GB2389918A

GB2389918A - De-activation of combustion chambers in a multi-combustion chamber i.c. engine

Info

Publication number: GB2389918A
Application number: GB0214413A
Authority: GB
Inventors: James William Griffith Turner; Ralph Purvis; Paul Anthony Birch; Simon James Hill
Original assignee: Lotus Cars Ltd
Current assignee: Lotus Cars Ltd
Priority date: 2002-06-21
Filing date: 2002-06-21
Publication date: 2003-12-24
Also published as: GB0214413D0; AU2003250373A1; WO2004001210A1

Abstract

A first throttle valve 17 controls flow of air to first combustion chambers 11,14 while a second throttle valve 18 controls flow of air to second combustion chambers 12,13. Fuel injectors 19,22 deliver fuel to the first combustion chambers 11,14 while second fuel injectors 20,2 1 deliver fuel to the second combustion chambers 12,13. Exhaust gas from the first combustion chambers 11,14 and the second combustion chambers 12,13 is passed through first and second catalytic converters 26,29, respectively. At high engine operating loads, fuel and air is supplied to all combustion chambers and both throttle valves 17,18 are effective. At low engine operating loads, the method comprises deactivating in turn the first combustion chambers 11,14 and then the second combustion chambers 12,13 in a cyclical fashion so that at any time during such operation some combustion chambers (11,14 or 12,13) are active while the other combustion chambers are deactivated by ceasing supply of fuel and opening wide the relevant throttle 17,18. The invention keeps the catalytic converters at their operating temperatures and is particularly applicable to V8 and V12 engines.

Description

- 1 2389918

A METHOD OF DE-ACTIVATING A MULTI-COMBUSTION CHAMBER

INTERNAL COMBUSTION ENGINE, A MULTI-COMBUSTION CHAMBER

INTERNAL COMBUSTION ENGINE OPERATING ACCORDING TO THE

METHOD, A CATALYTIC CONVERTER UNIT FOR THE MULTI

5 COMBUSTION CHAMBER ENGINE AND A METHOD OF MANUFACTURE

OF A CATALYTIC UNIT

The present invention relates to a method of de-activating a multicombustion chamber internal 10 combustion engine, to a multi-combustion chamber internal combustion engine operating according to the method, to a catalytic converter system for a multi combustion chamber (e.g. multicylinder) internal combustion engine and to a method of manufacture of a 15 catalytic converter unit.

It is known that at low load operating conditions it can be preferable to de-activate some cylinders of a multi-cylinder internal combustion engine, with the 20 remaining cylinders operating at higher loads. This improves the overall operating efficiency of the engine and reduces fuel consumption. Deactivation typically takes the form of closing all of the engine valves completely for a combustion chamber.

In a first aspect, the present invention provides a method of operating a multi-combustion chamber internal combustion engine comprising: using a first throttle valve to control flow of 30 air to a first combustion chamber; using a second throttle valve to control flow of air to a second combustion chamber; using a first fuel injector to deliver fuel to the first combustion chamber; 35 using a second fuel injector to deliver fuel to the second combustion chamber; passing gas expelled from the first combustion

2 - chamber through a first catalytic converter; passing gas expelled from the second combustion chamber through a second catalytic converter; at high operating loads of the engine supplying 5 fuel and air to both the first and second combustion chambers, combusting the supplied fuel and air in both the first and second combustion chambers and using both the first and second throttle valves to control flow of air to the first and second combustion 10 chambers; and at low operating loads of engine deactivating in turn the first combustion chamber and then the second combustion chamber in a cyclical fashion so that at any time during such operation one combustion chamber 15 is active and the other combustion chamber deactivated, with deactivation of a combustion chamber achieved by both stopping delivery of fuel to the combustion chamber by the relevant fuel injector and opening wide the relevant throttle for the combustion 20 chamber. Also in the first aspect, the present invention provides a method of operating a multi-combustion chamber internal combustion engine comprising: 25 using a first throttle valve to control flow of air to a first plurality of combustion chambers; using a second throttle valve to control flow of air to a second plurality of combustion chambers; using first fuel injection means to deliver fuel 30 to the first plurality of combustion chambers; using second fuel injection means to deliver fuel to the second plurality of combustion chambers; passing gas expelled from the first plurality of combustion chambers through a first catalytic 35 converter; passing gas expelled from the second plurality of combustion chambers through a second catalytic

