Background Art At present, a factor which limits the use of electrical vehicles is the difficuity in charging the electrical battery. Electrical batteries have a much lower energy/weight ratio than the liquid fuel now in use. Therefore, electrical vehicles require "refueling" more often than regular cars. Moreover, the charging process takes more time, because of the limited charging rate of the battery and the large amount of energy to be transferred thereto.

The charging station of the future is perceived to be similar to the gas station of today, with the oil pump and delivery device being replaced with electrical connectors to couple the electrical energy to the car.

The connector installed in the vehicle should not be heavy, to save battery energy- any decrease in the weight of the vehicle reduces the energy required to accelerate it and to overcome friction, and thus contributes to increase the time to the next recharge.

An important consideration is the human engineering of the device, that is the connector should be easy to use. Cumbersome, heavy connectors are not practical for this environment.

Another consideration is reliability, since the charging devices are to be used by nonprofessionals, in a rough environment. Electrical connectors are usually devised to be attached by technicians or other qualified persons, in a laboratory or factory or other clean, controlled environment. Clearly, these conditions cannot be met in charging stations for large scale use.

Still another requirement is high efficiency, that is to transfer electrical energy at minimum losses. This is important both to preserve energy and to protect the delivery system. Energy preservation is important at the company level as well as for the country and worldwide.

Energy losses usually result in energy being dissipated in the connector or other transfer means, which result in overheating and possible damage.

Considering the high power involved, of more than 6 kWatts, even a small percentage of losses may result in undesirable effects.

A system known in the art uses inductive couplers as the electrical connector. Here, electrical energy is transferred through the alternating magnetic field, without a physical contact being required between the two halves of the connector.

The advantage is that there are no electrical contacts to wear down, thus lower losses are achieved. The device is also easier to use.

The magnetic material in these connectors is ferrite.

One disadvantage of these connectors is the relatively large weight; a total weight of about 2.6 kg is typical for such a connector. This makes the connector cumbersome and not so easy to handle.

Another disadvantage is that ferrites are relatively brittle, may break or develop cracks, which result in undesired losses during charging.

Carosa, Paul F., US Patent 5216402, details a separabie inductive coupler for transferring electric power.

Hulsey, US Patent 5264776, Patent Assignee: HUGHES AIRCRAFT CO, details an electric vehicle inductive coupling charge port - includes primary and secondary coil assemblies to form transformer when primary and secondary windings are mated.

The apparatus includes a primary coil assembly which comprises a removable primary winding and an electrical cable coupled between the primary winding and the power source. A secondary coil assembly comprises a housing disposed in the vehicle, a transformer core having a first portion disposed in the housing that has cavity disposed there.

Use: Inductive charging unit that couples electrical power from power source to battery of electric vehicle, allowing safe charging without need for conventional electrical plug.

Gresser, DE 4115568 , details an electric vehicle which uses inductive pick-up from cable buried in street surface through tyres or subframe and homopolar motor.

There is inductive coupling between the subterranean cable (which may be superconducting) and the vehicle. One possible site of the energy receiver (inductive loops) is on an undercarriage which can be lowered from the vehicle subframe. Alternatively inductive pick-up loops are embedded in the vehicle tyres or in the airspace inside the tyres.

NORVIK TECHNOLOGIES INC, US 5202617 / WO 9308630 / EP 610258/ JP 7503837, details a charging station for electric vehicle, which has interface carrying status and control signals between vehicle and controller and lockout preventing delivery of power when connector is not in place.

It is an objective of the present invention to provide for a device with means for solving the above problems.

Disclosure of Invention It is an object of the present invention to provide an inductive oupler device for charging the batteries in electrical vehicles, which s easy to use, is reliable, has a high efficiency and a relatively low cost. This object is achieved with an inductive coupler for vehicles as disclosed in claim 1.

Accordingly, an objective of the present invention is to achieves a robust structure, with low losses and lower weight. This objective is achieved with a device where the magnetic loop in he coupler uses thin ferromagnetic ribbons made of a nanocrystalline amorphous material.

It is another objective of the invention to achieve lower losses and a lighter structure. The objective is achieved with a coupler using a magnetic structure with a minimal air gap and reduced magnetic reluctance.

Moreover, the coupler uses a combination of toroidal cores and planar coils to achieve a concentric structure which is easy to use, can be manufactured at a lower cost and achieves an efficient magnetic field flow.

Another aspect of the present invention is a coupler structure including a magnetic core made of a plurality of thin ribbons oriented along the magnetic flux lines such as to present a minimal magnetic reluctance, while minimizing eddy losses, and including a controlled gap covered with a resistant plastic material, to both minimize losses because of the hysteresis effect and protecting the magnetic ribbons from tear and wear.

Additionally, another embodiment of the coupler uses physical, electrical contacts in lieu of the inductive means. Especially shaped contacts and mechanical coupling means facilitate the efficient transmission of the desired electrical power, while minimizing losses and keeping weight to a minimum.

