GB2432900A

GB2432900A - A cooler having a valve to control the amount of cooling

Info

Publication number: GB2432900A
Application number: GB0524690A
Authority: GB
Inventors: Roy Clissold; Jon Edward Caine; Marcus Timothy Davies; Duncan James Kay
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2005-12-02
Filing date: 2005-12-02
Publication date: 2007-06-06
Also published as: GB0524690D0; GB2432901B; GB2432901A; GB0621302D0

Abstract

A cooler 11 for cooling a fluid comprises an inlet 28, an outlet 31 and at least one passage 30 for the fluid, at least one coolant passage 32 through which a coolant passes for heat transfer with the at least one passage 30 for the fluid, and a butterfly valve 25 moveable between a direct flow position (fig 4) whereby a minimum resistance is exhibited to the flow of the fluid from the inlet 28 to the outlet 31 and substantially no fluid flows through the at least one passage 20 for the fluid, and a transfer position (fig 5) whereby all of the fluid in the cooler 11 is diverted through the at least one passage 20 for the fluid before flowing out of the outlet 31. The fluid may be exhaust from an engine (5, fig 1) and the cooler 11 may be used in an air conditioning system or as an oil cooler. The at least one passage 30 for the fluid and coolant passage 32 may be C-shaped (figs 7 and 8) and comprise of plates stacked together. Cooler 11 may be combined into a single unit with an emission control device (12) after the cooler 11 or before the cooler 11 and combined with a further emission control device (figs 9 and 10, 12B). Emission control device 12 may be a catalytic converter (12A) or NOx trap (12B).

Description

An Exhaust Gas Cooler for an Engine This invention relates to heat

exchangers and in particular to an exhaust gas cooler for an internal combustion engine.

It is known to provide an internal combustion engine that can be operated in more than one combustion mode such as, a lean combustion mode, a stoichiometric combustion mode and a rich combustion mode.

To reduce emission from such an engine it is known to use one or more emission control devices to reduce the emissions from the engine. A three way catalyst is an emission control device used when the combustion is stoichiometric or rich but such a catalyst is not effective for converting NOx when the engine is operating in the lean combustion mode and so an emission control device in the form of a lean NOx trap is normally also used for these periods of lean combustion.

Such emission control devices require a minimum exhaust gas temperature in order to begin functioning efficiently and this temperature is often referred to as the light-off temperature of the device. It is desirable for an emission control device to reach this light-off temperature as soon as possible after start-up of the engine so as to keep to a minimum the time period when the emission control device is not performing efficiently thereby reducing start-up emissions. It is therefore desirable to position an emission control device of this type as close as possible to an exhaust outlet from an engine so as to maximise the temperature of the exhaust gas entering the emission control device and reduce the time delay before the light-off temperature is reached. It is therefore becoming common practice to attach the emission control device directly to an exhaust manifold of the engine and such emission control devices are often referred to as direct or close coupled devices. However, the performance of such an emission control device will deteriorate rapidly if the temperature of the exhaust gasses passing through it is too high for too long a period of time.

It is known from, for example, GB-A-2337710 to provide an exhaust system for a lean burn engine having a lean NOx trap (LNT) and a heat exchanger located upstream of the lean NOx trap to control the temperature of the exhaust gases entering the lean NOx trap. Such an arrangement is advantageous because in order for the lean NOx trap to operate at peak efficiency the temperature of the gases passing through the trap must be maintained between 300 and 425 C.

It is an object of this invention to provide a heat exchanger that is of a compact design and is economical to manufacture.

According to a first aspect of the invention there is provided an exhaust gas cooler for connection to an exhaust gas flow from an internal combustion engine, the cooler comprising a cooler inlet through which in use exhaust gas enters the cooler and a cooler outlet from which in use exhaust gas flows out of the cooler, at least one coolant flow passage through which in use coolant flows, at least one exhaust gas transfer passage arranged for heat transfer with the at least one coolant flow passage and a butterfly valve moveable between a direct flow position in which exhaust gas flows directly from the cooler inlet to the cooler outlet with minimum resistance to flow and a transfer position in which all of the exhaust gas entering through the cooler inlet is diverted though the at least one exhaust gas transfer passage before flowing out via the cooler outlet wherein each exhaust gas transfer passage has a gas inlet through which diverted exhaust gas enters the exhaust gas transfer passage and a gas outlet from which cooled exhaust gas leaves the exhaust gas transfer passage and the gas inlet and outlet for each exhaust gas transfer passage are positioned the same distance from the cooler inlet so that, when the butterfly valve is positioned in the direct flow position, substantially no exhaust gas flows through the or each exhaust gas transfer passage.