converter; at high operating loads of the engine supplying fuel and air to both the first and second pluralities of combustion chambers, combusting the supplied fuel 5 and air in all of the first and second pluralities of combustion chambers and using both the first and second throttle valves to control flow of air to the first and second plurality of combustion chambers; and at low operating loads of the engine deactivating I 10 in turn the combustion chambers of a first plurality of combustion chambers and then the combustion chambers of the second plurality of combustion chambers in a cyclical fashion so that at any time during such operation the combustion chambers of one 15 plurality of combustion chambers are active and the -

combustion chambers of the other plurality of combustion chambers are deactivated, with deactivation of each plurality of combustion chambers being achieved by both stopping delivery of fuel to the -

20 combustion chambers by the relevant injection means and opening wide the relevant throttle valve for the combustion chambers.

In modern engines it is important to keep 25 catalytic converters at elevated operating -

temperatures in order to meet emissions requirements for the engines. The de-activated combustion chambers operated in the manner described above will have passing through them clean air which is not heated by 30 combustion. This air when passing through the exhaust -

system will have the effect of cooling the catalytic converter connected to the de-activated cylinders.

Eventually, the catalytic converter will cool below its operating temperature. The present invention 35 avoids this by de-activating different cylinders in the engine in accordance with a thermal management model in the engine management system.

4 - In a second aspect the present invention provides a multi-combustion chamber internal combustion engine operating according to a method as described above and comprising: -

5 at least first and second combustion chambers; at least first and second electronically con trolled throttle valves respectively controlling the flow of gas to the first and second combustion chambers; lo at least first and second electrically controlled fuel injectors for delivering fuel respectively for the first and second combustion chambers; an electronic engine management controller which controls operation of the throttle valves and the fuel 15 injectors; and -

a catalytic converter system comprising a first catalytic converter that receives gas expelled from the first combustion chamber and not from the second -

combustion chamber and a second catalytic converter -

20 which receives gas expelled from the second combustion chamber and not from the first combustion chamber.

In a third aspect the present invention provides -

a catalytic converter unit suitable for use in the 25 multi-combustion chamber internal combustion engine described above comprising a first inner catalytic converter arranged concentrically within an outer cat alytic converter, each capable of receiving a gas flow supplied independently thereto.

The catalytic converter unit described above is ideally suited to an engine operated by the method of the first aspect of the invention. The catalytic converter system is arranged so that the inner 35 catalytic converter of the concentric catalytic converters receives exhaust gases from the activated combustion chambers, whilst the outer catalytic

- 5 - converter receives the air passing through the deactivated cylinder, or vice versa. The inner catalytic converter is kept hot by the exhaust gases and heat from the inner catalytic converter will pass 5 into the outer catalytic converter to keep the outer catalytic converter hot, or vice versa. This may mean i that it is not necessary to cyclically switch between combustion chambers in order to keep both catalytic converters at operating temperature. At the least, it 10 will reduce the rate of cooling by each catalytic converter when each catalytic converter is connected to deactivated combustion chambers so that the limit for reactivating deactivated cylinders is increased.

15 In a further aspect of the invention there is provided a method of manufacture of a catalytic converter suitable for use in the catalytic converter system described above. The method comprises a method of manufacture comprising the steps of: 20 forming a catalytic converter block with a plurality of parallel passages extending therethrough all opening onto two spaced apart end faces of the block; machining a first end of the catalytic converter i 25 block to provide a recess therein with the recess being able to receive therein an end of a first pipe relaying gas to the catalytic converter unit; whereby: the manufactured unit is formed with an inner catalytic converter comprising the parallel passages 30 which open on to the recessed part of the first end face and an outer catalytic converter comprising the parallel passages which open on to the non-recessed part of the first end face, the first catalytic converter being able to receive gas only from the 35 first pipe and the second catalytic converter being able to receive gas only from a second pipe independent of the first pipe.

- 6 - Two preferred arrangements of multi-cylinder reciprocating piston internal combustion engines and catalytic converter systems according to the present invention will now be described with reference to the 5 accompanying drawings, in which: Figure 1 is a schematic representation of a first arrangement of a multi-cylinder internal combustion engine and catalytic converter system according to the invention; 10 Figure 2 is a schematic representation of a second arrangement of internal combustion engine and catalytic converter system according to the present invention; Figure 3 is a cross-section taken through the 15 lines A-A' shown in Figure 2, depicting the internal structure of a first embodiment of a catalytic converter block; and Figure 4 is a cross-section showing the internal structure of a second embodiment of a catalytic 20 converter block.

Turning first to Figure 1, there can be seen in the figure a multicylinder internal combustion engine 10 having cylinders 11, 12, 13 and 14. The flow of 25 air into the cylinders 11 and 14 through inlet runners 15 and 16 is controlled by an electronic butterfly valve 17 common to both cylinders 11 and 14. Flow of air into cylinders 12 and 13 is controlled by an electronic butterfly valve 18 common to both cylinders 30 12 and 13.

Each cylinder is provided with its own individual fuel injector and in Figure 1 there can be seen a fuel injector 19 for the cylinder 11, a fuel injector 20 35 for cylinder 12, a fuel injector 21 for cylinder 13 and a fuel injector 22 for cylinder 14. The operation of the fuel injectors 19, 20, 21 and 22 as well as the

f - 7 operation of the butterfly valves 17 and 18 are controlled by an electronic engine management controller 23. The fuel injectors could be port injectors or direct injectors. Also a single injector 5 could be used for a pair of cylinders, eg by locating two injectors one of each near the throttle valves 17,18.

Two exhaust runners 24 and 25 lead gas expelled 10 from the cylinders 11 and 14 to a catalytic converter 26 common to both the cylinder 11 and the cylinder 14.

Exhaust runners 27 and 28 lead gases expelled from the cylinders 12 and 13 to a catalytic converter 29 common to both of the cylinders 12 and 13.

Once the gases expelled from all of the cylinders have passed through the catalytic converters 26 and 29 they are then mixed together and are passed through a second stage catalytic converter 30.

An oxygen sensor 31 is provided upstream of the catalytic converter 29 to measure the oxygen content of the gases passing into the catalytic converter 29.

Similarly, an oxygen sensor 32 is provided upstream of 25 the catalytic converter 26 to measure the oxygen content of the gases passing into the catalytic converter 26. The feedback signals provided by these oxygen sensors will be used in a known manner by the engine management controller 23 to control the ratio 30 of fuel to air in the fuel/air charges delivered for combustion in the cylinders 11 to 14.

A third oxygen sensor 33 is provided downstream of the catalytic converters 26 and 29 but upstream of 35 the catalytic converter 30, in order to measure the oxygen content of the gases passing into the catalytic converter 30. This oxygen sensor 33 provides a

- 8 - feedback signal to the electronic engine management controller 23 which will enable the electronic engine management controller 23 to carry out diagnostic tests to check the adequate functioning of the catalytic 5 converters 26 and 29. The diagnostic tests will be carried out only when all the cylinders 11 to 14 are active. The engine 10 and the catalytic converter system 10 associated therewith are designed for use in a motor vehicle. When the engine is operated at high speeds and loads then all four cylinders 11 to 14 will be in active operation and the engine management system 23 will control the electronic throttles 17 and 18 in 15 tandem to control the amount of fresh air delivered to the cylinders 11 to 14, whilst also controlling the amount of fuel delivered to the cylinders by the injectors 19 to 22. The engine 10 will be operated in a standard manner, albeit that it is unusual to have 20 two throttle valves controlling the output of the engine rather than one.

At low loads the engine management system 23 will operate to deactivate two of the four cylinders, 25 leaving the remaining two in operation. This has the advantage of efficiency and fuel economy. It is sufficient to operate only two cylinders at low engine loads to provide the power output needed from the engine. By operating just two cylinders there is 30 inherent saving in fuel and reduced CO2 emissions, whilst at the same time the two cylinders in active operation will operate at higher loading than if they were two of four operating cylinders and the higher loading on the two active cylinders will mean more 35 efficient operation of each of the active cylinders.

