GB2452920A

GB2452920A - Multi-cylinder Internal Combustion Engine with Cabin and De-activated Cylinder Heating using Coolant Flow

Info

Publication number: GB2452920A
Application number: GB0718189A
Authority: GB
Inventors: Darren Blake; Andrew Hawley Green; James William Griffith Turner
Original assignee: Lotus Cars Ltd
Current assignee: Lotus Cars Ltd
Priority date: 2007-09-18
Filing date: 2007-09-18
Publication date: 2009-03-25
Also published as: WO2009037453A2; GB0718189D0; WO2009037453A3

Abstract

The coolant of a multi-cylinder internal combustion engine may flow through two cylinder banks 11, 12 in series when one bank 11 is de-activated or through the two cylinder banks 11, 12 in parallel when both banks are active, the coolant also flowing through vehicle cabin heater 18. The flow may be controlled by electrical 3-way 14 and 2-way 15 valves. Coolant may flow only through the cylinder bank 12 and heater 18 whilst cylinder bank 11 is de-active, for example at start-up for rapid windscreen demisting and cabin warm-up. Series flow through both cylinder banks 11, 12 may be initiated when the coolant has reached a predetermined temperature, detected by sensor T1, warming up cylinder bank 11 before it is activated, or keeping it warm after it is de-activated. A thermostat 16 may be provided to bypass a cooling radiator 17 if the coolant is below a predefined temperature. The coolant may flow in series through the cylinders and cylinder heads of each block (figs 7-8) or through the cylinder heads alone. Starter catalysts may be provided on the exhaust outlet of cylinder bank 12 (fig 9).

Description

MULTI-CYLINDER INTERNAL COMBUSTION ENGINE

WITH CYLINDER DE-ACTIVATION.

The present invention relates to a multi-cylinder internal combustion engine with cylinder de-activation.

More specifically, the invention relates to a multi-cylinder engine which has its cylinders arranged in a plurality of banks and in which the cylinders in at least one bank can be de-activated whilst the cylinders in one or more of the other banks remain active.

It is known to de-activate one or more cylinders of an internal combustion engine. It is also known for large engines, such as a V12 engine, to arrange the 12 cylinders in two banks of 6 cylinders and to de-activate all the cylinders of one bank. Typically, it is desired to run the engine with the cylinders de-activated on start up and initial idle. However, this leads to difficulties in warming up the de-activated cylinders and also this leads to difficulties in achieving catalytic converter light-off.

Furthermore, during use the de-activated bank of cylinders cannot be allowed to cool below a certain temperature and so must be periodically activated. This limits the amount of time that the cylinders can be de-activated e.g. when the engine is in an automobile which is cruising.

The present invention provides a multi-cylinder internal combustion engine comprising: cylinders arranged in at least two banks; a cylinder de-activating system which can de-activate all cylinders of a first bank of cylinders; a cooling system for supplying exhaust to the banks of cylinders; wherein: the coolant system has: a first mode of operation when the first bank of S cylinders are de-activated in which first mode of operation coolant flows in series from pumping means sequentially through an active bank of cylinders, then through the de-activated bank of cylinders and then subsequently back to the pumping means; and a second mode of operation when the cylinders of the banks of cylinders are all active, in which second mode of operation coolant flows in parallel from the pumping mean through a first coolant path through the first bank of cylinders and through a second coolant path, independent of the first coolant path, through a second bank of cylinders.

The present invention provides an internal combustion engine in which the de-activated cylinders are warmed up whilst they are de-activated by control of the flow of coolant through the engine as a whole.

A preferred embodiment of the present invention will now be described with reference to the accompanying drawings in which: Figure 1 is a schematic illustration of an internal combustion engine according to the present invention having a plurality of cylinders arranged in banks, the figure in particular showing the arrangement of the cooling system of the engine; Figure 2 shows the engine of Figure 1 with its cooling system operating in a "start and initial warm-up" mode; Figure 3 shows the engine of Figures 1 and 2 in a "warming de-activated bank" mode; Figure 4 shows the internal combustion engine of Figures 1 to 3 in operation with a bank of cylinders de-activated and with coolant cooled by a radiator; Figure 5 shows the internal combustion engine of the previous Figures in a mode in which all cylinders are active and the coolant is below a thermostat threshold temperature; Figure 6 shows the internal combustion engine of the earlier Figures in a mode in which all the cylinders are active and the coolant is above the thermostat threshold temperature; Figure 7 is a schematic illustration of the flow of coolant through the cylinder block; Figure 8 is a schematic illustration of the flow of coolant through the cylinder head of the engine of Figures 1 to 6; and Figure 9 is a schematic illustration of the exhaust system of the engine of Figures 1 to 6.

