Patent Publication Number: US-2011065541-A1

Title: Sprocket assembly

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a sprocket assembly of human-powered vehicle, and more particularly to a multispeed sprocket assembly. 
     2. Description of the Prior Art 
     A sprocket assembly is common installed at a center of a bicycle back wheel and has a unidirectional transmission relationship with a hub. Thus, the sprocket assembly is driven by a chain to rotate the hack wheel. A conventional sprocket assembly includes several sprockets, each has different diameter to provide different transmission ratio to achieve the effects of high speed or strength saving. 
     U.S. Pat. No. 4,889,521 discloses a sprocket assembly having a larger diameter sprocket and a smaller diameter sprocket. The lager diameter sprocket has a chain guide portion disposed at an inner surface thereof. More specifically, the chain guide portion is formed of a cutout that overlaps at least a tooth of the smaller diameter sprocket for the chain to easily shift from the smaller diameter sprocket to the larger diameter sprocket. 
     SUMMARY OF THE INVENTION 
     The main object of the present invention is to provide a sprocket assembly allowing the chain to shill easily. 
     To achieve the above object, a sprocket assembly of the present invention includes a first sprocket and a bigger second sprocket. The first sprocket has a first face and a second face opposite to the first face. The sprockets are co-axially and parallel disposed. A plurality of small-diametered teeth are spaced and radially extended from a periphery of the first sprocket, and a plurality of large-diametered teeth are spaced and radially extended form a periphery of the second sprocket. At least one of the small-diametered teeth has a beveled edge, which is tapered from a first face to a second face along a transmission direction. At least one of the larger-diametered teeth has a thinner section clockwise adjacent to the small-diametered tooth having the beveled edge. The thinner section is stepped at an outer face of the second sprocket. 
     The present invention will become more obvious from the following description when taken in connection with the accompanying drawings, which show, for purpose of illustrations only, the preferred embodiments in accordance with the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view of a sprocket assembly having several sprockets of the present invention; 
         FIG. 2  is a front view of a sprocket assembly of the present invention; 
         FIG. 3  is a partial pictorial drawing showing first sprocket of a sprocket showing assembly of the present invention; 
         FIG. 4  is a rear view of a sprocket assembly of the present invention; 
         FIG. 5  is a partial pictorial drawing showing a second sprocket of a sprocket assembly of the present invention; 
         FIG. 6  is a front view of a sprocket assembly showing the relative position of a first tooth and a second tooth of the present invention; 
         FIG. 7  is a partial front view showing a chain shifting from a first sprocket to a second sprocket; 
         FIG. 8  is a partial front view showing a chain shifting from a second sprocket to a first sprocket. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Please refer to  FIG. 1 . The present invention provides a sprocket assembly for a human-powered vehicle. The sprocket assembly has several sprockets assembled together or integrally formed, and it is installed in a transmission system of the human-powered vehicle and is driven by a chain, which can shift between the sprockets to vary the transmission ratio. 
     Please refer to  FIG. 2 . The present embodiment merely shows two sprockets to interpret the features of the present invention. Note that such features disclosed hereinafter can be applied on any two adjacent sprockets of the sprocket assembly as shown in  FIG. 1 . The sprocket assembly includes a circular first sprocket  10  and a second sprocket  20 . The first sprocket has a first face  11  and a second face opposite to the first face. A clockwise rotational direction of the first face  11  is defined as a transmission direction A. A plurality of small-diametered teeth  12  is spaced and radially extended front a periphery of the first sprocket  10 . Each small-diametered tooth  12  has a first corner  121  and a second corner  122  sequentially formed on a distal end thereof along the transmission direction A. At least one of the small-diametered teeth  12  is defined as a first tooth  13 , and the first tooth  13  has a beveled edge  131 . 
     As shown in  FIG. 3 , the beveled edge  131  is tapered from the first face  11  to the second face along the transmission direction A, and the beveled edge  131  makes an angle O of 5-15 degrees to the second face. In addition, a curve surface  132  is formed between the beveled edge  131  and the first face  11 . The curve surface  132  is perpendicular to the first face  11  and concave toward a center of the first sprocket  10 . The curve surface  132  has a first end close to the first corner  121  and a second end away from the first corner  121 . The second end of the curve surface  132  is closer to the center of the first sprocket  10  than the first end is. Thus the curve surface  132  generally faces the second corner  122  of the first tooth  13 . 
     Refer to  FIG. 2  again. The second sprocket  20  is co-axial with and parallel to the first sprocket  10 , and it is spaced disposed near the second face. A diameter of the second sprocket  20  is bigger than that of the first sprocket  10 . A plurality of big-diametered teeth  21  are spaced and radially extended from a periphery of the second sprocket  20 . Each big-diametered tooth  21  has a first corner  211  and a second corner  212  sequentially disposed on a distal end thereof along the transmission direction A. At least one of the big-diametered teeth is defined as a second tooth  22 , and the second tooth  22  has a thinner section. 
     As shown in  FIGS. 4 and 5 , the thinner section is stepped at an outer face of the second sprocket  20 , such that it has a thickness smaller than the second sprocket  20 . The outer face of the second sprocket  20  faces opposite to the first sprocket  10 . Specifically, the second tooth  22  is cut from the outer face to form the stepped thinner section. 
     Please refer to  FIG. 2  again. The first tooth  13  and the second tooth  22  are adjacent to each other to make a shifting guide set. To more specifically indicate the relative position of the first and second teeth  13  and  22 , please refer to  FIG. 6 . A polar coordinate system is defined on the first face  11  of the first sprocket  10 . The center of the first sprocket  10  is defined as a pole of the polar coordinate system, and a ray defined from the pole and passing through the second corner  122  of the first tooth  13  is a polar axis of the polar coordinate system. A positive polar angle is measured from the polar axis along the counterclockwise direction B. As such, the second corner  122  or the first tooth  13  has a polar angle of 0 degree. The first corners  211  of the big-diametered teeth  21  have projection points on the polar coordinate system. The projection point of the second tooth  22  has a polar angle being the most close to but not exceeding 360 degrees among all the projection points. As such, the first and second teeth  13  and  22  are adjacent to each other with desired interval. 
     Please refer to  FIG. 7 . When the chain  30  is shifting from the second sprocket  20  to the first sprocket  10 , the chain  30  is inclined from the second tooth  22  to approach the first sprocket  10 , and the first tooth  13  has a beveled edge  131  for the chain  30  to easily and smoothly engage therewith. To further smooth the shifting movement, the big-diametered tooth  21 ′ clockwise adjacent to the second tooth  22  may also have a thinner section, and the small-diametered tooth  12 ′ counterclockwise adjacent to the first tooth  13  may have a beveled edge as well. 
     Refer to  FIG. 8 . When the chain  30  is shifting from the first sprocket  10  to the second sprocket  20 , the chain  30  is inclined from the beveled edge  131  of the first tooth  13  to approach and thereafter engage with the second sprocket  20 . 
     The sprocket assembly of the present invention may have multiple shilling guide sets. Each two adjacent shifting guide sets are separated by one to seven small-diametered teeth  12 . Preferably, two to five shifting guide sets may be provide on two adjacent sprockets. 
     In summarization, the sprocket assembly of the present invention has shilling guide set(s) to smooth the shilling movement of the chain. Although the beveled edge is tapered, the first tooth still has a thicker surface, which provides sufficient mechanical strength, near the first corner for the chain to transmit driving force thereto. The sprocket assembly of the present invention may be provided with the chain guide portion as disclosed in U.S. Pat. No. 4,889,521 to further enhance the shilling efficiency.