The decision to deactivate cylinders will be

- 9 taken by the electronic engine management controller 23 having regards to a number of inputs including input indicative of a torque demanded by an operator; of the engine, eg a driver of a vehicle.

As shown in Figure 1, the cylinders 11 and 14 are deactivated. The cylinders 11 and 14 are deactivated by stopping the delivery of fuel to the cylinders by the injectors 19 and 22 and by opening wide open the 10 throttle valve 17. The engine management system 23 will control the injectors 19 and 22 and the throttle valve 17 in order to achieve this.

The deactivated cylinders 11 and 14 when 15 deactivated in the manner described above will simply L in each cycle draw in fresh air via the butterfly valve 17 and then expel fresh air to the catalytic converter 26. There will be no combustion in the cylinders 11 and 14.

In order to function properly, a catalytic converter must be maintained at an elevated operating temperature. When the engine 10 is operated at high loads then each of the cylinders 11 to 14 will expel 25 combusted gases at a high temperature and the high temperature of the combusted gases will keep at operating temperatures both of the catalytic I converters 29 and 26. However, when a pair of cylinders, e.g. 11 and 14, are deactivated the gas 30 expelled from each cylinder in each exhaust stroke will be fresh air at a temperature significantly below the temperature of combusted gases expelled from an active cylinder. This lower temperature fresh air will act to cool the relevant catalytic converter, e.g. the 35 catalytic converter 26 in the case of the cylinders 11 and 14. If the catalytic converter is allowed to cool below its operating temperature then when the

- 10 cylinders associated therewith are reactivated the catalytic converter will not function for a number of operating cycles and the engine will therefore have; unacceptable emissions to atmosphere.

To avoid the problem above in the present invention it is proposed that when the engine is operated at low loads, then the engine management controller 23 switches between pairs of cylinders, 10 first of all deactivating the pair of cylinders 11 and 14 and then deactivating the pair of cylinders 12 and 13 (whilst reactivating cylinders 11 and 14), then next deactivating the pair of cylinders 11 and 14 i (while reactivating cylinders 12 and 13), and so on.

15 The electronic engine management controller 23 will L switch between the pairs of cylinders by controlling i separately the fuel injectors 19 to 22 and by controlling independently the electronic throttle valves 17 and 18. It will decide when to switch 20 between the pairs of cylinders by using a catalyst thermal management model embedded in its software, which will enable the controller 23 to predict, using modelled behaviour, when a catalyst will cool below its operating temperature.

When deactivating a pair of cylinders, the engine management control system will move to wide open I throttle the throttle valve associated with the pair of cylinders whilst deactivating the fuel injectors 30 associated with the pair of cylinders so that no further fuel is delivered to the cylinders. When reactivating the pair of cylinders, the engine management controller 23 will bring back into operation a throttle valve previously held at wide 35 open throttle and will vary the throttle position to control the output of the engine. At the same time, the electronic engine management controller 23 will

( - 11 -

reactivate a pair of fuel injectors to recommence delivery of fuel.

Testing will be conducted of the characteristics 5 of the catalytic converters 26 and 29 so that it can be determined how quickly the catalytic converters 26, 29 fall below their operating temperatures when fresh air is passed through them. This information can be used to calibrate the model used in operation of the 10 controller 23 so that the controller 23 switches between the pairs of cylinders in a cyclical fashion at a frequency sufficient to ensure that neither the catalytic converter 26 nor the catalytic converter 29 is exposed to a throughput of fresh air (as opposed to 15 combusted gases) for a period of time sufficient to cool the catalytic converter below operating temperature. Figure 2 shows an evolution of the arrangement of 20 engine and catalytic converter shown in Figure 1.

Features common to both arrangements are given the same reference numerals and will not be separately described. The difference between the Figure 1 system and the Figure 2 system is that the in Figure 2 the 25 catalytic converters 26 and 29 are replaced by two concentric catalytic converters, an outer catalytic converter 126 and an inner catalytic converter 129.

