CIRCUIT BOARD AND POWER SUPPLY DEVICE

A power supply device includes: a generator including a stator which rotates with a tire wheel, and a rotor which rotates around a rotation axis of the tire wheel; an inertial component fixed to the rotor and configured to maintain a consistent attitude by an own weight of the inertial component; a circuit board fixed to the tire wheel and arranged such that a plate thickness direction is oriented parallel to the rotation axis; a rectifier circuit mounted on the circuit board and rectifies a current output from the generator to supply the current to a load; a plurality of smoothing capacitors provided in the rectifier circuit and positioned on a common imaginary circle around the rotation axis so that the plurality of smoothing capacitors as a whole has a center of gravity located in a central area of rotation.

TECHNICAL FIELD

The present disclosure relates to a circuit board attached to a rotating body and a power supply device.

BACKGROUND ART

A circuit board of this type, which is attached for example to a tire wheel, is known (see, for example, Patent Document 1).

PATENT DOCUMENTS

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

Durability is sometimes an issue with a circuit board attached to a rotating body or a device that contains the circuit board such as the example described above because of the centrifugal force of rotation they are subjected to. The present disclosure provides a technique for improving the durability of a circuit board attached to a rotating body and a device that includes same.

Means of Solving the Problems

The circuit board according to the present disclosure made to solve the above problem is a circuit board fixed to a rotating body, with a plate thickness direction oriented parallel to a rotation axis, including either a plurality of devices mounted on the circuit board to be distributed around the rotation axis so that the circuit board as a whole has a center of gravity located in a central area of rotation, or a single device mounted on the circuit board in an annular shape to have a center coinciding with the rotation axis.

MODE FOR CARRYING OUT THE INVENTION

First Embodiment

A power supply device10A according to a first embodiment of the present disclosure will be described with reference toFIG.1toFIG.7. This power supply device10A is attached to a central part of each wheel101of a vehicle100, as shown inFIG.1. In the central part of the tire wheel11of each wheel101is provided a circular recess14that is open at the outer end and closed at the inner end as shown inFIG.2for attaching the power supply device10A. The circular recess14has a step inside at the open end where the diameter is increased to provide a large-diameter part14A. A small-diameter part14B on the inner side from a step surface14D is formed with locking grooves14N for locking protrusions26to be described later of the power supply device10A to engage with. The step surface14D is formed with a plurality of engaging recesses14K for anti-rotation protrusions27to be described later of the power supply device10A to fit in and engage with.

As shown inFIG.3andFIG.4, the power supply device10A is structured as a unit in which a generator30and a circuit board50are attached to a housing20. The housing20is made of resin, for example, and has a separate housing body21and a lid member22. The housing body21includes a flat, substantially cylindrical tubular wall24that is small in axial length compared to its outside diameter, and positioned such that its center axis coincides with the rotation axis J1(seeFIG.2) of the tire wheel11(which corresponds to the “rotating body” of the present disclosure). Hereinafter the directions parallel to the rotation axis J1of the power supply device10A shall be referred to as “front to back direction.”

The interior of the tubular wall24is divided into two, first chamber24A on the front side and second chamber24B on the rear side, by a partition wall23provided at a midway point in the front to back direction. The lid member22closes the opening at the front end of the tubular wall24, so that the first chamber24A is a tubular compartment closed at both ends. The lid member22and the tubular wall24are processed to be water-proof. The lid member22further has an emblem22A formed on the outer face.

While the tubular wall24of this embodiment is provided with the first chamber24A and second chamber24B, the tubular wall24may instead include only the first chamber24A, with the partition wall23provided at the rear end, or the tubular wall24may be divided in the axial direction into three chambers.

The tubular wall24is formed with a step surface24D on the outer face near the rear end, and a small-diameter part24S on the rear side of the step surface24D. A plurality of locking lugs25protrudes from the rear surface of the tubular wall24, slightly inside of the outer face. These locking lugs25are configured to extend backward in a cantilevered manner and have a locking protrusion26at the tip. A plurality of anti-rotation protrusions27protrudes from an outer edge portion on the rear surface of the tubular wall24. The plurality of locking lugs25and the plurality of anti-rotation protrusions27are circumferentially distributed around the tubular wall24so that the center of gravity of the entire housing20lies on the center axis of the tubular wall24.

