THREE-SPEED GEAR MECHANISM IN A POWER TOOL

Abstract: A three-speed gear mechanism for a power tool includes a high speed gear (38) and a low speed gear (34) journalled to the output spindle (26) and an intermediate speed gear (36) keyed to the spindle between the high and low speed gears. The intermediate speed gear serves the dual function of providing a direct torque couple between the idler shaft (68) and spindle (26) in the intermediate speed position and a clutch for transmitting torque from the high and low speed gears to the output spindle in the high and low speed conditions. In addition, in connection with the application of the present invention to a hammer drill to which it is particularly suited, the present invention includes novel means for accommodating the reciprocatory movement of the output spindle while maintaining proper relative positioning between the high and low speed gears.

Description: Three-Speed Gear Mechanism For A Power Tool The present invention relates to power tools and in particular to a multiple speed gear mechanism for a power tool such as a drill or hammer drill. Multiple speed gear mechanisms are known in the power tool art and are generally utilized where it is desired to provide a tool, such as a drill, with the capability of operating at different speeds while main taining the speed of the motor at a fixed predetermined rate. Prior art multiple speed gear mechanism (U.S. Patents, Nos. 2,911,841; 3,396,593; and 3,785,443) typic ally comprise an output spindle having disposed thereon a pair of gears for selectively imparting either a high or low rotational speed to the output spindle. A shift mechanism is provided to alter the position of torque transmitting means coupled to the output spindle for selectively coupling the output spindle to a motor drive through either the high or low speed gear. The primary object of the present invention is to provide an improved three-speed gear mechanism that is durable and capable of maintaining positive engagement even when utilized in high vibration power tools such as hammer drills. An additional object of the present invention is to provide an improved three-speed gear mechanism which includes an intermediate speed gear that also serves as a clutch in the high and low speed positions for transmit ting torque from the high and low speed gears to the output spindle. A further object of the present invention is to provide an improved three-speed gear mechanism that is adapted to accommodate reciprocatory movement of the output spindle which occurs during the operation of certain power tools such as hammer drills. In general, the three-speed gear mechanism of the present invention includes three output gears, of which the intermediary gear serves as a clutch for transmitting torque to the output spindle from one or the other of the remaining two output gears in the high and low speed conditions. In addition, in the intermediate speed condition, the intermediary gear also serves to impart torque directly to the output spindle. More particularly, the present three-speed gear mechanism comprises an idler shaft that is geared to the motor shaft and which has fixedly mounted thereon three rotary gears of varying diameter. The two outer gears on the idler shaft are in turn permanently engaged to two output gears, both of which are journalled freely to the output spindle A third output gear, located intermediate the aforesaid two output gears, is keyed to the spindle so as to rotate therewith, and is slideable along the axis thereof. In addition, the intermediate output gear has pins fixedly mounted therein that are adapted to engage corresponding detents in the faces of the remaining two output gears. A shift mechanism. is provided which is connected to the intermediate output gear and is adapted to slide said gear along the shaft of the output spindle to one of three positions such that in a first position the intermediate output gear is rotationally engaged with the low speed output gear so that the rotational speed imparted to the output spindle through the intermediate output gear corresponds to the rotational speed of the low speed output gear, in a second position the intermediate output gear is directly engaged with the intermediate sized gear on the idler shaft so that the rotational speed imparted to the output spindle corresponds to the rotational speed of the intermediate output gear, and