Communications: electrical – Land vehicle alarms or indicators – Internal alarm or indicator responsive to a condition of the...
Reexamination Certificate
2002-09-03
2004-11-23
Hofsass, Jeffery (Department: 2636)
Communications: electrical
Land vehicle alarms or indicators
Internal alarm or indicator responsive to a condition of the...
C340S444000, C340S461000, C340S443000
Reexamination Certificate
active
06822561
ABSTRACT:
BACKGROUND OF THE INVENTION
Motor vehicles, which are equipped with an electronic system for controlling the driving dynamic, such as ABS, ASR or ESP, usually have a unit for measuring the angular velocity of the vehicle wheels. A measurement of the angular velocity of the vehicle wheels can especially take place with the aid of active wheel rpm sensors. It is already known that the monitoring of a change in the angular velocity of the wheels is suitable for tire pressure loss detection.
The known systems for detecting a pressure loss practically always proceed from the situation that an increase of the wheel rpm or a drop of the dynamic wheel radius results when there is a lowering pressure.
To detect the wheel rpm information, some systems store the actual wheel velocity first in a memory and evaluate this actual wheel velocity at a later time point. Compared to systems which undertake no storage of data, a conclusion can be drawn as to the actual driving situation from the trace of the wheel velocities so that fluctuations of the wheel angular velocities can be removed from the data which is necessary for an adequate accuracy of the pressure loss detection. The fluctuations of the wheel angular velocities are superposed on the tire pressure loss.
It is common for practically all known tire pressure detection systems that the detection system must first be advised when the desired rated pressure P
0
of the mounted wheels is adjusted. This starting condition for the tire pressure detection can be told to the electronic system, for example, by means of a reset switch which must be pressed by the operator of the vehicle. If, after a specific time, a pressure loss occurs at one or more wheels, the tire pressure of the affected wheel drops by the pressure difference AP. As a consequence of the pressure loss, the dynamic rolling radius of the affected wheel changes in a characteristic manner dependent upon the tire. As mentioned above, in known pressure loss detection systems, a pressure loss is detected when the dynamic rolling radius of the affected wheel is reduced by a specific minimum value whereby the wheel rpm increases.
Numerous methods for detecting a pressure loss have been suggested by evaluating the wheel velocity. Known methods for detecting pressure loss on the basis of wheel rpm information often are concerned with carrying out the pressure loss detection with still greater reliability and accuracy. The difficulty of carrying out a pressure loss detection with high accuracy is to distinguish a change of the dynamic rolling radius based on a pressure loss from changes of the dynamic rolling radius which can be caused, inter alia, by dynamic driving situations, especially driving in a curve, acceleration, deceleration, et cetera and roadway defects (potholes, various friction values) and are, as a rule, greater than the influence of a pressure loss on the dynamic rolling radius (disturbance effects).
For a pressure loss detection with high detection accuracy even during dynamic driving maneuvers, a method has been suggested in German patent application 199 61 681. Here, additional physical data, such as yaw rate, acceleration, brake actuation, engine torque, et cetera are included in the detection algorithm for pressure loss detection so that a pressure loss detection can be carried out even during dynamic driving maneuvers (driving in a curve, acceleration, braking, et cetera).
In U.S. Pat. No. 6,439,045, a pressure loss detection method is described, which is integrated into an electronic anti-blocking system CABS), wherein, after triggering the reset switch, when the rated pressure of the wheels is adjusted, first a time limited learning phase is run through in which a microcontroller follows wheel angular velocities while considering the driving situation and from the time-dependent trace of the reference values, upper and lower limit values (G
1
and G
2
) are fixed. The reference values are formed from the wheel angular velocities. After the learning phase, a comparison phase starts in which a check is made as to whether the actual specific reference values lie within the range defined by the learned limit values.
The method considers the actual driving situation by excluding, during the learning phase and during the comparison phase, reference values during unsuitable dynamic driving situations.
Known methods detect a pressure loss in the tire based on an increase of the angular velocity or a drop of the dynamic rolling radius for one or more wheels. The quality of the detection is, however, often not reliable enough because the criterion for detecting is based on a comparatively small change of the wheel rpm and the wheel rpm is influenced by a plurality of unwanted effects to a larger extent than the effect to be measured.
SUMMARY OF THE INVENTION
The task of the invention is to provide a method for detecting a pressure loss on the basis of the wheel rpm signals which is less sensitive relative to unwanted effects than known methods. Such unwanted effects are, for example, changes of the wheel rpm because of travel in a curve.
The present invention is based on the principle of detection of a pressure loss based on a drop of the angular velocity or an increase of the dynamic rolling radius for one or more wheels.
The pressure measurement takes place in a manner known per se by evaluating angular velocities of all wheels of the vehicle or evaluating informations which indicate the angular velocities on the basis of time intervals. The angular velocities are determined by sensor means.
In the detection method of the invention, the surprising effect is utilized that, when a tire has lost so much pressure that the tire rolls essentially on the emergency tread, this tire indicates an increase of the dynamic rolling radius, that is, a detectable drop of the wheel velocity.
Preferably, the wheel has an emergency tread arranged within the tire casing, especially, the wheel is a run-flat wheel having an emergency tread arranged on the rim.
According to the invention, the detection of the increase of the dynamic rolling radius of a wheel can preferably take place in that:
M
1
: a check is made as to whether a fixed pregiven or learned desired value is exceeded by the measured dynamic rolling radius; or,
M
2
: a check is made as to whether the dynamic rolling radius increases after it has previously dropped.
The method M
2
, which is especially preferred, can also be a method combined with the methods Prog A and Prog B described below. For example, an initially weak drop of the dynamic rolling radius as a consequence of a pressure loss before the tire casing seats on the emergency body (time point of the start of the flat) can be determined first with the methods Prog A and Prog B. If, thereafter, the dynamic rolling radius increases sharply, then a flat is present.
In a further preferred embodiment and according to the method of the invention, a tire pressure loss is exclusively detected in that a check is made whether the angular velocity or the dynamic rolling radius of the observed wheel increases by more than a pregiven threshold value.
According to the invention, suitable wheels for the vehicle are, for example, conventional tires having standard rims or preferably tires having emergency running characteristics, especially run-flat wheels having an emergency tread or run-flat tires having side walls reinforced for emergency running. Especially preferred are run-flat wheels having an emergency tread which is mounted on the rim. To generate a velocity pattern, the emergency tread can be modified in a run-flat wheel or run-flat tire in such a manner that during the rotation of the tire in a flat tire run during travel, a defined velocity pattern is generated.
A run-flat wheel which is preferably usable according to the method of the present invention is described in U.S. Pat. No. 6,591,668 which is incorporated herein by reference. In the type of tire described, the emergency tread then comes into contact with the inner side of the tire when the tire pressure is no
Edling Frank
Griesser Martin
Köbe Andreas
Latarnik Christine
Latarnik Eva-Maria
Blount Eric
Continental Aktiengesellschaft
Hofsass Jeffery
Latarnik Christine
Latarnik Eva-Maria
LandOfFree
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