Because the inlet to and outlet from each exhaust gas transfer passage is positioned the same distance from the cooler inlet there is no significant pressure differential between them and so there is no pressure gradient causing exhaust gas to enter the exhaust gas transfer passage when the butterfly valve is in the direct flow position. This has the advantage that no cooling of the exhaust gas will occur to the exhaust gas flowing through the exhaust gas cooler when the butterfly valve is in the direct flow position and so the maximum possible exhaust gas temperature will be maintained at the outlet from the exhaust gas cooler.

The exhaust gas cooler may have a plurality of exhaust gas transfer passages.

Preferably, the plurality of exhaust gas transfer passages provide parallel exhaust gas flow paths.

The exhaust gas cooler may have a plurality of coolant flow passages.

The coolant flow passages may be arranged in parallel between a common inlet and a common outlet.

The coolant flow passages may be connected to a common coolant inlet by an inlet plenum and may be connected to a common coolant return by an outlet plenum.

Advantageously, the butterfly valve may have a shaft supported by a bearing and the shaft may extend from the bearing to a head of the butterfly valve through a gap formed between the inlet and outlet plenums so as to minimise the temperature of the bearing.

This has the advantage that the bearing used for the butterfly valve can be manufactured from a material that is less resistant to high temperatures and so a less expensive material can be used.

The cooler may further comprise a cylindrical body supporting a C-shaped heat exchange unit defining the plurality of coolant flow passages and the plurality of exhaust gas transfer passages.

The cylindrical body may be attached to a cylindrical tube defining a substantially cylindrical central flow passage extending through the exhaust gas cooler and the butterfly valve may be rotatably mounted in the central flow passage.

The C-shaped heat exchange unit may be comprised of a number of C-shaped plates stacked together so as to define the plurality of coolant flow passages and the plurality of exhaust gas transfer passages.

This has the advantage that a very compact heat exchange unit can be produced.

All of the C-shaped plates may be identical to one another.

This has the advantage that the heat exchange unit can be manufactured in a very cost effective manner.

Each C-shaped plate may have a front surface in which is formed at least one depression and a rear surface and the plates may be secured together in pairs such that their respective front surfaces face one another so as to define therebetween at least one coolant flow passage and the pairs of plates may be stacked one against another so that the rear surface of one plate of one pair faces the rear surface of one plate of an adjacent pair so as to define therebetween at least one exhaust gas transfer passage.

A spacer may be provided between each pair of plates so as to space the facing rear surfaces apart to form the at least one exhaust gas transfer passage. The spacer may be formed by a lip extending outwardly from the rear surface of each plate around an outer circumferential edge of each plate.

The cooler outlet may be formed as a divergent nozzle.

According to a second aspect of the invention there is provided a combined emission control device and exhaust gas cooler assembly for connection to an exhaust gas flow from an internal combustion engine the assembly comprising an exhaust gas cooler in accordance with said first aspect of the invention and at least one emission control device wherein the at least one emission control device and the exhaust gas cooler are connected directly together so that they form a single unit.

The exhaust gas cooler may be arranged to receive in use a flow of gas from the engine and the emission control device is positioned downstream from the exhaust gas cooler, the emission control device having an inlet through which exhaust gas enters the emission control device from the exhaust gas cooler and an outlet from which treated exhaust gas flows to atmosphere wherein the emission control device is connected directly to the exhaust gas cooler so that they form a single unit.

This has the advantage that there is less heat loss between the exhaust gas cooler and the emission control device than is the case if separate units are used and the addition of an exhaust gas cooler enables the emission control device to be positioned very close to an exhaust outlet from the engine thereby reducing the time to light-off the emission control device.

The exhaust gas cooler may have a divergent nozzle outlet which co-operates directly with the inlet to the emission control device.

This has the advantage that the exhaust gas entering the emission control device is uniformly dispersed across the inlet to the emission control device rather than being concentrated in a small area.

