Abstract:
A supporting structure for an engine timing chain comprising a chain guide for artificially limiting vertical movement of the timing chain near a camshaft sprocket, thereby reducing any abnormal engagement between the timing chain and camshaft sprocket while the camshaft sprocket is in motion, decreasing noise, and increasing the life of the components.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims priority of Korean Application No. 10-2003-0022621, filed on Apr. 10, 2003, the disclosure of which is incorporated fully herein by reference.  
         FIELD OF THE INVENTION  
         [0002]    The present invention relates to a supporting structure for an engine timing chain and, more particularly, to a chain guide for guiding movement of a timing chain.  
         BACKGROUND OF THE INVENTION  
         [0003]    In general, the interaction between a crankshaft and a camshaft that allows an intake and exhaust valve of an engine to open and close periodically causes the driving force to vary periodically because the driving force transmitted from the crankshaft to the camshaft is maximized when a cam lobe of the camshaft pushes against the intake or exhaust valve. In an engine using a timing chain around a crankshaft sprocket and a camshaft sprocket, a driving torque is periodically varied during a periodic opening and closing of intake and exhaust valves. The periodic variation of the driving torque forces the timing chain to move vertically (approximately 3-4 mm) in close proximity to the camshaft sprocket.  
           [0004]    However, a drawback in conventional engines using a timing chain is that vertical movement generated by the timing chain adjacent to the camshaft sprocket induces an uneven engagement between the sprocket and timing chain.  
           [0005]    There is another drawback in that operational noise occurs in the course of an engagement of the sprocket and timing chain for transmitting the driving force.  
           [0006]    There is still another drawback in that the chain link pins of the timing chain having relatively weak rigidity get damaged due to repetitive uneven engagement, thereby decreasing the life of components.  
         SUMMARY OF THE INVENTION  
         [0007]    Embodiments of the present invention provide an engine having a timing chain adapted to artificially restrict vertical movement of a timing chain in close proximity to a camshaft sprocket, thereby reducing any abnormal engagement between the camshaft sprocket and timing chain, decreasing noise, and increasing the life of components.  
           [0008]    In one preferred embodiment of the present invention, a supporting structure for an engine timing chain comprises a timing chain installed around a crankshaft sprocket and a camshaft sprocket to allow the camshaft to interact with the crankshaft for periodically opening and closing an intake and an exhaust valve. A chain guide guides movements of the timing chain in close proximity to the camshaft sprocket, such that the timing chain is restricted in vertical movement.  
           [0009]    The chain guide preferably further comprises a body part having a guide groove at its rear portion for allowing the timing chain to be inserted therein. A mounting boss part is integrally formed at a lower portion of the body part for fixing the chain guide.  
           [0010]    The chain guide is further preferably secured at a cam cap mounted on a journal part of the cylinder head, wherein the cam cap is integrally formed for simultaneously fixing the intake and exhaust camshafts at the journal part of the cylinder head.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    For fuller understanding of the nature and objects of the present invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings in which:  
         [0012]    [0012]FIG. 1 is a schematic drawing of a chain guide mounted on an engine timing chain according to an embodiment of the present invention;  
         [0013]    FIGS.  2 ( a ) and ( b ) respectively illustrate front and rear perspective views of the chain guide of FIG. 1;  
         [0014]    [0014]FIG. 3 is a perspective view illustrating a configuration and installation state of a cam cap for mounting a chain guide thereto according to the embodiment of the present invention; and  
         [0015]    [0015]FIGS. 4 and 5 respectively illustrate front and rear perspective views of the cam cap of FIG. 3. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings.  
         [0017]    As shown in FIG. 1, a timing chain  14  is installed around a crankshaft sprocket  10  and a camshaft sprocket  12 . A chain guide  16  is mounted adjacent to the camshaft sprocket  12  to restrict any vertical movement of the timing chain  14 .  
         [0018]    In a double overhead cam (DOHC) engine as shown in FIG. 1, the chain guide  16  is preferably installed between an intake camshaft sprocket  12   a  and an exhaust camshaft sprocket  12   b.    
         [0019]    With reference to FIGS.  2 ( a ) and ( b ), the chain guide  16  is formed with a mounting boss part  16   a  at its lower portion for fixing the chain guide  16  to an engine cylinder head or the like. A body part  16   b  having a guide groove  16   c  for fixing and supporting the timing chain  14  is formed at an upper portion of the mounting boss part  16   a.    
         [0020]    The chain guide  16  may be preferably installed at a cam cap  24  as shown in FIG. 3. The cam cap  24  is designed to fix an intake and an exhaust camshaft  20  and  22  at a journal part  18   a  of a cylinder head  18 . The cam cap  24  is, therefore, installed on the journal part  18   a  of the cylinder head  18  in close proximity to the camshaft sprocket  12 . A detailed configuration of the integral cam cap  24  is illustrated in FIGS. 4 and 5, respectively.  
         [0021]    The cam cap  24 , as shown in FIGS. 4 and 5, is formed with receptive grooves  24   a  at both ends of the journal part so as to support the intake and exhaust camshafts  20  and  22 . A mounting boss part  24   b  is disposed at a front center of the cam cap  24  to be correspondingly secured to the mounting boss part  16   a  of the chain guide  16 . A cut-out portion  24   c  is formed at a rear part of the mounting boss part  24   b  of the cam cap  24  to reduce the weight of the components.  
         [0022]    The chain guide  16  may be integrally manufactured with the cam cap  24 .  
         [0023]    The crankshaft sprocket  10  and camshaft sprocket  12  interact with each other via the timing chain  14  for periodically opening and closing an intake and exhaust valve of an engine. The chain guide  16 , for restricting the vertical movement of the timing chain  14 , is installed either at an adjacent portion of the camshaft sprocket  12  or between the intake camshaft sprocket  12   a  and the exhaust camshaft sprocket  12   b , such that vertical movement of the timing chain  14  according to the driving torque variation periodically generated from the camshaft sprocket  12  can be forcibly restricted.  
         [0024]    If the timing chain  14  is restricted in vertical movement via the chain guide  16 , the camshaft sprocket  12  and timing chain  14  uniformly engage with each other, so that noise emitted during the engagement is reduced. Furthermore, wear and tear on the components due to an uneven engagement is prevented, contributing to an increase in durability of the components.  
         [0025]    The cam cap assembled at the journal part  18   a  of the cylinder head  18  thus described for fixing the intake and exhaust camshaft  20  and  22  may be replaced by a cam cap  24  which fixes the intake and exhaust camshaft  20  and  22  at the same time, resulting in a reduction of the number of cam caps required during an engine assembly in comparison with the typical decoupled cam cap, and facilitation of maintaining the components.  
         [0026]    The cam cap  24  used for installing the chain guide  16  is formed with the cut-out portion  24   c  at the rear portion of the mounting boss part  24   b , thus reducing the weight of the cam cap integrally manufactured.  
         [0027]    As apparent from the foregoing, there is an advantage in that the supporting structure of the engine timing chain includes the chain guide  16  and the timing chain  14 , which transmits power between the crankshaft sprocket  10  and the camshaft sprocket  12 , thereby restricting vertical movement of the timing chain  14  in conjunction with the periodic change of the driving torque from the camshaft sprocket  12 , reducing noise generated by an abnormal meshing between the camshaft sprocket  12  and timing chain  14 , and optimizing the life of components.