Abstract:
The disclosure includes specifying an electrical connection arrangement, in particular for a rechargeable battery arrangement, having an electrical connecting element which permits the electrical energy to be transmitted between the rechargeable battery cells with as little loss as possible. In addition, there is disclosed an advantageous electrical connecting element in the form of a sheet-metal strip for the electrical connection arrangement.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of and priority to German Patent Application No. 10 2010 033 437.5, filed Aug. 4, 2010, and International Application No. PCT/EP2011/003678, filed Jul. 22, 2011, the entire disclosures of which are incorporated herein by reference for all purposes. 
     BACKGROUND 
     The present application relates generally to the field of batteries and battery systems. More specifically, the present application relates to batteries and battery systems that may be used in vehicle applications to provide at least a portion of the motive power for the vehicle. 
     A rechargeable battery arrangement having a plurality of rechargeable battery cells usually has electrical connecting elements for connecting the poles of the rechargeable battery cells. The rechargeable battery cells are generally connected in series, if appropriate also connected groupwise in a parallel connection, by means of the electrical connecting elements. The electrical connecting elements may be embodied, for example, in the form of a sheet-metal strip, as is known, for example, from US 2010/0015519 A1. Such electrical connecting elements are also referred to as bridge connectors or as busbars. In order to transmit the electric current from one rechargeable battery cell to the next, it is desirable to minimize the contact resistances and therefore the losses. 
     SUMMARY 
     The disclosure includes specifying an electrical connection arrangement, in particular for a rechargeable battery arrangement, having an electrical connecting element which permits the electrical energy to be transmitted between the rechargeable battery cells with as little loss as possible. In addition, there is disclosed an advantageous electrical connecting element in the form of a sheet-metal strip for the electrical connection arrangement. 
     This permits a reduction in the contact resistance from one electrical terminal to the other electrical terminal by means of electrical connecting element with simple cost-effective means. The present techniques may begin with optimizing the contact faces at which the electrical connecting element is in contact with the electrical terminals. According to the previously acknowledged teaching, it has been attempted to configure the surfaces of these contact faces to be as smooth and level as possible in order in this way to maximize the contact and therefore minimize contact resistances. However, such optimization in the direction of ideal surface quality does not in fact lead to the desired objective since even smooth surfaces which have been optimized with a large degree of expenditure on manufacture and therefore at high cost have tolerances which in the microscopic range do not cause the contact faces of the connecting element and of the electrical terminal to bear one against the other in a uniform, two-dimensional planar fashion. This inherently gives rise to relatively high contact resistance, which according to the previous teaching would require a further increase in the fabrication precision of the surfaces. 
     The present technique departs from the prevalent teaching and instead proposes that at least one of the contact faces of the electrical connecting element and/or of the first or second electrical terminal be intentionally manufactured with a structured surface, and that the latter be configured in such a way that as a result of attachment of the electrical connecting element to the first and/or second electrical terminal, the structured surface is plastically deformed compared to the state present before the attachment of the electrical connecting element. As a result, a significant reduction in contact resistances is possible in a cost-effective way since the structured surface permits plastic adaptation at the contact face which is respectively located opposite, which gives rise to a maximization of the entire contact face. Depending on the configuration of the material hardnesses of the first and second electrical terminals and of the electrical connecting element, the structured surface can also plastically deform the contact face which is respectively located opposite, for example by means of stamping, as a result of the attachment of the electrical connecting element to the first and/or second electrical terminal. It is also possible to have a combination such that the structured surface itself is deformed plastically and the structured surface also plastically deforms the contact face lying opposite. Overall, this results in optimum adaptation of the profiles of the contact faces which bear one against the other. 
     There is provision here that the plastic deformation occurs as a result of attachment of the electrical connecting element to the first and/or second electrical terminal, for example in that the connecting element is attached to a thread on the electrical terminal by means of a screw or an attachment nut, and the screw or the attachment nut is correspondingly tightened until a desired plastic deformation is achieved. The tightening of the screw or of the attachment nut advantageously occurs with a prescribed tightening torque. 
     Particularly low-resistance junctions can be implemented with the present techniques since as a result of the surface structuring the contact faces not only bear against one another in a two-dimensional level fashion but also a three-dimensional structure is provided, as a result of which a larger overall contact face is produced than the two-dimensional extent of the contact faces. 
     The structured surface can have a regular or irregular shape. As a result, large degrees of freedom are permitted in the determining and the manufacture of the structured surface, which has the advantage that in each case particularly cost-effective manufacturing methods can be used. The structured surface may have, for example, a random pattern. 