The at least one emission control device may be one of a catalytic converter and a NOx trap.

Alternatively, there may be two emission control devices and an exhaust gas cooler formed as a single unit.

One emission control device may be positioned upstream from the exhaust gas cooler and one emission control device may be positioned downstream from the exhaust gas cooler.

Preferably a catalyst may be positioned upstream from the exhaust gas cooler and a lean NOx trap may be positioned downstream from the exhaust gas cooler.

According to a third aspect of the invention there is provided a fluid cooler for connection to a fluid flow requiring selective cooling, the cooler comprising a cooler inlet through which in use fluid enters the cooler and a cooler outlet from which in use fluid flows out of the cooler, at least one coolant flow passage through which in use coolant flows, at least one fluid transfer passage arranged for heat transfer with the at least one coolant flow passage and a butterfly valve moveable between a direct flow position in which fluid flows directly from the cooler inlet to the cooler outlet with minimum resistance to flow and a transfer position in which all of the fluid entering through the cooler inlet is diverted though the at least one fluid transfer passage before flowing out via the cooler outlet wherein each fluid transfer passage has a fluid inlet through which diverted fluid enters the fluid transfer passage and a fluid outlet from which cooled fluid leaves the fluid transfer passage and the fluid inlet and outlet for each fluid transfer passage are positioned the same distance from the cooler inlet so that, when the butterfly valve is positioned in the direct flow position, substantially no fluid flows through the or each fluid transfer passage.

Preferably, the fluid cooler may have a plurality of fluid transfer passages and may have a plurality of coolant flow passages. The coolant flow passages may be arranged in parallel between a common inlet and a common outlet.

The cooler may further comprises a cylindrical body supporting a C-shaped heat exchange unit defining the plurality of coolant flow passages and the plurality of fluid transfer passages.

The cylindrical body may be attached to a cylindrical tube defining a substantially cylindrical central flow passage extending through the fluid cooler and the butterfly valve may be rotatably mounted in the central flow passage.

Preferably, the C-shaped heat exchange unit may be comprised of a number of C-shaped plates stacked together so as to define the plurality of coolant flow passages and the plurality of fluid transfer passages.

Advantageously, all of the C-shaped plates may be identical to one another.

Each C-shaped plate may have a front surface in which is formed at least one depression and a rear surface and the plates may be secured together in pairs such that their respective front surfaces face one another so as to define therebetween at least one coolant flow passage and the pairs of plates may be stacked one against another so that the rear surface of one plate of one pair faces the rear surface of one plate of an adjacent pair so as to define therebetween at least one fluid transfer passage.

The invention will now be described by way of example with reference to the accompanying drawing of which:-Fig.1 shows an internal combustion engine having a combined emission control device and exhaust gas cooler according to a preferred embodiment of the invention; Fig.2 is a pictorial end view of the combined emission control device and cooler shown in Fig.1; Fig.3 is a pictorial side view of the combined emission control device and cooler shown in Fig.1 Fig.4 is a cross-section through an exhaust gas cooler forming part of the combined emission control device and exhaust gas cooler shown in Figs. 2 and 3 and shows a butterfly valve in a direct flow position; Fig.5 is a cross-section similar to Fig.4 but showing the butterfly valve in a transfer position; Fig.6 is a view similar to Fig.4 but showing only an upper half of the exhaust gas cooler; Fig.7 is a pictorial side view of the exhaust gas cooler shown in Figs.4 and 5 in a partially assembled state showing a coolant outlet plenum; Fig.8 is a pictorial side view of the exhaust gas cooler shown in Figs.4 and 5 in a partially assembled state showing the coolant outlet plenum and a coolant inlet plenum; Fig.9 is a schematic diagram of a second embodiment of a combined emission control device and exhaust gas cooler according to the invention; and Fig.lO is a schematic diagram of a third embodiment of a combined emission control device and exhaust gas cooler according to the invention.

With particular reference to Fig.l there is shown an internal combustion engine 5 having an exhaust manifold 6 to which is connected an exhaust pipe 7u leading to an inlet to a combined emission control device and cooler assembly 10.

The combined emission control device and cooler assembly 10 comprises of an emission control device 12 such a catalytic converter or NOx trap and an exhaust gas cooler 11 positioned upstream from the emission control device 12.

A second exhaust pipe 7d transfers exhaust gas from an outlet 13 of the emission control device 12 to atmosphere.

-10 -The exhaust gas cooler 11 includes a butterfly valve 25 (not shown on Fig.1) which is moveable between a direct flow position in which exhaust gas passes directly through the exhaust gas cooler 11 with no appreciable cooling and a transfer position in which all of the exhaust gas is cooled as will be described in more detail hereinafter. The butterfly valve 25 is rotated by an actuator mechanism including an electronically controlled actuator 9.

The electronically controlled actuator 9 is operably connected to an electronic control unit 8 which controls the positioning of the butterfly valve 25. A temperature sensor 4 is positioned at or near to an inlet to the emission control device 12 so as to measure the temperature of the exhaust gas entering the emission control device 12 and provides a signal indicative of the sensed temperature to the electronic control unit 8.

The electronic control unit 8 controls the positioning of the butterfly valve 25 based upon the signal received from the temperature sensor 4.

In an exemplary form of operation the electronic control unit 8 is operable to control the electronically controlled actuator 9 to move the butterfly valve 25 to the direct flow position when the signal from the temperature sensor 4 indicates that the temperature of the exhaust gas entering the emission control device 12 is below a first predetermined temperature. The first predetermined temperature may be the light-off temperature of the emission control device 12 or a temperature slightly above this temperature. It is a priority to reach light-off as quickly as possible in order to minimise emissions from the engine 5.

If the signal from the temperature sensor 4 indicates that the temperature of the exhaust gas entering the -11 -emission control device 12 is above a second higher predetermined temperature the electronic control unit 8 is operable to control the electronically controlled actuator 9 to move the butterfly valve 25 towards the transfer position s so as to reduce the temperature of the exhaust gas entering the emission control device 12 so as to bring the temperature back to the second predetermined temperature.

The second predetermined temperature is preferably a temperature where the emission control device 12 operates at or near to maximum efficiency without rapid temperature induced performance loss occurring. If the temperature falls below the second predetermined temperature then the electronic control unit 8 is operable to control the electronically controlled actuator 9 to move the butterfly valve 25 back towards the direct flow position so as to increase the temperature of the exhaust gas entering the emission control device 12. That is to say, the position of the butterfly valve 25 is controlled in a closed loop manner so as to maintain the temperature of the exhaust gas entering the emission control device 12 at or close to the second predetermined temperature whenever possible.

It will be appreciated that other forms of control are possible and that the invention is not limited to such closed loop temperature control.

It will also be appreciated that the electronic control unit 8 may be programmed to permit the temperature of the exhaust gas entering the emission control device 12 to exceed the second predetermined temperature in order to periodically regenerate the emission control device 12.

It will be further appreciated that the inlet to the exhaust gas cooler 11 could be connected directly to the exhaust manifold 6 of the engine 5 without the need for the exhaust pipe 7u. In this case the combined emission control -12 -device and exhaust gas cooler assembly 10 would be direct or close coupled to the engine 5.

With particular reference to Figs.2 to 6 the combined emission control device and exhaust gas cooler assembly 10 is shown in greater detail.

The combined emission control device and exhaust gas cooler assembly 10 has a cast cylindrical outer body 26 which is connected to a longitudinally extending central cylindrical tube 15 by a cooler outlet 27. The central cylindrical tube 15 and the cooler outlet 27 are both formed as an integral part with the body 26 and an end cap 16 is fastened to one end of the cylindrical body 26 and to the cylindrical tube 15 so as to form an enclosure for a C-shaped heat exchange unit. The cylindrical tube 15 defines a substantially cylindrical central flow passage extending through the exhaust gas cooler and the butterfly valve 25 is rotatably mounted in the central flow passage.

In this case the cooler outlet is in the form of a divergent nozzle 27 but it will be appreciated that the cylindrical tube could simply extend outwardly from the combined emission control device and exhaust gas cooler assembly 10 to form a cooler outlet.

An end portion of the cylindrical tube 15 forms a cooler inlet that is to say exhaust gas enters the combined emission control device and exhaust gas cooler assembly 10 through a free end of the cylindrical tube 15.

Exhaust gas can selectively enter and leave the C-shaped heat exchange unit through two apertures 21 or ports formed in the cylindrical tube 15 positioned between the end cap 16 and the cooler outlet 27.

