Abstract:
A manually operated impact tool is provided and includes: an impact mass; an anvil rotatably disposed relative to the impact mass; an input member operatively connected to one of the impact mass and anvil mass for imparting a relative rotation between the impact mass and the anvil; an output member connected to the other of the impact mass and anvil mass for transferring an impact to a fastener; and one or more elastic elements for storing potential energy upon the relative rotation between the impact mass and the anvil. Wherein conversion of the potential energy to kinetic energy causes the impact mass to impact the anvil and transfer of the impact to the output member.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Application Ser. No. 60/671,653, filed Apr. 16, 2005, the entire contents of which is incorporated herein by its reference. The manually operated impact wrenches described herein are similar to those described in U.S. Pat. Nos. 6,679,143 and 6,997,087 and U.S. application Ser. No. 11/333,852, the disclosures of which are also incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to impact tools and, more particularly, to a manually operated impact tool for loosening or tightening a fastener, such as a lug nut. 
   2. Prior Art 
   Impact based or impact assisted wrenches of the prior art operate using electric, pneumatic and in some cases hydraulic power to loosen and/or tighten fasteners such as nuts threaded on a mating treaded stud. The impact force generated by such wrenches greatly assists the loosening and tightening operation of such devices by generating a large impulsive force at the fastener interface. As the result, and in many cases due also to the generated stress waves that travels across the male and female fastener surfaces, such wrenches are operated with a significantly smaller operator effort. In certain situations, the large forces and/or moment and/or torque that has to be applied to a manually operated wrench to begin to open the fastener may cause its failure, particularly since such forces cannot usually be applied perfectly symmetrically, i.e., only in the direction that would open the fastener without unwanted added forces. For example, an operator applying a torque to a manually operated socket wrench to open a bolt may also apply a large shearing force and/or bending moment while exerting his maximum effort to open the fastener and thereby may cause the bolt to shear off during the procedure. Such failures seldom occur while using impact based wrenches since the operator does not have to exert his or her maximum effort in the above manner to operate the wrench. 
   It can safely be claimed that the relative ease with which impact based wrenches are operated to loosen or tighten various fasteners is well appreciated by their users. However, such wrenches require electric, pneumatic or some other type of generally electric based power in order to operate. In addition, such systems are generally heavy, bulky and expensive to be carried by the operator to all sites. This is particularly the case for the infrequent user such as a driver who may require the wrench in case of a flat tire to loosen and fasten the tire bolts or nuts. 
   A need therefore exists in the art for manually operated impact wrenches that are simple to use, light weight and inexpensive, particularly for the casual user and professional user who does not have access to a power source at the work site or who does not want to carry a heavy load to a site or may seldom face the need for its use. 
   SUMMARY OF THE INVENTION 
   Accordingly, a manually operated impact tool is provided. The manually operated impact tool comprising: an impact mass; an anvil rotatably disposed relative to the impact mass; an input member operatively connected to one of the impact mass and anvil mass for imparting a relative rotation between the impact mass and the anvil; an output member connected to the other of the impact mass and anvil mass for transferring an impact to a fastener; and one or more elastic elements for storing potential energy upon the relative rotation between the impact mass and the anvil; wherein conversion of the potential energy to kinetic energy causes the impact mass to impact the anvil and transfer of the impact to the output member. 
   The impact mass can comprise two impact masses and the anvil comprises two anvils disposed on an anvil member, each of the impact masses extending in opposite directions from an impact member and configured to impact one of the two anvils. The anvil member and impact member can rotate relative to each other about a central portion. Each of the anvil member and impact member can further have a reduced thickness portion at the central portion such that when assembled together, an overall thickness of the assembled anvil member and impact member is less than the combined thickness of the impact member and anvil member outside of the central portion. 
   The input member can comprise a frame rotatably disposed relative to one of the anvil and impact mass, the frame can have a portion which interferes with one of the anvil and impact mass such that rotation of the frame causes a rotation of the one of the anvil and impact mass relative to the other of the anvil and impact mass. The frame can further have a nut for facilitating rotation thereof. The one or more elastic elements can be attached between the frame and the one of the anvil and impact mass to bias the one of the anvil and impact mass towards the other of the anvil and impact mass. The one or more elastic elements can comprise two pairs of springs, each pair being disposed symmetrically around the one of the anvil and impact mass. 
   The output member can be an output shaft connected to the one of the anvil and impact mass. The output shaft can have a male socket at an end thereof. 
