Abstract:
Serious racers strive to squeeze as many revolutions per minute as possible out of their engines. They often use exotic metals like titanium in efforts to minimize the weight of some reciprocating parts. Almost exclusively, serious racers use titanium valve spring retainers to obtain higher speeds. This invention relates to an improved valve spring retainer for use in high performance engines. More particularly, it relates to an aluminum valve spring retainer which is lighter and less costly than titanium retainers of approximately equivalent strength.

Description:
BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic side elevation illustrating the valve lifter mechanism in a high performance push rod engine. 
     FIG. 2 is a cross-sectional view of an improved valve spring retainer of the type which forms the subject matter of this invention. 
     FIG. 3 is a cross-sectional view of the improved keeper. 
     FIG. 4 illustrates the valve spring retainers of the type known to the prior art. 
     FIG. 5 illustrates an embodiment of the present invention in which steel thrust plates are used to protect the aluminum retainer. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates the valve lifter mechanism in a typical internal combustion engine. Valve stem 10 is pivotably connected to rocker arm 15 which is pivotably connected to push rod 14 which engages lifter body 16 terminating in roller 18. Roller 18 bears against cam surface 20 on camshaft 22. Valve springs 24 and 26 bear against valve spring retainer 28 and against engine head 30 urging valve stem 10 upward into the closed position. Valve spring retainer 28 is held in position by keeper 32 comprised of retainer locks 34 and 36. 
     In racing engines, two valve springs 24 and 26 are used so that the valve can be made to open and shut as quickly as possible, of course, more springs can be used. Since valve springs 24 and 26 are normally very stiff, they exert a great deal of force on thrust surfaces 38 and 40 of valve spring retainer 28 often causing it to fracture at its weak point 42 or extrude the locks through the spring retainer. 
     As shown in FIG. 4, the valve spring retainers known to the prior art have a chambered disc portion 44 which joins a thicker intermediate disc portion 46 which in turn is joined to cylindrical body portion 48. The lower face of chamfered disc portion 44 defines thrust surface 38 while the lower face of intermediate disc portion 46 defines thrust surface 40. Tapered bore 50 passes through the centers of discs 44 and 46 and along the centerline of cylindrical body portion 48. As mentioned previously, weak point 42 occurs where intermediate disc portion 46 joins cylindrical body portion 48. The conventional valve spring retainer has a bore having an inner surface which is conical wherein the angle that the generators of the cone define with the centerline of the bore is approximately 7.5° to 10° . In an effort to strengthen valve spring retainers, many other tapers have been used. However, it has been found that when the taper is decreased to 71/2° , the extreme forces exerted by the springs on the retainer often actually extrude the keeper through the valve spring retainer. 
     The valve spring retainer of the present invention differs from those known to the prior art, the angle of taper of the bore is not constant. In particular, the taper angle increases in the regions of the valve spring retainer which are furthest from the springs. More particularly, in a preferred embodiment the initial angle of taper of the bore in the portion adjacent to the valve springs is substantially less than the terminal angle of the taper of the bore in the portion away from the valve springs. In a more preferred embodiment, the initial angle of taper of the bore is between 0° and 10° while the terminal angle of taper is between 10° and 40° . It is further preferred that the interior surface of the valve spring retainer be in the form of a smooth surface of revolution. In a still more preferred embodiment, the local radius of curvature of the generator of the interior surface is substantially constant over at least about 75% of the area of the interior surface. It is greatly preferred that the radius of curvature be constant since this enables the valve spring retainers to be easily formed. It is to be emphasized that the valve spring retainers of the present invention are not merely marginally stronger than conventional designs but are so unexpectedly stronger that aluminum can be substituted for titanium. 
     It is not essential that the interior surface of valve spring retainer 28 be a surface of revolution, substantial benefits can be obtained if the area of the interior surface increases more rapidly in a portion of the retainer away from the valve springs than in a portion closer to the valve springs. 
     The retainer locks 34 and 36 which hold the novel valve spring retainer of the present invention in place have exterior surfaces which are congruent with the interior surface of the valve spring retainer and therefore mate with the interior surface of valve spring retainer 28 when inserted therein. Protrusions 56 on retainer locks 34 and 36 engage congruent recess formed in valve stem 10. 
     In some cases, the ends of valve springs 24 and 26 will gouge thrust surfaces 38 and 40 of valve spring retainer 28 and, over time, weaken it. It has been found that this effect may be avoided by interposing thin annular thrust plates 52 and 54 between valve springs 24 and 26 and thrust surfaces 38 and 40 of valve spring retainer 28. Annular thrust plates 52 and 54 engage thrust surfaces 38 and 40 but may be held in place merely by the force of valve springs 24 and 26. Steel or any other suitably hard material may be used for thrust plates 52 and 54 and a substantial savings in weight realized since the flared interior surface construction of valve spring retainer 28 allows it to be comprised of aluminum. 
     EXAMPLE 
     Aluminum valve spring retainers were placed in a testing device having a cylindrical rod 11/32 inches in diameter similar to a valve stem and means for pressing against the thrust surfaces of the retainer while maintaining the retainer in place by means of retainer locks as in an engine. The initial angle of taper of the bore was 5° , the terminal angle of taper of the bore was 25° and the radius of curvature of the interior surface formed by the bore was 1.25 inches. The valve spring retainers failed under an average load of 6964 pounds. Conventional titanium valve spring retainers of similar construction but having an angle of taper of 71/2° failed under an average load of 4241 pounds.