GB2504953A

GB2504953A - Engine system with at least one deactivatable cylinder and an electric booster

Info

Publication number: GB2504953A
Application number: GB1214481.2A
Authority: GB
Inventors: Ian Graham Pegg; Andrew David Scarisbrick
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2012-08-14
Filing date: 2012-08-14
Publication date: 2014-02-19
Anticipated expiration: 2032-08-14
Also published as: GB2504953B; DE102013215536A1; GB201214481D0; CN103590912B; CN103590912A

Abstract

The system comprises a multi-cylinder engine 5 with at least one deactivatable cylinder, a turbocharger 10 and an electric booster 20. The booster supplies pressurised air to the compressor 11 of the turbocharger and is activated by an electronic controller 40 when at least one cylinder is deactivated and at least one booster operating condition is met. The operating conditions may be engine speed or torque demand ranges. The system may include exhaust gas recirculation and an after-treatment device 30. The system may be used in a vehicle with an energy recirculation arrangement and an electrical energy storage device to power the booster. Also claimed is a method of controlling the system.

Description

An Engine System and a Method of Controlling an Engine System This invention relates to an engine system having a turbocharged multi-cylinder engine and in particular to a method for controlling the engine system when one or more cylinders of the engine are deactivated.

It is known to provide a mechanism for deactivating one or more cylinders of a multi-cylinder internal combustion engine of a motor vehicle in order to reduce fuel consumption and/or the production of emissions. Such cylinder deactivation inoreases the load per cylinder thereby allowing the engine to operate closer to its maximum efficiency when the load on the engine is relatively low.

It is further known to provide forced induction for an internal combustion engine by the use of a turbocharger that uses exhaust gas emanating from the engine to drive a compressor thereby increasing the mass flow rate and pressure of air entering the engine.

It is a problem when combining cylinder deactivation and turbocharging that the efficient operating region in which the engine can be used is very limited. Although cruising of the motor vehicle at low speed is normally possible when cylinder deactivation is taking place, acceleration is not possible as it would take the operation of the engine outside the efficient operating region. This is primarily because the turbocharger cannot operate efficiently with the reduced mass flow rates that cylinder deactivation produces. In the case of a variable geometry turbocharger, the inlet area is normally reduced at such low loads in order to increase the flow velocity of the gas flowing through a turbine side of the turbocharger but this has the disadvantage that the back pressure on the engine is increased. Because the boost pressure deliverable at such low mass flow rates is also restricted, the combination of low inlet pressure and higher back pressure will often result in a high pressure difference between the inlet and outlet sides of the engine with consequential high pumping losses.

It is an object of the invention to provide an improved engine system and method of controlling such an engine system to minimise such problems and disadvantages.

According to a first aspect of the invention there is provided an engine system comprising a multi-cylinder engine having at least one deactivatable cylinder, a turbocharger having a compressor and a turbine operatively connected to the engine, an electric booster connected to the compressor of the turbocharger so as to selectively supply air at increased pressure to the compressor of the turbocharger and an electronic controller to control activation of the electric booster wherein the electronic controller is operable to activate the electric booster when at least one cylinder of the engine is deactivated and at least one electric booster operating condition is met.

The electric booster operating condition may be an engine speed range and the electronic controller is operable to only activate the electric booster if the engine is operating within a speed range defined by a lower speed limit and an upper speed limit.

Advantageously, when it is active, the electric booster is controlled by the electronic controller to meet a torgue demand for the engine.

A further electric booster operating condition may be that a torque demand for the engine is not greater than a maximum engine torque limit for the current engine speed.

A further electric booster operating condition may be that a torque demand for the engine is greater than a minimum engine torque limit for the current engine speed.

The system may further comprise a low pressure exhaust gas recirculaticn circuit having a low pressure exhaust gas recirculation control valve controlled by the electronic controller and, when the electric booster is active and the low pressure exhaust gas recirculation control valve is open, the electric booster may increase the flow through the low pressure exhaust gas recirculation circuit.