   The manually operated impact tool can further comprise: an engagement member disposed on one of the anvil and impact mass for engaging the other of the anvil and impact mass and maintaining the anvil and impact mass in a predetermined position relative to each other; and a release member disposed on one of the other of the anvil and impact mass and the input member for releasing the engagement and causing the conversion of the potential energy to kinetic energy. 
   Also provided is a manually operated impact tool comprising: an impact member having a pair of impact masses; an anvil member having a pair of anvil members, the anvil member being rotatably disposed relative to the impact member such that each of the impact masses corresponds to each of the anvils; an input member operatively connected to one of the impact member and anvil member for imparting a relative rotation between the impact member and the anvil member; an output member connected to the other of the impact member and anvil member for transferring an impact to a fastener; and one or more elastic elements for storing potential energy upon the relative rotation between the impact member and the anvil member; wherein conversion of the potential energy to kinetic energy causes each of the impact masses to impact a corresponding anvil and transfer of the impact to the output member. Each of the pair of impact masses can extend in opposite directions from the impact member. The anvil member and impact member can rotate relative to each other about a central portion. Each of the anvil member and impact member can further have a reduced thickness portion at the central portion such that when assembled together, an overall thickness of the assembled anvil member and impact member is less than the combined thickness of the impact member and anvil member outside of the central portion. 
   The input member can comprise a frame rotatably disposed relative to one of the anvil member and impact member, the frame can have a portion which interferes with one of the anvil member and impact member such that rotation of the frame causes a rotation of the one of the anvil member and impact member relative to the other of the anvil member and impact member. The frame can further have a nut for facilitating rotation thereof. The one or more elastic elements can be attached between the frame and the one of the anvil member and impact member to bias the one of the anvil member and impact member towards the other of the anvil member and impact member. The one or more elastic elements can comprise two pairs of springs, each pair being disposed symmetrically around the one of the anvil member and impact member. 
   The output member can be an output shaft connected to the one of the anvil member and impact member. The output shaft can have a male socket at an end thereof. 
   The manually operated impact tool can further comprise: an engagement member disposed on one of the anvil member and impact member for engaging the other of the anvil member and impact member and maintaining the anvil member and impact member in a predetermined position relative to each other; and a release member disposed on one of the other of the anvil member and impact member and the input member for releasing the engagement and causing the conversion of the potential energy to kinetic energy. 
   Still further provided is a method for manually imparting an impact, the method comprising: rotatably disposing an impact mass relative to an anvil; rotating an input member in a first direction to impart a relative distance between the impact mass and the anvil; storing potential energy upon the rotation in the first direction of the input member; and rotating the input member in a second direction to convert the potential energy to kinetic energy causing the impact mass to impact the anvil and transfer of the impact to an output member. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features, aspects, and advantages of the apparatus of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
       FIG. 1  illustrates a perspective view of an output side of an impact tool which is in an open or loaded position. 
       FIG. 2  illustrates a perspective view of an input side of the impact tool. 
       FIG. 3  illustrates an exploded view from the output side of the impact tool of  FIG. 1 . 
       FIG. 4  illustrates an exploded view from the input side of the impact tool of  FIG. 2 . 
       FIG. 5A  illustrates a side view of the input side of the impact tool of  FIG. 2  in which the impact tool is open and loaded for an impact. 
       FIG. 5B  illustrates an enlarged view of detail  5 B of  FIG. 5A . 
       FIG. 5C  illustrates an enlarged view of detail  5 C of  FIG. 5A . 
       FIG. 6A  illustrates a side view of the input side of the impact tool of  FIG. 5A  prior to the impact masses being released for impact. 
       FIG. 6B  illustrates an enlarged view of detail  6 B of  FIG. 6A . 
       FIG. 7A  illustrates a side view of the input side of the impact tool of  FIG. 5A  in which the impact masses are released for impact. 
       FIG. 7B  illustrates an enlarged view of detail  7 B of  FIG. 7A . 
       FIG. 8  illustrates a side view of the input side of the impact tool of  FIG. 5A  upon impact of the impact masses with corresponding anvil surfaces. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Although the present invention is applicable to numerous types of impact tools, it is particularly useful in the environment of impact wrenches for removing lug nuts from automobile wheels. Therefore, without limiting the applicability of the present invention to impact wrenches for removing lug nuts from automobile wheels, it will be described in such environment. 
