TECHNICAL FIELD The present disclosure relates to intake systems for automotive internal combustion engines. Aspects of the invention relate to an intake system for delivering air to an automotive internal combustion engine, and to a method of operating an intake system of an automotive internal combustion engine. The present disclosure relates also to a valve assembly for a gas flow system and particularly, but not exclusively, to a valve assembly for a gas flow system of an automotive internal combustion engine. Aspects of the invention relate to a valve assembly, to a gas flow system, and to an internal combustion engine. BACKGROUND

There is a current trend in the automotive industry towards the use of smaller capacity engines, primarily for reasons of fuel efficiency. In order to offset the reduced performance which may result from selecting a smaller capacity for an engine, it is common to provide an engine with a charging system to increase the density of air supplied to the engine, thereby increasing the torque and power available from the engine.

Conventional charging systems often include a supercharger (comprising a compressor that is driven by the engine via a belt, gear, shaft or other mechanical means) and/or a turbocharger (comprising a compressor that is driven by an exhaust gas driven turbine). A turbocharger generally provides increased torque and power with a high efficiency, but suffers from turbo lag as the turbine and compressor take time to spool up following an increase in throttle position. In contrast, a supercharger generally provides a rapid response to an increased throttle position, but is less efficient that a turbocharger. The disadvantages of each type of compressor may be offset to some degree by employing both a turbocharger and a supercharger in a single charging system, commonly known as a twin charged system. It is possible to provide a turbocharger with an electric motor which may be used to help spool up the compressor. Turbochargers including an electric motor for spooling up the compressor are known as electric turbochargers. Electric turbochargers may provide a quicker response to an increased throttle position than a regular turbocharger due to the ability of the electric motor to spool up the compressor. However, these systems are relatively complex, and are not common in automotive applications.

A more recent concept in the field of automotive engine charging is the use of electric superchargers. Electric superchargers are charging devices that use an electric motor to drive a compressor. In an electric supercharger, the compressor is driven only by the electric motor. (Electric superchargers are distinct from electric turbochargers, in which the compressor is arranged to be driven by an exhaust gas driven turbine in addition to being driven by an electric motor.) Electric superchargers can be used to increase the density of air supplied to an engine rapidly in response to an increased throttle position. However, the use of electric superchargers in automotive applications is still fairly uncommon, and electric superchargers have not been able to solve all of the disadvantages associated with conventional charging systems.

An intake or exhaust system of an automotive internal combustion engine may include two or more separate flow paths, each of which may be provided with a valve that is operable to control the flow of gases through its respective flow path. For example, an intake or exhaust system may include two (or more) alternative parallel flow paths in a selectively configurable arrangement, which may be controlled to cause gases flowing through the intake or exhaust system to flow either through a first one of the flow paths in a first configuration or alternatively through a second one of the flow paths in a second configuration.

Generally, each valve used to control the flow of gases through a flow path of an intake or exhaust system comprises a housing, a valve element located within the housing for controlling the flow of gases through its respective flow path, and an actuator for controlling the position of the valve element. While allowing multiple flow paths of the intake or exhaust system to be controlled as desired, the use of valves adds to the cost, weight, parts-count and control complexity of the overall intake or exhaust system.

It is an aim of the present invention to address disadvantages associated with the prior art.

SUMMARY OF THE INVENTION

According to an aspect of the present invention there is provided an intake system for delivering air to an automotive internal combustion engine, the intake system comprising two electric superchargers arranged to compress air passing through the intake system before delivery to the internal combustion engine in use. By providing the intake system with two electric superchargers it is possible to increase the torque and power available from an engine of a given displacement, and to provide a rapid response to an increased throttle position with a high level of efficiency.

By employing two electric superchargers it is possible to maximise the beneficial effects of the electric superchargers and provide a highly optimised charging system. In addition, the use of two electric superchargers instead of a single electric supercharger with a higher power rating allows the electric superchargers to be selected from a wider range of available models, allows greater flexibility for the lay-out and operation of the charging system, reduces response times to due lower inertia in each electric supercharger, and reduces the overall cost and weight for the charging system. The intake system may further comprise an additional charging device. The additional charging device may be, for example, a supercharger or a turbocharger. When used in combination with an additional charging device, the two electric superchargers may help to offset some of the disadvantages associated with the additional charging device. For example, particularly when used in combination with a turbocharger, the two electric superchargers may act to reduce lag and provide a more rapid response to an increased throttle position, especially at low engine speeds. The two electric superchargers may be arranged in series with (and preferably downstream of) the additional charging device, or alternatively in parallel with the additional charging device. The two electric superchargers may be arranged in series with each other. Where the two electric superchargers are arranged in series with each other, air flows through and is compressed by a first one of the electric superchargers before flowing through and being further compressed by a second one of the electric superchargers, in use. Arranging the two electric superchargers in series with each other provides maximised pressure boosting at low engine speeds, thereby allowing a more rapid response to an increased throttle position and more rapid acceleration.

Alternatively, the two electric superchargers may be arranged in parallel with each other. Where the two electric superchargers are arranged in parallel with each other, a portion of the air flowing through the intake system flows through and is compressed by a first one of the electric superchargers (but not a second one of the electric superchargers) while another portion of the air flowing through the intake system flows through and is compressed by the second one of the electric superchargers (but not the first one of the electric superchargers), in use. Arranging the two electric superchargers in parallel with each other allows a higher maximum air mass flow rate to be achieved through the two electric superchargers, thereby extending the engine speed range over which the two electric superchargers are effective in compressing air for delivery to an engine.

Alternatively, the two electric superchargers may be provided in a configurable arrangement that can be selectively switched during use of the intake system between a series configuration in which the two electric superchargers are arranged in series with each other and a parallel configuration in which the two electric superchargers are arranged in parallel with each other. By providing such a configurable arrangement it is possible to selectively achieve the advantages of both series and parallel arrangements, so that engine performance can be more fully optimised over a wider range of operating conditions (especially during transient modes of operation).

The intake system may comprise a first flow path for delivering air from an outlet of a first one of the two electric superchargers to an inlet of a second one of the two electric superchargers when the two electric superchargers are operated in the series configuration, a second flow path for delivering air from the outlet of the first electric supercharger and bypassing the second electric supercharger when the two electric superchargers are operated in the parallel configuration, and a third flow path for bypassing the first electric supercharger and delivering air to the inlet of the second electric supercharger when the two electric superchargers are operated in the parallel configuration.

The first flow path may be provided with a first valve element that may be opened to enable air to flow from the first electric supercharger to the second electric supercharger, the second flow path may be provided with a second valve element that may be opened to enable air to flow from the first electric supercharger bypassing the second electric supercharger, and the third flow path may be provided with a third valve element that may be opened to enable air to bypass the first electric supercharger and flow to the second electric supercharger.

The second and third valve elements may be arranged to be operated in phase with each other, and the first valve element may be arranged to be operated out of phase with the second and third valve elements.

Two or more of the first, second and third valve elements may be arranged to be operated together by a common actuator.

Two or more of the first, second and third valve elements may be coupled to a common shaft.

Two or more of the first, second and third valve elements may be provided within a common housing. The intake system may further comprise a common charge cooling device located downstream of both of the two electric superchargers arranged to cool air that has passed through one or both of the two electric superchargers. Alternatively, separate parallel charge cooling devices may be provided, each of the charge cooling devices being arranged to cool air that has passed through a respective one of the two electric superchargers. The charge cooling device(s) may be, for example, water charged air coolers.

