Indicator of the air pressure in the pneumatic tires of a vehicle based on a capacitive coupling

• US 5,531,109 A
• Filed: 07/11/1994
• Issued: 07/02/1996
• Est. Priority Date: 10/07/1992
• Status: Expired due to Fees

• Current Assignee: Nicolaos Tsagas
• Original Assignee: Nicolaos Tsagas
• Inventors: Tsagas, Nicolaos
• Primary Examiner(s): Chilcot, Richard
• Assistant Examiner(s): FELBER, JOSEPH LEON
• Application Number:
  US08/282,061
• Time in Patent Office: 722 Days
• Field of Search: 73/146.2, 73/146.3, 73/146.4, 73/146.5, 73/717, 73/723, 73/729.1, 340/442, 340/445, 340/448
• US Class Current: 73/146.5
• CPC Class Codes: B60C 23/0427 Near field transmission with inductive or capacitive coupling means
• CPC Class Codes: B60C 23/0428 using passive wheel mounted resonance circuits
• CPC Class Codes: B60C 23/043 using transformer type signal transducers, e.g. rotary transformers

Abstract

A device for monitoring tire air pressure in each one of the wheels of a vehicle at any time, and providing the driver of the vehicle with a warning signal in case the pressure in any one of the vehicle'"'"'s tires deviates from a normal predetermined value. The device includes a tire pressure gauge mounted onto the rotating tire, connected to a pair of air capacitors formed by four metallic annular strips, these capacitors being used as a timing capacitor in an oscillator producing two discrete frequencies depending on the ON-OFF position of the tire pressure gauge. Eventually a voltage comparator produces a square train pulse whenever its input falls below a certain level determined by a trimmer and the amplitude of the square train pulse is increased by a monostable multivibrator, the output of which drives an indicating LED to warn the vehicle'"'"'s driver of the faulty air pressure in one of his tires.

Claims

1. An indicator of the air pressure in the pneumatic tires of a vehicle, comprising for each one of the wheels of the vehicle a first metallic annular strip, a second metallic annular strip, a third metallic annular strip and a fourth metallic annular scrip, first pair comprised of said first and second metallic annular strips being concentrically mounted onto an insulating layer fixed onto the inner surface of a brake drum and a second pair comprised of said third and fourth metallic annular strips being concentrically mounted onto a nonrotating insulated base fixed on a nonrotating part of said vehicle, a pair of air capacitors being formed between said first pair, and said second pair of metallic annular strips said indicator further comprising an integrated electronic circuit which includes a high frequency oscillator and a frequency divider unit to produce a square train pulse, an amplifier and a set of tuned filters unit including a high-Q notch filter permitting the fundamental frequency of said square train pulse pass in order to convert said square train pulse to a sinusoidal signal, a system of LEDs, one LED for each one of the wheels of the vehicle, a unit including a half wave rectifier converting said sinusoidal signal to a D.C. level, a voltage comparator giving an output of a square train pulse whenever an input signal to said voltage comparator falls below a certain level and a monostable multivibrator increasing the amplitude of the square train pulse of said voltage comparator output, a single polarity D.C. power supply to a symmetrical polarity D.C. power supply converter and a tire pressure gauge to connect electrically as an ON- OFF switch said first pair of first and second metallic annular strips said pair of air capacitors being adapted to operate as a timing capacitor in said oscillator, wherein a first frequency range is produced to correspond to the ON position of said tire pressure gauge and a second frequency range is produced to correspond to the OFF position of said tire pressure gauge, wherein said first frequency range falls within a gap of notch filter of said amplifier and set of tuned filters unit and passes with an attenuation of the order of one hundred, while said second frequency range falls outside the gap of said notch filter and wherein said half wave rectifier converts the sinusoidal signal to the D.C. level, said voltage comparator providing said square train pulse output whenever the input signal to said voltage comparator falls below a certain level determined by a trimmer and said monostable multivibrator increasing the amplitude of the square train pulse of said voltage comparator output by using a timing circuit, an output of said monostable multivibrator driving one of said LEDs, corresponding to a tire with abnormal air pressure.

