Electricity: conductors and insulators – Conduits – cables or conductors – Combined
Reexamination Certificate
2000-02-24
2003-03-25
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
Conduits, cables or conductors
Combined
C174S08400S, C439S874000
Reexamination Certificate
active
06538203
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a connection of an electrical cable, especially one constructed of several aluminum wires or flexible leads and insulated aluminum cables, with a connection piece made of copper, copper alloy and/or brass or similar metal, for example with a battery clamp, a cable lug, a connection adapter, a plug element, a cable piece or the like, for the electrical system of a motor vehicle. The insulation of the aluminum cable ends before or at a distance from the contact point with the connection piece, and a support sleeve is provided, which encloses at least a region adjacent to the end face of the stripped (bared) part of the aluminum cable and is crimped and/or shrunk on the end of the aluminum cable, so that the wires of the aluminum cable are crimped together at least in the area of the end face.
The invention further relates to a process for connecting an electrical aluminum cable with a connection piece made of copper, copper alloy and/or brass or similar metal, for example a battery clamp, cable lug, connection adapter, plug element, cable or the like, for the electrical system of a motor vehicle. Here, the end face of the aluminum cable is brought into connection and electrical contact with the end face of the connection piece, and for this purpose the aluminum cable is bared (stripped of insulation) on the connection end. A support sleeve is crimped or shrunk on the stripped place, and the wires or flexible leads of the aluminum cable are thereby crimped together.
The idea is already known of replacing current-conducting leads of copper or copper alloys, especially energy leads, having a relatively large cross section in motor vehicles, with ones of aluminum, because aluminum even leads to a lower weight if the lead cross sections must be enlarged due to the somewhat lesser conductivity of aluminum in comparison with copper.
In this connection, experiments were conducted, and in U.S. Pat. No. 2,806,215, it was proposed to join the parts to be connected, i.e., an aluminum cable and a corresponding connection piece, by means of ferrules and clamps so as to conduct electricity. There, the problem nonetheless exists that, on the surface of aluminum under the influence of air oxygen, a thin oxide layer arises, whose thickness increases with time and which does not conduct electricity. The electrically conducting connection of an aluminum cable with a connection piece of another metal therefore requires the elimination or the penetration of such an oxide layer, and the prevention of a renewed formation of such an oxide layer.
Furthermore, with the connection of an aluminum cable made of individual wires or flexible leads with a connection piece, there results the necessity, for diminishing electrical resistance, of undertaking a clamp connection with high compressive force. This leads to deformations at the crimping site of the cross sections of the individual aluminum wires, so that these are weakened from the outset at the juncture point and can break under the dynamic stress in a motor vehicle in the course of time. Especially high dynamic stresses arise here in the area of the driving motor, the dynamo and even the battery.
On the other side, it is not possible to make the connection piece itself likewise of aluminum, because in the area of batteries or accumulators acid vapors cannot be entirely ruled out, which attack aluminum to a considerably greater extent than copper, copper alloys or brass, and because connections to units joined with a combustion motor, such as dynamos, are exposed to such a high dynamic stress that, in the course of time, the less stable aluminum material breaks or the connection juncture is destroyed.
Aluminum is also subject to a greater danger of corrosion than copper, which has a relatively good corrosion resistance, because aluminum is relatively electronegative. For this reason, aluminum has the tendency to convert to the more stable oxide form, from which is was created under the application of energy.
If metals of varying base character are conductively connected with one another, there exists the danger of a contact corrosion. Here, due to their electropositive potential, copper materials are less degradable than aluminum, but can also exert a degrading action on this metal in a connection with it. Since aluminum is the more electronegative metal in comparison with copper, it can also occur in a contact connection with high currents and longer stress times, chiefly in a humid, salt-containing climate, that the more electronegative metal, i.e., the aluminum, acts as the “sacrificial anode” and deteriorates. Thus, with time, a loss of material occurs on the contact surface, which has a negative effect on the contact resistance and stability.
Even with the use of an aluminum ferrule surrounding the stripped aluminum cable, and welding it with a connection piece of copper, according to FIG. 8 of U.S. Pat. No. 2,806,215, there exists the problem, within the aluminum ferrule, between the front ends of the aluminum wire and the connection piece made of copper, that a seam or a space remains and, in the course of time, the previously mentioned contact corrosion arises.
SUMMARY OF THE INVENTION
For this reason, there exists the object of creating a connection of the type mentioned at the beginning, which has a high degree of stability in relation to the dynamic stresses and a good conductivity, and which, on the one hand, eliminates an oxide layer or corrosion on the aluminum in the area of the juncture by the connection operation itself and/or, on the other hand, prevents an oxide layer in this area of mutual contacting of the different metals.
For accomplishing this objective, the initially mentioned connection of an electrical aluminum cable with a connection piece of another metal is wherein the connection piece is welded with the end face of the aluminum cable formed by the individual wires.
The connection is thus chiefly characterized by an additional support sleeve on the aluminum cable, which sufficiently stabilizes the individual wires or flexible leads by crimping them together and draws them closer to one another, in order to yield a metal surface on the end face of the cable, which is then at the same time the connection point or the place of welding with the connection piece. It is thereby possible to free this face of oxide, to the extent that it may have formed there, and then to butt weld this face with the connection piece, so that in the future as well no oxide can arise at this spot. As is well known, aluminum can be easily fused or welded with copper and thus, in the connection of the invention, even form a mutual alloy. Experiments have shown that the resistance to wear of such a connection can be higher than that of the aluminum cable and/or the connection piece themselves.
Since the individual wires of the aluminum cable themselves can be welded with the connection piece, and thereby also with themselves, there results a sub-metallic connection between the aluminum cable and its individual wires and the connection piece consisting of copper or a copper alloy, which can extend over the entire end face cross-sectional area. This sub-metallic connection layer, according to experiments, can be about 2 mm thick, so that an air or moisture access to this connection site is ruled out.
It is especially beneficial if the support sleeve reaches beyond the transition between the stripped region of the aluminum cable and the insulation, including a part of the insulation. The support sleeve thus expediently maintains a longer axial length than the stripped area of the aluminum cable, so that a good stiffening is attained in the area of the connection point up to under the insulation, which leads to an even distribution of the compressive forces in the connection area, without subjecting the individual aluminum wires too strongly to stress and to deformation. Consequently, such a connection point is also a match for shearing forces and dynamic stresses, as they can also occur in motor vehicl
Lietz Franz-Josef
Nölle Günther
Akin Gump Strauss Hauer & Feld L.L.P.
Auto Kabel Managementgesellschaft mbH
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