Electric power tool

Patent metadata

Field	Value
Publication number	US-2016197573-A1
Application number	US-201615073005-A
Country	US
Kind code	A1
Filing date	Mar 17, 2016
Priority date	Mar 18, 2011
Publication date	Jul 7, 2016
Grant date	—

Abstract

An electric power tool includes: a brushless motor having a plurality of stator windings and configured to rotate in accordance with voltages applied to the plurality of stator windings, an induced voltage being generated in accordance with a rotation of the brushless motor; a rectifier circuit configured to rectify an AC voltage; a smoothing capacitor configured to smooth the AC voltage rectified by the rectifier circuit to a pulsation voltage having a maximum value larger than the induced voltage and a minimum value smaller than the induced voltage; and an inverter circuit configured to perform switching operations to output the pulsation voltage to the plurality of stator windings by rotation.

First claim

What is claimed is:

1 . An electric power tool comprising:
a brushless motor including a stator and a rotor, the stator having a plurality of windings, the rotor being rotatable relative to the stator, an induced voltage being generated from the plurality of windings upon rotations of the rotor, the induced voltage having a voltage level determined depending upon number of rotations of the rotor; a rectifier circuit configured to rectify an AC voltage; a smoothing capacitor configured to produce from the rectified voltage a pulsating voltage in which ripples remain; an inverter circuit configured to sequentially switch the plurality of windings for energization by a capacitor voltage developed across the smoothing capacitor; a receiving unit configured to receive a drive instruction for driving the brushless motor by a user; and a control unit configured to control the inverter circuit, wherein the smoothing capacitor has such a capacity that a first period of time for which a current flows through the brushless motor and a second period of time for which the current does not flow through the brushless motor alternately take place, the current flowing through the brushless motor for the first period of time being caused by the capacitor voltage exceeding the induced voltage resulting from a variation in the capacitor voltage accompanying a variation in the rectified voltage, the current not flowing through the brushless motor for the second period of time being caused by a balance of the capacitor voltage with the induced voltage, wherein the control unit is configured to control the inverter circuit such that the inverter circuit performs the sequential switching during both the first period of time and the second period of time insofar as the drive instruction is being received at the receiving unit, and wherein the rectifier circuit and the smoothing capacitor are interiorly provided.

2 . An electric power tool comprising:
a brushless motor including a stator and a rotor, the stator having a plurality of windings, the rotor being rotatable relative to the stator, an induced voltage being generated from the plurality of windings upon rotations of the rotor, the induced voltage having a voltage level determined depending upon number of rotations of the rotor; a rectifier circuit configured to rectify an AC voltage; a smoothing capacitor configured to produce from the rectified voltage a pulsating voltage in which ripples remain; an inverter circuit configured to sequentially switch the plurality of windings for energization by a capacitor voltage developed across the smoothing capacitor; a receiving unit configured to receive a drive instruction for driving the brushless motor by a user; and a control unit configured to control the inverter circuit, wherein the smoothing capacitor has such a capacity that a first period of time for which a current flows through the brushless motor and a second period of time for which the current does not flow through the brushless motor alternately take place, the current flowing through the brushless motor for the first period of time being caused by the capacitor voltage exceeding the induced voltage resulting from a fluctuation of the capacitor voltage accompanying a fluctuation of the rectified voltage, the current not flowing through the brushless motor for the second period of time being caused by a balance of the capacitor voltage with the induced voltage, wherein the control unit is configured to control the inverter circuit such that the inverter circuit performs the sequential switching during both the first period of time and the second period of time insofar as the drive instruction is being received at the receiving unit, and wherein the rectifier circuit and the smoothing capacitor are interiorly provided.

3 . The electric power tool according to claim 1 or 2 , wherein the control unit is further configured to control the inverter circuit to halt the sequential switching when the current flowing through the brushless motor exceeds an overcurrent threshold value regardless of the drive instruction being received at the receiving unit.

Assignees

• Hitachi Koki Kk

Inventors

• Iwata Kazuhiko
• Koizumi Toshiaki

Classifications

• H02P27/06 Primary

  using DC to AC converters or inverters (H02P27/05 takes precedence) · CPC title

• H02K19/10

  for multi-phase current · CPC title

• H02P6/15 Primary

  Controlling commutation time · CPC title

• H02P27/04

  using variable-frequency supply voltage, e.g. inverter or converter supply voltage · CPC title

• H02P6/28

  Arrangements for controlling current (H02P6/10 takes precedence) · CPC title