Abstract:
A torque screw having a screw with a head and a threaded shaft, a knob having a central longitudinal axis coaxial with the screw and a one-directional ratchet disposed between the knob and the screw that engages to allow the screw to be disengaged in a counter-clockwise direction using the knob, and engages when rotated in a clockwise direction to a predetermined torque value. Once that predetermined torque value is reached, the ratchet is caused to slip such that the knob turns relatively freely with respect to the screw.

Description:
This application is a continuation-in-part application of U.S. application Ser. No. 08/811,872, filed on Mar. 5, 1997, now pending, which is a continuation of U.S. application Ser. No. 08/554,563, filed on Nov. 16, 1995, now U.S. Pat. No. 5,642,972. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to torque screws of the type generally used to attach an object to a panel or frame wherein it is desired to limit the torque the screw may place on either the object or frame such that potential damage caused by over tightening the screw is eliminated. 
     Various requirements in manufacturing and assembly of components have dictated the need for a screw fastener that cannot be over tightened such that damage to panels or other object to which the fastener is attached does not occur. Various torque limiting screws exist in the prior art, including U.S. Pat. No. 5,120,168 to Padula, and U.S. Pat. No. 4,109,691 to Wilson, each of which is a “single use only” screw which provides tamper resistance, but here, once the screw is installed, it cannot easily be unscrewed. U.S. Pat. No. 4,472,098 to Kiefer is an invention for a torque limiting nut that uses an elastomeric material to engage a threaded screw shaft. None of these patents disclose a torque screw that allows reuse an indefinite number of times and allows the screw to be unscrewed in a normal manner. 
     Additionally, none of these torque screws is of a captive screw style. 
     Finally, it would be advantageous to have an audible signal indicating that the torque screw has reached its predetermined torque limit. It is not believed that any screws of the present type have this audible feature. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a torque screws in general. The present invention provides a torquelimiting arrangement in which the screw may be tightened down to a particular torque. Once that torque value is reached, the knob of the screw rotates without significant further tightening down of the threads of the screw. The action is accomplished by means of a “C” shaped spring which acts as a driver to transmit torque from the knob to a flange on the screw in the tightening mode, but that deflects inwardly, thus disengaging the driving action when the knob is rotated clockwise at a point when a predetermined torque is reached. 
     The torque screw is hand tightenable to tighten, for example, a first panel to a second panel, but once the predetermined torque is reached, the torque screw “slips” and allows for substantially no more significant torque to be supplied to the screw threads. 
     The torque screw comprises a screw having a head and a threaded shaft, a knob having a central longitudinal axis coaxial with the screw, and a one-directional ratchet means disposed between the knob and the screw that engages to allow the screw to be disengaged in a counter-clockwise direction using the knob, and engages when the knob is rotated in a clockwise direction to a predetermined torque value. Then, the knob slips generally freely, such that further clockwise rotation causes the knob to slip relative to the knob. When the knob is rotated in a counterclockwise direction, the ratchet locks and causes the screw to rotate counterclockwise at all times during the counterclockwise rotation of the knob. 
     An alternate embodiment has the above mechanism, but has a ferrule that is attachable to a panel, where the knob is captivated on the panel. The captivation means of the knob on the ferrule allows for limited axial movement of the knob with respect to the ferrule and full rotational movement of the knob with respect to the ferrule, but limited by the ratchet means. 
     A driver recess is optionally placed on the top surface of the knob to aid in rotating the screw. 
     It is therefore an object of the present invention to provide a new and improved torque screw. 
     It is another object of the present invention to provide a new and improved torque screw that is reliable and simple to manufacture. 
     It is another object of the present invention to provide a new and improved torque screw that spins generally freely relative to the screw shaft once a predetermined torque is reached. 
     It is another object of the present invention to provide a new and improved torque screw that is in the form of a single article without the need for a separate torque wrench or driver. 
     It is a still further object of the present invention to provide a new and improved torque screw that provides a desired torque by hand or with a standard screwdriver or similar tool. 
     It is a further object of the present invention to provide a new and improved torque screw that provides audible indication of when the maximum torque allowed by the screw has been reached. 
     It is a still further object of the present invention to provide a new and improved torque screw that provides for the torque screw to be captivated on a panel such that loose items of hardware are eliminated. 