A complete system according to the present invention may include the inductive coupler with two halves, one mounted in the car and connected to the battery and charging electronics there, and the other half being installed in the charging device, with a structure which allows for a limited distance and including self-searching means for ease of use.

An object of the present invention is to provide an improved system for charging electric vehicles, and to automate the charging process.

Further objects, advantages and other features of the present invention will become obvious to those skilled in the art upon reading the disclosure set forth hereinafter.

Brief Description of Drawings The invention will now be described by way of example and with reference to the accompanying drawings in which: Fig. 1 illustrates the structure and operation of the inductive coupler using a planar coil.

Fig. 2 details the magnetic field circuit for the inductive connector.

Fig. 3 details the inductive connector (vehicle), cross-sectional view.

Fig. 4 details the structure of the inductive connector without ferromagnetic core.

Fig. 5 illustrates the inductive connector with planar ribbon layer, top view.

Fig. 6 details the inductive connector cross-section along lines A-A in Fig. 5.

Fig. 7 details the inductive connector cross-section, another embodiment.

Fig. 8 illustrates the ohmic contacts connector, side view.

Fig. 9 illustrates the ohmic contacts connector, front view.

Fig. 10 details the ohmic contact area.

Fig. 11 details the ohmic contact tooth, cross-sectional view along lines B-B in Fig. 10.

Fig. 12 details the current distribution around the ohmic contact tooth.

Fig. 13 illustrates an electrical charging system.

Fig. 14 details high frequency electrical current flowing through the electrical connector.

Modes for Carrying out the Invention A preferred embodiment of the present invention will now be described by way of example and with reference to the accompanying drawings.

Referring to Fig. 1, an example of an inductive coupler according to the present invention, one half of the coupler is detailed, the other half (not shown) being identical thereto. Outer ferromagnetic toroid 11 with inner ferromagnetic toroid 12 and ferromagnetic base 13 form the magnetic circuit which transfers the magnetic flux between the halves of the connector, to accomplish the inductive coupling as desired.

In the present invention, "ferromagnetic" is meant to include soft ferromagnetic materials, which have minimal residual magnetivity.

Planar coil 17 is connected to the AC electrical source (not shown) to create the magnetic field for the inductive coupler. Coil 17 has about 4 to 13 planar turns. For automotive charging purposes, the primary voltage is about 400 V, at a current of about 16.5 A, to transfer about 6.6 kWatts of electrical power for charging the battery in the car.

Terminals 172 at the ends of coil 17 are connected to the electrical source through openings (not shown) in toroid 12 or base 13.

The connector as shown features a circular symmetry, for ease of use.

Thus, the connector halves can be coupled in any relative orientation (that is, any angle of rotation therebetween), without any deterioration in performance.

Referring to Fig. 2, which details the magnetic field circuit for the inductive connector comprising halves 1 and 2, outer ferromagnetic toroid 11 in charger connector (primary), with inner ferromagnetic toroid 12 and ferromagnetic base 13 form the magnetic circuit in part 1.

The present disclosure includes several embodiments or variants of the invention.

Figs. 1 and 2, together with the related description, refer to the first variant of the invention.

The toroids comprising each half of the connector are mounted together so that the toroidal central axes coincide.

The system may be engineered so as to work in the 105 kHz to 370 kHz preferred frequency range.

Magnetic flux is coupled to outer ferromagnetic toroid 21 in vehicle connector 2 (secondary), which is mounted on the roof or the bottom of the vehicle (not shown). Inner ferromagnetic toroid 22 and ferromagnetic base 23 close the magnetic loop, with magnetic flux 3 coupling primary 1 to secondary 2. The alternating magnetic flux 3 flowing between primary 1 and secondary 2 thus transfers the electrical energy required to charge the battery (not shown) in the vehicle.

Fig. 3 details the inductive connector (vehicle), cross-sectional view.

The parts of the connector are shown separate from each other, for clarity.

Outer ferromagnetic toroid 11 comprises a ribbon of ferromagnetic amorphous material wound into a toroidal shape as shown. The cross section details the orientation of the ribbon layers, in the vertical direction. This is required such as to provide low magnetic reluctance to the flux passing in the vertical direction through toroid 11. This structure also minimizes losses in the toroid 11 because of eddy current, since the induced current cannot pass between adjacent layers but is confined to each single layer, which presents a high resistance because of the thin ribbon used.

Toroids 11 and 12 have the same height, thus the magnetic structure has a minimal air gap and reduced magnetic reluctance, to achieve lower losses and a lighter structure. The ribbon is made of nanocrystalline ferromagnetic material, having a relative magnetic permeability tr of about 160,000 to 300,000. Because of the large magnetic permeability tr and the reduction of the air gap, a smaller core is achievable. The weight is reduced by about 1.2 to 1.4 kg. Whereas previous connectors installed in the car had a weight of about 2.3 kg, the present connector has a weight installed in the car of only 0.6 to 0.7 kg.

