Patent Publication Number: US-6662693-B2

Title: Wrench with a fixed maximum operational torque

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a wrench with a fixed maximum operational torque to prevent damage to the object secured by a fastener driven by the wrench. 
     2. Description of the Related Art 
     FIG. 12A of the drawings illustrates a conventional wrench  1  having a hexagonal driving portion with six planar faces  2  for engaging with six faces of a hexagonal groove in a top face of a fastener. However, slide tends to occur between the planar faces of the driving portion of the wrench  1  and the faces of the fastener. FIG. 12B illustrates a so-called TROX wrench  3  having plural arcuate faces  4  for engaging with corresponding arcuate faces in a top face of a fastener. Such a TROX wrench  3  is used to tighten important parts of a car and cutting tools. As illustrated in FIG. 13, a blade  7  is tightened to a cutting tool  5  by a bolt  6 . However, the expensive blade  7  tends to be damaged when the bolt  6  is excessively tightened. But the blade  7  could fly away and thus cause injury if the bolt  6  is not tightened to the desired extent. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a wrench with a fixed maximum operational torque such that when the torque applied by the user is greater than the maximum operational torque, the wrench slides and the fastener is not turned. Thus, damage to the object secured by the fastener is prevented. 
     Another object of the present invention is to provide a wrench with a fixed maximum operational torque that can be altered in response to the actual use. 
     A wrench in accordance with the present invention comprises a rod, a slide control member, a casing for rotatably accommodating the slide control member, and a retaining means. The rod comprises a driving portion on an end thereof for engaging with a fastener. The slide control member is securely mounted to the rod to turn therewith. The retaining means is mounted in the casing and includes an end operably connected to the slide control member. When a rotational force applied to the casing is smaller than an engaging force between the slide control member and the end of the retaining means, the slide control member and the rod are turned to thereby turn the fastener. When a rotational force applied to the casing is greater than the engaging force between the slide control member and the end of the retaining means, the casing slides while the slide control member and the rod are not turned. 
     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 wrench in accordance with the present invention. 
     FIG. 2 is an exploded perspective view of the wrench in accordance with the present invention. 
     FIG. 3 is a sectional view taken along plane A—A in FIG.  1 . 
     FIG. 4 is a perspective view illustrating use of the wrench in accordance with the present invention. 
     FIG. 5 is a sectional view taken along plane B—B in FIG.  1 . 
     FIG. 6 is a sectional view similar to FIG. 5, illustrating operation of the wrench. 
     FIG. 7 is a sectional view similar to FIG. 5, illustrating a modified embodiment of the wrench in accordance with the present invention. 
     FIG. 8 is a sectional view similar to FIG. 7, illustrating operation of the wrench in FIG.  7 . 
     FIG. 9 is a perspective view of another modified embodiment of the wrench in accordance with the present invention. 
     FIG. 10 is a sectional view taken along plane A—A in FIG.  9 . 
     FIG. 11 is a sectional view taken along plane B—B in FIG.  9 . 
     FIG. 12A is an end view of a conventional hexagonal wrench. 
     FIG. 12B is an end view of a conventional TROX wrench. 
     FIG. 13 is a perspective view, partly cutaway, of a cutting tool. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1 and 2, a wrench in accordance with the present invention generally includes a rod  10 , a retaining means  40 , a slide control member  20 , and a casing  30 . The rod  10  comprises a first end  11  and a second end  12  with a driving portion  13  for engaging with a fastener. In this embodiment, the driving portion  13  is shaped as a TROX type wrench. The rod  10  further has an embossed section  14  that is preferably adjacent to the first end  11  thereof. 
     The slide control member  20  includes a longitudinal hole  21  for securely engaging with the embossed section  14  of the rod  10 . Thus, the slide control member  20  and the rod  10  rotate jointly. The slide control member  20  further includes an operative outer periphery  22 . In this embodiment, the operative outer periphery  22  includes plural ratchet teeth; namely, the slide control member  20  is a ratchet wheel. 
