Low tire pressure sensor and air switch therefor

• US 4,235,185 A
• Filed: 07/18/1979
• Issued: 11/25/1980
• Est. Priority Date: 07/18/1979
• Status: Expired due to Term

• Current Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Original Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Inventors: Byram, Robert J.
• Primary Examiner(s): Yasich, Daniel M.
• Application Number:
  US06/058,738
• Time in Patent Office: 496 Days
• Field of Search: 116/34 R, 73/146.2, 73/146.3, 73/146.8, 340/58, 137/227, 200/61.22, 200/61.25
• US Class Current: 116/34.00R
• CPC Class Codes: B60C 23/0405 Mechanically generated visible signals, e.g. by using a gauge needle
• 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 23/0494 Valve stem attachments positioned inside the tyre chamber

Abstract

A low tire pressure sensor for emitting a magnetic signal when the tire pressure reaches a low limit pressure includes a signal device having a magnet movable from a storage position to an actuated position by tire pressure applied to the magnet from an air switch. The air switch includes a bellows charged to a reference pressure and exposed to tire pressure for moving in response to tire pressure changes, and a three-way valve operated by the bellows for venting the signal device to atmospheric pressure when the tire pressure is normal and for closing the vent and applying tire pressure to the signal device to actuate it when the pressure drops below a preset low pressure.

Claims

1. An air switch for a low tire pressure sender to emit a pneumatic signal when tire pressure drops to a limit value, comprising:

a valve cavity having first, second, and third ports, means including the first port for selectively admitting air under pressure from the tire to the valve cavity, the second port vented to atmospheric pressure, the third port comprising an outlet, a control member movable within the cavity for selectively placing the said first and second ports into communication with the third port, and bias means for urging the control member into a normal position to close the first port, and

bellows means adapted to be exposed to the tire pressure and mounted in operative engagement with the control member, the bellows means being precharged to a reference pressure and adapted to expand with decreasing tire pressure for moving the control member from its normal position when the tire pressure decreases to a low limit value to open the first port to communication with the third port and emit a pneumatic signal to the outlet, the bellows means, upon expansion, further being effective to move the control member into position to close the second port thereby preventing passage of tire air through the second port.

2. An air switch for a low tire pressure sender to emit a pneumatic signal when tire pressure drops to a limit value, comprising:

a valve cavity having first, second, and third ports, means including the first port for selectively admitting air under pressure from the tire to the valve cavity, the second port being aligned with the first port along a common axis and vented to atmospheric pressure, the third port comprising an outlet, a poppet linearly movable within the cavity along the common axis for selectively placing the said first and second ports into communication with the third port, and bias means for urging the poppet into a normal position to close the first port, and

bellows means adapted to be exposed to the tire pressure and mounted in operative engagement with the poppet, the bellows means being precharged to a reference pressure and adapted to expand with decreasing tire pressure for moving the poppet from its normal position when the tire pressure decreases to a low limit value to open the first port to communication with the third port and emit a pneumatic signal to the outlet, the bellows, upon expansion, further being effective at a second lower limit value for moving the poppet into position to close the second port thereby preventing passage of tire air through the second port at tire pressures below the second limit value.

3. A low tire pressure sensor for emitting a signal when pneumatic tire pressure reaches a low limit pressure comprising:

a signal device normally subject to atmospheric pressure and maintained in a nonsignalling mode in the normal tire condition and subject to tire pressure for actuation to a signalling mode when the tire pressure reaches the low limit pressure, and

an air switch device having a chamber adapted to communicate with tire pressure, a bellows mounted within the chamber, a signal passage connected to the signal device, an air passage vented to atmosphere; and

a valve for selectively connecting the chamber and the air passage with the signal passage,

the valve comprising a cavity having first, second and third ports, the first port connecting the chamber with the cavity, the second port opposed to and aligned with the first port along a common axis and connecting the air passage to the cavity, the third port joining the signal passage to the cavity, and a control member in the cavity spring biased toward the first port to close the first port and open the second port during normal tire pressure condition to subject the signal passage and the signal device to atmospheric pressure supplied through the second port, and the control member being responsive to bellows movement for movement toward the second port for opening the first port and closing the second port when tire pressure drops to a low tire pressure condition thereby admitting tire air to the signal passage whereby the tire pressure is effective to actuate the signal device to signalling mode and the air passage to atmosphere is closed to avoid loss of tire air through the passage.