Capacitive pressure sensor

• US 20040159158A1
• Filed: 06/06/2002
• Published: 08/19/2004
• Est. Priority Date: 06/06/2002
• Status: Active Grant

• Current Assignee: NVIDIA Corporation
• Original Assignee: Mineral Lassen LLC (Intellectual Ventures LLC)
• Inventors: Forster, Ian J.
• Granted Patent: US 7,100,432 B2
• Time in Patent Office: Days
• US Class Current: 73/718
• CPC Class Codes: B60C 23/0408 transmitting the signals by non-mechanical means from the wheel or tyre to a vehicle body mounted receiver
• CPC Class Codes: B60C 23/0433 Radio signals
• CPC Class Codes: B60C 23/0442 the transmitted signal comprises further information, e.g. instruction codes, sensor characteristics or identification data

Abstract

A capacitive pressure sensor comprises a pair of conductive plates surrounding a compressible dielectric to form a capacitor. Changes in pressure create changes in the capacitance of the capacitor which in turn may be measured to determine the changes in pressure. The pressure sensor may be constructed to be temperature and centripetal force compensated so that it may be positioned in a tire. A further embodiment uses the conductive plates to form a radiating element for the sensor such that it may wirelessly communicate with a remote interrogator.

Claims

1. A pressure sensor, comprising:

a first conductive layer;

a compressible dielectric contiguous said first conductive layer;

a second conductive layer contiguous said compressible dielectric, wherein said first and second conductive layers form a capacitor; and

said capacitor adapted to reflect a capacitance in relation to pressure changes on said compressible dielectric.

2. The pressure sensor of claim 1, wherein said compressible dielectric comprises a resilient material.

3. The pressure sensor of claim 2, wherein said resilient material comprises a material selected from the group consisting of:

silicone foam material;

foam material;

rubber material;

synthetic rubber material;

neoprene;

polyurethane foam; and

PTFE foam.

4. The pressure sensor of claim 1, wherein said first conductive layer comprises two conductive plates.

5. The pressure sensor of claim 4, wherein said two conductive plates are co-planar.

6. The pressure sensor of claim 1, further comprising a remote communication device operatively associated with said capacitor for sending pressure related information to a remote location.

7. The pressure sensor of claim 6, wherein said remote communication device is co-planar with said first conductive layer.

8. The pressure sensor of claim 7, wherein said first conductive layer comprises two radiating elements operative to radiate as an antenna for said remote communication device.

9. The pressure sensor of claim 6, wherein said remote communication device is adapted to respond to interrogations from the remote location.

10. The pressure sensor of claim 1, further comprising a temperature measuring element.

11. The pressure sensor of claim 10, further comprising a remote communication device and wherein said temperature measuring element communicates temperature information to said remote communication device.

12. The pressure sensor of claim 1, further comprising a temperature compensating element associated with said capacitor.

13. The pressure sensor of claim 12, wherein said temperature compensating element comprises a ceramic element.

14. The pressure sensor of claim 13, wherein said ceramic element is disposed within said compressible dielectric.

15. The pressure sensor of claim 13, wherein said ceramic element comprises a second dielectric sandwiched between a third and fourth conductive layer, forming a second capacitor in parallel with said capacitor.

16. The pressure sensor of claim 12, wherein said temperature compensating element comprises a layered plastic and metal structure.

17. The pressure sensor of claim 1, wherein said conductive layers are formed from a conductive ink printed on said compressible material.

18. The pressure sensor of claim 1, wherein said conductive layers comprise metal foils.

19. The pressure sensor of claim 1, wherein said conductive layers comprise metalized polymers.

20. The pressure sensor of claim 10, wherein said temperature measuring element is selected from the group consisting of:

a thermistor, an anemometer, a semiconductor type, and a chemical device.

21. The pressure sensor of claim 1, wherein said first and second conductive layers sandwich said compressible dielectric.

22. The pressure sensor of claim 1, wherein said first and second conductive layers are substantially co-planar and form an interdigital structure.

23. A wheel, comprising:

a rim;

a tire surrounding said rim and sealing a gas under pressure within a cavity formed by said tire and said rim; and

a pressure sensor associated with said rim for measuring the gas under pressure within the cavity, said pressure sensor comprising;

a first conductive layer;

a compressible dielectric contiguous said first conductive layer;

a second conductive layer contiguous said compressible dielectric, wherein said first and second conductive layers form a capacitor; and

said capacitor adapted to reflect a capacitance in relation to pressure changes within the cavity.

24. The wheel of claim 23, wherein said pressure sensor is mounted on said rim.

25. The wheel of claim 24, further comprising a remote communication device associated with said capacitor for communicating pressure information to a remote location.

26. The wheel of claim 24, wherein said pressure sensor further comprises a rotational force compensator.

27. The wheel of claim 26, wherein said rotational force compensator comprises a bend in said first conductive layer such that said capacitor is mounted to said rim substantially perpendicular to a radius associated with the tire.

28. The wheel of claim 27, wherein said first conductive layer comprises two co-planar L-shaped pieces of metal, said L-shape containing said bend.

29. The wheel of claim 27, wherein said second conductive layer comprises a low mass when compared to a mass associated with said first conductive layer.

30. The wheel of claim 26, wherein said rotational force compensator comprises:

a second compressible material, both said compressible material and said second compressible material positioned between said first and second conductive layers; and

a pair of generally S-shaped conductors, at least a portion of each S-shaped conductor positioned between said second compressible material and said compressible material.

31. The wheel of claim 25, wherein said remote communication device is co-planar with said first conductive layer.

32. The wheel of claim 25, wherein said first conductive layer comprises two radiating elements operative to radiate as an antenna for said remote communication device.

