The invention relates to a battery terminal connecting cable with a strand consisting of numerous fine wires and a further section having a hole for a screw, whereby on the further section the numerous fine wires are welded together, a method for the manufacture of a battery terminal connecting cable and a device for the manufacture of such a cable.
Battery terminal connecting cables are used primarily to interconnect battery cells conductively. In this case one also talks of cell connectors. For the conduction of relatively high currents at low electrical resistance the strand usually consists of copper wires twisted into a strand having a cross-section of approximately 50 mm2. Depending on the field of application, however, both thicker and thinner strands are used.
In order to connect such a strand consisting of numerous fine copper wires to a battery terminal, a copper pipe section is first inverted over the strand and this pipe section is then pressed to an approximate plate shape. In this plate there is a hole which first passes through the upper side of the original pipe section, then through the compressed cable and finally through the lower side of the original pipe section. Finally in this hole there is inserted a screw which interacts with a thread in the battery terminal so that when the screw is tightened, the strand held together by means of the copper sleeving is pressed onto the battery terminal.
In practice it has been found that even a relatively strongly tightened screw works loose as a result of vibrations, as occur especially in batteries located in vehicles. This has the result that the end of the cable is no longer securely connected to the battery terminal. Contact is therefore made over smaller areas and is thus severely impaired. In cases of more severe loosening this leads to undesirable heating, even to the extent of sparking.
In order to prevent screws working loose, in known battery terminals a plastic section, such as preferably a plastic bead, is provided in the thread region between the screw and the battery terminal. This bead becomes deformed as the screw is turned and acts to prevent loosening of the screw.
The insertion of a bead or other plastic section has the result that expensive, special screws are required. Since battery terminal connectors are a mass-produced product manufactured in large quantities, any increase in the cost of the product leads to economic disadvantages.
A battery terminal connecting cable of appropriate type is known from EP-A-O 707 321. In practice the end of the cable strand produced by spot welding does not give the required strength values for the cable end so that the cables described have not proved suitable as battery terminal cables.
U.S. Pat. No. 4,325,760 discloses a cable whose end was soldered. However, soldering is an expensive procedure which leads to increased costs in the area of mass production.
The invention is based on the problem of preparing a connection between battery terminal connecting cable and battery terminal at a favourable cost, which ensures secure contact between the battery terminal connecting cable and the battery terminal even under severe vibration or thermal expansion.
The problem is solved using a battery terminal connecting cable of appropriate type where the strand is at least partly insulated and a further section is secured at the end of the strand.
The invention is based on the knowledge that the problem of screw loosening in the battery terminal is not primarily attributable to the screw being held inadequately in the battery terminal. The reason for loosening screws lies in the fact that at times fairly high temperatures occur at the contact piece of the battery terminal connecting cable as a result of the flowing currents. At varying temperatures the fine wires inside the copper sleeving are severely compressed from time to time and then remain in this severely compressed form. As a result after many temperature fluctuations the originally tightened screw is subject to less force so that the screw sits more loosely in the thread. Loosening of the screw can then only be impeded by the plastic section described above. The plastic section certainly impedes loosening of the screw but the fact that the screw at times exerts less pressure on the contact piece is not impeded by the plastic section. However, a constant pressure on the contact piece is required to ensure a continuous equally good current flow.
Practical tests have shown that when a cable end consisting of wires welded together, is screwed on, the compression of the connecting piece described above does not occur and consequently normal screws without protection against loosening can be used. Since the screw now presses the contact piece onto the battery terminal at a constant pressure, optimal electrical conditions are created and thus the heating in the contact region is reduced.
According to the invention a further section is secured at the end the strand. This further section can, for example, serve as a contact piece and can be connected in various ways to the end of the strand welded to form a solid material.
A particularly preferred embodiment of a battery terminal connecting cable is obtained if the further section is welded onto the end of the strand. In this way a specially favourably shaped contact piece can be used. This in particular allows the weight of the battery terminal connecting cable to be reduced.
It is also advantageous if the further section, preferably constructed as a contact piece, is made of copper.
In all known battery terminal connecting cables the longitudinal axis of the further section extends in the direction of the axis of the battery terminal connecting cable. Since the battery terminal connecting cable serves as a connecting element between two terminals, it seems to be logical to use a further section extending in the direction of the axis of the battery terminal connecting cable. However, tests have shown that in many cases it is of great advantage if this further section is configured such that its longitudinal extension runs at an angle to the longitudinal axis of the cable. Examples of this type of configuration are shown in FIGS. 6-9.
Depending on the configuration of the battery terminals, in practice the connecting cables are frequently very severely bent. In many cases, the angular configuration of the further section to the axis of the battery terminal connecting cable reduces the necessary bending of the cable and also allows shorter cables to be used. The configuration described thus has the result that the cable can be protected and material usage can be reduced.
The angular configuration described is also of great importance for battery terminal connecting cables regardless of the afore-mentioned characteristics and can thus also be used to advantage for clamp connections between the cable strand and a further section.
The problem according to the invention is also solved using a method for the manufacture of a battery terminal connecting cable in which a strand consisting of numerous fine wires is welded by means of ultrasound and the strand is welded to a contact piece or with a contact piece.
The use of ultrasound for making electrical connections is already known from EP-A-0 671 790. However, the welding of the strand to a contact piece or with a contact piece cannot be inferred from this document.
All types of welding or soldering of an end of a strand developed so far have failed in that the high heat input during the welding process is transferred from the copper cables normally used to the insulating layer. On the one hand, this leads to destruction of the insulation and on the other, the input heat is rapidly dissipated. Only welding by means of ultrasound produced such good results that the insulating layer can remain on the cable strand during welding. This surprising result reduces the energy input and allows known manufacturing methods for moulding plastic onto the connecting regions to be used even for the new battery terminal connecting cable.
For manufacture of the battery terminal connecting cable according to the invention a device is proposed which has a sonotrode, a strand feed device, a contact piece feed device and a pressure cylinder arranged so that the strand and the contact piece can be pressed onto one another by means of this device.
The device allows the battery terminal connecting cable to be manufactured automatically and rapidly.
Since during pressing of the wire strand the fine wires are pressed to the side, it is proposed that on the device according to the invention there should preferably be provided movable jaws which act on the strand at right angles to the axis of the pressure cylinder. These jaws together with the pressure cylinder and the sonotrode define a cross-section in which the wires should be welded together to form the most compact copper piece. At the end of the welding process the jaws are moved away from the strand and the pressure cylinder is retracted so that the strand connected to the contact piece can be removed from the device.