Abstract:
A ratchet wheel includes an inner periphery and an outer periphery. The outer periphery includes a number of arcuate concave teeth each having two sides and an intersection of the two sides. The ratchet wheel includes a center, a line from the center to the intersection dividing an angle between the two sides into two unequal portions, thereby forming asymmetric arcuate concave teeth to provide improved structural strength and improved torque. In another embodiment, the concave teeth are non-arcuate to reduce the formation time for the teeth, thereby reducing the production cost.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application is a reissue application of U.S. Pat. No. 6,148,695, issued Nov. 21, 2000, and filed on Aug. 3, 1999, with application Ser. No. 09/365,738. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a ratchet wheel with asymmetric arcuate concave teeth or non-arcuate concave teeth. The present invention also relates to a ratcheting tool, e.g., a ring spanner having a box end in which the ratchet wheel is mounted. The ratchet wheel with asymmetric arcuate concave teeth provides improved structural strength and improved torque. The ratchet wheel with non-arcuate concave teeth is easy to form and thus reduces the production cost. 
     2. Description of the Related Art 
     A wide variety of spanners and wrenches have heretofore been provided. Ring spanners are the best choice for driving fasteners (e.g., nuts, bolt heads, etc etc.) in a limited space that is uneasy not easy to access and where it is difficult to operate all kinds of ratcheting tools. Nevertheless, conventional ring spanners have low driving torque. Ratchet type ring spanners have been proposed to solve this problem. A ratchet wheel is mounted in the box end of a ring spanner for driving fasteners at high torque. It is, however, found that, the structural strength of the ratchet wheel is weak, as an outer periphery of the ratchet wheel is processed to form a plurality of arcuate concave teeth with a considerable depth. 
       FIGS. 11 through 13  of the drawings illustrate a conventional ratchet wheel  1  mounted in a box end (not shown) of a ring spanner (not shown) and having an inner periphery  4  for driving a fastener (not shown) and an outer periphery having a plurality of arcuate concave teeth  3 . Referring to  FIG. 12 , each arcuate concave tooth  3  is formed by means of feeding a cutter  2  along a direction transverse to a radial direction (see line OR). The resultant concave tooth  3  has a depth “d” and two sides that intersect at point “R”. The line OR divides the angle a defined by the two sides of the arcuate concave tooth  3  into two equal portions (usually 45° for each portion). As illustrated in  FIG. 12 , each arcuate concave tooth  3  is machined to have a considerable depth “d” that adversely affects the structural strength of the ratchet wheel  1 , as the remaining wall thickness “t” of the ratchet wheel  1  is relatively small. As a result, the driving torque provided by the ratchet wheel for driving the fastener is limited. 
       FIGS. 14 through 16  of the drawings illustrate a conventional ratchet wheel  5  mounted in a box end  9 a ( FIG. 17 ) of a ring spanner  9  ( FIG. 17 ) and having an inner periphery  8  for driving a fastener (not shown) and an outer periphery having a plurality of arcuate concave teeth  6 . Referring to  FIG. 15 , each arcuate concave tooth  6  is formed by means of feeding a cutter  7  along a radial direction. The resultant arcuate concave tooth  6  has a depth “d” and two sides that intersect at point “R”. The line OR divides the angle β defined by the two sides of the concave tooth  6  into two equal portions (usually 45° for each portion). As illustrated in  FIG. 15 , each arcuate concave tooth  6  is machined to have a considerable depth “d” that adversely affects the structural strength of the ratchet wheel, as the remaining wall thickness “t” of the ratchet wheel  5  is relatively small. As a result, the driving torque provided by the ratchet wheel for driving the fastener is limited. Such structure has been disclosed in U.S. Pat. No. 5,533,427 to Chow issued on Jul. 9, 1996, which is incorporated herein for reference. A further drawback of this conventional ratchet wheel is the low production rate for forming the arcuate concave teeth by cutting. 
