GB2365070A

GB2365070A - Control of electrically-driven supercharger for i.c. engines

Info

Publication number: GB2365070A
Application number: GB0102815A
Authority: GB
Inventors: Mark Anderton Criddle; Guy David Morris; Justin James Tindall; Simon Petrovich; Peter Austen Wintle
Original assignee: Visteon Global Technologies Inc
Current assignee: Visteon Global Technologies Inc
Priority date: 2000-07-28
Filing date: 2001-02-05
Publication date: 2002-02-13
Also published as: GB2365065A; GB0023776D0; GB0023773D0; GB2365068A; GB0023777D0; GB2364978A; GB0018428D0; GB0023770D0; GB2364976A; GB0023779D0; GB0023771D0; GB2365069A; GB2364977A; GB2365067A; GB2364980A; GB0023774D0; GB0023778D0; GB0102815D0; GB2364979A; GB0023772D0

Abstract

The engine (1) is responsive to an engine torque demand and is operable over a range of engine speeds (33,37,38) to provide an engine torque output in response to the engine torque demand. The engine comprises: a throttle valve (17) ; one or more combustion chambers (2); an air inlet (3) for admitting air into the combustion chambers (2) ; a compressor (10) for compressing said air admitted into the combustion chambers (2) in order to boost engine torque output (SCB) ; an electric compressor driver (14) by which the compressor (10) is driven when the engine torque demand cannot be met by natural aspiration alone and deactivated when the engine torque demand can be met by natural aspiration alone; an engine controller (22) responsive to the engine torque demand in order to control engine torque output, said engine torque output in the absence of the compressor torque boost (SCE) peaking at a moderate engine speed (33). The engine controller (22) is arranged to control the compressor driver (14), and when the throttle (17) is set for a maximum engine torque output the engine controller is arranged to control the boosted engine torque output by controlling the amount of aspirated compressed air via the compressor driver (14).

Description

2365070 Internal Combustion Engine Supercharger The present invention

relates to a supercharger for an internal combustion engine.

There are many factors that characterize the torque output of any given internal combustion engine, for example the swept volume within cylinders, cylinder configuration, the bore-to-stroke ratio, the compression ratio, valve train arrangement, and the inlet & exhaust arrangement.

Engine developers are constantly "tuning" engines, that is, adjusting these parameters and others in the search for improved fuel economy and performance. However, this does not necessarily result in increased power or torque as perceived by the driver. In real world driving conditions it is engine torque that is most important to the driver's perception of performance (or performance feel), and particularly engine torque delivered at lower engine speeds (RPM), for example, below 3500 rpm for a typical light duty passenger car application.

For this reason, an engine may need to be tuned to give higher torque at lower RPM, but this will typically result in a loss of to rque at higher engine speed, for example an engine speed that is above about 3500 rpm. This is particularly a problem with small capacity gasoline engines, for engines below about 1.8 litres for a gasoline engines and below about 2 litres for a diesel engine which tend to dominate in the European marketplace.

2 - The same engine could easily be Ire-tuned' to deliver the same torque but at much higher crank speeds. This results in significantly higher peak power but at the expense of 5 torque at lower rpm. Whilst this will appeal to the,sporting' driver, acceleration performance is reduced at lower engine speeds.

Engine designers have employed a multitude of techniques and technologies in an attempt to overcome this traditional compromise. Examples of such systems are variable geometry intake systems, variable camshaft timing and variable valve lift & timing. All of these approaches are designed to maintain more than one 'state of tune' depending on operating conditions.

Another commonly used technique is to reject engine tuning as a method for increased performance and instead pump air into the engine by means of a turbocharger or supercharger. Such forced induction generally results in significant increases in torque and power.

However, some types of turbochargers and superchargers (referred to collectively herein as "compressors") can add significantly to the cost of an engine, which is a particular barrier to using a compressor with smaller capacity engines in an economy car. Since turbochargers are driven by exhaust gasses, these are most useful at high engine RPM, and so do not in themselves help solve the problem of low RPM torque.

- 3 It is an object of the present invention to provide an internal combustion engine compressor that addresses these issues.

