Power tool

Abstract

 A power tool (11) includes a transmission mechanism (17) capable of selecting one of a plurality of transmission gear ratios by changing a combination of gears of a gear train (30) to be meshed with each other, a transmission ratio switching operation unit (25; 26) capable of turning around the thrust shaft and operating to change the combination of the gears, a gear operation mechanism (63, 29a, 42c, 46b) to move a transmission gear (42; 46) of the gear train in a thrust shaft direction in accordance with turning motion of the transmission ratio switching operation unit, and a biasing mechanism (32, 65) to bias the gear operation mechanism in accordance with the turning motion of the transmission ratio switching operation unit such that the transmission gear moves in the thrust shaft direction and meshes with a meshed gear corresponding to the selected transmission gear ratio.

Description

[0001] The present invention relates to a power tool including a transmission mechanism for changing a rotation speed of a drive source and a transmission ratio switching operation unit for changing a transmission gear ratio of the transmission mechanism.

[0002] An electric power tool which is one example of the power tool includes a motor as a drive source, a transmission mechanism for changing a rotation speed of the motor, a drive shaft which rotates at a transmission gear ratio of the transmission mechanism, and a transmission ratio switching operation unit for changing the transmission gear ratio of the transmission mechanism. Japanese Utility Model Publication No. 3175818, Japanese Laid-Open Utility Model Publication Nos. 62-65175 and 5-80611, and Japanese Laid-Open Patent Publication No. 2009-125909 describe examples of such power tools. For example, in an electric power tool described in the Publication No. 3175818 (e.g., see claim 1, paragraphs [0008] and [0015] in specification, and Figs. 1 to 4 and 8 to 13), when a transmission paddle (transmission ratio switching operation unit) is turned around a thrust shaft, a transmission ratio switching ring is turned, an inclined cam formed on the transmission ratio switching ring moves a pushpin in a thrust shaft direction. When the pushpin pushes a coil spring, a biasing force of the coil spring is applied to a ring gear (transmission gear) in the thrust shaft direction. As a result, the ring gear moves in the thrust shaft direction, and a gear which meshes with the ring gear (hereinafter, meshed gear) is changed. This changes a transmission gear ratio of the transmission mechanism.

[0003] However, in the power tool described in the Publication No. 3175818, when the transmission paddle is turned around the thrust shaft, if crests (convex portions) of teeth of the ring gear (transmission gear) and the meshed gear match with each other in the circumferential direction, the ring gear cannot move in the thrust shaft direction due to contact between the crests. At this time, in order to turn the transmission paddle to a changing position (operation position), it is necessary that the inclined cam presses the pushpin while compressing the coil spring in a state where the crests of the teeth of the ring gear and the meshed gear contact against each other. Hence, operability of the transmission paddle is poor.

[0004] Further, when the transmission paddle is operated to the changing position, the inclined cam of the transmission ratio switching ring is changed and the pushpin moves in the thrust shaft direction to compress the coil spring. Therefore, the ring gear is relatively strongly biased in the thrust shaft direction, and the crests of the teeth of the ring gear and the meshed gear abut against each other relatively strongly. In this state, even if the motor is driven and the transmission mechanism starts rotating, there is fear that the ring gear and the meshed gear do not smoothly mesh with each other. That is, a transmission ratio may not smoothly be switched. Hence, it is desired to enhance the operability when the transmission ratio is switched, and to smoothly mesh the transmission gear and the meshed gear with each other. This is not a problem of the electric power tool only, but power tools including an air-pressure type tool which is driven by air pressure and a hydraulic type tool which is driven by hydraulic pressure also have the same problem.

[0005] It is an object of the present invention to provide a power tool capable of enhancing operability of a transmission ratio switching operation unit, and capable of smoothly meshing a transmission gear and a meshed gear with each other.

[0006] One embodiment of the invention is a power tool. The power tool includes a power source including an output shaft which rotates around a thrust shaft; and a transmission mechanism including a gear train for changing a rotation speed of the output shaft between a plurality of transmission gear ratios and capable of selecting one of the transmission gear ratios by changing a combination of gears of the gear train to be meshed with each other. The power tool further includes a transmission ratio switching operation unit capable of turning around the thrust shaft and capable of operating to change the combination of the gears of the gear train, a holding spring configured to hold an operation position of the transmission ratio switching operation unit, a gear operation mechanism configured to move a transmission gear of the gear train in a thrust shaft direction in accordance with turning motion of the transmission ratio switching operation unit, and a biasing mechanism configured to bias the gear operation mechanism in accordance with the turning motion of the transmission ratio switching operation unit such that the transmission gear moves in the thrust shaft direction and meshes with a meshed gear corresponding a selected one of the transmission gear ratios.

[0007] In the power tool, it is preferable that the biasing mechanism functions as a turning biasing mechanism configured to engage with the transmission ratio switching operation unit to generate a biasing force around the thrust shaft. In this structure, it is preferable that the turning biasing mechanism is configured to bias the gear operation mechanism in the thrust shaft direction by the biasing force acting around the thrust shaft to make the transmission gear mesh with the meshed gear.

[0008] In the power tool, it is preferable that the biasing mechanism functions as a thrust biasing mechanism configured to change turning motion of the transmission ratio switching operation unit around the thrust shaft into movement of the gear operation mechanism in the thrust shaft direction and to generate a biasing force in the thrust shaft direction. In this structure, it is preferable that the thrust biasing mechanism is configured to bias the gear operation mechanism in the thrust shaft direction by a biasing force in the thrust shaft direction to make the transmission gear mesh with the meshed gear.

[0009] In the power tool, it is preferable that the transmission gear is an internal gear. It is preferable that the thrust biasing mechanism includes a spring capable of resiliently being deformed around the thrust shaft by engaging with the transmission ratio switching operation unit, a transmission ratio switching member disposed on an outer peripheral side of the internal gear so that the transmission ratio switching member can engage with the transmission ratio switching operation unit through the spring, and a converting mechanism configured to convert turning motion of the transmission ratio switching member around the thrust shaft into movement of the gear operation mechanism in the thrust shaft direction.

[0010] In the power tool, it is preferable that the transmission gear is an internal gear. In this structure, it is preferable that the thrust biasing mechanism includes a moving member configured to engage with the transmission ratio switching operation unit, a converting unit configured to convert the turning motion of the transmission ratio switching operation unit around the thrust shaft into movement of the moving member in the thrust shaft direction, and a wire spring disposed on an outer peripheral side of the internal gear and having one end fixed to the moving member and the other end locked to an outer periphery of the internal gear.

[0011] According to the present invention, it is possible to smoothly change a meshing state between the transmission gear and the meshed gear without deteriorating the operability of the transmission ratio switching operation unit.

