JP2014107964A - Electric tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric tool the magnet surface area on the outer peripheral side of which, in a configuration where the permanent magnet is disposed on the magnet insertion part of a rotor core, can be increased in comparison with the conventional.SOLUTION: The outer peripheral surface of a permanent magnet 23 is a curved surface (arcuate surface) curved so that the shaft 21 is the center of the curvature side, and is covered with the outer peripheral part 29 of the rotor core 22. The inner peripheral surface of the permanent magnet 23 consists of three planes (along the arcuate plane around the shaft 21) directly facing the shaft 21. Both end corners of the outer peripheral surface and the inner peripheral surface of the permanent magnet 23 are the chamfers 28, respectively.

Description

  The present invention relates to an electric tool including a brushless motor.

  In an electric tool such as an impact driver, a brushless motor is used as a drive source. A brushless motor generally has a rotor configuration in which a flat permanent magnet is inserted and held in a magnet insertion hole of a rotor core provided on the outer periphery of a shaft.

JP 2009-72889 A JP 2010-99823 A

  In order to increase the output, it is necessary to increase the amount of magnetic flux by increasing the surface area of the permanent magnet, particularly on the outer peripheral side. Here, there is a configuration in which a circular tube magnet is bonded to the surface of the rotor core, but there is a problem that the circular tube magnet idles when an impact is applied because of fixing only by bonding.

  The present invention has been made in view of such a situation, and an object of the present invention is to increase the magnet surface area on the outer peripheral side in comparison with the conventional structure in the configuration in which the permanent magnet is disposed in the magnet insertion portion of the rotor core. It is to provide a power tool.

  An aspect of the present invention is an electric tool including a brushless motor, and the brushless motor is disposed on a shaft, a rotor core provided on an outer periphery of the shaft, and a magnet insertion portion of the rotor core, and is provided on an outer periphery of the rotor core. A plurality of permanent magnets along the surface, and the surface on the outer peripheral side of each permanent magnet includes a curved surface curved so that the shaft is on the curvature center side.

  The magnet insertion portion may be a groove provided on the outer peripheral surface of the rotor core, and the curved surface of each permanent magnet may be exposed.

  The surface on the outer peripheral side of each permanent magnet has a stepped surface recessed from the curved surface on one end side or both end sides in the axial direction of the curved surface, and the rotor core engages with the stepped surface to You may have a retaining part which prevents the permanent magnet from coming off to the outer peripheral side.

  Another aspect of the present invention is an electric tool including a brushless motor, wherein the brushless motor is disposed on a shaft, a rotor core provided on an outer periphery of the shaft, and a magnet insertion portion of the rotor core. A plurality of permanent magnets along the outer peripheral surface of the rotor core, and the outer peripheral surface of each permanent magnet includes a plurality of flat surfaces along the curved surface where the shaft is on the curvature center side.

  At least a part of the corners of each permanent magnet viewed from the axial direction may be chamfered.

  The said rotor core may have a partition part which partitions off between adjacent permanent magnets.

  Another aspect of the present invention is an electric tool including a brushless motor, wherein the brushless motor is disposed on a shaft, a rotor core provided on an outer periphery of the shaft, and a magnet insertion portion of the rotor core. A plurality of permanent magnets along the outer peripheral surface of the rotor core, and the outer peripheral surface of each permanent magnet is a flat surface along the curved surface where the shaft is on the center of curvature, and two or more per one pole of the rotor The permanent magnet having the same polarity is provided.

  The curved surface may be a substantially arc surface.

  The inner peripheral surface of each permanent magnet may include a flat surface.

  A substantially T-shaped housing having a main body body portion and a handle portion extending from the main body body portion, wherein the brushless motor is present behind or extends from a base portion of the handle portion in the main body body portion; May be.

  An impact mechanism driven by the brushless motor may be provided in the main body body.

  A battery pack serving as a power source may be attached.

  It should be noted that any combination of the above-described constituent elements, and those obtained by converting the expression of the present invention between methods and systems are also effective as aspects of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the electric tool which can enlarge the magnet surface area of an outer peripheral side compared with the former in the structure which arrange | positions a permanent magnet in the magnet insertion part of a rotor core can be provided.

