Abstract:
The invention relates to an exhaust gas recirculation device ( 5 ) for an internal combustion engine ( 1 ), especially in a motor vehicle, said device comprising an exhaust gas recirculation line ( 6 ) and an exhaust gas cooler ( 7 ) which is built into the exhaust gas recirculation line ( 6 ) and connected to a cooling circuit ( 8 ) operating by means of a liquid coolant. The exhaust gas recirculation cooler ( 7 ) comprises a cooler housing ( 9 ) which comprises at least one exhaust gas inlet ( 10 ), an exhaust gas outlet ( 11 ), a coolant inlet ( 12 ) and a coolant outlet ( 13 ), and through which a coolant flows. In order to be able to improve the adjustment of the cooling power, the exhaust gas recirculation cooler ( 7 ) contains, in the cooler housing ( 9 ) thereof, a first cooling tube arrangement ( 14 ) and a second cooling tube arrangement ( 15 ) which enables a larger heating flow between the exhaust gas and the coolant than the first cooling tube arrangement ( 14 ).

Description:
TECHNICAL FIELD 
     The present invention relates to an exhaust gas recirculation device for an internal combustion engine, especially in a motor vehicle. 
     BACKGROUND 
     In internal combustion engines, an exhaust gas recirculation is increasingly used to thereby improve the emission values and the efficiency of the internal combustion engine. To avoid here an increase of NO x  emissions, it is necessary to cool the recirculated exhaust gases by means of an exhaust gas recirculation cooler, abbr. EGR cooler, since the NO x  generation in the combustion process increases disproportionately high with increasing temperature. 
     Accordingly, an exhaust gas recirculation device, abbr. EGR device, of the type mentioned above comprises typically an EGR cooler which is built into an exhaust gas recirculation line, abbr. EGR line, and which is connected to a cooling circuit operating with liquid coolant. For this, the EGR cooler has a cooler housing, which comprises an exhaust gas inlet, an exhaust gas outlet, a coolant inlet and a coolant outlet, and through which a coolant flows. 
     From WO 96/30 635 A1 such an EGR device is known, which in addition is characterized in that it has a bypass externally bypassing the EGR cooler and controllable by means of a switching valve. By means of such a bypass, the possibility is provided to bypass the EGR cooler with an activated bypass. This is desired, for example, for a cold start of the internal combustion engine to heat up the internal combustion engine as quickly as possible by means of the heat of the recirculated exhaust gases. With a hot internal combustion engine, the bypass is deactivated so that the recirculated exhaust gases then flow through the EGR cooler, thereby being cooled. 
     From DE 199 62 863 A1, another EGR device comprising an EGR cooler and a bypass is known. However, in this EGR device, the bypass bypasses the EGR cooler internally. This means that the bypass runs within the cooler housing, but is thermally insulated from the coolant. 
     SUMMARY 
     The present invention is concerned with the problem to provide for an EGR device of the type mentioned above an improved embodiment, which is in particular characterized by an increased variability of the adjustable cooling power of the EGR cooler. 
     This problem is solved according to the invention as disclosed below. Advantageous embodiments are disclosed herein below. 
     The invention is based on the general idea to provide in the EGR cooler two coolant tube arrangements through which a coolant can flow separately, and which are distinguished by different cooling power. The one or the first cooling tube arrangement has a smaller cooling power, and hence enables a smaller heating flow between the exhaust gas and the coolant. Unlike that, the other or the second coolant tube arrangement has a larger coolant power, and thus enables a larger heating flow between exhaust gas and coolant. By means of this construction, two separate EGR coolers with different cooling power are quasi integrated in a common housing, which results in an extremely compact construction. By means of the proposed construction of the EGR coolers, basically three different flow-through conditions are realizable. In a first flow-through condition, which is set, for example, when no cooling demand or only a low cooling demand is required, the exhaust gases are passed exclusively through the first cooling tube arrangement, which allows the lower heating flow. In a second flow-through condition, when a medium cooling demand is required, the exhaust gases are passed exclusively through the second cooling tube arrangement, which enables the higher heating flow. In a third flow-through, which is set, for example, for covering a high cooling demand, the exhaust gases flow through both coolant tube arrangements. For this it can be provided to configure the distribution of the exhaust gas flow to the two cooling tube arrangement in the third flow-through condition mobile in steps or continuously variable, whereby the cooling power provided by the EGR cooler can be adapted even better to the actual coolant demand. 
