System for transmitting information of reduced pneumatic pressure of tire

Abstract

A system for transmitting information of reduced pneumatic pressure of tires comprising an electromagnetic wave radiation mechanism of an electric field excitation system and at least one receiver antenna of an electromagnetic field sensing type for sensing a polarized wave of an electromagnetic field radiated from the radiation mechanism. The radiation mechanism includes an electromagnetic wave radiation member consisting of a substantially concentric metal body opposedly and substantially provided on each axle of a plurality of tire wheels for actuating as an electric dipole together with the wheels and an oscillator electrically coupled to the radiation member and energized by a switch actuated in response to reduced pneumatic pressure of tire. The receiver antenna is provided in the space between the ground surface and the lower surface of the bottom plate of the car body in order to screen external noise waves.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a system for transmitting information of reduced pneumatic pressure of tire by sensing reduction of pneumatic pressure of a tire and by informing the thus sensed information to an operator when the pneumatic pressure of any one of tires of vehicles is reduced by some reason while running or parking.

Reduction of the pneumatic pressure of a tire to less than a predetermined value while running, particularly running at high speed, is very dangerous because it causes a puncture or a lowering of steerage. Therefore, an operator should sense such reduction with the use of some means. In order to meet such requirement, various devices have hitherto been developed. However, this kind of conventional device has many defects, some of which are complication of an electromagnetic wave radiation mechanism to the signal of an oscillator for sensing reduction of pneumatic pressure of a tire and difficulty for mounting such device to a vehicle. Other defect is in the construction of an antenna mechanism for receiving an electromagnetic wave transmitted from such radiation mechanism. For example, in a system for receiving electromagnetic waves from oscillators of each wheel, it is difficult to mount the antenna mechanism on the vehicle, and in an antenna mechanism which utilizes the conventional antenna for receiving broadcasting or other antenna provided for the same purpose for the electromagnetic waves from the oscillators of each wheel, broadcast waves, communication waves and other noise waves are stronger than the electromagnetic waves from the oscillators to be used, so that it becomes difficult to discriminate a desired signal from others, and thus erroneous information is produced.

For example, a wave radiation mechanism of a conventional transmitter for sensed information of reduced pneumatic pressure shown in FIG. 1 consists of a signal oscillator 1, a sensing switch 2 for closing its contacts when the internal pressure of a tire is lowered to less than a predetermined value, an electric power supply source 3 for suppplying voltage to the oscillator through said switch 2 at the closing thereof, and a loop-shaped electromagnetic radiation member, i.e., a radiation coil 4, for transmitting the output of said oscillator 1. This oscillator 1 is provided with a resonance circuit 5 for carrying out oscillation and for amplifying an oscillated signal and an output coil 6 magnetically coupled thereto, so that voltage induced in the coil 6 is supplied through a conductor wire 7 to said electromagnetic radiation member 4, so as to flow an AC current therethrough and to radiate an induced electromagnetic field from the elctromagnetic radiation member 4.

The loop-shaped electromagnetic radiation member 4 of such wave radiation mechanism, as shown in FIG. 2, is actually constructed in such a manner that its diameter is made larger than the outer diameter D of a rim 11 of a disc wheel 10 and is embedded in a ring 12 made of rubber or the like, and an inner peripheral portion 13 of this rubber ring 12 is pressed between an inner wall portion 14 of the rim 11 and a contact surface 16 of the rim 11 of a tire 15. Accordingly, in case of mounting this rubber ring 12 on a wheel with a tire, the wheel is removed from a fitting portion 18 of a hub 17, air in the tire 15 is completely reduced, and the inner peripheral portion 13 of the rubber ring 12 embedded the loop-shaped electromagnetic radiation member 4 therein is pressed between the inner wall portion 14 of the rim 11 and the rim contact surface 16 of the tire 15, or the rubber ring 12 is mounted to the rim 11 and then the tire 15 is mounted to the rim 11, so that it becomes very difficult to fit the rubber ring 12 to the wheel with the tire. In FIG. 2, the internal pressure sensing switch 2, the power supply source 3 and the oscillator 1 are not illustrated, but they should be provided on the surface portion of the wheel and protected by a wheel cap or the like. Therefore, it also becomes difficult to fit these components to the wheel. In addition, the conductor wire 7 between the output coil 6 and the loop-shaped radiation coil 4 should be introduced into the rear surface side from the front surface side of the wheel through a gap provided in a portion of the wheel under the rim 11 therof, so that the fitting operation thereof becomes troublesome.

