Pneumatic switch for low tire pressure warning system

• US 3,982,225 A
• Filed: 12/08/1975
• Issued: 09/21/1976
• Est. Priority Date: 12/08/1975
• 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: Schlanzky, Manfred P. H.
• Primary Examiner(s): Waring, Alvin H.
• Application Number:
  US05/638,968
• Time in Patent Office: 288 Days
• Field of Search: 340/58, 200/61.22, 200/61.25, 200/83 R, 200/83 A, 200/83 C, 200/83 Q, 200/83 S, 200/83 SA
• US Class Current: 340/442
• CPC Class Codes: B60C 23/007 having multiple wheels arranged side by side
• CPC Class Codes: B60C 23/0408 transmitting the signals by non-mechanical means from the wheel or tyre to a vehicle body mounted receiver

Abstract

A pneumatic switch located within a tire emits a pulse of air from the tire when the tire pressure drops a preset amount below the normal operating pressure. A bellows in the switch is charged to normal operating pressure and when tire pressure drops, the bellows extends to open a valve to emit the air pulse to actuate a warning system. A valve in the bellows is opened manually to establish the pressure charge within the bellows at the level of the tire pressure when the tire is inflated. The same valve in the bellows is automatically opened during tire deflation after the air pulse is emitted to equalize the bellows charge with the lower tire pressure in order to avoid a pressure differential across the bellows sufficient to damage the bellows.

Claims

1. In a low pressure warning system for a vehicle mounted pneumatic tire assembly normally inflated to a normal operating pressure, a low pressure sensing unit for providing a signal when the tire inflation pressure drops to a certain amount below the normal operating pressure comprising

a support member secured to the said tire assembly,

an expansible chamber fixed to the support and including a wall portion movable in response to the differential of air pressures acting on the movable portion, the exterior of the chamber being exposed to the tire inflation pressure and the interior of the chamber being charged to a reference pressure,

the chamber including a normally closed valve effective when opened to provide air communication between the interior and exterior of the chamber thereby tending to equalize the interior and exterior air pressures,

valve actuating means,

means operating the valve actuating means to open the valve for charging the reference pressure in the chamber to the normal operating pressure when the tire is normally inflated, and

means actuated by the movable wall portion connected to signal actuating means for producing a signal when the tire inflation pressure drops a first amount below the chamber reference pressure and further connected to the valve actuating means for opening the valve when the tire inflation pressure drops a second amount larger than the said first amount below the chamber reference pressure to relieve pressure from the chamber interior whereby the pressure differential acting on the movable wall portion is limited to a value insufficient to damage the expansible chamber.

2. In a low pressure warning system for a vehicle mounted pneumatic tire assembly normally inflated to a normal operating pressure, a low pressure sensing unit for providing a signal when the tire inflation pressure drops to a certain amount below the normal operating pressure comprising

a support member secured to the said tire assembly,

an expansible chamber fixed to the support and including a wall portion movable in response to the differential of air pressures acting on the movable portion, the exterior of the chamber being exposed to the tire inflation pressure and the interior of the chamber being charged to a reference pressure,

the chamber including a normally closed first valve effective when opened to provide air communication between the interior and exterior of the chamber thereby tending to equalize the interior and exterior air pressures,

a second normally closed valve mounted on the support member and exposed to the tire inflation pressure effective when opened to emit a pneumatic signal by exhausting a portion of the tire air,

valve actuating means for operating the first and second valves,

manually controlled means operating the valve actuating means to open the first valve for charging the reference pressure in the chamber to the normal operating pressure when the tire is normally inflated,

means connected to the movable wall portion and responsive to a predetermined displacement of the wall portion for operating the valve actuating means to one position for opening the second valve to produce a signal when the tire inflation pressure drops a first amount below the chamber reference pressure, and responsive to a second predetermined displacement of the wall portion for operating the valve actuating means to another position for opening the first valve when the tire inflation pressure drops by an amount larger than the first amount below the chamber reference pressure to relieve pressure from the chamber interior whereby the pressure differential acting on the movable wall portion is limited to a value insufficient to damage the expansible chamber.

3. In a low pressure warning system for a vehicle mounted pneumatic tire assembly normally inflated to a normal operating pressure, a low pressure sensing unit for providing a signal when the tire inflation pressure drops to a certain amount below the normal operating pressure comprising

a support member secured to the said tire assembly,

a bellows having one end fixed to the support and having a free end movable in response to the differential of air pressures acting on the bellows, the bellows exterior being exposed to the tire inflation pressure and the interior of the bellows being charged to a reference pressure, the bellows having a low spring rate to provide sensitive response to pressure changes and being subject to damage in the event of large pressure differentials acting on the bellows,

means for adjustably setting the reference pressure in the bellows and for preventing a large pressure differential on the bellows including,

a normally closed valve in the support effective when opened to provide air communication between the bellows interior and exterior thereby tending to equalize interior and exterior air pressures,

valve actuating means,

manually controlled means operating the valve actuating means to open the valve for charging the reference pressure in the bellows to the normal operating pressure when the tire is normally inflated,

means actuated by bellows extension due to tire pressure drop and connected to the valve actuating means for opening the valve when the tire pressure drops a certain amount below the reference pressure insufficient to cause bellows damage to relieve pressure from the bellows interior thereby limiting the pressure differential on the bellows to a safe value;

and

the valve actuating means further being connected to signal actuating means and responsive to a bellows extention at a pressure differential less than that required to open the valve for producing a signal indicative of low tire pressure.