     In an advanced development of the EGR device, a bypass can be provided which bypasses the EGR cooler externally and which is activated when no cooling demand is required. Alternatively, in internal combustion engines, for example, which have a relatively short warm-up phase due to their construction, such a bypass can be abandoned. During the warm-up operation, the recirculated exhaust gases can be passed exclusively through the first cooling tube arrangement with the lower power. A thereby given extension of the warm-up phase compared to an embodiment comprising an external bypass, or an internal and insulated bypass, is accepted in this case. 
     To be able to configure the cooling power or the heating flow, respectively, between the exhaust gas and the coolant differently within the two cooling tube arrangements, a plurality of different measures are proposed, which can be realized cumulatively or alternatively. For example, the second cooling tube arrangement can have a larger surface on the exhaust gas side and/or the coolant side than the first cooling tube arrangement. The second cooling tube arrangement can have more cooling tubes than the first cooling tube arrangement. The cooling tubes of the second cooling tube arrangement can have smaller flow-through cross sections and/or higher flow-through resistances for the exhaust gas. The cooling tubes of the second cooling tube arrangement can be made of a different material than the cooling tubes of the first cooling tube arrangement and can have a higher heat transfer coefficient. In the cooling tubes of the second cooling tube arrangement, between exhaust gas and cooling tube and/or turbulators, ribs can be arranged for improvement of the heat transfer, which increase the flow resistance and the retention time of the exhaust gas in the respective cooling tube, and cause turbulences, which in each case contribute to the increase of the heat transfer between exhaust gas and cooling tube. Advantageously, the ribs can be formed as turbulators. 
     Further important features and advantages of the invention are apparent from the disclosure, the drawings, and tile associated description of tile figures by means of the drawings. 
     It is to be understood that the aforementioned and the following features still to be illustrated are not only usable in the respective mentioned combination, but also in other combinations or on its own, without departing from the scope of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       Preferred exemplary embodiments of the invention are illustrated in the drawings, and are explained in the following description in more detail, wherein identical reference numbers refer to identical, or similar, or functionally identical components. 
       In the figures 
         FIG. 1  shows schematically a greatly simplified diagram-like basic illustration of an internal combustion engine comprising an exhaust gas recirculation device, 
         FIGS. 2 and 3  show schematically perspective longitudinal sections of an exhaust gas recirculation cooler in different embodiments, 
         FIGS. 4 and 5  show schematically perspective longitudinal sections of another exhaust gas recirculation device comprising an exhaust gas valve arrangement in different viewing directions and sectional planes. 
     
    
    
     DETAILED DESCRIPTION 
     According to  FIG. 1 , an internal combustion engine  1 , which can be arranged in a motor vehicle, comprises an engine block  2  with cylinders which are not shown, a fresh gas system  3 , which supplies fresh gas to the cylinders of the engine block  2 , and an exhaust system  4 , which discharges exhaust gas from the cylinders of the engine block  2 . Furthermore, the internal combustion engine  1  is equipped with an exhaust gas recirculation device  5 , which is denoted hereinafter as EGR device  5 . The EGR device  5  comprises an exhaust gas recirculation line  6 , which is denoted hereinafter as EGR line  6 . The EGR line  6  serves for external recirculation of exhaust gas from the exhaust system  4  into the fresh gas system  3 . For this, the EGR line  6  is connected, on the one hand, to the exhaust system  4 , and on the other hand to the fresh gas system  3 . The EGR device  5  comprises in addition an exhaust gas recirculation cooler  7 , which is denoted hereinafter as EGR cooler  7 . The EGR cooler is arranged in the EGR line  6  so that the exhaust gas can flow through it. The EGR cooler  7  is connected to a cooling circuit  8  which operates by means of a liquid coolant. Preferably this concerns here the same cooling circuit  8 , which in the internal combustion engine  1  serves for cooling of the engine block  2 . The EGR cooler  7  allows a heat-transferring coupling between coolant and exhaust gas, and comprises a cooler housing  9  through which coolant can flow and which comprises at least an exhaust gas inlet  10 , an exhaust gas outlet  11 , a coolant inlet  12  and a coolant outlet  13 . 