Moreover, an electromagnetic wave radiation mechanism of a conventional device shown in FIG. 3 is composed by providing an electromagnetic wave radiation member or radiation members 4' at one or several portions of a rim bottom portion 19 of the wheel 10 and adjacent the rim bottom portion so as to radiate electromagnetic waves from an oscillator through a rubber layer of the tire 15. The electromagnetic wave radiation mechanism having such construction requires a suitable machining operation, i.e., machining of a screw hole 20, for securing the radiation member around the rim bottom portion 19, and the position for fitting the radiation member is so positioned that a plurality of radiation members can precisely keep their static and dynamic balancing to rotation of wheels, or in case of fitting one radiation member, it is necessary to fit a balance weight having the same mass as the radiation member at the position diametrically opposed to the wheel of the radiation member.

Further, in an antenna mechanism for receiving an electromagnetic wave from an electromagnetic wave radiation mechanism, in case of providing a receiver antenna corresponding to electromagnetic wave radiation member of each wheel, the electromagnetic wave (or inductive electromagnetic wave) from the radiation member is absorbed by metal members such as a mudguard or the like provided near the tire, so that it is necessary to set the receiver antenna in the space where the shilding and absorption hardly occur, and very near to each radiation member. Therefore, in the device having a receiver antenna 21, i.e., a senser coil for reception of the wave is fitted to a part of a wheel suspension portion such as a housing of the hub 17 which is at rest against rotation of wheels, and is not changed crossing of magnetic flux against vertical movement of wheels or against angle displacement of front wheels, i.e., a peripheral portion of a brake drum 22 by means of a metal fixture.

In a four-wheel vehicle, the senser coils 21 are secured as described above to the radiation coils 4 of wheels, respectively, and the output lead wires of the senser coil 21 are passed through the car body or connected to a receiver along the bottom portion of the car body.

The receiver of the aforementioned conventional device has the following defects.

That is, the radiation coil 4 and the senser coil 21 are magnetically coupled with each other, and when these coils are so mounted that relative intervals thereof are varied while running, the degree of magnetic coupling is varied, so that it is impossible to transmit signals with satisfaction. Particularly, the front wheels of the vechicle are accompanied by angle displacement for steering, so that mounting of these coils is very difficult. The induction magnetic field of the radiating coil 4 has sharp directivity, and large magnetic absorption and attenuation at the steel portions such as wheels, hubs or the like, so that large electric supply power is required for excitation of the coil.

From the above points, the radiation coil inevitably has the outer diameter larger than the diameter of the rim and it cannot be avoided to arrange the radiation coil along the tire side wall of the rear surface of the wheel. As a result, repair or exchange of a punctured tire becomes very inconvenient.

Further, in the device having the construction shown in FIG. 3, it is necessary to provide a receiver antenna 23 at the position opposed to the tire of a mudguard 24.

Then, fitting of the receiver antenna and wiring between the antenna and a receiver provided in the operator cabin become troublesome.

Further, in case of using the antenna for receiving broadcasting or the antenna mechanism corresponding thereto, provision is made of a receiver for receiving the induced voltage of the antenna regarded as the same potential as the ground surface in relation to the incoming wave through the electrostatic capacitance between the car body and the ground surface or for receiving the induced current flowing through said electrostatic capacitance from the antenna to the ground surface, but in case of receiving the electromagnetic wave from the radiation member of the oscillator near the wheel, the electromagnetic wave from each radiation member is reflected from or absorbed in the side surface of the car body so that radiation energy flowed to a desired receiver antenna becomes a little. On the contrary, the electromagnetic waves for broadcasting and communication and other incoming noise waves are received by the receiver with large energy, so that at an input path of the receiver, the ratio of the signal component of the elctromagnetic wave from said radiation member and the signal component (noise signal) of other incoming waves (the so-called signal-to-noise ratio) becomes lessened and discrimination of a desired signal becomes very difficult, so that stability of reception necessary for this kind of devices is spoiled.

