US 12,316,262 B2
Technique for protecting motor in electric work machine from over temperature
Dai Suzuki, Anjo (JP); Masayuki Okamura, Anjo (JP); and Itsuku Kato, Anjo (JP)
Assigned to MAKITA CORPORATION, Anjo (JP)
Filed by MAKITA CORPORATION, Anjo (JP)
Filed on Apr. 13, 2023, as Appl. No. 18/134,309.
Claims priority of application No. 2022-067526 (JP), filed on Apr. 15, 2022.
Prior Publication US 2023/0336105 A1, Oct. 19, 2023
Int. Cl. H02P 29/032 (2016.01); B25F 5/00 (2006.01); H02P 6/24 (2006.01)
CPC H02P 29/032 (2016.02) [B25F 5/00 (2013.01); H02P 6/24 (2013.01)] 20 Claims
OG exemplary drawing
 
1. An electric work machine comprising:
a holder (i) holding a driven tool in an undetachable manner or (ii) configured to hold the driven tool in a detachable manner;
a manual switch configured to be manually operated by a user of the electric work machine;
a motor configured to drive the driven tool;
a drive circuit configured to drive the motor based on the manual switch having been or being manually operated;
a time counting circuit configured to measure a load time, the load time corresponding to a time period during which a first load is continuously imposed on the motor, and the first load having a specified magnitude or more;
a heat estimation circuit configured to calculate an estimated heat value, the estimated heat value corresponding to an estimated heat generation amount of the motor, the heat estimation circuit being configured to (i) increase the estimated heat value in accordance with a rate of increase (ii) vary the rate of increase based on the load time; and
a protection circuit configured to perform a protective operation for over temperature protection of the motor based on the estimated heat value having reached a heat threshold.