Power tool with weight-reduced motor

Abstract

Power tool (1), with a motor (5) with a speed of 40,000 revolutions per minute or more, in which The rotational speed of the motor (5) is slowed down by a first-stage deceleration mechanism (37, 45) and a second-stage deceleration mechanism (47, 51) so that rotations of the motor (5) are transmitted to a tip tool (4), a delay ratio of the delay mechanism (37, 45) of the first stage is greater than a delay ratio of the delay mechanism (47, 51) of the second stage, and the rotational speed of the tip tool (4) is within a range of 1,000 revolutions per minute to 15,000 revolutions per minute, the delay mechanism (37, 45) of the first stage comprises a first gear (37) which is provided on a rotating shaft (31) of the motor (5) and a second gear (45) which is provided on an intermediate shaft (41) and engages with the first gear (37), the delay mechanism (47, 51) of the second stage comprises a third gear (47) provided on the intermediate shaft (41) and a fourth gear (51) provided on an output shaft (48) and engaged with the third gear (47), the rotating shaft (31), the intermediate shaft (41) and the output shaft (48) are arranged parallel to each other, and the second gear (45) overlaps with the output shaft (48) when viewed along the axis of the output shaft (48).

Description

TECHNICAL AREA

[0001] The present invention relates to power tools, such as a circular saw. STATE OF THE ART

[0002] Power tools, such as a circular saw, use a motor, such as a brushless motor or a commutator motor, as their drive source (see patent document 1). The aforementioned motor was used at a speed of approximately 25,000 to 30,000 revolutions per minute. DOCUMENTS ON THE STATE OF TECHNOLOGY PATENT DOCUMENTS [Non-Patent Document 1] Makita Product Catalogue 2013-4, [searched on 3 July 2013] via the Internet<http: / / www.makita.co.jp / product / ecatalog / sougou / index-html#1> JP H07-31 188 A discloses a rotary control for a brushless motor for a tooth polishing device. DE 11 2006 001 852 T5, DE 37 28 279 A1 and DE 41 16 343 A1 represent further prior art. BRIEF SUMMARY OF THE INVENTIONAL PROBLEM

[0003] With usability in mind, an attempt was made to reduce the weight of the power tool. However, the motor accounts for a large portion of the tool's weight, so only minor measures were taken to reduce the thickness or modify the shape of components. Consequently, significant weight reductions were not achieved.

[0004] It is therefore a task of the present teachings to provide a power tool in which a significant weight reduction can be achieved, so that it is excellent in its usability. SOLUTION TO THE PROBLEM

[0005] To solve the above-mentioned problem, a power tool according to claim 1 is provided.

[0006] According to aspect 1, a power tool has a motor with a speed of 40,000 revolutions per minute or more.

[0007] According to aspect 2, in the configuration according to aspect 1, the motor is decelerated at least by a first-stage deceleration mechanism or a second-stage deceleration mechanism to transmit the rotation of the motor to a tip tool, and a deceleration rate of the first-stage deceleration mechanism is greater than a deceleration rate of the second-stage deceleration mechanism.

[0008] According to aspect 3, in the configuration according to aspect 1 or 2, the rotational speed of the tip tool is within a range of 1,000 revolutions per minute to 15,000 revolutions per minute.

[0009] According to aspect 4, in the configuration according to aspect 2, the first stage delay mechanism includes a first gear provided on a rotating shaft of the motor, and a second gear meshing with the first gear, and a module of the first gear and the second gear is specified within 0.5 to 1.5.

[0010] According to aspect 5, in every configuration according to any of aspects 1 to 3, the deceleration is performed by a planetary gear deceleration mechanism located between the motor's rotating shaft and the tip tool.

[0011] According to aspect 6, in any configuration according to any of aspects 1 to 5, the motor is a brushless motor and the number of rotor poles is six or less.

