Method and device for an overload detection in hand-guided power tools

• US 8,018,182 B2
• Filed: 07/17/2006
• Issued: 09/13/2011
• Est. Priority Date: 08/12/2005
• Status: Active Grant

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Hirschburger, Wolfgang, Roehm, Heiko
• Primary Examiner(s): Benson; Walter
• Assistant Examiner(s): Luo; David S
• Application Number:
  US11/912,676
• Publication Number:
  US 20080170340A1
• Time in Patent Office: 1,884 Days
• Field of Search: 318/139, 318/374, 318/375, 318/756
• US Class Current: 318/139
• CPC Class Codes: B25F 5/001 Gearings, speed selectors, clutches or the like specially adapted for rotary tools
• CPC Class Codes: H02H 6/005 using digital thermal images
• CPC Class Codes: H02H 7/18 for batteries; for accumulators

Abstract

The invention relates to a method for detecting an overload in an electric hand tool (10) comprising an electric motor (12), in particular a battery-driven electric hand tool (10). According to the invention, an operating current (i_B) of the electric motor (12) is determined, the difference (I_D) between the value of the operating current (I_B) and at least one stored current value (I_G) is determined and a thermal overload of the electric hand tool (10) is deduced from said difference (I_D). The invention also relates to a corresponding monitoring device (22).

Claims

1. A method for detecting an overload situation in a battery-powered hand-guided power tool (10) equipped with an electric motor (12) and a DC battery pack (14) for supplying an operating current (I_B) to the electric motor (12), in particular for a battery-powered hand-guided power tool (10), in which the operating current (I_B) of the electric motor (12) is determined,

wherein a difference (I_D) between the value of the operating current (I_B) and at least one stored current value (I_G) is determined, in association with a maximum set point duration (t_a), which maximum set point duration (t_a) defines a maximum duration of said overload situation by taking into account an operating temperature (T₀) of the hand-guided power tool (10), particularly at a moment at which the tool is switched on, and based on the difference (I_D), a conclusion is drawn as to whether a thermal overloading of the power tool (10) is occurring.

2. The method as recited in claim 1, wherein the stored current value (I_G) is less than or equal to a maximum continuous current (I_M).

3. The method as recited in claim 1, wherein the difference (I_D) is continuously calculated and repeatedly compared to a system parameter (z) of the hand-guided power tool.

4. The method as recited in claim 3, wherein the difference (I_D) is raised to the power of a system-dependent exponent (n) before the addition is carried out.

5. The method as recited in claim 3, wherein the system parameter (z) is multiplied by a factor for the comparison.

6. The method as recited in claim 3, wherein the sum is set to zero at the moment that the hand-guided power tool is switched on.

7. The method as recited in claim 3, wherein a determination of the system parameter (z) takes into account an operating temperature (T₀) of the hand-guided power tool (10), particularly at the moment that it is switched on.

8. The method as recited in claim 1, wherein the operating current (I_B) is reduced or interrupted as a countermeasure to prevent the thermal overload.

9. The method as recited in claim 1, wherein the association of the thermal overload and the maximum set point duration (t_a) are stored in the form of a characteristic curve (30).

10. The method as recited in claim 9, wherein the characteristic curve (30) is hyperbola-shaped.

11. A monitoring device (22) for detecting an overload situation in a battery-powered hand-guided power tool (10) equipped with an electric motor (12) and a DC battery pack (14) for supplying an operating current (I_B) to the electric motor (12), particularly a battery-powered hand-guided power tool (10), which monitoring device (22) has a current measuring device (20) that determines the operating current (I_B) of the electric motor (12),

wherein the monitoring device (22) also has a logic device (28) that calculates a difference (I_D) between the operating current (I_B) and at least one stored current value (I_G), in association with a maximum set point duration (t_a), which maximum set point duration (t_a) defines a maximum duration of said overload situation by taking into account an operating temperature (T₀) of the hand-guided power tool (10), particularly at a moment at which the tool is switched on, and based on the resulting difference (I_D), determines whether a thermal overload is occurring.

12. The monitoring device as recited in claim 11, wherein the logic device (24) is embodied in the form of a digital controller.

13. A method for detecting an overload situation in a battery-powered hand-guided power tool (10) equipped with an electric motor (12) and a DC battery pack (14) for supplying an operating current (I_B) to the electric motor (12), in particular for a battery-powered hand-guided power tool (10), in which the operating current (I_B) of the electric motor (12) is determined,

wherein a difference (I_D) between the value of the operating current (I_B) and at least one stored current value (I_G) is determined and based on this difference (I_D), a conclusion is drawn as to whether a thermal overloading of the power tool (10) is occurring, which thermal overloading is associated with a maximum set point duration (t_a), and

wherein the association of thermal overloading and the maximum set point duration (t_a) is stored in the form of a characteristic curve (30).

14. The method as recited in claim 13, wherein the stored current value (I_G) is less than or equal to a maximum continuous current (I_M).

15. The method as recited in claim 13, wherein the difference (l_D) is continuously calculated and repeatedly compared to a system parameter (z) of the hand-guided power tool.

16. The method as recited in claim 15, wherein the difference (I_D) is raised to the power of a system-dependent exponent (n) before the addition is carried out.

17. The method as recited in claim 15, wherein the system parameter (z) is multiplied by a factor for the comparison.

18. The method as recited in claim 15, wherein the sum is set to zero at the moment that the hand-guided power tool is switched on.

19. The method as recited in claim 15, wherein a determination of the system parameter (z) takes into account an operating temperature (T₀) of the hand-guided power tool (10), particularly at the moment that it is switched on.

20. The method as recited in claim 13, wherein the operating current (I_B) is reduced or interrupted as a countermeasure to prevent the thermal overload.

21. The method as recited in claim 13, wherein the association of the thermal overload and the maximum set point duration (t_a) are stored in the form of a characteristic curve (30).

22. The method as recited in claim 21, wherein the characteristic curve (30) is hyperbola-shaped.

23. A monitoring device (22) for detecting an overload situation in a battery-powered hand-guided power tool (10) equipped with an electric motor (12) and a DC battery pack (14) for supplying an operating current (I_B) to the electric motor (12), particularly a battery-powered hand-guided power tool (10), which monitoring device (22) has a current measuring device (20) that determines the operating current (I_B) of the electric motor (12),

wherein the monitoring device (22) also has a logic device (28) that calculates a difference (I_D) between the operating current (I_B) and at least one stored current value (I_G) and based on the result, determines whether a thermal overload is occurring, which thermal overload is associated with a maximum set point duration (t_a), and

wherein the association of thermal overload and the maximum set point duration (t_a) is stored in the form of a characteristic curve (30).