     The present invention is intended to provide an improved ratchet wheel that mitigates and/or obviates the above problems. 
     SUMMARY OF THE INVENTION 
     It is a primary object of the present invention to provide an improved ratchet wheel has having asymmetric arcuate concave teeth for providing improved structural strength and improved torque. 
     It is another object of the present invention to provide an improved ratchet wheel that has non-arcuate concave teeth to allow higher production rate rates, as the non-arcuate concave teeth can be formed by means of roll squeezing method, investment casting, or molding. The non-arcuate concave teeth may be symmetric or asymmetric. The ratchet wheel with non-arcuate concave teeth may bear higher torque during ratcheting (i.e., tightening or loosening a fastener). 
     The present invention also provides a ratcheting tool, e.g., a spanner, equipped with a ratchet wheel in accordance with the present invention. In an embodiment of the invention, the spanner has a box end for receiving a ratcheting wheel with asymmetric arcuate concave teeth. In another embodiment of the invention, the spanner has a box end for receiving a ratcheting wheel with non-arcuate asymmetric concave teeth. In a further embodiment of the invention, the spanner has a box end for receiving a ratcheting wheel with non-arcuate symmetric concave teeth. 
     Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a ratchet wheel with asymmetric arcuate concave teeth in accordance with the present invention; 
         FIG. 2  is a side view of the ratchet wheel in accordance with the present invention; 
         FIG. 3  is a top view of the ratchet wheel in accordance with the present invention, illustrating formation of asymmetric arcuate concave teeth in an outer periphery of the ratchet wheel; 
         FIG. 4  is a top view of a box end of a ring spanner equipped with the ratchet wheel in accordance with the present invention; 
         FIG. 5  is a sectional view taken along line  5 - 5  in  FIG. 4 ; 
         FIG. 6  is a top view, in an enlarged scale, of the ratchet wheel in accordance with the present invention, wherein the position of symmetric concave teeth formed according to the prior art is illustrated to show difference therebetween; 
         FIG. 7a  is a perspective view of a pawl for cooperating with the asymmetric arcuate concave teeth of the ratchet wheel in accordance with the present invention; 
         FIG. 7b  is a top view of the pawl in  FIG. 7a ; 
         FIG. 7c  is a side view of the pawl in  FIG. 7a ; 
         FIG. 8a  is a perspective view of a conventional pawl for cooperating with the arcuate concave teeth of the ratchet wheel in  FIG. 14 ; 
         FIG. 8b  is a top view of the pawl in  FIG. 8a ; 
         FIG. 8c  is a side view of the pawl in  FIG. 8a ; 
         FIG. 9  is an enlarged fragmentary view illustrating operation of the pawl and the asymmetric arcuate concave teeth of the ratchet wheel in accordance with the present invention; 
         FIG. 10  is a schematic force diagram of the asymmetric arcuate concave tooth of the ratchet wheel in accordance with the present invention; 
         FIG. 11  is a perspective view of a ratchet wheel according to the prior art; 
         FIG. 12  is a top view of the ratchet wheel in  FIG. 11 ; 
         FIG. 13  is a side view of the ratchet wheel in FIG  11 ; 
         FIG. 14  is a perspective view of another ratchet wheel according to the prior art; 
         FIG. 15  is a top view of the ratchet wheel in  FIG. 14 ; 
         FIG. 16  is a side view of the ratchet wheel in  FIG. 14 ; 
         FIG. 17  is a top view of a box end of a ring spanner equipped with the ratchet wheel in  FIG. 14 ; 
         FIG. 18  is an enlarged fragmentary view illustrating operation of the conventional pawl and the symmetric arcuate concave teeth of the conventional ratchet wheel in the ring spanner in  FIG. 17 ; 
         FIG. 19  is a schematic force diagram of the ratchet wheel in  FIG. 14 ; 
         FIG. 20  is a sectional view taken along line  20 - 20  in  FIG. 17 ; 
         FIG. 21  is a perspective view of a ratchet wheel with non-arcuate concave teeth in accordance with the present invention. 
