Method for determining tire characteristic influencing variables and control device therefor

Abstract

A method is for determining a tire characteristic influencing variable and includes: a) detecting an acceleration of a measurement point on a tire inner side of a vehicle tire, wherein a deviation, caused by contact of the vehicle tire with a roadway, of the acceleration of the measurement point within an observation window is detected, b) deriving at least one analytical characteristic variable which is characteristic of the detected acceleration, wherein the at least one analytical characteristic variable characterizes the non-periodic profile of the detected acceleration within one tire rotation, c) determining at least one tire characteristic influencing variable in a manner dependent on the at least one analytical characteristic variable, wherein a mathematical mapping yields the dependency between the analytical characteristic variable and the tire characteristic influencing variable, wherein the mathematical mapping assigns at least one tire characteristic influencing variable to the at least one derived analytical characteristic variable.

Claims

1. A method for determining a tire characteristic influencing variable, the method: a) detecting an acceleration of a measurement point on a tire inner side of a vehicle tire by a sensor positioned on the tire inner side, wherein a deviation, caused by contact of the vehicle tire with a roadway, of the acceleration of the measurement point within an observation window is detected, where the acceleration comprises a radial acceleration and a tangential acceleration; b) deriving at least one analytical characteristic variable by the sensor which is characteristic of the detected acceleration, wherein the at least one analytical characteristic variable characterizes a non-periodic profile of the detected acceleration within one tire rotation, the at least one analytical characteristic variable comprising a rising gradient of the radial acceleration at a rising flank and a falling gradient of the radial acceleration at a falling flank; receiving the at least one analytical characteristic variable at a control unit by a radio signal from the sensor; and, c) determining at least one tire characteristic influencing variable by the control unit in a manner dependent on the at least one analytical characteristic variable, wherein a mathematical mapping yields the dependency between the analytical characteristic variable and the tire characteristic influencing variable, wherein the mathematical mapping assigns at least one tire characteristic influencing variable to the at least one derived analytical characteristic variable and wherein the at least one tire characteristic influencing variable is stored in the control unit, the at least one tire characteristic influencing variable comprising a profile depth and a wheel load of the vehicle tire, the profile depth is a tread depth of the tire; wherein a determination of the profile depth and the wheel load as at least one tire characteristic influencing variable includes using a mapping matrix (M) and a shift factor (V) having constant elements (a, b, c, d, C.sub.a, C.sub.b) which map analytical characteristic variables (S1, S2, B1) linearly onto the profile depth and the wheel load, wherein the analytical characteristic variables are dependent on the profile depth and the wheel load; and wherein the mapping matrix and the shift factor define a linear first-order equation system, the solution of which, for the two derived analytical characteristic variables yields, a wheel load and the profile depth.

2. The method of claim 1, wherein, for said determination of the at least one tire characteristic influencing variable as a mathematical mapping wherein the mathematical mapping maps the at least one analytical characteristic variable onto the at least one tire characteristic influencing variable, such that every value of the at least one analytical characteristic variable is assigned exactly one value of the at least one tire characteristic influencing variable.

3. The method of claim 2, wherein a determination of a wheel load as at least one tire characteristic influencing variable includes using a calibration curve which runs within a linear tolerance band, wherein the tolerance band runs with a deviation of less than 15% around a linear approximation to the calibration curve.

4. The method of claim 2, wherein a determination of a wheel load as at least one tire characteristic influencing variable includes using a calibration curve which runs within a linear tolerance band, wherein the tolerance band runs with a deviation of less than 5% around a linear approximation to the calibration curve.

5. The method of claim 2, wherein a determination of a wheel load as at least one tire characteristic influencing variable includes using a calibration curve which runs linearly, and the wheel load is determined from a multiplication of the at least one analytical characteristic variable by a gradient of the calibration curve taking into consideration a tire-specific constant.

6. The method of claim 1, wherein each analytical characteristic variable is assigned in each case one calibration curve.

7. The method of claim 1, wherein, as at least one analytical characteristic variable, a time interval or an angular interval or a distance difference along the rolling circumference between two acceleration states of the measurement point is derived from the detected acceleration.

