Abstract:
The invention relates to a current-sensing resistor ( 1 ) for measuring an electric current, in particular also for measuring a battery current in a vehicle power supply, having a plate-shaped first connecting part ( 3 ) for introducing the electrical current to be measured, wherein the plate-shaped first connecting part ( 3 ) consists of an electrically conductive conductor material; a plate-shaped second connecting part ( 2 ) for conducting away the electrical current to be measured, wherein the plate-shaped second connecting part ( 2 ) consists of an electrically conductive conductor material; and a plate-shaped resistance element ( 4 ), which is connected in the current path between the two connecting parts and through which the electrical current to be measured flows, wherein the resistance element ( 4 ) consists of a comparatively high-impedance resistance material. According to the invention an incision ( 10, 11 ) is arranged in the plate-shaped first connecting part ( 3 ) and/or in the plate-shaped second connecting part ( 2 ) in order to reduce the temperature dependency of the measurement and to eliminate the influence of the plate-shaped connecting parts (usually copper or aluminum).

Description:
BACKGROUND OF THE INVENTION 
     The invention concerns a current-sense resistor for measuring an electrical current, especially for measuring a battery current in a motor vehicle on-board electrical system. 
     EP 0 605 800 A1 discloses a current-sense resistor of this type, which consists of two copper plate-shaped connecting parts and an also plate-shaped low-ohm resistance element made of a resistance alloy (e.g. Cu84Ni4Mn12), wherein the resistance element is placed between the connecting parts and welded to the connecting parts. Such current-sense resistors are used to measure the electrical current as per the well-known four-wire technology, wherein the current to be measured is conducted through the resistance element via the plate-shaped connecting parts. The voltage drop over the resistance element then forms a measure for the electrical current to be measured in accordance with Ohm&#39;s law. The known current-sense resistor consequently has two voltage contacts on both plate-shaped connecting parts with the voltage contacts arranged near the resistance element and thus allowing a measurement of the voltage drop over the resistance element. Such current-sense resistors exhibit only a relatively low temperature dependency of the measurement, since, usually, the resistance material used (e.g. Cu84Ni4Mn12) has a very low temperature coefficient. However, the demands on temperature constancy of such current-sense resistors are still increasing. 
     U.S. Pat. No. 5,999,085 discloses a low-ohm current-sense resistor which has an incision on each connecting part which divides the connecting parts into a voltage contact and a current contact each. Both current contacts are used for introducing the current to be measured into or conducting it away from the current-sense resistor. Both voltage contacts serve, in contrast, to measure the electric voltage that decreases over the current-sense resistor according to the well-known four-wire technology. Here, the incision in the connecting parts runs parallel to the current flow direction between both connecting parts and therefore does not have a particularly favorable effect on the temperature stability of the current measurement. Here, the incisions in particular have a very limited influence on the current course in the connecting parts since they are oriented parallel to the main current direction. 
     Therefore, the object of the invention is to improve the temperature constancy of the above-described conventional current-sense resistor. 
     This object is achieved by a current-sense resistor according to the invention. 
     DESCRIPTION OF THE INVENTION 
     The invention is based on the technical-physical finding that the conductor material (e.g. copper) of the plate-shaped connecting parts has a much higher temperature coefficient than the resistance material (e.g. Cu84Ni4Mn12) of the plate-shaped resistance element. During the measuring of the electrical current that drops over the resistance element between both voltage contacts, there is, however, also an influence on the measurement caused by the material of the connecting parts. The temperature dependency of the voltage measurement thus is not only determined by the temperature coefficient of the resistance material, but also by the temperature coefficient of the conductor material. Here, it is important to take into consideration that the temperature coefficient of copper, for example, is α=83.9·10 −3  K −1  and thus greater by a factor of 195 than the temperature coefficient of Cu84Ni4Mn12 (Manganin®) with α=0.02·10 −3  K −1 . Due to the much greater temperature coefficient of copper, the plate-shaped connecting parts actually influence the temperature dependency of the entire measurement if only a small part of the voltage between the voltage contacts drops over the connecting parts. 
