JP2007143314A - Forward-backward rotation switching device for power tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the lifetime of a contact by always keeping a contact-separation speed of a contact constant. <P>SOLUTION: An operation ring 15 is connected to a brush base 14 of a forward-backward rotation switching device 12 while having a relatively rotatable play from a switching position of either of forward or backward rotation to a neutral position. The brush base 14 is formed with an engagement piece 26, and a unit base 13 is formed with fitting portions 30, 30 for fitting the engagement piece 26 at each switching position to generate resistance for the initial movement of the brush base 14 when moving from the each switching position to the neutral position. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a forward / reverse switching device provided in an electric tool driven by a motor for switching the rotation direction of the motor.

  A forward / reverse switching device for an electric power tool is slidably opposed to a commutator and a unit base having a pair of fixed contacts fixed to a stator of a motor in a housing and electrically connected to a coil of the stator. The brush base comprises a ring-shaped brush base that holds a pair of carbon brushes and is rotatably assembled to the unit base. Each brush base is provided with a pair of movable contacts located between fixed contacts. By switching the contact mode of the two movable contacts to the fixed contact by this brush base rotation operation, it is possible to select forward rotation or reverse rotation of the motor (for example, see Patent Document 1).

Japanese Patent Laid-Open No. 2003-180054

  In the forward / reverse switching device, since the brush base is manually rotated, the operation speed of the brush base is not constant, and the contact / separation speed between the contacts is increased or decreased. In particular, when a switching operation is performed while the motor is energized, contact welding may occur if the operation speed is slow, leading to a decrease in contact life. Although it is possible to assist switching by providing a spring that urges the brush base in the rotational direction, as long as it is a structure that manually operates the brush base directly, uneven operation speed is not eliminated and the effect on contact life is not affected. It will remain.

  Therefore, the present invention has an object to provide a forward / reverse switching device for an electric tool that can improve the contact life by constantly maintaining the contact / separation speed between the contacts regardless of the operation speed by the user. It is.

In order to achieve the above-mentioned object, the invention according to claim 1 has a play that allows the brush base to relatively rotate from a switching position of either forward rotation or reverse rotation to a neutral position where the movable contact moves away from the fixed contact. In this state, an operation member that can be rotated from the outside of the housing is connected, while the brush base is positioned at each switching position between the brush base and the unit base, and the brush base is first moved from each switching position to the neutral position side. It is characterized in that positioning means for generating resistance is provided.
In addition to the object of the first aspect, the invention according to claim 2 includes an engaging portion provided on either the unit base or the brush base, in order to easily form the positioning means, It is provided on the other side, and is a fitting portion in which the engaging portion is fitted at each switching position of the brush base.
According to a third aspect of the present invention, in addition to the object of the first or second aspect, in order to increase the certainty of the quick disconnection of the contact, the brush with a force smaller than the holding force of the brush base at each switching position by the positioning means. Biasing means for urging the base to the neutral position side is provided.

According to the first aspect of the present invention, the adoption of the operation member connected with the brush base with play allows the brush base to be switched regardless of the moving speed of the operation member that is directly operated. Therefore, the contact can be quickly cut at a constant speed, the possibility of contact welding being reduced, and the contact life can be expected to be improved.
According to the second aspect of the present invention, in addition to the effect of the first aspect, the positioning means can be easily formed by a simple fitting structure of the engaging portion and the fitting portion.
According to the third aspect of the present invention, in addition to the effect of the first or second aspect, more reliable quick disconnection can be achieved by the rotation biasing of the biasing means.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an overall view of an electric drill as an example of an electric tool provided with a forward / reverse switching device of the present invention, FIG. 2 is a perspective view of a state in which a handle cover is removed, and the electric drill 1 includes a motor 2. This is a well-known structure that includes a chuck 5 that protrudes in front of the housing 3 (left side in FIG. 1) and that can be fitted with a drill bit or the like at the tip of the spindle 4. On the rear side of the housing 3, a handle 7 is extended downward together with a handle cover 6 assembled from the rear, and a switch 9 that is turned on when the switch lever 8 is pushed in is provided in the handle 7. 10 is a speed change dial of the motor 2, and 11 is a stopper pole for setting a perforation depth.

