DC motor with a positive temperature coefficient thermistor

This application claims priorities from Japanese Patent Application No. 2016-190562 filed on Sep. 29, 2016, the entire subject matters of which is incorporated herein by reference.

The present disclosure relates to DC motor, and particularly to a DC motor including a PTC thermistor.

As a DC motor, there is a DC motor including a positive temperature coefficient (PTC) thermistor. The PTC thermistor is used as a circuit protection element, and functions as a current limiting element of which resistance rapidly increases when the temperature exceeds a predetermined temperature.

In JP-A-2014-226004, JP-A-2006-166646, and JP-A-2009-165209, a structure of a DC motor which uses a PTC thermistor is disclosed. The PTC thermistor is disposed between a power supply terminal and a brush. The PTC thermistor has a shape of a plate of which both surfaces are electrodes, a terminal on a power supply side is connected to one surface, a terminal to which the brush is connected is connected to the other surface, and the PTC thermistor is used while being interposed between the two terminals.

However, in a case where the PTC thermistor is disposed in the DC motor which has, for example, a cylindrical shape or an angular shape (which has an outer diameter having a substantially quadrangular shape on a section perpendicular to a rotation shaft (here, the substantially quadrangular shape has, for example, a shape having roundness of a radius R in a corner portion, or a shape to which chamfering is performed in the corner portion)), there is a problem that it is difficult to ensure a space for disposing the PTC thermistor on the inside of the motor as the size of the DC motor decreases. Specifically, in disposing the PTC thermistor on the inside of the DC motor, it is necessary to avoid a commutator, a brush, a terminal to which the brush is connected and the like. Therefore, in accordance with a decrease in size of the motor, it is necessary to use a small PTC thermistor.

Meanwhile, for example, in a PTC thermistor which is a type that is used in motors described in JP-A-2014-226004, JP-A-2006-166646, and JP-A-2009-165209 which are described above and is used being nipped, or in a so-called lead line type PTC thermistor, there is a problem that it is difficult to prepare a PTC thermistor which is small and satisfies required functions. In other words, such a small PTC thermistor type has a problem that internal resistance is relatively high and torque of the DC motor decreases. There is a case where trip time is extremely short, and there is a problem that there is a possibility that a continuous operation becomes impossible depending on use.

Regarding such problems, as a surface mounting type PTC thermistor, there are a PTC thermistor which has relatively low internal resistance, a PTC thermistor which has a relatively long trip time, and a PTC thermistor which has an appropriately required functions even when the size is small. However, in the related art, in mounting such a surface-mount type PTC thermistor on the inside of the DC motor, it is necessary to prepare an additional component, such as a substrate, and there is a problem that the number of components of the DC motor increases.

One of objects of the present disclosure is to provide a DC motor which is capable of usage of the surface-mount type PTC thermistor and has less number of components.

According to one aspect of the present invention, there is provided a DC motor including: a brush configured to be connectable with a commutator; a first terminal attached to the brush; a second terminal disposed at a position away from the first terminal, the second terminal being configured to be connectable with an external terminal; a bracket to which the first terminal and the second terminal are attached; and a positive temperature coefficient (PTC) thermistor disposed between the first terminal and the second terminal, the PTC thermistor including a first electrode bonded to the first terminal and a second electrode bonded to the second terminal, wherein the PTC thermistor is a surface-mount type thermistor in which the first electrode and the second electrode are exposed on one surface side, and wherein, on the one surface side of the PTC thermistor, the first electrode faces the first terminal and the second electrode faces the second terminal.

According to another aspect of the present invention, there is provided a motor including: a motor frame; a shaft rotatably supported by the motor frame and extended in an axial direction; a bracket attached to the motor frame and including a penetration hole through; which the shaft is passed and a groove; a positive temperature coefficient (PTC) thermistor having a first surface and a second surface opposite to the first surface, a first electrode portion exposed from the first surface and a second electrode portion exposed from the first surface; a first terminal arranged in the groove and attached to a brush; and a second terminal arranged in the groove and arranged at a position away from the first terminal, the second terminal being configured to be coupled with an external terminal, wherein the first electrode of the PTC thermistor is coupled to the first terminal and the second electrode of the PTC thermistor is coupled to the second terminal.

