Patent Publication Number: US-6334437-B1

Title: System for recirculating exhaust gas in an internal combustion engine

Description:
STATE OF THE ART 
     The invention relates to a system for recycling exhaust gas in an internal combustion engine according to the preamble of the principal claim. 
     In a system of this kind disclosed in DE 30 34 971 C2 exhaust gases of the internal combustion engine are returned to the intake duct for the internal combustion engine. The connecting duct is here embedded in a heat exchanger for cooling the recycled exhaust gas through a broad range. 
     Taken in itself, it is also known that the recycled exhaust duct is fastened by a flange with two screws to the air intake tube made of plastic. In order to insulate the exhaust gas duct thermally from the air intake tube, mixture air is fed in the area of the flange by means of a diffuser tube. With this arrangement the exhaust gas temperature can be lowered in the area of the flange from about 450° C. to about 125° C. at a recycling rate of about 20%. 
     Thermal peaks occur in such systems, especially in the areas of the gaskets, made of plastic as a rule, at the connection of the duct carrying the returned exhaust gas and in areas lying opposite the air entry opening. It is often difficult, due to the relatively small cross sections and relative long paths, to carry away sufficient heat. In many applications, in connection with direct injection motors, also on account of the exhaust gas return rate to be expected (up to 50%), there is frequently a call for cylinder-selective introduction of the exhaust gas, which leads to additional thermal problems. 
     STATEMENT OF THE PROBLEM 
     The invention is addressed to the problem of improving a system of the kind referred to above such that an optimum lowering of the temperature will be possible. 
     ADVANTAGES OF THE INVENTION 
     The system of the invention is advantageously suitable, setting out from the generic kind, for solving the stated problem by the distinctive features of the principal claim. Owing to the fact that a cooling element in the form of a cooling channel for a liquid coolant is placed in a connecting duct for the recycled gas, which is integrated into the flange-like attachment of the duct connecting to the intake tube, the thermal stress on the plastic intake tube can be reduced at high recycling rates by simple means. Also the temperature of the aspirated air in the air intake tube can thereby be positively influenced. 
     In general, with the system according to the invention the thermal stress of the internal combustion engine, the exhaust temperature, the NOx emission and the fuel consumption are reduced. If the motor coolant is used as the coolant, the result is a simpler and less expensive construction. 
     The coolant duct can advantageously be integrated into the air intake tube, which as a rule is made of plastic, the transition from the cooling channel into the internal combustion engine being situated in the cylinder head flange of the motor, and the interface being sealed with an additional gasket. Alternatively it is also possible to place a separate coolant line into the flange between the exhaust pipe and the air intake tube, or for the cooling passage also to be placed on a given length into or onto the exhaust pipe. In another embodiment of the invention, the cooling element is a massive heat-conducting part which is a component of the connecting line and is located on the cylinder head in the area of the flange-like connection of the air intake tube. Due to the massive attachment, of the manifold for the recycled exhaust, for example, to the cylinder head, the flowing gases can be cooled simply through the cylinder head flange which has cooling passages anyway. 
     Advantageously, the elements fastening the intake tube to the cylinder head can be used at least partially as means for fastening the massive part. 
     It is also advantageously possible to provide a cooling channel carrying coolant in the area of attachment of the massive part in the cylinder head or also at least partially in the massive part, whereby the cooling power can be further optimized. 
     In another embodiment, the massive heat conducting part is a tubular insert which is integrated internally into the intake tube. This insert is in thermal contact at one end with the cylinder head. With this arrangement, when the intake tube is mounted to the cylinder head a good thermal transfer is easily achieved between the insert, which is preferably made of metal, and the cylinder head. Through this heat transfer the thermal energy delivered by the exhaust gas can be removed into the cooled cylinder head. 
     This heat transfer can also, if necessary, be increased if the end face of the insert in contact with the cylinder head has an expanded diameter. 
     The pipe-like connecting duct for the recycled exhaust is brought out through the wall of the intake tube on the side of the insert. The connecting duct and the insert are joined together gas-tight, so that no gaskets are necessary between the connecting duct and the intake tube. The entering exhaust thus strikes against the inside wall of the cooled insert and therefore does not apply any elevated thermal stress to the plastic of the intake tube. 
     It is especially advantageous if in the area where the connecting duct is brought out there is a gap in the intake tube so as to form a radial space away from the connecting duct and thus to prevent any thermal stress on the intake tube in this area. 
     These and additional features of preferred embodiments of the invention will be found not only in the claims but also in the description and the drawings, the individual features being applicable individually or severally in the form of subcombinations in the embodiment of the invention and in other fields and may represent advantageous as well as independently patentable embodiments, for which protection is hereby claimed. 
    