The generator30is attached to the rear surface of the partition wall23and accommodated in the second chamber24B. The generator30has the same structure as an AC motor, for example, and outputs an alternating current. Specifically, the generator30is accommodated substantially entirely in a flat cylindrical case38with a quadrate flange39at one end. As shown inFIG.2, the stator33of the generator30is made up of the cylindrical case38and a cylindrical stator field coil33K fixed on the inner side face of the cylindrical case. The rotor32of the generator30on the other hand includes a rotor body32H accommodated in a central space inside the stator33, and a rotating shaft32S extending through a central part of the rotor body32H. The rotating shaft32S is rotatably supported by a pair of bearings32F fixed at both ends of the cylindrical case38. One end of the rotating shaft32S extends out of the cylindrical case38from a central part of the flange39and forms a rotation input part35. A pair of, for example pin-shaped, output electrodes37A and37B protrude rearward from a side face of the generator30, and the generated alternating current is output across these output electrodes37A and37B.

While the generator30of this embodiment includes a pair of output electrodes37A and37B to output the alternating current, the generator may include three output electrodes, for example, to generate a 3-phase alternating current. The generator30may have the same structure as a DC motor and output a direct current.

The partition wall23is formed with a through hole23A in a central part for attaching the generator30, and a plurality of screw holes23B therearound. The front end face of the generator30on a side the flange39is overlapped with the rear surface of the partition wall23(i.e., outer face at one end of the first chamber24A), and screws having passed through the through holes39A at four corners of the flange39are fastened into the screw holes23B of the partition wall23to secure the generator. The rotation input part35extends through the through hole23A in the partition wall23and protrudes into the first chamber24A (seeFIG.2).

Inside the first chamber24A, an inertial component is fixedly attached to the rotation input part35. The inertial component40is a metal circular plate, for example, having a slightly smaller outside diameter than the inside diameter of the first chamber24A, and cut into a form slightly smaller than a semicircle as a whole except for the central part. The rotation input part35is tightly fitted into a through hole40A extending through the remaining central part so that the inertial component and rotor32rotate integrally relative to the stator33.

The inertial component40is not limited to the shape described above; as long as it has the center of gravity shifted off the rotation axis J1, the inertial component may have any shape and may be made of any material.

The circuit board50is disposed behind the generator30. A plurality of support pillars45protrudes rearward from the partition wall23for supporting this circuit board50. Specifically, the support pillars45have a columnar structure, with screw holes in the center at both ends. Along the outer edge of the partition wall23, a plurality of through holes23C is formed at (e.g., 3) equidistant positions along an imaginary circle around the through hole23A. The plurality of support pillars45is secured to the partition wall23by screws having passed through respective through holes23C from the first chamber24A side, and extend rearward beyond the rear surface of the generator30.

The circuit board50is in the form of a circular plate, placed over the rear faces of the plurality of support pillars45, and fastened with screws at the plurality of points along the outer edge of the circuit substate50. The rotation axis J1extends perpendicularly to the center of the circuit board50. Between the rear surface of the generator30and the circuit board50is provided a slight clearance (seeFIG.2).

A rectifier circuit60is mounted on the circuit board50for converting the alternating current output by the generator30into a direct current. As shown inFIG.5(A), the rectifier circuit60includes a pair of input electrodes61A and61B which are connected to the output electrodes37A and37B of the generator30, and a pair of output electrodes62A and62B connected to a load. The pair of input electrodes61A and61B are provided as terminal fittings inside a connector50C fixed in an outer edge portion on a front face50A of the circuit board50. The pair of output electrodes37A and37B of the generator30are inserted in the connector50C and connected to the pair of input electrodes61A and61B. The pair of output electrodes62A and62B are provided as terminal fittings inside a connector50D fixed in an outer edge portion on the front face50A of the circuit board50, and connected to a load to be described later.

