Abstract:
A power driven tool for rotating a mechanical element. The tool includes a housing and motor. The motor has an output shaft. The shaft rotates relative to the housing. The tool also includes an impact drive axially fixed within the housing. The impact drive includes a base and an anvil shaft having an anvil. The impact drive includes an annular hammer having opposite impact lands pivotally mounted on the base for movement between three positions, including a forward position in which the hammer is positioned so one impact land engages the anvil, a reverse position in which the hammer is positioned so another of the impact lands engages the anvil, and a disengaged position in which neither of the impact lands engages the anvil. Further, the tool includes a ratchet mechanism. The ratchet mechanism includes an output drive mounted for rotation relative to the housing for rotating a mechanical element.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    Priority is claimed from U.S. Provisional Patent Application Ser. No. 61/108,756 filed Oct. 27, 2008, which is hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates generally to power driven tools, and more specifically to a power driven tool for tightening or loosening fasteners including an impact drive having an oversized hammer clutch. 
         [0003]    Power driven tools for tightening or loosening fasteners (e.g., nuts and bolts) are known, and power driven tools incorporating impact drives that can intermittently provide increased torque for tightening or loosening fasteners are common. 
         [0004]    An impact wrench incorporating a ratchet head is disclosed in co-owned U.S. Pat. No. 4,821,611, which is incorporated by reference. A pneumatic motor rotates a clutch case that coaxially houses an impact drive. Under normal operation, a cam ball in the clutch case engages a finger of an impact clutch and rotates the clutch with an output shaft for tightening or loosening the fastener. But when frictional resistance of the fastener exceeds a preselected torque output for the tool, the cam ball slides under the impact clutch finger and pushes the clutch axially forward along the output shaft. This action moves a pair of hammers forward into alignment with a corresponding pair of anvils of the output shaft. The hammers simultaneously impact the anvils producing an increased torque in the output shaft, increasing torque applied to the fastener and acting to overcome the frictional resistance of the fastener. Immediately following the impact, the hammers retreat axially rearward and when the cam ball makes one full rotation with the clutch case, the impact sequence repeats if frictional resistance exceeds the preselected torque of the tool. 
         [0005]    The clutch case and cam ball generally move at a rate equal to the output speed of the motor, which is relatively fast. Therefore, when the output shaft is unable to turn the fastener, the cam ball repeatedly pushes the impact clutch and hammers axially forward. This action often occurs so rapidly that the hammers impact the anvils before corresponding surfaces are fully aligned, or alternatively the hammers completely miss the anvils and fail to produce any additional torque. Moreover, when the frictional resistance of the fastener exceeds the additional torque produced by the hammers, the cam ball and impact clutch may unnecessarily push the hammers into repeated alignment with the anvils before an operator disengages the motor. This repeated impact and movement can damage components of the impact drive (e.g., the cam ball and impact clutch) or prematurely wear them out. 
         [0006]    Co-owned U.S. Pat. No. 7,080,578, which is incorporated by reference, includes a speed reducing mechanism in the power driven impact wrench. This particular design reduces the speed of the motor output and controls the impact rate of the hammers of the impact drive. Although the components of the impact drive are less prone to damage and wear, the speed reducing mechanism requires the use of additional components adding complexity to the tool. 
         [0007]    Accordingly, there is a need for a power driven ratchet tool having an impact drive capable of providing adequate damage and wear protection without using a speed reducing mechanism. 
       SUMMARY OF THE INVENTION 
       [0008]    This invention relates generally to a power driven tool for rotating a mechanical element. The tool comprises a housing and a motor positioned in the housing. The motor has an output shaft extending therefrom. The shaft rotates relative to the housing during motor operation. Further, the tool includes an impact drive axially fixed within the housing and operatively connected to the motor output shaft. The impact drive including a base, an anvil shaft having an anvil extending therefrom rotatably mounted on the base, and an annular hammer having opposite impact lands pivotally mounted on the base for movement between three positions. The three positions included a forward position in which the hammer is positioned so one of the impact lands engages the anvil, a reverse position in which the hammer is positioned so another of the impact lands engages the anvil, and a disengaged position in which neither of the impact lands engages the anvil. In addition, the tool comprises a ratchet mechanism operatively connected to the anvil shaft of the impact mechanism. The ratchet mechanism includes an output drive mounted for rotation relative to the housing for rotating a mechanical element in a selected direction. 
         [0009]    In another aspect of the invention, a power driven tool for tightening and loosening a mechanical fastener, the tool comprises a housing having first and second ends and a longitudinal axis extending between the first and second ends. The tool also includes an output drive rotatably mounted on the housing for operatively engaging the mechanical fastener and a motor positioned in the housing having an output shaft. Further, the tool includes an impact drive positioned in the housing and functionally connecting the motor and the output drive. The impact drive including a base, an anvil shaft having an anvil extending therefrom rotatably mounted on the base, and an annular hammer having opposite impact lands pivotally mounted on the base for movement between three positions, including a forward position in which the hammer is positioned so one of said impact lands engages the anvil, a reverse position in which the hammer is positions so another of said impact lands engages the anvil, and a disengaged position in which neither of the impact lands engages the anvil. 
