Power tool

Abstract

 A power tool includes a reversing restriction portion (46b (46c)) arranged in a pivot member (42). When a drive unit (33) pivots the pivot member (42) to switch the gear ratio of a gear mechanism (41), the reversing restriction portion (46b (46c)) engages with a support (47) to restrict pivoting of the pivot member (42) in a reverse direction that is caused by a reaction force which acts on the pivot member (42) at a limit position from where further pivoting of the pivot member (42) is prohibited.

Description

[0001] The present invention relates to a power tool that switches the gear ratio of a gear mechanism which transmits rotational power to a rotation output unit to which a bit is attachable.

[0002] One example of a power tool is an electric power tool such as an electric power driver. Japanese Laid-Open Patent Publication Nos. 2012-16760, 2012-30347, and 2009-56590 each describe an electric power tool including a motor, a gearshift device, and a rotation output unit. The motor is arranged in a body housing. The gearshift device changes the speed of the rotation produced by the motor. The rotation output unit is rotated at the speed changed by the gearshift device. Further, a bit is attachable to the rotation output unit.

[0003] The gearshift device described in each of the above publications includes a gear mechanism, a gear switching unit, and a gearshift actuator. A control unit drives the gearshift actuator to operate the gear switching unit and switch the gear ratio (reduction ratio) of the gear mechanism.

[0004] The gear switching unit includes a pivot plate (e.g., curved plate) that is pivotal along the outer surface of a gearshift device case. The pivot plate includes a cam hole extending in a direction inclined to the pivot direction. The gear mechanism includes a support coupled to a movable member, such as a ring gear. The support is inserted through the cam hole of the pivot plate and a slide hole which extends through the gear case in the axial direction. In this structure, the pivot plate pivots and moves the support along the cam hole so that the movable member slides in the axial direction of the gearshift device to shift gears engaged with the movable member. This switches the gear ratio of the gear mechanism. In such a gearshift device, the control unit drives the gearshift actuator based on the detected value of the acting load to automatically shift gears and switch the gear ratio. The gearshift device includes a gearshift switch that is operable by a user. The control unit drives the gearshift actuator in accordance with an operation signal from the gearshift switch to switch the gear ratio.

[0005] In the above gearshift device, the pivot plate should be stopped at a target position (target tolerable position) when shifting gears. A brake circuit may be used to stop the gearshift actuator. However, this would result in a complicated structure. Further, depending on the motor type (e.g., brush motor), early wear may occur in a gearshift actuator component (e.g., brush). Thus, to obtain a sufficient duration, the motor has to be enlarged in size. This, in turn, may enlarge the electric power tool.

[0006] When there is no brake circuit, the pivot plate is pivoted by inertia after the gearshift actuator stops operating. In this case, pivoting of the pivot plate is prohibited at a limit position that is set at a target position. However, when the pivot plate pivoted by inertia reaches the limit position and the support hits a terminal end of the cam hole, the retroaction may slightly pivot the pivot plate in the reverse direction. The reversed rotation of the pivot plate may move the pivot plate away from the target position. The cam hole includes an operation hole, which is inclined to the circumferential direction of the pivot plate, and holding holes, which are continuous with the two ends of the operation hole and extend in the circumferential direction of the pivot plate. The support is held at the terminal end of the holding hole to be immovable in the axial direction. However, when the reaction force produced at the terminal end of the holding hole pivots the pivot plate in the reverse direction, the support may be returned to near the operation hole. For example, even when the pivot plate is only slightly pivoted in the reverse direction by the vibration produced during operation of the electric power tool, the support may be returned to the operation hole. In this case, since movement of the movable member in the axial direction is no longer prohibited, the gear ratio may be switched in an unexpected manner.

[0007] Such a problem is not limited to electric power tools and applies to any power tool that includes a gear mechanism driven by a drive unit such as a gearshift actuator. For example, the same problem may occur in a pneumatic tool, which uses pneumatic pressure as a power source, or a hydraulic tool, which uses hydraulic pressure as a power source.

[0008] It is an object of the present invention to provide a power tool that allows for a movable member to be stopped at a given position even if a pivot member is pivoted by retroaction in a reverse direction from a limit position after a drive unit stops operating and the pivot member reaches the limit position.

[0009] In one embodiment, a power tool includes a power source, a rotation output unit to which a bit is attachable, a gear mechanism configured to transmit rotational power of the power source to the rotation output unit, a gearshift device case configured to accommodate the gear mechanism, and a housing configured to accommodate the power source and the gearshift device case. The gear mechanism includes gears and a movable member movable in an axial direction of the gears to be engaged with or disengaged from the gears. The gear mechanism is further configured to move the movable member to allow for switching between a plurality of gear ratios. The gearshift device case includes a slide hole formed in the gearshift case in the axial direction. The power tool further includes a pivot member that is pivotal about the axial direction along an outer surface of the gearshift device case. The pivot member includes a cam hole arranged at a location partially overlapped with the slide hole. The cam hole includes an operation hole that extends in a direction inclined to a circumferential direction of the pivot member. The power tool further includes a support arranged on the movable member. The support projects from the movable member and extends through the slide hole and the cam hole. The power tool further includes a drive unit configured to pivot the movable member along the outer surface of the gearshift device case. The power tool further includes a reversing restriction portion arranged in the pivot member. The reversing restriction portion is configured such that when the drive unit pivots the pivot member to switch the gear ratio, the reversing restriction portion engages with the support to restrict pivoting of the pivot member in a reverse direction that is caused by a reaction force which acts on the movable member at a limit position from where further pivoting of the movable member is prohibited. Here, the term "engagement" of the reversing restriction portion and the support includes "sliding" of the support on the reversing restriction portion, "restraint" of the support being moved, and "locking" of the support, as well as hitting the support to change a direction in which the pivot member receives a reaction force relative to a pivoting direction of the pivot member.

[0010] According to this structure, the power tool that allows for the movable member to be stopped at a given position even if the pivot member is pivoted by retroaction in a reverse direction from a limit position after the drive unit stops operating and the pivot member reaches the limit position.

[0011] In a preferred embodiment, the pivot member is arranged to be pivoted in the cam hole within a range including a first terminal end region and a second terminal end region, and the reversing restriction portion is configured to increase sliding resistance of the support and the pivot member in the first and second terminal end regions to apply a braking force to the pivot member and restrict pivoting of the pivot member in the reverse direction.

[0012] In a preferred embodiment, the reversing restriction portion includes holding holes that are continuous with two ends of the operation hole and extend in a direction inclined to the circumferential direction of the pivot member.

[0013] In a preferred embodiment, the pivot member further includes first hole portions that are continuous with two ends of the operation hole and extend in the circumferential direction of the pivot member, and the reversing restriction portion includes an inclined surface located at a terminal end of each first hole portion, wherein the inclined surface is configured to apply a reaction force to the support in a direction intersecting a longitudinal direction of the first hole portion when the support contacts the terminal end of the first hole portion.