The rectifier circuit60converts the alternating current applied to the input electrodes61A and61B to a pulsating current by a diode circuit63, smoothes the pulsating current by a smoothing circuit64, and outputs the current across the pair of output electrodes62A and62B. The diode circuit63is a common bridge circuit having, four diodes63A, for example as shown inFIG.6. The smoothing circuit64is a plurality of smoothing capacitors64A connected in parallel between the pair of output electrodes62A and62B of the rectifier circuit60. Additionally, a resistor65is connected as an element to reduce the current between the smoothing circuit64and one output electrode62A.

As described above, the smoothing circuit64of this embodiment has a plurality of parallel-connected smoothing capacitors64A between the pair of output electrodes62A and62B. Typically, however, one smoothing capacitor having an electrostatic capacity that equals to that of the plurality of smoothing capacitors64A combined is connected between the pair of output electrodes62A and62B. This is because it is generally more advantageous to provide a single smoothing capacitor64A than several divided smoothing capacitors64A in terms of installation space, total mass, cost, and wiring simplicity. Even so, this embodiment uses a plurality of smoothing capacitors64A for the smoothing circuit64in consideration of the fact that the circuit board50rotates with the tire wheel11. These smoothing capacitors64A have the same mass, and mounted on the front face50A of the circuit board50such that their respective centers of gravity are located at positions equally dividing a common imaginary circle around the rotation axis J1of the generator30, as shown inFIG.5(A). Therefore, the center of gravity of the circuit board50as a whole is located near the rotation axis J1(i.e., central part of the circuit board50).

The positions of the plurality of diodes63A and resistor65are also taken into account in order to make the center of gravity of the entire circuit board50closer to the rotation axis J1. Specifically, the plurality of diodes63A included in the diode circuit63has the same mass similarly to the plurality of smoothing capacitors64A, and is mounted on the rear side50B of the circuit board50such that their respective centers of gravity are located at positions equally dividing a common imaginary circle around the rotation axis J1of the generator30. The resistor65is mounted in a central part on the rear side50B of the circuit board50so that its center of gravity is located at the center of the circuit board50. Accordingly, as described above, the center of gravity of the circuit board50as a whole is located in the central part.

A central part of the circuit board50shall refer to a range of a circle around the rotation axis J1having 10% of surface area of either one of the front and rear side of the circuit board50.

The diode circuit63in the rectifier circuit60is not limited to the plurality of diodes63A that forms a bridge connection as described above. Namely, the rectifier circuit60is not limited to a bridge rectifier circuit and may have any configuration. Specifically, the rectifier circuit60may be, for example, a half wave rectifier circuit that is configured with only a single diode and uses only half cycle of alternating current, or a full wave or full wave voltage doubler rectifier circuit configured with a transformer and a pair of diodes. The circumferentially equally distributed configuration mentioned in the above description includes any arrangement that is not necessarily equally spaced but can counterbalance the centrifugal force, such as for example a line symmetric arrangement.

The housing20is fixed to the tire wheel11as described below. The plurality of anti-rotation protrusions27of the housing20and the plurality of engaging recesses14K of the tire wheel11(seeFIG.2) are brought to face each other, and the housing20is pushed into the circular recess14of the tire wheel11to insert the plurality of locking lugs25. This causes the plurality of locking lugs25to bend inward and closer to the center to allow the plurality of anti-rotation protrusions27to engage with the plurality of engaging recesses14K. At the point where the step surface24D of the housing20abuts on the step surface14D of the circular recess14, the plurality of locking lugs25elastically returns so that the locking protrusions26latch in the locking grooves14N of the tire wheel11. This way, the housing20is fixed to the tire wheel11such as to be integrally rotatable. Sealant is applied between the inner side face of the tubular wall24of the housing and the inner side face of the circular recess14so that the space on the inner side of the step surface14D of the circular recess14is sealed water tight, which makes the second chamber24B a water-proof space.