    
     THE DRAWINGS 
     Embodiments of a system of the invention for cooling recycled exhaust gas in an internal combustion engine will be explained with the aid of the drawings, wherein: 
     FIG. 1 is a schematic view of a cylinder head of the internal combustion engine with a liquid-cooled connection of the recycled exhaust gas to the intake tube. 
     FIG. 2 is a section through the connecting flange for the recycled exhaust gas with a cooling channel. 
     FIG. 3 is a schematic view of a manifold tube for the recycled exhaust gas with a massive connection to the cylinder head. 
     FIG. 4 is a section through the arrangement presented in FIG.  3 . 
     FIG. 5 is a detail of a modified design of the system of FIGS. 3 and 4. 
     FIG. 6 is a section through an embodiment with a heat-contacted insert, and 
     FIG. 7 a detail of a modified design of the system of FIG.  6 . 
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     In FIG. 1 is shown a cylinder head  1  of an internal combustion engine with the parts which are important here. On an air intake tube  2  through which the air reaches the combustion chambers of the internal combustion engine there is a connection  3  for a manifold  4  through which the exhaust gas tapped from the exhaust pipe is returned to the air intake tube  2 . The exhaust gas in the manifold  4  is at a high temperature due to the combustion in the motor, which can damage the intake tube and the adjacent units, since the latter are designed for normal air temperatures and are made mostly of plastic. 
     To the connecting flange  2  for the recycled gas a cooling duct  5  is connected through which the coolant needed by the motor flows according to the arrows  6   a  (in) and  6   b  (out). FIG. 2 shows how this coolant duct passes around the connecting flange  2  and thus around the manifold  4  bearing the recycled exhaust gas as shown in another view. The flange seen in FIG. 2 is fastened to the plastic intake tube  2  with two screws  7 . The connecting tube  4  is introduced into the center of this flange. 
     In FIG. 3 an embodiment is to be seen in which a manifold tube  10  for recycled exhaust gas is disposed on a cylinder block  11 . In FIG. 4 this arrangement can be seen in section. The recycled exhaust flows through the cross section  12  of the manifold  10  and is passed through pipes  13  and corresponding mounting flanges  14  into an air intake tube  15 . To fasten the manifold  10  to the cylinder head, bolt holes  16 , preferably already present, can be used for the intake tube, possibly with a metal sleeve  17 . 
     In the cylinder block  11  in FIG. 4 a coolant channel  18  is provided, through which the coolant liquid flows. In an embodiment according to FIG. 5 a coolant channel  19  can also be integrated at least partially into the manifold  10 , in which case additional gaskets  20  are necessary. 
     In FIG. 6 there is shown an embodiment which has a metal insert  21  placed in the plastic intake tube  22  such that one end  23  is in thermal contact with the cylinder head  24 . In the cylinder head  24  there is also a coolant channel  25 . A connecting tube  26  for the recycled exhaust gas is introduced laterally and affixed in a gas-tight manner. An open space  27  is here provided for the surrounding plastic of the intake tube  22 , since the relatively high temperatures of the connecting tube must not harm the plastic of the intake tube  22 . 
     The recycled exhaust gas flows according to arrows  28  into the relatively cool insert  21  and strikes against it such that the thermal stress on the plastic of the intake tube does not become too great. To improve the cooling of the insert  21  still further, according to FIG. 7 the area of the end  23  of the insert is enlarged, so that a still better thermal contact is achieved between the insert  21  and the cylinder head  24 .