Method for evaluating the transversal grip of a tire on a snow covered ground
View Patent ↗A method for evaluating the transversal grip of a type of tires on a snow-covered ground, of providing this type of tires to a vehicle, driving this vehicle at the transversal grip limit on a snow-covered track, and producing instantaneous measures of the vehicle transversal acceleration while it travels on the track. Track (P) includes a plurality of turns (V1, V2) making it possible to establish a transversal acceleration steady state, the transversal acceleration instantaneous measures being subjected to a low-pass filtering, and the transversal grip of a tire is judged as being even better the higher the transversal acceleration values obtained with this tire are.
1. A method for evaluating the transversal grip of a tire of a first type on a snow-covered ground, comprising the steps of:
providing tires of the first type to a wheeled vehicle;
driving said wheeled vehicle thus equipped at the transversal grip limit on a snow-covered track comprising at least one turn;
producing instantaneous measures of a transversal acceleration of the wheeled vehicle during its travel on the track, wherein said track includes at least two discriminating turns selected such that a time period required for the vehicle to cover each one of said discriminating turns is equal to at least one second, said time period being measured between the end of a phase of growth of the vehicle transversal acceleration starting from a given acceleration threshold and the beginning of a return phase of returning towards said vehicle transversal acceleration threshold;
a filtering step of producing transversal acceleration filtered measures by low-pass filtering the transversal acceleration instantaneous measures; and
a selection step of identifying, from among the filtered measures, a set of at least one transversal acceleration per discriminating turn, the transversal grip of said tire being rated according to a direct function of the transversal acceleration values obtained with said tire.
2. The evaluation method according to claim 1 , wherein the given transversal acceleration threshold is equal to zero.
3. The evaluation method according to claim 1 , wherein the discriminating turns comprise at least a left turn and a right turn.
4. The evaluation method according to claim 3 , comprising a correction step of correcting the transversal acceleration filtered measures from any possible local or overall deviation between the values taken by these measures for the left and right turns, respectively.
5. The evaluation method according to claim 1 , wherein the transversal acceleration measures are performed while the vehicle covers the track a plurality of times.
6. The evaluation method according to claim 5 , wherein the track is a looped car track, which the vehicle covers at least once in a clockwise direction and at least once in a counterclockwise direction.
7. The evaluation method according to claim 5 , comprising a statistical analysis taking into consideration plural sets of transversal acceleration values, recorded in each discriminating turn during respective travels on this turn.
8. The evaluation method according to claim 1 , wherein any the selection step comprises calculating, for each discriminating turn, the transversal acceleration filtered values average between a first peak corresponding to the end of the transversal acceleration growing phase and a last peak corresponding to the beginning of the phase of return towards the given transversal acceleration threshold.
9. The evaluation method according to claim 8 , wherein the given threshold is lower than 0.08 g.
10. The evaluation method according to claim 1 , wherein, for each discriminating turn, the selection step comprises:
determining a time window of at least a given duration in which the transversal acceleration filtered values are comprised within a range of a magnitude lower that a given threshold; and
calculating the filtered transversal accelerations average within this time window.
11. The evaluation method according to claim 10 , wherein the time window duration is equal to at least 1 second.
12. The evaluation method according to claim 1 , wherein the selection step comprises:
determining, for each discriminating turn, all the filtered transversal acceleration peaks within the given turn;
calculating the transversal acceleration filtered values average for all the peaks of the discriminating turns of the car track; and
discarding, from among the set of the previous transversal acceleration filtered values, those values of which absolute deviation relative to the average is higher than a given threshold.
13. The evaluation method according to claim 12 , wherein the given threshold is of about 15%.
14. The evaluation method according to claim 1 , wherein the selection step comprises determining, in each discriminating turn, the maximal filtered transversal acceleration value.
15. The evaluation method according to claim 1 , wherein the low-pass filtering is made through a symmetric moving average.
16. The evaluation method according to claim 1 , wherein the track comprises at least four discriminating turns.
17. The evaluation method according to claim 1 , wherein each discriminating turn is selected such that the time period required for the vehicle to cover it is higher than two seconds, and preferably at least equal to three seconds.
18. The evaluation method according to claim 1 , wherein the track comprises at least one non-discriminating turn, and wherein the selection step comprises discarding the transversal acceleration measures performed while the vehicle covers each non-discriminating turn.