The electrical load connected to the power supply device10A of this embodiment is a tire monitoring device provided to the wheel101as shown inFIG.7. The tire monitoring device90is provided at one end of a tire valve91fixed to the rim11A of the tire wheel11and positioned inside the tire102. The tire monitoring device detects the pressure and temperature inside the tire102and wirelessly transmits the detection results to a signal processor93mounted on the main body of the vehicle100. As shown inFIG.6, the tire monitoring device90is provided with a rechargeable battery90A as a power source, as well as a charging circuit90B for charging the rechargeable battery90A. A pair of input electrodes92A and92B of this charging circuit90B are connected to two components of the tire valve91and wired out of the tire102.

Specifically, the tire valve91has a valve stem91A which is fixed in a state such as to extend through the rim11A, and a valve shaft91B which moves linearly inside this valve stem91A, insulated from each other. These valve stem91A and valve shaft91B are connected to the pair of input electrodes92A and92B of the charging circuit90B described above inside the tire102, and connected to a pair of core wires13A and13B of a cable13outside the tire102.

The cable13is laid along a radial direction of the tire wheel11and secured on an outer face of the tire wheel11. As shown inFIG.2, the tire wheel11is formed with a communication hole12that connects the inner part of the circular recess14on the inner side of the step surface14D and the outer face of the tire wheel11lateral to the circular recess14. The cable13is passed through the communication hole12, with a connector13C provided to the end of the cable13inside the circular recess14. The communication hole12is filled with sealant to be water-proof. The connector13C of the cable13is coupled to the connector50D mentioned above of the circuit board50so that power can be supplied from the power supply device10A to the tire monitoring device90.

The structure of the power supply device10A according to this embodiment is as has been described above. This power supply device10A does not operate and does not generate power when the vehicle100is stopped. The charging circuit90B of the tire monitoring device90that is the load is provided with a diode90C so that no power is supplied from the rechargeable battery90A of the tire monitoring device90to the power supply device10A.

When the vehicle100runs, the stator33of the generator30fixed to the tire wheel11of the wheel101rotates with the tire wheel11relative to the road surface, while the rotor32of the generator30rotates relative to the stator33, because the self weight of the inertial component40restricts rotation of the rotor32relative to the road surface. Thus the power supply device10A of this embodiment can generate power by utilizing rotation of the tire wheel11to cause the rotor32to rotate relative to the stator33of the generator30. The generated alternating current is rectified by the rectifier circuit60and can be supplied to the tire monitoring device90serving as the load. When the rechargeable battery90A of the tire monitoring device90has little remaining power, the battery is charged.

The durability of the circuit board50of the power supply device10A is an issue because the circuit board is subjected to the centrifugal force when the tire wheel11rotates. In this regard, the power supply device10A of this embodiment has a plurality of devices including the plurality of smoothing capacitors64A distributed around the rotation axis J1such that the center of gravity of the circuit board50as a whole is located in a central area of rotation, because of which the circuit board50undergoes less vibration resulting from the centrifugal force. Typically, a single smoothing capacitor is used, rather than a plurality of smoothing capacitors64A. Here, a plurality of smoothing capacitors64A being electrically equivalent is used, and distributed around the rotation axis J1, which facilitates the arrangement of the center of gravity of the entire circuit board50in a central area of rotation. The use of the plurality of smoothing capacitors64A makes each of the smoothing capacitors64A more lightweight, which reduces the centrifugal force applied to each smoothing capacitor64A and in turn reduces the load which the support part of each smoothing capacitor64A on the circuit board50must carry. These all contribute to better durability of the circuit board50and therefore improves the durability of the power supply device10A equipped with the circuit board50.

The circuit board50is disposed opposite to the first chamber24A, with the stator33of the generator30interposed therebetween. The plurality of smoothing capacitors64A mounted on the circuit board50is disposed laterally to the stator33. This efficient use of the space lateral to the stator33allows the power supply device10A to be more compact along the direction of the rotation axis J1.

While the circuit board50may be fixed to the generator30, the circuit board50in the power supply device10A of this embodiment is fixed to the housing20by a plurality of support pillars45rather than to the generator30. As a result, the circuit board50can be fixed more stably, and this contributes to a better durability, too.

The power supply device10A of this embodiment includes the housing20that is fixed to the tire wheel11. The inertial component40is disposed inside the tubular first chamber24A, which is closed at both ends, of this housing20. Therefore entrance of foreign substances into the moving area of the inertial component40is prevented reliably.