According to yet another aspect of the present invention, there is provided a motor comprising: a motor frame; a shaft rotatably supported by the motor frame and extended in an axial direction; and a bracket assembly attached to the motor frame, wherein the bracket assembly comprises; a bracket body having a penetration hole and a groove, the shaft is passed through the penetration hole; a first terminal arranged in the groove; a second terminal arranged in the groove, and a positive temperature coefficient (PTC) thermistor having a first surface and a second surface opposite to the first surface and arranged in the groove so that the first and second surfaces are arranged at a plane parallel to the axial direction, only one of the first and second surfaces being faced to the first and second terminals.

In the accompanying drawings:

FIG. 1 is a side sectional view illustrating a DC motor according to an embodiment of the present disclosure;

FIG. 2 is a perspective view illustrating a structure of a bracket unit;

FIG. 3 is an exploded perspective view illustrating a first terminal, a second terminal, and a PTC thermistor;

FIG. 4 is an exploded perspective view illustrating a third terminal and a bracket; and

FIG. 5 is a view describing an attaching structure of the PTC thermistor.

Hereinafter, a DC motor according to an embodiment of the present disclosure will be described.

FIG. 1 is a side sectional view illustrating a DC motor 1 according to an embodiment of the present disclosure.

As illustrated in FIG. 1 , the DC motor (hereinafter, simply referred to as a motor) 1 roughly includes a frame assembly 1 a , and an armature assembly (hereinafter, simply referred to as an armature) 1 b which is supported to be rotatable around a rotation shaft 2 with respect to the frame assembly 1 a.

The armature assembly 1 b includes the rotation shaft (shaft) 2 , an armature portion 4 , a commutator portion 6 and the like. The armature portion 4 is attached to the rotation shaft 2 . The armature portion 4 includes an armature core 5 which has a plurality of salient poles which protrude in a radial direction, a winding wire (not illustrated) wound around each of the salient poles. The commutator portion 6 is provided in the vicinity of a base end portion (end portion on a right side in FIG. 1 ) of the rotation shaft 2 , and rotates together with the rotation shaft 2 . The commutator portion 6 has a commutator 7 or the like which comes into contact with a brush 20 attached to the frame assembly 1 a as will be described later.

The frame assembly 1 a is configured of a frame 10 , a bracket 30 , a plate 41 , a magnet 70 and the like.

The frame 10 has a tubular shape. A tip end portion (end portion on a left side in FIG. 1 ) of the rotation shaft 2 protrudes from one end portion of the frame 10 to block the one end portion. An opening portion of the other end portion (end portion on the right side in FIG. 1 ) of the frame 10 is blocked by the plate 41 . In a frame configured of the frame 10 and the plate 41 , the armature 1 b is accommodated. One end portion of the rotation shaft 2 of the armature 1 b protrudes from the frame 10 . A bearing 18 is held in a center portion of the one end portion of the frame 10 . A bearing 19 is held in a center portion of the plate 41 . The rotation shaft 2 is held to be rotatable with respect to the frame 10 by the bearings 18 and 19 at two locations.

The bracket 30 is attached to an inner side of the plate 41 . The bracket 30 is made of, for example, resin. The bracket 30 and the plate 41 are attached to the opening portion on the other end side of the frame 10 .

FIG. 2 is a perspective view illustrating a structure of a bracket unit 40 .

As illustrated in FIG. 2 , the bracket unit 40 includes the bracket 30 , the brush 20 , a first terminal 24 , a second terminal 25 , a PTC thermistor 26 , and a third terminal 28 .

In the embodiment, the brush 20 is held by the bracket 30 via the first terminal 24 and the third terminal 28 such that a part in the vicinity of a tip end of a brush arm made of a metal plate comes into contact with the commutator 7 . The brush arm roughly has a shape of a rectangular plate of which one direction on a plane perpendicular to the rotation shaft 2 is a longitudinal direction and a direction parallel to the rotation shaft 2 is a width direction.

The brush 20 is used in a state where the part in the vicinity of the tip end comes into contact with the commutator 7 and is slightly bent from a natural state. The brush arm is held by the first terminal 24 or the third terminal 28 to have flexibility (similar to a cantilever beam).

