TECHNICAL FIELD The present disclosure relates to a supercharger assembly for an internal combustion engine. In particular, but not exclusively, the present disclosure relates to a supercharger assembly that incorporates a generator. Aspects of the invention relate to a supercharger assembly and to a related method of operation, to a vehicle, and to related computer program products, controllers and computer readable mediums.

BACKGROUND

A conventional supercharger has an impeller positioned upstream of an engine intake to elevate the intake pressure above ambient, to raise engine performance. Typically, the impeller is driven mechanically via a pulley by a belt coupled to the engine. For example, the belt may form part of a front end accessory drive (FEAD) of the engine. As the impeller raises the load on the engine there is typically an overall increase in fuel consumption.

Superchargers are therefore distinct from turbochargers, in which an impeller performing the same function of raising engine intake pressure is driven by an exhaust-driven turbine. Turbochargers recover waste heat from exhaust gases and so can help to improve vehicle efficiency. The exhaust gas flow rate needs to reach a threshold level before the turbine is driven effectively, causing the problem of 'turbo lag'. As superchargers are driven mechanically, they do not suffer from lag, and so they are favoured for some applications. However, as superchargers do not recover energy in the way that a turbocharger does, in the current climate of prioritising reduced vehicle fuel consumption, superchargers need to operate as efficiently as possible.

Figure 1 shows a known supercharger assembly 10 that includes an impeller 12 that is driven indirectly by a pulley 14 through an epicyclic gearbox, or 'epicycloid' 16. The impeller 12 is disposed within a duct 18 leading to an intake of an engine (not shown) such that, on rotating, the impeller 12 pumps air through the duct 18 and into the engine for increased output. The pulley 14 is driven by a belt that is in turn driven by the engine FEAD (not shown). The supercharger pulley 14 is sized so as to produce a speed ratio of around 3:1 relative to the FEAD output speed, which corresponds to the engine speed. The internal features of the epicycloid 16 are not shown in Figure 1 , but the skilled reader will appreciate that such a gearbox comprises three rotating elements held in concentric relation: an outer gear ring or 'annulus', a plurality of inner planet gears or 'planets', and a central gear or 'sun'. The planets are supported by a common planet carrier which maintains the relative positions of the planets. Although not visible in Figure 1 , it should be appreciated that coaxial input and output shafts extend from opposite sides of the epicycloid, with each shaft being attached to a different one of the epicycloid's three elements. The input shaft is coupled at its other end to the pulley 14, while the output shaft drives the impeller 12.

The input shaft carries an armature 20 of a first electric machine 22, which is the main generator for the vehicle in which the supercharger 10 resides. Therefore, as the input shaft is driven by the FEAD through the pulley 14, the armature 20 is rotated to generate electrical energy in the first electric machine 22. This provides a compact and versatile packaging arrangement.

The uncoupled element of the epicycloid 16, namely the element that is not connected to either the input shaft or the output shaft, may be held stationary to provide a fixed speed increase or decrease between the input and output shafts, typically at a gear ratio of about 10:1 .

Alternatively, the uncoupled element can be driven forwards or backwards so as to vary the gear ratio. To this end, an armature 24 of a second electric machine 26 is disposed between the epicycloid 16 and the impeller 12, and is used to drive the uncoupled element to enable the effective gear ratio to be varied to provide a desired output speed that is decoupled from the variable input speed that is governed by the engine speed.

The speed at which the vehicle engine operates is variable within a range of, for example, 500 to 7000 revolutions per minute (rpm). If the uncoupled element were held stationary, the assembly would produce a speed increase of around 30:1 , through a combination of a 3:1 increase from the pulley, and a 10:1 increase from the epicycloid 16. Therefore, the expected operating range for the supercharger impeller 12 would be 15,000 to 210,000 rpm.

However, for optimal performance it is desirable to maintain the speed of rotation of the supercharger impeller 12 at a relatively constant level during operation, generally at around 120,000 rpm; although it is noted that the desired speed may vary within a relatively narrow range according to instantaneous engine speed and load. Therefore, the second electric machine 26 is controlled so as to vary the gear ratio of the epicycloid 16 to deliver the desired output speed at all times as the engine speed varies.

While the use of an epicycloid 16 is effective in optimising the speed of the impeller 12, thereby raising engine performance, the epicycloid 16 places an additional load on the engine and so overall efficiency is compromised.

