Wirelessly rechargeable battery and power transmitter

A wirelessly rechargeable battery is provided having coils oriented off major battery axes to facilitate good coupling with power transmitter magnetic fields. A magnetic core may house charging electronics for a compact form factor. A wireless power transmitter that produces fields to maximize coupling with receiver coils.

This application is a National Stage Application of PCT/NZ2011/000241, filed 16 Nov. 2011, which claims benefit of Serial No. 589312, filed 16 Nov. 2010 in New Zealand and which applications are incorporated herein by reference. To the extent appropriate, a claim of priority is made to each of the above disclosed applications.

FIELD OF THE INVENTION

This invention relates to a wirelessly rechargeable battery and a power transmitter. More particularly, but not exclusively, this invention relates to wirelessly rechargeable batteries where the coils are offset to facilitate charging in any direction and a power transmitter generating arcing flux distributions between adjacent coils energised with alternating polarities.

BACKGROUND OF THE INVENTION

Rechargeable batteries are increasingly replacing single use batteries due to economic, performance convenience and environmental factors. Rechargeable batteries have been integrated into electric devices, such as cordless toothbrushes, for some time. Such devices typically locate the device with respect to a charger to ensure good coupling for efficient power transfer.

There is a demand for wirelessly rechargeable batteries to be provided in a standard battery casing. There is limited space within the casing for the electrochemical cell, charging circuit and coils. Further it would be desirable to be able to charge a battery in any orientation within a general charging region and when located within an electronic device.

Batteries are typically housed in an orientation parallel or orthogonal to the faces of an electronic device. Power transmitters in the form of charging mats etc. typically generate a field normal to the charging surface. Thus in some orientations there may be limited coupling between the coils within a wirelessly rechargeable battery and the coils of the power transmitter. Power transmitters may also be wasteful in generating a full charging field whether batteries are present or not.

It is an object of the invention to provide a battery and/or power transmitter enabling charging in all typical orientations in an energy efficient manner or to at least provide the public with a useful choice.

SUMMARY OF THE INVENTION

According to one exemplary embodiment there is provided a wirelessly rechargeable battery comprising:a. an elongate battery casing having a longitudinal axis;b. a rechargeable storage device;c. a plurality of power receiving coils disposed at an angle of between 30 to 60 degrees to the longitudinal axis; andd. a charging circuit for controlling the supply of power from the coils to the storage device.

According to another exemplary embodiment there is provided a wirelessly rechargeable battery comprising:a. a battery casing;b. a rechargeable storage device;c. one or more power receiving coils mounted on a ferrite core; andd. a charging circuit for controlling the supply of power from the coils to the storage device at least partially housed within the ferrite core.

According to another exemplary embodiment there is provided a wireless power transmitter including:a. a plurality of power transmission coils arranged in a planar array; andb. a driving circuit for driving the coils such that at least a first coil is driven so as to produce an alternating magnetic field of opposite polarity to that produced by a second coil.

It is acknowledged that the terms “comprise”, “comprises” and “comprising” may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, these terms are intended to have an inclusive meaning—i.e. they will be taken to mean an inclusion of the listed components which the use directly references, and possibly also of other non-specified components or elements.

Reference to any prior art in this specification does not constitute an admission that such prior art forms part of the common general knowledge.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1shows a first embodiment of wirelessly rechargeable battery having a cylindrical casing consisting of lower section2, that may be metallic, and an upper section3, that is non-metallic. The casing contains a storage device4that is typically a rechargeable electrochemical cell but could be a capacitor or other energy storage device. Orthogonal coils5and6are wound on magnetic core7(typically ferrite) and oriented transverse to the longitudinal axis of the battery. Charging circuit1may be located within the magnetic core to minimise the form factor of the charging circuit (as shown inFIG. 7). This topology is compact but may result in week coupling if the coils5and6are normal to the charging field.

FIG. 2shows an alternate topology in which coils8and9are oriented at 45 degrees to the longitudinal axis of the battery. This ensures that for any standard orientation with respect to a power transmitter (i.e. up, down or flat in any orientation) that there will be sufficient coupling between power transmitter coils and battery coils. The offset angle may be within a range of about 30 to 60 degrees. This allows the preferred battery orientation to have the most favoured coupling whilst providing adequate coupling for less preferred orientations. Charging circuit10may be housed within the magnetic core11. It will be appreciated that the magnetic core11may simply be a cylindrical block of ferrite with grooves on the exterior for the coils and an internal cavity for the charging circuit (as shown inFIG. 7).

