AIR PRESSURE INDICATOR FOR A VEHICLE TYRE

Abstract: The present invention relates to a device which indicates the safety limits of the air pressure in each one of the pneumatic tyres of a vehicle by transmitting appropriate information from the wheels to the driving control board. Transmission of information is based on the capacitive coupling between rotating and non-rotating conductive annular surfaces (2-5, 12-19, 72-75) which are mounted into channels of insulated bases (6-9) fixed in the available space between the bearing flange, the braking system and the wheel bearings (66) and are forming cylindrical and plane capacitors. An electronic circuit incorporates these capacitors as basic elements for its operation, and also an AC bridge (20) to give an automatic compensation by measuring the differential capacitance for each pair of the wheels to avoid faulty indication due to causes like humidity, temperature, etc. Also a simple electronic circuit can be used for each one of the wheels. A tyre pressure sensor (1) comprises a semiconductor membrane (30) with an electrode (33) which is shorting out the rotating conductive surfaces (2, 3, 12, 13, 16, 17, 72, 73) when the tyre pressure deviates from the safety limits resulting in a change of the original frequency and giving visual display or audio indication.

Description: AIR PRESSURE INDICATOR FOR A VEHICLE TYRE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device which indicates the safety limits of the air pressure in the pneumatic tyres of a vehicle by transmitting information from the rotating wheel to the driving control board. The operation of the device is based on a capacitive coupling between rotating and nonrotating conductive (metallic, carbon, etc.) coaxial cylindrical, coaxial annular and concentric annular surfaces mounted onto insulated bases. They are fixed into any available and suitable space between the rotating and the nonrotating part of the wheel assembly, which can be the space between the rotating bearing flange and nonrotating braking system or the space between the bearings of the wheel. For each one of the wheels of the vehicle the system includes a tyre pressure sensor mounted on the wheel which operates as an ON-OFF mechanical switch, according to the variations of the air pressure in the pneumatic tyres. When the air pressure, in any one of the pneumatic tyres of the vehicle, deviates from a normal predetermined value, the tyre pressure sensor electrically connects the rotating conductive surfaces, thereby effecting an enhanced capacitive coupling between the above mentioned conductive surfaces which can be detected by an electronic circuit, by means of a visual or audio indication. Over-or under-inflated tyres are dangerous and could be avoided by the device of the present invention, which can operate as a road safety device. The present invention eliminates all the disadvantages of the various patents which have been awarded in the past to the same inventor N. F. Tsagas from USA 5,531,109/2.7.96, EPO 550701 Bl/16.10.95 and Australia 671583/5.3.97. 2. Description of the Prior Art. Various devices have been developed in the prior art to control the faulty air pressure in anyone of the tyres of a vehicle. Basically the following principles of operation are used in those prior art devices. a) The current collector system, wherein a current collector ring is used on the rotating part of the wheel and a collector brush is fixed at the nonrotating part of the wheel assembly to connect the tyre pressure sensor and indicator of the device. b) The wireless system, wherein a wireless frequency transmitter is mounted on the rotating part of the wheel, and a receiver is placed at the driving control board. c) Resonance circuit system, wherein a detecting switch, an antenna and a circuit with inductance and capacitance are mounted onto the rotating tyre and a transmitter and receiver at the nonrotating part of the vehicle, wherein an intermittent retransmission of the abovementioned circuit occurs in response to the variations in tyre air pressure, this retransmission being of the same frequency as the resonance frequency of the circuit. Various disadvantages are associated with the aforementioned systems of the prior art, wherein degradation of performance tends to occur, sooner or later, due to a) wear of the parts, b) batteries mounted onto the rotating wheels, c) integrated electronic circuits for the transmitter which are sensitive to the strains mounted onto the rotating wheels, d) complicate mechanism which tends to exhibit deviations in resonance and in general e) the installation of systems which make the device unreliable, under worsh conditions and needs employment of severe maintenance standards. In the previous Tsagas's systems described in the aforementioned patents, various disadvantages being due to improper shape and locality of metallic strips, the electronic circuit and the pressure gauge made the device unreliable and caused installation difficulties. SUMMARY OF THE INVENTION The first object of the present invention is to provide an air pressure monitoring device in the pneumatic tyres of a vehicle, which eliminates all the abovementioned disadvantages in order to achieve a) an accurate and reliable operation, b) a convenient and easy installation, c) a low cost with maintenance requirements close to zero and d) an additional safety capability to the driver. A second object of the present invention is to provide an air pressure monitoring device in the pneumatic tyres of a vehicle, with a special configuration and dimensions of rotating and nonrotating conductive coaxial cylindrical and annular surfaces within the wheel assembly, in order to achieve the highest possible capacity of the nonrotating conductive surfaces by shorting out the rotating conductive, metallic or carbon, surfaces and to eliminate parasitic capacitances. A third object of the present invention is to provide a proper positioning for the conductive surfaces within the wheel assembly, so as to offer protection from temperature, humidity, water, dust, etc. The fourth object of the present invention is to provide a proper electronic circuit so as to obtain optimum efficiency in the operation of the device in the desired limits of capacity changes. Finally, a fifth object of the present invention is to provide a reliable tyre pressure sensor of very small dimensions to operate as a mechanical switch of shorting out the rotating conductive surfaces after exceeding the safety limits of air pressure in the pneumatic tyres of a vehicle. The abovementioned objects of the present invention are implemented with the use of rotating conductive coaxial and concentric cylindrical and annular surfaces surrounding the nonrotating conductive cylindrical and annular surfaces mounted, rotating and nonrotating surfaces, onto insulated bases or metallic bases insulated by ceramic. They are fixed