GB2496407A

GB2496407A - Three cylinder engine in which a cylinder may be selectively deactivated.

Info

Publication number: GB2496407A
Application number: GB1119370.3A
Authority: GB
Inventors: Timothy James Bowman
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2011-11-10
Filing date: 2011-11-10
Publication date: 2013-05-15
Anticipated expiration: 2031-11-10
Also published as: DE102012219807A1; GB2496407B; RU2012147907A; RU2612544C2; CN103104355A; GB201119370D0; CN103104355B

Abstract

A three cylinder inline reciprocating piston internal combustion engine is disclosed in which an inner cylinder 12 of the three cylinders 11, 12 and 13 may be selectively deactivated in order to improve fuel consumption or assist with engine heat-up by for example increasing the exhaust gas temperature thereby assisting with light-off of an exhaust gas after treatment device 20 such as a NOx trap, soot trap diesel or catalytic convertor. The engine 5 has a flat plane crankshaft 40 having three throws 11T, 12T, 13T. The throws 11T, 13T for the two outer cylinders 11, 13 are in phase and the throw 12T for the inner cylinder 12 is 180 degrees out of phase. The inner cylinder 12 is deactivated by cutting off a fuel supply to the cylinder 12.

Description

A Three Cylinder Engine with a Deactivatable Cylinder.

This invention relates to an internal combustion engine and in particular to a three cylinder inline reciprocating piston engine in which one cylinder is deactivatable in order to improve fuel consumption.

It is well known that an engine is often run at a power output level well below that which it is capable of producing. Such part load operation will often result in the engine operating at a thermal efficiency level well below that achievable by the engine thereby compromising fuel economy.

It is therefore desirable to better match the output available from an engine with the load placed upon the engine so that the engine operates as close as possible to its maximum operating efficiency at all times. The inventor has realised that such matching can best be achieved by selectively deactivating one of the cylinders of a three cylinder engine when the engine is operating at part load.

Furthermore, if an aftertreatment device, such as a catalytic converter, NOx trap or soot trap, is fitted to the engine in order to reduce emissions from the engine it is normally required to heat the aftertreatment device beyond a temperature where it becomes sufficiently active to perform its designated function, such a temperature is often referred to as the light-off temperature' . However, when an engine is operating at low or part load with all cylinders operating the exhaust temperature is relatively low compared to that produced when the engine is operated at full load. The inventor has therefore realised that a further advantage of selective cylinder deactivation is that by deactivating one of the cylinders the exhaust temperature from the remaining operating cylinders can be increased thereby reducing the time taken for any aftertreatment devices to reach their respective light-off temperature following a start-up from cold.

It is an object of the invention to provide a three cylinder engine with improved fuel economy.

According to a first aspect of the invention there is provided a three cylinder inline reciprocating piston internal combustion engine comprising two outer primary cylinders and & secondary cylinder interposed between the two outer primary cylinders, each of the cylinders slidingly supporting a respective piston operatively connected by a respective connecting rod to a respective throw of a three throw flat plane crankshaft wherein the throws for the two primary cylinders are arranged in phase and the throw for the secondary cylinder is arranged 180 degrees out of phase with respect to the two primary cylinders and the secondary cylinder is selectively deactivatable.

The secondary cylinder may be deactivated to improve fuel economy.

The secondary cylinder may be deactivated to increase the temperature of at least one of the exhaust gases exiting the engine, lubricating oil flowing through the engine and coolant flowing through the engine.

A power stroke may occur in one of the two primary cylinders for each revolution of the crankshaft and the power stroke for the secondary cylinder may be out of phase with the power strokes of the primary cylinders.

Deactivating the secondary cylinder may include shutting off a fuel supply to the secondary cylinder.

The secondary cylinder may include at least one inlet valve and at least one exhaust valve and deactivating the secondary cylinder may include maintaining all inlet and all exhaust valves in their respective closed positions.

The secondary cylinder may be deactivated based upon a comparison of an engine torque demand with an engine torque demand limit.

The secondary cylinder may be deactivated based upon a comparison of a rate of change of engine torque demand with an engine torque demand rate of change limit.