There is isolation between adjacent layers because the ribbon is coated with an isolating layer. Usually, the ribbon as is produced with the rapid quench process has an isolating layer thereon; if not, then the isolation layer is applied at a later stage.

Whereas toroids 11 and 12 are shown separated from base 13 for the sake of clarity, it is to be understood that they are firmly attached to base 13 such as to minimize any possible air gaps therebetween, to minimize the magnetic reluctance.

Inner ferromagnetic toroid 12 is also made of a ferromagnetic amorphous ribbon, wound around itself. Whereas toroid 11 is made with a central hole therein, toroid 12 is a full or almost full cylinder.

Ferromagnetic base 13 is preferably made of thin layers of amorphous ribbon, cut into a circular shape (not shown). Thus, magnetic flux passes along the ribbons in toroid 11, base 13 and toroid 12 and to the other half (not shown) of the inductive connector. The structure presents minimal reluctance to the magnetic flux, for efficient, wideband magnetic coupling.

At the same time, the structure offers a large resistance to the eddy currents, to minimize losses in the coupler.

Whereas toroids 11 and 12 are shown separated from base 13 for the sake of clarity, it is to be understood that they are firmly attached to base 13 such as to minimize any possible air gaps therebetween, to minimize the magnetic reluctance.

Planar coil 17 is mounted between toroids 11 and 12, such that passage of alternating current in coil 17 results in an alternating magnetic flux in toroids 11 and 12 and in base 13, in a path as depicted in Fig. 2 above.

The layers of base 13 are preferably made of circular sheets stamped out of a long, wide ribbon of ferromagnetic amorphous material. If a large diameter of base 13 is required, which may require too wide a ribbon, then half circles (not shown) may be cut off the ribbon, such that a ribbon half as wide (width equal to radius of circle) is required.

Circle halves are mounted side by side to form a complete circle. Adjacent layers preferably have the layers at different angle, to increase mechanical strength. The dividing line between the half circles does not interfere with the magnetic flux passage, since magnetic flux (not shown) flows along radial lines, thus in parallel with the line between the half circles.

Fig. 4 details the structure of the inductive connector without a ferromagnetic core.

The inductive coupler works as follows: High frequency current passing through coil 17, creating magnetic flux 3 (see Fig. 2). The magnetic flux 3 passes through toroids 21, 22 and 23, creating an alternating flux through coil 27 (see Fig. 4) . The alternating flux induces the secondary voltage across the terminals of secondary coil 27.

The secondary coil 27, through its terminals 272, is connected to the electric battery (not shown) in the vehicle, through a voltage rectifier means (not shown). Thus, the induced voltage in the secondary coil of the connector is used to charge the battery.

Planar coil 17 (primary) is mounted on an isolating, non-ferromagnetic case (not shown), which protects the coil 17 from the environment, and also includes a handle for holding it.

Coil terminals 172 are used to connect coil 17 to a source of electrical energy (not shown). Similarly, planar coil 27 (secondary) with coil terminals 272 is enclosed in a non-ferromagnetic case and connected to the charging means and battery in the vehicle (not shown).

The structure of coils 17 and 27, together with their corresponding cases, is such as to place coils 17, 27 close to each other and in the proper relative orientation, to allow good inductive coupling therebetween.

The advantage of this structure is lower losses, since core losses (in the ferromagnetic material) are eliminated. The losses in the air and in isolators are minimal. This structure also has a lower cost, since no ferromagnetic material is required.

A possible disadvantage of this structure is the inductance in the circuit, because of the magnetic flux spreading. This may decrease the electrical power transferred to the secondary. One possible way to correct this effect is to increase the power in the primary. Another method is to use a matching unit, to connect a capacitor in the circuit. The inductance is fixed, deriving from the geometry of the coils 17, 27 and their relative position. The capacitor may include means (not shown) for changing its value, to match the varying inductance which depends on the operating frequency.

Another disadvantage of this circuit is the magnetic alternating flux surrounding the connector. Undesired currents may be induced in any conducting material close to the connector. To prevent or minimize this effect, outer magnetic shields 18 and 28 (optional) are used to confine the magnetic field in the space close to coils 17 and 27.

Shields 18 and 28 preferably have a circular shape, adapted to the shape and size of coils 17 and 27.

Fig. 5 illustrates the inductive connector with a planar ribbon layer, top view.

Outer magnetic shield 18 is used to confine the magnetic field close to the coils (not shown), as detailed above with respect to Fig. 4.

Shield 18 includes alternate layers, each including ferromagnetic ribbons at a predetermined angle of orientation, which is different from the orientation of ribbons in adjacent layers. In the embodiment illustrated in Fig. 5, this feature of the present invention is illustrated with a layer of amorphous ribbons 182 with an horizontal orientation, and an adjacent layer of amorphous ribbons 183 with a vertical orientation.

The angle difference between adjacent layers may have other values, for example 30 degrees or 60 degrees. A difference not a submultiple of 360 degrees may be used, such that every layer defines a different direction, and a multitude of thin layers provide virtually all the desired radial directions for the magnetic flux.

