Power tool

Patent metadata

Field	Value
Publication number	US-10898985-B2
Application number	US-202016855234-A
Country	US
Kind code	B2
Filing date	Apr 22, 2020
Priority date	Nov 24, 2017
Publication date	Jan 26, 2021
Grant date	Jan 26, 2021

Abstract

A power tool includes a direct current (DC) unit, a motor, a driving circuit, a capacitor circuit, and a control unit. The capacitor circuit includes a switching element and a capacitor. The control unit drives the switching element to realize the control of charging or discharging of the capacitor. The capacitor circuit is connected between the DC unit and the driving circuit, and can buffer the impact on the power supply side of the power tool, making the power tool compact in structure.

First claim

What is claimed is:

1. A power tool, comprising:
a motor, comprising a stator and a rotor;
a transmission device, operably connected to the rotor and configured to output a power to drive a tool accessory;
a driving circuit, configured to output an on-off signal to drive the rotor of the motor to operate;
a control unit, configured to output a driving signal to control the driving circuit;
a rectifier module, configured to convert an alternating current (AC) power to a direct current (DC) power to power up the motor, the driving circuit, and the control unit; and
a capacitor circuit, connected between the rectifier module and the driving circuit;
wherein the capacitor circuit comprises a capacitor C and a power switch transistor Q that are connected in series;
and the control unit is electrically connected to the power switch transistor Q and is configured to output a pulse width modulation (PWM) duty cycle signal depending on a characteristic parameter related to a rotational speed of the motor to control the power switch transistor Q to be turned on and off.

2. The power tool as recited in claim 1 , wherein when the power switch transistor Q is turned off, a duty ratio of the PWM duty cycle signal is gradually reduced.

3. The power tool as recited in claim 2 , wherein the control unit is configured to output a PWM duty cycle signal depending on the characteristic parameter related to the rotational speed of the motor to control the power switch transistor Q to be turned on and off and is configured to output a PWM duty cycle signal to turn on the switching element in response to the rotational speed of the motor reaching a first rotational speed, causing the capacitor circuit to enter a charging state.

4. The power tool as recited in claim 1 , wherein the capacitor is an electrolytic capacitor, and a ratio of a capacitance value of the electrolytic capacitor to a rated power of the motor lies in the range of 20 μμF/kW to 80 μμF/kW.

5. An angle grinder, comprising:
a motor, comprising a stator and a rotor;
a transmission device, operably connected to the rotor and configured to output a power to drive a grinding disc;
a driving circuit, configured to output an on-off signal to drive the rotor of the motor to operate;
a control unit, configured to output a driving signal to control the driving circuit;
a rectifier module, configured to convert an alternating current (AC) power to a direct current (DC) power to power up the motor, the driving circuit, and the control unit; and
a capacitor circuit, connected between the rectifier module and the driving circuit;
wherein the capacitor circuit comprises a capacitor C and a power switch transistor Q that are connected in series;
and the control unit is electrically connected to the power switch transistor Q, and is configured to output a pulse width modulation (PWM) duty cycle signal depending on a rotational speed of the motor to control the power switch transistor Q to be turned on, and is configured to output a PWM duty cycle signal in response to the rotational speed of the motor reaching a first rotational speed to control the power switch transistor Q to be turned on, causing the capacitor circuit to enter a charging state.

6. The angle grinder as recited in claim 5 , wherein when the power switch transistor Q is turned on, a duty ratio of the duty cycle signal is gradually increased.

7. The angle grinder as recited in claim 5 , wherein the capacitor C is an electrolytic capacitor, and a ratio of a capacitance value of the electrolytic capacitor to a rated power of the motor lies in the range of 20 μF/kW to 80 μF/kW.

8. A power tool, comprising:
a brushless motor, comprising a stator and a rotor;
a transmission device, operably connected to the rotor and configured to output a power to drive a tool accessory;
a driving circuit, configured to output an on-off signal to drive the rotor of the brushless motor to operate;
a control unit, configured to output a driving signal to control the driving circuit;
a direct current (DC) unit, configured to supply power to the brushless motor, the driving circuit, and the control unit; and
a capacitor circuit, connected in parallel between a positive electrode and a negative electrode of the DC unit;
wherein the capacitor circuit comprises a capacitor C and a switching element that are connected in series;
and the control unit is electrically connected to the switching element, and is configured to output a pulse width modulation (PWM) duty cycle signal depending on a rotational speed of the brushless motor to control the switching element to be turned on, and is configured to output a PWM duty cycle signal in response to the rotational speed of the brushless motor reaching a first rotational speed to control the switching element to be turned on, causing the capacitor circuit to enter a charging state.

9. The power tool as recited in claim 8 , wherein the control unit is configured to output a PWM duty signal to turn on the switching element in response to the rotational speed of the brushless motor reaching the first rotational speed, causing the capacitor circuit to enter a charging state, and output a PWM duty signal to turn off the switching element in response to the rotational speed of the brushless motor reaching a second rotational speed, causing the capacitor circuit to enter a discharging state, wherein the first rotational speed is less than the second rotational speed.

10. The power tool as recited in claim 8 , wherein the DC unit comprises a rectifier module that is at least operative to couple to an alternating current (AC) power source and that is configured to convert the AC power into a DC power.

11. The power tool as recited in claim 8 , wherein the capacitor circuit is connected between the rectifier module and the driving circuit.

12. An angle grinder, comprising:
a housing;
a brushless motor, received in the housing and comprising a stator and a rotor;
a motor shaft, driven by the rotor;
a tool accessory shaft, configured to support and drive a grinding disc;
a transmission device, configured to couple the motor shaft to the tool accessory shaft;
a driving circuit, configured to output an on-off signal to drive the rotor of the brushless motor to operate;
a control unit, configured to output a driving signal to control the driving circuit;
a direct current (DC) unit, configured to supply power to the brushless motor, the driving circuit, and the control unit; and
a capacitor circuit, connected in parallel between a positive electrode and a negative electrode of the DC unit;
wherein the capacitor circuit comprises a capacitor C and a power switch transistor Q that are connected in series;
and the control unit is electrically connected to the power switch transistor Q, and is configured to: output a pulse width modulation (PWM) duty cycle signal depending on a rotational speed of the brushless motor, and output a PWM duty cycle signal in response to the rotational speed of the brushless motor reaching a first rotational speed, to control the power switch transistor Q to be turned on, causing the capacitor circuit to enter a charging state; and in response to the rotational speed of the brushless motor reaching a second rotational speed, output a PWM duty cycle signal to turn off the power switch transistor Q, causing the capacitor circuit to enter a discharging state, wherein the first rotational speed is less than the second rotational speed.

13. The angle grinder as recited in claim 12 , wherein when the power switch transistor Q is turned on, a duty ratio of the PWM duty cycle signal is gradually increased.

Assignees

• Nanjing Chervon Ind Co Ltd

Inventors

• Wang Hongwei
• Chen Weipeng

Classifications

• Y02P70/10

  Greenhouse gas [GHG] capture, material saving, heat recovery or other energy efficient measures, e.g. motor control, characterised by manufacturing processes, e.g. for rolling metal or metal working · CPC title

• H02P6/06

  Arrangements for speed regulation of a single motor wherein the motor speed is measured and compared with a given physical value so as to adjust the motor speed · CPC title

• B24B47/12

  by mechanical gearing or electric power (B24B47/16 takes precedence) · CPC title

• B24B23/028 Primary

  Angle tools · CPC title

• H02P25/03

  with brushless excitation · CPC title