[0014] In a preferred embodiment, the reversing restriction portion further includes a second hole portion continuous with the terminal end of each first hole portion and extending in a direction in which the support receives the reaction force from the inclined surface.

[0015] In a preferred embodiment, the pivot member further includes a guide surface configured to guide the support from the second hole portion to the first hole portion when the pivot member starts to pivot from the second hole portion.

[0016] Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.

[0017] The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

Fig. 1 is a cross-sectional view of a power tool in a first embodiment;

Fig. 2 is a schematic diagram of an automatic gearshift device installed in the power tool of Fig. 1;

Fig. 3 is a schematic front view of a gearshift unit arranged in the automatic gearshift device of Fig. 2;

Figs. 4A to 4C are schematic cross-sectional view illustrating the switching of gear ratios of a gear mechanism in the gearshift unit of Fig. 3;

Fig. 5 is a side view illustrating a reversing restriction portion of the gearshift unit (gear switching unit) of Fig. 3;

Fig. 6 is a side view illustrating another example of a reversing restriction portion of the gearshift unit (gear switching unit) of Fig. 3;

Figs. 7A and 7B are schematic diagrams illustrating a gear switching unit in a comparative example;

Fig. 8 is a side view illustrating a reversing restriction portion of a gear switching unit in a second embodiment; and

Fig. 9 is a side view illustrating the operation of the reversing restriction unit in Fig. 8.

[First Embodiment]

[0018] An electric power tool 10 will now be described with reference to Figs. 1 to 6 as one example of a power tool. In Fig. 1, a housing 13 is partially removed from the power tool 10.

[0019] Referring to Fig. 1, the electric power tool 10 is portable and may be held with a single hand. The electric power tool 10 may be used as, for example, an electric drill driver. The electric power tool 10 includes a main body 11 and a battery pack 12, which is attached in a removable manner to the main body 11. The housing 13, which forms the shell of the main body 11, includes a tubular barrel 14 (only one half illustrated in Fig. 1) and a handle 15. The barrel 14 has a closed end, and the handle 15 is continuous with the barrel 14. The handle 15 extends from a longitudinally middle portion of the barrel 14 in a direction intersecting the axis L (axial direction) of the barrel 14. The electric power tool 10 also includes a tetragonal battery pack connector 15a arranged on the lower end of the handle 15. The electric power tool 10 of the present example is chargeable and uses the electric power of the battery pack 12.

[0020] The barrel 14 includes a basal portion (left portion in Fig. 1) that accommodates a motor 16, which is driven by the power from the battery pack 12. The motor 16 is arranged in the barrel 14 so that a rotation shaft of the motor 16 is aligned with the axis L of the barrel 14. The motor 16 is, for example, a brush motor or a brushless motor. A gearshift unit 17 is arranged next to an output shaft of the motor 16 (right side in Fig. 1) to change (reduce) the rotation speed of the motor 16.

[0021] The gearshift unit 17 reduces the rotation speed of the motor 16 and transmits the rotation to a power transmission mechanism 18. The power transmission mechanism 18 transmits rotation, of which the speed has been reduced by the gearshift unit 17, to a drive shaft 19. The drive shaft 19 is connected to a rotation output unit 20, which is arranged on the distal end of the barrel 14. In the present embodiment, the rotation output unit 20 includes a chuck. A bit 21 is arranged in a removable manner to the distal end of the chuck. Accordingly, the bit 21 rotates together with the rotation output unit 20, which is rotated at a speed reduced by the gearshift unit 17. Although not illustrated in the drawings, the power transmission mechanism 18 includes a torque limiter, a lock mechanism, and the like. The torque limiter cuts the transmission of power to the drive shaft 19 when a load greater than or equal to a predetermined value is applied to the drive shaft. The lock mechanism locks the drive shaft 19 to prohibit rotation. The rotation output unit 20 does not have to include the chuck and may instead include a threaded portion that allows for a bit to be fastened.

[0022] As illustrated in Fig. 1, a trigger switch 22 is arranged at the front side of the handle at a position located slightly downward from where the barrel 14 is connected. The trigger switch 22 is located at a position corresponding to where the index finger of a user would be located when the user holds the handle 15. The trigger switch 22 includes a trigger lever 23 and a switch 24. The user operates the trigger lever 23 to drive the power tool 10. The switch 24 is located in the handle 15 and activated or deactivated in accordance with the operation of the trigger lever 23. The trigger lever 23 is urged and projected toward the front from the handle 15 by, for example, a spring. The switch 24 outputs a signal having a value corresponding to the operation amount (pulled amount) of the trigger lever 23.

[0023] As illustrated in Fig. 1, a forward/reverse switch 25 (rotation direction switch lever) is arranged proximal to the portion where the barrel 14 and the handle 15 are connected. The user operates the forward/reverse switch 25 to switch the rotation direction of the rotation output unit 20 between forward and reverse. The forward/reverse switch 25 is a two-position switch that is movable between a forward rotation position and a reverse rotation position. Alternatively, the forward/reverse switch 25 may be a three-position switch that is movable between a forward rotation position, a reverse rotation position, and a neutral position, which is used when restricting rotation of the rotation output unit 20.

[0024] A gearshift switch 26 is arranged on an upper surface of the barrel 14 to switch the gear ratio of the gearshift unit 17. The gearshift switch 26 is one example of a gearshift operation unit. The gearshift unit 17 is capable of switching the gear ratio with a plurality of gears. The gearshift switch 26 is used to select automatic gear shifting or a certain gear ratio, which fixes the rotation speed of the rotation output unit 20. The gearshift switch 26 is, for example, a slide switch. In the present embodiment, the gearshift switch 26 is a three-position switch that allows for the selection of one of three drive modes, namely, a high speed/low torque drive mode (H gear), a low speed/high torque drive mode (L gear), and an automatic gearshift mode (AUTO). The gearshift switch 26 outputs a signal corresponding to the selected one of the three modes.

[0025] As illustrated in Fig. 1, a control unit 27 is arranged in the battery pack connector 15a. The control unit 27, which is, for example, a control board, is electrically connected to the motor 16 through the trigger switch 22 and a wire to electrically control the motor 16. The forward/reverse switch 25 and the gearshift switch 26 are also connected to the control unit 27. When the user pulls the trigger lever 23, the motor 16 produces rotation in the rotation direction that corresponds to the position of the forward/reverse switch 25. Further, when the user pulls the trigger lever 23, the rotation speed of the motor 16 is reduced by the gearshift unit 17 in correspondence with the position of the gearshift switch 26, and the rotation output unit 20 is rotated at the reduced speed. When the load applied to the drive shaft 19 exceeds a predetermined value, the power transmission mechanism 18 functions to produce an impact by striking an anvil with a hammer using the urging force of a spring so that the rotation output unit 20 outputs high torque.

[0026] A structure for switching the gear ratio of the gearshift unit 17 will now be described with reference to Figs. 2 and 3.

