Patent Publication Number: US-6666117-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. 10A of the drawings illustrates a conventional wrench  1  having a hexagonal driving portion with six planar faces 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. 10B illustrates a so-called TORX wrench  3  having plural arcuate faces for engaging with corresponding arcuate faces in a top face of a fastener. Such a TORX wrench  3  is used to tighten important parts of a car and cutting tools. As illustrated in FIG. 11, a blade  7  is tightened to a cutting tool  5  by a bolt  6 . However, it was found that the expensive blade  7  tends to be damaged when the bolt  6  is excessively tightened. However, 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 comprises a rod comprising a driving portion for engaging with a fastener, a retainer having an end securely engaged with the rod to move therewith, and a casing comprising a compartment for accommodating the retainer. The casing comprises a retaining section defining a retaining space for retaining the other end of the retainer in place. When a rotational force applied to the casing is smaller than an engaging force between the retaining section of the casing and a retaining device that is attached between the retaining section and the retainer, the retainer and the rod are turned to thereby turn the fastener. When a rotational force applied to the casing is greater than the engaging force, the casing slides while the retainer 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 in a direction. 
     FIG. 7 is a sectional view similar to FIG. 5, illustrating operation of the wrench in a different direction. 
     FIG. 8 is a sectional view similar to FIG. 3, illustrating a modified embodiment of the wrench in accordance with the present invention. 
     FIG. 9 is a sectional view similar to FIG. 5, illustrating the modified embodiment of the wrench in accordance with the present invention. 
     FIG. 10A is an end view of a conventional hexagonal wrench. 
     FIG. 10B is an end view of a conventional TROX wrench. 
     FIG. 11 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 retainer  30 , and a casing  40 . 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  adjacent to the first end  11  thereof. 
     The retainer  30  comprises a first end  31  and a second end  32 . A transverse through-hole  33  is defined in the first end  31  of the retainer  30  and securely engages with the embossed section  14  of the rod  10  to move therewith. A receptacle  34  is defined in an end face of the second end  32  of the retainer  30  for receiving a retaining means  35  comprised of an elastic element  351  and a ball  352 . 
     The casing  40  comprises a first end  41  and a second end  42 . A grip portion  49  is formed on the second end  42  of the casing  40  for manual turning operation. A compartment  43  is defined in the casing  40  for accommodating the retainer  30 . As illustrated in FIGS. 2 and 5, a wall defining a portion of the compartment  43  and facing the retainer  30  comprises two peg holes  44  each having an opening (not labeled) communicated with the compartment  43 . A steel peg  46  is anchored in each peg hole  44 . As illustrated in FIG. 5, a portion not greater than a half of each steel peg  46  is exposed in the compartment  43 . And a retaining space  46 ′ is defined between the exposed portions of the steel pegs  46  that forms a retaining section. Normally, the ball  352  is biased by the elastic element  351  to enter and thus be retained in the retaining space  46 ′. In this embodiment, the ball  352  presses against the exposed portions of the steel pegs  46  under the action of the elastic element  351 . 
     Referring to FIG. 3, a positioning hole  45  is defined in the first end  41  of the casing  40  and communicated with the compartment  43 . The first end  11  of the rod  10  is received in the positioning hole  45  of the casing  40 , and a ball  47  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  45  of the casing  40  to provide a smooth rotation therebetween. A recessed portion  48  surrounds the compartment  43  of the casing  40 , and a lid  50  is mounted in the recessed portion  48  for enclosing the compartment  43 . The lid  50  has a hole  51  through which the rod  10  extends. 
     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  40  is then turned by means of gripping and turning the grip portion  49 . Referring to FIG. 5, when the rotational force applied to the wrench is smaller than a predetermined engaging force between the ball  352  and the steel pegs  46 , the retainer  30  and the rod  10  turn together with the casing  40  to thereby drive the bolt  61 . When the rotational force applied to the wrench is greater than the predetermined engaging force between the ball  352  and the steel pegs  46 , the casing  40  slides relative to the ball  352 . Thus, the casing  40  is moved to a position shown in FIG. 6 or FIG. 7; namely, the ball  352  is disengaged from the retaining space  46 ′, but the retainer  30  and the rod  10  are not turned. As a result, the bolt  61  is not turned. The casing  40  returns to its original position shown in FIG. 5 under the action of the elastic element  351  when the force is released. 
     It is noted that the engaging force, which largely depends on the elastic coefficient of the elastic element  351 , determines a maximum operational torque for turning the retainer  30  and the rod  10 . Namely, when the torque applied to the casing  40  is smaller than the maximum operational torque, the retainer  30  and the rod  10  are turned, and when the torque applied to the casing  40  is greater than the maximum operational torque, the retainer  30  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  40  would be greater than the maximum operational torque such that the casing  40  slides. Thus, the user will notice the sliding motion of the casing  40  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. 
     FIGS. 8 and 9 illustrate a modified embodiment of the invention, wherein the steel pegs  46  forming the retaining section are replaced by two protrusions  432 ″ that are integrally formed with the wall defining the portion of the compartment  43  of the casing  40 . Thus, the protrusions  432 ″ and the casing  40  can be made by means of injection molding. In addition, the ball  352  is replaced by a cylinder  352 ″ that can also be made of plastic material. 
     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.