     The casing  30  comprises a first end  31  and a second end  32 . A grip portion  33  is formed on the second end  32  of the casing  30  for manual turning operation. A receiving section  34  is defined in the casing  30  for accommodating the retaining means  40  and the slide control member  20 . The receiving section  34  includes a first compartment  341  for receiving the slide control member  20 , a second compartment  342  for receiving a pressing member  42  of the retaining means  40 , and a third compartment  343  for receiving an elastic element  41  of the retaining means  40 . The three compartments  341 ,  342 , and  343  are communicated with each other. 
     Referring to FIGS. 2 and 3, a positioning hole  35  is defined in the first end  31  of the casing  30  and extends through the first compartment  341 . The first end  11  of the rod  10  is received in the positioning hole  35  of the casing  30 , and a ball  15  is provided between an end face of the first end  11  of the rod  10  and an end wall defining a portion of the positioning hole  35  of the casing  30  to provide smooth rotation therebetween. A recessed portion  36  surrounds the receiving section  34  of the casing  30 , and a lid  50  is mounted in the recessed portion  34  for closing the receiving section  34 . The lid  50  has a hole  51  through which the rod  10  extends. 
     Referring to FIG. 5, the pressing member  42  is biased by the elastic element  41  to press against the operative outer periphery  22  of the slide control member  20 . Namely, a predetermined engaging force exists between the operative outer periphery  22  of the slide control member  20  and the pressing member  42  under the action of the elastic element  41 . 
     Referring to FIG. 4, when driving a TROX type bolt  61  for a cutting tool  60 , the driving portion  13  of the second end  12  of the rod  10  is engaged with the bolt  61 , and the casing  30  is then turned by means of gripping and turning the grip portion  33 . Referring to FIG. 5, when the rotational force applied to the wrench is smaller than the predetermined engaging force between the pressing member  42  and the slide control member  20 , the slide control member  20  and the rod  10  turn together with the casing  30  to thereby drive the bolt  61 . 
     When the rotational force applied to the wrench is greater than the predetermined engaging force between the pressing member  42  and the slide control member  20 , as illustrated in FIG. 6, the pressing member  42  is moved away from the slide control member  20  and compresses the elastic element  41 , as the elastic force of the elastic element  41  is overcome by the rotational force. Thus, the casing  30  slides relative to the slide control member  20 ; namely, the slide control member  20  and the rod  10  are not turned. As a result, the bolt  61  is not turned. The casing  30  returns to its original position shown in FIG. 5 under the action of the elastic element  41  when the rotational force is released. 
     It is noted that the engaging force, which largely depends on the elastic coefficient of the elastic element  41 , determines a maximum operational torque for turning the rod  10 . Namely, when the torque applied to the casing  30  is smaller than the maximum operational torque, the slide control member  20  and the rod  10  are turned, and when the torque applied to the casing  30  is greater than the maximum operational torque, the slide control member  20  and the rod  10  are not turned. During tightening of the bolt  61 , the bolt  61  before being tightened is turned by means of applying a torque smaller than the maximum operational torque. When the bolt  61  is tightened, the torque required to turn the casing  30  would be greater than the maximum operational torque such that the casing  30  slides. Thus, the user will notice the sliding motion of the casing  30  and be aware of tightening of the bolt  61 . The maximum operational torque can be altered by means of selecting elastic elements of different elastic coefficients. The maximum operational torque is a constant and thus allows accurate operation. This advantageous design can be used in a limited space, and the manufacturing cost of the wrench is largely reduced. 
     FIGS. 7 and 8 illustrate a modified embodiment of the invention, wherein the slide control member  20  is a gear having an operative outer periphery  22 ′. This allows rotation of the casing  30  in either direction, while the casing  30  in the first embodiment can be turned in only one direction. 
     FIGS. 9 through 11 illustrate another modified embodiment of the invention, wherein the casing  30  is substantially rectangular. In addition, there are two receiving sections  34  and two retaining means  40 . Operation of this embodiment is substantially the same as that of the first embodiment. 
     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 scope of the invention as hereinafter claimed.