METHOD FOR DETECTING A WEAR-RELEVANT LOAD ON A VEHICLE WHEEL

Abstract

A method for detecting a wear-relevant load on a vehicle wheel uses a tire pressure monitoring unit mounted on the vehicle wheel containing an acceleration sensor. A rotational frequency of the vehicle wheel is determined for a time interval from a series of measured values of the acceleration sensor at first time intervals. A centrifugal acceleration value is determined for the time interval. A proportionality factor is determined from the rotational frequency and centrifugal acceleration value, linking the square of the rotational frequency with the centrifugal acceleration. A rotational frequency of the wheel is continuously calculated from measured values of the centrifugal acceleration, which have been determined at second time intervals that are greater than the first time intervals, and from the proportionality factor. A load value is respectively calculated from the rotational frequency and the second time intervals. These load values are continuously added up to an overall load.

Claims

1. A method for detecting a wear-relevant load on a vehicle wheel by means of a tire pressure monitoring unit that is mounted on the vehicle wheel and comprises at least one acceleration sensor, the method comprising the steps of: determining a rotational frequency of the vehicle wheel for a time interval from a series of measured values of the acceleration sensor at first time intervals; determining a centrifugal acceleration value for the time interval, determining a proportionality factor from the rotational frequency and centrifugal acceleration value, linking the square of the rotational frequency with the centrifugal acceleration; successively calculating a rotational frequency of the wheel from measured values of the centrifugal acceleration, which have been determined at second time intervals that are greater than the first time intervals, and from the proportionality factor; calculating a load value from the rotational frequency and the corresponding second time interval; and successively adding these load values up to an overall load.

2. The method according to claim 1, wherein the second time intervals are at least 100 times as large as the first time intervals.

3. The method according to claim 1, wherein the rotational frequency is determined for the time interval from 4 to 100 measured values of the acceleration sensor.

4. The method according to claim 1, wherein the first time intervals are less than 30 milliseconds.

5. The method according to claim 1, wherein the second time intervals are at least 2 seconds.

6. The method according to claim 1, wherein the rotational frequency is determined for the time interval from measured values of tangential acceleration.

7. The method according to claim 1, wherein the proportionality factor is statistically calculated from several series of measured values of the acceleration sensor for different time intervals and centrifugal acceleration values determined in each case for these time intervals.

8. The method according to claim 1, wherein the load value corresponds to the number of wheel revolutions made in the second time interval.

9. The method according to claim 1, wherein the load value is calculated from the number of wheel revolutions made in the second time interval and from the tire pressure.

10. The method according to claim 1, wherein the overall load is set to zero if the tire pressure falls below a predetermined threshold.

11. The method according to claim 10, wherein the overall load, before it is set to zero, is stored as the load value.

12. Tire pressure monitoring device comprising a pressure sensor, an acceleration sensor and a control unit, wherein the control unit is designed to carry out a method according to claim 1 in operation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 shows a flowchart of a method for detecting a wear-relevant load on a vehicle wheel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Step 1 of the method checks whether the vehicle is travelling. This can be done with an acceleration sensor of a tire pressure monitoring device mounted on a wheel of the vehicle. If the vehicle is travelling, i.e., a wheel revolution is detected, step 2 checks whether there is a valid value of a proportionality factor, which links the square of the rotational frequency with the centrifugal acceleration. Such a value can, for example, be stored in a memory of a tire pressure monitoring unit or central unit of the vehicle, with which the tire pressure monitoring unit communicates, wherein a flag can indicate whether the stored value is valid.

[0019] If there is no valid value of the proportionality factor, the proportionality factor is determined in step 3. For this purpose, an acceleration value is determined with an acceleration sensor of the tire pressure monitoring device at first time intervals of, for example, 5 ms to 10 ms, for example a value of the tangential acceleration X.sub.acc or the centrifugal acceleration X.sub.acc. In this way, a series of measured values from an acceleration sensor is determined for a time interval formed from several first time intervals, for example 8 to 50 measured values. These measured values show a sinusoidal curve or their curve has a sinusoidal component. The frequency f of the sinusoidal curve or sinusoidal component of the signal curve can thus be measured by evaluating the series of measured values. For example, by smoothing the signal curve with low-pass filtering and determining the number of zero crossings.

[0020] The frequency determined in this way in step 3 is the rotational frequency of the wheel in the respective time interval. In step 3, at least one value of the centrifugal acceleration is measured during the time interval. The centrifugal acceleration is preferably measured several times in the time interval and an average formed from the measured values, which is then used as a centrifugal acceleration value for the time interval. If the rotational frequency is determined from a series of values of the centrifugal acceleration, these values can also be used to determine a centrifugal acceleration value for the time interval by averaging. If the rotational frequency is determined from a series of values of the tangential acceleration, values of the centrifugal acceleration can also be measured at first time intervals, and a centrifugal acceleration value can be determined therefrom for the time interval.

[0021] A proportionality factor is then determined from the value for the rotational frequency determined for the time interval and from the centrifugal acceleration value, which proportionality factor links the square of the rotational frequency with the centrifugal acceleration, for example by dividing the value for the rotational frequency by the centrifugal acceleration value. At the end of step 3, the determined proportionality factor is stored as a valid value of the proportionality factor, for example in a memory of the tire pressure monitoring unit or a central unit of the vehicle.

[0022] If it has already been established in step 2 that there is a valid value of the proportionality factor or after step 3 has been carried out, the method is continued with step 4.

[0023] In step 4, the centrifugal acceleration is measured at second time intervals Δt.sub.2, which are larger than the first time intervals Δt.sub.1, and then a value for the rotational frequency ω is calculated therefrom using the stored proportionality factor, for example by multiplying a measured value of the centrifugal acceleration by the proportionality factor. A load value of the tire is then calculated from the rotational frequency in step 5. In the simplest case, as a product of frequency f and second time interval Δt.sub.2. However, tire pressure can also be included in the load value, as tire revolutions lead to increased wear if the tire pressure is too high or too low. At the end of step 4, the calculated load value is added to an overall load value stored in the tire pressure monitoring unit or a central unit of the vehicle.

[0024] Provided that a tire revolution is detected, step 4 is carried out again and again such that the overall load value continuously increases and makes it possible to evaluate the wear condition of the tire. When using the tire pressure monitoring device for the first time, the overall load value is zero and will then increase with time.

[0025] The second time intervals Δt.sub.2 can be substantially larger than the first time intervals Δt.sub.1, for example 100 to 1,000 times larger. In order to keep the energy consumption associated with the method low, it is advantageous if the second time intervals Δt.sub.2 are at least 2 seconds, preferably at least 5 seconds, for example 5 seconds to 15 seconds.

[0026] One variant of the method described above envisages that the overall load value is set to zero if a fall in the tire pressure below a predetermined threshold is detected. This can prevent a new tire being assigned the overall load value determined for a previously used tire following a tire change. However, it is also possible that the overall load value is reset manually by a control signal every time a tire is changed.

[0027] In order to increase the reliability of the method, it is possible to determine the proportionality factor according to step 3 several times and then use an average of the determined proportionality factors in step 4.