8. The method of claim 7, wherein a maximum positive change of a radial acceleration within a tire contact patch region and a maximum negative change of the radial acceleration within a tire contact patch region are selected as acceleration states.

9. The method of claim 7, wherein a radial acceleration in both acceleration states is approximately identical, and the radial acceleration in both acceleration states corresponds to a value which lies between 25% and 75% of the maximum radial acceleration 5 within the tire contact patch region, and wherein the maximum radial acceleration is determined from at least one of a profile of the detected radial acceleration weighted and averaged over multiple tire rotations and a profile of the detected radial acceleration smoothed in accordance with the floating mean value principle.

10. The method of claim 8, wherein the derivation of the at least one analytical characteristic variable from the radial acceleration includes: forming a characteristic curve versus a time or a traversed rolling circumference or a traversed angle of the measurement point on the vehicle tire from the detected radial acceleration; selecting two observation points on the characteristic curve; and, deriving a peak width of a peak in the characteristic curve from an abscissa spacing of the two observation points.

11. The method of claim 10, wherein the derivation of the peak width includes forming a derivative of the characteristic curve formed by the radial acceleration versus the time or the traversed rolling circumference or the traversed angle of the measurement point on the vehicle tire.

12. The method of claim 7, wherein a maximum tangential acceleration within a tire contact patch region and a minimum tangential acceleration within the tire contact patch region are selected as acceleration states, wherein the maximum and the minimum tangential acceleration are determined from at least one of a profile of the detected tangential acceleration weighted and averaged over several tire rotations and a profile of the detected tangential acceleration smoothed in accordance with the floating mean value principle.

13. The method of claim 12, wherein the derivation of the at least one analytical characteristic variable from the tangential acceleration includes: forming a characteristic curve versus the time or the traversed rolling circumference or the traversed angle of the measurement point on the vehicle tire from the detected tangential acceleration; selecting two observation points on the characteristic curve; and, deriving an x-axis spacing within the characteristic curve from an abscissa spacing of the two observation points.

14. The method of claim 7, wherein local high points within a tire contact patch region are selected as acceleration states.

15. The method of claim 14, wherein a further analytical characteristic variable is derived from a change in a radial acceleration versus a time or the traversed rolling circumference or a traversed angle of the measurement point on the vehicle tire.

16. The method of claim 15, wherein, as a further analytical characteristic variable, a maximum negative change within a tire contact patch region, or a maximum positive change within the tire contact patch region, of the radial acceleration versus the time or the traversed rolling circumference or the traversed angle of the measurement point on the vehicle tire is derived.

17. The method of claim 16, wherein the derivation of the further analytical characteristic variable from the change of the radial acceleration includes: forming a characteristic curve from the detected radial acceleration; selecting at least one observation point on the characteristic curve; and, deriving the change of the radial acceleration from the at least one observation point.

18. The method of claim 15, wherein the determination of a profile depth and a wheel load from the two analytical characteristic variables includes forming a characteristic map, which defines a mapping matrix, wherein the characteristic map has intersecting iso-lines, and intersection points of the iso-lines yield the wheel load and the profile depth for the derived analytical characteristic variables.

19. The method of claim 1 further comprising at least one of averaging the profile of the detected acceleration in weighted fashion over multiple tire rotations and smoothing the profile of the detected acceleration in accordance with the floating mean value principle.

20. The method of claim 1, wherein the determination of the at least one tire characteristic influencing variable includes additionally compensating at least one of an influence of a tire pressure, a tire temperature, and a wheel speed on the detected acceleration of the measurement point.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described with reference to the drawings wherein:

(2) FIG. 1 shows a motor vehicle tire having a tire sensor module;

(3) FIG. 2 shows a characteristic curve for a radial acceleration;

(4) FIG. 2A shows a derivative of the characteristic curve as per FIG. 2 for the derivation of a wheel load in accordance with a first and a second embodiment;

(5) FIG. 2B shows a characteristic map for the determination of a wheel load and of a profile depth in accordance with the first embodiment;

(6) FIG. 2C show the wheel load F.sub.z.