The advantage of this variable orientation is that on average there are several ribbons leading from the center of shield 18 to its periphery, in every radial direction. Thus, a symmetrical structure is achieved, to close the magnetic circuit irrespective of the relative rotational orientation between the two halves of the connector.

The abovedetailed structure offers a low magnetic reluctance path for the magnetic flux generated in the coil (not shown) of the coupler, to guide the flux from the inner part of the coil to its outer part, thus to close the magnetic circuit.

Another advantage of this structure is that, although there are ribbons in various directions, the width of the shield 18 is constant.

In another embodiment (not shown), ribbons in each layer have a radial orientation, that is each ribbon spans the distance from the center of the circle of shield 18 to its periphery. This structure offers an improved, lower magnetic reluctance in the various radial directions, but the width of the shield 18 is no more uniform. The shield is thick at the center, and thin at the periphery.

The magnetic ribbons 182, 83 are made of soft ferromagnetic materials as known in the art, in a nano-crystalline or amorphous state. The ribbons are preferably about 2 to 20 wide and about 20 to 25 microns thick.

The distance between ribbons in the same layer should be about 0.2 mm to 1 mm. Thickness of insulation between adjacent layers should be minimal, for example about 5 microns.

The total number of layers is set according to the expected energy to transfer and the required magnetic flux, and such as not to bring the ribbons close to magnetic saturation, in which case losses increase rapidly.

Because the structure includes very thin ribbons, and considering the skin effect at these frequencies which results in current only on the surface of the conductors, the electrical resistance to eddy currents is very high, this minimizing losses in the magnetic core of the connector.

For example, at a frequency of 370 kHz, current passes on a depth of about 0.0184 mm, resulting in a resistance of about 400 ohm, and a resulting current of only 0.015 A.

To transfer a power of 6.6 kWatt at a frequency of 370 kHz, a connector having an external diameter of about 340 mm is used. The height of each half of the connector is about 4.0 mm. The minimal thickness of the magnetic layer is about 0.715 mm, and the mass of each connector half is 0.4 kg. The losses in the magnetic core are near 90 Watt, and the maximum magnetic induction is B= 0.179 T.

Variant 2 According to this variant, see Fig. 6, there is provided a high frequency air transformer with open core. The transformer consists of parts 1 and 2 for the transmission of the charging current. Parts 1 and 2 may have identical shape and form, or may have otherwise complementary shapes.

Part 1 consists of plane primary coil 17, which is fitted to an insulation base 185. Coil terminals 172 (see Fig. 4) are used to connect coil 17 to a source of electrical energy (not shown). Plane magnetic core 18 is situated at the output surface of the primary winding 17.

The magnetic core diameter is equal to the primary winding diameter.

Core 18 is formed of alternate layers of amorphous or nanocrystalline alloy ribbons 182,183.

Part 2 consists of secondary coil 27, insulation base 285 and magnetic core 28 with layers 282, 283 respectively (see Fig. 6). Secondary coil 27 is connected to the battery (not shown) in the vehicle, through coil terminals 272 and through a voltage rectifier (not shown).

Amorphous or nanocrystalline ribbons may preferably have a width of about 2 to 20 mm and a thickness of about 20 - 25 microns.

The ribbons in each layer are parallel to each other, with a distance between ribbons of about 0.2 to 1 mm. There is insulation between adjacent layers, of a thickness of about 5 microns for example.

The ribbons of each layer have a predetermined angle of orientation, which is different from the orientation of ribbons in adjacent layers.

For example, in the embodiment illustrated in Fig. 5, there is a layer of amorphous ribbon 182 with an horizontal orientation and an adjacent layer of amorphous ribbon 183 with a vertical orientation.

Similarly, magnetic core 28 includes layers of amorphous ribbons 282 and 283 with different orientations.

The angle difference between adjacent layers may be different from normal, for example 30 degrees or 60 degrees.

The operation of the inductive coupler is as follows: Coil 17 is connected to a high frequency electrical source (not shown).

High frequency current in coil 17 creates a magnetic field 3.

The magnetic field 3 passes through layers 182 and 183 and replaces the current of coil 17 to the coil surface, which faces coil 27 (see Fig. 6) . This improves the interaction between coils 17 and 27.

Magnetic flux 3 passes through coil 27 and induces a secondary voltage across terminals 272 at the ends of coil 27.

This voltage and its corresponding current are connected to the electric battery in the vehicle, through terminals 272 and a voltage rectifier (not shown).

Magnetic cores 18 and 28 include alternating layers of amorphous ribbon with a predetermined angle of orientation, which is different from the orientation of ribbons in adjacent layers. Thus a symmetrical structure is achieved, due to the multitude of thick alternate ribbons, and consequently an optimal path for the magnetic flux is achieved. This structure offers a lower magnetic reluctance for the magnetic flux 3.

