JP2005246542A - Power tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power tool capable of reducing noise and increasing air capacity by applying optimal blade shape to the fan diameter of a centrifugal fan. <P>SOLUTION: The outer diameter d2 of a fan body 21 is 45mm≤d2≤50mm, and a blade 22 is provided at the fan body 21 so that an axial height h1 in an approximately middle position C of the blade 22 to the outer diameter of the fan body 21 is 0.2≤h1/d2≤0.3 and that an axial height h2 at the outer peripheral edge of the blade 22 to the outer diameter d2 of the fan body 21 is 0.12≤h2/d2≤0.17. Further, the number of blades 22 is 23-30. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electric tool including a centrifugal fan that cools a motor.

  Due to the demands for miniaturization, high output, and low noise of electric tools, there is an increasing need for development of a motor cooling fan and a fan periphery that are small, have high cooling capacity, and have low noise. Therefore, optimization of the blade shape has been proposed for the purpose of increasing air volume and reducing noise. (For example, refer to Patent Document 1).

JP-A-10-153194

  As shown in FIG. 10 and FIG. 11, the plurality of blades 222 of the centrifugal fan 220 described in Patent Document 1 are arranged on the one surface side of the fan main body 221 in order to discharge air radially outward of the fan main body 221. The main body 221 extends from a predetermined radial position to the outer edge, is arranged at a predetermined pitch along the circumferential direction of the fan main body 221, and is provided so as to protrude from the one surface side in the axial direction of a drive shaft (not shown).

  When the centrifugal fan 220 is rotated, energy is given to the air by centrifugal action, and the air passes through the air passage formed by the blades 222 and the fan guide 211 from the inlet portion which is the inner end of the blades 222, so It is discharged radially outward from the outlet portion which is the outer peripheral portion.

  Here, the centrifugal fan 220 includes a fan main body 221 between portions D1 of the inner ends of the pair of blades 222 positioned in the same radial direction, a protruding length H1 at the inner ends of the blades 222, and portions facing each other at the inner ends of the blades 222. The product of the circumferential distance L1, the outer diameter D2 of the fan body 221, the protruding length H2 of the outer periphery of the blade 222, and the distance L2 of the fan body 221 in the circumferential direction between the opposing portions of the outer edge of each blade 222 Are substantially equal to each other. That is, the air smoothly flows so that D1 × H1 × L1≈D2 × H2 × L2, and the noise reduction effect is exhibited.

  However, there is an increasing demand for lower noise in power tools, and it is necessary to optimize the shape of the centrifugal fan to reduce noise. In general, fluid noise is said to be proportional to the sixth power of the flow velocity. In the case of a centrifugal fan, if the rotational speed is the same, the flow velocity decreases when the fan outer diameter is reduced. Therefore, noise can be reduced by reducing the fan outer diameter. Further, when the fan outer diameter is reduced, the flow rate is reduced, but by increasing the fan blade height, the amount of air to which centrifugal force is applied can be increased to compensate for the flow rate. However, when the blade height is increased, it becomes necessary to form deeper grooves in the part corresponding to the blades of the mold of the fan, and it is difficult to process because the end mill easily shakes when forming the grooves. Therefore, there arises a problem that the manufacturing cost is significantly increased.

  Accordingly, an object of the present invention is to provide an electric tool that can set an optimum blade height with respect to the fan diameter of a centrifugal fan, and can achieve low noise and increase in air volume at an appropriate manufacturing cost.

In order to achieve the above object, the present invention includes an inlet for sucking air, a housing in which an outlet for discharging the air is formed, a rotor and a stator housed in the housing. And a centrifugal fan that is coaxially fixed to the rotor and rotates together with the rotor. The centrifugal fan includes a disk-shaped fan body and air along the axial direction of the rotor. A plurality of blades extending from a predetermined radial position of the fan main body to an outer peripheral edge and formed at a predetermined pitch along a circumferential direction of the fan main body, and the stator and the housing. A first flow path is defined between the stator and the rotor, and a second flow path is defined between the stator and the rotor. The first flow path is perpendicular to the axial direction of the rotor. The smallest value S of the cross-sectional areas of the first flow path and the second flow path among the cross-sections arranged in the direction. But the power tool is 350mm ² ≦ S0 ≦ 650mm ^2, the outer diameter d2 of the fan body is 45 mm ≦ d2 ≦ 50 mm, and the axial direction of the height h1 in becomes highest point of the vane The electric power tool is characterized in that 0.2 ≦ h1 / d2 ≦ 0.3 with respect to the outer diameter of the fan body.

