GB2528506A

GB2528506A - Forced air induction unit

Info

Publication number: GB2528506A
Application number: GB1413167.6A
Authority: GB
Inventors: Ross Murphy; Michael John Cade; Steve Johnson
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2014-07-24
Filing date: 2014-07-24
Publication date: 2016-01-27
Also published as: DE102015111101A1; CN204900058U; GB201413167D0

Abstract

A forced air induction unit 101 for an engine comprises a compressor housing 103 having a compressor chamber 105 in which a first compressor impeller 107 and a second compressor impeller 109 are disposed. The first compressor impeller 107 is coupled to a first drive shaft 111 driven by engine exhaust gases and the second compressor impeller 109 is coupled to a second, eg coaxial, drive shaft 113 which may be driven by an output shaft of the engine via pulley 125, an ancillary device of the engine, eg a starter motor, or a motor, eg an electric motor which is part of a vehicle hybrid drive system. The first compressor impeller 107 may be driven by an exhaust turbine impeller 119 in a turbine chamber 117. One or more additional drive shafts coupled to additional compressor impeller(s) may be provided, eg a further compressor impeller (129, fig.2) may be driven by an additional exhaust turbine (133).

Description

Forced Air Induction Unit This disclosure relates to a forced air induction unit for an engine, and in particular, but not exclusively, relates to a forced air induction unit comprising a first compressor impeller driven by engine exhaust gases, and a second compressor impeller driven by an output shaft of the engine.

Introduction

It is common for a vehicle to use one or more turbochargers and/or superchargers to force an increased amount of air, or air-fuel mixture, into an engine. This increases the combustion pressure and the engine power, which enables a comparatively small engine to deliver increased fuel economy during normal driving conditions and increased power when needed. Turbochargers and superchargers have been incorporated into both gasoline and diesel engines, for both commercial and passenger vehicle applications.

Despite turbocharger technology being relatively mature, turbochargers used with modern gasoline and diesel vehicles have many performance drawbacks. In particular, one of the most significant compromises relates to the turbine wheel size. A smaller turbine wheel spools up quickly, which is beneficial in terms of transient response, i.e. reduced turbo lag. However, a smaller turbine wheel may not offer sufficient levels of maximum boost. A larger turbine wheel enables higher levels of maximum boost, but spools up more slowly, which may cause unacceptable levels of turbo lag.

A recent evolution in turbocharger technology has seen the use of regulated two-stage sequential turbochargers, in which two comparatively small turbochargers are used as an alternative to a single, larger turbocharger. These regulated two-stage turbocharger systems typically have a small, high-pressure turbocharger in series with a larger, low-pressure turbocharger, As an alternative to two-stage turbocharger systems, a separate supercharger system may be provided in series and/or in parallel with a standard turbocharger system in order to provide sufficient boost pressure at lower engine speeds whilst the turbocharger is spooling up.

Two-stage turbocharger systems take up a great deal of space within the vehicle's engine as they are made up of two compressor housings, two turbine housings, two centre housings, as well as the associated ducting. Typically, such two-stage systems are integrated with the exhaust manifold in an effort to minimize the packaging requirements, which may further increase cost.

Turbocharger technology for use in diesel vehicles is based on specific power break- points and has seen fixed-geometry turbine technology be replaced by variable-geometry turbine technology to increase performance and fuel economy. However, variable-geometry turbine technology can significantly increase the cost of the turbocharger system relative to fixed-geometry turbine technology. Variable-geometry turbochargers must also make compromises in regard to the size of the turbine wheel and spooling-up time.

Due to material requirements, design complexity and packaging issues, two-stage turbocharger systems can be significantly more expensive than the sum of the component parts, for example a two-stage turbocharger system using variable-geometry turbines may cost more than double that of standard turbocharger systems.

Statements of Invention

According to an aspect of the present invention there is provided a forced air induction unit for an engine. The forced air induction unit comprises a compressor housing having a compressor chamber. The forced air induction unit comprises a first compressor impeller disposed within the compressor chamber. The forced air induction unit comprises a second compressor impeller disposed within the compressor chamber. The first compressor impeller is coupled to a first rotational drive shaft driven by engine exhaust gases. The second compressor impeller is coupled to a second rotational drive shaft which is not driven by engine exhaust gases. The second rotational drive shaft may instead be driven from at least one of: an output shaft of the engine; an ancillary device of the engine; or a motor. The first compressor impeller and the second compressor impeller may be disposed within a common compressor chamber.

