Cable holder for a motor vehicle

Abstract

A cable holder (300) for use in a motor vehicle (105), the cable holder (300) comprising: a receptacle (325) for the cable (225); a fastening element (355) for attachment to the motor vehicle (105); a temperature sensor (345) for sensing a temperature of the cable (225); a processing device (340) for determining a frequency-dependent electrical property of the cable (225) based on the temperature.

Description

The present invention relates to a cable holder for a motor vehicle. In particular, the invention relates to a cable holder for a high-voltage or high-current cable.A motor vehicle is configured to be electrically driven. For this purpose, the motor vehicle comprises an electric drive machine which is operated with current from an electrical energy store. The energy store can have a rated voltage of several 100 V, for example about 400, about 800 or about 1,000 V. A current flowing through the electric drive machine may reach a magnitude of about 100 A or more. A cable which transmits electrical current between the energy store and the drive machine can no longer be regarded as being electrically neutral under such loads. Rather, an electrical resistance of the cable and its behavior in the transmission of alternating current must be taken into account in order to keep the electrical drive system balanced and low-loss.Even if the cable is installed on board the motor vehicle relatively briefly and carefully, after a certain operating time of the motor vehicle, a poor electrical coordination can become noticeable, in particular due to aging of the cable. As a result, for example, reactive power between the energy store and the drive machine can increase. The reactive power can heat the cable and further load it electrically, but does not contribute to the drive of the motor vehicle.CN 1 06 353 579 A discloses an apparatus and a method for integrated monitoring of cable current, conductor temperature and internal partial discharge.An object underlying the present invention is to provide an improved technique for electrically adapting a cable on board a motor vehicle. The invention achieves this object by means of the subject matter of the independent claims. Dependent claims represent preferred embodiments.According to a first aspect of the present invention, a cable holder for use on a motor vehicle comprises a receptacle for the cable; a fastening element for attachment to the motor vehicle; a temperature sensor for sensing a temperature of the cable; and a processing device for determining a frequency-dependent electrical property of the cable on the basis of the temperature.It has been recognized that a tuning of the cable to an electrical power to be transmitted is dependent on its temperature. The cable holder may combine a mechanical attachment of the cable to the motor vehicle with a sensor and processing system. The cable holder can thus determine a property of the cable and provide it to a control system. The control system may control a source or sink of electrical energy connected to the cable in an improved manner depending on the particular electrical characteristic. Adaptation of the source to the depression can be improved. The controllability of the overall system can be improved. Electrical losses in the region of the cable can be minimized. The cable can heat up less strongly, as a result of which its frequency-dependent tuning can be influenced less strongly.The frequency dependent property may comprise an electrical impedance. In this case, the impedance can specify a ratio of an applied electrical voltage to a current intensity flowing through the cable. In other words, an influence of the cable on the transmission of alternating current can be expressed. It is particularly preferred that the frequency-dependent property comprises a frequency response. The frequency response can relate in particular to a profile of the impedance over the frequency of a transmitted electrical power. Thus, knowing a frequency of a transmitted electric current, the impedance of the cable can be easily determined. The frequency response can be present, for example, in the form of a table, a graph or a formula description.It is particularly preferred that the processing device is configured to determine an ageing state of the line on the basis of a time profile of its temperature. In addition, the processing device is preferably configured to determine the frequency-dependent electrical property on the basis of the determined state of aging.The cable comprises one or more wires and an insulation surrounding them. Optionally, the cable can also comprise an electrically conductive protective screen which is then usually re-insulated from the outside. The structure of the cable can be varied depending on a longer temperature load. In addition, dielectric properties of an insulating material can be changed by temperature influence. The insulating material may comprise a plastic which may change its chemical structure under the influence of time and temperature. Further, a mechanical structure of the cable may change slightly, for example, by increasing or decreasing a distance between a wire and a shield. Such effects can be mapped or predicted by determining the state of