Method for determining a pivoting angle of a wheel unit mounted onto a snap-in inflation valve

Abstract

A method for determining a pivoting angle () of a wheel unit (12) mounted onto a snap-in inflation valve (10) includes the following three phases: observation of a curve representing the effect of gravity on the radial acceleration A.sub.mes of a wheel of the vehicle on a sensing axis Y which is related to the wheel unit and is not parallel to the axis of rotation of the wheel, by spectrum analysis of the gravity curve at a sampling frequency F.sub.s greater than an assumed rotation speed of the wheel, deduction of the actual rotation speed of the wheel, and determination of the pivoting angle according to the formula $\cos =\frac{\stackrel{\_}{A_{\mathrm{mes}}}}{{}^{2}R},$ where is the actual angular speed deduced from the observation of the curve, A.sub.mes is a mean value of the corrected radial acceleration, and R is a standardized radius of the wheel.

Claims

1. A method for determining a pivoting angle () of a wheel unit (12) mounted onto a snap-in inflation valve (10), said valve being placed on a wheel of a motor vehicle, said method including the following: with an inner end (15) of the inflation valve (10) positioned on a rim opening of the wheel and with the wheel unit (12) fastened to a head (19) of the inflation valve (10) so that the wheel unit (12) is mounted fixed to the inflation valve (10) with respect to rotation, rotating the wheel so that a pivoting angle of a wheel unit occurs while the wheel is rotating, wherein the wheel unit has a measurement axis (Y) for measuring acceleration that allows the wheel unit, in an initial, non-pivoting position, to directly measure a radial acceleration (Arad) of the wheel, wherein during rotation of the wheel when the wheel unit pivots about the rotation axis (X) in a first direction (P), the measurement axis (Y) is displaced from the initial, measurement position by a pivoting angle to a new position corresponding to a sensing axis (Y), wherein when the wheel unit pivots about the rotation axis (X), the sensing axis (Y) is non-parallel to an axis of rotation of the wheel, the wheel unit pivots from the measurement axis (Y) to the sensing axis (Y) that deviates from the measurement axis (Y) by the pivoting angle and measures a radial acceleration (A.sub.mes) on the sensing axis (Y), wherein, the method further includes the following phases: Phase 1: with the wheel pivoted and in rotation, measuring the radial accelerations (Ames) on the sensing axis (Y), observation of a gravity curve C representing the effect of gravity on the radial acceleration (A.sub.mes) of a wheel of the vehicle on the sensing axis (Y), by performing spectrum analysis of the gravity curve at a sampling frequency F.sub.s greater than an assumed rotation speed .sub.0 of the wheel, Phase 2: deduction of an actual rotation speed of the wheel, where is the actual angular speed deduced from the observation of the gravity curve, and Phase 3: determination of the pivoting angle according to the formula $\cos =\frac{\stackrel{\_}{A_{\mathrm{mes}}}}{{}^{2}R},$ where A.sub.mes is a mean value of the measured radial accelerations, and R is a standardized radius of the wheel.

2. The method as claimed in claim 1, wherein in the spectrum analysis the curve C is assumed to be sinusoidal, and the spectrum analysis includes an identification between a discrete sampling of the acceleration value and a sinusoidal expression of said curve, with changing of the sampling frequency to provide convergence towards the actual rotation speed of the wheel.

3. The method for determining a pivoting angle as claimed in claim 2, further comprising the following steps: 1a) measuring a radial acceleration A.sub.mes of the wheel at a predetermined sampling frequency $F_s=\frac{16{}_0}{2},$ where .sub.0 is the assumed rotation speed of the wheel, 1b) filtering and determining a first sinusoidal curve C representing the variations of the radial acceleration sampled in step 1a), as a function of the rotation of the wheel, by eliminating noise and centering this curve on the origin, 1c) determining a surface area S.sub.1 of this first sinusoidal curve C and a surface area S.sub.2 of a second sinusoidal curve representing the integral of the first sinusoidal curve, 2a) determining a rotation speed .sub.1 of the wheel by finding the ratio of these two surface areas according to the formula $\frac{S_1}{S_2}={}_1,$ 2b) verifying that the determined rotation speed .sub.1 does match the sampling frequency F.sub.s of step 1a), and: 3a) when the determined rotation speed .sub.1 is verified to match the sampling frequency F.sub.s of step 1a), determining the pivoting angle after determination of a mean value of the radial acceleration A.sub.mes according to the relation: $\cos =\frac{\stackrel{\_}{A_{\mathrm{mes}}}}{{}_1^{2}R}$ where A.sub.mes is the mean value of the radial acceleration, .sub.1 is the actual rotation speed of the wheel determined in step 2a, and R is a standardized radius of the wheel, and 3b) if this is not the case, repeating steps 1a) to 2b).

