Abstract:
The invention provides a coil apparatus ( 100 ) for inductive power transmission, comprising an electromagnetic coil ( 102 ) for emitting and/or picking up an electromagnetic field ( 112 ) on a transmission side ( 106 ) of the coil apparatus ( 100 ), and comprising a housing wall ( 104 ), which covers the coil ( 102 ) on the transmission side ( 106 ) and is transmissive to the electromagnetic field ( 112 ). Furthermore, the coil apparatus ( 100 ) comprises a housing medium ( 108 ), which is enclosed by the housing wall ( 104 ) in such a way that, when a through-opening ( 110 ) is formed in the housing wall ( 104 ), the housing medium ( 108 ) passes through the through-opening ( 110 ). Alternatively, a housing vacuum is provided which is enclosed by the housing wall in such a way that, when a through-opening is formed in the housing wall, atmospheric air ( 118 ) passes through the through-opening. Among further aspects, a vehicle comprising such a coil apparatus and a method for inductive power transmission are provided. The method comprises steps of providing an electromagnetic coil ( 102 ) for emitting and/or picking up an electromagnetic field ( 112 ), covering the coil ( 102 ) on a transmission side ( 106 ) with a housing wall ( 104 ) which is transmissive to the electromagnetic field ( 112 ), enclosing a fluid ( 116 ) with an internal pressure which is different than the atmospheric air by the housing wall ( 104 ),

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a method and a coil apparatus for inductive power transmission. The invention also relates to a vehicle comprising a coil apparatus of this type. 
         [0002]    Although applicable to any coil apparatuses for inductive power transmission, the present invention will be presented, without loss of generality, on the basis of the example of coil apparatuses for contactless, inductive charging of batteries of electrically operated vehicles. 
         [0003]    Electric vehicles, which nowadays are tested as prototypes or in test fleets, are equipped with coil apparatuses of this type, which comprise one or more electromagnetic coils installed in an insulating plastics housing and which are usually mounted on the vehicle underbody or are embedded therein, such that they constitute the lowest parts on the vehicle underbody. This makes it possible to start the charging process comfortably without delay as soon as the vehicle is stopped at a charging point equipped with a corresponding further coil apparatus arranged on the ground. 
         [0004]    When traveling over curbs or poor-quality stretches of road, however, it is routinely expected in the case of road vehicles of conventional design that the underbody will contact or scrape along the curb/road surface. Such contact leads to damage at the lowest parts of the vehicle underbody. In the event of mechanical damage with damage to the insulation of the coil apparatus, an electric shock caused by insufficiently insulated voltage is to be anticipated in the event of contact. The same is true for coil apparatuses arranged on the ground, which apparatuses for example lie on the floor of a garage or on the ground at a parking space or are embedded therein and may be damaged when driven over or when scraped over. It is thus desirable to avoid the risk of electrical accidents with electric shock when using coil apparatuses for inductive power transmission. 
       SUMMARY OF THE INVENTION 
       [0005]    Accordingly, a coil apparatus for inductive power transmission is provided, comprising an electromagnetic coil for emitting and/or picking up an electromagnetic field on a transmission side of the coil apparatus, and comprising a housing wall, which covers the coil on the transmission side and is transmissive to the electromagnetic field. The coil apparatus may also comprise a plurality of coils and may be designed for inductive power transmission also on other sides. The coil apparatus has a housing medium, which is enclosed by the housing wall in such a way that, when a through-opening is formed in the housing wall, the housing medium passes through the through-opening. As the housing medium passes through the through-opening, the housing medium thus leaves the space in which it is enclosed by the housing wall. The housing medium may be a suitable chemical substance or a suitable substance mixture, wherein the type of the housing medium and the conditions of the enclosure are coordinated with one another, such that, when a through-opening is formed, the housing medium is discharged, for example by diffusion, by vibration as the through-opening itself is formed, or by an existing or subsequently produced pressure difference. 
