US Patent No. 10,461,674

ELECTRIC WORKING MACHINE, AND METHOD OF DETECTING OVERLOAD OPERATION THEREOF


Patent No. 10,461,674
Issue Date October 29, 2019
Title Electric Working Machine, And Method Of Detecting Overload Operation Thereof
Inventorship Michisada Yabuguchi, Anjo (JP)
Kouichi Takeda, Anjo (JP)
Masumi Nishimura, Anjo (JP)
Hiroshi Nojiri, Anjo (JP)
Assignee MAKITA CORPORATION, Anjo-shi (JP)

Claim of US Patent No. 10,461,674

1. An electric working machine comprising:a motor configured to generate a driving force for driving a tool portion attached to the electric working machine;
a drive circuit configured to drive the monitor;
a speed setting unit configured to set a rotation speed of the motor;
a load detection unit configured to detect a magnitude of a load on the motor;
a determination unit configured to calculate an estimated value of a heat generation amount of the motor from the magnitude of the load detected by the load detection unit when the motor rotates, and to determine that the motor is in an overload operation state when the estimated value reaches a predetermined threshold; and
a parameter setting unit configured to set a parameter used for calculating the estimated value in accordance with the rotation speed without being coupled to a detection circuit that detects a temperature of the motor and/or a temperature of the drive circuit, the parameter setting unit being further configured to set the parameter so that the estimated value quickly reaches the threshold as the rotation speed set by the speed setting unit decreases,
wherein the load detection unit k configured to detect a current flowing through a conduction path provided between a power source and the motor,
wherein the estimated value of the heat generation amount of the motor is based on the current detected by the load detection unit,
wherein the determination unit includes a heating counter,
wherein the parameter includes a count parameter for incrementing the heating counter,
wherein the parameter setting unit is configured to set the count parameter to quickly increment the heating counter as the rotation speed set by the speed setting unit decreases,
wherein the determination unit is configured to increment a count value of the heating counter based on the count parameter, and
wherein the count value of the heating counter corresponds to the estimated value.