Patent Publication Number: US-8973559-B2

Title: Gear subassembly and exhaust gas recirculation system

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based on Japanese Patent Application No. 2011-116984 filed on May 25, 2011, the disclosure of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates mainly to a gear subassembly obtained by integrating a gear which constitutes a part of reduction gears, and a cam which constitutes a part of a link mechanism. 
     BACKGROUND 
     Conventionally, a system, in which a gear subassembly is configured as a single component, is widely known for an exhaust gas recirculation system (hereinafter referred to as an EGR system) that recirculates exhaust gas discharged from an internal combustion engine into an intake-air passage (see, for example, JP-A-2010-190116 corresponding to US2010/0206274A1). 
     A system provided with a turbocharger that rotates an exhaust turbine by exhaust gas and compresses intake air through a compressor coaxial with the exhaust turbine is known for an air intake and exhaust system of the engine. In the air intake and exhaust system equipped with the turbocharger, the EGR system recirculates exhaust gas into an intake passage mainly through a low-pressure EGR passage that communicates between an exhaust passage on a downstream side of the exhaust turbine in an exhaust gas flow direction, and the intake passage on an upstream side of the compressor in an intake air flow direction. 
     The EGR system includes an EGR valve that changes an opening degree of the low-pressure EGR passage so as to increase or decrease the amount of exhaust gas recirculated, an electric motor that generates output for driving the EGR valve, reduction gears that decelerate the output of the electric motor to transmit it to the EGR valve, an intake throttle valve that reduces a flow of intake air in the intake passage on an upstream side of an exhaust-gas merging part in the intake air flow direction, and a link mechanism that synchronizes movement of the intake throttle valve with movement of the EGR valve. 
     The gear subassembly is configured, for example, by integrating a gear that is a part of the reduction gears and is fastened to a rotatable shaft of the EGR valve, and a cam having a cam profile that is a part of the link mechanism and shows a synchronization pattern of the intake throttle valve relative to the EGR valve, and the subassembly thereby serves as one component of the EGR system. Recent demand for high fuel efficiency of a vehicle is extremely great. To cope with such demand for fuel efficiency, request for weight saving of the gear subassembly becomes high, too. 
     SUMMARY 
     According to the present disclosure, there is provided a gear subassembly for an exhaust gas recirculation (EGR) system including an EGR valve and a rotatable shaft provided for the EGR valve. The gear subassembly includes a gear and a cam. The gear is a part of reduction gears and is fastened to the rotatable shaft to rotate therearound. The cam is fastened to the gear and is a part of a link mechanism. The gear includes a metal shaft-fastening part used for fastening the gear to the rotatable shaft, and a metal cam-fastening part used for fastening the gear to the cam. The gear is formed by resin-molding with the shaft-fastening part and the cam-fastening part serving as insert parts. 
     According to the present disclosure, there is also provided an exhaust gas recirculation (EGR) system that is a part of an air intake and exhaust system for an internal combustion engine. The air intake and exhaust system includes a turbocharger, an exhaust passage for exhaust gas, and an intake passage for intake air. The turbocharger has an exhaust turbine and a compressor coaxial with the exhaust turbine, and is configured to rotate the exhaust turbine by exhaust gas discharged from the engine and to compress intake air drawn into the engine through the compressor. The EGR system includes the gear subassembly, an EGR passage, the EGR valve, an electric motor, and an intake throttle valve. A part of exhaust gas is recirculated through the EGR passage from the exhaust passage on a downstream side of the exhaust turbine in a flow direction of exhaust gas into the intake passage on an upstream side of the compressor in a flow direction of intake air. The EGR valve is configured to open or close the EGR passage. The electric motor is configured to generate output to drive the EGR valve. The intake throttle valve is disposed in the intake passage to reduce a flow of intake air on an upstream side of a connecting portion between the intake passage and the EGR passage in the flow direction of intake air. The reduction gears are configured to decelerate the output of the electric motor and transmit the decelerated output to the EGR valve. The rotatable shaft is a rotation center of the EGR valve. The link mechanism is configured to synchronize movement of the intake throttle valve with movement of the EGR valve. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: 
         FIG. 1  is a diagram illustrating a configuration of an air intake and exhaust system of an internal combustion engine in accordance with a first embodiment; 
         FIG. 2  is a diagram illustrating a configuration of an EGR system in accordance with the first embodiment; 
         FIG. 3A  is a plan view illustrating a gear subassembly in accordance with the first embodiment; 
         FIG. 3B  is a sectional view taken along a line IIIB-IIIB in  FIG. 3A ; 
         FIG. 4  is an exploded perspective view illustrating the gear subassembly of the first embodiment; 
         FIG. 5A  is a perspective view illustrating a plate and a nut in accordance with the first embodiment; 
         FIG. 5B  is a perspective view illustrating a gear in accordance with the first embodiment; 
         FIG. 6A  is a plan view illustrating a gear subassembly in accordance with a second embodiment; 
         FIG. 6B  is a sectional view taken along a line VIB-VIB in  FIG. 6A ; 
         FIG. 7  is a perspective view illustrating an integrated object of a plate and a nut in accordance with the second embodiment; 
         FIG. 8  is a diagram illustrating a production method for the integrated object of the second embodiment; 
         FIG. 9  is a diagram illustrating a production method for an integrated object in accordance with a modification; and 
         FIG. 10  is a diagram illustrating a production method for an integrated object in accordance with a modification. 