The engine system may include at least one exhaust aftertreatment device connected downstream from the turbine of the turbocharger and the low pressure exhaust gas recirculation circuit may include a low pressure exhaust gas flow passage extending from a position downstream from the at least one aftertreatment device to a position upstream from the electric booster.

The electric booster may comprise a compressor driven by an electric motor.

According to a second aspect of the invention there is provided a motor vehicle having an engine system constructed in accordance with said first aspect of the invention.

The motor vehicle may be a motor vehicle having an energy recirculaticn system to capture electrical energy during use of the motor vehicle and store it in an electrical energy storage device and electrical energy stored in the electrical energy storage device may be used to power the electric booster.

According to a third aspect of the invention there is provided a method of controlling an engine system comprising a multi-cylinder engine having at least one deactivatable cylinder, a turbocharger and an electric booster wherein the method comprises activating the electric booster when at least one cylinder of the engine is deactivated and at least one electric booster operating condition is met.

The at least one electrio booster operating condition may be an engine speed range and the method may further comprise only activating the electric booster if the engine is operating within a speed range defined by a lower speed limit and an upper speed limit.

Advantageously, when it is aotive, the electric booster may be oontrolled to meet a torque demand for the engine.

An electric booster operating condition may be that a torque demand for the engine is not greater than a maximum engine torque limit for the current engine speed.

An electric booster operating condition may be that a torque demand for the engine is greater than a minimum engine torque limit for the current engine speed.

The invention will now be described by way of example with reference to the accompanying drawing of which:-Fig.1 is a schematic diagram of a motor vehicle according to a second aspect of the invention having a first embodiment of an engine system acoording to a first aspect of the invention; Fig.2 is a schematic diagram similar to Fig.l but showing a second embodiment of an engine system according to the first aspect of the invention; Fig.3 is a flow chart showing a method according to a third aspect of the invention; Fig.4 is a torque versus engine speed chart showing various operating regions for the engine; and Fig.5 is a block diagram showing further features of the motor vehicle shown in Figs.1 and 2.

With particular reference to Fig.1 there is shown a motor vehicle 1 having an engine system to provide motive power for the motor vehicle 1 via a transmission system (not shown) The engine system comprises a multi-cylinder engine in the form of a four cylinder diesel engine 5, a turbocharger operatively connected to the engine 5, an electric booster 20, an air filter 4, a high pressure exhaust gas recirculation valve 8, an intercooler 14, a torque demand input means in the form of an accelerator pedal 15 and an accelerator pedal position sensor 16, an aftertreatment device 30 and an electronic controller 40.

The turbocharger 10 comprises a compressor 11 and a turbine 12 connected by a shaft so that the turbine 11 drives the compressor 11 when exhaust flows from the engine via an exhaust manifold 7. The compressor 11 is connected to an inlet manifold 6 of the engine 5 so as to supply air to the engine 5.

The engine 5 has a number of fuel injectors (not shown) to provide the engine 5 with fuel as is well known in the art.

The electric booster 20 comprises an electric motor 21 which is driveably connected to a compressor 22 by a shaft.

As shown in Fig.5, the electric booster 20 or to be more accurate, the electric motor 21 is controlled by the electronic controller 40 via a power controller 41. The electric booster 20 has an active state in which the electric motor 21 drives the compressor 22 and a deactivated state in which no electrical energy is supplied to the electric motor 21. Tjhen the electric booster 20 is in the active state the electronic controller 40 varies the speed of the electrio motor 21 so as to control the electric booster 20 so as to meet a torque demand for the engine 5.

When the engine 5 is operating, air enters an inlet air flow path as indicated by the arrow "IN" flows through the air filter 4 to an inlet side of the compressor 22, passes through the compressor 22 to an inlet side of the compressor 11 of the turbocharger 10 and then flows to the engine via the inlet manifold 6. The compressors 11, 22 of the turbocharger and electric booster respectively are therefore operatively connected in a series arrangement.

In an alternative arrangement (not shown) a bypass passage is arranged around the electric booster 20. The flow through the bypass passage is controlled by an electronically controlled valve under the control of the electronic controller 40. When the electric booster 20 is not operating and/or when the engine 5 is running under high load the electronically controlled valve is opened to allow inlet air to bypass the electric booster 20. This prevents the inlet air flow being unnecessarily restricted by the electric booster 20 when the electric booster 20 is not in use.

Exhaust gas flows from the engine 5 via the exhaust manifold 7 to an inlet side of the turbine 12 of the turbocharger 10 through the turbine 12 to an outlet side of the turbine 12 and on to an aftertreatment device 30. The exhaust gas then flows from the aftertreatment device 30 to atmosphere as indicated by the arrow "EX". It will be appreciated that one or more noise reducing devices or silencers are normally located between the aftertreatment device 30 and the point at which exhaust gas is returned to atmosphere.

A high pressure exhaust gas recirculation circuit is also shown on Fig.i having a high pressure exhaust gas recirculation valve 8 controlled by the electronic controller 40 so as to recirculate when required some of the exhaust gas exiting the engine 5 back to the inlet side of the engine 5 as is well known in the art.

Referring now to Fig.4 there is shown a relationship between torque and engine speed for the engine 5 in various conditions -The maximum torque curve I shows the relationship between torque and engine speed for a throttle wide open condition, that is to say, the relationship between torque and engine speed when the accelerator pedal 15 is fully depressed with all cylinders active.

The exact shape and magnitude of the maximum torque curve I will depend upon a number of factors including but not limited to, engine displacement, maximum permitted cylinder pressure, maximum permitted boost pressure, maximum available boost pressure, maximum permitted exhaust gas temperature and gearbox torque capacity.

The curve IIjri-rhr, shows the maximum torque available from the engine 5 when all of deactivatable cylinders of the engine 5 are in their deactivated state and only the turbocharger 10 is being used to increase the mass flow rate or inlet pressure. The operating region bounded by the quadrilateral c, e, f, d is the efficient operating region for the engine 5 using only the turbocharger 10.

The curve mhcI:r shows the maximum torque available from the engine 5 when the deactivatabie cylinders of the engine 5 are in their deactivated state and the turbocharger and the electric booster 20 are being used to increase the mass flow rate or inlet pressure. The operating region bounded by the quadrilateral a, b, e, I is the efficient operating region for the engine 5 using both the turbocharger 10 and the electric booster 20 and the operating region bounded by the quadrilateral a, b, c, ci is the additional efficient operating region provided by the use of the electric booster 20 when the engine 5 is operating with its cylinders deactivated.

It will be appreciated when the cylinders are deactivated the electric booster 20 can be used all the time or only when the demanded torque exceeds the torque defined by the curve LL'[bL but it is normaily more efficient to use the electric booster 20 whenever additional pressure or mass flow is required while the cylinders are deactivated.

The line Nnur represents the lowest engine speed for which cylinder deactivation is practical. This limit is normally determined based upon NVH considerations for the engine 5.

The line Nax represents the highest engine speed for which cylinder deactivation is possible. This limit is normally determined based upon the maximum speed that cylinder deactivation can be disengaged without causing damage to the engine 5. That is to say, this limit is based upon the mechanical attributes of the mechanism used to effect deactivation.

During normal running of the engine 5, fuel will be supplied to the engine 5 in response to torque demands from an operator as indicated by the position of the accelerator pedal 15. The electronic controller 40 either directly or via a separate engine control unit (not shown) varies the fuel supplied to match the air flow into the engine 5 to provide a predefined air/fuel ratio based upon various faotors including engine speed and controls the turbocharger to produce the required boost to achieve the requested demand.

If the torque demand on the engine 5 is relatively low the electronic controller 40 will decide whether or not to deactivate the deactivatable cylinders of the engine 5.

This decision is based on various factors including but not limited to the current engine speed compared to the upper and lower engine speed limits Nex and N-1 respectively, predicted engine efficiency in the deactivated and ncn-deactivated states, predicted emissions in the deactivated and non-deactivated states, predicted exhaust gas temperature in the deactivated and non-deactivated states and the cylinder temperatures in the deactivated and non-deactivated states.

If the conditions for deactivation are met then the electronic controller 40 will proceed and deactivate the deactivatable cylinders of the engine 5 which in this case are cylinders 2 and 3 and at the same time will activate the electric booster 20.

As previously mentioned, if the torque demand for the engine 5 is below the torque output shown as T!jwUrhn on Fig.4 then additional boosting using the electric booster 20 is not actually required but can be used because it will result in improved engine efficiency. This is because the use of electric boosting permits the inlet to the turbocharger 10 to remain in a more open position thereby reducing the back pressure on the engine 5 and consequently the pressure difference across the engine 5. This is possible because the turbine 12 is not required to drive the compressor 11 to produce the required boost pressure as most of the boost pressure is provided by the electric booster 20.

-10 -If the torque demand for the engine 5 is above the torque output shown as T!!]rh!: on Fig.4 then additional boosting using the electrio booster 20 is always required.

As before, the use of the electric booster 20 permits the inlet to the turbocharger 10 to remain in a more open position thereby reducing the back pressure on the engine 5 and consequently the pressure difference across the engine 5 because the turbine 12 is not required to drive the compressor 11 to produce the required boost pressure.

The torque demand for the engine 5 is met primarily by controlling the electric booster 20 so that if an increase in torque is demanded by a user of the engine 5, such as is the case if acceleration of the motor vehicle is required, then the electronic controller 40 increases the speed of the electric motor 21 so as to provide more boost pressure from the compressor 22 and more torque from the engine 5 and increases the amount of fuel being supplied to the engine 5.

It will be appreciated that the maximum torque that can be produced is limited by the maximum allowable torque limit ThaEbocuLcr for the current engine operating speed. If the torque demand reduces, the electronic controller 40 will reduce the speed of the electric motor 21 to reduce the boost provided by the electric booster 20.

Once activated the electric booster 20 is controlled by the electronic controller 40 to meet the current torque demand in the most efficient manner which may mean that a large proportion of the required boost is provided by it or that the boost is shared by the turbocharger 10 and the electric booster 20. If during the time the electric booster 20 is active, a torgue demand is received which exceeds the maximum torque limit then the electric booster 20 is controlled so as not to exceed the maximum torque limit Lf[r and, if the demand continues for more than a very short period of time, the electronic controller will switch the engine 5 out of the deactivated mode so -11 -as to better meet the requested torque demand. It will be appreciated that the maximum torque limit TImI!!!n!)ster only applies to the situation where the cylinders are deactivated it is otherwise limited by the limit Trnax.

The maximum torque limit TlirnEtcoster represents one electric booster operating condition that must be met. That is to say, if a torque demand for the engine is not greater than maximum torque limit TIrnI!!h!)oster for the current engine speed then the electric booster 20 can be used and the operating condition is met otherwise it cannot.

In some embodiments a further electric booster operating condition is that a torque demand for the engine is greater than a minimum engine torque limit TrTh1Lr.; for the current engine speed. That is to say, in some embodiments the electric booster 20 is only used when the turbocharger cannot efficiently provide the required boost.

It will also be appreciated that, when all of the cylinders of the engine 5 are active, the electric booster could also be used to supplement the turbocharger 10 but in such a case different operating limits would be defined.

That is to say, when all cylinders of the engine 5 are operating the limits T!jrLhone.-p, and do not apply.

One particularly advantageous use of the invention is in relation to a hybrid motor vehicle. Fig.5 shows in block diagram form the motor vehicle configured as a hybrid motor vehicle 1 having in addition to the engine 5 a secondary source of motive power in the form of a traction motor 50.

The traction motor 50 is driveably connected to at least one road wheel 2 of the motor vehicle 1 so as to permit it to either drive the road wheel 2 or be driven by the road wheel 2. In practice a coupling such as a clutch may be interposed between the traction motor and the road wheel 2 to allow the drive therebetween to be disconnected. The -12 -traction motor 50 is electrically connected to an electric energy storage device 51 which could be in the form of a battery or ultra-capacitor. As indicated by the double headed arrow, electrical energy (current) can flow from the electric energy storage device (EESD) 51 to the traction motor 50 or from the traotion motor 50 to the EESD 51. That is to say, the traction motor 50 is a motor/ generator. The flow of electrical energy will depend upon the current operating state of the motor vehicle 1 and the electronic controller 40 controls the flow of electrical energy between the traction motor 50 and the EESD 51 via a power controller 42 based upon predefined operating parameters.

Electrical energy is also supplied from the EESD 51 to the electric booster 20 or more specifically the electric motor 21 of the electric booster 20 via the power controller 41.

Therefore electrical energy for the electric booster 20 comes from the EESD 51. The traction motor 50 and the EESD 51 form parts of an energy recirculation system that is able to capture energy during use of the motor vehicle 1 and store it for future use.

For example, if the motor vehicle is reguired to reduce speed, the traction motor 50 can be operated as a generator to store electrical energy in the EESD 51 for later use either by the traction motor 50 or by the electric booster 20.

One advantage of using the electric power stored in the FESD 51 to power the electric booster 20 is that no fuel is wasted generating the electricity by using the engine 5 to drive a generator. A second advantage is that it provides an opportunity to use the stored electrical energy at times when there is no current need for the electrical power to drive the traction motor 50.

-13 -Furthermore, if the traotion motor 50 and the engine 5 are being used at the same time with the deactivatabie cylinders of the engine 5 deactivated then the stored electrical power provides not only direct drive the motor vehicle 1 via the traction motor 50 but improves the performance of the engine 5 thereby improving the overall efficiency of the motor vehicle 1.

A second particularly advantageous application of the invention is in respect of a motor vehicle that can recover energy during periods of deceleration and store the recovered energy for future use. With such an arrangement the saved electrical energy can be used to power the electric booster 20 and so the electrical energy required producing any engine boosting from the electric booster 20 is provided with no additional fuel penalty. For example an engine fitted with a front of engine accessory drive driving a generator could be used to recapture electrical energy by producing electricity from the generator when the engine is in an overrunning condition. Such a motor vehicle can be said to have an energy recirculation system to capture electrical energy during use of the motor vehicle and store it in an electrical energy storage device.

Referring now to Fig.2 there is shown a second embodiment of an engine system that is in most respects identical to that previously described with reference to Figs.1 and 4 and is not discussed again in detail.

Identical components use the same reference numbers in Fig.2 as in Fig.1.

The second embodiment differs from the first embodiment in that the engine system has two aftertreatment devices in the form of a diesel oxidation catalyst 31 and a diesel particulate trap 32 rather than a single aftertreatment device and that the engine system of the second embodiment -14 -also includes a low pressure exhaust gas recirculation circuit along with the high pressure exhaust gas recirculaticn circuit already discussed with respect to Fig.i.

The low pressure exhaust gas recirculation circuit has a low pressure exhaust gas recirculation control valve 9 controlled by the electronic controller 40 and includes a low pressure exhaust gas flow passage extending from a position downstream from the diesel particulate filter 32 to a position upstream from the compressor 22 of the electric booster 20. The position at which the low pressure exhaust gas recirculation circuit joins the inlet air path to the engine 5 is located between the air filter 4 and the compressor 22 of the electric booster 20.

