Patent Publication Number: US-6662687-B2

Title: Ratchet wrench with improved force distribution

Description:
FIELD OF THE INVENTION 
     The present invention relates to a ratchet wrench for selectively applying torque to a fastener. 
     BACKGROUND OF THE INVENTION 
     FIG. 5 illustrates a prior art ratchet wrench  100 . The prior art wrench has a wrench body  102  including a handle portion (not shown) and a head portion  106 . A pawl  102  is shown in its gear driving position. In this gear driving position, the head portion  104  engages the pawl  102  so as to apply force to it during torque application is a “sidewards” direction of the pawl  102  (indicated by arrow F). That is, the force is applied mostly circumferentially with respect to the axis about which the gear  108  rotates. As a result, the force transmitted to the gear  108  by the pawl  106  tends to be focused at the teeth closest to the point of engagement. Specifically, the force is primarily focused at the outermost tooth of the pawl closest to the point of engagement. As a result, the remainder of the pawl teeth transmit considerably less force. This is an unsatisfactory load distribution. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention provides a ratchet wrench for applying torque to a fastener. The wrench comprises a wrench body having a handle portion configured to be manually grasped and a head portion providing a pawl engaging surface; and a ratchet gear constructed and arranged to be removably engaged with the fastener such that torque applied to the gear is transmitted to the fastener to affect rotation thereof. The ratchet gear is mounted to the wrench body such that the gear and the body are rotatable relative to one another about a gear axis, the ratchet gear having a plurality of gear teeth arranged on a radially outer peripheral surface thereof in circumferential relation with respect to the gear axis. A pawl is mounted to the wrench body and having a plurality of ratcheting teeth arranged in an arc essentially complementary to the gear teeth and a load receiving surface facing generally opposite the ratcheting teeth. The ratcheting teeth include a pair of outermost teeth provided at opposing ends of the arc and inner teeth therebetween. 
     The pawl has a gear driving position wherein the ratcheting teeth of the pawl are positioned for driving engagement with the gear teeth and the pawl engaging surface is positioned for driving engagement with the load receiving surface of the pawl such that a manual force applied in a first direction to the handle portion of the wrench body is transmitted from the wrench body to the pawl via the driving engagement between the pawl engaging surface and the load receiving surface and from the pawl to the ratchet gear via the driving engagement between the ratcheting teeth and the gear teeth so as to apply torque to the gear. The pawl is constructed and arranged with respect to the gear teeth and the pawl engaging surface such that, as the manual force is being transmitted to the gear via the pawl, the total amount of force applied to the gear is distributed among the ratcheting teeth in such a manner that an amount of force applied to the gear by each of the inner ratcheting teeth is greater than or equal to an amount of force applied to the gear by either of the outermost ratcheting teeth. 
     The wrench further comprises a biasing element engaged with the pawl and biasing the pawl to the gear driving position. The biasing element is constructed and arranged such that a manual force applied to the handle portion in a second direction opposite the first direction causes rotation of the wrench body relative to the ratchet gear with the ratcheting teeth of the pawl repeatedly ratcheting over the gear teeth against the biasing of the biasing element. 
     Another aspect of the invention provides a ratchet wrench for applying torque to a fastener. The wrench comprises a wrench body having a handle portion configured to be manually grasped and a head portion providing a pawl engaging surface; and a ratchet gear constructed and arranged to be removably engaged with the fastener such that torque applied to the gear is transmitted to the fastener to affect rotation thereof The ratchet gear is mounted to the wrench body such that the gear and the body are rotatable relative to one another about a gear axis. The ratchet gear has a plurality of gear teeth arranged on a radially outer peripheral surface thereof in circumferential relation with respect to the gear axis. A pawl is mounted to the wrench body and has a plurality of ratcheting teeth arranged in an arc essentially complementary to the gear teeth and a load receiving surface facing generally opposite the ratcheting teeth. The ratcheting teeth include a pair of outermost teeth provided at opposing ends of the arc and inner teeth therebetween. 
     The pawl has a gear driving position wherein the ratcheting teeth of the pawl are positioned for driving engagement with the gear teeth and the pawl engaging surface is positioned for driving engagement with the load receiving surface of the pawl such that a manual force applied in a first direction to the handle portion of the wrench body is transmitted from the wrench body to the pawl via the driving engagement between the pawl engaging surface and the load receiving surface and from the pawl to the ratchet gear via the driving engagement between the ratcheting teeth and the gear teeth so as to apply torque to the gear. The load receiving surface is positioned on or between two outer radial lines of four imaginary radial lines dividing the arc into five equal imaginary arcuate sectors. 
     The wrench also comprises a biasing element engaged with the pawl and biasing the pawl to the gear driving position. The biasing element is constructed and arranged such that a manual force applied to the handle portion in a second direction opposite the first direction causes rotation of the wrench body relative to the ratchet gear with the ratcheting teeth of the pawl repeatedly ratcheting over the gear teeth against the biasing of the biasing element. 
    
    
     Other objects, advantages, and features of the present invention will become apparent from the following detailed description, the accompanying drawings and the appended claims. 
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is an exploded view of an exemplary ratchet wrench constructed in accordance with the principles of the present invention; 
     FIG. 2 is a bottom plan view showing the pawl in a gear driving position with other components of the wrench removed for clarity; 
     FIG. 3 is a bottom plan schematic view showing the stress distribution between the pawl and the ratchet gear in a gray scale plot, the units being expressed in terms of pounds per square inch (PSI). 
     FIG. 4 is a view isolating the pawl and a portion of the gear  18  to illustrate imaginary lines dividing the area of teeth. 
     FIG. 5 is a bottom plan schematic view similar to FIG. 4 showing a prior art construction. 
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT 
     FIG. 1 is an exploded perspective view of a ratchet wrench, generally indicated  10 , constructed in accordance with the present invention. The illustrated wrench  10  is merely an exemplary embodiment of the invention and is not intended to be limiting. The wrench  10  includes a wrench body, generally indicated at  12 . The wrench body  12  includes a handle portion  14  configured to be manually grasped and a head portion  16 . In the illustrated embodiment, the head portion  16  is formed integrally with the handle portion  14 . The head portion  16 , however, may be formed separately from the handle portion  14  and movably connected thereto by a pivot pin for angular adjustment. 
     The wrench  10  includes a ratchet gear  18 . The ratchet gear  18  is constructed and arranged to be removably engaged with a fastener such that torque applied to the gear  18  is transmitted to the fastener to affect rotation thereof. In the illustrated embodiment, the gear  18  is provided with an axially extending lug  19  on which removable sockets are received. Alternatively, the gear  18  could be of the ring gear type with a hole formed therethrough. The hole has an internal periphery configured for suitable engagement with a polygonally-headed fastener, such as a nut or bolt. In general, the ratchet gear  18  can have any configuration for directly or indirectly engaging a fastener for torque application. 
     The ratchet gear  18  is mounted to the wrench body such that the gear  18  and the wrench body  12  are rotatable relative to one another about a gear axis. In the illustrated embodiment, the gear  18  is retained in the cavities of the head portion  16  by a cover plate  20 . 
     The gear  18  has a plurality of gear teeth  22  arranged on a radially outer peripheral surface thereof in circumferential relation with respect to said gear axis. Each of the gear teeth having opposing tooth surfaces. The teeth  22  may be symmetrical or asymmetrical. The teeth  22  may be recessed or protruding outwardly from the gear  18 . 
     The wrench  10  further comprises a pawl  24  mounted to the wrench body  12 . The pawl  24  has a plurality of ratcheting teeth  26  arranged in an arc. The arc is essentially complementary to the gear teeth  22 . The pawl  24  also has a load receiving surface  28  facing generally opposite the ratcheting teeth  26 . The ratcheting teeth  26  include a pair of outermost teeth  30  provided at opposing ends of the arc and inner teeth  32  therebetween. 
