Abstract:
A silent chain and sprocket system for power transmission that includes a toothed sprocket and a chain with multiple links. At each point of engagement between the sprocket teeth and the chain link teeth, the sprocket teeth have a curved surface that makes contact with a curved surface on the chain link teeth.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a silent chain power transmission device. Such devices are used in automotive transmissions, transfer cases, engine timing systems, and the like. More specifically, the present invention relates to a silent chain power transmission device in which the sprocket teeth have a curved surface that makes contact with a curved surface on the link plate teeth at each point of engagement. The result is an increase in surface area of the engagement between the link plate teeth and the sprocket teeth, which in turn reduces the contact surface pressure and improves the overall durability as compared with conventional silent chain power transmission devices. 
     Silent chain transmission devices are formed by an arrangement of link plates in lateral and longitudinal directions. The links are interlaced and joined, forming a chain that is used in conjunction with a sprocket. A typical chain is composed of inner links, which contact the teeth of the sprocket to provide power transmission, and guide links, which do not provide power transmission. Guide links are employed to maintain the chain on the center of the sprocket. A row of link plates, arranged in the lateral direction, typically has a number of inner links combined with guide links in the center or at both edges of the row. 
     Conventional silent chain transmission devices face durability problems. In the conventional device, power is transmitted by the contact of the flat or convex surface of the link plate with the convex surface of the sprocket teeth. Thus, both surfaces experience wear due to high contact surface pressure. As a result, the durability of the power transmission device is decreased. The present invention is directed at solving this problem. It decreases the wear on the link plates and sprocket teeth by increasing the surface area of the contact between them. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to increase the durability of silent chain power transmission devices. The area of contact between the link plate teeth and the sprocket teeth is increased in surface area. This increase is accomplished by curving the surfaces of both the link plate tooth and the sprocket tooth at the location of contact. The link plate teeth and the sprocket teeth thereby cradle into each other. The increase in surface area of the contact location results in lower contact pressure and thus increased durability of the device. 
     The silent chain and sprocket system that a preferred embodiment of the present invention comprises has multiple link plates joined by pins inserted into apertures in the link plates. Each of the link plates has teeth that are curved, either concavely or convexly, on either their inside flanks or their outside flanks. In addition, the system&#39;s sprocket has multiple teeth that have curved surfaces for engagement with the link plates. 
     U.S. Pat. No. 5,154,674 to Avramidis and Ledvina also teaches curved link plate teeth. Unlike the present invention, however, the &#39;674 patent teaches link plates that are asymmetrical in order to modify the noise pattern of the chain they comprise. In contrast, the present invention teaches symmetrical link plates in order to increase link plate durability. 
     For a better understanding of the invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE INVENTION 
     In the drawings, which are not to scale: 
     FIG. 1 is a partially cut front elevational view of a silent chain composing one embodiment of the present invention; 
     FIG. 2 is a top plan view of the silent chain of FIG. 1; 
     FIG. 3 is a front elevational view of a link plate that is part of the silent chain of FIG. 1; 
     FIG. 4 is a front elevational view of the area of engagement of the link plate of FIG. 3 with a sprocket; 
     FIG. 5 is a front elevational view of the area of engagement of a link plate with a sprocket in an alternative embodiment of the present invention; 
     FIG. 6 is a front elevational view of the area of engagement of a link plate with a sprocket in a second alternative embodiment of the present invention; 
     FIG. 7 is a front elevational view of the area of engagement of a link plate with a sprocket in a third alternative embodiment of the present invention; 
     FIG. 8 is a front elevational view of a link plate and the area of engagement between the link plate and a sprocket in a fourth alternative embodiment of the present invention; and 
     FIG. 9 is a front elevational view of a link plate and the area of engagement between the link plate and a sprocket in a conventional silent chain power-transmission device. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is explained below in greater detail with reference to the attached figures. 
     FIG. 1 is a partially cut front elevational view of a silent chain that comprises one embodiment of the present invention; FIG. 2 is the corresponding plan view. In both FIG.  1  and FIG. 2, silent chain  1  has multiple link plates  2 , each with a pair of teeth  21  and apertures or pinholes  22 . Link plates  2  are connected by insertion of connecting pins  3  into pinholes  22  of link plate  2 . Guide links  4  are attached to the outermost link plates  2 . 
     FIG. 3 is a front elevational view of a link plate that is part of the silent chain of FIG.  1 . Each tooth  21  of link plate  2  comprises inside flank  23  and outside flank  24 . Inside flank  23  has a nearly straight flat surface or slightly curved surface. Outside flank  24  has a concave surface  24   a  near the tip of tooth  21  and convex surface  24   b  that is near pinhole  22 . The dotted lines show the conventional, nearly-straight outside flank. 
