Gm Global Technolgoy Operations, Inc.

John A Stewart

Wayne C Nichols

Roy G Hynes

David G Beyerlein

John B Force

Harold A Haven

A low tire pressure transducer coupled to a tire rim includes a diaphragm subject to tire pressure on one side and to a mechanical spring force on the other side. A magnet within the transducer is coupled with a shunt which minimizes the external magnetic field when tire pressure is at its proper value. However, movement of the diaphragm occasioned by low tire pressure also moves the shunt so that the external magnetic field increases substantially. Movement of the shunt also opens a valve which relieves any air pressure buildup in the transducer on the spring side of the diaphragm thereby avoiding premature actuation of the transducer due to air leakage into the transducer. A retaining ring holds the transducer to the rim and contains vents for allowing the exhaust of air from the transducer.

Low tire pressure transducer

A low tire pressure detector and magnetic signal sending unit includes a bellows charged to a reference pressure for moving a magnet from a shielded position to a signal emitting position when tire pressure operating outside the bellows decreases to a predetermined value. A latching force is established by the magnet to operate against the bellows force to help maintain the magnet in the shielded or non-signalling position. The magnitude of the latching force is controlled by a polepiece of thin cross section which saturates under the influence of the magnet to limit the latching force to a fixed value. The spring force of the bellows is sufficient in the absence of a pressure differential to overcome the latching force and move the magnet to signalling position. A ferrous slug mounted on the movable end of the bellows is magnetically coupled to the magnet assembly to form a releasable connection between the magnet assembly and the bellows.

Low tire pressure detector

In a system having a pressure sensor on a vehicle tire for generating a magnetic field when tire pressure reaches a predetermined value, an indicating circuit includes a stationary reed switch which is closed when subjected to the magnetic field, a coil in series with the reed switch which develops a magnetic flux when the switch closes to latch the switch closed, and an indicator lamp in series with the reed switch which is continually illuminated when the switch is closed to provide a low tire pressure warning. A test circuit energized when the vehicle ignition key switch is in 'start' position includes a pulse forming circuit for generating a current pulse in the latching coil to close the reed switch and provide an indicator light if the indicator circuit is operative. Power to the indicator circuit is interrupted when the key switch is moved from the 'start' position to 'run' position so that the coil is momentarily de-energized and the switch opened thereby placing the indicator circuit in readiness for sensing a magnetic field from the pressure sensor.

Low tire pressure indicator circuit

A circuit is provided for a tractor/trailer combination to provide a warning in the tractor of an event such as low tire pressure occurring at the trailer utilizing only conventional wiring connections between the tractor and trailer. When low tire pressure occurs, a flasher circuit on the trailer flashes the trailer marker lamps which are normally energized so that the flashing lamps are visible to the operator. The electrical pulses in the marker lamp circuits are sensed by a detector in the tractor to illuminate an indicator lamp in the tractor.

Warning circuit for a tractor/trailer combination

A vehicle pneumatic tire low pressure warning system including a low pressure air switch carried on the vehicle rotating wheel assembly which compares a reference pressure and the tire pressure and couples the tire air to an actuator on the rotating wheel assembly when the difference exceeds a specified amount. The tire air operates the actuator to position a magnet to actuate a reed switch sensor on a stationary member of the vehicle. A signal is provided in response to the reed switch actuation to warn the vehicle operator of the low tire pressure.

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Flint, MI, United States of America

John A Stewart