  Here, the axial height h1 at the highest point of the blade is preferably 0.25 ≦ h1 / d2 ≦ 0.3 with respect to the outer diameter d2 of the fan body.

  The axial height h2 of the outer peripheral edge of the blade is preferably 0.12 ≦ h2 / d2 ≦ 0.17 with respect to the outer diameter d2 of the fan body.

  Further, the number n of the blades is preferably 23 ≦ n ≦ 30, and the number n of the blades is more preferably 25 ≦ n ≦ 28.

  Further, the product of the distance L1 along the circumferential direction of the fan body between the mutually opposing portions at the highest point of the blades adjacent to each other and the axial height h1 at the highest point of the blade. A first area S1 composed of the same, an inner diameter d1 which is a distance between the highest portions of the pair of blades located in the same diameter direction of the fan body, and portions facing each other on the outer peripheral edges of the blades adjacent to each other A second area S2 formed by a product of a distance L2 along the circumferential direction of the fan body between the fan body and a height h2 in the axial direction at the outer peripheral edge of the blade, and an outer diameter d2 of the fan body is S1 · It is preferable to be configured to satisfy the relationship of d1 = (1 ± 0.3) S2 · d2.

  The blade includes an inner part from the predetermined radius position to the highest point and an outer part from the highest point to the outer peripheral edge, and the outer peripheral edge of the outer part. The vicinity is inclined at a first predetermined angle α1 in a direction opposite to the rotational direction of the centrifugal fan with respect to a straight line connecting the center of the fan and the outer peripheral edge of the outer portion, and the inner portion is Is inclined at a second predetermined angle α2 in a direction opposite to the rotational direction of the centrifugal fan with respect to a straight line connecting the center of the center and the predetermined radial position, and the first predetermined angle α1 is 30 ° ≦ α1 ≦ 50 °. The second predetermined angle α2 is preferably 0 ° ≦ α2 ≦ 10 °.

  Here, the first predetermined angle α1 is preferably 35 ° ≦ α1 ≦ 45 °, and the second predetermined angle α2 is preferably 2.5 ° ≦ α2 ≦ 7.5 °.

  According to the electric tool of claim 1 of the present invention, the outer diameter d2 of the fan body is 45 mm ≦ d2 ≦ 50 mm, and the height h1 in the axial direction at the highest point of the blade is outside the fan body. Since 0.2 ≦ h1 / d2 ≦ 0.3 with respect to the diameter, it is possible to realize a reduction in noise and an increase in air volume at an appropriate manufacturing cost.

  According to the electric tool of claim 2, the axial height h1 at the highest point of the blade is 0.25 ≦ h1 / d2 ≦ 0.3 with respect to the outer diameter d2 of the fan body. Therefore, it is possible to achieve a reduction in noise and an increase in air volume at a more appropriate manufacturing cost.

  According to the electric power tool of claim 3, since the axial height h2 at the outer peripheral edge of the blade is 0.12 ≦ h2 / d2 ≦ 0.17 with respect to the outer diameter d2 of the fan body, a large air volume is obtained. And a low noise centrifugal fan can be realized.

  According to the power tool of the fourth aspect, since the number n of blades is 23 ≦ n ≦ 30, vortices causing noise are not generated, and air passage can be sufficiently secured. Therefore, it is possible to reduce noise while ensuring a sufficient air volume.

  According to the electric power tool of claim 5, since the number n of blades is 25 ≦ n ≦ 28, it is possible to reduce noise while securing a sufficient air volume as compared with the configuration of claim 4. .

  According to the electric tool of claim 6, since it is configured to satisfy the relationship of S1 · d1 = (1 ± 0.3) S2 · d2, the air flow between adjacent blades is hardly disturbed, and noise Can be reduced.

  According to the electric tool of claim 7, since the first predetermined angle α1 is 30 ° ≦ α1 ≦ 50 °, the air flow rate in the vicinity of the outer peripheral edge of the centrifugal fan can be set to an appropriate speed. Low noise can be achieved while maintaining a large air volume. Further, since the second predetermined angle α2 is 0 ° ≦ α2 ≦ 10 °, the stress generated at the base of the blade can be relieved, the blade can be prevented from being broken, and turbulence that causes noise is generated. Can be suppressed.

