Patent Publication Number: US-RE37529-E

Title: Clutch mechanism for reciprocating saws

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application  reissue application  09 / 500 , 252 , is a continuation of co- pending Reissue application Ser. No.  09 / 164 , 985 , filed Oct.  1 ,  1998  both of which are reissues of U.S. Pat. Nos.  5 , 689 , 891   ( filed May  30 ,  1996  as Ser. No.  08 / 658 , 889   )  which  is a continuation-in-part of U.S. patent applications Ser. No. 08/444,069, now U.S. Pat. No. 5,566,458, and Ser. No. 08/443,784, now U.S. Pat. No. 5,607,023, both filed May 18, 1995, and both of which are continuation-in-part applications of U.S. patent applications Ser. No. 08/354,518, abandoned, and Ser. No. 08/354,560, abandoned, both filed Dec. 13, 1994. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to the field of reciprocating saws. 
     BACKGROUND OF THE INVENTION 
     Reciprocating drive mechanisms are known in the art. See, for example, U.S. Pat. No. 5,050,307, issued to Palm on Sep. 24, 1991, U.S. Pat. No. 5,025,562, issued to Palm on Jun. 25, 1991, and U.S. Pat. No. 5,079,844, issued to Palm on Jan. 14, 1992, each of which is assigned to the assignee of the present invention, and is incorporated herein by reference. 
     Reciprocating drive mechanisms are found, for example, in reciprocating saws. Such reciprocating saws typically include a housing including a gear case, a motor in the housing having a motor shaft, a jackshaft mounted in the housing parallel to the motor shaft, and a gear and pinion connecting the motor shaft to the jackshaft. A primary wobble plate, including a drive arm, is mounted on the Jackshaft, and a tubular spindle is mounted in the gear case for reciprocating motion. The spindle has a longitudinal slot, and the drive arm projects through the slot where it is connected to the portion of the spindle opposite the slot on the other side of the axis of the spindle. The drive arm reciprocates the spindle as the jackshaft is rotated. A secondary wobble plate is mounted on the Jackshaft, and includes a drive arm for reciprocating a counterbalance that is coaxial with the spindle, to reduce vibration. 
     Some hand held electric tools, such as electric screwdrivers, include clutch mechanisms that activate at a torque less than the stalling torque of the motor in the tool. For example, when a screw driven by an electric screwdriver has been driven all the way into a wall, the clutch will activate to prevent stripping of the threads. Because the clutch activates at a torque less than the stalling torque of the motor, the motor in the tool continues to rotate after the clutch has activated. 
     Attention is directed to U.S. patent application Ser. No. 08/275,151, filed Jul. 14, 1994, now U.S. Pat. No. 5,588,496, which is assigned to the assignee of the present invention, and which is incorporated herein by reference. 
     SUMMARY OF THE INVENTION 
     The inventor of the present invention has recognized that in a reciprocating saw, the saw bit occasionally locks or binds, for example if a blade encounters a knot in wood being sawed, or is otherwise overloaded. Also, the spindle of a saw occasionally hits a work piece. Either situation creates a high energy impulse of short duration on the drive mechanism of the saw. Such an impulse can cause failure to occur in the saw. For example, wobble plates may bend, or bearings may be damaged. Such an impulse can cause failure to occur at the gear and pinion. This is the most serious type of failure, as these parts are expensive to replace. 
     The invention provides a reciprocating saw comprising a housing, a spindle mounted for reciprocating motion within the housing, a gear rotatably mounted within the housing, a wobble shaft rotatably mounted within the housing, a wobble plate rotatably mounted on the wobble shaft and connected to the spindle, and a clutch drivingly connecting the gear to the wobble shaft. In accordance with one aspect of the present invention, the clutch includes a clutch driver rotatably positioned within the housing adjacent the wobble shaft, and the clutch driver includes a recess for insertably receiving a portion of the wobble shaft. By virtue of the recess, the transfer of power from the clutch driver to the wobble shaft occurs through a larger surface area, thereby reducing the likelihood of failure. 
     Preferably, the saw further comprises a shaft rotatably mounted within the housing, and the clutch driver and the wobble shaft are positioned about the shaft. For example, the clutch driver can include an orifice for receiving the shaft, and the recess can extend substantially completely around the orifice. The clutch driver and the wobble shaft are mounted for rotation about a rotational axis, and the recess is preferably asymmetrical with respect to the rotational axis. In another embodiment, the recess includes an inner contour, the wobble shaft includes an end facing the clutch driver and having an outer contour, and the outer contour of the end substantially matches the inner contour of the recess. 