     Other objects and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cutaway elevational view of a torque screw in accordance with one embodiment of the present invention. 
     FIG. 2 is an exploded perspective view of a knob, screw, C-spring, ratchet wheel, and retainer ring of the embodiment of FIG.  1 . 
     FIG. 3 is a perspective view depicting the interrelationship of the C-spring and ratchet wheel of FIG.  1 . 
     FIG. 4 is cutaway elevational view of a torque screw in accordance with a second embodiment of the present invention, including a means to captivate the torque screw on a panel. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now in detail to the drawings, wherein like reference numerals indicate like elements throughout the several views, there is shown in FIGS. 1 and 2, a torque screw  10  in accordance with one preferred embodiment of the present invention. The illustrative device  10  is shown generally comprising a knob  20 , a screw  30 , a ratchet wheel  40 , a C-spring  50 , and a retainer ring  60 . 
     Screw  30  is rotationally disposed within knob  20  as depicted in FIGS. 1 and 2. Knob  20  is substantially hollow with an end cap  22  that has a substantially planar inner surface  24 . Screw  30  likewise has a substantially planar surface  32  on its head  34 . Additionally, the head  34  of screw  30  has an annular flange  36  with a notch  38 , the purpose of which will be described in more detail below. 
     As can be seen in FIGS. 2 and 3, C-spring  50  has an downwardly extending pawl  54  which engages notch  38  on the annular flange  36  of screw  30 . As screw  30  rotates in either clockwise or counterclockwise directions, C-spring  50  also must rotate with screw  30 . As can be seen in FIG.  1  and in more detail in FIG. 3 which details only the relationship between the ratchet wheel  40  and C-spring  50 , C-spring  50  fits snugly within ratchet wheel  40 , but is free to rotate within ratchet wheel  40  but is limited by the ratchet action. Upwardly extending pawl  52  engages ratchet wheel teeth  42  as will be described below. 
     Upon assembly of the torque screw  10  of the present invention, ratchet wheel  40  is pressed into place within the knob  20  as shown in FIG. 1, thereby preventing relative motion of the ratchet wheel  40  with respect to the knob  20 . Ratchet wheel  40  preferably has axial knurled teeth  41  on its outer surface, and is preferably constructed of a harder material than that of the knob to allow for the ratchet wheel  40  to be pressed rigidly into position in knob  20 . However, ratchet teeth could also be formed integral to the knob  20  (not shown). As described above, C-spring  50  then fits snugly within the ratchet wheel  40 , free to rotate, with upwardly extending pawl  52  engaging the teeth of ratchet wheel  40 . Screw  30  is then inserted into the knob  20  with the downwardly extending pawl  54  of C-spring  50  engaging screw notch  38 . 
     Finally, retainer ring  60  is placed against the bottom of the annular flange  36  on screw head  30  and the lower portion  26  of the knob  30  is rolled over to secure the screw  30  and C-spring  50  within the ratchet wheel  40  and knob  20 . Clearance is provided to allow screw  30  to turn relative to knob  20 . Note that FIG. 2 depicts the knob  20  in a condition prior to rolling over. Therefore, when knob  20  is rotated relative to screw  30 , upwardly extending pawl  52  interacts with teeth  42  on ratchet wheel  40 . The screw  30  is secured from movement in the longitudinal direction within the knob  20 , but is free to rotate axially in the clockwise direction once the limit of torque of the screw is reached. 
     As can be seen in FIG. 3, when ratchet wheel  40  is rotated in a counterclockwise direction, C-spring  50  must also rotate counterclockwise due to the shape of ratchet teeth  42 . That is, the teeth  42  have a leading edge that is generally perpendicular to the C-spring  40  such that the teeth  42  positively engage upwardly extending pawl  52 . However, when ratchet wheel  40  is rotated in a clockwise direction, C-spring also will rotate to a certain value of torque. As the torque on the threaded shaft  31  of screw  30  increases, the upwardly extending pawl  52  of C-spring  50  will begin to deflect radially inwardly. Note that clearance  39  is provided between the screw head  34  and the ratchet wheel  40  by means of the extended annular surface  36  of the screw  30  to allow for such deflection to take place. See FIG.  1 . The occurring friction of the upwardly extending pawl  52  with respect to the teeth  42  on ratchet wheel  40  and the displacement of the C-spring  50  by the teeth  42  provide the desired resistance to rotation thereby supplying a limit to torque that is capable of being supplied to the screw  30  by rotating the knob  20 . This torque can be varied by varying the strength of the C-spring  50 , for example by increasing its thickness, or changing tooth shape or tooth angle to provide increased axial spring force. 