The internal block diagram of the electric tool (impact driver) which concerns on embodiment of this invention. The enlarged view of the brushless motor 2 vicinity of FIG. The front view of the rotor of the brushless motor 2 (view seen from the axial direction). The front view of the brushless motor 2 (the figure seen from the axial direction). The characteristic view of the magnetic flux amount (vertical axis) and the teeth width (horizontal axis) flowing through the tooth part 33. FIG. 6 is a characteristic diagram of the number of rotations (horizontal axis) of the brushless motor 2, time required for screw tightening of 120 mm (vertical axis on the left side), and operating current (vertical axis on the right side). The characteristic diagram of the number of turns of the coil 35 and the number of rotations of the brushless motor 2. FIG. 5 is a characteristic diagram of torque and rotation speed of the brushless motor 2.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same or equivalent component, member, etc. which are shown by each drawing, and the overlapping description is abbreviate | omitted suitably. In addition, the embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

  FIG. 1 is an internal configuration diagram of a power tool (impact driver) according to an embodiment of the present invention. A housing 1 of this electric tool has a main body body portion 1a and a handle portion 1b. A handle portion 1b extends downward from an intermediate portion of the main body body portion 1a, and the housing 1 is generally T-shaped as a whole. A brushless motor 2 and a rotary striking mechanism are provided in the main body body 1a. That is, in the main body body portion 1 a, the spindle 4 is connected to the brushless motor 2 via a speed reduction mechanism 3 (for example, a planetary gear mechanism), and the hammer 4 is connected to the spindle 4 via a spring 5 (compression spring) and a steel ball 6. Are connected, and an anvil 8 is provided on the tip side of the hammer 7. A tip tool mounting hole 9 for mounting a tip tool such as a driver bit is provided at the tip of the anvil 8. When the user grips the handle portion 1b and pulls the trigger 10 during work such as screw tightening, power is supplied to the brushless motor 2 from the battery pack 11 attached to the lower end of the handle portion 1b. , The spindle 4 and the hammer 7 rotate, and the hammer 7 applies a rotational impact force to the anvil 8. In addition, since the structure and operation | movement of such a rotation impact mechanism are known, the detailed description beyond this is abbreviate | omitted.

  FIG. 2 is an enlarged view of the vicinity of the brushless motor 2 of FIG. FIGS. 3A to 3E are front views (views seen from the axial direction) showing preferred examples of the rotor of the brushless motor 2. FIG. 4 is a front view of the brushless motor 2 (viewed from the axial direction). However, in FIG. 4, illustration of the insulator 34 and the coil 35 shown in FIG. 2 is omitted. As shown in FIG. 2, the brushless motor 2 exists or extends behind the base portion of the handle portion 1 b of the main body body portion 1 a of the housing 1.

  A rotor core 22 is provided around the shaft 21. The rotor core 22 is formed, for example, by stacking electromagnetic steel plates into a cylindrical shape. As shown in FIG. 3, the rotor core 22 has a shaft insertion hole 27 in the center. In the present embodiment, the rotor has four poles, and the rotor core 22 has four magnet insertion portions 24 around the shaft insertion hole 27. The adjacent magnet insertion parts 24 are partitioned by a partition part 25. The shaft 21 passes through the shaft insertion hole 27, and the permanent magnet 23 is inserted and held in each magnet insertion portion 24.

  As shown in FIG. 4, a stator core 31 is held by the main body body 1 a of the housing 1 on the outer periphery of the rotor core 22. The stator core 31 has a yoke part 32 and a tooth part 33. The yoke portion 32 surrounds the rotor core 22 in a cylindrical shape. The teeth portion 33 extends from the yoke portion 32 to the rotor core 22 side. In the present embodiment, the stator has six slots, and six tooth portions 33 extend from the yoke portion 32 at equal angular intervals. As shown in FIG. 2, a coil 35 is wound around each tooth portion 33 via an insulator 34.

  Variations on the shape of the permanent magnet 23 will be described with reference to FIGS.