The forced air induction unit may comprise a turbine housing having a turbine chamber.

The forced air induction unit may comprise a first turbine impeller disposed within the turbine chamber. The first turbine impeller may be configured to be driven by engine exhaust gases.

The first rotational drive shaft may be configured to couple the first compressor impeller to the first turbine impeller. The first rotational drive shaft may extend between the compressor chamber and the turbine chamber.

The second rotational drive shaft may extend through the turbine chamber. The second rotational drive shaft may extend through an opening in a wall of the turbine housing. A first end of the second rotational drive shaft may be disposed in the compressor chamber. A second end of the second rotational drive shaft may be disposed outside of the forced air induction unit. The second rotational drive shaft may be configured to couple the second compressor impeller to a rotational drive member, for example a rotational drive member of the output shaft of the engine, a rotational drive member of the ancillary device or a rotational drive member of the motor. The rotational drive member may be a pulley wheel, for example a belt-or chain-driven pulley wheel. The second rotational drive shaft may be coupled to the output shaft of the engine, the ancillary device of the engine or the motor by virtue of a mechanical, electrical and/or magnetic coupling. The second rotational drive shaft may be coupled to the output shaft of the engine, the ancillary device of the engine or the motor by virtue of a geared coupling such that the rotational speed of the second rotational drive shaft is different, for example a slower or faster rotational speed, than the rotational speed of the output shaft of the engine, the ancillary device of the engine or the motor.

In one embodiment, the second rotational drive shaft may extend into the compressor chamber from outside of the compressor housing, for example the second rotational drive shaft may extend into the compressor chamber through an opening in a wall of the compressor housing. The first and second rotational drive shafts may be spaced apart form each other and may extend into the compressor chamber from different directions.

The first rotational drive shaft may be at least partially disposed within the second rotational drive shaft. The second rotational drive shaft may be at least partially disposed within the first rotational drive shaft. The first and second rotational drive shafts may be coaxially arranged. The first and second rotational drive shafts may be concentrically arranged. The first and second rotational drive shafts may be axially spaced apart, The first and second rotational drive shafts may be provided within a common housing. For example the first and second rotational drive shafts may be provided within the compressor housing and/or the turbine housing. The compressor housing and the turbine housing may be integral, for example the compressor chamber and the turbine chamber may be formed within a common housing.

The forced air induction unit may comprise one or more additional compressor impellers. Each additional compressor impeller may be driven by an addition rotational drive shaft.

One or more additional compressor impellers may disposed in the compressor chamber. One or more additional compressor impellers may disposed in an additional compressor chamber of the compressor housing.

Each additional rotational drive shaft may be driven by engine exhaust gases, an output shaft of the engine, an ancillary device of the engine or a motor.

Each additional rotational drive shaft may be coupled to an additional turbine impeller.

Each additional turbine impeller may be configured to be driven by engine exhaust gases. Each additional turbine impeller may be disposed in the turbine chamber. Each additional turbine impeller may be disposed in an additional turbine chamber of the turbine housing.

The forced air induction unit may comprise one or more pressure regulators, for example one or more waste gates and/or one or more dump valves. The forced air induction unit may comprise a pressure sensor and/or a mass flow rate sensor. The forced air induction unit may comprise a control device configured to control the output boost pressure of the forced air induction unit and/or the mass flow rate of air through the forced air induction unit.

The compressor impellers may be selected to meet different performance requirements of the engine, for example a small compressor impeller may be selected in order to reduce spooling-up time to reduce lag or a larger compressor impeller may be selected in order to deliver high pressure output for increased boost.

One or more of the first, second and/or additional compressor impellers may be a fixed-geometry impeller or a variable-geometry impeller. One or more of the first, second and/or additional compressor impellers may be an axial-flow, radial-flow or mixed4low impeller.

One or more of the first, second and/or additional turbine impellers may be a fixed-geometry impeller or a variable-geometry impeller. One or more of the first, second and/or additional turbine impellers may be an axial-flow, radial-flow or mixed-flow impeller.