According to a second aspect of the invention there is provided an engine system comprising a three cylinder engine constructed in accordance with said first aspect of the invention, an input indicative of a demanded engine torque and an electronic controller operable to receive the input indicative of demanded engine torque wherein the electronic controller is operable to determine whether to operate the engine using all three cylinders or deactivate the secondary cylinder so as to operate the engine using only the two primary cylinders based upon at least the input indicative of demanded engine torque.

The input indicative of demanded engine torque may be produced by a cruise control system.

The engine system may further comprise an accelerator pedal operable by an operator of the engine and an accelerator pedal position sensor to monitor the position of the accelerator pedal and provide the input indicative of demanded engine torque and the electronic controller may be operable to receive the input from the accelerator pedal position sensor and determine whether to operate the engine using all three cylinders or deactivate the secondary cylinder so as to operate the engine using only the two primary cylinders based upon at least the input received from the accelerator pedal position sensor.

If the demanded engine torque is greater than a first predefined torque demand limit, the engine may be operated using all three cylinder and, if the demanded torque is less than the first predefined torque demand limit, the engine may be operated as a two cylinder engine with the secondary cylinder deactivated.

The engine system may further comprise a temperature indicator means to provide an input tc the electronic controller indicative of an engine related temperature and the electronic controller may be operable to deactivate the secondary cylinder if the engine related temperature is below a predefined temperature limit.

The engine system may further comprise an exhaust gas aftertreatment device, the engine related temperature may be exhaust gas temperature, the temperature indicator means is an exhaust gas temperature sensor tc provide an input to the electronic controller indicative of the temperature of the exhaust gas entering the aftertreatment device and the predefined temperature limit is a required operating temperature of the aftertreatment device.

The engine related temperature may alternatively be the temperature of a coolant circulating through the engine, the temperature sensor may be a coolant temperature sensor to provide an input to the electronic controller indicative of coolant temperature and the predefined temperature limit may be a required operating temperature of the coolant.

The engine related temperature may alternatively be the temperature of oil circulating through the engine, the temperature indicator means is an oil temperature sensor to provide an input to the electronic controller indicative of oil temperature and the predefined temperature limit is a required operating temperature of the oil.

According to a third aspect of the invention there is provided a method of operating an engine constructed in accordance with said first aspect of the invention wherein the method comprises determining whether the secondary cylinder can be deactivated and, if the secondary cylinder can be deactivated, terminating a fuel supply to the secondary cylinder to deactivate it.

The secondary cylinder of the engine may be deactivated if the torgue output reguired from the engine can be met by operating the engine on only two cylinders.

The engine may be operated using three cylinders if an engine torque demand is greater than a predefined limit.

The secondary cylinder may include at least one inlet valve and at least one exhaust valve and the method may further comprise deactivating the secondary cylinder by maintaining all inlet and all exhaust valves in their respective closed positions.

The invention will now be described by way of example with reference to the accompanying drawing of which:-Fig.1 is a block diagram showing an engine system according to a second aspect of the invention; Fig.2 is a schematic cross-section through an inline three cylinder engine according to a first aspect of the invention; Fig.3 is a view in the direction of arrow "A" on Fig.2 showing the relative orientation of three throws of a crankshaft of the engine shown in Fig.2; Fig.4 is a flow chart of a first embodiment of a method of operating an engine according to a third aspect of the invention; Figs.5A and SB are flow charts showing a second embodiment of a method of operating an engine according to the third aspect of the invention; and Figs. 6A and 6B show alternative timing charts for the engine shown in Figs. 1 to 3.

With particular reference to Figs. 1 to 3 there is shown a motor vehicle 50 having an engine system 1 comprising a four stroke three cylinder reciprocating piston is internal combustion engine 5, an exhaust aftertreatment device 20 for the engine 5, an electronic controller 30, an operator demand input device in the form of an accelerator pedal 15 and an associated accelerator pedal position sensor 32.

It will be appreciated that the electronic controller may comprise of several interlinked electronic controllers, control units or electronic processors and is shown as a single unit for the purpose of illustration only.

The engine system 1 also includes an exhaust gas temperature sensor 33 to provide an output indicative of the temperature of the exhaust gas entering the aftertreatment device 20, an electronically controlled fuel injection unit 10, an electronically controlled variable valve actuation mechanism 14 and an engine speed sensor 31 associated with a toothed ring on a flywheel 9 of the engine 5. It will be appreciated that other means for measuring engine speed could be used and that the invention is not limited to the use of a toothed ring and engine speed sensor.

