WIRELESS POWER SUPPLY DEVICE

Abstract

A wireless power supply device includes an electrically-conductive case that accommodates a power transmitting circuit board and a power receiving LC circuit in a resonant cavity formed therein and surrounded by an electrically-conductive plate with both ends of a power transmitting LC circuit being connected to the electrically-conductive plate. In the resonant cavity, a power transmitting coil and a power receiving coil resonate magnetically so as to supply power of an AC voltage signal to a load. The both ends of the power transmitting LC circuit are electrically connected to the electrically-conductive case using a pair of electrically-conductive attachment units configured to attach the power transmitting circuit board to an inner wall surface of the electrically-conductive case.

Claims

1. A wireless power supply device comprising: a power transmitting LC circuit having a power transmitting coil and a power transmitting capacitor connected in parallel or in series; a power transmitting circuit board on which the power transmitting LC circuit is formed; a power source circuit configured to apply an AC voltage signal having a resonance frequency f.sub.0 of the power transmitting LC circuit to the power transmitting LC circuit; a power receiving LC circuit having a power receiving coil and a power receiving capacitor connected in parallel or in series and having a resonance frequency f.sub.0 the same as the resonance frequency f.sub.0 of the power transmitting LC circuit; a load to be supplied with power of the AC voltage signal via the power receiving coil of the power receiving LC circuit; and an electrically-conductive case configured to accommodate the power transmitting circuit board and the power receiving LC circuit in a resonant cavity formed therein and surrounded by an electrically-conductive plate with both ends of the power transmitting LC circuit being connected to the electrically-conductive plate, wherein in the resonant cavity, the power transmitting coil and the power receiving coil resonate magnetically so as to supply the power of the AC voltage signal to the load.

2. The wireless power supply device according to claim 1, further comprising at least a pair of electrically-conductive attachment units configured to attach the power transmitting circuit board to an inner wall surface of the electrically-conductive case, and wherein the both ends of the power transmitting LC circuit are electrically connected to the electrically-conductive case via the pair of electrically-conductive attachment units.

3. The wireless power supply device according to claim 1, wherein the resonant cavity is surrounded by the electrically-conductive plate and an electrically-insulating plate integrally coupled to the electrically-conductive plate, and the electrically-insulating plate is covered with any of an electromagnetic shield film and an electromagnetic shield coating electrically connected to the electrically-conductive plate integrally coupling to the electrically-insulating plate.

4. The wireless power supply device according to claim 1, wherein the power transmitting coil is formed on the power transmitting circuit board so as to be close to a voltage conversion coil connected to the power source circuit, so that electromagnetic induction coupling made between the voltage conversion coil and the power transmitting coil causes an AC voltage signal having a resonance frequency f.sub.0 to flow through the power transmitting coil.

5. The wireless power supply device according to claim 1, wherein the power transmitting coil is a pattern coil formed by a conductive pattern of the power transmitting circuit board electrically connecting between the pair of electrically-conductive attachment units.

6. A wireless power supply device comprising: a power transmitting LC circuit having a power transmitting coil and a power transmitting capacitor connected in parallel or in series; a power transmitting circuit board on which the power transmitting LC circuit is formed; a power source circuit configured to apply an AC voltage signal having a resonance frequency f.sub.0 of the power transmitting LC circuit to the power transmitting LC circuit; a power receiving LC circuit having a power receiving coil and a power receiving capacitor connected in parallel or in series and having a resonance frequency f.sub.0 the same as the resonance frequency f.sub.0 of the power transmitting LC circuit; a load to be supplied with power of the AC voltage signal via the power receiving coil of the power receiving LC circuit; and an electrically-conductive case configured to accommodate the power transmitting circuit board and the power receiving LC circuit in a resonant cavity formed therein and surrounded by an electrically-conductive plate with both ends of the power transmitting LC circuit being connected to the electrically-conductive plate, wherein in the resonant cavity, the power transmitting coil and the power receiving coil resonate magnetically so as to supply the power of the AC voltage signal to the load, the load is a strain sensor configured to detect a running torque of a crankshaft that rotates together with a pedal of a power-assisted bicycle, a power receiving circuit board on which the strain sensor and the power receiving LC circuit are formed is fixed to the crankshaft, and the power transmitting circuit board and the power receiving circuit board are accommodated in the resonant cavity surrounded by the electrically-conductive plate of the electrically-conductive case fixed to a main body of the power-assisted bicycle.