According to another aspect of the present invention there is provided a forced air induction unit for an engine. The forced air induction unit comprises a compressor housing having a compressor chamber, The forced air induction unit comprises a first compressor impeller disposed within the compressor chamber. The forced air induction unit comprises a second compressor impeller disposed within the compressor chamber. The first compressor impeller is coupled to a first rotational drive shaft driven by engine exhaust gases. The second compressor impeller is coupled to a second rotational drive shaft driven by an output shaft of the engine, an ancillary device of the engine or a motor. The second rotational drive shaft extends from outside of turbine housing, through the turbine chamber and into the compressor chamber. The second rotational drive shaft may extend from outside of the turbine housing through an opening in the wall of the turbine housing into the turbine chamber.

The first compressor impeller may be a turbocharger impeller. The second compressor may be a supercharger impeller. The additional compressor impeller may be either another turbocharger impeller or another supercharger impeller.

A motor vehicle and/or an engine may comprise one or more of the forced air induction

units according to the present disclosure.

According to another aspect of the present invention there is provided a method of optimising the output boost pressure of a forced air induction unit for an engine of a motor vehicle. The method comprises driving a first rotational drive shaft coupled to a first compressor impeller. The first compressor impeller is disposed within a compressor chamber of a compressor housing of the forced air induction unit. The first rotational drive shaft is driven by the engine exhaust gases. The method comprises driving a second rotational drive shaft coupled to a second compressor impeller The second compressor impeller is disposed within the compressor chamber. The second rotational drive shaft is not driven by engine exhaust gases. The second rotational drive shaft may instead be driven from at least one of: an output shaft of the engine; an ancillary device of the engine; or a motor.

The method may comprise driving an additional rotational drive shaft coupled to a further compressor impeller of the forced air induction unit. The additional rotational drive shaft may be driven by engine exhaust gases, an output shaft of the engine, an ancillary device of the engine or a motor.

The method may comprise adjusting the output boost pressure of the forced air induction unit depending upon the performance requirements of the engine and/or the vehIcle. The method may comprise adjusting independently the respective rotational speed of the first, second and/or addition rotational drive shafts of the forced air induction unit.

The invention also provides software, such as a computer program or a computer program product for carrying out any of the methods described herein, and a computer readable medium having stored thereon a program for carrying out any of the methods described herein. A computer program embodying the invention may be stored on a computer-readable medium, or it could, for example, be in the form of a signal such as a downloadable data signal provided from an Internet website, or it could be in any other form.

Brief Description of the Drawings

For a better understanding of the present disclosure, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 shows a forced air induction unit according to the present disclosure; and Figure 2 shows another forced air induction unit according to the present disclosure.

Detailed Description

The present disclosure relates to a forced air induction unit 101, for example an integrated supercharger-turbocharger unit, for an engine of a motor vehicle. At lower engine speeds, the initial boost pressure output from the forced air induction unit is provided by a compressor impeller, for example a supercharger compressor wheel, driven by an output shaft of the engine, an ancillary device of the engine and/or a motor. At a higher engine speed, subsequent and/or additional boost pressure is provided by another compressor impeller, for example a turbocharger compressor wheel, which is driven by the engine exhaust gases.

Figure 1 shows a forced air induction unit 101 according to the present disclosure. The forced air induction unit 101 comprises a compressor housing 103 having a compressor chamber 105, in which a first compressor impeller 107 and a second compressor impeller 109 are disposed. In the example of figure 1, the first compressor impeller 107 is a mixed-flow type impeller and the second compressor impeller 109 is an axial-flow type impeller. It is appreciated, however, that the configuration of each of the first compressor impeller 107 and the second compressor impeller 109 may be of any appropriate type, for example, radial-flow, mixed-flow or axial flow.

The first compressor impeller 107 is coupled to a first rotational drive shaft 111 and the second compressor impeller 109 is coupled a second rotational drive shaft 113. The first rotational drive shaft 111 is driven by engine exhaust gases. The second rotational drive shaft 113 is driven by an output shaft of the engine, for example a crankshaft, an ancillary device of the engine, for example a starter motor of the engine, and/or a motor, for example an electric motor which may be part of a hybrid drive system of the vehicle.