  In FIG. 3A, the outer peripheral surface of the permanent magnet 23 is a curved surface (preferably an arc surface centered on the shaft 21) curved so that the shaft 21 is on the curvature center side, and the outer periphery of the rotor core 22. Covered by the portion 29. The inner peripheral surface of the permanent magnet 23 is composed of three planes (three planes along an arc surface centered on the shaft 21) that face the shaft 21. Both end corners of the outer peripheral surface and the inner peripheral surface of the permanent magnet 23 are chamfered portions 28, respectively. As shown in FIG. 3 (A), the surface on the outer peripheral side of the permanent magnet 23 is compared with the conventional case where a flat permanent magnet 23 is used by making the outer peripheral surface of the permanent magnet 23 a curved surface. Is large, and the amount of magnetic flux increases, which is advantageous for high output. In addition, since the inner peripheral surface of the permanent magnet 23 is a combination of flat surfaces with better processing accuracy compared to the curved surface, it is easy to receive an impact on the surface and is not easily damaged when an impact is applied. Furthermore, since the chamfered portion 28 is provided to eliminate the sharp portion, stress concentration is eliminated and the permanent magnet 23 is not easily damaged. Further, the portion of the main body body portion 1a of the housing 1 that protrudes rearward from the base portion of the handle portion 1b is easily bent, and the brushless motor 2 extends here, so that (1) the outer peripheral portion 29 functions as a buffer spring. In order to alleviate the radial shock applied to the permanent magnet 23, the permanent magnet 23 can be thin and advantageous for cost reduction, and (2) the radially extending partition 25 serves as a buffer spring. Further, since the impact in the circumferential direction applied to the permanent magnet 23 is reduced, the idling of the permanent magnet 23 can be prevented.

  Although the permanent magnet 23 having this configuration can be used for all electric tools, it is particularly effective to use it for an impact driver that has a larger impact on the motor during operation than an electric tool such as a driver drill. As is well known, the impact driver is configured to generate torque when the hammer 7 strikes the anvil 8 and transmit the rotational force to the tip tool attached to the tip tool attachment hole 9. The impact generated by the hammer 7 and the anvil 8 is hit is transmitted to the brushless motor 2. This impact is transmitted to the permanent magnet 23 inserted in the magnet insertion portion 24. When a plate-like permanent magnet is used as in the prior art, the outer peripheral portion 29 located on the outer peripheral side of the permanent magnet has a large thickness from the permanent magnet to the rotor outer peripheral portion in the radial direction. The impact force transmitted to the rotor is applied to the permanent magnet, but since the outer peripheral portion 29 is thick, it cannot be deformed and buffered by the impact force. Therefore, the permanent magnet may be damaged. In contrast, in the present embodiment, since the outer peripheral portion 29 can be made thin by configuring the permanent magnet in an arc shape, the outer peripheral portion 29 can be deformed to mitigate the impact even if an impact is applied to the permanent magnet. In addition, the permanent magnet can be prevented from being damaged. This is particularly effective when a samarium cobalt magnet that is easily broken is used as a permanent magnet, or when a thin neodymium magnet is used. That is, by combining the shape and arrangement of the permanent magnet as described above, it can be used for an electric power tool that generates impact force such as an impact driver.

  3B, unlike FIG. 3A, the surface on the outer peripheral side of the permanent magnet 23 is 3 along a curved surface (preferably an arc surface centered on the shaft 21) on which the shaft 21 is on the curvature center side. It consists of two planes. Also in this case, the surface area on the outer peripheral side of the permanent magnet 23 is large and the amount of magnetic flux is increased, which is advantageous for high output as compared with the case where a flat permanent magnet is used as in the prior art. The other points in FIG. 3B are the same as those in FIG. 3A and have the same effects.

  3C, unlike FIG. 3A, the inner peripheral surface of the permanent magnet 23 is a single flat surface. Further, the chamfered portions 28 are not provided at both ends of the inner peripheral surface of the permanent magnet 23. The other points in FIG. 3C are the same as those in FIG. 3A, and have the same effects.

