Electric power tool having a conductive elastic body connected to a yoke

An electric power tool of an embodiment of the present invention uses a motor provided with a yoke as a drive source, and is configured such that an end portion of an electric component mounted on a drive circuit of the motor is electrically connected to the yoke of the motor through a conductive elastic body.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electric power tool provided with a yoke as a drive source.

2. Description of the Related Art

As a measure for suppressing noise produced in an electric power tool, a neutral line of a noise-protection capacitor is connected to a yoke of a motor, as shown in Japanese Laid-Open Utility Model Publication No. S62-101365.

That is, the yoke itself has a low impedance, and thus noise emitted from the electric power tool outwardly can be suppressed by inducing noise current to the yoke via the neutral line of the capacitor and making a loop smaller in which noise current flows.

In the electric power tool in Japanese Laid-Open Utility Model Publication No, S62-101365, the neutral line of the noise-protection capacitor is electrically connected to the yoke of the motor by pressing a terminal provided in the neutral line of the noise-protection capacitor toward the yoke of the motor by use of spring force.

However, in a construction in which a part of the noise-protection capacitor is electrically connected to the yoke of the motor by use of the neutral line, the terminal, and the spring etc., it is necessary to create storage space for housing wires and the spring etc. within the housing of the electric power tool.

Further, the terminal of the neutral line is configured to press the yoke of the motor by use of the spring force, and thus vibration of the electric power tool can, over time, cause contact failure.

Thus, there is a need in the art to connect an end portion of an electric component to the yoke of the motor by a space-saving and vibration-proof member.

SUMMARY OF THE INVENTION

One embodiement is an electric power tool that uses a motor provided with a yoke as a drive source. An end portion of an electric component mounted on a drive circuit of the motor may be electrically connected to the yoke of the motor through a conductive elastic body.

According to one embodiment, the conductive elastic body can be electrically connected to the yoke of the motor by inserting the conductive elastic body between the end portion of the electric component and the yoke of the motor. As compared to a construction in which the electric component is electrically connected to the yoke of the motor by use of lead wires, terminals, and the spring etc., the electric power tool of the embodiment will be advantageous in terms of space, Further, the electric power tool of this embodiment can prevent contact failure between the electric component and the yoke of the motor caused by vibration of the electric power tool.

According to another embodiment, a thickness size of the elastic body where external force is not applied to the elastic body is configured to be larger than a gap between the end portion of the electric component and the yoke of the motor.

Because of this, it is ensured that the end portion of the electric component is electrically connected to the yoke of the motor by inserting the elastic body into the gap between the end portion of the electric component and the yoke of the motor.

According to another embodiment, the elastic body includes an elastic main body and a conductive cloth that covers the elastic main body.

Because of this, deformation amount can be widely adjusted by changing the material of the elastic main body etc.

According to another embodiment, the elastic body is a conductive cloth that is folded and piled up.

In this way, the configuration is simple and thus the invention will be advantageous in terms of cost.

According to another embodiement, the electric component is an FET and the end portion of the electric component is a heatsink of the FET.

According to the above embodiements, the end portion of the electric component can be electrically connected to the yoke of the motor by the vibration-proof configuration.

DETAILED DESCRIPTION FO THE INVENTION

An explanation about an embodiment 1 of the present invention will be described below with reference toFIG. 1toFIG. 6. An electric power tool according to an embodiment of the present invention may be a battery-operated hammer drill that is provided with a direct-current motor as a power source.

<Outline of the Electric Power Tool>

The hammer drill10(hereinafter referred to as the electric power tool10) includes a tubular housing main body12and a handle part15that is formed so as to protrude from a lower part of a rear portion of the housing main body12, as shown inFIG. 1.

A direct-current motor20(hereinafter referred to as the motor20) is housed in the rear portion of the housing main body12, and a gear mechanism (not shown) that increases the rotational force of the motor20is housed in front of the motor20. Further, an output shaft of the gear mechanism is linked to a tool applied part29that is placed at the tip of the housing main body12.

Further, at a base end portion, there is provided a variable speed switch18having a trigger18tthat can be pulled by a finger of a user. And, at the tip (bottom part) of the handle part15, there is provided a battery connection part15bconfigured to be able to be connected to a battery19.

<About the Motor20and the Motor Drive Circuit30>

The motor20includes an armature22(rotor22) having a commutator22s, a cylindrical yoke24yand a permanent magnet24m(refer toFIG. 2), and a stator having a brush25(refer toFIG. 3), as shown inFIG. 1. The armature22is not shown inFIG. 2.

