Patent Publication Number: US-8528529-B2

Title: Exhaust gas recirculation cooler

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional and claims priority under 35 U.S.C. §120 to U.S. Ser. No. 12/841,297 filed Jul. 22, 2010 which claims foreign priority benefits under 35 U.S.C. §119(a)-(d) to GB 0913479.2, filed Aug. 1, 2009, which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     This disclosure relates to exhaust gas recirculation (EGR) systems and in particular to an EGR assembly combining EGR flow control and EGR cooling. 
     2. Background Art 
     EGR systems are used to recirculate part of the exhaust gas produced by an internal combustion engine, of a vehicle for example, to suppress the generation of nitrogen oxides. EGR systems may incorporate an EGR cooler, a bypass of the EGR cooler, and an EGR valve. See for example EP-A-1933023 which describes a water-cooled, in-line EGR cooler comprising a cylindrical shell. 
     GB 2062749 A describes an EGR cooler which has the form of a U-shaped tube and is adapted to be mounted directly onto an engine intake manifold. 
     One known type of EGR valve for regulating the flow of recirculated exhaust gas is described in EP 1918 566. This type of valve, often known as a poppet valve, is electrically controllable in accordance with engine operating conditions. The term ‘EGR valve’ as meant herein is a poppet valve. 
       FIGS. 1A and 1B  illustrate two alternative arrangements of a known EGR circuit. 
     In  FIG. 1A , a portion of the exhaust gas from an internal combustion engine is directed from the exhaust manifold region  1  to the inlet manifold region  2 , via an in-line EGR cooler  3 . An EGR valve  4  is positioned on the hot side of the cooler and regulates EGR flow. An EGR cooler is provided to cool the hot exhaust gases to reduce NOx formation even further. A butterfly valve  5  deflects EGR gas either through the cooler  3  or around a bypass link  6 . A problem with this arrangement is that as the valve  4  is always cooled, it cools the EGR gas flowing through it, even when engine operating conditions dictate that there is no requirement for the EGR gas to be cooled prior to reaching the intake manifold. This problem can be overcome by re-positioning the valve  4  as shown in  FIG. 1B . 
     In  FIG. 1B , the EGR valve  4  is located on the cold side of the cooler  3 . However, any contaminants settling on the valve mechanism tend not to get burned off and the valve  4  eventually starts to stick. A further drawback with both of the above arrangements is that the butterfly valve  5  tends to leak so that either not all of the EGR gas reaching the intake manifold is cooled or else not all the EGR gas bypasses the cooler. Furthermore, butterfly valves are often operated by a vacuum system which can be prone to external contamination, creating premature wear of the actuation system. 
     An EGR system which mitigates the above disadvantages would be advantageous. 
     SUMMARY 
     An EGR cooler for use in an EGR system of an internal combustion engine is disclosed. The EGR cooler has a housing having an inlet and an outlet, an EGR cooler passage within the housing and coupled to the inlet, a bypass passage within the housing and coupled to the outlet, a first EGR valve disposed in the housing, and a second EGR valve disposed in the housing. The first EGR valve is disposed between the bypass passage and the EGR cooler passage. The first EGR valve prevents flow from the inlet into the bypass passage when closed; the second EGR valve is disposed between the bypass passage and the EGR cooler passage; and the second EGR valve prevents flow between the EGR cooler and the outlet when closed. The bypass passage is connected in parallel to the EGR cooler so as to selectively permit exhaust gas to bypass the EGR cooler passage. The first EGR valve controls the flow of exhaust gas through the bypass passage and the second EGR valve controls the flow of exhaust gas through the EGR cooler passage. At least one cooler element is disposed in the EGR cooler passage. In one embodiment, a first cooler element is disposed in a first leg of the EGR cooler passage, a second cooler element is disposed in a second leg of the EGR cooler passage, an intermediate passage is provided between the first and second legs of the EGR cooler passage, and a third EGR valve couples the bypass passage and the intermediate passage. In another embodiment, a first cooler element is disposed in a first leg of the EGR cooler passage and a second cooler element is disposed in a second leg of the EGR cooler passage. The first and second legs of the EGR passage form a U-shape. The cooler elements may be water cooled and the EGR valves may be poppet valves which may be commanded to an open position, a closed position, or positions in between. 
     According to the disclosure there is provided an exhaust gas recirculation (EGR) assembly comprising an EGR cooler passage housing an EGR cooler, a bypass passage connected in parallel to the EGR cooler so as to selectively permit exhaust gas to bypass the EGR cooler without cooling, a first EGR valve for controlling the flow of exhaust gas through the bypass passage and a second EGR valve for controlling the flow of exhaust gas through the EGR cooler passage. 
     An advantages of the disclosure is that the bypass and cooling functions are controlled by EGR valves, therefore, eliminating the leakage problem suffered by butterfly or flap valves. 
     The first EGR valve may control the flow of gas entering the bypass passage. 
     Advantageously, the second EGR valve may control the flow of gas exiting the EGR cooler passage. 
     This has the advantage that the second EGR valve is never exposed to un-cooled exhaust gas. 
     The assembly may further comprise a housing having an inlet and a outlet, the EGR cooler passage and the bypass passage are formed as an integral part of the housing and the EGR cooler passage and the bypass passage are connected in parallel between the inlet and outlet of the housing. 
     This has the advantage that the assembly is economical to manufacture. 
     The EGR cooler passage is a U-shaped EGR cooler passage. 
     This has the advantage of allowing the use of a longer EGR cooler passage without increasing the length of the EGR assembly. 
     The exhaust gas may make two passes through the EGR cooler when passing through the EGR cooler passage. 
     This has the advantage of providing increased cooling effect. 
     The EGR cooler has two cooler elements and the exhaust gas passes through at least one of the two EGR cooler elements when passing through the EGR cooler passage. 
     The assembly may further comprise an intermediate bypass passage located between the two EGR cooler elements so as to selectively connect the EGR cooler passage to the bypass passage and a third EGR valve for controlling the flow of exhaust gas through the intermediate bypass passage to the bypass passage. 
     This has the advantage of improved controllability of cooling effect. 
     Further advantages of the disclosure are that the EGR valves do not require cooling as they never need to be exposed to hot exhaust gas while they are open and periodic burn-off of contaminants from one of the valves is possible thus ameliorating the sticking problem mentioned above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are schematic block diagrams of known prior art EGR systems; 
         FIGS. 2A to 2E  are schematic sectioned views of an EGR assembly in accordance with a first embodiment of the disclosure; 
         FIGS. 3A to 3B  are schematic sectioned views of an EGR assembly in accordance with a second embodiment of the disclosure; and 
         FIGS. 4A to 4E  are schematic sectioned views of an EGR assembly in accordance with a third embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. 
     With reference to  FIG. 2 , there is shown a first embodiment of an exhaust gas recirculation (EGR) assembly having a housing  7  which has an inlet port  8  for receiving exhaust gas from an engine exhaust and an outlet port  9  for discharging exhaust gas to an engine intake. 
     The housing  7  defines a U-shaped EGR cooler passage  12  and a bypass passage  11 . An EGR cooler  10  is housed in the U-shaped passage  12 . The EGR cooler  10  has a series of tubes through which and around which exhaust gas and liquid coolant can flow, respectively. 
     Adjacent to the inlet and outlet ports  8 ,  9  are two EGR valves  14 ,  13 . A first (“hot”) EGR valve  14  of the two EGR valves  14 ,  13  controls the flow of EGR gas between the inlet port  8  and the outlet port  9  via the bypass passage  11 . 
     A second (“cold”) EGR valve  13  of the two EGR valves  14 ,  13  controls the flow of EGR gas between the inlet port  8  and the outlet port  9  through the EGR cooler  10  via the U-shaped EGR cooler passage  12 . 
     The bypass passage  11  is connected in parallel to the EGR cooler  10  between the inlet port  8  and the outlet port  9  so as to selectively permit exhaust gas to bypass the EGR cooler  10  without cooling. 
     The first EGR valve  14  controls the flow of gas entering the bypass passage  11 , that is to say, it is located at an upstream end of the bypass passage  11 . The second EGR valve  13  controls the flow of gas exiting the U-shaped EGR cooler passage  12 . That is to say, the second EGR valve  13  is located at a downstream end of the U-shaped EGR cooler passage  12 . This is advantageous in that the second EGR valve  13  is never exposed to very high exhaust gas temperatures. Furthermore, because the first EGR valve  14  is always closed when the exhaust gas is extremely high, this allows the use of un-cooled EGR valves  14 ,  13 . 
     Some modes of operation of the first embodiment will now be described. 
     The valves  14 ,  13  are controlled electrically using known techniques in accordance with an EGR engine management strategy. 
     When both of the first and second EGR valves  14 ,  13  are closed (as in  FIG. 2A ), no exhaust gas flows from an engine exhaust to an engine intake. That is to say, there is no EGR flow. 
     When the first (hot) EGR valve  14  is open and the second (cold) EGR valve  13  is closed (as in  FIG. 2B ), exhaust gas is allowed to flow from the engine exhaust to the engine intake but via the bypass passage  11  only, bypassing the EGR cooler  10 , (as indicated by the direction of the arrow). This mode of operation is typically employed at engine start-up when the exhaust gas is relatively cool. 
     As neither of the first and second EGR valves  14 ,  13  are cooled, the exhaust gas does not suffer any unnecessary cooling on its way to the engine intake. There is a further advantage over the system shown in  FIGS. 1A and 1B  in that there is a minimal pressure loss due to the short bypass flow path. 