According to the invention, there is provided an internal combustion engine, the engine being responsive to an engine torque demand and operable over a range of engine speeds to provide an engine torque output in response to the engine torque demand, and comprising: one or more combustion chambers; an air inlet for aspirating the combustion chambers, the engine torque output being dependent at least in part on the amount of air aspirated into the combustion chambers; a throttle in the air inlet that can be set to regulate the aspiration of the combustion chambers and hence engine torque output; a compressor in the inlet for compressing air aspirated into the combustion chambers in order to boost engine torque output above that available when the engine is naturally aspirated; compressed air control means separate from the throttle by which the amount of compressed air aspirated into the combustion chambers may be controlled; an engine controller responsive to the engine torque demand in order to control engine torque output; wherein, the engine controller is arranged to control the compressed air control means, and when the throttle is set for a maximum engine torque output the engine controller is arranged to control the boosted engine torque output by controlling the amount of aspirated compressed air via the compressed air control means.

The engine is therefore operated in a fuel-efficient manner when the engine torque demand is below the maximum available when naturally aspirated. When the engine torque demand is at or above this level, the throttle setting will be a maximum setting, and the compressor boost is activated and controlled in such a such a way that the engine torque output is controlled not by the changing the setting of the throttle, but at least in part by controlling the amount of compressed air aspirated into the combustion chambers.

The engine may comprise an air by-pass across the compressor. The compressed air control means may then include means by which the amount of air bypassing the compressor may be controlled.

Additionally or alternatively, the compressor may include adjustable impeller vanes. The compressed air control means then includes means by which the impeller vanes may be adjusted to control the amount of air compressed by the compressor.

In a preferred embodiment of the invention, the compressed air control means includes a compressor driver for driving the compressor over a range of compressor speeds, the amount of air aspirated into the combustion chambers being dependent on the compressor speed.

Preferably, the compressor driver is an electrically driven motor. The power and hence speed of such an electric motor can readily be controlled by suitable control electronics, giving precise and sufficiently rapid control of the amount of torque output boost.

The engine will normally include fuel delivery means by which the amount of fuel entering the combustion chambers may be controlled. The engine torque output will then depend at least in part on the amount of fuel delivered to the combustion chambers. Sensor means can then be provided to detect the composition of exhaust gasses from the combustion chambers. This is useful, because the engine controller can then be arranged to control the fuel delivery means, dependent on an output received from the sensor means indicative of the exhaust gas composition. The engine controller is then responsive to the sensed exhaust gas composition to control the amount of compressed air and/or the amount of delivered fuel.

In a preferred embodiment of the invention, the compressor is enabled only after the engine torque demand has closely approached or reached the maximum un-boosted engine torque output at that engine speed. This helps to maximise fuel efficiency.

The compressor is then driven when the engine torque demand cannot be met by natural aspiration alone and deactivated when the engine torque demand can be met by natural aspiration alone.

The engine aspiration then is normal when the compressor is not enabled.

Usually, the engine torque output in the absence of the compressor torque boost peaks at a moderate engine speed and falls at a high engine speed. The engine controller may then enable use of the compressor driver when the engine speed is relatively low or moderate and disable use of the compressor when engine speed is relatively high.

The internal combustion engine may be a reciprocating internal combustion engine. In the context of the present invention, the term "moderate" as regards engine speed, means an engine speed at or near the mid-range of engine speeds, between and idle engine speed and a maximum rated engine speed.

Preferably, the engine is tuned to optimize power at higher engine speeds in the absence of the compressor boost, even if this means a loss in engine torque at moderate or low engine speeds. The compressor boost may then be employed solely at such moderate and low engine speeds in order to provide additional engine power and torque at those engine speeds.

Preferably, the engine controller therefore enables use of the compressor driver when the engine speed is relatively low or moderate and disables use of the compressor when engine speed is relatively high.

If the engine is a reciprocating piston engine in a motor car, then the moderate speed is preferably at least about 3soo rpm, and may be as high as about 5500 rpm. This permits the engine, particularly if it is relatively small capacity engine of less than about 1.8 litres capacity, to be tuned to provide its maximum torque in the region of about 5500 rpm, which is a relatively high speed for such an engine. This will help to provide good fuel economy at highway speeds. The consequent decrease in torque at lower RPM would be noticed by the driver even during moderate driving, particularly when the driver needs to accelerate quickly at lower rpm, however, the lower torque can be boosted by use of the compressor. Because the compressor does not work at relatively high RPM, fuel economy at such speeds is preserved. The invention also provides the benefit of not increasing the maximum vehicle speed, which for most types of vehicle in most countries is in any event normally well in excess of national speed limits. This provides a safety benefit, and may give the vehicle a lower insurance rating, particularly for younger drivers. At the same time, the invention provides good acceleration at lower engine speeds, which in many circumstances can be a safety feature.

when the engine is of the reciprocating type, the engine will have a number of intake/outlet valves arranged to operate at predetermined times in the engine cycle. Because of the performance boost provided by the supercharger, it is therefore possible for the timing of said valve operation to be fixed. This helps avoid unnecessary cost in construction and maintenance of the engine.