2. The indicator of the air pressure in the pneumatic tires of a vehicle, as claimed in claim 1, wherein the operation efficiency of said indicator is improved when:

a thin layer of dielectric material of high dielectric constant is inserted within said air capacitors;

the surfaces of said first, second, third and fourth metallic annular strips of said air capacitors that face each other are coated with a paste of high dielectric constant mixed with an epoxy resin;

the separation coupling distance between said first and third metallic annular strips and said second and fourth metallic annular strips is selected to be approximately 1 mm;

the area of each one of said first, second, third and fourth metallic annular strips is selected to be the maximum allowed by the dimensions of said brake drum;

a parasitic capacitive coupling occurring between said first and second metallic annular strips, said third and fourth metallic annular strips, said second and third metallic annular strips, said first and fourth metallic annular strips and between said first, second, third and fourth metallic annular strips and adjacent metallic parts of the vehicle is minimized, minimization of said parasitic capacitive coupling being effected when;

said first, second, third and fourth metallic annular strips are fixed at a distance which is selected to be the maximum from adjacent metallic surfaces of said wheel assembly, allowed by the dimensions of said brake drum;

said first, second, third and fourth metallic annular strips are fixed at a minimum distance of the order of 2 mm from adjacent metallic parts of said wheel assembly;

a minimum spacing between said first and second concentric metallic annular strips and between said third and fourth concentric metallic annular strips is approximately 2 mm;

each one of said insulating layer and said insulated base have a low dielectric constant and a thickness which is selected to be the maximum allowed by the dimensions of said wheel assembly;

a minimum thickness of each of said insulating layer and said insulating base is approximately 2 mm;

high frequency sinusoidal signals are applied at said third and fourth metallic annular strips so that the surrounding metallic frame of said wheel assembly does not follow the fast changes of high frequency oscillation;

the cables connecting said integrated electronic circuit to each one of said LEDs are coated with thick insulating material of low dielectric constant.

3. An indicator of the air pressure in the pneumatic tires of a vehicle, as claimed in above claim 1, wherein said integrated electronic circuit comprises a plurality of LEDs corresponding to the number of the wheels of the vehicle, so that a single integrated electronic circuit is used for all the wheels of the vehicle.

4. An indicator of the air pressure in the pneumatic tires of a vehicle, as claimed in claim 1, said tire pressure gauge comprising a pair of durable rubber layers of a certain thickness, said pair of durable rubber layers containing therebetween a thin curved zig-zag steel wire, said durable rubber layers closing air-tightly a chamber, said chamber communicating through a tube with the interior of said tire, wherein a sensitive ON-OFF microswitch is electrically connected to said first and second metallic annular strips, an electrode being mounted at the middle of said pair of rubber layers, said electrode being connected with said steel wire, wherein a regulating screw is used to adjust the position of said microswitch.

5. An indicator of the air pressure in the pneumatic tires of a vehicle as claimed in above claim 4, said tire pressure gauge further comprising a plurality of small elastic rubber balls and foamy material with elastic properties filling said chamber, soft springs being diagonally disposed within said chamber so as to enhance elasticity of said foamy material and said small elastic rubber balls.

6. An indicator of the air pressure in the pneumatic tires of a vehicle as claimed in above claim 4, said tire pressure gauge further comprising compressed gas filling a portion of said chamber, said portion of said chamber being closed on the top by a rubber layer, said rubber layer being held in position by a pair of springs being fixed to the walls of said tire pressure gauge.

7. An indicator of the air pressure in the pneumatic tires of a vehicle as claimed in claim 4, said tire pressure gauge being disposed onto an air inlet valve opening, said air inlet valve opening being fixed externally onto a metallic rim of said wheel assembly.

8. An indicator of the air pressure in the pneumatic tires of a vehicle as claimed in claim 4, said tire pressure gauge being disposed onto an air inlet valve opening, said air inlet valve opening being fixed internally onto a metallic rim of said wheel assembly.

9. An indicator of the air pressure in the pneumatic tires of a vehicle as claimed in claim 1, said tire pressure gauge comprising a small chamber with folding walls made by rubber and thin metallic layers, wherein one end of an electrode is fastened on the base of said small chamber and the other end of said electrode moves between a pair of contact points of a microswitch, wherein a first wall is fixed mounted on the internal walls of a metallic box, a second wall moves freely along an axis parallel to said folding walls and a base of said metallic box, said base being fixedly mounted on the internal side of said wheel'"'"'s rim and wherein the interior of said tire communicates with the interior of said box through an opening of the side wall of said metallic box, wherein said chamber is filled up with a heavy gas with a pressure equivalent to a normal tire pressure.

10. An indicator of the air pressure in the pneumatic tires of a vehicle as claimed in claim 9, wherein said small chamber is filled up with air through an inlet valve, said inlet valve being fixed on said first wall and projecting outward from a metallic rim of said wheel assembly.