     When the first (hot) valve  14  is closed and the second (cold) valve  13  is open, EGR gas is directed through the EGR cooler passage  12  through the EGR cooler  10  and out through the outlet port  9 , allowing maximum cooling of exhaust gas (as in FIG.  2 C). Note that because of the use of a U-shaped EGR cooler passage  12  the exhaust gas makes two passes through the EGR cooler  10  when passing through the EGR cooler passage  12  thereby maximising the cooling effect on the exhaust gas. 
     Variable cooling can be achieved by partially opening each of the first and second EGR valves  14 , 13  so that some exhaust gas flows through the EGR cooler  10  and some flows through the bypass  11  (as in  FIG. 2D ). 
     The valves  13 ,  14  can be regenerated by closing the second (cold) valve  13  and opening the first (hot) valve  12  once the engine has reached normal operating temperature. This procedure can be used to burn off any contaminants which might have accumulated and, if necessary, the engine can be run so as to temporarily increase the exhaust gas temperature thereby speeding up the burn-off. During this process, all exhaust gas flows through the bypass passage  11  (as in  FIG. 2E ). External test equipment (not shown) can be used to monitor valve operation. If sticking (or slow operation) is suspected, then an engine control module (not shown) can be used to run a valve regeneration cycle for a preset time period whereby engine load is set high so that the EGR gas is hot enough to burn off contaminants. 
     A second embodiment will now be described with reference to  FIGS. 3A and 3B . 
     The EGR assembly is much as before having a housing  18  with an inlet port  19  and an outlet port  21 . The housing  18  defines a U-shaped EGR cooler passage  17  having two limbs in which are mounted an EGR cooler having two cooler elements  26 ,  27 , one located in each of the limbs. 
     The housing  18  further defines a bypass passage  22  that is arranged in parallel to the U-shaped EGR cooler passage  17  between the inlet and outlet ports  19  and  21  of the housing  18 . 
     The housing further defines an intermediate bypass passage  20  connected between the U-shaped EGR cooler passage  17  and the bypass passage  22  at a position between the two EGR cooler elements  26 ,  27 . 
     Mounted in the housing  18  are three EGR valves  23 ,  24 ,  25 . A first, “hot” EGR valve  23  controls the exhaust gas flow between the inlet port  19  through the bypass passage  22  to the outlet port  21 . A second, (cold) EGR valve  25  controls the flow of exhaust gas through the U-shaped EGR cooler passage  17  from the inlet port  19  to the outlet port  21 . A third, (intermediate) EGR valve  24  controls the flow of exhaust gas through the intermediate bypass passage  20  to the bypass passage  22 . 
     Because the EGR cooler has two separate cooling elements  26 ,  27 , exhaust gas can be diverted through one cooling element  27 , both cooling elements  26 ,  27  or bypass both cooling elements  26 ,  27  depending on the state of the EGR valves  23 ,  24 ,  25 . This embodiment therefore, permits a greater degree of control over the cooling of the exhaust gas in addition to bypassing the EGR cooler altogether when no cooling is required. 
     The third EGR valve  24  controls the flow of gas exiting the intermediate bypass passage  20  that is to say, the third EGR valve  24  is located at a downstream end of the intermediate passage  20  and downstream from the EGR cooler element  27 . The second EGR valve  24  is not exposed to very high exhaust gas temperatures and so does not require cooling. 
     The second EGR valve  25  controls the flow of gas exiting the EGR cooler passage  17  that is to say, the second EGR valve  25  is located at a downstream end of the EGR cooler passage  17  and downstream from the EGR cooler elements  26 ,  27 . The second EGR valve  25  is not exposed to very high exhaust gas temperatures and so does not require cooling. 
     Furthermore, because the first EGR valve  23  is closed when the exhaust gas temperature is extremely high, this allows the use of an un-cooled EGR valve for the first EGR valve  23 . 
       FIG. 3A  shows a low level cooling mode of operation where the first and second EGR valves  23 ,  25  are closed and the third EGR valve  24  is open. This permits EGR gas to flow through just one cooling element  27  of the EGR cooler. This low level cooling can be of use in certain engine operating conditions to achieve optimum combustion without reducing exhaust gas velocity too much in the EGR cooler. 
       FIG. 3B  illustrates a high level cooling mode of operation where the first and third EGR valves  23 ,  24  are closed and the second EGR valve  25  is open. This allows exhaust gas to flow through both of the cooling elements  26 ,  27  of the EGR cooler so as to maximise the cooling. 
     While  FIGS. 3A ,  3 B show an in-line arrangement for the three valves,  23 ,  24 ,  25 , they may be packaged differently to suit external packaging requirements. 