In general, it is desirable if the engine controller progressively disables use of the compressor in the vicinity of said moderate engine speed. The vicinity may include a region of engine speed slightly above said moderate speed. The engine controller may, in fact, disable any use of the compressor above said moderate engine speed, but preferably the disabling of the compressor use is substantially below said high engine speed.

Another way of expressing this is to say that the compressor torque boost does not significantly increase the engine power output above said moderate engine speed.

Also according to the invention, there is provided a motor vehicle, comprising an internal combustion engine for powering the vehicle, an accelerator pedal movable by the driver, and an internal combustion engine, wherein the internal combustion engine is as described above as being according to the invention, the engine torque demand being set at least in part by the position of the accelerator pedal.

Also according to the invention, there is provided a method of operating an internal combustion engine, the engine being responsive to an engine torque demand and operable over a range of engine speeds to provide an engine torque output in response to the engine torque demand, the engine comprising: one or more combustion chambers; an air inlet for aspirating the combustion chambers, the engine torque output being dependent at least in part on the amount of air aspirated into the combustion chambers; a throttle in the air inlet that can be set to regulate the aspiration of the combustion chambers and hence engine torque output; a compressor in the inlet for compressing air aspirated into the combustion chambers in order to boost engine torque output above that available when the engine is naturally aspirated; compressed air control means separate from the throttle by which the amount of compressed air aspirated into the combustion chambers may be controlled; an engine controller responsive to the engine torque demand in order to control engine torque output; wherein the method comprises the steps of:

a) using the engine controller is to control the compressed air control means; b) setting the throttle for a maximum engine torque output; c) using the engine controller to control the boosted engine torque output by controlling the amount of aspirated compressed air via the compressed air control means.

The invention will now be described by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic diagram of a motor vehicle having a 1.4 litre, four cylinder engine system with an air intake apparatus that includes an electrically powered intake compressor, according to the invention; Figure 2 is a graph plotting engine torque against engine speed for the 1.4 litre engine of Figure 1 when naturally aspirated, tuned either for maximum torque at moderate engine speed, or maximum engine power at higher engine speed; is Figure 3 is a graph similar to that of Figure 2, showing also the effect on engine torque output with the engine of Figure 1 when using the intake compressor; Figure 4 is a graph plotting engine compressor torque boost against driver throttle engine demand for the engine of Figure 1; Figure 5 is a graph of compressor demand against driver throttle angle demand for the engine of Figure 1; Figure 6 is a perspective view of the air intake apparatus used with the engine of Figure 1; Figure 7 is an exploded view of a housing and internal components that form the air intake apparatus of Figure 6; Figure 8 is a top plan view of the air intake apparatus of Figure 7, showing two separate removable access panels on upper surfaces of the housing; Figure 9 is a top plan view of the air intake 10 apparatus similar to that of Figure 8, but with the two access panels removed, and no components within the housing; Figure 10 is a perspective view of the empty housing 15 of Figure 9; Figure 11 is a perspective view of a portion of the housing, with an access panel removed to show the compressor within the housing, and an air outlet pipe 20 from the compressor extending through an air diffuser chamber to an air outlet from the housing; Figure 12 is a different perspective view of the portion of the housing shown in Figure 11, looking 25 into the air outlet to show the arrangement of the air outlet pipe with respect to the air outlet and the diffuser chamber; Figure 13 is a perspective view from underneath of a 30 portion of a divider plate that covers the air compressor and air diffuser chamber of Figures 11 and 12, showing an air flap valve in the diffuser plate in a closed position; Figure 14is a perspective view similar to that of Figure 13, with the air flap valve removed to show an air grille through the divider plate by which bypass air flows into the diffuser chamber to the housing air outlet.

Figure 1 shows schematically part of a motor vehicle 7 having a supercharged reciprocating piston internal combustion engine 1, with four in-line cylinders 2, an air inlet manifold 4 and an exhaust manifold 6 leading to and from each of the cylinders 2, and a fuel injection system 8 for supplying fuel to cylinders 2 in a manner well-known in the art. An electrically driven supercharger 10 is provided upstream of the inlet manifold 4.

Air flows to the inlet manifold 4 through the supercharger 10 when this is operational, and when the supercharger is operating at below full capacity, or is disabled, also through an air bypass conduit 12 in parallel with the supercharger 10. Air is supplied to the supercharger 10 and/or the bypass 12 along an inlet air path 3.

The air bypass conduit 12 has an air valve 13 that automatically opens to permit inlet air 5 to bypass the supercharger when the supercharger airflow is is insufficient to charge the engine cylinders 2 with air.

I The air supply to the engine 1 is then controlled by the setting of a throttle valve 17 downstream of the supercharger 10 and bypass 12, and the activation of the supercharger 10. When the supercharger 10 is not activated, the engine 1 is normally aspirated, and when the supercharger 10 is activated, the airflow to the engine is increased.

The supercharger is driven only by an electrical motor (M) 14 powered by a conventional 12-volt lead/acid vehicle battery 16. The battery 16 also lies within the air supply path 3, so that inlet air flows around the battery 16.

An air filter 9 is provided in the air supply path 3 downstream of the battery 16 and upstream of the supercharger 10 and air bypass 12.

As will be explained in more detail below, the battery 16, filter 9, supercharger 10 and air bypass 12 are all housed within a hollow enclosure 50.

The vehicle driver (not shown) can control the engine power via a movable accelerator pedal assembly 18, that provides an electrical signal 20 to an engine control unit (ECU) 22. The engine control unit receives a number of input signals indicative of engine and vehicle operating parameters, including an engine speed signal 24 from an engine speed sensor 26. The engine control unit 22 calculates an engine torque demand from the various input signals, and provides a number of output signals to control various vehicle and engine operating parameters, including a fuel injection control signal 28, throttle valve control signal 30 and a supercharger motor control signal 32. The engine torque demand is therefore set at 5 least in part by the position of the accelerator pedal.

As will be explained in more detail below, when the driver moves the accelerator pedal to demand engine torque in excess of that which can be delivered by the engine 1 when naturally aspirated, the throttle valve 17 moves to a maximum setting to admit the maximum volume of air into the cylinders, and engine control unit 22 then activates the supercharger motor 14 under certain engine moderate or low engine speeds, but not at high engine speeds.

Thereafter, the boosted engine torque output is controlled by the supercharger speed and the amount of fuel supplied to the cylinders. If the engine is an injection engine, the engine control unit 22 can control the amount of injected fuel by electrical control of the injectors.

Preferably, the engine includes an exhaust gas sensor 31 for monitoring engine combustion conditions. The sensor 31 may be an exhaust gas oxygen (EGO) sensor. This can be sued to determine if the engine is running lean or rich.

The engine control unit 22 first sets both the supercharger speed and delivered fuel amount according to the current torque demand. The engine control unit monitors the output from the sensor 31, and then adjusts the supercharger speed and/or the amount of delivered fuel to achieve an appropriate level of rich or lean engine operation.

Figure 2 shows a graph of engine torque against engine speed for a conventional four-cylinder in-line engine, such as that described above, but without supercharging. As can be seen from curve 30 of Figure 2, the engine can be tuned to provide either good power at high engine speeds ("power tune"), but at the expense of lowend torque.

Alternatively, as shown by curve 32, the engine can be tuned to give good torque at low and moderate engine speeds Ptorque tune"), but at the expense of top-end power. Whilst "power tune" will appeal to the 'sporting, driver, it will result in lower levels of satisfaction for the majority of car owners. The requirement to deliver good real world 'performance feel, commonly results in an engine torque output as shown in the "torque tune" curve, where power at high engine speeds has been compromised in order to promote torque output below 3500 rpm. Although engine gearing can be selected to minimize undesirable characteristics, in practice conventional engines are tuned to achieve a compromise.