         [0006]    In accordance with a further aspect a method for inductive power transmission is provided. The method comprises steps of providing an electromagnetic coil for emitting and/or picking up an electromagnetic field, covering the coil on a transmission side with a housing wall which is transmissive to the electromagnetic field, enclosing a fluid with an internal pressure that is different from the atmospheric air by means of the housing wall, sensing the internal pressure, assessing whether the internal pressure reaches a predefinable internal pressure threshold value, and emitting a signal when the internal pressure reaches the internal pressure threshold value. 
         [0007]    The inventive coil apparatus makes it possible to reliably avoid electric accidents with a coil used for inductive power transmission, even in the event of mechanical damage from the transmission side. With normal operation the housing wall, since it covers the coil on the transmission side, firstly prevents any direct contact of live parts of the coil by the user. Even with a relatively small amount of damage, for example caused by mechanical impacts on the coil apparatus which might not break through the housing wall, the user remains protected against electric accidents by the housing wall still providing an intact covering of the coil. Lastly, in the event of damage so significant that the coil may be exposed, a through-opening is also inevitably created in the housing wall between the coil and the object acting mechanically from the transmission side, such that, in accordance with the invention, the housing medium passes through the through-opening. This makes it possible to determine the presence of the damage by suitable monitoring of the housing medium, without having to accurately locate the damage itself, such that, for example by being switched off, the inductive power transmission is immediately terminated and a continued endangerment by exposed live parts can be avoided. 
         [0008]    In accordance with a preferred development of the coil apparatus the housing medium has a dye. On the basis of the leaked dye this allows a user of the coil apparatus to notice in a particularly simple manner, merely by visual inspection, any damage to the coil apparatus where the housing wall has been broken through, so as to then be able to take safety measures, such as switching off the coil apparatus, or to carry out a repair. The dye is preferably formed as a colored powder, which is particularly easily noticeable, since it quickly distributes over a large area once it has passed through the through-opening. 
         [0009]    In accordance with a preferred development the housing medium has a fluid with an internal pressure that is increased compared with atmospheric air. By way of example, the pressurized fluid can be formed as air, another gas, or a liquid. If the through-opening is formed, the fluid thus passes outwardly through said through-opening, which leads to a particularly reliable drop of the internal pressure in the space enclosed by the housing wall, which drop in internal pressure can be determined for example with the aid of a pressure gauge. The fluid preferably comprises a liquid and/or a gel. This enables a particularly reliable determination even of damage with minimal through-openings, since, on account of the virtual incompressibility of liquids and gels, even minimal amounts of fluid discharging through the through-opening lead to a drastic, easily determinable drop of the internal pressure. 
         [0010]    In accordance with a preferred development the coil apparatus also comprises an internal pressure sensor, which senses the internal pressure, and a signal unit, which outputs a signal when the internal pressure falls below a predefinable internal pressure threshold value. This makes it possible to monitor the coil apparatus continuously in an automated manner for the presence of potentially endangering damage, such that a particularly high level of safety is attained alongside comfortable use. 
         [0011]    In an alternative aspect, the invention provides a coil apparatus, in which, instead of the housing medium, which is enclosed by the housing wall in such a way that when a through-opening is formed in the housing wall the housing medium passes through the through-opening, a housing vacuum is used, which is enclosed by the housing wall in such a way that, when a through-opening is formed in the housing wall, atmospheric air passes through the through-opening. Here, the signal unit, by contrast, is configured to output the signal when the internal pressure exceeds the predefinable internal pressure threshold value. The term “housing vacuum” is not only understood to mean an ideal vacuum, but in the further sense is also understood to mean a housing medium that comprises a fluid, in particular air or another gas or gas mixture, with an internal pressure that is reduced compared to atmospheric pressure. 