The transformer may operate in a 105 kHz to 370 kHz preferred frequency range, and it is necessary to consider the skin effect at these frequencies, which results in current only on the surface of the ribbons. Moreover, it is necessary to consider such ribbon characteristics as magnetic resistance m and electrical resistance r For amorphous ribbons, m =3000 and r = 150E-8 Ohm* m.

Thus, due to skin effect and such values of magnetic and electrical resistance, the electrical resistance to eddy current is very high and this minimizes losses in magnetic core.

Following are examples of several embodiments of the inductive coupler which were manufactured and tested.

The inductive couplers were made with different coil winding numbers and different external coil winding diameters. The winding number (number of turns) was between 4 to 17 and the external diameter was between 130 mm and 440 mm. The windings were made of copper sheet 1.2 mm thick, using a laser. The magnetic core was made of amorphous ribbons 22 micron thick and 20 mm wide.

Tests of these inductive couplers were conducted, with the following parameters: Power = 4.5 kWatt Frequency = 330 kHz Load resistance = 24 Ohm The tests indicated good results for these embodiments.

Fig. 6 details the inductive connector, in a view in cross-section along lines A-A in Fig. 5.

Outer magnetic shield 18 (primary) is used to confine the magnetic field close to coil 17. Layers of amorphous ribbons in one direction, illustrated here with ribbons 182 in a horizontal orientation or in the plane of the drawing, are deposited alternating with layers of ribbons in a normal direction to the adjacent layer, illustrated here with ribbons 183 in a normal orientation or normal to the plane of the drawing.

Planar coil 17 (primary) is located close to the other coil, 27, with the shield 18 and a corresponding shield 28 being located on the outer part of the volume including coils 17 and 27.

Inner isolation layer 185 is used to isolate between the connectors, to avoid undesired electrical currents. Outer isolation layer 184 is used to protect users and the public at large from the high energy in the connector.

Outer magnetic shield 28 (secondary) serves to confine the magnetic field close to coils 17, 27.

Layers of amorphous ribbons like 282 with a horizontal orientation are interspersed with layers of amorphous ribbons like 283 with a normal orientation thereto. Planar coil 27 (secondary) is located close to coil 17 to allow inductive coupling therebetween.

Inner isolation layer 285 is used to isolate between the connectors, to avoid undesired electrical currents. Outer isolation layer 284 is used to protect users and the public from the high energy in the connector. Part of the magnetic flux 3 coupling primary to secondary is illustrated as well.

Fig. 7 details the inductive connector cross-section, another embodiment.

Variant 3 According to this variant, see Fig. 7, there is provided a high frequency transformer with two parts 1 and 2 for thn transmission of the charging current therebetween.

Parts 1 and 2 may be identical or similar to these in Variant 2 detailed above, however the magnetic core structure is different.

Part 1 consists of plane primary coil 17 with insulation layers 185 and magnetic core 18. The magnetic core 18 is made amorphous or nanocrystalline alloy ribbons 182,183.

Respectively, part 2 consists of secondary coil 27, insulation layers 285 and magnetic core 28 with layers 282, 283.

Unlike Variant 2, the magnetic cores 18 and 28 are made of ribbons having a radial orientation in each layer, that is each ribbon spans the distance from the center of the magnetic core circle 18 or 28 to its periphery.

Thus the ribbons are curved so that they fill a zone 41 of internal winding diameter 17 and 27 and a zone 43 of external winding diameter.

Due to such magnetic core performing the magnetic flow way across an air gap is reduced. This results in reduced no-load current and accordingly in lower core losses and higher efficiency of the inductive coupler.

A possible disadvantage of this magnetic core structure may be the complexity of its production technology, however this structure may be used for high power electric vehicles. There the coupler achieves significant savings in electrical energy, due to its higher efficiency.

Electrical energy is transferred from planar coil 17 (primary) to planar coil 27 (secondary), with said coils being located close to each other and in the same orientation, such that a sizable part of the alternating magnetic flux from coil 17 is coupled into coil 27.

Inner isolation layer 185 and inner isolation layer 285 are used to isolate the electrical circuits in the primary and secondary, respectively, from the outside environment. These layers may be made of a thin sheet of plastic or other electrical isolate, not ferromagnetic material.

Outer magnetic core 18 (primary) and outer magnetic core 28 (secondary) are used to confine magnetic field (not shown) close to coils 17 and 27. Cores 18 and 28 also serve as magnetic shields, to protect users from magnetic fields inside the connector. Thus, parts 18 and 28 are referred to as "cores" or "shields".

Core 18 includes layers of ferroelectric ribbons, each in a different orientation from ribbons in adjacent layers, as illustrated with layer of amorphous ribbons 182 with a horizontal orientation, and adjacent layer of amorphous ribbons 183 with a normal orientation. Similarly, shield 28 includes layers at different orientations, as illustrated with layer of amorphous ribbons 282 with a horizontal orientation and layer of amorphous ribbons 283 with a normal orientation.

