JP2006123034A - Portable power tool with earth - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a portable power tool with earth, reducing the occupied space of a noise eliminating member in a housing, reducing a noise level (an electromagnetic interference wave terminal voltage level), and having a metal outer frame as the housing. <P>SOLUTION: In the portable power tool with earth, the housing 15 has an outer frame made of a metallic material surrounding the outer periphery of an electric motor section body and electrically connected in common to an earth connection line 30 together with a stator core 7. A rotating shaft 2 of a rotor 1 is electrically insulated from a rotor core 3 by an insulating material layer 4, and a first capacitor 9 for eliminating normal mode noise generated from the electric motor section is electrically connected between feeder lines 31, 32. A series circuit of a resistance 10 and a second capacitor 11 for eliminating common mode noise generated from the electric motor section, is electrically connected in parallel with a stator coil 8. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a grounded portable power tool, and more particularly to a grounded portable power tool having a noise prevention circuit in which a housing of the portable power tool is made of a metal material and suppresses noise generation.

  In general, portable power tools suppress the propagation of noise (noise or electromagnetic interference) caused by commutators and stator windings of a series commutator type motor used as a tool drive source. Or it is required to prevent. Furthermore, it is required to reduce the size of the tool in consideration of weight reduction or workability improvement.

  It is known that noise generated from an electric motor propagates to a power supply line connected to the electric motor and interferes with other electric or electronic devices such as radios and televisions connected to other power supply lines as electromagnetic interference. ing. Therefore, a regulation value as shown in FIG. 5 is defined for this noise in CISPR publication 14 (International Committee for Radio Interference), which is an international standard. In a grounded power tool, the propagation of noise generated from the motor is divided into normal mode noise that propagates between a pair of feed lines and common mode noise that propagates between the feed lines and the ground line. Is known to be able to be suppressed or prevented independently, and the technology shown in FIG.

  The noise removal circuit shown in FIG. 6 is disclosed in FIG. In FIG. 6, the stator core SI in which the stator winding SC of the electric motor is formed is electrically connected to the ground together with the motor housing (housing). In order to remove common mode noise generated from the electric motor, a pair of capacitors C2 and C3 connected in series are electrically connected between the power supply lines, and a midpoint of the pair of capacitors C2 and C3 is electrically connected to the ground. ing. Further, it discloses that the capacitor C1 is electrically connected between the feeder lines in order to remove normal mode noise generated from the electric motor. Further, FIG. 2 of Patent Document 1 also discloses that a common mode choke coil L including a pair of choke coils is inserted into the feed line in order to further reduce common mode noise.

JP 58-10471 A

  However, in the conventional noise removal circuit shown in FIG. 6, a single capacitor C1 and a pair of series-connected capacitors C2 and C3 are connected in parallel between the power supply lines, and the pair of series-connected pairs are connected. Because the midpoint of the capacitor must be electrically connected to the motor housing or ground connection, the wiring within the motor housing is complicated, and more space is required to place the three capacitor blocks And

On the other hand, the common mode choke coil L for removing the common mode noise used in the above prior art is generally used as an electromagnetic interference wave countermeasure element. Since it constitutes a part of the power supply line of the power supply, a relatively thick wire winding is formed on the ferrite core. For example, when the common mode choke coil L requires an inductance of 5 mH or more for noise removal and the rated current of the power tool requires 5 A or more, the common mode choke coil L realizes a required inductance value and a rated current value, and In order to adapt the temperature rise of the coil to a standard value or less, it is necessary to wind a lead wire having a conductor cross-sectional area of 1.25 mm ^{2 around} a hollow ferrite core having a size of about 20 mm × 20 mm × 40 mm. For this reason, the electromagnetic interference wave suppression countermeasure by the common mode choke coil L requires a large mounting space in the housing of the power tool, and the power tool cannot be miniaturized. Furthermore, there is a problem that the cost is increased.

  Accordingly, an object of the present invention is to provide a grounded portable electric tool that reduces the space occupied by a noise removing member in the housing and reduces the noise level (electromagnetic interference terminal voltage level). Another object of the present invention is to provide a grounded portable power tool having a metal outer frame as a housing.

  The above and other objects and novel features of the present invention will become apparent from the following description of the present specification and the accompanying drawings.

  According to one aspect of the present invention, an electric motor unit comprising a housing, a stator having a stator winding held by the housing, and a rotor having a rotating shaft rotatably supported by the housing. And a grounded portable electric tool comprising a power supply line connected to the motor unit, wherein the housing has an outer frame made of a metal material surrounding an outer periphery of the motor unit main body, and the outer frame is connected to the ground Electrically connected to the wire, the rotating shaft of the rotor has an insulating layer, a first capacitor is electrically connected between the feeder lines, and a second capacitor is electrically connected to the stator winding. Connected in parallel.

  According to another feature of the invention, a series circuit including a resistor connected in series to the second capacitor is electrically connected in parallel to the stator winding.

