CAPACITIVE PRESSURE SENSOR

• US 20090027184A1
• Filed: 09/30/2008
• Published: 01/29/2009
• 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 7,880,600 B2
• Time in Patent Office: Days
• US Class Current: 340/447
• 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 wheel, comprising:

a rim;

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

a pressure sensor positioned within the cavity, wherein the pressure sensor is configured to sense the pressure of the gas within the cavity, and wherein the pressure sensor comprises;

a first conductive layer;

a compressible dielectric contiguous to the first conductive layer;

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

a temperature compensating element associated with the capacitor;

wherein the capacitor is configured to vary a capacitance in response to pressure changes within the cavity.

2. The wheel of claim 1, wherein the pressure sensor is positioned on the rim.

3. The wheel of claim 2, further comprising a remote communication device associated with the capacitor, wherein the remote communication device is configured to communicate pressure information to a remote location.

4. The wheel of claim 3, wherein the remote communication device is co-planar with the first conductive layer.

5. The wheel of claim 3, wherein the first conductive layer comprises two radiating elements operative to radiate as an antenna for the remote communication device.

6. The wheel of claim 3, wherein the remote communication device is configured to respond to an interrogation from the remote location.

7. The wheel of claim 2, wherein the pressure sensor further comprises a rotational force compensator.

8. The wheel of claim 7, wherein the rotational force compensator comprises a bend in the first conductive layer so that the capacitor is positioned on the rim substantially perpendicular to a radius associated with the tire.

9. The wheel of claim 8, wherein the first conductive layer comprises two co-planar, L-shaped pieces of metal, and wherein the L-shape includes the bend.

10. The wheel of claim 8, wherein the second conductive layer comprises a low mass when compared to a mass associated with the first conductive layer.

11. The wheel of claim 7, wherein the rotational force compensator comprises:

a second compressible material, wherein both the compressible material and the second compressible material are positioned between the first and second conductive layers; and

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

12. The wheel of claim 1, wherein the temperature compensating element comprises a ceramic element.

13. The wheel of claim 12, wherein the ceramic element is disposed within the compressible dielectric.

14. The wheel of claim 12, wherein the ceramic element comprises a second dielectric sandwiched between a third and fourth conductive layer to form a second capacitor in parallel with the capacitor.

15. The wheel of claim 1, wherein the temperature compensating element comprises a layered plastic and metal structure.

16. The wheel of claim 1, further comprising a temperature sensor associated with the pressure sensor.

17. A pressure sensing system, comprising:

a vehicle, including;

a control system; and

a wheel, comprising;

a rim;

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

a pressure sensor positioned within the cavity, wherein the pressure sensor is configured to sense pressure within the tire, and wherein the pressure sensor includes;

a first conductive layer;

a compressible dielectric contiguous to the first conductive layer;

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

a temperature compensation element;

wherein the capacitor has a capacitance that varies according to pressure changes within the cavity; and

a remote communication device associated with the pressure sensor, wherein the remote communication device is configured to communicate information from the pressure sensor to a remote location.

18. The pressure sensing system of claim 17, wherein the pressure sensor comprises a rotational force compensator.

19. The pressure sensing system of claim 17, wherein the first conductive layer comprises radiating elements for the remote communication device.

20. The pressure sensing system of claim 19, wherein the remote communication device is generally co-planar with the radiating elements.

21. The pressure sensing system of claim 17, wherein the vehicle further comprises an interrogator operatively connected to the control system, and wherein the remote communication device is configured to communicate with the interrogator.

22. The pressure sensing system of claim 17, wherein the first and second conductive layers sandwich the compressible dielectric therebetween.

23. The pressure sensing system of claim 17, further comprising a temperature sensor associated with the pressure sensor and the remote communication device.

24. The pressure sensing system of claim 17, further comprising a rotational force compensator associated with the pressure sensor.

25. The pressure sensing system of claim 17, wherein the pressure sensor is positioned on the rim.

26. A method of sensing pressure of a gas in a cavity, comprising:

measuring capacitance associated with a capacitor positioned within the cavity and comprising a compressible dielectric material and a pair of conductive layers, wherein changes in capacitance are related to changes in pressure as a function of the compressible dielectric; and

compensating for temperature changes.

27. The method of claim 26, further comprising communicating information about the changes in capacitance to a remote location through a remote communication device.

28. The method of claim 27, wherein said communicating information comprises using at least one of the pair of conductive layers as a radiating element for the remote communication device.

29. The method of claim 26, further comprising compensating for rotational forces.

30. The method of claim 29, wherein said compensating for rotational forces comprises positioning the capacitor parallel to a direction associated with the rotational forces.

31. The method of claim 29, wherein said compensating for rotational forces comprises providing a second capacitor associated with the capacitor, and wherein the capacitor experiences compression during rotational force application and the second capacitor experiences expansion during rotational force application.

32. The method of claim 26, wherein said compensating for temperature changes comprises measuring a temperature proximate the capacitor.

33. The method of claim 26, wherein said compensating for temperature changes comprises providing structure associated with the capacitor that changes the capacitance in a predictable fashion as a function of temperature.

34. The method of claim 33, wherein said providing structure comprises associating an element whose shape changes as a function of temperature.

35. The method of claim 33, wherein said providing structure comprises inserting a dielectric whose dielectric constant changes as a function of temperature.

36. The method of claim 26, wherein the compressible dielectric of the capacitor is sandwiched between the pair of conductive layers.

37. A method of sensing pressure in a tire, comprising:

determining tire pressure changes based on changes in a compressible material of a pressure sensor positioned within a cavity between the tire and a rim associated with the tire, wherein the changes in the compressible material affect a capacitance of a pair of conductive layers of the pressure sensor;

compensating for temperature changes within the cavity; and

interrogating a remote communication device associated with the pressure sensor to convey information about tire pressure changes in the cavity.

38. The method of claim 37, further comprising measuring the temperature within the cavity.

39. The method of claim 37, further comprising compensating for rotational forces as the tire rotates.

40. The method of claim 37, further comprising using at least one of the conductive layers as a radiating element for the remote communication device.

41. The method of claim 37, wherein the pressure sensor is mounted on the rim associated with the tire.