Over-current and thermal protection device

• US 6,570,749 B1
• Filed: 09/27/2000
• Issued: 05/27/2003
• Est. Priority Date: 07/14/2000
• Status: Expired due to Term

• Current Assignee: GP Batteries International Limited (Gold Peak Industries Limited)
• Original Assignee: Advanced Battery Technologies Incorporated (Hudson Bay Capital Management LP)
• Inventors: Ling, Peter, Magnuson, Doug
• Primary Examiner(s): Patel, Rajnikant B.
• Application Number:
  US09/671,383
• Time in Patent Office: 972 Days
• Field of Search: 361/102, 429/56, 429/58, 429/62, 429/97, 429/98, 429/66, 429/325, 338/32.R, 338/221, 337/108, 337/140, 337/102, 337/38, 337/393, 337/372, 337/365, 337/139, 337/141
• US Class Current: 361/102
• CPC Class Codes: H01H 37/323 making use of shape memory materials in thermal relays H01H61/0107; release mechanism H01H71/145; treatment of SMF alloys C22F1/006; for control of temperature G05D23/024
• CPC Class Codes: H01H 71/145 using shape memory materials H01H71/16 takes precedence
• CPC Class Codes: H01H 71/164 Heating elements
• CPC Class Codes: H01M 2200/10 Temperature sensitive devices
• CPC Class Codes: H01M 50/107 having curved cross-section, e.g. round or elliptic H01M50/103, H01M50/109, H01M50/11 take precedence
• CPC Class Codes: H01M 50/3425 in the form of rupturable membranes or weakened parts, e.g. pierced with the aid of a sharp member
• CPC Class Codes: H01M 50/574 Devices or arrangements for the interruption of current
• CPC Class Codes: H01M 50/581 in response to temperature
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

An over-current and thermal protection device adaptable for use as an electrical interrupt and in a battery environment. The protection device has a pair electrical conductors, an electrically conductive resilient switch member engageable in contact with the conductors to define an electrical conductivity pathway. The switch member is actuated by a thermally responsive shape memory alloy strip and activatable in response to a change in temperature at a predetermined level to effect a change in the metallurgical state of the shape memory alloy and position of the engagement of the switch member with one of the conductors.

Claims

1. An over-current and thermal protection device comprising:

(i) a pair of electrical conductors;

(ii) an electrically conductive resilient switch member interposed between the conductors and engageable with the conductors to define and electrical conductivity pathway, and

(iii) a thermally responsive actuator comprising a shape memory alloy cooperatively engaged with said switch member and activatable in response to a change in temperature thermally conducted from a surface of said switch member, at a predetermined temperature level, to effect a change in the position of the engagement of the switch member with one of the conductors.

2. The over-current and thermal protection device according to claim 1 wherein the switch member comprises an elongated member resiliently engageable in contact with one of the conductors to define the electrical conductivity pathway.

3. The over-current and thermal protection device according to claim 1 wherein in response to the change in temperature to the predetermined level, the actuator overcomes the resilient engagement of the switch member with the said one of the conductors.

4. The over-current and thermal protection device according to claim 1 wherein the thermally responsive actuator comprises an elongated shape memory strip secured along the length of the elongated member and adaptable to effect heat and mechanical stress transfer between the actuator and the elongated member.

5. The over-current and thermal protection device according to claim 1 wherein the change in temperature is caused by electric current passing through the electrical pathway.

6. The over-current and thermal protection device according to claim 1 wherein the change in temperature causes a change in the metallurgical state of the shape memory alloy from a martensitic state to a austenitic state at the predetermined temperature level.

7. The over-current and thermal protection device according to claim 1 wherein the martensitic state of the shape memory alloy is at a temperature below the predetermined temperature level and the austenitic state is at a temperature above the predetermined temperature level.

8. The over-current and thermal protection device according to claim 1 wherein predetermined level is effected by heat-treating the shape memory actuator material to an elevated temperature to at least approximately 500°

C. for at least approximately 5 minutes and by cooling the material between 0°

C. and 50°

C. thereafter.

9. The over-current and thermal protection device according to claim 2 wherein the elongated member has a portion of reduced cross section adaptable to bear greater amount of resistive heat relative to other portions of the elongated member when subject to an electrical current along the electrical pathway.

10. The over-current and thermal protection device according to claim 1 wherein the temperature change is substantially due to electrical current passing through the electrical conductivity pathway.