In the preferred embodiment shown, the two 30 catalytic converters 126 and 129 are formed from a single catalytic converter block 130. A catalytic converter block when viewed in transverse cross section as shown in Figure 3 is a honeycomb arrangement of parallel passages each extending along 35 the length of the block. Gas passing through each one of the plurality of passages is kept separate from gas passing through the other passages. In the present

- 12 invention it is proposed that an end face of a catalytic converter block is machined to provide a recess. The recess is shown at 131 in Figure 2. A pipe 132 leading from the cylinders 12 and 13 will be 5 fitted in the recess 131 with a suitable seal 133 acting between the end of the pipe 132 and the catalytic converter block. In this way, a single catalytic converter block is effectively divided into two separate catalytic converters arranged 10 concentrically with each other. For illustration purposes only the passages in the catalytic converter block 130 through which gas expelled from the cylinders 12 and 13 passes are shaded in Figures 2 and 3. This shows that these passages are distinct and 15 separate from those passages in the catalytic converter block 130 through which passes gas expelled from the cylinders 11 and 14. In the manner described above, a single and standard catalytic converter block is converted into a pair of concentric catalytic 20 converters, 126 and 129, the inner catalytic converter 129 being totally surrounded by the outer concentric catalytic converter 126.

In Figure 2 the cylinders 11 and 14 are shown 25 deactivated and therefore fresh air passes through the outer catalytic converter 126, with a cooling effect.

Also as shown the cylinders 12 and 13 remain active and hot combusted gases are expelled through the inner catalytic converter 129. The combusted gases keep hot 30 the inner catalytic converter 129 and heat from the inner catalytic converter 129 will pass through the outer catalytic converter 126 and keep the outer catalytic converter 126 hot.

35 The heat exchange between the inner catalytic converter 129 and the outer catalytic converter 126 may be sufficient to keep the outer catalytic

- 13 converter 126 at or above its operating temperature.

In this case, it will not be necessary for the engine management controller 123 to switch between pairs of cylinders, deactivating first one pair, and then the 5 next. However, it is more likely that the arrangement shown will have the effect of slowing down the rate of cooling of each catalytic converter when it has passing therethrough clean air expelled from a pair of cylinders. This will mean that the rate of switching 10 between the pairs of cylinders can be reduced, with each pair of cylinders being deactivated for a longer time period before it is necessary to reactivate, with simultaneous deactivation of the other pair of cylinders. When the cylinders 12 and 13 are deactivated then hot exhaust gas will pass from the cylinders 11 and 14 through the outer catalytic converter 126 and heat from the outer catalytic converter 126 will pass to 20 the inner catalytic converter 129.

Whilst the arrangements described above are described with reference to a four-cylinder engine, the invention is applicable to any multi-cylinder 25 engine, having two or more cylinders.

Whilst the catalytic converter 30 shown in Figures 1 and 2 will be a three-way catalytic converter, during period of deactivation the gas 30 mixture it receives will be very rich in oxygen due to the passage of air through the deactivated cylinders.

Consequently during periods of deactivation the three-

way catalytic converter will in fact operate as an oxidation catalytic converter only.

During periods of cylinder deactivation, the engine management controller 23 will have regard only

- 14 to the oxygen sensor (31 or 32) upstream of the catalytic converter which receives combusted gases.

The signal provided by the other oxygen sensor will be; meaningless. Heated oxygen sensors are commonly used 5 and thus there will be no difficulties caused by cooling of the oxygen sensors during deactivation.

The engine management controller 23 will use the signal provided by the oxygen sensor 33 to determine lO the effectiveness of the catalytic converters only during periods when all four cylinders are activated.

Whilst above the machining of a catalytic converter block to provide two concentric catalytic 15 converters is described with reference to the use of the final product in an arrangement according to the invention, the machined catalytic converter block comprising two concentric catalytic converters could be of general utility. The machining operation 20 involved is not complex, because only one face of the block needs to be machined, the upstream face, whilst the downstream face is conventional.

The present invention has the advantage that the 25 existing engine can easily be adapted to provide for cylinder deactivation. The cylinder head and cylinder block and other components of the engine will remain standard, the present invention only requiring the attachment of a new inlet manifold and a new exhaust 30 system and two electronic throttles. It is envisaged that the existing engines could easily be adapted to implement the present invention.