The engine system 1 may also comprise a cruise control system (not shown) to provide an input to the electronic controller 30 of a required engine torque demand in order to maintain a set vehicle speed. It will be appreciated that the logic for the cruise control system could be formed as part of the electronic controller 30 or could be a separate unit.

The engine 5 comprises three cylinders 11, 12 and 13 arranged inline, therebeing two outer primary cylinders 11, 13 and a centre secondary cylinder 12 interposed between the two outer primary cylinders 11, 13.

The primary cylinders 11, 13 operate at all times while the engine 5 is operating and the secondary cylinder 12 is selectively deactivatable as described in more detail hereinafter.

An exhaust manifold 6 directs exhaust gas leaving the engine 5 through an exhaust conduit 7 to the aftertreatment device 20 and a tailpipe 8 conducts exhaust gas from the aftertreatment device 20 to atmosphere as indicated by the arrow E' . It will be appreciated that the aftertreatment device 20 can be of any known type suitable for reducing the emissions from the engine 5 and that there may be more than one type of exhaust aftertreatment device connected to the exhaust conduit 7 in series. For example and without limitation, a catalyst and a soot trap may both be arranged in series. It will also be appreciated that one or more devices to reduce exhaust noise may be fitted into the tailpipe 8 downstream from the aftertreatment device or devices.

The exhaust gas temperature sensor 33 may be directly attached to an inlet end of the aftertreatment device 20 or may be located upstream from the aftertreatment device 20 so as to measure the temperature of the exhaust gas flowing through the exhaust conduit 7 at a position close to an inlet to the aftertreatment device 20. It will be appreciated that the temperature could be inferred from other operating parameters rather than be directly measured using a temperature sensor. As meant herein the phrase temperature indicator means' means the determination of a temperature by either direct temperature measurement using a sensor or by use of an inferred temperature.

The position of the accelerator pedal 15 is sensed by the accelerator pedal position sensor 32 and the output from the sensor 32 is supplied as an input to the electronic controller 30 where it is processed so as to provide an indication of operator engine torque demand.

The output from the engine speed sensor 31 is used by the electronic controller 30 as an indication of current engine speed.

Referring now in particular to Figs 2 and 3 the first primary cylinder 11 slidingly supports a piston 11P which is connected to a first throw 111 of a three throw flat plane crankshaft 40 by a connecting rod lic. The connecting rod iic is rotatably connected to the piston liP via a little end bearing liE and gudgeon pin hG and is rotatably connected to the first throw (crank pin) liT of the crankshaft 40 by a big end bearing liD.

The second primary cylinder 13 slidingly supports a piston i3P which is connected to a third throw 131 of the three throw flat plane crankshaft 40 by a connecting rod 13C. The connecting rod 130 is rotatably connected to the piston i3P via a little end bearing 13E and gudgeon pin 13G and is rotatably connected to the first throw (crank pin) 131 of the crankshaft 40 by a big end bearing 13D.

The secondary cylinder 12 slidingly supports a piston 12P which is connected to a second throw 121 of the three throw flat plane crankshaft 40 by a connecting rod 120. The connecting rod 120 is rotatably connected to the piston 12P via a little end bearing 12E and gudgeon pin 12G and is rotatably connected to the first throw (crank pin) 12T of the crankshaft 40 by a big end bearing 12D.

The secondary cylinder 12 is interposed between the two outer primary cylinders 11, 13. The secondary cylinder 12 may be of the same capacity as the two primary cylinders 11, 13 or may be of a different capacity due either to a different bore diameter or to a different stroke or a combination of these, however in the example being described all three cylinders 11, 12 and 13 are of the same capacity and the bore and stroke is the same for all three cylinders 11, 12 and 13.

Each of the cylinders 11, 12 and 13 has a respective inlet and exhaust valve ha, llb; l2a, 12b; 13a, l3b however it will be appreciated that in practice there may be a different number of inlet and exhaust valves for example two inlet and two exhaust or three inlet and two exhaust.

Furthermore it is possible for the secondary cylinder 12 to have a different number of inlet valves and exhaust valves than the primary cylinders 11, 13.