FIG. 3 is an exploded perspective view illustrating the first terminal 24 , the second terminal 25 , and the PTC thermistor 26 .

As illustrated in FIG. 3 , the second terminal 25 is disposed at a position separated from the first terminal 24 . In the embodiment, each of the first terminal 24 and the second terminal 25 is formed by bending one metal plate or by performing other sheet metal working. The first terminal 24 includes an attaching portion 24 a to which the brush arm of the brush 20 is attached, a fixing portion 24 b linked to the attaching portion 24 a , and a bonding portion 24 f which extends toward the second terminal 25 from the fixing portion 24 b . The second terminal 25 includes a fixing portion 25 b , a connection portion 25 c for external connection linked to the fixing portion 25 b , and a bonding portion 25 f which is linked to the fixing portion 25 b and is disposed to be positioned substantially on the same plane as the bonding portion 24 f.

The entire PTC thermistor 26 has a shape of a rectangular plate. In two side portions of the PTC thermistor 26 , a first electrode 26 c and a second electrode 26 d are disposed. Each of the electrodes 26 c and 26 d is exposed on one surface 26 a of the PTC thermistor 26 , a surface 26 b on the other side, and a side surface. In other words, the PTC thermistor 26 is a surface-mount type thermistor in which two electrodes 26 c and 26 d are exposed to one surface 26 a side (mounting surface side).

The PTC thermistor 26 is disposed between the first terminal 24 and the second terminal 25 . On one surface 26 a in the PTC thermistor 26 , the electrode 26 c is disposed to face the bonding portion 24 f of the first terminal 24 , and the electrode 26 d is disposed to face the bonding portion 25 f of the second terminal 25 . The bonding portion 24 f of the first terminal 24 is bonded to the electrode 26 c by soldering. The bonding portion 25 f of the second terminal 25 is bonded to the electrode 26 d by soldering. Accordingly, the first terminal 24 and the second terminal 25 are electrically connected to each other via the PTC thermistor 26 . In other words, the connection portion 25 c of the second terminal 25 and the brush 20 attached to the attaching portion 24 a of the first terminal 24 are conductive to each other. In the drawing, the solder is omitted. As a bonding method of each of the first terminal 24 and the second terminal 25 and the electrodes 26 c and 26 d of the PTC thermistor 26 , other methods may be employed.

FIG. 4 is an exploded perspective view illustrating the third terminal 28 and the bracket 30 .

As illustrated in FIG. 4 , the third terminal 28 includes an attaching portion 28 a to which the brush arm of the brush 20 is attached, a fixing portion 28 b linked to the attaching portion 28 a , and a connection portion 28 c linked to the fixing portion 28 b . In the embodiment, the third terminal 28 is formed by bending one metal plate. The attaching portion 28 a , the fixing portion 28 b , and the connection portion 28 c have a shape of a plate.

The bracket 30 is a resin molded article having a thickness in a shaft direction (axial direction or longitudinal direction) of the rotation shaft 2 . The bracket 30 is formed such that the rotation shaft 2 penetrates therethrough. The bracket 30 is formed such that the connection portion 28 c of the third terminal and the connection portion 25 c of the second terminal 25 are exposed to the outside of the frame assembly 1 a , and an external terminal can be inserted thereinto. By connecting the external terminal to each of the connection portions 25 c and 28 c and by applying the driving voltage between the connection portions 25 c and 28 c , the motor 1 can be driven.

In the bracket 30 , three groove portions 31 , 32 , and 33 are formed. Each of the groove portions 31 , 32 , and 33 is formed such that the shaft direction (axial direction or longitudinal direction) of the rotation shaft 2 is a depth direction. In the bracket 30 , a columnar projection (one example of a positioning portion) 35 is formed.

The groove portion 31 is formed to hold the fixing portion 24 b of the first terminal 24 . As illustrated in FIG. 3 , in the fixing portion 24 b of the first terminal 24 , a bump portion 24 d is formed. The first terminal 24 is fixed to the bracket 30 in a state where the fixing portion 24 b is press fitted into the groove portion 31 by partially nipping the bracket 30 between the bump portion 24 d and the attaching portion 24 a.

