Methods for assessing contamination and cleaning of a rail, in particular for a railway vehicle

Abstract

A method for assessing contamination of a rail, in particular for a railway vehicle, comprises the steps of imposing a first sliding value lower than a first threshold between the wheels of a first controlled axle and the rail, the first controlled axle being the head axle of the railway vehicle, imposing a second sliding value greater than a second threshold between the wheels of a second controlled axle and the rail, the second axle following the first axle and the second threshold being greater than the first threshold, and determining the trend of an adhesion curve between the wheels belonging to a plurality of controlled axles and the rail, based on a first adhesion value between the wheels of the first axle and the rail, and a second adhesion value between the wheels of the second axle and the rail.

Claims

1. A method for assessing contamination of a rail, in particular for a railway vehicle, the method comprising the steps of: imposing a first sliding value lower than a first predetermined threshold between the wheels of a first controlled axle of a railway vehicle and the rail, the first controlled axle being the head axle of the railway vehicle according to a direction of travel of the railway vehicle; imposing a second sliding value greater than a second predetermined threshold between the wheels of a second controlled axle and the rail, the second axle following said first axle according to the direction of travel of the, railway vehicle and the second predetermined threshold being greater than said first predetermined threshold; determining trend of an adhesion curve between the wheels belonging to a plurality of controlled axles of the railway vehicle and the rail, based on a first adhesion value between the wheels of said first axle and the rail, and a second adhesion value between the wheels of said second axle and the rail.

2. The method of claim 1, wherein the step of determining the trend of the adhesion curve between the wheels belonging to a plurality of controlled axles of a railway vehicle and the rail comprises the steps of: measuring the first adhesion value between the wheels of said first axle and the rail, and the second adhesion value between the wheels of said second axle and the rail; determining that the adhesion curve between the wheels belonging to the plurality of controlled axles of a railway vehicle and the rail is an adhesion curve having an adhesion peak at a sliding value greater than the second predetermined threshold, if the second adhesion value is greater than the first adhesion value; and determining that the adhesion curve between the wheels belonging to a plurality of controlled axles of a railway vehicle and the rail is an adhesion curve having an adhesion peak at a sliding value lower than said first predetermined threshold, if the second adhesion value is lower than the first adhesion value.

3. The method of claim 2, wherein: a) if it has been determined that the adhesion curve between the wheels belonging to a plurality of controlled axles of a railway vehicle and the rail is an adhesion curve having an adhesion peak at a sliding value greater than the second predetermined threshold, said method comprises the step of: imposing a sliding value greater than the second predetermined threshold between the wheels of all controlled axles and the rail; b) if it has been determined that the adhesion curve between the wheels belonging to the plurality of controlled axles of a railway vehicle and the rail is an adhesion curve having an adhesion peak at a sliding value lower than the first predetermined threshold, said method further comprises the steps of: calculating a value of an adhesion difference by means of the difference between the first adhesion value and the second adhesion value; imposing the second sliding value greater than the second predetermined threshold between the wheels of at least one third axle and the rail; said at least one third axle following said second axle according to the direction of travel of the train; calculating a value of an adhesion difference generated by a cleaning effect of the wheels of the second axle to the benefit of the wheels of the third axle; said value of the adhesion difference generated by the cleaning effect being obtained by means of the difference between a third adhesion value between the wheels of the third axle and the rail, and the second adhesion value between the wheels of the second axle and the rail; imposing a sliding value greater than the second predetermined threshold between the wheels of all controlled axles and the rail, if the value of the adhesion difference generated by the cleaning effect of the wheels is predominant with respect to the value of the adhesion difference multiplied by an adaptive factor the value of which is inversely proportional to the number of axles; imposing a sliding value lower than the first predetermined threshold between the wheels of all controlled axles and the rail, if the value of the adhesion difference generated by the cleaning effect of the wheels is not predominant with respect to the value of the adhesion difference multiplied by an adaptive factor the value of which is inversely proportional to the number of the axles.

