Power tools

Abstract

To suppress heat generation at the time of braking to prevent deterioration of brake characteristic and product life cycle.SOLUTION: A grinder 1 comprises: a switch 7 which performs ON / OFF action in accompany with operation of a switch lever 8 in a body housing 2; an output shaft 17 which rotates at the time of ON action of the switch 7; and a brake mechanism 75 which brakes the output shaft 17 at the OFF state of the switch 7, and releases the braking of the output shaft 17 in conjunction with operation of the switch lever 8 performing the ON action of the switch 7. A circular braking drum 40 is fixed to the output shaft 17, and the brake mechanism 75 uniformly presses the braking drum 40 at two portions from a radial direction outer side to the center to brake the output shaft 17.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a power tool, such as a grinder, that rotates a tool bit. [Background technology]

[0002] Power tools such as grinders that rotate a tool bit such as a disc-shaped grinding wheel to perform work are provided with a brake mechanism to quickly stop the inertial rotation of the tool bit when work is finished. As exemplified in Patent Document 1, this brake mechanism brakes the output shaft by pressing a brake plate provided at the rear end of the motor's output shaft with a brake shoe biased by a coil spring. When the tool is in use, pressing an operating member such as a paddle switch turns the switch ON, and a lever that rotates in conjunction with the operating member separates the brake shoe from the brake plate, thereby releasing the brake. When the operating member is released from the pressing operation, the switch turns OFF and the brake shoe is pressed against the brake plate, applying the brake. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6953252 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when braking, the brake shoes come into contact with the rotating brake plate, which increases the heat generated by the brake mechanism, potentially leading to a decrease in braking performance and component life.

[0005] Therefore, an object of the present disclosure is to provide a power tool that can suppress heat generation during braking and prevent deterioration of braking characteristics and component life. [Means for solving the problem]

[0006] In order to achieve the above object, the present disclosure provides a power tool that includes, within a housing, a switch that operates on / off in response to operation of an operating member, a rotating shaft that rotates when the switch is turned on, and a brake mechanism that brakes the rotating shaft when the switch is turned off and releases the brake on the rotating shaft in conjunction with operation of the operating member that turns the switch on. And the axis of rotation End of for, Separately A circular brake member is fixed, and the brake mechanism brakes the rotating shaft by pressing the brake member at multiple points with pressing members so that a uniform force acts from the radial outside toward the center. In another aspect of the present disclosure, the brake member has a spiral groove on its outer circumferential surface that opens onto front and rear end surfaces in the axial direction of the rotary shaft. In another aspect of the present disclosure, a circular brake member is fixed to a rotating shaft, and a brake mechanism expands and contracts a pair of holding members each holding a pressing member, centering on a fulcrum set on the radial outside of the brake member, to move each pressing member toward and away from the outer circumferential surface of the brake member, and when each pressing member comes into contact with the brake member, the brake member is pressed so that a uniform force acts from the radial outside toward the center, thereby braking the rotating shaft, while Each holding member is formed in a semicircular shape extending radially outside the brake member, The brake mechanism is characterized by further including a wedge member that is positioned on the opposite side of the fulcrum sandwiching the brake member and moves back and forth between the ends of the pair of holding members to expand and contract the pair of holding members. [Effects of the Invention]

[0007] According to the present disclosure, cooling air can be easily guided to the sliding surface between the brake member and the pressing member, thereby suppressing heat generation during braking and preventing deterioration of braking characteristics and component life. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. [Figure 2] FIG. 2 is a central vertical cross-sectional view of the grinder (switch OFF state). [Figure 3] FIG. 3 is an enlarged view of the brake mechanism portion of FIG. 2. [Figure 4] FIG. 2 is an exploded perspective view of the brake mechanism and the right half housing as viewed from the rear. [Figure 5] FIG. 2 is an exploded perspective view of the brake mechanism and the left half housing as viewed from the front. [Figure 6] FIG. [Figure 7] FIG. 4 is a cross-sectional view taken along line AA in FIG. [Figure 8] FIG. 4 is a cross-sectional view taken along line BB in FIG. 3. [Figure 9] FIG. 2 is a perspective view of only the brake mechanism portion as viewed from below. [Figure 10] FIG. 4 is a cross-sectional view taken along line CC in FIG. [Figure 11] FIG. 2 is a plan view of the brake mechanism portion with the main body housing omitted. [Figure 12] FIG. 4 is a cross-sectional view taken along line DD in FIG. 3. [Figure 13] FIG. 4 is a cross-sectional view taken along the line EE in FIG. [Figure 14] This is a side view of the brake mechanism with the left half housing omitted (switch OFF state). [Figure 15] A side view of the brake mechanism with the left half housing omitted (switch ON state) [Figure 16] FIG. 4 is an enlarged view of the brake mechanism portion corresponding to FIG. 3 in a switch-on state. [Figure 17] FIG. 17 is a cross-sectional view taken along the line FF in FIG. 16. DETAILED DESCRIPTION OF THE INVENTION

