DESCRIPTION

ELECTRIC TOOL

Technical Field

The present invention relates to an electric tool such as a rotary hammer drill using a DC motor as a drive source.

Background Art The electric tool using the DC motor as the drive source has come into wide use (as referred to JP-A-2002-254337, for example) . A rotary hammer drill as one example of the electric tool of this kind has a DC motor housed as the drive source in the housing. This DC motor has a magnet assembly 130 (or a stator) constituted, as specifically shown in Figs . 1OA, 1OB, to include a generally cylindrical yoke 131 made of a ferromagnetic material such as iron, and two arcuately curved magnets 132 arranged inside of the yoke 131 while leaving an equal circumferential spacing between the two magnets 132. Fig. 1OA is a sectional side elevation (or a section of line H - H of 10B) of the magnet assembly 130, and Fig. 1OB is a front elevation (as taken in the direction of arrow J of 10A) of the same magnet assembly 130.

Here, the two magnets 132 are so fixed on the inner circumference of the yoke 131 by adhering means that they may

be prevented from axially coming out and circumferentially rotating. By inserting magnetic holders 135 formed of wires or the like into a U-shape and having spring properties, into the circumferential clearances between those magnets 132, the force to push the magnets 132 to the outside is caused to push the magnets 132 onto the inner circumference of the yoke 131, so that the magnets 132 may not come out even in case the adhesion becomes weak.

In the circumferential edge of the opening in one axial end of the yoke 131, as shown in Fig. 1OA, there is fitted a ring-shaped dust guard 133, which performs functions to prevent powder dust from invading into the DC motor and to improve the flow of air thereby to enhance the cooling efficiency of the DC motor. Disclosure of Invention

Here, Fig. 11 and Fig. 12 show the comparisons of wind passage areas between the cases, in which magnet holders 135 shown in Fig. 1OA are used and not.

Fig. 11 is a front elevation of the magnet assembly 130 of the case, in which the magnet holders 135 are not provided. In this case, the entirety of the space (as hatched in Fig. 11) between the yoke 131 and an armature 141 by the circumferential clearance between the magnets 132 becomes the cooling wind passage. On the contrary, Fig. 12 is a front elevation of the magnet assembly 130 of the case, in which the

magnet holders 135 are provided. In this case, the space to be formed between the yoke 131 and the armature 141 by the circumferential clearance between the magnets 132 has its sectional area reduced by the magnet holders 135, so that the sectional area (as hatched in Fig. 12) of the cooling wind passage is reduced by that area reduction thereby to lower the cooling efficiency.

As shown in Figs. 1OA, 1OB, moreover, the yoke 131 is usually provided with a notch 131a, in which the (not-shown) protrusion of the housing is fitted to prevent the circumferential rotation of the yoke 131.

Even if the rotation of the yoke 131 is prevented by the structure thus far described, the magnets 132 in the constitution shown in Fig. 11 may come out in the axial direction or rotate in the circumferential direction, as the adhesion of the magnets 132 to the yoke 131 becomes weak, by the influences of the rotational reaction of the armature 141.

In the constitution having the magnet holders 135 shown in Fig.

12, on the other hand, the magnets 132 do not come out, but the magnets 132 may rotate circumferentially along the inner circumference of the yoke 131 together with the magnet holders

135.

The invention has been conceived in view of the problems thus far described, and has an object to provide an electric tool, which can prevent magnets easily from coming out and

rotating.

Another object of the invention is to provide an electric tool, which can improve a cooling efficiency.

In order to achieve the aforementioned objects, according to the invention as set forth in claim 1, there is provided an electric tool comprising: a generally cylindrical yoke; a plurality of magnets fixed through a circumferential clearance to the inner circumference of said yoke; an armature rotatably arranged on the inner side of said yoke through a radial clearance between said yoke and the magnets; and a dust guard fitted in one axial end of said yoke. The dust guard is equipped integrally with a plurality of engaging protrusions engaging with the circumferential clearance between said magnets in said yoke. In the invention of claim 1, the invention as set forth in claim 2 is characterized in that said dust guard includes a ring-shaped body portion protruding outward of the axial direction from the axial end face of said yoke, and in that said engaging protrusions are protruded integrally with said body portion.