[0012] According to aspect 7, in every configuration according to any of aspects 1 to 6, the motor uses mains current as a power source and a controller which has a rectifier circuit is included and the controller does not use an electrolytic capacitor which has a large capacitance. ADVANTAGEOUS EFFECTS OF THE TEACHINGS

[0013] According to the teachings, the motor speed is set at 40,000 or more per minute, so that the motor is reduced in weight and the power tool as a whole can be reduced in weight while still being excellent in handling. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a side view of a circular saw. Fig. Figure 2 is a top view of the circular saw. Fig. Figure 3 is a cross-sectional view of Fig. 1 along line AA. Fig. Figure 4 is a cross-sectional view of Fig. 2 along line BB. Fig. Figure 5 is a longitudinal sectional view of a grinding device (does not show all features of the claims). DETAILED DESCRIPTION OF THE TEACHINGS

[0014] The following describes embodiments of the present teachings based on the drawings. Fig. Figure 1 is a side view of a circular saw, which is an example of a power tool. Fig. 2 is a top view of it, Fig. Figure 3 is a cross-sectional view of Fig. 1 along line AA, and Fig. is a cross-sectional view of Fig. 2 along line BB. Above a base 2, which has a rectangular shape in a plan view, a circular saw 1 is configured to have a main body 3, which has a circular, disc-shaped saw blade 4 as a tip tool, driven by a brushless motor 5. The main body 3 consists of a motor housing 6, which accommodates the brushless motor 5, a gearbox housing 7, which is connected to the right side (right side of Fig. 1 (referred to as the front side) of the motor housing 6, and a blade housing 8, which covers an upper part of the saw blade 4, while being connected to the right side of the gearbox housing 7. Above the gearbox housing 7, a handle housing 9, mounted in a loop-shaped manner, is provided between the gearbox housing 7 and a protruding housing 56 described below.

[0015] The front side of the blade housing 8, in the cutting direction of the base 2, which is rotatable in the vertical direction, is pivotally mounted to a connecting plate 10, which has a U-shape in plan view, by means of a screw 11. The connecting plate 10 is connected to a guide plate 12, which rests transversely on the base 2 and has an arcuate guide groove, in a rotatable manner by a pin in the reciprocating direction and in a manner that can be fixed at any position along the guide groove by means of a wing nut 13. Meanwhile, a guide plate 14, which has an arcuate guide groove, rests transversely on the base 2 at the rear side of the blade housing 8.A depth guide 15, which curves forward in an arc along one side of the blade housing 8, is connected to the guide plate 14 in a rotatable manner by a pin in the reciprocating direction and in a manner that can be fixed at any position along the guide groove by a wing screw 16. A roller 17, provided on a lateral surface of the blade housing 8, passes through the depth guide 15, so that any clamping operation is possible by a lever 18, which is provided on an extension of the rotating shaft of the roller 17.

[0016] Accordingly, the cutting depth of the saw blade 4 on the main body 3 can be adjusted downwards through an angled hole 19 provided at the base 2 by changing the clamping position of the blade housing 8 along the depth guide 15 by rotating it around the screw 11. Additionally, the main body 3 can be fixed within a range of any tilt angle, from a right-angle position in which the saw blade 4 is perpendicular to the base 2, to a maximum tilt position in which the saw blade 4 is inclined to the right at an angle of 45° with respect to the base 2, by changing the fixed position of the connecting plate 10 and the depth guide 15 on the front and rear guide plates 12 and 14.Furthermore, notches 20 and 20, whose side edges are positioned on the extension of the saw blade 4 in the right-angle (0°) position and the 45° position of the saw blade 4, are formed at the front end of the base 2. Accordingly, it is possible to easily perform a cut along a marked line by causing the side edge of the notch 20 to coincide with the marked line, which is marked on a top surface of a material to be cut.

[0017] Meanwhile, the handle housing 9 is formed by assembling a split housing half 9a on the left side, which is subsequently connected to the motor housing 6, and a split housing half 9b on the right side using screws 21, 21 and so on, and the rear side serves as a handle part 22. A switch 23, from which a push button 24 projects downwards, is mounted on the front side of the handle part 22, and a power cable 25 is connected to the rear side of the handle part 22.

[0018] The brushless motor 5 is an internal rotor type comprising a stator 26 and a rotor 27. The stator 26 contains a stator core 28, which consists of a plurality of laminated steel plates, a front insulating component 29, and a rear insulating component 30 (furthermore, for the simplicity of describing the interior of the main body 3, which is in Fig. The rotor 27 comprises (as shown in Figure 3, where the side of the saw blade 4 is referred to as the front side and the side of the brushless motor 5 is referred to as the rear side), which are provided on the front and rear sides of the stator core 28, and six coils (not shown) which are wound around the stator core 28 over the front insulating component 29 and the rear insulating component 30. Additionally, the rotor 27 includes a rotating shaft 31 positioned at the shaft center, a cylindrical rotor core 32 arranged around the rotating shaft 31, a cylindrical permanent magnet 33 arranged on the outside of the rotor core 32 whose polarity is reversed in the circumferential direction, and a plurality of permanent magnets (not shown) for a sensor, arranged radially on its rear side.A sensor circuit board 34 is fixed at the rear end of the rear insulating component 30, on which three rotation detection elements are mounted, which output rotation detection signals for a sensor of the rotor 27 by detecting a position of the permanent magnets.

