Inductive power transmitter

Abstract

An inductive power transmitter for use in on-the-move dynamic charging of motor vehicles includes an elongate ribbon structure 22 for deployment on a road. The ribbon structure has a plurality of prim

Description

The present invention is concerned with charging of electric vehicles ("EVs"). At the time of writing a major transition is underway in the automotive industry, away from vehicles driven by internal combustion engines and toward EVs. But despite advances in battery technology, 5 concerns remain about the performance of EVs with respect to their range (the distance they can travel between battery charges), the mass of their batteries, and the time taken for the batteries to charge using plug-in chargers. There have been various proposals for systems to charge EVs inductively on the move, potentially alleviating the above concerns. Electrically conductive primary coils are embedded in the road and an 10 applied alternating current causes them to create a time-varying magnetic field extending above the road surface. The EV is fitted with a secondary coil in which, as the vehicle passes over the primary coil, an electromotive force is generated by the time-varying magnetic field, and the current thus induced in the secondary coil is used to charge the EV's onboard batteries. The term "dynamic charging" is commonly used to refer to systems for charging automotive vehicles 15 on the move, and will be adopted herein. US5821728A1 provides an example of an inductive dynamic charging system. There are at the time of writing various commercial projects underway relating to inductive dynamic charging systems, one such being by Qualcomm® Technologies, Inc. and referred to as Qualcomm Halo. There are several pilot sites for dynamic induction charging for electric vehicles around the world. These include projects in Detroit, Michigan, Stockholm, Sweden, Gotland, Sweden and Tel Aviv, Israel. Cars, buses and heavy-duty trucks are used on such systems. Dynamic charging makes possible a significant reduction in the size of the vehicle battery, enabling EVs to be smaller, lighter and more efficient. Additionally or alternatively, it may extend effective EV range and avoid the need to break journeys for charging. Thus, dynamic charging has the potential both to increase uptake of EVs and to improve their efficiency, thereby significantly reducing global carbon emissions. But an obstacle to widespread adoption of inductive dynamic charging is the cost of its installation. Existing proposals contemplate that the primary coils along with the necessary cabling will be installed beneath the road surface. Retrofitting such a system to an existing road thus involves excavation, fitting 30 of the equipment and then resurfacing of the road, at considerable expense. High-traffic roads typically require resurfacing every 7 to 10 years, thereby adding long-term maintenance costs. There is a need for a dynamic vehicle charging system able to be more straightforwardly deployed on existing and newly built roads. According to a first aspect of the present invention there is an inductive power transmitter for use in 35 on-the-move charging of motor vehicles, the inductive power transmitter comprising an elongate ribbon structure for deployment on a road, the ribbon structure having an undersurface, a top surface, a plurality of primary coils for generating a magnetic field, the coils being housed between the undersurface and the top surface of the ribbon structure and being disposed at intervals along the ribbon structure's length, and a plurality of elongate magnetic core members which are housed in the 40 elongate ribbon structure between the undersurface and the top surface and at least some of which are provided with and contained in respective elongate, hollow-section protector members. By incorporating the primary coils in a ribbon structure, the invention makes it possible for them to be deployed simply by positioning the ribbon on the road and securing it in place. A protective covering may also be applied over the ribbon structure in situ. According to a second aspect of the present invention, there is a method of installing inductive power-5 transmission coils on a road for on-the-move charging of motor vehicles, the method comprising:- - housing the power-transmission coils in an elongate ribbon structure having an undersurface and a top surface, the power-transmission coils being disposed at intervals along the ribbon structure's length, - housing in the elongate ribbon structure a plurality of elongate magnetic core members, 10 - providing at least some of the magnetic core members with elongate, hollow-section protector members; - laying the ribbon structure along the road and - securing the ribbon structure to the road. Specific embodiments of the present invention will now be described, by way of example only, with 15 reference to the accompanying drawings, in which:- Figure 1 is a schematic depiction of a motor vehicle on a road equipped with an inductive power transmitter according to the present invention; C\J Figure 2 is a further depiction of a motor vehicle on a road equipped with the inductive power transmitter of Figure 1, showing lines of magnetic field (B-field lines) created by the charging system; Figure 3 depicts the relationship of a vehicle-mounted receiver to the road-mounted power transmitter; Figure 4 is a plan view of the inductive power transmitter which is partly shown in section to reveal primary coils; Figure 5 is a section through the inductive power transmitter of Figure 4 in a vertical plane; 25 Figure 6 is a detail view showing