onto the rotating and nonrotating parts of the wheel assembly, in the location between the bearing flange and braking system and between the bearings of the wheel form cylindrical and plane air capacitors. An air pressure sensor, as a tyre pressure sensor, of a vehicle operating as an ON-OFF mechanical switch can electrically short out the rotating conductive cylindrical and annular surfaces by means of a silicon membrane being curved accordingly to the air pressure changes. This tyre pressure sensor can be positioned either on the existing valves or on a hiding place of the rim. The capacitance increase of nonrotating conductive surfaces, by shorting out the rotating conductive surfaces, can change the operating frequency of the electronic circuit. This can activate visual and audio indications corresponding to the tyre with the faulty pressure. One of the main advantages of the present invention is the coaxial and concentric cylindrical and annular configuration of the rotating conductive surfaces mounted onto insulated bases and surrounding the cylindrical and annular nonrotating conductive surfaces being mounted, by metal or carbon -plated, into shallow circular channels, which are opened onto the periphery of insulated bases. Some nonconductive concentric rings with negligible j friction coefficient like ceramic and with small thickness surround and cover the conductive concentric annular surfaces and a spring is pressing the insulated base from back side. By this configuration the rotating and nonrotating conductive surfaces can be very close, in a constant distance, without touching each other. This coaxial cylindrical and annular configuration of conductive surfaces together with their proper positioning onto the insulated bases results to a maximum enhanced capacitive coupling between the abovementioned conductive surfaces, which thereby increases very much the operational efficiency of the device. Also the parasitic capacitances, due to mechanical defaults and vibrations of the rotating wheels, dust, water, humidity, temperature, surrounding metallic surfaces etc, are negligible. BRIEF DESCRIPTION OF THE DRAWINGS The application of the invention is described below by reference to the accompanying drawings, wherein the abovementioned objects and other novel features of this invention will become apparent to those skilled in the art. FIG. 1 provides a general view of the device and the shaft of the wheel assembly, wherein the mechanical part of the proposed device, in accordance to a first preferred embodiment, is comprising a system of rotating and nonrotating conductive coaxial cylindrical and annular surfaces mounted onto insulated bases fixed in the space between the bearing flange, the braking system, the bearings and the shaft of the wheel assembly. Also shown is a block diagram of the tyre pressure sensor and the electronic circuit of the proposed device. FIG. 2 shows various longitudinal sectional views of the shaft of the wheel assembly, wherein the mechanical parts of the proposed device, in accordance to a second preferred embodiment, are comprising various configurations of rotating and nonrotating conductive coaxial and concentric cylindrical and annular surfaces onto different insulated bases fixed in a suitable space of the wheel assembly. Also shown is a block diagram of a resonance electronic circuit which can activate a visual display and a audio indication, when the rotating conductive surfaces are shorted out by the tyre pressure sensor in case of ubnormal air pressure in any pneumatic tyre. FIG. 3 shows air pressure sensor with silicon membranes and- substrates. FIG. 4 shows various longitudinal sectional views of shaft of the wheel assembly, wherein the mechanical part of the device, in accordance to the third preferred embodiment, is comprising rotating and nonrotating conductive coaxial cylindrical and concentric annular surfaces mounted by carbon or metal-plated into shallow channels, being opened onto bases made by dense insulated material or insulated metallic bases, being fixed in the space between bearing flange and braking system onto the rotating oil collector and nonrotating shaft of the wheel assembly. The insulated cylindrical bases and the conductive surfaces are divided into two half pieces which are connected by means of bolts and nuts assemblies, for convenient and easy installation, and elastic spring washers being used to confront a metallic expansion of shaft due to heat. Nonconductive concentric rings with negligible friction coefficient like ceramic and with small thickness surround and cover the conductive concentric annular surfaces and a spring is pressing the insulated base from back side. The associated block diagram of the electronic circuit is the same as that of FIG 2. FIG. 5 shows a cross sectional view of a vehicle's twin wheels assembly wherein the mechanical part of the proposed tyre pressure sensor, in accordance to a third preferred embodiment, again is comprising one pair of rotating and one pair of nonrotating conductive coaxial cylindrical surfaces, mounted onto insulated bases, fixed in the space between the bearing flange and the braking system. The above nonrotating surfaces are surrounded by the rotating surfaces. Also within this wheel assembly is shown rotating and nonrotating conductive, metallic or carbon, concentric annular surfaces mounted onto insulated bases which are fixed in the space between the bearing flange and the braking system or between the bearings of the wheel. FIG. 6 shows a cross sectional view of a vehicle's wheel assembly, wherein the mechanical part of the proposed tyre pressure sensor mounted onto insulated bases, fixed in the space between the bearings and the shaft of the wheel, in accordance to a second preferred embodiment, again comprises two rotating and two nonrotating conductive annular surfaces, wherein the first nonrotating conductive surface is surrounded by two rotating conductive surfaces and the second rotating conductive surface is surrounded by two nonrotating conductive surfaces. Also within the wheel assembly, rotating and nonrotating conductive coaxial cylindrical or concentric annular surfaces can be mounted onto insulated bases fixed in the space between the bearing flange and the braking system of the wheel. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The detailed description of preferred embodiments and drawings herein, after being made by reference to the accompaning drawings, does not intend to limit the scope of the invention, and it will be readily understood by one skilled in the art that the present invention is not anticipated by the prior art. The proposed device of the air pressure sensor in the pneumatic tyres of a vehicle, in accordance to the present invention, employs for each one of the wheels of the vehicle, a pair of rotating conductive, metallic or carbon, surfaces connected to a tyre pressure sensor, mounted onto the wheel and another pair of nonrotating conductive, metallic or carbon, surfaces connected to an electronic circuit. Whenever the air pressure in any one of the tyres of the vehicle deviates from a normal predetermined value, the tyre pressure sensor shorts out the rotating conductive surfaces mounted onto the rotating part of the wheel assembly, thereby increasing the capacitance of the nonrotating conductive surfaces. This results to the activation of the abovementioned electronic circuit, by means of which a visual display or audio indication is given to the driver of the vehicle. Referring to any one of the accompanying FIGS 1, 2, 3 or 4 the device is shown to include a tyre pressure sensor (1), a system of conductive coaxial annular surfaces (2, 3, 4, 5), conductive coaxial cylindrical surfaces (12, 13, 14, 15, 16, 17, 18, 19) and conductive concentric annular surfaces (72, 73, 74, 75) mounted onto insulated bases (6, 7, 8, 9), a high frequency oscillator in the MHz region (21), an amplifier (22), a magnitude and phase comparator (23), a sequential circuit (24), two diodes (25) for change of pressure into two wheels, a bridge (20) with three resistors (Rl, R2, R3), a variable capacitor (C5), four capacitors (Cl, C2, C3, C4) which are connected with two pairs of nonrotating conductive coaxial annular, and cylindrical surfaces for each pair of wheels. In accordance to a first preferred embodiment of the invention, depicted in FIG 1, there are two rotating conductive annular surfaces (2, 3) surrounded by two nonrotating conductive annular surfaces (4, 5), being fixed onto insulated bases (7, 6) in the space between the bearings (66) and two nonrotating conductive cylindrical surfaces (14, 15), surrounded by two rotating, conductive cylindrical surfaces (12, 13) being fixed onto insulated bases (9, 8) in the space between the bearing flange (10) and the braking system of the wheel assembly (60). The abovementioned conductive, metallic or carbon, surfaces are adapted to operate as a variable capacitor which can show, by means of a visual display or audio indication, a deviation from normal of the air pressure in any one of the tyres. This can be achieved by using, in the electronic circuit, a bridge assembly (20) which is supplied with a high frequency sinusoidal signal, and which is one of the usual cases of a reference stable voltage Vref (Clock oscillation). By using as a reference the capacitances of the conductive surfaces (Cl, C2) of one wheel to the first branch of the bridge (20) and the capacitances of the conductive surfaces (C3, C4) of the other wheel to the second branch of the same bridge (20), it is possible to detect the faulty air pressure in anyone of the two pneumatic tyres with the same circuit. This can be done by detecting both the change of the signal width at the points Al and A2 and the change of signal phase at the point Al , A2 in relation to the clock which shows the tyre in which the air pressure has been changed. The change of the signal width under normal conditions R1=R2 and C1=C2 is zero because of the bridge balance. The advantage of applying the bridge method is that it requires only the half number of circuits in comparison to the number of the vehicle's wheels. The bridge method presupposes an unlikely appearance of a faulty pressure at the same time in both tyres. In this case the possibility of faulty pressure appearance is small and it can become very small by examining various statistical data to select the proper pairs of the wheels. A change of the value of one of the capacitances Cl or C2 causes an appearance of voltage and a change of the signal phase in relation to the reference sinusoidal signal. The new signal is driven to the instrumentation amplifier (22) which produces a sinusoidal signal with reference to the earth. The following circuits amplify initially the signal and the F/F which follow can distinguish which one of the capacitances have been changed. The electronic circuit includes a gate NAND Schmidt Trigger, a resistor and a capacitor producing a square wave with frequency inversely proportional to the RC value. The system of rotating and nonrotating conductive coaxial cylindrical and annular surfaces, being used as a capacitance C, and the value of this capacitance depends on the ON- OFF position of the tyre pressure sensor (1) which affects the frequency of the oscillator output signal. Therefore the problem of detecting the faulty air pressure in the pneumatic tyres is to distinguish two different frequencies by the abovementioned electronic circuit. The AC bridge gives the possibility of automatic compensation of the system measuring differential capacitance, and therefore it can avoid to give faulty indications from changes of the capacitance due to reasons other than the faulty pressure (for example an increase of environmental humidity). The different weak signals of the bridge are amplified by high speed video instrumentation amplifiers, and for further signal amplification and construction of filters a quadruple operational amplifier of high speed and accuracy is used. In case of a low value of capacitances, due to the long distances between the conductive surfaces and their small area, makes necessary the operation of the system in high frequency. In accordance to a second preferred embodiment of the invention, depicted in FIG. 2, a various number of rotating conductive annular surfaces (2, 3, 72, 73) and conductive cylindrical surfaces (12, 13, 17, 16) and nonrotating conductive annular surfaces (4, 5, 74, 75) and conductive cylindrical surfaces (14, 15, 18, 19), being fixed onto insulated bases (7, 6), (8, 9) in a suitable space of the wheel assembly, are taking alternately various combined positions and orientations in relation to each other and the axis of the wheels rotation. The non conductive concentric rings (77, 78, 79) with negligible friction coefficient like ceramic and with small thickness surround and cover the conductive concentric annular surfaces (72, 73, 74, 75) in order to prevent them from touching each other. The spring (76) is pressing the insulated base (9) to keep the conductive surfaces (72, 73, 74, 75) in a constant distance from each other. All the aforementioned conductive surfaces, metallic or carbon, are adapted to operate as a variable capacitor of a resonance circuit which includes a square signal generator (26), a comparator (e.g. a digital gate) (27), RLC of sinusoidal signal transformer (28) and a signal display indicator (29). The frequency of the waveforms produced by the generator (26) depends on the capacitance of the nonrotating conductive surfaces which in turn depends on the position ON-OFF of the air pressure sensor (1) which electrically connects and disconnects the rotating conductive surfaces. The first edge of the comparator is connected to the output of the RLC filter and the second is connected to a