Abstract:
An exhaust gas recirculation cooler, typically of the drawn cup design, with a bypass and control valve is disclosed. The control valve can direct a proportion of the exhaust gas to the cooler and a proportion to bypass the cooler depending on the input temperature of the exhaust gas and the required temperature of the exhaust gas. The proportion of the exhaust gas directed to the cooler/bypassing the cooler can be varied as required and so the temperature of the exhaust gas can be controlled. One benefit of certain embodiments of the invention is that engine damaging chemicals, such as sulphuric acid, which result from over-cooling the exhaust gas are reduced.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a cooler for use in an exhaust gas recirculation (EGR) system in an internal combustion engine and particularly to a bypass around said cooler. 
   2. Description of the Related Art 
   Emissions regulations are requiring reduced emissions from vehicles, particularly the Euro 5, Bin 5 and US 06 regulations. To reduce the generation of nitrous oxides, it is known to recirculate exhaust gas through the engine. Under normal conditions the exhaust gas must be cooled before recirculation and it is known to pass the exhaust gas through an exhaust gas cooler. However, under “cold start” or low operating conditions, the gas can be over-cooled resulting in increased hydrocarbon emission and CO 2  production. 
   SUMMARY OF THE INVENTION 
   Thus an object of the present invention is to recirculate exhaust gas without over-cooling. 
   According to a first aspect of the present invention there is provided an exhaust gas cooler comprising:
         an exhaust gas inlet;   an exhaust gas outlet;   at least one coolant channel arranged between the exhaust gas inlet and exhaust gas outlet;   a coolant inlet and a coolant outlet in fluid communication with the coolant channel;
 
at least one exhaust gas passage adjacent to the at least one coolant channel and in fluid communication with the exhaust gas inlet and exhaust gas outlet;
   a bypass passage; and,   a gas direction mechanism moveable to at least three positions, each position adapted to direct a different proportion of the exhaust gas between the at least one exhaust gas passage and the bypass passage.       

   The at least one exhaust gas passage is typically adapted to exchange more heat than the bypass passage. Preferably the heat exchange within the bypass passage is minimized, although for certain embodiments the bypass passage may provide a heat exchanger with less efficiency in terms of heat exchange than the exhaust gas passage. Preferably the coolant channels are formed from a pair of plates attached to one another. 
   Preferably the gas direction mechanism comprises a valve. Preferably the gas direction mechanism is adapted to move from a first position where substantially all of the exhaust gas is directed through the bypass passage, to a second position where substantially all the exhaust gas is directed through the exhaust gas passage and also to at least one further position where a proportion of exhaust gas is directed through the bypass passage and a proportion of the exhaust gas is directed through the exhaust gas passage. The gas direction mechanism is typically able to move from each said position to any other said position directly. For example the gas direction mechanism can move from the first position to the at least one further position directly without moving to the second position. 
   Preferably there are more than three positions. Indeed the gas direction mechanism can preferably be adapted to adopt any intermediate position between the first and second positions. 
   Typically the gas direction mechanism has a first face adapted to close a first aperture in order to direct the exhaust gas through the bypass passage and has a second face adapted to close a second aperture in order to direct the exhaust gas through the exhaust gas passage. 
   Preferably the cross-sectional size of the gas direction mechanism is greater than the cross-sectional size of the aperture such that the gas direction mechanism is supported by the area around each aperture when in the respective first and second positions. 
   Preferably the gas direction mechanism comprises a first face which possesses rotational symmetry. Preferably the gas direction mechanism comprises opposite faces, each comprising rotational symmetry. 
   Optionally a face of the gas direction mechanism has a conical shape. The gas direction mechanism can comprise a first conical face and a second conical face. 
   The first and second faces may be at an angle of between 20–40° to each other although larger angles of, for example, up to 80° are also possible. For certain embodiments the first and second faces are not at an angle to each other—that is the second face is on the opposite side of the first face. 
   Preferably the bypass passage is enclosed in a housing. Preferably the housing is provided with a series of corrugations, typically to eliminate fatigue failure due to differential thermal expansion stress. 