[0009] In one embodiment of the present disclosure, a pair of pressing members may be arranged at positions that are point-symmetric with respect to the center of the brake member. With this configuration, a uniform force can be easily applied to the brake member from the radially outer side toward the center. In one embodiment of the present disclosure, the brake member may have a spiral groove on its outer circumferential surface that opens onto front and rear end surfaces in the axial direction of the rotation shaft. According to this configuration, the grooves have the effect of expelling foreign matter such as dust, making it difficult for foreign matter to become lodged between the sliding surfaces of the brake member and the pressing member, and making it possible to more effectively prevent deterioration of braking characteristics. In one embodiment of the present disclosure, the brake mechanism may be configured to move a pair of holding members, each holding a pressing member, toward and away from the outer peripheral surface of the brake member by expanding and contracting the holding members around a fulcrum set radially outside the brake member. According to this configuration, the pressing member can press the brake member from the radially outer side in a well-balanced and compact manner. In one embodiment of the present disclosure, each retaining member may include a pair of anti-slip members that clamp the pressing member together with the retaining member, and a clip that holds and fixes the pair of anti-slip members in a clamped state between the retaining member and the pressing member. According to this configuration, the pressing member can be easily and reliably assembled to the holding member, and the pressing member can be easily replaced. In one embodiment of the present disclosure, each retaining member is formed in a semicircular shape extending radially outside the brake member, and the brake mechanism may further include a wedge member that is arranged on the opposite side of the fulcrum that sandwiches the brake member and moves back and forth between the ends of the pair of retaining members to expand and contract the pair of retaining members. According to this configuration, the expansion and contraction movements of the pair of holding members can be easily synchronized.

[0010] In one embodiment of the present disclosure, the brake mechanism further includes a link member that moves the wedge member back and forth between the ends of the pair of holding members in conjunction with the operation of the operating member, and the wedge member and the link member may be connected by fitting their tapered shapes together. According to this configuration, the wedge member and the link member can be easily connected, and the wedge member can be smoothly moved up and down in conjunction with the rotation of the link member. In one embodiment of the present disclosure, the link member may include a first link member that cooperates with the operating member, and a second link member that is rotatably connected to the first link member and cooperates with the wedge member. According to this configuration, even if the operating member and the wedge member are separated from each other, the wedge member can be smoothly advanced and retreated in response to the operation of the operating member. In one embodiment of the present disclosure, at least the first link member may include a pair of arms. With this configuration, even if a component such as a controller is present between the operating member and the wedge member, it can be placed in the space between the arms without interfering with the operation. In one embodiment of the present disclosure, the pair of retaining members and the wedge member may be axially positioned between two components arranged in the housing in the axial direction of the rotation shaft. According to this configuration, the pair of holding members and the wedge member can be positioned easily and in a space-saving manner by utilizing the gap between the two constituent members. In one embodiment of the present disclosure, the brake member may be threadably engaged with and fixed to the rotating shaft. With this configuration, the brake member can be easily fixed to the rotating shaft. [Example]

[0011] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. Fig. 1 is a perspective view of a grinder as an example of a power tool, and Fig. 2 is a central vertical cross-sectional view of the grinder. The grinder 1 has a cylindrical main housing 2 extending in the front-to-rear direction. The main housing 2 is made of resin, and a metal gear housing 3 is provided on the front side. The main housing 2 is formed by a pair of left and right half housings 2a, 2b screwed together from the left and right. The main housing 2 has a front main body portion 4 and a rear grip portion 5. Multiple air intakes 6, 6... extending in the front-to-rear direction are formed on the left and right side surfaces of the rear of the main body portion 4. The grip portion 5 has a smaller diameter than the main body portion 4 and extends rearward, tilting downward from a position eccentric above the axis of the main body portion 4. The grip portion 5 is equipped with a switch 7 and a switch lever 8. A power cord 9 is connected to the rear end of the grip portion 5. A motor housing 10 is held inside the front side of the main body 4 via a rubber sleeve 11. The gear housing 3 is screwed to the motor housing 10 from the front via a gear housing cover 12. Mounting portions 14, 14 for side handles 13 are provided on the left and right sides of the main body 4. A fixing ring 15, which is fitted onto the exterior of the rubber sleeve 11, is provided inside the mounting portions 14, 14 on the front side of the main body housing 2. The mounting portions 14, 14 are screwed to the fixing ring 15.

[0012] The motor housing 10 is made of resin and houses a motor 16 (here, a commutator motor). The motor 16 is housed in the motor housing 10 with its output shaft 17 facing forward and backward. The front portion of the output shaft 17 penetrates the gear housing cover 12 and protrudes into the gear housing 3. The gear housing cover 12 is provided with a bearing 18 that supports the output shaft 17. A fan 19 is fixed to the output shaft 17 behind the gear housing cover 12. A plurality of exhaust ports 20, 20... that communicate with the interior of the motor housing 10 are formed in the front surface of the gear housing 3.