     The invention therefore comprises the general technical teaching of providing an incision in at least one of the plate-shaped connecting parts to reduce the temperature dependency of the measurement. 
     The incision preferably runs at least partially transversely (e.g. at a right angle) with respect to the current flow direction between both connecting parts. The incision is therefore oriented at least partially transversely (e.g. at a right angle) to the connecting line between both connecting parts. In other words, the incision preferably runs parallel to the connecting line between the resistance element and the neighboring connecting parts for at least a portion of its length. The current-sense resistor according to the invention thus differs from the known current-sense resistor according to U.S. Pat. No. 5,999,085 as described at the beginning which has an incision oriented parallel to the current flow direction. 
     In a preferred exemplary embodiments, the current-sense resistor according to the invention corresponds to a great extent to the current-sense resistor described in EP 0 605 800 A1, so that the content of this patent application is to be incorporated in full in the present description as regards the design of the current-sense resistor. It should merely be mentioned at this point that the current-sense resistor according to the invention has two plate-shaped connecting parts that consist of an electrically conductive conductor material (e.g. copper) and are used for introducing or conducting away the electrical current to be measured. In addition, the current-sense resistor according to the invention has a plate-shaped resistance element connected in the current path between both connecting parts and through which the electric current to be measured flows, wherein the resistance element consists of a low-ohm resistance material (e.g. Cu84Ni4Mn12) which is low-ohm from an absolute point of view, but has a greater specific resistance than the conductor material. 
     The current-sense resistor according to the invention preferably has two voltage contacts to measure the electrical current dropping over the resistance element as a measure for the electrical current to be measured as per Ohm&#39;s law, which voltage contacts are connected electrically and mechanically with both plate-shaped connecting parts, wherein both voltage contacts are preferably arranged as close as possible to the resistance element on the plate-shaped connecting parts. 
     For example, the voltage contacts can be an embossment as described e.g. in DE 10 2009 031 40, so that the content of this patent application is to be incorporated in full in the present description as regards the constructional design of the voltage contacts. 
     Alternatively, there is the option of designing the voltage contacts as contact surfaces, as described, for example, in EP 0 605 800 A1, so that the content of this patent application is to be incorporated in full in the present description as regards the constructional design of the voltage contacts. 
     In addition, in the framework of the invention, there are also different other options for the constructional design of the voltage contacts. 
     With such design of the current-sense resistor according to the invention with two voltage contacts, there is a preference for at least one incision in each of both associated plate-shaped connecting parts in order to reduce temperature dependency of the measurement. 
     Here, both incisions in both plate-shaped connecting parts are preferably arranged in such a way as to transform the current lines and the equipotential lines in the plate-shaped connecting parts in such a way that the equipotential lines in the plate-shaped connecting parts running through the voltage contacts directly reach the contact point (joining point) with the resistance element, i.e. usually the weld seam between the plate-shaped connecting parts and the resistance element. The advantage of this is that the voltage contacts are then at the same electrical potential as the edges of the resistance element, so that the voltage measurement is not in the least distorted by the conductor material of the plate-shaped connecting parts. 
     Both incisions in both plate-shaped connecting parts are therefore preferably arranged on the side of the respective voltage contact that is facing away from the resistance element. Thus, both incisions preferably run between the voltage contacts and the respective current contacts, which serve for introducing or conducting away the electrical current to be measured and which are electrically and mechanically connected to the respective plate-shaped connecting part. 
     There are also several options in the context of the invention as regards the constructional design of the current contacts, some examples of which are described in EP 0 605 800 A1 and DE 10 2009 031 408, so that the content of this patent application is to be incorporated in full in the present description as regards the constructional design of the voltage contacts. 
     It should also be mentioned that the incisions are preferably arched, wherein the incisions extend over an arc angle of more than 30°, 40°, 50°, 60° or even 70°. 
     Furthermore it should be mentioned that the incisions in the plate-shaped connecting parts in the preferred exemplary embodiment are each arched or angled away from the current contacts and towards the resistance elements. 
     The incision preferably exhibits a width that is essentially constant over the length of the incision. The incisions are thus preferably slit-shaped, although other shapes are also possible. 