         [0012]    In accordance with a preferred development the coil apparatus also comprises an external pressure sensor, which senses an external pressure of the atmosphere. Here, the signal unit comprises a threshold value determination unit, which determines the internal pressure threshold value depending on the external pressure. This makes it possible to avoid false signals as a result of fluctuations of the atmospheric pressure and thus makes it possible to achieve a particularly high level of safety, without the need for an internal pressure deviating excessively from atmospheric pressure and for corresponding structural outlay, such as an excessive thickness of the housing wall. 
         [0013]    In accordance with a preferred development the housing wall comprises an inner wall and an outer wall, which cover the coil on the transmission side. This means that the housing wall is designed on the transmission side in a double-walled manner. This on the one hand makes it possible to configure the coil apparatus with a very low volume of the housing medium, which is advantageous in terms of material costs and the overall weight of the coil apparatus, depending on the housing medium used. In addition, since the coil itself is located outside the space filled by the housing medium, maintenance and inspection of the coil are facilitated. In accordance with an alternative development the housing wall surrounds the coil, which allows a saving of wall material, since a double-walled embodiment of the housing wall is unnecessary. 
         [0014]    In a further aspect the invention provides a vehicle comprising an electric accumulator, which comprises a coil apparatus of this type for inductive power transmission to the electric accumulator. The coil apparatus is preferably arranged on an underbody of the vehicle, wherein the transmission side points downward. This makes it possible to arrange the coil apparatus particularly low above the ground for efficient power transmission with further coil apparatuses located on or in the ground without the risk of increasing electric accidents. The housing wall more preferably covers the coil downwardly and to the side. The protection against electric accidents thus extends to a threat of mechanical damage of the coil apparatus not only from below, but also from the side. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1A  shows a schematic cross-sectional view of a coil apparatus in accordance with an embodiment of the invention; 
           [0016]      FIG. 1B  shows a schematic cross-sectional view of the coil apparatus from  FIG. 1  in a damaged state; 
           [0017]      FIGS. 2 and 3  show schematic cross-sectional views of coil apparatuses in accordance with two different embodiments; 
           [0018]      FIG. 4  shows a schematic side view of a vehicle in accordance with an embodiment; and 
           [0019]      FIG. 5  shows a flow diagram of a method for inductive power transmission in accordance with an embodiment. 
       
    
    
       [0020]    Unless expressly mentioned otherwise, like reference signs in the figures refer to like or equivalent elements. 
       DETAILED DESCRIPTION 
       [0021]      FIG. 1A , in a schematic cross-sectional view, shows a coil apparatus  100 , arranged on the ground  119 , for inductive power transmission by means of an electromagnetic field  112  to a further coil apparatus (not shown), which can be arranged above the upper side of the coil apparatus  100 , designated as the transmission side  106 , and for example can be mounted on an electric vehicle (not shown), which is to stop above the coil apparatus  100 . The coil apparatus  100  comprises a coil  102 , of which the windings are wound on the whole in the form of a flat cylinder, of which the axis of symmetry  101  lies in the drawing plane, and also a housing, which surrounds the coil  102  and likewise has a cylindrical wall  104 . 
         [0022]    The wall  104  of the housing of the coil apparatus  100  is double-walled peripherally with an inner wall  104 ′ and an outer wall  104 ″ made of an electrically non-conductive material, wherein, in order to support the inner wall  104 ′ on the underside of the coil apparatus facing away from the transmission side, spacers  107  are inserted between the inner wall  104 ′ and an outer wall  104 ″. A two-core feed line  103  for feeding electrical power into the coil  102  is guided outwardly through one of the spacers  107 . The space located within the inner wall  104 ′, in which space the coil  102  is located, is filled with a suitable medium, for example an oil, a protective gas, or with air, which for example can be connected via the spacers  107  to the external air of the atmosphere  118  or can be sealed off with respect thereto. 