The intake system may further comprise a bypass line operable to selectively bypass at least one of the two electric superchargers. The bypass line may be provided with a valve which is openable in order to selectively bypass the electric supercharger(s). The intake system may comprise a first bypass line operable to selectively bypass a first one of the two electric superchargers, and a second bypass line operable to selectively bypass a second one of the two electric superchargers.

The bypass line may be operable to selectively bypass both of the two electric superchargers.

The two electric superchargers may be located within the intake system so as to be located on opposite sides of an engine to which the intake system may be fitted.

The intake system may further comprise a throttle device, wherein the two electric superchargers are both arranged upstream of the throttle device. The two electric superchargers may have the same power rating. The two electric superchargers may be of the same model. Alternatively, the two electric superchargers may be different models, in which case they may have different power ratings and/or other different operating characteristics. At least one of the two electric superchargers may have a rated power of at least 2kW, preferably at least 3kW, and most preferably at least 5kW. Other power ratings are also possible, for example 10kW or higher.

The two electric superchargers may be arranged to be powered by a main battery of a vehicle in which the intake system may be installed, or by one or more separate batteries or capacitors. The one or more separate batteries or capacitors may be comprised in (for example mounted to) the intake system, and may be arranged to be charged, for example, by an engine to which the intake system may be fitted and/or by regenerative braking. A further aspect of the present invention provides an automotive internal combustion engine fitted with an intake system as described above. The engine is preferably a 4- stroke piston engine. The engine may have a displacement of no more than 4L or no more than 3L or no more than 2L, although larger engine displacements are also possible.

A further aspect of the present invention provides a vehicle comprising an internal combustion engine as described above. The vehicle may be, for example, a road vehicle such as a car or van, or alternatively an off-road vehicle.

The vehicle may comprise a control module arranged to control operation of the two electric superchargers. The control module may be arranged to provide the same power to each of the two electric superchargers in use. By always providing the same power to each of the two electric superchargers the control complexity is minimised. Alternatively, the control module may be arranged to control the power supplied to each of the two electric superchargers individually and supply different power to each of the two electric superchargers in use, for example to maximise their operational efficiency.

The control module may be arranged to actuate the electric superchargers only during transient modes of operation of the engine. This may be, for example, in response to an increased throttle position. Alternatively, the control system may be arranged to also actuate the electric superchargers at other times, for example when there is a gap between target power and measured power or a gap between target boost pressure and measured boost pressure.

It will be appreciated that the intake system is not limited to having exactly two electric superchargers, and that an intake system according to the present invention may also comprise additional electric superchargers. For example, the intake system may include a third electric supercharger arranged in series with, or in parallel with, or in a configurable arrangement with the two electric superchargers. A further aspect of the present invention provides a method of operating an intake system of an automotive internal combustion engine, the method comprising delivering air to the internal combustion engine through the intake system; passing air through two electric superchargers provided in the intake system; and using the two electric superchargers to compress air passing through the intake system before delivery to the internal combustion engine. The two electric superchargers may be arranged in series with each other or in parallel with each other. The method may be used in operating an intake system as described above, and may include any steps associated with the normal operation of an intake system including any of the above-described features. The method may be used in operating an intake system in which the two electric superchargers are permanently arranged in series with each other, or in which the two electric superchargers are permanently arranged in parallel with each other, or in which the two electric superchargers are provided in a configurable arrangement that can be selectively switched between a series configuration and a parallel configuration.

The method may comprise switching the two electric superchargers between a series configuration in which the two electric superchargers are arranged in series with each other and a parallel configuration in which the two electric superchargers are arranged in parallel with each other during use of the engine.

According to a further aspect of the present invention there is provided a valve assembly for a gas flow system, comprising:

first and second valve elements, wherein the first valve element is movable between an open position for allowing gas flow through a first flow path of the gas flow system and a closed position for restricting gas flow through the first flow path of the gas flow system, and wherein the second valve element is movable between an open position for allowing gas flow through a second flow path of the gas flow system and a closed position for restricting gas flow through the second flow path of the gas flow system; and

a common actuator arranged to control the position of each of the first and second valve elements;

wherein the first and second valve elements are arranged to be operated out of phase with each other. The valve assembly may optionally be a valve assembly for a gas flow system of an automotive internal combustion engine.

The first and second valve elements are capable of controlling gas flow through first and second flow paths when the valve assembly is incorporated in a gas flow system including the first and second flow paths. However, it will be appreciated that the valve assembly may be provided separately to the gas flow system in which it is to be incorporated. The valve assembly of the present invention allows a gas flow system (for example a gas flow system of an automotive internal combustion engine) in which the valve assembly may be incorporated to open a first flow path while closing a second flow path (and vice-versa) without requiring the use of two separate valves operated by two separate actuators. The present invention therefore allows a reduction in the cost, weight, parts count and control complexity of a gas flow system (for example a gas flow system of an automotive internal combustion engine). The present invention maybe used in any gas flow system of an automotive internal combustion engine in which it is desired to open at least one flow path while closing at least one other flow path. The common actuator may be arranged to control the position of each of the first and second valve elements simultaneously using a single output to which each of the first and second valve elements is coupled.

The actuator may be a rotary actuator or alternatively a linear actuator.

The first and second valve elements may be arranged to be operated 90 degrees out of phase with each other such that when the first valve element is in its closed position the second actuator is in a position of maximum opening, and vice-versa. The first and second valve elements may have a fixed phase relationship with each other.

The first and second valve elements may be arranged to be rotated between their respective open and closed positions. The first and second valve elements may be butterfly valve elements. Alternatively any other form of valve element suitable for selectively restricting or preventing gas flow through a flow passage may be employed.

The first and second valve elements may be arranged along a common pivot axis about which each of the first and second valve elements is arranged to rotate between its open and closed positions. Alternatively the first and second valve elements may be arranged to pivot about separate pivot axes, which may be parallel pivot axes.

The first and second valve elements may be angularly offset from each other in order to operate out of phase with each other. For example, the first and second valve elements may be offset from each other by approximately 90 degrees about the common pivot axis (or about their respective pivot axes). Angular offsets of less than 90 degrees are also possible, for example where each of the valve elements is arranged to rotate by less than 90 degrees between its closed position and its position of maximum opening.

The first and second valve elements may be fixed to a common shaft. The common shaft may be coupled directly to a rotary output of the actuator. Alternatively the common shaft may be coupled to a rotary or linear output of the actuator via a coupling mechanism for enabling the common actuator to rotate the common shaft. Such a coupling mechanism may include, for example, one or more gears, cranks or levers.

Alternatively the first and second valve elements may be fixed respectively to separate shafts. In this case a first one of the shafts may be coupled directly to a rotary output of the actuator, or alternatively coupled to a rotary or linear output of the actuator via a coupling mechanism. The second one of the shafts may also be coupled to the output of the actuator via a further coupling mechanism, or alternatively may be coupled to the first one of the shafts via a further coupling mechanism in order to enable the actuator to control the position of both of the first and second valve elements. The first and second valve elements may be arranged to at least substantially prevent gas flow through their respective flow paths when in their closed positions. It may therefore be possible to substantially or alternatively completely seal either of the first and second flow paths when its respective valve element is in its closed position.

The valve assembly may further comprise a biasing system for biasing the valve assembly into a position in which one of the first and second valve elements is in its open position and the other one of the first and second valve elements is in its closed position.

The first and second flow paths may run substantially parallel to each other at the location of the valve elements.