part of Figure 5 at an enlarged scale; Figure 7 depicts the inductive power transmitter of Figures 4 to 6, internal detail including primary coils and magnetic cores being included; Figure 8 depicts a further inductive power transmitter embodying the present invention, internal detail including primary coils and magnetic cores being included; 30 Figure 9 is a side view of an arrangement of a magnetic core, a protector member and wires forming a primary coil. This arrangement is found in the inductive power transmitter of Figures 4 to 7; Figure 10 depicts the arrangement of Figure 9, but includes multiple magnetic cores and is a plan view; 35 Figure 11 again depicts an arrangement of a magnetic core, a protector member and wires forming the primary coil; Figure 12 depicts a drum which carries the inductive power transmitter and which is mounted on a frame; Figure 13 depicts a vehicle and trailer combination for laying a covering on the power transmitter. The broad principle of operation of the vehicle charging system can be understood from Figures 1, 2 and 3, depicting an inductive power transmitter 8 mounted on a road 10 upon which travels a motor vehicle 12. The inductive power transmitter 8 comprises primary coils 14 at intervals along the road 17 09 24 which are supplied with alternating current to create a local magnetic field 16. The motor vehicle 12 is provided at its underside with a receiver comprising a secondary coil 18 in which alternating current is induced as the motor vehicle 12 passes over the primary coils 14. In this way, energy is transmitted to the motor vehicle 12 and this energy may be used to charge the vehicle's batteries and / or may be supplied to its electric motor(s) to propel the vehicle, reducing or altogether avoiding the need to halt the motor vehicle 12 for charging. The primary coils 14 may be driven selectively for the sake of efficiency. In particular, they may be energised only in the presence of a motor vehicle 12. This may for example be achieved by providing the motor vehicle 12 with a short-range transmitter to send a signal to a receiver controlling energisation of a set of the primary coils 14. As shown in Figure 3, there is typically an air gap 20 between the road-mounted primary coil 14 and the vehicle-mounted secondary coil 18. The size of the airgap depends on the ground clearance of the motor vehicle 12 and on the mounting height of the secondary coil 18 in the motor vehicle 12, but for example a design gap size of 230mm is suitable to accommodate a typical ground clearance of 140-160mm for cars and 170-200mm for sports utility vehicles. The inductive power transmitter 8 comprises a ribbon structure 22 which carries the primary coils 14 and which is prefabricated (i.e. it is manufactured, complete with the primary coils 14 and necessary electrical connections to them, prior to its deployment) and is then laid upon the road 10 and secured to it. In this way, installation of the charging system on the road 10 is greatly simplified and the cost of the charging system, compared with conventional systems reliant on buried coils, is greatly reduced. Figures 4, 5 and 6 depict the ribbon 22 according to one exemplary embodiment, having an undersurface 24 which rests upon the road surface 25 beneath and a top surface 26, both of them being substantially planar. The depth of the ribbon 22 (i.e. the separation of its undersurface 24 from its top surface 26) is small. It may be 44mm or less. Lateral edge regions 28 of the top surface 26 may be inclined downward so that the depth of the ribbon 22 tapers away at the edges, giving the ribbon 22 a trapezoidal shape in cross section. Hence a step change in height at the edge of the ribbon is avoided, enabling the wheels of motor vehicles 12 to move safely onto and off the ribbon 22 laterally. The ribbon 22 is elongate in the direction of travel along the road 10. It may be manufactured in elongate sections to be deployed end-to-end, with each section incorporating multiple primary coils 14 at longitudinal intervals. Thus it is not necessary to install and connect each primary coil 14 individually on site. Instead, long prefabricated sections of the ribbon carrying multiple primary coils 14 are laid in place, greatly expediting installation. The length of one elongate section of the ribbon 22 may be tens of metres. The ribbon 22 of the present embodiment is sufficiently flexible to be wound on a drum prior to installation, making its transport and deployment especially straightforward. Other embodiments may be more rigid, in which case the length of individual ribbon sections may be chosen to facilitate transportation. For example, the ribbon sections may be of a length that enables them to be carried in a stack on the bed of a lorry. According to the present embodiment, the internal structure of the ribbon 22 comprises conductive primary coils 14 and magnetic cores 32 disposed between upper and lower skins 34, 36 and surrounded by infill 39, creating a robust sealed structure able to withstand the harsh environment in which it is to be deployed. The upper and lower skins 34, 36 may comprise a tough, flexible polymer material. Polyvinyl chloride is used in the present embodiment. The ribbon 22 incorporates a magnetic shield 38 beneath (and in the present embodiment to either side of) the primary coils 14 whose purpose is to reduce magnetic field strength beneath the ribbon 22, which is a potential source of inefficiency. The magnetic shield 38 focusses the magnetic field upwards, reducing radial losses and eddy currents. In the present embodiment the magnetic shield 38 comprises an aluminium tray