EXHAUST GAS RECIRCULATION SYSTEM

Abstract: An exhaust gas recirculation system for an internal combustion engine has a housing (10) with an exhaust gas flow passage therein. The housing (10) is adapted to be mounted directly on the internal combustion engine. An adjustable flow control valve member (40) is mounted in a chamber (20) in the housing (10) for controlling the flow of exhaust gas through the flow passage. An exhaust gas heat exchanger (42) is mounted in a chamber (16) in the housing (10) so that, in use, the exhaust gas being recirculated flows through the heat exchanger (42). A coolant flow passage is provided for passing coolant through the heat exchanger (42) to cool exhaust gas flowing therethrough in use. Exhaust gas inlet and outlet connections (68 and 26) communicate with the exhaust gas flow passage in the housing (10) and are connectable, respectively, to an exhaust gas system and a combustion air inlet system of the internal combustion engine.

Description: EXHAUST GAS RECIRCULATION SYSTEM This invention relates to an exhaust gas recirculation system for an internal combustion engine such as a direct injection diesel or gasoline engine, and to an internal combustion engine including the same. Exhaust gas recirculation assemblies are used in direct injection diesel engines in order to reduce NO x emissions which are particular problem in engines designed to run at high temperature. In a known exhaust gas recirculation system, a proportion of the exhaust gas is led from the exhaust system into the body of a heat exchanger through which liquid coolant from the engine is passed in order to cool the exhaust gases which then pass out of the body of the heat exchanger through an outlet connection. From there, the cooled exhaust gases pass, possibly via a linking tube, into the inlet connection of a separate flow control valve having an outlet connection which communicates via another tube with the air intake manifold of the engine. The flow control valve is controlled by the engine management system to give the required amount of exhaust gas recirculation depending upon the amount of NO x being produced under the prevailing engine conditions. Such a known exhaust gas recirculation system is relatively heavy, bulky and expensive to produce. It is also complicated to cool the various parts of the system which require cooling. Additionally, it is also prone to the development of leaks which can have serious consequences on the ability of the engine management system to deliver the correct proportion of fuel to air. It is an object of the present invention to obviate or mitigate at least some of the above disadvantages. According to one aspect of the present invention, there is provided an exhaust gas recirculation system for an internal combustion engine, said system comprising a housing having an exhaust gas flow passage therein; an adjustable flow control valve member mounted in the housing for controlling the flow of exhaust gas through the passage; an exhaust gas heat exchanger mounted in the housing so that, in use, the exhaust gas being recirculated flows through the heat exchanger; a coolant flow passage for passing coolant through the heat exchanger to cool exhaust gas flowing therethrough in use; and exhaust gas inlet and outlet connections communicating with the exhaust gas flow passage in the housing and connectable, respectively, to an exhaust gas system and a combustion air inlet system of the internal combustion engine. Thus, in the exhaust gas recirculation system of the present invention, the flow control valve member and the heat exchanger are mounted in a common housing, thereby enabling a compact system which is less prone to leakage to be achieved since the housing can be provided by a one-piece body, e.g. a casting. The coolant flow passage can be formed in such a housing which can be adapted to be attached directly to the engine so that an inlet of the coolant passage in the housing is in registration with a coolant outlet from engine. However, it is within the scope of the present invention to form the housing integrally with either a cylinder block or a cylinder head or an inlet manifold or an outlet manifold of the internal combustion engine. In which case, it is possible to dispense with a joint between the housing and one of these parts of the internal combustion engine. The housing may also be adapted to receive a thermostat for controlling the temperature of the coolant. Such thermostat may actually replace the standard engine coolant thermostat or it may be an additional thermostat. Mounting of the valve member in the housing to which coolant is supplied in use for the heat exchanger can enable cooling of the valve member and ancillary control equipment to be facilitated. In this regard, if the housing is formed of material having good heat transfer characteristics, then cooling may take place via conduction through the housing. Alternatively, the coolant flow passage in the housing may be extended to the region of the valve. The valve member is preferably located downstream of the heat exchanger relative to the direction of flow of exhaust gas since this enables the gas flow to be controlled very close to where it enters the air inlet system, thereby reducing response delays. Also, locating the valve member downstream of the heat exchanger means that the gases have been cooled by the time they reach the valve member, thereby reducing the potential problem of overheating of the latter. In order to mitigate condensation problems in the region of the valve, it is preferred for the system to be designed so that, in operation, the valve is disposed at a higher level than the heat exchanger. In a preferred embodiment, the exhaust gas heat exchanger is mounted in a first chamber in the housing. Preferably, the