharger arrangement 40 shown in Figure 3 which are substantially similar to those of the turbocharger shown in Figure 1 are given the same reference numbers as those features of the turbocharger shown in Figure 1.

The turbocharger arrangement 40 shown in Figure 3 differs from the turbocharger shown in Figure 1 in that it has a generator 42 mounted to the shaft 8 axially (i.e. along the axis of rotation of the turbocharger) outboard of the compressor wheel 6. In this arrangement the turbine wheel 4, compressor wheel 6 and generator 42 are all mounted to a single shaft 8.

In order to provide the compressor 2 of the turbine arrangement 40 with air, the turbocharger arrangement 40 comprises a generally annular air inlet passageway 44. The inlet passageway 44 is defined between a radially inner wall 45a and a radially outer wall 45b. Struts (not shown) extend between the inner wall 45a and outer wall 45b to support the walls 45a, 45b relative to one another. The inlet passageway 44 defines a first open end 44a through which air is admitted into the inlet passageway 44. The inlet passageway then extends around the generator 42 and terminates with a second end 44b which directs air onto an inducer portion 46 of the compressor wheel 6. The first and second ends 44a, 44b of the inlet passageway 44 extend in a direction that is generally parallel to the axis of rotation of the turbocharger.

Locating the generator 42 axially outboard of the compressor wheel 6 reduces the amount of heat transferred to the generator 42 from the turbine 1 as compared to arrangements of the kind shown in Figure 2 in which the generator is located in the bearing housing. This is because the compressor 2, which is adjacent to the generator in this turbocharger arrangement 40, is supplied with relatively cool air from the atmosphere. In some cases, the movement of relatively cool air (for example from the atmosphere) flowing through the compressor 2 may extract heat from the turbocharger arrangement and thus reduce the temperature of at least part of the turbocharger arrangement, in particular the generator 42. It is also possible to draw air past the rotor of the generator 42 to aid cooling of the generator 42. Although locating the generator 42 axially outboard of the compressor 2 may reduce the problems caused by heat transfer from the turbine 1 this type of arrangement still suffers from disadvantages.

As previously described, it is common for the compressor of a turbocharger to be configured such that is has a substantially axial inlet. This may be problematic in a case where the generator is located axially outboard of the compressor because the generator is located on the axis of the turbocharger axially outboard of the compressor wheel, where the compressor inlet would otherwise be located. In order to overcome this problem the turbocharger shown in Figure 3 incorporates a generally annular inlet passageway 44 which extends away from the turbocharger axis, around the generator 42 and then back towards the turbocharger axis before extending axially towards the compressor 2. As a result the generator 42 is located further from the bearing housing 3 than would otherwise be necessary and the turbocharger incorporating the generator 42 has a greater axial length and therefore overall size than would otherwise be necessary.

The use of additional material in order to make the inlet passageway 44 increases the overall weight of the turbocharger arrangement 40 compared to a turbocharger without a generator and in some cases a turbocharger with a generator mounted within the bearing housing as depicted in Figure 2. Locating the generator 42 axially outboard of the compressor 2 increases the mass overhang of the compressor end of the shaft 8. The mass overhang of the compressor end of the shaft 8 is a function of the product of the mass axially outboard of the bearing assembly 13a (the mass of the compressor wheel 6, the rotor of the generator 33, and the portion of the shaft 8 which extends beyond the bearing assembly 13a closest to the compressor 2) and the distance between the bearing assembly 13a and the point at which the mass axially outboard of the bearing assembly 13a can be considered to act. An increased mass overhang necessitates a thicker shaft 8 to overcome shaft bending and various bearing and/or oil-film vibration modes but results in the shaft 8 being heavier and more costly to produce. The use of a thicker shaft 8 requires the use of larger bearings 13, 14, 15 within the bearing assemblies 13a that support the shaft 8 which are therefore likely to be heavier and more costly to produce. Additionally, larger bearings tend to be less efficient, thereby generating greater amounts of heat and causing greater frictional losses. Finally, the use of a thicker shaft 8 may result in a greater conduction of heat from the bearing assembly 13a to the compressor 2 and generator 42, which may reduce the operating performance of the compressor 2 and/or generator 42 and necessitate increased cooling of the bearing assembly 13a.

