GB2573953A

GB2573953A - Power tool

Info

Publication number: GB2573953A
Application number: GB1912066.6A
Authority: GB
Inventors: Miyagi Takanori; Shimizu Hiroyuki; Endo Daisuke
Original assignee: Nitto Kohki Co Ltd
Current assignee: Nitto Kohki Co Ltd
Priority date: 2017-03-29
Filing date: 2018-03-22
Publication date: 2019-11-20
Anticipated expiration: 2038-03-22
Also published as: TWI677412B; CN110520251A; KR20190116429A; GB2573953B; KR102303876B1; WO2018180835A1; CN110520251B; TW201900356A; JP6581725B2; GB201912066D0; DE112018001786T5; JPWO2018180835A1

Abstract

The purpose of the present invention is to provide a power tool that can make access to the interior of a housing easier and safer to perform. The present invention is a power tool (10) provided with a commutator motor (14) in a housing (12), wherein the housing (12) has a first housing unit (30), a second housing unit (32) that can move with respect to the first housing unit (30), a tapping screw (34) that fixes these, and a cover (36) that is attached by being sandwiched between the first housing unit (30) and the second housing unit (32). When the tapping screw (34) is loosened, the tapping screw (34) engages with an engaging ring (50) of the second housing unit (32) by being displaced in a direction away from the first housing unit (30) and displaces the second housing unit (32) in the away direction. In this manner, the cover (36) is in a removable state. In addition, when the tapping screw (34) is tightened, a state in which the cover (36) is attached is restored by the second housing unit (32) being displaced in a direction toward the first housing unit (30) by the tapping screw (34).

Description

Power Tool

Technical Field:

[0001] The present invention relates to a power tool having a power unit in a housing. Background Art:

[0002] A power tool having a power unit in a housing is generally configured to allow a worker to perform maintenance of the power unit, etc. disposed in the housing by disassembling the housing. For example, Patent Literature 1 discloses a grinder having a commutator motor as a power unit in a housing comprising a motor housing and a rear cover. Generally, a commutator motor has carbon brushes brought into contact with a commutator rotating together with a rotor to supply an electric current to the rotor. The carbon brushes need to be periodically replaced because the carbon brushes gradually become worn by friction with the rotating commutator. In this grinder, the carbon brushes are replaced after the rear cover has been detached by removing a securing screw securing the rear cover to the motor housing.

Citation List:

Patent Literature:

[0003] Patent Literature 1: Japanese Patent Application Publication No. 2007-152479 Summary of Invention:

Technical Problem:

[0004] With regard to power tools that require removal of a part of the housing in order to perform maintenance of the power unit disposed in the housing as in the abovedescribed conventional grinder, the removed screw may be lost, and a delicate operation is required to reinstall the screw removed temporarily, which is troublesome. In addition, if a part of the housing is removed, components disposed in the housing, such as an electronic circuit and wiring, are exposed, which may result in breakage of these components.

[0005] The present invention has been made in view of the above-described problems with the conventional technique, and an object of the present invention is to provide a power tool having a power unit in a housing, which allows easier and safer access to the interior of the housing.

Solution to Problem:

[0006] The present invention provides a power tool having a power unit in a housing. The housing includes the following: a first housing part; a second housing part displaceable relative to the first housing part; a securing device for securing the second housing part to the first housing part; an interior access opening for accessing the interior of the housing; and a cover held between the first housing part and the second housing part secured to each other by the securing device to close the interior access opening. The securing device is configured such that, when rotated in a first direction, the securing device is displaced in a direction away from the first housing part, and that, when rotated in a second direction reverse to the first direction, the securing device is displaced in a direction toward the first housing part. When the securing device is rotated in the first direction and thus displaced in the direction away from the first housing part, the securing device engages the second housing part in the direction away from the first housing part and displaces the second housing part in the direction away from the first housing part to release the cover from being held between the first housing part and the second housing part, thereby allowing removal of the cover from between the first housing part and the second housing part. When the securing device is rotated in the second direction and thus displaced in the direction toward the first housing part, the securing device engages the second housing part in the direction toward the first housing part and displaces the second housing part in the direction toward the first housing part to hold the cover between the first housing part and the second housing part.