     The pawl  24  has a gear driving position, shown in FIGS. 2 and 3. In the paw&#39;s gear driving position, the pawl  24  is positioned for driving engagement with the gear teeth  22  and a pawl engaging surface  34  of the wrench body  12  is positioned for driving engagement with the load receiving surface  28 . As a result of these driving engagements, a manual force applied in a first direction (indicated with arrow  36 ) is transmitted (a) from the wrench body  12  to the pawl  24  via the driving engagement between the pawl engaging surface  34  and the load receiving surface  28  and (b) from the pawl  24  to the ratchet gear  18  via the driving engagement between the ratcheting teeth  26  and the gear teeth  22 . This applies torque to the gear  18  for rotating the fastener. 
     The wrench  10  also comprises a biasing element, which in the illustrated embodiment is in the form of a coil spring  38 . Any suitable biasing element may be used in place of a coil spring  38 . For example, a leaf spring could be used. Likewise, any resilient structure suitable for applying a biasing force to the pawl  24  may be used. The spring  38  is engaged with the pawl  24  and biases the pawl  24  to its gear driving position. The spring  38  is constructed and arranged such that a manual force applied to the handle portion  14  in a second direction (indicated with arrow  40 ) opposite the first direction  36  causes rotation of the wrench body  12  relative to the ratchet gear  18  with the ratcheting teeth  26  of the pawl  24  repeatedly ratcheting over the gear teeth  22  against the biasing of the spring  38 . 
     In the illustrated embodiment of FIG. 1, the ratchet wrench  10  is of the reversible type. Thus, the wrench body  12  has an opposite pawl engaging surface  34   a . The pawl  24  is movable generally circumferentially with respect to the ratchet gear  18  to an opposite gear driving position opposite the one illustrated in FIG.  2 . In this opposite gear driving position, the ratcheting teeth  26  are positioned for an opposite driving engagement with the gear teeth  22  and the opposite pawl engaging surface  34   a  is positioned for an opposite driving engagement with the load receiving surface  28  of the pawl  24 . As a result of these opposite driving engagements, a manual force applied in the second direction  40  the handle portion  14  of the wrench body  12  is transmitted (a) from the wrench body  12  to the pawl via the opposite driving engagement between the opposite pawl engaging surface  34   a  and the load receiving surface  28  and (b) from the pawl  24  to the ratchet gear  18  via the opposite driving engagement between the ratcheting teeth  26  and the gear teeth  22 . This applies an opposite torque to the gear  18  for rotating a fastener in an opposite direction. 
     The wrench  10  in the illustrated embodiment further comprises a reversing switch member  42  mounted to the head portion  16 . The switch member  16  enables the user to switch the pawl  24  between the two gear driving positions. In the illustrated embodiment, the spring  38  is positioned between the pawl  24  and the switch member  16 . The spring  38  is arranged such that (a) when the pawl  24  is in the gear driving position, a manual force applied to the handle portion  14  in the second direction  40  causes rotation of the wrench body  12  relative to the gear  18  with the ratcheting teeth  26  repeatedly ratcheting over the gear teeth  22  against the biasing of the spring  38  and (b) when the pawl  24  is in the opposite gear driving position, a manual force applied to the handle portion  14  in the first direction  36  causes rotation of the wrench body  12  relative to the ratchet gear  18  with the ratcheting teeth  26  repeatedly ratcheting over the gear teeth  22  against the biasing of the spring  38 . 
     In the illustrated embodiment, the pawl  24  is pivotally mounted on the upright leg of an L-shaped member  39 , which leg is received in a bore  41  on the pawl  24 . The spring  38  is mounted on the other leg of the L-shaped member  39 , which other leg is received in a bore in the switch member  42 . As the switch member  42  is pivoted between positions, the spring  38  changes angular positions and moves the pawl  24  circumferentially relative to the gear  18 . The pawl  24  pivots on the leg of the L-shaped member  39  during this travel. The switch member  42  also includes a spring  42  and a detent member in the form of a detent ball  45  that engages a pair of recesses  47  on the head portion  16  to retain the switch member  42  in either of its two positions. For further details on this aspect of the illustrated, non-limiting construction, reference may be made to U.S. application Ser. No. 09/805,434, filed Mar. 14, 2001, entirety of which is hereby incorporated herein by reference. The construction used in U.S. Pat. No. 5,957,009 may also be used. Regardless of the construction, any type of suitable mechanism may be used for switching the pawl  24  between its gear driving positions. 