aging. The more heavily and the longer the cable is thermally stressed, the more it can be exposed to aging. The more the ageing is, the more a difference of a valid electrical property can deviate from an originally present electrical property. Depending on the state of aging, an applicable value of one or more electrical parameters of the cable may be determined.In a further embodiment, a temperature sensor for sensing a temperature at the surface of the cable is provided on the sensor. The processing device is configured to determine the temperature in a deeper layer of the cable. Optionally, the surface temperature of the cable may be compared to a temperature of an environment to determine how much the cable is heated due to current flowing. The heating by flowing electrical current takes place in a core of the cable, which may be insulated from the surface or from the sensor by layers of one or more materials. By determining a temperature prevailing in the interior of the cable, aging effects can be taken into account in an improved manner. In one embodiment, the processing device is configured to determine a profile of the temperature of the cable over its cross section. In a preferred embodiment, in which the cable contains only a single core, a radial temperature profile can be determined.According to a further embodiment, the cable holder comprises a mechanical adjustment device which is configured to move the receptacle with respect to the fastening element in order to change a course of the cable in the region of the cable holder. By changing the profile, the frequency-dependent electrical property can be influenced. The adjustment device can be controlled to influence the course of the cable in such a way that the property corresponds to an originally applicable or otherwise predefined property. The adjusting device can comprise, for example, a servomotor or a thermal adjusting element.According to a further embodiment, a magnetizable element is arranged in the region of the cable, wherein the course of the cable with respect to the element can be changed by means of the adjusting device. By varying a geometric distance of the cable or a core comprised by the cable from the magnetizable element, the frequency-dependent electrical parameter can be influenced. The material may comprise a ferromagnetic material such as iron or steel. In order to be able to adapt the parameter more precisely even at higher frequencies, the material can also comprise a pressing material which contains iron in powder form. In one embodiment, the magnetizable element is comprised by the motor vehicle. In another embodiment, the magnetizable element is comprised by the cable holder.A plurality of cables can be used between an energy source and an energy sink on board the motor vehicle. Accordingly, a plurality of cable holders can also be used. The frequency-dependent parameter of one of the cables can also be changed by changing its distance or its position with respect to an adjacent cable. In one embodiment, the cable holder comprises a further receptacle for a further cable and a further mechanical adjustment device. The adjusting device is configured to move the further receptacle relative to the other receptacle of the cable holder. A movement of the further receptacle relative to the fastening element can likewise be provided.According to a particularly preferred embodiment, the cable holder comprises receptacles for three cables. Each cable preferably comprises a core and the three cables together are capable of carrying a three phase alternating current. For tuning the cables between an energy source and an energy sink, one, two or all three cables can be mechanically influenced in their course in the manner described.In a further embodiment, the cable holder comprises a coil in the region of the receptacle and a matching circuit for providing a predetermined voltage on the basis of an alternating voltage provided by the coil when alternating current has flowed through the cable. Thus, an integrated voltage source can be provided on the cable holder in order to supply the processing device or the adjusting device with electrical energy, for example. An operating voltage can also be supplied to a temperature sensor in this way. The coil can be adapted in terms of winding number, diameter, conductor cross section and position with respect to the cable in order to provide a sufficient amount of electrical energy as a function of an expected current which flows through the cable. The matching circuit may comprise a boost converter and / or a buck converter. Preferably, the matching circuit provides a regulated voltage.A plurality of coils in the region of the cable or the receptacle can also be cascaded with one another. In one embodiment, a plurality of coils are provided that are connected to the matching circuit. Different coils may be attached to the same cable or to different cables. Two coils may be included in the same cable holder or different cable holders.It is generally preferred that the cable is configured to conduct an electric driving current flowing through an electric drive machine of the motor vehicle. The driving current preferably comprises an alternating current, the frequency of which can be variable