  3 (D), unlike FIG. 3 (A), the arcuate curved surface 30a on the outer peripheral side of the permanent magnet 23 is exposed from the rotor core 22, and the arcuate curved surface is formed on both ends of the arcuate curved surface 30a in the axial direction. A step surface 30b recessed from 30a is provided. 3A, the magnet insertion portion 24 is a hole, but in FIG. 3D, the magnet insertion portion 24 is a groove provided on the outer peripheral surface of the rotor core 22. The rotor core 22 has a retaining portion 26 that covers the step surface 30 b of the permanent magnet 23. Since the retaining portion 26 engages the step surface 30b, the permanent magnet 23 is prevented from coming off to the outer peripheral side. The other points in FIG. 3D are the same as those in FIG. 3A and have the same effects. Further, since the retaining portion 26 is thinner than the conventional outer peripheral portion, like the outer peripheral portion 29 in FIG. 3A, etc., the impact force applied to the permanent magnet can be reduced, so that the permanent magnet Can be prevented from being damaged.

  In FIG. 3E, eight plate-like permanent magnets 23 are used for the four poles of the rotor, that is, two permanent magnets 23 are used for one pole of the rotor. The two permanent magnets 23 forming each pair are arranged along a curved surface (preferably an arc surface centered on the shaft 21) on which the shaft 21 is on the curvature center side. The four magnet insertion portions 24 (holes) insert and hold two permanent magnets 23 belonging to the same pole of the rotor. As shown in FIG. 3E, by using two permanent magnets 23 for one pole of the rotor, the outer periphery of the permanent magnet 23 is compared with the conventional case where only one permanent magnet 23 is used for one pole of the rotor. The side surface area (surface area per pole) can be increased, and the amount of magnetic flux can be increased, which is advantageous for higher output. In addition, since the thickness of the outer peripheral portion 29 can be reduced, the impact can be mitigated by deformation when an impact is applied to the permanent magnet 23, so that the permanent magnet can be prevented from being damaged.

  Hereinafter, various parameters on the stator side will be described.

  The outer diameter of the stator (outer diameter of the stator core 31) is 48.5 ± 2 mm. As the stator outer diameter is increased, the yoke portion 32 of the stator core 31 is made thicker to easily generate magnetic flux (which is advantageous for high output) and a coil with a thick wire diameter can be wound, so that the temperature rise can be reduced by reducing copper loss. Conventionally, the maximum outer diameter of the main body body portion 1 a that houses the brushless motor 2 is determined by the outer diameter of the mechanism portion (for example, the mechanism from the speed reduction mechanism 3 to the hammer 7) on the tip side of the brushless motor 2. Under the restriction that the maximum outer diameter of the main body body portion 1a is not increased because it affects workability, the stator outer diameter is set to 48.5 ± 2 mm, which is substantially equal to the outer diameter of the mechanism portion. In addition, the stator thickness (the axial length (stacked thickness) of the stator core 31) is 8 to 12 mm, which is as long as possible within the constraints of the overall length of the electric power tool.

  The teeth width (the width of the tooth portion 33) is 5.4 to 6.6 mm, and the yoke width (the width of the yoke portion 32) is 1/2 of the teeth width. FIG. 5 is a characteristic diagram of the amount of magnetic flux (vertical axis) and the tooth width (horizontal axis) flowing through the tooth portion 33. The vertical axis indicates the ratio with the amount of magnetic flux at a tooth width of 4.8 mm being 100%. As shown in the figure, it can be seen that even if the teeth width is increased to 6 mm or more, the amount of magnetic flux is hardly changed and does not contribute to high output, and the optimum value of the teeth width is 6 mm. For this reason, the teeth width is in the vicinity of 6 mm (6 mm ± 10%). Further, in the stator core 31, the amount of magnetic flux flowing through the yoke portion 32 is ½ of the amount of magnetic flux flowing through the teeth portion 33 as shown in FIG. For this reason, the yoke width is ½ of the teeth width.