     It should furthermore be mentioned that the incision preferably extends from an edge of the respective connecting part towards the inside, wherein the incisions in both connecting parts preferably extend from the same edge. 
     In addition, it should be noted that the incision preferably does not reach the position of the resistance element or the opposite edge of the respective plate-shaped connecting part, so that the voltage contacts can come into contact with the resistance element on its entire width over the plate-shaped connecting part despite the incision. 
     Through the arrangement, according to the invention, of incisions in the plate-shaped connecting parts, it is possible in the framework of the invention that the temperature coefficient of the resistance of the entire current-sense resistor is by at least 30%, 40%, 50% or 60% smaller than for a current-sense resistor with the otherwise identical construction without such an incision. 
     For the preferred exemplary embodiment of the invention, copper or a copper alloy is used as the conductor material for the plate-shaped connecting parts. However, with regard to the conductor material used, the invention is not limited to the aforementioned examples. 
     It should also be noted that the resistance material for the resistance element is preferably a copper alloy, in particular a copper-manganese-nickel alloy such as Cu84Ni4Mn12 (Manganin®). However, with regard to the resistance material used for the resistance element, the invention is not limited to the aforementioned examples. However, the resistance materials of the resistance element preferably exhibits a lower conductivity resp. a greater specific resistance than the conductor material of the plate-shaped connecting parts. 
     It should also be mentioned that the resistance element is preferably connected to both connecting parts electrically and mechanically, in particular through a welded connection, wherein electron beam welding is particularly suitable as already described in detail in EP 0 605 800 A1, so that the content of this patent application is to be incorporated in full in the present description as regards the design and manufacturing method of the current-sense resistor according to the invention. 
     Finally, it should also be mentioned that both connecting parts are preferably arranged on opposite sides of the resistance element, so that the resistance element is located between both connecting parts. There is, however, the alternative option of arranging both connecting parts on the same side of the resistance element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantageous developments of the invention are explained in more detail below together with the description of the preferred exemplary embodiment of the invention on the basis of the figures. The figures show as follows: 
         FIG. 1  a perspective view of a current-sense resistor according to the invention, 
         FIG. 2  a plan view of the current-sense resistor from  FIG. 1 , 
         FIG. 3  a side view of the current-sense resistor from  FIGS. 1 and 2 , 
         FIG. 4  a detailed view of the current-sense resistor from  FIG. 2 , 
         FIG. 5A  a plan view of a conventional current-sense resistor with the distribution of the current lines and the equipotential lines between the voltage contacts. 
         FIG. 5B  for the purpose of comparison, a plan view of the current-sense resistor according to the invention, as well as 
         FIG. 6  a diagram to show the temperature dependency of the resistance value of the current-sense resistor according to the invention compared with a conventional current-sense resistor. 
     
    
    
       FIGS. 1 to 4  and  5 B show a preferred exemplary embodiment of a current-sense resistor  1  according to the invention, which may, for example, be used to measure a current according to the known four-wire technology in a motor vehicle on-board electrical system. 
     The current-sense resistor  1  according to the invention largely corresponds to a conventional current-sense resistor as it is described e.g. in EP 0 605 800 A1, so that additional reference is made to this patent application. 
     The current-sense resistor  1  according to the invention essentially consists of two plate-shaped connecting parts  2 ,  3  made of a conductor material (e.g. copper) and an also plate-shaped resistance element  4  made of a low-ohm resistance material (e.g. Cu84Ni4Mn12) which is inserted between both plate-shaped connecting parts  2 ,  3 . Here, both plate-shaped connecting parts  2 ,  3  are arranged on opposite sides of the also plate-shaped resistance element  4  and welded to the plate-shaped resistance element  4 . 
     In addition, the current-sense resistor  1  according to the invention has two current contacts  5 ,  6  which are electrically and mechanically connected with both plate-shaped connecting parts  2 ,  3 , wherein the current contact  6  used for introducing an electrical current I to be measured, while current contact  5  serves for conducting away the electrical current I to be measured, as is particularly clear from the side view in  FIG. 3 . 