Figure 1 illustrates an internal combustion engine which has 12 cylinders arranged in a V12 configuration of two banks of 6 cylinders, a left-hand bank 11 and a right-hand bank 12. The internal combustion engine is provided with cylinder de-activation. The internal combustion engine can be operated with the cylinders of the left-hand bank 11 de-activated, so that the engine runs only with the 6 cylinders of the right-hand bank 12 active.

Figure 1 shows the cooling system for the V12 engine which comprises a pump 13 to pump coolant around the cooling circuit. Flow of water around the cooling circuit is controlled by a 3-way valve 14 and a 2-way valve 15.

Furthermore, a thermostat 16 is included in the cooling circuit along with a radiator 17 and a heater 18, the heater comprising a heating matrix for heating air supplied to a cabin of a vehicle incorporating the engine.

The illustrated valves 14 and 15 are electrically-controlled valves and are controlled by an electronic control unit (not illustrated) . The electronic control unit receives a temperature signal from a temperature sensor 24 illustrated in Figure 1, which measures the temperature of coolant leaving the bank of cylinders 12.

Figure 2 shows the engine operating in a first "start and initial warm-up" operating mode, in which the valves 15 and 14 are both closed for a cold engine start. The Figure shows that on starting the coolant water flows solely around a loop comprising the bank of cylinders 12 and the heater 18. The water flcws around the pipes 20, 21 and 22, as shown by the arrow 23. The flow of water is driven by the water pump 13. The closed 3-way valve 14 prevents flow of coolant water from the bank 12 to the rest of the coolant system and the closed 2-way valve 15 forces all coolant flow from the pump 13 through the right-hand cylinder bank 12.

Since the cylinders of the left-hand cylinder bank 11 are de-activated, the load on the cylinders in the right-hand cylinder bank 12 is increased. This will lead to a rapid warm-up of the coolant flowing through the engine block 12 and the pipes 20,21,22 and 23; the fact that the volume of coolant in this part of the total coolant system is only a fraction of the total volume of coolant in the whole coolant system will also assist greatly. This rapid warm-up enables the heater 18 to provide de-misting of vehicle windscreens rapidly.

The temperature sensor 24 monitors the temperature of the coolant flow leaving the bank 12 of active cylinders and supplies a temperature signal to the ECU (not shown). When the ECU determines that the detected temperature has reached a first threshold (and therefore the bank 12 is warm), the ECU then controls the 3-way valve 14 to open to permit flow to the left-hand cylinder bank 11, as shown in Figure 3.

Figure 3 shows a mode of operation designed to warm the left-hand cylinder bank 11 with a series flow of coolant through the cylinder bank 12 and then through the cylinder bank 11. In Figure 3 it can be seen that the valve 14 allows flow of hot coolant through a small bore pipe 30 to a fluid conduit 31 and then through the cylinder bank 11, the fluid then flowing along a fluid conduit 32 and a conduit 33 to the thermostat 16. The thermostat 16 is closed because of the low coolant temperature reaching it and therefore the coolant flow bypasses the radiator 17 to flow through a bypass passage 34 and a conduit 35 back to the fluid conduit and the water pump 13. In this mode, the 2-way valve 15 remains closed so that all coolant leaving the water pump 13 flows into the active cylinder bank 12. In this way, the de-activated left-hand cylinder bank 11 is warmed and the temperature of the bank 11 increases progressively. If, in this mode, the temperature of the coolant leaving the de-activated bank 11 reaches the operating temperature of the thermostat 16 then the thermostat 16 can open to allow the coolant to flow via the radiator 17 back to the pump 13.

This is illustrated in Figure 4.