7. The wireless power supply device according to claim 6, further comprising at least a pair of electrically-conductive attachment units configured to attach the power transmitting circuit board to an inner wall surface of the electrically-conductive case, and wherein the both ends of the power transmitting LC circuit are electrically connected to the electrically-conductive case via the pair of electrically-conductive attachment units.

8. The wireless power supply device according to claim 6, wherein the resonant cavity is surrounded by the electrically-conductive plate and an electrically-insulating plate integrally coupled to the electrically-conductive plate, and the electrically-insulating plate is covered with any of an electromagnetic shield film and an electromagnetic shield coating electrically connected to the electrically-conductive plate integrally coupling to the electrically-insulating plate.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0053] FIG. 1 is a partial cutaway perspective view illustrating a wireless power supply device 1 according to an embodiment of the present invention.

[0054] FIG. 2 is a vertical cross-sectional view of a part cut vertically along a pair of electrically-conductive screws 4′ for attaching a power transmitting circuit board 10 to an electrically-conductive case 3.

[0055] FIG. 3 is a block diagram illustrating a circuit configuration of the wireless power supply device 1.

[0056] FIG. 4 is a perspective view illustrating a main part of a related wireless power supply device 100.

[0057] FIG. 5 is a block diagram illustrating a circuit configuration of the wireless power supply device 100.

DESCRIPTION OF EMBODIMENTS

[0058] A wireless power supply device 1 according to an embodiment of the present invention will now be described with reference to FIGS. 1 to 3. The wireless power supply device 1 according to the present embodiment is attached to a power-assisted bicycle to supply driving power to a torque sensor 6 from a battery (not shown) attached to a frame body of the power-assisted bicycle. The torque sensor is attached to a crankshaft 5, which rotates together with a pedal of the power-assisted bicycle, to detect a running torque of the crankshaft 5.

[0059] The crankshaft 5 is rotatably supported by being inserted through a bearing (not shown) provided in a bottom bracket 7 formed integrally with the frame body of the power-assisted bicycle. As shown in FIG. 1, an electrically-conductive case 3 is fixed along an outer side surface of the bottom bracket 7. The electrically-conductive case 3 is formed in the shape of a cylindrical box having its entire peripheral surface surrounded by an electrically-conductive metal plate 31. A lid surface (not shown) opposed to a bottom surface 3a of the box shape is pierced so as to have a through hole 32 for allowing the crankshaft 5 to be passed therethrough. One end of the crankshaft 5 projected from the bottom bracket 7 passes through the electrically-conductive case 3.

[0060] A portion of the upper part of the electrically-conductive case 3 in FIG. 1 is covered with an electrically-insulating synthetic resin plate 33. Inserted through the electrically-insulating synthetic resin plate 33 are a power cable 8 for providing a power source from the battery to circuit components mounted on a power transmitting circuit board 10 to be described later, and a signal cable 9 for outputting detection data of the torque sensor 6 to a drive control circuit (not shown) that controls the driving of an electric motor. In order to completely shield the interior of the electrically-conductive case 3, an electromagnetic shield film 34 electrically connected to the electrically-conductive metal plate 31 therearound is deposited over a front surface of the electrically-insulating synthetic resin plate 33. Although the electrically-insulating synthetic resin plate 33 may be shielded by depositing an electromagnetic shield coating on the front surface thereof, an aluminum-evaporated polyester film is used as the electromagnetic shield film 34 in the present embodiment.

[0061] As described above, since the entire peripheral surface of the electrically-conductive case 3 is surrounded by the electrically-conductive metal plate 31 and the electromagnetic shield film 34, the interior of the electrically-conductive case 3 forms a resonant cavity 35 in which a power transmitting coil 13 and a power receiving coil 22 to be described later magnetically resonate.

[0062] In this resonant cavity 35, the power transmitting circuit board 10 and a power receiving circuit board 20 are accommodated as shown in FIG. 3. On the power transmitting circuit board 10, a power transmitting LC circuit 11, a voltage conversion coil 12, a matching circuit unit 14, a microcomputer 15 equipped with a clock signal source, and a phototransistor 16 are formed. On the power receiving circuit board 20, a power receiving LC circuit 21, a full-wave rectifying circuit 23, a power receiving circuit unit 24, the torque sensor 6, an LED driver 25, and an infrared LED 26 to be photo-coupled with the phototransistor 16 are formed. Each circuit or circuit element being formed on a circuit board herein means that a circuit element constituting a circuit or a circuit element is mounted on a circuit board or formed by a conductive pattern on a circuit board.