whose bottom panel 40 lies above the lower skin 34 and whose longitudinally extending edges 42 are upturned laterally outboard of the primary coils 14, shielding against lateral spread of the magnetic field. In other embodiments the magnetic shield may additionally or alternatively comprise a ferrite layer, which may be disposed atop the bottom panel 40. Magnetic field strength is maximised by virtue of the magnetic cores 32, which may comprise ferrite material. In the present embodiment the magnetic cores comprise multiple elongate members which extend laterally with respect to the ribbon 22 (across the direction of traffic flow, and more specifically in the present embodiment at right angles to it) and which are spaced from one another along the length of the ribbon 22. The cross-sectional shape of the magnetic cores 32 is semicircular in the present embodiment but other shapes may be used. The magnetic cores 32 may be provided with protector members 44 to protect them from damage. The protector members 44 may be configured to act as stiffeners to prevent breakage of the magnetic cores 32 by bending and / or they may provide crush resistance. In the embodiment depicted in Figure 5, the protector members 44 comprise elongate hollow arches each containing a respective semicircular magnetic core 32. Figure 8 depicts a different embodiment comprising circular magnetic cores 32a within hollow tubular protector members 44a. The primary coils 14 comprise electrical conductors which extend in directions substantially parallel with the undersurface 24 of the ribbon 22 and which are embedded in the structure of the ribbon 22 and protected by it. The configuration of the primary coils 14 (especially their shape, viewed in plan) may vary from one embodiment to another-various coil configurations are known for inductive power transfer and may be adopted in embodiments of the present invention. But in the present embodiment the coils are continuous loops and their configuration is of the type known as "Double D." The primary coils 14 are arranged in laterally adjacent pairs as seen in Figures 4 and 8. This is known to be an advantageous coil configuration. Pairsof primary coils Mare provided at regular intervals along the length of the ribbon 22. Each section of ribbon 22 comprises multiple pairs of coils. The number of pairs of coils per section may be three or more. In the present embodiment, and purely byway of example, each primary coil 14 is approximately 1.8 metres in length and 0.85 metres in width. The vehicle-mounted secondary coil 18 is approximately 0.66 metres in length, and receives a power of the order of 200kW. Other dimensions and powers may be chosen in other systems embodying the present invention. The primary coils 14 may be formed of wires 46 comprising multiple insulated strands (commonly referred to as Litz wires), able to efficiently conduct the supplied alternating current. In the depicted embodiments, the wires 46 are laid on the protector members 44 or 44a, being received in preformed channels therein. Where the wires 46 cross the protector members 44,44a these channels run laterally across the protector members 44, 44a (see Figures 9 and 10). In end regions 50 of the primary coils 14, the wires 46 run lengthwise along the protector members 44, 44a, being received in channels extending along the protector members 44 as seen in Figure 11. The protector members 44 thus give protection to the primary coils 14 as well as to the magnetic cores 32. In alternative embodiments, the primary coils 14 may be formed by electrically conductive strips (e.g. of copper, or another suitable conductor) in place of the Litz-type wires 46, which may assist in maximising flexibility of the ribbon 22 to enable it to be rolled on a drum prior to deployment. complete charging system comprises not only the inductive power transmitter 8 but also the electrical systems to provide and control the AC signal needed to drive the primary coils 14. However suitable electrical systems are known in the art, and will not be described in detail herein. For information on this topic, reference may be made to the paper Modular Power Electronics Approach for High Power Dynamic Wireless Charging System, Xue et al, published in IEEE Transactions on Transport Electrification, Volume 10, Issue 1, March 2024. The electrical system may provide for adjustment of power level based on the position and speed of the motor vehicle 12, with communication between the motor vehicle 12 and the charging infrastructure to coordinate charging and to ensure proper vehicle alignment. It may comprise a high-frequency inverter receiving power from the national electrical grid to provide the AC power supply to the primary coils 14. Manufacture of the ribbon 22 may involve laying the magnetic cores 32, the protector members 44, 44a and the primary coils 14 atop a sandwich formed by the lower skin 36 and the magnetic shield 38, supplying infill 39 in a liquid, settable form, and applying the upper skin 34. Polyvinyl chloride is a suitable settable material for the infill 39. At edges and ends of a section of the ribbon 22 the upper and lower skins 34, 36 will be sealed to one another (e.g. by vulcanisation), making a physically robust structure sealed against water ingress. Installation of the power transmitter 8 involves suitably cleaning the road 10, where necessary, and then positioning the ribbon 22 suitably on the road 10 and securing the ribbon 22 to the road 10. Additionally, according to the embodiments to be described herein, a covering 52 is applied over the ribbon 22. According to the present embodiment the ribbon 22 is