in a third position the intermediate output gear is engaged with the high speed output gear so that the rotational speed imparted to the output spindle through the intermediate output gear corresponds to the rotational speed of the high speed output gear. Furthermore, in connection with the application of the present invention to a hammer drill to which it is particularly suited, the three-speed gear mechanism in the preferred embodiment includes novel means for accommodating the reciprocating movement of the output spindle when the tool is operated in the hammer drill mode. In particular, the spline key which rotationally connects the intermediate output gear to the spindle has a predetermined length equal to the distance between the low speed and high speed output gears to constrain axial movement thereof. In addition the spline key is slideably engaged in a groove formed in the output spindle which has a length that exceeds the length of the spline key to accommodate the reciprocating movement of the spindle. Thus, it will be appreciated that the spline key serves to maintain the fixed positions of the low speed and high speed output gears while at the same time permitting the percussive movement of the tool spindle. Additional objects and advantages of the present invention will become apparent from a reading of the detailed description of the preferred embodiment which makes reference to the following set of drawings in which: FIG. 1 is a side elevational view, partly in longitudinal section, illustrating a hammer drill incorporating a three speed gear mechanism according to the present invention; FIG. 2 is an enlarged sectional view of the three speed gear mechanism illustrated in FIG. 1; FIG. 3 is a transverse sectional view taken along line 3-3 in FIG. 2; FIG. 4 is a diagrammatic view illustrating the shift mechanism of the present invention; FIG. 5 is a diagrammatic view illustrating the three-speed gear mechanism in the low-speed position; FIG. 6 is a diagrammatic view illustrating the three-speed gear mechanism in the intermediate-speed position; ; FIG. 7 is a diagrammatic view illustrating the three-speed gear mechanism in the high-speed position; and, FIG. 8 is a diagrammatic view illustrating an alternative embodiment of the three-speed gear mechanism of the present invention. Referring to FIG. 1, an impact or hammer drill 10 incorporating a three-speed gear mechanism 12 according to the present invention is shown. Again, it is to be emphasized that although the preferred embodiment herein discloses a hammer drill to which the present invention is particularly suited, the multiple-speed gear mechanism of the present invention is applicable to power tools in general, and may for example be utilized in other tools such as a conventional drill. The hammer drill 10 is conventional in overall layout, comprising a motor 14 (partly shown) disposed within a casing 16 in part defining a pistol grip-type handle 18 incorporating a trigger-type on/off switch 20. Power to the tool 10 is supplied via the usual power cord 22 extending from the bottom of the handle 18. A fan 24 is affixed to the shaft 25 of the motor 14 to facilitate cooling of the tool 10. The motor 14 drives an output spindle 26 through the three-speed gear mechanism 12 which is disposed in a gear case 15 fastened to the forward end of casing 16. The spindle 26 extends outwardly beyond the front of gear case 15 and has affixed to its exposed end a chuck 28 for securing a drill bit thereto. An additional depending handle 30 is mounted to the front end of gear case 15 to provide means for supporting the forward end of the tool 10. Furthermore, a rotary select knob 32 exposed through an opening in the top of the casing 16 is provided for selecting between hammer drill or drill only operation of the tool 10 in a manner to be subsequently described. Turning now to FIG. 2, a detailed sectional view of the three-speed gear mechanism 12 of the present invention is shown. The gear mechanism 12 includes three output gears 34, 36 and 38, comprising the low, intermediate and high speed gears, respectively. The low speed 34 and high speed 38 gears are freely journalled to the output spindle 26 which is in turn journalled in and supported by ball bearings 40 and 42 mounted in the forward end and rear wall, respectively, of the gear case 15. The intermediate speed gear 36 is keyed to spindle 26 via a spline key 44 