  According to still another aspect of the present invention, the first capacitor is disposed in the housing, and a series circuit of the second capacitor and the resistor is mounted on a stator of the electric motor.

  According to the present invention, since a capacitor or a resistor is used as a noise removing member, a grounded portable electric tool that reduces the occupied space and cost of the noise removing member in the housing of the electric tool and suppresses the noise level. Can provide. Moreover, the portable electric tool with a ground which has the outer frame of a metal material as a housing can be provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiments, and the repetitive description thereof will be omitted.

  1 to 4 are drawings for explaining a grounded portable power tool according to an embodiment of the present invention. FIG. 1 is a grounded portable power tool when the present invention is applied to a disc grinder (cutting tool). 2 is a sectional view (side view) of the tool, FIG. 2 is a partially enlarged view of a rotor in the grounded portable electric tool according to the present invention shown in FIG. 1, and FIG. 3 is a ground according to the present invention shown in FIG. FIG. 4 shows a circuit diagram of the grounded portable electric tool according to the present invention shown in FIG. 1, respectively.

  As shown in FIG. 1, a disc grinder according to the present invention includes a motor housing portion 15 made of a metal material such as aluminum, a switch housing portion (switch case portion) 24 made of an insulating material such as a metal material or a plastic material, and a metal material. Gear housing part (gear case part) 25 and a tip tool 28 such as a grindstone.

  In the switch housing portion 24, a switch (not shown) for controlling power supply of a commercial power source to an electric motor described later, a capacitor 9 for removing noise, that is, an electromagnetic interference wave, and a capacitor 11 and a resistor 10 described later. The series circuit is provided. Further, a power cord 23 including power supply lines 31 and 32 for supplying commercial power to the motor is drawn out from the switch housing portion 24, and is inserted through plugs 22a and 22b of a plug 22 provided at the end thereof. Electrically connected to a commercial power outlet. In addition, the power cord 23 includes a ground connection wire 30 electrically connected to the motor housing portion 15 by screwing or the like in parallel with the feed lines 31 and 32, and is electrically connected to the ground 21 via the clip 16. (See FIG. 4).

  A part of the grindstone 28 is covered with a protective cover 29. A pair of bevel gears 26 and 27 constituting a rotation conversion portion are mounted on the gear housing portion 25, and the rotational force generated on the shaft 2 of the electric motor mounted on the motor housing portion 15 is transmitted to the tip tool 28.

  The motor housing portion 15 is composed of an outer frame made of a metal material that surrounds the outer periphery of the electric motor portion. In the motor housing portion 15, an AC / DC power supply motor (universal motor) is mounted. As shown in FIG. 3, the electric motor includes a stator 34 attached to the housing 15. The stator 34 includes a stator core 7 and a stator winding 8. The electric motor further includes a rotor 1 having a shaft (rotating shaft) 2 rotatably supported by the housing 15.

  As shown in FIG. 2, a commutator 5 is attached to the shaft 2 in addition to the rotor core 3 and the rotor winding 6. The rotor core 3, the rotor winding 6 and the commutator 5 are electrically insulated from the shaft 2 made of a metal material by the insulating material layer 4 covering the shaft 2 to constitute the rotor 1 of the electric motor. .

  Although not shown in FIG. 1, the capacitor 9 of the noise removing electrical component according to the present invention shown in the equivalent circuit diagram of FIG. 4 is disposed in the switch housing portion 24, and the capacitor 11 of the noise removing electrical component and The resistor 10 is provided in the space of the stator 34 in the form of a circuit block (module) 33 as shown in FIG. Thereby, the occupied space in the switch housing portion 24 is remarkably reduced as compared with the conventional case. Of course, the capacitor 9 may be mounted in the motor housing portion 15 if the space of the motor housing portion 15 is allowed. In FIG. 4, one end (the end opposite to the clip 16) of the ground connection wire 30 is electrically connected to the motor housing portion 15 made of a metal material by screwing as described above. The features of the present invention will be described below with reference to FIG.

  First, as shown in FIG. 2, according to the present invention, the rotor 1 has a structure in which the rotor winding 6 is electrically insulated from the rotor shaft 2 by the insulating material layer 4 as described above. With the structure in which the rotor winding 6 is electrically insulated from the shaft 2 by the insulating material layer 4, the rotor winding 6 is electrically insulated from the motor housing portion 15, that is, the ground connection line 30. As a result, common mode noise in a frequency band of 0.15 MHz to 30 MHz transmitted from the rotor winding 6 to the housing portion 15 can be suppressed.

  Furthermore, according to the present invention, the capacitor 11 alone or a series circuit of the resistor 10 and the capacitor 11 is electrically connected in parallel to the stator winding 8 serving as a noise generation source. When the capacitor 11 is singly connected in parallel to the stator winding 8, the resonance frequency of the noise frequency formed by the capacitor 11 by the stator winding 8 and its parallel distributed capacitance (for example, 1 MHz is the center). Frequency) to a lower frequency, and as a result, has a function of reducing the impedance of the noise with respect to the resonance frequency. Accordingly, it is possible to suppress propagation of common mode noise around the resonance frequency determined by the stator winding 8 and the distributed capacitance of the stator winding 8 to the feed lines 31 and 32.