     It will be appreciated that by using a U-shaped EGR cooler passage in the above referred to embodiments a very compact EGR assembly can be produced. In addition, by forming the EGR cooler passage and the bypass passage as part of a common housing, the EGR assembly can be manufactured for relatively low cost. 
     One advantage of the use of a U-shaped EGR cooling passage is that the length of the cooling passage can be longer without increasing the length of the housing. The use of a longer EGR cooling passage provides the opportunity to provide a greater degree of cooling. 
     A third embodiment will now be described with references to  FIGS. 4A to 4E . 
     With reference to  FIG. 4 , an EGR assembly comprises a housing  28  which has an inlet port  29  for receiving exhaust gas from an engine exhaust and an outlet port  30  at the opposite end of the cooler  28  for discharging exhaust gas to an engine intake. Inside the housing  28  is a water-cooled, in-line EGR cooler  31  housed in an EGR cooler passage  35  formed as part of the housing  28 . The EGR cooler  31  has a series of tubes through which and around which exhaust gas and liquid coolant can flow, respectively. 
     Integral with the housing  28  and extending away from the outlet port  29  is a bypass passage  32 . Mounted in the housing  28  are two EGR valves  33 ,  34 . 
     A first (“hot”) EGR valve  33  of the two EGR valves controls the flow of exhaust gas between the inlet port  29  and the outlet port  30  via the bypass passage  32 . 
     A second (“cold”) EGR valve  34  of the two EGR valves controls the flow of exhaust gas between the inlet port  29  and the outlet port  30  via the EGR cooler  31 . The second (cold) EGR valve  34  controls the flow of exhaust gas exiting the EGR cooler passage  35 . That is to say, it is located downstream from the EGR cooler  31 . 
     Some modes of operation of the third embodiment will now be described. The EGR valves  33 ,  34  are controlled electrically using known techniques in accordance with an EGR engine management strategy. 
     When both valve  33 ,  34  are closed ( FIG. 4A ), no exhaust gas flows from engine exhaust to engine intake. 
     When the first (hot) EGR valve  33  is open and the second (cold) EGR valve  34  is closed ( FIG. 4B ), exhaust gas is allowed to flow from engine exhaust to engine intake but only via the bypass passage  32 . The exhaust gas bypasses the EGR cooler  31 , as indicated by the direction of the arrow in  FIG. 4B . This mode of operation is typically employed at engine start-up when the exhaust gas is relatively cool. As neither of the EGR valves  33 ,  34  are cooled, the exhaust gas does not suffer any unnecessary cooling on its way to the engine intake. 
     When the first (hot) EGR valve  33  is closed and the second (cold) EGR valve  34  is open, exhaust gas is directed through the EGR cooler  31  producing maximum cooling of exhaust gas (see the arrow in  FIG. 4C ). 
     Variable cooling can be achieved, as shown in  FIG. 4D , by partially opening each of the two EGR valves  33 ,  34  so that some EGR gas flows through the cooler  28  and some through the bypass  32  (see the arrows in  FIG. 4D ). 
     The valves can be regenerated (as shown in  FIG. 4E ) by closing the second (cold) EGR valve  34  and opening the first (hot) EGR valve  33  once the engine has reached normal operating temperature. This procedure can be used to burn off contaminants which might have accumulated. During this process, all exhaust gas flows through the bypass duct  32 . (See the arrow in  FIG. 4E ). External test equipment (not shown) can be used to monitor valve operation. If sticking or slow operation is suspected then an engine control module (not shown) can be used to run a valve regeneration cycle for a preset time period whereby engine load is set high so that the exhaust gas is hot enough to burn off contaminants. 
     One advantage of the disclosure is that the valves used to control exhaust gas recirculation flow and those used to control selective cooling of the recirculating exhaust are the same valves. That is to say, the EGR assembly can provide both EGR control and exhaust gas cooling control using the same valves. 
     A further advantage according to embodiments of the disclosure is that because only EGR valves are used, when these valves are in their respective closed positions there is no leakage past the EGR valves unlike the situation when butterfly or flap valves are used. Therefore when no cooling is required, there is no leakage through the EGR cooler; and when maximum cooling is required, there is no leakage through the bypass passage. 
     A further advantage of the disclosure is that cooling of the EGR valves is not required because when the exhaust gas temperature is very high the hot EGR valve is closed and the other EGR valve used are located downstream from at least one EGR cooler and so are not exposed to very high exhaust gas temperatures. 
     While the best mode has been described in detail, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. Where one or more embodiments have been described as providing advantages or being preferred over other embodiments and/or over background art in regard to one or more desired characteristics, one of ordinary skill in the art will recognize that compromises may be made among various features to achieve desired system attributes, which may depend on the specific application or implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described as being less desirable relative to other embodiments with respect to one or more characteristics are not outside the scope of the disclosure as claimed.