4. The method of claim 3, wherein if it has been determined that the adhesion curve of the wheels belonging to a plurality of controlled axles of a railway vehicle is an adhesion curve having an adhesion peak at a sliding value lower than the first predetermined threshold, said method further comprises the step of: after having imposed a second sliding value greater than the second predetermined threshold between the wheels of all controlled axles and the rail, due to non-predominance of the value of the adhesion difference generated by the cleaning effect of the wheels with respect to the value of the adhesion difference multiplied by an adaptive factor the value of which is inversely proportional to the number of axles, if the adhesion value of the wheels of a previous axle is coincident with the adhesion value of the wheels of the next axle, imposing a first sliding value lower than the first predetermined threshold between the wheels of at least one following axle and the rail.

5. The method of claim 1, wherein the method for assessment of contamination of a rail is repeated after a predetermined time interval.

6. The method of claim 1, wherein the method for assessment of contamination of a rail is repeated after a predetermined distance has been traveled by the railway vehicle.

7. The method of claim 1, wherein the first predetermined threshold has a sliding value lower than 5%, and the second predetermined threshold has a sliding value comprised between 15% and 25%.

8. A method for assessing cleaning of a rail for a railway vehicle, comprising the steps of: imposing a first sliding value lower than a first predetermined threshold between the wheels of a first controlled axle of a railway vehicle and the rail, the first controlled axle being the head axle of the railway vehicle according to a direction of travel of the railway vehicle; imposing a second sliding value greater than a second predetermined threshold between the wheels of a second controlled axle and the rail; the second axle following said first axle according to the travel direction of the railway vehicle, and said second predetermined threshold being greater than said first predetermined threshold; imposing a third sliding value equal to said second sliding value between the wheels of at least one third axle and the rail; said at least one third axle following said second axle according to the travel direction of the railway vehicle; determining effectiveness of the cleaning of the rail generated by the sliding of the second axle to the benefit of the at least one third axle based on a first adhesion value between the wheels of said second axle and the rail and a second adhesion value between the wheels of said at least one third axle and the rail.

9. The method of claim 8, wherein the step of determining the effectiveness of the cleaning of the rail comprises the steps of: measuring the first adhesion value and the second adhesion value; and determining the effectiveness of the cleaning by performing a subtraction operation between the second adhesion value and the first adhesion value.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is a block diagram of an anti-skid control system of the wheels of a railway vehicle;

(2) FIG. 2 is a graph showing qualitatively the trend of the adhesion coefficient μ of the wheels of an axle, shown on the y-axis, as a function of the sliding δ, shown on the x-axis;

(3) FIG. 3 is a diagram illustrating the forces applied to an axle's wheel;

(4) FIGS. 4A, 4B are graphs showing qualitatively the trends of the adhesion coefficient μ of the wheels of four axles of a vehicle in two different operating conditions;

(5) FIG. 4C illustrates the trend of an average adhesion curve μ around the peak value;

(6) FIG. 5 is a graph illustrating an adhesion curve having an adhesion peak at a sliding value lower than the first predetermined threshold;

(7) FIG. 6 is a graph illustrating an adhesion curve having an adhesion peak at a sliding value greater than the second predetermined threshold;

(8) FIG. 7 shows four adhesion curves, respectively of wheels belonging to four consecutive axles, in case of a cleaning effect of the rail;

(9) FIG. 8 shows four adhesion curves respectively of wheels belonging to four consecutive axles, in the case wherein the sliding value is imposed to correspond with the adhesion peak between the wheels of the axles and the rail, and consequently there is no cleaning effect of the rail;

(10) FIG. 9 shows four adhesion curves respectively of wheels belonging to four consecutive axles, in the case wherein the adhesion curve of the wheels belonging to a plurality of controlled axles of a railway vehicle exhibits an adhesion peak at a sliding value lower than the first predetermined threshold, and the sliding value imposed between the wheels of the axles and the rails is a higher sliding value than the second predetermined threshold; and

(11) FIG. 10 shows four adhesion curves respectively of wheels belonging to four consecutive axles, in the case wherein the adhesion curves exhibit an adhesion peak at a sliding value greater than the second predetermined threshold and the sliding value imposed between the wheels of the axles and the rails is a higher sliding value than the second predetermined threshold.