exhaust gas heat exchanger is a sub-assembly comprising heat exchange pipework, the exhaust gas inlet connection, and means for securing the sub-assembly to the housing. The sub-assembly may be detachably secured to the housing so that it can be removed for cleaning, servicing or replacement purposes. Preferably also, the housing comprises a second chamber in which the adjustable flow control valve member is mounted, the second chamber communicating with the first chamber so that the exhaust gas flow passage extends through these chambers. Preferably also, the housing is formed with a coolant outlet which may have two connections to enable coolant which has passed through the heat exchanger to be connected to one or both of a radiator for cooling the internal combustion engine coolant and a heater for heating a passenger compartment of a vehicle in which the internal combustion engine is fitted. Preferably also, the housing includes a connector communicating with the coolant flow passage for enabling a temperature sensor to be attached whereby to monitor the temperature of coolant flowing from the internal combustion engine in use into the exhaust gas recirculation system. According to a second aspect of the invention, there is provided an internal combustion engine in combination with an exhaust gas recirculation system according to said first aspect of the present invention, wherein the exhaust gas inlet connection of the system is connected to an exhaust system of the internal combustion engine, and wherein the exhaust gas outlet connection of the recirculation system is connected with an air intake system of the internal combustion engine. In a convenient embodiment, the air intake system includes a manifold formed of plastics lined with a suitably heat-resistant liner, such as stainless steel. In order to accommodate for any tolerance-build-up, it is preferred for the exhaust gas inlet connection of the system to be connected with the exhaust system of the internal combustion engine via a duct which can be swivelled. However, as an alternative or in addition, the exhaust gas inlet connection to the system may itself be designed so its position can be varied relative to the housing. This can be conveniently achieved by arranging for the exhaust gas heat exchanger sub-assembly to be adjustably mounted in the housing. An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Fig. 1 is a part cut-away schematic view of an exhaust gas recirculation system according to one example of the present invention, and Fig. 2 is a schematic sectional view of a flow control valve used in the system of Fig. 1. Referring now to Fig. 1, the system comprises a housing 10 in the form of a unitary aluminium casting. The housing 10 comprises a main body part 12 with an integral mounting flange 14. The main body part 12 is of generally stepped cylindrical form. Within the main body part 12 there is defined a first chamber 16 which opens onto one end face of the main body part 12 at which there is first flange 18. A second chamber 20 is also provided internally of the main body part 12 and is co-axially arranged with respect to the first chamber 16. The second chamber 20 opens on to an opposite end of the main body part 12 at which there is a second flange 22. The first and second chambers 16 and 20 communicate with one another via a tapered passage through the centre of an annular rib 24 which is formed internally of the main body part 12. The opening tapers inwardly away from the first chamber 16. The housing 10 is further formed with a cooled exhaust gas outlet duct 26 terminating in an external flange 28. An inner end of the duct 26 opens into the second chamber 20 adjacent the inner end thereof and on the opposite side of the rib 24 to the first chamber 16. The housing 10 additionally includes a coolant inlet duct 30 which opens at one of its ends onto the rear face (not illustrated) of the mounting flange 14. The illustrated front face of the flange 14 is that to which the main body part 12 is joined. The inlet duct 30 opens at its opposite end into the first chamber 16. In Fig. 1, this is illustrated as being towards the inner end of the first chamber 16. However, this end of the inlet duct 30 may be located somewhat closer to the inner end of the first chamber 16 or it may be inclined so as to direct cooling water to the inner end of the first chamber 16. The coolant inlet duct 30 is formed with a mounting 32 for receiving a coolant temperature sensor 34 for sensing the temperature of coolant from the internal combustion engine. The housing 10 is further provided with a coolant outlet duct 36 which opens into the first chamber 16 adjacent the open end thereof. All of the ducts 26, 30 and 36 and the chambers 16 and 20 are formed integrally with the remaining parts of the housing 10 so that the number of joints requiring sealing is minimised. In addition to the housing 10, the exhaust gas recirculation system according to the present invention further comprises a flow control valve indicated generally by arrow 40, and an exhaust gas heat exchanger 42, each of which is formed as a separate sub-assembly. The valve 40 comprises a body 44 containing, in this embodiment, a stepper motor or DC motor 46 (Fig. 2) acting on a slidable valve stem 48 carrying a valve closure member 50 at its inner end. The valve body 44 has a flange 52 by means of which it can be bolted to the second flange 22 of the main body part 12. As shown in Fig. 2, the valve 40 has an inner sleeve region 54 which extends into the second chamber 20 so that its inner end abuts against the annular rib 24. The inner end of the sleeve region 54 carries an annular valve seat 56 with which the valve closure member 50 co-operates. The inner end of the sleeve region 54 is sealed with the annular rib 24 by means of a heat- resistant stainless steel spring seal. The sleeve region 54 has an aperture 58 therethrough which is aligned with the inner end of the exhaust gas outlet duct 26. The valve stem 48 passes through an annular bush 60 which is supported internally of the sleeve region 54 and which serves to remove any carbon deposits which may be formed on the stem 48 in use. It will therefore be understood that the valve 40 can be formed as a sub-assembly which is inserted into the second chamber 20 and secured in position by means of bolts 62 (not shown) to the second flange 22 with an interposed O-ring seal or the like. The stepper motor/DC motor 46 is arranged to be precisely controlled by the engine management system of the internal combustion engine to which the system of the present invention is fitted so as to control the position of the valve closure member 50 relative to the annular valve seat 56. In this way, the proportion of exhaust gas being recirculated through the system can be accurately controlled in accordance with the prevailing engine conditions. The heat exchanger 42 is likewise formed as a sub-assembly which can be inserted into the first chamber 16. The heat exchanger 42 comprises a bundle of mutually parallel, heat exchange pipes 64 extending axially from a manifold 88 having a mounting flange 67. An exhaust gas inlet connection 68 extends outwardly from the manifold 66. In the drawing, this inlet connection 68 is shown simply as a short tube. However, it can be of any size, shape or length to enable it to be connected to the exhaust system of the internal combustion engine. The inlet connection 68 may include a sealed ball-and-socket arrangement to facilitate connection to the exhaust system. The bundle of heat exchange pipes 64 extends to the inner end of the first chamber 16 into which the inner ends of the pipes 64 open. The pipe bundle is fitted with O-ring seals 70 and 72 which seal with the wall of the first chamber 16. As can be seen from Fig. 1, the O-ring seals 70 and 72 are disposed so that the coolant inlet and outlet ducts 30 and 36 open into the first chamber 16 between these seals 70 and 72. The inner end of the bundle of heat exchange pipe 64 abuts against the annular rib 24 and is sealed therewith by a heat-resistant stainless steel spring seal (not shown). The heat exchange pipes 64 in the bundle are mutually spaced apart to allow for passage of coolant between them. A rib 74 is provided around the bundle so as to lie against a land 76 between the ducts 30 and 36. In this way, coolant from the inlet duct 30 is constrained to flow between the heat exchange pipes 64 and through the centre of the rib 74 before it can leave the system via the coolant outlet duct 36. The mounting flange 67 of the heat exchanger 42 is connected by bolts (not shown) to the first flange 18 so that there is an effective seal between these two flanges. A gasket may be interposed between these flanges. The coolant outlet duct 36 is connected via a hose to a heater matrix (not shown) which is provided for heating a passenger compartment of an automobile to which with the internal combustion engine and the system of the present invention are fitted. The coolant outlet duct 36 also has a connector which leads to a radiator which is provided in the vehicle for cooling the engine coolant. However, because the system of Fig. 1 is shown partly cut-away, this is not illustrated. If desired, there may be provided a by-pass duct extending directly between the ducts 30 and 36 so that a proportion of the coolant can by-pass the heat exchanger 42. The by-pass duct is provided, if required, to avoid excessive cooling of the recirculated exhaust gas. If desired, the housing may further include a connection leading from the outlet duct 36 which enables de-gassing of the coolant. In use, the system is secured by bolts (not shown) through the mounting flange 14 to the engine so that the coolant duct 30 is sealed by means of a gasket in registration with a coolant outlet from the engine through which coolant normally passes from the block to the engine cooling radiator and to the passenger compartment heater. Also, the cooled exhaust gas outlet duct 26 is connected via the flange 28 with an inlet manifold of the internal combustion engine so that exhaust gas from the exhaust of the vehicle can be recirculated back into the engine to reduce NO x emissions. The proportion of exhaust gas which is recirculated is controlled by the engine management system in a manner known per se using the valve 40. The exhaust gas path is illustrated by the arrow 80 whilst the coolant liquid path through the system is illustrated by the arrows 82. The siting of the valve 40 downstream of the heat exchanger 42 means that it is contacted by cooled rather than uncooled gas so mitigating the problem of overheating of the valve and ancillary control equipment. Cooling of the valve may take place by thermal transfer through the housing 10. If required, the coolant passage in the housing may be extended to the region of the housing adjacent to the valve. Additionally, siting of the valve 40 downstream of the heat exchanger permits it to be located close to the gas outlet duct 26, thereby enabling the gas flow to be controlled very close to where it enters the air inlet system. This enables response delays to be reduced. It will be appreciated from the above that the number of joints required is considerably reduced as compared with known exhaust gas recirculation assemblies. The system of the present invention is relatively light, compact and easy to install. Additionally, the number of bends in the exhaust gas flow is relatively small, thereby limiting turbulence and reducing the system mass flow properties, as well as limiting dead flow areas where deposits may build up.