     In accordance with another aspect of the present invention, the clutch includes a clutch driver rotatably positioned within the housing adjacent the wobble shaft, a first clutch disk connected with the gear and positioned between the gear and the clutch driver, and a second clutch disk connected with the clutch driver and positioned between the gear and the first clutch disk. Preferably, the clutch driver includes a hub portion, and the first and second clutch disks are mounted about the hub portion. The gear can also be mounted about the hub portion. 
     In one embodiment, the gear includes a plurality of grooves, and the first disk includes a plurality of splines positioned within the grooves. The clutch driver can also include a plurality of grooves, and the second clutch disk can include a plurality of splines positioned within the grooves. Preferably, the gear includes a recess, and the first and second clutch disks are positioned within the recess. 
     In accordance with another aspect of the present invention, the clutch includes a clutch driver rotatably positioned within the housing adjacent the wobble shaft, the clutch driver including a relief ledge for providing clearance between the clutch driver and the wobble plate. 
     Other features and advantages of the invention will become apparent to those of ordinary skill in the art upon review of the following detailed description, claims, and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is side elevation view, partly in section, of a reciprocating saw embodying various features of the invention. 
     FIG. 2 is an enlarged view of a clutch mechanism included in the saw of FIG.  1 . 
     FIG. 3 is a side elevation view, partly in section, showing an alternative embodiment of the invention. 
     FIG. 4 is an enlarged view of a clutch mechanism included in the saw of FIG.  3 . 
     FIG. 5 is a perspective assembly view of an alternative clutch mechanism. 
     FIG. 6 is a side section view of the clutch mechanism of FIG.  6 . 
    
    
     DETAILED DESCRIPTION 
     FIGS. 1-4 illustrate a reciprocating saw  9  embodying some of the features of the present invention. The saw  9  includes a main body  10  which includes a handle portion  12 . The saw  9  includes a motor  16  supported by the main body  10 , and an on-off trigger switch  14  supported by the handle portion  12  and electrically connected to the motor  16  for controlling energization of the motor  16 . The motor  16  includes a motor shaft  18 . 
     The saw  9  further includes a gear case  26  and a diaphragm  25  in the main body  10 , and a jackshaft  24  journaled in the gear case  26  and the diaphragm  25  by roller bearings  21  and needle bearings  23 , respectively. The jackshaft  24  is positioned parallel to the motor shaft  18 . The saw  9  further includes a urethane or rubber insulating “boot”  27  covering the gear case  26 . 
     The saw  9  further includes means for converting rotary motion into reciprocating motion. In the illustrated embodiment, such means comprises a wobble plate drive member in the form of a wobble shaft  28  rotatably mounted on the jackshaft  24 , and two wobble plate assemblies  30  mounted on the wobble shaft  28 . Other means can be employed for converting rotary motion into reciprocating motion. For example, the counterbalanced reciprocating mechanism described in U.S. Pat. No. 5,079,844, issued to Palm, can be employed. 
     The wobble plate assemblies  30  convert rotary motion into reciprocating motion. Each wobble plate assembly  30  has an input bearing  32  mounted on the wobble shaft  28 . The wobble plate assembly  30  on the left (in the figures) is a primary assembly, and the wobble plate assembly  30  on the right (in the figures) is a secondary assembly. Each wobble plate assembly  30  has a drive arm. The primary wobble plate assembly has a drive arm  34  having a somewhat spherical tip  36 . The secondary wobble plate assembly has a drive arm  35  also having a somewhat spherical tip  43 . 
     The saw  9  further includes a reciprocating tubular spindle  40  mounted in the gear case  26  for reciprocating motion and parallel to the jackshaft  24 . The spindle  40  includes a socket or hole  38  receiving the spherical tip  36  of the primary wobble plate assembly  30 , and the spindle  40  is reciprocated by the primary wobble plate assembly  30 . The spindle  40  further includes a slot  54  in the lower portion of the spindle  40 , opposite the hole  38 , for receiving the drive arm  34  of the primary wobble plate assembly  30 . The spindle  40  selectively carries a saw blade  42  or other tool bits, outside of the main body  10 . The saw blade  42  is attached to or removed from the spindle  40  using a screw or other suitable attachment mechanism. 
