JP3736120B2 - Electric tool - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric tool such as a portable electric circular saw using a helical gear, and particularly to reduce gear noise at start-up.
[0002]
[Prior art]
When the power tool is started, a large current flows and a high torque is generated, the motor is accelerated rapidly and rotational fluctuation occurs at a frequency twice the current frequency. This phenomenon causes vibration and noise peculiar to the start-up in an electric tool having a reduction gear using a helical gear, for example. Conventionally, an elastic body described in Japanese Utility Model Publication No. 37-15604 is generally provided in the bearing chamber to prevent vibrations and resonances associated with rotational fluctuations. Since it is limited by the frictional force with the elastic body and the elastic force acting on the side surface of the bearing, there is little effect on the unique phenomenon at the start of the motor, and a drastic solution has been demanded.
[0003]
[Problems to be solved by the invention]
An object of the present invention is to eliminate the above-described drawbacks of the prior art, to reduce the collision energy of the helical gear when the electric tool is activated, and to reduce gear noise peculiar to the activation.
[0004]
[Means for Solving the Problems]
The object is to provide a gap between the outer periphery of the bearing that supports the motor rotation shaft and the bearing chamber that houses the bearing so that the motor rotation shaft and the bearing can be easily moved in the thrust direction. This is achieved by providing an elastic body with a small spring constant having a plurality of hemispheres in contact with the bearing side surface between the chamber and the chamber.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention in which a power tool is round will be described. As shown in FIG. 1, the circular saw decelerates the rotation of the motor, that is, the rotary shaft 7a by the helical gear 2 attached to one end of the rotary shaft 7a of the armature 7 and the helical gear 1 attached to the output shaft 14. The saw blade 13 mounted on the output shaft 14 via the washer 11 and the washer 12 is rotated and cut. Both ends of the rotating shaft 7 a are supported by bearings 3 and 4, and the bearings 3 and 4 are stored and held in the bearing chambers 5 and 6. Since the motor is normally driven by an AC power supply, at the time of start-up, the rotation of the rotating shaft 7a increases while rotating. In particular, a power tool in which a disc-shaped blade such as a saw blade 13 having a large inertial mass is attached to the output shaft 14 like a circle in order to rapidly rotate the helical gear 1 and the saw blade 13 that are stopped at the time of activation. Then, the collision of the helical gears 1 and 2 occurs, and the helical gears 1 and 2 are accelerated while repeating the collision, coupled with the rotational fluctuation of the rotating shaft 7a. The impact due to the collision of the helical gears 1 and 2 is transmitted to the saw blade 13 via the output shaft 14 and also transmitted to the main body 15 via the bearing 3 and the like, thereby generating vibrations in various places. In particular, since the saw blade 13 is formed of a thin metal plate, vibration due to impact force is large, which causes a large generation of gear noise. The present invention focused on the fact that the impact force of the helical gears 1 and 2 is separated into a radial component force and a thrust component force, and the impact force can be absorbed and relaxed by moving the helical gears 1 and 2 in the direction of action of these forces. Specifically, a gap is provided between the outer periphery of the bearing 4 that supports the round rotating shaft 7a using the helical gears 1 and 2 and the bearing chamber 6 that houses and holds the bearing 4, so that the rotating shaft 7a, that is, the armature 7 is provided. The bearing 4 is integrated with the bearing 4 and is movable in the axial direction, and has a hemispherical projection 9 in contact with the side surface of the bearing 4 between the side surface of the bearing 4 and the bearing chamber 6. By providing the body 8 and buffering the thrust component force at the time of the collision of the helical gears 1 and 2 by the axial movement of the armature 7 and reducing the collision energy, the gear noise can be reduced.
[0006]
Since the hemispherical projection 9 has a tapered shape, the spring constant when the contact area is small is small, and the axial displacement of the armature 7 can be easily performed when the motor is started. Easy to absorb energy. Since the rotational fluctuation twice as large as the current frequency occurs as described above at the time of starting the motor, it is desirable that the period of the axial displacement of the armature 7 is an elastic body 8 having a spring constant that synchronizes with the rotational fluctuation period. . When a large thrust component is applied to the elastic body 8, the contact area gradually increases according to the axial displacement, and further, the elastic body 8 receives a force on the plane 10 without the hemispherical projection 9, so the spring constant increases. It has a shape that can withstand high loads during practical use. In the case where the slit is formed as in the above-mentioned Japanese Utility Model Publication No. 37-15604, the elastic body 8 having the tapered hemispherical projection 9 is formed when the high load is repeatedly applied, compared to the case where the slit is likely to be the starting point of destruction. Provides a stable strength. Moreover, since the hemispherical protrusion 9 is formed on the plane of the elastic body 8, it can be manufactured with good mass productivity and at low cost. Furthermore, the spring constant of the elastic body 8 can be arbitrarily set by changing the number, height, shape, and material of the hemispherical protrusions 9.
[0007]
In the above embodiment, the elastic body 8 is provided between the bearing 4 and the bearing chamber 6. However, the elastic body 8 is provided between the bearing 3 and the bearing chamber 5 or between both the bearings 3 and 4 and the bearing chambers 5 and 6. May be.
[0008]
【The invention's effect】
As described above, according to the present invention, it is possible to reduce gear noise generated at the time of startup.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment in which the present invention is applied to a circular saw.
FIG. 2 is a front view of an elastic body constituting the present invention.
3 is an enlarged side view showing a protrusion of FIG. 2. FIG.
[Explanation of symbols]
1, 2 are helical gears, 3, 4 are bearings, 5 and 6 are bearing chambers, 7 is an armature, 7a is a rotating shaft, 8 is an elastic body, 9 is a spherical protrusion, 10 is a flat portion, and 11 and 12 are washers. , 13 is a circular saw blade, 14 is an output shaft, and 15 is a main body.

Claims (2)

An electric tool having a tool attached to the tip of an output shaft equipped with a helical gear that meshes with a helical gear provided at one end of a motor rotating shaft,
A clearance is provided between a bearing that supports the rotating shaft and a bearing chamber that houses the bearing, and an elastic body having a plurality of hemispherical protrusions is provided between the bearing and the bearing chamber. Electric tool to do.   The power tool according to claim 1, wherein the protrusion protrudes in an axial direction of the rotating shaft.

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