In the invention of claim 1 or 2, the invention as set forth in claim 3 is characterized in that said engaging protrusions are arcuately curved along the inner circumference shape of said yoke. In the invention of any of claims 1 to 3, the invention

as set forth in claim 4 is characterized in that axially extending slits are formed in said engaging protrusions.

In the invention of any of claims 1 to 4, the invention as set forth in claim 5 is characterized in that a first engaging portion is formed in a portion of said trunk portion of the housing having a cylindrical trunk portion, and in that a second engaging portion for engaging with said first engaging portion in the rotational direction is formed in said dust guard.

In the invention of claims 5, the invention as set forth in claim 6 is characterized in that said dust guard is arranged in the front end portion of the assembling direction of said yoke to be assembled in said housing.

According to the invention as set forth in claim 1, there is adopted the constitution, in which the engaging protrusions formed integrally with the dust guard are made to engage with the circumferential clearance formed between the magnets in the yoke. It is, therefore, possible to suppress the magnet from axially coming out and from circumferentially rotating. Moreover, the engaging protrusions for preventing the magnets from axially coming out and from circumferential rotating are formed integrally with the dust guard. It is possible to reduce the number of parts and to improve the assemblage and reduce the cost.

According to the invention as set forth in claim 2, the ring-shaped body portion of the dust guard is protruded axially

outward from the axial end face of the yoke. It is, therefore, possible to improve the function to block the invasion of powder dust such as iron powder.

According to the invention as set forth in claim 3, the engaging protrusions formed on the dust guard are arcuately curved along the inner circumference shape of the yoke. It is, therefore, possible to minimize the sectional area by the engaging protrusions of the wind passage which formed between the yoke and the armature by the circumferential clearance between the magnets, and to suppress the throttling of the flow rate of the cooling wind to pass through the wind passage, thereby to enhance the cooling efficiency of the DC motor. According to the invention as set forth in claim 4, the axially extending slits are formed in the engaging protrusions . When the dust guard is fitted in the yoke while inserting the engaging protrusions between the magnets, the engaging protrusions can be easily brought into engagement with the magnets without obstructing the assemblage of the dust guard, so that the function to prevent the magnets from coming out can be exercised. Moreover, the reaction for the engaging protrusions to push the circumferential end faces of the magnets can be increased to prevent the magnets from axially coming out. Moreover, the sectional area of the wind passage, which is formed between the yoke and the armature by the circumferential clearances between the magnets, is increased

to the extent of the slits so that the flow rate of the cooling wind to pass through the wind passage increases to enhance the cooling efficiency of the DC motor.

According to the invention as set forth in claim 5, the magnet assembly having the dust guard is assembled in the trunk portion of the cylindrical housing while the engaging protrusions on the housing side being held in engagement with the engaging grooves formed in the dust guard. Then, the magnet assembly is precisely positioned with respect to the housing so that the assemblage of the magnet assembly is enhanced. It is also possible to suppress the rotations relative to the housing through the dust guard and the magnets.

According to the invention as set forth in claim 6, the dust guard is arranged in the front end portion of the assembling direction of the yoke to be assembled in the housing. Before the magnet assembly is assembled in the housing, the engaging protrusions on the housing side can be brought into engagement with the engaging grooves formed in the dust guard. It is, therefore, possible to assemble the magnet assembly easily in a workable manner into the housing while positioning the magnet assembly and preventing the rotation of the same from the first.

Brief Description of the Drawings Fig. 1 is a sectional side elevation of an electric tool

(or a rotary hammer drill) according to the invention.

Fig. 2A is a sectional side elevation (or a section of line A - A of 2B) of a magnet assembly of the electric tool according to the invention; Fig. 2B is a front elevation of the same magnet assembly; and Fig. 2C is a section of line C

- C of 2A.

Fig. 3 is an exploded perspective view of the magnet assembly of the electric tool according to the invention.

