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 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 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; 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 ; 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 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 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 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.

Also in the 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 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 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 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 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 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 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 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 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 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 avoids this by de-activating different cylinders in the engine in accordance with a thermal management model in the engine management system.

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 : 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; 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 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 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 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 catalytic converter of the concentric catalytic converters receives exhaust gases from the activated combustion chambers, whilst the outer catalytic

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 into the outer catalytic converter to keep the outer catalytic converter hot, or vice versa. This may mean 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 will reduce the rate of cooling by each catalytic converter when each catalytic converter is connected to de-activated combustion chambers so that the limit for reactivating deactivated cylinders is increased.

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: 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 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 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 first pipe and the second catalytic converter being able to receive gas only from a second pipe independent of the first pipe.

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 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; 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 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 converter block.

Turning first to Figure 1, there can be seen in the figure a multi-cylinder internal combustion engine 10 having cylinders 11,12, 13 and 14. The flow of 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 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 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

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 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 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 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 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 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

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 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 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 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 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, 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 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 efficient operation of each of the active cylinders.

The decision to deactivate cylinders will be

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 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 deactivated in the manner described above will simply 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 combusted gases at a high temperature and the high temperature of the combusted gases will keep at operating temperatures both of the catalytic converters 29 and 26. However, when a pair of cylinders, e. g. 11 and 14, are deactivated the gas 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 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

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, 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 (while reactivating cylinders 12 and 13), and so on.

The electronic engine management controller 23 will switch between the pairs of cylinders by controlling separately the fuel injectors 19 to 22 and by controlling independently the electronic throttle valves 17 and 18. It will decide when to switch 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 throttle the throttle valve associated with the pair of cylinders whilst deactivating the fuel injectors 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 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

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

Testing will be conducted of the characteristics 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 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 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 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 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 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 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

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 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 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 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 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 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 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.

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

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 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 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 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 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 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

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 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 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 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 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 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 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 be particularly useful with a V8 or a V12 engine.

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

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 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 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 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 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 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 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

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 converters provided concentrically as illustrated in Figure 4.