     According to one advantageous development, the structured surface is embodied as a third-order shape deviation according to Deutsches Institut für Normung (i.e., German Institute for Standardization or “DIN”) 4760. The structured surface therefore has a certain degree of roughness which may be embodied, for example, in the form of grooves. The structured surface may have a simple-groove arrangement and a cross-groove arrangement. The grooves may be profiled in different ways in a cross section, for example in a V shape or U shape. 
     The structured surface may be provided only on the electrical connecting element. The first and second electrical terminals therefore may not provided with a structured surface. This results in further cost advantages with respect to the manufacture of the electrical connection arrangement. It is therefore possible for the electrical terminals, for example the poles of rechargeable battery cells, to be manufactured in the same way as before. Switching over manufacturing steps is necessary only for the manufacture of the electrical connecting element. In addition, simple exchange and replacement of the electrical connecting elements is made possible since by using a new electrical connecting element here a new structured surface, which is not yet plastically deformed, is also used. 
     The electrical connecting element may be composed, at least in the region of its contact faces, of another material with a different material hardness than the first and/or the second electrical terminals in the region of its contact face. It is basically technically irrelevant which contact partner is made harder or softer. The material selection can therefore be made according to economic criteria, in particular according to the criteria of re-usability and costs of parts. It is advantageous, when connecting rechargeable battery cells, to make the electrical connecting element softer than the first and the second pole of the rechargeable battery cell, for example by soft annealing the electrical connecting element. In particular, soft-alloyed types of copper are advantageously used. Lead and aluminum and their alloys are also possible, for example. 
     When selecting the material hardnesses it may be desirable to ensure that when the electrical connecting element is attached to the first and/or the second electrical terminal, a sufficient pressing force can be applied without one of the connecting materials flowing away under this force or the attachment means being damaged, for example tearing off. Advantageous material hardnesses are in the range from 45 to 100 HV, for example. 
     The structured surface may have a peak-to-trough depth in the range from 0.25 to 1 mm. The peak-to-trough depth is measured here between the highest and the lowest point of the surface, for example between the upper edge and the trough of a groove. The peak-to-trough depth may be defined, in particular, as a function of the size of the electrical connecting element. 
     The structured surface may be stamped with a stamping tool. This has the advantage that the structured surface can be configured with less sharp edges, as a result of which notch effects and an associated risk of fracture in the region of the contact faces lying one against the other is reduced. 
     The electrical connecting element may have in each case a passage opening for feeding through an attachment means in the region of the contact faces of said connecting element. The attachment means may have, in particular, a thread embodied, for example, as a screw. 
     The disclosure also relates to an electrical connecting element in the form of a sheet-metal strip for connecting a first electrical terminal to a second electrical terminal, in particular for connecting a first rechargeable battery cell to a second rechargeable battery cell of a rechargeable battery arrangement of the type described above. The electrical connecting element has the structured surface on at least one of its contact faces. 
     The disclosure also relates to a rechargeable battery arrangement having at least a first rechargeable battery cell, a second rechargeable battery cell and an electrical connection arrangement of the type described above. Here, the first electrical terminal is a first pole of the first rechargeable battery cell, and the second electrical terminal is a second pole of the second rechargeable battery cell. As is apparent, the electrical connection arrangement according to the disclosure can, however, also be used advantageously for all types of electrical connections between two electrical terminals. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be explained in more detail below with reference to exemplary embodiments and using drawings, in which: 
         FIG. 1  shows a rechargeable battery arrangement, 
         FIG. 2  shows an electrical connection arrangement, 
         FIG. 3  shows the electrical connection arrangement according to  FIG. 2  after the attachment of the electrical connecting element, 
         FIG. 4  shows the connection arrangement according to  FIG. 3  from a lower view, 
         FIG. 5  shows a first embodiment of an electrical connecting element, 
         FIG. 6  shows a second embodiment of an electrical connecting element, 
         FIG. 7  shows an embodiment of a terminal pole of a rechargeable battery cell, 
         FIG. 8  shows a third embodiment of an electrical connecting element in a plan view, 
         FIG. 9  shows the electrical connecting element according to  FIG. 8  in a side view, and 
         FIG. 10  shows a groove in an enlarged illustration. 
     
    
    
     DETAILED DESCRIPTION 
     In the figures, the same reference symbols are used for corresponding elements. 
