TECHNICAL FIELD

The present disclosure relates to an air induction apparatus and method and particularly, but not exclusively, to a diesel engine air induction apparatus and method and to improvements in stop/start control technology for engines fitted in conventional and hybrid vehicles.

Aspects of the invention relate to a diesel engine air induction apparatus, methods of stop/start control, a controller and a vehicle.

BACKGROUND

Some modern vehicles are fitted with automatic engine stop/start systems to aid with reducing fuel consumption. These engine stop/start systems automatically stop and restart the engine of the vehicle when the engine is not needed to power the vehicle, for example when the vehicle is stationary at traffic lights and the driver has their foot on the brake pedal, the engine can be switched off to save the fuel used during engine idling. Stop/start technologies apply to both conventional and hybrid vehicles where internal combustion engines are fitted. For vehicles fitted with automatic engine stop/start systems it is desirable for the engine to have both a refined shutdown sequence avoiding Noise Vibration Harshness (NVH) problems and also a quick and refined engine restart time that will enable fast vehicle launch times from rest. Both acceptable NVH and vehicle restart times are important for delivering acceptable customer satisfaction.

To improve NVH on engine shutdown it is known on diesel engines to deliberately create an inlet manifold depression (i.e. an inlet pressure lower than atmospheric pressure) by closing the inlet manifold throttle valve. Alternately 'in cylinder' depression may be induced by closing the cylinder head inlet valves when the engine shutdown command is received. If the inlet manifold throttle or cylinder head valves are closed during engine shutdown then a lower pressure is created in each cylinder during an inlet induction stroke as the engine piston is effectively trying to draw inlet air through a closed or restricted inlet valve. This manifold or cylinder depression creates a known damping effect which reduces undesirable engine judder or cyclic oscillations during shutdown thus improving the NVH during the shutdown event. However, when intake manifold or cylinder depression is used to reduce judder during engine shutdown, the subsequent reduced pressure in the intake manifold and cylinder can prevent ideal engine restart conditions on the next restart by reducing the amount of available air in the next cylinder charge. The amount of air in the cylinder during an engine restart is critical as it limits the amount of fuel which can be injected into the cylinder to avoid excessive smoke creation and therefore reduced air/fuel content will increase the restart time due to lower power output which may disappoint the driver.

One possible disadvantageous use case for creating cylinder depression to improve NVH is the 'change of mind' situation where the driver of a stop/start vehicle is braking the vehicle to rest and then changes their mind and decides to accelerate while the engine is shutting down. This could happen in a traffic light stop situation, for example. In the 'change of mind' situation the driver would naturally transfer their foot from the brake to demand throttle which in turn would initiate an immediate engine restart request. It will be appreciated that during the preceding engine shutdown, the vehicle will have closed the inlet throttle valve to provide the inlet manifold depression to improve NVH but the subsequent manifold depression could still be present during the immediate restart request, which would be detrimental to the ideal restart condition of having maximum air present on the first induction air stroke of the engine. Other situations may arise where inlet manifold depression is present such as after a short vehicle stop during a journey, where the inlet manifold depression may remain due to good sealing of a closed intake throttle. A blocked air inlet filter or debris in the air intake could also cause retained intake manifold depression before an engine start. It is known to have an electrically driven boost device in the inlet air system as shown in JP201018071 1 A, however this device is aimed at improving diesel engine cold starting by raising the inlet manifold pressure above atmospheric pressure.

At least in embodiments, the present invention seeks to overcome or ameliorate at least some of the shortcomings associated with prior art arrangements.

SUMMARY OF THE INVENTION

Aspects of the present invention relate to relate to an air induction apparatus, a method, a controller and a vehicle.

According to an aspect of the present invention there is provided an air induction apparatus for an engine operable to perform automatic shutdown and startup functions. The air induction apparatus may comprise an inlet conduit for supplying air to the engine. The air induction apparatus may comprise an inlet flow valve operable to restrict airflow through the inlet conduit during automatic engine shutdown to reduce air pressure in the inlet conduit below atmospheric pressure. The air induction apparatus may comprise at least one controllable boost device operable to increase the inlet conduit air pressure. The air induction apparatus may comprise a controller for controlling the at least one controllable boost device. The controller may be configured to activate the at least one controllable boost device following operation of the inlet flow valve to restrict airflow through the inlet conduit. The activation of the at least one controllable boost device can increase air pressure in the inlet conduit. At least in certain embodiments the increased air pressure can improve the engine restart time, for example immediately after a 'change of mind' situation or where intake manifold depression below atmospheric reduces engine start performance.