The valve assembly may further comprise a common housing, wherein the first and second valve elements are located within and/or mounted to the common housing. Where the first and second valve elements are fixed to a common shaft the common shaft may be rotatably mounted to the housing. Alternatively the gas flow system may comprise separate housings for the first and second valve elements. The valve assembly may comprise first and second flow passages, wherein the first valve element is operable to control the flow of gas through the first flow passage, and wherein the second valve element is operable to control the flow of gas through the second flow passage. The first flow passage may be arranged to form part of the first flow path and the second flow passage may arranged to form part of the second flow path when the valve assembly is incorporated into a gas flow system including the first and second flow paths. The first and second flow passages may be provided by the common housing, or alternatively by separate housings. In either case the first and second flow passages may run substantially parallel to each other. The first valve element may be arranged in the first flow passage, and the second valve element may be arranged in the second flow passage. Alternatively one or both of the first and second valve elements may be arranged outside the first and second flow passages, for example at ends of the first and second flow passages. The valve assembly may further comprise a third valve element that is movable between an open position for allowing gas flow through a third flow path of the gas flow system and a closed position for restricting gas flow through the third flow path of the gas flow system. It will be appreciated that any features of the first and/or second valve elements described above may equally apply to the third valve element. In particular, the common actuator may additionally be arranged to control the position of the third valve element. It will further be appreciated that the valve assembly may, in some embodiments, comprise more than three valve elements. The third valve element may be arranged to be operated out of phase with the first valve element and in phase with the second valve element.

A further aspect of the present invention provides a gas flow system (for example a gas flow system of or for an automotive internal combustion engine) comprising first and second flow paths and a valve assembly as described above. The first valve element may be operable to control the flow of gas through the first flow path and the second valve element may be operable to control the flow of gas through the second flow path. However, as mentioned above, it will be appreciated that the valve assembly may be provided separately to the gas flow system in which it is to be incorporated. The first flow path may be opened while the second flow path is closed by operating the actuator to move the first valve element into (or maintain the first valve element in) its open position and to move the second valve element into (or maintain the second valve element in) its closed position, and vice-versa. The first and second flow paths may be alternative flow paths arranged in parallel with each other. The valve assembly may be operable to selectively cause gases flowing through the gas flow system to flow either via the first flow path (but not the second flow path) or via the second flow path (but not the first flow path).

Where the valve assembly comprises a third valve element, the gas flow system may further comprise a third flow path, with the third valve element being operable to control the flow of gas through the third flow path. In this case the first, second and third flow paths may each be opened or closed as required by operating the common actuator. The first, second and third flow paths may be alternative flow paths arranged in parallel with each other. The valve assembly may be operable to selectively cause gases flowing through the gas flow system to flow either via the first flow path (but not the second or third flow paths) or via the second and third flow paths (but not the first flow path). The gas flow system may be an intake system (for example an intake system of or for an automotive internal combustion engine).

Where the intake system comprises first and second flow paths, the first flow path may be arranged to deliver air from an outlet of a first electric supercharger to an inlet of a second electric supercharger; and the second flow path may be arranged to deliver air from the outlet of the first electric supercharger and bypass the second electric supercharger, or alternatively the second flow path may be arranged to bypass the first electric supercharger and deliver air to the inlet of the second electric supercharger. Where the intake system comprises first, second and third flow paths, the first flow path may be arranged to deliver air from an outlet of a first electric supercharger to an inlet of a second electric supercharger; the second flow path may be arranged to deliver air from the outlet of the first electric supercharger and bypass the second electric supercharger; and the third flow path may be arranged to bypass the first electric supercharger and deliver air to the inlet of the second electric supercharger.

The gas flow system may be an exhaust system (for example an exhaust system of or for an automotive internal combustion engine). In this case the first flow path may be a first exhaust gases flow path and the second flow path may be an alternative exhaust gases flow path arranged in parallel with the first exhaust gases flow path.

The valve assembly of the present invention may equally be used in any other gas flow system of an automotive internal combustion engine (besides those described above) in which it is desired to open at least one flow path while closing at least one other flow path.

A further aspect of the present invention provides an internal combustion engine (for example an automotive internal combustion engine) fitted with a gas flow system as described above. A further aspect of the present invention provides a vehicle comprising an engine as described above. The vehicle may be, for example, a road vehicle such as a car or a van, or alternatively an off-road vehicle.

A further aspect of the present invention provides a valve assembly for a gas flow system (for example a gas flow system of an automotive internal combustion engine), comprising:

first and second flow passages arranged to allow a gas to flow therethrough; first and second valve elements, wherein the first valve element is movable between an open position in which gas flow through the first flow passage is permitted and a closed position in which gas flow through the first flow passage is restricted, and wherein the second valve element is movable between an open position in which gas flow through the second flow passage is permitted and a closed position in which gas flow through the second flow passage is restricted; and

a common actuator arranged to control the position of each of the first and second valve elements;

The first and second valve elements may be are arranged to be operated out of phase with each other.

The valve assembly may generally include any of the features described above in connection with the first aspect of the present invention. A further aspect of the present invention provides a valve assembly for a gas flow system (for example a gas flow system of an automotive internal combustion engine), comprising:

first and second valve elements, wherein the first valve element is movable between an open position for allowing gas flow through a first flow path of the gas flow system and a closed position for restricting gas flow through the first flow path of the gas flow system, and wherein the second valve element is movable between an open position for allowing gas flow through a second flow path of the gas flow system and a closed position for restricting gas flow through the second flow path of the gas flow system; and a common actuator arranged to control the position of each of the first and second valve elements.

The first and second valve elements may be fixed to a common shaft upon which each of the first and second valve elements is arranged to rotate between its open and closed positions.

Optionally, the first and second valve elements may be arranged to be operated out of phase with each other. However, this is not required in all embodiments, and in some embodiments the first and second valve elements may be arranged to be operated in phase with each other. In particular, where the first and second valve elements are arranged to be operated in phase with each other, the valve assembly may be comprised in an intake system of or for an automotive internal combustion engine comprising first and second flow paths, wherein the first flow path is arranged to deliver air from an outlet of a first electric supercharger and bypass a second electric supercharger, and wherein the second flow path is arranged to bypass the first electric supercharger and deliver air to an inlet of the second electric supercharger. The valve assembly may generally include any of the features described above in connection with the first aspect of the present invention.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 illustrates a car including an automotive internal combustion engine fitted with an intake system in accordance with one possible embodiment of the present invention;

Figure 2 schematically illustrates the engine, intake system and exhaust system of the vehicle of Figure 1 ;

Figures 3 to 8 schematically illustrate various automotive internal combustion engines fitted with intake systems according to alternative embodiments of the present invention; Figures 9a and 9b schematically illustrate a valve assembly from the embodiment illustrated in Figures 7 and 8; and

Figures 10 and 1 1 schematically illustrate automotive internal combustion engines fitted with intake systems according to still further embodiments of the present invention.

Figure 12 schematically illustrates the engine, intake system and valve assembly of the vehicle of Figure 1 ;

Figures 13, 14 and 15 schematically illustrate the valve assembly during different modes of operation of the intake system;

Figures 16 and 17 schematically illustrate various automotive internal combustion engines fitted with intake systems comprising valve assemblies in accordance with other possible embodiments of the present invention; and

Figure 18 schematically illustrates a portion of an exhaust system comprising a valve assembly according to another possible embodiment of the present invention.

DETAILED DESCRIPTION

Embodiment of Figures 1 and 2

Figure 1 illustrates a car 100 comprising an automotive internal combustion engine 1 . The engine 1 is fitted with an exhaust system 2 for removing combustion gasses from the engine and an intake system 3 for delivering air to the engine, as schematically illustrated in Figure 2. The intake system 3 is an intake system in accordance with one possible embodiment of the present invention. The engine 1 generally may be any type of automotive engine, for example a 4-stroke engine with 4 cylinders and a displacement of approximately 2L.