It is against this background that the present invention has been devised. SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide a supercharger assembly, a method, a vehicle, a computer program product, a controller and a computer readable medium as claimed in the appended claims.

According to an aspect of the invention there is provided a vehicle supercharger assembly. The assembly comprises an impeller and an input adapted for drive, for example permanent drive, from a source of motive power. The assembly also comprises a magnetic gear comprising an input member that is coupled to the input, an output member arranged to drive the impeller, and a rotatable control member which is rotatable with a rotational speed that determines a speed ratio between the input member and the output member. The supercharger assembly further comprises a first electric machine coupled to the control member and operable to drive rotation of the control member to adjust the rotational speed of the impeller.

Thus, embodiments of the present invention provide a supercharger arrangement in which, by virtue of the magnetic gearbox, a speed increase between coaxial input and output shafts is enabled and, moreover, at a gear ratio that is controllable so as to provide a desired impeller speed, whilst simultaneously and advantageously reducing frictional losses. Therefore, the supercharger assembly of the above aspect of the invention can operate more efficiently than known arrangements.

In some embodiments, the input member, the output member and the rotatable control member are arranged concentrically, in which case the output member may be disposed centrally within the magnetic gear. In such arrangements, the rotatable control member is optionally disposed between the input and output members. The first electric machine may be arranged to drive the rotatable control member mechanically. Alternatively, the first electric machine may comprise a set of windings that is operable to produce a rotating magnetic field that interacts with a set of magnets on the rotatable control member so as to drive the rotatable control member.

The supercharger assembly may comprise a lock that is engageable to prevent rotation of the output member. This beneficially enables the first electric machine to drive the input member indirectly through the rotatable control member when the lock is engaged, thereby to supply a drive force to the source of motive power creating further modes of operation such as start-assist, where torque is supplied to a vehicle engine during start-up, or torque- assist, where torque is supplied to the engine after start-up, for example to assist with high load conditions. Also, the first electric machine may be operable as a generator when the lock is engaged, enabling the assembly to provide a regeneration function. The supercharger assembly may comprise a second electric machine, in which case an armature of the second electric machine is driven by the input. In such embodiments, the second electric machine may be operable as a generator when driven by the input. Furthermore, in embodiments also including the lock to prevent rotation of the output member, the second electric machine may be operable to drive the input when the lock is engaged, optionally in combination with the first electric machine, thereby to supply a drive force to the source of motive power.

The impeller is optionally coaxial with the input, thereby creating a compact packaging arrangement.

The input may comprise a pulley, providing a convenient means for coupling the input to the source of motive power.

The supercharger assembly may comprise means for sensing a rotational speed of the input, in which case the first electric machine is operable in dependence on the sensed input speed so as to adjust the speed of the impeller to a desired level. The means for sensing may be, for example, a sensor configured to produce a signal indicative of the rotational speed of the input. The signal may be processed by a controller associated with the first electric machine, or by the first electric machine itself. A further aspect of the invention provides a vehicle comprising above summarised supercharger assembly, in which case the source of motive power may be an engine of the vehicle. Another aspect of the invention provides a method of operating a vehicle supercharger assembly. The supercharger assembly comprises an input adapted for drive, for example permanent drive, from an engine of the vehicle, an impeller driven by the input through a magnetic gear, and a first electric machine coupled to a control member of the magnetic gear and operable to drive rotation of the control member, thereby to adjust the rotational speed of the impeller. The method comprises sensing a rotational speed of the input, and adjusting the speed of the impeller to a desired level by operating the first electric machine in accordance with the sensed input speed.

When the supercharger assembly comprises a lock that is arranged to prevent rotation of the impeller when engaged, the method may comprise determining whether impeller rotation is required, and engaging the lock in the event that impeller rotation is not required. The method may also comprise operating the first electric machine to drive the input in the event that impeller rotation is not required. If the supercharger assembly comprises a second electric machine that has an armature that is driven by the input when the input speed is non-zero, the method may comprise operating the second electric machine to drive the input in the event that impeller rotation is not required. The method may comprise driving the first and second electric machines in combination to drive the input in the event that impeller rotation is not required. Other aspects of the invention provide a computer program product arranged to implement the method of the above aspect, a controller, and a non-transitory computer readable medium comprising such a computer program product.

Yet further aspects of the invention provide a computer program product comprising instructions, which when executed on an electronic processor configure the electronic processor to implement the method of the previously summarised aspect.

