Method and device for detecting a deflated tire on a vehicle

Details Method and device for detecting a deflated tire on a vehicle Method and device for detecting a deflated tire on a vehicle

1994-11-16

1996-12-31

Hofsass, Jeffery

Communications: electrical

Land vehicle alarms or indicators

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

340442, 731465, B60C 2300

Patent

active

055898165

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to a method of detecting a deflated tire on a vehicle suitable for cars, trucks or the like.


BACKGROUND ART

Prior applications such as French Patent Publication No. 2568519 and European Patent Publication No. 291 217 propose using wheel speed signals from the vehicle wheels such as for example the signals from an anti-lock braking system which are multi-pulse signals of typically 48 to 96 pulses per revolution of each wheel. The prior art system compares the speed derived signals in various ways, and also attempts to overcome errors due to vehicle factors such as cornering, braking, accelerating, uneven or changing loads, etc., which can cause changes in the speed signals which are larger than those caused by a tire deflation of, for example, 0.4 bar.
French Patent Publication No. 2568519 avoided errors of this type by monitoring the speeds of the diagonally opposed pairs of wheels for a long time or distance period so that it averaged out effectively cornering of the vehicle. The result however was that the device operated very slowly taking many kilometers to sense a pressure loss.
European Patent Publication No. 291 217 improved the situation by calculating the lateral and longitudinal acceleration of the vehicle using the same four wheel speed signals and setting fixed limits above which the detection system was inhibited to avoid false signals due to cornering and acceleration. This inhibition of detection however meant that for a proportion of the time of vehicle running the system was not sensing punctures, the actual proportion depending upon the type of roads and the way the vehicle was being driven.
The real difficulty with these types of systems is that, apart from the lateral acceleration of the vehicle which occurs during cornering causing increased deflection of the outer pair of wheels compared to the inner pair of wheels, each vehicle has different characteristics due to the position of the center of gravity and the type of suspension. These different characteristics, when concerning, produce additional deflections in the outer pairs of tires with regard to the inner pairs of tires.
However, the vehicle characteristics make the tire deflections different in each of the tires. Similar problems occur due to vehicle characteristics in the deflections in the front pair of tires compared to the rear pair tires when the vehicle brakes, and vice-versa when the vehicle accelerates.


SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method of detecting a deflated tire on a vehicle which accommodates the above changes, avoiding false signals and detecting deflation for substantially all the time when the vehicle is running.
According to one aspect of the present invention there is provided a method of detecting a deflated tire on a vehicle by comparing the rolling radii of the tires by means of comparing angular velocity speed signals from wheel speed sensors one at each wheel characterised by calculating an error value DEL' where ##EQU2## where C1, C2, C3 and C4 are angular velocity values for left-hand front, right-hand front, left-hand rear and right-hand rear wheels of the vehicle respectively, determining a correction factor LAT, calculating a corrected error value DEL where indicator provided in the vehicle to indicate that at least one tire is deflated when it is sensed that the magnitude of the corrected error value DEL is in the range 0.05 to 0.5.
Preferably the tire warning indicator is operated when the magnitude of the corrected error value is in the range 0.1 to 0.3.
The vehicle related constants A and B may have values in the range -5.0E-7 to +5.0E-7 and -4.01E-9 to +4.0E-9 respectively.
The correction factor LAT is found by calculating from the four angular velocity values C1, C2, C3 and C4 respective first, second, third and fourth deciding factors (MC1, MC2, MC3, MC4) where centralizing constant (K) to give a central deciding factor (MPSD) and selecting the correction factor (LAT) as follows, if the first or se

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