The engine may comprise a diesel engine.

Opening the inlet flow valve whilst requesting an immediate engine restart may not be enough to raise the inlet conduit air pressure quickly enough to meet the engine start demand and having a controllable boost device to aid the rate of pressure increase will be advantageous.

In an embodiment of an air induction apparatus as described herein, wherein the controller is configured to control said at least one controllable boost device to increase the inlet conduit air pressure, the increased inlet conduit air pressure can increase the amount of air in each induction stroke thereby improving the amount of fuel/air mixture possible prior to the excessive smoke limitation ratio in the cylinder. Air can be measured in terms of either mass or volume.

The activation of the at least one controllable boost device can increase air pressure in the inlet conduit to a pressure less than or equal to atmospheric pressure. Increasing the inlet conduit pressure can provide improved start conditions for the engine. This can be used in a variety of situations, such as after an engine stop condition

The controller can be configured to activate the at least one controllable boost device in dependence on an automatic engine startup request. The air pressure can be raised to less than or equal to atmospheric pressure ready for the engine intake air induction stroke. The controller can be configured to activate the at least one controllable boost device after one or more of the following conditions:

a) following completion of an automatic engine shutdown;

b) at any time after an engine restart request is received during the engine shutdown;

c) at any time after an engine restart request is received and up to 5 seconds after engine shutdown has completed;

d) a pressure sensor in the inlet conduit detects a pressure less than atmospheric pressure in the inlet conduit and an engine restart request is received. These conditions represent at least some of the scenarios representing lower than optimum inlet conduit pressure. Activating the at least one controllable boost device to raise air inlet conduit pressure can aid engine restart in certain embodiments.

The controller can be configured to reopen the inlet flow valve at the same time as an engine restart request is received, or at any time after an engine restart request is received. This can allow the intake flow valve to allow higher pressure air into the inlet conduit as soon as it is known that a restart is required, again allowing improved restart conditions. It may also allow any low pressure region disposed between the inlet flow valve and the cylinder intake valve to increase in pressure or to equalise pressure across the inlet flow valve.

The at least one controllable boost device can be fitted in any conduit in series with the inlet conduit. This may be beneficial by aiding the in-vehicle package layout such that components fit in the available space. Alternatively, the at least one controllable boost device can be fitted in any conduit in parallel with the inlet conduit. This may be beneficial by aiding the in-vehicle package layout such that components fit in the available space.

The controller can be configured to activate the at least one controllable boost device when reduced air filter performance is detected causing low inlet conduit pressure; and/or a partial blockage of the engine air inlet system is detected causing low inlet conduit pressure. The low inlet conduit pressure can be overcome by increasing the inlet conduit pressure through use of the at least one controllable boost device, thus counteracting the effects of defective air filters or a blocked engine air inlet system.

According to another aspect of the present invention there is provided a method of controlling the controllable boost device in an air induction apparatus for a diesel engine operable to perform automatic shutdown and startup functions, the air induction apparatus comprising: an inlet conduit; an inlet flow valve operable to restrict airflow through the inlet conduit during automatic engine shutdown to reduce air pressure in the inlet conduit below atmospheric pressure; at least one controllable boost device operable to increase the inlet conduit air pressure; and the method comprising controlling the at least one controllable boost device following operation of the inlet flow valve to restrict airflow through the inlet conduit. In this way the at least one controllable boost device is controlled in the right way to deliver an increase the inlet conduit air pressure at the right time. In another embodiment of a method as claimed, the method comprises controlling the inlet conduit air pressure to a pressure less than or equal to atmospheric pressure. Being able to be selective about the air pressure within the inlet conduit ensures that the right amount of fuel can be injected into the fuel/air mixture. In another embodiment of a method as claimed, the method comprises controlling the at least one controllable boost device in dependence on an automatic engine startup request, thus being able to deliver the correct inlet conduit pressure when the engine startup request is made. In another embodiment of a method as claimed, the method comprises controlling the at least one controllable boost device after one or more of the following conditions:

a) following completion of an automatic engine shutdown;

b) at any time after an engine restart request is received during the engine shutdown;

c) at any time after an engine restart request is received and up to 5 seconds after engine shutdown has completed;

d) a pressure sensor in the inlet conduit detects a pressure less than atmospheric pressure in the inlet conduit and an engine restart request is received.

These engine start time scenarios cover all possible situations where lower than optimum inlet conduit start pressure could exist and therefore be able to activate at least one controllable boost device to raise air intake conduit start pressure in a beneficial way to aid engine restart.