Figure 4 shows a turbocharger arrangement 50 which represents a significant improvement to the turbocharger arrangement 40 shown in Figure 3. Features of the turbocharger arrangement 50 which are substantially similar to those of the turbocharger shown in Figure 1 are again labelled using numerical references which correspond to those of the turbocharger shown in Figure 1.

The turbocharger arrangement 50 comprises a turbocharger 52 and a generator 54. The turbocharger 52 comprises a turbine 1 having a turbine wheel 4, and a compressor 56 having a compressor wheel 58. The turbine 1 is joined to the compressor 56 via a central bearing housing 3. The turbine wheel 4 and compressor wheel 58 are mounted to a shaft 8. The turbocharger shaft 8 rotates on two bearing assemblies 60 within the bearing housing 3, although it will be appreciated that any desirable number of bearing assemblies may be used. The turbine wheel 4 rotates within the turbine housing 5. Similarly, the compressor wheel 58 rotates within a compressor chamber defined by a compressor housing 62.

The turbine housing 5 defines an exhaust gas inlet volute 9 arranged around an annular inlet which is in turn arranged around the turbine wheel 4. The turbine housing 5 also defines an axial exhaust gas outlet 10.

The turbine wheel 4 and compressor wheel 58 are mounted to the shaft 8 which is supported by the bearing assembly 60 located in the bearing housing 3 intermediate the turbine 1 and the compressor 56, such that the shaft 8 may rotate about an axis X-X. The axis X-X about which the shaft 8, and attached turbine wheel 4 and compressor wheel 58 rotate, may also be referred to as the turbocharger axis.

The generator 54 is located axially outboard of the compressor 56 in a generally similar manner to the turbocharger arrangement 40 described above in relation to Figure 3. The generator 54 comprises a generator housing 64 which depends from the compressor housing 62. The generator 54 has a rotor portion 55 which is mounted to the shaft 8 such that the rotor portion 55 of the generator 54, the compressor wheel 58, the turbine wheel 4 and the shaft 8 all co-rotate about the turbocharger axis X-X. The generator 54 also has a stator portion 57 which is fixed relative to the generator housing 64. The generator 54 operates in a conventional manner whereby rotation of the rotor portion 55 relative to the stator portion 57 of the generator 54 generates electrical power. It will be appreciated that the generator 54 may also be controlled so as to act as a motor to drive rotation of the shaft 8 and the associated components if desired.

The compressor wheel 58 is mounted on the shaft 8 such that it is between the generator 54 and the bearing assembly 60 within the bearing housing 3. The compressor wheel 58 has an inducer portion 58a and an exducer portion 58b. The inducer portion 58a of the compressor wheel 58, when in use, receives air from a compressor intake 66. The air from the compressor inlet 66 then passes from adjacent the inducer portion 58a of the compressor wheel 58 to adjacent the exducer portion 58b of the compressor wheel 58. The air is then passed from the adjacent exducer portion 58b of the compressor wheel 58 to a compressor outlet 68. In this case the compressor outlet 68 is generally radial. That is, in use gas passing out of the compressor outlet 68 travels in a generally radially outward direction relative to the turbocharger axis X-X.

The compressor wheel 58 is mounted to the shaft 8 such that the inducer portion 58a of the compressor wheel 58 is between the exducer portion 58b of the compressor wheel 58 and the bearing assembly 60 within the bearing housing 3. That is, the inducer portion 58a of the compressor wheel 58 is between the exducer portion 58b of the compressor wheel 58 and the bearing housing 3. Arranging the compressor wheel 58 so that it faces inboard (i.e. towards the bearing assembly 13a and turbine 1) is different to the arrangement of a conventional compressor wheel, such as those shown in Figures 1 to 3 described above, in which the compressor wheel faces outboard with the exducer portion of the compressor wheel in between the inducer portion of the compressor wheel and the bearing assembly 13a.

