Electrical transmission or interconnection systems – Switching systems – Condition responsive
Reexamination Certificate
1999-03-16
2001-06-19
Fleming, Fritz (Department: 2836)
Electrical transmission or interconnection systems
Switching systems
Condition responsive
C200S05200R
Reexamination Certificate
active
06249063
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrical switching device utilizing a frangible actuator, specifically to a device for bypassing (i.e., isolating) a failed battery cell utilizing an improved frangible actuator.
2. Description of the Related Technology
A multi-cell battery typically has the cells connected in series so that their voltages will be summed to produce a battery with a higher voltage than could be obtained with a single cell. Unfortunately, when a battery cells fails, it generally develops a high resistance. Since this resistance is in series with the other cells, it effectively disables the entire battery, even though the remaining good cells would be sufficient to keep the battery operating in a slightly degraded mode. For large batteries, where battery cost is high and replacement is difficult, it makes sense to use actuators to detect and isolate failed cells so that the battery can keep operating. Since a defective cell generally cannot be repaired, such actuators are generally one-way single-use actuators, and can be frangible (i.e., they activate by separating).
Conventional actuators (used for a variety of purposes) have a number of deficiencies. For the switch portion, a commonly-used structure provides a conductive tube with the end slightly bent in. A slightly smaller conductive cylinder fits within the tube so that it just touches the inwardly indented portion of the tube's rim. A second tube with a similarly indented end faces the first. Upon activation, the cylinder passes into the second tube, contacting its rim and providing an electrical connection between the two tubes. Unfortunately, such devices can only be used as simple on-off switches. In addition, they provide a minimal contact area, which limits the amount of occurrent that can be conducted. Also, the degradation of contact force due to heating is reduced.
Another problem with conventional actuators is that they employ frangible cylinder-type actuators, which are prone to mechanical failure, due to the manner in which certain portions can interfere with other portions during actuation. An actuator is needed that maintains the simplicity of conventional actuators, but with improved reliability and higher current capacity.
SUMMARY OF THE INVENTION
A frangible actuator may contain a plurality of separable parts, preferably in the form of two cylinder halves pressed together to form an overall cylinder shape. The cylinder halves may be held together by wrapping a restraining wire around them multiple times, and securing the ends of the restraining wire so that it stays in this position. One end of the restraining wire may be secured to one of the separable halves, while the other end may be secured by a sensor that detects when an electrical current exceeds a predetermined threshold. The sensor is preferably a fusible link which melts, separates, deforms or otherwise fails in tension when the current through it exceeds the threshold, thereby releasing the end of the restraining wire. Once the restraining wire is released, the cylinder halves may be free to separate.
A spring-loaded plunger may be held in place by the cylinder halves in their restrained position, with the end of the plunger pressed against a conical surface formed between the two halves. When the cylinder halves are allowed to separate, the force of the plunger against this conical surface may force the cylinder halves apart, allowing the plunger to continue moving forward between the cylinder halves until stopped by a physical obstacle. This motion of the plunger may activate a switch.
The sensor may be attached to an insulator at one end of the cylinder, so that the electrical connections to the sensor are held away from the cylinder halves to avoid physically interfering with them during separation. The insulator may also include two pins disposed between the cylinder halves to prevent them from rotating under the urging of the restraining wire, which can be made of a spring-like material and be spring loaded in its restraining position.
The actuator can activate an electrical switch. The switch may include a contact base formed as a conductive cylinder which slides axially within the bore of multiple electrical terminals. By attaching the contact base to the end of a non-conductive cylinder of the same diameter, the total conductive
on-conductive cylinder may slide within the terminal bores, making or breaking contact with each terminal according to which portion of the cylinder is within that terminal. Reliable electrical contact may be achieved by placing toroidal contact elements within annular grooves in the conductive cylinder. Each contact element may be in the form of a coiled spring with its two ends attached to each other, thus forming a toroid having a spiral spring traversing the circle of the toroid. By sizing the various elements so that outermost portions of the toroid are slightly larger than the diameter of the terminal bore, the contact element may be slightly compressibly deformed when within the terminal bore, thus creating a spring-loaded force at each contact point. Switches formed in this manner may be configured with one or more poles, single- or double-throw, make-before-break or break-before-make, or any combination of these, simply by changing the number and spacing of contact elements and the spacing between terminals.
REFERENCES:
patent: 5438173 (1995-08-01), Rudoy et al.
Courtney Craig W.
McCormick Larry Leroy
Rudoy Edward
Vega Edwin E.
DeBeradinis Robert L
Fleming Fritz
NEA Electronics, Inc.
Sternfels Lewis B.
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