     
    
    
     DETAILED DESCRIPTION 
     In accordance with a first embodiment, a gear subassembly is for an exhaust gas recirculation (EGR) system including an EGR valve and a rotatable shaft provided for the EGR valve. The gear subassembly includes a gear and a cam. The gear is a part of reduction gears and is fastened to the rotatable shaft to rotate therearound. The cam is fastened to the gear and is a part of a link mechanism. The gear includes a metal shaft-fastening part used for fastening the gear to the rotatable shaft, and a metal cam-fastening part used for fastening the gear to the cam. The gear is formed by resin-molding with the shaft-fastening part and the cam-fastening part serving as insert parts. 
     An exhaust gas recirculation (EGR) system is a part of an air intake and exhaust system for an internal combustion engine. The air intake and exhaust system includes a turbocharger, an exhaust passage for exhaust gas, and an intake passage for intake air. The turbocharger has an exhaust turbine and a compressor coaxial with the exhaust turbine, and is configured to rotate the exhaust turbine by exhaust gas discharged from the engine and to compress intake air drawn into the engine through the compressor. The EGR system includes the gear subassembly, an EGR passage, the EGR valve, an electric motor, and an intake throttle valve. A part of exhaust gas is recirculated through the EGR passage from the exhaust passage on a downstream side of the exhaust turbine in a flow direction of exhaust gas into the intake passage on an upstream side of the compressor in a flow direction of intake air. The EGR valve is configured to open or close the EGR passage. The electric motor is configured to generate output to drive the EGR valve. The intake throttle valve is disposed in the intake passage to reduce a flow of intake air on an upstream side of a connecting portion between the intake passage and the EGR passage in the flow direction of intake air. The reduction gears are configured to decelerate the output of the electric motor and transmit the decelerated output to the EGR valve. The rotatable shaft is a rotation center of the EGR valve. The link mechanism is configured to synchronize movement of the intake throttle valve with movement of the EGR valve. 
     In accordance with a second embodiment, the shaft-fastening part and the cam-fastening part are in direct contact with each other without molding-resin therebetween. The shaft-fastening part and the cam-fastening part are configured as an integrated object. The gear is formed by resin-molding with the integrated object serving as a single insert part. The integrated object is provided by press-fitting one of the shaft-fastening part and the cam-fastening part into the other one of the shaft-fastening part and the cam-fastening part. 
     (First Embodiment) 
     Configuration of the gear subassembly of the first embodiment will be described. The gear subassembly of the first embodiment (hereinafter referred to as “subassembly”)  1  will be explained with reference to  FIGS. 1 to 5B . The subassembly  1  is obtained by integrating a gear  3  which is a part of reduction gears  2 , and a cam  5  which is fastened to the gear  3  and is a part of a link mechanism  4 . For example, the subassembly  1  is one component of an EGR system  8  that returns exhaust gas discharged from an internal combustion engine  6  into an intake passage  7 . 
     The EGR system  8  serves as a part of an air intake and exhaust system  10  of the engine  6 . For example, the EGR system  8  includes a low-pressure EGR system  12  that recirculates exhaust gas to the intake passage  7  through a low-pressure EGR passage  11 , and a high-pressure EGR system  14  that recirculates exhaust gas to the intake passage  7  through a high-pressure EGR passage  13 . 