In this case the inlet and exhaust valves are operated by the electronically controlled variable valve actuation mechanism 14 so that the opening and closing of the valves ha, llb; l2a, 12b; 13a, 13b can be controlled and, in particular, can be controlled to disable the inlet and exhaust valves 12a, 12b of the secondary cylinder 12 so that they remain closed when the secondary cylinder 12 is deactivated. Various mechanisms to achieve such disabling are known, see for example and without limitation, GB patent -10 -publications 2,319,300, 2,447,111 and 2,454,314 and US Patent publication 6,805,079.

The crankshaft 40 is rotatable about a central axis 42 and is suppcrted in this case by four main bearings 43. As best seen in Fig.3 the throws UT, 13T for the two primary cylinders 11, 13 are arranged in phase with cne ancther and the throw 121 for the secondary cylinder 12 is arranged or orientated so as to be out of phase by an angle B with respect to the throw liT, 131 for the two primary cylinders 11, 13. The angle 8 is an angle of 180 degrees so that the throws 111 and 131 for the primary cylinders 11, 13 can be said to be 180 degrees out of phase to the throw 121 for the secondary cylinder 12. The effect of this is that whenever the pistons liP, l3P of the primary cylinders 11, 13 are at top dead centre, the piston 12P of the secondary cylinder 12 is at bottom dead centre and vice-versa.

In this case the engine 5 is a four stroke diesel engine and the means for deactivating the secondary cylinder 12 is the shutting off or termination of the fuel supply to the secondary cylinder 12. In addition, the inlet and exhaust valves 12a, 12b are both disabled by the electronic controller 30 via commands sent to the electronically controlled variable valve actuation mechanism 14. The closing of the inlet and exhaust valves i2a, 12b has the advantage that pumping losses are reduced while the secondary cylinder 12 is deactivated. It will however be appreciated that in other embodiments no means for disabling the inlet and exhaust valves 12a, l2b may be provided so that they operate normally during deactivation. It will also be appreciated that other valve operating arrangements could be provided so that, for example, only the inlet valve is kept closed or only the exhaust valve is kept closed during deactivation of the secondary cylinder 12.

-11 -It will be appreciated that if the engine 5 were a spark ignited engine then both the ignition and the fuel supply to the secondary cylinder 12 may be cut during deactivation cr the ignition may be kept in a normal operating state with only the fuel supply being cut-off.

Operation of the engine system 1 is as follows, when a high torque output is required from the engine 5 the electronic controller 30 is cperable to operate the engine 5 in a three cylinder operating mode with all three cylinders 11, 12 and 13 operating. The determination of what constitutes a high tcrque output is in this case the engine torque demanded by an cperator of the engine 5 based upon the input received by the electronic controller 30 from the accelerator pedal position sensor 32. It will however be appreciated that it could also or alternatively be an engine torque demand from a cruise control system.

In one example the output from the accelerator pedal position sensor 32 varies between 0.OV and 4.2V and, after signal conditioning, the 0.OV output corresponds to a 0% accelerator pedal position indicating that the operator is not depressing the accelerator pedal 15 and the 4.2V output corresponds to a 100% accelerator pedal position indicating that the accelerator pedal 15 has been fully depressed by the operator. In will be appreciated that these accelerator pedal positions may directly relate to demanded engine torque or there may be a non-linear relationship between accelerator pedal position and demanded engine torque.

With such an arrangement, if the output from the accelerator pedal position sensor 32 indicates that the operator is depressing the accelerator pedal 15 more than a predefined amount, which corresponds to a predefined engine torque demand limit, then operation using all three cylinders 11, 12 and 13 is selected. Tf the accelerator pedal 15 is depressed less than this predefined amount, then -12 -operation using only the two primary cylinders 11, 13 is selected and the secondary cylinder 12 is deactivated. In the case of deactivation this is effected by the electronic controller 30 acting to cut off the supply of fuel tc the secondary cylinder 12 and controlling the valve actuation unit 14 to disable the inlet and exhaust valves 12a, 12b.

