EP1924449A2

EP1924449A2 - Method and device for determining the condition of at least one tyre of a vehicle wheel

Info

Publication number: EP1924449A2
Application number: EP06808305A
Authority: EP
Inventors: Denis Le Bret; Zahir Djama
Original assignee: Peugeot Citroen Automobiles SA
Current assignee: PSA Automobiles SA
Priority date: 2005-09-16
Filing date: 2006-09-11
Publication date: 2008-05-28
Also published as: WO2007031677A2; FR2890899B1; FR2890899A1; WO2007031677A3; US20090151439A1

Abstract

The invention concerns a method for diagnosing the condition of at least one tyre of a vehicle wheel connected to the body shell thereof via a suspension, including, for the or each tyre, a step (102) of acquiring the vertical acceleration of the wheel in a reference model of the vehicle. Said method includes a step (108) of filtering the acquired acceleration to eliminate the frequencies thereof lower than a predetermined filtering frequency, a step (110) of determining a vertical excitation applied to the tyre based on the filtered acceleration, and a step (112, 114, 116, 118, 120) of determining the condition of the tyre based on the determined excitation.

Description

Method and system for determining the condition of at least one tire of a vehicle wheel

The present invention relates to a method for diagnosing the state of at least one tire of a vehicle wheel connected to the body thereof by means of a suspension, of the type comprising, for the or each tire, a stage of acquisition of the vertical acceleration of the wheel in a reference system of the vehicle. The present invention also relates to a diagnostic system implementing such a method.

There are methods using the measurement of the rotation speed of a motor vehicle wheel to diagnose the state of the tire thereof, and in particular its underinflation. However, a rapid uncorrected under-inflation causes an irreversible alteration of the dynamic behavior of the tire, even once it is re-inflated, that the methods of the state of the art do not allow to diagnose.

The object of the present invention is to solve the aforementioned problem by providing a method and a system capable of diagnosing abnormalities of a tire, such as unbalance or hernia, even if it is properly inflated. .

For this purpose, the subject of the invention is a method for diagnosing the state of at least one tire of a vehicle wheel connected to the body thereof by means of a suspension, of the type comprising, for the or each tire, a step of acquiring the vertical acceleration of the wheel in a reference system of the vehicle, characterized in that it comprises:

a step of filtering the acceleration acquired to eliminate the frequencies thereof that are lower than a predetermined filtering frequency;

a step of determining a vertical excitation applied to the tire as a function of the filtered acceleration; and

a step of determining the state of the tire as a function of the determined excitation. According to particular modes of implementation, the method may comprise one or more of the following characteristics:

the filtering frequency is greater than the rolling resistance frequency range of the wheel; the filtering frequency is greater than 25 Hz;

the filtering step is a high-pass filtering step;

the step of determining the vertical excitation applied to the tire comprises a step of calculating it from an inverse model of a single-wheel mechanical model of the wheel connected to the vehicle body by means of suspension ;

the step of determining the state of the tire comprises a step of comparing the determined excitation with a predetermined threshold value and a step of diagnosing the state of the tire, suitable for determining that the latter has an anomaly if the determined excitation is greater than at least once at the threshold value;

the threshold value is substantially equal to 1 millimeter;

the method further comprises a step of acquiring the speed of the vehicle and a supervision step adapted to trigger the diagnosis of the pneumatic state or to validate the determined state of the tire if at least the speed of the vehicle is greater than one. predetermined threshold speed; and

- The threshold speed is substantially equal to 50 km / h. The invention also relates to a system for diagnosing the condition of at least one tire of a vehicle wheel connected to the body thereof by means of a suspension, of the type comprising, for the or each pneumatic means for acquiring the vertical acceleration of the wheel in a reference system of the vehicle, characterized in that it is adapted to implement a method of the aforementioned type.

The invention will be better understood on reading the description which will follow, given solely by way of example, and in relation to the appended drawings, in which:

- Figure 1 is a mechanical model of a motor vehicle wheel connected to the body thereof by a suspension; FIG. 2 is a schematic view of a system according to the invention; and

FIG. 3 is a flowchart of the method implemented by the system of FIG. 2. FIG. 1 shows a single-wheel mechanical model of a wheel R of a four-wheeled motor vehicle, connected to FIG. the body C of the latter by means of a suspension Su, the wheel R being in contact with the ground So.

The body C is modeled by a mass brought back to the wheel of M _c occupying, on a vertical axis OZ of the vehicle, an altitude Z _c with respect to a reference level NRef, for example the altitude of the ground So at the start of the vehicle .

The suspension Su is modeled by a stiffness coefficient spring K _c in parallel with a damping damping coefficient R _c . The wheel R is modelized by a mass M _r occupying on the axis OZ an altitude Z _r compared to the reference level Nref. The tire of this latter is modeled by a spring of coefficient of stiffness K _r in contact with the ground So which occupies on the axis OZ an altitude Z _s with respect to the level of reference

Nref. When the vehicle moves, the behavior of this mechanical system is controlled by the evolution over time of the altitude Z _s of the ground.