     The EGR cooler  7  includes in its cooler housing  9  two cooling tube arrangements, in particular a first cooling tube arrangement  14  and a second cooling tube arrangement  15 . Each cooling tube arrangement  14 ,  15  connects in the housing  9  the exhaust gas inlet  10  with the exhaust gas outlet  11 , and thus allows the flow of exhaust gas through the EGR cooler  7 . At the same time, the two cooling tube arrangements  14 ,  15  are coupled heat-transferring with the coolant passing through the cooler housing  9 . The two cooling tube arrangements  14 ,  15  are matched to each other or formed such that the second cooling tube arrangement  15  allows a higher heating flow between the exhaust gas and the coolant under the same basic conditions than the first cooling tube arrangement  14 . Same basic conditions means, in particular, the same volume flows of exhaust gas and coolant as well as the same temperature difference between exhaust gas and coolant. 
     The EGR device  5  comprises in addition an exhaust gas valve arrangement  16  which is arranged here at the exhaust gas inlet  10 . Principally, an embodiment is thinkable which is arranged at the exhaust gas outlet  11 . The exhaust gas valve arrangement  16  is formed such that it allows different switching positions. In a first switching position, it passes the exhaust gas exclusively through the first cooling tube arrangement  14 . The first switching position is, for example, selected by a control, which is not shown here, of the EGR device  5  when there is only a low cooling demand for the exhaust gas to be recirculated. The first switching position can in particular also be selected when there is no cooling demand for the exhaust gas to be recirculated, which is the case, for example, during a warm-up phase of the internal combustion engine  1 . In a second switching position, the exhaust gas arrangement  16  passes the recirculated exhaust gas exclusively through the second cooling tube arrangement  15 . The second switching position is selected, for example, when a considerably higher or medium cooling demand is required for the exhaust gas. 
     The exhaust gas valve arrangement  16  preferably allows in addition the setting of at least a third switching position, in which the exhaust gas valve arrangement  16  passes the exhaust gas through both cooling tube arrangements  14 ,  15 . This third switching position can be selected for cooling demand in the exhaust gas, which is again higher or large. Here it is basically possible to form the exhaust gas valve arrangement  16  such that within this third switching position, basically any intermediate position is adjustable, whereby the distribution of the recirculated exhaust gas flow to the two cooling tube arrangements  14 ,  15  is adjustable as desired between 0% and 100%, and, in particular, in steps or continuously variable. 
     In addition, the EGR device  5  can be equipped optionally with a bypass  17 , which is only indicated here by a broken line, and which allows bypass of the EGR cooler  17  externally. For this, the exhaust gas valve arrangement  16  is preferably formed for adjusting a fourth switching position, in which it passes the recirculated exhaust gases exclusively through the bypass  17 , which is particularly useful in the case when no cooling demand in the exhaust gas exists. For achieving of a particularly compact construction, this bypass  17  is preferably abandoned. 