[0063] As shown in FIG. 1, the power transmitting circuit board 10 is attached by screwing electrically-conductive screws 4, which are electrically-conductive attachment units configured to attach the power transmitting circuit board 10 to the electrically-conductive case 3, into four corners of the power transmitting circuit board 10 so as to secure the power transmitting circuit board 10 to the bottom surface 3a of the electrically-conductive case 3 by screws. Of these electrically-conductive screws, a pair of electrically-conductive screws 4′ are screwed at positions of land patterns 11a on both sides of the power transmitting LC circuit 11 on the power transmitting circuit board 10 as shown in FIG. 2, and both ends of the power transmitting LC circuit 11 are electrically connected to the electrically-conductive case 3 at Earth 1 and Earth 2.

[0064] The microcomputer 15, the matching circuit unit 14, and the phototransistor 16 formed on the power transmitting circuit board 10 are operated using the power source to which power is supplied by the battery via the power cable 8. The microcomputer 15 generates an AC voltage signal with the same frequency as a resonance frequency f.sub.0 (which will be described later) of the power receiving LC circuit 21 on the basis of a clock outputted from the clock signal source. The microcomputer 15 then applies the generated AC voltage signal to the voltage conversion coil 12 via the matching circuit unit 14 that matches the output of the microcomputer 15 with the impedance of the voltage conversion coil 12. The microcomputer 15 is also connected to the phototransistor 16 to demodulate the detection data of the torque sensor 6 from an infrared signal received by the phototransistor 16 and output the demodulated data to the drive control circuit disposed outside the electrically-conductive case 3 via the signal cable 9.

[0065] Although the voltage conversion coil 12 may be a conductive pattern formed in a helical shape on the power transmitting circuit board 10, the voltage conversion coil 12 in the present embodiment is a chip inductor surface-mounted on a conductive pattern of the power transmitting circuit board 10.

[0066] The voltage conversion coil 12 and the power transmitting coil 13 of the power transmitting LC circuit 11 are formed on the power transmitting circuit board 10 so as to be close to, and opposed to, each other. With such an arrangement, the voltage conversion coil 12 and the power transmitting coil 13 are coupled with each other by electromagnetic induction. A ratio of a voltage generated in the power transmitting coil 13 coupled by electromagnetic induction or the power receiving coil 22 having magnetic field resonance with the power transmitting coil 13 to a voltage of the AC voltage signal applied to the voltage conversion coil 12 is proportional to the number of turns of the voltage conversion coil 12 and the power transmitting coil 13. Thus, the number of turns of the voltage conversion coil 12 and the power transmitting coil 13 is determined on the basis of an operating voltage of loads in the power receiving circuit board 20, such as the torque sensor 6 and the infrared LED 26, which are operated by receiving wireless power supply.

[0067] The power transmitting LC circuit 11 is formed by the power transmitting coil 13 and a power transmitting capacitor 17 connected in series between the land patterns 11a of the power transmitting circuit board 10. Circuit constants for the inductance of the power transmitting coil 13 and the capacitance of the power transmitting capacitor 17 are set so that a series resonance frequency f.sub.0 of the power transmitting LC circuit 11 is identical with the resonance frequency f.sub.0 of the power receiving LC circuit 21. As the result, the power transmitting coil 13 and the power receiving coil 22 generate magnetic field resonance inside the electrically-conductive case 3. Although the power transmitting coil 13 and the power transmitting capacitor 17 can be produced by conductive patterns formed on the power transmitting circuit board 10, the power transmitting coil 13 and the power transmitting capacitor 17 in the present embodiment are provided as discrete components mounted on the power transmitting circuit board 10 in an easily replaceable manner in order to facilitate fine tuning of the series resonance frequency f.sub.0.