In another embodiment of a method as claimed, the method comprises controlling the inlet flow valve to reopen at the same time as an engine restart request is received, or at any time after an engine restart request is received. This advantageously allows the intake flow valve to allow higher pressure air into the inlet conduit as soon as it is known that a restart is required, again allowing best restart air conditions. It may also allow any low pressure region trapped between the inlet flow valve and the cylinder intake valve to increase in pressure or equalise pressure across the inlet flow valve. In another embodiment of a method as claimed, the method comprises controlling the at least one controllable boost device when reduced air filter performance is detected causing low inlet manifold pressure; and/or a partial blockage of the air inlet system is detected causing low inlet manifold pressure. Advantageously the low inlet conduit pressure can be overcome by controlling the inlet conduit pressure through use of the at least one controllable boost device, thus counteracting the effects of defective air filters or a blocked engine air inlet system.

According to another aspect of the present invention there is provided a system for controlling an engine of a vehicle as described above, wherein:

controller means are provided for receiving one or more signals each indicative of a value, comprising one or more electronic processors having an electrical input for receiving said one or more signals each indicative of a value; and

one or more electronic memory devices electrically coupled to the electronic processors and having instructions stored therein; and

a communication network connecting said electronic processors and providing communication of said signals from one processor to another.

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 shows a diesel engine air induction apparatus in accordance with an embodiment of the present invention;

Figure 2 shows another embodiment of a diesel engine air induction apparatus in accordance with an embodiment of the present invention;

Figure 3 shows a further embodiment of a diesel engine air induction apparatus in accordance with an embodiment of the present invention; Figure 4 is a first graph comparing engine speeds immediately after a 'change of mind' restart event for a standard diesel engine and a diesel engine having an air induction apparatus in accordance with an embodiment of the invention; and

Figure 5 is a second graph comparing manifold pressure immediately after a 'change of mind' restart event for a standard diesel engine and a diesel engine having an air induction apparatus in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

An air induction apparatus in accordance with an embodiment of the present invention is described herein with reference to the accompanying figures. The air induction apparatus is configured for connection to a conventional diesel engine (10) for a vehicle, such as an automobile.

Figures 1 , 2 and 3 represent three embodiments of the diesel engine air induction apparatus by way of example. The features common to each of these embodiments will now be described and like reference numerals used for like components. The embodiments each have a turbocharger (20), a fuel injection system (40) and a controller (50). A common pre- turbocharger inlet system comprising an air filter (8), an air mass flow measuring device (9), a low pressure (LP) exhaust gas recirculation (EGR) valve (7), a LP EGR transfer conduit (5), a high pressure (HP) EGR valve (44, 144, 244) and a HP transfer conduit (37, 137, 237). All example embodiments have common post-turbocharger exhaust systems including catalyst (6). An air pressure sensor (not shown) can be provided to monitor air pressure in an engine air intake. The air pressure sensor can be fitted in an inlet conduit (34, 134, 234) fluidly connected to the engine air intake, or anywhere between the electric supercharger (30) and the engine air intake. An embodiment of an air induction apparatus (39) in accordance with the present invention is shown in Figure 1 . The air induction apparatus (39) comprises an air inlet (Inlet) fluidly connected to the air inlet filter (8), fluidly connected to the air mass flow measuring device

(9) , fluidly connected to the LP EGR valve (7), fluidly connected to the inlet conduit of turbocharger (20). The LP EGR valve (7) is provided selectively to open and close the LP

EGR transfer conduit (5). The LP EGR valve (7) is fluidly connected to the inlet of the turbocharger (20) via air inlet conduit (38), the outlet of the turbocharger (20) is connected to the engine air intake via first and second intermediate inlet conduits (31 , 32), the intake throttle (33) and the inlet conduit (34).

The engine (10) has an attached exhaust system (1 1 ). The exhaust gases exit the engine