as a function of a driving speed of the motor vehicle.In accordance with another aspect of the present invention, an electric drive axle includes a cable holder described herein. The electric drive axle can additionally comprise an electric inverter and / or an electric drive machine for the motor vehicle. In addition, the drive axle may include a transmission. The electric drive axle acts on a drive wheel of the motor vehicle. The transmission can comprise an input for a further drive machine, in particular an internal combustion engine.In accordance with yet another aspect of the present invention, a motor vehicle includes a cable holder or an electric drive axle described herein. The motor vehicle is preferably designed as a motorcycle, as a passenger car, as a truck or as an omnibus.According to yet another aspect of the present invention, a method comprises steps of detecting a temperature at a surface of a cable; and determining a frequency dependent electrical property of the cable based on the temperature. More preferably, a temperature of the cable in a deeper layer is determined on the basis of the determined temperature, and the property is determined with respect to this temperature.The method is carried out according to the invention by means of a cable holder described herein and in particular a processing device comprised by it. For this purpose, the processing device can be designed electronically and comprise a programmable microcomputer or microcontroller. The method can be in the form of a computer program product with program code means. The computer program product can be stored on a computer-readable data carrier or can be transmitted via a data line. Features or advantages of the method can be transferred to one of the described devices or vice versa.The invention will now be described in more detail with reference to the accompanying figures, in which: FIG. 1 shows a motor vehicle having an electric drive axle; FIG. 2 is a circuit diagram of an electric drive axle; FIG. 3 shows a cable holder with a cable; and FIG. 4 shows a flow diagram of a methodis.FIG. 1 shows a system 100 having a motor vehicle 105 and an electric drive axle 110. The drive axle 110 comprises an electric drive machine 115 to which electrical energy is supplied from an electrical energy store 125 by means of a current transformer 120. The drive engine 115 acts on a drive wheel 130 of the motor vehicle 105.The electrical energy store 125 provides a DC voltage, which is converted into usually a plurality of AC voltages by means of the current transformer 120. Three alternating voltages phase-shifted by 120° with respect to one another are customary. A rotational speed or a torque of the drive engine 115 and thus also of the drive wheel 130 can be influenced by controlling voltages and frequencies of the alternating voltages accordingly.FIG. 2 shows a circuit diagram of an electric drive axle 110. The current transformer 120 situated between the energy store 125 and the electric drive machine 115 comprises, by way of example, three half bridges 205, each of which comprises an upper and a lower current valve 210. The current valves 210 of a half bridge 205 are connected in series between different potentials of the electrical energy store 125 and a connection between two current valves 210 is led to a phase of the electric drive machine 115. A control device 215 is configured to alternately open and close the current valves 210 of a half bridge 205, wherein a duty cycle of duty cycles of the current valves 210 controls a voltage provided to the electric machine 115. An intermediate circuit capacitor 220 attenuates alternating currents between the current transformer 120 and the energy store 125.Three cables 225 run between the current transformer 120 and the electric drive machine 115, which are each shown with the symbol for a connection in the circuit diagram shown. A further two cables 225 are provided between the energy store 125 and the current transformer 120; the same applies for these connections as for the cables 225 leading to the electric drive machine 115, but a DC voltage component is higher here and usually only two instead of three cables 225 are led in the same way.A current flows through a cable 225 between the drive machine 115 and the current transformer 120 or the energy store 125. This current may assume different frequencies and the cable 225 may have a frequency dependent electrical property that may affect the transmission of electrical energy. In particular, an adaptation of electrical parameters of the energy store 125 or of the current transformer 120 as energy source and of the electric drive machine 115 as energy sink can be influenced by an electrical property of a cable 225.FIG. 3 shows a cable holder 300 with a cable 225. In the embodiment shown, the cable 225 comprises a plurality of elements mounted radially with respect to one another. In the middle is a core 305 made of an electrically conductive material, through which an electrical current can flow along the cable 225. The core 305 is surrounded by a first insulator 310, on the outer side of which a shield 315 can be provided. The shield 315 serves to suppress electrical interference and is also electrically conductive. It can be realized, for