     Alternatively, the ratchet wrench  10  may be of the one-way ratcheting type wherein the pawl  24  only has a single gear driving position. This type of wrench  10  is devoid of a reversing switch  42 . In this type of wrench  10 , the gear  18  is preferably of the ring gear type illustrated with a hole formed therethrough for receiving a fastener. This enables the wrench  10  to be flipped over for rotating the fastener in an opposite direction. 
     The pawl  24  is constructed and arranged with respect to the gear teeth  22  and the pawl engaging surface  34   a  (and, in the reversible type of wrench, pawl engaging surface  34   a ) such that, as the manual force is being transmitted to the gear  18  via the pawl  24 , the total amount of force applied to the gear  18  is distributed among the ratcheting teeth  26  in such a manner that an amount of force applied to the gear  18  by each of the inner ratcheting teeth  32  is greater than or equal to an amount of force applied to the gear teeth  26  by either of the outermost ratcheting teeth  30 . That is, the force is distributed among the teeth  26  such that it is not focused to a greater extent on either of the outermost teeth  32 , and instead is distributed more broadly across all the teeth  26 . This distribution can be appreciated from the stress distribution plot provided as FIG. 3, wherein the units shown in the legend are expressed in the units of pounds per square inch (PSI). A comparison of this stress. distribution with that shown in FIG. 5 of the prior art illustrates the improved distribution. 
     Color versions of FIGS. 3 and 5 are being filed herewith in an Appendix for better clarity. This Appendix is incorporated into the present application by reference. 
     The force distribution discussed in the above paragraph may be achieved by positioning the load receiving surface  28  such that it is on or between two outer radial lines of four imaginary radial lines  44  dividing the arc of the ratcheting teeth  26  into five equal imaginary arcuate sectors. Preferably the load receiving surface  28  is positioned on or between two outer radial lines of three imaginary radial lines  46  dividing the arc into four imaginary arcuate sectors. More preferably, the load receiving surface  28  is positioned on or between two imaginary radial lines  48  dividing the arc into three equal imaginary sectors. Still more preferably, the load receiving surface  28  is positioned on or between two inner radial lines of the four imaginary radial lines  44  dividing the arc into five equal imaginary sectors. In the illustrated embodiment, the load receiving surface  28  is positioned on an imaginary line (which is the middle line of lines  46 ) bisecting the arc into two imaginary equal sectors. 
     It should be understood that while the geometric configuration discussed in the preceding paragraph preferably achieves the load distribution discussed in the secondmost preceding paragraph, that load distribution may be achieved using other geometries and the geometries mentioned are not specifically necessary achieve such a load distribution The aforementioned geometries discussed above achieve superior load distribution compared to prior art ratchet wrenches; however, the load distribution achieved need not be limited to the type wherein the force applied by the inner teeth  32  is greater than or equal to the force applied by the outermost teeth  32 . Other variations of improved load distribution may occur. 
     Most preferably, the total force is distributed essentially evenly between all the ratcheting teeth  26 . Such a distribution, however, is only preferred and the invention is not limited to such distribution. 
     In the illustrated embodiment, the load receiving surface  28  is provided on a back wall  50  of the pawl  24  opposite the ratcheting teeth  26 . However, this arrangement is not intended to be limiting. For example, the load receiving surface  28  may be spaced inward toward the teeth  26  from the back wall  50 . 
     The foregoing description has been provided solely for illustrating the structural and functional principles of the present invention and is not intended to be limiting. To the contrary, the present invention is intended to encompass all modifications, substitutions, and alterations within the spirit and scope of the appended claims.