reference voltage Vref(80)which is about lvolt. Also, it has been added another circuit which produces a different pulse, when the device has any problem. So the driver is being informed (with different indications), when there is a problem with the tyre (1 st indication), and when there is a problem with the device (2 nd indication). Last it has been developed a digital device in order to detect the change of the capacitance and to transfer the information from the wheels to the driver only through a cable. The function of this device is based on a CAN bus telecommunication system. This device is mainly consisted of a multivibrator connected to the aforementioned conductive surfaces variable capacitor and microcontrollers. In accordance to a first preferred embodiment of the invention the tyre pressure sensor, depicted in FIG. 3. comprises a silicon membrane of p-type (30) closing air-tightly, a small cavity (36) with metal-plated semiconductor substrate of n-type (37) and a silicon layer (40) being oxidized for insulation, wherein the curvature of the membrane's surface (30) is proportional to the air pressure, and the device pressure sensitivity is proportional to the area of the membrane (30) and inversely proportional to the intrinsic tensile stress, to the thickness of the membrane (30) and the gap spacing between membrane (30) and substrate (37), wherein the elastic feature of the membrane (30) is reinforced by the elastic properties of springs (31) and furthermore by a pressurized heavy gas filling up a chamber (36), with pressure equivalent to a normal tyre pressure, wherein one end of a special shape electrode (33) with adjustable length is fastened on metal-plated membrane (30) and the other end of the electrode (33) moves between a pair of contact points (35, 41) or (39) being formed inside of the semiconductor substrate (37). The rotating conductive surfaces are connected with the tyre pressure sensor (1) through a thin cable (11) being covered by a thick insulating substrate of small dielectric constant. In order to increase the capacitance of the nonrotating conductive surfaces after shorting out the rotating conductive surfaces and therefore to increase the reliability of the device, various combinations of more rotating and nonrotating conductive surfaces can be made. Mainly the reliability of the device is increased by reducing the distance between the rotating and nonrotating conductive surfaces and enlarging their area. The device is operating as follows: Whenever the air pressure in any one of the pneumatic tyres of the vehicle deviates from a normal predetermined value, the tyre pressure sensor (1) electrically connects, by mechanical way, the rotating conductive surfaces [(2, 3), (72, 73), (12, 13) and (16, 17)] and thereby increases the capacitance of the nonrotating surfaces [(4, 5), (74, 75), (14, 15) and (18, 19)]. The system of rotating and nonrotating conductive surfaces, metallic or carbon, behaves as a variable capacitor being an element of the electronic circuit (20, 21, 22, 23, 24, 25) and (26, 27, 28, 29). The change of capacitance of this variable capacitor alters the frequency of the waveforms being produced by the generator (26), and this affects the digital gate (27) resulting to the activation of the electronic circuit, by means of which a warning display indication (29) is given to the driver of the vehicle. In accordance to a third preferred embodiment of the invention depicted in FIG. 4, shallow circular channels on both sides of the insulated bases (7, 8) or (6, 9) are opened to obtain a significant increment of the capacitance after shorting out the rotating surfaces. These channels can be either carbon or metal-plated (by various ways, eg sputtering) or by fixing the metallic surfaces (12, 13, 14, 15), (72, 73, 74, 75) on the periphery of the channels and covering these metallic surfaces by a thin insulating layer (e.g. ceramic). The insulated bases (7, 8), (6, 9) (e.g. metallic covered by ceramic, dense plastic, polyamidio etc) and the conductive, metallic or carbon, surfaces (12, 13, 14, 15), (72, 73, 74, 75) are divided into two half pieces and are fixed by bolts (62), nuts (64) and elastic washers (63) onto the rotating oil collector (61) and the nonrotating shaft (69) of the wheel assembly. In accordance to a third preferred embodiment of the invention, the device in FIG. 5 comprises one pair of nonrotating conductive cylindrical surfaces surrounded by another pair of rotating conductive cylindrical surfaces, mounted onto insulated bases, fixed in the space between the bearing flange and braking system (51, 60) of a vehicle's twin wheels assembly. The tyre pressure sensor (1) is placed onto the air inlet valve (50). Also within this wheel assembly the conductive concentric annular surfaces (72, 73) and (74, 75) are mounted onto insulated bases, fixed in the space between the bearing and the shaft of the wheel. The rotating conductive surfaces, metallic or carbon, are connected with the air pressure sensor (1) by two thin cables through a hole along the bolt (53) by connecting plugs (54). In accordance to a second preferred embodiment of the invention, the device in FIG. 6 comprises two rotating (2, 3) and two nonrotating (4, 5) conductive annular surfaces, wherein the first nonrotating surface (4) is surrounded by two rotating surfaces (2, 3) and the second rotating surface (3) is surrounded by two nonrotating surfaces (4, 5) onto insulated bases fixed in the space (45) between the bearings (66) of a vehicle's wheels assembly. Also within the wheel assembly, rotating and nonrotating conductive coaxial cylindrical or concentric annular surfaces can be mounted onto insulated bases fixed in the space between the bearing flange and the braking system of the wheel. A contact coupling method is using two collecting brushes mounted onto the nonrotating part of the wheel assembly, which in turn are on a continuous contact with two rotating concentric rings which can be shorted out by the tyre pressure sensor (1) which operates as a switch and results in passing a current through the collecting brushes to activate a visual or an audio indicator of the device, warning the driver for the deviation from normal air tyre pressure. Also a magnetic coupling method is using two or more coils being mounted onto the rotating part of the wheel and the same number of coils onto the nonrotating part of the wheel. Finally the electromagnetic coupling method is using photodiodes (OD) p.i.n and p.n without internal gain and photoemitters (LED) being mounted onto the rotating part of the vehicle's wheel. Also photodiodes (OD) with internal gain, phototransistors (APD) and photoemitters (LED) is mounted onto the nonrotating part of the wheel assembly. When the rotating OD and LED are shorted out by the tyre pressure sensor (1), a light is emitted to the nonrotating OD resulting to the activation of a display indication.

