Electric working machine, and method of detecting overload operation thereof

Patent metadata

Field	Value
Publication number	US-10461674-B2
Application number	US-201715670242-A
Country	US
Kind code	B2
Filing date	Aug 7, 2017
Priority date	Aug 10, 2016
Publication date	Oct 29, 2019
Grant date	Oct 29, 2019

Abstract

An electric working machine according to one aspect of the present disclosure comprises a motor, a speed setting unit, a load detection unit, a determination unit, and a parameter setting unit. The determination unit calculates an estimated value of a heat generation amount of the motor, and determines that the motor is in an overload operation state when the estimated value reaches a predetermined threshold. The parameter setting unit sets a parameter to be used for calculating the estimated value and/or the threshold in accordance with a rotation speed set by the speed setting unit.

First claim

What is claimed is:

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.

2. The electric working machine according to claim 1 , further comprising:
a motor protection unit configured to stop the motor and/or decelerate the motor when the determination unit determines that the motor is in the overload operation state.

3. The electric working machine according to claim 2 ,
wherein the parameter setting unit is configured to set the threshold so that the threshold decreases as the operation of the motor protection unit increases.

4. The electric working machine according to claim 1 ,
wherein the parameter setting unit is configured to set the threshold so that the estimated value rapidly reaches the threshold as the rotation speed decreases.

5. The electric working machine according to claim 1 ,
wherein the parameter setting unit is configured to set the threshold so that the threshold increases as the rotation speed increases.

6. The electric working machine according to claim 1 ,
wherein the parameter includes a heating addition value,
wherein the parameter setting unit is configured to set the heating addition value so that the heating addition value increases as the rotation speed decreases,
wherein the determination unit comprises a heating counter, and the determination unit is configured to increment the heating counter using the heating addition value set by the parameter setting unit when the magnitude of the load on the motor is higher than a predetermined set value, and
wherein a count value of the heating counter corresponds to the estimated value.

7. The electric working machine according to claim 1 , further comprising:
a control unit configured to control rotation of the motor in accordance with the rotation speed set by the speed setting unit.

8. The electric working machine according to claim 7 ,
wherein the electric working machine comprises a current path provided between a power source and the motor,
wherein the load detection unit is configured to detect a value of a motor current flowing through the current path as the magnitude of the load on the motor,
wherein the control unit is configured to PWM-control a conduction current to the motor in accordance with the rotation speed,
wherein the determination unit is configured to (i) calculate a value of an actual current flowing to the motor by dividing the value of the motor current detected by the load detection unit by a drive duty ratio of the PWM control, and (ii) calculate the estimated value using the value of the actual current.

9. The electric working machine according to claim 7 :
wherein the drive circuit is configured to supply power to the motor to rotate the motor,
wherein the control unit is configured to output a conduction command in accordance with the rotation speed to the drive circuit to rotate the motor,
wherein the parameter setting unit changes the parameter and/or the threshold in synchronization with the output of the conduction command to the drive circuit so that the estimated value quickly reaches the threshold as the rotation speed decreases.

10. The electric working machine according to claim 1 , further comprising
a cooling fan provided on a rotation shaft of the motor.

11. The electric working machine according to claim 1 ,
wherein the parameter includes a set value,
wherein the parameter setting unit is configured to set the set value so that the set value decreases as the rotation speed decreases,
wherein the determination unit includes a heating counter, the determination unit being configured to increase a count value of the heating counter when the magnitude of the load on the motor is higher than the set value, and
wherein the count value of the heating counter corresponds to the estimated value.

12. The electric working machine according to claim 1 ,
wherein the parameter setting unit is configured to set the parameter in accordance with the rotation speed set by the speed setting unit and the magnitude of the load detected by the load detection unit.

13. The electric working machine according to claim 1 ,
wherein the determination unit is configured to start calculating the estimated value when a soft start ends and when a predetermined time elapses after a start of driving of the motor, the soft start gradually increasing the rotation speed of the motor to the rotation speed set by the speed setting unit.

14. A method of detecting that a motor of an electric working machine is in an overload operating state, the method comprising:
setting a rotation speed of the motor;
detecting a magnitude of a load on the motor by detecting a current flowing through a conduction path provided between a power source and the motor;
calculating, with a heating counter, an estimated value of a heat generation amount of the motor based on the magnitude of the load, wherein the estimated value of the heat generation amount of the motor is based on the current flowing through the conduction path;
determining that the motor is in an overload operation state when the estimated value reaches a predetermined threshold; and
setting a parameter used for calculating the estimated value based on the magnitude of the load 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,
wherein the parameter is set so that the estimated value quickly reaches the threshold as the rotation speed decreases,
wherein the parameter includes a count parameter for incrementing the heating counter,
wherein setting a parameter used for calculating the estimated value based on the magnitude of the load in accordance with the rotation speed w

Assignees

• Makita Corp

Inventors

• Yabuguchi Michisada
• Takeda Kouichi
• Nishimura Masumi
• Nojiri Hiroshi

Classifications

• H02P29/032

  Preventing damage to the motor, e.g. setting individual current limits for different drive conditions · CPC title

• B25F5/00

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

• H02P6/24

  Arrangements for stopping · CPC title

• H02P6/28 Primary

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