Using the fundamental principle of dynamics, it can be shown that the single-wheel mechanical model of Figure 1 satisfies the following relationships:

^A _r (p) _ _πr ^ _ K _r p ² (M _c p ² ₊ R _c P ₊ K _c ) Z _s (p) ^W L (p) (1)

L (p) = M _r M _c p ⁴ + R _C (M _C + M _r ) p ³ + (M _r K _c + M _c (K _r + K _c )) p ² + R _c K _r p + K _c K _r

where p is the Laplace variable and A _r is the vertical acceleration along the OZ axis of the center of the R wheel. It can be shown that the model according to relations (1) is invertible.

It will now be described with reference to FIG. 2, a system according to the invention for diagnosing the state of a tire of a motor vehicle wheel, connected to the body thereof by means of a suspension.

This system is based on the single-wheel model according to the relations (1) and more particularly on a discretization of these relations.

This system is designated by the general reference 10 and comprises a single-axis accelerometer 12 arranged at the center of the wheel and measuring the vertical acceleration A _r of it along the axis OZ.

The accelerometer 12 is adapted to provide, via a wire link 14, a signal representative of the vertical acceleration to means 20 provided for extracting from this signal the vertical acceleration Ar.

The means 20 are connected to an analog / digital converter 22, for example a 0-order sample-and-hold, adapted to digitize with a predetermined sampling period Te, for example between about 0.001 seconds and 0.02 seconds, acceleration

A _r measured and thus output a numerical acceleration A _r (k) of the wheel, where k represents the k ' ^th sampling time. The analog / digital converter 22 is connected to a filter

24. This filter 24 is adapted to process the digital acceleration A _r (k) of the wheel by applying a high-pass filtering of the higher frequencies to a predetermined filter frequency f _c .

This frequency f _c is greater than the rolling resistance frequency range of the wheel in which the power of the wheel modes is essentially concentrated. Typically, this range is substantially equal [8; 20] Hz and in a preferred embodiment of the invention, the frequency f _c is substantially equal to 25 Hz. Thus, the frequencies below f _c of the digital acceleration A _r (k) are substantially eliminated by the filter 24. The high-pass filter 24 is moreover connected to a unit 26 able to implement a diagnosis of the state of the tire as a function of the filtered digital acceleration A _rf (k).

This unit 26 comprises a computation module 28 adapted to reconstruct a digital excitation Z _s (k) applied to the tire by the ground from a model inverse to that of the relations (1) as a function of the acceleration A _rf (k) filtered digital. The reconstruction of such an excitation by the module 28 is carried out, for example, from a bilinear discretization of sampling period Te of the model H ^"1 (p), which is possible because of the property of inversion of the model H (ρ).

The diagnostic unit 26 also comprises a comparison module 30 connected to the calculation module 28 and suitable for comparing the reconstructed digital excitation Z _s (k) with a predetermined threshold value Z threshold, for example substantially equal to 1 millimeter. The unit 26 also comprises a diagnostic module 32 connected to the comparison module 30 and adapted to diagnose that the state of the tire is defective if the reconstructed excitation Z _s (k) has at least N values greater than the threshold values. Zseuil, where N is a predetermined integer for example equal to 100. The unit 26 is connected to an alarm system 34 housed in the passenger compartment of the vehicle and adapted to deliver a light signal and / or sound if the state tire is diagnosed as defective.

Finally, the system 10 according to the invention comprises a supervision module 36 connected to a speed sensor 38 of the vehicle to receive a measurement of the speed thereof. The supervision module 36 is able to activate the high-pass filter 24 and the calculation unit 26 when the measured speed of the vehicle is greater than a predetermined speed substantially equal to 50 km / h. Indeed, it can be shown that the diagnostic accuracy achieved by the system according to the invention is increased for vehicle speeds greater than 50 km / h. FIG. 3 is a flowchart of the diagnostic method implemented by the system of FIG. 2.

In a first initialization step 100, for example activated after starting the vehicle, an error counter is initialized to zero.

A next acquisition step 102 is to measure the vertical acceleration A _r of the wheel and the speed V of the vehicle and to digitize these measurements according to the sampling period Te.

Then, a first test is performed in 104 to know if the speed of the vehicle acquired at 102 is greater than a predetermined threshold, for example 50 km / h. If the result of this test is negative, the anomaly counter is reset to zero in a step 106. Step 106 then loops to acquisition step 102.

If the result of the test at 104 is positive, a high pass filter is applied at 108 to the digitized vertical acceleration A _r (k) to substantially eliminate the frequencies thereof lower than the frequency f _c .