A further aspect of the invention provides a controller comprising an electronic processor configured with a computer program product comprising instructions, which when executed on the electronic processor configure the electronic processor to implement the method of the previously summarised aspect. 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 DRAWINGS

Figure 1 shows a perspective cut-away view of a known supercharger assembly, and has already been described in the background. Embodiments of the present invention will now be described, by way of example only, with reference to the remaining figures, in which like components are assigned like numerals, and in which:

Figure 2 is a schematic illustration of a supercharger assembly according to an embodiment of the invention;

Figure 3 is a schematic illustration of a supercharger assembly according to another embodiment of the invention;

Figure 4 is a schematic illustration of a supercharger assembly according to another embodiment of the invention;

Figure 5 is a schematic illustration of a supercharger assembly according to another embodiment of the invention; Figure 6 is a graph showing possible gear ratios achievable in the supercharger assemblies of Figures 2, 4 and 5;

Figure 7 is a graph showing possible gear ratios achievable in the supercharger assembly of Figure 3; and

Figure 8 is a flow diagram showing the steps comprised in a process for operating the supercharger assembly of any one of Figures 2 to 5. DETAILED DESCRIPTION

In overview, embodiments of the invention provide supercharger assemblies that are similar in general form to the known arrangement already described with reference to Figure 1 , but in which a magnetic gearbox is used in place of the epicycloid. Figures 2 to 5 show four particular implementations and are described below, following a discussion of some of the benefits of using a magnetic gearbox in place of an epicycloid. Firstly, the epicycloid has been identified as one of the primary sources of efficiency loss in known supercharger arrangements, and this is mainly due to friction at the mechanical interfaces between the annulus and the planets, and between the planets and the sun. In contrast, as shall be described later, a magnetic gearbox comprises rotating members that are not in contact with each other, requiring fewer bearings, and thus friction is minimised. Therefore, replacing the epicycloid with a magnetic gearbox minimises frictional losses in the supercharger assembly, thereby improving efficiency.

A related benefit is that a magnetic gearbox requires little or no lubrication, meaning that various auxiliary systems associated with an epicycloid, such as traction feeds, oil seals and an oil pump, can be dispensed with, and sealed bearings used instead, thereby reducing the overall part count in a vehicle.

As the rotating members are not in mechanical contact, a magnetic gearbox also provides vibration isolation between the input and the output. Similarly, the rotating members do not generate vibration, and so magnetic gears are generally noiseless.

Turning now to Figure 2, a supercharger assembly 30a according to an embodiment of the invention is shown in which an impeller 32 is driven by a FEAD 34 of an internal combustion engine 36 through a magnetic gearbox 38. As in the known arrangement described above, the impeller is disposed within a duct leading to an intake of an engine (not shown) such that, on rotating, the impeller 32 pumps air through the duct and into the engine for increased output.

The magnetic gearbox 38 is composed of three tubular rotating members that are supported in concentric relation about a common central axis 40: an outer member 42, an inner member 44 and an intermediate member 46 disposed between the inner and outer members 42, 44. For simplicity, the housing and bearings containing and supporting the rotating members 42, 44, 46 are not shown.

An input shaft 48 extends coaxially with the central axis 40 between the outer member 42 of the magnetic gearbox 38 and a pulley 50 that is driven by a belt 52 which in turn is driven by the FEAD 34. The input shaft 48 and the pulley 50 therefore together form an input that delivers torque to the magnetic gearbox 38. Therefore, the outer member 42 of the magnetic gearbox 38 is driven by the FEAD 34, and so the outer member 42 acts as an input member. As in the known arrangement described previously, the pulley 50 is typically configured to provide a pulley ratio of approximately 3:1 from the FEAD 34 output.

An output shaft 54 is driven by the inner member 44 of the magnetic gearbox 38, and extends coaxially with the central axis 40 to support the impeller 32, the output shaft 54 being journalled on bearings 56 within a central aperture in the intermediate member 46. Accordingly, the inner member 44 of the magnetic gearbox 38 acts as an output member and drives the impeller 32. A clutch 58 is provided that is operable to act as a brake to lock the output shaft 54 to prevent impeller 32 rotation, for reasons that shall become clear later. An additional one-way clutch (not shown) may be provided between the clutch 58 and the impeller 32 to enable the impeller 32 to freewheel when the output shaft 54 is locked by the clutch 58 so as to minimise the restriction created within the duct leading to the engine intake.