One of various defects of the aforementioned device according to the conventional technique is that in case of utilizing an electric characteristic of the electromagnetic wave radiation member for the oscillator, i.e., induction magnetic field in radio engineering, the receiver antenna mechanism must be arranged near each radiation member of wheels. Therefore, in this point these defects cannot be avoided. When a receiver antenna mechanism of one system is arranged at the upper portion of the car body, the electromagnetic wave radiated from the radiation member for the oscillator can be received, but the received energy is weakened as described in the foregoing.

SUMMARY OF THE INVENTION

An object of the present invention is to eliminate the aforementioned various defects and to provide a system for transmitting information of reduced pneumatic pressure of tires comprising a plurality of electromagnetic wave radiation members corresponding to each tire wheel and an antenna mechanism for reliably receiving electromagnetic waves from each radiation member.

Another object of the invention is to provide a system for transmitting information of reduced pneumatic pressure of tires, which can easily be mounted on the car body and manufactured inexpensively.

Further object of the invention is to provide a system for transmitting information of reduced pneumatic pressure of tires, in which electromagnetic wave radiation having wide directivity can be possible by means of an oscillation circuit having low electric supply power, and instead of providing a number of sensing receiver coils corresponding to a number of wheels, only one antenna can receive information, and the system being easily mounted on the surface of a wheel.

The system for transmitting information of reduced pneumatic pressure of tires according to the present invention comprises an electromagnetic wave radiation mechanism of an electric field excitation system and a receiver antenna of an electric field sensing type or a magnetic field sending type. The electromagnetic wave radiation mechanism includes an electromagnetic wave radiation member consisting of loop-shaped metal body opposedely provided on the wheel surface of a plurality of tire wheels and an oscillator coupled to the radiation member and energized in response to reduced pneumatic pressure of the tire. The receiver antenna is provided in space between the surface of the ground and the lower surface of the bottom plate of the car body and sense a horizontally polarized wave of an electric field or a vertically polarized wave of a magnetic field radiated from said radiation mechanism, respectively. The electromagnetic wave radiation member is a metal ring having a common axis to metal wheels for holding the tire. The metal ring is electrically insulated and opposedely arranged to the metal wheel and is used as a radiation antenna for the output of an oscillator energized in response to reduced pneumatic pressure of the tire. The metal ring is embedded in an annular insulator which is fitted to a rim of wheel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a transmitter for reduced pneumatic pressure signals of tires according to a conventional system;

FIGS. 2 and 3 are cross-sectional views of the conventional system;

FIG. 4 is a schematic circuit diagram of transmitter of the system according to the present invention;

FIG. 5 is a cross-sectional view showing the positional relation of an electromagnetic wave radiation mechanism according to the present invention which consists of a tire wheel and an electromagnetic wave radiation member opposedly provided thereto;

FIG. 6 is a cross-sectional view showing another embodiment of the electromagnetic wave radiation mechanism according to the present invention;

FIG. 7A is a schematic side view showing a receiver antenna mechanism mounted at the bottom surface of a car body;

FIG. 7B is a schematic bottom view of the receiver antenna mechanism shown in FIG. 7A;

FIG. 8 is a plan view showing a receiver antenna of an electric field sensing type particularly a dipole antenna for use in the system according to the present invnetion;

FIG. 9 is a perspective view showing a receiver antenna of a magnetic field sensing type for use in the system according to the invention;

FIG. 10 is a fundamental view showing another embodiment of tire wheel provided with the transmitter device according to the invention;

FIG. 11 is a partially sectional view of the tire wheel provided with the transmitter device shown in FIG. 10;

FIG. 12 is a partially perspective view of wheel provided with the transmitter shown in FIG. 11;

FIG. 13 is a view showing distribution of electric field in case of cutting the radiation mechanism in the plane inclusive of the wheel of the vehicle; and

FIG. 14 is an explanatory view showing strength of electric field which is received by a receiver antenna AB from the center (0) of a radiation member.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 4, one embodiment of a fundamental construction of the system according to the present invention is shown. An electromagnetic wave radiation mechanism of the system comprises an oscillator 1 and an electromagnetic wave radiation member 4 in each wheel.