[0013] A bevel gear 21 is provided at the front end of the output shaft 17 within the gear housing 3. A bearing box 22 is attached to the lower part of the gear housing 3. A spindle 23 is provided vertically within the gear housing 3 and the bearing box 22. The spindle 23 has a bevel gear 24 at its upper part. The bevel gear 24 meshes with the bevel gear 21 of the output shaft 17. The spindle 23 is journaled by upper and lower bearings 25, 25 held within the gear housing 3 and the bearing box 22. The lower end of the spindle 23 protrudes downward from the bearing box 22. A tool tool (e.g., a disc-shaped grinding wheel) 28 can be attached to the lower end of the spindle 23 via an inner flange 26 and a lock nut 27. A wheel cover 29 is attached to the bearing box 22, covering the upper and rear sides of the rear part of the tool tool 28.

[0014] As shown in FIG. 3 , a bearing holder 30 is integrally formed at the rear of the motor housing 10. The output shaft 17, which protrudes rearward from the commutator 31, is supported by a bearing 32 held by the bearing holder 30. A pair of support protrusions 33, 33 are provided on the top and bottom of the bearing holder 30. The support protrusions 33, 33 are arranged coaxially in the vertical direction perpendicular to the axis of the output shaft 17. Each support protrusion 33 is covered with a cap-shaped rubber ring 34. As shown in FIGS. 4 and 5 , upper and lower holders 35, 35 are provided on the inner surfaces of the left and right half housings 2a, 2b, protruding toward the center in the horizontal direction and holding the upper and lower rubber rings 34, 34 in their centers. Thus, the motor housing 10 is elastically supported within the main housing 2 via the front rubber sleeve 11 and the rear rubber rings 34, 34.

[0015] The rear end of the output shaft 17 extends rearward through the bearing holder 30. A brake drum 40 is fixed to the rear end of the output shaft 17, rearward of the bearing holder 30. As shown in FIG. 6 , the brake drum 40 includes a hub 41, a plurality of spokes 42, 42..., and a rim 43. The hub 41 is threadedly engaged with the output shaft 17 from the rear, and is coaxially and integrally connected to the output shaft 17. The tightening direction of the hub 41 is opposite to the rotation direction of the output shaft 17 (so-called tightening direction). A disk-shaped magnetic sleeve 44 is attached to the rear end of the hub 41. A disc portion 45 is formed on the outer periphery of the hub 41. A circular rib 46 extending rearward is provided on the outer periphery of the disc portion 45. The spokes 42, 42... are formed to extend radially from the outer periphery of the circular rib 46. The rim 43 is connected to the radial ends of each spoke 42 and is arranged coaxially on the radial outside of the disc portion 45. The rim 43 is in the shape of a strip ring that protrudes front and rear from the spokes 42, and has a spiral groove 47 formed on its outer circumferential surface. The front and rear ends of the groove 47 reach the front and rear end faces of the rim 43 and open onto each end face.

[0016] A coil holder 50 is provided within the main body 4 behind the brake drum 40. As shown in FIG. 7, the coil holder 50 is a rectangular box extending in the vertical direction. The coil holder 50 is screwed to the bearing holder 30 from the rear at two diagonal points. A circular recess 51 that opens forward is provided in the center of the coil holder 50. The circular recess 51 accommodates the rear end of the hub 41 of the brake drum 40 and the magnet sleeve 44 without contacting them. The front end of the circular recess 51 protrudes inside the circular rib 46 of the hub 41. The circular rib 46 and the front end of the circular recess 51 overlap radially without contacting each other. A storage compartment 52 for a pickup coil 53 is formed above the circular recess 51 in the coil holder 50. The pickup coil 53 is stored in the storage compartment 52 with its detection surface facing downward. The detection surface is located directly above the magnet sleeve 44. A boss 54 that protrudes to the left is formed on the inner surface of the right-hand housing half 2b. A rubber pin 55 is held at the tip of the boss 54. The rubber pin 55 abuts against the right side surface of the pickup coil 53, pressing the pickup coil 53 against the left inner surface of the storage compartment 52.

[0017] A controller 60 is disposed within the main body 4 behind the coil holder 50. As shown in FIG. 8, the controller 60 is held vertically in the center in the left-right direction by a lower support rib 61 and a rear support rib 62 that protrude from the inner surface of the left half housing 2a. The controller 60 includes a control circuit board 63 therein. An adjustment dial 64 is provided on the upper front side of the control circuit board 63. As shown in FIGS. 1 to 3, the upper part of the adjustment dial 64 is exposed above the main body housing 2. The rotation speed of the motor 16 can be adjusted by rotating the adjustment dial 64. The switch 7 is held at the top inside the grip part 5 with the button part 7a facing downward. Retaining ribs 65 that hold the upper part of the switch 7 are formed on the inner surfaces of the left and right half-housings 2a, 2b. A switch base 66 that holds the lower part of the switch 7 is held inside the grip part 5. The switch base 66 is plate-shaped and extends in the front-to-rear direction along the slope of the grip part 5. The button part 7a penetrates the switch base 66 and protrudes downward. A stopper piece 67 and a locking piece 68 are provided on the front and rear of the front of the switch base 66, facing downward. A shaft part 69 that protrudes to both the left and right is formed on the lower surface of the rear of the switch base 66.