  According to the power tool of claim 8, the first predetermined angle α1 is 35 ° ≦ α1 ≦ 45 °, and the second predetermined angle α2 is 2.5 ° ≦ α2 ≦ 7.5 °. Noise can be reduced while maintaining a sufficient air volume than the configuration of Item 7.

  An embodiment in which the electric power tool of the present invention is applied to a grinding tool (disc grinder) will be described with reference to FIG. FIG. 1 shows the overall structure of the disc grinder 1. If the left side of the drawing is the front end, the resin handle portion 2, the resin motor housing 3, and the aluminum alloy gear cover 4 are connected in this order from the rear. And the housing is configured. And the space defined in each of the handle | steering-wheel part 2, the motor housing 3, and the gear cover 4 is connecting. A power cable 5 is attached to the handle portion 2 and a switch mechanism 6 is built in. The switch mechanism 6 is provided with a lever 2A that can be operated by a user. The power cable 5 connects the switch mechanism 6 to an external power source (not shown) and operates the lever 2A to switch between connection and disconnection of the switch mechanism 6 and the power source. A first air inlet 2a is formed at the rear end of the handle portion 2, and second and third air inlets (not shown) are formed at the front end.

  A motor 9 having a rotor 7 and a stator 8 is accommodated in the motor housing 3, and the rotor 7 has a drive shaft 10 coaxially. A fan guide 11 is fixed to the motor housing 3 in front of the motor 9.

  In the gear cover 4 and in front of the fan guide 11, a centrifugal fan 20 is concentrically fixed to the drive shaft 10 and is rotatably provided with the drive shaft 10. In the gear cover 4, a first exhaust port 4 a, a second exhaust port 4 b, and a third exhaust port (not shown) are formed at a radially outward position of the centrifugal fan 20. A power transmission mechanism including a pinion gear 12 fixed to one end of the drive shaft 10 and a gear 14 fixed to the output shaft 13 as an output unit is disposed in the gear cover 4, and the pinion gear 12 meshes with the gear 14. Thus, the rotation of the rotor 7 is transmitted to the output shaft 13. A grindstone 15 is fixed to the output shaft 13.

  Next, the internal structure of the motor housing 3 will be described with reference to FIG. FIG. 2 is a cross-sectional view taken along line II-II in FIG. As described above, the motor 9 has the rotor 7 and the stator 8. The stator 8 is fixedly held by the motor housing 3, and a hollow portion 8 a for loosely inserting the rotor 7 is formed in the stator 8. A plurality of first air flow paths 3 a are defined by the motor housing 3 and the stator 8, and a plurality of second air flow paths 3 b are defined by the stator 8 and the rotor 7, respectively. Yes.

  Next, the operation of the disc grinder 1 will be described. By pressing the lever 2A against the handle portion 2, an electric current is supplied from an external power source (not shown) to the motor 9, and the rotor 7 rotates. The drive shaft 10 is rotated with the rotation of the rotor 7, the rotation is transmitted to the output shaft 13 and the grindstone 15 by the pinion gear 12 and the gear 14, and the grinding operation is performed by pressing the rotating grindstone 15 against the work material. .

  At this time, the rotation of the centrifugal fan 20 fixed to the rotor 7 causes air to flow as indicated by an arrow c1 in a boosting space 20a, which will be described later, and the pressure decreases on the inner diameter side of the centrifugal fan 20 and the pressure on the outer diameter side. Get higher. As a result, air is introduced from the first air inlet 2a of the tail cover 2 and the second and third air inlets (not shown) as indicated by arrows a1, a2, and a3. Next, the air passes through the first air flow path 3a and the second air flow path 3b as indicated by arrows b1 and b2, and cools the motor 9. Thereafter, the air flows through the pressure increasing space 20a as indicated by an arrow c1, and flows out to the outside as indicated by arrows e1, e2, and e3 through the first exhaust port 4a, the second exhaust port 4b, and a third exhaust port (not shown).

  Next, the structure of the centrifugal fan 20 will be described with reference to FIG. 3 is a cross-sectional view of the centrifugal fan 20, and FIG. 4 is a front view of the centrifugal fan 20 viewed from the direction IV in FIG. Centrifugal fan 20 has a fan main body 21 and a plurality of blades 22 provided integrally with fan main body 21 and projecting in the axial direction of fan main body 21, and rotates in the direction indicated by arrow A (FIG. 4). . The fan main body 21 has a disc shape, and includes a hub 21A having a rotor insertion hole 21a for engaging with the drive shaft 10 and a main plate 21B. The plurality of blades 22 extend from the predetermined radial position B of the fan main body 21 to the outer peripheral edge along the circumferential direction of the fan main body 21 in order to flow air along the axial direction of the rotor 7 outward in the radial direction of the fan main body 21. It is formed at a predetermined pitch.

  As shown in FIG. 4, the blades 22 are inclined in a direction opposite to the rotational direction A with respect to a direction extending radially outward from the predetermined radial position B of the fan main body 21. Each blade 22 includes an inner portion 22A from a predetermined radius position B to a substantially intermediate position C, and an outer portion 22B from a substantially intermediate position C to the outer peripheral edge. The inner portion 22A has a shape in which the axial height gradually increases outward in the radial direction. Conversely, the outer portion 22B has an axial height gradually increasing in the radial outward direction. It has a lower shape. Further, the pressure increasing space 20a through which air flows is defined by the blades 22 adjacent to each other, and a part of the pressure increasing space 20a faces the fan guide 11 (FIG. 1).

  Here, the distance between the substantially intermediate positions C of the pair of blades 22 located on opposite sides of the centrifugal fan 20 in the same diameter direction (hereinafter referred to as fan inner diameter) is d1, and the diameter of the fan main body 21 (hereinafter referred to as fan outer diameter). D2, the axial height at the substantially intermediate position C of the blade 22 (hereinafter referred to as the blade inner height) h1, and the axial height (hereinafter referred to as the blade) of the outer peripheral edge of the outer portion 22B of the blade 22 H2). In addition, an angle formed by the extending direction of the outer portion 22B and a straight line connecting the center of the centrifugal fan 20 and the outer peripheral edge of the outer portion 22B is α1, the extending direction of the inner portion 22A, and the center of the fan main body 21. The angle formed by the straight line connecting the predetermined radius position B is α2. Further, the distance along the circumferential direction of the centrifugal fan 20 between the portions facing each other at the substantially intermediate position C of the blades 22 adjacent to each other (hereinafter, the distance between the substantially intermediate positions C) is L1, and the outer peripheral edges of the blades 22 adjacent to each other The distance along the circumferential direction of the centrifugal fan 20 between the parts facing each other in FIG.

  In this embodiment, the fan inner diameter d1 = 35 mm, the fan outer diameter d2 = 48 mm, the blade inner height h1 = 13 mm, and the blade outer height h2 = 7 mm. The dimensions of the conventional centrifugal fan were: fan inner diameter d1 '= 33 mm, fan outer diameter d2' = 52 mm, blade inner height h1 '= 9 mm, blade outer height h2' = 3.5 mm. Further, α1 = 40 °, α2 = 5 °, and the number of blades 22 is 27. Since there are measurement errors and variations in the dimension value, the symbol “=” used to represent the dimension value will be used as substantially meaning “≈”.

Next, the reason why the fan outer diameter d2 is changed from the conventional 52 mm to 48 mm will be described. In selecting the fan outer diameter d2, the relationship between the sound pressure p [pa] of the noise generated by the fluid and the flow velocity v [m / sec] is approximately p∝v ^6.
It is based on the property of becoming. In the centrifugal fan, the relationship between the fan outer diameter d2 and the flow velocity v at the fan outlet is approximately d2∝v.
So when these are combined,
p∝d2 ⁶
It becomes. Further, the relationship between the conventional fan outer diameter d2 ′ and the sound pressure p ′ is similarly p′∝d2 ′ ^6.
It becomes. Therefore,
(P / p ′) ∝ (d2 / d2 ′) ⁶
It becomes. That is, the fan outer diameter d2 is selected based on the property that if the fan outer diameter d2 is made smaller, the flow velocity v becomes smaller in proportion to it, and the sound pressure p becomes smaller in proportion to the sixth power. In this embodiment,
(P / p ′) ∝ (48/52) ⁶ ≈0.62
Theoretically, the sound pressure p is reduced to about 0.62 times compared to the conventional case. Further, as a result of the experiment, the conventional noise value was about 81 dB, whereas in the present embodiment, it was about 77.5 dB, which was about 3.5 dB smaller. In addition, if the fan outer diameter d2 is in the range of 45 mm ≦ d2 ≦ 50 mm, substantially the same effect can be obtained.