   Referring now to  FIGS. 1 and 2 , there is illustrated an impact tool in the form of an impact wrench, generally referred to by reference numeral  100 . The impact wrench  100  has an output side shown in  FIG. 1  with a male socket part  102  for holding a socket (not shown) which is in turn disposed on a nut, such as a lug nut. Alternatively, the output side can have a particular size socket permanently mounted thereon. Furthermore, the output side can have a different type of tool either permanently or removable mounted thereon, such as a plain or Philips type screwdriver head or an allen key. The impact wrench  100  further has an input side shown in  FIG. 2  with a hexagonal nut  104 . The impact wrench  104  is operated, as discussed below, by rotating the hexagonal nut  104  a predetermined amount of rotation. The hexagonal nut is rotated by disposing a tool over the same and rotating the tool (not shown). For example, a lug wrench (not shown) can be used to turn the hexagonal nut  104  or other tool, such as an adjustable wrench, open or closed end wrench, or a socket wrench. Other shaped nuts or configurations can also be used at the input side. Furthermore, a handle can be permanently or releasably mounted at the input side. Although shown open, the impact wrench  100  can be covered, wholly or partially by a cowl (not shown). However, the hexagonal nut  104  (or other means disclosed above) as well as the male socket  102  (or other means disclosed above) must be exposed from the cowl to permit operation on the impact wrench as well as operation on the fastener to be loosened. Lastly, although the impact wrench is described as loosening a fastener, those skilled in the art will appreciate that the same can be provided in a mirrored configuration to tighten a fastener. 
   Referring now also to  FIGS. 3 and 4 , the impact wrench  100  has an impact member  106  having impact masses  108  arranged at opposite ends of the impact member  106 . The impact masses  108  extend from the impact member  106  in opposite directions culminating in an impact surface  108   a  and are equally distanced from a central bore  110 . The impact member  106  further has spring posts  112  disposed at each end. The spring posts  112  can be pins that are fit into corresponding holes or threaded studs that are threaded into mating threaded holes. The impact member  106  further has an engagement widow  114  at one end disposed between the central bore  110  and one of the impact masses  108 . The impact member  106  has a reduced thickness portion  116  at a central portion thereof. The impact member  108  can be fabricated from a durable material, such as machine steel. 
   The impact wrench  100  also has an anvil member  118  having first and second anvil members  120  disposed at ends thereof. The anvil member further has a central bore  122  in which is disposed an output shaft  124 . The output shaft  124  can also be integral with the anvil member  118 . The output shaft  124  has a first end  126  which is rotatably disposed in the central bore  110  of the impact member  106  and a second end  128  which has the male socket part  102  at an end thereof. The anvil member  118  further has a reduced thickness portion  130  corresponding to the reduced thickness portion  116  of the impact member  106  such that the impact member  106  and anvil member  118  mate together and rotate relative to each other within a predetermined angle range, as shown in  FIGS. 1 and 2 . When mated, anvil surfaces  128   a  of the anvil member  118  correspond to the impact surfaces  108   a  of the impact member  106 . The first end  126  of the output shaft may be provided with a female thread  132  and a fastener (not shown) may be provided through the central bore  110  of the impact member  106  to retain the impact member  106  and anvil member  118  together. In this regard, the central bore  110  of the impact member  106  may have a counter bore (not shown) for acceptance of a head of the fastener so as not to interfere with other parts of the impact wrench  100 . The anvil member  118  further has an engagement member  134  which is rotatably disposed on one end of the anvil member  118  by a pin  136  or the like. The rotation of the release member can be limited by stops such that it rotates only through a small angle and it biased in direction A by a spring or other biasing member (not shown). As shown clearly in  FIGS. 5A and 5C , the engagement member  134  has a stepped portion  138  at a free end thereof that is disposed in the engagement window  114  of the impact member  106 . 