(10) via exhaust conduit (15). The engine (10) is fluidly connected to the inlet of the turbocharger (20) via the exhaust conduit (15) and an intermediate conduit (19). An exhaust exit conduit (17) of the turbocharger (20) is fluidly connected to the inlet of the catalyst (6); the exit of the catalyst (6) exhausts to atmosphere via the exhaust outlet (outlet). The turbocharger (20) comprises a turbine wheel (22) and a compressor wheel (24) and operates conventionally as would be understood by a person skilled in the art. The embodiments described herein each have separate EGR conduit flow paths in the form of LP EGR and HP EGR conduit flow paths. As an example the embodiment shown in Figure 1 has a HP EGR valve (44) and a HP transfer conduit (37) which fluidly connects the intermediate exhaust conduit (19) and the inlet conduit (34) when HP EGR is required. The LP EGR valve (7) and the LP EGR transfer conduit (5) fluidly connect the exhaust gas exiting the catalyst (6) to the inlet of the turbocharger compressor wheel (24) when required. Figure 1 further comprises an electric supercharger (30) connected in parallel to an inlet intermediate conduit (32). The exit of the compressor wheel (24) is fluidly connected to the first intermediate conduit (31 ). In turn, the first intermediate conduit (31 ) is fluidly connected to an inlet of a bypass valve (60). The exit of the bypass valve (60) is fluidly connected to a supercharger inlet conduit (36) which is fluidly connected to an inlet of the electric supercharger (30). An outlet of the electric supercharger (30) is fluidly connected via an electric supercharger outlet conduit (35) back into the second intermediate conduit (32). The second intermediate conduit (32) is fluidly connected to an inlet of an intake throttle (33), the outlet of the intake throttle (33) being fluidly connected to the engine (10) via the inlet conduit (34).

An alternate embodiment of an air induction apparatus (139) is shown in Figure 2. The air induction apparatus (139) differs from the air induction apparatus (39) shown in figure 1 in that the electric supercharger (130) is placed in parallel to a turbocharger inlet conduit (156) upstream of a turbocharger compressor wheel (124). All other induction and exhaust system architecture is similar and carries like reference numerals for like components albeit incremented by 100 for clarity. The bypass valve (160) comprises an inlet fluidly connected to an air inlet conduit (138) and an outlet fluidly connected to an inlet of the electric supercharger (130).An outlet of the electric supercharger (130) is fluidly connected to a turbocharger inlet conduit (156) via supercharger outlet conduit (135).

An alternate embodiment of an air induction apparatus (239) is shown in Figure 3. The air induction apparatus (239) differs from the air induction apparatus (39; 139) shown in figures 1 and 2 in that there is only one boost device in the system but with two (2) options to power it. Essentially an electrically driven turbocharger (220) of Figure 3 is placed in the position that a conventional turbocharger (20) occupies in air induction apparatus (39) shown in figure 1 . The separate parallel connected electrically driven supercharger (30) is therefore not required in the embodiment of Figure 3.

It will be appreciated that in the air induction apparatus (239) shown in Figure 3 the inlet air enters an engine (210) via air induction apparatus (239). A turbocharger inlet conduit (218) is connected to the inlet of the compressor wheel (224) of a turbocharger (220), the outlet of the compressor wheel (224) is fluidly connected to a conduit (232) which is fluidly connected to the inlet of an engine (210) via an intake throttle (233) and inlet conduit (234). Exhaust gases of the engine (210) exhaust into an exhaust system (21 1 ). The exhaust exits the engine (210) into an intermediate exhaust conduit (219) which is fluidly connected to an exhaust conduit (215). The exhaust conduit (215) is fluidly connected to an inlet of the turbine wheel (222) of the turbocharger (220). The exit of the turbine wheel (222) is fluidly connected to atmosphere via a turbocharger exhaust conduit (217), the catalyst (6) and the outlet (outlet).

An electric machine or motor (226) is optionally drivingly connectable to the turbocharger drive shaft (not shown) via a clutch (225) and can be controlled by a controller (250). Functionally the turbocharger could operate purely as a conventional turbocharger system by opening the clutch (225). Optionally the turbocharger could be connected to the motor (226) via the clutch (225) to allow the motor (226) to drive the turbocharger (220). An additional advantage of this system is that energy can be taken from the turbocharger (220) by connecting the motor (226) via clutch (225) and regenerating energy into a storage device (not shown) in a hybrid vehicle application, for example. The air induction apparatus (39) shown in Figure 1 will now be described. As shown in Figure 1 , the air induction apparatus (39) is incorporated into a system including the diesel engine (10), the fuel injection system (40), and the exhaust system (1 1 ). During normal running operation, the diesel engine (10) is exhausting the combusted gases through the exhaust conduit (15) and into the turbocharger (20) and then exhausting the gases to the atmosphere through the turbocharger exhaust conduit (17), the catalyst (6) and the exhaust outlet (outlet). As the exhaust gases enter the turbocharger (20), the gases act on the turbine wheel (22) and via a shaft drives the compressor wheel (24) which in turn provides a pressure boost to the air being drawn in through the air inlet conduit (38) (i.e. the pressure of the air entering the air inlet conduit (38) is increased above atmospheric pressure). The pressure boosted air is directed through the first and second intermediate conduits (31 , 32) and through the intake throttle (33) and finally through the inlet conduit (34) into the engine cylinder in conventional manner. In Figure 1 an example electrically driven supercharger (30) is connected in parallel with the conventional first and second intermediate conduits (31 , 32) and the inlet conduit (34). The supercharger (30) is optionally able to draw inlet air through the bypass valve (60), through the electric supercharger inlet conduit (36) into the electric supercharger (30) and deliver controllable boosted pressure back into the air inlet conduit (32) towards the engine cylinders via the supercharger outlet conduit (35), the inlet conduit (34) and the intake throttle (33). A controller (50) controls the amount of fuel required to be injected into the engine (10) based on driver demand.