-13 -An advantage of using a divergent nozzle 27 is that the exhaust gas leaving the exhaust gas cooler 11 is able to spread out into a more uniform flow so as to be more uniformly distributed when it impinges against the brick or bricks forming part of the emission control device 12. This increases the efficiency of the emission control device 12 compared to the situation where a small diameter concentrated flow is supplied to a central portion of the first or inlet brick. This is because the full surface area of the brick is immediately utilised whereas with a concentrated flow arrangement there is often a dead zone around the perimeter of the first brick through which virtually no exhaust gas flows.

The C-shaped heat exchange unit is formed by a number of C-shaped plates 20 which are stacked together to define a plurality of exhaust gas transfer passages 30 and a plurality of coolant flow passages 32.

The C-shaped heat exchange unit defines a substantially cylindrical central flow passage extending through the exhaust gas cooler 11 and the butterfly valve 25 is rotatably mounted in the central flow passage. The central flow passage extends along a longitudinal axis X-X as shown on Fig.4.

The butterfly valve 25 has a shaft or spindle 23 supported by a bearing (not shown) located in a boss 18 formed on the body 26. The spindle 23 extends from the bearing to a head 24 of the butterfly valve 25 through a gap formed between a coolant inlet plenum 41 and a coolant outlet plenum 40 so as to minimise the temperature of the bearing. A lever 14 is attached to one end of the spindle 23 for use in connecting the spindle 23 to the electronically controlled actuator 9.

-14 -The coolant inlet plenum 41 has an inlet formed by a tube 17 which is connected in use to a source of coolant such as a cooling circuit of the engine 5 and the coolant outlet plenum 40 has an outlet formed by a tube 19 used to connect the coolant outlet plenum 40 to a return conduit to return coolant to the source from which the coolant is derived. In use coolant enters the coolant inlet plenum 41 through the tube 17 and flows from the coolant inlet plenum 41 through all of the coolant flow passages 32 in parallel to the coolant outlet plenum 40 and then back to the source of coolant via the tube 19.

With particular reference to Figs.6 to 8 the construction of the C-shaped heat exchange unit will now be described in more detail.

The C-shaped heat exchange unit comprises of a stack of identical plates 20. Each of the plates has a front surface in which is formed a depression 33 between in and outer circumferentially extending flanges 34, 36 and a rear surface from which extends a lip 35 around the outer periphery of each plate 20.

The plates 20 are secured together by brazing in pairs such that their respective front surfaces face one another so as to define therebetween a coolant flow passage 32.

That is to say the inner and outer circumferentially extending flanges 34, 36 abut one another and are brazed together and the two depressions 33 form in combination a single coolant flow passage 32. The pairs of plates 20 are stacked one against another so that the rear surface of one plate 20 of one pair faces the rear surface of one plate 20 of an adjacent pair so as to define therebetween an exhaust gas transfer passage 30. The two lips 35 abut against one another when the two pairs of plates abut one another and are brazed together to prevent exhaust gas leakage. The height of the lips 35 on the two abutting plates 20 is such -15 -that they act as a spacer separating the two rear surfaces to form an exhaust gas transfer passage 30 between the two adjacent rear surfaces. Such a stacked plate construction provides a heat exchange unit that is very compact and cost effective to manufacture and, in particular, the axial length of the heat exchange unit is relatively small.

Each of the exhaust gas transfer passages 30 has a gas inlet 28 and a gas outlet 31. The distance of the gas inlet 28 from the cooler inlet for each of the exhaust gas transfer passages 30 is the same as the distance of the gas outlet 31 from the cooler inlet so that there is substantially no pressure difference between the gas inlet 28 and the gas outlet 31 when the butterfly valve 25 is in the direct flow position. This means that no exhaust gas will flow through the exhaust gas transfer passages 30 when the butterfly valve 25 is in the direct flow position and so the maximum possible exhaust gas temperature will be produced at the cooler outlet 27. This is advantageous during engine start-up from cold as it will minimise the time taken for the emission control device 12 to reach its light-off temperature.

As can best be seen with reference to Fig.8 (in which only one plate 20 is shown) each of the plates 20 is fastened to the inlet and outlet plenums 41, 40 by brazing so as to form a fluid tight seal between the plenums 40, 41 and the coolant flow passages 32.