         FIG. 22  is a side view of the ratchet wheel in  FIG. 21 ; 
         FIG. 23  is a top view of a box end of a ring spanner equipped with the ratchet wheel in  FIG. 21 ; 
         FIG. 24  is a sectional view taken along line  24 - 24  in  FIG. 23 ; 
         FIG. 25  is a top view of the ratchet wheel in  FIG. 21 , wherein the position of symmetric concave teeth formed according to the prior art is illustrated to show difference therebetween; 
         FIG. 26a  is a perspective view of a pawl for cooperating with the non-arcuate concave teeth of the ratchet wheel in  FIG. 23 ; 
         FIG. 26b  is a lop view of the pawl in  FIG. 26a ; and 
         FIG. 26c  is a side view of the pawl in  FIG. 26a . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIGS. 1 through 9  and initially to  FIGS. 1 through 3 , a ratchet wheel  20  in accordance with the present invention generally includes first and second axial ends 21a and 21b, an inner periphery  24  for driving a fastener (not shown) and an outer periphery having a plurality of arcuate concave teeth  22 . The plurality of concave teeth 22 have an axial extent less than that between the axial ends 21a and 21b. The plurality of concave teeth 22 are axially spaced from the axial ends 21a and 21b to define first and second axially spaced portions 23a and 23b. The first axially spaced portion 23a includes a radially extending annular recess. Each arcuate tooth 22 is defined by two sides, with an intersection of radially outer linear edges 22b of teeth 22 being arcuate in shape in a direction parallel to the outer periphery. 
     Referring to  FIG. 3 , each arcuate concave tooth  22  is formed by means of feeding a cutter  26  along a direction transverse to a radial direction (see line OR). The resultant concave tooth  22  has a radial depth “d 1 ” and two sides RA and RB that intersect at point “R”. The line OR divides the angle θ defined by the two sides RA and RB of the concave tooth  22  into two unequal portions (e.g., 30° and 60°, 40° and 50°, etc etc.). Namely, every concave tooth  22  thus formed is “asymmetric”, or the two sides for each teeth concave tooth  22  is not equal, which is the most important feature of this embodiment of the present invention. As illustrated in  FIG. 3 , each concave tooth  22  is machined to have a depth “d 1 ” that will not adversely affect the structural strength of the ratchet wheel, as the remaining wall thickness “t 1 ” of the ratchel wheel  20  is still relatively large. As a result, the ratchet wheel  20  may bear a relatively large driving torque for driving the fastener. 
     DifferenceThe difference in the depth of the concave tooth  22  of the ratchet wheel  20  of the present invention and the depth of the concave tooth  6  of the conventional ratchet wheel  5  ( FIG. 14 ) is illustrated in  FIG. 6 . Namely, the remaining narrowest wall thickness “t 1 ” of the ratchet wheel  20  of the present invention is greater than the remaining wall thickness “t” of the conventional ratchet wheel  5  that has the same size as the ratchet wheel  20 . Referring to  FIGS. 4 and 17 , the narrowest wall thickness (t 1 =1.01 mm in  FIG. 4  for a ratchet wheel having an outer diameter of 25.76 mm) of the ratchet wheel  20  of the present invention is almost twice as the narrowest wall thickness (t=0.51 mm in  FIG. 17  for a ratchet wheel having an outer diameter of 25.76 mm) of the conventional ratchet wheel  5 . Thus, the structural strength and the driving torque of the ratchet wheel of the present invention are both improved. 