The connection of the low pressure exhaust gas recirculation circuit to the inlet air flow path upstream from the electric booster 20 has the advantage that, when the electric booster 20 is active and the low pressure exhaust gas recirculation control valve 9 is open, the electric booster 20 will increase the flow of low pressure exhaust gas through the low pressure exhaust gas recirculation circuit. That is to say, the electric booster 20 acts as a pump drawing recirculated exhaust gas from the exhaust through the low pressure exhaust gas recirculation circuit into the inlet air flow path.

Normally, causing low pressure exhaust gas to flow through a low pressure exhaust gas recirculation circuit at low engine speeds is problematic because of its inherent low pressure. In some prior art system a flow restrictor valve is positioned in the exhaust pipe downstream from the position where the exhaust gas enters the low pressure exhaust gas flow passage to encourage the flow of low pressure exhaust gas through the low pressure exhaust gas recirculation circuit. That is to say, the restrictor valve -15 -is positioned between the juncture of the low pressure exhaust gas flow passage with the exhaust pipe and the point "EX" at which the exhaust gas enters the atmosphere. With such an arrangement, when low pressure exhaust gas flow is reguired, the low pressure exhaust gas recirculation control valve 9 is opened and the flow restrictor valve is adjusted to increase the pressure in the exhaust pipe so as to provide a pressure differential between the exhaust pipe end of the low pressure exhaust gas recirculation circuit and the inlet air end of the low pressure exhaust gas recirculation circuit. However, increasing the pressure in the exhaust pipe is disadvantageous as it reduces the flow through the two exhaust gas aftertreatment devices 31, 32 and through the turbine 12 thereby further reducing the ability of the turbocharger 10 to provide boost when the deactivatable cylinders of the engine 5 are deactivated.

The use of low pressure exhaust gas recirculaticn is also problematic at low engine loads due to the low cylinder temperatures produced by low load running. This can be improved by deactivating the deactivatable cylinders as the load per cylinder is increased thereby increasing the cylinder temperatures in the cylinders still operating.

It is therefore normally difficult to combine low pressure exhaust gas recirculation with cylinder deactivation.

The ability to operate the engine 5 in the cylinder deactivated state with low pressure exhaust gas recirculation is considerably enhanced by using the electric booster 20 as proposed by this invention as the flow of low pressure exhaust gas is aided by the electric booster 20.

It will also be appreciated that the use of the electric booster 20 may produce a positive pumping effect rather than the normal pumping losses if the pressure -16 -entering the cylinders is greater than that in the exhaust manifold 7.

With reference to Fig.3 there is shown a method 100 of controlling an engine system according to the invention.

The method starts in box 110 which in the case of a motor vehicle such as the motor vehicle 1 could be a key-on event. The method then advances to box 115 to determine whether cylinder deactivation is required to achieve efficient running of the engine 5. This determination could be made by the electronic controller 40 or by another controller such as an engine control unit. As is well known in the art there are many factors that need to be taken into account when deciding whether to deactivate any deactivatable cylinders of the engine 5. However, in the case of the example being described, a first test is whether the current engine speed (N) is within a predetermined operating range. That is to say is N::Ljfl < N < N; where N is the current engine speed, Nitjr. is the lowest engine speed for which cylinder deactivation is practical which is normally determined based upon NVH considerations for the engine 5 and is the highest engine speed for which cylinder deactivation is practical and is normally determined based upon the maximum speed that cylinder deactivation can be disengaged without causing damage to the engine 5.

A secondary test is whether the demanded torque (Tjeitr:j) is below a torgue limit TI!!h!)o;ter which in this case is the maximum torque that it is predicted can be produced with the deactivatable cylinders of the engine 5 deactivated without the exhaust gas temperature in the active cylinders exceeding a predefined limit. It will however be appreciated that other factors could be used with or instead of the cylinder temperature limit such as an exhaust gas temperature limit for the turbine 12 or high cylinder -17 -pressure limit. The temperatures and/or pressure could be modelled or sensors could be provided to measure them.

