Abstract:
An EGR system includes an intake and an exhaust valve arranged in a cylinder head of an engine, a first link pivotally supported by the cylinder head using a first pivot member for actuating the intake valve, a second link pivotally supported by the cylinder using a second pivot member for actuating the exhaust valve, an EGR adjuster connected to a proximal end of the first link and contacted a lower surface of the second link for adjusting exhaust valve opening.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    (a) Field of the Invention  
           [0002]    The present invention relates to an exhaust gas recirculation (EGR) system, and more particularly, to an improved exhaust gas recirculation system capable of controlling an amount of recirculating exhaust gas according to exterior temperature.  
           [0003]    (b) Description of the Related Art  
           [0004]    The EGR system is a system for recirculating a portion of exhaust gas to an intake part of an engine so as to reduce generation of nitrogen oxides (NOx). Typically, the EGR system comprises an EGR valve connecting the exhaust and intake manifolds and which controls an amount of recirculating exhaust gas according to a state of the intake manifold such that some of the exhaust gas flows into the intake manifold having a relatively lower pressure than the exhaust manifold, when the EGR valve is opened. There are two kinds of EGR valves, i.e., a pneumatic EGR valve using pressure difference between the intake and exhaust manifolds, and an electronic EGR valve using solenoid valves. The pneumatic EGR valve is used in small size engines requiring an EGR amount of 5˜10% and the electronic EGR valve in relative large size engines requiring an EGR amount of 15˜20%.  
           [0005]    [0005]FIG. 1 is a schematic view of a conventional pneumatic EGR system. As shown in FIG. 1, intake air is supplied to an engine  20  via an air cleaner  12 , throttle body  14  and intake manifold  18 . The amount of intake air is adjusted by a throttle valve  16  arranged in the throttle body  14 . The intake air is mixed with fuel in combustion chambers of the engine and the exhaust emission after combustion of the mixed gas is exhausted through the exhaust manifold  22 . From an initial closed state, the EGR valve  26  opens by pressure difference between the intake and exhaust manifolds  18  and  22  of the engine  20  when the throttle valve  16  is closed, that is, the intake part pressure becomes lower than the exhaust part pressure such that a valve plate  23  moves upward by overcoming an elastic force of a spring  27  of the EGR valve  22  so as to open an EGR passage  24 , resulting in exhaust gas flowing into the intake part. A reference numeral  28  indicates an EGR-back pressure transducer (EGR-BPT) valve which adjusts pressure level applied to the EGR valve  26 .  
           [0006]    However, this conventional EGR system has a drawback in that the structure is complicated and requires many parts. Also, the electronic EGR valve requires a complicated EGR logic system and gives much processing burden to a controller.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention has been made in an effort to solve the above problems of the prior art.  
           [0008]    It is an object of the present invention to provide an improved EGR system capable of adjusting an amount of exhaust gas recirculated into a combustion chamber according to exterior temperature.  
           [0009]    To achieve the above object, an EGR system comprises an intake and an exhaust valve arranged in a cylinder head of an engine, a first link pivotally supported by the cylinder head using a first pivot member for actuating the intake valve, a second link pivotally supported by the cylinder head using a second pivot member for actuating the exhaust valve, and an EGR adjuster connected to a proximal end of the first link and contacting a lower surface of the second link for adjusting exhaust valve opening. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and together with the description, serve to explain the principles of the invention:  
         [0011]    [0011]FIG. 1 is a schematic view showing a prior art EGR system;  
         [0012]    [0012]FIG. 2 is a front view illustrating an EGR system according to a preferred embodiment of the present invention when an EGR amount is small; and  
         [0013]    [0013]FIG. 3 is a front view illustrating the EGR system of FIG. 2 when the EGR amount is large. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]    A preferred embodiment of the present invention will be described hereinafter with reference to the accompanying drawings. In the following detailed description, only the preferred embodiment of the invention has been shown and described, simply by way of illustration of the best mode contemplated by the inventor of carrying out the invention. As will be realized, the invention is capable of modification in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not restrictive.  
         [0015]    [0015]FIG. 2 and FIG. 3 are respective front views illustrating an EGR system according to a preferred embodiment of the present invention when an EGR amount is small and large.  
         [0016]    The EGR system of the present invention comprises an intake and an exhaust valve  110  and  120 , a first link  130  pivotally supported by a cylinder head (not shown) using a first pivot  132  approximately at its middle portion and one end of which is perpendicularly contacting an upper end  112  of the intake valve  110 , a second link  140  pivotally supported by a cylinder head using a second pivot  142  approximately at its middle portion and one end of which is perpendicularly contacting an upper end  122  of the exhaust valve  120 , and an EGR adjuster  150  interposed between the first and second links  130  and  140 , the EGR adjuster  150  being connected to the other end of the first link  130  and contacting the other end of the second link  140 .  
         [0017]    The first and second links  130  and  140  can be rocker arms appropriately modified for being adapted to the present invention or separate members that can cooperate with the corresponding rocker arms.  