         [0010]    In yet another aspect of the invention, a pneumatic tool for tightening and loosening a mechanical fastener comprises an elongate tubular housing sized for being held in one hand. The tool includes a pneumatic motor in the housing having an output shaft adapted for rotation and an impact drive axially fixed within the housing and operatively connected to the motor output shaft. The impact drive includes a base and an anvil shaft having an anvil extending therefrom rotatably mounted on the base. The impact drive also includes an annular hammer having opposite impact lands pivotally mounted on the base for movement between three positions, including a forward position in which the hammer is positioned so one of said impact lands engages the anvil, and a reverse position in which the hammer is positioned so another of said impact lands engages the anvil. The hammer impacts the anvil on the shaft in response to loading on the impact drive exceeding a predetermined torque to instantaneously increase torque provided to the anvil shaft. Further, the tool includes a ratchet mechanism operatively connected to the anvil shaft of the impact mechanism. The ratchet mechanism includes an output drive mounted for rotation relative to the housing for rotating a mechanical element in a selected direction. 
         [0011]    Other objects and features will be in part apparent and in part pointed out hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a perspective of a hand-held pneumatic ratchet wrench of the invention incorporating an impact drive and pneumatic motor; 
           [0013]      FIG. 2  is an elevation of the wrench of  FIG. 1  in partial section to show internal construction; 
           [0014]      FIG. 3  is a perspective of an impact drive of the wrench; 
           [0015]      FIG. 4  is a separated perspective of the impact drive; and 
           [0016]      FIG. 5  is a separated perspective of a ratchet mechanism of the wrench. 
       
    
    
       [0017]    Corresponding reference characters indicate corresponding parts throughout the drawings. 
       DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0018]    Referring now to the drawings, and particularly to  FIGS. 1 and 2 , a hand-held, pneumatically-driven, ratchet wrench is generally indicated at reference numeral  10 . The wrench  10  includes a tubular grip, indicated generally at  12 , and a head, indicated generally at  14 . As shown in  FIG. 2 , the grip  12  and head  14  are connected by a tubular threaded coupling, generally indicated at  16 , so the grip, coupling and head form a housing that houses the functional components of the wrench  10 . The grip  12  houses a motor, which is generally indicated at  18 . The coupling  16  houses an impact drive, generally designated by  20  and the head  14  houses a ratchet mechanism, generally designated by  22  ( FIG. 3 ). Each of these components will be described in greater detail below. For convenience of description, when describing orientations of components, a forward end of the wrench  10  will be understood to be at an end having the head  14  and a rearward end will be understood to be at an end having the grip  12 . The motor  18  illustrated and described is a standard, air-driven motor of the type commonly used in pneumatic tools. Because the motor  18  is conventional, it will not be described in further detail. 
         [0019]    Referring to  FIG. 1 , an air inlet fitting  30  provided at the rearward end of the grip  12  is capable of connecting the wrench  10  to a conventional external pressurized air source (not shown). A lever  32  provided adjacent the grip  12  controls fluid flow to the motor  18 . The lever  32  is pivotally mounted on the grip  12  and is spring biased to an extended position as shown so that it can be squeezed toward the grip to open a valve  34  to selectively permit pressurized air to flow through the air inlet fitting  30  to the motor  18 . As shown in  FIG. 2 , the motor  18  includes a rotor  36  rotatably mounted on the grip  12  for rotation about a centerline  38 . The rotor  36  rotates in response to air passing through the motor  18  when the valve  34  is open. The rotor  36  includes an output shaft  40  centered on the centerline  38 . Although the output shaft  40  may has other shapes without departing from the scope of the present, in one embodiment the shaft has a generally cylindrical, splined (i.e., ridged) exterior for connecting the shaft to the impact drive. 
