Overload protection arrangement for an electric motor, especially of a hand-held power tool
US4430681A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | May 22, 1981 |
| Grant date | Feb 7, 1984 |
| Priority date | — |
| Expiry date | May 22, 2001 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH02H7/0858
- WIPO fieldElectrical machinery, apparatus, energy
- WIPO sectorElectrical engineering
Abstract
An overload protection arrangement for an electric motor, especially of a hand-held power tool, includes an electronic speed of rotation control arrangement which is, in turn, controlled by an overload circuitry which includes a positive temperature coefficient resistor situated in the winding of the electric motor and incorporated in a voltage divider. The output of the PTC-resistor is amplified by an amplifier and, when the temperature of the winding increases above an acceptable level, the maximum current which can be drawn by the electric motor is reduced to a level at which the winding cannot burn out even if the rotor of the electric motor is blocked. If the rotor can rotate freely, the speed of rotation thereof even at the reduced power input will be sufficient to assure rapid cooling of the device powered by the electric motor. A time-delay member consisting of a capacitor and a resistor is arranged in parallel with the operational amplifier.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.