Patent ID: 12218522

DETAILED DESCRIPTION

While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts that are embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention. Those of ordinary skill in the art will recognize numerous equivalents to the specific apparatus and methods described herein. Such equivalents are considered to be within the scope of this invention and are covered by the claims.

In the drawings, not all reference numbers are included in each drawing, for the sake of clarity. In addition, positional terms such as “upper,” “lower,” “side,” “top,” “bottom,” etc. refer to the apparatus when in the orientation shown in the drawing. A person of skill in the art will recognize that the apparatus can assume different orientations when in use.

As shown inFIGS.1-4, one aspect of the present disclosure is a wireless power transfer device10that includes at least a first coil layer12and a second coil layer14, each coil layer including two coil windings16positioned adjacent to one another in a lateral direction18; wherein the two coil windings16in each corresponding coil layer12and14are connected in series and are wound in the same rotational direction, and the first and second coil layers12and14are stacked in layers on top of one another. The magnetic fields of the coil layers12and14can interact with one another in a constructive manner such that the overall efficiency and power transmission of the wireless power transfer device10can be enhanced. The wireless power transfer device10inFIG.1depicts a transmitter coil11connected to a power source15for transferring power to a receiver coil17, as shown inFIG.2. In some embodiments, a wireless power transfer device10can include only a transmitter coil11that can be configured to interact and transfer power via induction to various receiver coils15that come into close enough proximity to the magnetic fields generated by the transmitter coil11.

Another aspect of the present disclosure is a wireless power transfer device10including a first coil layer12having a first pair of coil windings16apositioned laterally adjacent to one another, wherein the first pair of coil windings16aare connected in series to one another and wound in the same rational direction. The device10can include a second coil layer14having a second pair of coil windings16bpositioned laterally adjacent to one another, wherein the second pair of coil windings16bare connected in series to one another and wound in the same rational direction. The first coil layer12can be stacked on the second coil layer14in a direction22transverse to the lateral direction18.

Having the coil windings16in a coil layer12or14oriented laterally adjacent to one another can mean that the coil windings16are each wound about corresponding axes24aand24bthat are substantially parallel and separate from one another, such that the coil windings16in a coil layer12or14are oriented in a side by side orientation. In some embodiments, one coil winding16from each coil layer12and14can be wound about the same axis24band the other coil windings16in each coil layer12and14can be wound around the other axis24b, the that corresponding coil windings in successive coil layers12and14can be vertically aligned with one another.

Having the coil windings16in each corresponding coil layer12or14connected in series and wound in the same rotational direction with respect to the direction of current flow through the coil windings16can produce a divergent or repellant magnetic interaction between the coil windings16of a coil layer12or14, which can help increase the range of the magnetic flux produced by an individual coil layer12or14. In some embodiments, the first and second coil layers12and14can be configured such that all coil windings16of the wireless power transfer device10can be wound in the same rotational direction with respect to the flow of current through the coil windings16, such that the magnetic fields20in each coil layer12or14interfere constructively with respect to the magnetic fields20produced in the other coil layers12or14, respectively, as shown inFIG.4. Magnetic fields interfering constructively with one another can mean that while there may be some converging of the interfering magnetic fields at certain points along the wireless power transfer device10, the overall mutual inductance of the layered coil layers12and14can be increased as opposed to decreased, when the coil layers12and14are stacked together, and particularly along the axes24aand24bof vertically aligned coil windings16, as shown inFIGS.4and5.

As shown inFIG.1, in some embodiments all coil windings16in the first and second coil layers12and14can be wound in a clockwise direction with respect to the flow of current through the coil windings16. It will be readily appreciated that the coil windings16could be wound in either a clockwise or counterclockwise direction, provide that all coil windings16are wound in the same rotational directional, and the resulting magnetic fields and fluxes produced by the transmission coil11of the device10would be substantially equivalent, but reversed in polarity. The constructive nature of the magnetic fields20of the different coil layers12and14can help increase the range, transmission power, and transmission efficiency of the wireless power transfer device10. The layering of the DD coils in the wireless power transfer device10can also help minimize the lateral space or area occupied by the wireless power transfer device10, which can help provide an increased power transmission without substantially increasing the lateral space or footprint of the power transfer device10.