Fig. 4 is a front elevation showing the section of a wind passage formed in the magnet assembly of the electric tool according to the invention.

Fig. 5A is a sectional side elevation of the magnet assembly, and Fig. 5B is a section of line D - D of Fig. 5A.

Fig. 6A is a sectional side elevation of the magnet assembly, and Fig. 6B is a section of line E - E of Fig. 6B.

Fig. 7A is a sectional side elevation of the magnet assembly, and shows another embodiment, and Fig. 7B is a front elevation (as taken in the direction of arrow G of 7A) of the same magnet assembly. Fig. 8 is an exploded perspective view of a magnet assembly of an electric tool according to Embodiment 2 of the invention.

Fig.9 is a front elevation of the rear half of the housing of an electric tool according to Embodiment 2 of the invention. Fig. 1OA is a sectional side elevation (or a section of

line H - H of 10B) of the magnet assembly of the electric tool of the background art, and Fig. 1OB is a front elevation (as taken in the direction of arrow J of 10A) of the same magnet assembly. Figs. 11 and 12 are front elevations showing the section of a wind passage formed in the magnet assembly of the electric tool of the background art. Best Mode for Carrying Out the Invention

Embodiments of the invention are described in the following with reference to the accompanying drawings.

Fig. 1 is a longitudinal section showing a rotary hammer drill 1 as one mode of an electric tool according to the invention. The shown rotary hammer drill 1 has a DC motor 3 or a drive source housed in a housing 2 or an outer member made of a resin. This DC motor 3 has a spindle (or a motor shaft) 4 supported rotatably at its two ends by bearings 5 and 6. To this spindle 4, moreover, there is bound a cooling fan 7, around which a fan guide 8 is arranged. Moreover, a pinion 9 is formed at such a front end portion of the spindle 4 as protrudes forward from the bearing 5.

On the other hand, the housing 2 is constituted by jointing longitudinally split halves 2A and 2B together. To a handle portion 2B-1 of the split half 2B, there is connected a power cord 10 for feeding the power to the DC motor 3. Moreover, the handle portion 2B-1 of the split half 2B is

equipped with a circuit (or AC/DC converter) 11 for converting the AC power into a DC one, and a switch 12 for turning ON/OFF the feed the electric power to the DC motor 3.

In front of the DC motor 3 in the housing 2, an intermediate shaft 13 is arranged in parallel with the spindle 4 and is rotatably supported at its two ends by bearings 14. The intermediate shaft 13 is equipped with a reciprocating bearing 15 and gears 16 and 17, and the pinion 9 meshes with the pinion 9 formed at the front end of the spindle 4. Here, the gear 16 has a larger diameter than that of the pinion 9, and constitutes a speed reducing mechanism.

In the front end portion of the housing 2, a cylinder 18 is rotatably arranged in parallel with the spindle 4 and the intermediate shaft 13. The cylinder is equipped on its outer circumference with a gear 19, which meshes with the gear 17 disposed at the intermediate shaft 13. Here, the gear 19 has a larger diameter than that of the gear 17, and these gears 17 and 19 constitute a speed reducing mechanism.

In the cylinder 18, a bottomed cylindrical piston 20 having one end (or a front end) opened is so fitted as to slide back and forth, and forms a pressure chamber 22 defined by an intermediate member 21. The arm 15a of the reciprocating bearing 15 is connected to the rear end portion of the piston 20, and a tip tool (or a drill bit) 23 is removably mounted in the leading end of the cylinder 18. This tip tool 23 can

slide back and forth with respect to the cylinder 18 and can rotate integrally with the cylinder 18. An impacter 24 is interposed between the cylinder 18 and the intermediate member 21. When the switch 12 is turned ON to drive the DC motor 3, the rotations of the spindle 4 are reduced in speed through the pinion 9 and the gear 16 and transmitted to the intermediate shaft 13 so that the intermediate shaft 13 is rotationally driven at a predetermined speed. Then, the arm 15a of the reciprocating bearing 15 is rocked back and forth to reciprocate the piston 20 back and forth in the cylinder 18. As a result, the pressure in the pressure chamber 22 of the cylinder 18 fluctuates to cause an impact. This impact resulting from the pressure fluctuations is transmitted through the intermediate member 21 and the impacter 24 to the tip tool 23 so that the impacting force is applied to the tip tool 23.

