A method and equipment for identifying a deflated tyre on a motor vehicle

Abstract: The angular velocity (ω 1 - ω 4 ) each wheel (1-4) is detected and corresponding velocity signals are generated and processed in an electronic processing unit (EPU) programmed to calculate the difference between the sum of the velocity signals relating to two diagonally opposite wheels (1, 4) and the sum of the signals relating to the other two wheels (2, 3). The processing unit (EPU) generates an alarm signal when the value of this difference is greater than a reference value. The sign of this difference identifies the diagonal (1, 4; 2, 3) on which the at least partially deflated tyre is located. The processing unit (EPU) calculates a number of successive values of the radii of curvature (R) of the paths followed by the front axle (1, 2) and the rear axle (3, 4) of the vehicle (V) from a predetermined equation, and compares the radii (R) thus calculated for the front axle (1, 2) and the rear axle (3, 4) with respective predetermined reference values. The processing unit (EPU) counts the number of the radii of curvature (R) values relating to each axle (1, 2; 3, 4) which are less than the corresponding reference value and identifies that axle having the greater number of radii of curvature (R) values less than the corresponding reference value as the axle of the vehicle (V) having a partially deflated tyre.

Description: The present invention relates to a method and equipment for detecting the presence of an at least partially deflated tyre on a motor vehicle with four wheels each fitted with a tyre. More specifically, the subject of the invention is a method which includes the steps of: measuring the angular velocity of each wheel and generating corresponding velocity signals or data; processing the velocity signals or data in a processing unit programmed to calculate the difference between the sum of the velocity signals or data relating to one pair of diagonally opposite wheels and the sum of the velocity signals or data relating to the other pair of wheels, and to generate an alarm signal indicating that a tyre is at least partially deflated when the difference is greater than a predetermined reference value; the sign of this difference being indicative of the diagonal on which the at least partially deflated tyre is located. A method of this type is known, for example, from French Patent Application FR-A-2 568 519. European Patent EP-B1-0 291 217 describes a method of this type in which, in order to identify the specific tyre which is at least partially deflated, the angular velocity signals or data for each tyre are compared with the average velocity for the four wheels and a signal is generated when the difference between the angular velocity of one wheel and the average angular velocity of the wheels exceeds a predetermined value. Another method for identifying a deflated tyre is known from EP-A-0 466 535. This method is based on a first criterion for determining the diagonal wherein the deflated tyre is located, and a second criterion for precisely identifying the deflated tyre. The first criterion consists of the observation of a function of the squares of the speeds of the wheels. The second criterion consists of comparing the average longitudinal speeds of the wheels of the front axle with that of the wheels of the rear axle. The object of the present invention is to provide an improved method and equipment which enables a specific tyre which is partially deflated to be identified reliably. This object is achieved according to the invention by a method as claimed in claim 1 and by an equipment as claimed in claim 3; the method is characterised by the following additional operations: the calculation, in the processing unit, of a predetermined number of successive values of the radii of curvature of the paths followed by the front and rear axles of the vehicle from a predetermined equation as a function of the angular velocities of the front and rear wheels respectively; the comparison of the radii of curvature thus calculated for the front axle and the rear axle with respective predetermined reference values; the counting, for each axle, of the number of the radius of curvature values which are less than their corresponding reference value; the identification of the vehicle axle on which the partially deflated tyre is located as the axle for which the greater number of values of the radius of curvature were found to be less than the corresponding reference value, and the generation of signals identifying the at least partially deflated tyre on the basis of the sign of the said difference and of the axle identified by means of the said additional operations. The method of the invention enables the specific tyre which may be deflated to be detected, that is identified, by the identification both of the diagonal and the axle of the vehicle on which this tyre is located. In order to identify the axle on which the deflated tyre is located, the invention relies on the fact that, when a tyre is deflated, the effective radius of rolling of the corresponding wheel is reduced and the angular velocity of this wheel increases relative to the angular velocity of the other wheel on the same axle of the motor vehicle, just as if this axle were travelling along a curved path. According to the invention, a given number of successive values of the radii of curvature (real or apparent) of the paths of the front and rear axles are thus calculated from a predetermined equation as a function of the angular velocities measured for the front and rear axles. These values are then compared with respective predetermined reference values. When the calculated radii of curvature are greater than the reference values, it is assumed that the paths of the vehicle's axles are substantially rectilinear. When, on the other hand, the calculated radii of curvature are less than the reference values, it is assumed that the vehicle's axles are following curved paths. If there is a partially deflated tyre on one axle, the number of the radius of curvature values which are less than the reference value will be greater for that axle than for the other axle. It is thus possible to identify the axle having the deflated tyre. Additional characteristics and advantages of the present invention will become apparent from the detailed description which follows, provided purely by way of non-limitative example, with reference to the appended drawing which is a block diagram of a system which operates in accordance with the present invention. In the appended drawing, a motor vehicle indicated V has four wheels 1,2,3 and 4 with respective tyres. Respective sensors of the so-called phonic wheel type, indicated S1 to S4 are associated with these wheels. In the embodiment illustrated, each of these sensors comprises essentially a toothed wheel W, rotatable with the corresponding vehicle wheel, and an associated magnetic pick-up P. The pick-ups P of the sensors S1 to S4 are connected to corresponding inputs of an electronic processing unit EPU. It is convenient, though not essential, for the sensors S1 to S4 to be of the type currently used in anti-skid, or so-called ABS, systems. In a vehicle V fitted with such an anti-skid or ABS system, the sensors S1 to S4 can be the same ones as those used in the anti-skid system and the processing unit EPU may consist of the electronic control unit of the anti-skid system. This has the advantage that the system of the invention is integrated with the anti-skid system of the vehicle. In any case, the electronic processing unit EPU consists conveniently of a microprocessor with associated memories and devices for interfacing with the sensors S1 to S4. Indicator devices I1 to I4 are also connected to the processing unit EPU, each being associated with a respective wheel 1 to 4. For convenience, these indicator devices may be arranged in the instrument panel of the vehicle. The processing unit EPU is programmed to receive signals transmitted by the sensors S1-S4 indicative of the angular velocities ω 1 , ω 2 , ω 3 , and ω 4 of the vehicle's wheels and to process these signals in the manner described below. The processing unit EPU calculates the difference between the sum of the angular velocities ω 1 + ω 4 of the diagonally opposite wheels 1 and 4 and the sum of the angular velocities ω 2 + ω 3 of the other two diagonally opposite wheels 2 and 3. The absolute value of the difference thus calculated is compared with a predetermined reference value. If the difference is greater than the reference value, the processing unit EPU deduces that there is a tyre which is at least partially deflated in one of the two diagonals. In this event, the processing unit EPU is able to identify the diagonal on which the at least partially deflated tyre is located on the basis of the sign (negative or positive) of the calculated difference. In parallel or in sequence with the operations described above, the processing unit EPU calculates a predetermined number of successive values of the radii of curvature of the respective paths of the front axle 1, 2 and of the rear axle 3, 4 of the motor vehicle. These radii of curvature may be calculated, for example, from the following equation: R = (V r + V l ) C / 2 mod (V r - V l ) where R is the radius of the path of an axle measured between the centre of curvature of the path and the centre line of the axle, V r is the speed at which the right wheel advances, V l is the speed at which the left wheel advances, C is the track-width of the axle, that is, the distance between the wheels, and mod is an absolute value. The processing unit EPU can calculate the speeds of advance V r and V l by multiplying the angular velocities of the right and left wheels respectively (transmitted by the sensors) by the nominal radii of these wheels. The processing unit EPU may be programmed, for instance, to calculate one hundred successive values of the radii of curvature of the paths of the front and rear axles, corresponding, for example, to one hundred successive rotations of the wheels. After having calculated the radii of curvature values, the processing unit EPU compares these values with a predetermined reference value of for example, 1km. In general, the reference value may be different for the front and back axles, for example to take into account any difference in the lengths of these two axles. In particular, the processing unit EPU is also programmed to count the number of values of the radii of curvature which are less than the corresponding reference value for each axle and to identify the axle containing the partially deflated tyre as that for which the greatest number of radius of curvature values were less than the corresponding reference value. At this point, having identified the diagonal and the axle on which the at least partially deflated tyre is located, the EPU activates the indicator device I corresponding to this tyre. For convenience, so as to eliminate, or at least greatly reduce, the number of possible false indications, the processing unit EPU may be programmed to assume that there is an at least partially deflated tyre on one axle of the motor vehicle when the difference between the number of radius of curvature values that are smaller than the corresponding reference value for one axle and the number of corresponding values for the other axle exceeds a predetermined number. Naturally, the principle of the invention remaining the same, the embodiments and manufacturing details thereof may be varied widely from those described and illustrated here purely by way of non-limitative example without departing thereby from the scope of the present invention as defined in the attached Claims.