Claims: CLAIMS 1. A device indicating the safety limits of the air pressure in the tyres of a vehicle, comprising for each one of the wheels of the vehicle a first conductive cylindrical surface, a second conductive cylindrical surface, a third conductive cylindrical surface and a fourth conductive cylindrical surface, the first pair being comprised of said first and second conductive cylindrical surfaces of different radius, being coaxially mounted onto an insulated cylindrical base fixed onto a rotating shaft, between the bearing flange and the braking system, and a second pair comprised of said third and fourth conductive cylindrical surfaces of different radius, being coaxially mounted onto an insulated cylindrical base, fixed onto a nonrotating shaft between said bearing flange and said braking system, a pair of cylindrical air capacitors being formed between said first pair and said second pair of the conductive cylindrical surfaces with optimum combined positioning between said conductive, metallic or carbon, surfaces, said device is further comprising an electronic circuit which includes a high frequency oscillator, a differential instrumentation amplifier with adjustable gain, a magnitude and phase comparator, a sequential circuit, two diodes for pressure change into two tyres, a bridge with three resistors, four capacitors which are connected with the nonrotating conductive cylindrical surfaces for each pair of wheels, a square pulse generator, a comparator (e.g. a digital gate), RLC sinusoidal wave transformer, a system of visual display LEDS and a tyre pressure sensor converting the air pressure variations in the interior of said pneumatic tyre into mechanical displacement of a semiconductor membrane, p-type silicon, moving an electrode to connect electrically, as an ON-OFF switch, said first pair of first and second conductive cylindrical surfaces of different radius, said pair of cylindrical air capacitors being adapted to operate as a variable capacitor in said electronic circuit wherein a first frequency range is produced to correspond to the ON position of said tyre pressure sensor, and a second frequency range is produced to correspond to the OFF position of said tyre pressure sensor, resulting to the activation of said electronic circuit to drive one of said visual display LEDS corresponding to a tyre with abnormal air pressure. 2. The device indicating the safety limits of the air pressure in the pneumatic tyres of a vehicle, as claimed in claim 1, comprising for each one of the wheels of the vehicle a first conductive annular surface, a second conductive annular surface, a third conductive annular surface and a fourth conductive annular surface, the first pair comprised of said first and second conductive annular surfaces of the same radius, being coaxially mounted onto an insulated cylindrical base, fixed onto a rotating cylindrical housing within the bearings space of the rotating wheel, wherein said conductive, metallic or carbon, surfaces are connected with the pressure sensor by thin cables through a hole in a bolt along its axis by connecting plugs and a second pair comprised of said third and fourth conductive annular surfaces of the same radius being coaxially mounted onto an insulated cylindrical base, fixed onto said nonrotating cylindrical shaft within said bearings space of the rotating wheel, a pair of plane air capacitor being formed between said first pair and said second pair of conductive annular surfaces, with optimum combined positioning between said surfaces. 3. The device indicating the safety limits of the air pressure in the pneumatic tyres of a vehicle, as claimed in claims 1 and 2, comprising for each one of the wheels of the vehicle two conductive, metallic or carbon, concentric annular surfaces of different radius and two conductive coaxial annular surfaces of the same radius, being mounted onto insulated cylindrical bases fixed onto said nonrotating parts of the wheel assembly and another two conductive concentric annular surfaces of different radius and two conductive coaxial annular surfaces of the same radius, being mounted onto insulated cylindrical bases, fixed onto said rotating parts of the wheel assembly,, wherein said rotating and nonrotating conductive, metallic or carbon, surfaces taking alternately various combined positions and orientations in relation to each other and to the axis of the wheel's rotation, wherein non conductive concentric rings with negligible friction coefficient like ceramic and with small thickness surround and cover the conductive concentric annular surfaces in order to prevent them from touching each other and a spring is pressing said insulated base to keep said conductive surfaces in a constant distance from each other . 4. The device indicating the safety limits of the air pressure in the pneumatic tyres of a vehicle, as claimed in claims 1, 2 and 3, comprising for each one of the wheels of said vehicle two groups with more than two rotating conductive, metallic or carbon, annular surfaces of the same radius for each group, being surrounded by two said nonrotating conductive annular surfaces of the same radius in a very close distance to the last conductive annular rotating surfaces, further many nonrotating conductive annular surfaces of the same radius in two groups being surrounded by two rotating conductive annular surfaces of the same radius, wherein many rotating conductive cylindrical surfaces of different radius in two groups are surrounded by two said nonrotating conductive cylindrical surfaces, and further many nonrotating conductive cylindrical surfaces of different radius in two groups are surrounded by two rotating cylindrical surfaces of different radius, wherein the axis of rotation of said surfaces is coinciding with the axis of the wheels rotation and said conductive rotating annular and cylindrical surfaces being connected with said air pressure sensor by two thin cables through a hole in a bolt by conecting plugs and said conductors being surrounded by an insulating material with a small dielectric constant. 5. The device indicating the safety limits of the air pressure in the pneumatic tyres of a vehicle, as claimed in claims 1 and 4, comprising for each one of the wheels of said vehicle two rotating conductive coaxial cylindrical surfaces of the same radius, electrically separated by a thin insulating layer, said rotating conductive surfaces being mounted onto an insulated cylindrical base, fixed onto a rotating shaft of the wheels assembly and two nonrotating conductive coaxial cylindrical surfaces of the same radius, electrically separated by a thin insulating layer, said nonrotating conductive surfaces being mounted onto a nonrotating insulated base and said nonrotating conductive surfaces being surrounded by said rotating conductive cylindrical surfaces, wherein the axis of said rotating and nonrotating conductive cylindrical surfaces and the axis of cylindrical insulated bases coincide with the wheel's rotation axis and a cylindrical capacitor being formed by said rotating and nonrotating conductive, metallic or carbon, cylindrical surfaces, being an element of said electronic circuit and said rotating conductive cylindrical surfaces being connected with the tyre pressure sensor by said two thin cables through a hole in said bolt by connecting plugs surrounded by said insulating material with a small dielectric constant and high temperature resistance, and said nonrotating conductive cylindrical surfaces being connected with said electronic circuit through two thin conductors surrounded by said insulating material. 