  Note that the dimensions of the centrifugal fan 20 according to the present embodiment and the conventional centrifugal fan are designed so as to satisfy the formula (1) described later, which smoothes the air flow in the centrifugal fan and reduces noise. Therefore, the noise value is reduced by about 3.5 dB only because the fan outer diameter d2 is changed to 48 mm.

  Next, the reason why the blade inner height h1 = 13 mm with respect to the fan outer diameter d2 = 48 mm will be described. Ratio of blade inner height h1 and fan outer diameter d2 (hereinafter referred to as first blade height ratio): h1 / d2 is h1 / d2 = 0.27, and conventional h1 ′ / d2 ′ = It is larger than 9 / 52≈0.17. This is to compensate for the decrease in the flow rate due to the fan outer diameter d2 being reduced to reduce the flow velocity.

Hereinafter, factors affecting the flow rate will be described. Flow from the inlet (first intake port 2a, second and third inlet ports not shown) to the outlet (first exhaust port 4a, second exhaust port 4b, third exhaust port not shown) in the air flow path A pressure difference P [Pa] between the inlet and the outlet of the pressurizing space 20a, which is a fan blowing capacity necessary for generating a flow rate Q [m ³ / min], is expressed by the following equation.
P = aQ ²
Here, a is a channel resistance coefficient. The above formula is Q = √ (P / a)
It becomes. That is, the factors affecting the flow rate Q are the pressure difference P and the channel resistance coefficient a. Hereinafter, the channel resistance coefficient a will be described. It is known that the channel resistance coefficient a is an eigenvalue determined by the shape of the channel, and the value of the channel resistance coefficient a is almost determined by the size of the cross-sectional area (referred to as S0) of the narrowest portion in the channel. ing.

  The minimum cross-sectional area S0 in the cooling flow path of the disc grinder 1 of the present embodiment is perpendicular to the axial direction of the rotor 7 and out of the cross sections aligned in the axial direction of the rotor 7, the first air flow path 3a and the second air flow path 3a. The cross-sectional area of the air flow path 3b is the smallest value (hereinafter referred to as a motor cross-sectional area: S0). The cross-sectional area of the first air flow path 3a is naturally determined from the demand for miniaturization to make the outer diameter of the motor housing 3 as small as possible and the outer diameter of the stator 8 necessary for obtaining desired power. Further, the second air flow path 3b is naturally determined from the need to efficiently convert the magnetic force into the rotational force.

As a result of examining the in-motor flow path cross-sectional area S0 for a general portable electric tool, it was about 350 mm ² ≦ S0 ≦ 650 mm ² . FIG. 5 shows the results of examining changes in the flow rate Q [mm 2] when a pressure difference (pressure difference) P [Pa] is generated between the air inlet and the outlet. The curve X in FIG. 5 is the result at S0 = 350 mm ² , and the curve Y is the result at S0 = 650 mm ² . Further, the channel resistance coefficient a in the curve X was about 3000, and the channel resistance coefficient a in the curve Y was about 2000. Therefore, the channel resistance coefficient a in the portable power tool of 350 mm ² ≦ S0 ≦ 650 mm ² is about 2000 ≦ a ≦ 3000.

Hereinafter, the ventilation capability of a fan is demonstrated. The factor that has a great influence on the fan blowing capacity is the first blade height ratio. Change of flow rate Q when the fan outer diameter is changed in the range of 45 mm ≦ d2 ≦ 50 mm and the first blade height ratio (h1 / d2) is changed for a portable power tool of 350 mm ² ≦ S0 ≦ 650 mm ² FIG. 6 shows the result of the investigation. When the first blade height ratio is in the range of h1 / d2 <0.2, the flow rate increases in proportion to the increase in the first blade height ratio. This is because, in this region, the ratio of the channel resistance to the fan blowing capacity is sufficiently small, so that air easily flows between the blades 22 and the flow around the fan is smooth.

  Further, the rate of increase in the flow rate is reduced around 0.2 ≦ h1 / d2 ≦ 0.3, and the flow rate hardly increases when 0.3 <h1 / d2. This is because, in the range of 0.3 <h1 / d2, the ratio of the channel resistance to the fan capacity is too large, so that it is difficult for air to flow between the blades 22 and the fan energy is used to stir the surrounding air. This is because fine vortices are generated between the blades 22 and the blades 22. That is, in these electric power tools, if the range is 0.2 ≦ h1 / d2 ≦ 0.3, the blade inner height h1 can be set to an appropriate height in flow rate and manufacturing cost.

More preferably, if it is set in the range of 0.25 ≦ h1 / d2 ≦ 0.3, a more appropriate height can be set, and if it is set so that h1 / d2 = 0.27, the most appropriate height can be set. Can be set. In this embodiment, since the fan outer diameter d2 is 48 mm,
h1 / d2 = 0.27
To h1 = 0.27 × 48 ≒ 13mm
Therefore, h1 = 13 mm is set.

From the above, in an electric tool having a cooling flow path for cooling a motor by a centrifugal fan and having a motor cross-sectional area S0 in the range of 350 mm ² ≦ S0 ≦ 650 mm ² , the fan outer diameter Is set to a range of 45 mm ≦ d2 ≦ 50 mm, and the blade inner height h1 is set to satisfy 0.2 ≦ h1 / d2 ≦ 0.3, thereby reducing noise and increasing the air volume at an appropriate manufacturing cost. Can be realized.

Next, the reason why the fan inner diameter d1 is 35 mm and the blade outer height h2 is 7 mm will be described. In Japanese Patent No. 3391199, the area indicated by the product of the distance L1 between the substantially intermediate positions C and the blade inner height h1 is defined as the inlet portion area S1 (= L1 × h1), the blade outer peripheral edge distance L2, the blade outer height, and h2. When the area indicated by the product is the exit area S2 (= L2 × h2),
S1 · d1 = μ · S2 · d2 (1)
0.7 ≦ μ ≦ 1.3
By designing the shape of the blades 22 so as to satisfy the relationship, the ratio between the radial velocity and the rotational velocity between the blades 22 is such that the inlet portion (substantially intermediate position C of the blade 22) and the outlet portion. It is described that it becomes equal between (the outer peripheral edges of the blades 22), the air flow is hardly disturbed, and noise is reduced.

Therefore, it should be designed in this embodiment so as to satisfy the relationship of the expression (1). Specifically, from the equation (1) (in this embodiment, μ = 1), (π · d1 / n) · h1 · d1 = (π · d2 / n) · h2 · d2
And d1 ² · h1 = d2 ² · h2 (2)
It becomes. Here, since d2 = 48 mm and h1 = 13 mm in the present embodiment, Equation (2) is
d1 ² · 13 = 48 ² · h2
Thus, d1 = 35 mm and h2 = 7 mm are set so as to satisfy this relationship.

From the above, the inventors set the first blade height ratio: h1 / d2 and the ratio of the blade outer height h2 to the fan outer diameter d2 (hereinafter referred to as the second blade height ratio): h2 / d2 as a predetermined value. Experiments were performed with variation within the range. In FIG. 7, the second blade height ratio and the first blade height ratio are (10.0%, 22.0%), (14.5%, 27.0%), (20.0%, 32 0.0%), and the results of the experiments conducted in each. The vertical axis on the left is the noise ratio, which is a value obtained by dividing the obtained noise value by a predetermined noise value. The vertical axis on the right is the air volume [m ³ / min].

  From FIG. 7, in the region where the second blade height ratio and the first blade height ratio are less than (12.0%, 25.0%), the noise is small, but there is a sufficient air volume to cool the motor 9. In addition, it can be seen that in a region exceeding (17.0%, 30.0%), a sufficient air volume can be obtained, but the noise increases. Therefore, if the second blade height ratio is within a range of 12.0 to 17.0% and the first blade height ratio is within a range of 25.0 to 30.0%, noise is reduced while maintaining a sufficient air volume. It is possible to make it. More preferably, if it is in the vicinity of (14.5%, 27.0%), the centrifugal fan 20 that generates a large air volume and is low noise can be realized.