     The air intake and exhaust system  10  includes a turbocharger  18  that rotates an exhaust turbine  17  by exhaust gas and compresses intake air through a compressor  16 , which is coaxial with the exhaust turbine  17 . The low-pressure EGR system  12  returns exhaust gas into the intake passage  7  through the low-pressure EGR passage  11  that communicates between an exhaust passage  19  on a downstream side of the exhaust turbine  17  in an exhaust gas flow direction, and the intake passage  7  on an upstream side of the compressor  16  in an intake air flow direction. The high-pressure EGR system  14  returns exhaust gas into the intake passage  7  through the high-pressure EGR passage  13  that communicates between the exhaust passage  19  on an upstream side of the exhaust turbine  17  in the exhaust gas flow direction, and the intake passage  7  on a downstream side of a throttle device  20  in the intake air flow direction. 
     Except for the EGR system  8  and the turbocharger  18 , the air intake and exhaust system  10  includes, for example, an air cleaner  21 , an inter cooler  22 , and a diesel particulate filter (DPF)  23 , which are widely known. Moreover, the air intake and exhaust system  10  includes a predetermined electronic control unit (not shown: hereinafter referred to as an ECU). The ECU controls operations of the devices provided for the low-pressure and high-pressure EGR systems  12 ,  14  to realize air intake and exhaust in accordance with an operational state of the engine  6 . 
     The low-pressure EGR system  12  includes a low-pressure EGR valve  25  that changes an opening degree of the low-pressure EGR passage  11  so as to increase or decrease the amount of exhaust gas recirculated; an electric motor  26  that generates output for driving the low-pressure EGR valve  25 ; the reduction gears  2  that decelerate the output of the electric motor  26  to transmit it to the low-pressure EGR valve  25 ; an intake throttle valve  27  that reduces a flow of intake air at the intake passage  7  on an upstream side of its connecting portion with the low-pressure EGR passage  11  in the intake air flow direction; the link mechanism  4  that synchronizes movement of the intake throttle valve  27  with movement of the low-pressure EGR valve  25 ; and a low-pressure EGR cooler  28  that cools exhaust gas on an upstream side of the low-pressure EGR valve  25  in the exhaust gas flow direction. 
     The reduction gears  2  include a major diameter gear  3  that is fastened to the rotatable shaft  30  of the low-pressure EGR valve  25  to rotate with the rotatable shaft  30  serving as the rotation center; a minor diameter gear  31  that is fastened to an output shaft of the electric motor  26 ; and an intermediate gear  32  having in a coaxial manner major diameter gear teeth engaged with the teeth of the gear  31  and minor diameter gear teeth engaged with the teeth of the gear  3 . 
     The intake throttle valve  27  is for promoting the recirculation of exhaust gas via the low-pressure EGR passage  11  through the reduction of the intake passage  7  to increase a differential pressure between the exhaust passage  19  and the intake passage  7 . The link mechanism  4  transmits the output of the electric motor  26  serving as an actuator of the low-pressure EGR valve  25  to the intake throttle valve  27  so as to rotate the intake throttle valve  27  by the output of the electric motor  26 . Accordingly, the link mechanism  4  eliminates an actuator for the intake throttle valve  27  to achieve cost reduction of the low-pressure EGR system  12 . 
     The link mechanism  4  includes the cam  5  serving as a driving-side member that is incorporated coaxially with the low-pressure EGR valve  25  and the gear  3  and rotated by the output of the electric motor  26 ; and a linking lever  34  serving as a driven-side member that is incorporated coaxially with the intake throttle valve  27  and rotated upon transmission of the output of the electric motor  26  from the cam  5 . The cam  5  includes a cam profile  35  that shows a synchronization pattern of the intake throttle valve  27  relative to the low-pressure EGR valve  25 . The linking lever  34  includes a driven pin  36  which is in contact with the cam profile  35  and to which the output of the electric motor  26  is transmitted from the cam  5 . The linking lever  34  rotates the intake throttle valve  27  by the rotation of the lever  34  as a result of the output transmitted through the driven pin  36 . 
     A synchronization relationship between the low-pressure EGR valve  25  and the intake throttle valve  27  through the link mechanism  4  is set such that when the low-pressure EGR valve  25  rotates on an open side (direction to open the low-pressure EGR passage  11 ), the intake throttle valve  27  rotates on a closed side (direction to close the intake passage  7 ). 