[0012] 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 partial side sectional view illustrating an electric power tool in a first embodiment;

Fig. 2 is a partial plan view illustrating peripheries of a transmission ratio switching operation unit in the electric power tool illustrated in Fig. 1;

Figs. 3A to 3D are schematic diagrams illustrating a corresponding relation between an operation position and a gear mode of the transmission ratio switching operation unit;

Fig. 4 is a side sectional view illustrating a transmission mechanism and a transmission ratio switching mechanism;

Fig. 5 is a side sectional view illustrating the transmission mechanism and the transmission ratio switching mechanism in a first speed mode;

Fig. 6 is a side sectional view illustrating the transmission mechanism and the transmission ratio switching mechanism in a third speed mode;

Fig. 7 is a side sectional view illustrating the transmission mechanism and the transmission ratio switching mechanism in a fourth speed mode;

Fig. 8 is a perspective view illustrating the transmission mechanism and the transmission ratio switching mechanism;

Fig. 9 is an exploded perspective view illustrating the transmission mechanism and the transmission ratio switching mechanism;

Fig. 10 is a front sectional view illustrating the transmission mechanism and the transmission ratio switching mechanism;

Fig. 11 is a side view illustrating the transmission mechanism and the transmission ratio switching mechanism;

Fig. 12 is a side view illustrating the transmission mechanism and the transmission ratio switching mechanism in a state where an operation position of an operation unit is different from that illustrated in Fig. 11;

Fig. 13 is a perspective view illustrating a transmission mechanism and a transmission ratio switching mechanism in a second embodiment;

Fig. 14 is a side view illustrating the transmission mechanism and the transmission ratio switching mechanism;

Fig. 15 is a plan view illustrating the transmission mechanism and the transmission ratio switching mechanism;

Fig. 16 is an exploded perspective view illustrating the transmission mechanism and the transmission ratio switching mechanism; and

Fig. 17 is a front sectional view illustrating the transmission mechanism and the transmission ratio switching mechanism.

(First Embodiment)

[0013] A first embodiment will now be described based on Figs. 1 to 12. Fig. 1 schematically illustrates an electric power tool 11 which is one example of a power tool.

[0014] As illustrated in Fig. 1, the electric power tool 11 of the first embodiment is a hand-hold type tool which can be grasped with one hand, and the electric power tool 11 can be used as a concrete electric driver. The electric power tool 11 includes a body housing 12 as an exterior. The body housing 12 includes a bottomed cylindrical barrel 13 (only left half thereof is illustrated in Fig. 1), and a handle 14 extending from the barrel 13 in one direction (downward in Fig. 1) which intersects with an axis of the barrel 13.

[0015] A motor 15 is accommodated in the barrel 13 at a position on the side of a base end of the barrel 13 (left side in Fig. 1). The motor 15 has a rotation axis which matches with an axis of the barrel 13, and includes an output shaft 16 projecting toward a tip end of the barrel 13 (right side in Fig. 1). The motor 15 is a brush motor or a brushless motor for example. A transmission mechanism 17 which changes a speed of rotation of the output shaft 16 of the motor 15 is disposed at a position adjacent to the output shaft 16 of the motor 15. The transmission mechanism 17 is a decelerating mechanism for example.

[0016] In the example illustrated in Fig. 1, the transmission mechanism 17 decelerates rotation of the motor 15, and transmits the decelerated rotation to a power transmitting mechanism 18. The power transmitting mechanism 18 is accommodated in the barrel 13 on the side of a tip end of the barrel 13 (right side in Fig. 1). The power transmitting mechanism 18 transmits rotation decelerated by the transmission mechanism 17 to a drive shaft 20 of a rotation output unit 19 provided on the side of the tip end of the barrel 13. The power transmitting mechanism 18 includes a power shutoff mechanism (torque limiter) which shuts off transmission of power to the drive shaft 20 when a load exceeding a set value is applied to the drive shaft 20, and a lock mechanism which locks the drive shaft 20 such that the drive shaft 20 cannot rotate in a state where the electric power tool 11 stops.

[0017] A tip end tool 21 is detachably attached to the drive shaft 20 (rotation shaft) projecting from a tip end of the rotation output unit 19. In this example, the drive shaft 20 includes a cylindrical tip end, and thread portions 20a are formed on an inner peripheral surface and an outer peripheral surface of the cylindrical tip end (only one of the thread portions 20a formed on the outer peripheral surface is illustrated in Fig. 1). The tip end tool 21 is threadedly engaged with any one of the thread portions 20a formed on the inner peripheral surface and the outer peripheral surface of the drive shaft 20. When the electric power tool 11 is driven, the tip end tool 21 rotates coaxially with the rotation output unit 19. A mounting unit provided on the drive shaft 20 for mounting the tip end tool 21 may be a chuck instead of the thread portion 20a.

[0018] As illustrated in Fig. 1, the handle 14 is provided with a trigger lever 22 (operation lever) which is operated by a user for driving the electric power tool 11. A trigger switch 23 is disposed in the handle 14 at a position corresponding to the trigger lever 22. The trigger switch 23 is for switching between ON and OFF of the motor 15 in accordance with operation of the trigger lever 22. The electric power tool 11 includes a switching lever 24 (forward/reverse instructing lever) which is operated by a user for switching between forward and reverse directions of rotation of the tip end tool 21, and a plurality of (two in this example) transmission ratio switching operation units 25 and 26 for switching between transmission gear ratios of the transmission mechanism 17.

[0019] As illustrated in Fig. 1, a battery pack attaching portion 27 including a substantially square box-shaped accommodation case is detachably attached to a lower end of the handle 14. A battery pack 28 which is a secondary battery is accommodated in the accommodation case of the battery pack attaching portion 27. The electric power tool 11 of this example operates using the battery pack 28 as a driving power source. That is, the motor 15 is driven by electric power supplied from the battery pack 28.

[0020] The electric power tool 11 decelerates a rotation speed of the output shaft 16 of the motor 15 by the transmission mechanism 17 at a deceleration ratio selected in accordance with operation positions of the two transmission ratio switching operation units 25 and 26, and the electric power tool 11 drives the drive shaft 20 at the decelerated rotation speed and with torque. The transmission mechanism 17 of the first embodiment includes a cylindrical gear case 29 and a four gear type transmission gear mechanism 30 (see Fig. 4) accommodated in the gear case 29. The transmission gear mechanism 30 selects one of four transmission gear ratios based on a combination of the operation positions of the two transmission ratio switching operation units 25 and 26. The transmission gear mechanism 30 is one example of a gear train.

[0021] As illustrated in Fig. 1, a control substrate C is disposed in the vicinity of a lower end in the handle 14. The control substrate C controls drive of the motor 15 and the like. The control substrate C is electrically connected to the motor 15 through the trigger switch 23 and a wiring 23a. A switch circuit (not illustrated) which switches a rotation direction of the tip end tool 21 in accordance with operation of the switching lever 24 is also electrically connected to the control substrate C. When a user pushes the trigger lever 22, the motor 15 is rotated and driven in a rotation direction in accordance with a position of the switching lever 24. When the user pushes the trigger lever 22, the transmission mechanism 17 decelerates a rotation speed of the motor 15 at a deceleration ratio in accordance with the combination of the operation positions of the transmission ratio switching operation units 25 and 26, and the transmission mechanism 17 rotates the drive shaft 20 at the decelerated rotation speed. The power transmitting mechanism 18 may be provided with such a hammer function that when a load applied to the drive shaft 20 exceeds a predetermined load, a hammer which receives a biasing force of a spring hits a base end of the drive shaft 20, thereby outputting high torque to the drive shaft 20.