adhered to the road 10 using a suitable adhesive, which may for example comprise a polyurethane-based adhesive or may comprise an epoxy resin. Mechanical fasteners may additionally or alternatively be used to secure the ribbon 22 to the road 10. Where the ribbon 22 is supplied to the installer on a drum 54 (see Figure 12), positioning the ribbon 22 on the road 10 can be carried out very straightforwardly by mounting the drum 54 on a vehicle through a frame 56 and simply paying the ribbon 22 off the drum as the vehicle moves along the road 10. A typical flatbed trailer can carry up to five drums 54, ends of neighbouring sections of the ribbon 22 being joined to one another by factory-stitched joints and mechanical wire fastening. Note that it is not necessary to provide a trench in the road 10 to receive the ribbon 22. According to the present embodiment, the ribbon 22 will simply be applied to the (typically substantially flat) surface of the road 10. The ribbon 22 will thus stand slightly proud of the adjacent road surface 25, but due to its shallow depth and its trapezoidal shape, with tapered edge regions, this does not present an unacceptable obstacle for motor vehicles 12. The covering 52 can be chosen to provide desired properties including coefficient of friction with vehicle wheels, appearance, wear resistance and resistance to water ingress. A settable polymer material is used in the present embodiment, which may comprise a thermoplastic or a thermosetting plastic. Epoxy resin may be used, but the present embodiment uses thermoplastic road-marking paint, which is known to be both durable and capable of providing adequate traction for vehicle tyres, and is available in a range of colours. The covering 52 may incorporate glass beads to increase durability and provide reflectivity, making the ribbon 22 visible to road users. Other settable materials may be used in the covering 52. Tar may be used, and can be laid hot to set as it cools. It may comprise glass beads or fine stone. Thermoplastic road-marking paint is typically applied hot. For this purpose a marking vehicle 60 (see Figure 12) is provided with a boiler / heater and holding tank 62 for the molten thermoplastic paint. The vehicle also has water storage, gas fuel storage and storage for glass beads. The marking vehicle 60 is able to discharge sufficient volume of the thermoplastic paint and accompanying materials on top of the ribbon 22 to cover its whole area and to seal it onto the road surface 25. A purpose-designed 4-wheel trailer 64 is pulled directly behind the marking vehicle 60 and operated by the driver utilizing sensors and remote cameras to lay the thermoplastic paint. A sluice 65 delivers the hot thermoplastic paint from the holding tank 62 to a delivery trough 66 from which the thermoplastic paint is applied to the road surface 25. The width of the covering 52 thus formed is sufficient to cover the ribbon 22 and to extend laterally a short distance onto the road 10. This lateral extent may be of the order of 150mm. A splined roller 68 follows the delivery trough 66 to rib the covering 52. Glass beads will then be applied from a distribution box 70 and water is dispensed from a distribution tank 72 to cool the covering 52. Depth of the covering 52 may be of the order of 13mm, or less. The depicted marking vehicle 60 and trailer 64 may be used to lay other settable materials , such as tar, to form the covering 52. The ribbon 22 is typically placed along the centre of a road lane. On multi-lane roads - dual carriageways, motorways and freeways - ribbons 22 may be placed along all lanes or along selected lanes. Motor vehicles 12 are intended to straddle the ribbon 22 whilst charging, the vehicle's wheels lying to left and right of the ribbon 22 so that the vehicle-mounted secondary coils 18 suitably align with the road-mounted primary coils 14. The aforementioned ribbing of the covering 52, and the raised surface formed by the ribbon 22 and its covering 52, assist the driver in this respect by providing sensory feedback in the manner of a rumble strip if the motor vehicle 12 strays from the desired road position, causing its wheels to contact the ribbon 22. In some embodiments, raised studs 74 may be provided (see Figure 4), in addition or as an alternative to the ribbing of the covering 52 and either along edges of the ribbon 22 or along lines on the road 10 outboard of the said edges, to provide an additional or alternative means of signaling improper alignment to the driver. The ribbing deters vehicles from travelling with a wheel on top of the belt, although the ribbon 22 and its covering 52 are able to be driven over without damage. It is envisaged that a gap will be left between belts at intervals along the road 10, to allow vehicles to change lanes, although this may prove unnecessary. The above description and the appended drawings are presented by way of example and not of limitation. Numerous variations, substitutions and modifications are possible without departing from the scope of the invention determined by the claims below. For example, while in the above-described embodiments the ribbon 22 stands proud of the road 10 on which it is installed, it would be possible to place the ribbon 22 in a shallow trench so that it - or its covering 52 - would lie flush with the adjacent road surface 25. As another example, while the power induced in the primary coil 14 is described as being used for "charging", and will typically be used to charge an electric battery, it may be used to directly drive the motor vehicle 12, or for example to charge an energy store of another type, such as super capacitors.