     The gear  3  is urged by a torsion spring  37  in a direction to rotate the low-pressure EGR valve  25  on its closed side, and the linking lever  34  is urged by a torsion spring  38  in a direction to rotate the intake throttle valve  27  on its open side. The output of the electric motor  26  is transmitted to the low-pressure EGR valve  25  through the reduction gears  2  so as to rotate the low-pressure EGR valve  25  on its open side against urging force of the torsion spring  37 . The output of the electric motor  26  is transmitted to the intake throttle valve  27  through the reduction gears  2  and the link mechanism  4  so as to rotate the intake throttle valve  27  on its closed side against urging force of the torsion spring  38 . 
     In addition, the high-pressure EGR system  14  includes, for example, a high-pressure EGR valve  40  that changes an opening degree of the high-pressure EGR passage  13  so as to increase or decrease the amount of exhaust gas recirculated; a high-pressure EGR cooler  41  that cools exhaust gas on an upstream side of the high-pressure EGR valve  40  in the exhaust gas flow direction; a cooler bypass  42  that bypasses the high-pressure EGR cooler  41  to guide exhaust gas into the intake passage  7 ; and a changeover valve  43  that switches a recirculation passage for exhaust gas between the high-pressure EGR cooler  41  and the cooler bypass  42 . 
     Next, the subassembly  1  will be described with reference mainly to  FIGS. 3A to 5B . The subassembly  1  is obtained as a result of integrating the gear  3  that constitutes the reduction gears  2  and the cam  5  that constitutes the link mechanism  4 , by fastening via a screw  45 . 
     The gear  3  is provided by resin-forming whereby a metal plate (shaft-fastening part)  46  used for fastening of the gear  3  to the rotatable shaft  30 , and a metal nut (cam-fastening part)  47  used for screw-fastening of the gear  3  to the cam  5  are insert parts. A fitting hole  49 , into which one end part  48  of the rotatable shaft  30  is fitted, is formed through the metal plate  46 . The rotatable shaft  30  and the plate  46  are fastened together as a result of the one end part  48  being fitted into the fitting hole  49 . In addition, a permanent magnet  50  is attached on an inner peripheral surface of the gear  3 , and the permanent magnet  50  serves as a part of a rotational angle sensor that detects a rotation angle of the low-pressure EGR valve  25 . 
     Effects of the subassembly  1  of the first embodiment will be described. The subassembly  1  of the first embodiment includes the gear  3  which is a part of reduction gears  2 , and the cam  5  which is fastened to the gear  3  and is a part of the link mechanism  4 . The gear  3  is provided by resin-forming whereby the metal plate  46  used for fastening of the gear  3  to the rotatable shaft  30 , and the metal nut  47  used for fastening of the gear  3  to the cam  5  are insert parts. 
     Therefore, in the gear  3 , which constitutes the subassembly  1 , a part which requires high strength is formed from metal, and a part which does not require very high strength is made from resin. Accordingly, the weight of the gear  3  can be reduced compared to a case of the entire gear  3  being made from metal. As a result, weight saving of the subassembly  1  obtained by integrating the gear  3  which constitutes a part of reduction gears  2 , and the cam  5  which constitutes a part of the link mechanism  4  can be achieved. 
     The subassembly  1  is applied to the low-pressure EGR system  12  including the intake throttle valve  27  in the air intake and exhaust system  10  of the engine  6 . The gear  3  is configured as a part of the reduction gears  2  that decelerate the output of the electric motor  26  to transmit it to the low-pressure EGR valve  25 . The cam  5  is configured as a part of the link mechanism  4  that synchronizes the movement of the intake throttle valve  27  with the movement of the low-pressure EGR valve  25 . 
     The torsion springs  37 ,  38  that urge the low-pressure EGR valve  25  and the intake throttle valve  27  respectively in the opposite directions from directions of their movements due to the output of the electric motor  26  are provided for the low-pressure EGR system  12  having the intake throttle valve  27 . The torsion springs  37 ,  38  strongly urge the low-pressure EGR valve  25  and the intake throttle valve  27  respectively. For this reason, the strong urging force of the torsion spring  37  is transmitted to the plate  46  through the rotatable shaft  30 , and the strong urging force of the torsion spring  38  is transmitted through the link mechanism  4  to the nut  47 . 