DETAILED DESCRIPTION

(12) Before describing in detail a plurality of embodiments, it should be clarified that the present invention is not limited in its application to the details of construction or to the configuration of the components provided in the following description or illustrated in the drawings. The invention may assume other embodiments and may be implemented or achieved in essentially different ways. It should also be understood that the phraseology and terminology have descriptive purposes and should not be construed as limiting. The use of “include” and “comprise” and the variations thereof are to be understood as encompassing the elements stated hereinafter and the equivalents thereof, as well as additional elements and the equivalents thereof.

(13) The method according to the present invention allows to determine the position of the adhesion peak along the adhesion curves of the wheels belonging to a plurality of controlled axles of a vehicle, and, consequently, to obtain improved control and possible recovery of the adhesion of the wheels of a controlled axle of a railway vehicle.

(14) Initially referring to adhesion curves shown in FIG. 5, the adhesion peak μ.sub.p is obtained for small sliding values of the order of 1-2%.

(15) Defining δ.sub.p as the sliding value for which the adhesion peak μ.sub.p is obtained, it is clear that: if the axle is brought to slide close to δ.sub.p (small slide), there will be a negligible cleaning effect to the benefit of the local adhesion which assumes the peak value μ.sub.p. conversely, if the axle is brought to slide at higher sliding values δ, there will be a loss of local adhesion to the benefit of a possible cleaning effect for the following axles. Such effect will be more or less effective depending on the type and amount of contaminant present. The effectiveness of the cleaning is an unknown datum a priori.

(16) In order to maximize the average adhesion of the axles, two factors should be considered when choosing sliding points to make the axles work: benefit of cleaning on the following axles (increasing as the local sliding increases); and local adhesion value (decreasing as the sliding increases).

(17) Conversely, in case of an adhesion curve as shown FIG. 6, literature and results of experimental tests carried out on rolling stock, demonstrate that the trend of the adhesion curves depends on many factors, among which, type and amount of contaminant, and weight of the vehicle. Not all adhesion curves necessarily exhibit an adhesion peak μ.sub.p for small sliding values, such as that of FIG. 5. There are cases wherein the adhesion peak μ.sub.p is obtained for higher sliding values (δ.sub.p≈20%), like the curve in FIG. 6.

(18) In such case: if the axle is brought to slide at small sliding values (e.g. δ=1-2%), the cleaning effect will be practically zero and the local adhesion will be reduced with respect to the peak value. conversely, if the axle is brought to slide at higher values δ (e.g. δ≈20%), there will be a benefit both on the local adhesion and on a possible cleaning effect for the following axles.

(19) In the case of adhesion curves such as those of FIG. 6, therefore, regardless of the effectiveness of the cleaning, the most appropriate choice is to bring all the axles into large slides (δ≈20%≈δ.sub.p) maximizing both the local adhesion and the possible cleaning effect.

(20) Based on the above concepts, the method for assessing contamination of a rail, particularly for a railway vehicle, comprises the steps of: imposing a first sliding value δ.sub.1 lower than a first predetermined threshold t.sub.1 between the wheels W.sub.1 of a first controlled axle A.sub.1 of a railway vehicle and the rail, the first controlled axle A.sub.1 being the head axle of the railway vehicle according to the direction of travel of the railway vehicle; imposing a second sliding value δ.sub.2 greater than a second predetermined threshold t.sub.2 between the wheels of a second controlled axle A.sub.2 and the rail, the second axle A.sub.2 being the axle following said first axle A.sub.1 according to the direction of travel of the train, and the second predetermined threshold t.sub.2 being greater than said first predetermined threshold t.sub.1; determining the trend of the adhesion curve between the wheels W belonging to a plurality of controlled axles A.sub.n of the railway vehicle and the rail based on a first adhesion value μ.sub.1 between the wheels of said first axle A.sub.1 and the rail, and a second adhesion value μ.sub.2 between the wheels of said second axle A.sub.2 and the rail.