Operation of the exhaust gas cooler 11 is best understood with reference to Figs 4 and 5.

Fig.4 shows the butterfly valve 25 in the direct flow position. In this position the butterfly valve 25 is aligned with the exhaust gas flow entering the exhaust gas cooler 11 and produces virtually no resistance to flow.

Therefore when the butterfly valve 25 the exhaust gas is in -16 -this position the exhaust gas enters the exhaust gas cooler 11 through the cylindrical tube 15 and flows through the exhaust gas cooler 11 with no appreciable cooling to the cooler outlet 27 from where it enters the emission control device 12.

If it is desired to reduce the temperature of the exhaust gas exiting the exhaust gas cooler 11 the butterfly valve 25 is rotated (in this case in a clockwise direction) sO that it is no longer aligned with the flow of exhaust gas entering the exhaust gas cooler 11. The effect of this rotation is to produce a pressure differential between each gas inlet 28 and the corresponding gas outlet 31 thereby causing exhaust gas to begin flowing through the exhaust gas transfer passages 30 from the gas inlets 28 to the gas outlets 31. As exhaust gas passes through each of the exhaust gas transfer passages 30 it passes over the plates defining the exhaust gas transfer passage 30 which are cooled by the coolant flowing through the coolant flow passages 32. The exhaust gas is therefore cooled as it moves from the gas inlet 28 to the gas outlet 31. It will be appreciated that as shown and described the heat exchange unit is a contraflow unit in that the direction of flow of coolant is the opposite to the direction of flow of exhaust gas through the exhaust gas transfer passages 30 however this need not be the case and the coolant could be arranged to flow in the same direction as the exhaust gas.

The percentage of exhaust gas that passes through the exhaust gas transfer passages 30 depends upon the angle of the butterfly valve 25 to the direction of the exhaust gas entering the exhaust gas cooler 11 or more accurately to the magnitude of the pressure differential between each gas inlet 28 and gas outlet 31 produced by the inclined position of the butterfly valve 25.

-17 -One of the advantages of the heat exchange unit shown is that the exhaust gas transfer passages are arranged in parallel so that, when exhaust gas is diverted therethrough, a relatively large area gas flow passage is provided which minimises the back pressure upstream from the exhaust gas cooler 11.

When maximum cooling of the exhaust gas is required the butterfly valve 25 is moved to the transfer position shown in Fig.5 in which the butterfly valve 25 abuts against an inner wall of the cylindrical tube 15 and a cylindrical portion of the cooler outlet 27. In this position substantially all of the exhaust gas entering the exhaust gas cooler 11 through the cylindrical tube 15 as indicated by the arrow A' enters the gas inlets 28, as indicated by the arrow B', passes through the exhaust gas transfer passages 30, leaves the exhaust gas transfer passages 30 via the gas outlets 31, as indicated by the arrow D', and exits the exhaustgas cooler 11 via the cooler outlet 27, as indicated by the arrow E'.

It will therefore be appreciated that by varying the angle of rotation of the butterfly valve 25 a seamless and infinitely variable change in the proportion of exhaust gas being cooled can be produced between the limits of zero cooling and maximum cooling. The controllability of such a design is therefore very good which can be important particularly if the temperature of the emission control device has to be kept within relatively small limits as is the case with some formulations of NOx trap.

With reference to Fig.9 there is shown a second embodiment of a combined emission control device and exhaust gas cooler according to the invention. The construction of the combined emission control device and exhaust gas cooler is substantially as described above and so will not be described again in detail.

-18 -The primary difference with this embodiment compared to that previously described is that instead of the exhaust gas flowing through the exhaust gas cooler first and then into the emission control device the opposite arrangement is used. That is to exhaust gas enter an emission control device such as a catalyst 12A flows through the catalyst 12A and then flows into an exhaust gas cooler 11. As before the catalyst 12A and the exhaust gas cooler 11 are formed as a single unit so that the outlet from the catalyst 12A forms the inlet to the exhaust gas cooler 11 or the inlet to the exhaust gas cooler 11 forms the outlet from the catalyst 12A. The exhaust gas from the exhaust gas cooler 11 can then be fed to a further emission control device such as a lean NOx trap 12B which is very temperature sensitive.