On the other hand, the rotations of the intermediate shaft 13 are reduced in speed through the gears 17 and 19 and are transmitted to the cylinder 18 so that the cylinder 18 and the tip tool 23 mounted thereon are rotationally driven at a predetermined speed.

Thus, the rotations and the impacting force are applied to the tip tool 23 so that the tip tool 23 performs the operation to drill the not-shown work. The rotary hammer drill 1 is

equipped with a mode switching mechanism, although not shown, so that it can select the rotation mode, in which only the rotation is applied to the tip tool 23, and the rotation/impact mode, in which the rotation and the impact are applied, as described hereinbefore.

Here, the DC motor 3 acting as the drive source is constituted by housing an armature (or rotor) 41 rotatably in a generally cylindrical magnet assembly (or a stator) 30. The magnet assembly 30 is constituted to include a generally cylindrical yoke 31 made of a ferromagnetic material such as iron, and two arcuate magnets 32 arranged on the inner side of the yoke 31. Equidistant circumferential clearances, as will be described hereinafter, are formed (as referred to Fig. 2B) between the two magnets 32. Moreover, the fan guide 8 is fitted at its outer circumference in the inner circumference of the housing 2, and abuts, at its rear end portion (as the front is located on the lefthand side in Fig. 1), against the inner circumference of the front end of the yoke 31 of the magnet assembly 30. A ring-shaped dust guard 33 is fitted in the inner circumference of the rear end portion of the yoke 31. In Fig. 1, reference numeral 25 designates carbon brushes.

Next, the gist of the invention is described with reference to Fig. 2A to Fig. 4. <Embodiment 1>

Fig. 2A is a sectional side elevation (or a section of line A - A of (b) ) of the magnet assembly; Fig. 2B is a front elevation (or a view in the direction of arrow B of (a) ) of the same magnet assembly; Fig. 2C is a section of line C - C of (a) ; Fig. 3 is an exploded perspective view of the magnet assembly; and Fig. 4 is a front elevation showing the section of a wind passage formed in the magnet assembly.

In the inner circumference of the rear end portion (or the right end portion of Fig. 2A) of the yoke 31, as shown in Fig. 2A, there is fitted the dust guard 33, which is made of a resin to have two engaging protrusions 33b formed integrally and protruded from a ring-shaped body portion 33a. In one portion of the other end portion (or the front end portion) of the yoke 31, there is formed a, rectangular notch 31a, with which the not-shown protrusion formed at the aforementioned fan guide 8 (as referred to Fig. 1) engages to stop the rotation of the yoke 31.

The body portion 33a of the dust guard 33 is protruded a predetermined distance backward (or rightward of Fig. 2A) from one axial end of the yoke 31 thereby to suppress invasion of dust such as iron powder into the yoke 31. On the other hand, the two engaging protrusions 33b, as formed from that body portion 33a, are formed to confront each other at positions circumferentially spaced by 180 degrees, and are shaped into such arcuate shapes as can have their outer circumferences

closely fitted on the inner circumference of the yoke 31, as shown in Fig. 2B. Moreover, axially long slits 33b-1 are formed at the widthwise centers of the individual engaging protrusions 33b. Thus, the dust guard 33 is mounted in the yoke 31 by positioning its individual engaging protrusions 33b to engage with the circumferential clearances between the magnets 32 thereby to push the dust guard 33 forward into the yoke 31, and by fitting the outer circumference of the body portion 33a into the inner circumference of the rear end portion of the yoke 31. As shown in Figs. 2A and 2B, the two engaging protrusions 33b of the dust guard 33 engage with the circumferential clearances, as formed in the yoke 31 between the two magnets 32, to position the individual magnets 32 circumferentially thereby to block the rotations of those magnets 32 along the inner circumference of the yoke 31.