  A forward / reverse switching device 12 for switching the rotation direction of the motor 2 is assembled behind the motor 2. As shown in FIGS. 3 and 4, the forward / reverse switching device 12 is assembled to a disk ring-shaped unit base 13 fixed to the stator of the motor 2, and is assembled to the rear of the unit base 13. It consists of a brush base 14 having a disk ring shape of the same shape, and an operation ring 15 as an operation member assembled to the rear of the brush base 14. The unit base 13, the brush base 14, and the operation ring 15 are all made of synthetic resin. In the following description of the forward / reverse switching device 12, the vertical direction will be described in the state shown in FIG. Further, in the bottom explanatory view of FIG. 4 and subsequent figures, the unit base 13 is omitted except for the contact points and the terminal fittings for convenience.

First, the unit base 13 has a pair of planar arcuate fixed contacts 16, 16 arranged symmetrically in point symmetry, and the end portions 17, 17 of each fixed contact 16 are the end portions 17, 17 of the other fixed contact 16, respectively. Are opposed to each other at a predetermined interval in the circumferential direction. In addition, each fixed contact 16 is provided with a downwardly connecting plug 18 that is inserted into and electrically connected to one pair of terminal terminals on the coil side of the stator. 19 and 19 are terminal fittings whose lower ends are inserted into the other pair of terminal terminals on the coil side, and whose upper ends pass through the brush base 14 and are connected to the switch 9 via lead wires (not shown).
Further, a pair of hooks 20, 20 with their upper ends folded back outwardly project from the inner periphery of the unit base 13. The hooks 20, 20 penetrate the brush base 14 and the operation ring 15 and are locked to the upper surface of the operation ring 15, so that the brush base 14 and the operation ring 15 are respectively integrated on the unit base 13 so as to be rotatable. Yes.

  Next, on the upper surface of the brush base 14, cylindrical portions 21, 21 for inserting and holding the metal brush holders 22, 22 with square sleeves are integrally formed in a straight line at point symmetry positions. , 22 can be held in sliding contact with the commutator of the motor 2. Reference numeral 24 in FIG. 2 denotes a bearing portion that passes through the forward / reverse switching device 12 and supports the output shaft of the motor 2. On the bottom surface of each brush holder 22, a movable contact 25 hangs downward at a point-symmetrical position and protrudes between end portions 17, 17 between the fixed contacts 16, 16 of the unit base 13. Accordingly, the movable contacts 25, 25 are moved in the circumferential direction along with the rotation of the brush base 14, so that the movable contacts 25, 25 are either of the pair of end portions 17, 17 that are paired symmetrically with respect to the fixed contacts 16, 16. It can be selectively contacted.

  Further, below the front end of each cylindrical portion 21 in the brush base 14, on the line connecting the movable contacts 25, 25 in a plan view, an engaging piece 26 that is an engaging portion protrudes downward. . On the other hand, on the inner peripheral side of the unit base 13, stoppers 27, 27 with which the engagement pieces 26 abut at the left and right positions in the circumferential direction where the movable contacts 25, 25 are in contact with the end portions 17, 17 of the fixed contact 16, Projected toward the center. At the center between the stoppers 27, 27, a support piece 28 protrudes toward the center side at a height that does not interfere with the engagement piece 26, and gradually increases toward the left and right sides of the support piece 28 as the distance from the support piece 28 increases. In the vicinity of the apex, the elastic pieces 29 and 29 are formed symmetrically so as to be higher and interfere with the engagement piece 25 and gradually lower after the apex position.