example, by a wire mesh, a foil or a tube. On the outside of the shield 315, a second insulator 320 may be provided.The cable 225 may also be constructed in a manner other than that shown. Elements of the cable 225, in particular the insulators 310 and 320, can age during operation of the cable 225 and change their influence on a frequency-dependent electrical parameter of the cable 225.The cable 225 lies in a receptacle 325 of the cable holder 300. In one embodiment, the cable holder 300 includes a coil 330 that preferably wraps around the cable 225. The coil 330 may be provided in the area of the receptacle 325 or at another location along the cable 225. The coil 330 is connected to a matching circuit 335. If an alternating electric current flows through the cable 225, an alternating electromagnetic field is formed in its environment, which induces an electric voltage in the coil 330. The matching circuit 335 conditions the voltage to supply an electric power of a predetermined voltage to another component. In the illustrated embodiment, matching circuit 335 feeds a processing device 340. Optionally, a battery or capacitor may be provided to store energy harvested via coil 330. If no coil 330 is provided, a supply voltage can also be provided by another route, for example via an on-board power supply system or a battery.In the region of the receptacle 325 or at another suitable location along the cable 225, at least one temperature sensor 345 is located. In the present case, two temperature sensors 345 are provided, which are arranged offset relative to one another by approximately 90° with respect to a direction of extension of the cable 225. The temperature sensors 345 are each configured to detect a temperature at the surface of the cable 225. A corresponding sensor value can be passed on to the processing device 340.The processing device 340 may determine a temperature in a lower layer of the cable 225 based on the sensor values. Thus, a temperature influence on different layers or elements 305 to 320 of the cable 225 can be determined. Based on a determined heating, a state of aging of the cable 225 may be determined. On the basis of the state of aging, a frequency-dependent electrical parameter of the cable 225 can be determined.In order to adapt the frequency-dependent electrical parameter, one or more adjusting devices 350 may be provided in order to move the receptacle 325 with respect to a fastening element 355 which is configured to be attached to the motor vehicle 105. In the embodiment shown, two adjustment devices 350 are provided, which are mounted offset relative to one another by approximately 90° with respect to a direction of extension of the cable 225. An adjustment device 350 can be configured to move the cable 225 on one side or two sides along a predetermined line. With respect to the illustration in FIG. 3, one adjustment device 350 is provided for the horizontal adjustment and another for the vertical adjustment of the receptacle 325 with respect to the fastening element 355. The adjusting devices 350 can be actuated by the processing device 340.A position of the receptacle 325 controls a course of the cable 225 in the region of the cable holder 300. An influence on a frequency-dependent electrical parameter of the cable 225 can be brought about by a distance of the cable 225 from the fastening element 355, the motor vehicle 105, an adjacent cable 225 or an optional element 360 which can be provided in the region of the cable 225. The element 360 may be magnetizable and interact with an alternating electromagnetic field which is formed in the vicinity thereof on the basis of a current flowing through the cable 225.FIG. 4 shows a flow diagram of an example method 400. The method 400 can be implemented in particular by means of a cable holder 300.In a step 405, a magnetic field in the region of the cable 225 can be converted into a voltage. The magnetic field may be formed depending on a current flowing through the cable 225. An electrical voltage can be derived from the magnetic field by means of the coil 330, which electrical voltage can be processed by means of the matching circuit 335 into a voltage which can be used for operating a further element of the cable holder 300 and thus for carrying out the remaining method 400.In a step 410, a temperature prevailing at the surface of the cable 225 can be determined. For this purpose, sensor values of one or more temperature sensors 345 may be determined. In a step 415, a depth temperature prevailing below the surface at a predetermined depth in the cable 225 may be determined. The temperature is essentially caused by heating of a wire 305 due to an electric current flowing through it. This heating can be conducted outward through further layers 310 to 320 as far as the surface of the cable 225. A temperature profile along the cable 225 at a predetermined depth may be substantially constant.In a step 420, a state of aging of the cable 225 may be determined based on a temperature of the cable 225. In a step 425, a frequency response of the cable 225 can be determined on the basis of the state of aging. The frequency response may describe the progression of a predetermined electrical parameter over the frequency of a current flowing through