Here, said radiation mechanism means a mechanism comprising a tire wheel 10 and a radiation member 4 for forming an electric dipole. The radiation member 4 consisting of a metal body is electrically connected to the output side of the oscillator 1 through a conductor wire 7. The oscillator 1 is further connected to a switch 2 having an electric contact 2a which closes when a pneumatic pressure of the tire is lowered to less than predetermined value and an electric power supply source 3. The oscillator 1 operates when the contact 2a is closed by lowering the pneumatic pressure of the tire and a closed circuit containing the power supply source 3 is formed. The operation of the oscillator is continued while the contact 2a is closed. Then, an electromagnetic wave is radiated from the radiation member 4 by this oscillation.

In the embodiment of the present invention, as shown in FIG. 5, the radiation member 4 is arranged on the same axis as that of an axle at the position opposed to the surface of the wheel 10, so as to form an electric dipole between the radiation member 4 and the surface of the wheel 10 and to connect the wheel surface to the surface of the ground (connect a feedback path 8 of the oscillator to the wheel). The power supply source 3 is preferablly a small mercury dry cell.

That is, the elctromagnetic radiation body can be formed into a dome, a loop, a ring or a disc having no hole, or a polygon, and can concentrically be arranged and fitted to the wheel. Accordingly, the shape of the enveloping surface of an electric line of force 9 formed between the surface of the radiation member 4 and the wheel surface becomes dome-shape or cylindrical under the condition that it coindides with the axis of the wheel. The more preferable enveloping surface by means of the electric line of force is, as shown in another embodiment of FIG. 6, is obtained by providing a loop-shaped projection member 10a on the surface of the wheel 10 and by arranging the radiation member 4a opposedely thereto. Its shape is therefore cylindrical or drum-shape. As described in the foregoing, the loop-shaped radiation member 4 or 4a has its axis coincided with the axis of the wheel and is provided opposedly to the surface of the wheel 10, so that lowering of the output of the oscillator caused by increasing electrostatic capacitance between a projection 10b of a supporting member of a bearing provided in the front wheels or the like of the vehicle and the radiation member 4 or 4a can be prevented. It means that the output of the electromagnetic wave radiation is made equal as possible as compared with the case of the surface of the wheel having no projection such as rear wheels.

The shape and arrangement of the antenna mechanism according to the invention will be explained with reference to embodiments shown in FIGS. 7A and 7B.

A receiver antenna mechanism suitable for receiving the horizontally polarized wave of a radiation electric field from the electromagnetic wave radiation mechanism of the transmitter is arranged in the space sandwiched by a bottom plate 30 of a car body and the ground surface 31 at the position adjacent the bottom plate 30 and in flat plane 32 almost paralled to said bottom plate 30. When an antenna 33 is secured to the car body at a right angle between the front wheels and the rear wheels, the antenna 33 receives an electric field wave component polarized in the direction at right angles to the forward direction of the vehicle, while the antenna 33a secured parallel to the car body receives an electric field wave component polarized paralled to the forward direction of the vehicle. These antennas 33 and 33a can be used separetely or together as an electrostatic field antenna. Further, the receiver antenna can be a crossed dipoles consisting of a pair of antennas 34a and 34b, i.e., the so-called shortened type, which make the length of one segment shorter than or in a fraction of the wave length of the electromagnetic wave radiated from the radiation member 4.

