Abstract:
A power tool is provided which includes a motor assembly having a rotatable motor shaft mechanism, and a motor control coupled to the motor assembly and operable between a normal off condition de-energizing the motor and an on condition energizing the motor. The tool includes a rotatable tool shaft mechanism, and a clutch shiftable between a normal disengaged condition decoupling the motor shaft mechanism from the tool shaft mechanism and an engaged condition coupling the motor shaft mechanism to the tool shaft mechanism. A trigger member is engageable with both the motor control and the clutch and is moveable between a first position, wherein the motor control is in its off condition and the clutch is in its disengaged condition, and a second position holding the motor control in its on condition and the clutch in its engaged condition for driving the tool shaft mechanism. The trigger member is designed to prevent premature energization of the motor assembly.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to power tools, and more particularly, to drive train couplers. 
     2. Description of the Prior Art 
     In the past, power tools have included trigger activated clutches to couple the motor shaft to the tool output shaft. These tools normally required a first trigger to engage the clutch and a second trigger to energize the motor and had very complicated clutching mechanisms. 
     These complicated clutch mechanisms were thus costly to make and complicated for an operator to use. 
     SUMMARY OF THE INVENTION 
     It is a general object of the invention to provide an improved trigger-operated power tool clutch arrangement, while affording structural and operating advantages. 
     An important feature of the invention is the provision of a trigger-operated power tool clutch which is of relatively simple and economical construction. 
     A further feature of the invention is the provision of a clutch of the type set forth which is not easily damaged in use. 
     Another feature of the invention is the provision of a clutch of the type set forth which includes a trigger which operates the motor as well as the clutch. 
     In connection with the foregoing feature, another feature of the invention is provision of a trigger of the type set forth which prevents premature energization of the tool motor. 
     Certain ones of these or other features may be attained by providing a power tool which includes a motor assembly having a rotatable motor shaft mechanism, and a motor control coupled to the motor assembly and operable between a normal off condition de-energizing the motor and an on condition energizing the motor. The tool includes a rotatable tool shaft mechanism, and a clutch shiftable between a normal disengaged condition decoupling the motor shaft mechanism from the tool shaft mechanism and an engaged condition coupling the motor shaft mechanism to the tool shaft mechanism. A trigger member is engageable with both the motor control and the clutch and is moveable between a first position, wherein the motor control is in its off condition and the clutch is in its disengaged condition, and a second position holding the motor control in its on condition and the clutch in its engaged condition for driving the tool shaft mechanism. 
     The invention consists of certain novel features and a combination of parts hereinafter fully described, illustrated in the accompanying drawings, and particularly pointed out in the appended claims, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For the purpose of facilitating an understanding of the invention, there is illustrated in the accompanying drawings a preferred embodiment thereof, from an inspection of which, when considered in connection with the following description, the invention, its construction and operation, and many of its advantages should be readily understood and appreciated. 
     FIG. 1 is a perspective view of a power ratcheting screwdriver in accordance with the present invention; 
     FIG. 2 is an enlarged, side elevational view, partially broken away, of the screwdriver of FIG. 1; 
     FIG. 3 is a further enlarged sectional view of a portion of FIG. 2 showing the clutch and the motor control of the present invention in a non-engaged and off conditions; 
     FIG. 4 is a sectional view taken generally along line  4 — 4  of FIG. 3; 
     FIG. 5 is a view similar to FIG. 3 showing the clutch and the motor control in engaged and on conditions; 
     FIG. 6 is a sectional view taken generally along line  6 — 6  of FIG. 5; 
     FIG. 7 is a view similar to FIG. 3 illustrating the trigger partially depressed and with the clutch in its non-engaged condition and the motor control in its off condition; 
     FIG. 8 is a view similar to FIG. 7, wherein the trigger has been further depressed and the motor control is in an on condition, and the clutch is not engaged; and 
     FIG. 9 is an exploded view of the clutch, the clutch actuator and a portion of the drive train assembly of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, an electrically-powered ratcheting screwdriver  20  is illustrated. The screwdriver  20  includes an outer housing  21  enclosing a motor assembly  22 . As seen in FIG. 2, the motor assembly  22  includes a DC motor  24 . Referring also to FIG. 9, the motor assembly  22  also includes a motor shaft mechanism including a rotatable motor shaft  26  coupled to a drive train assembly  28 , in a known manner. The drive train assembly  28  includes a first pinion gear (not shown) fixed to the motor shaft  26  and a first gear carrier  29  having planetary gears (also not shown) engaging the first pinion gear and a ring gear  30  to rotate the first carrier  29 . A pinion gear  29   a  is fixed to the first carrier  29 , and planetary gears  32 , rotatably mounted on a second gear carrier  34 , engage the pinion gear  29   a  and the ring gear  30  for rotating the carrier  34  in response to rotation of the motor shaft  26 . The gear carrier  34  includes a cavity  35  having a central cylindrical portion  35   a  and three part-triangular arms  35   b . As seen in FIGS. 1 and 2, the motor  24  is electrically powered by a battery pack  36 . 