     FIG. 4 is a front elevational view of the area of engagement of the link plate of FIG. 3 with a sprocket. Sprocket tooth  5  makes contact with concave surface  24   a  on the outside flank of link plate  2 . Sprocket tooth  5  has convex surface  51 , which corresponds to concave surface  24   a . The engagement between outside flank  24  of link plate  2  and sprocket tooth  5  is via the contact between concave surface  24   a  and convex surface  51 , so that the contact surface pressure on both surfaces is reduced and the durability of the device is improved. 
     FIG. 5 is a front elevational view of the area of engagement of a link plate with a sprocket in an alternative embodiment of the present invention. Outside flank  24  of link plate  2  has convex surface  24 ′ a  near the tip of tooth  21 . In addition, sprocket tooth  5  has corresponding concave surface  52 . As in the embodiment of FIG. 4, engagement between link plate  2  and sprocket tooth  5  is achieved via contact between a concave surface and a convex surface, so that the contact surface pressure on the inside flank of link plate  2  and the sprocket tooth is reduced and durability of the device is improved. 
     FIG. 6 is a front elevational view of the area of engagement of a link plate with a sprocket in a second alternative embodiment of the present invention. The inside flank of link plate  2  has concave surface  23   a , and sprocket tooth  5  has corresponding convex surface  53 . Convex curved surface  24   b  and nearly straight surface  24   c  are formed on the outside flank. In this embodiment, as in the other embodiments, engagement between link plate  2  and sprocket  5  is via the contact between the concave surface and the convex surface so that the contact surface pressure between the inside flank of link plate  2  and the sprocket tooth is reduced, and the overall durability of the device is improved. 
     FIG. 7 is a front elevational view of the area of engagement of a link plate with a sprocket in a third alternative embodiment of the present invention. The inside flank of link plate  2  has convex surface  23 ′ a . In addition, sprocket tooth  5  has corresponding concave surface  54 . Convex curved surface  24   b  and nearly straight surface  24   c  are formed on the outside flank. Convex curved surface  24   b  is formed near a pinhole on the outside flank so that the material thickness near the pinhole of link plate  2  is increased so that the strength of the link plate is thereby increased. As in the above embodiments, engagement between link plate  2  and sprocket  5  is via the contact between the concave surface and the convex surface, so that the contact surface pressure between the inside flank of link plate  2  and the sprocket tooth is reduced, and the overall durability of the device is improved. 
     FIG. 8 is a front elevational view of a link plate and the area of engagement between the link plate and a sprocket in a fourth alternative embodiment of the present invention. A link plate of a back-driving silent chain is shown. Link plate  6  has teeth  61 ,  61 ′ on both sides of center line L-L′. Tooth  61  comprises inside flank  63  and outside flank  64 ; tooth  61 ′ comprises inside flank  63 ′ and outside flank  64 ′. Inside flanks  63 ,  63 ′ have a straight or slightly curved surface. Outside flank  64  has concave surface  64   a  on the lower portion of tooth  61  and convex surface  64   b  near pinhole  62 . Outside flank  64 ′ has concave surface  64 ′ a  on the upper portion of tooth  61 ′ and convex surface  64 ′ b  near pinhole  62 . The dotted lines show the surfaces of a conventional outside flank. Sprocket  5  has convex surface  55 , which engages with concave surface  64   a  on outside flank  64  of link plate  6 . A similar engagement takes place between a second sprocket, not shown, and outside flank  64 ′ of link plate  6 . Thus, the engagement between link plate  6  and the sprockets is via contact between a concave surface and a convex surface, thereby reducing the contact surface pressure and improving the durability of the device. The present invention could also be practiced by modifying FIG. 8 so that the sprocket has a concave surface and the corresponding flank of the link plate has a convex surface. Similarly, the area of engagement with the sprocket could be the inside flank of the link plate, in which case the inside flank would be concave or convex, depending on the curvature of the sprocket tooth. 
     FIG. 9 is a front elevational view of a link plate and the area of engagement between the link plate and a sprocket in a conventional silent chain power-transmission device. In the figure, link plate  100  has a pair of pinholes  101 ,  012  for insertion of the connecting pin and a pair of teeth  103 ,  104  which mesh with sprocket  10 . Tooth  103  is composed of inside flank  105  and outside flank  106  and tooth  104  is composed of inside flank  105  and outside flank  107 . Inside flank  105  is composed of a slightly curved surface and outside flanks  106 ,  107  are composed of a nearly straight, flat surface. The teeth of sprocket  110  that mesh with outside flanks  106 ,  107  are composed of a convex curved surface  110   a , such as an involute curve. 
     Those skilled in the art to which the invention pertains will be able to make modifications and other employing the principles of this invention without departing from its spirit or essential characteristics, particularly upon considering the foregoing teachings. The described embodiments are to be considered in all respects only as illustrative and not restrictive, and the scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. Consequently, while the invention has been described with reference to particular embodiments, modifications of structure, sequence, materials and the like would be apparent to those skilled in the art and fall within the scope of the invention.