System and method for inductively transferring ac power and self alignment between a vehicle and a recharging station

Abstract

A method and apparatus for hands free inductive charging of batteries for an electric vehicle is characterized by the use of a transformer having a primary coil connected with a charging station and a secondary coil connected with a vehicle. More particularly, the when the vehicle is parked adjacent to the charging station, the primary coil is displaced via a self alignment mechanism to position the primary coil adjacent to the secondary coil to maximize the inductive transfer of charging current to the secondary coil. The self alignment mechanism preferably utilizes feedback signals from the secondary coil to automatically displace the primary coil in three directions to position the primary coil for maximum efficiency of the transformer.

1 . A power transformer, comprising:
 a first core including first, second, and third pole areas; and   a second core including first, second, and third pole areas, and wherein   the first core and the second core are separated by first, second, and third air gaps,   the first air gap separating the first pole of the first core and the first pole of the second core, the second air gap separating the second pole of the first core and the second pole of the second core, and the third air gap separating the third pole of the first core and the third pole of the second core.   
     
     
         2 . The power transformer according to  claim 1 , wherein
 the first core further comprises a first winding area wrapped about a first conductive material connected with a primary voltage source;   the second core further comprises a second winding area wrapped about a second conductive material configured to provide current;   the first, second, and third poles of the first core, and the first, second, and third poles of the second core are substantially similar in size and shape;   the first and second windings are substantially similar in cross sectional area; and   a ratio of surface area of the first pole to the cross sectional area of the first winding area is between about a 2.0 and about 5.0.   
     
     
         3 . The power transformer according to  claim 2 , wherein the ratio of surface area of the first pole to the cross sectional area of the first winding area is about 3.2. 
     
     
         4 . The power transformer according to  claim 1 , wherein power input to the primary core is inductively coupled through the first, second, and third air gaps to the second core. 
     
     
         5 . The power transformer according to  claim 1 , wherein the first core and the second core are shaped like a flared “C”. 
     
     
         6 . A system for charging a rechargeable battery, comprising:
 a power transformer including
 a first core, the first core including first, second, and third pole areas; and 
 a second core, the second core including first, second, and third pole areas, and wherein
 the first core and the second core are separated by first, second, and third air gaps, 
 the first air gap separating the first pole of the first core and the first pole of the second core, the second air gap separating the second pole of the first core and the second pole of the second core, and the third air gap separating the third pole of the first core and the third pole of the second core; and 
 
   a semi-permeable magnetic membrane comprising an epoxy binder and a ferromagnetic material embedded within the epoxy binder, wherein
 the semi-permeable magnetic membrane coats each of the first, second, and third poles on the first core, and 
 the semi-permeable magnetic membrane coats each of the first, second, and third poles on the second core, 
 the first core is electrically connected to a primary voltage source, and 
 the second core is located apart from the first core until recharging occurs and further is electrically connected to the rechargeable battery. 
   
     
     
         7 . The system for recharging according to  claim 6 , wherein the ferromagnetic material includes at least one of iron and steel. 
     
     
         8 . The system for recharging according to  claim 6 , wherein the semi-permeable magnetic material comprises a mixture of between 30% and 90% iron or steel filings in an epoxy binder. 
     
     
         9 . An inductively coupled battery recharging system, comprising:
 a first inductive winding coupled to an exterior power source and including
 a first core, 
 a first winding area of the first core including a first winding cross sectional area A WC1 ; 
 a first pole section of the first core including a first pole sectional area A C1P1 , a second pole section of the first core including a second pole sectional area A C1P2 , and a third pole section of the first core including a third pole section area A C1P3 , wherein A C1P1 , A C1P2 , and A C1P3  are substantially similar in shape and size; and 
   a second inductive winding coupled to a rechargeable battery and including
 a second core, 
 a second winding area of the second core including a second winding cross sectional area A WC2 ; 
 a first pole section of the second core including a first pole sectional area A C2P1 , and a second pole section of the second core includes a second pole sectional area A C2P2 , and a third pole section of the second core including a third pole sectional area A C2P3 , wherein A C2P1  and A C2P2  and A C2P3  are substantially similar in shape and size, A WC1  and A WC2  are substantially similar in shape and size, and A C1P1  and A C1P2  and A C1P3  and A C2P1  and A C2P2  and A C2P3  are substantially similar in shape and size, and further wherein,
 when the ratio of the area of the pole of the core to the area of the winding of the core is between 2.0- and 5.0, both a first magnetic flux area formed between the first pole of the first core and the first pole of the second core, and a second magnetic flux area formed between the second pole of the first core and the second pole of the second core, and a third magnetic flux area formed between the third pole of the first core and the third pole of the second core are substantially contained, respectively, within a first volume formed by the cross sectional areas of the first pole of the first core and the first pole of the second core, and the second pole of the first core and the second pole of the second core, and the third pole of the first core and the third pole of the second core. 
 