   The impact wrench  100  further has an outer frame  140  including an input side frame  140   a  and an output side frame  140   b . The input side frame  140   a  is rectangular in shape and has the hexagonal nut  104  fixed at a central position thereof, such as by welding or the like. The hexagonal nut  104 , or any other input means can also be integral with the input side frame  140   a . The input side frame  140   a  further has a projection  142 . The input side frame  140   a  also has a release member  144  fixed thereto, such as by welding, screws or the like and may also be integrally formed with the input side frame  140   a . The output side frame  140   a  is also rectangular shaped and has a central bore  146  in which the output shaft  124  is rotatably disposed. The output side frame  140   b  also has a projection  148  corresponding to the projection  142  of the input side frame  140   a . The input side frame  140   a  and output side frame  140   b  are assembled around the impact member  106  and anvil member  118  with the output shaft  124  disposed in the central bore  146  of the output side frame  140   b  and separated by a predetermined distance by spring pins  150  and cam pin  152 . The spring pins  148  have stepped portions  154  at each end thereof which are disposed in mating holes  156  in each end of the input side frame  140   a  and output side frame  140   b . The portion between the stepped portions  154  maintains the input side frame  140   a  and output side frame apart by the predetermined distance such that the impact member  106  and anvil member  118  can rotate within the frame  140 . Nuts (not shown) can be disposed on threaded portions of the stepped portions  154  to secure the input side frame  140   a  and output side frame  140   b  together. The cam pin  152  is secured between the projections  142 ,  148  of the input side frame  140   a  and output side frame  140   b , respectively. The cam pin  152  can have female threads  158  at each end thereof and the same can be secured by screws (not shown) disposed through holes  160  on the projections  142 ,  148  which mate with the female threads  158 . 
   Elastic members, such as springs  162  bias the impact member  106  towards the frame  140 . The springs  162  (shown broken in the figures for clarity) attach at one end to the spring posts  112  of the impact member  106  and attach at the other end to the stepped portion  154  of the spring pins  150 . The spring ends can be secured to the spring posts  112  and spring pins  150  by any means known in the art such as the spring posts  112  and spring pins  150  having small holes for acceptance of the spring ends. The impact wrench  100  shown in the Figures utilizes two pairs of springs  162 , two at each end of the impact member  106 . Other elastic members can also be used, such as rubber members. 
   The operation of the impact wrench  100  will now be explained with reference to  FIGS. 5A-8 . Referring first to  FIG. 5A , the impact member  106  is rotated clockwise relative to the anvil member  118  by turning the hexagonal nut  104  (and frame  140  connected thereto) into the position shown in  FIG. 5A  (from a starting position shown in  FIG. 8 ). Upon the clockwise rotation, the cam pin  152  urges against a surface  164  of the impact member  106  relative to the anvil member  118  as shown clearly in  FIG. 5B . The impact member  106  rotates relative to the anvil member  118  until the stepped portion  138  of the engagement member  134  catches in the engagement window  114  of the anvil member, as shown clearly in  FIG. 5C . At this point, the springs  162  will be stretched and the impact wrench is loaded for an impact. Also at this point, the position of the impact member  106  relative to the anvil member  118  is fixed by engagement of the stepped portion  138  of the engagement member  134  with the engagement window  114 . As discussed above, the engagement member  134  is biased in the direction of Arrow A to maintain the engagement. 
   Referring now to  FIGS. 6A and 6B , the hexagonal nut  104  (and frame  140  attached thereto) is rotated counterclockwise until the release member  144  begins to engage the stepped portion  138  of the engagement member  134  in a direction opposite to Arrow A against the biasing of the engagement member  134 . As can be seen clearly in  FIG. 6B , the engagement of the release member  144  moves the stepped portion  138  from engagement with the engagement window  114 . 
   Referring now to  FIGS. 7A and 7B , continued counterclockwise rotation of the hexagonal nut  104  (and frame  140  attached thereto) causes the stepped portion  138  of the engagement member  134  to completely disengage from the engagement window  114 , as clearly shown in  FIG. 7B . Therefore, the potential energy in the springs  162  will be converted to kinetic energy and accelerate the impact member  106  towards the anvil member  118 . As shown in  FIG. 8 , the impact surfaces  108   a  of the impact masses  108  will impact the corresponding anvil surface  120   a  of the anvils  120 . The impact is transferred through the impact member  118  to the male socket part  102  of the output shaft  124  which is attached to the anvil member  118 . The output shaft  124  in turn transfers the impact to a fastener to be loosened (or tightened in a mirrored configuration). Since the impact masses  108  extend from the impact member  106  in opposite directions, their impacts each contribute to rotating the anvil member  118  and output shaft  124  connected thereto in the same direction. 
   The size and number of the impact masses and/or number and strength of the springs can be varied to scale the magnitude of the impact for the particular application. For example, a smaller impact can be used for use with hand tools to loosen stubborn nuts, while a larger impact can be used for use in removing lug nuts from automobiles and trucks. 
   While there has been shown and described what is considered to be preferred embodiments of the invention, it will, of course, be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is therefore intended that the invention be not limited to the exact forms described and illustrated, but should be constructed to cover all modifications that may fall within the scope of the appended claims.