the cable 225.Optionally, the frequency response of the cable 225 may be adjusted by adjusting its geometric profile in a predetermined manner. For this purpose, a horizontal course of the cable 225 in the region of the cable holder 300 can be adapted in a step 430 and / or a vertical course can be adapted in a step 435. For this purpose, respectively assigned adjusting devices 350 can be suitably controlled. Directions along which an adjustment can take place are preferably perpendicular to one another and do not have to run parallel to the vertical or horizontal. The adjustment can change the parameter by bending the cable 225, so that geometric relationships of its structure change. The parameter can also be changed because a distance to a magnetizable element 105, 355, 360 or to a further cable 225 is changed.By the control, the frequency response can be approximated to a predetermined frequency response which, for example, was originally mastered for the cable 225. With regard to the predetermined frequency response, the energy store 125 or the current transformer 120 can be adapted with regard to the electric drive machine 115. By changing the course of the cable 225, this adjustment can be restored if an electrical parameter of the cable 225 changes due to aging.Reference numerals denote reference numerals100 System 105 Motor vehicle 110 Electric drive axle 115 Electric drive machine 120 Current transformer 125 Electric energy store 130 Drive wheel 205 Half bridge 210 Current valve 215 Control device 220 Intermediate circuit capacitor 225 Cable 300 Cable holder 305 Core 310 First insulator 315 Shield 320 Second insulator 325 Receptacle 330 Coil 335 Matching circuit 340 Processing device 345 Temperature sensor 350 Adjusting device 355 Fastening element 360 Element 400 Method 405 Provide voltage from magnetic field 410 Surface temperature determine 415 Depth temperature determine 420 Aging state determine 425 Frequency response determine 430 Horizontal profile match 435 Vertical profile

Claims

Cable holder (300) for use in a motor vehicle (105), wherein the cable holder (300) comprises: a receptacle (325) for the cable (225); a fastening element (355) for attachment to the motor vehicle (105); a temperature sensor (345) for sensing a temperature of the cable (225); a processing device (340) for determining a frequency-dependent electrical property of the cable (225) on the basis of the temperature.The cable holder (300) of claim 1, wherein the frequency dependent characteristic comprises a frequency response.Cable holder (300) according to Claim 1 or 2, wherein the processing device (340) is configured to determine a state of aging of the line on the basis of a temporal profile of its temperature; and to determine the frequency-dependent electrical property on the basis of the determined state of aging.Cable holder (300) according to one of the preceding claims, wherein the temperature sensor (345) is configured to sense a temperature at the surface of the cable (225); wherein the processing device (340) is configured to determine the temperature in a lower layer of the cable (225).Cable holder (300) according to one of the preceding claims, further comprising a mechanical adjustment device (350) which is configured to move the receptacle (325) with respect to the fastening element (355) in order to change a course of the cable (225) in the region of the cable holder (300).Cable holder (300) according to claim 5, wherein a magnetizable element is arranged in the region of the cable (225); wherein the course of the cable (225) can be changed with respect to the element by means of the adjustment device (350).Cable holder (300) according to either of Claims 5 and 6, comprising a further receptacle (325) for a further cable (225) and a further mechanical adjustment device (350) which is configured to move the further receptacle (325) with respect to the other receptacle (325) of the cable holder (300).Cable holder (300) according to claim 7, wherein receptacles (325) for three cables (225) are provided.Cable holder (300) according to one of the preceding claims, further comprising a coil (330) in the region of the receptacle (325); and a matching circuit (335) for providing a predetermined voltage on the basis of an alternating voltage provided by the coil (330) when alternating current has flowed through the cable (225).The cable holder (300) of claim 9, wherein a plurality of coils (330) are provided that are connected to the matching circuit (335).Cable holder (300) according to one of the preceding claims, wherein the cable (225) is configured to conduct an electric travel current flowing through an electric drive machine (115) of the motor vehicle (105).An electric drive axle (110) comprising a cable holder (300) according to any preceding claim.Motor vehicle (105) comprising a cable holder (300) according to one of the preceding claims.Method (400) carried out by means of a cable holder (300) according to one of claims 1 to 11, wherein the method comprises the following steps: detecting (410) a temperature at a surface of a cable (225); and determining (420) a frequency-dependent electrical property of the cable (225) on the basis of the temperature.

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