In figure 1, the forced air induction unit 101 comprises a turbine housing 115 having a turbine chamber 117. A first turbine impeller 119 is disposed within the turbine chamber 117 and is configured to be driven by the engine exhaust gases. In the example of figure 1, the first turbine impeller 119 is a mixed-flow type impeller, although it is appreciated that the configuration of first turbine impeller 119 may be of any appropriate type, for example, radial-flow, mixed-flow or axial flow. a

The first rotational drive shaft 111 is configured to extend between the turbine chamber 117 and the compressor chamber 105, and rotationally couple the first turbine impeller 119 to the first compressor impeller 107 such that the engine exhaust gases drive the first compressor impeller 107 to rotate.

The first rotational drive shaft 111 and second rotational drive shaft 113 are arranged coaxially with the second rotational drive shaft 113 extending axially through the first rotational drive shaft 111, such that the first rotational drive shaft 111 and second rotational drive shaft 113 may rotate independently from each other. The first compressor impeller 107 and the first turbine impeller 119 are provided towards opposite ends of the first rotational drive shaft 111, although it is appreciated that the first compressor impeller 107 and the first turbine impeller 119 may be provided at any point along the length of first rotational drive shaft 111. The first compressor impeller 107 and the first turbine impeller 119 each comprise a central opening extending axially through the compressor and turbine impellers 107, 119. In this manner, as shown in figure 1, the second rotational drive shaft 113 extends axially through the first rotational drive shaft 111, the first compressor impeller 107 and the first turbine impeller 119.

The compressor housing 103 and the turbine housing 115 are spaced axially apart along the rotational axis of the first and second rotational drive shafts 111, 113, the compressor housing 103 and the turbine housing 115 being connected by a housing portion 121. In an alternative example the compressor housing 103 and the turbine housing 115 may be proximate to each other, next to each other, fixed directly to each other or integral. For example, the compressor housing 103 and the turbine housing 115 may be integrally formed. In this manner, the first and second rotational drive shafts 111, 113 may be provided in a common housing. It is appreciated that the compressor housing 103 and the turbine housing 115 may be spaced apart by any appropriate distance, or indeed not spaced apart at all, depending on the packaging requirements of the engine.

The second compressor impeller 107 is provided towards a first end 122 of the second rotational drive shaft 113 that extends through the first compressor impeller 107 and into the compressor chamber 105, such that the first and second compressor impellers 107, 109 are axially spaced apart. The other end 124 of the second rotational drive shaft 113 extends though the first turbine impeller 119, through the turbine chamber 117, and though an opening in a wall 123 of the turbine housing 115, such that the other end 124 of the second rotational drive shaft 113 is disposed outside of the turbine housing 115. A bearing housing (not shown) may define the opening in the wall 123 and may support a bearing (for example, a sealed bearing) in which the second rotational drive shaft 113 runs. The second rotational drive shaft 113 is configured to couple the second compressor impeller 109 to a rotational drive member 126 disposed outside of the forced air induction unit 101, In the example shown in figure 1, the second rotational drive shaft 113 is coupled to a pulley wheel 125, which may, for example, be driven by a belt or chain connected to the crankshaft of the engine. In an alternative example, the second rotational drive shaft 113 may be coupled to an output shaft of a motor, for example an electric motor of a hybrid vehicle. In a further example, the second rotational drive shaft 113 may be coupled to an ancillary device drive member, for example an output shaft of a starter motor or an oil pump. n one example, the second rotational drive shaft 113 may be coupled to the drive member by virtue of a mechanical, electrical and/or a magnetic coupling. Additionally and/or alternatively, the second rotational drive shaft 113 may be coupled to the rotational drive member 126 by a geared coupling such that the rotational speed of the second rotational drive shaft 113 may be different, for example greater than or less than, the rotational speed of the rotational drive member 126. In another example, the rotational drive member 126, for example the pulley wheel 125, may be fixed to or integrally formed with the second rotational drive shaft 113. In one example the pulley wheel 125 may be fitted to a tapered end of the second rotational drive shaft 113.

For engines fitted with a standalone turbocharger device, at lower engine speeds the mass flow rate of engine exhaust gases may be insufficient to drive an impeller of the turbocharger at a rotational speed corresponding to a desired output boost pressure of the turbocharger. It is common, therefore, for engines to be provided with a separate supercharger device to supplement the output boost pressure. Since the supercharger device may be driven directly from the output shaft of the engine, the supercharger is able to provide sufficient levels of boost at lower engine speeds. A standalone supercharger device may however be unable to provide sufficient levels of boost at higher engine speeds.