[0018] The switch lever 8 extends in the front-to-rear direction below the switch base 66. The rear end of the switch lever 8 is rotatably connected to a shaft portion 69 of the switch base 66. The front portion of the switch lever 8 is exposed downward from an opening 70 provided in the lower surface of the grip portion 5. The switch lever 8 has a pressing portion 71 located below the button portion 7a. As shown in Figures 3 and 6, a locking hole 8a is formed in the front surface of the switch lever 8. The lower end of the stopper piece 67 is inserted into the locking hole 8a. The switch lever 8 can swing up and down between an upper position and a lower position. When the switch lever 8 is in the upper position, the lower edge of the locking hole 8a abuts against the lower end of the stopper piece 67, and the pressing portion 71 presses the button portion 7a (the switch 7 is turned ON). When the switch lever 8 is in the lower position, the lower end of the stopper piece 67 engages with the upper edge of the engagement hole 8a, and the pressing portion 71 moves away from the button portion 7a (the switch 7 is OFF). A coil spring 72 is interposed between the switch base 66 and the switch lever 8. The coil spring 72 normally biases the switch lever 8 to the lower position. A lock-on lever 73 is provided at the lower front end of the switch lever 8. The lock-on lever 73 can be rotated when the switch lever 8 is in the upper position to engage with the engagement piece 68, thereby locking the switch lever 8 in the upper position. A pair of connecting pins 74, 74 are provided on the left and right side surfaces of the front part of the switch lever 8, protruding outward to the left and right.

[0019] A brake mechanism 75 is provided inside the main body 4. As shown in Figures 6, 8, 9, and 10, the brake mechanism 75 includes the brake drum 40, a pair of brake arms 76A, 76B, a pair of brake shoes 77, 77, a pair of shoe holders 78, 78, a pair of coil springs 79, 79, a wedge plate 80, a front link 81, and a rear link 82. The brake arms 76A, 76B are disposed radially outward from the brake drum 40. The brake arms 76A, 76B are semicircular in front view and are symmetrical about the output shaft 17. As shown in FIG. 11 , the upper portions of the brake arms 76A, 76B are bent so that the left brake arm 76A is bent rearward and the right brake arm 76B is bent forward. Due to this bending, the left and right brake arms 76A, 76B, excluding the upper portions, are positioned on the same plane perpendicular to the axis of the brake drum 40.

[0020] Ring-shaped fulcrum portions 83, 83 that overlap in the axial direction are provided at the upper ends of the brake arms 76A, 76B. A fulcrum pin 84 penetrates the front and rear fulcrum portions 83, 83 in the front-rear direction. As shown in FIG. 3, the front end of the fulcrum pin 84 is supported by the rear surface of the bearing holder 30, and the rear end is supported by the front surface of the coil holder 50. Therefore, the brake arms 76A, 76B are supported so as to be rotatable left and right about the fulcrum pin 84. Bulging portions 85, 85 that bulge outward in an arc shape to the left and right are formed at the circumferential middle portions of the brake arms 76A, 76B. The lower ends of the brake arms 76A, 76B are rounded and formed in a semicircular shape when viewed from the front. The brake shoes 77 are disposed radially inward of the bulging portions 85. Each brake shoe 77 is strip-shaped and has a width in the front-to-rear direction greater than that of the brake arms 76A and 76B. The brake shoes 77 are formed in an arc shape that follows the outer peripheral surface of the rim 43 of the brake drum 40.

[0021] The shoe holders 78, 78 are provided on the bulging portions 85, 85. Each shoe holder 78 has a pair of front and rear clamping plates 86, 86 and a clip 87. Each clamping plate 86 has an outer peripheral portion 88 that clamps the bulging portion 85 from the front and rear, and an inner peripheral portion 89 that clamps the outer peripheral side of the brake shoe 77 from the front and rear inside the bulging portion 85. Engagement recesses 90 for the clip 87 are formed on the front and rear outer sides of each outer peripheral portion 88, respectively. The clip 87 is a leaf spring formed to fit the outer shape of the outer peripheral portions 88, 88 of the clamping plates 86, 86, including the engagement recesses 90, 90. With the clamping plates 86, 86 clamping the bulge 85 and brake shoe 77 from the front and rear, the clip 87 engages both ends with the engagement recesses 90, 90 of the outer peripheral portions 88, 88 to clamp the clamping plates 86, 86 from the outside. Then, the shoe holder 78 is fixed to the bulge 85 while holding the brake shoe 77. The clamping plates 86, 86 have a bottomed hole 91 that opens radially outward at the joint between the outer peripheral portions 88, 88. The clip 87 has a through hole 92 that opens coaxially radially outward of the bottomed hole 91.

[0022] The coil springs 79 are disposed radially outward of the shoe holders 78. The inner end of each coil spring 79 is inserted through a through hole 92 in the clip 87 into a bottomed hole 91 in the clamping plates 86. The outer end of each coil spring 79 is fitted onto a receiving protrusion 93 protruding from the inner surface of each of the half housings 2a and 2b. Therefore, in a normal state, the left and right brake arms 76A, 76B are biased radially inward, reducing the distance between them, by the coil springs 79, 79. As a result, the brake shoes 77, 77 held by the brake arms 76A, 76B via the shoe holders 78, 78 simultaneously press against the outer peripheral surface of the rim 43 of the brake drum 40 from the left and right, as shown in Figure 10.