         [0020]    As illustrated in  FIGS. 3 and 4 , the impact drive  20  of the wrench  10  generally comprises a clutch base  50 , a hammer  52  and an anvil shaft  54 . As further illustrated in  FIG. 4 , the base  50  includes forward and rearward bushing plates  60 ,  62 , respectfully, separated by integral spacers  64  creating a space  66  between the plates for receiving the hammer  52 . Each of the bushing plates  60 ,  62  includes a respective machined central opening  68 ,  70  for receiving the shaft  54 . Holes  72  are provided on opposite sides of the openings  68 ,  70  for receiving pins  74 ,  76  that capture the hammer  52  in the space  66  formed between the plates  60 ,  62 . A portion  78  of the rearward central opening is  68  splined for receiving the splined output shaft  40  of the motor  18 . Thus, the base  50  turns with the motor rotor  36 . The hammer  52  includes a lobed central opening  80 , a semi-circular slot  82  on one side and broad slot  84  on an opposite side. The slots  82 ,  84  receive the pins  74 ,  76  so they extend between the plates  60 ,  62  for retaining the hammer  52  in the space  66 . As will be appreciated by those skilled in the art, the semi-circular slot  82  and the pin  74  permit the hammer  52  to pivot. The broad slot  84  and pin  76  limit rotation of the hammer  52  as it pivots on pin  74 . The anvil shaft  54  extends through the central openings  68 ,  70  of the bushing plates  60 ,  62  and the lobed central opening  80  of the hammer  52 . The shaft  54  also has spaced journals  88 ,  90  corresponding to the central openings  68 ,  70  in the plates  60 ,  62 . The journals  88 ,  90  engage the central openings  68 ,  70  for supporting the shaft  54  and permitting the shaft to rotate in the base  50 . An anvil  92  is provided on the shaft  54  between the journals  86 ,  88  so lands  94 ,  96  in the lobed opening  80  of the hammer  52  can intermittently engage the anvil to provide increased torque as will be explained in greater detail below. In addition, the shaft  54  includes a crank  98  at its forward end for driving the ratchet mechanism  22 . 
         [0021]      FIG. 5  illustrates the ratchet mechanism  22  of the wrench  10  which converts orbital motion of the crank  98  to rotational motion in a selected direction. The crank  98  drives an internal ring gear  100  to oscillate back and forth in a yoke  102  of the head  14 . The crank  98  and ring gear  100  are operationally connected by a bushing  104  that is received in a generally cylindrical opening  106  of an arm  108  extending from the ring gear. A drive body  110  is rotatably mounted inside the ring gear  100 . The drive body  110  includes square output drive  112  and a dog carrier  114 . A pivotal ratchet dog or ratchet pawl  120  is pivotally captured in the dog carrier  114  by a pin  122 . The dog  120  is biased to pivot in one selected direction by a selector knob  124 . The selector knob  124  includes a shaft  126  that extends inside the dog carrier  114 . The shaft  126  has a recess  128  that holds a spring  130  for biasing a pusher  132  against the dog  120 . The pusher  132  pushes the dog  120  in a selected direction so the ring gear  100  drives the drive body  110  in one direction but not in the other direction as the ring gear oscillates back and forth. A axial bushing pad  140  is positioned between the shaft  126  of the selector knob  124  and the drive body  110 , and a keeper  142  is positioned between the drive body and the yoke  102  of the head  14 . Spring biased bearings  144  and a race  146  allow the drive body  110  to spin freely in the head  14 . A snap ring  148  retains the race  146  in position in the head  14 . The illustrated ratchet mechanism  22  is similar to that shown in U.S. Pat. No. 4,346,630, generally including an output drive  112  rotatably mounted on the head  14  for engaging a mechanical fastener. The ratchet mechanism  22  selectively limits rotation of the output drive  112  in one direction. Because the ratchet mechanism  22  is conventional, it will not be described in further detail. 
         [0022]    In general operation of the wrench  10 , air enters through the air inlet fitting  30  at the rearward end of the grip  12  when the lever  32  is squeezed toward the grip. The air enters the motor  18  where it rotates the rotor  36  including the output shaft  40 . The motor shaft  36  rotates the clutch base  50 . When required torque is low, the clutch base  50  turns the hammer  52  which engages the anvil  92  to turn the shaft  54 . The crank  98  orbits the wrench centerline  38 , oscillating the ring gear  100 . As the ring gear  100  oscillates in one direction, the dog  120  pivots into the dog carrier  114  so the output drive  112  does not turn. As the gear  100  oscillates in another direction, the dog  120  engages the gear so the output drive  112  turns with the gear. When the required torque exceeds some preselected value, the hammer  52  pivots on the pin  74 , disengaging the engaged hammer land  94  or  96  from the anvil  92  on the shaft  54  and temporarily preventing the crank  98  from driving the ratchet mechanism  22 . After the anvil  92  passes the hammer land  94  or  96 , the hammer  62  pivots back to a position in which the land engages the anvil  92  on the next revolution. When the combined spinning mass of the motor rotor  36 , base  60  and hammer  52  acts through the hammer to impact the anvil  92  on the next revolution, an instantaneous torque increase occurs. The torque increase acts to overcome the friction in the mechanical fastener. If the torque exceeds the preselected value on the next revolution the sequence repeats. Otherwise, the impact drive  20  delivers continuous toque. 
         [0023]    It is envisioned that the wrench of the present invention can operate at relatively high pressures thus producing relatively high rotational speeds with the motor shaft of the motor. It is therefore a benefit of this wrench  10  that the impact drive  20  is capable of handling high pressures without a speed reducing mechanism or excessively wearing components. 
         [0024]    Components of the wrench of this invention are made of a suitable rigid material, such as metal (ex., cold-forged steel). But a wrench having components made of different materials does not depart from the scope of this invention. 
         [0025]    When introducing elements of the present invention or the preferred embodiments(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
         [0026]    In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained. 
         [0027]    As various changes could be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.