The exact value chosen for this predefined engine torgue demand limit will depend upon the exact configuration of the engine 5 and is chosen so that, if, as in this case, the engine 5 is fitted to the motor vehicle 50, the acceleration performance of the motor vehicle 50 is not severely affected by operating on two cylinders 11, 13 and also the need to operate all three cylinders 11, 12 and 13 as close as possible to their optimum efficiency. That is to say, operation is controlled so that the overall efficiency achieved by operating on two cylinders exceeds that obtainable if the engine 5 were to be operated on three cylinders -Figs.6A and 63 show two possible timing charts for the engine 5 the main difference between these timing charts is that in Fig.6A the timing of secondary cylinder 12 is 360 degrees different to that in Fig.6B. It will be appreciated that the actions listed in Figs. 6A and 6B for secondary cylinder 12 are those which occur when the secondary cylinder 12 is operating and the engine 5 is using all three cylinders 11, 12 and 13 to produce power.

It will also be noted that when the secondary cylinder 12 is deactivated the engine S operates as a conventional two cylinder engine with power being produce in alternate cycles from the two primary cylinders 11, 13. That is to say, each phase of operation of primary cylinder 11 is timed to occur 360 degrees from the same phase of operation in the other primary cylinder 13 and vice-versa. Therefore, every time one of the pistons liP, 13P in the primary cylinders -13 - 11, 13 traverses from top dead centre towards bottom dead centre power is produced from the engine 5. Therefore a power stroke occurs in one of the two primary cylinders 11, 13 for every crankshaft revolution. In addition, a power stroke of the secondary cylinder 12 never occurs at the same time as a power stroke in either of the two primary cylinders 11, 13.

Therefore by selectively deactivating the secondary cylinder 12 it is possible to operate the engine 5 closer to is maximum efficiency thereby reducing fuel consumption.

So far deactivation has been described as being effected based solely on demanded engine torque which in this case is inferred from accelerator pedal position however this need not be the case. For example, the rate of change of demanded engine torgue as indicated by accelerator pedal position could be used in combination with the predefined torque demand limit. In such a case, if the rate at which the accelerator pedal is being depressed is above a predefined limit, then, even if the actual engine torque demand is below the engine torque demand limit, the engine could be operated using all three cylinders 11, 12 and 13.

This could be achieved using logic such as, for example and without limitation:-If dTd > dTd-11 OR Id > Td11 then use three cylinders; Else use two cylinders Where: -dTd is the current rate of change of accelerator pedal position; dTd-111 is the limit for the rate of change of accelerator pedal position; -14 -Id is the current torque demand based upon accelerator pedal position; and IdLj-is the predefined torque demand limit.

It will be appreciated in the above logic equation that the rate of change of engine torque demand could alternatively be inferred from a rate of change of engine torgue demand from a cruise control system.

One advantage of using such a combination is that a sudden change in accelerator pedal position is indicative that the engine operator such as a driver of the motor vehicle 50 requires to rapidly increase torque production and therefore it is desirable to reflect this by using all three cylinders 11, 12 and 13 to operate even if the current level of engine torque demanded is below the predefined torque demand limit (TdJHmj-) . For example, in an overtaking manoeuvre, the accelerator pedal 15 may be moved rapidly from 15% depressed to 90% depressed but without the use of rate of change logic the secondary cylinder 12 would remain deactivated until the accelerator pedal 15 physically moves past the predefined engine torque demand limit. However by using rate of change logic the secondary cylinder 12 can be brought back into use as soon as a rate of change of accelerator pedal position exceeds the accelerator pedal rate of change limit (dTdt) thereby reducing the engine response time and anticipating the need for three cylinder operation.

Although the accelerator pedal position is referred to above as being a percentage demand it will be appreciated that this need not be the case and the operator torque demand could be derived based upon variations in output voltage from the accelerator pedal position sensor 32 or variations in output value if a digital position sensor is used.

-15 -It will be appreciated that transiticning between the deactivated and active states may not occur instantaneously the conditions for such transitioninq to occur are established. For example and without limitation, the secondary cylinder 12 may be reactivated when it enters its induction stoke and may only be deactivated at the end of an exhaust stroke.

Referring now to Fig.4 there is shown a first embodiment of a method of operating a three cylinder engine of the type and construction previously described.

The method starts in box 100 which in the case of a motor vehicle would be a key-on event. The method then advances to box 110 where it is checked whether the conditions for operating the engine 5 as a two cylinder engine are present. In its simplest form this test could be: Is Id < ? Where: -Id is the current torque demand based in this case upon accelerator pedal position; and is the predefined engine torque demand limit.