Outer isolation layers 184 and 284 protect the users from the electrical energy in the connector. Central obstruction 186 is made in shield 18, with a corresponding central obstruction 286 in shield 28, to provide a low magnetic reluctance path around coils 17 and 28. Additionally, outer rim magnetic contact 187 with a corresponding outer rim magnetic contact 287 in shield 28 serve to close the magnetic circuit surrounding coils 17, 27.

Central obstructions 186, 286 and outer rims 187, 287 can be created by using a suitable mold (not shown). Circular shields 18 and 28 are inserted in the mold, and pressure is appiied to achieve the desired shape. A combination of pressure and heating may be used. Alternately, the ribbons and the isolator may be placed on the mold, such as to make the shield directly in the desired shape.

Variant 4 According to this variant, there is provided a high frequency contact connector. The connector includes two parts 5 and 6 (see Fig. 8) for the transmission of the charging current therebetween. Parts 5 and 6 may have an identical size and shape, or may have otherwise complementary forms.

The connector is devised to be used in the 105 kHz to 370 kHz preferred frequency range. At these frequencies, it is impossible to use the usual conductivity models, because of the peculiar current distribution across an electrical contact at high frequency.

It is necessary to consider the skin effect at these frequencies, which results in current only on the external surface of the conductor, and in a small superficial area close to that surface, to a depth Delta 93, see Fig. 14.

A preferred material for the contacts is copper, because of its good electrical conductivity. If r = 1.84E-8 Ohm m, m =1 and for the frequency range of 105 It to 370 kHz, the skin depth Delta = 0.1 to 0.2 mm.

Therefore, current will pass on the conductor surface only to that depth Delta 93, irrespective of the total contact area. There is no current through conta3t area 94 in Fig. 14.

The electrical current flows as follows: current 68 flows through part 6 of the connector, which is part of the charger system (not shown).

Current 69 then passes to the other part 5 of the connector, and continues as current 58 in part 5. Part 5 of the connector is mounted on the electrical vehicle (not shown).

Due to this effect, if simple conductive contacts were used at these high frequencies, then the contact surface would burn out.

For example, if a current 1=45 Ampere passes through a contact of cross sectional dimensions 3 x 3 mm2 made of copper, then the current density is j= 5.0 A/mm2 and the copper bus is not overheated. If the same current passing through the same contact, however, has a frequency f=370 kHz, then the current density is j= 37.5 A/mm2. This results in the contact surface being overheated or burnt.

To transfer a high current at high frequency through a connector, we must force the current to flow through all the contact area.

This is implemented with a contact connector including two halves 5 and 6 (see Fig. 8) . Part 5 is mounted in the electric vehicle and part 6 is made moveable and is connected to support 72. In one implementation, part 5 may consist of copper hard busses 51 and 52 with hard insulation 53. The busses 51,52 are connected to battery 62 by cable (see Fig. 13).

Busses 51 and 52 are provided by one of the two contact plates 54.

Part 6 of the contact connector includes two hard copper busses 61 and 62 with contact plates 64. Part 6 is situated between contact plates 54.

Contact plates 54 and 64 have a contact zone length 44 and width 45 (see Figs. 8, 9) . There are produced grooves 56 on the contact plate surface 54 and 64. The grooves 56 are perpendicular to each other.

Thereby each contact plate 54 and 64 has a multipoint contact area, including a plurality of contact teeth 55 and 65 respectively.

Fig. 12 details the current distribution around the contact tooth 55.

The tooth 65 is formed identical so only tooth 55 will be detailed.

The calculations were performed with the following parameters: Current 1= 16.5 A Frequency f= 370 kHz Voltage U= 400 V Power P= 6.6 kWatt For this contact connector, the grooves may be produced with a width and depth each of 2 mm, the contact area of teeth 55 and 65 each being about 3 x 3 mm2. A hole 57 is made in each of teeth 55 and 65, the hole diameter 46 being about 0.5 mm, and the opening of the phase 47 of about 1.0 mm.

To decrease the contact wear during use, a lubricant with graphite powder may be used to cover the contact area.

Part 6 is moveable, therefore both contact plates 64 with busses 61, 62 are moveable. With this purpose there may be may be included an elastic insulator material, for example sylphon, between contact plates 64.

The sylphon 66 may be implemented, for example, with hydraulic means and is used to bring plates 64 to couple to plates 54. It is necessary to achieve the coupling between all the teeth 55 and 65.

The high frequency current passes through cable 73 to busses 61 and 62, and across contact plates 64 to contact tooth area 65, then to contact tooth area 55 and across contact plates 54 and busses 51, 52 to the vehicle battery 62 (see Fig. 13).

The process of passing the high frequency current along the contact plate with teeth 55 is illustrated in Fig. 12 The high frequency current passes along all bus surface at a depth equal to Delta.

This current flows almost evenly between all grooves 56 at the depth Delta.

Current raises along the four sides of tooth 55 at depth Delta and on contact area 55 along the perimeter will be formed a zone with he current flowing through a depth Delta.

Therefore the ideal tooth size is 2 Delta x 2 Delta = 4 Delta 2. For the frequency as detailed above, the size is maximum 0.4 x 0.4 = 0.16 mm2.