     As seen in FIG. 2, the ratcheting screwdriver  20  also includes a rotatable tool shaft mechanism  38  which includes, bevel gears  40 ,  42 , coupled to a conventional ratcheting mechanism  44  including a bit holder  46 . Bevel gear  40  includes, as seen in FIG. 9, a shaft  41  having a plurality of splines  41   a.    
     Referring to FIG. 3, the ratcheting screwdriver  20  also includes a trigger button  50  having a pad  51  engageable with a motor control switch  52 , electrically coupled to the motor  24  for energizing and de-energizing the same. The switch  52  includes a housing  54  and an actuator button  56 . The button  56 , as seen in FIG. 3, is normally biased out of the housing  54 , to a normal off condition de-energizing the motor  24 . The motor button  56 , as seen in FIGS. 5 and 8 can be pushed into the housing  54  by the pad  51  of trigger button  50  to place the switch  52  in an on condition to energize the motor  24 . 
     Referring to FIG. 9, the screwdriver  20  also includes a clutch  58  to couple the tool shaft mechanism  38  to the motor shaft mechanism. The clutch  58  includes a clutch driver  60  and a clutch jaws member  62 . The clutch driver  60  includes an annular plate  64  and a hollow cylindrical collar  66  projecting axially from one side of the plate  64  and having a splined interior portion  68  (see FIG.  3 ). The clutch driver  60  also has an annular cavity  70  and two diametrically-opposed arcuate teeth  72  projecting axially from the other side of the plate  64 . The splined interior portion  68  of the cylindrical collar  66  is disposed about and slidable axially on the splined shaft  41  of the bevel gear  40  such that the splines  41   a  are engaged with splines  69  (FIGS.  3  and  5 ), thereby coupling the clutch driver  60  to the tool shaft mechanism  38 . 
     Referring to FIG. 9, the clutch jaws member  62  has a circular base  74  with three radially-projecting arms  76  and a central cylindrical portion  78  disposed on the base  74  having two diametrically opposed arcuate teeth  80  projecting radially outwardly therefrom. The central cylindrical portion  78  has a cylindrical cavity  82  formed axially in one end thereof (FIG.  3 ). As discussed below, the teeth  80  are engageable with the teeth  72  to couple the drive train assembly  28  and motor shaft  26  with the tool shaft mechanism  38 . 
     A compression spring  84  is disposed in the cylindrical cavity  82  and bears against the gear carrier  34  at the central portion  35   a  of the cavity  35 . A retaining plate  86  is disposed over the arms  76  and fastened by three screws  88  to the gear carrier  34 . A retaining ring  90  has tabs  91  receivable in notches  91   a  in the ring gear  30  and is frictionally engaged with the ring gear  30  to maintain the gear carrier  34  and clutch jaws member  62  in place. 
     The spring  84  biases the clutch jaws member  62  outwardly, holding the arms  76  against the plate  86 . The depth of the cavity  35  is such that the member  62  is slidably moveable axially thereinto. 
     The ratcheting screwdriver  20  also includes a thrust bearing  92  disposed upon the plate  64  and having a plurality of roller bearings  94  and a thrust washer  96  disposed upon the thrust bearing  92 . The ratcheting screwdriver  20  also, as discussed further below, includes a compression spring  97  seated in the annular cavity  70  and bearing against the retained plate  86 . 
     The ratcheting screwdriver  20  also includes a clutch actuator, in the form of a bell crank  98 , which couples the trigger button  50  to the clutch  58 . Referring to FIGS. 3 and 9, the bell crank  98  includes two arms  100  engageably coupled to a backside  102  of the trigger button  50  and two legs  104  straddling the cylindrical collar  66  and resting on the thrust washer  96 . The bell crank  98  also includes two coaxially-aligned stub shafts  106  respectively disposed in cavities  108  in the housing  21  (FIGS.  1  and  2 ), the bell crank  98  being rotatable about the axis of the rods  106 . Thus, the spring  97 , acting through the clutch driver  60 , the bearing  92  and the washer  96 , urges the bell crank  98  against the trigger button  50 . This bias, together with that of the switch actuator button  56 , urges the trigger button  50  outwardly to the rest position of FIG.  3 . 