With reference to Fig.1O there is shown a third embodiment of a combined emission control device and exhaust gas cooler according to the invention.

The construction of the exhaust gas cooler is as previously described and so will not be described again in detail.

In this embodiment the exhaust gas cooler 11 is combined in a single unit with two emission control devices 12A, 12B. That is to say exhaust gas from an engine enters the combined emission control device and exhaust gas cooler and passes first through an emission control device able to withstand relatively high temperatures such as a three way catalyst 12A and then passes into the exhaust gas cooler 11 where the exhaust gas is selectively cooled and then passes through a second emission control device that is temperature sensitive such as a lean NOx trap 12B before passing out to atmosphere. --,

-19 -It will be appreciated that a further embodiment is also possible in which the two emission control devices 12A, 12B are both positioned downstream from the exhaust gas cooler 11 in a single unit this embodiment is not shown.

Although the invention has been described so far in relation a preferred embodiment in which the exhaust gas cooler 11 and the emission control device 12 are attached directly to one another to form a single combined emission control device and exhaust gas cooler assembly it will be appreciated that the emission control device 12 and the exhaust gas cooler 11 could be separate self contained units connected together by a conduit or pipe. In this case the exhaust gas cooler 11 will be positioned upstream from the emission control device 12 and the outlet from the exhaust gas cooler 11 will be connected to the inlet to the emission control device 12. In this case the outlet from the exhaust gas cooler 11 may be formed by a cylindrical outlet pipe and need not be of a divergent nozzle form.

Therefore in summary, the design of the valve for an exhaust gas cooler is fundamental since it accounts for a large proportion of the overall cost of the device. The design described herein enables the valve spindle bearings to be kept cool using the coolant jacket at approximately 10000 and this results in a substantial cost saving over a design in which the bearings must be specified to be leak free at 900 C.

In addition, by using a butterfly valve, the actuation forces are dramatically lower than for a flap valve having a spindle at one edge because the exhaust gas forces that act against a top half of the butterfly valve are balanced to some degree by the forces that act against a lower half of the butterfly valve. This allows a lower power actuation system to be used which is both more compact and less expensive to produce.

-20 -Further the positioning of the gas inlets and gas outlets to the cooler matrix mean that as soon as the butterfly valve starts to move away from the horizontal or direct flow position, some flow is deflected through the cooler due to higher pressure in front of the valve face, and exits into a lower pressure region immediately behind the valve face. This results in a very controllable partial cooling mode in which the proportion of gas flowing through the cooler varies relatively linearly with the angle of the control valve. This is an important requirement for such a device since the amount of gas cooling required will be dictated by the limitations of the vehicle cooling system to which the exhaust gas cooler is connected. If fine control of temperature is not possible, either the vehicle cooling system will overheat or insufficient gas cooling will be provided.

Although the invention has thus far been described with respect to a preferred use for selectively cooling exhaust gas from an engine it will be appreciated that it could be applied to any other situation where heat exchange is required with minimum parasitic loss and a fluid flow requires selective cooling such as for example an air conditioning unit requiring cooled gas or an oil cooler in which hot oil needs to be cooled by coolant from an engine cooling circuit.

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

Claims

-21 -Claims 1. An exhaust gas cooler for connection to an exhaust gas

flow from an internal combustion engine, the cooler comprising a cooler inlet through which in use exhaust gas enters the cooler and a cooler outlet from which in use exhaust gas flows out of the cooler, at least one coolant flow passage through which in use coolant flows, at least one exhaust gas transfer passage arranged for heat transfer with the at least one coolant flow passage and a butterfly valve moveable between a direct flow position in which exhaust gas flows directly from the cooler inlet to the cooler outlet with minimum resistance to flow and a transfer position in which all of the exhaust gas entering through the cooler inlet is diverted though the at least one exhaust gas transfer passage before flowing out via the cooler outlet wherein each exhaust gas transfer passage has a gas inlet through which diverted exhaust gas enters the exhaust gas transfer passage and a gas outlet from which cooled exhaust gas leaves the exhaust gas transfer passage and the gas inlet and outlet for each exhaust gas transfer passage are positioned the same distance from the cooler inlet so that, when the butterfly valve is positioned in the direct flow position, substantially no exhaust gas flows through the or each exhaust gas transfer passage.