Claims

1. An inductive power transmitter for use in on-the-move charging of motor vehicles, the inductive power transmitter comprising an elongate ribbon structure for deployment on a road, the ribbon structure having an undersurface, a top surface, a plurality of primary coils for generating a magnetic 5 field, the coils being housed between the undersurface and the top surface of the ribbon structure and being disposed at intervals along the ribbon structure's length, and a plurality of elongate magnetic core members which are housed in the elongate ribbon structure between the undersurface and the top surface and at least some of which are provided with and contained in respective elongate, hollowsection protector members.10 2. An inductive power transmitter as claimed in claim 1 comprising at least three primary coilsseparated from one another at intervals along the ribbon structure's length.

3. An inductive power transmitter as claimed in claim 1 or claim 2 in which the separation of the undersurface from the top surface is no more than 60mm.

4. An inductive power transmitter as claimed in any preceding claim in which the ribbon has a width 15 between 0.3 metres and 1.5 metres.

5. An inductive power transmitter as claimed in any preceding claim in which the ribbon structure has a continuous length in excess of 5 metres.C\J,nzu6. An inductive power transmitter as claimed in any preceding claim in which the ribbon structure comprises a lower skin and an upper skin, the primary coils being housed between the upper and the lower skins.

7. An inductive power transmitter as claimed in claim 6 in which the primary coils are embedded in infill disposed between the upper and the lower skin.

8. An inductive power transmitter as claimed in any preceding claim in which at least one of the primary coils is provided with at least one magnetic core housed in the ribbon structure between the25 undersurface and the top surface.

9. An inductive power transmitter as claimed in claim 8 in which at least one of the primary coils is provided with multiple elongate magnetic core members.

10. An inductive power transmitter as claimed in any preceding claim in which the ribbon structure is flexible and is disposed on a drum or in a roll.30 11. An inductive power transmitter as claimed in any preceding claim in which the ribbon structurehas longitudinally extending edge regions which taper in depth, becoming less deep at the ribbon structure's longitudinal edges.

12. An inductive power transmitter as claimed in any of claims 1 to 11, further comprising a magnetic shield disposed above the undersurface and beneath the primary coils.35 13. An inductive power transmitter as claimed in claim 12 in which the magnetic shield comprises ametal layer.

14. An installation for vehicle charging on the move, comprising an inductive power transmitter as claimed in any preceding claim extending along and secured to a road, and a covering layer over the ribbon structure.

15. An installation for vehicle charging on the move as claimed in claim 16, in which the covering layer comprises a layer of thermoplastic or thermosetting plastic material extending beyond the ribbon structure onto the road.

16. An installation for vehicle charging on the move as claimed in claim 16 or claim 17 in which the 5 undersurface of the ribbon structure is secured to the road by adhesive.

17. A method of installing inductive power-transmission coils on a road for on-the-move charging of motor vehicles, the method comprising:-- housing the power-transmission coils in an elongate ribbon structure having an undersurface and a top surface, the power-transmission coils being disposed at intervals along the ribbon structure's 10 length,- housing in the elongate ribbon structure a plurality of elongate magnetic core members,- providing at least some of the magnetic core members with elongate, hollow-section protector members;- laying the ribbon structure along the road and15 - securing the ribbon structure to the road.

18. A method as claimed in claim 17 further comprising providing a cover layer over the ribbon structure after laying the ribbon structure on the road.C\J 19. A method as claimed in claim 18 in which providing the cover layer comprises applying a settable or curable material over the ribbon structure followed by setting or curing of the material to form the 20 cover layer.

20. A method as claimed in claim 18 or 19 in which the cover layer extends laterally beyond the ribbon I structure and onto the road.I-21. A method as claimed in any of claims 17 to 20 further comprising shaping a top surface of the cover layer to provide a rumble-strip effect.25 22. A method as claimed in any of claims 17 to 21 in which securing the ribbon structure is secured tothe road using adhesive to adhere the undersurface of the ribbon to an upper surface of the road.

23. A method as claimed in any of claims 17 to 22 which further comprises comprising winding the ribbon structure on a drum or in a roll and in which laying the ribbon structure along the road comprises paying the ribbon structure off the drum or roll onto the road.30

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