Further, an embodiment of the receiver antenna having a mechanism different from the above electrostatic field receiver antenna is shown in FIG. 9. The antenna in this embodiment is made by applying a winding 36 to a bar-shaped magnetic core 35 which has axis on a perpendicular dropped from the bottom surface of the car body onto the ground surface. Around the outer periphery of the winding 36 is provided a metal plate for compensating the electrostatic potential caused by the electric field of the electromagnetic wave, and further provided an electrostatic shielding cylinder 37 having such a structure that a part of the periphery thereof is not short circuited against the induced voltage caused by the core 35. These are a magnetic field type antenna for obtaining the voltage induced in the winding 36 by a change of the flux passed through the magnetic core 35 at the output terminal 38. Such magnetic field type antenna as shown in the drawing is provided at the middle of the front and rear wheels or at the rear of the rear wheels of the car body.

The system of the above described construction according to the invention is operated as follows.

When pneumatic pressure of either one or a plurality of tires of a vehicle is lowered to less than a lower limit value, the contact of the switch 2 is closed to form the closed circuit inclusive of the power supply source 3 so that the voltage of the power supply source 3 is applied to the oscillator 1, and thus the oscillator 1 is energized. The output of the oscillator is supplied to the radiation member 4 through the line 7. The line 8 of the oscillator 1 is connected to the surface of the wheel 10 and the radiation member 4 and the surface of the wheel 10 are opposedly provided with each other to form electric dipole, so that if they are excited by the oscillator, the electric lines of force 9 generated between both of them become an alternating electric lines of force equal to the excitation frequency. These electric lines of force are, as shown in FIG. 5, enveloped around the axis of the wheel in the form of a dome. Further, in another embodiment shown in FIG. 6, the electric lines of force form a drum-shaped by the loop-shaped projection 10a on the wheel surface. Therefore, the so-called electromagnetic wave is generated by groups of these electric lines of force, and three-dimensionally propagated around the dipole.

A preferable embodiment for securing the system according to the invention to the wheels of the vehicle will be explained with reference to FIGS. 10, 11 and 12. In the present embodiment, the electromagnetic wave radiation member consists of a loop-shaped radiation antenna 4b made of a metal wire as shown in FIG. 10, the radiation antenna 4b is embedded in a ring-shaped insulator body 12 made of a material selected from hard plastics and hard rubbers or the like as shown in FIGS. 11 and 12, the loop antenna 4b is arranged adjacent the outer wall of the rim 11 in the space of the outer wall portion of the rim, and the ring-shaped insulator body 12 is fitted to the rim 11 by means of a ring-shaped fitting jig 39, 40 so as to coincide the axis of the ring with the axis of the wheel 10. Further, the power supply source 3 and the oscillator 1 are accommodated in a part of the ring-shaped insulator body 12 as shown in FIG. 11. The power supply source 3 is preferablly a small mercury dry cell. One end 5A of the resonance circuit 5 of the oscillator 1 is connected to the antenna 4b, while the other end 5B is grounded to the rim 11 by means of a grounded fixture (not shown) provided at a part of the insulator body 12. The internal pressure sensing switch 2 of the tire is secured to a valve and connected to the oscillator through the conductor wire as shown in FIG. 10.

In the above described construction, when the internal pressure of the tire is lowered to less than a predetermined value and the sensing switch 2 is closed, the voltage of the power supply source 3 is applied to the oscillator 1 and a resonance voltage is generated between the terminals 5A and 5B of the resonance circuit 5. The terminal 5B is at grounded potential, so that the voltage applied to the terminal 5A, i.e., the antenna 4b, is generated by the driving of a constant current from an active element for oscillation in a parallel circuit consisting of the coil 5L, capacitor 5C and the capacitance 4C, provided that the value of electrostatic capacitance 4C of the wheel to the antenna 4b is Ca and the value of the leakage resistance 4R of the wheel to the antenna 4b is Ra, so that if the current is i and the impedance of the parallel circuit is z, the voltage applied to the antenna becomes iz, which is in proportion to the impedance z. The impedance z is z.apprxeq.Ra during resonating, so that in order to make the impedance large, it is preferable to provide the large leakage resistance of the ring-shaped insulator body 12.