[0068] The inner diameter of the power receiving circuit board 20 is approximately equal to the outer diameter of the crankshaft 5. The power receiving circuit board 20 is formed in a circular plate shape perpendicular to the axial direction of the crankshaft 5, and attached around the axis of the crankshaft 5 inside the electrically-conductive case 3. The power receiving LC circuit 21 provided on the power receiving circuit board 20 is formed by the power receiving coil 22 and a power receiving capacitor 27 connected in series. Of these components, the power receiving coil 22 in the present embodiment is formed by a helical conductive pattern provided on a back surface of the power receiving circuit board 20, as opposed to a mounting surface 20a on which other circuit components such as the power receiving capacitor 27 are mounted, because the circular plate-shaped power receiving circuit board 20 attached around the crankshaft 5 has a small mounting area. The power receiving coil 22 is connected in series with the power receiving capacitor 27 provided on the mounting surface 20a via a through hole of the power receiving circuit board 20.

[0069] A series resonance frequency f.sub.0 of the power receiving LC circuit 21 is represented by:

f.sub.0=1/(2π√LC)  (1)

[0070] wherein L denotes an inductance of the power receiving coil 22 in the power receiving LC circuit 21, and C denotes a capacitance of the power receiving capacitor 27.

[0071] When an AC voltage signal having the same resonance frequency f.sub.0 flows through the power transmitting coil 13 to form standing electromagnetic waves having the resonance frequency f.sub.0 inside the electrically-conductive case 3, the power receiving coil 22 generates magnetic field resonance. As a result of induced electromotive force of the power receiving coil 22, the AC voltage signal having the resonance frequency f.sub.0 flows through the power receiving LC circuit 21.

[0072] The full-wave rectifying circuit 23 connected to the latter part of the power receiving LC circuit 21 converts the AC voltage signal to a DC voltage power and outputs the power to the power receiving circuit unit 24. On the basis of the inputted power, the power receiving circuit unit 24 provides a DC power source to the torque sensor 6 and the LED driver 25 so as to operate these circuit components.

[0073] The torque sensor 6 detects a torque being applied to the crankshaft 5 on the basis of a shearing strain generated on a surface of the crankshaft 5. As shown in FIG. 1, the torque sensor 6 includes: a strain sensor 6a fixed to the crankshaft 5; and an input and output unit 6b mounted on the mounting surface 20a of the power receiving circuit board 20 for outputting detection data of the strain sensor 6a to the LED driver 25 and receiving the driving power source from the power receiving circuit unit 24.

[0074] The LED driver 25 controls the blinking of the infrared LED 26 on the basis of the detection data inputted from the torque sensor 6, and causes an infrared signal modulated by the detection data to be outputted from the infrared LED 26. As mentioned above, the phototransistor 16 and the infrared LED 26 are photo-coupled together, so that the infrared signal emitted by the infrared LED 26 is received by the phototransistor 16. However, since the infrared light reflects at an inner wall surface of the electrically-conductive case 3, the phototransistor 16 is not necessarily required to be disposed within a directivity angle of the infrared LED 26.

[0075] In the thus configured wireless power supply device 1, the circuit components, such as the microcomputer 15, the matching circuit unit 14, and the phototransistor 16, mounted on the power transmitting circuit board 10 fixed to the frame body of the power-assisted bicycle are supplied with the power source from the battery via the power cable 8, and the AC voltage signal having the same frequency as the resonance frequency f.sub.0 of the power receiving LC circuit 21 is outputted to the voltage conversion coil 12.

[0076] The resonance frequency f.sub.0 of the power transmitting LC circuit 11 is identical with the resonance frequency f.sub.0 of the voltage conversion coil 12. Thus, when the AC voltage signal having the resonance frequency f.sub.0 flows through the voltage conversion coil 12, the power transmitting coil 13 coupled with the voltage conversion coil 12 by electromagnetic induction oscillates at the resonance frequency f.sub.0, thereby forming electromagnetic waves having the resonance frequency f.sub.0 around the power transmitting coil 13. Since an area around the power transmitting coil 13 is surrounded by the grounded electrically-conductive case 3 including the electrically-conductive metal plate 31 and the electromagnetic shield film 34, no electromagnetic waves formed around the power transmitting coil 13 leak out from the electrically-conductive case 3, thus forming a magnetic field of standing electromagnetic waves having the resonance frequency f.sub.0 in the resonant cavity 35 inside the electrically-conductive case 3.