   The bypass passage may be spaced away from the at least one exhaust gas passage by an insulating channel. The insulating channel may, in use, be evacuated or may contain gas, preferably hot gas. 
   In alternative embodiments the gas direction mechanism may comprise a sleeve with an inlet and at least one outlet. 
   The sleeve may be axially displaceable. Preferably the sleeve is axially displaceable such that the outlet is alignable substantially exclusively with the exhaust gas passage, substantially exclusively with the bypass passage or an intermediate position where a proportion of the exhaust gas is directed to the exhaust gas passage and a proportion of the exhaust gas is directed to the bypass passage. 
   In alternative embodiments the sleeve may be rotatably displaceable rather than axially displaceable. Preferably such a sleeve comprises two apertures, rotationally spaced from each other, more preferably longitudinally spaced away from each other. Typically the sleeve is adapted to direct exhaust gas exclusively to the exhaust gas passage, exclusively to the bypass passage or an intermediate position where a proportion of the exhaust gas is directed to the exhaust gas passage and a proportion of the exhaust gas is directed to the bypass passage. 
   Optionally there are at least two coolant channels which are adapted to allow coolant to flow therethrough at differing rates. Typically the first of the at least two coolant channels is adapted to allow coolant to flow therethrough at a greater rate compared to the rate at which coolant is allowed to flow through the second of the at least two coolant channels. 
   Typically coolant inlets of the respective coolant channels are sized to provide for such differing flow rate of coolant. Optionally an obstacle, such as a plate, is provided within the second of the at least two coolant channels to slow the rate at which coolant can flow therein. Typically the second coolant channel is adjacent the bypass passage. 
   According to a second aspect of the present invention there is provided a bypass assembly for connection to an exhaust gas cooler; the bypass assembly comprising a gas direction mechanism to direct a proportion of the exhaust gas to an exhaust gas cooler and a proportion of the exhaust gas to a bypass passage. 
   Preferably the gas direction mechanism is the gas direction mechanism according to earlier aspects of the invention. 
   According to a further aspect of the invention, there is provided a method of manufacturing an exhaust gas cooler, wherein:
         the exhaust gas inlet;   the exhaust gas outlet;   the at least one coolant channel;   the coolant inlet and the coolant outlet; and   the at least one exhaust gas passage;   are first brazed together in a furnace and then the bypass passage and gas direction mechanism are attached thereto.       

   According to a yet further aspect of the present invention there is provided a method of cooling exhaust gas, the method comprising:
     (i) providing an exhaust gas cooler comprising:
       an exhaust gas inlet;   an exhaust gas outlet;   at least one coolant channel arranged between the exhaust gas inlet and exhaust gas outlet and having a coolant inlet and a coolant outlet in fluid-communication with the coolant channel;   at least one exhaust gas passage adjacent to the at least one coolant channel and in fluid communication with the exhaust gas inlet and exhaust gas outlet;   a bypass passage; and,   
       (ii) directing a proportion of the exhaust gas to the at least one exhaust gas passage and a proportion of-the exhaust gas to the bypass passage.   

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
       FIG. 1  is a sectional side view of a first embodiment of an exhaust gas cooler with bypass in accordance with the present invention; 
       FIG. 2  is an enlarged view of the exhaust gas cooler with bypass of  FIG. 1 ; 
       FIG. 3  is a further sectional side view of the exhaust cooler with bypass of  FIG. 1 , showing a variety of valve positions; 
       FIG. 4  is a sectional side view of a second embodiment of the exhaust cooler with bypass in accordance with the present invention; 
       FIG. 5  is an enlarged view of the exhaust gas cooler with bypass of  FIG. 4 ; 
       FIG. 6  is an external perspective view of the exhaust gas cooler with bypass of  FIG. 4 ; 
       FIG. 7   a  is a side view of a valve used within the exhaust gas cooler with bypass of  FIG. 4 ; 
       FIG. 7   b  is a top view of the valve of  FIG. 7   a;    
       FIG. 7   c  is a side view of the bypass assembly of the  FIG. 4  exhaust gas cooler with bypass; 
       FIG. 8  is a partial side sectional view of a third embodiment of an exhaust gas cooler with bypass in accordance with the present invention; 
       FIG. 9   a  is a top view of a sleeve which forms part of the exhaust gas cooler with bypass of  FIG. 8 ; 
       FIG. 9   b  is a side view of the sleeve of  FIG. 9   a ; and, 
       FIG. 9   c  is a bottom view of the sleeve of  FIG. 9   a.    