It is envisaged that the present invention would 35 be particularly useful with a V8 or a V12 engine.

However, with certain configurations of engine it may be necessary to chance the firing order of the

- 15 cylinders during periods of deactivation, otherwise a false imbalance will result. Therefore it is within the ambit of the present invention to run two different firing orders, one for when the cylinders 5 are all active and a separate one for the period when some cylinders are deactivated.

The present invention is applicable in a turbo charged engine, but separate turbo chargers would be 10 needed for each set of cylinders, e.g. one turbo charger for the cylinders 11 and 12 and another turbo charger for the cylinders 13 and 14.

To minimise the effects noticed by a driver IS during change-over from full cylinder activation to deactivation of some of the cylinders, it is proposed that change-overs could be coincided with gear shifts.

Whilst above the invention has been described 20 with reference to a reciprocating piston internal combustion engine, the invention is also applicable to a Wankel engine, the Wankel engine having at least two rotors with an electronic throttle controlling the flow of air to each rotor.

Whilst above the catalytic converted unit 130 is shown with only two concentric catalytic converters 126, 129 the manufacturing method could be used to form a catalytic converter unit with a number of 30 different catalytic converters. This possibility is illustrated in Figure 4 in which it can be seen that an end face of a catalytic converter block is machined with a number of concentric recesses of differing depths to form a plurality of catalytic converters 35 120, 121, 122, 123, each of which is connected to an exhaust pipe individual thereto. Whilst above the example given is of a four cylinder engine in which

- 16 two pairs of cylinders are separately controlled, the invention could be used with e.g. an eight cylinder engine with four pairs of cylinders sequentially controlled by four throttles with four catalytic 5 converters provided concentrically as illustrated in Figure 4.

Claims

1. A method of operating a multi-combustion chamber internal combustion engine comprising: 5 using a first throttle valve to control flow of air to a first combustion chamber; using a second throttle valve to control flow of air to a second combustion chamber; using a first fuel injector to deliver fuel to 10 the first combustion chamber; using a second fuel injector to deliver fuel to the second combustion chamber; passing gas expelled from the first combustion chamber through a first catalytic converter; 15 passing gas expelled from the second combustion chamber through a second catalytic converter; at high operating loads of the engine supplying fuel and air to both the first and second combustion chambers, combusting the supplied fuel and air in both 20 the first and second combustion chambers and using both the first and second throttle valves to control flow of air to the first and second combustion chambers; and at low operating loads of engine deactivating in 25 turn the first combustion chamber and then the second combustion chamber in a cyclical fashion so that at any time during such operation one combustion chamber is active and the other combustion chamber deactivated, with deactivation of a combustion chamber 30 achieved by both stopping delivery of fuel to the combustion chamber by the relevant fuel injector and opening wide the relevant throttle for the combustion chamber.

- 18

2. A method of operating a multi-combustion chamber internal combustion engine comprising: using a first throttle valve to control flow of air to a first plurality of combustion chambers; 5 using a second throttle valve to control flow of air to a second plurality of combustion chambers; using first fuel injection means to deliver fuel to the first plurality of combustion chambers; using second fuel injection means to deliver fuel 10 to the second plurality of combustion chambers; passing gas expelled from the first plurality of combustion chambers through a first catalytic converter; passing gas expelled from the second plurality of 15 combustion chambers through a second catalytic converter; at high operating loads of the engine supplying fuel and air to both the first and second pluralities of combustion chambers, combusting the supplied fuel 20 and air in all of the first and second pluralities of combustion chambers and using both the first and second throttle valves to control flow of air to the first and second plurality of combustion chambers; and at low operating loads of the engine deactivating 25 in turn the combustion chambers of a first plurality of combustion chambers and then the combustion chambers of the second plurality of combustion chambers in a cyclical fashion so that at any time during such operation the combustion chambers of one 30 plurality of combustion chambers are active and the combustion chambers of the other plurality of combustion chambers are deactivated, with deactivation of each plurality of combustion chambers being achieved by both stopping delivery of fuel to the 35 combustion chambers by the relevant injectors and opening wide the relevant throttle valve for the combustion chambers.