     The EGR device  5  or the cooling circuit  8 , respectively, can be equipped with a coolant valve arrangement  18  which allows to switch over or to distribute the coolant flow between the coolant inlet  12  and an additional connection  19 , which is also connected to the housing  9 , and, in particular, in steps or continuously variable between 0% and 100%. By means of the additional connection  19 , in the cooler housing  9 , a changed coolant flow can be realized which, for example, improves the cooling power of the first cooling tube arrangement  14 . An embodiment provided with the additional connection  19  is addressed in more detail below with reference to  FIG. 3 . The coolant valve arrangement  18  can also be arranged in the return line of the cooling circuit  8 , instead of being in the flow line, as shown here, whereby it then switches or distributes the coolant flow between the coolant outlet  13  and the additional connection  19 . 
     According to  FIGS. 2 and 3 , the first cooling tube arrangement  14 , for example, is formed by a single cooling tube  20 , which connects the exhaust gas inlet  10  with the exhaust gas outlet  11 . Unlike this, the second cooling tube arrangement  15  is formed here by a plurality of cooling tubes  21 , which also connect the exhaust gas inlet  10  with the exhaust gas outlet  11 . In the present case, six parallel cooling tubes  21  are provided in the second cooling tube arrangement  15 . The cooling tubes  20 ,  21  of the two cooling tube arrangements  14 ,  15  each extend straight and parallel to each other. 
     The cooler housing  9  encloses a cooling chamber  22 , which in the embodiments of  FIGS. 2 and 3  is called main cooling chamber  22 . The cooling chamber  22  is bounded in the region of the exhaust gas inlet  10  and in the region of the exhaust gas outlet  11  by a bottom  23 , respectively, and closed tightly. The cooling tubes  20 ,  21  of the two cooling tube arrangements  14 ,  15  run within the cooling chamber  22  and penetrate the bottoms  23 . 
     The cooling tubes  21  of the second cooling tube arrangement  15  have, on the exhaust gas side as well as on the coolant side, in total a larger surface than the cooling tube  20  of the first cooling tube arrangement  14 . Furthermore, each of them are provided with smaller flow-through cross sections than the cooling tube of the first cooling tube arrangement  14 . In addition, the cooling tubes  21  of the second cooling tube arrangement hereby can have a higher flow resistance than the cooling tube  20  of the first cooling tube arrangement  14 . Optionally, it can also be provided to manufacture the cooling tubes  21  of the second cooling tube arrangement  15  from a different material than the cooling tube  20  of the first cooling tube arrangement  14 , such that they have a higher heat transfer coefficient. For example, the cooling tubes  21  of the second cooling tube arrangement  15  are made of aluminum or copper, while the cooling tube  20  of the first cooling tube arrangement  14  is made of stainless steel. 
     In the embodiments of  FIGS. 2 and 3 , a partition wall  24  is arranged in the cooler housing  9  in a manner that it completely encloses, but spaced apart, the cooling tube  20  of the first cooling tube arrangement  14  in circumferential direction, thus transverse to the longitudinal direction of this cooling tube  20 , so that between the partition wall  24  and said cooling tube  20 , an additional cooling chamber  25  is formed, which completely encloses the cooling tube  20  of the first cooling tube arrangement  14  in circumferential direction. The partition wall  24  thereby separates the additional cooling chamber  25  within the cooler housing  9  from the remaining cooling chamber  22  or main cooling chamber  22 , respectively. However, this separation is not complete since the partition wall  24  includes at least one opening  26  through which the additional cooling chamber  25  communicates with the main cooling chamber  22 . In this manner, the coolant can flow through the additional cooling chamber  25  as well. The cooling tube  20  of the first cooling tube arrangement  14  hence extends within the additional cooling chamber  25 , while the cooling tubes  21  of the second cooling tube arrangement  15  extend within the main cooling chamber  22 . The partition wall  24  causes a systematic restriction of the flushing around the cooling tube  20  in the first cooling tube arrangement  14  compared to the flushing of the cooling tubes  21  of the second cooling tube arrangement  15 . The partition wall  24  is hence a measure for the realization of a reduced cooling power for the first cooling tube arrangement  14 . 