FIG. 6 is a characteristic diagram of the rotation speed (horizontal axis) of the brushless motor 2, the time required for screw tightening of 120 mm (vertical axis on the left side), and the operating current (vertical axis on the right side). The rotational speed of the brushless motor 2 is the rotational speed at 0.15 N · m in the torque range (for example, 0.15 to 0.20 N · m) of the brushless motor 2 during actual work, and the number of turns of the coil 35 is changed. It is changed with. The rotational speed at a predetermined torque can be measured by a motor characteristic measuring device. The voltage applied to the brushless motor 2 (voltage of the battery pack 11) is 14.4V, and the duty ratio is 100%. In general, there is a relationship in which the motor rotation speed increases when the number of coil turns is reduced, and the motor rotation speed decreases when the coil turns is increased. In order to increase the speed of screw tightening to, for example, 5 seconds or less, it is necessary to set the rotational speed of the brushless motor 2 to 14600 min ^-1 (rpm) or more as is apparent from FIG. On the other hand, as shown in FIG. 6, even if the rotational speed of the brushless motor 2 is increased to 19000 min ⁻¹ or more, the time required for screw tightening is not shortened but rather is increased. This is presumably because the rotary impact mechanism will not follow if the rotational speed of the brushless motor 2 is too high. Therefore, it is important to set the rotation speed of the brushless motor 2 to 14600 to 19000 min ⁻¹ (within the dotted line in FIG. 6). When the rated voltage of the battery pack 11 is 14.4 to 18 V (maximum voltage 16 to 20 V), the rotation speed of the brushless motor 2 is a torque range of the brushless motor 2 during actual work (for example, 0.15 to 0.20 N · It is preferable to be able to be 14600-19000 min ⁻¹ in the entire area of m). For this reason, the stator outer diameter, the stator thickness, the teeth width, and the yoke width are set in the above ranges, and the number of turns of the coil 35 is set to 8.5 to 11.5 turns / slot. In particular, considering the balance between the operating current and the screw tightening time, the optimal number of rotations of the brushless motor 2 is 15600 min ^{−1 and the} optimal number of turns of the coil 35 is 10.5 turns / slot.

FIG. 7 is a characteristic diagram of the number of turns of the coil 35 and the number of rotations of the brushless motor 2. In the prior art (▲ in the figure), since the number of turns is as large as 12.5 turns / slot, the number of revolutions is as low as 13500 min ⁻¹ . On the other hand, if the number of turns of the coil 35 is 8.5 to 11.5 turns / slot (● in the figure), the number of rotations can be 14600 to 19000 min ⁻¹ . On the other hand, if the operating current is increased too much, the temperature rise of the brushless motor 2 may become a problem. It is preferable to reduce the copper loss by making the wire diameter of the coil 35 as large as possible, and here, it is 1.1 to 1.3 mm in consideration of the relationship with the slot size. Moreover, as shown in FIG. 1, the full length of an electric tool shall be 120-138 mm. The slot area (slot size) is proportional to the square of the outer diameter when the stator outer diameter is 48.5 ± 2 mm (46.5 mm to 50.5 mm). Since the slot area when the stator outer diameter is 48.5 mm is 28.7 mm ² , the minimum value of the slot area is 28.7 × (46.5 / 48.5) ² = 26.4 mm ² . The maximum value is 31.1 mm ² . Therefore, the slot area is optimally 26.4 mm ^{2 to} 31.1 mm ² .

FIG. 8 is a characteristic diagram of torque and rotation speed of the brushless motor 2. In the prior art (◯ in the figure), it was not possible to achieve a high rotational speed of 14600 min ⁻¹ or higher in a torque range of 0.15 to 0.20 N · m. On the other hand, by setting the stator outer diameter, stator thickness, teeth width, and yoke width within the above ranges (□ in the figure), the brushless in the region where the torque is 0.15 to 0.20 N · m. It becomes possible to make the rotation speed of the motor 2 14600-19000min- ¹ . This characteristic is the case when the battery pack 11 applied to the brushless motor 2 is fully charged at a rating of 14.4 V, the teeth width is 6.0 mm, and the yoke width is 3.0 mm.

  According to the present embodiment, the following effects can be achieved.

(1) As described with reference to FIGS. 3A to 3E, the surface area on the outer peripheral side of the permanent magnet 23 is larger than that in the prior art, so that the amount of magnetic flux is increased, which is advantageous for high output. Further, even if an inexpensive neodymium magnet is used instead of an inexpensive samarium cobalt magnet, a necessary amount of magnetic flux can be obtained, which is advantageous for cost reduction.

