Abstract:
A cam assembly for a click-type torque wrench includes an elongated plunger body having opposed ends and having a deep cavity formed axially in one end and terminating at an end face disposed with intermediate the ends, the end face having a cam seat formed therein and extending laterally theracross and having opposed sloping side cam surfaces. A sleeve may be disposed about the cam plunger for sliding engagement within a tubular lever arm of the torque wrench. The cam seat cooperates with an end of the wrench pivot arm for trapping therebetween the wrench trip block.

Description:
RELATED APPLICATION 
   This application claims the benefit of the filing date of now abandoned U.S. Provisional Application No. 60/510,704, filed Oct. 10, 2003. 

   BACKGROUND 
   This application relates to torque wrenches of the click type and, in particular, to click mechanisms for such wrenches. 
   Click-type torque wrenches derive their name from the fact that they signal the achievement of a predetermined torque level by generating an audible and/or tactile “click.” Such torque wrenches typically have an elongated tubular lever arm coupled at one end to a workpiece-engaging head by a pivot arm which extends into the tube, a handle being provided at the other end of the tube. The click mechanism includes a spring-loaded cam plunger which is slidably disposed within the tube and is biased toward the inner end of the pivot arm, for trapping therebetween a trip block or pawl which is seated in recesses formed in the facing ends of the pivot arm and cam plunger. The spring force, which is adjustable, drives the trip block axially against the inner end of the pivot arm so as to hold the pivot arm in a position aligned substantially coaxially with the tube until the applied torque reaches a level which causes the pivot arm to overcome the spring force and pivot, moving its inner end laterally to tip the trip block, camming the cam plunger rearwardly in the tube and allowing the inner end of the pivot arm to strike the inner surface of the tube, creating the click. When torque is released, the spring drives the parts back to their original positions. 
   While this arrangement works well, it has created several problems. When the trip block tips, it applies a lateral force against the front end of the cam plunger tending to cause its front end to move laterally more than the rear end, which can cause the front peripheral edge of the cam plunger to create surface galling of the inner surface of the tube as the cam plunger moves axially back and forth. Heretofore, this problem has been overcome by internal surface hardening of the tube through a heat-treating process. However, this heat treating process can cause distortion of the thin-walled tube and can create a significant degree of surface finish degradation. This surface finish damage and physical distortion of the tube then necessitates secondary processing operations to create surface finish and tube straightness, which add cost to the tool. 
   Furthermore, it has been found that in prior tools the lateral movement of the inner end of the pivot arm to create the click is sometimes sufficient to completely roll over the trip block or pawl so that it does not return to its proper position when torque is released. In order to alleviate this problem it has been necessary in prior designs to add a spacer ring press-fitted onto the end of the pivot arm to restrict the lateral or side-to-side movement of the pivot arm, thereby further adding cost to the tool. 
   SUMMARY 
   There is disclosed herein an improved click-type torque wrench and click mechanism therefore which avoid the disadvantages of prior techniques while affording additional structural and operating advantages. 
   An important aspect is the provision of a click mechanism which utilizes an improved cam assembly which effectively eliminates surface galling of the inner surface of the lever arm tube and obviates the use of a spacer on the pivot arm. 
   In an embodiment, a cam assembly for a click-type torque wrench includes an elongated plunger body having opposed ends and having a deep cavity formed axially in one end and terminating at an end face disposed intermediate the ends, the end face having a cam seat formed therein and extending laterally thereacross and having opposed sloping side cam surfaces. 
   In an embodiment, the cam assembly may be used in a click-type torque wrench which includes a tubular lever arm having a longitudinal axis, a pivot arm disposed within the lever arm for pivotal movement relative thereto and adapted to be coupled to a workpiece-engaging head, the plunger body being disposed within the lever arm for axial movement therealong and resiliently biased toward the pivot arm, and a trip block trapped between the seat and the distal end of the pivot arm for holding the pivot arm substantially coaxially within the lever arm and allowing it to pivot when a predetermined torque is reached. 
   The cam assembly may include a sleeve extending about the cam plunger for sliding engagement with the inner surface of the lever arm. 
   There is also disclosed a method of providing a click indication in a click-type torque wrench having a tubular lever arm and a pivot arm disposed within the lever arm, a cam plunger biased toward the distal end of the pivot arm and a trip block trapped between the cam plunger and the distal end of the pivot, the method comprising providing a deep axial cavity in the cam plunger into which the distal end of the pivot arm is received, and disposing the trip block at the inner end of the cavity. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For the purpose of facilitating an understanding of the subject matter sought to be protected, there are illustrated in the accompanying drawings embodiments thereof, from an inspection of which, when considered in connection with the following description, the subject matter sought to be protected, its construction and operation, and many of its advantages should be readily understood and appreciated. 