     Therefore, in such a low-pressure EGR system  12 , high strength is required for the plate  46  and the nut  47 , and the plate  46  and the nut  47  have a substantial need to be formed from metal. Thus, to increase the strength of the gear  3  by making only the plate  46  and the nut  47  out of metal is an extremely effective method for achieving the weight saving of the subassembly  1 . 
     (Second Embodiment) 
     In the subassembly  1  of the second embodiment, as illustrated in  FIGS. 6A to 7 , a plate  46  and a nut  47  are configured as an integrated object  52 , and a gear  3  is provided by resin-forming with the integrated object  52  as a single insert part. As illustrated in  FIG. 8 , a hole  53  for press-fitting is provided for the plate  46 , and the nut  47  is press-fitted into the plate  46 , so that the integrated object  52  is provided. 
     As a result, the plate  46  and the nut  47  are in direct contact with each other without molding-resin therebetween. Consequently, force can be transmitted from the plate  46  to the cam  5  without the molding-resin therebetween, and reliability of the subassembly  1  can thereby be improved. 
     Furthermore, the gear  3  is provided by resin-forming with the integrated object  52  as a single insert part. Accordingly, the number of insert parts that should be set in a die for forming the gear  3  can be reduced compared to the case of the plate  46  and the nut  47  being separately provided. For this reason, the production cost of the subassembly  1  can be reduced. 
     Modifications of the above embodiments will be described. The mode of the subassembly  1  is not limited to the above embodiments, and various modifications can be possible. For example, in the subassembly  1  of the second embodiment, the hole  53  for press-fitting is provided for the plate  46 , and the nut  47  is press-fitted into the plate  46 , so that the integrated object  52  is provided; but alternatively, a hole  53  for press-fitting may be provided for a nut  47 , and a projection for press-fitting may be provided for a plate  46 , and an integrated object  52  may be provided by press-fitting the plate  46  into the nut  47 . 
     In addition, an integrated object  52  can be configured as one casting (see  FIG. 9 ), or a burring hole may be made to rise through press-working of a plate-like metallic material and then the burring hole may be formed to have a part corresponding to a screw hole of a nut  47  (see  FIG. 10 ). 
     Moreover, instead of forming the plate  46  and the nut  47  as the integrated object  52 , the gear  3  may be resin-formed such that the plate  46  and the nut  47  are in direct contact with each other inside the gear  3 . In this case, although in resin-forming of the gear  3 , the number of insert parts increases compared to the case of the integrated object  52  being used as an insert part, the force can be transmitted from the plate  46  to a cam  5  without molding-resin therebetween, since the plate  46  and the nut  47  are in direct contact inside the gear  3 . Thus, the reliability of the subassembly  1  can be improved. 
     Furthermore, the subassembly  1  of the above embodiments is applied to the low-pressure EGR system  12  including the intake throttle valve  27 , in the air intake and exhaust system  10  of the engine  6 . The gear  3  is configured as a part of the reduction gears  2  that decelerate the output of the electric motor  26  to transmit it to the low-pressure EGR valve  25 . The cam  5  is configured as a part of the link mechanism  4  that synchronizes the movement of the intake throttle valve  27  with the movement of the low-pressure EGR valve  25 . Nevertheless, the subassembly  1  may be applicable to other uses. 
     To sum up, the gear subassembly  1  and the exhaust gas recirculation (EGR) system  8  in accordance with the above embodiments may be described as follows. 
     A gear subassembly  1  is for an exhaust gas recirculation (EGR) system  8  including an EGR valve  25  and a rotatable shaft  30  provided for the EGR valve  25 . The gear subassembly  1  includes a gear  3  and a cam  5 . The gear  3  is a part of reduction gears  2  and is fastened to the rotatable shaft  30  to rotate therearound. The cam  5  is fastened to the gear  3  and is a part of a link mechanism  4 . The gear  3  includes a metal shaft-fastening part  46  used for fastening the gear  3  to the rotatable shaft  30 , and a metal cam-fastening part  47  used for fastening the gear  3  to the cam  5 . The gear  3  is formed by resin-molding with the shaft-fastening part  46  and the cam-fastening part  47  serving as insert parts. 
     Therefore, in the gear  3 , which constitutes the gear subassembly  1 , a part which requires high strength is formed from metal, and a part which does not require very high strength is made from resin. Accordingly, the weight of the gear  3  can be reduced compared to a case of the entire gear  3  being made from metal. As a result, weight saving of the gear subassembly  1  obtained by integrating the gear  3  which constitutes a part of reduction gears  2 , and the cam  5  which constitutes a part of the link mechanism  4  can be achieved. 
