Torque signalling wrench
BACKGROUND OF THE INVENTION 
     The present invention relates to a torque signalling wrench, and, more particularly, to a simplified structure for such a wrench enabling low cost production of the wrench including cost of manufacturing parts and assembly. 
     Torque limiting wrenches are known. The known wrenches have a wrench shank structure associated with a handle for the wrench and a torque responsive unit comprising a swivel type connection is also associated with the handle and provides for relative movement between elements of the torque responsive unit for limiting the torque applied by the wrench. In the known wrenches, the torque responsive unit is a unit which is fabricated separately and incorporated into the handle for the wrench. These units complicate the manufacture of torque wrenches because of the nature of the parts and the assembly operations required, thereby, increasing the cost of such wrenches. 
     It is an object of the present invention to provide a torque wrench which signals when the applied torque exceeds an adjustable threshold and in which requires a minimum of simple parts which are such that prefabricated torque responsive units are not necessary, the fabrication the parts only requiring simple machine or forming operation with the assembly of the torque signalling wrench being a simple assembly operation and the design enabling standard production wrench heads with handle shanks to be utilized. 
     SUMMARY OF INVENTION 
     In accordance with the preferred design of the invention, a wrenching head, which may be a conventional flat type open-end wrench head, having a shank, preferably a relatively flat shank, extending outwardly from the wrenching head into a tubular handle member with the shank terminating in an outer end disposed within the handle member toward the outer end of the handle member. The shank is pivoted to the handle member near the inner end of the handle to provide limited relative angular movement of the shank and handle member about a pivot, preferably relative movement to either side of a centered position along the centerline of the handle member. The maximum crosswise dimension of the shank is somewhat smaller than the internal diameter of the handle to permit the relative angular movement with the movement being limited by the engagement of the outer end of the shank and the internal wall of the handle member. Preferably the shank is normally held along the center line of the handle by torque responsive means which will yield to allow relative angular movement between the shank and the handle when a predetermined wrenching threshold is reached. In the preferred embodiment, the torque responsive means includes a movable ball element having a surface of which a portion thereof is received in a recess in the outer end of the shank between opposed walls defining the recess. The outer end portions of the opposed walls engage the ball surface on opposite sides of the handle centerline equidistant therefrom. A moveable centering member supports the ball element on the centerline of the handle member is axially moveable along the centerline. A spring disposed within the outer end portion of the handle urges the centering member and the ball element inwardly toward the outer end of the shank to yieldingly force the ball surface into the notch or recess in the shank end to center the shank on the centerline of the handle and to hold it centered unless sufficient torque force is applied to effect a camming of the ball away from the shank end by the walls of the engaging the ball surface. The outer end of the spring abuts an adjustable spring stop member which is adjustable axially of the handle member to adjust the biasing force of the spring to determine the torque threshold for the wrench. When the torque threshold is reached, the applied torque forces on the handle cause the walls defining the recess or notch to cam the ball outwardly of the handle and to allow relative movement between the handle member and the shank to signal that the torque threshold has been reached. In the preferred and illustrated embodiment, the construction is such that the assembly operation for the wrench is simple. After inserting a pin to pivotally mount the shank inside the handle and preferably filler plates which are loosely associated with the shank to laterally position the shank on the centerline of the handle, the ball, the ball centering member for the ball and the spring can merely be dropped into the handle and the adjustable spring stop member moved into engagement with the outer spring end, preferably by threading. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     Referring to the drawings which illustrate a preferred embodiment hereof and which are part of the present specification for all subject matter disclosed therein, and in which: 
     FIG. 1 is a longitudinal cross-sectional view of a wrench embodying the present invention; 
     FIG. 2 is a fragmentary perspective view of a portion of the wrench of FIG. 1 showing the outer end of the shank and the cooperating ball element; 
     FIG. 3 is a cross-sectional view of the wrench of FIG. 1 taken as indicated by the line 3--3 of FIG. 1; 
     FIG. 4 is an enlarged fragmentary sectional view of the right hand end portion of the wrench of FIG. 1 showing the spring adjustment stop member and an end portion of the spring within the handle of the wrench; and 
     FIG. 5 is fragmentary showing of FIG. 1 illustrating the wrench shank and handle of FIG. 1 when in a torque signalling position. 
    
    
     DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates a torque signalling wrench 10 embodying the preferred embodiment of the present invention. The torque signalling wrench 10 includes as the wrenching member a conventional flat type open-ended wrench 12 having a flat type wrenching head 14 and a generally flat shank 16 which extends outwardly from the wrenching head 14 into a tubular handle member 18 of the handle 20 of the torque signalling wrench 10. The maximum crosswise dimensions of the shank 6 are somewhat smaller than the inside diameter of the tubular member 18 to allow the wrench to be supported for limited angular movement within the handle by a pivot pin 22. The pivot pin 22 is mounted in diametrically opposed openings 24 in the side wall of the tubular member 18 and extends through an aligned crosswise opening 26 in the wrench shank 16, and through aligned openings in filler flats 27, one on either side of the shank 16. The filler plates 27 are chordal segments of a cylinder to provide a flat side 27a which lies along the adjacent side of the shank and a cylindrically curved side 27b which corresponds to the internal curvature of the tubular handle member 18. The openings in the filler plates are located so that when the openings are aligned with the openings 24, the filler plates extend to and terminate at the inner end of the tubular member. This simplifies locating the filler plates in the handle during assembly. The pivot pin axis is perpendicular to the plane of wrenching movement of the wrench, as well as perpendicular to the center line of the length of the shank 16. The pivot pin and filler plates allow the wrench to have limited angular movement about the pivot pin inside the tubular handle. The shank 16 extending from the pivot pin is maintained along the center line of the tubular member 18 by means comprising a spherically shaped element, preferably a ball 30, of somewhat smaller diameter than the inside of the tubular member 18. The ball 30 is of a size such that a portion of its surface (less that 180 degrees) is received in a notch, or recess, 32 formed in the outer end of the shank to effect a centering of the shank along the centerline of the handle. The notch or recess 32 has a bottom surface 34 which extends essentially crosswise of the shank and side walls 36 extending axially outwardly from the bottom at an angle of approximately 45 degrees to form a space for receiving a portion of the surface of the ball between the walls with the walls engaging the ball on opposite sides of the center line substantially equidistantly from the center line when the shank is lying along the center line of the handle. The walls defining the recess or notch are centered on the plane of wrenching movement of the handle extending through the centerline of the handle. 