Other possible solutions to proving adequate boost output pressure over a full range of engine speeds include: variable-geometry (VG) compressor and/or turbine impellers; and parallel, sequential, staged or compound turbocharger/supercharger systems.

However, such systems are heavy, expensive and have complicated packaging requirements.

The forced air induction unit 101 provides a single device that is configured to operate over the full range of required boost output pressures. The forced air induction unit 101 is advantageous as the compressor chamber 105 is provided with two independently rotating compressor impellers 107, 109, wherein the compressor impellers 107, 109, are driven by different means. For example, the second compressor impeller 109, which may be driven from the crankshaft of the engine, can provide the majority of an initial boost output pressure, for example at lower engine speeds. When sufficient mass-air flow is available, for example at higher engine speeds, the second compressor impeller 109, which is driven by the engine exhaust gases, can provide the majority of the output boost pressure. The level of boost output pressure is a function of a first boost pressure provided by the first compressor impeller 107 and a second boost pressure provided by the second compressor impeller 109. The first andfor second rotational drive shafts 111, 113 may be selectively disengagable, for example by virtue of one or more crutch mechanisms, from the first and/or second compressor impellers respectively. Depending on the performance requirements of the engine, the first and/or second compressor impellers 107, 109 may be selectively disengaged. For maximum boost output pressure, both the first and second compressor impellers 107, 109 may operate simultaneously.

Figure 2 shows another example of the forced air induction unit 101 according to the present disclosure, which may comprise similar features to those described above, the features and benefits of which apply equally to the example described below. In the example of figure 2, the forced air induction unit 101 comprises an additional compressor impeller 129 disposed in the compressor chamber 105. The additional compressor impeller 129 is coupled to an additional turbine impeller 133 disposed in the turbine chamber 117 by an additional rotational drive shaft 131. The additional compressor impeller 129 and the additional turbine impeller 133 are provided towards opposite ends of the additional rotational drive shaft 131. The additional turbine impeller 133 is configured to be driven by engine exhaust gases. In the example of figure 2, the additional compressor impeller 129 and the additional turbine impeller 133 are axial-flow type impellers! although it is appreciated that each additional impeller 129, 133 may be of any appropriate configuration.

Whilst figure 2 shows only one additional compressor impeller 129, it is appreciated that the forced air induction unit 101 may comprise any appropriate number of additional compressor impellers. Each additional compressor impeller may be provided in the compressor chamber 105 or in an additional compressor chamber of the forced air induction unit 101. For example, the compressor housing may comprise a plurality of compressor chambers each having a respective compressor chamber inlet 135 and compressor chamber outlet 137. In a similar manner, the forced air induction unit 101 may comprise any appropriate number of additional turbine impellers. Each additional turbine impeller may be provided in the turbine chamber 117 or in an additional turbine chamber of the forced air induction unit 101. For example, the turbine housing may comprise a plurality of turbine chambers each having a respective turbine chamber inlet 139 and turbine chamber outlet 141.

In figure 2, the additional rotational drive shaft 131 is coaxially arranged with respect to the first and the second rotational drive shafts 111, 113. The additional rotational drive shaft 131 is disposed radially in between the first and second rotational drive shafts 111, 113, such that the second rotational drive shaft 113 extends axially through the first and the additional rotational drive shafts 111, 131. The second rotational drive shaft 113 extends through an opening in the wall 123 of the turbine chamber such that the second end of the second rotational drive shaft 113 is disposed outside of the turbine housing 115. In the example shown in figure 2, the second rotational drive shaft 113 is coupled to a rotational drive member of a motor 143, the motor 143 being configured to drive the second compressor impeller 109 to rotate. As with the example of figure 1, the second rotational drive shaft 113 may be coupled to any appropriate rotational drive mechanism, which may for example by located remote from the force air induction unit 101.

In an alternative embodiment, the additional drive shaft 131 may extend through an opening in the waIl 123 of the turbine chamber such that an end of the additional rotational drive shaft 133 is disposed outside of the turbine housing 115. The end of the additional rotational drive shaft 133 that is disposed outside of the turbine housing 115 may be rotationally coupled to a rotational drive member of the motor 143 and/or one or more alternative rotational drive members. In this manner, it is appreciated that the additional rotational drive shaft 133 may be driven by the engine exhaust gases, an output shaft of the engine, an ancillary device of the engine or the motor 143.

In an alternative embodiment (not shown), the second and/or the additional rotational drive shaft 113, 133 may extend into the compressor chamber 105 from outside of the forced air induction unit 101 through an opening in a wall of the compressor chamber 103. The second and/or additional rotational drive shaft 113, 133 may be arranged coaxially and/or spaced axially apart from the first rotational drive shaft such that the second and/or the additional rotational drive shaft 113, 133 are not disposed within the first rotational drive shaft 111.

The forced air induction unit 101 may comprise one or more pressure regulator, for example a waste gate or a dump valve. The forced air induction unit 101 may comprise one or more pressure sensors and/or mass flow rate sensors configured to determine the pressure and the mass flow rate of air through the forced air induction unit 101 respectively. The one or more pressure regulation devices, pressure sensors and/or mass flow rate sensors may be located at any appropriate point on or remote from the forced air induction unit 101.

The forced air induction unit 101 may comprise a control device configured to control the boost pressure of and/or mass flow rate of air though the forced air induction unit 101. The control device may be configured to control one or more of the pressure regulation devices in order to regulate the boost pressure of the forced air induction unit 101 according to the performance requirements of the engine.

The present disclosure provides a method of optimising the boost pressure of the forced air induction unit 101. The method comprises driving the first rotational drive shaft 111, which is coupled to the first compressor impeller 107, by the engine exhaust gases. The method further comprises driving the second rotational drive shaft 113, which is coupled to a second compressor impeller 109, by an output shaft of the engine, an ancillary device of the engine or a motor.

The method may further comprise driving one or more additional rotational drive shafts coupled to a further compressor impeller of the forced air induction unit, wherein the additional rotational drive shaft is driven by engine exhaust gases, an output shaft of the engine, an ancillary device of the engine or a motor. The method may further comprise controlling and/or modifying the rotational speed of one or more of the first.

second and/or additional rotational drive shafts according to the performance requirements of the engine and/or the vehicle.

The forced air induction unit 101 according to the present disclosure is advantageous as it may provide a broader boost pressure range, improved transient response, and could enable higher levels of performance across the full range of engine speeds when compared to the above-mentioned alternative solutions, for example when compared to variable-geometry impeller technology.

The forced air induction unit 101 may improve the packaging requirements, i.e. may reduce the space occupied by the forced air induction unit 101 in an engine bay, when compared, for example, to two-stage series sequential turbocharger systems. The forced air induction unit 101 removes the requirement for a separate compressor housing, turbine housing, centre housing, and associated ducting which would otherwise be required. Typically a two-stage series sequential turbocharger system is manufactured separately to a standard turbocharger system, due to significant differences in that manufacturing bill of parts/processes. The forced air induction unit 101 according to the present disclosure allows much greater commonality with a standard turbocharger system, and may therefore obviate the need for separate manufacturing and/or assembly requirements.

It is known to manufacture components of a standard turbocharger system from expensive materials, such as titanium aluminide, to help minimize turbo lag. The forced air induction unit 101 according to the present disclosure may reduce or negate the need for these expensive materials.

Compared to the forced air induction unit 101, a known turbocharger system, for example a two-stage series sequential turbocharger system, requires a greater volume of air to fill due to the extra ducting, for example, which tends to lead to transient losses of power during operation. Due to the compact design of the present disclosure, the forced air induction unit 101 reduces loss of output boost pressure during transition as there is less air in the system, when for example compared to a two-stage series sequential turbocharger system.

It will be appreciated by those skilled in the art that although the invention has been described by way of example with reference to one or more examples, it is not limited to the disclosed examples and that alternative examples could be constructed without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