  Next, the reason why the number of blades 22 is 27 will be described. Hereinafter, the number of blades 22 is n. As a result of examining the change in the air volume when the number n of the blades 22 was changed for the centrifugal fan 20 with the fan outer diameter d2 of 45 mm ≦ d2 ≦ 50 mm, the fan outer diameter d2 was not greatly changed by the difference in the fan outer diameter d2, and both The tendency as shown in FIG. 8 was shown. The vertical axis represents the air volume ratio, which is a value obtained by dividing the air volume value obtained for each number by the air volume value when the number is 27. As can be seen from FIG. 8, the most air volume was obtained at n = 27, and when the number of blades 22 was in the range of 23 ≦ n ≦ 30, no significant decrease in the air volume was observed compared to n = 27. In the range of n <23, since the number n of the blades 22 is smaller than the fan outer diameter d2, the distance between the adjacent blades 22 near the outer diameter of the centrifugal fan 20 increases. For this reason, the air flow between the blades 22 is disturbed, and the air volume is reduced.

  Further, in the range of n> 30, since the number n of the blades 22 is larger than the fan outer diameter d2, the distance between the adjacent blades 22 on the inner diameter of the centrifugal fan 20 is narrowed. For this reason, it becomes difficult for air to flow between the blades 22, and the air volume is reduced. From the above, in the centrifugal fan 20 having the fan outer diameter d2 of 45 mm ≦ d2 ≦ 50 mm, the noise n can be reduced while ensuring a sufficient air volume by setting the number n of the blades 22 as 23 ≦ n ≦ 30. It becomes possible. More preferably, if the number n of blades 22 is set to 25 ≦ n ≦ 28, it is possible to reduce noise while ensuring a sufficient air volume. If n = 27, it is possible to reduce the noise while ensuring the maximum air volume. In this embodiment, the number of blades 22 is set to 27.

  Next, the reason why α1 = 40 ° and α2 = 5 ° will be described. The inventors changed the angle between α1 and α2 and examined changes in noise and air volume. As a result, it was found that a sufficient air volume can be obtained and noise reduction can be realized in the range of 30 ° ≦ α1 ≦ 50 ° and 0 ° ≦ α2 ≦ 10 °.

  This is because if α1 is less than 30 °, the flow velocity of air near the outer peripheral edge of the centrifugal fan 20 increases, causing noise. If α1 exceeds 50 °, the outside of the centrifugal fan 20 is reversed. This is because the flow velocity of the air near the peripheral edge becomes slow and a sufficient air volume cannot be obtained. Further, if α2 is less than 0 ° or α2 exceeds 10 °, a large stress tends to occur at the base of the blade 22 and turbulence tends to occur, which is not desirable. 0 ° ≦ α2 ≦ 10 ° This is because the turbulent flow can be suppressed within the range.

  Further, if the range is 35 ° ≦ α1 ≦ 45 ° and 2.5 ° ≦ α2 ≦ 7.5 °, it is possible to achieve a further sufficient air volume and noise reduction, α1 = 40 °, α2 = 5 °. It was found that the highest air volume can be obtained with the lowest noise.

  The power tool according to the present invention is not limited to the above-described embodiment, and various modifications and improvements can be made within the scope described in the claims. For example, the shape of the centrifugal fan 20 may be a taper shape that is inclined in the direction opposite to the direction in which the blades 122 project rather than the disk shape, as in the centrifugal fan 120 shown in FIG. Good. Further, the ridge line from the substantially intermediate position C to the outer peripheral edge of the blade 22 is a straight line, but is not limited thereto, and may be a circular arc shape or the like like the centrifugal fan 120. Furthermore, the electric tool is not limited to a vibration drill or a disc grinder, and can be applied to a cutting tool, an electric drill, a screw tightener, or the like.