(7) FIG. 3 shows a characteristic curve for a tangential acceleration for the determination of a wheel load in accordance with a third embodiment; and,

(8) FIG. 4 shows calibration curves for the determination of the wheel load in accordance with the second and third embodiments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

(9) FIG. 1 illustrates a vehicle tire 1, on the tire inner side 2 of which there is arranged a tire sensor module 3. The tire sensor module 3 is arranged such that, via the tire sensor module 3, it is possible in particular to determine an acceleration, influenced by a deformation of the vehicle tire 1, of a measurement point MP. The acceleration may be in particular a radial acceleration a.sub.r or a tangential acceleration a.sub.t of the measurement point MP. The tire sensor module 3 can in particular transmit analytical characteristic variables, which may be derived from the measured acceleration a.sub.r, a.sub.t, for example via a radio signal 20 to a control unit 4, which can correspondingly further process the radio signals 20.

(10) In a first and a second embodiment, the radial acceleration a.sub.r is observed. In this regard, by way of example, FIG. 2 illustrates a characteristic curve K.sub.1 in which the radial acceleration a.sub.r measured by the tire sensor module 3 is plotted versus the time t. Outside an observation window 5, the radial acceleration a.sub.r is approximately constant. Within the observation window 5, the radial acceleration a.sub.r initially rises to a high point, then has a falling flank 6 which hereafter falls approximately to zero and subsequently transitions into a rising flank 7, which rises up to a second high point. At greater time values t, the radial acceleration a.sub.r falls again to a constant value outside the observation window 5, wherein the exact profile is dependent on the orientation of the tire sensor module 3 within the vehicle tire 1. Thus, in this example, the observation window 5 corresponds to a tire contact patch region L, in which a curvature of the tire inner side 2 changes owing to the deformation of the vehicle tire 1, such that the radial acceleration a.sub.r, observed at the tire inner side 2, also changes.

(11) The radial acceleration a.sub.r becomes minimal, that is, ideally zero, when the measurement point MP is situated in the region of a ground contact area 9 of the vehicle tire 1, within which the vehicle tire 1 is in contact with a roadway 8. The vehicle tire 1 deforms in the region of the ground contact area 9 such that the tire inner side 2 runs ideally parallel to the roadway 8 in a region which is situated opposite a tread 12, lying on the roadway 8, of the vehicle tire 1; the radial acceleration a.sub.r thus ideally becomes zero at these points.

(12) In the first embodiment, for the determination of at least one tire characteristic influencing variable which, in this embodiment, is given by a profile depth D of the vehicle 1 and a wheel load F.sub.z, firstly an x-axis spacing B.sub.1 between two observation points P.sub.A1, P.sub.B1 on the characteristic curve K.sub.1 is determined as an analytical characteristic variable. Here, the two relative high points of the characteristic curve K.sub.1 are selected as observation points P.sub.A, P.sub.B, wherein the relative high point before the falling flank 6 corresponds to the radial acceleration a.sub.r at the run-in into the tire contact patch, and the relative high point after the rising flank 7 corresponds to the radial acceleration a.sub.r at the run-out from the tire contact patch of a rotating vehicle tire 1.

(13) The x-axis spacing B.sub.1 is dependent both on the wheel load F.sub.z acting on the vehicle tire 1 and on the profile depth D of the vehicle tire 1. To be able to determine the respective influence of the two parameters F.sub.z, D, firstly a further analytical characteristic variable S.sub.1, S.sub.2 is determined, which is likewise dependent on the wheel load F.sub.z and the profile depth D.

(14) For this purpose, a maximum negative gradient S.sub.1 or a maximum positive gradient S.sub.2 of the characteristic curve K.sub.1 within the observation window 5 is determined as analytical characteristic variable, wherein the maximum negative gradient S.sub.1 is assigned to the falling flank 6 and the maximum positive gradient S.sub.2 is assigned to the rising flank 7. It is then preferably possible to form a derivative K.sub.2 of the characteristic curve K.sub.1 with respect to the time t, which derivative is illustrated in FIG. 2A. An ordinate value (y value) of a low point and of a high point of the derivative K.sub.2 then yields the maximum negative gradient S.sub.1 and the maximum positive gradient S.sub.2 respectively.