Claims 1. A forced air induction unit for an engine, the forced air induction unit comprising: a compressor housing having a compressor chamber; a first compressor impeller disposed within the compressor chamber; and a second compressor impeller disposed within the compressor chamber, wherein the first compressor impeller is coupled to a first rotational drive shaft driven by engine exhaust gases and the second compressor impeller is coupled to a second rotational drive shaft driven by an output shaft of the engine, an ancillary device of the engine or a motor.
2. A forced air induction unit according to claim 1, the forced air induction unit further comprising: a turbine housing having a turbine chamber; and a first turbine impeller disposed within the turbine chamber, the first turbine impeller being configured to be driven by engine exhaust gases.
3. A forced air induction unit according to claim 2, wherein the first rotational drive shaft is configured to couple the first compressor impeller to the first turbine impeller.
4. A forced air induction unit according to claim 2 or 3, wherein the first rotational drive shaft extends between the compressor chamber and the turbine chamber.
5. A forced air induction unit according to any of claims 2 to 4, wherein the second rotational drive shaft extends through the turbine chamber.
6. A forced air induction unit according to any of the preceding claims, wherein the second rotational drive shaft is configured to couple the second compressor impeller to a drive member of the output shaft of the engine, the ancillary device of the engine or the motor.
7. A forced air induction unit according to any of the preceding claims, wherein the second rotational drive shaft extends into the compressor chamber from outside of the compressor housing.
8. A forced air induction unit according to any of the preceding claims, wherein the second rotational drive shaft is coupled to the output shaft of the engine, the ancillary device of the engine or the motor by virtue of a mechanical, electrical and/or magnetic coupling.
9. A forced air induction unit according to any of the preceding claims, wherein one of the first rotational drive shaft and the second rotational drive shaft is at least partially disposed within the other of the first rotational drive shaft and the second rotational drive shaft.
10. A forced air induction unit according to any of the preceding claims, wherein the first and second rotational drive shafts are coaxially and/or concentrically arranged.
11. A forced air induction unit according to any of the preceding claims, wherein the first and second rotational drive shafts are provided within a common housing.
12. A forced air induction unit according to any of the preceding claims, wherein the forced air induction unit further comprises one or more additional compressor impellers each driven by an addition rotational drive shaft.
13. A forced air induction unit according to claim 12, wherein each additional compressor impeller is disposed in the compressor chamber or in an additional compressor chamber of the compressor housing.
14. A forced air induction unit according to claim 12 or 13, wherein each additional rotational drive shaft is driven by engine exhaust gases, an output shaft of the engine, an ancillary device of the engine or a motor.
15. A forced air induction unit according to any of claims 12 to 14, wherein one or more of the additional rotational drive shafts are each coupled to an additional turbine impeller respectively, each additional turbine impeller being configured to be driven by engine exhaust gases.
16. A forced air induction unit according to claim 15, wherein each additional turbine impeller is disposed in the turbine chamber or in an additional turbine chamber of the turbine housing.
17. A forced air induction unit according to any of the preceding claims, the forced air induction unit further comprising one or more pressure regulators.
18. A forced air induction unit according to any of the preceding claims, the forced air induction unit further comprising a pressure sensor and/ar a mass flow rate sensor.
19. A forced air induction unit according to any of the preceding claims, the forced air induction unit further comprising a control device configured to control the boost pressure of the forced air induction unit and/or the mass flow rate of air through the forced air induction unit.
20. A forced air induction unit according to any of claims 2 to 19, wherein the compressor housing and the turbine housing are integral.
21. A motor vehicle and/or an engine comprising one or more forced air induction units according to any preceding claim.
22. A method of operating a forced air induction unit for an engine, the method comprising driving a first rotational drive shaft coupled to a first compressor impeller disposed within a compressor chamber of a compressor housing of the forced air induction unit, wherein the first rotational drive shaft is driven by the engine exhaust gases; and driving a second rotational drive shaft coupled to a second compressor impeller disposed within the compressor chamber of the compressor housing of the forced air induction unit, wherein the second rotational drive shaft is driven by an output shaft of the engine, an ancillary device of the engine or a motor.
23. A method according to claim 26, the method further comprising driving an additional rotational drive shaft coupled to a further compressor impeller of the forced air induction unit, wherein the additional rotational drive shaft is driven by engine exhaust gases, an output shaft of the engine, an ancillary device of the engine or a motor.
24. Software which when executed by a computing apparatus causes a computing apparatus to perform the method of claim 22 or 23.
25. A forced air induction unit as described herein, with reference to, and as shown in the accompanying drawings.