The groove portion 32 is formed to hold the fixing portion 25 b of the second terminal 25 . As illustrated in FIG. 3 , each of the connection portion 25 c and the bonding portion 25 f is connected to the fixing portion 25 b to be bent. In addition, in the groove portion 32 , in the end portion on the side on which the PTC thermistor 26 is disposed, a protrusion portion 32 a which protrudes toward the PTC thermistor 26 is formed. The second terminal 25 is fixed to the bracket 30 in a state where the fixing portion 25 b is press fitted into the groove portion 32 by biasing the bonding portion 25 f such that the protrusion portion 32 a widens an angle between the connection portion 25 c and the bonding portion 25 f.

The groove portion 33 is formed to hold the fixing portion 28 b of the third terminal 28 . The third terminal 28 is fixed to the bracket 30 in a state where the fixing portion 28 b is press fitted into the groove portion 32 .

As illustrated in FIG. 3 , in the embodiment, in the first terminal 24 , on a surface of the bonding portion 24 f which faces the PTC thermistor 26 , a claw portion (one example of a first projection) 24 g formed to protrude from the surface is provided. The claw portions 24 g are provided at two locations to nip the center of the bonding portion 24 f in the shaft direction (axial direction or longitudinal direction) of the rotation shaft 2 . In addition, in the second terminal 25 , on a surface of the bonding portion 25 f which faces the PTC thermistor 26 , a claw portion (one example of a second projection) 25 g formed to protrude from the surface is provided. The claw portions 25 g are also provided at two locations to nip the center of the bonding portion 25 f in the shaft direction (axial direction or longitudinal direction) of the rotation shaft 2 . The claw portions 24 g and 25 g protrude to the side on which the PTC thermistor 26 is disposed. The protrusion height of the claw portions 24 g and 25 g is, for example, approximately the same as or slightly less than the thickness of the PTC thermistor 26 , but the protrusion height is not limited thereto.

FIG. 5 is a view describing an attaching structure of the PTC thermistor 26 .

As illustrated in FIG. 5 , the PTC thermistor 26 is disposed between the claw portion 24 g and the claw portion 25 g . A position of a side end portion on the first electrode 26 c of the PTC thermistor 26 is regulated by the claw portion 24 g such that the electrode 26 d is not separated from the second terminal 25 to the first terminal 24 side. A position of a side end portion of the electrode 26 d of the PTC thermistor 26 is regulated by the claw portion 25 g such that the electrode 26 c is not separated from the first terminal 24 to the second terminal 25 side. In other words, on each of the surface which faces the PTC thermistor 26 of the first terminal 24 and a surface which faces the PTC thermistor 26 of the second terminal 25 , the claw portions 24 g and 25 g are formed to protrude from the surfaces and to be capable of positioning the PTC thermistor 26 , respectively. Accordingly, when bonding the PTC thermistor 26 to the first terminal 24 or the second terminal 25 , it is possible to easily position the PTC thermistor 26 with respect to the first terminal 24 or the second terminal 25 .

In the embodiment, the columnar projection 35 is provided in the bracket 30 . The PTC thermistor 26 can be positioned with respect to the first terminal 24 and the second terminal 25 by the columnar projection 35 . Specifically, the columnar projection 35 has a positioning surface 35 a which faces the surface 26 b on a side opposite to the mounting surface 26 a of the PTC thermistor 26 in a state where the mounting surface 26 a side of the PTC thermistor 26 faces the first terminal 24 and the second terminal 25 .

In this manner, the claw portions 24 g and 25 g are provided in the first terminal 24 and the second terminal 25 , respectively. The columnar projection 35 is provided in the bracket 30 . When attaching the PTC thermistor 26 , in a state where the first terminal 24 and the second terminal 25 are fixed to the bracket 30 , first, the PTC thermistor 26 is disposed in a space surrounded by the bonding portion 24 f , the bonding portion 25 f , the claw portions 24 g , the claw portions 25 g , and the columnar projection 35 . At this time, the PTC thermistor 26 is in a state of being positioned with respect to the first terminal 24 , the second terminal 25 , and the bracket 30 by each portion on the periphery thereof. In other words, the PTC thermistor 26 is in a state of being temporarily fixed to the first terminal 24 , the second terminal 25 , and the bracket 30 . In addition, in the state, by soldering the electrode 26 c and the bonding portion 24 f , and by soldering the electrode 26 d and the bonding portion 25 f , it is possible to easily bond the PTC thermistor 26 to the first terminal 24 and the second terminal 25 . The number or the shape of the claw portions is not limited to the description above. In the bracket 30 , a positioning portion of the structure having a positioning surface that faces the surface 26 b of the PTC thermistor 26 may be formed in another shape which is not a columnar shape.