The motor20is configured to be driven by a motor drive circuit30, as shown in FIG.3. The motor drive circuit30includes a FET32that adjusts the electric power supplied to the armature22of the motor20(winding wires of the armature (not shown)), and a motor control section38that controls the FET32via a signal from the variable speed switch18. Accordingly, electric power supplied from the battery19to the motor can be adjusted through pressing of the trigger18tof the variable speed switch18. In this way, the rotational speed of the electric power tool10can be controlled.

<About a Measure against Noise from the Electric Power Tool10>

Since the motor20includes the commutator22sand the brush25as described above, noise is generated by slide movement of the commutator22swith respect to the brush25at the time of driving the motor20. As shown inFIG. 3, noise (common mode noise) is generated such that noise current Ic flows from the motor20, which is a noise source, toward a power supply (the battery19) through an outward path31fand a return path31bof a power line31of the motor drive circuit30.

In the electric power tool10according to an embodiment the present invention, a part Ic2of the noise current Ic that flows toward the battery19is urged to the yoke24yof the motor20and a loop in which noise current flows is made smaller, and thus noise emitted from the electric power tool10is reduced. In order to do this, a heatsink33of the FET32that is electrically connected to the return path31bof the power line31is electrically connected to the yoke24yof the motor20through a conductive elastic body40.

As described above, the yoke24yhas a low impedance, and thus the part Ic2of the noise current Ic can be urged to the yoke24ythrough the elastic body40.

As shown inFIG. 4, the elastic body40includes an elastic main body45having a sponge that is formed in a band plate shape, and a conductive cloth43that covers the elastic main body45,. The conductive cloth43is formed, for example, by weaving resin fiber plated by conductive metal in a cloth shape.

Here, a thickness size T of the elastic body40is configured to be sufficiently larger than that of a gap between the heatsink33of the FET32that makes up the motor drive circuit30and the yoke24yof the motor20.

Due to this, the elastic body40is disposed so as to extend in a circumferential direction along an outer periphery of the yoke24yof the motor20. The elastic body40is inserted between the yoke24yand the heatsink33of the FET32, and thus the yoke24ycan be electrically connected to the heatsink33.

That is, the FET32corresponds to an electric component of an embodiment of present invention and the heatsink33of the FET32corresponds to an end portion of the electric component of the present invention.

<Advantage of the Electric Power Tool10According to the Present Embodiment>

According to the electric power tool10of the present embodiment, by inserting the conductive elastic body40between the heatsink33of the FET32and the yoke24yof the motor20, the yoke24yis electrically connected to the elastic body40. Compared to the prior art construction in which the electrical component (noise-protection capacitor) is connected to the yoke of the motor by use of lead wires, the terminal, and the spring etc., the present embodiment will be advantageous in terms of space. Further, the present embodiment can prevent contact failure between the heatsink33of the FET32and the yoke24yof the motor20caused by vibration of the electric power tool10.

Further, the thickness size T of the elastic body40in a condition where external force is not applied to the elastic body40is configured to be larger than the gap between the heatsink33of the FET32and the yoke24yof the motor20. Because of this, it is ensured that the heatsink33of the FET32is electrically connected to the yoke24yof the motor20by inserting the elastic body40between the heatsink33of the FET32and the yoke24yof the motor20.

Further, the elastic body40may include the elastic main body45and the conductive cloth43that covers the elastic main body45, and thus deformation amount of the elastic body40can be widely adjusted by changing material of the elastic main body45etc.

Here, the present invention is not limited to the above embodiment and various modifications can be made without departing from the scope of the invention. The above embodiment shows that the elastic body40is inserted between the heatsink33of the FET32and the yoke24yof the motor20. However, as shown inFIG. 5, in a motor drive circuit30in which a noise-protection capacitor Cn is provided, it is possible that by inserting the elastic body40between a neutral terminal Cnx of the noise-protection capacitor Cn and the yoke24yof the motor20, the neutral terminal Cnx may be electrically connected to the yoke24y.

Further, the above embodiment shows that the elastic body40includes the elastic main body45and the conductive cloth43. However, as shown inFIG. 6, a conductive cloth43that is folded and piled up can be used as the elastic body40. This will enable the construction of the elastic body40to become simple and will be advantageous in terms of cost.

Further, the present embodiment shows the hammer drill as the electric power tool10. However, any electric power tools that use the motor provided with the yoke24ycan be applied to embodiments of the present invention.

Explanation of Symbols