Therefore, if all contact plate surface 54 is made as a multipoint contact area, including a plurality of contact teeth 55, then the high frequency current will pass through all the contact plate surface, but not along contact plate perimeter.

In this case, the current density sharply decreases, and contact overheating will be greatly diminished.

For practical implementations, the contact plate may be produced with grooves about 2 mm deep and wide, and the contact area of teeth 55 and 65 having a cross section of about 3 x 3 mm2.

For this embodiment of the invention, the real contact area, that is the area through which current flows, is equal to 0.1 x 3 x 4 = 1.2 mm2.

For a current density of j= 1A/mm2, then to transfer a current of 1= 16.5 A, the number of teeth on each plate is n= 16.5/1.2= 14 Therefore, 14 contact surfaces are required, each of cross section 3 x 3 mm2 .

Considering the adjoining grooves, the total contact plate area may be about 350 mm2, and for a practical implementation the contact plates 54 and 64 are produced with sizes of 40 x 50 mm2.

Fig. 8 illustrates another embodiment of the present invention, using ohmic contacts connector, side view. The ohmic contacts connector comprises halves 5 and 6. Ohmic contacts allow direct flow of electrical current therebetween, using electrical conductive surface in direct contact.

In this embodiment, electrical energy is transferred using physical contacts between the (not shown) vehicle and charging device. This achieves a simple and effective connection, with low losses and low weight.

Electrical bus means 51, 52 are mounted in vehicle (not shown), and leading to battery charging means (not shown). Bus means 51, 52 are connected each to one of the two outer contact plates 54. Piates 54 each has a multipoint electrical contact area, including a plurality of contact teeth 55.

While the connector halves 5 and 6 are coupled to each other to transfer electrical energy therethrough, contact teeth 55 come into contact with contact teeth 65 on each of the two inner contact plates 64.

The contact area as illustrated has a contact zone length 44, of about 40 mm. The width of the contact area is preferably about 25 mm.

A plurality of contact teeth is used in lieu of a continuous, plane contact surface to minimize contact losses because of the skin effect.

Should a continuous surface contact be used, the electrical current would flow only through the periphery of the connection surface, because of the skin effect which is present at the high frequency being used. Thus, the effective contact area is much smaller than the physical contact area of the connector. A small contact area results in high contact resistance, and high losses because of resistive losses.

In the present invention, however, the continuous contact surface is replaced with a plurality of small teeth, with a resulting distribution of the current between these teeth. The current has a generally uniform distribution between the contact teeth 55.

The effective contact area is greatly increased, it now comprising the sum of the areas on the periphery of each tooth 55.

Contact plates 64 with electrical bus means 61, 62 are part of the charging system.

An electrical energy source (not shown) is connected through electrical bus means 61, 62 to plates 64, to transfer energy to charge the battery in the vehicle.

A simple and effective means is used to couple the connector halves 5, 6 and disconnect them after charging. Rigid insulator layer 53, or a similar isolating case means (not shown), are used to hold plates 54 at a fixed distance from each other, and at a fixed orientation therebetween. This forms the fixed "female" part of the connector, which is mounted on the vehicle.

Plates 64 are mounted such as to allow their movement with respect to each other, for example by being connected through an axis of rotation (not shown). That connection should be of an isolating material, to prevent shorting the voltage between the plates 64.

A contacts actuator 66, implemented with pneumatic or hydraulic means, is used to bring plates 64 close to each other or to force them apart.

This is the "male" part of the connector, to be installed in the charging station.

While plates 64 are close to each other, the device 6 is coupled to device 5, with plates 64 being placed between the plates 64.

Actuator 66, under actuator controller 67 control, then forces plates 64 apart, such that each of plates 64 is pressed against one of the corresponding plates 54, with each of teeth 65 making good contact with a corresponding tooth 55.

To achieve this coupling between all the teeth 55 and 65, mechanical guiding means (not shown) are required such that each of the plates 64 should engage each of the plates 54 in a fixed, predefined relative location and orientation. The connector with parts 5, 6 thus coupled is left in that state during battery charging.

Fig. 9 illustrates the ohmic contacts connector, front view.

Electrical bus means 51 in vehicle (not shown), are leading to battery charging means, and connected to outer contact plate 54.

Contacts actuator 66, implemented for example using pneumatic or hydraulic means (shown in the circular, dotted lines) brings a contact plate (not shown) underneath plate 54. Electrical bus means 61 in charging device is connected to electrical energy source (not shown).

The contact zone has a width 45, which is preferably about 25 mm, for the charger of the rated power of about 6 kWatt.

Fig. 10 details part of the ohmic contact area on outer contact plate 54.

Contact plate 54 includes contact teeth 55 as shown, separated with two groups of grooves 56, one group running in parallel in one direction and the other group in a direction generally normal to that of the grooves in the first group. The teeth should have a generally equal size and shape, to achieve a generally equal distribution of the electrical current therebetween.