[0027] As illustrated in Fig. 2, the gearshift unit 17, which is coupled to the rotation shaft of the motor 16, includes a gearshift device 31, a gear switching unit 32, and a gearshift actuator 33, which is one example of a drive unit that drives the gear switching unit 32. The gearshift device 31 includes a ring gear RG (internal gear), which is one example of a movable member. The gear switching unit 32 moves the ring gear RG in the axial direction to switch the gear ratio of the gearshift device 31. The control unit 27, which controls the electric power tool 10, is electrically connected to input system components such as the gearshift switch 26, the trigger switch 22, and the forward/reverse switch 25.

[0028] The control unit 27 drives a motor drive circuit 34 based on an input signal from the trigger switch 22 to activate and deactivate the motor 16 and regulate the rotation speed of the motor 16. The control unit 27 controls the rotation speed of the motor 16 in accordance with the operation amount of the trigger switch 22, that is, the pulled amount of the trigger lever 23.

[0029] The control unit 27 drives a gearshift drive circuit 35 to move the gearshift actuator 33 to a drive position corresponding to the designated gear ratio. The control unit 27 provides the gearshift drive circuit 35 with a control signal to control the rotation direction of the gearshift actuator 33 and the driver power supplied through PWM control.

[0030] In the automatic gearshift mode (automatic gearshift control), the control unit 27 detects the load torque applied to the bit 21, which is attached to the rotation output unit 20, based on the value of the current flowing through the motor 16 and the gear ratio of the gearshift unit 17. Then, the control unit 27 drives the gearshift actuator 33 to switch to a gear ratio corresponding to the detected load torque. Further, the control unit 27 stops driving the motor 16 when detecting locking of the motor 16 based on at least one of the detected load torque and the detected rotation speed of the motor 16.

[0031] As illustrated in Figs. 2 and 3, the gearshift device 31 includes a generally tubular gearshift device case 40 and a gear mechanism 41, which is accommodated in the gearshift device case 40. The gear mechanism 41 of the present embodiment is, for example, a planetary gear mechanism including three gears. Fig. 3 illustrates only the ring gear RG of the gear mechanism 41.

[0032] The gear mechanism 41 includes a plurality of gears and the ring gear RG, which includes teeth that are engageable with the teeth of the plurality of gears. The ring gear RG is moved in the axial direction (sideward direction in Fig. 2) of the drive shaft 19 (refer to Fig. 1) to switch the gear mechanism 41 between two gear ratios.

[0033] As illustrated in Figs. 2 and 3, a pivot plate 42, which serves as a cam member, is located at the outer side of the ring gear RG. The ring gear RG is pivotal about the axis of the ring gear. The pivot plate 42 is semi-cylindrical (arcuate) and partially cut out in the circumferential direction. The pivot plate 42 includes a main body portion 43, which is semi-cylindrical and arranged along the outer surface of the ring gear RG, and an engagement portion 44, which projects toward the outer side in the radial direction (lower side in Figs. 2 and 3) from the main body portion 43.

[0034] Referring to Fig. 2, the gearshift actuator 33 is driven in the axial direction to move the ring gear RG in the axial direction and switch the gear ratio. The gearshift actuator 33 includes a gearshift motor 33a, a speed reduction unit 33b, and an output gear 33c. The gearshift motor 33a produces rotation in forward and reverse directions. The speed reduction unit 33b reduces the speed of the rotation, or drive force, produced by the gearshift motor 33a. The output gear 33c is rotated by the drive force transmitted from the speed reduction unit 33b.

[0035] Referring to Fig. 3, the output gear 33c is engaged with teeth 44a of the engagement portion 44. Thus, when the gearshift actuator 33 is rotated in forward and reverse directions, the engagement of the output gear 33c and the engagement portion 44 pivots the pivot plate 42 back and forth in a predetermined angular range. The gear switching unit 32 includes stoppers 45 that restrict the range in which the pivot plate 42 may be pivoted. In the present example, two stoppers are arranged at positions that allows for contact with the two end surfaces of the engagement portion 44 in the pivot direction. In Fig. 3, when the pivot plate 42 is pivoted in the clockwise direction, the left stopper 45, which contacts the left end surface of the engagement portion 44, prohibits further pivoting of the pivot plate 42. Under this situation, the ring gear RG is located at a first engagement portion (position illustrated by broken lines in Fig. 2). When the pivot plate 42 is pivoted in the counterclockwise direction, the right stopper 45, which contacts the right end surface of the engagement portion 44, prohibits further pivoting of the pivot plate 42. Under this situation, the ring gear RG is located at a second engagement portion (position illustrated by double-dashed lines in Fig. 2).

[0036] As long as the stoppers 45 are able to limit the pivotal range of the pivot plate, the location and mechanism of the stoppers 45 may be changed in any manner. For example, the stoppers may be arranged to contact the main body portion 43 of the pivot plate 42. In this case, the pivot plate 42 may include an insertion portion formed by a hole or a slit, and the stopper may be a rod inserted through the insertion portion. In this structure, contact of the stopper with the inner end surfaces of the insertion portion limits the range in which the pivot plate 42 may be pivoted. Further, stoppers may come into contact with a component pivoted together with the pivot plate 42 to limit the range in which the pivot plate 42 may be pivoted.

[0037] As illustrated in Figs. 2 and 3, two cam holes 46 are formed in the main body portion 43 near the two circumferential ends. As illustrated in Fig. 2, each cam hole 46 includes an operation hole 46a, which extends in a direction inclined to the circumferential direction of the pivot plate 42, and holding holes 46b, which are continuous with the two ends of the operation hole 46a and which substantially extend in the circumferential direction. Each holding hole 46b is an example of a reversing restriction portion in the first embodiment.

[0038] As illustrated in Fig. 3, the ring gear RG is accommodated in the gearshift device case 40 and movable in the axial direction. A groove RGa is formed in the outer surface of the ring gear RG extending in the circumferential direction. A support 47, which is formed by a metal wire rod, is fitted in the groove RGa. The support 47 includes an arcuate support portion 47a, which is arranged along the outer surface of the ring gear RG, and two projections 47b, which extend straight toward the outer side in the radial direction from the two ends of the support portion 47a. Two slide holes 40a extend through the gearshift device case 40 at locations partially overlapped with the two cam holes 46 of the pivot plate 42. The slide holes 40a extend in the axial direction of the gearshift device case 40 (refer to Figs. 5 and 6). Each projection 47b of the support 47 is inserted into the corresponding cam hole 46 of the pivot plate 42 through the corresponding slide hole 40a of the gearshift device case 40. The slide holes 40a are, for example, elongated holes or slits extending in the axial direction.

[0039] In Fig. 2, the gearshift actuator 33 pivots the pivot plate 42 of the gear switching unit 32 to move the ring gear RG in the axial direction. Further, the gearshift actuator 33 shifts the gear engaged with the ring gear RG to switch the gear ratio of the gear mechanism 41. The gearshift actuator 33 includes a position detector 33d, which detects from the rotation amount of the output gear 33c that the ring gear RG has been moved to the proper target position. The control unit 27 drives the gearshift actuator 33 based on the detection signal from the position detector 33d until the ring gear RG reaches the target position. The control unit 27 stops driving the gearshift actuator 33 when the ring gear RG reaches the target position. In this case, the control unit 27 may stop driving the gearshift actuator slightly before the ring gear RG reaches the target position taking into consideration inertial rotation after cutting the supply of power to the gearshift actuator 33.

[0040] In the present embodiment, the ring gear RG is engaged with the high (H) gear (high-speed gear) when located at the first engagement position illustrated by the broken lines. This sets the gearshift unit 17 in the high speed/low torque mode (hereinafter, simply referred to as the high-speed mode). When the ring gear RG moves toward the front from the first engagement position, the ring gear RG is disengaged from the H gear. Further, the ring gear RG is engaged with the low (L) gear (low-speed gear) when located at the second engagement position illustrated by the double-dashed lines. This sets the gearshift unit 17 in the low speed/high torque mode (hereinafter, simply referred to as the low-speed mode).

[0041] The structure of the gear mechanism 41 will now be described with reference to Figs. 4A to 4C.

[0042] As illustrated in Fig. 4A, the gear mechanism 41, which is accommodated in the gearshift device case 40 of the gearshift device 31, is a planetary gear mechanism including a plurality of planetary gear trains, for example, three planetary gear trains 51 to 53. The first planetary gear train 51 includes a sun gear 54, planet gears 55, a carrier 56, and a ring gear 57. The sun gear 54 is located at an input side and driven by a motor 16. The planet gears 55 are arranged around the sun gear 54. The carrier 56 rotatably supports the planet gears 55, and the ring gear 57 is located at the outer side of the planet gears 55. The carrier 56 includes a central gear 58 and teeth extending toward the outer side in the radial direction. The central gear 58 functions as an input gear of the second planetary gear train 52.

[0043] The second planetary gear train 52 includes planet gears 59 arranged around the central gear 58, a carrier 60 rotatably supporting the planet gears 59, and a ring gear RG arranged at the outer side of the planet gears 59. The ring gear RG is movable in the axial direction. The carrier 60 includes a central gear 61. The third planetary gear train 53 includes planet gears 62 arranged around the central gear 61, a carrier 63 rotatably supporting the planet gears 62, and a ring gear 64 arranged at the outer side of the planet gears 62. The ring gear 64 is engaged with the planet gears 62. The carrier 63 rotates when the planet gears 62 revolve and includes an output shaft 65 rotated at a speed corresponding to the present gear ratio.

[0044] The ring gear 57 in the first planetary gear train 51 is fixed to the inner wall of the gearshift device case 40 so that the ring gear 57 does not rotate. The ring gear RG in the second planetary gear train 52 includes teeth extending inward in the radial direction from the inner circumferential surface and teeth extending outward in the radial direction from an output side end.

[0045] The gearshift device case 40 includes fixed teeth 66 projecting inward in the radial direction from the inner wall surface of the gearshift device case 40. The ring gear RG moves between a position where the ring gear RG engages with the teeth of the carrier 56 and the teeth of the planet gears 59 and a position where the ring gear RG engages with the teeth of the planet gears 59 and the fixed teeth 66. In the present example, the carrier 56, the planet gears 59, and fixed teeth 66 form gears engaged with and disengaged from the ring gear RG.

[0046] When the ring gear RG is engaged with the carrier 56 and the planet gears 59 as illustrated in Fig. 4A, the power tool 10 is set in the high speed/low torque mode (non-speed reduction mode). When the ring gear RG is engaged with the planet gears 59 and the fixed teeth 66 as illustrated in Fig. 4C, the power tool 10 is set in the low speed/high torque mode (sped reduction mode).

[0047] The ring gear 64 arranged at the outer side of the planet gears 62 is fixed to the gearshift device case 40. As illustrated in Fig. 4A, the planet gears 55 are arranged between and engaged with the sun gear 54 and the ring gear 57. The planet gears 59 are arranged between and engaged with the central gear 58 and the ring gear RG. The planet gears 62 are arranged between and engaged with the central gear 61 and the ring gear 64.

[0048] The two projections 47b of the support 47, which is received in the groove RGa of the ring gear RG, extend through the two slide holes 40a (refer to Fig. 5) of the gearshift device case 40 and project out of the gearshift device case 40.

[0049] As the projections 47b of the support 47 move along the slide hole 40a in the axial direction, the ring gear RG rotates and moves in the axial direction.

[0050] As illustrated in Fig. 5, each cam hole 46 of the pivot plate 42 includes an operation hole 46a, which is inclined to the circumferential direction (pivot direction) of the pivot plate 42, and holding holes 46b, which are continuous with the two ends of the operation hole 46a and extend in the circumferential direction. Thus, in each cam hole 46, the two holding holes 46b define first and second terminal end regions. The pivot plate 42 is arranged on the gearshift device case 40 so that each cam hole 46 is partially overlapped with the corresponding slide hole 40a. The projection 47b extending through each slide hole 40a is inserted through the corresponding cam hole 46.

[0051] When the pivot plate 42 pivots along the outer surface of the gearshift device case 40, the projections 47b of the support 47 move along the operation holes 46a. This moves the projections 47b along the slide holes 40a in the axial direction. Further, referring to Figs. 2 and 4A to 4C, the ring gear RG follows the movement of the projections 47b in the axial direction.

[0052] Referring to Fig. 5, when the projection 47b is located at the first terminal end (L side in Fig. 5) of the corresponding cam hole 46, the ring gear RG is engaged with the planet gears 59 and the fixed teeth of the gearshift device case 40. This sets the low speed/high torque mode. When the projection 47b is located at the second terminal end (H side in Fig. 5) of the corresponding cam hole 46, the ring gear RG is engaged with the carrier 56 and the planet gears 59. This sets the high speed/low torque mode.

[0053] The structure of the reversing restriction portion in the first embodiment will now be described with reference to Figs. 5 and 6.

[0054] As illustrated in Fig. 5, each holding hole 46b of the cam hole 46 is inclined by a predetermined angle θ to the circumferential direction of the pivot plate 42. In the example illustrated in Fig. 5, each holding hole 46b is inclined in a direction opposite to the direction in which the operation hole 46a is inclined. More specifically, each holding hole 46b includes two inner wall surfaces (first and second inner wall surfaces) 46c opposed to each other in the widthwise direction (axial direction). Further, each inner wall surface 46c is inclined at the predetermined angle θ. For example, when switching the gearshift unit 17 to the low (L) gear, as the pivot plate 42 pivoted by inertia reaches the pivot limit position (hereinafter simply referred to as the limit position), each projection 47b hits the first terminal end (L side) of the corresponding cam hole 46. As a result, a pivot force acts on the pivot plate 42 in a reverse direction. When the pivot plate 42 is pivoted in the reverse direction, the projection 47b slides along the first inner wall surface 46c (left inner wall surface 46c as viewed in Fig. 5). As a result, the slide friction (slide resistance) between the projection 47b and the first inner wall surface 46c restricts pivoting of the pivot plate 42 in the reverse direction that would be caused by the retroaction after the projection 47b hits the first terminal end (L side) of the corresponding cam hole 46. In the same manner, when switching the gearshift unit 17 to the high (H) gear, pivoting of the pivot plate 42 in a reverse direction is caused by the retroaction after the pivot plate 42 reaches the limit position and the projection 47b hits the second terminal end (H side) of the corresponding cam hole 46. In this case, when the pivot plate 42 is pivoted in the reverse direction, the projection 47b slides along the first inner wall surface 46c (right inner wall surface 46c as viewed in Fig. 5). As a result, the sliding friction produced with the first inner wall surface 46c restricts pivoting of the pivot plate 42 in the reverse direction. In the example illustrated in Fig. 5, each holding hole 46b functions as the reversing restriction portion.

[0055] The holding hole 46b, which serves as the reversing restriction portion, is not limited to the structure illustrated in Fig. 5 and may have the structure illustrated in Fig. 6. In Fig. 6, each holding hole 46b is inclined in the same direction as the direction in which the operation hole 46a is inclined. More specifically, each holding hole 46b includes first and second inner wall surfaces 46d inclined at a predetermined angle θ relative to the circumferential direction of the pivot plate 42. In this structure, when switching the gearshift unit 17 to the L gear, pivoting of the pivot plate 42 in a reverse direction is caused by the retroaction after the pivot plate 42 reaches the limit position and the projection 47b hits the first terminal end (L side) of the corresponding cam hole 46. In this case, when the pivot plate 42 is pivoted in the reverse direction, the projection 47b slides along the first inner wall surface 46d (right inner wall surface 46d as viewed in Fig. 6). As a result, the slide friction produced with the first inner wall surface 46d restricts pivoting of the pivot plate 42 in the reverse direction. In the same manner, when switching the gearshift unit 17 to the H gear, pivoting of the pivot plate 42 in a reverse direction is caused by the retroaction after the pivot plate 42 reaches the limit position and the projection 47b hits the second terminal end (H side) of the corresponding cam hole 46. In this case, when the pivot plate 42 is pivoted in the reverse direction, the projection 47b slides along the first inner wall surface 46d (left inner wall surface 46d as viewed in Fig. 6). As a result, the sliding friction produced with the first inner wall surface 46d restricts pivoting of the pivot plate 42 in the reverse direction.

[0056] The predetermined angle θ is set to increase the sliding resistance between the first inner wall surface 46c or 46d of the holding hole 46b and the projection 47b when the pivot plate 42 acts to move in the reverse direction due to the retroaction after the pivot plate 42 is pivoted by inertia to the limit position and the projection 47b hits the terminal end. The sliding resistance restricts pivoting of the pivot plate 42. As a result, the projection 47b is held closer to the terminal end of the holding hole 46b than the operation hole 46a.

[0057] In one example, the predetermined angle θ is preferably one degree or greater and thirty degrees or less. More particularly, the predetermined angle θ is three degrees or greater and fifteen degrees or less. When the predetermined angle θ is less than one degree, due to the gap corresponding to the difference between the width of the holding hole 46b and the diameter of the projection 47b, the projection 47b may move without substantially sliding along the inner wall surface 46c or 46d of the holding hole 46b. Even when the projection 47b slides along the inner wall surface 46c or 46d of the holding hole 46b, the sliding resistance would be small and a sufficient braking force would not be obtained. When the predetermined angle θ is three degrees or less, although it is within a tolerable range, sufficient sliding resistance is not obtained. Thus, movement of the projection 47b from the terminal end of the holding hole 46b to the operation hole 46a may not be sufficiently restricted. When the predetermined angle θ is three degrees or greater, sufficient sliding resistance is easily obtained. This holds the projection 47b proximal to the terminal end of the holding hole 46b.

[0058] To obtain sufficient sliding resistance, it is desirable that the predetermined angle θ be set so that the deviation in the axial direction between the two longitudinal ends of each holding hole 46b is greater than the gap corresponding to the difference between the width of the holding hole 46b and the diameter of the projection 47b. In the present example, the predetermined angle θ that obtains the necessary sliding resistance is set taking into consideration such a gap that is in accordance with tolerable values set when designing the electric power tool 10.

[0059] When the predetermined angle θ is greater than thirty degrees, the sliding resistance produced by the projection 47b and the first inner wall surface 46c or 46d of the holding hole 46b becomes excessive when the pivot plate 42 is pivoted. As a result, the drive load on the gearshift motor 33a increases and smooth shifting of gears becomes difficult in the gearshift unit 17. When the predetermined angle θ is thirty degrees or less, gears may be shifted in a relatively smooth manner while reducing sliding resistance so that it does not become excessive. In particular, when the predetermined angle θ is fifteen degrees or less, sufficient sliding resistance is obtained, and gears may be shifted in a relatively smooth manner.

[0060] When taking into consideration reversed pivoting of the pivot plate 42 resulting from vibrations produced when operating the electric power tool 10, the length of the holding hole 46b is preferably set to be, for example, two times or greater than the diameter of the projection 47b. In this case, when the predetermined angle θ is set to be greater than fifteen degrees, displacement of the projection 47b in the holding hole 46b caused by deviation of the pivot plate 42 may displace the ring gear RG in the axial direction. To reduce such axial displacement of the ring gear RG, it is preferable that the predetermined angle θ be set to fifteen degrees or less. The predetermined angle θ is not limited to fifteen degrees or less and may be any angle as long as the effects described above may be obtained.

[0061] The operation of the power tool 10 described above will bow be described.

[0062] When the trigger lever 23 is operated, the rotation output unit 20 and the bit 21, which is attached to the rotation output unit 20, are rotated. This allows for the bit 21 to perform a task. For example, if the bit 21 is a driver, a screw may be tightened with the driver. If the bit 21 is a drill, a bore may be drilled.

[0063] When the trigger lever 23 is operated, the gearshift unit 17 reduces the speed of the rotation produced by the motor 16. The power transmission mechanism 18 transmits the rotational power of the motor 16 at the speed reduced by the gearshift unit 17 to the rotation output unit 20. As a result, the bit 21 rotates in a forward direction or a reverse direction in accordance with the operation of the forward/reverse switch 25.

[0064] To shift gears of the electric power tool 10, a user operates the gearshift switch 26. For example, to drive the electric power tool 10 in the low speed mode, the user moves the gearshift switch 26 to the low speed position. As a result, the gearshift switch 26 provides the control unit 27 with a low speed selection signal. To drive the electric power tool 10 in the high speed mode, the user moves the gearshift switch 26 to the high speed position. As a result, the gearshift switch 26 provides the control unit 27 with a high speed selection signal.

[0065] When the control unit 27 detects a switching operation of the gearshift switch 26, the control unit 27 drives the gearshift actuator 33 and pivots the pivot plate 42 to slide the ring gear RG. For example, when the control unit 27 receives a low speed selection signal, the control unit 27 drives the gearshift motor 33a to produce forward rotation. This switches the gearshift unit 17 from the H gear to the L gear. Further, when the control unit 27 receives a high speed selection signal, the control unit 27 drives the gearshift motor 33a to produce reverse rotation. This switches the gearshift unit 17 from the L gear to the H gear. When the gearshift motor 33a is being driven and the control unit 27 detects with the position detector 33d that the output gear 33c has been rotated by a predetermined rotation angle thereby reaching a target position, the control unit 27 stops driving the gearshift motor 33a.

[0066] When the gearshift motor 33a does not have a braking function (function stopping the motor with a regenerated diode or the like immediately after the power supply is cut), inertial rotation continues after the power supply is cut. The inertial rotation of the gearshift motor 33a also pivots the pivot plate 42 with inertia. Due to the inertial pivoting, the pivot plate 42 may hit the stopper 45, and the projection 47b may hit the terminal end of the corresponding holding hole 46b. The retroaction after the pivot plate 42 reaches the limit position may produce a pivoting force that acts on the pivot plate 42 in the reverse direction. For example, the force that returns the pivot plate 42 to its original shape after being momentarily deformed when the projection 47b hits the terminal end acts as a pivoting force on the pivot plate 42 in the reverse direction.

[0067] However, as illustrated in Fig. 5 or 6, the holding holes 46b are inclined by the predetermined angle θ relative to the circumferential direction (i.e., pivoting direction) of the pivot plate 42. Thus, when the pivot plate 42 acts to pivot in the reverse direction, the projection 47b slides on the first inner wall surface 46c or 46d while applying a relatively strong force. This produces a sliding resistance that acts as a braking force functioning to restrict pivoting of the pivot plate 42 in the reverse direction. Further, the predetermined angle θ is set as a value that keeps the projection 47b within a tolerable range so that the projection 47b does not return to near the operation hole 46a. As a result, pivoting of the pivot plate 42 in the reverse direction is restricted, and the pivot plate 42 is not greatly displaced from the target position. That is, the projection 47b stops at a position within the tolerable range and is held in the proximity of the terminal end in the holding hole 46b.

[0068] Figs. 7A and 7B illustrate comparative examples when the holding hole of the cam hole extends in the circumferential direction (i.e., predetermined angle θ = 0). As illustrated in Fig. 7A, a cam hole 71 formed in the pivot plate 70 includes an operation hole 71a, which extends in a direction inclined to the axial direction and the circumferential direction, and holding holes 71b, which extend in the circumferential direction of the pivot plate 70 (i.e., predetermined angle θ = 0).

[0069] In the same manner as described above, when switching gear ratios (e.g., when switching to the L gear), the gearshift motor 33a continues to produce rotation due to inertial even after the power supply is cut. The retroaction after the projection 47b hits the terminal end of the corresponding holding hole 71 b as the pivot plate 42 reaches the limit position produces a pivoting force that acts on the pivot plate 70 in the reverse direction. Here, the holding hole 71b of the pivot plate 70 extends in the circumferential direction. This pivots the pivot plate 70 in the reverse direction without receiving a large sliding resistance from the projection 47b of the support 47. Consequently, for example, as illustrated in Fig. 7B, the projection 47b moves close to the operation hole 71a in the holding hole 71b. In this case, even a slight pivoting movement of the pivot plate 70 caused by vibration during operation of the electric power tool 10 may move the projection 47b to the operation hole 71a and thereby permit axial movement of the support 47. Under this situation, the vibration produced during operation of the electric power tool 10 may easily move the projection 47b in the operation hole 71a. This may move the ring gear RG and cause unexpected switching of the gear ratio.

[0070] In this regards, the pivot plate 42 of the first embodiment includes the cam hole 46. When the projection 47b hits the terminal end of the corresponding cam hole 46, the retroaction acts to pivot the pivot plate 42 in the reverse direction. However, the pivot plate 42 receives a braking force that is produced by the sliding resistance of the projection 47b and the first inner wall surface 46c or 46d. Thus, even if the pivot plate 42 pivots in the reverse direction, the pivot amount (returning amount) in the reverse direction would be minimized. Consequently, the projection 47b is arranged near the terminal end of the holding hole 46b in the cam hole 46. Thus, even if the pivot plate 42 is pivoted due to vibration when the electric power tool 10 is being operated, the projection 47b remains held in the holding hole 46b. This restricts axial movement of the support 47. As a result, the ring gear RG does not move in the axial direction, and unexpected switching of the gear ratio is limited. Moreover, when the pivot plate 42 is pivoted by inertia after the power supply to the gearshift actuator 33 is cut, the projection 47b slides on the second inner wall surface 46c or 46d of the holding hole 46b. For example, in Fig. 5, when switching the gearshift unit 17 to the L gear, the projection 47b slides on the second inner wall surface 46c (right inner wall surface 46c in Fig. 5). The sliding friction (sliding resistance) between the second inner wall surface 46c and the projection 47b reduces the pivoting speed of the pivot plate 42. Such speed reduction effect of the pivot plate 42 also helps to hold the projection 47b at the proximity of the terminal end of the holding hole 46b. Although not described here, the same applies when switching to the H gear in Fig. 5 and in the structure of Fig. 6.

[0071] If the trigger switch 22 is operated when the gearshift switch 26 is located at the AUTO position, the control unit 27 drives the gearshift actuator 33 in accordance with the detected value of the operation load (load torque). This automatically switches the gear ratio of the gearshift unit 17 in accordance with the operation load. In this case, the projection 47b of the support 47 is also held in the tolerable range at a location proximal to the terminal end of the holding hole 46b.

[0072] The first embodiment has the advantages described below.

(1) The pivot plate 42 is pivoted by inertia after cutting the supply of power to the gearshift actuator 33. Each holding hole 46b of the cam hole 46 functions as a reversing restriction portion that restricts pivoting of the pivot plate 42 in the reverse direction that would be caused by the retroaction when the pivot plate 42 hits the projection 47b of the support 47 at the limit position. Each holding hole 46b extends to be inclined at a predetermined angle θ relative to the circumferential direction of the pivot plate 42. Thus, when the projection 47b slides on (engages with) the first inner wall surface 46c or 46d of the holding hole 46b, braking force (sliding resistance) that restricts pivoting of the pivot plate 42 in the reverse direction is applied to the pivot plate 42. As a result, the pivoting amount of the pivot plate 42 in the reverse direction is small, and the pivoting of the pivot plate 42 in the reverse direction may be restricted without a brake circuit. This allows for the pivot plate 42 to be stopped at the target position in the tolerable range. Thus, even when the pivot plate 42 is pivoted in the reverse direction by the vibration produced when the electric power tool 10 is operating, the projection 47b is held in the holding hole 46b.
This limits unexpected switching of the gear ratio.

(2) The reversing restriction portion is formed by the holding hole 46b that is inclined by the predetermined angle θ relative to the circumferential direction of the pivot plate 42. Accordingly, the reversing restriction portion may be formed relatively easily just by changing the shape of the cam hole 46 in the pivot plate 42.

(3) The predetermined angle θ is in the range of one to thirty degrees and allows for the generation of a sufficient sliding resistance. Thus, the application of excessive load to the gearshift motor 33a that would be caused by an excessive sliding resistance is limited, and gear ratios are smoothly switched. In particular, when the predetermined angle θ is set to the range of three to fifteen degrees, a further sufficient braking force produced by the sliding resistance is applied to the pivot plate 42. This further smoothly switches the gear ratio.

[Second Embodiment]

[0073] A second embodiment will now be described with reference to Figs. 8 and 9. In the second embodiment, the shape of the terminal regions in the cam hole is changed. To avoid redundancy, like or same reference numerals are given to those components that are the same as the corresponding components of the first embodiment. Such components will not be described. The description will focus on components that differ from the first embodiment.

[0074] As illustrated in Fig. 8, the cam hole 46 of the second embodiment includes an operation hole 46a similar to that of the first embodiment. The cam hole 46 further includes two holding holes 46b and two extended holes 46e. Each holding hole 46b is an example of a first hole portion, and each extended hole 46e is an example of a second hole portion. The holding holes 46b are continuous with the two ends of the operation hole 46a and extend in the circumferential direction of the pivot plate 42. Each extended hole 46e is continuous with the terminal end of the corresponding holding hole 46b and extends in a direction intersecting the circumferential direction of the pivot plate 42 (longitudinal direction of holding hole 46b). The terminal end of each holding hole 46b includes an inclined surface 46f. When the projection 47b of the support 47 hits the terminal end (inclined surface 46f), the inclined surface 46f applies a reaction force to the projection 47b in a direction intersecting the longitudinal direction of the holding hole 46b. In the example of Fig. 8, the inclined surface 46f produces a reaction force that moves the projection 47b, which hits the inclined surface 46f, to the extended hole 46e. In other words, the extended hole 46e extends in a direction in which the projection 47b receives a reaction force from the terminal end (inclined surface 46f) of the holding hole 46b.

[0075] Each extended hole 46e includes a guide surface 46g at a location opposing the inclined surface 46f. The guide surface 46g guides the projection 47b from the extended hole 46e to the holding hole 46b when the pivot plate 42 starts to pivot to switch the gear ratio.

[0076] The operation of the gearshift unit 17 in the second embodiment will now be described.

[0077] When switching the gear ratio, the gearshift motor 33a continues to produce rotation due to inertia even after power supply is cut. This pivots the pivot plate 42 due to inertia. As a result, the projection 47b hits the inclined surface 46f, which is located at the terminal end of the holding hole 46b in the pivot plate 42. In this case, the projection 47b receives a reaction force from the inclined surface 46f in a direction intersecting the longitudinal direction of the holding hole 46b (direction of large arrow in Fig. 9). This moves the projection 47b to the extended hole 46e and holds the projection 47b in the extended hole 46e, as illustrated by the double-dashed line in Fig. 9.

[0078] Further, the pivot plate 42 receives a reaction force in a direction intersecting the pivoting direction (left direction as viewed in Figs. 8 and 9) when the projection 47b hits the inclined surface 46f. The reaction force reduces the force that pivots the pivot plate 42 in the reverse direction. This lowers the pivoting speed of the pivot plate 42 in the reverse direction when the projection 47b moves in the extended hole 46e. As a result, the projection 47b is held in the extended hole 46e.

[0079] Since the projection 47b is held in the extended hole 46e, pivoting of the pivot plate 42 in the reverse direction is restricted, and the projection 47b is held at the terminal end of the holding hole 46b. Further, since the projection 47b is held in the extended hole 46e, pivoting of the pivot plate 42 is restricted even when, for example, the electric power tool 10 vibrates during operation. This limits unexpected switching of the gear ratio.

[0080] The second embodiment has the advantages described below.

(4) The reversing restriction unit includes the inclined surface 46f formed at the terminal end of the holding hole 46b. The inclined surface 46f hits the inclined surface 46f and applies reaction force to the projection 47b in a direction intersecting the longitudinal direction of the holding hole 46b. This decreases the pivoting force of the pivot plate 42 in the reverse direction and restricts reversed pivoting of the pivot plate 42.

(5) The reversing restriction portion further includes the extended hole 46e. The extended hole 46e extends in the direction in which the projection 47b receives reaction force from the terminal end (inclined surface 46f) of the holding hole 46b. Thus, the projection 47b that contacts the inclined surface 46f may be held in the extended hole 46e, and pivoting of the pivot plate 42 in the reverse direction may be limited.

(6) The cam hole 46 includes the guide surface 46g that guides the projection 47b from the extended hole 46e to the holding hole 46b when the pivot plate 42 starts to pivot to switch the gear ratio. Thus, the pivoting of the pivot plate 42 and the switching of the gear ratio may be smoothly performed.

[0081] It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms.

[0082] In the first embodiment, the second inner wall surface 46c of the holding hole 46b may be extended parallel to the circumferential direction. In this structure, when the pivot plate 42 is pivoted in the reverse direction, the sliding resistance (braking force) between the projection 47b and the first inner wall surface 46c is applied to the pivot plate 42. Alternatively, the second inner wall surface 46c may be formed to include a non-inclined portion, which is parallel to the circumferential direction, and an inclined portion, which is inclined at a predetermined angle θ. In this structure, the projection 47b moves along the non-inclined portion of the second inner wall surface 46c until the power supply to the gearshift actuator 33 is cut. Further, the projection 47b moves along the inclined portion of the second inner wall surface 46c after the power supply is cut. This decreases the load on the gearshift actuator 33 when the gearshift actuator 33 is driven and applies a braking force produced by a sliding resistance to the pivot plate 42 that is pivoted by inertia.

[0083] In the first embodiment, the first inner wall surfaces 46c and 46d are straight (flat) as illustrated in Figs. 5 and 6. Instead, the first inner wall surfaces 46c and 46d may be curved. Even when the inner wall surface of the holding hole 46b is curved, a sliding resistance may be applied to the pivot plate 42 between the projection 47b and the inner wall surface. In this case, it is preferable that a curved surface be formed so that the predetermined angle θ (angle between a hypothetical line extending in the circumferential direction of the pivot plate 42 and a hypothetical line contacting the curved surface) increases as the terminal end of the holding hole 46b becomes closer. In this structure, the projection 47b is held further easily near the terminal end of the holding hole 46b.

[0084] In the second embodiment, the extended holes 46e (second hole portions) may be omitted. This is because the reaction force (force in a direction intersecting circumferential direction) acting on the projection that hits the inclined surface 46f decreases the pivoting amount of the pivot plate 42 in the reverse direction.

[0085] In the second embodiment, the extended holes 46e may extend from the holding hole 46b in the opposite direction. That is, the two extended holes 46e may extend toward each other in the axial direction (sideward direction in Fig. 8). This structure obtains the same advantages as the second embodiment.

[0086] In each of the above embodiments, the reversing restriction portion may restrict pivoting of a pivot member in the reverse direction by hooking the support. For example, a concave surface may be formed in the terminal end of the holding hole 46b. The concave surface has substantially the same radius of curvature as the outer surface of the projection 47b so as to allow for the projection 47b to be hooked. In this structure, when the pivot plate 42 reaches the limit position, the projection 47b is hooked to the terminal end (concave surface) of the holding hole 46b.

[0087] In each of the above embodiments, the structure of the portion that prohibits further pivoting of the pivot plate 42 at the limit position is not limited to the stopper 45 and the terminal end of the holding hole 46b. The structure of the restricting portion is not particularly limited as long as the pivoting of the pivot plate may be prohibited at the restriction position.

[0088] The pivot member is not limited to the pivot plate 42 that is formed by a plate. For example, the pivot member may be formed by a pivotal block having a curved surface extending along the outer surface of the gearshift device case 40.

[0089] The gear mechanism 41, which switches the gear ratio, is not limited to a planetary gear mechanism, and may be replaced by a different known gear mechanism. In this case, the movable member is not limited to a ring gear and may be replaced by any component that may be engaged with and disengaged from gears in a gear mechanism. Further, the movable member does not have to be movable in the axial direction and may be movable in the radial direction as long as the gear ratio may be switched.

[0090] The drive unit is not limited to an actuator that includes a motor. For example, as long as the drive unit outputs power for pivoting a pivot plate under the control of a control unit, the drive unit may be a motor, a motor-driven cylinder, a solenoid, or an electrostrictive actuator.

[0091] In each of the above embodiments, the gearshift unit 17 (gear mechanism 41) is operated in two speed modes, namely, the low speed/high torque mode and the high speed/low torque mode. However, the gearshift unit 17 may be operated in three or more speed modes, for example, four, five, or six speed modes. In this case, the pivot plate may include a plurality of cam holes as described in Japanese Laid-Open Patent Publication Nos. 2012-16760, 2012-30347, and 2009-56590. Further, the cam hole 46 of Fig. 5 or 6 or the cam hole 46 of Figs. 8 and 9 may be used as one of the cam holes.

[0092] In each of the above embodiments, the gear mechanism 41 is a speed reduction mechanism. Instead, the gear mechanism 41 may be a speed increasing mechanism or may combine a speed reduction mechanism and a speed increasing mechanism. The gear mechanism 41 may also include a constant speed mechanism.

[0093] The electric power tool may be a non-chargeable AC electric power tool.

[0094] The electric power tool is not limited to an electric drill driver. The present invention may be applied to any electric power tool that pivots a pivot member along an outer surface of a gearshift device case with the power of a drive unit such as a gearshift actuator to move a movable member of a gear mechanism that changes the speed of the power from the power source and moves the movable member to switch the gear ratio of the gear mechanism. For example, the electric power tool may be applied to a motor-driven impact driver, a hammer drill, an impact wrench, a radial arm saw, a jigsaw, a screw driver, a vibration driver, a grinder, and a nail gun.

[0095] The power tool is not limited to an electric power tool and may be a power tool powered by pneumatic pressure or hydraulic pressure. As long as a drive unit (e.g., actuator) switches the gear ratio of a gear mechanism, any known power source such as that of an electric type, a pneumatic type, or a hydraulic type may be used as a power source that outputs power for changing the speed of the gear mechanism.

Claims

1. A power tool (10) comprising:

a power source (16);

a rotation output unit (20) to which a bit (21) is attachable;

a gear mechanism (41) configured to transmit rotational power of the power source (16) to the rotation output unit (20);

a gearshift device case (40) configured to accommodate the gear mechanism (41); and

a housing (13) configured to accommodate the power source (16) and the gearshift device case (40), wherein:

the gear mechanism (41) includes gears (56, 59, 66) and a movable member (RG) movable in an axial direction of the gears (56, 59, 66) to be engaged with or disengaged from the gears (56, 59, 66);

the gear mechanism (41) is further configured to move the movable member (RG) to allow for switching between a plurality of gear ratios; and

the gearshift device case (40) includes a slide hole (40a) formed in the gearshift case (40) in the axial direction,

the power tool (10) being characterized by further comprising:

a pivot member (42) that is pivotal about the axial direction along an outer surface of the gearshift device case (40), wherein the pivot member (42) includes a cam hole (46) arranged at a location partially overlapped with the slide hole (40a), and the cam hole (46) includes an operation hole (46a) that extends in a direction inclined to a circumferential direction of the pivot member (42);

a support (47) arranged on the movable member (RG), wherein the support (47) projects from the movable member (RG) and extends through the slide hole (40a) and the cam hole (46);

a drive unit (33) configured to pivot the pivot member (42) along the outer surface of the gearshift device case (40); and

a reversing restriction portion (46b (46c/46d) or 46e-46f) arranged in the pivot member (42) and configured such that when the drive unit (33) pivots the pivot member (42) to switch the gear ratio, the reversing restriction portion (46b (46c/46d) or 46e-46f) engages with the support (47) to restrict pivoting of the pivot member (42) in a reverse direction that is caused by a reaction force which acts on the pivot member (42) at a limit position from where further pivoting of the pivot member (42) is prohibited.

2. The power tool (10) according to claim 1, being characterized in that:

the pivot member (42) is arranged to be pivoted in the cam hole (46) within a range including a first terminal end region (46b) and a second terminal end region (46b); and

the reversing restriction portion (46b (46c/46d)) is configured to increase sliding resistance of the support (47) and the pivot member (42) in the first and second terminal end regions (46b, 46b) to apply a braking force to the pivot member (42) and restrict pivoting of the pivot member (42) in the reverse direction.

3. The power tool (10) according to claim 1 or 2, being characterized in that the reversing restriction portion (46b (46c/46d)) includes holding holes (46b) that are continuous with two ends of the operation hole (46a) and extend in a direction inclined to the circumferential direction of the pivot member (42).

4. The power tool (10) according to claim 1, being characterized in that:

the pivot member (42) further includes first hole portions (46b) that are continuous with two ends of the operation hole (46a) and extend in the circumferential direction of the pivot member (42); and

the reversing restriction portion (46e-46f) includes an inclined surface (46f) located at a terminal end of each first hole portion (46b), wherein the inclined surface (46f) is configured to apply a reaction force to the support (47) in a direction intersecting a longitudinal direction of the first hole portion (46b) when the support (47) contacts the terminal end of the first hole portion (46b).

5. The power tool (10) according to claim 4, being characterized in that the reversing restriction portion (46e-46f) further includes a second hole portion (46e) continuous with the terminal end of each first hole portion (46b) and extending in a direction in which the support (47) receives the reaction force from the inclined surface (46f).

6. The power tool (10) according to claim 5, being characterized in that the pivot member (42) further includes a guide surface (46g) configured to guide the support (47) from the second hole portion (46e) to the first hole portion (46b) when the pivot member (42) starts to pivot from the second hole portion (46e).

Drawing