         [0018]    The EGR adjuster  150  comprises a cylindrical housing  152  integrally connected to the end of the first link  130  in a longitudinal direction, a piston rod  154  with a plunger  156  tightly inserted into the housing so as to separate an inner space of the housing into left and right compartments, with one end of the piston rod  154  protruding outside the housing  152  such that a distal end of the piston rod  154  contacts a lower surface of the second link  140 , a coil spring  158  installed in the right compartment defined so as to bias the plunger  156  in a left direction, a thermal sensitive material stored in the left compartment of the housing  152 , and an air port  160  connected to the compartment where the thermal sensitive material is stored such that the thermal sensitive material expands to push the plunger  156  by overcoming the elastic force of the coil spring  158  when it is exposed to high temperature air from the air port  160 . The air port  160  is connected to an air passage  162  which communicates outside for guiding outside air.  
         [0019]    The operation of the above structured EGR system will be described hereinafter.  
         [0020]    The first and second links  130  and  140  act as rocker arms so as to actuate the intake and exhaust valves  110  and  120 . The second link  140  independently actuates the exhaust valve  120  during an exhaust stroke of the engine. At the same time the first link  130  actuates the intake valve  110  to be opened, it causes the second link  140  to responsively actuate the exhaust valve  120  to be opened. That is, during an intake stroke of the engine, the first link  130  rotates in a clockwise direction such that the distal end of the first link  130  pushes down the intake valve  110  and the other end of the first link  130  moves upward. Accordingly, the distal end of the piston rod  154  of the EGR adjuster  152  pushes up the one end of the second link  140  since the distal end of the piston rod  154  contacts the lower surface of the second link  140  such that the second link  140  rotates in a counter clockwise direction, resulting in the distal end of the second link  140  pushing down the exhaust valve  120  and opening it.  
         [0021]    During this intake operation of the engine, an opening amount of the exhaust valve  120  is determined by a rotational angle of the second link  140  and the rotational angle of the second link is determined by a distance “B” between the second pivot  142  and a contact point where the second link contacts the end of the piston rod  154 . That is, the shorter the distance “B”, the larger the rotational angle of the second link  140  and also the opening amount of the exhaust valve  120 .  
         [0022]    The distance “B” varies according to how much the piston rod  154  is protruded out of the housing  152  of the EGR adjuster  150  by the elastic force of the spring  158 . Protrusion of the piston rod  154  is limited by a volume of the thermal sensitive material stored in the left compartment of the housing  152 . The thermal sensitive material can be a material that sensitively expands and contracts according to temperature, such wax pellets used in thermostats.  
         [0023]    As shown in FIG. 2, the thermal sensitive material expands when it is exposed to high temperature air guided through the air port  160  and air passage  162 . In this case, the thermal sensitive material expands to push the plunger  156  to the right by overcoming the elastic force of the coil spring  158  such that the piston rod  154  withdraws into the housing  152 , resulting in the length “B” being maximized. Accordingly, the second link  140  rotates a small angle in the counter clockwise according to the rotation of the first link  130  in a clockwise direction during the intake stroke of the engine such that the exhaust valve  120  opens a small amount in order to let in a small amount of the exhaust gas remaining in an exhaust manifold (not shown).  
         [0024]    In FIG. 3, the thermal sensitive material is contracted when it is exposed to a lower temperature air from outside, such that the plunger  156  moves to the left by the elastic force of the coil spring  158 . This causes the piston rod  154  to be fully protruded out of the housing  152  such that the length “B” is shortened to cause the second link  140  to sensitively rotate in a counter clockwise direction in response to the rotation of the first link  130  in a clockwise direction during the intake stroke of the engine. Accordingly, the exhaust valve  120  opens so as to let in a relatively large amount of the exhaust gas remaining in the exhaust manifold.  
         [0025]    It is preferred that a ratio among the distances “A” between the second pivot  142  and the contact point of the second link  140  with the upper end of the exhaust valve  120 , “B” between the second pivot  142  and the contact point of the second link  140  with the distal end of the piston rod  154 , “C” between the contact point of the second link  140  with the distal end of the piston rod  154  and the first pivot  132  of the first link  130 , and “D” between the first pivot  132  and the contact point of the first link  130  with the upper end of the intake valve  110  is 1:1:1:8 when the air temperature from the air port  160  is higher than a first predetermined threshold temperature, i.e., when the piston rod  154  is fully withdrawn into the housing  152  such that the intake and exhaust valves open in a ratio of 8:1 during the intake stroke of the engine, as show in FIG. 2.  
         [0026]    Also, it is preferred that the ratio among the distances “A,” “B,” “C,” and “D” is 1:0.5:1.5:8 when the air temperature from the air port  160  is lower than a second predetermined threshold temperature, i.e., when the piston rod  154  is fully extended out of the housing  152  such that the intake and exhaust valves open in a ratio of 8:3 during the intake stroke of the engine, as shown in FIG. 3.  
         [0027]    The opening ratio can continuously vary between the ratios 8:1 and 8:3 according to the outside temperature change.  
         [0028]    As described above, the EGR system of the present invention can adjust the EGR amount by controlling the exhaust valve opening according to the outside temperature such that the EGR amount increases in the cold weather of winter and decreases in the hot weather of summer, resulting in efficiently reducing nitrogen oxide (NOx) emissions.  
         [0029]    Furthermore, since this EGR system works without the requirement of the conventional elements such as EGR valves and passages for recirculating the exhaust gas, the structure and EGR operation are simplified and EGR performance is improved.