In the example as illustrated, the teeth 55 have a generally square cross section of size 3 x 3 mm. Other shapes are possible, however, for example a circular cross section. To decrease the contacts wearing during use, a lubricant with graphite powder should be used to fill the grooves 56.

Fig. 11 details the ohmic contact tooth 55, cross-sectional view along lines B-B in Fig. 10.

Outer contact plate 54 holds a plurality of contact teeth 55 like that illustrated.

There is a groove 56 between adjacent contact teeth 55, to separate therebetween.

In a preferred embodiment, there is made a hole in contact tooth 57, with a hole diameter 46 of about 0.5 mm and hole phased opening diameter 47 of about 1.0 mm. The hole further increases the mechanical pressure on the external part of the contact, that is on the electrical effective contact.

Fig. 12 details the current distribution around the ohmic contact tooth 55. Current elements 542 in plate 54 are leading to conducting tooth 55 and to the contact area 555 in the upper part of tooth 55. Tooth width 48 of tooth 55 of rectangular cross section, defines the contact area on surface 555.

A current density of no more than 1 A/m is preferred, this defining the required contact area for the required current of about 16.5 A.

For the frequency range as detailed above, a tooth width 48 of about 0.2 mm is recommended. This is about the order of magnitude of the skin effect depth at this frequency.

This is a trade-off between the tendency to make the teeth 55 as small as possible, to increase the effective contact area, and the requirement to make them larger, to prevent the increased fragility and more complex procedures required to make these smaller teeth. This is the best attainable tooth size from the electrical viewpoint, since further decreasing the size of teeth 55 will not result in a further decrease in the contact area, which is already limited by the skin depth.

For practical implementations, teeth 55 may have a larger width, like 3 mm. This is according to mechanical considerations, because of the low relative mechanical strength of copper, of which these contacts are usually made. At a preferred pressure of about 0.5 atmosphere between the contacts, copper may deform during use, if teeth of too fine dimensions are used. For teeth 55 of about 3 mm width, the groove between the teeth should be about 2 mm wide, and the recommended height of the teeth is about 2 mm. This structure may increase the rated power up to three times over the plane contact structure.

Fig. 13 illustrates an electrical charging system.

Eiectric vehicle 8 is depicted close to charging device support means 72, with charging device cable 73 holding inductive connector (primary) 1 and transferring electrical energy thereto.

An object of the present invention is to provide an improved system for charging electric vehicles, and to automate the charging process.

As shown in Fig. 13, there is provided a system for charging electric vehicles, which includes a high frequency generator (not shown), and high frequency connector including a first part 1 connected to the generator at the charging station, and a second part 2 mounted in the vehicle 8. When parts 1 and 2 of the connector are attached to each other, charging current flows from the high frequency generator to the electrical battery 62 in the vehicle 8.

Part 1 of the connector is connected to the high frequency generator through cable 73. Cable 73 may include both (not shown) electrical wires for the transmission of electric current. and support wires to hold part 1 suspended from support 72. The electrical wires may be made of a good conductor like copper, and the support wires may be made from steel.

In a preferred embodiment, part 1 is movably attached to support 72, for example using flexible wires and/or a robotic arm or other means.

This allows part 1 to search for part 2 and be moved so as to connect to part 2.

Part 2 of the connector is mounted on top of the vehicle 8 or in any other suitable location which may be reached by part 1 of the connector.

Part 2 is connected to the electrical battery 62, through charging circuits. The charging circuits may include detector means, to transform the alternative current (AC) into direct current (DC) which may be transferred to the battery. The charging circuits may also include voltage regulator means, to regulate the charging rate of the battery.

When the vehicle 8 approaches the charging station, a self searching system connects parts 1 and 2 for the transmission of charging current therebetween. At the end of the charging process, part 1 disengages from part 2, and the charging system is ready to charge the next vehicle.

The high frequency connector including parts 1 and 2 may be implemented using either inductive or conductive embodiments.

The inductive connector (secondary) 2, mounted on top of vehicle 8 and connected to battery and charger means 62 as shown, is located in close proximity to connector 1. When connector 1 is lowered down, preferably with automatic and/or robotic means (not shown), the magnetic attraction forces align the two connector halves 1 and 2, compensating for any small inaccuracy in alignment therebetween.

Thus, the connector 1 mounted on means including a measure of lateral degree of freedom, results in a self-aligning connector.

Although the connector 2 as illustrated is mounted on top of vehicle 8, it also may be mounted (not shown) on a side wall or the floor of the vehicle 8, with a corresponding connector 1 at a suitable location and orientation.

For any orientation of connector 1, a suitable cover means should be used, to protect the connector from rain, snow or dust.

A charging station may contain a plurality of vehicle service as that depicted, to concurrently charge a plurality of electrical vehicles.

It will be recognized that the foregoing is but one example of an apparatus and method within the scope of the present invention and that various modifications will occur to those skilled in the art upon reading the disclosure set forth hereinbefore.