An air pressure sensor (not shown) can optionally be provided to measure inlet air pressure. The air pressure sensor could be placed in the intermediate conduit (32) or the inlet conduit (34), for example, for detecting air pressure for the purpose of calculating air mass flow for fuelling purposes. An alternate use of the air pressure sensor may be to determine if either the air pressure in the intermediate conduit (32) or the inlet conduit (34) is below atmospheric pressure. The measured air pressure can optionally be used to control operation of the electric supercharger (30)

It will be understood that the conventional turbocharger (20) can work independently of the electric supercharger (30) and the electric supercharger (30) can optionally provide additionally pressure boosted air through the throttle valve (33) into the engine (10) via the inlet conduit (34). The controllable boost device is described herein as an electrically driven supercharger, but it will be appreciated that any type of controllable boost device can be utilised. By way of example, an on board storage means such as flywheel or accumulator could be used to drive a controllable boost device or indeed the accumulator could directly provide pressurised air as a means of quickly raising the air pressure in and around the cylinder inlet.

An exhaust gas recirculation (EGR) valve (44) is positioned in the HP transfer conduit (37) to optionally control flow between the intermediate exhaust conduit (19) and the inlet conduit (34) when necessary to benefit engine emissions and efficiency.

The intake throttle (33) is an inlet flow valve which could be a butterfly valve, a globe valve, a gate valve or any suitable valve able to restrict the air flow in the inlet air conduit.

In this example embodiment, when an engine has received an engine shutdown request and the intake throttle valve (33) has been flow restricted (partially or fully closed) to cause a deliberate intake depression in the inlet conduit (34), it is known that NVH shutdown benefits previously described will be delivered. However if the driver then requests an engine restart either during the shutdown event or shortly after when the pressure in the inlet conduit (34) will be lower than atmospheric pressure then this will cause a reduced engine restart capability or slower start time, as the amount of air in the next induction stroked will be reduced because of the lower pressure generated by the restricted intake valve (33). This in turn reduces the amount of fuel which can be provided to the air charge in the cylinder and the power developed in the next combustion event of that cylinder.

In a diesel engine shutdown sequence known to improve NVH, it is known to immediately close the intake throttle valve (33) as soon as the engine shutdown command is received. Simultaneously the fuelling to the engine can reduce from idle fuelling to zero fuelling over a time period circa 0.5 seconds (the time it takes the engine to come to rest approximately) to maintain engine rotational stability during engine shutdown. It is further known to reopen the intake throttle valve (33) within a time period of circa 0.5 seconds after the engine stop has been confirmed to allow the inlet air pressure to rise to atmospheric pressure naturally, ready for the next engine restart request. Note that a restricted inlet air filter (8) and other induction system restrictions could delay the rise in inlet air pressure to return to atmospheric. if an engine restart is requested immediately after an engine shutdown request is received and the engine speed is still above a restart limit threshold then it is possible to immediately reopen the intake throttle valve (33) and re-establish fuelling without the need for engine restart assistance. For a V6 diesel engine where the natural idle point is circa 650rpm the restart limit threshold may be circa 500rpm, below which restart assistance is required. A 4 cylinder restart limit threshold may be 600rpm below which restart assistance is required. Other restart limit thresholds are possible.

If an engine restart is requested shortly after an engine shutdown request is received in a 'change of mind' case and the engine speed is above the limit threshold speed then the reopening of the intake throttle valve (30) and re-instigation of refuelling command is all that is required to restart the engine fully. No restart assistance is required in this instance.

If an engine restart is requested shortly after an engine shutdown request is received in a 'change of mind' case and the engine speed is below the limit threshold speed then the engine may fail to restart by just reopening the intake throttle valve (30) and refuelling alone. In this case engine restart assistance is required as follows.