On the other hand, in case that the resonance circuit 5 actuates with the same frequency, the output voltage thereof is in proportion to Q of the coil 5L, i.e., the ratio of the reactance .omega.L and the internal resistance re of the coil 5L, .omega.L/re, so that in order to make L large, the even electrostatic capacitance of the wheel to the antenna should be made small, and in order to make the radiation efficiency of the antenna large, it is necessary to make the radiation effective area large. The loop or ring-shaped antenna made of a metal conductor according to the invention is to make the even electrostatic capacitance of the wheel to the ring conductor small and make the radiation area large by an envelope effect to the high frequency voltage, so that only a small power is required for electric field excitation, the directivity becomes maximum on the plane parallel to the bottom surface of the car body, and in the vehicle, the electromagnetic wave from the radiation antenna of each wheel can be received by only one receiver antenna.

Further, it is possible to provide the radiation antenna and circuit elements such as oscillator or the like inside the wheel cap, but if all the circuit elements are embedded in the ring-shaped insulator body 12 and integrated by arranging the mounting jig 39 to the outer wall portion of the rim 11 as shown in the present embodiment, not only detachability to the wheel 10 becomes very easy, but also connection of the internal pressure senser fitted to the valve with the transmitter becomes easy. In addition, there is another advantage that the outer diameter of the metal ring as a radiation antenna can be made large.

As described in the foregoing, the electromagnetic wave three-dimensionally propagated around the dipole for one radiation mechanism is designated by cut by planes inclusive of axle of each wheel of the vehicle as shown in FIG. 13. In FIG. 13, the forward directions by propagation of the electric field polarized wave of the electromagnetic wave along the x-y plane becomes radial around the radiation member, and thus groups of electric line of force (.alpha.) are estimated on any plane. The density of electric line of force at any point (P) on this plane (flux of electric line of force passing through a unit area .DELTA.s parallel to the z coordinate at this point) becomes maximum when the unit area is at a right angle to the line. Supporting that this maximum state is D, when the unit area is at an angle .theta. to the x-y plane, it becomes D.sub..theta.=D.sub.cos.sub..theta.. From this equation, when the unit area becomes at right angles to the x-y plane the density of electric line of force is maximum.

A receiver antenna 33 or 33a consisting of a straight metal conductor is placed at its center portion of diagonal lines of wheels in the x-y plane or the parallel plane adjacent the x-y plane.

The antenna 33 receives the effective mean electric field shown by a curved line portion MN which is extended along the mean intensity of electric line c of force is the electric lines a and b of force passing through the segment AB of the antenna for the electromagnetic wave radiated from the wave radiation mechanism of one of wheels and which is determined by the intersections of the mean intensity of electric line c of force and the normal lines m and n through both ends A and B or the segment from the center 0 of the electromagnetic wave radiation member as shown in FIG. 11. The middle point P of the segment AB is at equal distances from the wave radiation mechanism of each wheel, so that the voltage induced in the antenna becomes almost equal even by any radiation member. The antenna 33a shown in FIG. 7B corresponds to the segment AB of the antenna shown in FIG. 14 rotated 90.degree. around the middle point P, and the electric field intensity where the segment is positioned is slightly different from in the antenna 33, but the distance from each wave radiation member is same as that of the antenna 33, so that almost equal induced voltage for the electromagnetic wave from any wave radiation member can be obtained. In the receiver antenna consisting of two lines perpendicularly intersecting each other shown in FIG. 8, when the impedance of a path inclusive of the load Z induced by the receiver paths r and s from each middle point P and Q of the segments AB and CD of two antennas 34a and 34b is properly chosen and one of the segments AB or CD is made one-half or one-fourth of the wave length of the electromagnetic wave generated from the radiation member, the phase of the potential or current of the middle points P and Q can be made an opposite pole relation which is phase shifted by 180.degree., so as to form a dipole antenna and a large antenna gain can be obtained as compared with the antenna 33 or 33a.