The intake system 3 comprises an air filter 4 through which air enters the intake system. The intake system 3 further comprises a conventional turbocharger 5 comprising a turbine arranged to be driven by exhaust gasses flowing through the exhaust system 2 and a compressor that is driven by the turbine and that is arranged to compress air flowing through the intake system. Conventional turbochargers are well known to those skilled in the art, so the features and operation of the turbocharger 5 will not be discussed further.

The intake system 3 further comprises first and second electric superchargers 6, 7. Each of the electric superchargers 6, 7 comprises a compressor arranged to compress air flowing through the intake system 3 before delivery to the engine 1 , and an electric motor arranged to drive the compressor. The electric superchargers 6, 7 are of the same model and each have an identical power rating of 5kW.

The first and second electric superchargers 6, 7 are powered by a main battery 20 of the car 100, and their operation is controlled by a control module 21 , which may be the main ECU of the car 100 or alternatively a separate controller. The control module 21 is arranged to operate the first and second electric superchargers 6, 7 together and to always provide the same power to each of the first and second electric superchargers 6, 7 in order to minimise the complexity of controlling the charging system.

The first and second electric superchargers 6, 7 are arranged in series with each other along a supercharged flow path 8 such that air flowing along the supercharged flow path 8 flows through and is compressed by the first electric supercharger 6 before flowing through and being further compressed by the second electric supercharger 7. The first and second electric superchargers 6, 7 are also arranged in series with and downstream of the turbocharger 5, and so are each arranged to further compress air that has already been compressed by the turbocharger, although in other embodiments the first and second electric superchargers could equally be arranged in parallel with the turbocharger.

The first and second electric superchargers 6, 7 are arranged on opposite sides of the engine 1 , although could equally be arranged on the same side of the engine.

The supercharged flow path 8 is provided with a common charge cooling device 9 in the form of a water charged air cooler for cooling air that has been compressed by the first and second electric superchargers 6, 7.

The supercharged flow path 8 leads to a throttle device 10 that is operated in order to control operation of the engine 1 , and an intake manifold 1 1 for delivering air from the intake system 3 directly into cylinders of the engine 1 , the first and second electric superchargers 6, 7 being arranged upstream of the throttle device 10 and the intake manifold 1 1 .

The intake system 3 further comprises a bypass line 12 operable to selectively bypass the first and second electric superchargers 6, 7. The bypass line 12 is arranged in series with and downstream of the turbocharger 5, but runs in parallel with the supercharged flow path 8 in which the first and second electric superchargers 6, 7 are provided. The bypass line 12 is provided with a bypass valve 13 which may be selectively opened to allow air flowing through the intake system 3 to bypass the first and second electric superchargers 6, 7, and closed to shut the bypass line 12 such that air flowing through the intake system flows via the supercharged flow path 8 and through the first and second electric superchargers 6, 7. The bypass line 12 is provided with its own charge cooling device 14 in the form of a water charged air cooler for cooling air that has been compressed by the turbocharger 5 and is flowing through the bypass line 12 (instead of via the supercharged flow path 8). The bypass line 12 also leads to the throttle device 10 and the intake manifold 1 1 .

In other embodiments the two charge cooling devices 9, 14 may be replaced by a single charge cooling device arranged in series with and downstream of the turbocharger 5 and both of the first and second electric superchargers 6, 7. Operation of the intake system 3 will now be described.

During normal steady state operation of the engine 1 , the bypass valve 13 is maintained in its open position by an actuator. In this state, air being delivered to the engine 1 by the intake system 3 is compressed by the turbocharger 5, and then flows through the bypass line 12, thereby bypassing the supercharged flow path 8 and the first and second electric superchargers 6, 7. The compressed air is then cooled by the bypass line charge cooling device 14 before passing through the throttle device 10 and entering the engine 1 via the intake manifold 1 1 .

When the throttle position is increased, the actuator of the bypass valve 13 is controlled to move the bypass valve into its closed position, thereby closing the bypass line 12 and causing air flowing through the intake system 3 to flow via the supercharged flow path 8. The first and second electric superchargers 6, 7 are actuated by the control module 21 , and act to further compress the air that has already been compressed by the turbocharger 5, providing a further boost in air pressure. The further compressed air is then cooled by the supercharged flow path charge cooling device 9 before passing through the throttle device 10 and entering the engine 1 via the intake manifold 1 1 . In this mode of operation the first and second electric superchargers 6, 7 provide additional compression of the air being delivered to the engine 1 to thereby increase the torque and power available from the engine after the throttle position is increased, thereby providing a more rapid response to the increased throttle position. The first and second electric superchargers 6, 7 also spool up faster than the turbocharger 5, and so act to reduce the effects of turbo lag that are inherent with the turbocharger .

When the engine 1 returns to steady state operation the first and second electric superchargers 6, 7 may be deactivated and the bypass valve 13 may be opened to reopen the bypass line 12. Since the maximum air flow through the first and second electric superchargers 6, 7 is limited by the size and speed of the electric superchargers, the supercharged flow path 8 may be used only below a predetermined engine speed and/or a predetermined air mass flow rate. Embodiment of Figure 3

Figure 3 schematically illustrates an engine 101 that is fitted with an intake system 103 according to a further possible embodiment of the present invention. The embodiment of Figure 3 is generally similar to the embodiment of Figure 2, and so will not be described in its entirety, and instead only differences compared to the embodiment of Figure 2 will be described. Features already described in connection with the embodiment of Figure 2 are given equivalent numbers in the 100 series. As with the embodiment of Figure 2, the first and second electric superchargers 106, 107 are arranged in series with each other, and also in series with and downstream of a conventional turbocharger 105. However, in this embodiment, instead of a single bypass line that is operable to bypass both the first and second electric superchargers 106, 107, the intake system 103 instead includes a first bypass line 1 12a that is operable to bypass the first electric supercharger 106, and a separate second bypass line 1 12b that is operable to bypass the second electric supercharger 107.

In this embodiment it is possible to bypass both of the first and second electric superchargers 106, 107 by maintaining bypass valves 1 13a, 1 13b of the bypass lines 1 12a, 1 12b in open positions. The bypass valves 1 13a, 1 13b may then be moved into closed positions when it is desired to operate the first and second electric superchargers 106, 107 to further compress air being delivered to the engine 101 by the intake system 103. As with the embodiment of Figure 2, the intake system 103 comprises two charge cooling devices 109, 1 14. However, instead of a first charge cooling device 9 in the supercharged flow path 8 for cooling air that has been compressed by the first and second electric superchargers 6, 7 and a second charge cooling device 14 in the bypass line 12 for cooling air that has been compressed by the turbocharger 5 but that is bypassing the first and second electric superchargers, the intake system 103 of Figure 3 includes a first charge cooler 109 in series with and downstream of both the turbocharger 105 and the first electric supercharger 106 for cooling air that has been compressed by the turbocharger and optionally also by the first electric supercharger, and a second charge cooling device 1 14 in series with and downstream of the second electric supercharger 107 for cooling air that has additionally been compressed by the second electric supercharger.

Embodiment of Figure 4

Figure 4 schematically illustrates an engine 201 that is fitted with an intake system 203 according to a further possible embodiment of the present invention. The embodiment of Figure 3 has many similarities to the embodiment of Figure 2, and so will not be described in its entirety, and instead only differences compared to the embodiment of Figure 2 will be described. Features already described in connection with the embodiment of Figure 2 are given equivalent numbers in the 200 series, and are not described individually.