[0023] The wedge plate 80 is disposed below the brake drum 40 in the center in the left-right direction. The wedge plate 80 is a symmetrical plate with protruding portions 95, 95 that protrude semicircularly upward on the left and right sides. The protruding portions 95, 95 are located below the lower ends of the brake arms 76A, 76B. As shown in FIG. 3 , the rear surface of the bearing holder 30 and the front surface of the coil holder 50 are close to or abut the front and rear surfaces of the wedge plate 80. Therefore, the front-rear movement of the wedge plate 80 is restricted between the bearing holder 30 and the coil holder 50. A coupling groove 96 is formed in the lower part of the wedge plate 80 in the center in the left-right direction, penetrating from the front to the rear and opening downward. The coupling groove 96 is tapered, with its width decreasing downward from the top end, which forms the bottom.

[0024] The front link 81 is disposed in the left-right center below the magnet sleeve 44 and the brake drum 40. The front link 81 is a strip-shaped plate that is bent into an L shape in a side view, and is disposed vertically below the circular recess 51 of the coil holder 50. A support pin 97 passes through the bent portion of the front link 81 in the left-right direction. As shown in FIG. 12 , this support pin 97 is supported by a receiving boss 98 that protrudes from the inner surface of the left half housing 2a. A pin receiving portion 99 that positions the right end of the support pin 97 is provided on the right side of the front link 81 and below the coil holder 50. Therefore, the front link 81 is supported within the main body housing 2 so as to be rotatable about the support pin 97 .

[0025] The front link 81 has a forearm 100 and a rear arm 101. The forearm 100 protrudes forward from a support pin 97 and is inserted into a coupling groove 96 of the wedge plate 80. The rear arm 101 extends obliquely upward and rearward from the support pin 97. As shown in FIG. 10 , the cross-sectional shape of the forearm 100 is tapered, similar to the coupling groove 96, with the width decreasing from the upper end downward. Therefore, by fitting the forearm 100 into the coupling groove 96, the wedge plate 80 is coupled to the forearm 100 in a state where it is prevented from slipping out upward, and moves up and down integrally with the forearm 100. The receiving boss 98 is provided with a restricting portion 102 that restricts downward rotation of the forearm 100. 3 and 10, when the front link 81 is rotated to a position where the forearm 100 abuts against the restricting portion 102 (a counterclockwise rotation position about the support pin 97 in FIG. 3), the wedge plate 80 is in its lowest position. In this lowest position, the wedge plate 80 is spaced downward from the left and right lower ends of the brake arms 76A, 76B. An elongated hole 103 extending in the longitudinal direction is formed at the upper end of the rear arm 101.

[0026] The rear link 82 includes a pair of left and right arms 105 and a connecting shaft 106. The arms 105 are disposed on the left and right outer sides of the coil holder 50 and the controller 60 and extend in the front-rear direction. The rear portions of the arms 105 are bent toward the center in the left-right direction, narrowing the left-right spacing, and protrude into the grip portion 5. The rear ends of the arms 105 are rotatably connected to the connecting pins 74 of the switch lever 8. Fulcrum holes 107 extending in the longitudinal direction are formed in the middle portions of the arms 105. As shown in FIG. 13 , support bosses 108, the tips of which engage with the fulcrum holes 107, protrude from the inner surfaces of the left and right half housings 2a and 2b, respectively. The connecting shaft 106 is disposed in the left-right direction and passes through a long hole 103 in the rear arm portion 101 of the front link 81. Both left and right ends of the connecting shaft 106 are rotatably connected to the front ends of the arms 105, 105.

[0027] When the switch lever 8 is in the lower position, the arms 105, 105 are in a substantially horizontal position with the support bosses 108, 108 located behind the fulcrum holes 107, 107, as shown in Figure 14. At this time, the connecting shaft 106 is in the forward position, and the front link 81 is in the counterclockwise rotation position. Therefore, the wedge plate 80 is in the lowest position located below the brake arms 76A, 76B. When the switch lever 8 swings from this position to the upper position, the connecting pins 74 move upward. Then, as shown in FIG. 15 , the rear ends of the arms 105 are pulled upward together with the connecting pins 74, causing the support bosses 108 to move relatively within the fulcrum holes 107, causing the arms 105 to rotate counterclockwise approximately around the support bosses 108. As a result, the front ends of the arms 105 move backward together with the connecting shaft 106. Then, the front link 81 rotates clockwise around the support pin 97, raising the forearm 100 as shown in FIG. 16. Therefore, the wedge plate 80 reaches its upper limit position, inserted between the left and right lower ends of the brake arms 76A and 76B.