     The saw  9  further includes a reciprocating counterweight  46 , mounted in the gear case  26  coaxial with the spindle  40  for reciprocation opposite to the reciprocation of the spindle  40  so as to reduce vibration. The counterweight  46  has a hole  44  receiving the spherical tip  43  of the secondary wobble plate assembly  30  and the counterweight  46  is reciprocated by the secondary wobble plate assembly  30 . 
     The saw  9  includes a spindle bearing  48  fixed in the gear case  26 . The reciprocating spindle  40  slides inside of and is guided by the spindle bearing  48 . The saw  9  further includes a sleeve  50  fixed on the outside of the bearing  48 . The counterweight  46  slides on the outside of the sleeve  50 . The sleeve  50  has opposed slots  52 , and the drive arm  34  of the primary wobble plate assembly  30  projects through the bottom slot  52  in the sleeve  50 , through the slot  54  in the spindle  40 , so that the tip  36  can engage the socket or hole  38  in the top of the spindle  40 . The sides of the slot  54  engage a cylindrical exterior portion of the drive arm  34 , and this engagement prevents the spindle  40  from rotating about the spindle axis of reciprocation. 
     The saw  9  further includes means drivingly connecting the motor shaft  18  to the jackshaft  24  and providing slippage between the motor shaft  18  and the Jackshaft  24  if there is binding of the spindle  40 , such as if the blade  42  encounters a knot or a nail in a workpiece, or the spindle  40  hits the workpiece. 
     In one embodiment of the invention, shown in FIGS. 1-2, the motor shaft  18  includes a driving pinion  56  oriented to rotate about an axis parallel to the jackshaft  24 , and the means providing slippage comprises a clutch mechanism including a clutch driver  58  mounted on the jackshaft  24  and drivingly engaging the wobble shaft  28 . More particularly, the clutch driver  58  includes a tab or projection  59  which fits in and engages a keyway  61  in the wobble shaft  28 . 
     The clutch mechanism further includes a driven gear  60  rotatably mounted on the Jackshaft  24 , adjacent the clutch driver  58 . More particularly, in the embodiment shown in FIGS. 1-2, the driven gear  60  is rotatably mounted on a hub portion  62  of the clutch driver  58 . The clutch driver  58  has a discoidal surface perpendicular to the Jackshaft  24 . The driven gear  60  has a circumference that is greater than the circumference of the clutch driver  58 , and includes a discoidal surface perpendicular to the jackshaft  24  which faces the discoidal surface of the clutch driver  58 . The clutch mechanism may include a clutch disk  64  located axially between the clutch driver  58  and the driven gear  60 , mounted on the hub portion  62 , and having a first side frictionally engaging the discoidal surface of the clutch driver  58  and having an opposite side frictionally engaging the discoidal surface of the driven gear  60 . 
     The driving pinion  56  drivingly engages the driven gear  60 . The clutch mechanism further comprises a spring  66  biasing the driven gear  60  into engagement with the clutch driver and providing slippage if there is binding of the spindle  40 . In the illustrated embodiment, the spring  66  is a disk spring. The jackshaft  24  further includes an end having an enlarged diameter portion  70 , and the saw  9  further includes a spring retainer  72  mounted on the jackshaft  24 , against the enlarged diameter portion  70 , and retaining the disk spring  66  against the driven gear  60 . 
     The disk spring  66  controls frictional engagement of the clutch disk  64  with the driven gear  60  and clutch driver  58 . If a clutch disk  64  is not used, the disk spring  66  controls frictional engagement between the driven gear  60  and the clutch driver  58 . The disk spring  66  is compressed to a predetermined load setting during manufacture of the saw  9  by tightening an axle nut  68  to squeeze all the pieces mounted on the jackshaft  24 , including the disk spring  66 . The clutch mechanism will slip when the load on the saw spindle  40  or blade  42  exceeds the force applied by the disk spring  66 . More particularly, the clutch disk  64  will slip relative to either or both of the driven gear  60  and the clutch driver  58 . This prevents damage to the wobble plate assemblies  30  and the driving pinion  56  when the blade locks or binds, hits something like a knot or nail, or is otherwise overloaded. 