A drive shaft 60 of an electric machine 62a is coupled to the intermediate member 46 by a gearing or by other suitable means, such that the electric machine 62a is operable to drive rotation of the intermediate member 46. Alternatively, in some situations the intermediate member 46 may drive the electric machine 62a, as shall become clear in the description that follows. The electric machine 62a draws power from a battery 64 via an inverter 66 which converts the DC output of the battery 64 into an AC input for the electric machine 62a. The inverter 66 is also operable in reverse as a rectifier to enable the electric machine 62a to charge the battery 64. In other embodiments, the electric machine 62a may be a DC motor, in which case a DC motor controller would be provided in the place of the inverter 66.

The outer member 42 of the magnetic gearbox 38 comprises a first set of magnets 68, and the inner member 44 comprises a second set of magnets 70. The first and second sets of magnets 68, 70 are evenly distributed around their respective members 42, 44, separated by air gaps. The first and second sets of magnets 68, 70 are oriented such that the sources and sinks of magnetic flux are aligned perpendicular to the common central axis 40, and with alternating polarity. In other embodiments, other magnetic profiles may be used to enhance the magnetic flux in the air gaps, for example a Halbach array.

The intermediate member 46 carries a set of pole pieces or 'core members' (not shown) of ferromagnetic material. Like the magnets 68, 70, the core members are spaced evenly and separated by air gaps. The core members may be formed integrally with the intermediate member 46 as teeth in a castellated structure.

The first set of magnets 68 creates a magnetic field that extends radially inwardly across the core members. As the outer member 42 is driven by the input shaft 48, this magnetic field rotates. The core members interact with the rotating magnetic field to create a modulated rotating magnetic field between the intermediate member 46 and the inner member 44. This modulated field couples to the second set of magnets 70 to drive rotation of the inner member 44. In this way, torque is transferred from the outer member 42 to the inner member 44, and in turn from the input shaft 48 to the output shaft 54.

It is noted that, similarly to an epicycloid, if the intermediate member 46 of the magnetic gearbox 38 is held stationary the inner member 42 will rotate in the opposite sense to the outer member 44. Therefore, the connection to the FEAD 34 may be configured so as to ensure that the impeller 32 spins in the required sense.

The inner member 44 rotates at the same speed as the modulated field, which in turn rotates at a speed that is governed by the relative speed of the outer and intermediate members 42, 46. If the core members are held stationary, the magnetic gearbox 38 provides a fixed speed increase between the input and output shafts 48, 54. However, if the electric machine 62a is used to rotate the intermediate member 46 and its core members, thereby altering the relative speed of the outer and intermediate members 42, 46, the gear ratio can be controlled so as to provide a desired output speed. Therefore, in this embodiment the intermediate member 46 acts as a control member.

Accordingly, the magnetic gearbox 38 provides the same functionality as the epicycloid of the known arrangement, namely to apply a variable speed increase to the engine output so as to control the impeller speed at an optimum level. The functions of the outer member 42, the intermediate member 46 and the inner member 44 correspond to the functions of the annulus, the planets and the sun of the epicycloid respectively. It is noted that, as with an epicycloid, rotation of each of the rotating members 42, 44, 46 of the magnetic gearbox 38 is governed by the movement of the other two members, and so alternative modes of operation are possible. In particular, if the inner member 44 is held stationary the outer member 42 drives the intermediate member 46 with a fixed speed increase.

In operation, if boosting is required in a vehicle in which the supercharger assembly 30a resides, the clutch 58 is deactivated so that the input shaft 48 effectively drives the impeller 32. The electric machine 62a is operated so as to control the gear ratio of the magnetic gearbox 38 to provide a desired impeller speed that is decoupled from the engine speed. It is noted that the electric machine 62a is switched off so that the intermediate member 46 is held stationary whenever the resulting fixed speed ratio is acceptable for instantaneous boost demand. This eliminates the power consumption of the electric machine 62a, thereby raising efficiency.

When boosting is not required, for example when a vehicle is coasting or braking, the supercharger assembly 30a is placed into a regeneration mode by activating the clutch 58 to lock the output shaft 54 and prevent rotation of the impeller 32. The outer member 42 of the magnetic gearbox 38 is permanently driven by the FEAD 34 and so continues to rotate, which as noted above effects rotation of the intermediate member 46 while the inner member 44 is locked. This in turn drives the electric machine 62a as a generator, and the electric power generated is used to charge the battery 64. In this way, the supercharger assembly 30a is operable as an energy recovery device when boosting is not required. The supercharger assembly 30a finds further utility as an engine start-assist device, in that the electric machine 62a can be used to drive the FEAD 34 to aid engine starting. For this, the clutch 58 is activated so that rotation of the intermediate member 46 drives the outer member 42, in turn transmitting torque to the FEAD 34 via the input shaft 48 and the pulley 50. This mode of operation can also be used to provide torque assist to the engine 36 following engine start.