  Therefore, between the tips of the elastic pieces 29, 29 and the stoppers 27, 27, the engaging pieces 26 are fitted, and the fitting portions 30, 30 that hold the contact state between the fixed contact 16 and the movable contact 25 are provided. It is formed. The fitting portion 30 and the previous engagement piece 26 serve as positioning means. In FIG. 4, the rotation position of the brush base 14 in which the engagement piece 26 is fitted to the left fitting portion 30 that appears in the back is the forward rotation, and the brush base 14 in which the engagement piece 26 is fitted to the right fitting portion 30. The rotation position of each is a reverse rotation switching position (hereinafter referred to as “forward rotation position” and “reverse rotation position”, respectively), and the vicinity of the support piece 28 is a neutral position where the contacts 16 and 25 are not in contact with each other.

The operation ring 15 is a ring-shaped frame having an inner diameter that is substantially the same as the inner diameter of the brush base 14. Inverted U-shaped loose fitting portions 31, 31 that are slightly wider in the circumferential direction than 21 are formed point-symmetrically. That is, between the brush base 14 and the operation ring 15, a play that allows relative rotation of either of the left and right vertical bar portions 32, 32 of each loose fitting portion 31 until it abuts the side surface of the cylindrical portion 21. Are provided in the rotational direction. However, this play is set by the amount of rotation of the brush base 14 until the engagement piece 26 reaches the neutral position from the forward rotation position or the reverse rotation position.
Further, on the outer periphery of the operation ring 15 whose phase is shifted by approximately 90 degrees from the loosely fitting portions 31, 31, connecting pieces 33, 33 project outwardly in the radial direction. The connecting pieces 33, 33 face windows 34 formed on both side surfaces of the housing 3, respectively, so that the operation ring 15 can be rotated from the outside of the housing 3.

  In the forward / reverse switching device 12 configured as described above, when the operation ring 15 is rotated from the neutral position in FIG. 4 to the normal rotation side (left rotation in FIG. 4A), one of the loose fitting portions 31, 31. The vertical bar portions 32 and 32 come into contact with the cylindrical portions 21 and 21 to rotate the brush base 14 integrally. At this time, the engaging pieces 26, 26 receive resistance by interfering with the elastic piece 29 as it goes to the apex side of the moving elastic piece 29. This resistance is maximum near the apex. Here, by setting the length of the end portion 17 of the fixed contact 16, the movable contacts 25 and 25 come into contact with the ends 17 and 17 of the fixed contact 16 on the positive rotation side and are electrically connected in the vicinity of the apex where the resistance is maximum. Has been made. Therefore, at the time of entering the switching position, the contact speed of the contacts 16 and 25 becomes slow due to the resistance of the elastic piece 29. When the engagement piece 26 gets over the apex position, as shown in FIG. 5, the engagement piece 26 is fitted to the fitting portion 30 and is held in the forward rotation position.

  Next, when switching from forward rotation to reverse rotation, when the operation ring 15 is rotated clockwise from the state of FIG. 5 to the reverse rotation side, the other vertical bar portions 32, 32 of the loose fitting portions 31, 31 are cylindrical. The brush base 14 is rotated integrally with the parts 21 and 21. At the time of the initial movement of the brush base 14, the engagement pieces 26, 26 fitted in the fitting portion 30 are each caused to resist in the rotational direction by interfering with the elastic pieces 29, and therefore, via the operation ring 15. It is necessary to apply a strong force to the brush base 14 to some extent. Then, when each engagement piece 26 gets over the apex position of the elastic piece 29 and leaves the fitting portion 30 with force applied, the brush base 14 moves away from the vertical bar portions 32 and 32 first. As shown in FIG. 6, each engagement piece 26 quickly reaches a neutral position located above the support piece 28. Therefore, the movable contact 25 that has been in contact with the end portion 17 of the fixed contact 16 is quickly separated from the end portion 17 (rapid disconnection). This switching speed is constant regardless of the operating speed of the operating ring 15. That is, even when the operation ring 15 is slowly rotated, a force to get over the elastic piece 29 is necessary, so that the brush base 14 is faster than the loose fitting portions 31, 31 immediately after leaving the fitting portion 30. This is because the action of rotating the play amount does not change.

