Electrically conductive materials

• US 6,172,344 B1
• Filed: 07/25/1996
• Issued: 01/09/2001
• Est. Priority Date: 12/24/1993
• Status: Expired due to Fees

• Current Assignee: Gorix USA Inc.
• Original Assignee: Gorix Limited
• Inventors: Rix, John Robert, Gerrad, Graham, Gordon, John Yeats
• Primary Examiner(s): PAIK, SANG YEOP
• Application Number:
  US08/495,504
• Time in Patent Office: 1,629 Days
• Field of Search: 219/528, 219/529, 219/543, 219/545, 219/548, 219/569, 219/202, 219/211, 219/212, 219/217, 219/490, 219/497
• US Class Current: 219/529
• CPC Class Codes: H05B 1/0227 Applications
• CPC Class Codes: H05B 2203/007 using multiple electrically connected resistive elements or resistive zones
• CPC Class Codes: H05B 2203/011 Heaters using laterally extending conductive material as connecting means
• CPC Class Codes: H05B 2203/014 Heaters using resistive wires or cables not provided for in H05B3/54
• CPC Class Codes: H05B 2203/017 Manufacturing methods or apparatus for heaters
• CPC Class Codes: H05B 2203/029 Heaters specially adapted for seat warmers
• CPC Class Codes: H05B 2203/035 Electrical circuits used in resistive heating apparatus
• CPC Class Codes: H05B 2203/036 Heaters specially adapted for garment heating
• CPC Class Codes: H05B 3/34 flexible, e.g. heating nets or webs
• CPC Class Codes: H05B 3/36 heating conductor embedded in insulating material

Abstract

A conductive element useable as a resistance heater comprises a carbonized fabric (12) which has electrical terminals (18, 20) connected thereto and is encapsulated in or sandwiched between layers of plastic insulating material. The element generally is flexible and can be embodied in for example blankets for animals, vehicle seats and clothing. It is preferably provided with an electrical control circuit for controlling the temperature to which the fabric heats.

Claims

1. An electrically conductive resistance heating system, comprising:

a carbonised fabric heating element having a characteristic that as the temperature of said carbonised fabric heating element increases, the resistance of said carbonised fabric element decreases;

means for applying a potential difference across said carbonised fabric heating element, and an electrical control circuit arranged to control the temperature of said carbonised fabric heating element, and to derive a control signal from an electrical current passing through said carbonised fabric heating element, said electrical control circuit further comprising comparative switching means first and second inputs and acting to selectively apply and remove said potential difference across said carbonised fabric heating element;

wherein said electrical control circuit further comprises;

thermostat means having an output, said comparator switching means receiving at the first input the output of said thermostat means and at a second input either the control signal when the potential difference is being applied across said carbonised fabric heating element or the output of a gradual decay circuit when the potential difference is not applied, said gradual decay circuit output being initially representative of said control signal but gradually decaying;

the operation of said comparator switch means being to apply the potential difference across said carbonised fabric heating element only when the first input signal is greater than the second input signal.

2. A heating system according to claim 1 wherein said electrical control circuit further comprises:

a current detecting circuit arrange to detect said current flowing through said heating element.

3. A heating system according to claim 2, wherein said current detecting circuit comprises a resistor.

4. A heating system according to claim 1, wherein said heating element includes a carbonised polyacrilonitrile woven fabric, said fabric being carbonised after being woven.

5. A heating system according to claim 1, wherein said comparator switching means includes a relay.

6. A heating system according to claim 1, wherein said thermostat means includes a potentiometer arranged to allow adjustment of the level of the output of said thermostat means.

7. A heating system according to claim 1, wherein said thermostat means includes a voltage device.

8. A heating system according to claim 1, wherein the electrical control circuit includes:

a resistor coupled in series with said carbonised fabric heating element;

a switch coupled between and in series with said resistor and said heating element;

a first amplifier coupled to said resistor, said first amplifier producing an output signal in accordance with a voltage across said resistor;

a source of reference voltage derived from said thermostat means;

a second amplifier coupled to said source of reference voltage and said first amplifier, said second amplifier producing an output signal in accordance with said reference voltage and said output of said first amplifier; and

a transistor coupled to said second amplifier, said transistor controlling a state of said switch in accordance with said output of said second amplifier.