[0028] In the grinder 1 configured as described above, when the switch 7 is in the OFF state of the brake mechanism 75, the brake shoes 77, 77 press from the left and right against the outer peripheral surface of the rim 43 of the brake drum 40, which rotates integrally with the output shaft 17, as described above. Therefore, the output shaft 17 is braked via the brake drum 40. From this position, the switch lever 8 is pressed down with the hand holding the grip portion 5. Then, as shown in Figures 15 and 16, the switch lever 8 swings to the upper position, pressing the button portion 7a and turning on the switch 7. As a result, the controller 60 energizes the motor 16. Meanwhile, as the switch lever 8 swings to the upper position, as described above, the arms 105, 105 of the rear link 82 rotate left, causing the front link 81 to rotate right and moving the wedge plate 80 to the upper limit position. Then, as shown in FIG. 17 , the brake arms 76A, 76B spread outward to the left and right around the fulcrum pin 84, separating the brake shoes 77, 77 from the rim 43 of the brake drum 40. This causes the output shaft 17, whose brake is released, to rotate. The rotation of the output shaft 17 is transmitted to the spindle 23 via the bevel gears 21, 24, causing the bit 28 to rotate.

[0029] Meanwhile, rotation of the output shaft 17 rotates the fan 19. This causes outside air to be drawn in through the intake ports 6, 6··· of the main body 4. The drawn-in air passes through the controller 60 and the coil holder 50, in that order. The air then flows between the spokes 42, 42 of the brake drum 40 and along the radially outer side of the rim 43 to the motor 16. After passing through the motor 16, the air passes through the gear housing cover 12 and is discharged from the exhaust ports 20, 20···. This airflow cools the controller 60, the coil holder 50, the brake drum 40, and the motor 16. In particular, the brake drum 40 is cooled effectively by heat dissipation from the entire rim 43, coupled with contact with the airflow. Furthermore, even if dust or other particles are emitted from the brake shoes 77, 77, they are blown forward by the airflow and are less likely to adhere to the outer circumferential surface of the rim 43. Dust or other particles that enter the grooves 47 are expelled back and forth through the grooves 47 as the brake drum 40 rotates.

[0030] When the switch lever 8 is released from the depressed state, the switch lever 8 swings to the lower position due to the bias of the coil spring 72. Therefore, the button portion 7a is released from the depressed state and the switch 7 is turned OFF. Meanwhile, as the switch lever 8 swings to the lower position, the rear link 82 advances to the position shown in FIGS. 3 and 14 while rotating clockwise approximately about the support bosses 108. Then, the front link 81 rotates counterclockwise about the support pin 97, swinging the forearm 100 downward. Therefore, the wedge plate 80 moves to the lower limit position shown in FIG. 10 and separates from between the lower ends of the brake arms 76A and 76B. Then, the brake arms 76A and 76B rotate toward the center in the left-right direction due to the bias of the coil springs 79, pressing the brake shoes 77 against the outer peripheral surface of the rim 43 of the brake drum 40. Therefore, braking is applied to the output shaft 17 via the brake drum 40, and the braking force is transmitted to the spindle 23, stopping the tool bit 28.

[0031] During braking, the brake shoes 77, 77 press against the rim 43, which has a larger diameter than the output shaft 17, from the radially outer side. In other words, the brakes indirectly apply brakes to the output shaft 17 from a position radially away from the axis of the output shaft 17. This allows a high braking force to be exerted even with a small pressing force (multiplying effect). In addition, the grooves 47 on the outer peripheral surface of the rim 43 make it difficult for foreign matter such as dust to accumulate. This allows the braking force to be transmitted efficiently from the brake shoes 77, 77 to the rim 43, without affecting braking performance.

[0032] In this way, the grinder 1 of the above form is provided with, within the main body housing 2 (an example of a housing), a switch 7 that operates on / off in response to operation of a switch lever 8 (an example of an operating member), an output shaft 17 (an example of a rotating shaft) that rotates when the switch 7 is turned on, and a brake mechanism 75 that brakes the output shaft 17 when the switch 7 is in the OFF state and releases the brake of the output shaft 17 in conjunction with operation of the switch lever 8 that turns the switch 7 on. A circular brake drum 40 (an example of a brake member) is fixed to the output shaft 17, and the brake mechanism 75 brakes the output shaft 17 by pressing the brake drum 40 at two locations using brake shoes 77, 77 (an example of a pressing member) so that a uniform force acts from the radial outside toward the center. This configuration makes it easier to guide cooling air to the sliding surface between the rim 43 of the brake drum 40 and the brake shoe 77. This reduces heat generation during braking, preventing a decrease in braking characteristics and component life.

[0033] A pair of brake shoes 77 are arranged at positions point-symmetrical with respect to the center of the brake drum 40 . Therefore, a uniform force can be easily applied to the brake drum 40 from the radially outer side toward the center. The brake drum 40 has a spiral groove 47 on the outer peripheral surface of the rim 43 that opens onto the front and rear end surfaces in the axial direction of the output shaft 17 . Therefore, the grooves 47 have the effect of discharging foreign matter such as dust. As a result, foreign matter is less likely to become trapped between the sliding surfaces of the rim 43 and the brake shoe 77, making it possible to more effectively prevent deterioration of braking characteristics. The brake mechanism 75 expands and contracts a pair of brake arms 76A, 76B (an example of a holding member), each of which holds a brake shoe 77, around a fulcrum pin 84 (an example of a fulcrum) set radially outside the brake drum 40, thereby moving each brake shoe 77 toward and away from the outer peripheral surface of the brake drum 40. Therefore, the brake shoes 77 can press the brake drum 40 from the radially outer side in a well-balanced and compact manner.