FIG. 3shows an embodiment with three orthogonal coils12,13and14. This arrangement ensures that there is good coupling between the battery coils and the charging circuit in any orientation but does require an additional coil that may be redundant if the battery will always be in one of the three standard orientations (i.e. up, down or flat in any orientation).

FIG. 4shows an embodiment in which a tubular ferrite15houses both the storage device16and the charging circuit17. Coils18and19are wound at an angle of between 30 to 60 degrees to the longitudinal axis of the battery to ensure good coupling in the three standard orientations. This design may be suitable where a storage device is of lesser diameter (e.g. AAA) than the casing (e.g. an AA) and there is limited room at each end for coils and the charging circuit.

FIG. 5shows a similar embodiment toFIG. 4except that the coils19aand19bare wound longitudinally around the magnetic core21containing storage device20.

FIG. 6shows another variant in which3coils22,23and24are wound on magnetic core25so as to be oriented to each other at about 60 degrees. This eliminates the dead zone caused when the receiver coil is at 45° to the track and simplifies the electronics design. The pickup coils may be mounted so that none of the coils are in line with the elongate axis of the battery to maximize coupling.

FIG. 7shows a magnetic core26formed in a generally cylindrical form with grooves to accommodate windings27and28and a cavity29to accommodate a charging circuit. This technique may be applied to the embodiments previously described.

The charging circuit in each embodiment may rectify the power received from each coil to avoid any cancellation between coils. The charging circuit may also provide resonant tuning by way of series or parallel resonant tuning techniques. One particularly preferred tuning technique is that disclosed in PCT/NZ2009/000137 as it is easily implemented using a compact integrated circuit design. This circuit may also be used to regulate power supplied to the storage device by detuning the charging circuit. The charging circuit may also pulse its power demand to signal to a power transmitter. The pattern of power demand may encode information as to the charge state of the storage device, charging current, temperature, identifier of the battery etc. depending upon the economics for a given application.

Referring now toFIG. 8there is shown a wireless power transmitter in which a driving circuit42drives a plurality of coils30to41so as to produce arcing flux lines suitable for coupling with the receiving coils of wirelessly rechargeable batteries in any orientation. A variety of drive patterns may be employed to optimise coupling.FIG. 8shows coils30to32and36to38driven to produce alternating magnetic fields with a first time varying polarity and coils33to35and39to41driven with a second time varying polarity to produce arcing flux lines as shown (showing a snapshot in time as the fields alternate and maintain opposite polarity). This will provide strong coupling when a coil of a battery is oriented along the axes as shown by the arrows.FIG. 9shows coils31,34,37and40driven to produce a first time varying polarity and the other coils driven to produce a second time varying polarity, opposite to the first, to produce arcing flux lines as shown (at an instant in time). This will provide strong coupling when a coil of a battery is oriented as shown by the arrows.

Referring toFIG. 10the location of a battery43may be determined by sensing its affect on fields generated by coils of the wireless power transmitter44or by other sensing techniques. Coil pairs34and37may be energised to produce time varying fields of opposite polarity as shown for a snapshot in time inFIG. 10. This ensures that only the best coupled coils are driven. By driving adjacent coils to produce time varying magnetic fields of opposite polarity the magnetic field may be shaped and the drive load distributed amongst multiple coils.FIG. 11shows a variant to this approach where coil37is driven to produce a time varying magnetic field having a first time varying polarity and a plurality of surrounding coils34,36,38and40are driven to have a time varying magnetic field having a time varying polarity opposite to that produced by coil37.

For “dumb” batteries the power transmitter may detect the presence of batteries by the load on the power transmitter. In one embodiment the coils may be driven at a relatively low level or intermittently when no batteries are present and when the presence of a battery is detected (by the load drawn) the power level may be increased. When the batteries are charged the low load may again be detected and operation may revert to a relatively low drive level or intermittent drive. The charge circuit may also revert to a relatively low drive level or intermittent drive when disrupting metallic bodies are detected.

For batteries that can communicate (as described above) the power transmitter may receive information as to charge state of the storage device, charging current, temperature, identifier of the battery etc. The power transmitter may then alter the power supplied by coils30to41to adjust the amount of power supplied and the field pattern to optimise power transfer. Charging can be controlled on an individual coil30to41to battery relationship or a many to one or many to many relationship.

There are thus provided wirelessly rechargeable batteries that have an efficient form factor and/or allow efficient charging in all standard orientations using two coils. There is also provided a power transmitter for optimizing efficient charging with wirelessly rechargeable batteries.