Sectional drawing which shows embodiment which applied the electric tool by this invention to the grinding tool. Sectional drawing along the II-II line | wire of FIG. Sectional drawing of the centrifugal fan with which the electric tool by this invention is equipped. The front view of the centrifugal fan with which the electric tool by this invention is equipped. The figure which showed the change of the flow volume of air when a pressure difference is added to the inlet and outlet of air. The figure which showed the change of the flow volume of air when changing a 1st blade | wing height ratio. The figure which showed the relationship between each combination of a 1st blade | wing height ratio and a 2nd blade | wing height ratio, and a noise ratio and an air volume. The figure which showed the relationship between the number of blades and the air volume ratio. Sectional drawing of the modification of the centrifugal fan with which the electric tool by this invention is equipped. The front view of the conventional centrifugal fan. Sectional drawing of the conventional centrifugal fan.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Disc grinder 3 Motor housing 2a 1st inlet 3a 1st air flow path 3b 2nd air flow path 4a 1st exhaust port 4b 2nd exhaust port 7 Rotor 8 Stator 9 Motor 20, 120, 220 Centrifugal fan 21, 121, 221 Fan body 22A Inner part 22B Outer part 22, 122, 222 Blade B Predetermined radial position C Approximately intermediate position d1 Fan inner diameter d2 Fan outer diameter h1 Blade inner height h2 Blade outer height L1 Between approximately intermediate positions C Distance L2 Blade outer peripheral distance n Number of sheets S0 Motor cross-sectional area S1 Inlet area S2 Outlet area α1 First predetermined angle α2 Second predetermined angle

Claims (8)

A housing formed with a suction port for sucking air and a discharge port for discharging the air;
A motor housed in the housing and having a rotor and a stator;
A centrifugal fan that is coaxially fixed to the rotor and rotates together with the rotor, the centrifugal fan having a disk-shaped fan main body and air along an axial direction of the rotor outside the radial direction of the fan main body. A plurality of blades extending from a predetermined radial position of the fan main body to the outer peripheral edge and formed at a predetermined pitch along a circumferential direction of the fan main body in order to flow in the direction,
A first flow path is defined between the stator and the housing,
A second flow path is defined between the stator and the rotor,
Of the cross-sections perpendicular to the axial direction of the rotor and aligned in the axial direction of the rotor, the value S0 having the smallest cross-sectional area of the first flow path and the second flow path is 350 mm ² ≦ S0 ≦ 650 mm ² . In an electric tool,
The outer diameter d2 of the fan body is 45 mm ≦ d2 ≦ 50 mm, and the axial height h1 at the highest point of the blade is 0.2 ≦≦ the outer diameter of the fan body. An electric tool characterized by satisfying h1 / d2 ≦ 0.3.   2. The axial height h1 at the highest point of the blade is 0.25 ≦ h1 / d2 ≦ 0.3 with respect to the outer diameter d2 of the fan body. The electric tool as described in.   The height h2 in the axial direction at the outer peripheral edge of the blade is 0.12 ≦ h2 / d2 ≦ 0.17 with respect to the outer diameter d2 of the fan body. Electric tool.   The power tool according to claim 1, wherein the number n of the blades is 23 ≦ n ≦ 30.   The power tool according to claim 4, wherein the number n of the blades satisfies 25 ≦ n ≦ 28. It consists of the product of the distance L1 along the circumferential direction of the fan body between the portions facing each other at the highest point of the blades adjacent to each other and the axial height h1 at the highest point of the blade. A first area S1 and an inner diameter d1 which is a distance between the highest points of the pair of blades located in the same diameter direction of the fan body;
A second area S2 formed by a product of a distance L2 along the circumferential direction of the fan body between the mutually opposing portions on the outer peripheral edges of the blades adjacent to each other, and the axial height h2 on the outer peripheral edge of the blades; The electric tool according to claim 1, wherein the outer diameter d2 of the fan body is configured to satisfy a relationship of S1 · d1 = (1 ± 0.3) S2 · d2. The blade is composed of an inner part from the predetermined radial position to the highest point and an outer part from the highest point to the outer peripheral edge,
The direction in which the outer portion extends is inclined by a first predetermined angle α1 in a direction opposite to the rotational direction of the centrifugal fan with respect to a straight line connecting the center of the fan and the outer peripheral edge of the outer portion,
The inner portion is inclined at a second predetermined angle α2 in a direction opposite to the rotational direction of the centrifugal fan with respect to a straight line connecting the center of the fan and the predetermined radial position,
The centrifugal fan according to claim 1, wherein the first predetermined angle α1 is 30 ° ≦ α1 ≦ 50 °, and the second predetermined angle α2 is 0 ° ≦ α2 ≦ 10 °.   The first predetermined angle α1 is 35 ° ≦ α1 ≦ 45 °, and the second predetermined angle α2 is 2.5 ° ≦ α2 ≦ 7.5 °. Centrifugal fan.

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