(2) Since the rotation speed of the brushless motor 2 can be set to 14600 to 19000 min ⁻¹ in the actual working torque range of the impact tool by the above configuration, it can be compared with the conventional configuration (12800 to 13500 min ⁻¹ ). The screw tightening time can be shortened, and the working efficiency is improved.

  The present invention has been described above by taking the embodiment as an example. However, it is understood by those skilled in the art that various modifications can be made to each component and each processing process of the embodiment within the scope of the claims. By the way. Hereinafter, modifications will be described.

  Regarding the increase in the output by devising the shape of the permanent magnet 23, the power tool is not limited to the impact driver exemplified in the embodiment, and may be another type of power tool, and various parameters on the stator side are not particularly limited. .

DESCRIPTION OF SYMBOLS 1 Housing 1a Body part 1b Handle part 2 Brushless motor 3 Reduction mechanism 4 Spindle 5 Spring 6 Steel ball 7 Hammer 8 Anvil 9 Tip tool mounting hole 10 Trigger 11 Battery pack 21 Shaft, 22 Rotor core, 23 Permanent magnet, 24 Magnet insertion part, 25 Partition part, 26 Detachment part, 27 Shaft insertion hole, 28 Chamfered part, 29 Core outer peripheral part, 30a Arc-shaped curved surface, 30b Stepped surface, 31 Stator core, 32 Yoke part, 33 Teeth part, 34 Insulator, 35 Coil

Claims (12)

  An electric tool including a brushless motor, wherein the brushless motor includes a shaft, a rotor core provided on an outer periphery of the shaft, and a plurality of permanent magnets disposed on a magnet insertion portion of the rotor core along the outer peripheral surface of the rotor core. And an outer peripheral surface of each permanent magnet includes a curved surface curved so that the shaft is on the curvature center side.   The electric tool according to claim 1, wherein the magnet insertion part is a groove provided on an outer peripheral surface of the rotor core, and the curved surface of each permanent magnet is exposed.   The surface on the outer peripheral side of each permanent magnet has a stepped surface recessed from the curved surface on one end side or both end sides in the axial direction of the curved surface, and the rotor core engages with the stepped surface to The electric tool according to claim 2, further comprising a retaining portion that prevents the permanent magnet from coming off to the outer peripheral side.   An electric tool including a brushless motor, wherein the brushless motor includes a shaft, a rotor core provided on an outer periphery of the shaft, and a plurality of permanent magnets disposed on a magnet insertion portion of the rotor core along the outer peripheral surface of the rotor core. And an outer peripheral surface of each permanent magnet includes a plurality of flat surfaces along a curved surface where the shaft is on the curvature center side.   The power tool according to any one of claims 1 to 4, wherein at least some of the corners of each permanent magnet as viewed from the axial direction are chamfered.   The power tool according to any one of claims 1 to 5, wherein the rotor core has a partition portion that partitions between adjacent permanent magnets.   An electric tool including a brushless motor, wherein the brushless motor includes a shaft, a rotor core provided on an outer periphery of the shaft, and a plurality of permanent magnets disposed on a magnet insertion portion of the rotor core along the outer peripheral surface of the rotor core. The surface of each permanent magnet on the outer peripheral side is a plane along a curved surface where the shaft is the center of curvature, and two or more permanent magnets having the same polarity are provided for each pole of the rotor. A power tool.   The power tool according to any one of claims 1 to 7, wherein the curved surface is a substantially arc surface.   The electric tool according to any one of claims 1 to 8, wherein a surface on an inner peripheral side of each permanent magnet includes a flat surface.   A substantially T-shaped housing having a main body body portion and a handle portion extending from the main body body portion, wherein the brushless motor is present behind or extends from a base portion of the handle portion in the main body body portion. The power tool according to any one of claims 1 to 9.   The electric tool according to claim 10, wherein an impact mechanism driven by the brushless motor is provided in the main body body part.   The power tool according to claim 1, wherein a battery pack serving as a power source can be attached.

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