JPH09164501A - Electric circular saw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance safety by suppressing the temp. rise of the peripheral housing in which a resistor is arranged low without impairing brake function. SOLUTION: An electromotive circular saw is equipped with a resistor for a motor short-circuiting brake. A resistor 2 is disposed to the peripheral part of a circular saw blade 1 so as to be cooled by the wind generated by the rotating circular saw blade 1. The temp. rise of the resistor 2 for the motor short-circuiting brake is suppressed to prevent a lowering of brake capacity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric circular saw for cutting an object to be cut such as wood or metal by rotating a rotary saw blade. More specifically, the invention relates to an electric circular saw which is operated when a switch is turned off. The present invention relates to the arrangement structure of the brake resistance of.

[0002]

2. Description of the Related Art Conventionally, there is an electric circular saw provided with a brake function so that the circular saw blade stops in a short time when the switch is turned off after the cutting work. This is unsafe for work if the circular saw blade continues to rotate due to the inertial force of the circular saw blade after the switch is turned off, and the stop time is also defined in JIS standards.

At present, many brakes use a back electromotive force by short-circuiting the positive terminal and the negative terminal of the motor when the switch is turned off.
However, when the above method is adopted, especially in a DC motor or the like using a permanent magnet, the braking current is 100 A or more, and the life of the motor brush and the off contact of the switch is significantly shortened. For this reason, a brake current is reduced by inserting a resistor between the motor short circuits to extend the life of the motor and the switch.

[0004]

However, in the work in which the switch is repeatedly turned on and off frequently, the temperature of the housing in which the resistance is arranged rises because the resistance between the motor short circuits continues to generate heat. However, it may cause the housing to melt, which may cause burns, and the resistance value rises due to the temperature rise of the resistance, resulting in longer braking time and failure to meet the standard value. It is easy and, at worst, may damage the resistor.

An object of the present invention is to solve the above problems, and to improve safety without impairing the braking function and by suppressing the temperature rise of the surrounding housing where the resistor is arranged to be low. It is intended to provide a circular saw.

[0006]

In order to achieve the above object, according to the invention of claim 1, in an electric circular saw having a resistance for a motor short-circuit brake, cooling is performed by wind generated by a rotating circular saw blade 1. Thus, the resistor 2 is arranged in the peripheral portion of the circular saw blade 1, and it is possible to suppress the temperature rise of the resistor 2 for the motor short-circuit brake and prevent the braking performance from deteriorating.

According to a second aspect of the present invention, in the first aspect, a partition wall 4 for separating the circular saw blade 1 and the interior of the housing 3 is interposed between the circular saw blade 1 and the resistor 2, and a vent hole formed in the partition wall 4. The wind is introduced into the housing 3 through the filter 6 arranged in the position 5. While reliably preventing the chips generated during cutting from entering the housing 3, The resistor 2 can be cooled efficiently.

According to a third aspect of the present invention, in the first aspect, a partition wall 4 made of a material having high thermal conductivity is provided between the circular saw blade 1 and the resistor 2 so as to isolate the circular saw blade 1 and the inside of the housing 3 from each other. This is characterized in that the resistor 2 is interposed and brought into contact with the partition wall 4, and the cooling efficiency of the resistor 2 can be further improved.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION As an electric circular saw according to the present invention,
A detailed description will be given based on an embodiment of a battery-powered circular saw that uses a battery as a driving source. As shown in FIG. 2, the electric circular saw includes a main body 7 and a base 8 arranged below the main body 7 and abutted on the outer surface of the member to be cut when the member to be cut is cut.

A main switch 9 is provided at the center of the housing 3 which constitutes the main body 7, and a motor case 10 is provided below the main switch 9. Further, a handle portion 11 is integrally provided at the rear portion of the housing 3, and a battery portion 12 to which a battery is detachably attached is provided at the rear portion of the handle portion 11. A circular saw blade 1 is installed in the front part of the housing 3, and the circular saw blade 1 is housed in a motor case 10 via a speed reduction block provided in the housing 3 by a motor 13 which is housed in FIGS. , And is driven to rotate in the direction of arrow a in FIG. Here, when the circular saw blade 1 rotates in the direction of arrow A in the drawings, wind is generated so as to flow in the direction of arrow B in FIGS. 1 and 4. A transparent cover 14 is fixed to the front end of the housing 3 so as to suppress the scattering of chips generated when the circular saw blade 1 cuts a member to be cut and to make it easy to see the cutting edge of the circular saw blade 1.

The circular saw blade 1, the motor 13, the handle portion 11 and the battery portion 12 arranged on the main body 7 are arranged on the same axis line, and the main body 7 is balanced (especially in the left-right direction) and easily pushed during cutting work. In addition, it has a structure that makes it easy to cut, and normally has a transparent cover 14 as a fixed cover of the circular saw blade 1.
Is the housing 3 at a position away from the grip position and the axis.
It is composed of something different from.

A dustproof rib 15 as a partition wall 4 is provided on the housing 3 in such a manner that the housing 3 is divided into two so that chips generated when the member to be cut is cut by the circular saw blade 1 does not enter the motor 13 and the switch portion. And a resistor 2 for the motor short-circuit brake so that it contacts the side surface of the dustproof rib 15.
(Lead wire) is provided. That is, the portion where the lead wires are bundled is arranged so as to be in contact with the side surface of the partition wall 4, and a long lead wire is used so that a large current can be made to flow by increasing the resistance value.