     The shaft-fastening part  46  and the cam-fastening part  47  may be in direct contact with each other without molding-resin therebetween. Accordingly, the force can be transmitted from the shaft-fastening part  46  to the cam  5  without molding-resin therebetween. Thus, the reliability of the gear subassembly  1  can be improved. 
     The shaft-fastening part  46  and the cam-fastening part  47  may be configured as an integrated object  52 . The gear  3  may be formed by resin-molding with the integrated object  52  serving as a single insert part. Accordingly, the number of insert parts that should be set in a die for forming the gear  3  can be reduced compared to the case of the shaft-fastening part  46  and the cam-fastening part  47  being separately provided. For this reason, the production cost of the gear subassembly  1  can be reduced. 
     The integrated object  52  may be provided by press-fitting one of the shaft-fastening part  46  and the cam-fastening part  47  into the other one of the shaft-fastening part  46  and the cam-fastening part  47 . Furthermore, the integrated object  52  may be a casting. In addition, the integrated object  52  may be formed from a plate-like metallic material and configured as a burring hole, which is made to rise from the metallic material through press-working of the metallic material. At least one of the shaft-fastening part  46  and the cam-fastening part  47  may be provided by processing the burring hole. 
     An exhaust gas recirculation (EGR) system  8  is a part of an air intake and exhaust system  10  for an internal combustion engine  6 . The air intake and exhaust system  10  includes a turbocharger  18 , an exhaust passage  19  for exhaust gas, and an intake passage  7  for intake air. The turbocharger  18  has an exhaust turbine  17  and a compressor  16  coaxial with the exhaust turbine  17 , and is configured to rotate the exhaust turbine  17  by exhaust gas discharged from the engine  6  and to compress intake air drawn into the engine  6  through the compressor  16 . The EGR system  8  includes the gear subassembly  1 , an EGR passage  11 , the EGR valve  25 , an electric motor  26 , and an intake throttle valve  27 . A part of exhaust gas is recirculated through the EGR passage  11  from the exhaust passage  19  on a downstream side of the exhaust turbine  17  in a flow direction of exhaust gas into the intake passage  7  on an upstream side of the compressor  16  in a flow direction of intake air. The EGR valve  25  is configured to open or close the EGR passage  11 . The electric motor  26  is configured to generate output to drive the EGR valve  25 . The intake throttle valve  27  is disposed in the intake passage  7  to reduce a flow of intake air on an upstream side of a connecting portion between the intake passage  7  and the EGR passage  11  in the flow direction of intake air. The reduction gears  2  are configured to decelerate the output of the electric motor  26  and transmit the decelerated output to the EGR valve  25 . The rotatable shaft  30  is a rotation center of the EGR valve  25 . The link mechanism  4  is configured to synchronize movement of the intake throttle valve  27  with movement of the EGR valve  25 . 
     This aspect of the disclosure uses the gear subassembly  1  for the EGR system  8  that recirculates exhaust gas into the intake passage  7  through the low-pressure EGR passage  11 . The gear subassembly  1  is obtained by combining together the gear  3  fastened to the rotatable shaft  30  of the EGR valve  25 , and the cam  5  having the cam profile  35  that shows a synchronization pattern of the intake throttle valve  27  relative to the EGR valve  25 . 
     In the EGR system  8  having these EGR valve  25  and intake throttle valve  27 , urging means such as the torsion springs  37 ,  38  that urge the EGR valve  25  and the intake throttle valve  27  respectively in the opposite directions from directions of their movements due to the output of the electric motor  26  are provided, and these urging means strongly urge the EGR valve  25  and the intake throttle valve  27 . For this reason, the strong urging force is transmitted through the rotatable shaft  30  from the urging means  37  for urging the EGR valve  25  to the shaft-fastening part  46 , and the strong urging force is transmitted through the link mechanism  4  to a cam-fastening part  47  from the urging means  38  for urging the intake throttle valve  27 . 
     Thus, in such an EGR system  8 , the shaft-fastening part  46  and the cam-fastening part  47  need high strength, and they have a substantial need to be formed from metal. Accordingly, the above-described effects can be significantly produced. 
     Additional advantages and modifications will readily occur to those skilled in the art. The disclosure in its broader terms is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described.