[0022] As illustrated in Fig. 1, an outer peripheral side of the gear case 29 of the transmission mechanism 17 is provided with two transmission ratio switching mechanisms 31. When deceleration ratios of the transmission mechanism 17 are switched, each of the transmission ratio switching mechanisms 31 transmits an operation forces of the corresponding transmission ratio switching operation units (also simply called operation units, hereinafter) 25 and 26 to a corresponding transmission gear in the transmission gear mechanism 30 of the transmission mechanism 17. The transmission ratio switching mechanisms 31 connected to the operation units 25 and 26 include transmission ratio switching plates 32 which are one example of the transmission ratio switching member. Each of the transmission ratio switching plates 32 has a semi-ring plate-shape for example, and is disposed between the transmission mechanism 17 and corresponding one of the operation units 25 and 26. The transmission ratio switching plate 32 can reciprocate and turn within a predetermined angle range around the thrust shaft along an outer peripheral surface of the gear case 29 in tandem with the operation units 25 and 26. The transmission ratio switching mechanism 31 converts a turning operation force around the thrust shafts of the operation units 25 and 26 into a force in the thrust shaft direction, and transmits the converted force to a transmission gear in the transmission mechanism 17.

[0023] As illustrated in Fig. 2, the two operation units 25 and 26 are disposed adjacent to each other in a longitudinal direction (thrust shaft direction, and vertical direction in Fig. 2) of the barrel 13. The operation units 25 and 26 include knobs 25a and 26a (operation convex portions) respectively exposed from two rectangular openings 13a which open from upper surfaces (front surfaces in Fig. 2) of the body housing 12. The knobs 25a and 26a can be operated in a circumferential direction (lateral direction in Fig. 2) in the openings 13a, and can be switched between two operation positions in a lateral direction in Fig. 2.

[0024] The knob 25a of the operation unit 25 can be switched between "ON" and "OFF" which are two operation positions, and the knob 26a of the operation unit 26 can be switched between a "first gear" and a "second gear" which are two operation positions. The transmission gear ratio of the transmission mechanism 17 can be switched between four gears (i.e., four speeds) depending upon a combination of the operation positions of the two knobs 25a and 26a.

[0025] For example, as illustrated in Fig. 3A, in a state where the knob 25a is at an "OFF" position and the knob 26a is at a "first gear" position, a first speed mode (first gear) is selected. As illustrated in Fig. 3B, in a state where the knob 25a is at the "OFF" position and the knob 26a is at a "second gear" position, a second speed mode (second gear) is selected. As illustrated in Fig. 3C, in a state where the knob 25a is at an "ON" position and the knob 26a is at the "first gear" position, a third speed mode (third gear) is selected. As illustrated in Fig. 3D, in a state where the knob 25a is at the "ON" position and the knob 26a is at the "second gear" position, a fourth speed mode (fourth gear) is selected. The first speed mode and the second speed mode correspond to high torque low speed rotation, and the third speed mode and the fourth speed mode correspond to low toque high speed rotation.

[0026] Next, the transmission mechanism 17 and the transmission ratio switching mechanism 31 will now be described with reference to Fig. 4. First, the structure of the transmission mechanism 17 will now be described.

[0027] As illustrated in Fig. 4, the transmission gear mechanism 30 accommodated in the transmission mechanism 17 includes four planet gear mechanisms 33 to 36. The first planet gear mechanism 33 includes a sun gear 41 which can integrally rotate with the output shaft 16 of the motor 15, a ring gear 42 (outer gear) which is one example of an internal gear, a plurality of (three in this example) planet gears 43, and a carrier 44 which holds the planet gears 43. The second planet gear mechanism 34 includes a sun gear 45 which can integrally rotate with the sun gear 41, a ring gear 42 which can move in the thrust shaft direction, a ring gear 46 (outer gear) which is one example of the internal gear, a plurality of (three in this example) planet gears 47, and a carrier 48 which holds the planet gears 47. The third planet gear mechanism 35 includes a plurality of sun gears 49 which are integrally provided on the carrier 48, a ring gear 46, a plurality of (six in this example) planet gears 50, and a carrier 51 which holds the planet gears 50. The fourth planet gear mechanism 36 includes a sun gear 52 which is integrally provided on the carrier 51, a ring gear 53, a ring gear 54, a plurality of (six in this example) planet gears 55, and a carrier 56 which holds the planet gears 55.

[0028] As illustrated in Fig. 4, output of the carrier 56 is transmitted to the drive shaft 20 through an interlocking pin 57 projecting from the carrier 56, a lock plate 58 disposed on an outer periphery of the drive shaft 20, and a lock member (not illustrated) located between the lock plate 58 and the interlocking pin 57. When the motor 15 stops, the interlocking pin 57, the lock plate 58, the lock member and a lock ring 59 fix the drive shaft 20 to the gear case 29. Normally, the ring gears 53 and 54 of the fourth planet gear mechanism 36 cannot rotate, but when fastening torque exceeds set torque, the ring gears 53 and 54 start rotating to cut transmission of power to the drive shaft 20. The ring gears 53 and 54 configure torque limiters which limit the fastening torque.

[0029] The ring gear 42 of the first planet gear mechanism 33 cannot rotate around its axis and can move in its axial direction. Teeth 42a which can mesh with the planet gear 43 (see Fig. 8) of the first planet gear mechanism 33 are formed on an inner peripheral surface of on a rear side in an axial direction (left side in Fig. 4) of the ring gear 42. Teeth 42b which can mesh with the planet gear 47 of the second planet gear mechanism 34 are formed on the inner peripheral surface of on a front side in the axial direction (right side in Fig. 4) of the ring gear 42.

[0030] The ring gear 46 of the second planet gear mechanism 34 can rotate around its axis and can move in its axial direction. When the ring gear 46 moves rearward (left side in Fig. 4) in the axial direction, teeth 46a formed on an inner peripheral surface of the ring gear 46 can mesh with teeth on an outer periphery of the carrier 48 of the second planet gear mechanism 34. When the ring gear 46 moves forward (right side in Fig. 4) in the axial direction, the teeth 46a can mesh with the planet gears 50 of the third planet gear mechanism 35.

[0031] Next, speed changing operation of the transmission mechanism 17 will now be described using Figs. 4 to 7. According to the transmission mechanism 17, one of the four speed modes, i.e., one of the first speed mode, the second speed mode, the third speed mode and the fourth speed mode is selected based on a combination of four positions of the ring gears 42 and 46 which move between two positions in the thrust shaft direction in the four gear type transmission gear mechanism 30.

[0032] As illustrated in Fig. 5, in the first speed mode, the ring gear 42 is located on a front side (right side in Fig. 5) in the axial direction and meshes with the planet gear 47, and the ring gear 46 is located on a front side (right side in Fig. 5) in the axial direction and meshes with the planet gear 50. In this state, the second and third planet gear mechanisms 34 and 35 carry out decelerating operations. Therefore, in the first speed mode, the drive shaft 20 is rotated and driven at a low speed with high torque.

[0033] As illustrated in Fig. 4, in the second speed mode, in a state where the ring gear 46 is held at a position in the first speed mode (front position in the axial direction (right position in Fig. 4)), the ring gear 42 moves rearward (leftward in Fig. 4) and is located on the rear side in the axial direction, and meshes with the planet gear 43 as illustrated in Fig. 8. In this state, only the third planet gear mechanism 35 carries out decelerating operation. In the second speed mode, the drive shaft 20 is rotated and driven at a low speed with high torque.

[0034] As illustrated in Fig. 6, in the third speed mode, the ring gear 42 is located on the front side (right side in Fig. 6) in the axial direction and meshes with the planet gear 47, and the ring gear 46 is located on the rear side (left side in Fig. 6) in the axial direction and meshes with the carrier 48. In this state, only the second planet gear mechanism 34 carries out decelerating operation. Therefore, the drive shaft 20 is rotated and driven at a high speed with low torque in the third speed mode.

[0035] As illustrated in Fig. 7, in the fourth speed mode, in a state where the ring gear 46 is held at a position in the third speed mode (rear side in the axial direction (left side in Fig. 7)), the ring gear 42 moves rearward (leftward in Fig. 7) and meshes with the planet gear 43 as illustrated in Fig. 8. In this state, a carrier 44 of the first planet gear mechanism 33 and a carrier 51 of the third planet gear mechanism 35 are directly connected to each other. Hence, in the fourth speed mode, the drive shaft 20 is rotated and driven at a high speed with low torque. The structure of the transmission gear mechanism 30 for switching between the deceleration ratios is not limited to this example, and the transmission gear mechanism 30 may be changed to other known gear mechanism.

[0036] Next, the structure of the transmission ratio switching mechanism 31 will now be described using Figs. 8 to 11. Since structures of the two transmission ratio switching mechanisms 31 are substantially the same, the structure of one of the transmission ratio switching mechanisms 31 which corresponds to the operation unit 25 will now be described below.

[0037] As illustrated in Fig. 8, the transmission ratio switching plate 32 of the transmission ratio switching mechanism 31 engages with a back surface of the operation unit 25 (26), and can slide in a circumferential direction (around thrust shaft) along an outer peripheral surface of the gear case 29. Two guide holes 32a are formed in both ends of the transmission ratio switching plate 32 in the longitudinal direction (circumferential direction). Fig. 8 illustrates only the guide hole 32a on the side of one end. Each of the guide holes 32a extends around the thrust shaft, and has a path extending in the thrust shaft direction and in a direction inclining with respect to a direction around the thrust shaft. Ends 63a of switching spring 63 projecting outward from the gear case 29 are engaged into the guide holes 32a. In reality, both the ends 63a of the switching spring 63 project from the gear case 29, Fig. 8 illustrates only one of the ends 63a. A click spring 62 for holding the operation position of the operation unit 25 (26) is interposed between the operation unit 25 (26) and the gear case 29. The click spring 62 is a leaf spring for example. In the first embodiment, the click spring 62 is one example of a hold spring which holds the operation position of the operation unit 25 (26).

[0038] Fig. 9 is an exploded perspective view partially illustrating the transmission mechanism 17 and the transmission ratio switching mechanism 31 illustrated in Fig. 8. In Fig. 9, the gear case 29 is illustrated by phantom lines so that the transmission gear mechanism 30 in the transmission mechanism 17 can be seen. Fig. 10 is a front sectional view illustrating the transmission mechanism 17 and the transmission ratio switching mechanism 31 taken along a position of the ring gear 42. As illustrated in Figs. 9 and 10, annular circumferential grooves 42c and 46b are formed in the circumferential direction in outer peripheral surfaces of the ring gears 42 and 46. The switching springs 63 are accommodated in the circumferential grooves 42c and 46b. The switching spring 63 is a semi-annular wire spring for example. Both the ends 63a of the switching springs 63 project from the circumferential grooves 42c and 46b outward in a radial direction of the ring gears 42 and 46.

[0039] As illustrated in Figs. 10 and 11, both the ends 63a of the switching spring 63 project outward through openings 29a of the gear case 29, and are engaged into the guide holes 32a of the transmission ratio switching plate 32. A plurality of convex portions 42d projecting radially outward from an outer peripheral surface of the ring gear 42 in a substantially radial form are engaged with a plurality of guide grooves 29b formed in an inner peripheral surface of the gear case 29 and extending in parallel to the axial direction. Therefore, the ring gear 42 cannot move around the thrust shaft and can move in the thrust shaft direction.

[0040] As illustrated in Fig. 11, the openings 29a of the gear case 29 are provided at positions corresponding to both the ends 63a of the switching spring 63, and have lengths slightly longer than movable distances of the ring gears 42 and 46 in a direction parallel to the axial direction. Both the ends 63a of the switching spring 63 are guided in the thrust shaft direction along the opening 29a so that the ring gears 42 and 46 move in the thrust shaft direction together with the switching spring 63.

[0041] As illustrated in Fig. 9, a square frame-shaped accommodating portion 64 is provided at circumferentially central portion of the outer peripheral surface of the transmission ratio switching plate 32. A coil spring 65 which is one example of a resilient body is accommodated in the accommodating portion 64. The coil spring 65 has an axial direction which is in parallel to a tangential direction with respect to a circumferential direction of the transmission ratio switching plate 32, and the coil spring 65 resiliently deforms in the tangential direction. A pair of openings 64a is formed in the accommodating portion 64 at positions corresponding to axially both ends of the coil spring 65. The openings 64a are formed as notches for example. A pair of plate portions 25b is formed on a back surface of the operation unit 25. Each of the plate portions 25b has such a thickness that the plate portion 25b can be inserted into the opening 64a, and the plate portion 25b extends in an operation direction (circumferential direction). The pair of plate portions 25b is opposed to each other at a predetermined distance in the circumferential direction, and the plate portions 25b are located on both ends of the coil spring 65 in the axial direction through the openings 64a in a state where the operation unit 25 is mounted on the transmission ratio switching plates 32. Similarly, a pair of plate portions 26b which is opposed to each other at a predetermined distance in the circumferential direction is formed on a back surface of the operation unit 26. The pair of plate portions 26b is located on axially both ends of the coil springs 65 through the openings 64a in a state where the operation unit 26 is mounted on the transmission ratio switching plate 32.

[0042] Hence, as illustrated in Fig. 10, when the operation unit 25 (26) is turned toward one side, one of the pair of plate portions 25b (26b) enters the opening 64a and pushes one end of the coil spring 65. According to this, the coil spring 65 is compressed. An operation force (turning force) of the operation unit 25 (26) is transmitted to the transmission ratio switching plate 32 through the coil spring 65 and the accommodating portion 64. At this time, even if the teeth 42a and 42b of the ring gear 42 and the teeth 46a of the ring gear 46 contact against teeth of a gear (meshed gear) to be meshed and the operation unit 25 (26) cannot move in the thrust shaft direction, since the coil spring 65 is resiliently compressed, and the operation unit 25 (26) can smoothly be operated to a desired operation position.

[0043] As illustrated in Fig. 9, the click spring 62 is fixed to an upper portion of an outer peripheral surface of the gear case 29 at a position adjacent to the transmission ratio switching plate 32 in the axial direction. The click spring 62 is provided at its longitudinally central portion with a lock convex portion 62a. A pair of lock concave portions 25c is formed in a back surface of the operation unit 25 in the vicinity of its longitudinally (circumferentially) central portion. The pair of lock concave portions 25c is disposed at a predetermined distance in the circumferential direction. Similarly, a pair of lock concave portions 26c is formed in a back surface of the operation unit 26. Therefore, when the operation unit 25 (26) moves toward one side and one of the pair of lock concave portions 25c (26c) is locked to the corresponding lock convex portion 62a, the operation unit 25 (26) is held at one of the operation positions. When the operation unit 25 (26) moves toward the other side and the other one of the pair of lock concave portions 25c (26c) is locked to the corresponding lock convex portion 62a, the operation unit 25 (26) is held at the other operation position.

[0044] In Figs. 9 and 10, when the ring gears 42 and 46 and the meshed gears are not completely meshed with each other due to contact between the teeth, the coil spring 65 disposed between the transmission ratio switching plate 32 and the operation unit 25 (26) utilizes inclination of the guide holes 32a of the transmission ratio switching plate 32 and biases the ring gears 42 and 46 in the thrust shaft direction. According to this, when a force for rotating the output shaft 16 around the thrust shaft is generated, the ring gears 42 and 46 can be made smoothly mesh with the meshed gears to appropriately change a speed.

[0045] Even when the teeth and the teeth do not smoothly mesh with each other through the transmission ratio switching plate 32 and the switching spring 63, contact resistance of the teeth and the teeth is absorbed by the coil spring 65. Therefore, by providing the coil spring 65, it is possible to easily change a speed without deteriorating the operability of the operation units 25 and 26.

[0046] Next, the structure of each of the transmission ratio switching mechanisms 31 for switching between deceleration ratios of the transmission mechanism 17 in accordance with operations of the operation units 25 and 26 will now be described. Since structures of the two transmission ratio switching mechanisms 31 are substantially the same, the structure of one of the transmission ratio switching mechanisms 31 which corresponds to the operation unit 25 will now be described below.

[0047] As illustrated in Fig. 9, each of the transmission ratio switching mechanisms 31 includes the click spring 62 for locking and holding the operation unit 25 (26) at the operation position, the coil spring 65 which resiliently deforms in accordance with a turning amount when the operation unit 25 (26) is operated to the operation position, and the semi-ring plate-shaped transmission ratio switching plate 32 which engages with the operation unit 25 (26) through the coil spring 65.

[0048] As illustrated in Fig. 9, the transmission ratio switching mechanism 31 includes the semi-annular switching spring 63 which engages with portions of the outer peripheral surfaces of the ring gears 42 and 46 and which can transmit a force in the thrust shaft direction to the ring gears 42 and 46. Both the ends 63a of the switching spring 63 project outward from the openings 29a of right and left both sides (only one side is illustrated in Fig. 9) of the gear case 29, and the ends 63a of the switching spring 63 are engaged into the pair of guide holes 32a formed in longitudinally both the ends of the transmission ratio switching plate 32. As illustrated in Fig. 11, each of the guide holes 32a extends around the thrust shaft, and has a path extending in the thrust shaft direction and in a direction inclining with respect to a direction around the thrust shaft.

[0049] The guide holes 32a function as cams, the ends 63a of the switching spring 63 engaged into the guide holes 32a function as cam followers. When the operation unit 25 is turned from one of the operation positions illustrated in Fig. 11 to the other operation position illustrated in Fig. 12 for example, the transmission ratio switching plate 32 is turned around the thrust shaft. According to this, the ends 63a of the switching spring 63 are guided along the corresponding guide holes 32a, and the turning motion of the transmission ratio switching plate 32 around the thrust shaft is converted into movement of the switching spring 63 in the thrust shaft direction. A moving force of the switching spring 63 in the thrust shaft direction is transmitted to the ring gears 42 and 46. According to this, the ring gears 42 and 46 move in the thrust shaft direction. In the first embodiment, the pair of guide holes 32a and both the ends 63a of the switching spring 63 configures a converting mechanism. The transmission ratio switching plate 32 and the coil spring 65 configure a biasing mechanism. The biasing mechanism is one example of a turning biasing mechanism and one example of a thrust biasing mechanism. The switching spring 63, the openings 29a, and the circumferential grooves 42c and 46b configure a gear operation mechanism.

[0050] Next, the operation of the electric power tool 11 having the above-described structure will now be described.

[0051] When the trigger lever 22 is operated, the electric power tool 11 is driven, the drive shaft 20 rotates, and the tip end tool 21 attached to the drive shaft 20 rotates. According to this, it is possible to carry out operation suitable for the tip end tool 21. When the tip end tool 21 is a driver bit for example, it is possible to fasten a concrete screw by a driver. When the tip end tool 21 is a drill bit for example, it is possible to form a hole in a concrete by a drill.

[0052] When the trigger lever 22 is operated, a rotation speed of the output shaft 16 of the motor 15 is changed (decelerated) through the transmission mechanism 17, and the speed-changed rotation is transmitted to the rotation output unit 19 through the power transmitting mechanism 18. As a result, the tip end tool 21 attached to the drive shaft 20 rotates in accordance with a transmission gear ratio of the transmission mechanism 17. At this time, the tip end tool 21 rotates normally or reversely in accordance with a selected position of the switching lever 24.

[0053] When a speed of the electric power tool 11 is to be changed, at least one of the two operation units 25 and 26 is operated. In the electric power tool 11 of the first embodiment, When an operation position of at least one of the knobs 25a and 26a of the operation units 25 and 26 is switched, one of the four speed modes is selected based on a combination of operation positions of the knobs 25a and 26a.

[0054] For example, transmission ratio switching operation is carried out when the electric power tool 11 (motor 15) is stopped. When the motor 15 is stopped, since the drive shaft 20 does not rotate, a crest of a tooth of the ring gear 42 or 46 matches, in some cases, with a crest of a tooth of the meshed gear which is to be meshed with the ring gear 42 or 46. In this case, it is not possible to move the ring gear 42 or 46 in the thrust shaft direction any more. In the first embodiment, when the operation unit 25 (26) is operated, one of the pair of plate portions 25b (26b) pushes one end of the coil spring 65 as illustrated in Fig. 10. At this time, since the ring gear 42 or 46 cannot move any more, the coil spring 65 is compressed and deformed in accordance with a turning amount of the operation unit 25 or 26 in a state where the transmission ratio switching plate 32 cannot move around the thrust shaft. Hence, the transmission ratio switching plate 32 is biased around-the thrust shaft by the compressed and deformed coil spring 65. That is, the ring gear 42 or 46 is biased in the thrust shaft direction by the guide holes 32a and the switching spring 63 whose ends 63a are engaged into the guide holes 32a.

[0055] When the operation unit 25 (26) is turned to the operation position, the lock convex portion 62a of the click spring 62 is locked to the lock concave portion 25c (or 26c), and the operation unit 25 (26) is held at that operation position. Hence, a state where the transmission ratio switching plate 32 is biased around the thrust shaft is held by the compressed and deformed coil spring 65, and a state where the ring gear 42 or 46 is biased in the thrust shaft direction is held by the switching spring 63.

[0056] Thereafter, when the trigger lever 22 is operated, the motor 15 is driven and the output shaft 16 rotates. Therefore, a rotating force is generated in the transmission mechanism 17. When the rotating force is generated in the transmission mechanism 17, a state where the tooth (crest) of the ring gear 42 or 46 is in abutment against the tooth (crest) of the meshed gear in the thrust shaft direction is released, and the crest of the ring gear 42 or 46 matches with a valley (concave portion) of the meshed gear. At this time, the ring gear 42 or 46 is biased in the thrust shaft direction by the compressed and deformed coil spring 65. Hence, the ring gear 42 or 46 smoothly moves in the thrust shaft direction and meshes with the meshed gear. Also when the crests of the two gears (ring gear and meshed gear) which are meshed with each other are in abutment against each other in the thrust shaft direction as described above, the two gears smoothly mesh with each other by the biasing force of the compressed and deformed coil spring 65.

[0057] The first embodiment has the following advantages.

(1) The operation position of the operation unit 25, 26 is held by the click spring 62. When the operation unit 25, 26, is operated, the coil spring 65 is compressed, and the transmission ratio switching plate 32 is biased around the thrust shaft by the compressed coil spring 65. That is, the transmission ratio switching plate 32 is resiliently biased in the circumferential direction. The biasing force of the coil spring 65 holds a state where a tooth (crest) of the ring gear 42, 46 abuts against a tooth (crest) of the meshed gear in the thrust shaft direction. Thereafter, when the trigger switch 23 is operated and the motor 15 is driven, a rotating force is generated in the transmission mechanism 17. When the rotating force is generated, the ring gear 42, 46 is moved in the thrust shaft direction by the biasing force. As a result, the teeth of the ring gear 42, 46 smoothly mesh with the teeth of the meshed gear. In this manner, the speed changing operation of the transmission mechanism 17 can smoothly be carried out. It is also possible to enhance the operability when a speed of the operation unit 25, 26 is changed.

(2) The coil spring 65 is disposed such that its axial direction is parallel to a tangential direction around the thrust shaft. Therefore, the operation units 25 and 26 can be operated to desired operation positions while engaging the operation units 25 and 26 with the corresponding coil springs 65 and compressing the coil springs 65.

(3) The converting mechanism which converts movement of the operation unit 25, 26 around the thrust shaft into movement of ring gear 42, 46 in the thrust shaft direction is employed. The converting mechanism includes the guide holes 32a each including the path which is formed in the transmission ratio switching plate 32, which extends around the thrust shaft and which is inclined in the thrust shaft direction and around the thrust shaft. The converting mechanism also includes both the ends 63a of the switching spring 63 which are accommodated in the circumferential grooves 42c, 46b in the outer peripheral surface of the ring gear 42, 46, and which are engaged into the guide holes 32a. According to this structure, it is possible to smoothly change a speed of the electric power tool 11. In the electric power tool described in the Publication No. 3175818 for example, when a ring block is turned, an inclined cam which contacts against a pushpin is switched, and a relatively strong biasing force is applied from a spring to a transmission internal gear in the thrust shaft direction. In this case, an abutting pressure between a crest of the transmission internal gear and a crest of a meshed gear becomes excessively strong. This makes smooth meshing between the transmission internal gear and the meshed gear difficult. In the first embodiment, on the other hand, in a state where a crest of the tooth 42b of the ring gear 42, 46 contacts against a crest of a tooth of the meshed gear in the thrust shaft direction, even if the operation unit 25, 26 is operated to the operation position, the ends 63a of the switching spring 63 are held at a movement-starting position or a movement-halfway position in the inclined path of the guide hole 32a. Hence, the ring gear 42, 46 can be biased in the thrust shaft direction in a state where a crest of a tooth 42a, 42b, 46a of the ring gear 42, 46 is in abutment against a crest of the corresponding meshed gear with appropriate resiliency.

(4) The coil spring 65 which is one example of the biasing mechanism engages with the operation unit 25 (26) and biases the transmission ratio switching plate 32 around the thrust shaft. Therefore, the coil spring 65 functions as the turning biasing mechanism. A biasing force of the transmission ratio switching plate 32 in a direction around the thrust shaft applied by the coil spring 65 moves the switching spring 63 which is one example of the gear operation mechanism in the thrust shaft direction through engagement with the guide hole 32a, and biases the ring gear 42, 46 in a meshing direction with respect to the meshed gear. Hence, it is possible to enhance the operability of the operation unit 25, 26 when a speed is changed, and to smoothly change a speed.

(5) The transmission ratio switching mechanism 31 and the coil spring 65 also function as the thrust biasing mechanisms. The transmission ratio switching plate 32 which is engaged with the operation unit 25 (26) through the coil spring 65 converts a turning force of the operation unit 25 (26) around the thrust shaft into a biasing force of the switching spring 63 in the thrust shaft direction through engagement between the guide hole 32a as a cam and the switching spring 63 as a cam follower. Hence, when a rotating force is generated in the transmission mechanism 17, the ring gear 42, 46 can smoothly mesh with the meshed gear by the biasing force of the switching spring 63 in the thrust shaft direction.

(6) The thrust biasing mechanism includes the coil spring 65, and the transmission ratio switching plate 32 which engages with the operation unit 25 (26) through the coil spring 65 and which is disposed on the side of the outer periphery of the ring gear 42, 46. The thrust biasing mechanism also includes the converting mechanism (guide hole 32a and both ends 63a) which converts turning motion of the transmission ratio switching plate 32 into movement of the switching spring 63 in the thrust shaft direction. Since the transmission ratio switching plate 32 is disposed on the side of the outer periphery of the ring gear 42, 46, even if the ring gear 42, 46 is provided as a transmission gear, it is not so difficult to layout the thrust biasing mechanism. Further, the converting mechanism which converts turning motion of the transmission ratio switching plate 32 around the thrust shaft into movement of the switching spring 63 in the thrust shaft direction is composed of the guide hole 32a and both the ends 63a of the switching spring 63. Therefore, the structure of the converting mechanism is simple.

(7) The transmission gear mechanism 30 which realizes the four speed modes is employed. The transmission gear mechanism 30 includes the two operation units 25 and 26 which can be switched between the two different operation positions, and the two transmission ratio switching mechanisms 31 respectively provided corresponding to the operation units 25 and 26. According to this structure, even if the operation units 25 and 26 are operated to any one of the operation positions, it is possible to smoothly change a speed.

(Second Embodiment)

[0058] A second embodiment will now be described using Figs. 13 to 17. In the second embodiment, the structure of the transmission ratio switching mechanism 31 of the first embodiment is changed. The same symbols are allocated to the same constituent members as those of the first embodiment, and description thereof will not be repeated. In Figs. 13, 16 and 17, only ring gears 42 and 46 which are moved when a speed is changed are illustrated as a transmission gear mechanism 30, and other gear group is omitted.

[0059] As illustrated in Figs. 13 and 14, transmission ratio switching mechanisms 71 of the second embodiment are provided between operation units 25 and 26 and a transmission mechanism 17, an operation force of each of the operation units 25 and 26 around a thrust shaft is transmitted to a transmission gear mechanism 30 (see Fig. 4) in the transmission mechanism 17 as a force in the thrust shaft direction, thereby making the transmission mechanism 17 change a speed.

[0060] Each of the transmission ratio switching mechanisms 71 includes a switching spring 72 including a semi-annular wire spring. The switching spring 72 is provided between the operation units 25 and 26 and the transmission mechanism 17 illustrated in Fig. 13. The switching spring 72 extends in a circumferential direction along an outer peripheral surface of a gear case 29. As illustrated in Figs. 13 and 14, the switching spring 72 engages with back surfaces of the operation units 25 and 26. Both ends 72a of each of the switching springs 72 in the longitudinal direction are inserted into openings 29a from the gear case 29. As illustrated in Figs. 14 and 17, both the ends 72a of the switching spring 72 inserted into the openings 29a are engaged into circumferential grooves 42c and 46b concavely formed in outer peripheral surfaces of the ring gears 42 and 46.

[0061] As illustrated in Fig. 16, a rectangular parallelepiped guide member 73 extending in the circumferential direction is fixed to an upper portion of each of the switching springs 72. Each of the guide members 73 includes an opposed surface (upper surface in Fig. 16) which is opposed to the operation units 25 and 26, and a columnar convex portion 73a projects from the opposed surface. Guide grooves 25d are formed on the back surfaces of the operation units 25 and 26 which are opposed to the convex portion 73a. The guide groove 25d includes a groove path which is inclined with respect to both the thrust shaft direction and a direction around the thrust shaft. When the operation units 25 and 26 are mounted on an upper portion of the gear case 29, convex portions 73a of the guide member 73 are engaged into guide grooves 25d and 26d. In this state, when any one of a pair of lock concave portions 25c of the operation unit 25 is locked to a lock convex portion 62a of a corresponding click spring 62, the operation positions of the operation unit 25 are held. Similarly, when any one of a pair of lock concave portions 26c of the operation unit 26 is locked to another lock convex portion 62a of another click spring 62, the operation positions of the operation unit 26 are held.

[0062] As illustrated in Fig. 14, an outer peripheral surface of the gear case 29 is provided with guide rails 74 for guiding guide members 73 in the thrust shaft direction (lateral direction in Fig. 14). The guide members 73 can reciprocate within a predetermined range in the thrust shaft direction along the guide rails 74.

[0063] As illustrated in Fig. 15, the guide grooves 25d and 26d formed in the back surfaces of the operation units 25 and 26 are inclined with respect to both the thrust shaft direction and the direction around the thrust shaft as described above. When the operation units 25 and 26 are operated in the circumferential direction, the guide grooves 25d and 26d guide movements of the convex portions 73a of the guide members 73 to move the guide members 73 in the thrust shaft direction. Therefore, each of the transmission ratio switching mechanisms 71 converts an operation force (turning force) of the operation unit 25, 26 around the thrust shaft into a force of the switching spring 72 in the thrust shaft direction through movement of the convex portion 73a of the guide member 73 along the guide groove 25d, 26d. When the switching spring 72 moves in the thrust shaft direction, the ring gear 42, 46 also moves in the thrust shaft direction together with the switching spring 72.

[0064] In the second embodiment, the guide member 73 is one example of a moving member. The convex portion 73a of the guide member 73 functions as a cam, and the guide groove 25d, 26d functions as a cam follower. The convex portion 73a of the guide member 73 and the guide groove 25d, 26d configure a converting unit. The guide groove 25d, 26d, the guide member 73, and the switching spring 72 configure a biasing mechanism. This biasing mechanism also functions as a thrust biasing mechanism. The guide grooves 29b, the guide rail 74, the openings 29a and the circumferential groove 42c, 46b configure a gear operation mechanism.

[0065] Next, the operation of the electric power tool 11 will now be described.

[0066] When the knob 25a (26a) of the operation unit 25 (26) is moved around the thrust shaft and operated to a desired operation position, the convex portion 73a of the guide member 73 is guided along the inclined path of the guide groove 25d (26d). According to this, the guide member 73 moves in the thrust shaft direction. At this time, when a crest of a tooth 42a, 42b, 46a of the ring gear 42, 46 is in abutment against a crest of a tooth of the meshed gear which is to be meshed for changing a speed in the thrust shaft direction, the ring gear 42, 46 cannot move in the thrust shaft direction. In this case, in a state illustrated in Fig. 14 for example, positions of both the ends 72a of the switching spring 72 engaged into the circumferential groove 42c or 46b of the ring gear 42 or 46 are substantially maintained and while keeping this state, an upper end of the switching spring 72 fixed to the guide member 73 moves in the thrust shaft direction (lateral direction in Fig. 14). Therefore, in Fig. 14 which is a side view, the switching spring 72 deforms such that it inclines and extends. By the deformation of the switching spring 72, the ring gear 42 or 46 is biased in a direction in which the guide member 73 moved. That is, since the upper end of the switching spring 72 moves in the thrust shaft direction, the ring gear 42 or 46 is biased in the thrust shaft direction by resiliency of the switching spring 72.

[0067] When the operation unit 25 or 26 is operated to the operation position, the lock convex portion 62a of the click spring 62 is locked to the lock concave portion 25c or 26c. According to this, the operation position of the operation unit 25 or 26 is maintained. Hence, a state where the transmission ratio switching plate 32 is biased around the thrust shaft by the compressed and deformed coil spring 65 and the ring gear 42 or 46 is biased in the thrust shaft direction is maintained.

[0068] After the operation unit 25, 26 is operated to an operation position of a desired speed mode, when the trigger lever 22 is pushed in, the motor 15 starts to be driven. The output shaft 16 of the motor 15 rotates and a rotating force is generated in the transmission mechanism 17. When the rotating force is generated in the transmission mechanism 17, a state where the tooth (crest) of the ring gear 42 or 46 is in abutment against the tooth (crest) of the meshed gear in the thrust shaft direction is released, and the crest of the ring gear 42 or 46 matches with a valley of the meshed gear. At this time, the ring gear 42 or 46 is biased in the thrust shaft direction by the resiliently deformed switching spring 72. Hence, the ring gear 42 or 46 smoothly moves in the thrust shaft direction and meshes with the meshed gear. Also when the crests of the two gears (ring gear and meshed gear) which are meshed with each other are in abutment against each other in the thrust shaft direction as described above, the two gears smoothly mesh with each other by the biasing force of the compressed and deformed coil spring 65. According to this, a speed changing operation of the transmission mechanism 17 is excellently carried out.

[0069] Also when teeth are not smoothly meshed with each other through the switching spring 72 and the operation units 25 and 26, contact resistance between the teeth is absorbed by resiliency of the switching spring 72. Hence, it is possible to easily change a speed without deteriorating the operability of the operation unit 25, 26.

[0070] In addition to the advantages of the first embodiment, the second embodiment exerts the following advantages.

(8) The ring gear 42, 46 moves in the thrust shaft direction utilizing resiliency of the switching spring 72 which is the wire spring. Hence, the transmission ratio switching plate 32 of the first embodiment is unnecessary. Therefore, it is possible to reduce the number of parts, and the structure of the transmission ratio switching mechanism 31 can relatively be simplified.

(9) The guide groove 25d, 26d is formed in the back surface of the operation unit 25, 26. The guide groove 25d, 26d engages with the convex portion 73a of the guide member 73 to which the switching spring 72 is fixed, and guides movement of the guide member 73 in the thrust shaft direction. The convex portion 73a and the guide groove 25d, 26d function as the converting units. The converting unit converts turning motion of the operation unit 25, 26 around the thrust shaft into movement of the guide member 73 in the thrust shaft direction. According to this, the switching spring 72 can give a biasing force in the thrust shaft direction to the ring gear 42, 46.

[0071] It should be apparent to those skilled in the art that the above embodiment may be embodied in many other specific forms without departing from the scope of the present invention. Particularly, it should be understood that the above embodiment may be embodied in the following forms.

[0072] In the first embodiment, a guide notch may be formed in the transmission ratio switching plate 32 instead of the guide hole 32a of the transmission ratio switching plate 32. Alternatively, a guide cam surface may be formed on longitudinally both end surfaces of the transmission ratio switching plate 32. With the notch or the cam surface also, it is possible to guide both the ends 63a of the switching spring 63 in the thrust shaft direction in accordance with the operation of the operation unit 25, 26.

[0073] In the first embodiment, it is possible to use a relatively thick metal or synthetic resin wire material having high rigidity instead of the switching spring 63.

[0074] In the first embodiment, a columnar projection fixed to the ring gear 42, 46 may be engaged into the guide hole instead of the switching spring 63. A known fixing method such as an integrally forming method and a threadedly engaging method may be used as a fixing method between the projection and the ring gear 42, 46.

[0075] The shape of the transmission ratio switching member is not limited to the semi-ring plate shape like the transmission ratio switching plate 32, and the shape thereof may appropriately be changed. For example, a reversed U-shaped block member may be used.

[0076] The transmission mechanism is not limited to the decelerating mechanism. The transmission mechanism may be an accelerating mechanism or may be able to both decelerate and accelerate.

[0077] Although the transmission gear mechanism 30 can switch between the four speed modes in the embodiments, the transmission gear mechanism 30 may switch between two speed modes (low torque high speed rotation and high torque low speed rotation), or between three or five or more speed modes.

[0078] One of the two transmission ratio switching operation units 25 and 26 provided on the electric power tool having the four speed modes may be of a turning-operation type which can turn around the thrust shaft, and the other transmission ratio switching operation unit may be of a conventional slide-operation type which can slide in the thrust shaft direction. When other multi-stage transmission mode is employed also, at least one of a plurality of transmission ratio switching operation units 25, 26 may employ the turning-operation type.

[0079] Although the electric power tool is rechargeable, the above embodiments may be applied to a non-rechargeable AC electric power tool.

[0080] The embodiments are not limited to a concrete electric driver, and may likewise be applied to other electric power tools using a motor as a drive source. For example, the embodiments can be applied to an electric impact driver, a hammer drill, an impact wrench, a circular saw, a jigsaw, a screw driver, a vibration driver, a grinder, a box nailing machine and the like. In this case, the electric power tool is not limited for concrete, and material to be treated by the electric power tool may be wood, plastic, metal or ceramic.

[0081] The power tool is not limited to the electric power tool, and the power tool may be driven by air pressure as a power source. The power tool may be driven by hydraulic pressure as the power source. That is, the power tool may be driven by power obtained by a known method such as electricity, air pressure and hydraulic pressure.

[0082] The present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.

Claims

1. A power tool (11) comprising:

a power source (15) including an output shaft (16) which rotates around a thrust shaft; and

a transmission mechanism (17) including a gear train (30) for changing a rotation speed of the output shaft (16) between a plurality of transmission gear ratios and capable of selecting one of the transmission gear ratios by changing a combination of gears of the gear train (30) to be meshed with each other, wherein

the power tool (11) is characterized by further comprising:

a transmission ratio switching operation unit (25; 26) capable of turning around the thrust shaft and operating to change the combination of the gears of the gear train (30),

a holding spring (62) configured to hold an operation position of the transmission ratio switching operation unit (25; 26),

a gear operation mechanism (63, 29a, 42c, 46b) configured to move a transmission gear (42; 46) of the gear train (30) in a thrust shaft direction in accordance with turning motion of the transmission ratio switching operation unit (25; 26), and

a biasing mechanism (32, 65) configured to bias the gear operation mechanism (63, 29a, 42c, 46b) in accordance with the turning motion of the transmission ratio switching operation unit (25; 26) such that the transmission gear (42; 46) moves in the thrust shaft direction and meshes with a meshed gear corresponding to a selected one of the transmission gear ratios.

2. The power tool (11) according to claim 1, wherein the biasing mechanism (32, 65) functions as a turning biasing mechanism configured to engage with the transmission ratio switching operation unit (25; 26) to generate a biasing force around the thrust shaft, and the turning biasing mechanism (32, 65) is configured to bias the gear operation mechanism (63, 29a, 42c, 46b) in the thrust shaft direction by the biasing force acting around the thrust shaft to make the transmission gear (42; 46) mesh with the meshed gear.

3. The power tool (11) according to claim 2, wherein the biasing mechanism (32, 65) further functions as a thrust biasing mechanism configured to change the turning motion of the transmission ratio switching operation unit (25; 26) around the thrust shaft into movement of the gear operation mechanism (63, 29a, 42c, 46b) in the thrust shaft direction, and the thrust biasing mechanism (32, 65) is configured to generate a biasing force in the thrust shaft direction and bias the gear operation mechanism (63, 29a, 42c, 46b) in the thrust shaft direction by the biasing force in the thrust shaft direction to make the transmission gear (42; 46) mesh with the meshed gear.

4. The power tool (11) according to claim 3, wherein
the transmission gear (42; 46) is an internal gear, and
the thrust biasing mechanism (32, 65) includes
a spring (65) capable of resiliently being deformed around the thrust shaft by engaging with the transmission ratio switching operation unit (25; 26),
a transmission ratio switching member (32) disposed on an outer peripheral side of the internal gear (42; 46) so that the transmission ratio switching member (32) can engage with the transmission ratio switching operation unit (25; 26) through the spring (65), and
a converting mechanism (32a, 63a) configured to convert turning motion of the transmission ratio switching member (32) around the thrust shaft into movement of the gear operation mechanism (63, 29a, 42c, 46b) in the thrust shaft direction.

5. The power tool (11) according to claim 3, wherein
the transmission gear (42; 46) is an internal gear,
the thrust biasing mechanism (25d, 26d, 72, 73) includes
a moving member (73) configured to engage with the transmission ratio switching operation unit (25; 26),
a converting unit (73a, 25d, 26d) configured to convert the turning motion of the transmission ratio switching operation unit (25; 26) around the thrust shaft into movement of the moving member (73) in the thrust shaft direction, and
a wire spring (72) disposed on an outer peripheral side of the internal gear (42; 46) and having one end fixed to the moving member (73) and the other end locked to an outer periphery of the internal gear (42; 46).

Drawing