A further possible mode of operation is to deactivate both the clutch 58 and the electric machine 62a. In this mode, no energy is generated in the electric machine 62a, but equally the assembly 30a does not consume any electrical energy either. As the electric machine 62a holds the intermediate member 46 stationary when switched off, the assembly 30a provides boosting at a fixed speed increase in this mode. Figures 3 to 5 show further embodiments of the supercharger assembly 30b, 30c, 30d and shall now be described. It is noted that each of these embodiments uses a broadly similar underlying structure, in which an input shaft 48 driven by a FEAD 34 drives an impeller 32 supported by an output shaft 54 through a magnetic gearbox 38. The magnetic gearbox 38 itself is unchanged in each embodiment, although the rotating members 42, 44, 46 of the gearbox 38 are not always coupled to the same components of the assembly 30b, 30c, 30d. The description of each embodiment shall therefore focus on the differences with respect to the embodiment shown in Figure 2. In the supercharger assembly 30b shown in Figure 3, the output shaft 54 is coupled to the inner member 44 of the magnetic gearbox 38, as in the Figure 2 embodiment. However, the input shaft 48 is coupled to the intermediate member 46 rather than to the outer member 42. Therefore, the intermediate member 46 is the input member in this embodiment. It follows that the outer member 42 performs the role of the control member. Accordingly, the outer member 42 is driven by the electric machine 62b.

Another difference in the Figure 3 arrangement is that the electric machine 62b does not include a drive shaft, and instead comprises a set of windings 71 disposed concentrically around the outer member 42. The magnetic gearbox 38 is therefore embedded within the electric machine 62b in this embodiment. The windings 71 can be energised (e.g. by passing a current through them) to create a rotating field that couples to a set of drive magnets (not shown) provided on the exterior surface of the outer member 42 to effect rotation of the outer member 42. As the rotational speed of any of the members 42, 44, 46 of the magnetic gearbox 38 is dependent on the speeds of the other two members, as in the previous embodiment, the electric machine 62b is operable to provide a desired output speed against a varying input speed.

The Figure 3 embodiment is therefore functionally equivalent to the embodiment of Figure 2. Accordingly, as in the earlier embodiment, in the Figure 3 arrangement the clutch is deactivated when boost is required and the electric machine 62b controls the rotational speed of the outer member 42 so as to control the speed of the output shaft 54. As before, the clutch can be activated to lock the output shaft 54 for regeneration, start-assist or torque assist when boost is not required. As the windings 71 cooperate with the outer member 44 in this embodiment, this provides a favourable gearing arrangement for the purposes of start assist or torque assist, meaning that less power will be required from the electric machine 62b than in the embodiment of Figure 2. Configuring the electric machine 62b to envelop the outer member 42 of the magnetic gearbox 38 results in an axially compact arrangement and so may be useful in vehicles in which axial packaging space is limited. Conversely, the arrangement shown in Figure 2 may be more suitable where space around the magnetic gearbox 38 is restricted.

A further advantage with the embodiment shown in Figure 3 is that the windings 71 of the electric machine 62b are very close to the outer member 42 which is ideal for regeneration.

Figures 4 and 5 show supercharger assemblies 30c, 30d according to alternative embodiments in which the input shaft 48 carries an armature 72 of a second electric machine 74. Accordingly, for these embodiments the electric machine 62c, 62d associated with the intermediate member 46 is referred to as the first electric machine 62c, 62d.

Aside from the additional electric machine, the Figure 4 embodiment is identical to the embodiment of Figure 2. The Figure 5 embodiment differs from that of Figure 4 only in that the first electric machine 62c, 62d does not include a drive shaft, and instead comprise a set of windings 76 that produces a rotating magnetic field that couples to a set of drive magnets 77 attached to a planar end surface of the intermediate member 46, thereby enabling the electric machine to drive, or be driven by, the intermediate member 46.

In the embodiments of both Figure 4 and Figure 5, the second electric machine 74 is operable as both a motor and as a generator. The second electric machine 74 is coupled to the same inverter/rectifier 66 as the first electric machine 62c, 62d, enabling the second electric machine 74 to charge or draw power from the battery 64.

When the clutch is deactivated so that the impeller 32 rotates to provide boost, the second electric machine 74 is operated as a generator to recover electrical energy from the kinetic energy of the input shaft 48. This electrical energy can optionally be used to power the first electric machine 62c, 62d for driving the intermediate member 46. As before, the first electric machine 62c, 62d can be deactivated to allow boosting with a fixed gear ratio without any electrical energy consumption in the supercharger assembly 30c, 30d.

In regeneration mode, both the first and second electric machines 62, 74 are operated as generators to maximise the amount of electrical energy recovered and to charge the battery 64. For start-assist or torque-assist, the first and second electric machines 62, 74 can operate in combination to supply maximum torque to the FEAD 34 via the pulley 50.

Figure 6 is a graph that shows simulation data relating to the gear ratios that are achievable with the configurations of Figures 2, 4 and 5. Figure 7 is a graph showing corresponding data for the configuration of Figure 3, noting that the differing connections to the magnetic gearbox 38 in Figure 3 entail different achievable gear ratios compared with the configuration of the other embodiments. The graphs show the speed ratio of the control gear and the input shaft 48 along the x-axis, and the ratio of the numbers of magnetic poles contained in the first and second sets of magnets 68, 70 on the y-axis. It is noted that the range of speed ratios is slightly lower in Figure 7 than for Figure 6. This is because Figure 7 corresponds to a configuration in which the control member has a larger diameter than the input member 42, and so the possible speed ratio produced between the two is inherently lower than when the situation is reversed as in the other embodiments. Moreover, for similar reasons higher gear ratios are achievable in the embodiments of Figures 2, 4 and 5.

More specifically, the speed ratio, the pole ratio (namely the ratio of the number of magnetic poles between the low speed member and the high speed member), and gear ratio can be determined from an energy balance within the magnetic gearbox 38. Ignoring power losses, the energy balance equations for the magnetic gearbox 38 are typically as follows:

Where 'N' refers to the number of magnetic poles, 'W' represents the rotational speed, and T is the developed magnetic torque, with the subscripts "PP", "HS" and "LS" denoting the intermediate member 46, the inner (high speed) member 44 and the outer (low speed) member 42 respectively. So, for example, TH _S , TL _S and Tpp are the developed magnetic torques in the inner member 42, the outer member 44 and the intermediate member 46 respectively.

Each graph includes a series of generally vertical lines 78, each of which corresponds to a particular gear ratio. The gear ratio increases by ten from each line to the next moving from left to right in the graphs. For any given point on one of the lines, the speed ratio can be cross-referenced with the ratio of the magnetic poles. For example, for a given physical configuration where the ratio of magnetic poles is known, the speed ratio required to achieve a desired gear ratio can be determined. These graphs therefore provide look-up data for implementing control of their respective supercharger assemblies 30a, 30b, 30c, 30d.

By way of summary, Figure 8 shows in overview a generic process 80 for operating a supercharger assembly 30a, 30b, 30c, 30d of any of the above embodiments. The process 80 begins with determining at step 82 whether boost is required by a vehicle in which the supercharger assembly 30a, 30b, 30c, 30d resides. This information will typically be provided by a vehicle control unit such as an engine control unit. Generally, boost will be required while the vehicle is driving unless the vehicle is coasting or decelerating.

If boost is required, the clutch is deactivated at step 84, and the first electric machine 62c, 62d is operated at step 86 so as to control the impeller speed. If a second electric machine 74 is determined at step 88 to be present, the second electric machine 74 is operated at step 90 in a generator mode so as to charge the battery 64. The process 80 then returns to the initial decision step 82 and continues to iterate so as to respond to changing vehicle operating conditions.

If boost is not required at step 82, the clutch is activated at step 92 to lock the output member of the magnetic gearbox 38. If start assist or torque assist are found to be required at step 94, the first electric machine 62c, 62d, in combination with the second electric machine 74 if present, is operated at step 96 so as to transmit torque to the FEAD 34. If start/torque assist is not required, the first electric machine 62c, 62d, in combination with the second electric machine 74 if present, is operated at step 98 as a generator to charge the battery 64. As above, the process 80 then returns to the initial decision step 82 and continues to iterate so as to respond to changing vehicle operating conditions. It will be appreciated by a person skilled in the art that the invention could be modified to take many alternative forms to that described herein, without departing from the scope of the appended claims.