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   An exhaust gas cooler with bypass  100  is shown in  FIGS. 1–3  and comprises an exhaust gas recirculation (EGR) cooler  80  and an attached bypass assembly  90 . 
   The bypass assembly  90  comprises a bypass housing  11  attached to the EGR cooler  80 . The bypass housing  11  comprises an exhaust gas inlet  3 , an exhaust gas outlet  4 , a bypass tube  9 , a sealing plate  8  and an open face  28  which interfaces with the EGR cooler  80 . 
   The bypass seal  8  comprises a plate with an aperture  25  and seals the bypass housing  11  with the cooler  80 , allowing exhaust gas to proceed only through the aperture  25  towards the outlet  4  or through open face  28  into the port  23  of the EGR cooler  80 . The bypass seal  8  is welded to the housing  11  at one end but interfaces with the EGR cooler  80  by way of an interference fit and is preferably not welded thereto. This allows the bypass seal  8  to move slightly should the components expand and contract due to temperature variances. 
   The bypass tube  9  is placed within the aperture  25 . Further supports  14 ,  16  may be provided to hold the bypass tube  9  in place. The bypass tube  9  is spaced away from the exhaust gas cooler  80  in order to reduce heat loss from the exhaust gas during the bypass mode. Thus a void  15  typically filled with warm gas is provided between the bypass tube  9  and the EGR cooler  80 . The bypass tube  9  is preferably straight in order to minimize manufacturing complexity, but can be bent as shown in  FIG. 2 . For packaging constraints, the housing  11  may be minimized at  12  in order to compact the bypass cooler  100 . Alternative embodiments may not include a bypass tube  9 —the bypassing gas can flow through the aperture  25  and thereafter through the outlet  4 . 
   The aperture  25  comprises a rim  26  extending out from the plane of the bypass seal  8  towards the inlet  3  which helps support the bypass tube  9  therein and form a seal with a valve  6 , as described below. 
   The open face  28  of the bypass assembly  90  is aligned with an inlet port  23  and an outlet port  27  of the EGR cooler  80 . The EGR cooler  80  is of a drawn cup design which comprises a series of plate pairs  81 ,  82  which form coolant flow channels therebetween through which a coolant, such as water, flows. Exhaust gas is directed in the passages  2  between these coolant channels and the heat in the exhaust gas is absorbed by the coolant flowing through the coolant flow channels. 
   The inlet  3  and outlet  4  of the bypass housing  11  can be mounted at a tilted angle as shown in the Figures, or at a vertical or horizontal angle depending on the specific requirements for connection to the engine. Any suitable interface may be used such as welded tubes, brazed tubes, integrated flanges, V band clamps, etc. 
   Exhaust gas can therefore proceed from the inlet  3  into the exhaust gas cooler  80  via the open face  28  and aligned port  23 , through the passages  2  between the plate pairs  81  &amp;  82 , out of the EGR cooler  80  through the aligned ports  27 ,  29  and out of the bypass housing  11  through the outlet  4 . Alternatively the exhaust gas can proceed from the inlet  3  through the bypass tube  9  and out of the outlet  4 —bypassing the EGR cooler  80 . A valve assembly  35 , described below, determines the proportion of exhaust gas which proceeds in each direction. 