The compressor inlet 66 is configured to feed air into the compressor 56 from a position axially inboard of the compressor 56, i.e. from the turbine or bearing assembly side of the compressor 56. In this way, the axial distance between the compressor inlet 66 and the turbine 1 is less than the distance between the compressor wheel 58 and the turbine 1. The compressor inlet 66 defines a first end 66a adjacent the inducer portion 58a of the compressor wheel 58 and a second end 66b remote from the compressor wheel 58. The compressor inlet 66 is generally volute shaped although any suitable shape may be used. A generally volute shaped compressor inlet is preferred since it can swirl, also sometimes referred to as “pre-swirl”, into air travelling along the inlet. Introducing pre-swirl into the air before it is interacts with the compressor wheel may increase the proportion of the energy of the air that is supplied to the compressor which is converted into useful work by the compressor and thereby increase the efficiency and operating performance of the turbocharger.

The first end 66a of the compressor inlet 66 is orientated such that, in use, the direction of air flow through the first end 66a of the compressor inlet 66 has a component which is substantially parallel to the turbocharger axis X-X, i.e. which is in a generally axial direction. The second end 66b of the compressor inlet 66 is orientated such that, in use, the direction of air flow through the second end 66b of the compressor inlet 66 is substantially perpendicular to the turbocharger axis X-X. A wall which defines the compressor inlet 66 comprises a first section that extends in a direction which is, or a component of which is, substantially parallel to the turbocharger axis X-X and which defines the first end 66a of the compressor inlet 66. The wall further comprises a second section that extends in a direction that is substantially perpendicular to the turbocharger axis X-X and which defines the second end 66b of the compressor inlet 66 and which. While this is a preferred configuration for the compressor inlet, it will be appreciated that alternative configurations may be employed, such as an arrangement in which air flow through the first end of the compressor inlet is substantially parallel to the turbocharger axis and air flow through the second end of the compressor inlet is non-parallel to the turbocharger axis X-X.

The turbocharger arrangement 50 has several advantages over the arrangements described above in relation to Figures 2 and 3.

The generator 54 is located axially outboard of the compressor 56 thereby reducing the amount of heat transmitted to the generator 54 from the turbine 1 and/or bearing housing 3. Arranging the exducer portion 58b so that it is axially outboard of the inducer portion 58a enables the generator to be located very close to the compressor 56 and, in particular, the compressor wheel 58. In some embodiments, a portion of the compressor wheel 58, such as an outboard or back face of the compressor wheel 58, which is generally radial and free of compressor blades, may be attached directly to a portion of the generator 54. This may reduce the overall length of the turbocharger arrangement.

Reducing or eliminating the need for a space between the compressor 56 and generator 54 reduces the mass overhang of the compressor end of the rotating portion of the turbocharger arrangement, i.e. the compressor wheel 58, the rotor portion of the generator 54 and the portion of the shaft which extends beyond the bearing arrangement closest to the compressor wheel 58 that supports the shaft. By reducing the mass overhang at the compressor end of the turbocharger arrangement 50 a thinner shaft can be used, which will be lighter and less expensive to produce, and which allows the use of smaller bearings that tend to be cheaper, more efficient and generate less heat due to friction compared to their larger counterparts.

The turbocharger arrangement 50 would be counterintuitive to a person skilled in the art because it would be thought that air would have to be supplied to the compressor wheel via a radial inlet to accommodate reversing the direction in which the compressor wheel faces, i.e. inboard rather than outboard, which in fact is not the case. Additionally, it might have been expected that air entering the compressor 56 via the compressor inlet 66 will be exposed to a greater amount of heat compared to a more conventional arrangement in which the compressor inlet is outboard of the compressor wheel. Once again, however, this is not the case.

Referring now to Figures 5 and 6 there is shown a cross-sectional view of a turbocharger arrangement incorporating a turbocharger and a generator according to the present invention. The fundamental configuration of the turbine (not shown), bearing assembly 13a (only partially shown), compressor wheel 6 and generator 70 is essentially the same as that described above in relation to Figure 3. That is, the generator 70 is provided axially outboard of the compressor wheel 6 such that the compressor wheel 6 is in between the generator 70 and the bearing assembly 13a. It will be appreciated that the arrangement shown in Figures 5 and 6 may be replaced with the alternative arrangement described above in relation to Figure 4 where the generator is still outboard of the compressor wheel but the compressor wheel faces inboard and received air from the bearing side of the turbocharger rather than the generator side.

In the embodiment shown in Figures 5 and 6 the single piece shaft 8 of the turbocharger arrangements shown in Figures 3 and 4 is replaced with a split shaft consisting of a turbocharger shaft 71, which supports the turbine wheel (not shown) and the compressor wheel 6, and a generator shaft 72, which supports a generator rotor 73 mounted for rotation within a generator stator 74. The two shafts 71, 72 are connected together via a screw thread 75 which is orientated to ensure there is no tendency for it to loosen during operation of the turbocharger arrangement. The generator shaft 72 defines a female formation 76 for mating receipt of a complementary male formation 77 defined by an end region 78 of the turbocharger shaft 71. In this way, the two shafts 71, 72 can be easily screwed together during assembly of the turbocharger arrangement and an axially inboard end wall 79 of the generator shaft 72 can be used to secure the compressor wheel 6 on to the turbocharger shaft 71 by the end wall 79 abutting a hub 80 of the compressor wheel 6. As a result, the generator shaft 72 can be considered as acting as a ‘nut’ holding the compressor wheel 6 in placed on the turbocharger shaft 71. A significant benefit afforded by this arrangement is that the turbocharger shaft 71 can be entirely conventional in structure and can be coupled to the generator shaft 72 via the screw thread which would have received a nut holding the impeller in place in a conventional turbocharger arrangement.

In the embodiment shown in Figures 5 and 6 the rotor 73 is integral with the generator shaft 72, that is, the rotor 73 and generator shaft 72 have been formed as a singlepiece component which therefore requires no assembly before being screwed to the turbocharger shaft 71. In an alternative embodiment, which is not shown, the rotor and generator shaft can be manufactured separately and then connected together using any appropriate means of connection to mount the rotor on the generator shaft. The rotor may be mounted on the generator shaft before screwing the generator shaft on to the turbocharger shaft, or the two shafts may be screwed together and the rotor then mounted on to the generator shaft.

The female formation 76 defined by the generator shaft 72 is adapted to define a substantially cylindrical recess which extends along approximately 25 % of the axial length of the generator shaft 72 from the end wall 79 of the generator shaft 72. While this represents a good balance between the strength of the connection between the two shafts 71, 72 and the advantages gained by using a shorter length turbocharger shaft, such as it being cheaper and easier to manufacture, the female formation may define a recess that extends over a proportion of the axial length of the generator shaft 72 that is greater or less than 25 %. That is, while it may be preferred that the end region 78 of the turbocharger shaft 71 that is matingly engaged by the female formation 76 defined by the generator shaft 72 extends along about 25 % of the axial length of the generator shaft 72, the end region 78 of the turbocharger shaft 71 may extend along any desirable proportion of the axial length of the generator shaft 72.

While a screw thread 75 is used to connect the two shafts 71, 72 together in the specific embodiment shown in Figures 5 and 6, it will be appreciated that alternative means of connection may be used. For example, the mating engagement between the two shafts may be achieved by forming a female formation on the turbocharger shaft and a complementary male formation on the generator shaft. Additionally or alternatively, any desirable size, shape and/or number of male and female formations may be defined by the two shafts being connected together.