A receiver antenna of magnetic field type will be explained hereinafter. As shown in FIG. 13, the antenna can receive a magnetic field polarized wave presenting in the vertical direction to the group of the electric lines of force on the x-y plane and the electric field intensity is the strongest on the x-y plane, so that it can easily be found that the magnetic field intensity at right angles thereto is also the strongest according to a well known therom of pointing. If the receiver antenna of magnetic field type is mounted vertical to the bottom plate 30 of the car body and at the central portion of the diagonal line of each wheel, a single antenna can equally receive magnetic field polarized waves from the radiation mechanism of each wheel at the magnetic field intensity corresponding to the aforementioned effective electric field intensity of the receiver antenna 33 or 33a of the electric field type.

The receiving function for the electromagnetic wave of the wave radiation mechanism is explained with reference to each embodiment of the antenna mechanism according to the present invention in the foregoing, and the effect for removing other electromagnetic waves transmitted from the radiation mechanism other than that of each antenna mechanism will be explained hereinafter. In the aforementioned embodiments, the receiver antenna mechanism of the electric field type according to the invention is arranged in the plane inclusive of each axle within the space between the bottom portion of the car body and the ground surface parallel thereto or along the plane adjacent the bottom portion of the car body, and the receiver antenna mechanism of the magnetic field type is so arranged that the bar-shaped antenna has the axial direction vertical to the plane of the bottom surface of the car body. Accordingly, the electromagnetic wave from the radiation member in the space can be received by an antenna mechanism of one system with the strongest magnetic field intensity. On the other hand, the communication or broadcasting wave is screened in said space from the antenna placed at this position through the electrostatic capacitance of the car body to the ground, so that the electric field intensity of the electromagnetic wave around the antenna is considerably reduced. Further, even if the ground potential of the car body caused by these waves is present, the car electrostatic capacitance of the antenna adjacent the bottom portion of the car body is considerably larger than the ground electrostatic capacitance of the antenna, so that the antenna per se becomes almost same potential as that of the car body. Therefore, the voltage induced by these undesirable incoming waves is reduced, and thus it has no influence as noises upon reception of the electromagnetic wave from the radiation mechanism of each desired wheel.

Next, how to treat noises generated from the ignition system of the engine of the vehicle and noise generator is explained. The electromagnetic noise wave generated by the vehicle itself is strongly present in the space extended from the lower opening portion of the engine room of the vehicle to the ground surface, and then such noise becomes disturbing in the receiver antenna arranged at the aforementioned position. In order to remove this noise, the mounting position of the receiver antenna mechanism is preferably shifted from the central position of the diagonal line of each wheel to the opposite side of the engine room. An embodiment of this case (antennas 33b, 40a shown by a dot-dash line in FIG. 7) belongs to the category of the present invention.

As explained in detail, the electromagnetic wave radiation mechanism according to the present invention can radiate the electromagnetic wave with a constant intensity regardless of rotation and rest of wheels, and further radiate the strongest electric field polarized wave or magnetic field polarized wave in the vertical direction thereto on the plane inclusive of each axle or in the space between this plane and the bottom surface of the car body. Accordingly, if one system of the electric field type or magnetic field type receiver antenna mechanism is arranged in the space, any electromagnetic wave from any radiation member of the wheel can be received with almost equal electric and magnetic field intensity. Further, the ring-shaped or dome-shaped radiation member is arranged on the same axis as that of the wheel by facing to the wheel surface, while the oscillator circuit and the power supply source are also accommodated in the central portion of the radiation member and integrally formed with each other, so that any fault caused by unbalanced mass to rotation of the wheels can be eliminated. The device according to the present invention can easily be mounted by the use of a hub bolt for fitting the wheel of a vehicle or by operation similar to the fitting operation of the wheel cap. Furthermore, the receiver antenna mechanism can receive the electromagnetic wave from the desired radiation member with the strong intensity of electric or magnetic field, and reduces unnecessary waves by screening effect provided by utilizing the electric ground characteristic of the car body, and can stabilize reception of desired electromagnetic wave. The receiver antenna mechanism according to the present invention is not a conventional system for arranging a plurality of antennas but one system, so that the mounting of the antenna and the installation of the conductor wire to the receiver can be simplified.