Here, the brake circuit is constructed as shown in FIG. 3, and when the switch SW is turned on, the power is turned on and the motor 13 is driven. At this time, a current flows through the resistor 2 for the motor short circuit braking. Does not flow. Next, the motor 13
If the switch SW is turned off during driving, the power supply is cut off, but the motor 13 and the circular saw blade 1 try to continue rotating due to the rotational inertia force. At this time, the motor 13 is short-circuited, so that a counter electromotive voltage is generated in the motor 13, and the resistance 2 and the motor 1
A counter electromotive current flows through the motor 3, and a force for stopping the motor 13 works.

However, when the switch SW is turned on, the dustproof lip 15 is constantly cooled by the wind (arrow B) obtained by rotating the circular saw blade 1 in the direction shown by the arrow A in FIG. At the same time, the resistor 2 (lead wire) arranged in close contact with the dustproof rib 15 is also cooled. Due to this effect, it is possible to suppress the heat generated by the back electromotive force at the time of turning off, and in the work in which the switch SW is repeatedly turned on and off frequently, the motor 1
Even if the resistor 2 between the three short circuits continues to generate heat,
It is possible to efficiently cool the resistor 2 and prevent the temperature of the housing 3 in which the resistor 2 is placed from melting and melting the housing 3 or causing a burn or the like. It is possible to prevent the situation where the value rises and the braking time becomes longer and the standard value is not satisfied, and the braking performance is improved in the work in which the switch SW is repeatedly turned on and off frequently. It can be used safely without deterioration.

In the above embodiment, the dustproof rib 15 as the partition wall 4 is formed integrally with the housing 3, but the partition wall 4 is made of a material having a high thermal conductivity such as a copper plate or an aluminum plate in order to improve the cooling efficiency. If the partition wall 4 is made of a material having a high thermal conductivity, the heat radiation effect can be enhanced and the cooling effect of the resistor 2 can be enhanced. is there.

Further, in order to improve the cooling efficiency, as shown in FIGS. 4 and 5, a part of the dustproof rib 15 is cut to provide a vent hole 5, which has air permeability and dust intrusion. A filter 6 is installed to prevent the chips from entering the housing 3 while preventing the chips from entering the housing 3.
Alternatively, the wind generated by the rotation of the circular saw blade 1 may be directly applied to cool the resistor 2. In this case resistor 2
Can be directly cooled by the wind generated by the rotation of the circular saw blade 1, and the cooling efficiency of the resistor 2 can be improved. In addition, in the illustrated one, the vent hole 5
Shows a pair of partition walls 4 each having a long hole shape with one end open to the side, but a large number (two or more) of narrow ventilation holes 5 are provided adjacent to each other. Alternatively, one round-shaped ventilation hole 5 may be provided, and the essential point is that the wind can be directly directed to the resistance 2 while preventing the intrusion of chips.

[0017]

According to the invention of claim 1, in an electric circular saw having a resistance for a motor short-circuit brake, the resistance is arranged in the peripheral portion of the circular saw blade so as to be cooled by the wind generated by the rotating circular saw blade. Therefore, even if the work of turning on / off the switch obtained by providing a resistor is frequently performed, it has the effect of suppressing the shortening of the life of the motor and the switch, and the temperature rise of the resistor for motor short-circuit braking It is possible to provide an electric circular saw that suppresses the above and does not reduce the braking performance.

According to a second aspect of the present invention, a partition for separating the circular saw blade and the inside of the housing is interposed between the circular saw blade and the resistor, and a wind is passed through a filter arranged in a ventilation hole formed in the partition. Since it is introduced into the housing, in addition to the effect of claim 1, it is possible to reliably prevent the chips generated when the object to be cut from entering the housing, and to improve the resistance. The air can be sent to efficiently cool the resistance.

According to a third aspect of the present invention, in the first aspect, a partition wall made of a material having a high thermal conductivity is interposed between the circular saw blade and the resistor so as to isolate the circular saw blade from the inside of the housing, and the resistance is increased. Since it is brought into contact with the partition wall, in addition to the effect of the first aspect, the cooling efficiency of the resistance can be further improved.

[Brief description of the drawings]

FIG. 1 is a partially omitted sectional view showing an internal configuration.

2A is a front view with a part omitted, and FIG. 2B is a side view with a part omitted.

FIG. 3 is a circuit diagram showing a brake circuit.

FIG. 4 is a partially omitted cross-sectional view showing another example.

FIG. 5 is an explanatory diagram illustrating an arrangement state of ventilation holes and filters.

[Explanation of symbols]

 1 Circular saw blade 2 Resistance 3 Housing 4 Partition wall 5 Vent hole 6 Filter

Claims (3)

[Claims] 1. An electric circular saw having a resistance for a motor short-circuit brake, wherein the resistance is arranged in the peripheral portion of the circular saw blade so as to be cooled by wind generated by the rotating circular saw blade. Circular saw. 2. A partition wall that separates the circular saw blade from the inside of the housing is interposed between the circular saw blade and the resistor, and the wind is introduced into the housing through a filter arranged in a ventilation hole formed in the partition wall. The electric circular saw according to claim 1, wherein: 3. A partition wall made of a material having high thermal conductivity is interposed between the circular saw blade and the resistor so as to isolate the circular saw blade and the inside of the housing, and the resistor is brought into contact with the partition wall. The electric circular saw according to claim 1.