With reference to Figure 3, in the preferred embodiment of the invention, a relatively low capacity engine, for example below about 1.8 litres capacity, is tuned to give good power at high rpm, at the expense of torque at low engine speed, as illustrated by curve 30. This has the secondary effect of allowing good fuel economy at steady highway cruising speeds. As can be seen from curve 34, an increase in maximum engine torque is then provided with a supercharger torque boost (or equivalently engine power boost) when the driver demands power in excess of that available from a naturally aspirated engine, as shown by the curve with supercharger boost 11SCBIl. The boost is made available under control of the engine control unit 22 only in a region of low 38 and moderate engine speeds 33, and is progressively limited to transition smoothly into engine power at point 35 without compressor torque boost in a region of higher engine speeds 36. This is done by progressively limiting the maximum allowable supercharger boost proximate a transition point 40, which in this example is taken at the maximum un-boosted engine torque.

It is, however, possible to deviate either above or below this point, although a deviation too far below this point (in this example below about 3500 rpm) reduces the potential benefits provided by the supercharger, and a deviation too far above this point (in this example above about 5750 rpm) will lead to excess torque in a region of engine operation where this is not needed under most driving conditions, or desired from the point of view of fuel economy.

Thus, the engine controller enables use of the compressor driver only in such a way that the engine torque output with the compressor torque boost peaks in the region of moderate engine speed.

The boosted torque curve could, however, transition - 17 smoothly into the un-boosted torque curve 30 in a region of lower engine speeds 38, as shown by dashed line 39.

Figure 4 shows a graph of engine torque supercharger boost against driver throttle angle demand between 00 and 900.

The diagonal straight lines on the graph are labelled with engine speed in RPM, between 1250 RPM and 5400 RPM. The vertical scale corresponds between the difference in engine torque in Figure 3 between the boosted torque curve 34 and the un-boosted torque curve 30. At the maximum throttle angle 900, the engine torque supercharger boost is the maximum value shown in Figure 3. As throttle angle demands declines from 900, so does the engine torque supercharger boost, until this declines to 0 boost corresponding to curve 30 of Figure 3.

As can be seen from Figure 4, as the engine speed increases towards the transition point 35 of Figure 3, the slope of the engine torque supercharger boost curve declines, until at the transition point 35, there is no engine torque supercharger boost. This shows graphically the progressive disabling of the supercharger boost.

Figure 5 shows the operation of the supercharger in another way, with compressor demand plotted against driver ',throttle angle" demand between 00 and 900. Except at high engine speeds when operation of the supercharger is disabled, the driver "throttle angle" does not correspond with the actual angle of the throttle 17. At engine speeds where supercharger operation is permitted, the actual throttle angle will reach 900 (i.e. the maximum setting) before the driver "throttle angle" reaches 900. Thereafter, as driver throttle angle increases towards 900, the actual throttle angle remains at the maximum setting, and the boosted engine torque output is controlled by the amount of electrical power supplied to the supercharger motor, in conjunction with an appropriate amount of fuel delivered to the cylinders.

The various lines in Figure 5 are labelled with the engine speed in RPM. The compressor demand is equivalent to the electrical power supplied to the supercharger motor 14. The plots begin at a compressor demand at about 0.2, at which point the air supplied by the supercharger begins to have an appreciable effect on engine torque. As can be seen from Figure 5, as engine speed increases, so does the minimum compressor demand needed to appreciably boost torque. This is due to the increased air flow to the inlet manifold 4 as engine speed increases.

Figures 6 to 14 all show detailed views of the air intake apparatus according to the invention. Figure 6 shows an external perspective view of the unitary housing 50 that holds the battery 16, filter 9, compressor 10 and air bypass 12. The air supply path 3 through the unitary housing 50 begins at an air inlet 52 in a lower portion of the housing 50, and terminates at an air outlet 54 at a higher level in the housing 50.

The housing 50 includes the battery compartment 56 and the supercharger compartment 58. Each compartment 56, 58 has a corresponding access panel 60, 62 which is removably attached by screws 64 to a unitary housing base 66 that forms a lower part of the enclosure 50.

The battery compartment access panel 60 has a pair of apertures 61,63, by which a pair of battery terminals 65,67 can protrude through the housing 50 when the battery access panel is affixed to the housing base 66.

The unitary housing base 66 is mounted at a number of supports 68 extending downwards from the housing base 66 to a steel mounting plate 70, which is itself bolted to an inner surface of an engine compartment (not shown).

is The hollow enclosure 50 is formed from a moulded plastics material, for example ABS, or glass-filled nylon.