In the embodiment, on a surface that faces the PTC thermistor 26 of the first terminal 24 , at the position separated from the bonding portion 24 f bonded to the PTC thermistor 26 , a flow suppressing portion 24 h which is formed to protrude from the surface is provided. The flow suppressing portion 24 h is formed by performing drawing such that a part of the first terminal 24 projects. In addition, on a surface that faces the PTC thermistor 26 of the second terminal 25 , at the position separated from the bonding portion 25 f bonded to the PTC thermistor 26 , a flow suppressing portion 25 h which is formed to protrude from the surface is provided. The flow suppressing portion 25 h is formed while a part of the second terminal 25 is bent. A flow of the solder (not illustrated) for bonding the electrode 26 c of the PTC thermistor 26 to the bonding portion 24 f is blocked by the flow suppressing portion 24 h . A flow of the solder (not illustrated) for bonding the electrode 26 d to the bonding portion 25 f is blocked by the flow suppressing portion 25 h . In other words, as the flow suppressing portion 24 h is provided in this manner, in manufacturing the motor 1 , it is possible to prevent generation of a defect caused by the flow of the solder into a region in which the armature assembly 1 b is disposed or other regions inside of the motor 1 . The flow suppressing portion 24 h or the flow suppressing portion 25 h may be formed to be recessed from the surface on which the bonding portions 24 f and 25 f are provided. The flow suppressing portion 24 h or the flow suppressing portion 25 h may be provided only in any one of the first terminal 24 and the second terminal 25 .

As described above, in the embodiment, in the DC motor 1 , the surface mounting type PTC thermistor 26 is disposed between the first terminal 24 and the second terminal 25 , and the first terminal 24 and the second terminal 25 are connected to each other via the PTC thermistor 26 . In other words, by using the surface mounting type PTC thermistor 26 , since it is possible to perform current limiting of the DC motor 1 , without increasing the size of the DC motor 1 , it is possible to use the PTC thermistor 26 having required characteristics. Specifically, for example, since it is possible to use the PTC thermistor 26 having relatively low internal resistance compared to the size of the element, it is possible to prevent deterioration of torque characteristics of the DC motor 1 . Since the PTC thermistor 26 is bonded to the first terminal 24 and the second terminal 25 , it is not necessary to use an additional mounting substrate or the like, and it is possible to suppress the number of components of the DC motor 1 to be small.

As described above, before bonding the PTC thermistor 26 to the first terminal 24 and the second terminal 25 , a state where the PTC thermistor 26 is temporarily fixed to the first terminal 24 and the second terminal 25 is possibly set. Therefore, it is possible to easily perform bonding work of the PTC thermistor 26 , and to suppress the manufacturing costs of the DC motor 1 to be low.

In the above-described embodiment, a structure in which the PTC thermistor is positioned by the claw portion and the columnar projection is achieved, but the claw portion and the columnar projection may not be provided. It is sufficient that a structure in which the surface mounting type PTC thermistor is bonded to the first terminal and the second terminal is provided. Not being limited to a case where the PTC thermistor is bonded to the first terminal and the second terminal in a state where the first terminal and the second terminal are fixed to the bracket, a module in which the PTC thermistor is bonded to the first terminal and the second terminal in advance may be fixed to the bracket.

In addition, shapes and positional relationships therebetween of each of the first terminal, the second terminal, the third terminal, and the brush are not limited to the description above. The shapes and the positional relationships may be appropriately changed in accordance with the shape or the size of the DC motor, a bonded state or the like between the second terminal or the third terminal and the external terminal or the like.

According to the present disclosure, there is provided a DC motor which is capable of usage of the surface-mount type PTC thermistor and has less number of components.

All the contents of the above-described embodiment are examples and are not considered as restrictive contents. It is intended that the range of the invention is indicated by the range of the claims without being limited to the above-described description, and includes all changes in the meaning and the range equivalent to the range of the claims.