   
     
     
         10 . An inductively coupled battery recharging system as defined in  claim 1 , wherein the ratio of the area of the pole of the core to the area of the winding of the core is about 3.2. 
     
     
         11 . An inductively coupled battery recharging system as defined in  claim 9 , and further comprising a semi-permeable magnetic material comprising an epoxy binder and a ferromagnetic material embedded within the epoxy binder for coating said first and second poles on said first and second cores, respectively. 
     
     
         12 . An inductively coupled battery recharging system as defined in  claim 11 , wherein the ferromagnetic material includes at least one of iron and steel. 
     
     
         13 . An inductively coupled battery recharging system as defined in  claim 11 , wherein the semi-permeable magnetic material comprises a mixture of between 30% and 90% of at least one of iron and steel filings in an epoxy binder. 
     
     
         14 . A method for increasing the efficiency of energy transfer in a transformer having at least two cores, each core having at least two poles, comprising the steps of
 embedding a ferromagnetic material into an epoxy binder to provide a semi-permeable magnetic material; and   applying the semi-permeable magnetic material to the at least two poles of each core.   
     
     
         15 . The method of claim, wherein said embedding step comprises forming a mixture of between 30% and 90% of at least one of iron and steel filings in the epoxy binder. 
     
     
         16 . Apparatus for inductively charging a battery in a vehicle, comprising
 (a) a fixture; and   (b) a transformer including
 (1) a primary coil mounted on said fixture; and 
 (2) a secondary coil mounted on the vehicle, 
   whereby when the vehicle is positioned adjacent to said fixture and said secondary coil is opposite said primary coil and power is supplied to said primary coil, inductive power is transmitted to said secondary coil to charge the vehicle battery.   
     
     
         17 . Apparatus as defined in  claim 16 , wherein said fixture includes a movable interface plate, said primary coil being mounted on said interface plate. 
     
     
         18 . Apparatus as defined in  claim 17 , and further comprising means for displacing said interface plate to position said primary coil proximate to said secondary coil. 
     
     
         19 . Apparatus as defined in  claim 18 , wherein said displacing means comprises a guide plate mounted on said interface plate, said guide plate engaging a member on said vehicle and being displaced relative to said vehicle member to displace said interface plate laterally and longitudinally relative to the vehicle to align said primary and secondary coils. 
     
     
         20 . Apparatus as defined in  claim 19 , wherein said interface plate is pivotally connected with said fixture. 
     
     
         21 . Apparatus as defined in  claim 20 , wherein said displacing means further comprises a spring for pivoting said interface plate vertically to position said primary coil proximate to said secondary coil. 
     
     
         22 . Apparatus as defined in  claim 18 , and further comprising a first control module connected with said fixture and a second control module connected with said second coil said first control module controlling the operation of said first coil and said second control module controlling the operation of said second coil. 
     
     
         23 . Apparatus as defined in  claim 22 , and wherein said first and second control modules include wireless communication devices for sending information between said first and second control modules. 
     
     
         24 . Apparatus as defined in  claim 23 , wherein said first control module is connected with said displacing means to control the movement of said interface plate. 
     
     
         25 . Apparatus as defined in  claim 24 , wherein said displacing means moves said interface plate laterally, longitudinally and vertically to position said first coil proximate to said second coil. 
     
     
         26 . Apparatus as defined in  claim 25 , wherein said communication devices transmit information between said first and second modules relating to the strength of the magnetic field generated by said coils in order to position said interface plate in a position where energy transferred from said first coil to said second coil is maximized. 
     
     
         27 . A method for inductively charging a battery in a vehicle, comprising the steps of
 (a) connecting the secondary coil of a transformer with the vehicle battery and the primary coil of a transformer with a fixture;   (b) positioning the vehicle adjacent to the fixture;   (c) aligning the primary coil with the secondary coil to maximize the inductive transfer of power from said primary coil to said secondary coil, thereby to deliver power to the battery.   
     
     
         28 . A method as defined in  claim 25 , wherein said aligning step includes the steps of
 (a) supplying a low level of AC current to said primary coil to induce AC current in the secondary coil;   (b) measuring the AC current induced in the secondary coil to determine the efficiency of the inductive transfer of power between said coils;   (c) positioning said primary coil to maximize the efficiency of the inductive transfer of power.   
     
     
         29 . A method as defined in  claim 28 , and further comprising the step of transmitting a signal corresponding to the level of induced current in the secondary coil to the fixture to control the positioning of said primary coil. 
     
     
         30 . A method as defined in  claim 29 , and further comprising the step of rectifying the AC current supplied to the primary coil of the transformer.