Therefore in this case, if N1 < N C Nrnax is true and Tjerarc is less than Iiimmcster, deactivation will occur and the method advances to box 120 and if either condition is not met then the method loops around box 115.

If the above conditions are met, the method advances to box 120 then the deactivatable cylinders of the engine 5 are deactivated. It will be appreciated by those skilled in the art that the number of cylinders deactivated may be dependent upon the demanded load and the configuration of the engine. For example in the case of an eight cylinder engine four cylinders may be deactivated for very low engine load running but only two cylinders may be deactivated for medium engine load running. Such engines are sometimes referred to as variable displacement engines.

The method then advances to box 130 where it is determined whether to activate the electric booster 20. In the case of the example being described, if the deactivatable cylinders have been deactivated then the electric booster 20 is activated. However it will be appreciated that for this to occur N1 < N < must be true and Tdenard must be less than TT-yip!hrflstpr and so these are effectively requirements for activation of the electric booster 20 as well as for the deactivation of the deactivatable cylinder or cylinders. It will also be appreciated that in this case, the torque limit TI!ffI!!hn!)sfer is based upon a relationship between engine speed and expected exhaust gas temperature in the non-deactivated cylinders.

Although in the preferred embodiment described, the tests used to determine whether the deactivatable cylinders should be deactivated are the same as those used to determine whether the electric booster 20 should be -18 -activated this need not be the case. For example, the deactivatable cylinders could be deaotivated when the engine speed is less than N1 such as when the engine is idling with substantially no request for torque other than that required maintaining the engine 5 operating at idle speed.

In such a case use of the electric bocster 20 is not required and so then there would be different conditions for cylinder deactivation and electric booster 20 activation.

In this case, the electric booster 20 is only active when the deactivatable cylinders are deactivated, N-± < N < Nax is true and is less than Linshocster* If these requirements are not met then the method loops back to box 115. Note that, if the conditions for cylinder deactivation are the same as those for activation of the electric booster 20, the test for electric booster 20 activation becomes "Are the deactivatable cylinders deactivated?" If "Yes" then activate electric booster if "No" then do not activate the electric booster 20.

Note that, if the cylinders are not deactivated, there could be a further test to see whether use of the electric booster 20 would be advantageous with all of the cylinders active.

If the electric booster 20 has been activated then the method advances to box 140 where the electric booster 20 is controlled by the electronic controller 40 to provide the currently demanded torque in the most efficient manner. For example, assuming that the demanded torque requires a boost pressure of 0.4 Bar (0.4 x l5 N/rn2), this can be provided in various combinations of turbocharger 10 provided boost and electric booster 20 provided boost. Generally, it is preferable to use the electric booster 20 to provide as much of the boost as possible as this will allow the turbocharger to be operated with minimal exhaust gas back pressure on -19 -the engine 5. For example, the ratio may be 0.3 Bar (0.3 x 10: N/rn2) boost from the eleotrio booster 20 and 0.1 Bar (0.1 lo* N/rn2) from the turbocharger 10. It will be appreciated that the turbocharger 10 will always produce a small amount of boost because it will continue to rotate during cylinder deactivation.

After box 140 a test is made in box 150 to see whether a key-off event has occurred and, if not, the method advances to box 155 but if a key-off event has occurred the method 100 ends at box 190.

In box 155 it is checked whether electric booster activation is still valid, that is to say whether all of the conditions required for electric booster 20 activation are still met and, if they are, the method returns to box 140 but, if they are not, the method returns to box 115.

It will be appreciated that if the conditions for cylinder deactivation and electric booster 20 activation are identical as is the case with the preferred embodiment then the box 130 could be deleted as the same check is carried out in box 115.

Although the invention has been described by way of example with reference to a four cylinder diesel engine it will be appreciated that it is not limited to such use and could be applied with advantageous effect to any multi-cylinder engine having at least one deactivatable cylinder.