To provide an improved engine restart response it is desirable to maximise the amount of air in the cylinder and so the invention proposes to increase the air pressure in the inlet conduit (34) by immediately after receiving the engine restart request, using the electrically driven supercharger (30) to draw air through the opened bypass valve (60) and to boost the inlet conduit pressure in and around the intake valve (33) and the inlet conduit (34). As soon as the 'change of mind' restart request is initiated and the engine speed is below the limit threshold speed, for example by the driver lifting his foot from the brake pedal and transferring to the throttle, the controller (50) commands the electrically driven supercharger (30) to increase boost pressure in supercharger outlet conduit (35) and the controller (50) simultaneously initiates an open request to valves (60 and 33) to allow the pressure boosted air to flow into inlet conduit (34) and then into the engine cylinder. To be clear, during the engine restart the air can be drawn from the outlet of the turbocharger compressor (24), through the first intermediate conduit (31 ), through the bypass valve (60) and into the electric supercharger inlet conduit (36) where it will be taken through the electrically driven supercharger (30), out through the supercharger outlet conduit (35) in a pressure boosted state and reintroduced into the conventional airstream in conduit (32). The air will be at a higher pressure as it passes through the intake throttle (33) and enters the engine via inlet conduit (34). As the amount of air is now increased on the restart induction strokes the fuel injection system (40) will increase the amount of fuel in the cylinder to give an improved power output giving a faster engine acceleration response. A variant (not shown) of the air induction apparatus (39) shown in figure 1 could place the electrically driven supercharger (30) in series with inlet conduit (32) such that the bypass valve (60), electric supercharger inlet conduit (36) and supercharger outlet conduit (35) are removed. Operation would then mean that the turbocharger compressor (24) outlet would feed directly into the inlet of the electrically driven supercharger (30) and the outlet of the electrically driven supercharger (30) would direct boosted flow straight into the intake throttle (33) in series. In this case the electrically driven supercharger (30) may have to be driven continually to allow the air throughput and additionally the electrically driven supercharger (30) could be used to extract kinetic energy from the gas flow from turbocharger (20) to regenerate electrical energy back into an electrical storage device for a Hybrid (not shown)

Figure 2 shows another example embodiment of a diesel engine air induction apparatus arrangement which could be utilised for the invention. The system layout is very similar to that described in Figure 1 but the position of the electrically driven supercharger (130) has been placed to direct boosted air pressure into the inlet of the turbocharger (120) in the turbocharger inlet conduit (156), so the electrically driven supercharger (130) is now downstream of the turbocharger (120) instead of being upstream.

Operation of the air induction apparatus (139) shown in figure 2 is similar to that of the air induction apparatus (39) shown in figure 1 and will now be described.

The air induction apparatus (139) is shown in Figure 2 in combination with the diesel engine (1 10), the fuel injection system (140) and the exhaust system (1 1 1 ). During normal running operation, the diesel engine (1 10) exhausts combusted gases through the exhaust conduits (1 19,1 15) and into the conventional turbocharger (120) and then exhausting to atmosphere through the rest of the exhaust after treatment system through turbocharger exhaust conduit (1 17). As the gases enter the turbocharger (120), the gases act on the turbine wheel (122) and via a shaft drives the compressor wheel (124) which in turn provides boost pressure to the fresh air inlet being drawn in through the air inlet conduits (138,156).

In the embodiment shown in Figure 2 an example electrically driven supercharger (130) is connected in parallel with the conventional inlet air conduits (138,156) and optionally is able to draw inlet air through the bypass valve (160), through the electric supercharger inlet conduit (136) into the electric supercharger (130) and deliver controllable boosted pressure back into the air inlet conduit (156) towards the engine cylinders via the supercharger outlet conduit (135). The conventional turbocharger (120) takes the boosted air from the electrically driven supercharger (130) and the turbo compressor (124) increases the inlet air pressure further. A controller (150) controls the amount of fuel required from the fuel injection system (140) to be injected into the engine (1 10) based on driver demand to the engine on a cylinder by cylinder basis. An exhaust gas recirculation (EGR) valve (144) is positioned in the conduit (137) to optionally control flow between the exhaust pipe (1 15) and inlet conduit (134) when necessary to benefit engine emissions and efficiency as is a known technique.

In the case where an engine has received an engine shutdown request and the intake throttle valve (133) has been flow restricted to cause a deliberate intake depression in the inlet conduit (134), it is know that NVH shutdown benefits previously described will be delivered. However if the driver then requests an engine restart either during the shutdown event or shortly after when the pressure in the inlet conduit (134) will be lower than atmospheric pressure then this will cause a reduced engine restart capability as the amount of air in the induction stroked will be reduced because of the engine suction against the restricted intake valve (133). This in turn reduces the amount of fuel which can be provided to the air charge in the cylinder and the power developed in the next combustion event.