[0007] The power tool is configured such that the second housing part is displaced to allow removal of the cover in response to rotation of the securing device securing the second housing part to the first housing part. With this configuration, the power tool can be brought into a state where the interior of the housing can be accessed without completely removing the securing device and the second housing part from the first housing part. Accordingly, it is possible to prevent the loss of the securing device when accessing the interior of the housing to perform maintenance or the like of the power unit in the housing. It is also possible to reduce the possibility of breakage of the power unit and other components in the housing due to excessive exposure thereof to the outside. Further, to restore the power tool to the previous state where the cover is held between the first and second housing parts, the securing device and the second housing part need not be aligned relative to the first housing part again for reinstallation, but it is only necessary to simply turn the securing device. Therefore, the reinstalling operation can be facilitated as compared with the conventional power tool.

[0008] The securing device may be a securing screw threadedly engaged with the first housing part, the securing screw being configured such that, when rotated in the first direction, the securing screw is loosened, and that, when rotated in the second direction, the securing screw is tightened.

[0009] More specifically, the arrangement may be as follows. The securing screw has a shank and a head. The second housing part has an insertion hole receiving the shank, a recess contiguous with the insertion hole to receive the head, and a screw head engaging portion disposed so as to cover a part of the head to hold the head in the recess. When the securing screw is loosened by being threadedly rotated, the head of the securing screw engages the screw head engaging portion to displace the second housing part in the direction away from the first housing part. In this case, the screw head engaging portion may be in the shape of a ring having a central opening, so that the securing screw can be threadedly rotated with a tool inserted through the central opening.

[0010] In addition, the arrangement may be as follows. The first housing part has a resin-made internally extending portion to be threadedly engaged with the securing screw. The securing screw is a self-tapping screw to be threaded into the internally extending portion.

[0011] With the above-described arrangement, there is no need to prepare an internally threaded portion to be threadedly engaged with the securing screw in the process of manufacturing the first housing part, and it is possible to reduce the cost of manufacturing components.

[0012] In addition, the arrangement may be as follows. The first housing part has a first locking portion, and the second housing part has a second locking portion engageable with the first locking portion. Engagement of the first locking portion and the second locking portion limits the range of displacement of the second housing part relative to the first housing part in the direction away from the first housing part, thereby preventing the securing device from completely disengaging from the first housing part within the range of displacement.

[0013] Specifically, the arrangement may be as follows. The second locking portion is a locking screw threadedly engaged with the second housing part, and the first housing part has a slot receiving the tip of the locking screw. The first locking portion is an end portion of the slot.

[0014] With the above-described arrangement, the second housing part is prevented from being displaced more than necessary. Further, because the securing screw is prevented from disengaging from the first housing part, it is possible to prevent the loss of the securing screw even more reliably.

[0015] Specifically, the arrangement may be as follows. The power unit is a commutator motor having a brush, and the brush is disposed where the brush can be replaced through the interior access opening.

[0016] Embodiments of a power tool according to the present invention will be explained below on the basis of the accompanying drawings.

Brief Description of Drawings:

[0017] Fig. 1 is a side view of a power tool according to an embodiment of the present invention.

Fig. 2 is a plan view of the power tool shown in Fig. 1.

Fig. 3 is a sectional side view taken along the line III-III in Fig. 2.

Fig. 4 is a sectional plan view taken along the line IV-IV in Fig. 3.

Fig. 5 is a first fragmentary sectional view of a main part of the power tool, showing a cover removing operation.

Fig. 6 is a second fragmentary sectional view of a main part of the power tool, showing the cover removing operation.

Fig. 7 is a third fragmentary sectional view of a main part of the power tool, showing the cover removing operation.

Fig. 8 is a fourth fragmentary sectional view of a main part of the power tool, showing the cover removing operation.

Fig. 9 is a sectional plan view taken along the line IV-IV in Fig. 3, showing the power tool in a state where a second housing part has been displaced to the position shown in Fig. 7.

Description of Embodiments:

[0018] As shown in Figs. 1 to 3, a power tool 10 according to an embodiment of the present invention is an electric motor-driven tool having a commutator motor 14 in a housing 12 as a power unit. The commutator motor 14 has a rotating output shaft 16 to which a tool output shaft 20 is drivingly connected through a bevel gear 18. A required member, e.g. a disk-shaped polishing pad, is attached to the tool output shaft 20 according to each particular application.