9. A heating system according to claim 8, wherein said thermostat means includes one of a potentiometer and a voltage divider.

10. A heating system according to claim 8, wherein said gradual decay circuit is coupled between said first amplifier and said second amplifier, said gradual decay circuit allowing for a gradual decay of said output of said first amplifier when said voltage across said resistor disappears.

11. A heating system according to claim 1, wherein said control circuit further includes an electronic circuit arranged to provide visual indication of a magnitude of said potential difference applied across said heating elements.

12. A heating system according to claim 11, wherein said electronic circuit includes an LED.

13. A heating system according to claim 1, wherein said heating element includes a polyacrilonitrile fabric, and said fabric is substantially 100% carbonised.

14. A heating system according to claim 1, wherein said heating element includes a woven fabric, and an electrical property of said fabric is determined at least in part by a selection of a wave parameter of said fabric.

15. A heating system according to claim 14, wherein said electrical property of said fabric is further determined at least in part by a selection of a carbonisation parameter of said fabric.

16. A heating system according to claim 14, wherein said electrical property of said fabric is determined at least in part by selectively restraining and relaxing said fabric in at least one of a weft direction and a warp direction during carbonisation of said fabric.

17. A heating system according to claim 1, wherein said means for applying a potential difference across said carbonised fabric heating element are electrodes connected to the element at spaced locations enabling the application of the potential difference across the area of the fabric between the electrodes.

18. A heating system according to claim 1, wherein the carbonised heating element has a protective layer on at least one side thereof.

19. A heating system according to claim 18, wherein the carbonised fabric heating element includes a pair of opposite sides and further comprises a pair of protective layers, the protective layers each being applied to a respective one of the opposite sides.

20. A heating system according to claim 17, wherein the protective layers cooperate with at least one edging strip to encapsulate the carbonised fabric heating element.

21. A heating system according to claim 20, wherein said means for applying the potential difference comprise at least two conductive bus bars at least partially encapsulated along with the carbonised fabric heating element by the protective layers.

22. A heating system according to claim 21, wherein said bus bars each comprise at least one of copper, electrically conductive metal foil, woven wire braid, woven wire strips, an electrically conductive plastics material, and conductive wires.

23. A heating system according to claim 22, wherein the bus bars are each at least one of a metal foil and a metal strip and are applied to the carbonised fabric by double sided electrically conductive self-adhesive tape.

24. A heating system according to claim 22, wherein the bus bars each comprise woven wire braid and are connected to the carbonised fabric by means of a carbon laden silicon elastomer.

25. A heating system according to claim 24, wherein the bus bars are each sewn to the carbonised fabric heating element and at

26. A heating system according to claim 19, wherein:

said protective layers each include one of a single layer and multiple layers of at least one of a pvc coating, a thermal polyurethane coating, polyurethane coating nylon lamination, a polyester lamination, nylon/polyester lamination, fibreglass, rubber and plastic mouldings and laminations, closed cell foams, open cell foams, coated foams, uncoated foams, adhesives, adhesive netting, and extrudate.

27. A heating system according to claim 1, wherein the resistance of the carbonised heating element is in the range 1.5 to 4.5 ohms/m² at 20°

C.

28. A heating system according to claim 27, wherein the carbonised fabric heating element is woven and has a resistance in the weft direction of 3.0 to 4.5 ohms/m² and 1.5 to 2.5 ohms/m² in the warp direction, at 20°

C.

29. A heating system according to claim 1, wherein the carbonised fabric heating element is of an oxidised polyacrilonitrile fibre of finished weight of 240 grammes/m² nominal of end per cm=12(30 nominal per inch) and 6 per cm=(22 nominal per inch).

30. A heating system according to claim 1, wherein the carbonised fabric heating element is embodied in a vehicle seat.