11. The over-current and thermal protection device according to claim 1 wherein the switch member includes an elongated member forming part of a conductor disc in contact with one of the pair of conductors, the elongated member being resiliently engageable in contact with the other one of the pair of conductors and a shape memory alloy strip secured along the length of the elongated member of the conductor disc and activatable in response to a change in temperature at a predetermined level to effect a change in the position of the engagement of the elongated member with the said other one of the pair of conductors.

12. The over-current and thermal protection device according to claim 4 wherein the shape memory strip has a circular cross-sectional geometry.

13. The over-current and thermal protection device according to claim 12 wherein the shape memory strip has a cross-section diameter of between 0.5 and 0.75 mm.

14. The over-current and thermal protection device according to claim 13 wherein the shape memory strip has a cross-section diameter of 0.60 mm.

15. The over-current and thermal protection device according to claim 4 wherein the shape memory strip is bent to result in having a material strain of between 2% to 4%.

16. The over-current and thermal protection device according to claim 5 wherein the shape memory strip is bent to result in having a material strain of 6%.

17. An over-current and thermal protection device comprising:

(i) a pair of electrical conductors;

(ii) an electrically conductive resilient switch member interposed between the conductors and engageable to be in contact with the conductors to define an electrical conductivity pathway, and

(iii) a thermally responsive actuator cooperatively engaged with said switch member, comprising a shape memory alloy in thermally conductive communication with a surface of said switch member and having a first metallurgical state below a predetermined temperature level and a second state above the predetermined temperature level wherein the switch member being in engagement with both conductors in one of the states and being in engagement with only one of the conductors in the other of said states.

18. An over-current and thermal protection device assembly for application to a battery cell comprising an electrically conductive cap member and an electrically conductive base member, which forms an enclosure housing a switch member and a thermally responsive actuator of a shape memory alloy in a thermally conductive communication with a surface of said switch member and defining a closed electrical pathway wherein the actuator is activatable in response to a change in temperature at a predetermined level to effect a break in the electrical pathway.

19. The over-current and thermal protection device assembly of claim 18 wherein the assembly is disposed and secured at the open end of a can of the battery cell.

20. The over-current and thermal protection device assembly of claim 19 wherein the assembly is disposed and secured at the open end of a can of the battery cell by a grommet having a first inner peripheral channel and a second inner peripheral channel resiliently securing the cap member and the base member in the respective inner channels in electrical insulation from each other, the switch member being formed as part of a conductor disc interposed between the cap member and the base member and secured by the grommet in contact with one of the cap member and the base member and having an elongated member engageable in contact with the other one of the cap member and the base member;

and wherein the thermally responsive actuator includes a shape memory alloy strip secured along the length of the elongated member and in response to a change in temperature at a predetermined level to effect a change in the position of engagement of the elongated member with the said other one of the cap member and the base member.

21. The over-current and thermal protection device end cap assembly of claim 18, which further comprises an electrically conductive pressure resistant plate having at least one aperture therethrough, wherein a portion of the pressure resistant plate and a portion of a weakened portion forms at least part of the electrically conductive pathway.

22. The over-current and thermal protection device assembly of claim 18, which further comprises an electrically conductive pressure resistant plate secured to a weakened portion of the base member, wherein the portion of the base member deforms to cause a break in the electrical pathway thereby severing electrical connection between the cap member and the base member when the internal gas pressure of the battery cell reaches a first predetermined level.

23. The over-current and thermal protection device assembly of claim 22 wherein the weakened portion ruptures when the assembly is applied to a battery cell and gas pressure within the cell reaches a second predetermined level greater than the first predetermined level, whereupon gas from the interior of the cell passes through said ruptured weakened portion and into the enclosure of the assembly.

24. The over-current and thermal protection device assembly of claim 22, wherein the first predetermined gas pressure level is between approximately 120-150 psi.

25. The over-current and thermal protection device-assembly of claim 23, wherein the second predetermined gas pressure level is between approximately 300-350 psi.

26. The over-current and thermal protection device end cap assembly of claim 18 wherein the based member has a burst groove therein of reduced thickness.

27. The over-current and thermal protection device end cap assembly of claim 26 wherein the burst groove conforms generally to a major portion of the outer peripheral shape of the base member wherein the burst groove provides a rupture path for the weakened portion of the base member.

28. The over-current and thermal protection device end cap assembly of claim 27 wherein the bust groove is of substantially “

C”

shape.

29. The over-current and thermal protection device end cap assembly of claim 18 wherein the cap member has at least one aperture therethrough so that gas from the interior of the cell which accumulates in the end cap assembly enclosure may pass through the aperture outside the end cap assembly.