     Referring to  FIG. 4 , the ratchet wind  20  in accordance with the present invention is rotatably mounted in a box end  38  of a ring spanner  40 . A web area  39  between the box end  38  and a handle  42  of the ring spanner  40  includes a compartment  36  for slidably receiving a pawl  30 .  FIGS. 7a through 7c  illustrate the pawl  30 . The pawl  30  includes a plurality of teeth  31  that are formed complimentary to the curvatures of the asymmetric arcuate concave teeth  22 . An end  33  of the pawl  30  is attached to an end of an elastic member  32  the other end of which is received in a cavity  34  defined in a wall  36 a defining the compartment  36 , best shown in  FIG. 4 .  FIG. 17  illustrates a conventional arrangement of a ratchet type ring spanner  9  that has a box end  9 a for rotatably receiving the ratchet wheel  5 . A web area (not labeled) of the ring spanner  9  includes a compartment  10  for slidably receiving a pawl  11 .  FIGS. 8a through 8c  illustrate the pawl  11 . The pawl  11  includes a plurality of teeth  11 a that are formed complimentary to the curvatures of the symmetric arcuate concave teeth  6 . An end (not labeled) of the pawl  11  is attached to an end of an elastic member  12 , the other end of which member is received in a cavity  10 a defined in a wall  10 b defining the compartment  10 , best shown in  FIG. 17 .  FIGS. 8a ,  8 b,  8 c, and  17  are illustrated for comparison purpose. In addition, the difference in the wall thickness “t 1 ” of the ratchet wheel  20  of the present invention and the wall thickness “t” of conventional ratchet wheel  5  can also be clearly seen in  FIG. 6  and by means of comparing  FIG. 5  with  FIG. 20 . 
     In use of the ring spanner equipped with the ratchet wheel  20  in accordance with the present invention, referring to  FIG. 9 , the angle δ between a force N normal to the operative side P and the tangent T to the intersection I between the pawl  30  and the wall  36 a defining the compartment  36  is smaller than that in the prior art ratchet wheel (see  FIG. 18 ). As a result, the pawl  30  in  FIG. 9  is reliably pushed toward the wall  36 a defining the compartment  36  and thus provides a reliable engagement between the concave teeth  22  of the ratchet wheel  20  and the teeth  31  of the pawl  30 . If the angle δ reaches 90°, the pawl moves toward the central area of the ratchet wheel compartment and thus results in an undesired “sliding” effect, as there is no horizontal force imparted to move the pawl toward the wall  36 a of the compartment  36 . Thus, the ratchet wheel  20  and the pawl  30  in accordance with the present invention provides an engagement more reliable than that between the conventional ratchet wheel  5  and the pawl  11  and thus less likely to “slide”. The spanner with the ratchet wheel/pawl combination in accordance with the present invention can be used in a relatively small space and can be operated in a convenient manner. More specifically, the spanner is allowed to rotate in a reverse direction without disengaging the box end from the fastener when the spanner is stopped by an obstacle during ratcheting. And, and the spanner is then ready for the next ratcheting movement. This is very convenient and timesaving. 
     Referring to  FIGS. 9 and 10 , when the operative side P of the concave tooth  22  of the ratchet wheel  20  in accordance with the present invention is subjected to a force F during ratcheting, the area filled by the pawl  30  for bearing such force F is 2/1.732 h 2 . Referring to  FIG. 19 , for a conventional ratchet wheel  5 , when either operative side P of the concave tooth  6  of the ratchet wheel  5  is subjected to a force F, the area filled by the pawl  11  for bearing such force F is h 2  which is smaller than that provided by the ratchet wheel/pawl combination in accordance with the present invention. Namely, the ratchet wheel  20  with asymmetric arcuate concave teeth  22  provides a higher torque for ratcheting (i.e., tightening or loosening a fastener such as a nut or bolt head). 