     A second embodiment of the present invention is illustrated in FIGS. 3-4. The embodiment shown in FIGS. 3-4 is substantially similar to the embodiment shown in FIGS. 1-2 which was just described. In this regard, like reference numerals indicate like components, except that in this embodiment, the driven gear  160  includes circumferentially spaced apertures which house ball bearings  110 , and the clutch driver  158  includes a pocket or depression  114  in its side facing the driven gear  160 . The ball bearings  110  are housed between, and engage, the pocket or depression  114  on one side of the driven gear  160  and the disk spring  66  on the other side of the driven gear  160 . Also, in this embodiment, the clutch disk  64  is removed. A spacer  112  is provided between the clutch driver  158  and the driven gear  160  radially interior of the ball bearings  110 . 
     By pressing against the driven gear  160  and ball bearings  110 , the disk spring  66  controls engagement of the ball bearings  110  with the pocket or depression  114  in the clutch driver  158 . The clutch mechanism will slip when the load on the spindle  40  or blade  42  exceeds the force applied by the disk spring  72 . This prevents damage to the wobble plate assemblies  30  and the driving pinion  56  when the blade locks or binds, hits something like a knot or nail, or is otherwise overloaded. 
     FIGS. 5-6 illustrate a third embodiment of the present invention. Similar to the above-described embodiments, the mechanism  170  of FIGS. 5-6 provides relative slippage between the drive pinion  172  (FIG. 6 only) and the jackshaft  174  (FIG. 6 only) of a reciprocating saw. Also similar to the previous embodiments, the illustrated mechanism includes a driven gear  176  having a recess  177 , a spring retainer  178 , a disk spring  180 , a clutch driver  182  having a hub portion  184 , and a wobble shaft  186  (FIG. 6 only). 
     The interface between the driven gear  176  and the clutch driver  182  is provided by a first clutch disk  188  interconnected with the driven gear  176  and a second clutch disk  190  interconnected with the clutch driver  182 . Both the first and second clutch disks  188 , 190  are positioned within the recess  177  in the gear  176 . The first clutch disk  188  includes a plurality of radially-outwardly projecting splines  192  that cooperate with corresponding axially-extending grooves  194  on the inner surface of the driven gear  176 . The second clutch disk  190  includes a plurality of radially-inwardly projecting splines  196  that cooperate with corresponding axially-extending grooves  198  on the hub portion  184  of the clutch driver  182 . In the described embodiment, the first clutch disk  188  is made of bronze and the second clutch disk  190  is made of steel. By virtue of the provision of two clutch disks, the illustrated mechanism has three friction surfaces, as opposed to the single friction surface of the previous embodiments. 
     The clutch driver  182  of the third embodiment (FIGS. 5-6) eliminates the tab  59  of the first and second embodiments, and instead interconnects with the wobble shaft  186  through a contoured recess  200  in the clutch driver  182 . The contoured recess  200  is shaped to match the end of the wobble shaft  186  so that rotation of the clutch driver  182  will result in rotation of the wobble shaft  186 . The full surface contact between the clutch driver  182  and the wobble shaft  186  is believed to enhance the strength, fatigue resistance and impact resistance of the interconnection. 
     The clutch driver  182  further includes a relief ledge  202 . The relief ledge provides extra clearance between the clutch driver  182  and the wobble plate  204  (FIG. 6 only), thereby facilitating closer spacing of the entire assembly. 
     One embodiment of the invention provides a hand held reciprocating saw including a motor, a driving shaft, a driven shaft, and a clutch in driven engagement between the driving shaft and the driven shaft, which clutch activates to provide slippage between the driving shaft and the driven shaft only at a torque higher than the stalling torque of the motor. For example, any of the clutch mechanisms disclosed above in connection with FIGS. 1-4 can be configured to slip only at a torque higher than the stalling torque of the motor. Thus, the motor stalls when the saw encounters an unexpected impediment to operation, preventing harm to the motor, and the impulse caused by the impediment is absorbed by the clutch. 
     While clutch mechanisms and other means providing slippage have been described in connection with a reciprocating drive mechanism that includes wobble plates, it should be understood that the clutch mechanisms and other means providing slippage can be used in reciprocating drive mechanisms that include other means for converting rotary motion into reciprocating motion. It should also be understood that the clutch mechanisms could be located at other locations in the saw; for example, a clutch mechanism can be located closer to the blade, or a clutch mechanism can be provided between slip motor shafts. The illustrated embodiment has been found to provide a more economical location for the clutch mechanism. 
     Modifications may be made to the preferred embodiment described and illustrated herein without departing from the spirit of the invention as expressed in the following claims.