   The valve assembly  35  comprises a main cooler valve  5  pivotally mounted to a valve stem  7  and adapted to, seal the open face  28  at the port  23  of the EGR cooler to prevent exhaust gas entering the EGR cooler  80  and being cooled. When the valve  5  is in the closed position (that is, sealing the port  23 ) the exhaust gas will proceed through aperture  25  in the bypass seal  8 , the bypass tube  9  and the outlet  4 , therefore bypassing the EGR cooler  80 . 
   Affixed to the bypass side of the main cooler valve  5  is a further valve, referred to as a bypass valve  6 . The bypass valve  6  pivots with the main cooler valve  5  and is adapted to seal the aperture  25  in the bypass seal  8  and prevent exhaust gas entering the bypass tube  9 . When the bypass valve  6  is in the closed position, it seals the bypass tube  9  and prevents exhaust gas extending therethrough. Also, since the main cooler valve  5  is affixed to the bypass valve  6 , the port  23  of the EGR cooler  80  is open when the bypass valve  6  is in its closed position. In this position therefore, all the exhaust gas proceeds through the open face  28  and port  23  of the EGR cooler  80  and is cooled. 
   The valves  5 ,  6  may also be pivoted to an intermediate position so that a proportion of the exhaust gas proceeds in each of the two directions. 
   Each valve  5 ,  6  comprises a flange portion  52 ,  62  respectively and an outwardly projecting conical portion  54 ,  64  respectively. The flange  52  of the valve  5  is sized to be greater than the circular port  23  and thus abuts with the main body  30  of the exhaust gas cooler  80  to provide a seal. In a similar manner, the flange portion  62  of the valve  6  is larger than the aperture  25  and thus abuts with the rim  26  in order to form a seal. 
   Advantages of certain embodiments of the present invention is the greater size of the valves than the ports/apertures which they are sealing. This reduces the load on the valve stem since the valves abut against the edge of the port or aperture when closed. This significantly reduces the likelihood of failure of the stem which is typically the weakest part in bypass configurations. 
   In use, the valves  5 ,  6  can be pivoted so that they are placed in an intermediate position allowing a proportion of the exhaust gas to pas through the open face  28  and onwards through the EGR cooler  80  and be cooled, and allowing a proportion to pass through the bypass tubing  9  without being cooled. In this way the degree of cooling of the exhaust gas is modulated providing for accurate temperature control of the exiting exhaust gases. The conical portions  54 ,  64  affect the exhaust gas flow over the valves  5 ,  6  and allow greater control of the modulation by increasing the degree of rotation required to direct various proportions of exhaust gas to the bypass  9  or EGR cooler  80 . For example, when the valve  5  is pivoted away from its closed position by a small degree (˜5°), much of the conical portion  54  will remain in the port  23  allowing the exhaust gas to proceed only through a ring-shaped space between the conical portion  54  and the edge of the port  23 . As the valve  5  is pivoted further away from the port  23  the ring-shaped space increases in size allowing more exhaust gas to enter the port  23 . This aids control of the proportion of exhaust gas to be cooled and thus accurate control of the temperature at which the exhaust gas exits the EGR cooler with bypass  100 . The proportion of the exhaust gas directed to the cooler  80  or bypass  9  can be varied as required. 
     FIG. 3  shows the exhaust gas cooler/bypass  100  with the valve in a number of different positions, each of which correspond to a degree of cooling of the exhaust gas entering the inlet  3 . 
   Alternative embodiments may include only a valve for opening or closing the route to the bypass assembly and do not include a valve for opening or closing the route to the EGR cooler. Thus if the bypass valve is open most of the air will proceed through the bypass assembly because the pressure drop of proceeding through the EGR cooler is greater. If valve is closed, the air will pass through the EGR cooler. Such embodiments save on the cost of providing two valves. 
   Alternative embodiments may also utilize a differently shaped portion on the valves in order to optimize flow modulation—the shape does not necessarily have to be conical. 
   Assembly of the EGR cooler/bypass  100  is straightforward. An existing EGR cooler may be used without modification and the bypass assembly attached thereto by either brazing or preferably welding. 