     In the embodiment shown here, the arrangement of the partition wall  24  and the cooling tube  20  enclosed thereof within the cooler housing  9  is carried out such that the main cooling chamber  22  also encloses the partition wall  24 , and hence the additional cooling chamber  25  in circumferential direction. Consequently, the partition wall  24  is flushed from all sides in circumferential direction by the coolant. Thereby a uniform cooling within the cooling tube  20  of the first cooling tube arrangement  14  is improved. In a different embodiment, the partition wall  24  can be arranged in the cooler housing  9  such that it separates, like an intermediate bottom, the additional cooling chamber  25  from the main cooling chamber  22 , whereby it then also allows communication through at least one opening  26  between the two cooling chambers  22 ,  25 . The additional cooling chamber  25  in this case is not arranged within the main cooling chamber  22  but quasi in parallel thereto. 
     In the embodiment shown in  FIG. 2 , the partition wall  24  includes at least two such openings  26 , which are arranged with respect to the flow of coolant through the housing  9  such that they form at least one inlet opening and at least one outlet opening for coolant. The flow-through of the additional cooling chamber  25  is indicated by arrows. 
     In the embodiment illustrated in  FIG. 3 , the partition wall  24  has, in addition to the at least one opening  26 , another opening  27 , which is connected to the additional connection  19  mentioned above with respect to  FIG. 1 . The additional connection  19  connected to the cooling circuit  8  extends through the cooler housing  9  and is connected to the additional cooling chamber  25 . Thereby the additional connection  19  penetrates the main cooling chamber  22  at least partially. The coolant valve arrangement  18  mentioned with respect to  FIG. 1 , which is connected with the additional connection  19 , and, for example, with the coolant inlet  12 , can be formed such that it allows a first switching position in which the coolant exclusively flows in through the coolant inlet  12  and flows out through the coolant outlet  13 ; compare to the arrows drawn with solid lines. Furthermore, it can realize a second switching position in which the coolant, according to the arrows drawn with a broken line, exclusively flows in through the additional connection  19  and flows out through the coolant outlet  13 . Alternatively, in the second switching position, the flow can also take place such that the coolant exclusively flows in through the coolant inlet  12  and flows out through the additional connection  19 . Furthermore, it is also principally possible to form the coolant valve arrangement  18  such that it allows a third switching position, in which the coolant flows in through the coolant inlet  12  and flows out through the coolant outlet  13 , as well as through the additional connection  19 . In addition, alternatively, a switching configuration is possible in which the coolant flows in through the coolant inlet  12  and the additional connection  19  and flows out through the coolant outlet  13 . Thinkable is also a bypass for the coolant, which is not shown here, bypassing an EGR cooler  7  internally or externally, wherein the coolant valve arrangement  18  then passes the coolant in a further, or fourth, switching position through said bypass. 
     In the embodiment shown in  FIGS. 4 and 5 , the cooling tubes  20 ,  21  of the two cooling tube sections  14 ,  15  are formed as identical parts. Hereby this embodiment is built more cost effective. To improve the efficiency of the second cooling tube arrangement  15  compared to the first cooling tube arrangement  14 , more cooling tubes  21  are allocated here to the second cooling tube arrangement  15  than to the first cooling tube arrangement  14 . Without restriction of the generality, the first cooling tube arrangement  14  comprises here two cooling tubes  20 , while the second cooling tube arrangement  15  comprises three cooling tubes  21 . Furthermore, the cooling tubes  21  of the second cooling tube arrangement  15  are equipped with ribs and/or turbulators  28  in their interior, which result in a known manner in an extreme improvement of the heat transfer between the exhaust gas and the cooling tubes  21 . Unlike this, the cooling tubes  20  of the first cooling tube arrangement  14  preferably include neither ribs nor turbulators. 
     The measures for realizing different heating flows in the two cooling tube arrangements  14 ,  15  in the embodiment shown in  FIGS. 4 and 5  and in the embodiment shown in  FIGS. 2 and 3  can be combined with each other as desired. 
     With reference to  FIGS. 4 and 5 , hereinafter a special embodiment of the exhaust gas valve arrangement  16  is explained in more detail. 