In the aforementioned embodiments, the radiation antenna is a closed ring, but the present invention does not limit it thereto. The radiation antenna can be a ring opened at one point. In this case, the central point to the segment is made a contact with the output of the oscillation circuit, so that a standing wave is generated to the whole length of the ring and the voltage feeding can be formed, or one end of the open ring is connected to the tap down point of the oscillation coil 5L, so that current feeding can be formed. In this case, the directivity of the radiation electric field becomes the strongest along the vertical plane to the bottom surface of the car body, but the effect thereof is as well as the aforementioned one.

Further, the tire can be used as an insulator body for the aforementioned radiation antenna. However, even if it is embedded in the tire, the same effect as the aforementioned embodiment can be obtained.

Claims

What is claimed is:

1. A system for transmitting information of reduced pneumatic pressure of tires, comprising an electromagnetic wave radiation mechanism of an electric field excitation system having an electromagnetic wave radiation member consisting of a substantially concentric metal body opposedly and substantially concentrically provided on each axle of a plurality of tire wheels for actuating as an electric dipole together with the wheels and having an oscillator electrically coupled to said radiation member and energized in response to reduced pneumatic pressure of tires; and at least one receiver antenna of an electromagnetic field sensing type provided in the space between the surface of the ground and the lower surface of the bottom plate of the car body for sensing a polarized wave of an electromagnetic field radiated from said radiation mechanism in order to screen external noise waves.

2. The system as claimed in claim 1, wherein said electromagnetic wave radiation body consists of a metal ring having a common axis to metal wheel for holding the tire, said metal ring is electrically insulated and opposedly arranged to said metal wheel, and is used as a radiation antenna for the output of an oscillator energized in response to reduced pneumatic pressure of the tire.

3. The system as claimed in claim 1, wherein said metal ring is formed into the shape of an open ring with a cutout portion, whereby the electromagnetic wave having a standing wave generated in the form of the metal ring is radiated.

4. The system as claimed in claim 2, wherein said metal ring is embedded in an annular insulating body made of a material selected from hard plastic materials, hard rubbers or the like, and said insulating body is fitted to a rim of the wheel.

5. The system as claimed in claim 1, further including a loop-shaped projected member positioned inwards in the radial direction from the rim portion of the wheel and substantially concentrically projected in the direction of the axle of the wheel, said projected member being integrally formed with the wheel, and an electromagnetic radiation member consisting of a loop-shaped metal body being provided in opposition to said projected member.

6. The system as claimed in claim 4, wherein the oscillator and a power supply source thereof are embedded in said annular insulating body.

7. The system as claimed in claim 4, wherein the annular insulating body is detachably fitted to the rim of the wheel by means of a jig along the inner surface in the radial direction thereof.

8. The system as claimed in claim 7, wherein the power supply source embedded in the annular isulating body is small mercury dry cell.

9. The system as claimed in claim 1, wherein said receiver antenna is an antenna of an electric field sensing type for sensing a horizontally polarized wave of an electric field radiated from said electromagnetic wave radiation mechanism.

10. The system as claimed in claim 1, wherein said receiver antenna is an antenna of a magnetic field sensing type for sensing a vertically polarized wave of a magnetic field radiated from said electromagnetic wave radiation mechanism.

11. The system as claimed in claim 10, wherein said antenna of magnetic field sensing type is consisted of a bar-shaped magnetic core, a sense winding wound around said magnetic core, and an electrostatic shielding cylinder provided around said winding, and the axis of said magnetic core is coinsided with a perpendicular dropped from the bottom surface of the car body onto the surface of the ground.

12. The system as claimed in claim 1, wherein the receiver antenna is a bar-shaped receiver antenna, and said antenna is substantially arranged along the axle direction of the car body.

13. The system as claimed in claim 12, wherein the bar-shaped receiver antenna is substantially arranged along the forward direction of the car body.

14. The system as claimed in claim 1, wherein use is made of two rod-shaped receiver antennas, and said antennas are so arranged that its axes are intersected each other.

15. The system as claimed in claim 1, wherein the substantial center of at least one receiver antenna is arranged at an intersection of diagonal lines from four wheels of a four-wheel vehicle.