(21) The step of determining the trend of the adhesion curve between the wheels W belonging to a plurality of controlled axles A.sub.n of the railway vehicle and the rail may comprise the steps of measuring the first adhesion value μ.sub.1 between the wheels of said first axle A.sub.1 and the rail, and the second adhesion value μ.sub.2 between the wheels of said second axle A.sub.2 and the rail; if the second adhesion value μ.sub.2 is greater than the first adhesion value μ.sub.1, determining that the adhesion curve between the wheels W belonging to the plurality of controlled axles A.sub.n of a railway vehicle and the rail is an adhesion curve having an adhesion peak μ.sub.p at a sliding value δ.sub.p greater than the second predetermined threshold t.sub.2; and if the second adhesion value μ.sub.2 is lower than the first adhesion value μ.sub.1, determining that the adhesion curve between the wheels W belonging to a plurality of controlled axles A.sub.n of a railway vehicle and the rail is an adhesion curve having an adhesion peak μ.sub.p at a sliding value δ.sub.p lower than said first predetermined threshold t.sub.1.

(22) By way of example, the first predetermined threshold t.sub.1 may coincide with a sliding value of about 5%, and the first sliding value δ.sub.1 less than the first predetermined threshold between the wheels of a first controlled axle A.sub.1 and a rail may be about 1-2%. The second predetermined threshold t.sub.2 may coincide with a sliding value between about 15% and 25%, and the second sliding value δ.sub.2, greater than the second predetermined threshold between the wheels of at least one second controlled axle A.sub.2 and the rail may be comprised between 20%-25%.

(23) Preferably, the second sliding value δ.sub.2 does not exceed a limit sliding value δ.sub.limit equal to about 25%.

(24) The method for assessing contamination of a rail, if it has been determined that the adhesion curve between the wheels W belonging to a plurality of controlled axles A.sub.n of a railway vehicle and the rail is an adhesion curve having an adhesion peak μ.sub.p at a sliding value greater than the second predetermined threshold t.sub.2, may comprise the step of: imposing a sliding value δ greater than the second predetermined threshold t.sub.2 between the wheels of all controlled axles and the rail.

(25) On the other hand, the method for assessing contamination of a rail, if it has been determined that the adhesion curve between the wheels W belonging to the plurality of controlled axles A.sub.n of a railway vehicle and the rail is an adhesion curve having an adhesion peak μ.sub.p at a sliding value δ.sub.p less than the first predetermined threshold t.sub.1, may comprise the steps of: calculating the value of the adhesion difference Δμ.sub.slide by means of the difference between the first adhesion value μ.sub.1 and the second adhesion value μ.sub.2; imposing the second sliding value δ.sub.2 greater than a second predetermined threshold t.sub.2 between the wheels of at least one third axle A.sub.3 and the rail, the at least one third axle A.sub.3 being the axle following said second axle A.sub.2 according to the direction of travel of the train; calculating the value of the adhesion difference Δμ.sub.clean generated by the cleaning effect of the wheels of the second axle A.sub.2 to the benefit of the wheels of the third axle A.sub.3, said value of the adhesion difference Δμ.sub.clean generated by the cleaning effect being obtained by means of the difference between the adhesion value μ.sub.3 between the wheels of the third axle A.sub.3 and the rail, and the adhesion value μ.sub.2 between the wheels of the second axle A.sub.2 and the rail; imposing a sliding value δ greater than the second predetermined threshold t.sub.2 between the wheels W of all the controlled axles A.sub.1, . . . , A.sub.n and the rail, if the value of the adhesion difference Δμ.sub.clean generated by the cleaning effect of the wheels is predominant with respect to the value of the adhesion difference Δμ.sub.slide multiplied by an adaptive factor F.sub.ad, the value of which is inversely proportional to the number of axles; imposing a sliding value δ lower than the first predetermined threshold t.sub.1 between the wheels W of all the controlled axles A.sub.1, . . . , A.sub.n and the rail, if the value of the adhesion difference Δμ.sub.clean generated by the cleaning effect of the wheels is not predominant with respect to the value of the adhesion difference Δμ.sub.slide multiplied by an adaptive factor F.sub.ad the value of which is inversely proportional to the number of axles.