6. The device indicating the safety limits of the air pressure in the pneumatic tyres of a vehicle, as claimed in claims 1, 4 and 5, said tyre pressure sensor, comprising a semiconductor membrane, p-type silicon, closing air-tightly, a small cavity with metal-plated semiconductor substrate, n-type silicon, and a silicon layer being oxidized for insulation, wherein the curvature of said membrane's surface is proportional to the air pressure, and the tyre pressure sensitivity is proportional to the area of said membrane and inversely proportional to the intrinsic tensile stress, to the thickness of said membrane and the gap spacing between said membrane and said substrate, wherein the elastic feature of said membrane is reinforced by the elastic properties of springs, and furthermore by a pressurized heavy gas filling up a chamber with pressure equivalent to a normal. tyre pressure, wherein one end of a special shape electrode with adjustable length is fastened on said metal-plated membrane and the other end of said electrode moves between a pair of contact points, being formed inside of said semiconductor substrate, said electrode being displaced proportionally to said air tyre pressure, shorting out said rotating metallic surfaces when the said air tyre pressure is ubnormal. 7. The device indicating the safety limits of the air pressure in the pneumatic tyres of a vehicle, as claimed in claims 1, 2, 3, 4 and 5, comprising for each one of the wheels of the vehicle said rotating and nonrotating conductive, metallic or carbon, cylindrical surfaces of different radius, annular surfaces of the same radius and concentric annular surfaces of different radius mounted coaxially onto said insulated bases or insulated metallic bases being divided into two half pieces and fixed by means of bolts, nuts and elastic spring washers to convenience installation in a suitable rotating and nonrotating space of said wheel assembly and to confront a conductive expansion of the shaft due to the heat, wherein the distance between said rotating and nonrotating conductive surfaces is minimized by opening shallow circular channels on the periphery of the insulated base and said channels being carbon or metal-plated and covered by a thin insulating layer, increasing the efficiency of the device and reducing the parasitic capacitance, wherein said rotating and nonrotating conductive cylindrical and annular surfaces are further embodied with said bearing flange and a spring is pressing said insulated bases to keep said conductive surfaces in a constant distance from each other. 8. The device indicating the safety limits of the air pressure in the pneumatic tyres of a vehicle, as claimed in claims 1 and 6, comprising for each one of the wheels of the vehicle an electronic circuit which includes a square pulse generator, a comparator (e.g. a digital gate), RLC sinusoidal signal transformer, a signal display indicator and a tyre pressure sensor converting the air pressure variations in the pneumatic tyres into displacements of said silicon membrane moving, said electrode to short-out said rotating conductive surfaces being adapted to operate as a variable capacitor, enhancing the capacitance of said nonrotating metallic surfaces, when the tyre pressure in any one of the tyres of the said vehicle deviates from a normal value resulting to a change of the signal frequency of said generator activating said comparator (e.g. a digital gate) to drive said signal display indicator, wherein said device is further comprising an electronic circuit which includes a high frequency oscillator, a differential instrumentation amplifier with adjustable gain, a magnitude and phase comparator, a sequential circuit, two diodes, an AC bridge with three resistors, four capacitors connected with said nonrotating conductive surfaces for each pair of wheels, wherein said AC bridge offers an automatic compensation by measuring the differential capacitance thus avoiding faulty indications due to other reasons like the change of humidity, temperature etc., wherein a digital device based on a CAN bus system includes a multivibrator connected to said variable capacitor and microcontrollers and is able to detect the change of the capacitance and transfer the signal through one cable. 9. The device indicating the safety limits of the air pressure in the pneumatic tyres of a vehicle, as claimed in claim 1 and 6, comprising two collecting brushes which are mounted onto the nonrotating part of the wheel assembly, being also in contact with two rotating metallic concentric rings and finally being shorted out by said tyre pressure sensor when air tyre pressure deviates from the safety limits, wherein photodiodes and photoemitters are further mounted onto the nonrotating and the rotating part of said wheel assembly for electromagnetic coupling, and furthermore coils being mounted onto rotating and nonrotating part of the wheel assembly for magnetic coupling. AMENDED CLAIMS [received by the International Bureau on 13 March 2000 (13.03.00); original claims 1 -9 replaced by amended claims 1 -9 (4 pages)] 1. A device indicating the safety limits of the air pressure in the tyres of a vehicle, comprising for each one of the wheels of the vehicle a first conductive surface, a second conductive surface, a third conductive surface and a fourth conductive surface, the first pair being comprised of said first and second conductive surfaces being mounted onto an insulated rotating base fixed onto a rotating part of the wheel assembly, and a second pair comprised of said third and fourth conductive surfaces, being mounted onto an insulated base, fixed onto a nonrotating shaft of said wheel assembly, a pair of air capacitors being formed between said first pair and said second pair of said conductive surfaces with optimum combined positioning between said conductive surfaces, said device is further comprising onto nonrotating part of the vehicle an electronic circuit which includes a high frequency oscillator, a differential instrumentation amplifier with adjustable gain, a magnitude and phase comparator, a sequential circuit, two diodes for pressure change into two tyres, a bridge with three resistors, four capacitors which are connected with said nonrotating conductive surfaces for each pair of wheels and further a square pulse generator, a comparator (e.g. a digital gate), RLC sinusoidal wave transformer, a system of visual display LEDS onto the rotating wheel and a tyre pressure sensor converting the air pressure variations in the interior of said pneumatic tyre into mechanical displacement of a semiconductor membrane to connect as an ON-OFF switch, said first with second conductive surfaces and further with the metallic frame of the wheel, wherein said third and fourth conductive surfaces are connected with said electronic circuit to the metallic frame of the vehicle, said pair of air capacitors being adapted to operate as a variable capacitor in said electronic circuit wherein a first frequency range is produced to correspond to the OFF position of said tyre pressure sensor, and a second frequency range is produced to correspond to the ON position of said tyre pressure sensor, wherein a resonance circuit (L-C) is resulting to appear a maximum voltage to activate of said electronic circuit to drive one of said visual display LEDS corresponding to a tyre with abnormal air pressure. 