   Alternatively a new EGR cooler may be manufactured which typically includes the step of brazing the EGR cooler. The bypass assembly is preferably welded to the EGR cooler after the brazing step. This increases the furnace capacity and eliminates the need to put the valve components  5 ,  6  through the brazing step. 
   The bypass valve  6  can be fixed to the valve  5  by any suitable method such as welding or crimping. 
   The valve stem  7  is bushed, optionally sealed and operated by an actuator or crank mechanism  49  (shown only in  FIGS. 6 ,  7   c ). The stem is raised off the top of the bypass housing  11  to allow clearances for manufacturing/operation strength on the housing  11  and space for packaging the bushes and seals (not shown). 
   Pneumatic or electric actuator (not shown) can be used to control the valve stem  7 . The actuator is controlled by an Engine Control Unit (ECU), which can take work in a number of different ways. It can take simple temperature measurements of the coolant and/or the exhaust gas and modulate the proportion of gases which bypass depending on the temperatures detected. Alternatively or additionally a load versus speed map may be programmed into the ECU to modulate the proportion of uncooled exhaust gas required. The richness of the air/fuel mix may be assessed as can the combustion temperature and the temperature of different engine components. All these factors can be used in a calculation to determine the proportion of exhaust gas which is cooled. A combination of these control mechanisms may also be utilized. 
   A second embodiment of a gas bypass cooler is shown in  FIGS. 4 and 5 . The second embodiment is largely similar to the previous embodiment and like parts share common reference numerals. 
   One particular difference is that a valve  40  is provided as a single piece with faces  45 ,  46  corresponding to the valves  5 ,  6  of the previous embodiment. Moreover, the face  45  if the valve  40  is at an angle of around 30° to the face  46  of the valve  40 . The single-piece valve  40  reduces the movement required to seal the cooler or the bypass which reduces the required height of the housing  31 . Manufacture of a single piece valve is also simpler than two valves  5 ,  6  fixed together. The valves  5 ,  6  may be manufactured at a variety of angles to each other, for example from 10°–80°. 
   In other embodiments the valves may be formed from two pieces attached to each other at an angle or formed as a single piece with no angle between them. 
   The side of housing  31  has corrugations  18  which cope with the thermal expansion of the bypass tube  9  and bypass housing  12  more rapidly than the EGR cooler  80 . (Typically the bypass housing  12  and tube  9  will be exposed to temperatures of over 500° C. to 600° C. whereas the EGR cooler  80  is exposed to temperatures of up to 120° C.) 
   A screw  41  may be provided for attachment to the exhaust gas recirculation tube/manifold (not shown). A perspective view of the exhaust gas coolers/bypasses shown in  FIGS. 6 ,  7   c . A pneumatic activator  49  to control the valve stem  7  is also shown there. 
   A third embodiment of a EGR cooler with bypass  300  is shown in  FIG. 8 . The EGR cooler is also of the drawn cup design and therefore includes a series of plate pairs  381 ,  382  which form coolant flow channels therebetween. (In practise, more plate pairs  381 ,  382  are commonly provided than shown in the drawings.) 
   The channels are in fluid communication with a coolant inlet  383  and coolant outlet (not shown). 
   Between the plate pairs  381  &amp;  382 , cooling passages  302  are formed through which hot exhaust gas can flow. A bypass passage  301  is provided between a lowermost plate pair  381 L,  382 L and a bottom  385  of the cooler  300 . 
   The bypass passage  301  is essentially an additional heat exchanger section with lower performance than that of the cooling passages  302  but will be referred to hereinafter as a bypass passage. A degree of heat exchange will take place in the bypass passage  301 , although this is less than the heat exchange which will take place in the cooling passages  302 . This is taken into account by an engine control unit and thus modulated temperature control of the exhaust gas can still be achieved. Thus the present embodiment allows for exhaust gas to pass through heat exchangers of differing performance. The heat exchange in the second heat exchanger or bypass passage  301  may be negligible if required, but not necessarily so. 