In some embodiments, each of the first and second coil layers12and14can be interconnected in series, such that not only are the coil windings16in each layer connected in series, but the various coil layers12and14are also connected in series. As such, the entire transmitter coil11and all of the coil layers12and14can be powered by a single power source15. The coil windings16in the wireless power transmission device10can be wound in the same rotational direction relative to the current flowing through the coil windings16connected in series. In other embodiments, the coil layers12and14can be connected in parallel to one another on parallel electrical paths, but again the coil windings16can be wound in the same direction with respect to the flow of current through a given parallel line of the transmitter coil11wiring. In still other embodiments, the coil layers12and14can be powered by separate power sources, though the coil windings in all separately powered layers can be wound in the same rotational direction with respect to the current flowing through the coil layers, such that the magnetic fields in each subsequent coil layer have like polarities.

It will be readily appreciated that various numbers of coil layers having the orientations taught for the first and second coil layers12and14can be utilized to further increase the mutual inductance and transmission power of the wireless power transfer device10. For instance, as shown inFIGS.1-4, in some embodiments, the wireless power transfer device10can include a third coil layer30stacked on the first and second coil layers12and14. The third coil layer30can have a third pair16cof coil windings16positioned adjacent to one another in a lateral direction, connected in series, and wound in the same rotational direction. In some embodiments, all coil windings16of the first, second, and third coil layers12,14, and30of the wireless power transfer device10can be wound in the same rotational direction with respect to the flow of electricity through the coil windings16, such that the coil windings16in each corresponding coil layer12,14, or30produce a diverging magnetic field20in a direction transverse to the lateral direction18, and the magnetic field20produced in each coil layer interferes constructively with the corresponding magnetic field20produced by the corresponding coil windings16of the other coil layers12,14, or30respectively.

As noted previously, one problem with wireless power transmission devices10can be exposure of people or other electronic circuitry (car electrical systems) to the magnetic fields20produced via the transmitter coil11of the transfer device10. To prevent against this exposure, in some embodiments, as shown inFIGS.2and5, the wireless power transfer device10can be equipped with one or more magnetic shield layers32and/or34. In some embodiments, a magnetic shield layer32can be located or positioned adjacent an outermost one of the first, second, or third coil layers12,14, or30. The magnetic shield layer32can be positioned so as not to interference with the extension of the magnetic field20produced by the transmitter coil11in a direction toward the receiver coil17, but can help block or shield the magnetic field21of the transmitter coil11on a side of the transmitter coil11opposite the receiver coil17.

The magnetic shield layer32can be made of a variety of materials, including but not limited to ferrite, neodymium, nickel, nickel-iron, steel, cobalt-iron, aluminum, etc. In one embodiment, ferrite is used for the magnetic shield layer32, as ferrite has been shown to demonstrate significant shielding properties for the magnetic shield, as shown inFIG.5.

In some embodiments, a receiver coil17can be spaced apart from the transmitter coil11, and the magnetic shield layer can be located on a side of the transmitter coil11opposite the receiver coil17. In some embodiments, the wireless power transfer device can include a receiver magnetic shield layer34positioned on a side of the receiver coil17opposite from the transmitter coil11. As such, magnetic shield layers32and34can be placed on corresponding outer sides of both the transmitter coil11and the receiver coil17, to allow power transfer between the transmitter and receiver coils11and17, but the magnetic shield layers32and34can help prevent the magnetic fields21produced by the wireless power transfer device10to extend beyond the device10which can reduce exposure of nearby persons or electronic circuitry to such magnetic fields21.

Mutual and self-inductance are two parameters that influence the transfer efficiency of a wireless power transfer device10. The impact of parameters such as coil structure, electromagnetic shielding, coupling coefficient, and mutual inductance upon the system's efficiency and quantity of power transfer over a large area have been studied. It has been learned that it is helpful to increase the mutual inductance between the coils to achieve high efficiency and power in wireless power transfer systems. The higher the mutual inductance between the coils, the more easily the coils will transmit power. The self-inductance determines the power density, which can be referred to as the amount of power the coil can store. The coupling factor also determines how well the coils will behave in wireless power transfer applications. To achieve an improved inductance, various types of coil structures, shielding materials, orientations, and configurations have been employed in current systems, chiefly including circular, double D (DD), DD quadrature (DDQ), and layered DD (LDD) coil structures. LDD coil structures having coil windings wound in the same rotational direction with respect to the current flowing through the coil windings were found to have an enhanced performance when compared to the other structures due to two things: (1) the improved inductance and power transmission of the device while maintaining the same lateral area or footprint of the device, and (2) the current path generates a resultant magnetic field that constructively results in an overall improvement in the magnetic field around the transmitter coil of the wireless power transfer device10. To achieve an increase in inductance, coils are conventionally wound with more turns, therefore, making them bigger and not being able to fit into a fixed or limited area. Rather than making bigger and bigger coil structures, implementing a layered coil configuration, like the embodiment of a LDD coil shown inFIGS.1-2, helps to account for size constraints and creates maximum flux linkage between the transmitting and receiving coils of the wireless power transfer device10. The disclosed LDD coil also increases the effective power transmission area or range while maintaining the same lateral area or footprint of the device10.