It will also be appreciated that although the electronic controller 40 is shown as a single unit it could be comprised of several electronic controllers and/or electronic processors linked to achieve the functionality described.

-20 -It will be appreciated by those skilled in the art that although the invention has been described by way of example with reference to one or more embodiments it is not limited to the disclosed embodiments and that alternative embodiments could be constructed without departing from the scope of the invention as defined by the appended claims.

Claims

-21 -Claims 1. An engine system comprising a multi-cylinder engine having at least one deactivatable cylinder, a turbocharger having a compressor and a turbine operatively connected to the engine, an electric booster connected to the compressor of the turbocharger so as to selectively supply air at increased pressure to the compressor of the turbocharger and an electronic controller to control activation of the electric booster wherein the electronic controller is operable to activate the electric booster when at least one cylinder of the engine is deactivated and at least one electric booster operating condition is met.
2. A system as claimed in claim 1 wherein the electric booster operating condition is an engine speed range and the electronic controller is operable to only activate the electric booster if the engine is operating within a speed range defined by a lower speed limit and an upper speed limit.
3. A system as claimed in claim 1 or in claim 2 wherein, when it is active, the electric booster is controlled by the electronic controller to meet a torque demand for the engine.
4. A system as claimed in any of claims 1 to 3 wherein, an electric booster operating condition is that a torque demand for the engine is not greater than a maximum engine torque limit for the current engine speed.
5. A system as claimed in any of claims 1 to 4 wherein, an electric booster operating condition is that a torque demand for the engine is greater than a minimum engine torque limit for the current engine speed.

-22 -
6. A system as claimed in any of claims 1 to 5 wherein the system further comprises a low pressure exhaust gas recirculation circuit having a low pressure exhaust gas recirculation control valve controlled by the electronic controller and, when the electric booster is active and the low pressure exhaust gas recirculation oontrol valve is open, the electric booster increases the flow through the low pressure exhaust gas recirculation circuit.
7. A system as claimed in claim 6 wherein the engine system includes at least one exhaust aftertreatment device connected downstream from the turbine of the turbocharger and the low pressure exhaust gas recirculation circuit includes a low pressure exhaust gas flow passage extending from a position downstream from the at least one aftertreatment device to a position upstream from the electric booster.
8. A system as claimed in any of claims 1 to 7 wherein the electric booster comprises a compressor driven by an electric motor.
9. A motor vehicle having an engine system as claimed in any of claims 1 to 8.
10. A motor vehicle as claimed in claim 9 in which the motor vehicle is a motor vehicle having an energy reciroulation system to capture electrical energy during use of the motor vehicle and store it in an electrical energy storage device wherein electrical energy stored in the electrical energy storage device is used to power the electric booster.
11. A method of controlling an engine system comprising a multi-cylinder engine having at least one deactivatable cylinder, a turbocharger and an electric booster wherein the method comprises activating the electric -23 -booster when at least one cylinder of the engine is deactivated and at least one electric booster operating condition Is met.
12. A method as claimed in claim 11 wherein the at least one electric booster operating oondition is an engine speed range and the method further comprises only activating the electric booster if the engine is operating within a speed range defined by a lower speed limit and an upper speed limit.
13. A method as claimed in claim 11 or in claim 12 wherein, when it is active, the electrio booster is controlled to meet a torque demand for the engine.
14. A method as claimed in any of claims 11 to 13 wherein, an electric booster operating condition is that a torque demand for the engine is not greater than a maximum engine torque limit for the current engine speed.
15. A method as claimed in any of claims 11 to 14 wherein, an electric booster operating condition is that a torque demand for the engine is greater than a minimum engine torque limit for the current engine speed.
16. A method of controlling an engine system substantially as described herein with reference to the a000mpanying drawing.
17. An engine system substantially as described herein with reference to the accompanying drawing.
18. A motor vehicle substantially as described herein with reference to the accompanying drawing.