       FIG. 1  is a longitudinal vertical sectional view through a portion of a prior-art, click-type torque wrench; 
       FIG. 2  is a fragmentary horizontal sectional view through the torque wrench of  FIG. 1 ; 
       FIG. 3  is a view similar to  FIG. 1  of an improved click-type torque wrench; 
       FIG. 4  is a view similar to  FIG. 2  of the torque wrench of  FIG. 3 ; 
       FIG. 5  is an enlarged sectional view taken along the same plane as  FIG. 4  of the cam assembly of the torque wrench of  FIG. 4 ; 
       FIG. 6  is a left-hand end elevational view of the cam assembly of  FIG. 5 ; and 
       FIG. 7  is a right-hand end elevational view of the cam assembly of  FIG. 5 . 
   

   DETAILED DESCRIPTION 
   Referring to  FIGS. 1 and 2 , there is illustrated a portion or a prior-art torque wrench, generally designated by the numeral  10 , having an elongated tubular lever arm  11 . An elongated pivot arm  12  is received in one end of the lever arm  11 , being mounted in a fulcrum block  13  for pivotal movement about the axis of a pivot pin  14 . The outer or proximal end of the pivot arm  12  is adapted to be coupled to a workpiece-engaging head (not shown) in a known manner, which head could be ratcheting or non-ratcheting. The distal or inner end of the pivot arm  12  defines a clevis  15 . A coupling pin  16  extends through aligned apertures  17  in the arms of the clevis  15  and also passes through a hole  18  in a tongue  19  of a secondary arm  20  to form a pivotal connection between the lever arm  11  and the secondary arm  20 . The secondary arm  20 , which may be cylindrical in shape, is mounted in a fulcrum block  21  for pivotal movement about the axis of a pivot pin  22 . The use of two pivoting arms is necessary only in high-torque applications. In lower-torque applications only the pivot arm  20  may be necessary, in which case it would have the appropriate length and be directly connected to the workpiece-engaging head. Such a torque wrench is disclosed, for example, in U.S. Pat. No. 3,599,515, the disclosure of which is incorporated herein by reference. 
   Extending diametrically across the inner or distal end face of the secondary arm  20  is a seat recess  23  having a flat base surface  24  and opposed sloping side surfaces  25 . An annular stop ring  26  may be press-fitted on the distal end of the secondary arm  20  to limit lateral pivotal movement of the inner end of the secondary arm  20 . A pawl or trip block  27  is seated in the recess  23 . The pawl  27  may be an elongated block which is substantially square in transverse cross section with rounded ends, having opposed flat faces  28  and  29 , with the face  28  being normally seated against the base surface  24  of the seat recess  23 . 
   The wrench  10  also includes a cam plunger  30 , which may be a substantially cylindrical block disposed for coaxial sliding movement within the lever arm  11  and having a pawl slot  31  extending diametrically across the forward or inner face thereof. The pawl slot  31  is shaped generally like the seat recess  23 , having a flat base surface  32  and opposed side surfaces  33 . The flat face  29  of the pawl  27  seats against the base surface  32 . The rear or outer end of the cam plunger  30  is hollowed out to define a deep cylindrical cavity  34  which communicates with the pawl slot  31  through a relatively small-diameter vent hole  35 . The hole  35  avoids differential pressure which could occur due to possible sealing from lubrication grease within the wrench assembly, which differential pressure could cause variation in torque readings. The cam plunger  30  is biased forwardly, toward the secondary arm  20 , by a bias spring  36 , which may be a helical compression spring having one end thereof seated against the rear end of the cam plunger  30  and the other end seated against an adjustment mechanism (not shown) for adjusting the pre-compression of the spring and, thereby, the predetermined torque level at which the wrench is designed to “click.” The spring pressure holds the pawl  27  seated firmly against the seat recess  23  of the secondary arm  20 , thereby holding the secondary arm  20  in a normal rest configuration substantially coaxial with the lever arm  11 . 