Moreover, each of the engaging protrusions 33b of the dust guard 33 has (such) a slightly larger width size than the circumferential length of the circumferential clearance between the magnets 32 (as to retain a predetermined press-fit allowance) . When those engaging protrusions 33b are brought into engagement with the circumferential clearances between the magnets 32, the individual engaging protrusions 33b are compressed and deformed in the widthwise direction so that their reactions (or elastic forces) act on the circumferential

end faces of the individual magnets 32. As a result, the two magnets 32 are urged radially outward to come into close contact with the inner circumference of the yoke 31. Even in case the adhesions of the individual magnets 32 to the inner circumference of the yoke 31 become weak, the magnets 32 are effectively prevented from axially coming out from the yoke 31. Moreover, the individual outer circumferences of the magnets 32 and the engaging protrusions 33b are shaped into the arcuate curves profiling the inner circumference of the yoke 31 and into close contact with the inner circumference of the yoke 31. Even in case the adhesion of the magnets 32 to the inner circumference of the yoke 31 is weakened, the radial offset of the magnets 32 is suppressed.

Here in this embodiment, the axially extending slits 33b-l are formed in the individual engaging protrusions 33b of the dust guard 33. When the dust guard 33 is fitted in the yoke 31 while the engaging protrusions 33b being inserted between the magnets 32, the engaging protrusions 33b can come into easy engagement with the magnets 32 without obstructing the assemblage of the dust guard 33, thereby to prevent the magnets 32 effectively from coming out. On the other hand, the reaction for the engaging protrusions 33b to push the circumferential end faces of the magnets 32 can rise to prevent the magnets 32 from axially coming out. Moreover, the sectional area of the wind passage, which is formed between

the yoke 31 and the armature 41 by the circumferential clearance between the magnets 32, increases to the extent of the slits 33b-l, so that the flow rate of the cooling wind to pass through the wind passage increases to enhance the cooling efficiency of the DC motor 3.

When the DC motor 3 shown in Fig. 1 is driven, the cooling fan 7 is rotated together with the spindle 4. The cooling wind, as induced by the cooling fan 7, is introduced along the fan guide 8 into the DC motor 3 and passes the DC motor 3 axially thereby to cool the DC motor 3.

Thus in this embodiment, the engaging protrusions 33b of the dust guard 33 are shaped into the arcuate shape to come into close contact with the inner circumference of the yoke 31, and the slits 33b-l are formed in the widthwise centers of the engaging protrusions 33b. As a result, the sectional area (as hatched in Fig. 4) of the wind passage, which is formed between the yoke 31, as shown in Fig. 4, and the armature 41 by the circumferential clearance between the magnets 32, increases to the extent of the slits 33b-l, becomes larger than the sectional area of the wind passage, as shown in Fig. 12, of the case using magnet holders 135 shown in Figs. 1OA, 1OB. As a result, in this embodiment, the flow rate of the cooling wind to pass through the wind passage increases to enhance the cooling efficiency of the DC motor 3. With reference to Fig. 5A and Fig. 6B, here are

investigated how the radial clearance between the dust guard 33 and the armature 41 changes in case the length of the slits 33b-l formed in the individual engaging protrusions 33b of the dust guard 33 is changed. Fig. 5A and Fig. 6A are sectional side elevations of the magnet assembly 30; Fig. 5B is a section of line D - D of Fig. 5A; and Fig. 6B is a section of line E - E of Fig. 6B.

As shown in Fig. 5A, short slits 33b-2 are formed in the individual engaging protrusions 33b of the dust guard 33, and their semicircular end portions a ¹ are positioned in front (as indicated by arrows) of core end face positions f of the armature 41, as shown in Fig. 5B. Then, the radial clearance Ll between the dust guard 33 and the armature 41 is reduced so that the cooling wind to flow through the clearance Ll is throttled and restricted in its flow rate thereby to lower the cooling efficiency.