Figure 5 shows a situation in which the cylinders of the left-hand bank are activated by a demand for increased engine speed and power. In this mode, the 3-way valve 14 is controlled to allow flow of coolant from the cylinder bank 12 directly to the thermostat 16, bypassing the cylinder bank 11. The 2-way valve 15 has been opened to allow coolant flow directly from the water pump 13 to the cylinder bank 11, the fluid leaving the cylinder bank 11 then flowing on to the thermostat 16. Thus the cooling system works in a "parallel flow" mode with the coolant flowing from the water pump 13 in parallel through the two banks 11 and 12 on to the thermostat 16. As illustrated in Figure 5, the coolant reaching the thermostat 16 has not reached the operating temperature of the thermostat. Thus, the coolant passing through the thermostat 16 flows through the bypass passage 34 onto the coolant passage 35 and back to the water pump 13. When the temperature of the coolant reaching the thermostat 16 reaches the threshold temperature of the thermostat 16 then the thermostat will operate to channel the flow of coolant through the radiator 17 as can be seen in Figure 6, all of the coolant passing through the thermostat 16 then passing through the radiator 17 and on to the coolant passage 35, back to the water pump 13.

In each of the modes of operation of Figures 2, 3, 4 and 5 a percentage of the coolant flow leaving the cylinder bank 12 is diverted via the heater 18 to enable operation of the heater.

Should the engine be operating with both banks of cylinders active in the Figure 5 or Figure 6 mode and then it is desired to de-activate the cylinders of the left-hand bank 11, on de-activation of the cylinders the 2-way valve is closed and the 3-way valve 14 moved to assume the -position shown in Figures 3 and 4. In other words, the engine will move from the parallel flow of Figures 4 and 5 to the series flow of Figure 3. Hence, the left-hand bank of cylinders 11 will be kept warm by heat from the continuingly active right-hand bank 12 of cylinders. The temperature of the active right-hand bank 12 will rise slightly on transfer from parallel to series mode since there will be some heat loss from radiation from the left-hand bank 11. This will give a benefit of a reduction of friction at part-load and will keep warm the gases trapped in the cylinders of the left-hand bank 11. Keeping the trapped gases warmer for longer will be of benefit since any de-activation strategy will have to reactivate a bank of de-activated cylinders to keep the cylinders warm to a certain degree, in order that there is not an abrupt change when an engine moves from de-activated to fully activated operation.

By keeping the gas trapped in the cylinders in the bank 11 for a longer period the interval between re-activation can be increased, all other factors remaining constant. This has the benefit of increasing the duration of cylinder de-activation during a cruising mode of an automobile having the engine, for instance.

As illustrated, the engine has a single water pump 13, but this could be replaced with twin electric water pumps which would lead to very accurate control of temperature in each of the banks 11 and 12 (one electric water pump would be provided for each bank of cylinders). The water pump 13 illustrated could be itself a single electric water pump or could be a clutched mechanical pump.

The V12 engine will have elongate banks of cylinders.

This presents particular difficulties for cooling. In the preferred embodiment of engine according to the invention the flow of coolant through each bank will be as shown in Figures 8 and 9, which should be viewed together. Figure 8 shows the flow of coolant through the cylinder block and Figure 9 shows the flow of coolant through the cylinder head on top of the cylinder block. Water will flow through a feed gallery 50 on an exhaust side of the cylinder block.

Apertures will be provided to meter flow past the cylinders 51-55, the flow being illustrated by arrows 56-62. The coolant flows from the feed gallery 50 to a collection gallery 63 on an inlet side of the block and then on to a block thermostat 64. When the block thermostat is open the collected coolant will flow from the block thermostat 64 on to join with the flow of coolant through the cylinder head, this being indicated by the arrow 65. When the thermostat 64 is closed then all the coolant flow will be forced through the cylinder head cooling jacket.

The flow of coolant through the cylinder head is shown in Figure 8. The feed gallery 60 is illustrated on the exhaust side which receives coolant and then a collection gallery 61 is indicated on the intake manifold side of the engine. The coolant will flow from the feed gallery through the cylinder head water jacket to the collection gallery 61.

As mentioned above, when the thermostat 64 of the cylinder block is closed then all the flow through the bank of cylinders will be through the cylinder head. Once the thermostat 64 is opened then two-thirds of the flow through the cylinder bank will be through the cylinder head and one-third of the coolant flow will be through the cylinder block.

The cylinder coolant flow illustrated will give sufficient control to ensure tight control of the knock limit in the cylinders to the benefit of performance, economy and omissions.

Moving on to Figure 9, this Figure shows that the left-hand cylinder bank 11 is provided with two exhaust pipes 70 and 71 and that the right-hand cylinder bank 12 is provided with two exhaust pipes 72 and 73. Each of the exhaust pipes 70, 71 and 72 and 73 will collect combusted gases from three cylinders. These exhaust pipes converge at the main catalytic converter 74, from which exhaust gases flow to atmosphere via two exhaust pipes 75 and 76. A pair of starter catalysts 77 and 78 are provided one each in the exhaust pipes 72 and 73 of the right-hand cylinder bank 12.