[0019] The rotating shaft 31 is rotatably mounted by a bearing 35, which is held in a rear part of the motor housing 6, and a bearing 36, which is held in the gearbox housing 7, such that the front end, on which a first gear 37 is formed, projects into the gearbox housing 7. A centrifugal fan 38 for motor cooling is fixedly attached to the rear side of the rotating shaft 31 behind the bearing 36. A plurality of inlet openings 39, 39, and so on are formed on the rear surface of the motor housing 6. A shell-shaped deflector plate 40, through which the rotating shaft 31 passes and which surrounds the circumference of the centrifugal fan 38, is provided on the front of the stator 26.

[0020] Additionally, the rear and front ends of an intermediate shaft 41, which is parallel to the rotary shaft 31, are rotatably mounted on the front side of the rotary shaft 31 by a bearing 42 held in the gearbox housing 7 and a bearing 44 held in a bearing bracket 43 mounted to the blade housing 8, respectively. A second gear 45, which has a large diameter, is provided on the rear part of the intermediate shaft 41 and meshes with the first gear 37 of the rotary shaft 31. Reference numeral 46 denotes a ring held in the bearing bracket 43 at the front of the bearing 44, which absorbs compressive loads from the bearing 44. A third gear 47, which has a smaller diameter than the second gear 45, is formed in the front part of the intermediate shaft 41.

[0021] Furthermore, at the front of the intermediate shaft 41, the rear and front ends of a discharge shaft 48, which is parallel to the intermediate shaft 41, are rotatably mounted by a bearing 49 held in the blade housing 8 and a bearing 50 held in the bearing bracket 43, respectively. The front end, which extends through the bearing bracket 43, projects into the blade housing 8. A fourth gear 51, which meshes with the third gear 47 of the intermediate shaft 41, is provided at the rear of the discharge shaft 48. At the front end of the discharge shaft 48, the cutting blade 4 is clamped by an outer flange 52 and an inner flange 53 and is secured by a bolt 54, which is screwed into the center of the discharge shaft 48 from the front. Reference numeral 55 denotes a safety cover, which is rotatably mounted to the bearing bracket 43 inside the blade housing 8.Normally, the safety cover is pre-tensioned to rotate in a position in which the lower side of the saw blade 4, as in . Fig. 1 is shown, covered.

[0022] Meanwhile, as in Fig. As shown in Figure 4, the protruding housing 56 is connected to the rear of the motor housing 6, and a controller 57 is housed inside the protruding housing 56. The controller 57 accommodates a control circuit board (not shown) on which a microcomputer and other components, such as a diode or smoothing capacitor, a switching element, and the like, are mounted to form a rectifier or inverter circuit. Here, instead of the large-volume smoothing capacitor (electrolytic capacitor) used in the prior art, a smoothing capacitor configured to have a small volume of approximately several hundred µF is provided on the output side of the rectifier circuit. That is, a capacitor-free controller, which does not use an electrolytic capacitor, is employed.

[0023] Additionally, the inner surface of the protruding housing 56 is connected to the motor housing 6, and an inlet opening 58 is formed in the left end surface of the protruding housing 56. Fins 59, 59, and so on for radiation are installed such that they project onto a surface of the control 57.

[0024] A weight reduction of the aforementioned brushless motor 5 is achieved by reducing the number of laminated layers of the steel plates 28a, 28a, and so on of the stator core 26 (here, 40 layers in the prior art are reduced to 8.4 layers) and by reducing its size in the axial direction. Accordingly, the rotating shaft 31 of the brushless motor 5 can rotate at high speed, at a speed of 40,000 revolutions per minute or more. However, the module of the first gear 37 and the second gear 45 is set to between 0.5 and 1.5, so that the speed of the output shaft 48 can be maintained within a range of 4,000 to 6,000 revolutions per minute, similar to the prior art, even when the speed of the rotating shaft 31 is increased.At the same time, a delay ratio between the first gear 37 and the second gear 45, which serve as a first-stage delay mechanism, is made to be greater than a delay ratio between the third gear 47 and the fourth gear 51, which serve as a second-stage delay mechanism.