  When the series circuit of the capacitor 11 and the resistor 10 is connected in parallel, the resistance value of the resistor 10 is selected to be smaller than the impedance with respect to the noise frequency (for example, 1 MHz is the center frequency) of the field winding 8. For example, the resistance value of the resistor 10 is selected to be 500Ω so that it is 1/10 or less of the impedance of the stator winding 8. Further, the capacitor 11 is selected to have a capacitance value large enough to conduct high frequency components. For example, the capacitor 11 is selected to have a capacitance value of 0.02 μF. The series circuit of the resistor 10 and the capacitor 11 can suppress common mode noise transmitted to the stator winding 8 and the power supply lines 31 and 32 near the resonance frequency determined by the distributed capacitance.

  Further, according to the present invention, the capacitor 9 is electrically connected between the feed lines 31 and 32 in order to remove normal mode noise propagating between the feed lines 31 and 32. The capacitance value of the capacitor 9 is selected to be 0.02 μF, for example. The connection of the capacitor 9 can suppress the generation of noise having a frequency band of 0.15 MHz to 0.3 MHz.

  As a result of the above noise countermeasures, as shown in FIG. 5, the noise voltage level (electromagnetic interference terminal voltage level) is lower than the characteristic curve 13 indicating the allowable limit value of the noise frequency band defined by the international standard. The characteristic curve 12 showing the voltage level can be improved.

  According to the present invention described above, the generation of noise is efficiently suppressed or prevented by the resistor 10 or the capacitors 9 and 10 having a small occupied space without using a large-sized electric component such as a common mode choke coil of the prior art. be able to. Further, as described above, the structure in which the rotor winding 6 is electrically insulated from the rotor shaft 2 by the insulating material layer 4 makes it possible to suppress noise generated from the stator winding 8 separately. The propagation of noise generated from the rotor 1 can also be suppressed. Accordingly, the length or thickness of the housing such as the switch housing portion 24 can be reduced, and the grounded portable power tool can be miniaturized.

  Further, since at least the outer frame portion of the motor housing portion 15 is made of a metal material and the ground connection wire 30 is electrically connected to the outer frame portion of the metal material, the midpoint of the conventional pair of noise countermeasure capacitors is Compared to the case of connecting to the ground connection line, the ground connection wiring 30 is simplified.

  Furthermore, in the above-described embodiment, if the switch housing portion 24 is made of a metal material, the switch housing portion 24 is electrically connected in common with the motor housing portion 15 made of a metal material. Therefore, even if the ground connection line is connected to the switch housing portion 24. Good.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the scope of the invention. It is.

Sectional drawing of the portable electric tool (disc grinder) with a ground which concerns on this invention. The elements on larger scale of the rotor in the portable electric tool with a ground concerning the present invention. The elements on larger scale of the stator in the portable electric tool with a ground concerning the present invention. FIG. 2 is a circuit diagram of the grounded portable power tool according to the present invention shown in FIG. 1. The frequency versus noise voltage level (electromagnetic interference terminal voltage level) characteristic curve diagram of the portable electric tool with a ground according to the present invention. The circuit diagram for noise countermeasures of the portable electric tool with a grounding by a prior art.

Explanation of symbols

1: Rotor 2: Rotor shaft (rotating shaft) 3: Rotor core 4: Insulating material layer 5: Commutator 6: Rotor winding 7: Stator core 8: Stator winding 9: Capacitor between feeder lines (First capacitor) 10: resistor 11: capacitor (second capacitor)
12: Noise voltage level of the grounded portable power tool of the present invention (FIG. 5)
13: Noise voltage level according to CISPR international standard (Figure 5)
14: Common mode choke coil 15: Motor housing portion 16: Earth clip 20: Commercial AC power supply 21: Ground potential 22: Plug 22a, 22b: Plug insertion portion 23: Power cord 24: Switch housing portion 25: Gear housing portion 26 27: Bevel gear 28: Tip tool 29: Protective cover 30: Ground connection line 31, 32: Feed line 33: Circuit block 34: Stator

Claims (3)

A housing, a stator having a stator winding held by the housing, an electric motor unit having a rotor having a rotating shaft rotatably supported by the housing, and a feed line connected to the electric motor unit In a portable electric tool with a ground provided with
The housing has an outer frame made of a metal material surrounding an outer periphery of the stator, the outer frame is electrically connected to a ground connection line, a rotating shaft of the rotor has an insulating layer, and A portable electric tool with a ground is characterized in that a first capacitor is electrically connected to the stator winding, and a second capacitor is electrically connected in parallel to the stator winding.   The grounded portable electric tool according to claim 1, wherein a series circuit of the second capacitor and a resistor is electrically connected in parallel to the stator winding. The grounded portable electric tool according to claim 2, wherein the first capacitor is disposed in the housing, and a series circuit of the second capacitor and the resistor is attached to the stator.

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