4. The method for determining a pivoting angle as claimed in claim 1, further comprising the following steps: 1a) measuring a radial acceleration A.sub.mes of the wheel at a predetermined sampling frequency $F_s=\frac{16{}_0}{2},$ where .sub.0 is the assumed rotation speed of the wheel, 1b) filtering and determining a first sinusoidal curve C representing the variations of the radial acceleration sampled in step 1a), as a function of the rotation of the wheel, by eliminating noise and centering this curve on the origin, 1c) determining a surface area S.sub.1 of this first sinusoidal curve C and a surface area S.sub.2 of a second sinusoidal curve representing the integral of the first sinusoidal curve, 2a) determining a rotation speed .sub.1 of the wheel by finding the ratio of these two surface areas according to the formula $\frac{S_1}{S_2}={}_1,$ 2b) verifying whether the determined rotation speed .sub.1 does match the sampling frequency F.sub.s of step 1a), and: 3a) when the determined rotation speed .sub.1 is verified to match the sampling frequency F.sub.s of step 1a), determining the pivoting angle after determination of a mean value of the radial acceleration A.sub.mes according to the relation: $\cos =\frac{\stackrel{\_}{A_{\mathrm{mes}}}}{{}^{2}R}$ where A.sub.mes is the mean value of the radial acceleration, .sub.1 is the actual rotation speed of the wheel determined in step 2a, and R is a standardized radius of the wheel, and 3b) when the determined rotation speed .sub.1 is not verified to match the sampling frequency F.sub.s of step 1a), changing the sampling frequency F.sub.s and repeating steps 1a) to 2b).

5. The method as claimed in claim 4, wherein the sampling frequency F.sub.s is changed iteratively by executing steps 1a) to 2b) in a loop until the frequency F.sub.s is equal to the rotation speed calculated in step 2a) of the preceding cycle.

6. The method as claimed in claim 4, wherein step 1b) is executed with the aid of a bandpass filter.

7. The method as claimed in claim 6, characterized in that the bandpass filter is a Butterworth filter.

8. The method as claimed in claim 4, wherein, in step 3a), the mean value of the radial acceleration is determined by measuring the radial acceleration four times per wheel revolution during four to five consecutive wheel revolutions.

9. The method as claimed in claim 1, wherein the initial sampling frequency F.sub.s is within the range from 316 to 3016 Hz.

10. The method as claimed in claim 1, wherein the sampling frequency F.sub.s is chosen in such a way that at least sixteen acceleration measurements are made in each period.

11. The method as claimed in claim 1, wherein the method is performed when the vehicle is moving at a steady speed between 50 and 130 km/h without any significant change in speed in the period when the measurement of the radial acceleration (Ames) on the sensing axis (Y), is being made.

12. The method as claimed in claim 1, wherein the pivoting angle is calculated when the wheel has previously been subjected to an acceleration of 200 g or more.