which engages a longitudinal slot 46 formed in the spindle 26. The spline key 44 can, for example, be of circular cross-section. It will be noted that the length of the spline key 44 is such that it maintains the proper spaced relationship between the low and high speed gears 34 and 38. In particular, the position of the low speed gear 34 is constrained by an axial bearing 95 in the front wall of gear case 15 on one side and spline key 44 on the other, and the high speed gear 38 is constrained by ball bearing 42 in the rear wall of gear case 15 on one side and spline key 44 on the other. Additionally, it will be noted that the length of the longitudinal groove 46 formed in spindle 26 exceeds the length of spline key 44. This is to permit the spline key 44 to slide within groove 46 to accommodate the reciprocating movement of spindle 26 when the tool 10 is operated in the hammer drill mode. One or more equally radially spaced pins 48 are fixedly mounted in the intermediate speed gear 36 so as to protrude from both sides thereof as shown. A corresponding number of equally radially spaced detents 50 are formed in the opposed face of both the low speed 34 and high speed 38 gears which are adapted to engage the pins 48 in intermediate speed gear 36 when the intermediate speed gear 36 is juxtaposed with either the low speed 34 or high speed 38 gear. The axial position of the intermediate speed gear 36 is controlled by a shift mechanism 52 which is best illustrated in FIGS. 3 and 4. The shift mechanism 52 comprises a guide fork 54 having prongs 56 that engage a circumferential groove 58 formed in intermediate speed gear 36. Guide fork 54 includes a flat portion having a slot 60 formed therein that is adapted to receive one end of an S-shaped pin 62 that is eccentrically mounted at its other end to a knob 64 that is rotatable through an angle of 1800. Rotation of the knob 64 rotates S-shaped pin 62 causing guide fork 54 to slide along guide pin 66 to one of three different positions corresponding to the respective positions of the intermediate speed gear 36 shown in FIGS. 5-7, to be subsequently described. Returning to FIG. 2, the low#speed 34 and high speed 38 gears are permanently engaged with a pair of idler gears, 70 and 74 respectively, mounted to an idler shaft 68 which is journalled in and supported by a pair of ball bearings 76 and 78 mounted in the front and rear walls respectively of gear case 15. Idler gear 70 actually comprises a pinion type gear formed on idler shaft 68. A third idler gear 72 is additionally mounted to idler shaft 68 and is adapted to engage intermediate speed gear 36 when gear 36 is in the position illustrated in FIGS. 2 and 6. A pinion gear 82 formed on the end of motor shaft 25 drives idler shaft 68 through a gear 80 fixedly mounted to the rearward end of idler shaft 68. Turning momentarily to FIG. 8, an alternative embo diment of the present three-speed gear mechanism 12 is diagrammatically illustrated. In this embodiment, the low speed 34 and high speed 38 output gears as well as the corresponding idler gears, 70 and 74 respectively, to which they are engaged have helical teeth. With this helical gear configuration, output gears 34 and 38, which are freely journalled to output spindle 26, will exert axially opposed thrust loads against and bearings 95 and 42 respectively, as represented by the arrows, when driven by idler gears 70 and 74 to thereby relieve any axial loading on spline key 44. As noted previously, the hammer drill 10 disclosed herein is adapted to operate in either one of two modes: the hammer drill mode or the drill only mode. Mode selection is made via knob 32 which has a shaft 84 that has affixed thereto a cam member 86 having a recess 88 formed in a radial segment thereof. A pair of juxtaposed gears 92 and 94 having ratchet teeth formed on their opposed faces is provided at the forward end of spindle 26. Gear 92 is fixedly mounted to spindle 26 so as to rotate therewith. Gear 94, however, is fixedly mounted to the wall of gear case 15 so that it remains stationary relative to gear 92. A spring 90 is provided to forwardly bias the spindle 26 so that a slight gap is created between the opposed faces of gears 92 and 94 as shown. Thus, it will be appreciated that when the modeselect knob 32 is rotated to the position illustrated in FIG. 2, the cam member 86 will abut the rearward end of output spindle 26 preventing reciprocal