Figure 7 shows the mounting plate, hollow enclosure 50 and a number of components inside the enclosure 50 in an exploded, perspective, view. The battery 16 is housed within the battery compartment 56, together with supercharger drive electronics 72.

The supercharger compartment 58 contains a larger number of components, including the filter 9, supercharger 10 and supercharger motor 14. Also in the supercharger compartment 58 are the divider plate 74 that extends horizontally across an approportion of the supercharger compartment 58 beneath the supercharger access cover 62, and the flap air bypass valve 13. The air filter 9 has a rectangular outline, and sits within a similar rectangular recess 56 within the divider plate 74. The divider plate 74 has an air grill 78 to the underside of which is attached the air flap 13, and a curved plate 80 to limit the deflection of the air flap 13 away from the grill 78.

The supercharger compartment 58 is divided into a main portion AV2, which houses the compressor 10, motor 14 and air filter 9, and a minor portion 84, which is referred to herein as a diffuser chamber 84. The divider plate air grill 78, and air flap 13 lie over the diffuser chamber 74, with a flexible seal 86 making an air-tight seal between the diffuser chamber 84 and divider plate 74.

The air supply path 3 between the air inlet 52 and air outlet 54 extends around the battery 16 and supercharger power electronics 72 within the battery compartment 56, through an aperture 90 in a partition wall 92 that separates the battery compartment 56 from the supercharger compartment 58. As can be seen from Figure 7, the air aperture 90 is at a higher level in the battery compartment 56 from the air inlet 52. The air supply path through the battery compartment 56 therefore generally rises towards the air aperture 90.

The air aperture 90 has a number of veins, one of which 94 is visible in Figure 7. These veins 94 direct the air flow into a lower portion of the supercharger compartment 58, in the vicinity of the supercharger motor 14. The air c supply path therefore helps cool the supercharger motor 14 when this is operational. The air supply path 3 after f lowing around the supercharger motor 14 rises vertically upwards through the air f ilter 9 in the divider plate 74.

Into an air volume between the divider plate 74 and supercharger access panel 62. In Figure 7, this enclosed air volume is indicated generally by reference numeral 96.

When the supercharger is not operational, the air section provided from the inlet manifold 4 holds the flap valve 13 downwards onto the flap valve limiting plate 80, so that air can flow through the air grill 78 in the divider plate 74, and into the diffuser chamber 84. From the diffuser chamber 84, the air is then f ree to pass into the air outlet 54. Although not shown, the air path then follows a conventional flexible hose to the throttle valve 17. When the supercharger is operational, some air from the enclosed air

volume 96 will be drawn into an inlet 98 in an upper central portion of the supercharger 10. The supercharger air is then compressed and expelled at up to 50% above atmospheric pressure through the supercharger outlet 100. A small rubber ring 102 connects the supercharger air outlet 100 to an inlet 104 to the diffuser chamber 84.

Until the supercharger 10 is operating at a high capacity, there will be some air also entering through the air flap 78 into the diffuser chamber 84. The air expelled by the supercharger 10 through the diffuser chamber air inlet 104 - 22 passes into a diffuser pipe 106 that tapers gradually outwards to a diffuser pipe outlet 108. The diffuser pipe outlet 108 has three radial fins 110 equilaterally spaced around the circumference around the space of the diffuser pipe outlet 108. The fins 110 slot into corresponding grooves 112 on inner surfaces of the air outlet 54 so that an annular gap 114 is maintained between the air diffuser pipe 106 and air outlet 54.

The air expelled by the supercharger 110 is therefore kept separate from air entering through the flap valve 13 into the diffuser chamber 84 until this air mixes downstream of the annular gap 114 surrounding the diffuser pipe outlet 108.

is It has been found that the air flow efficiency is increased by this arrangement, as energy in the air expelled by the supercharger 10 helps to pull. air out of the diffuser chamber 84 supplied through the air flap 20 valve 13.

In order to dampen noise and vibration, the supercharger and its motor 14 are physically mounted through three rubber posts 116 spaced equidistantly around a cup-shaped aluminium mounting bracket 118 to which the supercharger has been rigidly mounted. The three rubber mounts 116 sit on three corresponding posts 120 extendingupwards from a lower portion of the supercharger compartment 58.