         [0023]    The space located between the inner wall  104 ′ and outer wall  104 ″ of the housing is hermetically sealed with respect to the atmosphere  118  and is filled by a housing medium  108 , which, besides air at low atmospheric pressure, also contains a dye in the form of a colored powder  114  of any color. The colored powder  114  is selected such that, if released in the event of damage to the outer wall  104 ″, it quickly spreads over a radius of a number of cm or dm and leaves behind easily noticeable traces. In alternative embodiments the housing medium may be enclosed at overpressure between the inner wall  104 ′ and the outer wall  104 ″. 
         [0024]      FIG. 1B  shows the coil apparatus from  FIG. 1  in a damaged state following influence of mechanical force from above, i.e. from the transmission side  106 . Due to the force influence, a small through-opening  110  has formed in the housing wall  104  and extends through an opening in the outer wall  104 ″ and a slightly smaller opening in the inner wall  104 ′ as far as the space located within the inner wall  104 ′, such that the coil  102  located therein is exposed in part. Due to the vibration during the force influence, the housing medium  108  located between the outer wall  104 ″ and inner wall  104 ′ has passed through the through-opening  110  into the atmosphere  118  outside the outer wall  104 ″ and has distributed the colored powder  114  contained in the housing medium  108  at the outer side of the outer wall  104 ″ in a radius of a number of centimeters. In the case of embodiments in which the housing medium is at overpressure with respect to the atmosphere  118 , the overpressure assists the outward passage of the housing medium  108  and therefore the distribution of the colored powder  114 . Due to its arbitrary color, the colored powder  114  is easily noticeable as a colored stain to the user of the coil apparatus  100 , which allows the user to protect themself against the threat of an electric accident by switching off the electrical power feed via the feed line  103 , and allows the user to repair or replace the coil apparatus  100 . 
         [0025]      FIG. 2  shows a coil apparatus  100  in accordance with a further embodiment, said coil device being arranged fully recessed in the ground  119 , such that the housing wall  104  on the transmission side  106  terminates flush with the surface of the ground  119 . In contrast to the embodiment from  FIGS. 1A-B , the housing wall  104  is formed as a single wall, which hermetically surrounds an interior, in which the coil  102  is arranged. A housing vacuum  109  prevails in the interior enclosed by the housing wall  104 , wherein the term “housing vacuum” is not limited to an ideal vacuum, but generally designates a situation in which the interior is filled with air or another gas or gas mixture having an internal pressure p i  that is reduced compared with the atmosphere  118 . In the present embodiment the internal pressure p i  is 100 hPa by way of example. The feed line  103  is guided through the housing wall  104  in a hermetically sealed manner. 
         [0026]    The coil apparatus  100  of the present embodiment also comprises, in the interior enclosed by the housing wall  104 , an internal pressure sensor  120 , which senses the internal pressure p i  and at its output provides a corresponding pressure signal, a signal unit  122 , which is connected to the output of the internal pressure sensor  120  and which compares the internal pressure p i  according to the pressure signal received from the pressure sensor with a threshold value p th  stored previously in the signal unit, for example of 550 hPa, and provides, at its output, a signal  132  corresponding to the comparison result, an alarm device  134 , and a switching device  123 , which are both connected to the output of the signal unit  122 . The alarm device  134  is formed in the present embodiment by way of example as a warning lamp, which in alternative embodiments can be replaced by or supplemented by other warning devices, such as sound generators, or the like. The switching device  123  is formed by way of example in the present embodiment as a relay with a switch contact  133  arranged in the feed line  103 , which switch contact can be replaced in alternative embodiments by a semiconductor switching element, for example. 
         [0027]    In the case of fault-free operation of the coil apparatus  100 , the switch contact  133  is closed, such that the coil  102  is supplied with electrical power via the feed line  103  and generates an electromagnetic field  112  extending toward the transmission side  106 . The internal pressure sensor  120  continuously signals the internal pressure value p i =100 hPa prevailing within the housing wall  104  to the signal unit  122 , which determines that the internal pressure, p i  lies below the internal pressure threshold value p th =550 hPa and accordingly does not emit a signal at its output. Provided the switching device  123  does not receive a signal from the signal unit  122 , it leaves the switch contact  133  closed, such that the coil apparatus  100  continues the generation of the electromagnetic field  112  for inductive power transmission. 
