Power tool

Patent metadata

Field	Value
Publication number	US-10658957-B2
Application number	US-201716096449-A
Country	US
Kind code	B2
Filing date	Mar 31, 2017
Priority date	Apr 28, 2016
Publication date	May 19, 2020
Grant date	May 19, 2020

Abstract

A power tool includes a brushless motor, a supplying circuit, and a controller. The brushless motor is configured to drive and rotate when a voltage applied to the brushless motor is larger than or equal to an induced voltage. The supplying circuit is configured to apply a driving voltage to the brushless motor. The controller is configured to control the supplying circuit. The supplying circuit includes a rectifying circuit, a capacitor, and a switching circuit. The rectifying circuit is configured to rectify an alternating voltage and output a rectified voltage. The capacitor is configured to smooth the voltage inputted via the rectifying circuit. The switching circuit is configured to perform a switching operation based on a PWM signal to adjust a period during which the driving voltage is applied. The controller is configured to set a duty ratio within a prescribed range, and output the PWM signal of the set duty ratio to the switching circuit to control the switching operation. The controller is configured to perform a constant-number-of-rotation control for controlling the brushless motor to rotate at a target rotation number by changing the duty ratio. The capacitor has a capacitance allowing a smoothed voltage to be always larger than or equal to the induced voltage during the constant-number-of-rotation control.

First claim

The invention claimed is:

1. A power tool comprising:
a brushless motor configured to drive and rotate when a voltage applied to the brushless motor is larger than or equal to an induced voltage;
a supplying circuit configured to apply a driving voltage to the brushless motor; and
a controller configured to control the supplying circuit,
wherein the supplying circuit includes:
a rectifying circuit configured to rectify an alternating voltage and output a rectified voltage;
a capacitor configured to smooth the voltage inputted via the rectifying circuit; and
a switching circuit configured to perform a switching operation based on a PWM signal to adjust a period during which the driving voltage is applied,
wherein the controller is configured to set a duty ratio within a prescribed range, and output the PWM signal of the set duty ratio to the switching circuit to control the switching operation,
wherein the controller is configured to perform a constant-number-of-rotation control (constant rotational speed control) for controlling the brushless motor to rotate at a constant target rotation number by changing the duty ratio,
wherein the capacitor has a capacitance allowing a smoothed voltage to be always larger than or equal to the induced voltage during the constant-number-of-rotation control (constant rotational speed control),
wherein the controller is capable of maintaining the constant speed control when a load of the motor is smaller than or equal to a first load and incapable of maintaining the constant speed control when the load of the motor is larger than the first load,
wherein the capacitor has the capacitance which allows the smoothed voltage to be always larger than the pulsating induced voltage in a case where the load of the motor is smaller than or equal to the first load, and allows a minimum of the smoothed voltage to be smaller than the pulsating induced voltage in a case where the load of the motor exceeds a second load larger than the first load.

2. The power tool according to claim 1 , wherein the controller is configured to control the supplying circuit to stop application of the driving voltage to the brushless motor in a case where the current flowing in the brushless motor is larger than a maximum allowable current value,
wherein the capacitor has the capacitance allowing the driving voltage to be always larger than or equal to the induced voltage while the current flowing in the brushless motor is smaller than the maximum allowable current value.

3. The power tool according to claim 1 , wherein the capacitance is larger than or equal to 500 microfarads.

4. The power tool according to claim 1 , wherein the capacitor includes a plurality of capacitors connected in parallel.

5. The power tool according to claim 1 , wherein the brushless motor includes a rotor configured to rotate about a rotational axis,
the power tool further comprising:
a fan configured to rotate coaxially with the rotational axis; and
a housing accommodating the brushless motor, the supplying circuit, and the fan,
wherein the housing has an opening portion,
wherein the housing is formed with a wind path therein, the wind path extending from the fan to the opening portion,
wherein a longitudinal direction of the capacitor extends in a direction of a cooling air flowing in the wind path.

6. The power tool according to claim 5 , further comprising:
a circuit board to which the switching circuit is mounted; and
a board case accommodating the circuit board,
wherein the capacitor is positioned at an end of the board case at a side where the opening portion is formed.

7. The power tool according to claim 6 , wherein the switching circuit is in contact with the circuit board.

8. The power tool according to claim 6 , wherein a filler is filled between the capacitor and the circuit board.

9. The power tool according to claim 1 , wherein the brushless motor includes a rotor configured to rotate about a rotational axis,
the power tool further comprising:
a circuit board to which the switching circuit is mounted;
a fan configured to rotate coaxially with the rotational axis; and
a housing accommodating the circuit board, the brushless motor, the supplying circuit, and the fan,
wherein the housing has a first opening portion and a second opening portion which are formed at different positions,
wherein the housing is formed with a first wind path and a second wind path therein, the first wind path extending from the fan to the first opening portion, the second wind path extending from the fan to the second opening portion,
wherein the circuit board is disposed on the first wind path,
wherein the capacitor is disposed on the second wind path.

10. The power tool according to claim 9 , wherein the housing includes a first wall portion disposed at one end thereof in an extending direction of the rotational axis and a second wall portion disposed at another end thereof in extending direction, the first wall portion having the first opening portion, the second wall portion having the second opening portion,
wherein the first opening portion has a region overlapping with the fan in a vertical direction,
wherein the second opening portion is disposed above the fan.

11. The power tool according to claim 1 , wherein the brushless motor includes a rotor configured to rotate about a rotational axis,
the power tool further comprising:
a centrifugal fan configured to rotate coaxially with the rotational axis; and
a circuit board having one surface on which the capacitor is disposed and another surface on which the switching circuit is disposed,
wherein the circuit board extends in a radial direction of the rotational axis.

12. The power tool according to claim 1 , wherein the brushless motor includes a rotor configured to rotate about a rotational axis,
the power tool further comprising:
a centrifugal fan configured to rotate coaxially with the rotational axis; and
a circuit board to which the capacitor is mounted,
wherein the capacitor is disposed closer to the centrifugal fan than the circuit board to the centrifugal fan.

13. The power tool according to claim 1 , wherein the capacitor has the capacitance which allows a minimum of the smoothed voltage to be lower than the pulsating induced voltage in a case where the current flowing in the brushless motor is larger than a maximum allowable current value.

14. The power tool according to claim 1 , wherein the controller is to stop rotating of the motor when the load of the motor exceeds an overcurrent threshold value larger than the second load.

Assignees

• Koki Holdings Co Ltd

Inventors

• Kuragano Shinji
• Kumakura Takeru

Classifications

• B25F5/00

  Details or components of portable power-driven tools not particularly related to the operations performed and not otherwise provided for · CPC title

• H02K7/14

  Structural association with mechanical loads, e.g. with hand-held machine tools or fans (with fan or impeller for cooling the machine H02K9/06) · CPC title

• H02K11/0094

  Structural association with other electrical or electronic devices · CPC title

• B23D45/16

  Hand-held sawing devices with circular saw blades · CPC title

• B23D47/12

  of drives for circular saw blades · CPC title