     Referring to  FIGS. 21 and 22 , in a second embodiment of the ratchet wheel in accordance with the present invention, the ratchet wheel (now designated by  50 ) includes an inner periphery  54  for driving a fastener (not shown) and an outer periphery having a plurality of non-arcuate concave teeth  52 . The non-arcuate concave teeth  52  is are formed by means of roll squeezing method, investment casting, or molding, which is quicker than formation by a cutter. Each non-arcuate concave tooth  52  may be trapezoidal, triangular, or any other shape that results from formation other than cutting. The production cost for the ratchet wheel  50  with non-arcuate concave teeth  52  in accordance with the present invention is largely reduced, as the production time for the non-arcuate concave teeth  52  is relatively short. In addition, the non-arcuate concave teeth  52  may be symmetric or asymmetric. When the ratchet wheel  50  has non-arcuate symmetric concave teeth  52 , the resultant structure provides a driving torque approximately the same as that provided by the conventional ratchet wheel  5  with symmetric arcuate concave teeth  6 . When the ratchet wheel  50  has non-arcuate asymmetric concave teeth  52  configured similar to concave teeth  22 , the resultant structure provides a higher driving torque than that provided by the conventional ratchet wheel  5  with symmetric arcuate concave teeth  6 . 
     Each concave tooth 52 is defined by two sides each including a radially inner linear edge 52a and a radially outer linear edge 52b. Each concave tooth 52 is further defined by a first intersection of the radially inner linear edges 52a of each of the two sides with an adjacent tooth 52 and by a second intersection of the radially outer linear edges 52b of the two sides and which is substantially parallel to the first arcuate intersection. The plurality of concave teeth 52 have an axial extent less than that between the axial ends 51a and 51b and are axially spaced therefrom so that first and second axially spaced portions 53a and 53b are defined between each of the axial ends 51a and 51b and concave teeth 52. Each non-arcuate tooth 52 has third and fourth axial ends 53e that are spaced radially inside from the outer periphery of ratchet wheel 50. Inclined annular walls 53d extend between the outer periphery of the ratchet wheel 50 and the axial ends 53e, with the inclined annular walls 53d having decreasing radial spacing from the outer periphery of the ratchet wheel 50 to the axial ends 53e. 
     Referring to  FIG. 23 , the ratchet wheel  50  in accordance with the present invention may be rotatably mounted in a box end  38  of a ring spanner  40 . A web area  39  of the ring spanner  40  includes a compartment  36  for receiving a pawl  60 .  FIGS. 26a through 26c  illustrate the pawl  60 . The pawl  60  includes a plurality of teeth  61  that are formed complimentary to the curvatures of the non-arcuate concave teeth  52 . An end  62  of the pawl  60  is attached to an end of an elastic member  32 , the other end of which is received in a cavity  34  defined in a wall  36 a defining the compartment  36 , best shown in  FIG. 23 . A detail comparison between the conventional pawl  11  illustrated in  FIGS. 8a through 8c , the pawl  30  of the first embodiment of the present invention illustrated in  FIGS. 7a through 7c , and the pawl  60  of this embodiment illustrated in  FIGS. 26a through 26c  would be appreciated. In addition, difference in the wall thickness of the ratchet wheel  50  of the present invention and the wall thickness of conventional ratchet wheel  5  can also be clearly seen in  FIG. 25  and by means of comparing  FIG. 24  with  FIG. 20 . 
     According to the above description, it is appreciated that the ratchet wheel with asymmetric arcuate concave teeth in accordance with the present invention provides a higher torque for operation and has improved structural strength as having a thicker wall in the ratchet wheel. The engagement between the ratchet wheel with asymmetric arcuate concave teeth and the pawl with asymmetric arcuate concave teeth is more reliable. The ratchet wheel with non-arcuate concave teeth in accordance with the present invention reduces the production cost for the ratchet wheel. The ratchet wheel with non-arcuate concave teeth also provides a higher torque for operation when the non-arcuate concave teeth is asymmetric. A spanner with the ratchet wheel/pawl combination in accordance with the present invention can be used in a relatively small space. Nevertheless, the ratchet wheel/pawl combination in accordance with the present invention is not limited to be used in the box end of a ring spanner. Namely, the ratchet wheel/pawl combination may be used in other ratcheting tools such as ratchet wrenches. 
     Although the invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.