Electrical resistors – Resistance value responsive to a condition – Current and/or voltage
Reexamination Certificate
1999-07-26
2001-07-10
Easthom, Karl D. (Department: 2832)
Electrical resistors
Resistance value responsive to a condition
Current and/or voltage
C338S208000
Reexamination Certificate
active
06259349
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrical component with a PTC polymer element. Such components are known, for example, from EP 0 655 760 A2, according to which a PTC polymer element is used for overcurrent limitation and, for this purpose, the PTC polymer element is connected in series with a load interrupter. A current above a threshold value, determined by the design of the PTC polymer element, in this case produces a rapid non-linear rise in the electrical resistance of the PTC polymer element and thereby limits the overcurrents. The load interrupter can then completely interrupt the limited current.
2. Discussion of Background
With respect to the use of PTC polymer elements at relatively high voltages, various possibilities have been proposed in U.S. Pat. Nos. 5,313,184 and 5,414,403 for using resistance systems comprising PTC polymer elements and varistor elements or linear resistor elements for reducing local overvoltages in the PTC polymer material and locally distributing the non-linear response behavior of the PTC polymer material. In connection with the teaching of these two documents, it can be stated that in the case of the present invention the terms PTC polymer element and PTC polymer material definitely also cover such elements and materials to which constituents without PTC behavior, for example linear resistor elements or varistor elements, are added.
Furthermore, this invention relates to such an electrical component in which the PTC polymer element does not have a constant current-carrying cross-sectional area, but instead the line cross-sectional area is constricted. The main direction of flow defining this cross-sectional area is generally dictated by external contacts on the PTC polymer element or by the geometry. At the same time, however, it does not have to correspond to all local directions of flow occurring, but to a certain extent only to their mean value.
Such a constriction of the line cross section has the effect that the current density in relation to the remaining PTC polymer element is locally increased, so that it is predetermined at which point the non-linear rise in resistance of the PTC effect begins when corresponding current threshold values are reached.
EP 0 798 750 A2 in turn shows a resistance system comprising a PTC polymer element with varistor elements in which such constrictions are provided.
U.S. Pat. No. 3,351,882 likewise shows PTC polymer elements with constrictions, giving as the reason for this that, by suitable choice of the constrictions, overheating in the vicinity of the contact points of the PTC polymer element is to be avoided.
Also to be cited as prior art is European Patent EP 0 038 715 B1, in which a very rapid response behavior in the range of a few seconds or less is to be achieved by a specific design of a PTC polymer element with a constriction.
A PTC polymer element with a constriction is also shown, furthermore, by JP 4-130602 with Patent Abstract, DE 196 26 238 A1 as well as U.S. Pat. Nos. 4,317,027 and 4,352,083. The two last-mentioned documents also show in particular that constrictions can be formed by neighboring recesses in a PTC polymer material. In this case, the recesses are filled with an essentially non-conducting material or with air.
SUMMARY OF THE INVENTION
Accordingly, one object of the invention is to provide a novel electrical component with a PTC polymer element in which the PTC polymer element exhibits a particularly rapid response behavior and, in the normally conducting case, a good current-carrying capacity as well as reliable and durable operation.
For this purpose, the invention provides an electrical component with a PTC polymer element which has a constriction of the cross-sectional area perpendicular to a main direction of flow, an aperture angle of the constriction in a longitudinal sectional plane containing the main direction of flow being at least 100°.
The invention thus relates to PTC polymer elements in which the constriction known per se in the prior art runs at a particularly steep angle, in other words has a particularly large aperture angle. It should firstly be stated in this respect that in many cases the constriction is formed only by restricting the cross-sectional area in one direction, in other words the PTC polymer element has as it were a two-dimensional basic structure. To this extent, the definition of the invention relates to an aperture angle in a longitudinal sectional plane through the PTC polymer element, containing the main direction of flow.
There may of course also be a further constriction in a further dimension, perpendicular to the main direction of flow. The invention relates in this case to PTC polymer elements in which the value of 100° for the aperture angle is reached or exceeded in at least one longitudinal sectional plane.
The aperture angle is in this case defined from the perspective of the point of minimum cross section in the constriction, in other words in the sense of spreading out from the point of minimum cross section. Seen from the minimum cross-sectional area, in the longitudinal sectional plane on each side there respectively exists a right-hand aperture angle and a left-hand aperture angle. In the case of the invention, on one side the right-hand aperture angle and the left-hand aperture angle are combined to form a total aperture angle of at least 100°, which however occurs at different apex points in two parts. In this case, the apex points of the two parts of the aperture angle are separated from one another by the transverse extent of the minimum cross-sectional area in the longitudinal sectional plane considered. It is not necessary here for the two parts of the total aperture angle to be identical, but it is preferred. Moreover, according to the invention, the (total) aperture angle must be present at least to one of the two sides, seen from the minimum cross-sectional area, but this preferably applies to both sides.
The length segments on both sides of the constriction that are angled with respect to the main direction of flow and are necessary for the definition of the two parts of the total aperture angle do not necessarily have to be regularly shaped. It is sufficient if a length segment satisfying the angle condition according to the invention can be defined as the mean value. It is preferred, however, for the constriction flanks on both sides of the minimum cross-sectional area to be essentially straight and consequently define the aperture angle overall essentially without mean-value formation. This is because then there cannot be any significant local deviations from the steep formation of the constriction preferred according to the invention.
The value of 100° mentioned for the total aperture angle (that is for example a partial aperture angle to the right of 50° and a partial aperture angle to the left of 50°) forms the lower limit for the invention. In fact, however, even greater aperture angles are more favorable; thus aperture angles of, for example, 105°, 110°, 115° or 120° and above are increasingly preferred.
The effect according to the invention (increasing with greater angles) is that, on the one hand, very rapidly responding PTC polymer elements can be realized, which, on the other hand, exhibit relatively high current-carrying capacities in the non-responding or already responded state.
This is because it has been found in the development of the invention to be important for these two criteria to be satisfied well and as far as possible simultaneously, i.e. on the one hand to realize a great current-carrying capacity with limited overall space provided for the complete electrical component or the PTC polymer element, but on the other hand to be able to design the reduction in the like cross sections for a rapid response behavior. It has been found in this respect that particularly pronounced relative like cross-section reductions produce a particularly rapid response behavior and at the same time, on the other hand, particularly steep constriction
Glatz-Reichenbach Joachim
Rajala Erkki
Skindhoj Jorgen
Strumpler Ralf
ABB Research Ltd.
Burns Doane Swecker & Mathis L.L.P.
Easthom Karl D.
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