Prior art layered inductive coil orientations do not optimize self-inductance and mutual inductance values by having the coil windings wound in the same rotational direction as taught herein. However, in the embodiment of the LDD coil depicted inFIG.1, self-inductance values have been enhanced in the horizontal direction and mutual inductance values are enhanced in the vertical direction in an effort to maximize the mutual inductance values of the transmission coil11.

The coil winding structure shown inFIGS.1-2helps increase the efficiency and amount of power transfer for all types of wireless power transfer applications.

The software simulation tool ANSYS Maxwell was used to model and test the LDD coils disclosed herein. In one embodiment, the LDD coil can be made from Litz wire14AWG and comprise three interconnected vertical layers, each spaced five millimeters apart. Within each interconnected layer, the Litz wire is wound into a circular-spiral shape with a starting radius of ten millimeters and a total of ten turns, wherein each turn has a change in radius of five millimeters. For shielding, aluminum and ferrite sheets were used in the simulation shown inFIG.5to improve the overall influence on the flux lines. As modeled in the ANSYS Maxwell simulation, shielding with dimensions of 120 mm×260 mm×1 mm was placed both below the transmitter and above the receiver, covering their respective surface areas.

In addition to the ANSYS Maxwell virtual simulation, a physical experimentation was also performed, wherein the DD and layered DD coils taught in the present disclosure where constructed, and current was supplied to the transmitter coil via a function generator, and the electrical waveforms induced in the receiver coil was measured using an oscilloscope. The physical experimentation was performed under similar parameters as those used in the ANSYS Maxwell virtual simulation. The coil terminals of each layer are excited or terminated such that the coil windings in each coil layer produce diverging, opposing, or repelling magnetic fields20, or the mutual regions between the coil windings generate an opposing or repelling magnetic field. Such a configuration was found to lead to a minimization of the mutual inductance within the coil layers but constructively add magnetic flux lines across successive coil layers to provide a higher amount of mutual inductance between the transmitting and receiving coils than any of the individual constituting DD coils put together. This concept increases the efficiency and amount of power transfer for all kinds of wireless power transfer applications. The comparison of the received power transmission and efficiencies of the single DD coil and layered DD coils of the present disclosure are shown in Tables I and II below:

TABLE IMAXIMUM RECEIVED POWERMaterialg(mm)PDD(W)PLDD(W)Air15.244.69 × 10−37.49 × 10−3Air40.649.21 × 10−48.58 × 10−3FE115.244.74 × 10−37.47 × 10−3FE140.648.05 × 10−45.28 × 10−3FE215.245.10 × 10−38.12 × 10−3FE240.641.06 × 10−35.55 × 10−3AL115.241.02 × 10−35.78 × 10−3AL140.641.33 × 10−41.81 × 10−3AL215.243.57 × 10−44.30 × 10−3AL240.643.04 × 10−55.23 × 10−4

TABLE IIEFFICIENCY AT MAXIMUM POWERMaterialg(mm)Eƒ ƒDD(%)Eƒ ƒLDD(%)Air15.2561.8091.1Air40.6447.0793.56FE115.2481.1392.16FE140.6434.3391.84FE215.7488.1973.96FE240.6449.2374.23AL115.2431.1299.99AL140.644.4227.18AL215.2414.3451.51AL240.640.73210.75

As can be seen from the tables, the LLD coil of the present disclosure offered increased power transmission and efficiency over the single D coil. In contrast, in a similar prior experiment, a layered DD coil was tested against various coil structures, including a single layer DD coil, wherein the coil windings for each coil layer of the layered DD coil were wound in opposite rotational directions with respect to the flow of current through the windings. The received power and efficiency statistics for these prior tests are shown below in Tables 3 and 4:

TABLE IIIMaximum received power at resonant frequency (mW)No shieldFerriteNeodymiumNickel-IronNickelSteelCobalt-IronCircular Coil19.6995.8719.7898.3092.6696.3199.41Helical Coil10.163.1610.152.673.443.122.76DD Coil205002178343724970Layer DD Coil2.933276.362.9388.42190.56373.65475.93Square Coil0.0280.560.00070.00420.0860.0770.024

TABLE IVTransfer Efficiency at resonant Frequency in (%)No ShieldFerriteNeodymiumNickel-IronNickelSteelCobalt-IronCircular Coil0.001670.16320.0019190.062140.0358240.22660.026395Helical Coil0.00560.0006220.01860.01070.0006330.0000640.000059DD Coil0.013790.0072.885555.06710.6076.0581Layer DD Coil8.5525.30.0041.89.918.1968.74Square Coil0.0000050.0013410.0000020.0000060.000010.0002340.000035

As can be seen in Tables III and IV, while the Layered DD coil in the prior experiment, with oppositely wound coil windings, showed similar efficiencies in some scenarios to the single layer DD coil, the DD coil actually transferred more power to the receiver coil than the LLD coil in that experiment. Thus, a significant performance improvement is achieved, as demonstrated in Tables I and II, by winding the coil windings in each coil layer of the wireless power transfer device10in the same rotational direction with respect to the direction of current flow through the coil windings, as taught herein. This is particularly true of as the range of distance between the transmitter coil and receiver coil is increased, wherein the power transmission of the LDD coil of the present disclosure was an order or magnitude greater than the power transmission of the single layer DD coil, and the efficiency of the LDD coil was often more than double that of the DD coil depending on the shielding material utilized.

Referring now toFIGS.4-6, front and side view of the magnetic field distribution around an embodiment of the LDD coil with and without a shielding, as modeled in ANSYS Maxwell, can be seen. Notably, it can be observed that the overall magnetic field of the LDD coil converges above the LDD coil as opposed to being uniformly distributed around it. Due to the constructive interference of the magnetic field21, the directed flux lines converge above the LDD coil and gravitate towards the center of the LDD coil shown inFIGS.4-5. The mutual inductance between the LDD coil's layers12,14, and30is also constructive and in the upward direction or a direction toward the receiver coil17, thereby leading to an inductance value that is typically greater than three times the mutual inductance of a similarly situated DD coil, which in turn means the LDD coil provides a better efficiency than the DD coil.

While shielding materials help minimize the leakage of magnetic flux into the surrounding environment, they also play a pivotal role in increasing the power transfer efficiency of a coil structure. In both the modeling of the ANSYS Maxwell virtual simulation and the physical experimentation, ferrite and aluminum sheets were used as shielding to determine their effects on the self-inductance, mutual inductance, and transmitting efficiency of the LDD coil10. In some embodiments, ferrite can be used as a shield only at the transmitter coil site (FIG.5(a)), while in others, ferrite can be used as a shield at both the transmitter and receiver sides (FIG.5(b)). In some other embodiments aluminum shielding can be used as a shield on the transmitting side only (FIG.5(c)), or on both the transmitting and receiving sides (FIG.5(d)). It was found that the LDD coils had a more consistent performance when ferrite was used as a shield. The efficiency of power transfer at the resonant frequency was consistently better in ferrite than aluminum and air. By using ferrite as the shield, the magnetic field formed around the coil maintains a more consistent pattern, as seen inFIGS.5(a) and5(b). This ensures consistency in its performance both at resonance and at maximum power transfer point. In the case of aluminum, this consistency was not observed. It was observed that the aluminum shield does not affect the magnetic field as it can be seen covering the space around the coil. The performance experienced by the aluminum shield can be attributed to the fact that current was also induced in the shield since aluminum is conductive. This current in turn generates a magnetic field around itself to oppose its source, and as a result, the overall magnetic field is reduced—impacting how much power gets induced in the receiver and the overall efficiency of the system.

From the overall theoretical and experimental results obtained through both the virtual and physical simulations, the LDD coil structure with ferrite shielding gave the best performance due to the constructive interference of the magnetic field. Also, the LDD coil configuration with ferrite shielding only on the transmitter side yielded the highest wireless power transfer performance, making it incredibly suitable for next generation wireless power transfer applications.

Thus, although there have been described particular embodiments of the present invention of a new and useful layered DD coil for wireless power transfer applications, it is not intended that such references be construed as limitations upon the scope of this invention.