[0034] The brake arms 76A, 76B include a pair of clamping plates 86, 86 (an example of a retaining member) that clamp the brake shoe 77 together with the bulge portion 85, and a clip 87 that holds and fixes the pair of clamping plates 86, 86 in a clamped state between the bulge portion 85 and the brake shoe 77. Therefore, the brake shoes 77 can be easily and reliably attached to the brake arms 76A and 76B, and the brake shoes 77 can be easily replaced. The brake arms 76A, 76B are formed in a semicircular shape extending radially outside the brake drum 40. The brake mechanism 75 is arranged on the opposite side of the fulcrum pin 84 across the brake drum 40, and further includes a wedge plate 80 (an example of a wedge member) that moves back and forth between the ends of the brake arms 76A, 76B to expand and contract the brake arms 76A, 76B. Therefore, the expansion and contraction operations of the brake arms 76A and 76B can be easily synchronized.

[0035] The brake mechanism 75 further includes a front link 81 and a rear link 82 (an example of a link member) that move the wedge plate 80 back and forth between the ends of the brake arms 76A and 76B in conjunction with the operation of the switch lever 8, and the wedge plate 80 and the front link 81 are connected by fitting their tapered shapes together. Therefore, the wedge plate 80 and the front link 81 can be easily connected, and the wedge plate 80 can be smoothly moved up and down in conjunction with the rotation of the front link 81. The link member includes a rear link 82 (an example of a first link member) that links with the switch lever 8, and a front link 81 (an example of a second link member) that is rotatably connected to the rear link 82 and links with the wedge plate 80. Therefore, even if the switch lever 8 and the wedge plate 80 are spaced apart from each other in the front and rear direction, the wedge plate 80 can be moved forward and backward in conjunction with the operation of the switch lever 8 without any hindrance. The rear link 82 includes a pair of arms 105, 105. Therefore, even if the controller 60 or the like is present between the switch lever 8 and the wedge plate 80, it can be arranged in the space between the arms 105, 105 without interference.

[0036] The brake arms 76A, 76B and the wedge plate 80 are positioned axially between the motor housing 10 and the coil holder 50 (an example of two components) arranged in the axial direction of the output shaft 17 within the main housing 2. Therefore, the brake arms 76A, 76B and the wedge plate 80 can be positioned easily and in a space-saving manner by utilizing the gap between the motor housing 10 and the coil holder 50. The brake drum 40 is screwed onto the output shaft 17 and fixed thereto. Therefore, the brake drum 40 can be easily fixed to the output shaft 17.

[0037] Modifications of the present disclosure will be described below. The shape of the brake member can be modified as appropriate. For example, the number of spokes in the brake drum of the above example may be increased or decreased, or the shape of the hub or rim may be changed. The brake member is not limited to the brake drum of the above example, but may also be a single disk. There may be multiple grooves on the outer peripheral surface, or they may be omitted. The brake member can be fixed to the output shaft using a structure other than threaded engagement. The retaining members are not limited to the brake arms in the above example and can be modified as appropriate. For example, the brake arms in the above example do not need to be semicircular when viewed from the front, but may be bent along the outer periphery of the brake member. The fulcrum of the pair of retaining members can be located not only above the brake drum, but also below or to the side. The biasing force on the brake arms is not limited to the coil springs from the left and right outer sides, and may be achieved by providing a tension spring between the brake arms, for example. The number of brake shoes is not limited to two, but three or more may be provided around the circumferential direction of the brake member, and each may be capable of approaching and separating from the brake member from the radially outer side. The means for holding the brake shoes is not limited to the shoe holder in the above example. For example, the retaining member may be formed by connecting a pair of clamping plates with a hinge, or by engaging the clamping plates with each other to hold the brake shoes without using a clip. The brake shoes may be attached directly to the brake arm by adhesive or the like, without using a shoe holder. The structure of the brake shoes themselves may also be modified as appropriate.

[0038] The wedge member is not limited to the wedge plate in the above example. For example, the wedge member is not limited to a configuration in which the left and right pressing portions are semicircular, but may be tapered (trapezoidal or triangular) so that the width narrows toward the top. The connection with the front link is not limited to a structure using a tapered connecting groove, but a pin or the like may also be used. The wedge member may be formed in a block shape (for example, a cone shape) instead of a plate shape. The wedge member may be moved forward and backward between the holding member in the front-rear direction instead of the radial direction. The positioning of the holding member and the wedge member in the front-rear direction is not limited to the structure using the motor housing and coil holder as in the above example. Positioning may be performed using other components inside the main body housing. Positioning may also be performed without using components, using, for example, a rib protruding from the housing. The link member is not limited to the structure of the front link and rear link in the above example. For example, a portion equivalent to a wedge member can be integrally formed on the forearm of the front link. The front link may be formed from a pair of arms. The rear link does not have to be formed from a pair of arms if there are no components such as a controller. There may be three or more link members.