movement thereof. Accordingly, in this position, the tool will operate in the drill only mode. However, upon rotation of knob 32 through an angle of 1800, recess 88 in cam member 86 will align with the rearward end of output spindle 26. Therefore, when the tool bit is pressed against the workpiece, spindle 26 will move rearwardly against the bias of spring 90 enabling the ratchet teeth of gears 92 and 94 to mutually engage, thereby imparting a reciprocating motion to spindle 26 as it rotates. Referring now to FIGS. 5, 6 and 7, the operation of the three-speed gear mechanism 12 according to the present invention in each of its three operative positions will now be explained. Looking first to FIG. 5, the shift knob has been rotated so that intermediate speed gear 36 is juxtaposed with low speed gear 34. In this configuration, pins 48 affixed to gear 36 are engaged with detents 50 formed in the face of gear 34 causing gear 36 to rotate with gear 34. Accordingly, torque is transmitted to output spindle 26 from motor shaft 25 through pinion gear 82, gear 80, idler shaft 68, pinion gear 70, gear 34, pins 48, gear 36 and spline key 44, as indicated by the solid line designated 96. Thus, since torque is transmitted from idler shaft 68 to output spindle 26 through gears 70 and 34, spindle 26 will rotate at its low speed rate. In FIG. 6, the intermediate speed gear 36 has been shifted to its intermediary position in which it is engaged directly with idler gear 72 on shaft 68. In this configuration, torque is transmitted from motor shaft 25 to output spindle 26 through pinion gear 82, gear 80, idler shaft 68, gear 72, gear 36 and spline key 44, as indicated by the solid line designated 98. Accordingly, since torque is transmitted from idler shaft 68 to output spindle 26 through gears 72 and 36, spindle 26 will rotate at its intermediate speed rate. Finally, in FIG. 7 the intermediate speed gear 36 has been shifted into juxtaposed relation with high speed gear 38 such that pins 48 in gear 36 engage detents 50 formed in the face of gear 38 causing gear 36 to rotate with gear 38. Accordingly, in this position torque is transmitted from motor shaft 25 to output spindle 26 through pinion gear 82, gear 80, idler shaft 68, gear 74, gear 38, pins 48, gear 36 and spline key 44, as indicated by the solid line designated 100. Thus, since torque is transmitted from idler shaft 68 to output spindle 26 through gears 74 and 38, spindle 26 will rotate at its high speed rate. From the above description, it can be seen that in the low and high speed conditions illustrated in FIGS. 5 and 7, the intermediate speed gear 36 serves as a clutch transmitting torque from the low speed gear 34 and high speed gear 38, respectively, to the output spindle 26; whereas in the intermediate speed condition shown in FIG. 6, gear 36 serves as the primary output gear transmitting torque to spindle 26 directly from idler shaft 68. Also of significant note is the manner in which the present three-speed gear mechanism 12 accommodates the reciprocatory movement of the spindle 26 in the hammer drill mode while maintaining proper gear alignment between the output gears journalled to the spindle 26 and the idler gears mounted to the idler shaft 68. More specifically, it can be seen that while the high speed and low speed gears 34 and 38 must be freely journalled to spindle 26 to permit axial movement thereof, it is also essential that the low speed gear 34 and high speed gear 38 remain stationary relative to idler shaft 68. In this regard, the multiple functions served by spline key 44 can be appreciated. In particular, spline key 44 not only transmits torque from intermediate speed gear 36 to spindle 26 in all three operative positions of the gear mechanism, it also serves to constrain axial movement of low speed gear 34 and high speed gear 38. As discussed previously, this is accomplished by making the length of spline key 44 equal to the distance between gears 34 and 38 and by lengthening slot 46 in spindle 26 so that it exceeds the length of spline key 44. In this manner, when spindle 26 reciprocates, spline key 44 will remain stationary in the axial direction while continuing to transmit torque to the spindle 26 by maintaining a slid ing engagement with slot 44. While the above description constitutes the preferred embodiment of the present invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the accompanying claims.