     In constructing the torque screw  10  of the present invention, the ratchet wheel  40  is inserted into and pressed into knob  20  to rigidly hold the ratchet wheel  40  to the inside of the knob  20 . C-spring  50  is then placed such that the upwardly extending pawl  52  mates with teeth  42  on ratchet wheel  40 . Screw  30  is then placed into knob such that downwardly extending pawl  54  mates with notch  38  of screw  30 . Finally, retainer ring  60  is inserted and lower portion of knob  26  is rolled over to hold the assembly together and to allow the screw  30  to smoothly rotate within the knob  20 . 
     Thus, torque, applied-by fingers or a screwdriver of an operator, is transmitted from knob  20  to the ratchet wheel  40  to the C-spring  50  to the screw  30 . However, when knob  20  is rotated in the clockwise direction, once a specific torque value is reached, upwardly extending pawl  52  on C-spring  50  deflects generally radially inwardly, caused by the angled side of ratchet teeth  44 , disengaging the driving action. 
     A screwdriver recess may also be located on the top of the knob (not shown), if desired, but this would not affect the performance of the screw with respect to torque as described above. 
     The desired action can also be accomplished by using the opposite configuration of that as described above. In this embodiment, the C-spring is coupled directly to the knob rather than the screw. The screw has an integral toothed ratchet flange (i.e. a ratchet wheel) and thus the same action as the first embodiment is achieved. 
     A second embodiment of the torque screw  10 ′ is depicted in FIG. 4 which shows a ferrule which allows the torque screw to be captivated on a panel. This second embodiment  10 ′ is shown generally comprising a knob  20 ′, a screw  30 ′, a ratchet wheel  40 ′, a C-spring  50 ′, and a retainer ring  60 ′, each of which functions in a similar manner to the knob  20 , screw  30 , ratchet wheel  40 , C-spring  50  and retainer ring  60  respectively of the torque screw  10  of FIGS. 1-3. In this embodiment, the retainer ring  60 ′ is of a slimmer configuration, but holds the screw  30 ′ and ratchet assembly in place within the knob, preferably by a knurled surface on the outer perimeter of the retainer ring  60 ′ pressed into place within the knob  30 ′. This embodiment adds two new major features, a ferrule  70  and an optional spring  80 . The ferrule is held in place on a panel  90  by a panel captivation means as known in the art. Such captivation means may include a press-in style, swage-in style, snap-in style, as are well known in the field of captive screws. See, for example, U.S. Pat. No. 5,382,124 to Frattarola. The opposite end of the ferrule has an annular ring  72  which, along with the lower portion of the knob  26 ′ which is rolled over during the assembly to form an inwardly pointing annular surface, forms a captivation means that captivates the knob  30 ′ on the ferrule  70 , but allows for limited axial movement and full rotational movement of the knob  30 ′ with respect to the ferrule  70 , as limited by the ratchet means. This knob/ferrule attachment configuration is well known in the art. Optionally, a spring  80  is captivated between an inner surface in the ferrule and the bottom of the screw  30 ′ or the knob  20 ′ to bias the screw and ferrule apart, such that the screw  30 ′ is in a retracted position when no downward axial load is applied to the screw  30 ′. 
     A major feature which is of particular importance for torque screws in general, as designed into both of the above embodiments is that the ratchet means creates an audible indication of when the maximum torque has been reached. This feature allows the user of the torque screw to hear precisely when the maximum torque has been reached, thereby preventing overtightening of the torque screw and saving time by not spending excess time tightening screws, particularly when multiple screws are used. 
     It will be recognized by those skilled in the art that changes may be made in the above described embodiments of the invention without departing from the broad inventive concepts thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but is intended to cover all modifications which are within the scope and spirit of the invention as defined by the appended claims.