To provide an improved engine restart response in this embodiment it is desirable to maximise the amount of air in the cylinder and so the invention proposes to increase the air pressure in the inlet conduit up to atmospheric pressure.

As soon as the 'change of mind' restart request is initiated for example by the driver lifting his foot from the brake pedal and transferring to the throttle, the controller (50) commands the electrically driven supercharger (130) to increase boost pressure in supercharger outlet conduit (135) and the controller (50) simultaneously initiates an open request to valves (160 and 133) to allow the pressure boosted air to flow into conduit (134) and then into the engine cylinder. The inlet air is then drawn from conduit (138), through the bypass valve (160), into electric supercharger inlet conduit (136), through the electric supercharger (130) where the air pressure is increased, into supercharger outlet conduit (135) and then into the inlet of the conventional turbocharger (120) where the compressor wheel (124) additionally boosts the inlet air pressure into conduit (155), through the now opened intake throttle valve (133), through conduit (134) and finally into the engine (1 10). A variant of the air induction apparatus 139 shown in figure 2 could place the electrically driven supercharger (130) in series with the inlet conduit (138) such that the bypass valve (160), conduit electric supercharger inlet (136), and the supercharger outlet conduit (135) are removed. Operation would then mean that the turbocharger compressor (124) inlet would draw directly from the electrically driven supercharger (130) and the outlet of the electrically driven supercharger (130) would boost flow straight into the intake (156) of the turbocharger (120). As described in the first embodiment of figure 1 in this series installation the electrically driven supercharger (130) may need to operate continually to allow flow through it.

Operation of the air induction apparatus (239) shown in Figure 3 will now be described. In this embodiment there is only one boosting device (220) which is driven by exhaust gas pressure conventionally or can optionally be driven by electric machine (226) via optional clutch (225).

The diesel engine air induction apparatus in Figure 3 includes a diesel engine (210), a fuel injection system (240), an air induction apparatus (239) and an exhaust system (21 1 ). A single turbocharger (220) with conventional turbine (222) and compressor wheel (224) is installed conventionally between the inlet and exhaust conduits (21 1 ,239). The turbocharger (220) is optionally drivable via a clutch (225) using an electric machine (226) and power electronics (248). The system could operate without the clutch also in another embodiment. Power electronics (248) are identified as (48,148) on other figures. The clutch (225) could be a one way clutch.

In use, when clutch (225) is disconnected the turbocharger (220) can run in the conventional manner being driven through the turbine (222) by the engine exhaust gases provided through conduit (215) and then a shaft transfer's mechanical power to the compressor wheel (224). The compressor wheel (224) draws air from conduit (218) and delivers boosted inlet air pressure to conduit (232), through intake throttle valve (233) and then into conduit (234) before it enters the engine cylinder of engine (210)

The EGR function operates identically as described in Figures 1 and 2.

Figure 4 shows a comparison of engine speeds immediately after 'change of mind' engine restart events for systems with and without electric supercharger boost improvements during a restart. Figure 5 shows a comparison of an example inlet manifold pressure immediately after 'change of mind' restart events for systems with and without electric supercharger boost improvements as described in the invention embodiment. Assuming the architecture described in Figure 1 , Figure 5 describes two examples of the inlet manifold pressure measured in the conduit (34) by a sensor (not shown) which will now be described.

Inlet manifold pressure line (410) is the pressure measured in conduit (34) throughout an engine restart event when the engine has had a 'change of mind' restart request after a shutdown request, but no electric supercharger (30) boosting is available which is the current state of the art technology. The pressure line (410) shows a pressure of circa 430 hPa present in conduit (34) at the 4.8 second point and this is the residual depression remaining after the shutdown request, caused by the intake throttle valve (33) being closed. Once the 'change of mind' situation is realised and the controller (50) initiates an immediate restart request, the intake throttle valve (33) will begin to open which starts a pressure rise in the conduit (34) as the inlet air in adjoining conduits (31 ,22) are closer to atmospheric pressure. The resultant pressure of the inlet manifold pressure line (410) causes pressure in the conduit (34) to increase to circa 970hPa at the 5.4 seconds point. It then takes the pressure line (410) more time to stabilise and it can be seen that it takes greater than 5.5 seconds to reach atmospheric pressure (1000hPa) for the inlet air shown by label (420). The dip in pressure at label (41 1 ) is a resultant of one of the engine cylinders creating a depression during another induction stroke. In parallel with this Figure 4 shows the corresponding engine speed (320) achieved at 5.4 seconds as being circa 250rpm. Using the unboosted restart it can be seen that the intake manifold pressure (Figure 5) only achieves atmospheric pressure (1000hPa) at around the 5.5 second point shown by label (420). To be clear the prior art would not have bypass valve (60), electric supercharger inlet conduit (36), electric supercharger (30) or supercharger outlet conduit (35) in the system although all other components would remain.