(15) For the further evaluation, for this purpose, that point of the characteristic curve K.sub.1 which is assigned the lowest ordinate value in the derivative K.sub.2 is selected as a first observation point P.sub.A2, or that point of the characteristic curve K.sub.1 which is assigned the highest ordinate value in the derivative K.sub.2 is selected as a second observation point P.sub.B2. The gradients S.sub.1 and S.sub.2 of the first observation point P.sub.A2 and of the second observation point P.sub.B2 respectively are subsequently transmitted as analytical characteristic variables by the tire sensor module 3 to the control unit 4 via the radio signal 20, along with the determined x-axis spacing B.sub.1. Whether the maximum negative gradient S.sub.1 or the maximum positive gradient S.sub.2 is used may depend on the signal quality for a respective tire type. However, the two gradients S.sub.1, S.sub.2 may each be considered for the following calculations, possibly also as a weighted mean value.

(16) Then, in the control unit 4, via a mapping matrix M with constant elements a, b, c, d and with a shift vector V with tire-specific constants C.sub.a and C.sub.b, the two analytical characteristic variables S.sub.1 or S.sub.2 and B.sub.1 are uniquely assigned both a profile depth D and a wheel load F.sub.z. Here, the assignment may for example take the following form:

(17) $[\begin{matrix} S_{1} \\ B_{1} \end{matrix}] = [\begin{matrix} a & b \\ c & d \end{matrix}] .Math. [\begin{matrix} D \\ F_{z} \end{matrix}] + [\begin{matrix} C_{a} \\ C_{b} \end{matrix}] with$ $M = [\begin{matrix} a & b \\ c & d \end{matrix}] and$ $V = [\begin{matrix} C_{a} \\ C_{b} \end{matrix}] or [\begin{matrix} D \\ F_{z} \end{matrix}] = {[\begin{matrix} S_{1} \\ B_{1} \end{matrix}] - [\begin{matrix} C_{a} \\ C_{b} \end{matrix}]} .Math. {[\begin{matrix} a & b \\ c & d \end{matrix}]}^{- 1}$

(18) This assignment applies analogously to the gradient S.sub.2. Here, the elements a, b, c, d of the mapping matrix M and C.sub.a and C.sub.b of the shift vector V are constant, such that a linear mapping is provided. To determine the profile depth D and the wheel load F.sub.z, it is thus merely necessary to determine the constants a, b, c, d, C.sub.a, C.sub.b and the inverses of the mapping matrix M, which may be derived from measurements performed in advance. For this purpose, it is for example possible to determine the change in the respective analytical characteristic variable S.sub.1, S.sub.2, B.sub.1 as a function of a variation of the wheel load F.sub.z and of the profile depth D, wherein the constants a, b, c, d each specify the magnitude of the change. The gradients S.sub.1, S.sub.2 or the x-axis spacing B.sub.1 are read from the characteristic curve K.sub.1 or from the derivative K.sub.2.

(19) This assignment thus specifies a linear first-order equation system which can be represented by a characteristic map 10 shown in FIG. 2B. The characteristic map 10 has parallel-running iso-lines 10a with a positive gradient and parallel-running iso-lines 10b with an opposite, negative gradient. Each iso-line 10a has a constant value S.sub.1, S.sub.2 in the event of variation of the wheel load F.sub.z and of the profile depth D, and each iso-line 10b has a constant x-axis spacing B.sub.1 in the event of variation of the wheel load F.sub.z and of the profile depth D. The iso-lines 10a, 10b intersect at intersection points 15, wherein the intersection points 15 specify the solutions of the linear equation system, such that the intersection points 15 yield the wheel load F.sub.z and profile depth D determined for a particular analytical characteristic variable S.sub.1 or S.sub.2 and B.sub.1.

(20) Mapping matrices M or inverses of the mapping matrices and shift vectors V may be stored for different tire types in the control unit 4.