13. The method as claimed in claim 1, wherein the diameter R of the wheel is standardized to 40.64 cm (16 inches).

14. The method as claimed in claim 1, wherein the wheel unit is comprised of: temperature and pressure sensors, an accelerometer, a microprocessor, a memory, a battery, an RF (radio frequency) transmitter device, and an LF (low frequency) receiver device, and the accelerometer is used in measuring the radial acceleration (Ames) on the sensing axis (Y).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other objects, advantages and characteristics of the invention will also be made clear by the following description, provided by way of non-limiting example with reference to the attached drawings, in which:

(2) FIG. 1 is a schematic view showing a wheel unit mounted on a snap-in inflation valve in the correct operating position,

(3) FIG. 2 is a schematic view showing a a snap-in valve associated with a wheel unit which has pivoted about the axis of the rim opening,

(4) FIG. 3 is a diagram showing the various steps of the method according to the invention, and

(5) FIG. 4 is a schematic view showing the variations of the radial acceleration of the wheel as a function of time.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(6) In the embodiment shown in FIGS. 1 and 2, an inflation valve 10 of what is known as the snap-in type is associated with a wheel unit 12. In a known manner which is not described in detail here, this inflation valve is designed to be placed in a rim (not shown) of a vehicle wheel (not shown) so as to allow the inflation and/or deflation of a tire (not shown) associated with this rim.

(7) The inflation valve 10 is made of a resilient material such as rubber, and has a generally cylindrical body 13 having two ends, referred to as the outer end 14 and the inner end 15.

(8) The inner end 15 (intended to be positioned inside the tire) has a head 19 onto which the wheel unit 12 is fastened. The wheel unit mounted in this way is fixed to the inflation valve 10 with respect to rotation.

(9) The outer end 14 of the valve (intended to be accessible from outside the tire) carries a cap 17 for sealing an inflation passage (of a known type, not shown) running from one end of the body of the inflation valve to the other.

(10) The snap-in valve is placed in the rim opening in a known way, by force-fitting the valve body into the rim opening. The rubber forming the body of the inflation valve is adapted to stretch when it passes into the rim opening (in a known way) and to return to its initial shape when the perimeter of the rim opening is fitted into a groove 18 provided between the body of the valve and its inner end 15. When positioned in this way, the inflation valve allows the tire to be inflated and/or deflated (after the removal of its cap 17). Obviously, a one-way valve system (of a known type, not shown) prevents any leakage of air toward the outside of the tire.

(11) It should be noted that, in order to facilitate the positioning of the valve 10 in the rim opening, the valve body is very commonly (but not necessarily) lubricated before being positioned.

(12) The wheel unit 12 is a casing of generally parallelepipedal shape containing a plurality of electronic components. Thus this wheel unit includes at least: temperature and pressure sensors, an accelerometer (and/or an impact sensor), a microprocessor, a memory, a battery, an RF (radio frequency) transmitter device, and an LF (low frequency) receiver device.

(13) None of these elements is illustrated because they are of known types, and their illustration is not essential for an understanding of the present invention.

(14) The wheel unit is intended to monitor at least the pressure and temperature within the tire and to transmit an alert message toward a central unit (not shown) mounted in the vehicle, to warn the driver of any anomalies detected in a tire of the vehicle.

(15) The central unit and the wheel unit form a tire pressure monitoring system of a known type.

(16) The axis of the rim opening in which the valve is mounted is identified by an X in the drawings.

(17) When the wheel on which the wheel unit is mounted is caused to rotate at high speed (thus subjecting the wheel to an acceleration of about 200 g or more), the weight of the wheel unit causes the inflation valve to rotate about the axis X. In fact, the valve does not generally perform a number of revolutions, but pivots about the axis X before becoming locked in a stable position. It has been found that the pivoting of the wheel unit may take place in either a clockwise or an anticlockwise direction. Furthermore, the pivoting angle is not strictly defined, since each wheel unit may reach its own stable position.

(18) However, as shown in FIG. 1, the accelerometer mounted in the wheel unit has a measurement axis Y which enables it, when the wheel unit is initially put in position (without pivoting, as shown in FIG. 1), to measure the radial acceleration A.sub.rad of the wheel directly.

(19) When the wheel unit pivots about the axis X (FIG. 2) in the direction of the arrow P (for example), then the accelerometer mounted in this wheel unit pivots with it and the new direction of measurement Y of the accelerometer is no longer the radial direction Y of the wheel, but is a direction deviating therefrom by an angle . Consequently, the measurement of the acceleration A.sub.mes on the axis Y (due to the pivoting of the wheel unit through an angle ) is only the projection of the radial acceleration on the axis Y, rather than the direct measurement of the radial acceleration. The measurement that is made must therefore be corrected to allow for the pivoting. However, in order to correct it, the value of the pivoting angle must be known.