         [0028]    In the event of mechanical damage of the coil apparatus  100 , in which case a through-opening (not shown) is created in the housing wall  104 , air flows from the atmosphere  118 , which for example is at a typical pressure of 1000 hPa, into the interior enclosed by the housing wall  104 , whereby the internal pressure p i  adjusts to atmospheric pressure. The internal pressure sensor  120  signals the internal pressure p i =1000 hPa to the signal unit  122 , which determines that the internal pressure p i  has reached or exceeded the internal pressure threshold value p th =550 hPa and emits a corresponding signal  132  to the switching device  123  and the warning device  134 . Upon receipt of this signal  132 , the switching device  123  switches off the feed of electrical power to the coil  102 , whereas the warning device  134  emits a warning light in order to notify the user. 
         [0029]    In alternative embodiments the internal pressure p i  may be higher than the atmospheric pressure. By way of example the internal pressure may be p i =2000 hPa and the internal pressure threshold value p th  with 1500 hPa as in the present embodiment may be fixed at the mean value between the set internal pressure p i  and the typical atmospheric pressure of 1000 hPa, wherein the signal unit  122  is designed to emit the signal when the internal pressure p i  has reached or fallen below the internal pressure threshold value p th . 
         [0030]      FIG. 3  shows a coil apparatus  100  in accordance with a further embodiment, which is reassessed in the ground  119  up to approximately half the overall height. In the present embodiment the housing wall  104  in the wall portions recessed in the ground  119  is embodied as a single wall, but by contrast is double-walled at the portions of the side walls arranged above the ground  119  and on the transmission side  106 . The space located between the inner wall  104 ′ and outer wall  104 ″ is filled with a liquid as housing medium  108 , which is at an internal pressure p i  that is increased compared with the typical pressure of the atmosphere  118 . By way of example, the internal pressure set when filling the housing medium  108  is p i =3000 hPa. The internal pressure sensor  120  is arranged in the housing medium  108  between the inner wall  104 ′ and outer wall  104 ″, whereas the signal unit  122  connected to the internal pressure sensor  120  is located jointly with the coil  102  in a coil space  105 , which is filled with air at atmospheric pressure and which is enclosed by the inner wall  104 ′ and the portions of the housing wall  104  embodied as a single wall. 
         [0031]    In contrast to the embodiment of  FIG. 2 , the coil apparatus  100  of the present embodiment has an external pressure sensor  121  reaching as far as the outer side of the coil apparatus  100  for sensing the external pressure p o  prevailing in the atmosphere  118  and also a threshold value determination unit  124  arranged in the coil space  105  for determining the internal pressure threshold value p th  depending on the external pressure p o , for which purpose an output of the external pressure sensor  121  is connected to an input of the threshold value determination unit  124 , and an output of the threshold value determination unit  124  is connected to an input of the signal unit  122 . In alternative embodiments the coil space  105  can be connected by suitable pressure compensation openings to the atmosphere  118 , wherein in this case the external pressure sensor  121  may be arranged in the coil space  105 . The housing medium  108  may also alternatively be formed as a gel or a gas or gas mixture, such as air, and may contain a colored powder or another dye for additional safety. 
         [0032]    With fault-free operation of the coil apparatus  100 , the external pressure sensor  121  continuously determines the air pressure p o  in the atmosphere  118  and signals this to the threshold value determination unit  124 . The threshold value determination unit  124  determines the internal pressure threshold value p th  depending on the external pressure p o , for example by forming the mean value from the external pressure p o  and a standard internal pressure p s , which is stored previously in the signal unit and corresponds to the internal pressure p i  of the housing medium  108  set in the undamaged state of the coil apparatus  100 . 