- 19

3. A method as claimed in claim 2 wherein the first fuel injection means comprises a first plurality of fuel injectors, one for each of the first plurality of combustion chambers, and the second fuel injection 5 means comprises a second plurality of fuel injectors, one for each of the second plurality of combustion chambers.

4. A method as claimed in claim 2 wherein the first 10 fuel injection means comprises a first fuel injector common to the first plurality of combustion chambers and the second fuel injection means comprises a second fuel injector common to the second plurality of combustion chambers.

5. A method of operating a multi-combustion chamber internal combustion engine as claimed in any of claims 1 to 4, comprising additionally: mixing together the gas leaving the first 20 catalytic converter with the gas leaving the second catalytic converter; and passing the mixed gases through a third catalytic converter; wherein: the third catalytic converter is operated as a 25 three-way catalytic converter at high operating speeds and/or loads of the engine and as an oxidising catalytic converter at low operating speeds and/or loads of the engine.

30

6. A method of operating a multi-combustion chamber internal combustion engine as claimed in any one of the preceding claims comprising additionally: operating a first firing order for the combustion chambers at high operating loads of the engine; and 35 operating a second firing order for the combustion chambers different to the first firing order at low operating loads of the engine.

À 20

7. A multi-combustion chamber internal combustion engine operating according to a method as claimed in any one of the preceding claims and comprising: at least first and second combustion chambers; 5 at least first and second electronically controlled throttle valves respectively controlling the flow of gas to the first and second combustion chambers; at least first and second electrically controlled 10 fuel injectors for delivering fuel respectively for the first and second combustion chambers; an electronic engine management controller which controls operation of the throttle valves and the fuel injectors; and 15 a catalytic converter system comprising a first catalytic converter that receives gas expelled from the first combustion chamber and not from the second combustion chamber and a second catalytic converter which receives gas expelled from the second combustion 20 chamber and not from the first combustion chamber.

8. A multi-combustion chamber internal combustion engine as claimed in claim 7 comprising additionally: a first oxygen sensor which provides a signal 25 indicative of the oxygen content of the gas expelled from the first combustion chamber; and a second oxygen sensor which produces a signal indicative of the oxygen content of the gas expelled from the second combustion chamber; wherein: 30 the electronic engine management controller receives the signals produced by the first and second oxygen sensors and at high loads of the engine controls the amount of fuel delivered by the fuel injectors having regard to the signals of both of the 35 oxygen sensors and at low loads of the engine controls the amount of fuel delivered to the active combustion chamber(s) having regard only to the oxygen sensor

- 21 associated with the active combustion chamber(s).

9. A multi-combustion chamber internal combustion engine as claimed in claim 7 or claim 8 wherein the 5 first and second catalytic converters are arranged adjacent each other so that heat from one can pass therebetween.

10. A catalytic converter unit suitable for use in 10 the multi-combustion chamber internal combustion engine of claim 9 comprising a first inner catalytic converter arranged concentrically within an outer catalytic converter, each capable of receiving a gas flow supplied independently thereto.

11. A catalytic converter unit as claimed in claim 10 wherein each of the catalytic converters is cylindrical. 20

12. A catalytic converter unit as claimed in claim 10 or claim 11 wherein the first and second catalytic converters are formed integrally with one another.

13. A method of manufacture of the catalytic 25 converter unit of claim 12 comprising the steps of: forming a catalytic converter block with a plurality of parallel passages extending therethrough all opening onto two spaced apart end faces of the block; 30 machining a first end of the catalytic converter block to provide a recess therein with the recess being able to receive therein an end of a first pipe relaying gas to the catalytic converter unit; whereby: the manufactured unit is formed with an inner 35 catalytic converter comprising the parallel passages which open on to the recessed part of the first end face and an outer catalytic converter comprising the

- 22 parallel passages which open on to the non-recessed part of the first end face, the inner catalytic converter being able to receive gas only from the first pipe and the outer catalytic converter being 5 able to receive gas only from a second pipe independent of the first pipe.

14. A multi-combustion chamber internal combustion engine substantially as hereinbefore described with 10 reference to and as shown in the accompanying drawings.

15. A catalytic converter unit substantially as hereinbefore described with reference to and as shown 15 in the accompanying drawings.