In this embodiment, on the contrary, the slits 33b-l longer than the slits 33b-2, as shown in Figs .5A, 5B, are formed in the individual engaging protrusions 33b of the dust guard 33, and their semicircular end portions a of the slits 33b-l are positioned at the back (as indicated by arrows) of the core end face positions f of the armature 41, as shown in Fig. 2C. As a result, a larger radial clearance L2 (> Ll) than the radial clearance Ll, as shown in Fig. 5B, is formed between the dust guard 33 and the armature 41, so that the flow rate of the

cooling wind to flow through the clearance L2 is increased to enhance the cooling efficiency.

On the other hand, long slits 33b-3, as shown in Fig.

6A, are formed in the individual engaging protrusions 33b of the dust guard 33, and their semicircular end portions a" are positioned farther backward of this embodiment. Between the dust guard 33 and the armature 41, as shown in Fig. 6B, a radial clearance L3 (> LO) larger than the radial clearance LO between the yoke 31 and the armature 41 is formed so that the flow rate of the cooling wind to flow between the yoke 31 and the armature

41 is further increased to further enhance the cooling efficiency.

Here in this embodiment, the slits 33b-l are formed in the individual engaging protrusions 33b of the dust guard 33. However, these slits 33b-l are not indispensable, but no slit may be formed in the engaging protrusions 33b, as- shown in Figs .

7A, 7B. Here, Fig. 7A is a sectional side elevation (or a section of line F - F of 7B of the magnet assembly, and shows another constitution of the embodiment, and Fig. 7B is a view taken in the direction of arrow G of 7A.

<Embodiment 2>

Next, an embodiment of the invention is described with reference to Fig. 8 and Fig. 9.

Fig. 8 is an exploded perspective view of a magnet assembly of a DC motor or a drive source of an electric tool

(or a rotary hammer drill) according to this embodiment, and Fig. 9 is a front elevation of the rear half of the housing, into which the magnet assembly 30 is incorporated.

In this embodiment, too, the dust guard 33 made of a resin is fitted in one axial end of the yoke 31 of the magnet assembly 30. As in Embodiment 1, the dust guard 33 has the two engaging protrusions 33b formed integrally for engaging with the circumferential clearances between the two magnets 32 assembled in the yoke 31 for preventing the magnets 32 from rotating and coming out.

Thus in this embodiment, the ring-shaped body portion 33a of the dust guard 33 is provided at its portion with an integral protrusion 33c, which is protruded radially outward and has an engaging groove 33d formed axially in the outer face. Here, the housing 2 of the electric tool according to this embodiment is constituted by jointing and integrating the longitudinally split halves. As shown in Fig. 9, the rear half

(or the rear split half B) has a trunk portion 2B-2 of a rectangular cylinder formed integrally. In the lower corner portion of the trunk portion 2B-2, there is integrally formed a rib-shaped oblique engaging protrusion 2a, which extends in the axial direction (or normal to the drawing of Fig. 9) .

Thus, the magnet assembly 30, in which the dust guard 33 is fitted in the axial end portion of the yoke 31, is assembled, from this side to the depth of Fig. 9, with the trunk

portion 2B-2 of the split half 2B of the housing 2 with the dust guard 33 being positioned on this side. At this time, the magnet assembly 30 is so assembled into the trunk portion 2B-2 of the split half 2B that the engaging protrusion 2a on the housing 2 engages with the engaging groove 33d formed in the protrusion 33c integrated with the dust guard 33. Then, the magnet assembly 30 is precisely positioned with respect to the housing 2. Therefore, the magnet assembly 30 can be enhanced in its assemblage and suppressed in its rotation thereby to omit the notch, which has been so additionally worked to the yoke 31 in the background art as to prevent the rotation of the yoke 31.

In addition, effects similar to those of Embodiment 1 can also be obtained in this embodiment. Here, Embodiments 1 and 2 have been described heretofore on the constitution, in which the two magnets 32 are arranged to oppose each other in the yoke 31. The number of the magnets 32 is arbitrary, if it exceeds 2, and the engaging protrusions 33b of the same number as that of the magnets 32 are formed on the dust guard 33.

The invention can be applied not only to the rotary hammer drill using the DC motor as its drive source but also to another arbitrary electric tool such as a driver drill, a shaper saw or an impact tool.