2. An exhaust gas cooler as claimed in claim 1 wherein the exhaust gas cooler has a plurality of exhaust gas transfer passages.

3. An exhaust gas cooler as claimed in claim 1 or in claim 2 wherein the exhaust gas cooler has a plurality of coolant flow passages.

4. An exhaust gas cooler as claimed in claim 3 wherein the coolant flow passages are arranged in parallel between a common inlet and a common outlet.

-22 - 5. An exhaust gas cooler as claimed in claim 3 when claim 3 dependent upon claim 2 or in claim 4 when claim 3 is dependent upon claim 2 wherein the cooler further comprises a cylindrical body supporting a C-shaped heat exchange unit defining the plurality of coolant flow passages and the plurality of exhaust gas transfer passages.

6. An exhaust gas cooler as claimed in claim 5 wherein the cylindrical body is attached to a cylindrical tube defining a substantially cylindrical central flow passage extending through the exhaust gas cooler and the butterfly valve is rotatably mounted in the central flow passage.

7. An exhaust gas cooler as claimed in claim 5 or in claim 6 wherein the C-shaped heat exchange unit is comprised of a number of C-shaped plates stacked together so as to define the plurality of coolant flow passages and the plurality of exhaust gas transfer passages.

8. An exhaust gas cooler as claimed in claim 7 wherein all of the C-shaped plates are identical to one another.

9. An exhaust gas cooler as claimed in claim 8 wherein each C-shaped plate has a front surface in which is formed at least one depression and a rear surface and the plates are secured together in pairs such that their respective front surfaces face one another so as to define therebetween at least one coolant flow passage and the pairs of plates are stacked one against another so that the rear surface of one plate of one pair faces the rear surface of one plate of an adjacent pair so as to define therebetween at least one exhaust gas transfer passage.

-23 - 10. A combined emission control device and exhaust gas cooler assembly for connection to an exhaust gas flow from an internal combustion engine the assembly comprising an exhaust gas cooler as claimed in any of claims 1 to 9 and at least one emission control device wherein the at least one emission control device and the exhaust gas cooler are connected together so that they form a single unit.

11. A combined emission control device and an exhaust gas cooler assembly as claimed in claim 10 wherein the exhaust gas cooler is arranged to receive in use a flow of gas from the engine and the an emission control device is positioned downstream from the exhaust gas cooler, the emission control device having an inlet through which exhaust gas enters the emission control device from the exhaust gas cooler and an outlet from which treated exhaust gas flows to atmosphere wherein the emission control device is connected directly to the exhaust gas cooler so that they form a single unit.

12. An assembly as claimed in claim 11 wherein the exhaust gas cooler has a divergent nozzle outlet which co-operates directly with the inlet to the emission control device.

13. An assembly as claimed in any of claims 10 to 12 wherein the at least one emission control device is one of a catalytic converter and a NOx trap.

14. An assembly as claimed in claim 10 wherein there are two emission control devices and an exhaust gas cooler formed as a single unit.

15. A fluid cooler for connection to a fluid flow requiring selective cooling, the cooler comprising a cooler inlet through which in use fluid enters the cooler and a cooler outlet from which in use fluid flows out of the -24 -cooler, at least one coolant flow passage through which in use coolant flows, at least one fluid transfer passage arranged for heat transfer with the at least one coolant flow passage and a butterfly valve moveable between a direct flow position in which fluid flows directly from the cooler inlet to the cooler outlet with minimum resistance to flow and a transfer position in which all of the fluid entering through the cooler inlet is diverted though the at least one fluid transfer passage before flowing out via the cooler outlet wherein each fluid transfer passage has a fluid inlet through which diverted fluid enters the fluid transfer passage and a fluid outlet from which cooled fluid leaves the fluid transfer passage and the fluid inlet and outlet for each fluid transfer passage are positioned the same distance from the cooler inlet so that, when the butterfly valve is positioned in the direct flow position, substantially no fluid flows through the or each fluid transfer passage.

16. An exhaust gas cooler substantially as described herein with reference to the accompanying drawing.

17. A combined emission control device and cooler assembly substantially as described herein with reference to the accompanying drawing.

18. A gas cooler substantially as described herein with reference to the accompanying drawing.