The tire monitoring device90is typically driven only by a battery. In this embodiment, the power supply device10A that generates power as the vehicle100runs supplies power to the tire monitoring device90. Therefore, compared to a case where the tire monitoring device90is driven only by a battery, more power is available for the tire monitoring device90, which enables sophistication of the tire monitoring device90.

Second Embodiment

The power supply device10B of this embodiment is shown inFIG.8, and different in that a plurality of smoothing capacitors64A of the smoothing circuit64is mounted on the circuit board50as a single device unit68. Specifically, the device unit68has an annular insulating ring member69, with the plurality of smoothing capacitors64A fixed at several circumferentially equally spaced positions. The plurality of smoothing capacitors64A is connected in parallel between a pair of connection terminals69A and69B fixed to the ring member69. Namely, the device unit68is substantially a single capacitor having an annular shape as a whole. The device unit68is screwed to the front face50A of the circuit board50with an insulating spacer (not shown) therebetween such that its center axis coincides with the rotation axis J1of the tire wheel11. The pair of connection terminals69A and69B of the device unit68are connected between the pair of output electrodes62A and62B of the rectifier circuit60described in the first embodiment.

In addition to the similar effects of the power supply device10A of the first embodiment, the power supply device10B of this embodiment facilitates mounting of the plurality of smoothing capacitors64A onto the circuit board50because the plurality of smoothing capacitors64A is mounted as a device unit68on the circuit board50, in which the smoothing capacitors64A are connected in parallel between the pair of connection terminals69A and69B and fixed on the ring member69. The ring member69receives and balances the centrifugal force applied to the plurality of smoothing capacitors64A and reduces the load on the circuit board50resulting from the centrifugal force, so that the durability of the circuit board50is improved.

The ring member69may be an annular case, or an annular circuit board. In the case with an annular case, the case may be filled with a potting material to fix the plurality of smoothing capacitors64A. Alternatively, instead of the device unit68, a single annular smoothing capacitor64A may be specially produced and mounted on the circuit board50as shown inFIG.9.

Other Embodiments

(1) While the load connected to the power supply device10A of the first embodiment is a tire monitoring device90, the load is not limited to the tire monitoring device90. For example, the load connected to the power supply device10A may be a light-emitting device for decorative lighting of the tire wheel11.(2) While the power supply device10A of the first embodiment is equipped with a rechargeable battery as a load, the power supply device10A itself may include a rechargeable battery. The power supply device10A can then supply power to the load even during the time when the vehicle100is stopped.(3) In the embodiments described above, examples were shown in which the circuit board50was provided to a power supply device10A or10B. Instead, the circuit board may be fixed to other rotating bodies other than a power supply device, and may “include a plurality of devices mounted thereon such as to be distributed around the rotation axis so that the circuit board as a whole has a center of gravity located in a central area of rotation, or, a single device mounted thereon in an annular shape such as to have a center coinciding with the rotation axis.” The circuit mounted on the circuit board is not limited to a rectifier circuit, and the device is not limited to a smoothing capacitor. Specifically, the circuit board may include a divider circuit mounted thereon, with a plurality of resistors that are devices included in this divider circuit distributed around the rotation center. In a configuration where the generator has a similar structure as that of a DC motor and generates a direct current, and where a rotating board has an inverter circuit mounted thereon, a plurality of FETs included in the inverter circuit may be distributed around the rotation center.(4) While the second embodiment described above utilizes the device unit68as a smoothing capacitor, such a unit may be used not only as a smoothing capacitor but also for other capacitors for other purposes. The plurality of devices on the device unit and their connection structure may be changed as required. Specifically, a device unit having a plurality of resistors connected in series and fixed on a ring member, or a device unit having a plurality of switches connected in parallel and fixed on a ring member, may be used.

While specific examples of the techniques included in the claims are disclosed in the specification and drawings, the techniques set forth in the claims are not limited to these specific examples but rather include various modifications and alterations of the specific examples, as well as partial extracts from the specific examples.

DESCRIPTION OF THE REFERENCE NUMERAL