No equivalent starter catalysts are provided for the lef t-hand bank 11.

It is envisaged that the start up strategy run for the engine will comprise an initial starting and "flaring" on all 12 cylinders in the two banks 11 and 12. This will put an initial charge of hot gas into the left-hand cylinder bank 11. After this initial "flaring" then the left-hand bank 11 will be de-activated and the engine will idle with only the right-hand bank 12 activated. The right-hand bank 12 will then run in isolation until there is light-off of the starter catalytic converters 77, 78 and then subsequently light-off of the main catalytic converter 7.

-10 -In the de-activated mode only 6 cylinders of the 12 cylinders are activated therefore hydrocarbon omissions are reduced by more than 50% compared with 12 cylinder idle operation. This results not only from the fact that half of the cylinders are de-activated but also because there is more complete combustion in the active cylinders, which have a higher load. Carbon monoxide production is reduced due to the reduced fuel flow and increased combustion temperature.

However, the higher loading can increase NOX production and therefore it is envisaged that the engine will be provided with exhaust gas recirculation. This can be achieved by control of the operation of the poppet valves of the cylinders, with early closing of the exhaust valves trapping cornbusted gases in the cylinder for mixing with the fresh charge of fuel and air to achieve hinternalfl exhaust gas recirculation. It is also possible that hydraulically actuated valves could be used to replace throttle in the intake system.

Once the main catalyst 74 has been fired then the engine can be operated with all 12 cylinders. The strategy described above permits the omission of starter catalysts for the left-hand bank 11 and this saves costs. The hotter gas temperature produced by the active bank of cylinders 12 after starting also makes it possible to respecify the nature of the starter catalysts 77 and 78 to reduce cost and/or makes it possible for the starter catalysts 77 and 78 to be positioned further away from the active cylinders, i.e further distanced along the exhaust pipes 72, 73, to the benefit of full load performance of the engine.

-11 -Whilst the preferred embodiment of the invention described above has been described with reference to a V12 engine, the invention is applicable to any engine in which an entire bank can be de-activated, such as V6 engines, V4 engines and V-twin engines and also flat-plane crank V8 and yb and V12 engines.

-12 -

1. A multi-cylinder internal combustion engine comprising: cylinders arranged in at least two banks; a cylinder de-activating system which can de-activate all cylinders of a first bank of cylinders; a cooling system for supplying coolant to the banks of cylinders; wherein: the coolant system has: a first mode of operation when the first bank of cylinders are de-activated, in which first mode of operation coolant flows in series from pumping means sequentially through an active bank of cylinders, the de-activated bank of cylinders and then subsequently back to the pumping means; and a second mode of operation when the cylinders of the banks of cylinders are all active, in which second mode of operation coolant flow in parallel from the pumping mean through a first coolant path through a first bank of cylinders and through a second coolant path, independent of the first coolant path, through a second bank of cylinders.

2. A multi-cylinder internal combustion engine as claimed in claim 1 comprising: an air heater in which air can be heated by the coolant for supplying to a vehicle cabin, wherein: the coolant system can have a third mode of operation when the first bank of cylinders is de-activated, in which third mode of operation coolant from the coolant pumping means flows through only one bank of cylinders, then through the air heater and back to the pumping means, bypassing the first cylinder bank.

-13 - 3. A multi-cylinder internal combustion engine as claimed in claim 1 or claim 2 which comprises a radiator for cooling the coolant and a thermostat for controlling flow of coolant through the radiator, wherein in the first and second modes of operation coolant flowing from the cylinder bank(s) flows to the thermostat and the thermostat controls whether the coolant flow through the radiator back to the pumping means or bypasses the radiator.

4. A multi-cylinder internal combustion engine as claimed in any one or claims 1 to 3, which comprise an electrically controlled 3-way valve and an electrically controlled 2-way valve, wherein: the 3-way valve is connected in a coolant flow path downstream of a/the bank of cylinders which remain(s) active when the first bank of cylinders is de-activated; the 2-way valve is connected between the pumping means and the first bank of cylinders; in the first mode of operation the 2-way valve is closed and prevents flow of coolant directly from the pumping means to the first bank of cylinders and the 3-way valve connects the active bank(s) of cylinders to the first bank of cylinders; and in the second mode of operation the 2-way valve is open to allow flow of coolant from the pumping means to the first bank of cylinders and the 3-way valve directs flow of coolant from the other bank(s) of cylinders to a coolant path which bypasses the first bank of cylinders.

