Abstract:
To operate a poppet valve in an internal combustion engine, a valve operating mechanism comprises a valve spring retainer which has a taper bore, a pair of cotters which is inserted in the bore to support the poppet valve, and a valve spring between the valve spring retainer and a cylinder head. There is provided means for preventing the cotters from falling out the bore.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a valve operating mechanism for a poppet valve of an internal combustion engine, said mechanism comprising a spring retainer made of light alloy such as Al alloy which is mounted to the poppet valve via steel cotters, thereby increasing load of falling the cotters out of the lower end of the spring retainer. 
     FIG. 6 illustrates an example of a known valve operating mechanism of an internal combustion engine, in which an A 1  alloy valve spring retainer  23  which has a taper bore  22  and a spring-retaining flange  23   a  is engaged with the upper end of a poppet valve  21  via a pair of steel cotters  24 . An annular bead  24   a  of each of the cotters  24  is engaged in an annular groove  21   a  of the poppet valve  22  so that the valve spring retainer  23  may not come out upwards. 
     Between the lower surface of the spring-retaining flange  23   a  and a cylinder head (not shown), a valve spring  25  is provided, and the poppet valve  21  is always urged upwards by the valve spring retainer  23 . 
     The numeral  26  denotes a rocker arm which is engageable on the upper end of the poppet valve  21 , and is moved up and down by a rotary cam (not shown) to open and close the poppet valve  21 . In the valve operating mechanism, the cotters  22  and the valve spring retainer  23  are integrally secured to the poppet valve  21  by wedge-like engagement of the cotters  24  with the bore  22 . To increase securing force, taper angle of the bore is decreased, and roughness of contact surface between the bore  22  and the cotters  24  is decreased to decrease frictional resistance, thereby strengthening wedge-like engagement. 
     However, in a valve operating mechanism which has a relatively low mechanical strength Al alloy valve spring retainer  23 , when the bore  22  is plastically deformed and expanded owing to increase in wedge-like engagement, the cotters  24  fall gradually owing to low frictional resistance of the contact surface between the bore  22  and the cotters  24 . The valve spring retainer  23  moves up gradually, so that load to the valve spring  25  is decreased to decrease the maximum rotation number of surging, so that engine performance is deteriorated. 
     When the cotters  24  fall deeply, the lower end of the valve spring retainer  23  is liable to cause cracking and to be damaged,. so that the cotters  24  come out. To solve the problem, the valve spring retainer  23  or the lower portion thereof increases in external diameter to increase rigidity and load of the cotters  24 . 
     However, the valve spring retainer  23  becomes larger to increase its weight. For Al alloy valve spring retainer made to lighten its weight, it will not be advantageous. 
     SUMMARY OF THE INVENTION 
     In view of the disadvantages as above, it is an object of the present invention to provide a valve operating mechanism for a poppet valve of an internal combustion engine to prevent a pair of cotters from falling out of a bore of a valve spring retainer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and advantages of the invention will become more apparent from the following description with respect to embodiment as shown in appended drawings wherein: 
     FIG. 1 is a perspective view of cotters employed in the first embodiment a valve operating mechanism of the present invention; 
     FIG. 2 is a central vertical sectional view of FIG. 1; 
     FIG. 3 is a central vertical sectional front view which illustrates how to determine load by which cotters come out of a bore of a valve spring retainer; 
     FIG. 4 is a central vertical sectional front view of the second embodiment of a valve operating mechanism of the present invention; 
     FIG. 5 is a central vertical sectional front view of the third embodiment of a valve operating mechanism of the present invention; 
     FIG. 6 is a central vertical sectional front view of a conventional valve operating mechanism; and 
     FIG. 7 is a central vertical sectional front view thereof in which cotters are fallen. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The first embodiment of the present invention will be described. 
     FIG. 1 illustrates a pair of cotters  7 , 7  used in a valve operating mechanism according to the present invention which have outer rough surfaces  8 , 8  made by sand blasting. The surfaces  8 , 8  may comprise uneven surfaces which have a number of sharp protrusions using rigid broken grid having sharp corners and made of cast steel. 
     FIG. 2 is a sectional view of the valve operating mechanism which includes the cotter  7  which is engaged in a taper bore  10  of an Al alloy valve spring retainer  9 , a bead  7   a  thereof being engaged in an annular groove  1   a  of a poppet valve  1 . 
     In the valve operating mechanism which includes the cotter  7 , load of a valve spring  5  is applied upwards to a spring-retaining flange  9   a  of the valve spring retainer  9 , and the cotter  7  moves downwards in the bore  10 . Then, the outer sharp protrusions of the rough surface  8  fits with the inner circumferential surface of the bore  10  to cause large frictional resistance. 
     The cotters  7 , 7  are prevented from falling, and preset load of the valve spring  5  decreases, not to decrease the maximum rotation number of surging. Cracking at the lower portion of the valve spring retainer  9  is prevented and the cotter  7  is not liable to come off. 
     The flange  9   a  of the valve spring retainer  9  is supported by a cylindrical jig  11  as shown in FIG. 3, and the poppet valve  1  is pressed at the upper end by a pressing rod  12  of a pressing machine such as a hydraulic cylinder. 
     Load by which the cotters  7 , 7  are pressed out of the valve spring retainer  9  is determined. In a conventional valve operating mechanism which includes cotters having flat outer circumferential surface, load is about 9 kN, while load in the present invention is about 15 kN which is equivalent to that a steel valve spring retainer. Increase in load of the cotter would avoid necessity of increase in external diameter of the lower end of the valve spring retainer  9  to increase rigidity, thereby providing miniaturization and lightening of the retainer  9 . 
     The cotter  7  is engaged in the bore  10  by fitting the rough surface  8  into the inner circumferential surface of the bore  10 . Even if lubricating oil flows into the bore  10  during running of an engine, frictional force of the contact surface will not be decreased. Thus, if surging occurs in the valve spring  5 , the cotter  7  could not come out of the upper portion of the bore  10 . 
     The second embodiment of the present invention will be described. 
     In FIG. 4, an annular projection  13  is formed at the lower portion of a bore  10  of an Al alloy valve spring retainer  9 . When a pair of steel cotters  7 , 7  is engaged in the bore  10  and annular beads  4   a , 4   a  are engaged in an annular groove of a poppet valve  1 , the upper end of the annular projection  13  is positioned slightly lower than the lower end of the cotters  7 . 
     In a valve operating mechanism which includes the valve spring retainer  9 , load of a valve spring  5  is applied upwards to a spring-retaining flange  9   a  of the valve spring retainer  9  repeatedly, and the cotters  7  slides relatively downwards. The lower end of the cotters  7  contacts the annular projection  13 , thereby preventing further downward movement thereof. 
     Therefore, the cotters  7  are prevented from falling out to decrease preset load of the valve spring  5 , so that the maximum rotation number of surging is not decreased. 
     The annular projection  13  provides high shear strength, pressing load of the cotters  7  to the bore  10 , and in ordinary operation, there is no possibility that the cotters  7  would be pressed downwards to break the annular projection  13  to go out of the bore. 
     FIG. 5 is a sectional view of the third embodiment of the present invention in which a smaller diameter portion  14  is formed to have larger taper angle than that of a bore  10 , at a lower portion than the lower end of the cotters  7 . In the embodiment, the cotters  7  are prevented from falling out, by the smaller diameter portion  14 . 
     The foregoing relate to embodiments of the present invention. Various changes and modifications may be made by person skilled in the art without departing from the scope of claims wherein: