EP2181811A1

EP2181811A1 - Air introduction devices for electric power tools

Info

Publication number: EP2181811A1
Application number: EP09013419A
Authority: EP
Inventors: Atsushi Sakai
Original assignee: Makita Corp
Current assignee: Makita Corp
Priority date: 2008-10-30
Filing date: 2009-10-23
Publication date: 2010-05-05
Anticipated expiration: 2029-10-23
Also published as: CN101722507B; CN101722507A; JP5253966B2; EP2181811B1; JP2010105130A

Abstract

The present invention includes an air introduction device having at least one window (30; 40; 50; 60) for introducing air into a motor housing (10a) of a power tool (I). The at least one window (30; 40; 50; 60) includes a first air path (31; 51), a second air path (32; 61) and a third air path (33; 41) provided between the first air path (31; 51) and the second air path (32; 61). At least two of the first to third air paths (31, 32, 41; 51, 32, 33; 31, 61, 33) have bent path portions.

Description

This application claims priority to Japanese patent application serial number 2008-280005 , the contents of which are incorporated herein by reference.
The present invention relates to air introduction devices including air introduction windows mainly used for introducing cooling air for hand-held electric tools such as electric hammers.
Known electric tools, mainly hand-held electric tools, which include electric motors as power sources, have various measures in order to cool the electric motors with ambient air. In many cases, an air introduction window is provided, for example, at a rear portion of a main body housing for introducing cooling air from outside into a main body. The cooling air introduced into the main body is moved to a front side of the main body housing by a cooling fan or the like to cool the electric motor and is finally discharged to the outside from a front portion of the main body housing. In this case, the air introduction window for introducing ambient air is required to efficiently introduce the ambient air and at the same time, to prevent intrusion of dust, etc. as far as possible. A technique relating an air introduction window and for preventing the dust intrusion without causing reduction in flow rate of a cooling air for a motor is disclosed in Japanese Laid-Open Patent Publication No. 7-266260 . FIG. 7 shows a known air introduction window 70 as disclosed in Japanese Laid-Open Patent Publication No. 7-266260 . The air introduction window 70 includes air passages 72 of a main body housing 71 and air passages 76 of a cover 75, which is attached to a rear portion of the main body housing 71. The air passages 72 and the air passages 76 are alternately arranged so as to form flow paths having crank-shaped bent portions. The air passages 72 of the main body housing 71 and the air passages 76 of the cover 75 are formed to be straight without being bent.
According to the known air introduction window 70, the ambient air drawn into the air passages 76 of the cover 75 flows straight through the air passages 76 and collide against the main body housing 71. The direction of flow of the ambient air is then changed in left and right directions and introduced into the main body housing 71 after flowing straight through the air passages 72 of the main body housing 71. Accordingly, because the flow paths are bent in the course of flowing from the air passages 76 of the cover 75 to the air passages 72 of the main body housing 71, it is possible to prevent intrusion of dust, etc. into the main body housing 71.
However, according to the above-described known technique, because the flow paths, which extend into the main body housing 71, are bent only one time, the the dust intrusion preventing function is insufficient in some cases. It is also possible to reduce the intrusion of dust, etc., by reducing a cross sectional area of each air passage. However, because sufficient flow rate cannot be ensured in this case, sufficient cooling of the electric motor may not be achieved. Further, the intrusion of dust, etc., may be prevented by providing an additional filter, such as a net, on an outer surface of a cover. However, this structure may cause increase in the tool length.
Therefore, there is a need in the art to provide an electric tool having an improved dustproof performance without accompanying degradation in air introduction performance (cooling performance) and increase in the tool length.
One aspect according to the present invention includes an electric tool with an air introduction device having at least one air introduction window. The air introduction window includes a first air path, a second air path and a third air path provided between the first and the second air paths. The first air path may be provided on the side of a cover of a motor housing, and the second pair path may be provided on the side of the motor housing. At least two of the three air paths are bent. With this structure, it is possible to increase the number of bent path portions than with a structure in which a single bent path is provided by arranging straight air paths to be offset from each other. As a result, by suitably setting the cross sectional area of each path dustproof performance can be improved without accompanying degradation in air introduction performance.
In another aspect, each of the first air path, the second air path and the third air path has at least one bent path portion. Because all three air paths have bent path portions, dustproof performance can be further improved.
In a further aspect, each of the first air path, the second air path and the third air path has only one bent path portion. Therefore, ambient air is introduced into the motor housing through the bent path portions that are three in total, the dustproof performance can be further improved.
In a still further aspect, a brush holder unit is mounted to a rear portion of the motor housing, and the brush holder unit includes the cover. Because the air introduction window can be constituted by using a cover of a conventional brush holder unit, dustproof performance can be improved without accompanying substantial increase in cost and tool length.
Additional objects, features, and advantages, of the present invention will be readily understood after reading the following detailed description together with the claims and the accompanying drawings, in which:

FIG. 1 is a side view of an electric tool incorporating an air introduction device according to a first embodiment, with an internal structure around air introduction device shown in a vertical sectional view;
FIG. 2 is an enlarged vertical sectional view around the air introduction device according to the first embodiment;
FIG 3 is a cross sectional view showing air paths of one of air introduction windows of the air introduction device according to the first embodiment and schematically showing the configurations of bent passage portions;
FIG. 4 is a cross sectional view showing air paths of one of air introduction windows of an air introduction device according to a second embodiment;
FIG 5 is a cross sectional view showing air paths of one of air introduction windows of an air introduction device according to a third embodiment;
FIG. 6,is a cross sectional view showing air paths of one of air introduction windows of an air introduction device according to a fourth embodiment; and
FIG. 7 is a cross sectional view of a known air introduction window.

Each of the additional features and teachings disclosed above and below may be utilized separately or in conjunction with other features and teachings to provide improved air introduction devices for electric power tools. Representative examples of the present invention, which examples utilize many of these additional features and teachings both separately and in conjunction with one another, will now be described in detail with reference to the attached drawings. This detailed description is merely intended to teach a person of skill in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the invention. Only the claims define the scope of the claimed invention. Therefore, combinations of features and steps disclosed in the following detailed description may not be necessary to practice the invention in the broadest sense, and are instead taught merely to particularly describe representative examples of the invention. Moreover, various features of the representative examples and the dependent claims may be combined in ways that are not specifically enumerated in order to provide additional useful embodiments of the present teachings.
First to fourth embodiments according to the present invention will now be described with reference to FIGS. 1 to 6. FIG. 1 shows an entire electric power tool 1 with an air introduction device according to a first embodiment. In this embodiment, an electric hammer is illustrated as an example of the electric power tool 1 that is used for a chipping operation, etc. The electric power tool 1 has a main body 2 and a D-shaped handle portion 3. The main body 2 includes a hammering element for hammering a bit 4 attached at a tip portion of the main body 2, a piston reciprocally moved for imparting a hammering force to the hammering element with compressed air, a crank mechanism for reciprocally moving the piston, and an electric motor 10 as a power source for applying a rotational force to the crank mechanism. All of these mechanisms and members except for the electric motor 10 are accommodated within a cylindrical main body housing 2a. The bit 4 is attached so as to protrude from the tip portion of the main body housing 2a. A motor housing 10a for accommodating the electric motor 10 is integrally formed with a rear portion of the main body 2 and a front portion of the handle portion 3 and extends therebetween. With this embodiment, a rotational axis J of the electric motor 10 extends perpendicular to a hammering direction of the bit 4 (i.e., the reciprocating direction of the piston). Thus, the electric motor 10 is a vertically installed motor in this embodiment. The basic constructions of the main body 2 with an L-shaped configuration and the handle portion 3 are known in the prior art and thus the details will not be described.
The electric motor 10 is an AC motor having a rotor 11 and a stator 12 and is started by pulling a trigger switch lever (not shown) arranged on an inner peripheral side of the handle 3. A rotor shaft 11a (output shaft) of the rotor 11 is rotatably supported by a motor housing 10a via upper and lower bearings 13 (only the lower bearing 13 is shown in FIG. 1). A rotational axis of the rotor shaft 11a corresponds to the rotational axis J of the electric motor 10. The lower bearing 13 is mounted to a lower portion of the motor housing 10a.
A brush holder unit 20 is mounted on the lower portion of the motor housing 10a. The brush holder unit 20 is an assembly in which a pair of left and right carbon brushes (not shown) slidably contacting with a commutator 11b, and connector terminal portions and necessary electrical wiring lines for the side of the stator 12 etc. are assembled to a cover 21 for covering the lower portion of the motor housing 10a. An assembling operation of the carbon brushes to the commutator 11b and a necessary wiring operation for the stator 12 can be completed at one time when the brush holder unit 20 is mounted to the lower portion of the motor housing 10a. The brush holder unit 20 is known in the prior art and thus the details will not be described.
Because of the presence of the cover 21 for the brush holder unit 20, the lower portion of the motor housing 10a has a double bottom structure (or a double wall structure). According to this embodiment, the air introduction device includes a plurality of air introduction windows 30 as an air inlet for introducing cooling air (ambient air) that mainly serves to cool the electric motor 10. The air introduction device is provided by utilizing this double bottom structure. The cooling air introduced into the motor housing 10a via the air introduction windows 30 flows upwardly in order to cool the electric motor 10 and then is exhausted in an ambient environment via an exhaust port (not shown) that is provided adjacent to a rear portion of the main body housing 2a.
The details of each of the air introduction windows 30 of the air introduction device according to this embodiment are shown in FIG. 2. In this embodiment, two groups of three air introduction windows 30 are arranged symmetrically on the left and right sides as viewed from the lower side in FIG. 2, in the double bottom structure formed by the motor housing 10a and the cover 21 of the brush holder unit 20, which is attached to the rear portion of the motor housing 10a. The number of introduction windows 30 can be increased or decreased as occasion demands. The air introduction windows 30 have the same configuration and only one air introduction window 30 will be described in detail. The air introduction window 30 has a first air path 31 on the side of the cover 21 and a second air path 32 on the side of the motor housing 10a. A clearance for flow communication is formed between the cover 21 and the motor housing 10a and serves as a third air path 33.
The first air path 31 has a first crank-shaped bent path portion. More specifically, the first air path 31 includes inlet ports 31a (lower side ports) and outlet ports 31b (upper side ports) connected to the inlet ports 31a via crank-shaped bent passages, which communicate with each other and jointly define the first crank-shaped bent path portion. Similarly, the second air path 32 has a second crank-shaped bent path portion. More specifically, the second air path 32 includes inlet ports 32a (lower side ports) and outlet ports 32b (upper side ports) connected to the inlet ports 32a via crank-shaped bent passages, which communicate with each other and jointly define the second crank-shaped bent path portion. Each of the inlet ports 31a and the outlet ports 31b of the first air path 31 as well as each of the inlet ports 32a and the outlet ports 32b of the second air path 32 have a rectangular configuration elongated in a direction perpendicular to the sheet of FIGS. 2 and 3.
Further, the third air path 33 has a third crank-shaped bent path portion. More specifically, the third air path 33 is defined between the inlet ports 31b of the first air path 31 and the outlet ports 32a of the second air path 32 via crank-shaped bent passages that define the third crank-shaped bent path portion. These features are best shown in FIG. 3. In FIG. 3, a lower side of the cover 21 is an atmospheric side and an upper side of the motor housing 10a is an inner side of the motor housing 10a. The motor cooling air flows from the upper side to the lower side in FIG. 3. In this specification, the term "crank-shaped bent path portion" or "crank-shaped bent passage" is used to mean a path portion or a passage formed as a result of an offset (in left and right directions in FIG. 3) between an inlet port(s) and an outlet port(s) of an air path, so that an impinging portion(s) of air is(are) provided in the midway of the air path. Conversely, a term "straight path" used in this specification means a path or a passage, in which an inlet and an outlet are not offset from each other in a direction perpendicular to the direction of flow of air into the inlet.
In this embodiment, the width (in right and left directions in FIG. 3) of each of the inlet ports 31a of the first air path 31 is set to be the same as the width (in right and left directions in FIG. 3) of the outlet ports 31b. In addition, the distance between the inlet ports 31a of the first air path 31 is set to be the same as the width of each of the inlet ports 31a. Similarly, the distance between the outlet ports 31b is set to be the same as the width of each of the outlet ports 31a. Further, the width (in right and left directions in FIG. 3) of each of the inlet ports 32a of the second air path 32 is set to be the same as the width (in right and left directions in FIG. 3) of the outlet ports 32b. The distance between two adjacent inlet ports 32a of the second air path 32 is set to be the same as the width of each of the inlet ports 32a. Similarly, the distance between the outlet ports 32b is set to be the same as the width of each of the outlet ports 32a. Furthermore, the width of each of the inlet ports 31a and the outlet ports 31b is the same as the width of each of the inlet ports 32a and the outlet ports 32b. In this connection, the inlet ports 32a of the second air path 32 are offset in right and left directions from the outlet ports 31b of the first path 31 by a distance equal to the width of the inlet and outlet ports 31a, 31b, 32a and 32b.
The above arrangement enables to easily mold the cover 21 and the motor housing 10a having the first path and the second path, respectively, from resin, rubber or any other suitable material. For example, in the case that the cover 21 or the motor housing 10a is molded from resin by an injection molding process, dies having pins and movable relative to each other are used. As the dies are separated from each other after the molding process, the pins may form the inlet and outlet ports as well as the bent passage portions in the molded product.
According to the air introduction window 30 as shown in FIG. 3, the ambient air, which is introduced from the outlet ports 31a of the first air path 31, changes its flow direction for a first time in the first air path 31 (the first bent path portion). The ambient air exhausted from the outlet ports 31b of the first air path 31 changes its flow direction for a second time in the third air path 33 (the second bent path portion) communicating with the inlet ports 32a, Thereafter, the ambient air changes its direction for a third time in the second air path 32 and is introduced into the motor housing 10a via the outlet ports 32b and then flows upwardly to cool the electric motor 10. Accordingly, the flow of air is bent at three points as the air flows along the air paths from the atmospheric side of the cover 21 into the motor housing 10a via the air introduction window 30, and therefore, the intrusion of dust can be more efficiently prevented than in the known device. In addition, the total flow area of the air paths 31, 32, 33 can be set to be enough, and therefore, the flow rate of air flowing through the air introduction window 30 can be also ensured enough.
According to the above-mentioned air introduction window 30, the bent path portions that are three in total (i.e., three layers of bent paths) are provided in the double bottom structure formed by the motor housing 10a and the cover 21. Therefore, by setting the flow area of each of the air paths (or air path layers) to be enough, it is possible to obtain more improve dustproof performance without accompanying degradation in air introduction performance.
Further, according to this embodiment, three layered bent path portions are provided in the double bottom structure formed by the motor housing 10a and the cover 21 of the brush holder unit 20, which is attached to the rear portion of the motor housing 10a. Because members that are normally provided in this kind of power tool can be used for this structure, it is not necessary to incorporate additional members, such as a filter, and therefore, it is possible to achieve the above-mentioned effect without increase in the cost and a tool length.
Various modifications can be made to the above-described embodiment. For example, the present invention can be incorporated by another configuration into the double bottom structure formed by the motor housing 10a and the cover 21 of the brush holder unit 20 as shown in FIGS. 4 to 6.
One of air introduction windows 40 of an air introduction device according to a second embodiment is shown in FIG. 4. The air introduction window 40 is different from the air introduction window 30 in that a third air path 41 extending between the motor housing 10a and the cover 21 is not formed to have a bent path portion but is formed as a straight path. The other structures are the same as the first embodiment, and therefore, an explanation of these structures is omitted by affixing the same reference numerals in FIG. 4 for the same or similar components of the first embodiment. Because the third air path 41 is formed as a straight path, the inlet ports 31b of the first air path 31 and the outlet ports 32a of the second air path 32 are not offset from each other so that the inlet ports 31b and the outlet ports 32a are aligned with each other with respect to left and right directions. Therefore, the ambient air introduced from the inlet windows 31a changes its direction of flow for one time in the first air path 31 before the ambient air flows out of the outlet ports 31b. Afterwards, the ambient air flows straight into the outlet ports 32a of the second air path 32 through the third air path 41 without changing the direction of flow in the third air path 41. The ambient air introduced into the second air path 32 via the inlet ports 32a once more changes its direction of flow in the second air path 32 and then flows out of the outlet ports 32b into the motor housing 10a.
As described above, according to the air introduction device having the air introduction windows 40 of the second embodiment, each introduction window 40 provides three layered flow paths including the first, second and third air paths 31, 32, 41 in the double bottom structure formed by the motor housing 10a and the cover 21 of the brush holder unit 20. Two layers of the first and the second air paths 31, 32 have the crank-shaped bent path portions. Therefore, it is possible to improve the dustproof performance than in the known device having only one bent path portion in a single layer with respect to the introducing direction of the ambient air.
One of air introduction windows 50 of an air introduction device according to a third embodiment is shown in FIG. 5. The air introduction window 50 is different from the air introduction window 30 of the first embodiment in that a first air path 51 is not formed to have a bent path portion but is formed as a straight path. This straight first air path 51 is formed within the cover 21 of the brush holder unit 20. The ambient air introduced from inlet ports 51a of the first air path 51 flows straight and is exhausted out of outlet ports 51b. The ambient air exhausted from the outlet ports 51b changes in direction of flow in two path layers (the third air path 33 and the second air path 32) and then flows into the motor housing 10a.
As described above, according to the air introduction window 50 of the third embodiment, because the direction of flow of air is changed at the third and the second air paths 33, 32, it is possible to obtain more improved dustproof performance than in the known device.
One of air introduction windows 60 of an air introduction device according to a fourth embodiment is shown in FIG. 6. The air introduction window 60 is different from the air introduction window 30 of the first embodiment in that the second air path 61 is not formed to have a bent path portion but is formed as a straight path. According to the air introduction window 60, the ambient air introduced into the inlet ports 31a of the first air path 31 changes for a first time in the first air path 31 and is exhausted out of the outlet ports 31b. The ambient air exhausted from the outlet ports 31b changes its direction of flow again at the third air path 33 and flows into inlet ports 61a of second air path 61. The ambient air introduced into the inlet ports 61a flows straight through the second air path 61 without changing its direction of flow and thereafter flows into the motor housing 10a via outlet ports 61b.
As described above, according to the air introduction window 60 of the fourth embodiment, the direction of flow of air changes at two path layers of the first and third air paths 31, 33 out of the first, second and third air paths 31, 61, 33. Therefore, the dust intrusion can be considerably reduced compared with the case where ambient air is introduced into the motor housing 10a after changing its direction of flow for only one time. As a result, the air introduction window 60 is improved in the dustproof performance.
According to the air introduction windows 40, 50, 60 of the above described second to fourth embodiments, two air paths out of the first to third air paths 31, 32, 33; 41, 51, 61 provided in the double bottom structure formed by the motor housing 10a and the cover 21 of the brush holder unit 20 have bent path portions. Therefore, the intrusion of dust etc., can be more securely reduced than with a structure shown in FIG. 7 having a single bent path portion provided between straight air paths of the main body housing 71 and the cover 75 by shifting them to be offset in a direction perpendicular to the flow of air entering the passages 76.
Further, because additional members, such as a mesh filter, are not necessary by the use of the brush holder unit 20 and the cover 21, which are normally provided in this kind of power tool, it is possible to improve a dustproof property without increasing the cost and a tool length.

Claims

An air introduction device comprising at least one air introduction window (30; 40; 50; 60) for introducing air into a motor housing (10a) of a power tool (1),
wherein the at least one air introduction window (30; 40; 50; 60) comprises:
a first air path (31; 51);

a second air path (32; 61); and

a third air path (33; 41) provided between the first air path (31; 51) and the second air path (32; 61);
wherein at least two of the first to third air paths (31, 32, 41;51, 32, 33; 31, 61, 33) have bent path portions.
The air introduction device as in claim 1, wherein the motor housing (10a) has an electric motor (10) accommodated therein and the at least one air introduction window (30;40;50;60) is provided in a double wall structure formed by the motor housing (10a) and a cover (21).
The air introduction device as in claim 1 or 2, wherein each of the first air path (31), the second air.path (32) and the third air path (33) has at least one bent path portion.
The air introduction device as in claim 3, wherein each of the first air path (31), the second air path (32) and the third air path (33) has only one bent path portion.
The air introduction device as in any one of claims 2 to 4, wherein :
a brush holder unit (20) is mounted to a rear portion of the motor housing (10a), and

the brush holder unit (20) includes the cover (21).
The air introduction device as in claim 1, wherein:
the first air path (31; 51) includes a plurality of passages formed in a first member (21; 22), and the second path (32; 61) includes a plurality of passages formed in a second member (10a).
The air introduction device as in claim 6, wherein;
the passages of each of the first and third air pahs (31, 41) have bent passage portions jointly defining the bent path portion.
The air introduction device as in claim 6, wherein the passages of one of the first and third air paths (31, 41) have bent passage portions jointly defining the bent path portion.
The air introduction device as in claim 1, wherein:
the power tool (1) further includes a cover (21) for covering the motor housing (10a);

the first air path (31; 51) is formed in the cover (21);

the third air path (33; 41) is formed in the motor housing (10a); and

the second air path (32; 61) extends across a space defined between the cover (21) and the motor housing (10a).
The air introduction device as in claim 9, wherein the cover (21) is assembled with brushes of the motor (10).