     The ratcheting screwdriver  20  operates as follows. As seen in FIGS. 3 and 4, when the trigger button  50  is not depressed, the switch  52  is in its off condition and the clutch  58  is in a disengaged condition wherein the tool shaft mechanism  38  is disengaged from the drive train assembly  28  and motor shaft  26 . This is because the compression spring  97  biases the clutch driver  60  away from the clutch jaws member  62  so that teeth  72  of the clutch driver  60  are spaced axially from and not engaged with the teeth  80  of the clutch jaws member  62 . The spring  97  biases the clutch driver  60 , the thrust bearing  92 , and the thrust washer  96  so that the thrust washer  96  exerts upward force against the legs  104  of the bell crank  98  whose arms  100  in turn exert biasing pressure on the backside  102  of the trigger button  50  so the pad  51  of the trigger button  50  is biased away from the button  56  of the switch  52  to allow the switch  52  to remain in its normal off condition. 
     Referring to FIGS. 5 and 6, when a user pushes the trigger button  50  in the direction of arrow A, the pad  51  pushes the button  56  of the switch  52  into the housing  54  to energize the motor  24  to rotate the motor shaft  26  and drive train assembly  28  including the gear carrier  34  in a known manner. At the same time, the backside  102  of the trigger button  50  pushes arms  100  to rotate the bell crank  98  counter-clockwise (FIG. 5) so that the legs  104  push the thrust washer  96 , thrust bearing  92  and clutch driver  60  downward (still leaving splines  41   a  engaged with splines  69 ), compressing compression spring  97 . If the rotational positions of the parts are such that teeth  72  are aligned perpendicular to the direction of alignment of the teeth  80 , depression of the trigger button  50  causes the teeth  72  of the clutch driver  60  to move axially between the teeth  80  of the clutch jaws member  62  for engagement therewith. 
     The clutch jaws member  62  is trapped in and rotating with the gear carrier  34 . The engaged teeth  72  and  80  cause the clutch driver  60  to rotate along with the bevel gear  40  which is engaged thereto via splines  41   a  and  69 . Bevel gear  40  acts on bevel gear  42  to rotate the bit holder  46  in a known manner. 
     The bevel gear  40 , clutch jaws member  62  and clutch driver  60  are coaxially aligned. As seen in FIG. 6, the teeth  72  of the clutch driver  60  and the teeth  80  of the clutch jaws member  62  are located at the same radial distance from the axis of rotation Z. Referring to FIGS. 7 and 8, since the teeth  72 ,  80  are at the same radial distance, and if they are not aligned perpendicular to each other, the teeth  72  may, as seen in FIG. 7, contact the axial end faces of the teeth  80  so when the trigger button  50  is first depressed, prior to the button  56  being pushed into the housing  54  a distance great enough to place switch  52  to its on condition. 
     To allow the motor  24  to be energized, the clutch jaws member  62  must be moved axially a distance great enough to allow the bell crank  98  to be rotated to allow the trigger button  50  to be depressed far enough to push the button  56  the distance needed to place the switch  52  to its on position. As seen in FIG. 8, when the trigger button  50  is depressed further, the teeth  72  of the clutch driver  60  force the teeth  80  and the clutch jaws member  62  axially downward into the cavity  35  of the gear carrier  34  against the urging of the spring  84 , thereby allowing the button  56  to be depressed into the housing  54  a distance far enough to energize the motor  24 . Thus, the motor cannot be energized until the teeth  72  are in axial position for engagement with the teeth  80 . Once the motor  24  is energized, the clutch jaws member  62  is rotated, as previously described, and after it has turned about 90° its teeth  80  move to align with the spaces between the teeth  72  of clutch driver  60  and are pushed up into engagement by the spring  84  to the position shown in FIGS. 5 and 6. 
     The cross-sectional areas of central cylindrical portion  35   a  and part-triangular arms portion  35   b  of cavity  35  are respectively slightly larger than the cross-sectional areas of the base  74  and radially projecting arms  76  of the clutch jaws member  62  to provide clearance between the arms  76  and the part-triangular arm portions  35   b  of the cavity  35 . This allows the clutch jaws member  62  to be inclined with respect to the axis of the gear carrier  34  so that the clutch jaws member  62  can properly engage the clutch driver  60  should there be any slight misalignment between the two. 
     While particular embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects. Therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation. The actual scope of the invention is intended to be defined in the following claims when viewed in their proper perspective based on the prior art.