It will be appreciated that the engine torque demand could alternatively be an engine torque demand from a cruise control system.

If the current engine torque demand is lower than the predefined engine torque demand limit, the method advances to box 120 where the engine 5 is operated as a two cylinder engine with the secondary cylinder 12 deactivated by in this case the electronic controller 30 cutting off the supply of diesel fuel to the secondary cylinder 12 and disabling the -16 -inlet and exhaust valves 12a, 12b for the secondary cylinder 12 by means of the electronically controlled variable valve actuation mechanism 14. The method then advances from box to box 140 where it is determined whether a key-off event has occurred and, if it has, the method terminates in box 150 but, if a key-off event has not occurred, the method cycles back to box 110. The method will continue to cycle through boxes 110, 120 and 140 while the conditions for two cylinder operation remain and a key-off event has not occurred.

Referring back to box 110, if the current engine torque demand is greater than the predefined engine torque demand limit, the method advances to box 130 where the engine 5 is operated as a three cylinder engine 5 with all three cylinders 11, 12 and 13 operating. The method then advances from box 130 to box 140 where it is determined whether a key-off event has occurred and, if it has, the method terminates in box 150 but, if a key-off event has not occurred, the method cycles back to box 110. The method will continue to cycle through boxes 110, 130 and 140 while the conditions for three cylinder operation remain and a key-off event has not occurred.

As an alternative to the simple test described above in relation to box 110 the test could alternatively take the form: -If dTd > dTdr1jL OR Id > Td11 then use three cylinders; Else use two cylinders Where: -dTd is in this case the current rate of change of accelerator pedal position; -17 -dTdj1i is the limit for the rate of change of accelerator pedal position; Id is in this case the current engine torque demand based upon accelerator pedal position; and is the predefined engine torque demand limit.

It will be appreciated that the rate of change could alternatively be a rate of change of torque demand from a cruise control system.

If such a test is used then the result from box 110 would be to advance to box 120 if the current rate of change of accelerator pedal position is lower than the limit for the rate of change of accelerator pedal position and the current torque demand based upon accelerator pedal position is less than the predefined torque demand limit but to advance to box 130 if either the current rate of change of accelerator pedal position is greater than the limit for the rate of change of accelerator pedal position or the current engine torque demand based upon accelerator pedal position is greater than the predefined engine torque demand limit.

The method is otherwise unaffected by this change to the test in box 110.

It will be appreciated that the predefined engine torque demand limit could be varied based upon other operating conditions of the engine 5 and so is not necessarily a fixed value. For example and without limitation the value of the predefined torque demand limit could be varied with engine speed so that the limit is increased as the engine speed increases.

Referring now to Figs.5A and 5B there is shown a second embodiment of a method according to the invention.

-18 -The method starts in box 200 which in the case of a motor vehicle would be a key-on event. The method then advances to box 205 where it is determined whether heating is required. This test can be for example whether the temperature of the exhaust gases needs to be increased to speed up light-off of one or more aftertreatment devices or whether the temperature of lubricating oil flowing through the engine 5 needs to be increased to reduce its viscosity thereby reducing friction losses or whether the temperature of a coolant flowing through the engine 5 to cool it needs to be increased after say a cold start or a combination of these.

In either case the test will take the form of a comparison using the electronic controller 30 of a current temperature as sensed by, for example, the exhaust gas temperature sensor 33 with a predefined temperature limit such as an aftertreatment light-off temperature. If the exhaust gas temperature is above the light-off temperature then the test would be failed and the method would advance to box 210 and if the test is passed, indicating that the current exhaust gas temperature is below the predefined temperature limit and heating is required, the method advances to box 207.

Dealing first with a failure of the test in box 205 and the consequential advancing of the method to box 210 then in box 210 it is checked whether the conditions for operating the engine 5 as & two cylinder engine are present. This test is the same test as applied in box 110 on Fig.4 and will not be described again in detail.

If the current engine torque demand is lower than the predefined engine torgue demand limit, the method advances to box 220 where the engine 5 is operated as a two cylinder engine with the secondary cylinder 12 deactivated. The method then advances from box 220 to box 240 where it is -19 -determined whether a key-off event has occurred and if it has the method terminates in box 250 but, if a key-off event has not occurred, the method cycles back to box 205. The method will continue to cycle through boxes 205, 210, 220 and 240 while no heating is required, the conditions for two cylinder operation remain and a key-off event has not occurred.