2. The device indicating the safety limits of the air pressure in the pneumatic tyres of a vehicle, as claimed in claim 1, comprising for each one of the wheels of the vehicle a first conductive annular surface, a second conductive annular surface, a third conductive annular surface and a fourth conductive annular surface, the first pair comprised of said first and second conductive annular surfaces, being coaxially mounted onto a thick insulated base, fixed onto a rotating cylindrical housing between the bearing flanges and further between the bearing flange and the braking system, wherein said conductive, metallic or carbon, surfaces are connected with a coil and said pressure sensor by coaxial cables with thin wire and thick insulated material to the metallic frame of the wheel through a hole in a bolt along its axis by connecting plugs and a second pair comprised of said third and fourth conductive annular surfaces, being coaxially mounted onto a thick insulated base, fixed around onto a nonrotating shaft inside and outside said bearing flanges of the wheel assembly, wherein said nonrotating conductive surfaces are connected with said electronic circuit and metallic frame of the vehicle, a pair of plane air capacitor being formed between said first pair and said second pair of conductive annular surfaces, with optimum combined positioning between said surfaces. 3. The device indicating the safety limits of the air pressure in the pneumatic tyres of a vehicle, as claimed in claims 1 and 2, comprising for each one of the wheels of the vehicle one or more conductive, metallic or carbon, concentric and coaxial annular surfaces and one or more conductive coaxial cylindrical surfaces of the same radius, being mounted onto thick insulated bases fixed onto said rotating housing between the bearing flanges and further at the end of differential axle shaft of the wheel assembly and another one or more conductive concentric and coaxial annular surfaces and one or more conductive coaxial cylindrical surfaces of the same radius, being mounted onto thick insulated bases, fixed onto said nonrotating parts of the wheel assembly, wherein said rotating and nonrotating conductive surfaces taking alternately various combined positions and orientations in relation to each other and to the axis of the wheel's rotation to increase the facing area of said rotating and nonrotating conductive surfaces, wherein non conductive material with negligible friction coefficient and small thickness cover the conductive surfaces in order to prevent them from touching each other and a spring is pressing said insulated base to keep said conductive surfaces in a constant distance from each other wherein said rotating conductive surfaces are connected and disconnected to the metallic frame of the wheel by said tyre pressure and said nonrotating conductive surfaces are connected to said metallic frame of the vehicle by said electronic circuit, further many rotating conductive annular surfaces in two groups are facing the same number of said nonrotating conductive annular surfaces one by one in two groups, wherein many rotating conductive cylindrical surfaces of different radius in two groups are facing the same number of said nonrotating conductive cylindrical surfaces one by one in two groups, wherein the axis of rotation of said surfaces is coinciding with the axis of the wheels rotation and said conductive rotating annular and cylindrical surfaces being connected to the metallic frame of the wheel by said air pressure sensor and coaxial cables with a thin wire through a hole in a bolt by connecting plugs and said cables being surrounded by a thick insulating material with a small dielectric constant. 4. The device indicating the safety limits of the air pressure in the pneumatic tyres of a vehicle, as claimed in claims 1, 2 and 3, comprising for each one of the wheels of said vehicle two rotating conductive coaxial cylindrical surfaces of the same radius, electrically separated by a thin insulating layer, being mounted onto an insulated cylindrical base, fixed onto a rotating shaft of the wheels assembly between the bearing flanges and two nonrotating conductive coaxial cylindrical surfaces of the same radius, electrically separated by a thin insulating layer, said nonrotating conductive surfaces being mounted onto a nonrotating insulated base between said bearing flanges and said nonrotating conductive surfaces being surrounded by said rotating conductive cylindrical surfaces, wherein the axis of said rotating and nonrotating conductive cylindrical surfaces and the axis of cylindrical insulated bases coincide with the wheel's rotation axis and a cylindrical capacitor being formed by said rotating and nonrotating conductive surfaces being an element of said electronic circuit and further said rotating conductive cylindrical surfaces being connected or disconnected with a coil and the metallic frame of the wheel by said tyre pressure sensor, through a hole in said bolt by coaxial cables of small dielectric constant and high temperature resistance and connecting plugs and said nonrotating conductive cylindrical surfaces being connected with the metallic frame of the vehicle through said electronic circuit, furthermore one rotating conductive surface mounted onto an insulated base being fixed onto a rotating part of the wheel assembly is connected and disconnected with or without a coil to the metallic frame of the wheel by said tyre pressure sensor through said coaxial cable with floating metallic grid and one nonrotating conductive surface mounted onto an insulated base, being fixed onto a nonrotating part of the wheel assembly is connected to the metallic frame of the vehicle by said electronic circuit through said coaxial cables being activated to drive a LED wherein said rotating conductive surface is connected to the metallic frame of the vehicle by the tyre pressure sensor through the bearings and the shaft of the wheel assembly. 