Claims: A method for detecting the presence of an at least partially deflated tyre on a motor vehicle (V) with four wheels (1-4) each fitted with a tyre, including the steps of: measuring the angular velocity (ω 1 - ω 4 ) of each wheel (1-4) and generating corresponding velocity signals or data, processing the velocity signals or data in an electronic processing unit (EPU) programmed to calculate the difference between the sum of the velocity signals or data relating to one pair of diagonally opposite wheels (1, 4) and the sum of the velocity signals or data relating to the other pair of wheels (2, 3) and to generate an alarm signal indicating that a tyre is at least partially deflated when the said difference is greater than a predetermined reference value; the sign of this difference being indicative of the diagonal (1, 4; 2, 3) on which the at least partially deflated tyre is located; the method being characterised by the following additional operations: the calculation, in the processing unit (EPU), of a predetermined number of successive values of the radii of curvature (R) of the paths followed by the front axle (1, 2) and the rear axle (3, 4) of the motor vehicle (V) from a predetermined equation as a function of the angular velocities (ω 1 , ω 2 ; ω 3 , ω 4 ) of the front wheels (1, 2) and of the rear wheels (3, 4) respectively; the comparison of the radii of curvature (R) thus calculated for the front axle (1, 2) and the rear axle (3, 4) with respective predetermined reference values; the counting, for each axle (1, 2; 3, 4), of the number of values of the radii of curvature (R) which are less than their corresponding reference value; the identification of the axle of the vehicle (V) on which a partially deflated tyre is located as that for which the greater number of values of the radii of curvature (R) were found to be less than the corresponding reference value, and the generation of signals identifying the at least partially deflated tyre on the basis of the sign of the said difference and of the axle (1, 2; 3, 4) identified by means of the said additional operations. A method according to Claim 1, characterised in that the said processing unit (EPU) calculates the difference between the number of radii of curvature (R) values which are less than their corresponding reference value for one axle (1, 2; 3, 4) and the corresponding number of values counted for the other axle (3, 4; 1, 2), and assumes that there is an at least partially deflated tyre on one axle (1, 2; 3, 4) of the vehicle (V) when this difference is greater than a predetermined value. Equipment for detecting the presence of an at least partially deflated tyre on a motor vehicle (V) with four wheels (1-4) each with a tyre, including sensor means (S1 - S4) for providing signals or data indicative of the angular velocity of each wheel (1-4), and an electronic processing unit (EPU) connected to the sensor means (S1-S4) and programmed to calculate the difference between the sum of the velocity signals or data relating to one pair of diagonally opposite wheels (1, 4) and the sum of the velocity signals or data relating to the other pair of wheels (2, 3) and to generate an alarm signal indicating that a tyre is at least partially deflated when the said difference is greater than a predetermined reference value; the sign of the aforesaid difference being indicative of the diagonal (1, 4; 2, 3) on which the at least partially deflated tyre is located; characterised in that the electronic processing unit (EPU) is also programmed to calculate a predetermined number of successive values of the radii of curvature (R) of the paths of the front axle (1, 2) and the rear axle (3, 4) of the motor vehicle (V) from a predetermined equation as a function of the angular velocities ω 1 , ω 2 ; ω 3 , ω 4 ), measured for the front wheels (1, 2) and the rear wheels (3, 4); to compare the radii of curvature (R) thus calculated for the front axle (1, 2) and for the rear axle (3, 4) with respective predetermined reference values; to count the number of values of the radii of curvature (R) for each axle (1, 2; 3, 4) which are less than their corresponding reference value; to identify the axle of the vehicle (V) on which the partially deflated tyre is located as that axle for which the greater number of the radii of curvature (R) values were less than the corresponding reference value, and to generate signals identifying the at least partially deflated tyre on the basis of the sign of the said difference and of the identified axle. Equipment according to the preceding Claim, characterised in that the electronic processing unit (EPU) is programmed to determine the difference between the number of the radii of curvature (R) values relating to one axle (1, 2; 3, 4) that are less than the reference value and the corresponding number of the radii of curvature values relating to the other axle (3, 4; 1, 2) and to assume that one axle (1, 2; 3, 4) of the motor vehicle (V) has an at least partially deflated tyre when this difference is greater than a predetermined number.

Inventors: BARGIS ERICA, CASCIO FULVIO, CISTERNINO MAURIZIO, DE CRISTOFARO FRANCESCO, PONTI CESARE, BARGIS, ERICA, CASCIO, FULVIO, CISTERNINO, MAURIZIO, DE CRISTOFARO, FRANCESCO, PONTI, CESARE
Applicants: FIAT AUTO SPA, FIAT AUTO S.P.A.
Application year: 1996
Main classification: B60C23
IPC codes: B60C23