As with the embodiment of Figure 2, the intake system 203 comprises first and second electric superchargers 206, 207. However, in this embodiment, instead of being arranged in series with each other, the first and second electric superchargers are arranged in parallel with each other in parallel supercharged flow paths 208a, 208b. The first and second electric superchargers 206, 207 are also arranged in series with and downstream of a conventional turbocharger 205. By arranging the electric superchargers 206, 207 in parallel with each other, it is possible to increase the maximum air mass flow rate that is achievable through the two electric superchargers. It is therefore possible to increase the engine speed range over which the electric superchargers 206, 207 are effective in compressing air for delivery to the engine 201 (albeit with reduced boost pressure at lower engine speeds).

The first and second electric superchargers 206, 207 are arranged on the same side of the engine 101 , although could equally be arranged on opposite sides of the engine.

The intake system 203 comprises a single bypass line 212 including a bypass valve 213 that may be maintained in an open position to enable air flowing through the intake system to bypass the first and second electric superchargers 206, 207. The bypass valve 213 may then be moved into a closed position when it is desired to use the first and second electric superchargers 106, 107 to further compress air being delivered to the engine 101 by the intake system 103. The intake system 203 comprises a single charge cooling device 209 arranged to cool air that is bypassing the first and second electric superchargers 206, 207 (when the bypass line 212 is active) as well as to cool air that has been compressed by one of the electric superchargers in addition to the turbocharger 205 (when the bypass line 212 is closed). In other embodiments there may equally be multiple charge cooling devices, for example a first charge cooling device arranged in series with and downstream of the first and second electric superchargers 206, 207 to cool air that has been compressed by the first and second electric superchargers in addition to the turbocharger 205, and a second charge cooling device arranged in the bypass line 212 for cooling air that is bypassing the first and second electric superchargers 206, 207.

The intake system 203 of Figure 4 is generally operated in the same manner as that of Figure 2, with the first and second electric superchargers 206, 207 being activated to increase air pressure during transient modes of operation of the engine, but being bypassed during steady state operation and at higher engine speeds. However, due to the parallel arrangement of the electric superchargers 206, 207, it may be possible to operate the electric superchargers at higher engine speeds and higher air mass flow rates.

Embodiment of Figure 5

Figure 5 schematically illustrates an engine 301 that is fitted with an intake system 303 according to a further possible embodiment of the present invention. Features already described in connection with the embodiment of Figure 2 are given equivalent numbers in the 300 series, and are not described individually. The embodiment of Figure 5 is generally similar to the embodiment of Figure 4, and so only differences compared to the embodiment of Figure 4 will be described. As with the embodiment of Figure 4, the first and second electric superchargers 306, 307 are arranged in parallel with each other. However, in this embodiment, the first and second electric superchargers 306, 307 are arranged in parallel with the turbocharger 305 instead of in series with the turbocharger. Embodiment of Figure 6

Figure 6 schematically illustrates an engine 401 that is fitted with an exhaust system 402 and an intake system 403 according to a further possible embodiment of the present invention.

The intake system 403 comprises an air filter 404 through which air enters the intake system. The intake system 403 further comprises a conventional turbocharger 405 comprising a turbine arranged to be driven by exhaust gasses flowing through the exhaust system 402 and a compressor that is driven by the turbine and that is arranged to compress air flowing through the intake system. Conventional turbochargers are well known to those skilled in the art, so the features and operation of the turbocharger 5 will not be discussed further. The intake system 403 further comprises first and second electric superchargers 406, 407. Each of the electric superchargers 406, 407 comprises a compressor arranged to compress air flowing through the intake system 403 before delivery to the engine 401 , and an electric motor arranged to drive the compressor. The electric superchargers 406, 407 are of the same model and each have an identical power rating of 5kW.

The first and second electric superchargers 406, 407 are powered by a main battery 420 of the car, and their operation is controlled by a control module 421 , which may be the main ECU of the car or alternatively a separate controller. The control module 421 is arranged to operate the first and second electric superchargers 406, 407 together and to always provide the same power to each of the first and second electric superchargers 406, 407 in order to minimise the complexity of controlling the charging system.

The first and second electric superchargers 406, 407 are provided in a configurable arrangement that can be selectively switched during use of the engine 401 between a series configuration in which the two electric superchargers are arranged in series with each other, and a parallel configuration in which the two electric superchargers are arranged in parallel with each other. The first and second electric superchargers 406, 407 are both arranged in series with and downstream of the turbocharger 405, and so are each arranged to further compress air that has already been compressed by the turbocharger, although in other embodiments the first and second electric superchargers could equally be arranged in parallel with the turbocharger.

The first and second electric superchargers 406, 407 are arranged on opposite sides of the engine 401 , although could equally be arranged on the same side of the engine.

When the first and second electric superchargers 406, 407 are in the series configuration, the first electric supercharger 406 is arranged in series with and upstream of the second electric supercharger 407. An outlet of the first electric supercharger is connected to an inlet of the second electric supercharger 407 by a first flow path 408a for delivering air from the first electric supercharger to the second electric supercharger. The first flow path 408a is provided with a first valve 413a that is operated by an actuator for controlling the flow of air through the first flow path from the first electric supercharger to the second electric supercharger.

The intake system 403 further comprises a second flow path 408b for delivering air from the outlet of the first electric supercharger 406 and bypassing the second electric supercharger 407 when the first and second electric superchargers 406, 407 are in the parallel configuration. The second flow path 408b is provided with a second valve 413b that is operated by an actuator for controlling the flow of air through the second flow path.

The intake system 403 further comprises a third flow path 408c for bypassing the first electric supercharger 406 and delivering air to the second electric supercharger 407 when the first and second electric superchargers 406, 407 are in the parallel configuration. The third flow path 408c is provided with a third valve 413c that is operated by an actuator for controlling the flow of air through the third flow path.

The first, second and third valves 413a, 413b, 413c each comprise a valve element, for example a butterfly valve element, that is located within a housing. The housing of each of the first, second and third valves 413a, 413b, 413c forms a part of a respective one of the first, second and third flow paths 408a, 408b, 408c. The first, second and third flow paths 408a, 408b, 408c together provide a configurable supercharged flow path.

When it is desired to operate the first and second electric superchargers 406, 407 in the series configuration, the first valve 413a may be maintained in an open position to thereby open the first flow path 408a while the second and third valves 413b, 413c are maintained in closed positions to thereby close the second and third flow paths 408b, 408c. In this configuration, air flowing along the supercharged flow path flows through and is compressed by the first electric supercharger 306 before flowing through and being further compressed by the second electric supercharger 407.

Conversely, when it is desired to operate the first and second electric superchargers 406, 407 in the parallel configuration, the first valve 413a may be maintained in a closed position to thereby close the first flow path 408a while the second and third valves 413b, 413c are maintained in open positions to thereby close the second and third flow paths 408b, 408c. In this configuration, a portion of the air flowing along the supercharged flow path flows through and is compressed by the first electric supercharger 306 and the remainder of the air flowing through the supercharged flow path flows through and is compressed by the second electric supercharger 407.

The intake system 403 further comprises a bypass line 412 that is operable to selectively bypass the supercharged flow path 408a, 408b, 408c (including the first and second electric superchargers 406, 407). The bypass line 412 is arranged in series with and downstream of the turbocharger 5, but runs in parallel with the supercharged flow path 408a, 408b, 408c and each of the first and second electric superchargers 406, 407. The bypass line 412 is provided with a bypass valve 413d which may be selectively opened to allow air flowing through the intake system 403 to bypass the first and second electric superchargers 406, 407, and closed to shut the bypass line 412 such that air flowing through the intake system flows via the supercharged flow path 408a, 408b, 408c and through the first and second electric superchargers 406, 407.

The intake system further comprises a charge cooling device 409, a throttle device 410 and an intake manifold 41 1 arranged in series with and downstream of each of the turbocharger 405 and the first and second electric superchargers 406, 407. Operation of the intake system 403 will now be described.