     In addition, the current-sense resistor  1  according to the invention has two voltage contacts  7 ,  8  which are electrically and mechanically connected with both plate-shaped connecting parts  2 ,  3  and serve for measuring the electrical voltage that drops over the resistance element  4 . Both voltage contacts  7 ,  8  are therefore arranged very close to the resistance element  4  in the plate-shaped connecting parts  2 ,  3  to avoid distortion of the voltage measurement by the electric voltage drop over the connecting parts  2 , 3 . 
     It should be mentioned that the current-sense resistor  1  according to the invention has, on the side in the area of the resistance element  4 , an incision  9  which is used for calibrating or adjusting the desired resistance value of the current-sense resistor  1  by making the incision  9  larger or smaller in the framework of manufacturing. 
     It is, however, import for function according to the invention that one incision  10 ,  11  each is arranged in both plate-shaped connecting parts  2 ,  3  in order to reduce the temperature dependency of the measurement. Here, both incisions  10 ,  11  extend transversely from the same edge of the plate-shaped connecting part  2  or  3  inwardly and are then led around the respective voltage contacts  7  or  8  in an arched manner, wherein both incisions  10 ,  11  extend over an arc angle α≈70°, as is particularly visible in the detailed view provided in  FIG. 4 . 
     Furthermore, the detailed view in  FIG. 4  shows that both incisions  10 ,  11  are slit-shaped and have a width b that is essentially constant over the entire length of the incisions  10 ,  11 . 
     The function of both incisions  10 ,  11  becomes obvious when one compares both  FIGS. 5A and 5B , wherein  FIG. 5A  shows the course of the current lines  12  and equipotential lines in a conventional current-sense resistor  1 , whereas  FIG. 5B  shows the course of the current lines  12  and the equipotential lines  13  in the current-sense resistor according to the invention. Here, the current lines  12  define a main current direction, wherein the incisions  10 , are partly oriented transverse to this main current direction in order to influence the current course. 
     This comparison shows that in the conventional current-sense resistance  1  according to  FIG. 5A , the equipotential lines running through the voltage contacts  7 ,  8  are not at exactly the same electrical potential as the outer edges of the resistance element  4 . This means that the voltage measured between the voltage contacts  7 ,  8  partly consists of the voltage that drops over the plate-shaped connecting parts  2 , 3 . Thus, the measured voltage is also influenced by the relatively high temperature dependency of the conductor material of connecting parts  2 , 3 . 
     In the current-sense resistor  1  according to the invention as per  FIG. 5B , the incisions  10 ,  11 , in contrast, deflect the current course  12  and the equipotential lines  13  away in such a manner that the equipotential lines running through the voltage contacts  7 ,  8  reach the outer edges of the resistance element  4  and therefore are at the same electrical potential. During voltage measurement, only the voltage that drops over the resistance element  4  is thus measured. This is advantageous because the conductor material (e.g. copper) of the plate-shaped connecting parts  2 ,  3  usually exhibits a much higher temperature dependency with regard to the specific electrical resistance than the resistance material (e.g. Manganin®) of the resistance element  4 . Here, the equipotential lines  13  asymptotically adapt to the welding edge between the plate-shaped connecting parts  2 ,  3  and the resistance element  4 . 
     The design of the current-sense resistor  1  according to the invention with the incisions  10 ,  11  leads to a considerable decrease of the temperature dependency during current measurement as can be seen in the diagram in  FIG. 6 , which shows the temperature dependency of the resistance value R as a function of the temperature T. 
     The invention is not limited to the previously described preferred exemplary embodiment. Instead, a plurality of variants and modifications are possible, which also make use of the concept of the invention and thus fall within the scope of protection. Furthermore, the invention also claims protection for the subject-matter of the subclaims independently of the features of the claims to which they refer. 
     LIST OF REFERENCE NUMERALS 
     
         
           1  Current-sense resistor 
           2  Connecting part 
           3  Connecting part 
           4  Resistance element 
           5  Current contact 
           6  Current contact 
           7  voltage contact 
           8  voltage contact 
           9  Incision 
           10  Incision 
           11  Incision 
           12  Current lines 
           13  Equipotential lines