     The ball element 30 is maintained in a centered position inside the tubular handle 18 by a spring stop, or centering member 38 disposed inside the tubular handle member on the side of the ball remote from the end of the shank 16. The centering member 38 has a circular recessed surface 40 with a conically shaped bottom for receiving and holding the ball in a centered position with the ball element in engagement with the outer end of the shank 16. The rear side 44 of the centering member, which extends transversely of the tubular member 18, is engaged by the inner end of a biasing spring 46 for yieldably urging the centering member and in turn the ball against the outer end of the shank 16. Both the centering member 38 and the spring are axially moveable in the handle 18. 
     The outer end of the spring 46 engages an adjustable spring stop member 48 which, in the preferred embodiment, is shown as a set screw which threads into outer end of the tubular handle member 18. The outer end of the tubular handle member 18 is provided with internal threads 50 for this purpose. The end of the tubular member 18 is closed by the end of a plastic sheath 52 which fits over the outer end of the tubular member 18 and extends to approximately the center of the tubular member to provide a hand grip for wrenching. The plastic sheath has a close fit but is removable. 
     From the foregoing description, it can be seen that the biasing spring 46 will urge the ball element into the notch in the end of shank 16 to relatively center the shank and tubular handle member on the center line of the handle. When the wrench is used and torquing forces are applied to the handle, the forces will tend to move the ball laterally relatively to the shank in the direction of wrenching movement and cause reaction forces in the end portion of the notch wall which is disposed in the direction which the ball is being forced. When sufficient force is applied, the ball element will be cammed or cam itself along its spherical surface to move the ball axially in the handle in response the reaction forces in the shank, which is being held by the torque resistance of the element being wrenched. This causes the handle and shank to relatively move angularly until the end of the shank engages the internal side wall of the handle member as is shown in FIG. 5. It is to be understood that the angular movement is insufficient to allow both end walls to move to one side of the center line so as to prevent an over center lock-up condition which would prevent the return of the shank to a centered position when the torque force is relaxed or released. 
     It can be seen that the wrench is of simple construction requiring no prefabricated units such as a swivel unit to be mounted on the end of the wrench shank, the elements of the wrench being simple and readily available or simply manufactured with only simple machine operations. 
     The assembly of the wrench is simple, the filler plates along with wrench shank can be simply be inserted into the tubular handle at its inner end and the pin 22, which may be a conventional rivet pin, inserted to hold the parts in position. The ball then may be dropped into the outer end of the tubular handle followed by the ball centering member 38, in turn, followed by the spring 46 with the set screw 50 then being threaded into the opening to engage the end of the spring and to adjust it to set the proper compression in the spring. The plastic sheath then can be applied to close the open outer end of the handle and provide a hand grip on the tubular handle member 18. 
     In a preferred embodiment, the wrenching head and shank is a typical open-ended wrench head with a relatively flat shank with the flat shank provided with the notch 32 which formed with the head and shank or proved by a simple machining operation. The ball centering mechanism is a simple cylindrical block with only a simple recess formed in one end to receive and trap the ball. 
     In summary, when the wrenching head is used to wrench a part, such as the head of a bolt or nut, about an axis, the biasing spring will maintain an alignment of the shank along the center line of the tubular handle until a predetermined torque is reached. As this torque is exceeded, the reaction forces on the side walls of the notch will tend to move the ball axially against the biasing spring. Upon reaching the torque threshold setting of the spring, the ball element is cammed axially sufficiently to allow the tubular handle to move angularly relative to the shank of the wrench, the angular movement of the shank itself being resisted by the part being wrenched. It is noted that the internal dimension of the tubular handle is such relative to the notch in the end of the shank that the end walls of the notch in the shank in engagement with the ball cannot move over center so that the handle will return to a straight position when the torquing force is released. 
     It is the movement of the handle relative to the shank that signals that the desired torque threshold has been reached. However, it will further be noted that continued wrenching of the element can occur when the outer end of the wrench engages the internal side wall of the tubular wrench member 18. It is also clear that torque signalling will occur in either direction of movement of the wrench handle. 
     From the foregoing description, it will be obvious to those in the art that modifications can be made in the preferred embodiment to accomplish the objects of the preferred embodiment, i.e. simple parts, a reduced number of parts, and easy assembly, for example, it may be convenient for a manufacturer to form the ball 30 and its centering member 38 as one piece which may be cammed axially. Also, the wrench head may comprise a socket extending perpendicular from the head instead of the open ended wrenching slot.