[0039] The power tool may be a DC tool powered by a battery pack, instead of an AC tool powered by a commercial power source. The power tool is not limited to a grinder. The present disclosure can be applied to other grinding and polishing tools such as polishers and sanders, and cutting tools such as circular saws and cutters, as long as they use a brake mechanism that applies brakes to a rotating shaft that rotates the tool bit. Therefore, the brake mechanism may apply brakes to a rotating shaft other than the output shaft of the motor. The power tool is not limited to an electric power tool, and the present disclosure can also be applied to an air tool, an engine tool, or the like. [Explanation of symbols]

[0040] 1 Grinder, 2 Main body housing, 3 Gear housing, 4 Main body, 5 Grip, 7 Switch, 8 Switch lever, 10 Motor housing, 16 Motor, 17 Output shaft, 19 Fan, 23 Spindle, 28 Tip tool, 30 Bearing holder, 40 Brake drum, 41 Hub, 43 Rim, 47 Groove, 50 Coil holder, 60 Controller, 74 Connecting pin , 75 Brake mechanism, 76A, 76B Brake arm, 77 Brake shoe, 78 Shoe holder, 79 Coil spring, 80 Wedge plate, 81 Front link, 82 Rear link, 83 Fulcrum portion, 84 Fulcrum pin, 85 Bulging portion, 86 Clamping plate, 87 Clip, 95 Protruding portion, 96 Connecting groove, 97 Support pin, 100 Forearm portion, 101 Rear arm portion, 105 Arm, 106 Connecting shaft.

Claims

1. A power tool including a switch that is turned on / off in response to operation of an operating member, a rotating shaft that rotates when the switch is turned on, and a brake mechanism that brakes the rotating shaft when the switch is in an off state and releases the brake of the rotating shaft in conjunction with operation of the operating member that turns the switch on, within a housing; A power tool characterized in that a separate circular brake member is fixed to the end of the rotating shaft, and the brake mechanism brakes the rotating shaft by pressing the brake member at multiple locations with pressing members so that a uniform force acts from the radial outside toward the center.

2. A power tool having a housing containing a switch that is turned on / off in response to the operation of an operating member, a rotating shaft that rotates when the switch is turned on, and a brake mechanism that brakes the rotating shaft when the switch is in the off state and releases the brake on the rotating shaft in conjunction with the operation of the operating member that turns the switch on, A circular brake member is fixed to the rotating shaft, and the brake mechanism brakes the rotating shaft by pressing the brake member at multiple locations with pressing members so that a uniform force acts from the radial outside toward the center, and The power tool is characterized in that the brake member has a spiral groove on its outer peripheral surface that opens onto front and rear end faces in the axial direction of the rotary shaft.

3. 3. The power tool according to claim 1, wherein the pair of pressing members are arranged at positions point-symmetrical with respect to the center of the brake member.

4. 4. The power tool according to claim 1, wherein the brake mechanism expands and contracts a pair of holding members, each holding one of the pressing members, about a fulcrum set radially outside the brake member, to move each of the pressing members toward and away from the outer peripheral surface of the brake member.

5. Each of the retaining members is formed in a semicircular shape extending radially outside the brake member, The power tool according to claim 4, characterized in that the brake mechanism further includes a wedge member arranged on the opposite side of the fulcrum across the brake member and moving back and forth between the ends of the pair of retaining members to expand and contract the pair of retaining members.

6. A power tool having a housing provided with a switch that is turned on / off in response to the operation of an operating member, a rotating shaft that rotates when the switch is turned on, and a brake mechanism that brakes the rotating shaft when the switch is in the off state and releases the brake on the rotating shaft in conjunction with the operation of the operating member that turns the switch on, A circular brake member is fixed to the rotating shaft, and the brake mechanism causes a pair of holding members, each holding a pressing member, to expand and contract about a fulcrum set on the radial outside of the brake member, so that each pressing member comes into contact with and separates from the outer circumferential surface of the brake member, and when each pressing member comes into contact with the brake member, it presses each brake member so that a uniform force acts from the radial outside toward the center, thereby braking the rotating shaft, Each of the retaining members is formed in a semicircular shape extending radially outside the brake member, A power tool characterized in that the brake mechanism further includes a wedge member that is arranged on the opposite side of the fulcrum across the brake member and moves back and forth between the ends of the pair of retaining members to expand and contract the pair of retaining members.

7. 7. The power tool according to claim 4, wherein each of the holding members includes a pair of anti-slip members that sandwich the pressing member together with the holding member, and a clip that holds and fixes the pair of anti-slip members in a sandwiched state between the holding member and the pressing member.

8. The power tool described in claim 5 or 6, characterized in that the brake mechanism further includes a link member that moves the wedge member forward and backward between the ends of the pair of holding members in conjunction with the operation of the operating member, and the wedge member and the link member are connected by fitting their tapered shapes together.

9. 9. The power tool according to claim 8, wherein the link member includes a first link member that is linked to the operating member, and a second link member that is rotatably connected to the first link member and that is linked to the wedge member.

10. 10. The power tool according to claim 9, wherein at least the first link member includes a pair of arms.

11. A power tool according to any one of claims 8 to 10, characterized in that the pair of retaining members and the wedge member are positioned in the axial direction between two components arranged in the axial direction of the rotating shaft within the housing.

12. 12. The power tool according to claim 1, wherein the brake member is screwed and fixed to the rotary shaft.

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