During normal steady state operation of the engine 401 , the bypass valve 413d is maintained in its open position. In this state, air being delivered to the engine 401 by the intake system 403 is compressed by the turbocharger 405, and then flows through the bypass line 412, thereby bypassing the supercharged flow path and the first and second electric superchargers 406, 407. The compressed air is then cooled by the charge cooling device 409 before passing through the throttle device 410 and entering the engine 401 via the intake manifold 41 1 .

When the throttle position is increased, the first and second electric superchargers 406, 407 may be operated in order to further compress the air being delivered to the engine 401 by the intake system 403 to provide a more rapid response to the increased throttle position and combat turbo lag. The ECU of the vehicle determines which configuration should be used. This determination may be based on, for example, the throttle position and/or the engine speed or air mass flow rate. For example, the series configuration may be selected when a large increase in the throttle angle is detected and/or when the engine speed is low, and the parallel configuration may be selected at higher engine speeds.

If it is determined that the first and second electric superchargers 406, 407 should be operated in the series configuration, the first valve is moved into or maintained in its open position and the second and third valves are moved into or maintained in their closed positions. In this configuration, the first and second electric superchargers 406, 407 are operated together in series with each other to sequentially further compress air flowing through the intake system 403 via the first flow path 408a.

Alternatively, if it is determined that the first and second electric superchargers 406, 407 should be operated in the parallel configuration, the first valve is moved into or maintained in its closed position and the second and third valves are moved into or maintained in their open positions. In this configuration, the first and second electric superchargers 406, 407 are operated together in parallel and each compress a portion of the air flowing through the intake system 403 via the second and third flow paths 408b, 408c.

When the engine 401 returns to steady state operation the first and second electric superchargers 406, 407 may be deactivated and the bypass valve 413d may be opened to re-open the bypass line 412, thereby allowing air flowing through the intake system 403 to bypass the supercharged flow path and the first and second electric superchargers 406, 407. The configurable arrangement described above allows the most advantageous configuration of the two electric superchargers 406, 407 to be selected for any given operating condition of the engine 401 such that the overall performance of the charging system may be optimised over a wider range of operating conditions. Embodiment of Figure 7

Figure 7 schematically illustrates an engine 501 that is fitted with an intake system 503 according to a further possible embodiment of the present invention. The embodiment of Figure 7 is generally similar to the embodiment of Figure 6, and so will not be described in its entirety, and instead only differences compared to the embodiment of Figure 6 will be described. Features already described in connection with the embodiment of Figure 6 are given equivalent numbers in the 500 series.

The intake system illustrated in Figure 7 has the same general lay-out and is operated in the same manner as the intake system illustrated in Figure 6. However, instead of using three separate valves each operated by a separate actuator to control the configurable series/parallel arrangement of the first and second electric superchargers, the embodiment of Figure 7 replaces the three separate valves with a single integrated valve assembly 530, as illustrated in Figures 7, 8, 9a and 9b.

The valve assembly 530 comprises a common housing 531 providing three separate valve passages 532a, 532b, 532c. The first valve passage 532a forms part of the first flow path 508a for delivering air from the first electric supercharger 506 to the second electric supercharger 507 when the first and second electric superchargers are operated in the series configuration. The second valve passage 532b forms part of the second flow path 508b for delivering air from the first electric supercharger 506 and bypassing the second electric supercharger 507 when the first and second electric superchargers are operated in the parallel configuration. The third valve passage 532c forms part of the third flow path 508c for bypassing the first electric supercharger 506 delivering air to the second electric supercharger 507 when the first and second electric superchargers are operated in the parallel configuration.

Each of the first, second and third valve passages 532a, 532b, 532c is provided with a respective valve element 513a, 513b, 513c, for example a butterfly valve element. Each valve element 513a, 513b, 513c is movable between a closed position in which it acts to prevent the flow of air through its respective valve passage 532a, 532b, 532c (and therefore through a respective one of the first second and third flow paths 508a, 508b, 508c), and an open position in which fluid flow is enabled. Each valve element 513a, 513b, 513c may be arranged to at least substantially completely seal its respective valve passage 532a, 532b, 532c when in the closed position. In addition, one or more of the valve elements 513a, 513b, 513c may include spring bias.

The three valve elements 513a, 513b, 513c are arranged along and fixedly attached to a common shaft 534 which is rotatably mounted to the common housing 531 . The first valve element 513a is arranged to be out of phase with the second and third valve elements 513b, 513c such that when the first valve element 513a is in its open position the second and third valve elements 513b, 513c are in their closed positions and vice- versa.

The common shaft 534 is rotatable between a first position and a second position. When the common shaft 534 is in its first position the first valve element 513a is in its open position the second and third valve elements 513b, 513c are in their closed positions, as illustrated in Figure 9a. In this position the first flow path 508a is kept open while the second and third flow paths remain closed, and so it is possible to operate the first and second electric superchargers 506, 507 in the series configuration. When the common shaft 534 is in its second position the first valve element 513a is in its closed position the second and third valve elements 513b, 513c are in their open positions, as illustrated in Figure 9b. In this position the first flow path 508a is closed while the second and third flow paths are opened, and so it is possible to operate the first and second electric superchargers 506, 507 in the parallel configuration.

The valve assembly 530 is provided with a common actuator 535, for example a rotary actuator, which is operable to rotate the common shaft 534 to thereby control the position of the first, second and third valve elements. The valve assembly 530 is further provided with a biasing element 536 for biasing the common shaft 534 towards its first position. By biasing the common shaft 534 in this direction it is possible to achieve a fail safe mode with the first valve element 513a in its open position and the second and third valve elements 513b, 513c in their closed positions, such that the configurable electric supercharger arrangement defaults to the series configuration. However, in other embodiments a biasing element could equally act to bias the common shaft in the opposite direction. The intake system 503 of Figure 7 is operated in the same manner as that of Figure 6. However, with the intake system of Figure 7, when it is determined that the first and second electric superchargers 506, 507 should be operated in either the series configuration or the parallel configuration, the desired configuration may be achieved simply by controlling the single common actuator 535 to control the position of the first second and third valve elements 513a, 513b, 513c together.

By replacing the first, second and third valves of the embodiment of Figure 6 with a single valve assembly 530 comprising three valve elements that are provided within a common housing and operated by a common actuator, it is possible to reduce the parts count, cost, weight and complexity of the configurable electric supercharger arrangement.

In other embodiments it is possible for an integrated valve assembly to be arranged to control the flow of air through only two of the first, second and third flow paths 508a, 508b, 508c. For example, Figure 10 schematically illustrates an alternative integrated valve assembly 530 to that illustrated in Figure 7. In this alternative embodiment the valve assembly 530 includes only two valve elements 513b, 513c provided within a common housing and mounted to a common shaft that are arranged to control the flow of air through the second and third flow paths 508b, 508c. In this embodiment the two valve elements 513b, 513c are arranged to be operated in phase with each other. A separate valve 513a operated by a separate actuator is used to control the flow of air through the first flow path 508a. As another example, Figure 1 1 schematically illustrates another alternative valve assembly 530 which includes only two valve elements 513a, 513c provided within a common housing and mounted to a common shaft that are arranged to control the flow of air through the first and third flow paths 508a, 508c. In this embodiment the two valve elements 513a, 513c are arranged to be operated out of phase with each other. A separate valve 513b operated by a separate actuator is used to control the flow of air through the second flow path 508b.