Referring back to box 210, if the current engine torque demand is greater than the predefined engine torque demand limit, the method advances to box 230 where the engine 5 is operated as a three cylinder engine 5 with all three cylinders 11, 12 and 13 operating. The method then advances from box 230 to box 240 where it is determined whether a key-off event has occurred. If a key-off event has occurred the method terminates in box 250 but, if a key-off event has not occurred, the method cycles back to box 205. The method will continue to cycle through boxes 205, 210, 230 and 240 while no heating is required, the conditions for three cylinder operation remain and a key-off event has not occurred.

As described with respect to box 110 on Fig.4 the test in box 210 could include a test for rate of change of engine torgue demand as inferred by the rate of change of accelerator position.

Referring back now to box 205, if the test in box 205 is passed indicating that heating is required then the method advances via box 207 to box 215.

In box 215 it is checked whether the conditions for operating the engine 5 as a two cylinder engine are present.

This test is similar to the test as applied in box 210 but the value of predefined engine torque limit could be different. That is to say, the fuel efficiency of the engine 5 may be temporarily compromised in order to reduce -20 -the time needed to light-off the aftertreatment device or devices.

It will be appreciated that in the case of a three cylinder engine having cylinders of identical capacity when operating on two cylinders for the same power output, the airflow is reduced by one third but the heat rejected is the same and so the temperature of the exhaust gas is increased.

If the current engine torque demand is lower than the second predefined engine torque demand limit, the method advances from box 215 to box 225 where the engine 5 is operated as a two cylinder engine with the secondary cylinder 12 deactivated. The method then advances from box 225 to box 238 and then on to box 240 where it is determined whether a key-off event has occurred. If a key-off event has occurred the method terminates in box 250 and, if a key-off event has not occurred, the method cycles back to box 205. The method will continue to cycle through boxes 205, 207, 215, 225, 238 and 240 while heating is required, the conditions for two cylinder operation remain and a key-off event has not occurred.

Referring back to box 215, if the current engine torgue demand is greater than the second predefined engine torgue demand limit, the method advances to box 235 where the engine 5 is operated as a three cylinder engine 5 with all three cylinders 11, 12 and 13 operating. The method then advances from box 235 to box 238 and from box 238 to box 240 where it is determined whether a key-off event has occurred.

If a key-off event has occurred the method terminates in box 250 and, if a key-off event has not occurred, the method cycles back to box 205. The method will continue to cycle through boxes 205, 207, 215, 235, 238 and 240 while heating is required, the conditions for three cylinder operation remain and a key-off event has not occurred.

-21 -Therefore in summary the invention provides an engine, an engine system and a method that enables a three cylinder engine to be operated as a three cylinder engine or selectively as a two cylinder engine. The use of a flat plane crankshaft enables the engine to be produced more economically and the selective deactivation of one of the cylinders enables the engine to be operated more efficiently thereby reducing fuel usage and can also be used to promote rapid warm-up of for example the exhaust gas, coolant flowing through the engine and lubricating oil flowing through the engine. Because operating the engine on two cylinders compared to three cylinders moves the load point for the operating cylinders and reduces the mass gas flow proportionately, emission production such as soot, HO and CO can be optimised thereby potentially reducing these emissions from the engine.

It will be appreciated that the electronic controller could be responsive to both an operator torque demand and a cruise control system torques demand.

It will also be appreciated that the electronic controller 30 could be arranged to deactivate the secondary cylinder 12 when an aftertreatment regeneration event is occurring in order to assist with elevating the temperature of the exhaust gas exiting the engine 5.

Although the engine has been described with respect to a diesel three cylinder engine it will be appreciated that it could be applied to a three cylinder spark ignition engine. It will also be appreciated that the invention could be applied to a two stoke engine.

It will be appreciated that the fuelling and valve timing for the deactivatable cylinder need not necessarily be the same as that for the primary working cylinders.

-22 -By using the cylinder timing described a smoother flow of power is produced because the secondary cylinder produces power out of phase to the two primary cylinders.

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.