   When torque is applied to a workpiece with the wrench  10 , the torque tends to try to pivot the pivot arm  12  and, thereby, the secondary arm  20 , but this pivotal movement is resisted by the spring pressure on the cam plunger  30 . When the predetermined torque level is reached, the spring pressure is overcome and the arms  11  and  20  pivot, e.g., in the direction of the arrow in  FIG. 2 , thereby tipping the pawl  27  and moving the cam plunger  30  rearwardly against the urging of the bias spring  36 , the pivotal movement of the inner end of the secondary arm  20  being limited by engagement of the stop ring  26  with the inner side of the tubular lever arm  11  so that the pawl  27  will not roll over, all in a known manner. When the torque is released, the cam plunger  30  is driven back forwardly, resetting the pawl  27  and the secondary arm  20  in their original aligned positions. 
   When the secondary arm  20  pivots and the pawl  27  tips, a lateral force is applied to the front end of the cam plunger  30 . Since this lateral force is concentrated at the front end of the cam plunger  30 , it tends to try to tilt the cam plunger about its center of gravity so that, as the cam plunger  30  moves axially back and forth, its front edge may tend to gall the inner surface of the tubular lever arm  11 , as at  37  and  38 . 
   Referring now to  FIGS. 3–7 , there is illustrated a modified torque wrench  10 A, in which the cam plunger  30  has been replaced by a cam assembly  40  and the stop ring  26  has been eliminated. All other parts of the torque wrench  10 A are the same as those in the wrench  10 , so that like parts have the same reference numbers. 
   The cam assembly  40  includes an elongated cylindrical cam plunger  41 , having formed axially in the forward end surface thereof a deep cylindrical bore or cavity  42  which terminates at a circular end face  43 , which is disposed in the rear half of the cam plunger  41 . Formed diametrically across the end face  43  is a pawl slot  44 , having a flat base surface  45  and opposed sloping side surfaces  46 . Formed in the rear end face of the cam plunger  41  are two vent holes  47  which extend parallel to the axis of the cam plunger  41  on opposite sides thereof and respectively intersect the sloping side surfaces  46  for communication with the cavity  42 . Formed in the rear end face of the cam plunger  41  and extending diametrically thereacross midway between the vent holes  47  is a shallow channel  48 . Also formed in the end face of the cam plunger  41  at the periphery thereof is an annular recess  49 . 
   The cam assembly  40  also includes a cylindrical sleeve  50 , which covers the outer cylindrical surface of the cam plunger  41 , the sleeve  50  having an annular front lip  51  which overlaps the front end surface of the cam plunger  41  and a rear peripheral lip  52  which seats in the annular recess  49 . The sleeve  50  may also include a cross arm  53  which extends diametrically across the rear end thereof and fills the channel  48  of the cam plunger  41 . The sleeve  50  may be formed of a plastic material, such as a suitable friction-reducing polymer material, such as molybdenum-disulfide nylon, and may be overmolded on the cam plunger  41 . Alternatively, the sleeve  50  could be preformed and then fitted over the cam plunger  41 . The sleeve  50  could be formed of other materials, such as brass or other metals, or non-metals. The material of the sleeve  50  may be selected so that the outer surface of the sleeve  50  has a friction-reducing character and may be selected to have a hardness relative to that of the lever arm  11  so as to inhibit galling of the inner surface of the lever arm  11 . 
   The operation of the torque wrench  10 A is substantially the same as that described above with respect to the torque wrench  10 . However, the friction-reducing sleeve  50  significantly reduces part-to-part wear which had been associated with prior torque wrenches at the metal-to-metal interface between the prior cam plunger and the inner surface of the tubular lever arm  11 . This reduced wear also significantly increases the life expectancy of the product. Also, because the pawl seat  44  is disposed well within the cam plunger  41 , the side load forces on the cam plunger  41  resulting from pivoting of the secondary arm  20  are much more evenly distributed along the length of the cam plunger  41 , greatly reducing the tendency of the cam assembly  40  to tend to gall the inner surface of the lever arm  11 . This tendency may be even further reduced by the presence of a friction-reducing sleeve  50 . Thus, there is no need for surface hardening of the internal surface of the lever arm  11 . Also, the cavity  42  is dimensioned to have a diameter only slightly greater than that of the secondary arm  20 . Thus, the lateral movement of the inner end of the secondary arm  20  is limited to an extent such that rollover of the pawl  27  is prevented, so that the stop ring  26  is not necessary. The seating of the cross arm  53  of the sleeve  50  in the channel  48  inhibits any tendency toward rotational movement of the sleeve  50  relative to the cam plunger  41 . 
   The cam plunger  41  may be formed of a suitable metal, such as a powdered metal, and the other parts of the torque wrench  10 A may also be formed of suitable metals, although it may be possible to use other materials for some or all of these parts. 
   While particular embodiments have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made without departing from the principles of the ratcheting torque angle wrench in its broader aspects. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation.