Tire pressure indicator

• US 4,308,520 A
• Filed: 01/03/1979
• Issued: 12/29/1981
• Est. Priority Date: 07/30/1976
• Status: Expired due to Term

• Current Assignee: Edcliff Instruments
• Original Assignee: Edcliff Instruments
• Inventors: Darlington, William W.
• Primary Examiner(s): Caldwell, Sr., John W.
• Assistant Examiner(s): Nowicki, Joseph E.
• Application Number:
  US06/000,712
• Time in Patent Office: 1,091 Days
• Field of Search: 340/58, 340/60, 340/531, 340/539, 200/61.22, 200/61.25, 73/146.3, 73/146.5, 73/146.8
• US Class Current: 73/146.5
• CPC Class Codes: B60C 23/02 Signalling devices actuated by tyre pressure hand-held tyre pressure gauges G01L17/00
• CPC Class Codes: B60C 23/0428 using passive wheel mounted resonance circuits
• CPC Class Codes: B60C 23/0479 Communicating with external units being not part of the vehicle, e.g. tools for diagnostic, mobile phones, electronic keys or service stations
• CPC Class Codes: B60C 23/0496 Valve stem attachments positioned outside of the tyre chamber

Abstract

Tire pressure indicator having a wheel mounted transponder unit and a hand-held interrogator unit which can be positioned for coupling with the transponder unit. The transponder unit is a passive device which returns signals to the interrogator unit in accordance with the pressure in the tire mounted on the wheel. When the tire pressure is above a predetermined safe level, a "safe" light on the interrogator unit is illuminated, and when the pressure is below the safe level, a "low" light is illuminated. Operating power for the interrogator unit is supplied by a battery in the unit, and the lights are flashed at a visible rate when the battery voltage drops below a predetermined level.

Claims

1. In a system for checking the pressure in a tire:

a handheld interrogator unit comprising an elongated generally cylindrical housing of a size suitable to be gripped and held in the hand, transmitter and receiver means mounted in the housing, transmitting and receiving coils connected to the transmitter and receiver means and positioned toward one end of the housing, a wheel-mounted transponder unit including means responsive to the pressure in the tire and to signals from the transmitting coil for returning to the receiving coil a signal corresponding to the pressure in the tire when the interrogator unit is held up to the transponder unit, the interrogator unit housing having an end member defining an outwardly opening cavity which extends inwardly through the openings in the coils for receiving a portion of the transponder unit therein to provide close coupling between the coils and the transponder unit, and indicator means responsive to the returned signal and visible externally of the housing for indicating the level of the pressure in the tire.

2. The system of claim 1 wherein the transponder unit includes a bellows assembly to which the pressure in the tire is applied and switch means actuated by the bellows assembly to assume a first state when the pressure is above a predetermined level and a second state when the pressure is below the predetermined level.

3. The system of claim 2 wherein the bellows assembly is mounted in a chamber pressurized to a level corresponding to the predetermined level.

4. The system of claim 1 further including a power source within the housing and a manually operable switch accessible externally of the housing for controlling energization of the interrogator unit with power from the source.

5. The system of claim 1 wherein the indicator means includes first and second indicator lights mounted on the housing, and means for illuminating the first light if the pressure in the tire is above a predetermined level and illuminating the second light if the pressure is below the predetermined level.

6. The system of claim 5 further including a power source within the housing and means for applying power from the source to the lights as a duty cycle less than 100 percent.

7. The system of claim 6 further including means responsive to the output of the power source for decreasing the duty cycle to produce visible flashing of at least one of the lights in the event that the output drops to a predetermined level.

8. The system of claim 1 wherein the end member comprises an insulative block in which the coils are embedded and the inwardly extending cavity comprises a generally conical recess disposed coaxially of the coils.

9. The system of claim 1 wherein the indicator means comprises a light emitting element mounted on the housing, said light emitting element being energized to provide a positive indication when the tire pressure is below the predetermined level.

10. The system of claim 1 wherein the transponder unit is mounted on the wheel in place of a conventional valve stem and includes a housing defining an internal chamber in communication with the tire, and a valve stem carried by the housing and communicating with the tire through the chamber in the housing, said pressure responsive means being positioned within the chamber.

11. The system of claim 1 wherein the transmitting and receiving coils are tuned to first and second frequencies, respectively, the transmitter means includes means for applying to the transmitting coil a signal of the first frequency modulated with a signal of the second frequency, and the transponder unit includes means including a coil adapted for coupling with the transmitting and receiving coils and producing a signal of the second frequency in the receiving coil in response to the signal in the transmitting coil.

12. The system of claim 11 wherein the means for producing a signal in the receiving coil further includes first and second diodes of opposite polarities and switch means responsive to the pressure in the tire for connecting the first diode across the transponder coil when the pressure is above a predetermined level and connecting the second diode across the transponder coil when the pressure is below the predetermined level.

13. In a system for checking the pressure in a tire mounted on a wheel:

an interrogator unit having transmitting and receiving coils tuned to first and second frequencies, means for applying to the transmitting coil a signal of the first frequency modulated at the second frequency, a transponder unit mounted on the wheel in place of a conventional valve stem and having a generally cylindrical housing defining an internal chamber in communication with the tire, a nipple extending axially from the inner end of the housing and threadedly received in the valve stem opening of the wheel, a valve stem extending axially from the outer end of the housing and communicating with the tire through the chamber in the housing, a coil wound coaxially about the valve stem toward the outer end of the housing for coupling with the transmitting and receiving coils when the interrogator unit is held in close proximity to the transducer unit, pressure responsive switch means within the chamber for completing an electrical circuit with the transponder coil to condition the transponder to return a signal indicative of the tire pressure to the interrogator unit, and means forming a part of the interrogator unit responsive to the signal from the transponder unit for providing an indication of the pressure in the tire.