Figure 12 schematically illustrates an engine 1001 , which may be any type of automotive engine, for example a 4-stroke engine with 4 cylinders and a displacement of approximately 2L. The intake system 1003 comprises an air filter 1004 through which air enters the intake system. The intake system 1003 further comprises a conventional turbocharger 1005 comprising a turbine arranged to be driven by exhaust gasses flowing through the exhaust system 1002 and a compressor that is driven by the turbine and that is arranged to compress air flowing through the intake system. Conventional turbochargers are well known to those skilled in the art, so the features and operation of the turbocharger 1005 will not be discussed further.

The intake system 1003 further comprises first and second electric superchargers 1006, 1007. Each of the electric superchargers 1006, 1007 comprises a compressor arranged to compress air flowing through the intake system 1003 before delivery to the engine 1001 , and an electric motor arranged to drive the compressor. The electric superchargers 1006, 1007 are of the same model and each have an identical power rating of 5kW. The first and second electric superchargers 1006, 1007 are powered by a main battery

1020 of the car, and their operation is controlled by a control module 1021 , which may be the main ECU of the car or alternatively a separate controller. The control module

1021 is arranged to operate the first and second electric superchargers 1006, 1007 together and to always provide the same power to each of the first and second electric superchargers 1006, 1007 in order to minimise the complexity of controlling the charging system.

The first and second electric superchargers 1006, 1007 are provided in a configurable arrangement that can be selectively switched during use of the engine 1001 between a series configuration in which the two electric superchargers are arranged in series with each other, and a parallel configuration in which the two electric superchargers are arranged in parallel with each other. The series configuration is a configuration in which air flows through the first electric supercharger 1006 before flowing through the second electric supercharger 1007, while the parallel configuration is a configuration in which a first air stream flows through the first electric supercharger (but not the second electric supercharger) while a parallel second air stream flows through the second electric supercharger (but not the first electric supercharger). The configurable arrangement is arranged to be selectively switched between the series configuration and the parallel configuration by a valve assembly 1050 according to an embodiment of the present invention, which is described in more detail below.

The first and second electric superchargers 1006, 1007 are both arranged in series with and downstream of the turbocharger 1005, and so are each arranged to further compress air that has already been compressed by the turbocharger, although in other embodiments the first and second electric superchargers could equally be arranged in parallel with the turbocharger, or the turbocharger could be replaced by a conventional mechanical supercharger, or omitted altogether. The first and second electric superchargers 1006, 1007 are arranged on opposite sides of the engine 1001 , although could equally be arranged on the same side of the engine.

When the first and second electric superchargers 1006, 1007 are in the series configuration, an outlet of the first electric supercharger is connected to an inlet of the second electric supercharger 1007 by a first flow path 1008a for delivering air from the first electric supercharger to the second electric supercharger.

The intake system 1003 further comprises a second flow path 1008b for delivering air from the outlet of the first electric supercharger 1006 and bypassing the second electric supercharger 1007 when the first and second electric superchargers 1006, 1007 are in the parallel configuration.

The intake system 1003 further comprises a third flow path 1008c for bypassing the first electric supercharger 1006 and delivering air to the second electric supercharger 1007 when the first and second electric superchargers 1006, 1007 are in the parallel configuration.

The first, second and third flow paths 1008a, 1008b, 1008c all run in parallel with each other and together provide a configurable supercharged flow path.

The intake system is provided with a valve assembly 1050 for selectively switching the first and second electric superchargers 1006, 1007 between the series and parallel configurations. The valve assembly 1050 comprises a housing 1051 providing first, second and third flow passages 1052a, 1052b, 1052c, as schematically illustrated in Figures 13 and 14. The first, second and third flow passages run substantially parallel to each other. The first flow passage 1052a forms part of the first flow path 1008a for delivering air from the first electric supercharger 1006 to the second electric supercharger 1007 when the first and second electric superchargers are operated in the series configuration. The second flow passage 1052b forms part of the second flow path 1008b for delivering air from the first electric supercharger 1006 and bypassing the second electric supercharger 1007 when the first and second electric superchargers are operated in the parallel configuration. The third flow passage 1052c forms part of the third flow path 8c for bypassing the first electric supercharger 1006 delivering air to the second electric supercharger 1007 when the first and second electric superchargers are operated in the parallel configuration.

Each of the first, second and third flow passages 1052a, 1052b, 1052c is provided with a respective valve element 1053a, 1053b, 1053c, for example a butterfly valve element as schematically illustrated in Figures 13 and 14. Each valve element 1053a, 1053b, 1053c is rotatable between a closed position in which it acts to prevent the flow of air through its respective flow passage 1052a, 1052b, 1052c (and therefore through its respective flow path 1008a, 1008b, 1008c), and an open position in which fluid flow is enabled. Each valve element 1053a, 1053b, 1053c may be arranged to at least substantially completely seal its respective flow passage 1052a, 1052b, 1052c to thereby seal its reflective flow path 1008a, 1008b, 1008c when in the closed position.

The first, second and third valve elements 1053a, 1053b, 1053c are each arranged along a common pivot axis and fixed to a common shaft 1054, as schematically illustrated in Figure 15. The common shaft 1054 is rotatably mounted to the housing 1051 . The common shaft 1054 is coupled to an output of a common actuator 1055 (also shown in Figure 15) which is operable to rotate the common shaft to thereby control the position of each of the first, second and third valve elements 1053a, 1053b, 1053c.

The second and third valve elements 1053b, 1053c are both offset from the first valve element 1053a by approximately 90 degrees. The second and third valve elements are therefore arranged to be operated 90 degrees out of phase with the first valve element 1053a such that when the first valve element 1053a is in its closed position the second and third valve elements 1053b, 1053c are each in positions of maximum opening. The second and third valve elements 1053b, 1053c are not angularly offset from each other, and so are arranged to be operated in phase with each other. The first, second and third valve elements 1053a, 1053b, 1053b have a fixed phase relationship due to each being fixed to the common shaft 1054.

The common actuator 1055 is operable to rotate the common shaft 1054 into (or maintain the common shaft in) a first position in which the first valve element 1053a is in a position of maximum opening and the second and third valve elements 1053b, 1053c are in their closed positions, as schematically illustrated in Figure 13. In this position the first flow path 1008a is kept open while the second and third flow paths 1008b, 1008c remain closed, and so it is possible to operate the first and second electric superchargers 1006, 1007 in the series configuration. The common actuator is also operable to rotate the common shaft 1054 into (or maintain the common shaft in) a second position in which the first valve element 1053a is in its closed position and the second and third valve elements 1053b, 1053c are in their positions of maximum opening, as schematically illustrated in Figure 14. In this position the first flow path 1008a is closed while the second and third flow paths 1008b, 1008c are opened, and so it is possible to operate the first and second electric superchargers 1006, 1007 in the parallel configuration. The valve assembly 1050 is further provided with a biasing element 1056 for biasing the common shaft 1054 towards its first position. By biasing the common shaft 1054 in this direction it is possible to achieve a failsafe mode with the first valve element 1053a in its open position and the second and third valve elements 1053b, 1053c in their closed positions, such that the configurable electric supercharger arrangement defaults to the series configuration. However, in other embodiments a biasing element could equally act to bias the common shaft in the opposite direction.

The intake system 1003 further comprises a bypass line 1012 that is operable to selectively bypass the supercharged flow path 1008a, 1008b, 1008c (including the first and second electric superchargers 1006, 1007). The bypass line 1012 is arranged in series with and downstream of the turbocharger 1005, but runs in parallel with the supercharged flow path 1008a, 1008b, 1008c and each of the first and second electric superchargers 1006, 1007. The bypass line 1012 is provided with a bypass valve 1013 which may be selectively opened to allow air flowing through the intake system 1003 to bypass the first and second electric superchargers 1006, 1007, and closed to shut the bypass line 1012 such that air flowing through the intake system flows via the supercharged flow path 1008a, 1008b, 1008c and through the first and second electric superchargers 1006, 1007.