[0025] In the circular saw 1, which has the configuration described above, when the push button 24 is actuated by pulling it upwards, the switch 23 is switched on, thus supplying mains power. This drives the brushless motor 5 with direct current, which is rectified by the controller 57. This means that the microcomputer of the controller 57 receives the rotation detection signal output by the rotation detection elements of the sensor switching board 34. This signal indicates the position of the permanent magnets for a sensor on the rotor 27 and detects the rotation state of the rotor 27. The microcomputer then controls the ON and OFF states of the respective switching elements in accordance with the detected rotation state. Subsequently, the microcomputer causes an electric current to flow sequentially to the respective coils of the stator 26, thereby rotating the rotor 27.Accordingly, the rotating shaft 31 turns, thus rotating the intermediate shaft 41 via the first gear 37 and then via the second gear 45. Furthermore, the output shaft 48 turns via the third gear 47 and then via the fourth gear 51, thus rotating the saw blade 4 and enabling it to cut the material to be cut.

[0026] According to the rotations of the centrifugal fan wheel 38, which are accompanied by rotations of the rotating shaft 31, the cooling air drawn in through the inlet openings 39 to the inside of the motor housing 6 is directed, as indicated by arrow a, to the side of the gearbox housing 7 through the deflector plate 40 after passing the brushless motor 5, in order to cool the brushless motor 5. Additionally, as indicated by arrow b, the cooling air drawn in through the inlet opening 58 of the protruding housing 56 is moved into the motor housing 6 so that it is similarly directed to the side of the gearbox housing 7 through the deflector plate 40 after passing the controller 57, in order to cool the controller 57.A large portion of the cooling air directed to the side of the gearbox housing 7 is expelled into the blade housing 8, where it mixes with the airflow generated by the rotation of the saw blade 4. This mixture is then drawn out of an outlet opening 60 located on the right side surface of the blade housing 8. The remaining cooling air is directed to the front end of the blade housing 8 and passes through a passage 61 on the left side surface of the blade housing 8, blowing towards the front end of the base 2. This prevents the marked line from becoming covered with sawdust.

[0027] In this way, according to the circular saw 1 of the embodiment, the speed of the brushless motor 5 is set to 40,000 revolutions per minute, so that the weight of the brushless motor 5 is reduced and the power tool can be reduced in weight overall, while still being excellent in its handling.

[0028] Furthermore, a switched reluctance motor, a high-frequency motor, or similar can be used as a brushless motor. Additionally, the number of rotor poles can be suitably reduced to six or fewer. Furthermore, the number of coils required for driving the motor using a controller can be reduced by specifying six poles or fewer. Accordingly, it is possible to control the brushless motor in a simple manner.

[0029] In this embodiment, the number of laminated layers of the steel plates of the stator core is reduced to achieve a weight reduction. However, it is also possible to achieve the weight reduction by reducing the number of windings in the coils.

[0030] Additionally, the power tool is not limited to a circular saw, so the gauges can also be applied to garden tools, screwdrivers, grinders, cutting tools, and the like. Accordingly, as in the embodiment, a power tool is not limited to a structure for achieving deceleration by arranging an intermediate shaft and an output shaft at an eccentric position relative to a motor's rotating shaft. However, it is permissible to use a structure for achieving deceleration by means of a planetary gear deceleration mechanism arranged between a motor's rotating shaft and a tip tool. Therefore, the tip tool's rotational speed is not limited to the range of 4,000 to 6,000 revolutions per minute, but can instead range from 1,000 to 15,000 revolutions per minute.