5. A multi-cylinder internal combustion engine as claimed in claim 4 when dependent on claim 2 wherein:

--

in the third mode of operation the 3-way valve and the 2-way valve are both closed to prevent fluid flow therethrough.

6. A multi-cylinder internal combustion engine as claimed in claim 5 comprising an electronic controller for controlling the 2-way valve and the 3-way valve and a temperature sensor which measures temperature of coolant and provides a signal indicative thereof to the electronic controller, wherein: on starting of the engine the controller keeps the 2-way valve and the 3-way valve closed so the engine operates in the third operating condition; once the coolant reaches a first temperature threshold and when the first bank of cylinders is de-activated, then the controller controls the 3-way valve to connect the active cylinder bank(s) to the first cylinder bank whilst keeping the 2-way valve closed to prevent direct flow of coolant from the pumping means to the first bank of cylinders, whereby the first bank of cylinders is warmed; and when all cylinders are activated then the controller opens the 2-way valve to connect the pumping means to the first bank of cylinders while the 3-way valve is switched to connect the other bank(s) of cylinders to the thermostat, bypassing the first bank of cylinders.

7. A multi-cylinder internal combustion engine as claimed in any one of claims 4 to 6 wherein in the first mode of operation the 3-way valve connects the active bank(s) of cylinders to the first bank of cylinder(s) via a coolant passage which has a cross-sectional area less than the -15 -cross-sectional areas of the coolant passages connecting the pumping means to the banks of cylinders.

8. A multi-cylinder internal combustion engine as claimed in any one of the preceding claims wherein: each bank of cylinders has a cylinder head, a cylinder block, a feed gallery for coolant on an exhaust side of the bank and a collection gallery f or coolant on an inlet side of the bank; the cylinders in each bank are arranged in line along the cylinder block, which is elongate having a length greater than a width thereof; coolant flows across the width of each cylinder block and the matching cylinder head therefor from the feed gallery to the collection gallery.

9. A multi-cylinder internal combustion engine as claimed in claim 8 wherein a thermostat is connected to each collection gallery and controls flow of coolant through the respective cylinder block and below a selected threshold temperature the thermostat is closed and flow of coolant is solely through the cylinder head of the relevant bank of cylinders and above the selected threshold the thermostat opens and flow of coolant is through both the cylinder head and the cylinder block.

10. An internal combustion engine as claimed in any one of the preceding claims wherein: a first exhaust pipe connects the first bank of cylinders to a main catalytic converter; an exhaust pipe is provided for the/each other bank of cylinder(s) to connect the bank to the main catalytic -16 -converter independently of the first exhaust pipe, each such exhaust pipe being provided with a starter catalytic converter through which exhaust gas flows prior to reaching the main catalytic convert; and exhaust gas flowing through the first exhaust pipe flows from the first bank of cylinders to the main catalytic converter without passing through a starter catalytic converter.

l. An internal combustion engine substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

853749, AWP, Ct? 1\

Claims

Amendments to the claims have been filed as follows CLAIMS

1. A multi-cylinder internal combustion engine comprising: cylinders arranged in at least two banks; a cylinder de-activating system which can de-activate all cylinders of a first bank of cylinders; an air heater in which air can be heated by the coolant for supplying to a vehicle cabin; and a cooling system for supplying coolant to the banks of cylinders; wherein: the coolant system has: a first mode of operation when the first bank of cylinders are de-activated, in which first mode of operation: (1) coolant flows in series from pumping means sequentially through an active bank of cylinders, the de-activated bank of cylinders and then subsequently back to the pumping means; and (ii) at least some of the coolant leaving the active bank of cylinders is directed via the heater and *. then subsequently back to the pumping means; and a second mode of operation when the cylinders of the * banks of cylinders are all active, in which second mode of operation: .. 25 (i) coolant flows in parallel from the pumping * * * means through a first coolant path through a first bank * p of cylinders and through a second coolant path, independent of the first coolant path, through a second bank of cylinders; and (ii) at least some of the coolant leaving the active bank of cylinders is directed via the heater and then subsequently back to the pumping means.

2. A multi-cylinder internal combustion engine as claimed in claim 1 wherein: the coolant system can have a third mode of operation when the first bank of cylinders is de-activated, in which third mode of operation coolant from the coolant pumping means flows through only one bank of cylinders, then through the air heater and back to the pumping means, bypassing the first cylinder bank.