The intake system further comprises a charge cooling device 1009, a throttle device 1010 and an intake manifold 101 1 arranged in series with and downstream of each of the turbocharger 1005 and the first and second electric superchargers 1006, 1007.

Operation of the intake system 1003 and the valve assembly 1050 will now be described.

During normal steady state operation of the engine 1001 , the bypass valve 1013 is maintained in its open position. In this state, air being delivered to the engine 1001 by the intake system 1003 is compressed by the turbocharger 1005, and then flows through the bypass line 1012, thereby bypassing the supercharged flow path 1008a, 1008b, 1008c and the first and second electric superchargers 1006, 1007. The compressed air is then cooled by the charge cooling device 1009 before passing through the throttle device 1010 and entering the engine 1001 via the intake manifold 101 1 . When the throttle position is increased, the first and second electric superchargers 1006, 1007 may be operated in order to further compress the air being delivered to the engine 1001 by the intake system 1003 to provide a more rapid response to the increased throttle position and combat turbo lag. The ECU of the vehicle determines which configuration should be used. This determination may be based on, for example, the throttle position and/or the engine speed or air mass flow rate. For example, the series configuration may be selected when a large increase in the throttle angle is detected and/or when the engine speed is low, and the parallel configuration may be selected at higher engine speeds.

If it is determined that the first and second electric superchargers 1006, 1007 should be operated in the series configuration, the common actuator 1055 is operated to move the common shaft 1054 into (or maintain the common shaft in) its first position, such that the first flow path 1008a is open while the second and third flow paths 1008b, 1008c remain closed. In this configuration, the first and second electric superchargers 1006, 1007 are operated together in series with each other to sequentially further compress air flowing through the intake system 1003 via the first flow path 1008a. Alternatively, if it is determined that the first and second electric superchargers 1006, 1007 should be operated in the parallel configuration, the common actuator 1055 is operated to move the common shaft 1054 into (or maintain the common shaft in) its second position, such that the first flow path 1008a is closed while the second and third flow paths 1008b, 1008c are opened. In this configuration, the first and second electric superchargers 1006, 1007 are operated together in parallel and each compress a portion of the air flowing through the intake system 1003 via the second and third flow paths 1008b, 1008c.

When the engine 1001 returns to steady state operation the first and second electric superchargers 1006, 1007 may be deactivated and the bypass valve 1013 may be opened to re-open the bypass line 1012, thereby allowing air flowing through the intake system 1003 to bypass the supercharged flow path 1008a, 1008b, 1008c and the first and second electric superchargers 1006, 1007. The configurable arrangement described above allows the most advantageous configuration of the two electric superchargers 1006, 1007 to be selected for any given operating condition of the engine 1001 such that the overall performance of the charging system may be optimised over a wider range of operating conditions.

The use of a common valve assembly 1050 to control the opening and closing of the first, second and third flow paths 1008a, 1008b, 1008c allows a reduction in the cost, weight, parts count and control complexity compared to an alternative solution in which three separate valves controlled by three separate actuators are used to open and close the first, second and third flow paths 1008a, 1008b, 1008c.

In the above described embodiment, the valve assembly 1050 comprises three valve elements 1053a, 1053b, 1053c arranged to open and close three different flow paths 1008a, 1008b, 1008c arranged in parallel with each other in a gas flow system. However, in other embodiments, a valve assembly may comprise only two valve elements arranged to open and close two different flow paths. For example, Figures 16 and 17 illustrates two alternative embodiments that are generally similar in structure and operation to the embodiment of Figure 12. Features already described in relation to the embodiment of Figure 12 are given numbers in the 1 100 and 1200 series respectively, and only differences compared to the embodiment of Figure 12 will be described.

In the embodiment of Figure 16, the valve assembly 1 150 comprises only two flow passages, respectively forming part of a first flow path 1 108a for delivering air from the outlet of the first electric supercharger 1 106 to the inlet of the second electric supercharger 1 107 and a second flow path 1 108c for bypassing the first electric supercharger 1 106 and delivering air to the inlet of the second electric supercharger 1 107. In this embodiment, first and second valve elements 1 153a, 1 153c of the valve assembly 1 150 are fixed to a common shaft 1 154 and arranged to be controlled by a common actuator 1 155 to open and close the first and second flow paths 1 108a, 1 108c. The valve elements 1 153a, 1 153c are arranged to be operated out of phase with each other. A separate valve 1 153b controlled by a separate actuator is used to open and close a further flow path 1 108b for delivering air from the first electric supercharger 1 106 and bypassing the second electric supercharger 1 107. It will be appreciated that in another embodiment a similar valve assembly could equally be arranged to control the flow path 1 108a for delivering air from the outlet of the first electric supercharger 1 106 to the inlet of the second electric supercharger 1 107 and the flow path for 1 108b for delivering air from the first electric supercharger 1 106 and bypassing the second electric supercharger 1 107. In such an embodiment the flow paths 1 108a, 1 108b may be regarded as first and second flow paths within the meaning of the accompanying claims.

In the embodiment of Figure 17, the valve assembly 1250 comprises only two flow passages, respectively forming part of a first flow path 1208b for delivering air from the first electric supercharger 1206 and bypassing the second electric supercharger 1207 and a second flow path 1208c for bypassing the first electric supercharger 1206 and delivering air to the inlet of the second electric supercharger 1207. In this embodiment, first and second valve elements 1253b, 1253c of the valve assembly 1250 are fixed to a common shaft 1254 and are arranged to be controlled by a common actuator 1255 to open and close the first and second flow paths 1208b, 1208c. The valve elements 1253b, 1253c are arranged to be operated in phase with each other. A separate valve 1253a controlled by a separate actuator is used to open and close a further flow path 1208a for delivering air from the outlet of the first electric supercharger 1206 to the inlet of the second electric supercharger 1207.

It will be appreciated that a valve assembly according to the present invention may also be used in other inlet and exhaust systems where is it desired to open and close multiple gas flow paths. For example, Figure 18 schematically illustrates a portion of an exhaust system 1301 that splits into a first exhaust gases flow path 1302 and an alternative exhaust gases flow path 1303 arranged in parallel with the first exhaust gases flow path. The exhaust system 1301 is provided with a valve assembly 1304 comprising first and second flow passages respectively forming part of the first exhaust gases flow path 1302 and the alternative exhaust gases flow path 1303. The valve assembly 1304 further comprises first and second valve elements 1305, 1306 each arranged to open and close a respective one of the first exhaust gases flow path 1302 and the alternative exhaust gases flow path 1303. The first and second valve elements 1305, 1306 are fixed to a common shaft 1308 and are arranged to be operated out of phase with each other such that when the first valve element 1305 is in its open position the second valve element 1306 is in its closed position, and vice versa. The valve assembly 1304 comprises a common actuator 1307 for controlling the position of each of the first and second valve elements 1305, 1306. By operating the common actuator 1307 it is possible selectively open either one of the first exhaust gases flow path 1302 and the alternative exhaust gases flow path 1303 while closing the other one of the first exhaust gases flow path 1302 and the alternative exhaust gases flow path 1303 to thereby control the route taken by exhaust gases passing through the exhaust system 1301 .

Many modifications may be made to any of the above examples without departing from the scope of the present invention as defined in the accompanying claims. For example, the turbocharger included in each of the above-described embodiments may be replaced by another type of charging device such as a conventional mechanical supercharger, or alternatively omitted altogether. Other modifications and variations will be apparent to those skilled in the art.