[0019] The commutator motor 14 includes, as shown in Fig. 3, a rotor 22 rotatably mounted to the housing 12, a stator 24 disposed around the rotor 22 and secured to the housing 12, and two brushes 26 disposed so as to contact a commutator 23 attached to the rotor 22. A switch 28 is mounted to the housing 12. The driving of the commutator motor 14 is ON/OFF controlled by actuating the switch 28. The brushes 26 gradually become worn by sliding contact with the commutator 23 rotating at high speed. Therefore, the brushes 26 need to be replaced with new ones after the power tool 10 has been used for a certain period of time.

[0020] The housing 12 has the following: a first housing part 30 retaining the commutator motor 14; a second housing part 32 mounted at the rear of the first housing part 30; a self-tapping screw (securing device, securing screw) 34 securing the second housing part 32 to the first housing part 30; and two covers 36 held between the first housing part 30 and the second housing part 32. The second housing part 32 is secured to the first housing part 30 in such a manner that a forward end portion 32a of the second housing part 32 covers the outer peripheral surface 30a of a rear end portion of the first housing part 30. The second housing part 32 is slidingly displaceable relative to the first housing part 30 in the direction of a longitudinal axis L. An interior access opening 37 for accessing the interior of the housing 12 is formed between a rear end recess 30b of the first housing part 30 and a forward end recess 32b of the second housing part 32. The interior access opening 37 is closed with the associated cover 36 when the power tool 10 is in use. The first housing part 30 has an internally extending portion 38 extending into the second housing part 32. The internally extending portion 38 is provided with a hole 40 into which the self-tapping screw 34 is to be threaded. The self-tapping screw 34 is threaded into the hole 40 while forming a thread groove in the side wall of the hole 40 in the internally extending portion 38. In this way, the self-tapping screw 34 is secured. The first housing part 30 is formed of a resin in its entirety, thereby facilitating the threading of the selftapping screw 34 into the internally extending portion 38.

[0021] The second housing part 32 has an insertion hole 46 receiving a shank 42 of the self-tapping screw 34, a recess 48 contiguous with the insertion hole 46 and configured to receive a head 44 of the self-tapping screw 34, and a metallic engagement ring (screw head engaging portion) 50 press-fitted and secured in the recess 48 so as to cover the periphery of the head 44 of the self-tapping screw 34 in the direction of the longitudinal axis L. The head 44 of the self-tapping screw 34 is held in the recess 48 by the engagement ring 50. Accordingly, the self-tapping screw 34 is prevented from being removed from the second housing part 32. To tighten or loosen the self-tapping screw 34 relative to the first housing part 30, the self-tapping screw 34 is threadedly rotated with a tool, e.g. a screwdriver, inserted through a central opening 52 in the engagement ring 50. It should be noted that the structure in which the engagement ring 50 is press-fitted into the recess 48 may be replaced with a structure in which a groove is provided in the inner peripheral surface of the recess 48 and a retaining ring is fitted into the groove to thereby form a screw head engaging portion.

[0022] A circuit board 60 is disposed on the internally extending portion 38 of the first housing part 30 in such a manner as to be covered with the second housing part 32.

The circuit board 60 is equipped with an LED 62 for indicating the status of the power tool 10. The circuit board 60 is housed in a casing made of a resin and installed from the rear side (right-hand side as seen in the figures) of the first housing part 30 by being slid relative to the internally extending portion 38 of the first housing part 30. The second housing part 32 has a light-diffusing member 64 disposed at a position aligned with the LED 62 to diffuse light from the LED 62. Consequently, light emitted from the LED 62 is diffused by the light-diffusing member 64, so that the outer surface of the light-diffusing member 64 shines with substantially uniform brightness, thereby allowing light emission of the LED 62 to be visually recognized easily.

[0023] As shown in Fig. 4, a locking screw (second locking portion) 54 is threadedly engaged with the second housing part 32. The locking screw 54 extends in a direction perpendicular to the longitudinal axis L. The internally extending portion 38 has a slot 56 extending in the direction of the longitudinal axis L. The slot 56 is configured to receive the tip 58 of the locking screw 54.

[0024] The brushes 26 of the commutator motor 14 need to be replaced periodically because the brushes 26 gradually become worn by friction with the commutator 23.

The power tool 10 is configured to allow replacement of the brushes 26 according to the following procedure.