12. The indicator of the air pressure in the pneumatic tires of a vehicle as claimed in above claim 3, wherein the operation efficiency of said indicator is improved when:

a thin layer of dielectric material of high dielectric constant is inserted within said plane air capacitor and said cylindrical air capacitor;

the surfaces of said first, second third and fourth metallic strips of said plane air capacitor and said cylindrical air capacitor that face each other are coated with a paste of high dielectric constant mixed with an epoxy resin;

the separation coupling distance between said second and fourth metallic strips of said plane air capacitor and between the first and third metallic strips of said cylindrical air capacitor is selected to be approximately 1 mm;

the area of each one of said first, second, third and fourth metallic strips is selected to be the maximum allowed by the dimensions of said brake drum;

a parasitic capacitive coupling occuring between said first and second metallic strips, said third and fourth metallic strips, said second and third metallic strips said first and fourth metallic strips and between said first, second, third and fourth metallic strips and adjacent metallic parts of the vehicle is minimized, minimization of said parasitic capacitive coupling being effected when;

said first, second, third and fourth metallic strips are fixed at a distance which is selected to be the maximum from adjacent metallic parts of said wheel assembly allowed by the dimensions of said wheel assembly;

said first, second, third and fourth metallic annular strips are fixed at a minimum distance of the order of 2 mm from adjacent metallic parts of said wheel assembly;

a minimum spacing between said first and second metallic strips and between said third and fourth metallic strips is approximately 2 mm;

each one of said insulating layer and said insulating base has a low dielectric constant and a thickness which is selected to be the maximum allowed by the dimensions of said wheel assembly;

a minimum thickness of said insulating layer and said insulating base is approximately 2 mm;

high frequency sinusoidal signals are applied at said third and fourth metallic strips, so that the surrounding metallic frame of said wheel assembly does not follow the fast changes of high frequency oscillation;

the cables connecting said integrated electronic circuit to each one of said LEDs are coated with thick insulating material of a low dielectric constant.

11. An indicator of the air pressure in the pneumatic tires of a vehicle, comprising for each one of the wheels of the vehicle a first metallic strip, a second metallic strip, a third metallic strip and a fourth metallic strip, a first pair comprised of said first and second metallic strips being mounted onto an insulating layer fixed onto the inner surface of a brake drum and a second pair comprised of said third and forth metallic strips being mounted onto a nonrotating insulated base fixed on a nonrotating part of said vehicle, a pair of air capacitors being formed comprising a plane air capacitors and a cylindrical air capacitor, said plane air capacitor being formed between said second and fourth metallic strips wherein said second and fourth metallic strips are of plane annular construction and disposed in an orientation normal to the central rotating wheel shaft, and said cylindrical air capacitor being formed between said first and third metallic strips, wherein each of said first and third metallic strips is of cylindrical construction and disposed in an orientation parallel to the central rotating wheel shaft, said indicator further comprising an integrated electronic circuit which includes a high frequency oscillator and a frequency divider unit to produce a square train pulse, an amplifier and a set of tuned filters unit including a high-Q notch filter permitting the fundamental frequency of said square train pulse to pass in order to convert said square train pulse to a sinusoidal signal, a system of LEDs, one LED for each one of the wheels of the vehicle, a unit including a half wave rectifier converting said sinusoidal signal to a D.C. level, a voltage comparator giving an output of said square train pulse whenever an input signal to said voltage comparator falls below a certain level and a monostable multivibrator increasing the amplitude of the square train pulse of said voltage comparator output, a single polarity D.C. power supply to a symmetrical polarity D.C. power supply converter and a tire pressure gauge to connect electrically as an ON-OFF switch said first pair of metallic annular strips of said pair of air capacitors, said pair of air capacitors being adapted to operate as a timing capacitor in said oscillator, wherein a first frequency range is produced to correspond to the ON position of said tire pressure gauge and a second frequency range is produced to correspond to the OFF position of said tire pressure gauge, wherein said first frequency range falls within a gap of said notch filter of said amplifier and set of tuned filters unit and passes with an attenuation, of the order of one hundred while said second frequency range falls outside the gap of said notch filter and wherein said half wave rectifier converts the sinusoidal signal to the D.C. level, said voltage comparator providing said square train pulse output whenever the input signal to said voltage comparator falls below a certain level determined by a trimmer and said monostable multivibrator increasing the amplitude of the square train pulse of said voltage comparator output by using a timing circuit, an output of said monostable multivibrator driving one of said LEDs corresponding to a tire with abnormal air pressure.

13. An indicator of the air pressure in the pneumatic tires of a vehicle, as claimed in claim 11 said tire pressure gauge comprising a pair of durable rubber layers of a certain thickness containing therebetween a thin curved zig-zag steel wire and said closing air-tightly a chamber, said chamber communicating through a tube with the interior of said tire, wherein a sensitive ON-OFF microswitch is electrically connected to said first and second metallic annular strips, an electrode being fastened at the middle of said rubber layers, said electrode being connected with said steel wire, wherein a regulating screw is used to adjust the position of said microswitch.