Then, when the operation ring 15 is further rotated clockwise from the neutral position of the brush base 14 to the reverse rotation side, the vertical bar portions 32 and 32 come into contact with each other and the brush base 14 rotates as it is. As shown in FIG. 7, it fits into the fitting portion 30 (reverse rotation position) while overcoming the apex position while interfering with 29 and receiving resistance. At this time, as in the case of switching from the neutral position to the forward rotation position, the movable contact 25 is positioned at the ends 17 and 17 of the fixed contact 16 near the apex position of the elastic piece 29 where the resistance to the engagement piece 26 is maximized. To make electrical connection (loose entry).
Note that switching from the reverse rotation position to the forward rotation position has the same action, and quick disconnection from the reverse rotation position to the neutral position and slow entry from the neutral position to the forward rotation position.

As described above, according to the forward / reverse switching device 12 of the above embodiment, the brush base 14 has a play capable of relative rotation from the switching position of either forward rotation or reverse rotation to the neutral position where the movable contact 25 is separated from the fixed contact 16. In this state, the operation ring 15 that can be rotated from the outside of the housing 3 is connected, while the brush base 14 is positioned at each switching position between the brush base 14 and the unit base 13, and the neutral position side from each switching position. By providing positioning means for generating resistance to the initial movement of the brush base 14 to the brush base 14, the brush base 14 can be switched regardless of the moving speed of the operation ring 15 that is directly operated, and the contact point is always at a constant speed. Fast disconnection of 16 and 25 is possible. Therefore, the possibility of causing contact welding is reduced, and an improvement in contact life can be expected. Incidentally, compared with a conventional forward / reverse switching device to which the present invention is not applied, the forward / reverse switching device 12 of the present invention has confirmed a contact life approximately twice as long.
Further, the positioning means is formed of an engagement piece 26 provided on the brush base 14 and a fitting portion 30 provided on the unit base 13 and into which the engagement piece 26 is fitted at each switching position of the brush base 14. Thus, the positioning means can be easily formed by a simple fitting structure.

The forward / reverse switching device 12 of the above embodiment achieves a quick disconnection using only the engagement piece 26 on the brush base 14 side and the fitting portion 30 on the unit base 13 side, as shown in FIGS. As described above, the lower half of the coil spring 36 as the urging means is fitted into the grooves 35, 35 provided in the circumferential direction of the upper surface of the unit base 13, while both ends of the coil spring 36 are placed on the lower surface of the brush base 14 at the neutral position. Abutment portions 37, 37 that are close to each other may be provided.
In this case, when the brush base 14 is rotated to each switching position by the operation ring 15, as shown in FIG. 9 (the coil spring portion is notched), one contact portion 37 contracts the coil spring 36. Held in a state. Here, the holding force of the brush base 14 by the fitting of the engaging piece 26 and the fitting portion 30 is larger than the urging force of the coil spring 36. Therefore, when the operation ring 15 is rotated to the neutral position side in this state, the engagement piece 26 immediately moves to the neutral position by the rotational bias of the coil spring 36 as shown in FIG. Will do.

  As described above, if the biasing means for rotating and biasing the brush base 14 to the neutral position side with a force smaller than the holding force of the brush base 14 at each switching position by the positioning means is provided, a more reliable quick disconnection is possible. Become. Of course, the biasing means is not limited to a coil spring, and other forms such as a leaf spring, a torsion spring, and an elastic body may be employed. Here, the engaging piece 26 and the fitting portion 30 of the previous form are used as they are for holding the brush base 14 as they are. However, as long as a holding force larger than that of the urging means can be obtained, other types are available. A structure can also be adopted.