[0025] First of all, in a state where the second housing part 32 is secured to the first housing part 30 by the self-tapping screw 34 as shown in Fig. 5, the self-tapping screw 34 is loosened by being threadedly rotated counterclockwise (first direction). Consequently, the self-tapping screw 34 is displaced in a direction (rightward as seen in the figure) away from the first housing part 30 along the longitudinal axis L, and the head 44 engages the engagement ring 50 as shown in Fig. 6. As the self-tapping screw 34 is further loosened, the engagement ring 50 is pressed by the head 44 of the selftapping screw 34, and the second housing part 32, together with the self-tapping screw 34, is displaced in the direction away from the first housing part 30. When the second housing part 32 has been displaced to the position shown in Fig. 7, the covers 36 are released from being held between the first housing part 30 and the second housing part 32. Thus, it becomes possible to remove the covers 36 from between the first housing part 30 and the second housing part 32 as shown in Fig. 8.

[0026] It should be noted that when the second housing part 32 reaches the position shown in Fig. 7, the tip 58 of the locking screw 54 engages an end portion (first locking portion) 66 of the slot 56, as shown in Fig. 9, thereby preventing the second housing part 32 from being further displaced in the direction away from the first housing part 30. In other words, the combination of the locking screw 54 and the end portion 66 of the slot 56 limits the range of displacement of the second housing part 32 relative to the first housing part 30. The self-tapping screw 34 has a length sufficient to prevent the self-tapping screw 34 from disengaging from the first housing part 30 within the displacement range.

[0027] As shown in Fig. 8, when each cover 36 is removed, the associated interior access opening 37 is opened, which was closed until then by being covered by the cover 36. It is possible to detach the old brushes 26 from respective brush holders 70 and to attach new brushes 26 to the brush holders 70 through the interior access openings 37. After the new brushes 26 have been attached to the brush holders 70, the covers 36 are reinstalled, and the self-tapping screw 34 is tightened by being threadedly rotated

- 8 clockwise (second direction). Consequently, the self-tapping screw 34 is displaced in a direction toward the first housing part 30 and engages the second housing part 32 to displace the second housing part 32 in the direction toward the first housing part 30. When the second housing part 32 has returned to the position shown in Fig. 5 where the second housing part 32 is secured to the first housing part 30, the covers 36 are held between the first housing part 30 and the second housing part 32 again. In this way, the replacement operation of the brushes 26 is completed.

[0028] The power tool 10 allows replacement of the brushes 26 or other components disposed in the housing 12 without the need to remove the second housing part 32 and the self-tapping screw 34, which are parts of the housing 12. Accordingly, the components disposed in the housing 12, such as the circuit board 60 and the LED 62, will not be exposed to the outside, and there is therefore less possibility of these components being accidentally broken. It is also possible to prevent the loss of the self-tapping screw 34. Λ self-tapping screw is threaded into a hole in the mating part while forming a thread groove in the inner peripheral surface of the hole. In this regard, if a self-tapping screw that has been installed is removed and reinstalled into the same hole, a thread groove may be undesirably formed at a position different from the previous one. If so, the strength of the inner peripheral surface of the hole is degraded. If this is repeated many times, the inner peripheral surface may be destroyed, and eventually, it may become impossible to hold the self-tapping screw. The power tool 10 allows access to the brushes 26 and so forth in the housing 12 without the need to remove the self-tapping screw 34, as has been stated above. Therefore, it is possible to prevent damage to the threaded hole by the self-tapping screw 34. Further, the removal of the self-tapping screw 34 is disabled by limiting the displacement range of the second housing part 32 by using the combination of the locking screw 54 and the slot 56. Consequently, there is no possibility of the self-tapping screw 34 being accidentally removed, and it is possible to prevent the above-described problems even more reliably.

[0029] Although the power tool 10 according to an embodiment of the present invention has been explained, the present invention is not limited thereto but may be modified in a variety of ways. For example, the first housing part 30 need not necessarily be formed by a resin in its entirety, but it is only necessary that the internally extending portion 38 of the first housing part 30, into which the self-tapping screw 34 is to be threaded, should be formed of a resin. Further, as a securing screw for securing the second housing part 32 to the first housing part 30, a conventional screw may be used in place of the self-tapping screw 34. In this case, however, an internal thread needs to be formed in the internally extending portion 38 in advance. Further, the arrangement may be as follows. A washer integrated screw is used as a securing screw, and the second housing part 32 is configured to hold not the screw head 44 but the washer. Further, the securing device for securing the second housing part 32 and the first housing part 30 may be other than a screw. For example, the arrangement may be as follows. A member having a shank with a projection projecting radially outward is used as a securing device, and the first housing part is provided with a hole having an inclined groove (or a helical groove) formed in the inner peripheral surface thereof. The securing device is attached to the first housing part in such a manner that the projection is engaged with the inclined groove, thereby allowing the securing device to be displaced in a direction away from and in a direction toward the first housing part in response to rotation of the securing device. The present invention is not limited to power tools equipped with a commutator motor but may also similarly be applied to power tools equipped with other power units such as a brushless motor, an air motor, an engine, etc. Further, power tools include machine tools such as a portable or stationary drill and a drilling machine.