       FIG. 1  shows a rechargeable battery arrangement having a first rechargeable battery cell  4  and a second rechargeable battery cell  5 . The first rechargeable battery cell  4  has a first pole  1  as a first electrical terminal. The second rechargeable battery cell  5  has a second pole  2  as a second electrical terminal. The first pole  1  is electrically and mechanically connected to the second pole  2  via an electrical connecting element  3  which is embodied in the form of a sheet-metal strip. Respective further electrical connecting elements  3 , by which the rechargeable battery cells  4 ,  5  can be electrically connected to further rechargeable battery cells (not illustrated), are illustrated on the underside of the rechargeable battery cells  4 ,  5 . As a result of the embodiment of the electrical connecting element  3  as a sheet-metal strip, not only is the electrical connection produced but at the same time a relatively rigid and stable mechanical connection is produced between the rechargeable battery cells, with the result that in many cases additional mechanical stabilization can be simplified, or can even be dispensed with. 
       FIG. 2  shows the connection between the first pole  1  and the electrical connecting element  3  in an enlarged illustration of a detail, wherein the first rechargeable battery cell  4  is not illustrated. The first pole  1  has a contact face  14  which is provided to come to bear against a corresponding, assigned contact face  32  of the electrical connecting element  3 . The first pole  1  also has a passage opening  10  which is provided with an internal thread and runs in the longitudinal direction. The electrical connecting element  3  has a first passage opening  30  in the form of a drilled hole and a second passage opening  31  in the form of a drilled hole. In the region surrounding the second passage opening  31 , the electrical connecting element  3  has a second contact face  33 . The second passage opening  31  serves for feeding through a further attachment means in order to connect the electrical connecting element  3  to the second rechargeable battery cell  5 .  FIG. 2  also illustrates a screw  12  which serves as an attachment means. The screw  12  has, for example, a thread  13  which matches the internal thread of the passage opening  10  of the first pole  1 . Furthermore, a washer  11  is arranged between the head of the screw  12  and the electrical connecting element  3 . 
       FIG. 3  shows the arrangement according to  FIG. 2  in a state in which the electrical connecting element is attached to the first pole  1  by screwing the screw  12  into the internal thread of the passage opening  10 . 
       FIG. 4  shows the arrangement according to  FIG. 3  in a view from below onto the electrical connecting element  3 , i.e. in a view in which the second contact face  33  with its structured surface can be seen. 
       FIG. 5  shows a first embodiment of the electrical connecting element  3 . As is apparent, both the first contact face  32  and the second contact face  33  are provided with a structured surface. The structured surfaces are embodied at least in the region of the contact faces  32 ,  33  in the form of a cross-groove arrangement, i.e. a first multiplicity of grooves which run parallel to one another and a second multiplicity of grooves which also run parallel to one another are present, wherein the second multiplicity of grooves is arranged at an angle to the first multiplicity of grooves. 
       FIG. 6  shows a second embodiment of the electrical connecting element  3  in which, at least in the region of the contact faces  32 ,  33 , in each case a simple-groove arrangement is provided, i.e. in each case a multiplicity of grooves running parallel to one another is provided. 
       FIG. 7  shows the connecting pole  1  with the contact face  14 , wherein it is apparent that the contact face  14  is also structured. The surface structure of the contact face  14  has been generated in this case by plastic deformation of the previously substantially level (smooth) surface of the contact face  14  owing to attachment of an electrical connecting element provided with a cross-groove arrangement, for example according to  FIG. 5 . 
     The described structured surfaces of the contact faces, as illustrated in  FIGS. 5 and 6  with reference to the electrical connecting element, can also be provided on the respective contact face  14  of the first or second pole  1 ,  2 . In this case, a pole  1 ,  2  is produced with a contact face  14  which looks comparable to the one illustrated in  FIG. 7 . 
       FIG. 8  shows an electrical connecting element  3  in which, at least in the region of the respective contact faces  32 ,  33 , again a cross-groove arrangement is provided, for example by stamping with a stamping tool.  FIG. 8  shows the electrical connecting element  3  in a plan view, and  FIG. 9  shows the same electrical connecting element  3  in a side view. For example, details are given below of a groove  34  of the cross-groove arrangement in the region of the contact face  33 . The groove  34  is illustrated enlarged in  FIG. 10 . As is apparent, the groove has a V-shaped profile. The groove depth is advantageously embodied in such a way that it corresponds to approximately 0.85 times the value of the groove width t. It has become apparent that as a result, particularly small contact resistances can be achieved.