Now if we describe the restart but assume that controlled boosting will be provided by the electric supercharger (30) then the start performance proposed by the invention is much improved as follows.

The same initial start pressure on Figure 5 in line (430) shows a pressure of circa 430 hPa present in inlet conduit (34) at the 4.8 second point and again this is the residual depression remaining after the shutdown request, caused by the intake throttle valve being closed. Once the 'change of mind' situation is realised and the controller (50) initiates an immediate restart request, the intake throttle valve (33) and the bypass valve (60) will begin to open which starts a pressure rise in the inlet conduit (34) which can be seen on the graph to allow the pressure in inlet conduit (34) to rise to circa 550hPa at around 5.2 seconds. At this point in time the controller (50) commands the electric supercharger (30) to draw air from the output of the turbocharger compressor (24), through the first intermediate conduit (31 ), through bypass valve (60), through electric supercharger inlet conduit (36) into the compressor of the electric supercharger (30) to boost the pressure in supercharger outlet conduit (35). This now extra boosted air in supercharger outlet conduit (35) flows into intermediate conduit (32) and through the now open intake throttle valve (33) to increase the intake manifold pressure in inlet conduit (34) as shown by the dotted line between points (431 ) and (440) on figure 5.

When comparing the manifold pressure lines (410,430) it can be seen that there is a clear advantage of using the electric supercharger (30) to boost the air as the inlet manifold pressure has nearly fully risen to atmospheric pressure (950hPa) at around 5.3 seconds (Iabel440), whereas using no boost pressure from the electric supercharger (30) means that it takes longer to reach nearly full atmospheric pressure at circa 5.4 seconds. Additionally the provision of the extra boost pressure from the electric supercharger (30) solves the problem of having intake manifold pressure fluctuations in inlet conduit (34) which is indicated by the unboosted pressure line (410) at greater than 5.4 seconds (label 41 1 ). Label (41 1 ) indicates a transient dip in intake manifold pressure line (410) in inlet conduit (34) due to an induction stroke from the piston which normally would temporarily draw the intake pressure down. The invention solves this problem because the electric supercharger (30) is providing an extra pressure boosted intake air which is able to supply the demands of the next engine cylinder induction stroke. The electric supercharger (30) is able to substitute and build back up the lost inlet air pressure in inlet conduit (34) caused by the NVH reducing engine stop, as soon as the driver enters the 'change of mind' condition and the controller (50) can utilise the boosting capability of the electric supercharger (30). Assuming the system architecture shown in any of figures 1 ,2 and 3, an engine speed restart performance comparison is made between boosted and unboosted inlet air pressure shown in Figure 4. Engine speed line (310) represents the engine speed for a pressure boosted engine during a restart using the electrically driven supercharger (30,130 or 230). Engine speed line (320) shows the unboosted engine restart performance. The engine speed traces are overlaid in Figure 4 and assuming the engine restart request is received at around the 5 second point, it can be seen that at the 5.4 second point the conventional unboosted engine has a first peak speed of approximately 250rpm at label (340), whereas the engine with electrically driven supercharger (30, 130 or 230) boosted pressure delivers a peak engine speed of 600rpm at label (330). Further the engine idle speed can be seen to reach 800 rpm at around the 5.58 second point (Label 350) for the boosted pressure start, versus 5.7 seconds for the unboosted pressure start. The pressure boosted engine reaches target idle speed faster.

Throughout this description the example 'change of mind' use case has been discussed but the invention is not limited to that. Alternative situations may arise where inlet manifold depression is present such as after a conventional engine stop event where the driver has left the vehicle and returned after a short stop. It is quite possible for inlet depression (below atmospheric pressure) to be present even after a long stop if the intake throttle valve (33) is well sealed when closed.

Inlet manifold depression may also be present due to partial blockage of the engine air inlet system perhaps due to a poorly maintained inlet air filter (8) or debris present in the inlet (inlet). The air inlet system is described as being anywhere between the air inlet (inlet) and the inlet conduit (34,134,234).

A pressure sensor (not shown) may be fitted in the induction system (39,139,239) to detect the pressure of the intake air going into the engine (10) such that intake depression below atmospheric can be detected in all engine start conditions.

It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.