26. A method as described herein, with reference to, and as shown in the accompanying drawings.Amendments to the claims have been filed as follows iç Claims 1 A forced air induction unit for an engine, the forced air induction unit comprising: a compressor housing having a compressor chamber; a first compressor impeller disposed within the compressor chamber; and a second compressor impeller disposed within the compressor chamber, wherein the first compressor impeller is coupled to a first rotational drive shaft driven by engine exhaust gases and the second compressor impeller is coupled to a second rotational drive shaft driven by an output shaft of the engine, an ancillary device of the engine or an electric motor of a hybrid vehicle.2. A forced air induction unit according to claim 1, the forced air induction unit further comprising: LI') a turbine housing having a turbine chamber; and a first turbine impeller disposed within the turbine chamber, the first C\J turbine impeller being configured to be driven by engine exhaust gases.N-20 3. A forced air induction unit according to claim 2, wherein the first rotational drive ("I shaft is configured to couple the first compressor impeller to the first turbine impeller.4. A forced air induction unit according to claim 2 or 3, wherein the first rotational drive shaft extends between the compressor chamber and the turbine chamber.5. A forced air induction unit according to any of claims 2 to 4, wherein the second rotational drive shaft extends through the turbine chamber.6. A forced air induction unit according to any of the preceding claims, wherein the second rotational drive shaft is configured to couple the second compressor impeller to a drive member of the output shaft of the engine, the ancillary device of the engine or the motor.7. A forced air induction unit according to any of the preceding claims, wherein the second rotational drive shaft extends into the compressor chamber from outside of the compressor housing.8. A forced air induction unit according to any of the preceding claims, wherein the second rotational drive shaft is coupled to the output shaft of the engine, the ancillary device of the engine or the motor by virtue of a mechanical, electrical and/or magnetic coupling.9. A forced air induction unit according to any of the preceding claims, wherein one of the first rotational drive shaft and the second rotational drive shaft is at least partially disposed within the other of the first rotational drive shaft and the second rotational drive shaft.10. A forced air induction unit according to any of the preceding claims, wherein the first and second rotational drive shafts are coaxially and/or concentrically arranged.LI') 11. A forced air induction unit according to any of the preceding claims, wherein the first and second rotational drive shafts are provided within a common housing. (4O 12. A forced air induction unit according to any of the preceding claims, wherein the 1"-a 20 forced air induction unit further comprises one or more additional compressor (4 impellers each driven by an addition rotational drive shaft.13. A forced air induction unit according to claim 12, wherein each additional compressor impeller is disposed in the compressor chamber or in an additional compressor chamber of the compressor housing.14.A forced air induction unit according to claim 12 or 13, wherein each additional rotational drive shaft is driven by engine exhaust gases, an output shaft of the engine, an ancillary device of the engine or a motor.15. A forced air induction unit according to any of claims 12 to 14, wherein one or more of the additional rotational drive shafts are each coupled to an additional turbine impeller respectively, each additional turbine impeller being configured to be driven by engine exhaust gases.16. A forced air induction unit according to claim 15, wherein each additional turbine impeller is disposed in the turbine chamber or in an additional turbine chamber of the turbine housing.17. A forced air induction unit according to any of the preceding claims, the forced air induction unit further comprising one or more pressure regulators.18. A forced air induction unit according to any of the preceding claims, the forced air induction unit further comprising a pressure sensor and/or a mass flow rate sensor.19. A forced air induction unit according to any of the preceding claims, the forced air induction unit further comprising a control device configured to control the boost pressure of the forced air induction unit and/or the mass flow rate of air through the forced air induction unit. IC)20. A forced air induction unit according to any of claims 2 to 19, wherein the compressor housing and the turbine housing are integral. 0.21. A motor vehicle and/or an engine comprising one or more forced air induction units according to any preceding claim.22. A method of operating a forced air induction unit for an engine, the method comprising driving a first rotational drive shaft coupled to a first compressor impeller disposed within a compressor chamber of a compressor housing of the forced air induction unit, wherein the first rotational drive shaft is driven by the engine exhaust gases: and driving a second rotational drive shaft coupled to a second compressor impeller disposed within the compressor chamber of the compressor housing of the forced air induction unit, wherein the second rotational drive shaft is driven by an output shaft of the engine, an ancillary device of the engine or an electric motor of a hybrid vehicle.23. A method according to claim 26, the method further comprising driving an additional rotational drive shaft coupled to a further compressor impeller of the forced air induction unit, wherein the additional rotational drive shaft is driven by engine exhaust gases, ar output shaft of the engine, an ancUlary device of the engine or a motor.24. Software which when executed by a computing apparatus causes a computing apparatus to perform the method of claim 22 or 23.25. A forced air induction unit as described herein, with reference to, and as shown in the accompanying drawings.26. A method as described herein, with reference to, and as shown in the accompanying drawings. IC) (4N