Figures 7 and 8 are perspective schematic illustrations of the turbocharger shaft 71 and generator shaft 72 when unscrewed. As can be seen, the turbocharger shaft 71 extends only a relatively small axial distance beyond the outboard side of the compressor wheel 6, and the screw thread 75a defined by a radially outer surface of the end region 78 of the turbocharger shaft 71 affords a simple and convenient means for connection to the generator shaft 72 via the complementary screw thread (not visible) defined by a radially inner surface of the generator shaft 72.

It will be appreciated that any appropriate construction of the generator housing, compressor housing and bearing housing may be used. For example, each housing may be formed as separate pieces. Alternatively, at least two of the housings may be formed as one piece. Any interface between the bearing housing and the compressor housing, or between the compressor housing and the generator housing, may be secured together using any appropriate fastening method. The compressor outlet may be defined by the compressor housing alone, or a combination of the compressor housing and the bearing housing. Similarly, the compressor inlet may be defined by the compressor housing alone or by a combination of the compressor housing and the bearing housing.

Claims

CLAIMS:

1. A turbocharger arrangement comprising a turbocharger and a generator; the turbocharger comprising a turbine wheel and a compressor wheel mounted to a turbocharger shaft; the turbocharger shaft being supported by a bearing assembly located between the turbine wheel and the compressor wheel such that the turbocharger shaft may rotate about an axis; and the compressor wheel being provided between the generator and the bearing assembly; wherein the generator comprises a rotor portion and a stator portion, the rotor portion being associated with a generator shaft that defines a feature that is adapted to engage an end region of the turbocharger shaft.

2. A turbocharger arrangement according to claim 1, wherein said feature defined by the generator shaft is adapted to matingly engage the end region of the turbocharger shaft.

3. A turbocharger arrangement according to claim 1 or 2, wherein said feature defined by the generator shaft is a female formation configured to receive a complementary male formation defined by the end region of the turbocharger shaft.

4. A turbocharger arrangement according to any preceding claim, wherein said feature defined by the generator shaft is an internal screw thread configured to receive a complementary external screw thread defined by the end region of the turbocharger shaft.

5. A turbocharger arrangement according to any preceding claim, wherein said feature defined by the generator shaft defines a screw thread of complementary profile to a screw thread defined by the end region of the turbocharger shaft.

6. A turbocharger arrangement according to any preceding claim, wherein an end region of the generator shaft is configured to abut a hub of the compressor wheel mounted on the turbocharger shaft.

7. A turbocharger arrangement according to any preceding claim, wherein the end region of the turbocharger shaft that is engaged by the feature defined by the generator shaft extends along less than about 50 % of the axial length of the generator shaft.

8. A turbocharger arrangement according to any preceding claim wherein the rotor portion and the generator shaft are integrally formed.

9. A turbocharger arrangement according to any one of claims 1 to 8, wherein the rotor portion and the generator shaft are formed as separate components which are subsequently connected together.

10. A turbocharger arrangement according to any preceding claim, wherein an exducer portion of the compressor wheel is located between an inducer portion of the compressor wheel and the bearing assembly.

11. A turbocharger arrangement according to claim 10, wherein the compressor wheel is provided in a compressor housing which defines an inlet and an outlet, the inlet being located axially outboard of the compressor wheel.

12. A turbocharger arrangement according to any one of claims 1 to 9, wherein an inducer portion of the compressor wheel is located between an exducer portion of the compressor wheel and the bearing assembly.

13. A turbocharger arrangement according to claim 12, wherein the compressor wheel is provided in a compressor housing which defines an inlet and an outlet, the inlet being located axially inboard of the compressor wheel.

14. A turbocharger arrangement according to claim 12 or 13, wherein a portion of the generator is attached directly to a portion of a back face of the compressor wheel.

15. A turbocharger arrangement according to any preceding claim, wherein the compressor wheel and the generator are provided in a one-piece housing.

16. A turbocharger arrangement according to any preceding claim, wherein the compressor wheel and the bearing assembly are provided in a one-piece housing.