Reference Signs List:

[0030] Power tool 10; housing 12; commutator motor (power unit) 14; rotating output shaft 16; bevel gear 18; tool output shaft 20; rotor 22; commutator 23; stator 24; brush 26; switch 28; first housing part 30; outer peripheral surface 30a; rear end recess 30b;

second housing part 32; forward end portion 32a; forward end recess 32b; self-tapping screw (securing screw) 34; cover 36; interior access opening 37; internally extending portion 38; hole 40; shank 42; head 44; insertion hole 46; recess 48; engagement ring (screw head engaging portion) 50; opening 52; locking screw (second locking portion) 54; slot 56; tip 58; circuit board 60; LED 62; light-diffusing member 64; end portion (first locking portion) 66; brush holder 70; longitudinal axis L.

Claims

1. A power tool having a power unit in a housing;

the housing including:

a first housing part;

a second housing part displaceable relative to the first housing part;

a securing device for securing the second housing part to the first housing part; an interior access opening for accessing an interior of the housing; and a cover held between the first housing part and the second housing part secured to each other by the securing device to close the interior access opening;

the securing device being configured such that, when rotated in a first direction, the securing device is displaced in a direction away from the first housing part, and that, when rotated in a second direction reverse to the first direction, the securing device is displaced in a direction toward the first housing part;

wherein, when the securing device is rotated in the first direction and thus displaced in the direction away from the first housing part, the securing device engages the second housing part in the direction away from the first housing part and displaces the second housing part in the direction away from the first housing part to release the cover from being held between the first housing part and the second housing part, thereby allowing removal of the cover from between the first housing part and the second housing part; and wherein, when the securing device is rotated in the second direction and thus displaced in the direction toward the first housing part, the securing device engages the second housing part in the direction toward the first housing part and displaces the second housing part in the direction toward the first housing part to hold the cover between the first housing part and the second housing part.

2. The power tool of claim 1, wherein the securing device is a securing screw thrcadcdly engaged with the first housing part, the securing screw being configured such that, when rotated in the first direction, the securing screw is loosened, and that, when rotated in the second direction, the securing screw is tightened.

3. The power tool of claim 2, wherein the securing screw has a shank and a head;

the second housing part having an insertion hole receiving the shank, a recess contiguous with the insertion hole to receive the head, and a screw head engaging portion disposed so as to cover a part of the head to hold the head in the recess;

wherein when the securing screw is loosened by being threadedly rotated, the head of the securing screw engages the screw head engaging portion to displace the second housing part in the direction away from the first housing part.

4. The power tool of claim 3, wherein the screw head engaging portion is in a shape of a ring having a central opening, so that the securing screw can be threadedly rotated with a tool inserted through the central opening.

5. The power tool of any one of claims 2 to 4, wherein the first housing part has a resin-made internally extending portion to be threadedly engaged with the securing screw, the securing screw being a self-tapping screw to be threaded into the internally extending portion.

6. The power tool of any one of claims 1 to 5, wherein the first housing part has a first locking portion, the second housing part having a second locking portion engageable with the first locking portion;

wherein engagement of the first locking portion and the second locking portion limits a range of displacement of the second housing part relative to the first housing part in the direction away from the first housing part, thereby preventing the securing device from completely disengaging from the first housing part within the range of displacement.

7. The power tool of claim 6, wherein the second locking portion is a locking screw threadedly engaged with the second housing part, the first housing part having a slot to receive a tip of the locking screw, the first locking portion being an end portion of the slot.

8. The power tool of any one of claims 1 to 7, wherein the power unit is a commutator motor having a brush, the brush being disposed where the brush can be replaced through the interior access opening.