Measuring and testing – Tire – tread or roadway – Tire inflation testing installation
Reexamination Certificate
2001-01-19
2002-08-27
Oen, William (Department: 2855)
Measuring and testing
Tire, tread or roadway
Tire inflation testing installation
C340S444000
Reexamination Certificate
active
06439045
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of detecting pressure loss in vehicle tires.
BACKGROUND OF THE INVENTION
The prior published application No. WO 95/12498 discloses the learning of correction factors with respect to the individual wheels of a vehicle during a first phase which shall compensate for possible differences in the diameters of the individual wheels. In the current operation the established wheel rotational speeds are multiplied with the respective learned correction factors in order to determine the vehicle speed from the wheel rotational speeds. The correction factors shall also be actually determined during driving. When the currently determined correction factor differs from the correction factor established for this wheel in the learning phase by more than a defined threshold value, pressure loss in the vehicle tire is detected. The correction factors are acquired in response to the driving situation so that the effects of possible deviations of wheel rotational speeds are taken into account which are due to longitudinal or transverse acceleration, due to cornering and the possibly related oversteering or understeering of the vehicle, or due to different slip values caused by differing coefficients of friction on the left and right road sides.
Further, it is known from U.S. Pat. Nos. 4,876,528 and 5,192,929 to detect pressure loss in tires of a vehicle by summing up the rotational speeds of the diagonal wheels and by establishing the difference between the sums. When this difference ranges between 0.05% and 0.6% of the mean value of both sums, the rotational speed of each individual wheel is allowed to deviate at most 0.1% from the mean speed of all four wheels. Pressure loss is signalled in the event of a greater deviation. Monitoring of the pressure loss is performed only if the vehicle is travelling straight, at least approximately. In the contrary case, the difference adopts a too great value due to a possibly understeering or oversteering behavior of the vehicle during cornering.
An object of the present invention is to provide a method which permits identifying pressure loss in a tire in a most simple and nevertheless maximum reliable fashion.
SUMMARY OF THE INVENTION
According to the present invention, this object is achieved because pressure loss in vehicle tires is identified by using at least one reference value which is produced by dividing the sums of respectively two signals representative of the wheel rotational speeds.
For example, the reference values can be produced as follows:
Ref
1
=(
T
vl
+T
hr
)/(
T
vr
+T
hl
)
Ref
2
=(
T
vl
+T
vr
)/(
T
hr
+T
hl
)
Ref
3
=(
T
vl
+T
hl
)/(
T
vr
+T
hr
).
The quantity T
i
is the signal representative of the rotational speed of the wheel, and the indices i have the following meaning: vl=front left-hand, vr=front right-hand, hl=rear left-hand, hr=rear right-hand, and refer to the wheel concerned. In a particularly favorable manner, the quantity T
i
as the signal representative of the rotational speed of the wheel can be established by the implementation of the method of the invention.
Advantageously, numerical problems in determining the reference values are minimized by the method of the present invention. In the prior art, initially two quantities are summed which have almost the same value. Thus, differences will occur only after a few digits behind the decimal point, from which, however, first problems may arise. In another step, the difference between these two sums is produced in the state of the art. As stated hereinabove, the two sums also adopt rather exactly the same value. In any case, deviations of these two sums inhere already a certain inaccuracy. When, on top of that, these two quantities are differenced, possible inaccuracies will still rise considerably so that the established difference, under certain circumstances, is no longer apt to be utilized as a numerical value.
According to the present invention, the reference values produce the sums of respectively two signals representative of the wheel rotational speeds, and respectively two of these sums are divided. Advantageously, this permits minimizing the numerical problems because the method of the present invention obviates the need for summing two almost equally great quantities and thereafter subtracting the sums in the subsequent steps.
In a preferred embodiment, the signals representative of the rotational speeds of the individual vehicle wheels are produced because the time measurement of the individual wheels, after a joint start signal, is started individually with the respectively following signal edge initiated by the respective wheel and is concluded individually for each wheel upon termination of a full or partial number of wheel revolutions predetermined for all wheels. In systems which make available only the number of the signal edges and the time of the last signal edge per scanning interval, favorably, an interpolation is made with reference to the corresponding signal edge which corresponds to the end of the measuring section.
Further inaccuracies can be avoided compared to the procedure of determining wheel rotational speeds which observes how many signal edges pass by in a predefined time window. In this mentioned procedure, there is an inaccuracy at the beginning and the end of the time window, in which position the sensor wheel is placed with respect to the last signal edge passing. This is because it may be the case that the last signal edge passage has just about taken place, or that the last signal edge passage took place so long ago that the following signal edge passage is imminent. Consequently, matters depend on the position which the sensor wheel adopts in the interspace between two teeth of the sensor wheel opposite the sensor.
The method of the present invention advantageously minimizes this inaccuracy because the position of the sensor wheel with respect to the sensor is exactly fixed at the beginning and the end of the measuring operation. With a sensor wheel having 48 teeth, this means in each case a {fraction (1/48)} rotation at the beginning and the end of the measuring operation.
The number of wheel rotations is predetermined as a function of the vehicle speed.
This provision may be effected, for example, so that the number of the wheel rotations varies proportionally with the vehicle speed. It may e.g. be achieved that the measurement time in which the signal representative of the wheel rotational speed shall be established is maintained approximately constant.
The number of the wheel turns can be integral. It is also possible to predefine a number of wheel turns which is not integral. In this case, the measuring operation ends with the edge of a tooth other than the tooth where measurement began. In order to begin the measuring operation exactly with one edge and to have it end exactly with the edge of another tooth, it is necessary to fix that part of the rotations which is no more completed in conformity with the number of the teeth of the sensor wheel.
Further embodiments of this procedure may include that for sensors with scanning intervals (which are so rated that the time information is not gathered for each signal edge but in which sensors scanning intervals are opened and closed with individual signal edges, and the number of the signal edges disposed in the scanning interval and the beginning and end time of the scanning interval is stored) an interpolation with reference to the defined signal edge is effected unless this edge marks the end of a scanning interval. The interpolation may take place under the assumption of a constant speed in the scanning interval, for example.
Measuring can be effected for each individual wheel. A general start signal is issued. After this start signal, the measuring operation is started individually for each wheel when the corresponding edge of the tooth of the sensor wheel has been detected. A defined edge of a tooth may e.g. be detected because a tooth gap is
Griesser Martin
Latarnik and Sylvia-Monika
Latarnik Michael
Zenzen Markus
Continental Teves AG & Co. OHG
Latarnik and Sylvia-Monika
Oen William
Rader & Fishman & Grauer, PLLC
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