These three rubber mounts 116, together with the flexible short outlet hose 102 between the supercharger outlet 100 a and diffuser chain inlet 104, dampen down any vibration which might be transmitted from the supercharger 10 and its motor 14 through to the body of the unitary housing 66.

The supercharger 10 is also vibrationally isolated from the divider plate 74 by a rubber ring 122 that extends around the circumference of the supercharger air inlet 98. The rubber ring 122 sits within a circular boss 124 that extends downwards from an undersurface 126 of the divider plate 74. The boss 124 has a passage 126 there through to allow air to flow through the divider plate 74 into the supercharger 10.

Referring now to Figures 9 and 10, these show how the air inlet path 3 extends into the battery compartment 56 initially in a recess 128 in a lower surface 156 of the battery compartment 56. The recess 128 gradually disappears downstream of the air inlet 52. thereby forcing inlet air to move laterally away from an access 130 of the air inlet 52 towards lateral side portions 132 of the flower 156, where there are a number of upstanding ribs 134 projecting from the side portions 132. The ribs 143 support an undersurface 136 of the battery 16, so that air channels 138 extend between the ribs 134 laterally away from the air inlet access 130. Inlet air is therefore directed across nearly the full undersurface of the battery, which helps to keep the battery cool. once the inlet air reaches lateral side walls 140 of the battery compartment 56, the air is directed to flow upwards over T corresponding vertically extending sides 142 of the battery 16 by vertically extending ribs 144 that project laterally inwards from the battery housing vertical side walls 140. The vertical ribs 144 also help to locate the 5 battery 16 transversely within the battery compartment 56.

Some air will, however, flow downstream of the battery 16 at a lower level to encounter the supercharger power electronics 72, which is provided with metallic heat dissipation fins 146.

The temperature of the inlet air therefore increases as it passes through the battery compartment 56, but the air is still cool compared with the temperatures that may be reached by the supercharger motor 14. This therefore provides an efficient means of cooling the various components within the housing 50.

Although in there are many advantages to using a compressor that is an electrically driven supercharger, it may be possible to implement the invention in other ways, for example with a mechanically driven supercharger, or even an exhaust driven turbocharger, as long as suitable mechanical or electrical control is provided to limit the compressor operation at high engine speeds according to the invention.

The invention aims to combine the benefits of both engine tuning and forced induction in order to achieve both good low rpm torque and high rpm power. The given engine is deliberately tuned in order to achieve a high power output at the expense of low rpm torque. An electrically driven compressor is integrated into the air induction system of the engine and is energized under the control of the engine management system to increase torque output when required.

The characteristics of the electrically driven compressor will in general be such that prolonged operation (e.g.

achieving maximum vehicle speed) is not possible without discharging the battery or overloading the electric motor. The fact that the supercharger is not available at high engine speeds negates these issues. Also, by reducing the electrical power consumption in this way, the invention can help to avoid the need for a more expensive mechanical drive of the supercharger, for example using a belt driven drive from the engine. The result is that the engine can be tuned to achieve not only the peak power associated with the high power 'tune' but also achieves increases in low/mid rpm torque that only forced induction could normally achieve.

Claims

1. An internal combustion engine, the engine being responsive to an engine torque demand and operable over a range of engine speeds to provide an engine torque output in response to the engine torque demand, and comprising: one or more combustion chambers; an air inlet for aspirating the combustion chambers, the engine torque output being dependent at least in part on the amount of air aspirated into the combustion chambers; a throttle in the air inlet that can be set to regulate the aspiration of the combustion chambers and hence engine torque output; a compressor in the inlet for compressing air aspirated into the combustion chambers in order to boost engine torque output above that available when the engine is naturally aspirated; compressed air control means separate from the throttle by which the amount of compressed air aspirated into the combustion chambers may be controlled; an engine controller responsive to the engine torque demand in order to control engine torque output; wherein, the engine controller is arranged to control the compressed air control means, and when the throttle is set for a maximum engine torque output the engine controller is arranged to control the boosted engine torque output by controlling the amount of aspirated compressed air via the compressed air control means.

2. An internal combustion engine as claimed in Claim 1, in which the compressed air control means includes a compressor driver for driving the compressor over a range k 4 of compressor speeds, the amount of air aspirated into the combustion chambers being dependent on the compressor speed.

3. An internal combustion engine as claimed in Claim 1, in which the engine comprises an air bypass across the compressor, and the compressed air control means includes means by which the amount of air by-passing the compressor may be controlled.