   Coolant flows at a lower rate through the channel between the lowermost plate pair  381 L,  382 L in contrast to the other plate pairs by means of a smaller inlet port (not shown). A division plate  386  is also provided between the lowermost plate pairs  381 L,  382 L in order to increase the insulation between the bypass  301  and cooling  302  passages. The division plate  386  also serves to reduce the flow rate of the coolant and thus the heat exchange within the bypass passage  301 . 
   Circular ports are provided in the plates  381 ,  382  to allow for exhaust gas to enter the space between the plates  381 ,  382 . These ports are aligned and a cylindrical void  373  is created. 
   A rotatable cylindrical sleeve valve  342  is provided in the void  373 . A boss  345  on its bottom locates in recess  346  on the bottom  385  of the cooler/bypass  300 . The sleeve  342  and is open at its top end for communication with an exhaust gas inlet  303  and has exit ports  343 ,  344 . The exit ports  343 ,  344  are rotationally and longitudinally spaced apart from each other. 
   The first exit port  343  is longitudinally aligned with the cooling passages  302  whereas the second port is longitudinally aligned with the bypass passage  301 . The ports  343 ,  344  are rotationally spaced apart from each other such that rotation of the sleeve around its main axis can allow exhaust gas to selectively exit via one of the two ports  343 ,  344  exclusively or a combination of the two ports  343 ,  344 . Thus by rotating the sleeve  342 , exhaust gas can be directed through the cooling passages  302  and be cooled or through the bypass passage  301  where it is not cooled. 
   The sleeve  342  can also be turned so that a portion of the first and second ports  343 ,  344  are aligned with the cooling and bypass passages respectively. This provides for modulated cooling, that is allowing any proportion of exhaust gas to be cooled whilst allowing the rest of the exhaust gas to proceed through the bypass. Thus the temperature of the exhaust gas exiting the cooler can be accurately controlled and it is not necessary to have all the exhaust gas passing through the cooler or the bypass at one time. 
   In alternative embodiments (not shown) a similar cylindrical sleeve may be provided but with only a single axial exit port. The sleeve is then, in use, displaced axially in order to direct the exhaust gases through the cooling or bypass passages or a combination of cooling or bypass passages where partial cooling is required. 
   An L-shaped pipe  365  is attached to the cooler via a V-band connection such as Marmon™ flanges  367  and is onwardly connected to the exhaust gas output of the engine (not shown). 
   An actuator rod  366  controls the rotation of the sleeve  342 . The sleeve  342  can be pneumatically or electrically actuated. The rod  366  extends through the L-shaped pipe  365  and has a collar  368  and bushing  369  on either side of the pipe  365 . 
   Thus in use, coolant enters the coolant inlet  383  and proceeds through the passages formed between plate pairs  381 ,  382 . Coolant may or may not proceed through the lowermost plate pairs  381 L,  382 L. For certain embodiments, a small amount of cooling is preferred in the bypass passage  301  and coolant can proceed through the lowermost plate pairs  381 L,  382 L. For other embodiments, no coolant is allowed to flow through the lowermost plate pairs  381 L,  382 L in order to minimize cooling in the bypass passage  301 . 
   Exhaust gas enters the inlet  303  and proceeds through the pipe  365  into the bore of the sleeve  342 . Depending on the rotational orientation of the sleeve  342 , exhaust gas can proceed either through the exit port  343  and thereafter through the cooling passages and be cooled by contact with the plate pairs  381 , or through the exit port  344  and bypass the cooling passage  302 . If the sleeve  342  is rotated so that the port  343  is partially aligned with the cooling passages  302  and the port  344  is partially aligned with the bypass passage  301 , the net affect on the exhaust gas will be partial cooling. The extent of cooling can be controlled by the degree of rotation of the sleeve  342 . 
   An advantage of certain embodiments of the present invention is the compact size afforded by the sleeve valve. 
   Modifications and improvements may be made without departing from the scope of the invention for example, the exhaust gas may be directed through the EGR cooler/bypass in an opposite direction, with the valve therefore being provided at the colder, output end.