3. A multi-cylinder internal combustion engine as claimed in claim 1 or claim 2 which comprises a radiator for cooling the coolant and a thermostat for controlling flow of coolant through the radiator, wherein in the first and second modes of operation coolant flowing from the cylinder bank(s) flows to the thermostat and the thermostat controls whether the coolant flows through the radiator back to the pumping means or bypasses the radiator.

4. A multi-cylinder internal combustion engine as claimed in any one or claims 1 to 3, which comprise an electrically controlled 3-way valve and an electrically controlled 2-way * * S * valve, wherein: the 3-way valve is connected in a coolant flow path downstream of a/the bank of cylinders which remain(s) active * su * when the first bank of cylinders is de-activated; * p the 2-way valve is connected between the pumping means and the first bank of cylinders; in the first mode of operation the 2-way valve is closed and prevents flow of coolant directly from the pumping means to the first bank of cylinders and the 3-way valve connects the active bank(s) of cylinders to the first bank of cylinders; and in the second mode of operation the 2-way valve is open to allow flow of coolant from the pumping means to the first bank of cylinders and the 3-way valve directs flow of coolant from the other bank(s) of cylinders to a coolant path which bypasses the first bank of cylinders.

5. A multi-cylinder internal combustion engine as claimed in claim 4 when dependent on claim 2 wherein: in the third mode of operation the 3-way valve and the 2-way valve are both closed to prevent fluid flow therethrough.

6. A multi-cylinder internal combustion engine as claimed in claim 5 comprising an electronic controller for controlling the 2-way valve and the 3-way valve and a temperature sensor which measures temperature of coolant and provides a signal indicative thereof to the electronic . 20 controller, wherein: * .w on starting of the engine the controller keeps the 2-way valve and the 3-way valve closed so the engine operates *I*� * * * * in the third operating condition; once the coolant reaches a first temperature threshold *... 25 and when the first bank of cylinders is de-activated, then the controller controls the 3-way valve to connect the S.....

* active cylinder bank(s) to the first cylinder bank whilst keeping the 2-way valve closed to prevent direct flow of coolant from the pumping means to the first bank of cylinders, whereby the first bank of cylinders is warmed; and *tP when all cylinders are activated then the controller opens the 2-way valve to connect the pumping means to the first bank of cylinders while the 3-way valve is switched to connect the other bank(s) of cylinders to the thermostat, bypassing the first bank of cylinders.

7. A multi-cylinder internal combustion engine as claimed in any one of claims 4 to 6 wherein in the first mode of operation the 3-way valve connects the active bank(s) of cylinders to the first bank of cylinder(s) via a coolant passage which has a cross-sectional area less than the cross-sectional areas of the coolant passages connecting the pumping means to the banks of cylinders.

8. A multi-cylinder internal combustion engine as claimed in any one of the preceding claims wherein: each bank of cylinders has a cylinder head, a cylinder block, a feed gallery for coolant on an exhaust side of the bank and a collection gallery for coolant on an inlet side of the bank; the cylinders in each bank are arranged in line along *. the cylinder block, which is elongate having a length greater than a width thereof; S...

coolant flows across the width of each cylinder block * 25 and the matching cylinder head therefor from the feed *:*::* gallery to the collection gallery.

S *** * .

9. A multi-cylinder internal combustion engine as claimed in claim 8 wherein a thermostat is connected to each collection gallery and controls flow of coolant through the respective cylinder block and below a selected threshold temperature the thermostat is closed and flow of coolant is 2-" solely through the cylinder head of the relevant bank of cylinders and above the selected threshold the thermostat opens and flow of coolant is through both the cylinder head and the cylinder block.

10. An internal combustion engine as claimed in any one of the preceding claims wherein: a first exhaust pipe connects the first bank of cylinders to a main catalytic converter; an exhaust pipe is provided for the/each other bank of cylinder(s) to connect the bank to the main catalytic converter independently of the first exhaust pipe, each such exhaust pipe being provided with a starter catalytic converter through which exhaust gas flows prior to reaching the main catalytic convert; and exhaust gas flowing through the first exhaust pipe flows from the first bank of cylinders to the main catalytic converter without passing through a starter catalytic converter.

11. An internal combustion engine substantially as ****e hereinbefore described with reference to and as shown in the accompanying drawings. S.. * .. * S S * S.

S *