Then, in a calculation step 110, the digital excitation Z _s (k) applied to the tire by the ground is calculated as a function of the numerical acceleration A _rf (k) filtered from the discretization of the model H ^~! (ρ). In a next step 112, the excitation Z _s (k) is compared with the threshold value Z _se uii of 1 millimeter. Then, at 114, a second test is implemented to find out if the excitation Z _s (k) has values greater than 1 mm.

If the result of this test is negative, the step 114 loops on the acquisition step 102. If not, the anomaly counter is incremented at 116 by the number of excitation values Z _s (k) greater than 1. millimeter.

A third test is then performed at 118 to know if the value of the anomaly counter is greater than N. If the result of this test is negative, step 118 then loop on step 102. Otherwise, the state of the pneumatic is diagnosed as defective at 120. An audible and / or visual alarm the passenger compartment of the vehicle is then triggered at 122 to warn the driver of the vehicle.

The system and method according to the invention thus make it possible to diagnose tire anomalies, and in particular unbalance or herniation thereof, effectively, even if the tire is suitably inflated. Indeed, it is found that the component of the vertical acceleration of the wheel related to the adhesion of the tire to the ground and to the characteristics of the tire casing is in frequency beyond the range of rolling resistance of the tire. wheel. Beyond this frequency range, the actual excitations of the ground on the tire are less than a value of the order of a millimeter. Thus, for a healthy tire with no abnormality, no significant vertical acceleration of the wheel can be generated beyond the rolling resistance range. Also, if the reconstructed excitation has values higher than the threshold value Zthreshold, then this means that the tire has anomalies.

Although it has been described the diagnosis of the state of a tire of a motor vehicle wheel, the method and the system according to the invention can be applied to other types of vehicle, such as for example a motorcycle or a multi-train vehicle.

Similarly, although high pass filtering has been described to eliminate the frequencies of the vertical acceleration of the wheel below a predetermined frequency, alternatively, band pass filtering is used to also filter the noise in the high frequencies, for example above 100 Hz.

Similarly, although a supervision has been described which activates the diagnosis of the tire condition for vehicle speeds above 50 km / h, alternatively, the diagnosis is continuously activated and the supervision consists in validating the diagnostic results for vehicle speeds above 50 km / h.

Likewise, although a method and a system applied to a single tire have been described, alternatively, these apply to any number of tires of the vehicle. Finally, although it has been described a tire excited by the ground when the vehicle moves, it will be understood that the present invention also applies when the vehicle is placed on a running bench.

Claims

A method for diagnosing the condition of at least one tire of a vehicle wheel (R) connected to the body (C) thereof by means of a suspension (Su), of the type comprising, for the or each tire, a step (102) for acquiring the vertical acceleration of the wheel in a reference frame of the vehicle, characterized in that it comprises:

a step (108) for filtering the acceleration acquired to eliminate the frequencies thereof that are lower than a predetermined filtering frequency; a step (110) for determining a vertical excitation applied to the tire as a function of the filtered acceleration; and

a step (112, 114, 116, 118, 120) for determining the state of the tire as a function of the determined excitation.

2. Method according to claim 1, characterized in that the filtering frequency is greater than the rolling resistance frequency range of the wheel.

3. Method according to claim 2, characterized in that the filtering frequency is greater than 25 Hz.

4. Method according to any one of the preceding claims, characterized in that the step (108) of filtering is a high-pass filtering step.

5. Method according to any one of the preceding claims, characterized in that the step (110) of determining the vertical excitation applied to the tire comprises a step of calculating it from an inverse model of a single wheel mechanical model of the wheel connected to the vehicle body by means of the suspension.

6. Method according to any one of the preceding claims, characterized in that the step (112, 114, 116, 118, 120) for determining the state of the tire comprises a step (112) for comparing the excitation. determined to a predetermined threshold value and a step (120) for diagnosing the state of the tire to determine that it has an anomaly if the determined excitation is greater than at least once the threshold value.

7. Method according to claim 6, characterized in that the threshold value is substantially equal to 1 millimeter.

8. Method according to any one of the preceding claims, characterized in that it further comprises a step (102) for acquiring the speed of the vehicle and a step (104) supervision adapted to trigger the diagnosis of the pneumatic state or validate the determined state of the tire if at least the speed of the vehicle is greater than a predetermined threshold speed.

9. The method of claim 8, characterized in that the threshold speed is substantially equal to 50 km / h.

10. System for diagnosing the state of at least one tire of a vehicle wheel (R) connected to the body (C) thereof by means of a suspension (Su), of the type comprising, for the or each tire, means for acquiring the vertical acceleration of the wheel in a reference frame of the vehicle, characterized in that it comprises:

means (24) for filtering the acceleration acquired to eliminate frequencies thereof that are lower than a predetermined filtering frequency;

means (28) for determining a vertical excitation applied to the tire as a function of the filtered acceleration; and

means (30, 32) for determining the state of the tire as a function of the determined excitation, said means (24, 26, 36, 38) being adapted to implement a method according to any one of the claims 7 to 9.