[0031] Fig. Figure 5 shows an example of a grinding device (not showing all features of the claims) that employs a planetary gear delay mechanism. In the grinding device 70, a motor 72, formed by a stator 73 and a rotor 74, is accommodated inside a motor housing 71, which is attached at the rear (left side in Fig.5 is positioned at the front of the motor housing 71. Inside a gearbox housing 77, which is connected to the front of the motor housing 71, a planetary gear delay mechanism 78 is provided, in which carriers 79 and 79, which support a plurality of planet gears 80 and 80 that rotate inside an inner gear 81, are arranged in two stages in the axial direction. A drive pinion 76, which is provided at the tip of a rotating shaft 75 of the rotor 74, engages with the planet gears 80 of the first stage. Furthermore, an output shaft 82, which is provided on the carrier 79 of the second stage, projects into a front housing 83, which is connected to the front of the gearbox housing 77.Inside the front housing 83, a spindle 84 is mounted to rotate perpendicular to the output shaft 82, causing a bevel gear 85, provided on an intermediate part, and a bevel gear 86, provided on the output shaft 82, to mesh with each other. A disc-shaped grinding wheel 87, acting as a center tool, is provided at the lower end of the spindle 84, which projects from the front housing 83. Reference numeral 88 designates a switch located in the rear part of the motor housing 71.

[0032] Similarly, in the grinding device 70, the number of laminated layers of the stator 73 is reduced to ensure that the rotational speed of the rotating shaft 75 of the motor 72 is 40,000 revolutions per minute or more, while the rotational speed of the spindle 84 is fixed within the range of 6,000 to 15,000 revolutions per minute by being slowed down by the planetary gear reduction mechanism 78.

[0033] In this way, according to the grinding device 70 in the embodiment, the weight of the motor is reduced by setting the speed of the motor 72 to 40,000 revolutions per minute, so that the overall weight of the power tool can be reduced while maintaining excellent usability. REFERENCE MARK LIST

[0034] 1: Circular saw, 2: Base, 3: Main body, 4: Saw blade, 5: Brushless motor, 6: Motor housing, 7: Gearbox housing, 8: Blade housing, 26: Stator, 27: Rotor, 31: Drive shaft, 37: First gear, 41: Intermediate shaft, 45: Second gear, 47: Third gear, 48: Output shaft, 51: Fourth gear, 56: Protruding housing, 57: Control, 70: Grinding device, 72: Motor, 73: Stator, 74: Rotor, 75: Drive shaft, 78: Planetary gear mechanism, 79: Carrier, 80: Planetary gear, 81: Internal gear, 82: Output shaft, 84: Spindle.

Claims

[1] Power tool (1), with a motor (5) with a speed of 40,000 revolutions per minute or more, in which The rotational speed of the motor (5) is slowed down by a first-stage deceleration mechanism (37, 45) and a second-stage deceleration mechanism (47, 51) so that rotations of the motor (5) are transmitted to a tip tool (4), a delay ratio of the delay mechanism (37, 45) of the first stage is greater than a delay ratio of the delay mechanism (47, 51) of the second stage, and the rotational speed of the tip tool (4) is within a range of 1,000 revolutions per minute to 15,000 revolutions per minute, the delay mechanism (37, 45) of the first stage comprises a first gear (37) which is provided on a rotating shaft (31) of the motor (5) and a second gear (45) which is provided on an intermediate shaft (41) and engages with the first gear (37), the delay mechanism (47, 51) of the second stage comprises a third gear (47) provided on the intermediate shaft (41) and a fourth gear (51) provided on an output shaft (48) and engaged with the third gear (47), the rotating shaft (31), the intermediate shaft (41) and the output shaft (48) are arranged parallel to each other, and the second gear (45) overlaps with the output shaft (48) when viewed along the axis of the output shaft (48). [2] Power tool (1) according to claim 1, wherein a module of the first gear (37) and the second gear (45) is set within 0.5 to 1.

5. [3] Power tool (1) according to claim 1 or 2, wherein the motor (5) is a brushless motor and the number of rotor poles is six or less. [4] Power tool (1) according to any one of claims 1 to 3, wherein the motor (5) uses mains current as a power source, includes a control which has a rectifier circuit, and the control does not use an electrolytic capacitor which has a large capacitance. [5] Power tool (1) according to any one of claims 1 to 4, wherein each of the first gear (37), the second gear (45), the third gear (47) and the fourth gear (51) is a spur gear. [6] Power tool (1) according to any one of claims 1 to 5, wherein, among the first gear (37), the second gear (45), the third gear (47) and the fourth gear (51), the second gear (45) has the largest diameter. [7] Power tool (1) according to any one of claims 1 to 6, wherein the power tool (1) is a circular saw.

Images