     According to  FIGS. 4 and 5 , the cooler housing  9  has on the inlet side an inlet flange  29 , which forms the exhaust gas inlet  10 , and through which, in the present case, the exhaust gas valve arrangement  16  is connected. The cooler housing  9  includes in addition an outlet flange  30 , which forms the exhaust gas outlet  11 , and through which the cooler housing  9  is connectable to the EGR line  6 . In an alternative embodiment, the exhaust gas valve arrangement  16  can also be arranged accordingly on the outlet side. 
     The exhaust gas valve arrangement  16  comprises a valve housing  31 , which is formed, for example, as a metal casting. In this valve housing  31 , two control valves are arranged, namely a first control valve  32  and a second control valve  33 . The first control valve  32  controls the exhaust gas flow through the first cooling tube arrangement  14 , while the second control valve  33  controls the exhaust gas flow through the second cooling tube arrangement  15 . The two control valves  32 ,  33  are preferably built identical (identical parts) and can are mobile between a maximum open position and a closed position, wherein they can realize, in particular, one or more intermediate positions to allow a stepped or even continuously variable switching between the closed position and the open position. Thus, the control valves  32 ,  33  are not considered switching valves, which can be switched over exclusively between a closed position and an open position. 
     According to  FIG. 4 , the cooler housing  9  comprises an exhaust gas inlet chamber  34  which is separated by an inlet-side bottom  23  from the coolant in the cooling chamber  22 , and which is located in the region of the exhaust gas inlet  10 . The exhaust gas valve arrangement  16  or its valve housing  31 , respectively, is equipped with a dividing wall  35 , which extends parallel to the flow direction, and hence parallel to the cooling tubes  20 ,  21 , and thereby extends up to or close to the said bottom  23 . The dividing wall  35  divides the exhaust gas inlet chamber  34  into a first sub-chamber  36 , which communicates with the first cooling tube arrangement  14 , and into a second sub-chamber  37 , which communicates with the second cooling tube arrangement  15 . A fixed connection of the dividing wall  35  to the bottom  23  is not required. Leakages which might occur can be tolerated. The dividing wall  35  projects into a gap, which is formed between the free ends of the two adjacent tubes  20 ,  21  of the two cooling tube arrangements  14 ,  15 . 
     The dividing wall  35  of the valve housing  31  extends also within the valve housing  31 , namely within an exhaust gas discharge  38 , which is directed away from the two control valves  32 ,  33  and is directed towards the exhaust gas inlet  10  of the cooler housing  9 . Hereby, a separate flow conduction within the common valve housing for the exhaust gas is realized from the control valves  32 ,  33  to the exhaust gas inlet  10  and through the dividing wall  35 , which is extended up to the inlet-side bottom  23 , and additionally to the two cooling tube arrangements  14 ,  15 . 
     According to  FIG. 5 , the valve housing  31  comprises in addition exhaust gas inflow  39 , which is connectable to the EGR line  6 , and which supplies the exhaust gas to the two control valves  32 ,  33 . For this, in the exhaust gas inflow  39 , a dividing wall  40  can be arranged, which allows a separate flow conduction for the exhaust gas within the exhaust gas inflow  39  up to the respective control valve  32 ,  33 . By means of the two dividing walls  35 ,  40 , in the valve housing  31 , two completely separated flow paths are realized, whereby the one of them is controllable with the first control valve  32 , and the other one is controllable separately by the second control valve  33 . 
     According to  FIGS. 4 and 5 , the valve housing  31  comprises a cooling jacket  41 , which is integrated in the cooling circuit  8 . For this, an inlet port  42  formed at the valve housing  31  and the coolant outlet  13  of the cooler housing  9  are connected with each other via a connection piece  43 . If the exhaust gas valve arrangement  16  is arranged on the flow-off side with respect to the EGR cooler  7 , such a liquid cooling of the valve housing can be eliminated.