5. The device indicating the safety limits of the air pressure in the pneumatic tyres of a vehicle, as claimed in claims 1,2,3 and 4, said tyre pressure sensor, comprising any type of semiconductor membrane, p-type or n-type silicon thin film, closing air-tightly, a very small cavity with metal- plated any type of semiconductor substrate, thin film n-type or p-type silicon, and a semiconductor, silicon, layer being oxidized for insulation, wherein the curvature of said membrane's surface is proportional to the air pressure, and the tyre pressure sensitivity is proportional to the area of said membrane and inversely proportional to the intrinsic tensile stress, to the thickness of said membrane and the gap spacing between said membrane and said substrate wherein a pair of contact points is formed for lower and upper safety air pressure limits by using two said silicon chip tyre pressure sensors of few hundred μm in the same silicon base of few square mm and other sensors for temperature, humidity, etc, included in the same arrangement, wherein a T junction housing, as a schrader valve, for said tyre pressure sensor being serving at the same time as an air inlet valve, and furthermore other types of tyre pressure sensors comprising various membranes being used for pneumatic apparatus and reinforced by the properties of springs, capillary curved tubes, bellows and pressurized heavy gas filling up a chamber with pressure equivalent to a normal tyre pressure, wherein one end of an electrode with adjustable length is fastened on said metal-plated membrane and the other end of said electrode moves between a pair of contact points, said electrode being displaced proportionally to said air tyre pressure, shorting out said rotating conductive surfaces with the metallic frame of the wheel whenever said air tyre pressure is ubnormal. 6. The device indicating the safety limits of the air pressure in the pneumatic tyres of a vehicle, as claimed in claims 1, 2, 3, 4 and 5, comprising for each one of the wheels of the vehicle said rotating and nonrotating conductive, metallic or carbon, coaxial cylindrical surfaces or coaxial and concentric annular surfaces mounted onto thick insulated bases or metallic insulated bases, using ABS as a rotating base, being divided into two half pieces and joined by means of bridges, clamping rings, collars, bolts, nuts and spring washers for convenient installation in a suitable rotating and nonrotating space of said wheel assembly and to confront an expansion of the shaft due to the heat, wherein the distance between said rotating and nonrotating conductive surfaces is minimized by opening shallow circular channels on the insulated bases and said channels being carbon or metal- plated and covered by a thin hydrophobic insulating layer, increasing the efficiency of the device and reducing the parasitic capacitance, wherein said rotating and nonrotating conductive cylindrical and annular surfaces are further embodied on thick insulated bases with bearing flanges and extra ball bearings, while springs are pressing said insulated bases to keep said nonrotating conductive surfaces in a constant distance from rotating conductive surfaces and furthermore said nonrotating conductive surface is only a part of an annular or cylindrical surface and not a complete ring mounted on a thick insulated base after a floating isolated conductive surface for reducing the parasitic capacitance and distance from the rotating conductive surface and for better installation. 7. The device indicating the safety limits of the air pressure in the pneumatic tyres of a vehicle, as claimed in claims 1, 2, 3, 4 and 5, comprising for each one of the nonrotating part of wheels of the vehicle an electronic circuit which includes a square pulse generator, a comparator (e.g. a digital gate), RLC sinusoidal signal transformer, a signal display indicator and a tyre pressure sensor converting the air pressure variations in the pneumatic tyres into displacements of said silicon membrane moving, said electrode to short-out said rotating conductive surface with the metallic frame of the wheel and said surface being adapted to operate as a capacitor with said nonrotating conductive surface, enhancing the capacitance of said capacitor, when the tyre pressure in any one of the tyres of the said vehicle deviates from a normal value resulting to a change of the signal frequency of said generator activating said comparator (e.g. a digital gate) to drive said signal display indicator, wherein said device is furthermore comprising an electronic circuit which includes a high frequency oscillator, a differential instrumentation amplifier with adjustable gain, a magnitude and phase comparator, a sequential circuit, two diodes, an AC bridge with three resistors, four capacitors connected with said nonrotating conductive surfaces for each pair of wheels, wherein said AC bridge offers an automatic compensation by measuring the differential capacitance thus avoiding faulty indications due to other reasons like the change of humidity, temperature etc., wherein a digital device based on a CAN bus system includes a multivibrator connected to said variable capacitor and microcontrollers and is able to detect the change of the capacitance and transfer the signal through one cable, furthermore the electronic circuit is comprising a unit of detecting the self-inductance reduction of rotating and nonrotating conductive surfaces when said rotating conductive surface is connected to the metallic frame of the wheel by said tyre pressure sensor. 8. The device indicating the safety limits of the air pressure in the pneumatic tyres of a vehicle, as claimed in claims 1, 5, 6 and 7, comprising for each one of the wheels of the vehicle one nonrotating and one rotating conductive surfaces, mounted onto insulated bases, being adapted to operate as a resonance circuit of a capacitor, a coil and a resistance connected in series to induce a high frequency A.C. voltage from an A.C. generator through said conductive surfaces and the metallic frame of the vehicle to the rotating wheel or energizing a coil with ferite hybrid by electromagnetic coupling and rectifing it to D.C. voltage in order to recharge a battery for operating a miniature automated pumping system with micromotor and reciprocating compressor on each tyre responding when the tyre pressure has decreased from the safety limits to maintain a normal pressure in the tyre and further the battery being charged by an electromagnetic actuator converting the rotation of the wheel into electrical energy by using permanent magnets and a piezoelectric crystal embodied in the tyre and pressed whenever is near to the ground and furthermore said battery is operating a mini radio frequency transmitter mounted on the wheel. 9. The device indicating the safety limits of the air pressure in the pneumatic tyres of a vehicle, as claimed in claims 1, 5 and 6, comprising one or two collecting brushes which are mounted onto the nonrotating part of the wheel assembly, being in contact with one or two rotating metallic concentric rings and finally being shorted out by said tyre pressure sensor whenever air tyre pressure deviates from the safety limits, wherein furthermore photodiodes and photoemitters are mounted onto said rotating and nonrotating part of said wheel assembly for photoelectric coupling, and furthermore coils being mounted onto rotating and coils and magnets onto nonrotating part of the wheel assembly for electromagnetic coupling, during rotation, wherein said rotating conductive surface is an open loop or an open coil and said tyre pressure sensor being adapted to close the loop or coil for ubnormal tyre pressure causing an electromagnetic coupling with said nonrotating conductive surface being a closed loop or a closed coil and adapted to operate as a magnetic signal emmitter.

Inventors: TSAGAS FOTIOS, TSAGAS NICOLAOS, TSAGAS, FOTIOS, TSAGAS, NICOLAOS
Applicants: TSAGAS FOTIOS, TSAGAS NICOLAOS, TSAGAS, FOTIOS, TSAGAS, NICOLAOS
Application year: 1999
Main classification: B60C23
IPC codes: B60C23