Claims: CLAIMS 1. An exhaust gas recirculation system for an internal combustion engine, said system comprising a housing (10) having an exhaust gas flow passage therein; an adjustable flow control valve member (40) mounted in the housing (10) for controlling the flow of exhaust gas through the passage; an exhaust gas heat exchanger (42) mounted in the housing (10) so that, in use, the exhaust gas being recirculated flows through the heat exchanger (42); a coolant flow passage for passing coolant through the heat exchanger (42) to cool exhaust gas flowing therethrough in use; and exhaust gas inlet and outlet connections (68 and 26) communicating with the exhaust gas flow passage in the housing (10) and connectable, respectively, to an exhaust gas system and a combustion air inlet system of the internal combustion engine. 2. A system as claimed in claim 1, wherein the housing (10) is adapted to be attached directly to the engine so that an inlet (30) of the coolant passage in the housing is in registration with a coolant outlet from engine. 3. A system as claimed in claim 1, wherein the housing (10) is formed integrally with a cylinder block, a cylinder head, an inlet manifold or an outlet manifold of the internal combustion engine. 4. A system as claimed in any preceding claim, wherein the housing (10) is adapted to receive a thermostat for controlling the temperature of the coolant. 5. A system as claimed in any preceding claim, wherein the housing (10) is formed of a material having high heat transfer characteristics such that cooling of the valve member (40) is assisted by heat conduction through the housing (10). 6. A system as claimed in any one of claims 1 to 5, wherein the coolant flow passage extends in the housing (10) to the region of the valve member (40). 7. A system as claimed in any preceding claim, wherein the valve member (40) is located downstream of the heat exchanger (42) relative to the direction of flow of exhaust gas through the system. 8. A system as claimed in any preceding claim, wherein, in operation, the valve is disposed at a higher level than the heat exchanger. 9. A system as claimed in any preceding claim, wherein the exhaust gas heat exchanger (42) is mounted in a first chamber (16) in the housing (10). 10. A system as claimed in claim 9, wherein the exhaust gas heat exchanger (42) is a sub-assembly comprising heat exchange pipework (64), the exhaust gas inlet connection (68), and means (67) for securing the sub-assembly to the housing (10). 11. A system as claimed in claim 10, wherein the sub-assembly is detachably secured to the housing (10). 12. A system as claimed in any one of claims 9 to 11, wherein the housing (10) comprises a second chamber (20) in which the adjustable flow control valve member (40) is mounted, the second chamber (20) communicating with the first chamber (16) so that the exhaust gas flow passage extends through these chambers (16 and 20). 13. A system as claimed in any preceding claim, wherein the housing (10) is formed with a coolant outlet (36) which has two connections to enable coolant which has passed through the heat exchanger (42) to be connected to one or both of a radiator for cooling the internal combustion engine coolant and a heater for heating a passenger compartment of a vehicle in which the internal combustion engine is fitted. 14. A system as claimed in any preceding claim, wherein the housing (10) includes a connector (32) communicating with the coolant flow passage for enabling a temperature sensor (34) to be attached whereby to monitor the temperature of coolant flowing from the internal combustion engine in use into the system. 15. An internal combustion engine in combination with an exhaust gas recirculation system as claimed in any preceding claim, wherein the exhaust gas inlet connection (68) of the system is connected to an exhaust system of the internal combustion engine, and wherein the exhaust gas outlet connection (26) of the recirculation system is connected with an air intake system of the internal combustion engine. 16. An internal combustion engine as claimed in claim 15, wherein the air intake system includes a manifold formed of plastics lined with a heat-resistant liner. 17. An internal combustion engine as claimed in claim 15 or 16, wherein the exhaust gas inlet connection (68) of the system is connected with the exhaust system of the internal combustion engine via a duct which can be swivelled. 18. An internal combustion engine as claimed in claim 15 or 16, the position of the exhaust gas inlet connection (68) of the system is variable relative to the housing (10). 19. An internal combustion engine as claimed in claim 18, wherein a subassembly of the exhaust gas heat exchanger (42) including the exhaust gas inlet connection (68) is adjustably mounted in the housing (10).

Inventors: CERIO DARREN, MIYAKE TOSHIHIKO, MIYOSHI SOTSUO, CERIO, DARREN, MIYAKE, TOSHIHIKO, MIYOSHI, SOTSUO
Applicants: MITSUBISHI ELECTRIC CORP, TRANSTEC PLC, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 2000
Main classification: F02M25
IPC codes: F02M25, F28F27