Torque limiting device for an electric motor

• US 7,235,940 B2
• Filed: 09/03/2004
• Issued: 06/26/2007
• Est. Priority Date: 09/11/2003
• Status: Active Grant

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Bosch, Volker, Wirnitzer, Bernd
• Primary Examiner(s): DUDA, RINA I
• Application Number:
  US10/933,857
• Publication Number:
  US 20050057207A1
• Time in Patent Office: 1,026 Days
• Field of Search: 318432-434, 318/599, 318/811, 388/809, 388/811, 388/815, 388/822, 388/823, 388/937, 173/4, 173/11
• US Class Current: 318/432
• CPC Class Codes: B25B 23/147 specially adapted for electrically operated wrenches or screwdrivers
• CPC Class Codes: H02P 7/28 using semiconductor devices

Abstract

A rotary speed limiting device for an electric motor has a current detecting device for detecting a motor current of the electric motor, a nominal value setting for adjusting a torque, a control and/or regulating device which limits the motor current to a maximum value depending on the nominal value setting, a rotary speed detecting device for detecting a rotary speed of the electric motor, the control and/or regulating device determining a maximum value of the motor current depending on the rotary speed determined by the rotary speed detecting device.

Claims

1. A rotary speed limiting device for an electric motor, comprising a current detecting device for continuously detecting a motor current of the electric motor;

a nominal value setting for adjusting a torque;

a control and/or regulating device which limits the motor current to a maximum value depending on the nominal value setting;

a rotary speed detecting device for indirectly detecting a rotary speed of the electric motor, wherein said rotary speed detecting device determines a rotary speed as a function of values of the motor current of the electric motor and a motor voltage of the electric motor, said control and/or regulating device determining a maximum value of the motor current depending on the rotary speed determined by said rotary speed detecting device, wherein a maximum permissible torque is pre-set by an operator, wherein the operator-set maximum permissible torque comprises a sum of first and second torque components, wherein the first torque component results from kinetic energy of rotating masses and the second torque component is a function of the motor current.

2. A rotary speed limiting device as defined in claim 1;

wherein said control and/or regulating unit is formed so as to reduce the maximum value of the motor current when the rotary speed increases, in order to reduce the second torque component during operation.

3. A rotary speed limiting device as defined in claim 1;

and further comprising a road control element which limits and/or turns off the motor current when the maximum value determined by the control and/or regulating device is reached.

4. A rotary speed limiting device as defined in claim 1, wherein said and/regulating device is formed as a microcontroller.

5. A rotary speed limiting device as defined in claim 1, wherein said control and/or regulating device includes a microcontroller.

6. A rotary speed limiting device as defined in claim 1, wherein said rotary speed detecting device detects the rotary speed via a rotary speed sensor formed as an element which registers revolutions of a shaft.