(20) At the present time, no method exists for determining this angle in an automatic way. The present invention proposes a solution for the automatic determination of this angle .

(21) The method of determining the pivoting angle is used only if the vehicle is moving at a steady speed between 50 and 130 km/h without any significant change in speed in the period when the measurement is being made (typically four revolutions of a wheel). This enables the pivoting angle to be determined only when this angle is stable in one position; otherwise the determination would be of no value.

(22) The method of determining the pivoting angle is also only used if the vehicle has been previously subjected to acceleration forces in excess of 200 g. This is the type of acceleration that is liable to cause the wheel unit to pivot about the axis X of the rim opening. If the vehicle has not been subjected to this type of acceleration, there is no point in determining the pivoting angle, since this angle will probably not have changed since the last determination.

(23) According to the invention, the method for determining the pivoting angle () of a wheel unit mounted onto a snap-in inflation valve mounted on a motor vehicle wheel having a diameter R includes three main phases (FIG. 3).

(24) The first phase consists in the observation of the curve C representing the effect of gravity on the radial acceleration A.sub.mes of a wheel of the vehicle on a sensing axis Y which is related to the wheel unit and is not parallel to the axis of rotation of the wheel, by spectrum analysis of the gravity curve at a sampling frequency F.sub.s greater than the assumed rotation speed of the wheel. For this purpose (see FIG. 3):

(25) Step 1a (100):

(26) The acceleration of the wheel is measured at a predetermined sampling frequency

(27) $F_s=\frac{16{}_0}{2}.$
In this formula, .sub.0 is an (assumed) initial rotation speed of the wheel. This initial rotation speed is not the actual speed (with rare exceptions). More precisely, the measured radial acceleration is A.sub.mes. This value is therefore the projection of the actual radial acceleration on the axis Y. This measurement is made at a sampling frequency Fs (which is found to be greater than the assumed initial rotation speed of the wheel .sub.0). The wheel rotation frequency is expected to lie within the range from 3 to 30 Hz. The initial sampling frequency F.sub.s is therefore preferably in the range from 316 to 3016 Hz. The radial acceleration is preferably measured sixteen times per period (i.e. per wheel revolution). Consequently, applying the formula

(28) $F_s=\frac{16{}_0}{2},$
if the sampling frequency is fixed, this also fixes a first value .sub.0 as the assumed initial rotation speed of the wheel.

(29) Step 1b (200):

(30) The acceleration measurements A.sub.mes are then filtered, and a first sinusoidal curve C (FIG. 4) is determined, representing the variations in measured acceleration (due to gravity) sampled in step 1a), as a function of time (t). The noise is eliminated and this curve is centered on the origin. To eliminate the noise and center the curve, use is made, notably, of a Butterworth filter (or a bandpass filter). This gives us the curve C, whose equation is of the type (a sin .sub.0t+), and which is shown in FIG. 4. The period T of this sinusoidal curve is equal to one wheel revolution.

(31) Step 1c (300):

(32) The surface area S.sub.1 of this first sinusoidal curve C is then determined, and the surface area S.sub.2 of a second sinusoidal curve representing the integral of the first sinusoidal curve is also determined.

(33) Thus we have:
S.sub.1=|a sin(.sub.0t+)|

(34) where a is a correction factor, .sub.0 is the assumed initial rotation speed of the wheel, t is the time and is the pivoting angle.

(35) S.sub.2 is the surface area of the first curve C. In other words, it is the double integral of the curve C.

(36) Thus we have:

(37) $S_2=\frac{1}{}.Math.a\cos \left(t+\right).Math.$

(38) The second phase of the method according to the invention consists in calculating the actual angular speed .sub.1 of the wheel. For this purpose, the following steps are executed:

(39) Step 2a (400):

(40) The actual rotation speed .sub.1 of the wheel is then determined by finding the ratio of these two surface areas according to the formula

(41) 0$\frac{S_1}{S_{21}}{}_1,$
provided that the integral is taken on a whole number of periods, an integration time equal to the period corresponding to .sub.0 being advantageously used,

(42) In fact,

(43) $\frac{S_1}{S_2}=\frac{.Math.a\sin \left({}_{0}t+\right).Math.}{\frac{1}{}.Math.a\cos ({}_{0}t+.Math.}{}_1$

(44) Thus we can find a value for the rotation speed of the wheel, .sup.1, which is independent of the pivoting angle .

(45) Step 2b (500):

(46) The actual rotation speed .sub.1 calculated from the acceleration measurements made in step 1a) is compared with the assumed initial rotation speed .sub.0 fixed by default.

(47) The third phase of the method according to the invention consists in the determination of the pivoting angle .

(48) For this purpose, the following steps are executed:

(49) Step 3a (600):

(50) If the two values (.sub.0, .sub.1) are identical (in other words, if the actual value of the rotation speed of the wheel has been found), the angle is then determined according to the following formula:

(51) $\cos =\frac{\stackrel{\_}{A_{\mathrm{mes}}}}{{}_1^{2}R},$
where
A.sub.mes is the mean value of the measured radial acceleration, .sub.1 is the rotation speed of the wheel determined in step 2b), and R is a standardized radius of this wheel. This standardized mean radius is fixed arbitrarily at a value of 40.64 cm (i.e. 16 inches).

(52) The mean value of the radial acceleration A.sub.mes can be determined by calculating the mean of all the measurements made in the course of the determination of .sub.1. It is particularly advisable to verify at this time the stability of this mean acceleration during the preceding four to five wheel revolutions, by checking the minimum and maximum values. Thus it will remain possible to invalidate the result if the expected stability has not been achieved (it depends on the driver's behavior, in terms of braking for example).

(53) It is also possible to determine the mean value of the radial acceleration by measuring the radial acceleration four times per wheel revolution during four to five consecutive wheel revolutions.

(54) When cos is known, the value of the angle is deduced from it.

(55) Step 3b (500):

(56) If it has been found in step 2b) (500) that the rotation speeds (.sub.0, .sub.1) are different from one another, steps 1a) to 2b) are restarted, using .sub.1 as the new initial rotation speed.

(57) By restarting this cycle of determining the rotation speed .sub.1 several times, we finally converge toward the actual rotation speed of the wheel.

(58) It should be noted that the sampling frequency F.sub.s is determined iteratively by executing steps 1a) to 2b) in a loop until this frequency F.sub.s is equal to the rotation speed calculated in step 2a) of the preceding cycle.

(59) Since the pivoting angle is known, the wheel unit can measure exactly the radial acceleration of the wheel on which it is mounted by correcting the measured acceleration values.

(60) This knowledge of the actual radial acceleration makes it possible, for example, to arrange for the wheel unit to transmit messages toward the central unit while conforming to fixed transmission angles, or to discover automatically which wheel/sensor assemblies are mounted on the vehicle by correlation between the wheel speed and the vehicle speed.

(61) Thus the method according to the invention makes it possible, by successive iterations, to determine the actual speed .sub.1 of the wheel, and then the pivoting angle .

(62) The method for determining the pivoting angle () of a wheel unit mounted onto a snap-in inflation valve 10 therefore includes the following three main phases: Phase 1: observation of the curve C representing the effect of gravity on the radial acceleration A.sub.mes of a wheel of the vehicle on a sensing axis Y which is related to the wheel unit and is not parallel to the axis of rotation of the wheel, by spectrum analysis of the gravity curve at a sampling frequency F.sub.s greater than an assumed rotation speed of the wheel, Phase 2: deduction of the actual rotation speed .sub.1 of the wheel, and Phase 3: determination of the pivoting angle according to the formula:

(63) $\cos =\frac{\stackrel{\_}{A_{\mathrm{mes}}}}{{}_1^{2}R}$

(64) Clearly, the present invention is not limited to the embodiment described and illustrated in FIGS. 1 to 4. In particular, the spectrum analysis means used to observe the curve C may be different from that described, without departure from the scope of the present invention.