[0077] The power receiving LC circuit 21 formed on the power receiving circuit board 20 is disposed in the resonant cavity 35, and the power receiving coil 22 of the power receiving LC circuit 21 generates magnetic field resonance with the power transmitting coil 13 at the same resonance frequency f.sub.0. Thus, power obtained by the induced electromotive force of the power receiving coil 22 can be wirelessly supplied to the circuit components, such as the torque sensor 6 and the LED driver 25, formed on the power receiving circuit board 20, which rotates relative to the frame body of the power-assisted bicycle.

[0078] Thus, the torque sensor 6 operates using the induced electromotive force generated in the power receiving coil 22 as a power source, detects a torque being applied to the crankshaft 5 on the basis of the shearing strain of the crankshaft 5, and outputs the detection data to the microcomputer 15 via the infrared signal outputted to the phototransistor 16 from the infrared LED 26. The drive control circuit connected to the microcomputer 15 via the signal cable 9 controls the driving of the electric motor in accordance with the detection data detected by the torque sensor 6.

[0079] According to the present embodiment, since the power transmitting coil 13 and the power receiving coil 22 to generate magnetic field resonance are disposed in the resonant cavity 35 inside the electrically-conductive case 3 surrounded by the electrically-conductive metal plate 31, power can be wirelessly supplied to the loads connected to the power receiving coil 22 at a high transmission efficiency. Moreover, the electrically-conductive case 3 that provides its interior as the resonant cavity 35 may be a metal case that protects the loads such as the torque sensor 6 and the circuit components for wireless power supply from external forces.

[0080] Moreover, with the use of the electrically-conductive screws 4 for attaching the power transmitting circuit board 10 to the electrically-conductive case 3, the power transmitting LC circuit 11 can be connected to the electrically-conductive case 3 grounded at the both ends thereof and can be disposed in the resonant cavity 35 inside the electrically-conductive case 3. Furthermore, since the power transmitting LC circuit 11 is formed on the power transmitting circuit board 10, the resonance frequency f.sub.0 of the power transmitting LC circuit 11 can be easily adjusted by changing the circuit constants of the power transmitting coil 13 and the power transmitting capacitor 17.

[0081] In the above-described embodiment, the AC voltage signal having the resonance frequency f.sub.0 flows through the power transmitting coil 13 via the voltage conversion coil 12 coupled with the power transmitting coil 13 by electromagnetic induction. If there is no need for voltage conversion, however, the AC voltage signal having the resonance frequency f.sub.0 may be directly outputted across the power transmitting LC circuit 11.

[0082] The power transmitting coil 13 and the power transmitting capacitor 17 in the power transmitting LC circuit 11, and the power receiving coil 22 and the power receiving capacitor 27 in the power receiving LC circuit 21 are both connected in series. However, either one or both of these pairs may be connected in parallel as long as these circuits have the same resonance frequency f.sub.0. If the AC voltage signal having the resonance frequency f.sub.0 is directly outputted to the power transmitting LC circuit 11 in which the power transmitting coil 13 and the power transmitting capacitor 17 are connected in parallel using a switching element without providing the voltage conversion coil 12, however, a large current flows through the power transmitting capacitor 17 upon switching at which the polarity of the AC voltage signal changes. As the result, the power transmitting capacitor 17 fails to function as a resonant capacitor. It is therefore desirable that the power transmitting coil 13 and the power transmitting capacitor 17 in the power transmitting LC circuit 11 be connected in series.

[0083] Although a part of the electrically-conductive case 3 surrounding the resonant cavity 35 is formed by the electrically-insulating synthetic resin plate 33, the entire electrically-conductive case 3 may be formed by the electrically-conductive metal plate 31. The present invention is sufficiently applicable even when a part of the electrically-conductive case 3 is opened.

[0084] The embodiment of the present invention is suitable for a wireless power supply device for supplying power to a load operating inside an electrically-conductive case covered with an electrically-conductive plate such as a metal plate.

REFERENCE SIGNS LIST

[0085] 1 wireless power supply device [0086] 3 electrically-conductive case [0087] 4′ electrically-conductive screw [0088] 6 torque sensor (load) [0089] 10 power transmitting circuit board [0090] 11 power transmitting LC circuit [0091] 13 power transmitting coil [0092] 17 power transmitting capacitor [0093] 20 power receiving circuit board [0094] 21 power receiving LC circuit [0095] 22 power receiving coil [0096] 27 power receiving capacitor [0097] 31 electrically-conductive metal plate [0098] 33 electrically-insulating synthetic resin plate [0099] 34 electromagnetic shield film [0100] 35 resonant cavity