Circuit arrangement for monitoring pressure and temperature of t

Details Circuit arrangement for monitoring pressure and temperature of t Circuit arrangement for monitoring pressure and temperature of t

1990-05-17

1992-08-25

Woodiel, Donald O.

Measuring and testing

Tire, tread or roadway

Tire inflation testing installation

73708, 340448, 374143, B60C 2302, G01L 1904

Patent

active

051408511

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to on a circuit arrangement for monitoring the air volume in a vehicle tire and comprising pressure and temperature rotating sensors fastened at a vehicle wheel, and a transmitter for transmitting sensed values to an evaluating circuit. In order to monitor the air volume in the tire of a motor vehicle in a known circuit arrangement of this type, according to WO 87/041 23, the temperature and pressure of the air in the tire is sensed by semiconductor sensors and corresponding measurement values are transmitted cyclically via a multiplexing control from the rotating wheel via a converter to an evaluating circuit which is fixed with respect to the vehicle. The air volume with which the tire is filled, is determined from the ratio of tire pressure and tire air temperature (PT) and is compared with an allowable limiting value. As soon as the air volume in one of the vehicle tires reaches or falls below the predetermined limiting value, an optical or acoustic signal is issued, and the driver of the vehicle is accordingly alerted to the risk of overstressing the tire.
In order to monitor the air volume in the vehicle tire, it is necessary that the pressure and the temperature of the air in the tire be known as exactly as possible. However, since the air in the tire and the wheel rim can have different temperatures when driving and, since the temperature sensor is inserted in the wheel rim and can therefore be thermally uncoupled from the wheel rim only incompletely, the air temperature in the tire can not be measured with the required accuracy. There is always a temperature difference between the tire air and the measurement value of the temperature sensor.


SUMMARY OF THE INVENTION

The object of invention is to compensate for the temperature measurement error when determining the tire air temperature and air volume in the tire.
The object of the invention is achieved by providing a correction circuit which outputs a measurement value in accordance with appropriate correction parameters.
The circuit arrangement, according to the invention has the advantage that the measurement error of the temperature sensor in the vehicle wheel need no longer be kept as small as possible by costly steps of thermal uncoupling from the wheel rim, rather the parameters producing the measurement value error are now detected in a correction circuit in order that the temperature measurement value or the air volume in the tire calculated from the latter together with the air pressure is corrected as accurately as possible to the actual value independently of these parameters. Another advantage consists in that the correction parameters required for this are, in many cases, already present in the vehicle and are to be determined once for certain vehicle types and/or vehicle wheels, so that the parameters can be fed to the correction circuit without considerable added expenditure. Moreover, costly constructions for the thermal uncoupling of the temperature sensor from the rim temperature can be avoided, since the tire air temperature during driving can be determined with favorable accuracy by the correction parameters, so that the reliability of the monitoring system is considerably increased.
It is particularly advantageous that the correction circuit be integrated in the centrally arranged evaluating circuit, which is fixed with respect to the vehicle, and that variable parameters as well as fixed parameters be fed to the correction circuit. The tire pressure and a signal concerning the state of the roadway, wet or dry, and a driving or speed signal are provided as variable correction parameters. The signal for a wet or dry tire is preferably provided by a moisture sensor of the correction circuit, which moisture sensor is fastened in the area of the wheel of the vehicle and is sprayed by the tire on wet roadways. However, this signal can also be tapped in the simplest manner from the windshield wiper system of the vehicle. The driving signal can be tapped from the speedometer. Corre

REFERENCES:
patent: 4703650 (1987-11-01), Dosjoub et al.
patent: 4909074 (1990-03-01), Gerresheim et al.

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