33. The wheel of claim 25, wherein said remote communication device is adapted to respond to interrogations from the remote location.

34. The wheel of claim 23, wherein said pressure sensor further comprises a temperature compensating element associated with said capacitor.

35. The wheel of claim 34, wherein said temperature compensating element comprises a ceramic element.

36. The wheel of claim 35, wherein said ceramic element is disposed within said compressible dielectric.

37. The wheel of claim 35, wherein said ceramic element comprises a second dielectric sandwiched between a third and fourth conductive layer, forming a second capacitor in parallel with said capacitor.

38. The wheel of claim 34, wherein said temperature compensating element comprises a layered plastic and metal structure.

39. The wheel of claim 23 further comprising a temperature sensor associated with said pressure sensor.

40. A pressure sensing system, comprising:

a vehicle, comprising;

a control system; and

a wheel, comprising;

a rim;

a tire surrounding said rim and sealing a gas under pressure within a cavity formed by said tire and said rim;

a pressure sensor positioned on said rim for sensing pressure within said tire; and

a remote communication device associated with said pressure sensor and wirelessly communicating to pass information from said pressure sensor to a remote location.

41. The pressure sensing system of claim 40, wherein said pressure sensor comprises:

a first conductive layer;

a compressible dielectric contiguous said first conductive layer;

a second conductive layer contiguous said compressible dielectric, wherein said first and second conductive layers to form a capacitor; and

said capacitor adapted to reflect a capacitance in relation to pressure changes within the cavity.

42. The pressure sensing system of claim 41, wherein said pressure sensor comprises a temperature compensation element.

43. The pressure sensing system of claim 41, wherein said pressure sensor comprises a rotational force compensator.

44. The pressure sensing system of claim 41, wherein said first conductive layer comprises radiating elements for said remote communication device.

45. The pressure sensing system of claim 44, wherein said remote communication device is generally co-planar with said radiating elements.

46. The pressure sensing system of claim 41, wherein said vehicle further comprises an interrogator operatively connected to said control system and said remote communication device communicates with said interrogator.

47. The pressure sensing system of claim 41 wherein said first and second conductive layers sandwich said compressible dielectric therebetween.

48. The pressure sensing system of claim 40 further comprising a temperature sensor associated with said pressure sensor and said remote communication device.

49. The pressure sensing system of claim 40 further comprising a rotational force compensator and a temperature compensator associated with said pressure sensor.

50. A method of sensing pressure, comprising:

forming a capacitor from a compressible dielectric material and a pair of conductive layers; and

measuring capacitance associated with the capacitor, wherein changes in capacitance are related to changes in pressure as a function of the compressible dielectric.

51. The method of claim 50, further comprising communicating information about the changes in capacitance to a remote location through a remote communication device.

52. The method of claim 51, wherein communicating information to a remote location comprises using one of the pair of conductive layers as a radiating element for the remote communication device.

53. The method of claim 50, further comprising compensating for temperature changes.

54. The method of claim 50, further comprising compensating for rotational forces.

55. The method of claim 53, wherein compensating for temperature changes comprises measuring a temperature proximate the pressure sensor.

56. The method of claim 53, wherein compensating for temperature changes comprises providing structure associated with the capacitor that changes the capacitance in a predictable fashion as a function of temperature.

57. The method of claim 50 wherein forming a capacitor comprises sandwiching the compressible dielectric between the pair of conductive layers.

58. The method of claim 54 wherein compensating for rotational forces comprises mounting the capacitor parallel to a direction associated with the rotational forces.

59. The method of claim 54 wherein compensating for rotational forces comprises providing a second capacitor associated with the capacitor, said capacitor experiencing compression during rotational force application and said second capacitor experiencing expansion during rotational force application.

60. The method of claim 56 wherein providing structure comprises associating an element whose shape changes as a function of temperature.

61. The method of claim 56 wherein providing structure comprises inserting a dielectric whose dielectric constant changes as a function of temperature.

62. A method of sensing pressure in a wheel comprising a tire and a rim, comprising:

forming a pressure sensor from a compressible material and a pair of conductive layers, thereby creating a capacitance;

placing the pressure sensor in the tire; and

determining pressure changes by changes in the compressible foam which affect the capacitance of the pressure sensor.

63. The method of claim 62 further comprising mounting the pressure sensor on the rim.

64. The method of claim 62 further comprising associating a remote communication device with the pressure sensor.

65. The method of claim 62 further comprising measuring a temperature proximate the pressure sensor.

66. The method of claim 62 further comprising compensating for rotational forces acting on the pressure sensor.

67. The method of claim 62 further comprising compensating for temperature changes proximate the pressure sensor.

68. The method of claim 64 further comprising communicating with a remote location through the remote communication device.

69. The method of claim 67 wherein compensating for temperature changes comprises inserting a ceramic material in the compressible dielectric.

70. A method of sensing pressure in a tire on a vehicle, comprising:

forming a pressure sensor from a compressible material and a pair of conductive layers;

associating a remote communication device with the pressure sensor;

placing the pressure sensor in a tire;

determining pressure changes by changes in the compressible material which affect the capacitance of the pressure sensor; and

interrogating the remote communication device to convey information to the vehicle'"'"'s control system about pressure changes in the tire.

71. The method of claim 70 further comprising compensating for temperature changes within the tire.

72. The method of claim 70 further comprising measuring the temperature within the tire.

73. The method of claim 70 further comprising compensating for rotational forces as the tire rotates.

74. The method of claim 70 further comprising using the conductive layers as radiating elements for the remote communication device.

75. The method of claim 70 further comprising mounting the pressure sensor on a rim associated with the tire.