US 9,808,927 B2
Voltage control at low temperature to avoid undervoltage switch-offs in battery-powered, hand-operated electric tools
Benedikt Beckert, Augsburg (DE); and Thomas Mueller, Klosterlechfeld (DE)
Assigned to Hilti Aktiengesellschaft, Schaan (LI)
Appl. No. 15/36,645
Filed by Hilti Aktiengesellschaft, Schaan (LI)
PCT Filed Nov. 14, 2014, PCT No. PCT/EP2014/074573
§ 371(c)(1), (2) Date May 13, 2016,
PCT Pub. No. WO2015/071400, PCT Pub. Date May 21, 2015.
Claims priority of application No. 13193102 (EP), filed on Nov. 15, 2013.
Prior Publication US 2016/0279781 A1, Sep. 29, 2016
Int. Cl. B25F 5/00 (2006.01); H02K 7/14 (2006.01); H02P 7/29 (2016.01)
CPC B25F 5/00 (2013.01) [H02K 7/145 (2013.01); H02P 7/29 (2013.01)] 9 Claims
OG exemplary drawing
 
1. An electric tool, operated independently of the mains, comprising:
an electric motor;
a battery;
a monitoring device for monitoring a monitoring operation-value limit, wherein the monitoring operation-value limit lies above an operation-value limit of the battery;
an adjustable resistor component; and
an operation-value controller for setting at least one operation-value of the electric motor by pulse width modulation (PWM);
wherein a PWM duty cycle of the operation-value controller is specified to set the at least one operation-value, which corresponds to a first value or a second value, wherein the first value is derivable from a current setting of the adjustable resistor component and wherein the second value corresponds to a PWM duty cycle last used for setting the at least one operation-value plus an offset value;
wherein for setting the at least one operation-value, a lower of the first value or the second value is selected for the PWM duty cycle, if an operation-value of the battery lies above the monitoring operation-value limit;
and wherein the offset value corresponds to a percentage of a last used PWM duty cycle for controlling the electric motor.