4. An internal combustion engine as claimed in Claim 1, in which the compressor includes adjustable impeller vanes, and the compressed air control means includes means by which the impeller vanes may be adjusted to control the amount of air compressed by the compressor.

5. An internal combustion engine as claimed in any preceding claim, in the engine including: fuel delivery means by which the amount of fuel entering the combustion chambers may be controlled, the engine torque output depending at least in part on the amount of fuel delivered to the combustion chambers; and sensor means arranged to detect the composition of exhaust gasses from the combustion chambers; in which the engine controller is arranged to control the fuel delivery means, and receives an output from the sensor means indicative of the exhaust gas composition, the engine controller being responsive to the sensed exhaust gas composition to control the amount of compressed air and/or the amount of delivered fuel.

1. 1 1 1.

6. An internal combustion engine as claimed in any preceding claim, in which the compressor is enabled only after the engine torque demand has closely approached or reached the maximum unboosted engine torque output at 5 that engine speed.

7. An internal combustion engine as claimed in any preceding claim, in which the engine torque output in the absence of the compressor torque boost peaks at a moderate engine speed and falls at a high engine speed, the engine controller enables use of the compressor driver when the engine speed is relatively low or moderate and disables use of the compressor when engine speed is relatively high.

is

8. An internal combustion engine as claimed in Claim 7, in which the engine controller enables use of the compressor driver only in such a way that the engine torque output with the compressor torque boost peaks in the region of moderate engine speed.

9. An internal combustion engine as claimed in claim 7 or Claim 8, in which the engine is a reciprocating piston engine, and the moderate engine speed is at least about 25 3500 rpm.

10. An internal combustion engine as claimed in any of Claims 7 to 9, in which, the capacity of the combustion chambers is below about 1.8 litres, said moderate engine speed is about at least 3500 rpm, and the maximum engine 29 - torque boost provided by the compressor in the vicinity of said moderate engine speed declines towards higher engine speeds.

11. An internal combustion engine as claimed in any of Claims 7 to 10, in which the engine controller progressively disables use of the compressor in the vicinity of said moderate engine speed.

12. An internal combustion engine as claimed in Claim 11, in which the engine controller disables any use of the compressor above said moderate engine speed.

13. An internal compression engine as claimed in Claim 11, in which the compressor torque boost does not significantly increase the engine torque output above said moderate engine speed.

14. An internal combustion engine as claimed in any of Claims 7 to 13, in which the engine torque output with compressor torque boost in a region of low or moderate engine speeds transitions smoothly into a region of engine torque output not having compressor torque boost at a higher engine speed.

15. An internal combustion engine as claimed in any preceding claim, in which the compressor is an electrically driven supercharger.

16. A motor vehicle, comprising an internal combustion 1 engine for powering the vehicle, an accelerator pedal movable by the driver, and an internal combustion engine, wherein the internal combustion engine is as claimed in any preceding claim, the engine torque demand being set at 5 least in part by the position of the accelerator pedal.

17. A method of operating an internal combustion engine, the engine being responsive to an engine torque demand and operable over a range of engine speeds to provide an engine torque output in response to the engine torque demand, the engine comprising: one or more combustion chambers; an air inlet for aspirating the combustion chambers, the engine torque output being dependent at least in part on the amount of air aspirated into the combustion chambers; a throttle in the air inlet that can be set to regulate the aspiration of the combustion chambers and hence engine torque output; a compressor in the inlet for compressing air aspirated into the combustion chambers in order to boost engine torque output above that available when the engine is naturally aspirated; compressed air control means separate from the throttle by which the amount of compressed air aspirated into the combustion chambers may be controlled; an engine controller responsive to the engine torque demand in order to control engine torque output; wherein the method comprises the steps of:

a) using the engine controller is to control the compressed air control means; 1 4 A, b) setting the throttle for a maximum engine torque output; c) using the engine controller to control the boosted engine torque output by controlling the amount of aspirated compressed air via the compressed air control means.

18. An internal combustion engine substantially as herein 10 described, with reference to or as shown in Figures 1, 3, 4 or 5 of the accompanying drawings.

19. A method of operating an internal combustion engine, substantially as herein described, with reference to 15 Figures 1, 3, 4 or 5 of the accompanying drawings.

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