Process and circuit for monitoring tire pressure

Details Process and circuit for monitoring tire pressure Process and circuit for monitoring tire pressure

1995-09-14

1997-03-25

Hofsass, Jeffery

Communications: electrical

Land vehicle alarms or indicators

Internal alarm or indicator responsive to a condition of the...

340442, 731465, 116 34R, B60C 2302

Patent

active

056148828

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention pertains to a process for monitoring the tire pressure of the wheels of a vehicle by measuring, comparing and evaluating the rotating speeds of the individual wheels of the vehicle. The present invention also includes a circuit for carrying out the process.
Processes for recognizing the loss of tire pressure, which are based on the measurement and the comparison of the rotating speeds of the individual wheels of the vehicle, already are known from U.S. Pat. Nos. 4,876,528 and 5,192,929. In principle, the rotating speeds of the diagonally opposite wheels are added according to both of these patents, and the difference between the two sums is determined. If this difference is between 0.05% and 0.60% of the mean value of the two sums, the rotating speed of every individual wheel may deviate by at most 0.1% from the mean speed of all four wheels as long as a sufficient tire pressure is present. Loss of pressure is signaled in the case of greater deviations.
The accuracy of these prior art techniques leaves something to be desired. When a spare tire or "emergency tire" with a different diameter is mounted, the method can fail completely.
Other processes, based, in principle, on the same algorithm, are known from U.S. Pat. No. 3,581,277, JP 63-305011(A), and FR-25 685 19-A.
A process for evaluating the speed signals, which reflect the rotation behavior of the individual wheels of a vehicle, is known from DE 39 15 879-A1, in which a speed correction factor is determined for each wheel. The multiplication of the instantaneous wheel speed by the speed correction factor yields a common basic speed, which is derived from, e.g., the speed of the instantaneous slowest wheel. The wheel speed multiplied by the corresponding correction factor is then used as the basis for further signal processing, instead of the actual wheel speed. The process is used to determine the rotation behavior of a wheel within the framework of an antilock system.


SUMMARY OF THE INVENTION

An objective of the-present invention is to provide a process for monitoring the tire pressure, which is characterized by higher accuracy and reliability compared with the prior art processes, and which can be used even when tires, which have different rolling circumferences as a consequence of manufacturing tolerances, uneven wear or the like, or because they are used only as emergency wheels, are mounted.
It has been found that this objective can be accomplished by a process in which velocity correction factors are formed for the individual wheels of the vehicle, and these factors, multiplied by the wheel speed, yield a basic speed, and the values of the individual correction factors are determined in a learning phase. Correlations are determined between the correction factors for typical driving situations. Band widths or "tolerances" that depend on the actual travel situation are determined for the correction factors. The deviations of the correction factors from the learned values are determined and evaluated in an identification phase, taking into account the tolerances that depend on the travel situation and the progression of the learning process. Loss of tire pressure is signaled when, taking the current deviation into account, the current correction factor for one wheel becomes smaller than the speed correction factor already learned during the learning phase for the corresponding wheel for the current travel situation, taking into account the tolerance already determined for the current travel situation during the learning phase.
The process according to the present invention for monitoring the tire pressure is consequently based on the formation and the evaluation of speed correction factors, which more or less compensate for the differences in the diameters of the individual wheels, and on the division of the process into a learning phase and an identification phase. The values of the individual correction factors and correlations between these factors in typical travel situations, e.g., during

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William, Roger: DWS--ein neues Druckverlust-Warnsystem fur Automobilreifen, ATZ Automobiltechnische Zeitschrift 94,6,1992, S.336-340.

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