(21) In a second embodiment, the peak 11 formed from the falling flank 6 and the rising flank 7 is observed, wherein, using a calibration curve 10c stored for this embodiment, a peak width B.sub.2 of the peak 11 illustrated in FIG. 2C yields the wheel load F.sub.z. In this embodiment, the peak width B.sub.2 is determined at those points of the peak 11 at which the maximum negative gradient S.sub.1 and the maximum positive gradient S.sub.2 is present. At these points, the peak width B.sub.2 is dependent virtually exclusively on the wheel load F.sub.z, and the influence of the profile depth D on the peak width B.sub.2 is insignificant and, depending on accuracy requirements, can be disregarded.

(22) This means an x-axis spacing that specifies the peak width B.sub.2 is formed between a first observation point P.sub.A3 and a second observation point P.sub.B3, wherein the ordinate values of the two observation points P.sub.A3, P.sub.B3 need not necessarily be equal. The peak width B.sub.2 at the points with the maximum gradient S.sub.1, S.sub.2 in terms of magnitude may in this case also be derived from the derivative K.sub.2, wherein, in the case of FIG. 2A, the peak width B.sub.2 can be derived from the x-axis spacing between the high point and low point of the derivative K.sub.2.

(23) Alternatively, as an ordinate value of the two observation points P.sub.A3, P.sub.B3, it is also possible for a value to be selected which corresponds to approximately 50% of the peak height H or to between 25% and 75% of the peak height H; that is, the radial acceleration ar has at these points fallen to approximately 50% or to between 25% and 75% of the radial acceleration a.sub.r at the high point of the characteristic curve K.sub.1, wherein the high point is determined from a profile weighted and averaged over several tire rotations, and/or from a profile smoothed in accordance with the floating mean value principle, of the detected radial acceleration a.sub.r. It is also possible to select, as an ordinate value, a value which corresponds to less than 25% or more than 75% of the peak height H. Then, however, the influence of the profile depth D must be taken into consideration again, wherein this may be performed through corresponding selection of a mapping matrix and of a shift vector, which take the influences of the two tire characteristic influencing variables into consideration in the mapping. At 50%, it is however possible here, depending on accuracy requirements, for an influence of the profile depth D to be disregarded.

(24) The respective peak width B.sub.2 yields the wheel load F.sub.z in accordance with F.sub.z=F.sub.c×B.sub.2+C.sub.c, wherein the factor F.sub.c specifies the gradient of the calibration curve 10c situated within a tolerance band F.sub.Tc, and C.sub.c represents a tire-specific constant. That is, the calibration curve 10.sub.c uniquely assigns a wheel load F.sub.z to the peak width B.sub.2, as illustrated in FIG. 4. The above linear assignment yields the wheel load F.sub.z at least for the wheel loads F.sub.z that are relevant in a vehicle, that is, in particular for wheel loads F.sub.z between an unladen and a fully laden vehicle. If the peak width B.sub.2 is not determined at the points of the maximum gradient S.sub.1, S.sub.2 in terms of magnitude, the peak width B.sub.2 and the x-axis spacing B.sub.1 are assigned a wheel load F.sub.z and a profile depth D via a corresponding mapping matrix, wherein the mapping matrix and the calculation may be performed analogously to the first embodiment.

(25) In a third embodiment, which is illustrated in FIG. 3, the tangential acceleration at versus the time t is observed and plotted as a characteristic curve K.sub.3. Within the observation window 5, the tangential acceleration firstly runs through a high point, has a zero crossing and transitions into a low point, wherein the exact profile is dependent on the orientation of the tire sensor module 3 relative to the direction of rotation of the vehicle tire 1. For the determination of the wheel load F.sub.z, firstly the point with the highest tangential acceleration at,1, that is, the high point of the characteristic curve K.sub.3, is selected as a first observation point P.sub.A4, and the point with the lowest tangential acceleration a.sub.t,2, that is, the low point of the characteristic curve K.sub.3, is selected as a second observation point P.sub.B4, wherein the maximum and the minimum tangential acceleration (a.sub.t,1, a.sub.t,2) are determined from a profile weighted and averaged over multiple tire rotations, and/or from a profile smoothed in accordance with the floating mean value principle, of the detected tangential acceleration (a.sub.t). The x-axis spacing B.sub.3 between the first observation point P.sub.A4 and the second observation point P.sub.B4 can be uniquely assigned a wheel load F.sub.z via the calibration curve 10d, such that the following applies: F.sub.z=F.sub.d×B.sub.3+C.sub.d, wherein F.sub.d is the gradient of a calibration curve 10d, which is provided for this third embodiment and which lies within the tolerance window F.sub.Td, for the tangential acceleration a.sub.t, and C.sub.d is a tire-specific constant. The above linear assignment yields the wheel load F.sub.z at least for the wheel loads F.sub.z that are relevant in a vehicle, that is, in particular for wheel loads F.sub.z between an unladen and a fully laden vehicle.

(26) To improve the signal quality, provision may additionally be made for the characteristic curves K.sub.1, K.sub.3 to be averaged in weighted fashion over multiple rotations of the vehicle tire 1. In this case, the same observation window 5 is averaged in weighted fashion over for example ten rotations, and the wheel load F.sub.z is determined from the averaged characteristic curve K.sub.1, K.sub.3 in accordance with the corresponding embodiment. In this way, it is possible in particular for noise and irregularities in the signal profile to be suppressed. Furthermore, it is also possible for a floating mean value to be applied for the purposes of smoothing the characteristic curves K.sub.1, K.sub.3.

(27) To improve the accuracy, it is additionally possible for further influences on the characteristic curves K.sub.1, K.sub.3 to be compensated. For example, a tire pressure p or a tire temperature T.sub.R or a wheel speed v.sub.R have influences on the radial acceleration a.sub.r and on the tangential acceleration a.sub.t. With the knowledge of the respective influencing variables, the influences can be compensated by the control unit 4 via characteristic curves which are stored in the control unit 4 and which describe the influence of the tire pressure p or of the tire temperature T.sub.R or of the wheel speed v.sub.R respectively.

(28) It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.

LIST OF REFERENCE SIGNS

(29) 1 Vehicle tire 2 Tire inner side 3 Tire sensor module 4 Control unit 5 Observation window 6 Falling flank 7 Rising flank 8 Roadway 9 Ground contact area 10 Characteristic map 10a, 10b Iso-lines 10c, 10d Calibration curves 11 Peak 12 Tread 15 Intersection point 20 Radio signal a, b, c, d Elements of the mapping matrix M a.sub.r Radial acceleration a.sub.t Tangential acceleration a.sub.t,1 Minimum tangential acceleration a.sub.t,2 Maximum tangential acceleration B.sub.1, B.sub.2, B.sub.3 x-axis spacing/peak width C.sub.a, C.sub.b, C.sub.c, C.sub.d Tire-specific constants D Profile depth F.sub.c, F.sub.d Gradient of 10c, 10d F.sub.Tc, F.sub.Td Tolerance band in 10c, 10d F.sub.z Wheel load H Peak height K.sub.1, K.sub.3 Characteristic curve K.sub.2 Derivative of K.sub.1 L Tire contact patch region M Mapping matrix MP Measurement point p Tire pressure P.sub.Ai, P.sub.Bi Observation point; i=1 . . . 4 S.sub.1/S.sub.2 Change or gradient of the radial acceleration at the falling/rising flank 6/7 t Time T.sub.R Tire temperature V Shift vector v.sub.R Wheel speed

Method for determining tire characteristic influencing variables and control device therefor

Assignee

Inventors

Cpc classification

Classification Explorer

G01G19/086

PHYSICS

Classification Explorer

B60C11/246

PERFORMING OPERATIONS; TRANSPORTING

Classification Explorer

G01G19/027

PHYSICS

International classification

Classification Explorer

G01G19/02

PHYSICS

Classification Explorer

B60C11/24

PERFORMING OPERATIONS; TRANSPORTING

Abstract

Claims

Description