Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle diagnosis or maintenance indication
Reexamination Certificate
2002-07-12
2004-11-30
Zanelli, Michael J. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle diagnosis or maintenance indication
C340S442000
Reexamination Certificate
active
06826462
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to a pressure detection system and more particularly relates to a method of detecting tire pressure drop in motor vehicles and a device for controlling the brake force or the driving dynamics.
BACKGROUND OF THE INVENTION
Motor vehicles equipped with an electronic system for brake pressure control or for the control of driving dynamics (ABS, TCS, ESP, etc.) usually include devices for measuring the angular velocity of the vehicle wheels, such as wheel speed sensors. It is already known in the art that observing a change in the angular velocity of the wheels is appropriate for detecting a pressure drop in tires because in the event of tire pressure drop the dynamic rolling circumference and, thus, the so-called dynamic wheel radius decreases. In addition, what is common with electronic brake pressure control systems, the current driving situation can be determined from the variation of the input data and, as the case may be, stored wheel speed data. Pressure drop detection may be performed most simply during driving situations with little influence on the difference of the wheel speeds, e.g. during straight travel without a force acting on the vehicle (longitudinal acceleration, transverse acceleration, yaw rate).
To achieve pressure drop detection with an increased accuracy especially in dynamic driving maneuvers, a method is disclosed in German patent application 199 61 681 wherein additional physical data such as yaw rate, acceleration, brake application, engine torque, etc., is included in the detection algorithm for pressure drop detection so that pressure drop detection can be carried out also during dynamic driving maneuvers.
In DE 197 21 480 A1 a pressure drop detection method which can be integrated into an electronic anti-lock system (ABS) is described, wherein after actuation of a reset switch which is triggered as soon as the nominal pressure of the wheels is set, a learning period within time limits is initially executed in which a microcontroller monitors wheel angle speeds in consideration of the driving situation and determines top and bottom limit values (G
1
and G
2
)from the time variation of the reference values calculated from the wheel angle speeds. Following the learning period is a period of comparison during which a check is made whether the currently determined reference values lie within the range defined by the learnt limit values.
The method takes into account the current driving situation by excluding reference values that result from inappropriate dynamic driving situations during the learning period and during the period of comparison.
Although various methods of detecting pressure drop by evaluating the wheel speed have already been disclosed, there is still the necessity to carry out pressure drop detection on the basis of wheel speed data in a still more reliable fashion, in particular to prevent undesirable wrong failure signalings as they may occur on e.g. snow or ice. The problem in pressure drop detection , among others, involves making a distinction between a comparatively insignificant variation of the dynamic rolling radius due to a pressure drop and major variations of the dynamic rolling radius due to cornering maneuvers, acceleration, deceleration, and roadway effects (bump holes, different coefficients of friction).
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a more reliable pressure drop detection on the basis of wheel speed data.
According to the present invention, this object is achieved by a method of detecting tire pressure drop in motor vehicles including the following steps:
a) producing at least two differently determined reference values Ref
i
which are produced from at least two wheel speed data of the group left front wheel VL, right front wheel VR, left rear wheel HL, and right rear wheel HR,
b) detecting a preliminary pressure drop by checking whether at least one reference value Ref
i
includes a predetermined minimum deviation from a nominal value S
i
for this reference value,
c) considering a final detection of a pressure drop to prevail in dependence on one or more methods for checking the plausibility
and a device for controlling the brake force and/or the driving dynamics and for detecting a pressure drop of tires in a motor vehicle, wherein a microcomputer which is connected to wheel speed sensors and, if necessary, additional driving dynamics sensors processes a method as described above and a per se known method for controlling the brake force and/or driving dynamics.
Initially, the following steps are performed according to the method of the present invention:
a) producing at least two differently determined reference values Ref
i
which are produced from at least two wheel speed data of the group left front wheel VL, right front wheel VR, left rear wheel HL, and right rear wheel HR.
b) detecting a preliminary pressure drop by checking
whether at least one reference quantity Ref
i
includes a predetermined minimum deviation from a nominal value for this reference quantity.
Subsequently, a final detection of a pressure drop (e.g. indication of a pressure drop alarm on the instrument panel) in dependence on one or more methods for checking plausibility is executed according to the present invention. The detection is additionally secured by this additional method. In case wrong failure signalings occur in steps a) and b), the predominant number of wrong failure signalings may be avoided by the plausibility check.
It is preferred that the predetermined minimum deviation is predefined by top and bottom limit values G
1
, G
2
while it is monitored whether these limit values are exceeded. The limit values can be produced by adding a suitable value to the nominal value, or by subtracting the said value from the nominal value.
The method of the present invention for measuring the pressure of vehicle tires is preferably implemented within a method of controlling the brake force and/or the driving dynamics (ABS, TSC, ESP).
The wheel rotational speed data is e.g. speed data of wheel speeds determined by sensors, or data indicating wheel speeds on the basis of time intervals. Preferably, the wheel speed data concerns data of currently determined wheel radii (dynamic wheel radius r
d
), which can be established according to the formula r
d
=v
ref
/&ohgr;, wherein v
ref
is the vehicle speed determined by the electronic brake system.
The nominal values with which the reference values are compared can be invariably fixed or learnt by means of a per se known learning method. WO 98/52780 e.g. describes a learning method that may be implemented according to the present invention. The purpose of the learning method that is preferred in application is to compensate for different running properties of the wheels which may occur due to different wear of the tires or different wheel diameters. An objective is to gather the data that is taken into consideration in the learning period during straight travel, if possible, when all wheels move at the same speed in relation to the underground. The learnt data can be averaged and stored as a nominal value. Following this action, the period of comparison can be performed according to steps a) and b).
To check the plausibility of a preliminary pressure drop which is detected according to steps a) and b), preferably, the amount of the deviation of a first reference value from a nominal value that is preferably learned, |&Dgr;Ref
f1
|=|Ref
f1
−S
f1
| and the amount of the deviation of another reference value from another nominal value |&Dgr;Ref
f2
|=|Ref
f2
−S
f3
| are compared to one another.
It may be expedient for the method that the reference values of the preliminary pressure drop detection in the steps a) and b) are produced in the same manner as the reference values in the plausibility check. However, this is not absolutely necessary. Therefore, it may also be provided that reference values are applied in
Griesser Martin
Ihrig Hans Georg
Continental Teves AG & Co. oHG
Honigman Miller Schwartz and Cohn LLP
Zanelli Michael J.
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