         [0033]      FIG. 4  shows a schematic side view of a vehicle  200 , which has an electric motor  202  fed from a rechargeable battery  206  as electric accumulator for driving the vehicle  200 . The battery  206  is connected via a feed line  103  for charging the battery  206  to a coil apparatus  100  mounted on the vehicle underbody  204 . The coil apparatus  100  contains a coil  102  for inductive power consumption from a transmission side  106 , which points downwardly in this case. Similarly to the coil apparatus in  FIG. 3 , the coil apparatus  100  of the vehicle  200  is located on the transmission side  106  and is covered in a lateral direction by a double-walled housing wall  104 , within which a gel  108  is located at overpressure as housing medium. 
         [0034]      FIG. 4  shows the vehicle  200  in a situation in which it is stopped above a further coil apparatus  100 ′, which is mounted on the ground  119  and which is connected to the mains grid via a supply feed line  103 ′ running in the ground  119 . The further coil apparatus  100 ′ may likewise be formed in accordance with an embodiment of the present invention. 
         [0035]    In the charging mode the further coil apparatus  100 ′ generates, with the aid of the grid power fed via the supply feed line  103 ′, an electromagnetic alternating field  112 , which also penetrates the coil  102  of the coil apparatus  100  mounted on the vehicle underbody  204 . An electrical voltage is hereby induced in the coil  102  and produces a charging current flowing through the coil  102  and the feed line  103  for charging the battery  206 . A signal unit  122  of the coil apparatus  100  monitors the internal pressure p i  by comparing this with a predefined threshold value, and, in the event that the threshold value is undershot, emits a signal  132 , which lights up a warning lamp  134  on the instrument panel of the vehicle  200 . 
         [0036]      FIG. 5  shows a flow diagram of a method for inductive power transmission. At the start of the method a coil for the inductive power transmission is provided in cooperation with a further coil in step  300 . In step  302  the coil is covered by a housing wall on a transmission side, on which the further coil is to be arranged during the inductive power transmission. 
         [0037]    In step  304  a fluid at a predefined internal pressure is arranged as a housing medium in a space enclosed by the housing wall, which space may enclose the coil or may be formed separately within the housing wall. The predefined internal pressure lies above a range in which fluctuations of the atmospheric pressure are to be expected for the intended use. In step  308  the external pressure currently prevailing in the surrounding atmosphere is detected by means of an external pressure sensor. In step  310  an internal pressure threshold value between the predefined internal pressure and the detected external pressure is determined, for example by forming the mean value from the predefined internal pressure and the external pressure detected in step  308 . 
         [0038]    In step  305  an inductive power transmission is started, in that a further coil is arranged on the transmission side covered by the housing wall in step  302  and an electromagnetic alternating field is generated with one of the coils and penetrates the other coil in order to induce an electrical voltage therein. In step  306  the internal pressure currently prevailing in the housing medium is detected by means of an internal pressure sensor arranged in the housing medium. In the branch step  312  it is assessed whether the internal pressure detected in step  306  lies above the internal pressure threshold value determined in step  310 . If this is the case the method reverts to step  306 . If, however, it is determined in the branch step  312  that the internal pressure has fallen since the enclosure of the housing medium in step  304  to such an extent that it reaches or has already undershot the internal pressure threshold value, for example on account of damage to the housing wall, the method jumps to step  314 , in which the coil is switched off in order to interrupt the inductive power transmission. In step  316  an acoustic or optical warning signal for example is emitted in order to notify the user of the incident. 
         [0039]    In a modified embodiment of the method the housing medium is enclosed in step  304  with a predefined internal pressure below the range in which fluctuations of the atmospheric pressure are to be expected for the intended use. In the case of such a modified embodiment the method in the branch step  312  jumps back to step  306  when the internal pressure detected in step  306  is below the internal pressure threshold value determined in step  310 , and jumps to step  314  when the detected internal pressure has risen to such an extent that it has reached or already exceeded the internal pressure threshold value.