Claims: CLAIMS 1. A three-speed gear mechanism for a power tool including a spindle having disposed thereon first, second and third output gears for selectively imparting low, medium and high speed rotation to said spindle by selectively coupling said output spindle to a motor drive through one of said three gears; the gear mechanism being characterized by: said second gear (36) being rotationally coupled to said spindle (26) in all operative positions of said gear mechanism, being disposed intermediate said first (34) and third (38) gears, and being movable in the axial direction relative to said first (34) and third (38) gears such that in a first operative position thereof (FIG.5) in which said first output gear (34) is coupled to said motor drive (25), torque is transmitted from said first output gear (34) to said second output gear (36), in a second operative position thereof (FIG.6) torque is transmitted directly from said motor drive (25) to said second output gear (36), and in a third operative position thereof (FIG.7) in which said output gear (38) is coupled to said motor drive (25), torque is transmitted from said third output gear (38) to said second output gear (36). 2. The gear mechanism of claim 1 caracterized by: first (70), second (72) and third (74) idler gears drivingly coupled to a motor shaft (25); said spindle (26) having disposed thereon said first (34),second (36) and third (38) output gears for providing low, medium and high speed rotation of said spindle (26), said second output gear (36) being disposed intermediate said first (34) and third (38) output gears and said first (34) and third (38) output gears being respectively engaged with said first (70) and third (74) idler gears; first torque transmitting means (44, 46) for transmitting torque from said second output gear (36) to said spindle (26) in all operative positions of said gear mechanism; ; shift means (52) for controlling the axial position of said second output gear (36) relative to said first (34) and third (38) output gears such that in said first operative position thereof (FIG.5) said second output gear (36) is juxtaposed with said first output gear (34), position in said second operative/thereof (FIG.6) said second output gear (36) is engaged with said second idler gear (72), and in said third operative position thereof (FIG.7) said second output gear (36) is juxtaposed with said third output gear (38), and, second torque transmitting means (48, 50) for transmitting torque from said first output gear (34) to said second output gear (36) in said first operative position (FIG.5) and from said third output gear (38) to said second output gear (36) in said third operative position (FIG.7). 3. The gear mechanism of claim 2, characterized in that said first (34) and third (38) output gears are freely journalled to said spindle (26) and said second output gear (36) is keyed to said spindle (26) by a spline key (44) engaged with a longitudinal slot (46) formed in said spindle (26). 4. The gear mechanism of claim 3 characterized in that the length of said spline key (44) is substantially equal to the distance between said first (34) and third (38) output gears for maintaining the proper relative position between said first (34) and third (38) output gears. 5. The gear mechanism of claim 2, characterized in that said first output gear (34) and said first idler gear (70) being mutually engaging helical gears and said third output gear (38) and said third idler gear (74) likewise being mutually engaging helical gears. 6. A three-speed gear mechanism of claim 1 - 5 for a hammer drill power tool having an output spindle and means for imparting reciprocatory movement to said spindle, the gear mechanism being characterized by: first (34) and third (38) output gears freely journalled to said spindle (26) and a second output gear (36) keyed to said spindle (26) intermediate said first (34) and third (38) output gears by a spline key (44) slideably engaged with a longitudinal groove t46) formed in said spindle (26) for accommodating the reciprocatory movement of said spindle (26), said spline key (44) having a length substantially equal to the axial distance between said first (34) and third (38) output gears for constraining axial movement of said first (34) and third (38) output gears; and select means (52) for selectively duping said output spindle (26) to a motor drive (25) through one ofsaid three output gears (34,36,38) for causing said spindle (26) to rotate at one of three predetermined speeds. 7. The gear mechanism of claim 6, characterized in that said spline key (44) is adapted to maintain the torque transmitting relationship between said second output gear (36) and said spindle (26) in all operative positions of said gear mechanism. 8. The gear mechanism of claim 6, characterized in that the length of said longitudinal groove (46) exceeds the length of said spline key (44) so that said spline key (44) will remain stationary relative to axial reciprocatory movement of said spindle (26). 9. The gear mechanism of claim 6, characterized by torque transmitting means (48, 50) associated with said second output gear (36) for transmitting torque from said first output gear (34) to said second output gear (36) in said first operative position (FIG.5) of said gear mechanism and from said third output gear (38) to said second output gear (36) in said second operative position (FIG.7) of said gear mechanism. 10. The gear mechanism of claim 9, characterized in that said second output gear (36) is slideably disposed on said spindle (26) and said select means (52) is adapted to shift the axial position of said second output gear (36) into juxtaposed relation with said first output gear (34) in said first operative position (FIG.5) and into juxtaposed relation with said third output gear (38) in -said second operative position (FIG.7).

Inventors: GROSSMANN, HORST
Applicants: BLACK & DECKER INC.
Application year: 1979
Main classification: B23B45
IPC codes: B23B45