Moreover, in the said form, although loose engagement is implement | achieved by setting it as a movable contact and a fixed contact contacting at the vertex position of the elastic piece before an engagement piece arrives at a fitting part, If the movable contact and the fixed contact come into contact with each other only after reaching the fitting portion, quick insertion can be realized.
Further, the positioning means is not limited to the above form, for example, the engaging piece is provided on the unit base and the fitting portion is provided on the brush base to reverse the above form, or the central supporting piece is eliminated and the elastic piece is attached to the unit base or Design changes such as projecting directly from the inner peripheral surface of the brush base or providing the stopper and the elastic piece integrally are possible. In addition, the pair is not limited to the one provided as in the above embodiment, and only one set of the engaging portion and the fitting portion may be provided, or may be provided between the unit base and the brush base or on the outer peripheral side.

The operation member is not limited to the frame-shaped operation ring, and may be a disk shape similar to the brush base. The play with the brush base may be set to a long groove provided in the operation member or the brush base, and the long groove. The design can be changed as appropriate, for example, depending on the protrusion to be loosely inserted in
In addition, the electric tool is not limited to the electric drill, and any electric tool having a motor forward / reverse switching function, such as an electric driver drill or an electric screwdriver, can be adopted.

It is a general view of an electric drill. It is a perspective view of the electric drill which removed the handle cover. It is a disassembled perspective view of a forward / reverse switching device. (A) is a perspective view of the forward / reverse switching device at the neutral position, and (B) is a bottom explanatory view thereof. (A) is a perspective view of the forward / reverse switching device at the forward rotation position, and (B) is an explanatory view of the bottom surface thereof. (A) is a perspective view of the forward / reverse switching device at the neutral position, and (B) is a bottom explanatory view thereof. (A) is a perspective view of the forward / reverse switching device at the forward rotation position, and (B) is an explanatory view of the bottom surface thereof. It is a disassembled perspective view of the forward / reverse switching device of the example of a change. It is a perspective view of the forward / reverse switching device of the example of a change (reverse rotation position). It is a perspective view of the forward / reverse switching device of the example of a change (neutral position).

Explanation of symbols

1 .. Electric drill, 2 .. Motor, 3 .. Housing, 7 .. Handle, 12 .. Forward / reverse switching device, 13 .. Unit base, 14 .. Brush base, 15 .. Operation ring, 16. Fixed contact, 17 ... end, 22 ... brush holder, 25 ... movable contact, 26 ... engagement piece, 29 ... elastic piece, 30 ... fitting part, 31 ... free fitting part, ... -Coil spring.

Claims (3)

A unit base having a pair of fixed contacts fixed in a housing of the electric tool and connected to a coil of the motor; and provided to be rotatable with respect to the unit base while holding the brush of the motor. A brush base having a pair of movable contacts located between them, and switching the contact manner of the movable contacts with respect to the fixed contacts by rotating the brush base to select forward rotation or reverse rotation of the motor A power tool forward / reverse switching device that is made possible,
An operation member that can be rotated from the outside of the housing in a state in which the brush base has a play that can be rotated relative to the neutral position where the movable contact moves away from the fixed contact from either the forward rotation position or the reverse rotation position. Positioning that positions the brush base at each switching position between the brush base and the unit base and causes resistance to the initial movement of the brush base from the switching position to the neutral position side A power tool forward / reverse switching device characterized in that means is provided.   The positioning means includes an engaging portion provided on one of the unit base and the brush base, and a fitting portion provided on the other and fitted with the engaging portion at each switching position of the brush base. The forward / reverse switching device for an electric tool according to Item 1. The forward / reverse switching of the electric power tool according to claim 1 or 2, further comprising an urging unit that urges the brush base to rotate toward the neutral position with a force smaller than a holding force of the brush base at each switching position by the positioning unit. apparatus.

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