(26) The method for assessing contamination of a rail, if it has been determined that the adhesion curve of the wheels W belonging to a plurality of controlled axles A.sub.n of a railway vehicle is an adhesion curve having an adhesion peak μ.sub.p at a sliding value δ.sub.p less than the first predetermined threshold t.sub.1, may comprise the step of: after having imposed a second sliding value δ.sub.2 greater than the second predetermined threshold t.sub.2 between the wheels of all the controlled axles A.sub.1, . . . , A.sub.0 and the rail, due to the non-predominance of the value of the adhesion difference Δμ.sub.clean generated by the cleaning effect of the wheels with respect to the value of the adhesion difference Δμ.sub.slide multiplied by an adaptive factor F.sub.ad the value of which is inversely proportional to the number of axles, if the adhesion value μ.sub.n of the wheels of a previous axle A.sub.n is coincident with the adhesion value μ.sub.n+1 of the wheels of the next axle A.sub.n+1, imposing a first sliding value δ.sub.1 lower than the first predetermined threshold t.sub.1 between the wheels of at least one following axle A.sub.n+1, A.sub.n+2, . . . and the rail.

(27) Due to this last step described above, it may be noted that the cleaning effect of the rail that was exhibited in the first axles according to the direction of travel no longer involves an increase in adhesion for the following axles (for example, because now the rail is completely clean), and consequently, it is appropriate to impose on the following axles the sliding value corresponding to the adhesion peak and not a sliding value useful for cleaning the rail.

(28) By way of example, considering the second axle as the previous axle A.sub.n and the at least one third axle as the following axle A.sub.n+1, after having imposed a second sliding value δ.sub.2 greater than the second predetermined threshold t.sub.2 between the wheels of all the controlled axles and the rail, due to the non-predominance of the value of the adhesion difference Δμ.sub.clean generated by the cleaning effect of the wheels with respect to the value of the adhesion difference Δμ.sub.slide multiplied by an adaptive factor F.sub.ad, a first sliding value δ.sub.1 may be imposed less than the first predetermined threshold t.sub.1 between the wheels of the axles following the third and the rail, if the adhesion value μ.sub.2 of the wheels of the second axle A.sub.2 (previous axle A.sub.n) coincides with the adhesion value μ.sub.3 of the wheels of the at least one third axle (following axle A.sub.n+1).

(29) By way of example, the method for assessing contamination of a rail may be repeated after a predetermined time interval (for example every 30 seconds) or it may be repeated after a predetermined distance has been traveled by the railway vehicle.

(30) The present invention comprises moreover a method for assessing cleaning of a rail for a railway vehicle, comprising the steps of: imposing a first sliding value δ.sub.1 lower than a first predetermined threshold t.sub.1 between the wheels W.sub.1 of a first controlled axle A.sub.1 of a railway vehicle and the rail; the first controlled axle A.sub.1 being the head axle of the railway vehicle according to the direction of travel of the railway vehicle; imposing a second sliding value δ.sub.2 greater than a second predetermined threshold t.sub.2 between the wheels of a second controlled axle A.sub.2 and the rail, the second axle A.sub.2 being the axle following said first axle A.sub.1 according to the direction of travel of the train, and said second predetermined threshold t.sub.2 being greater than said first predetermined threshold t.sub.1; imposing a third sliding value δ.sub.3 equal to said second sliding value δ.sub.2 between the wheels of a controlled third axle A.sub.3 and the rail, the third axle A.sub.3 being the axle following said second axle A.sub.2 according to the direction of travel of the train; determining the effectiveness of the cleaning of the rail generated by the sliding of the second axle A.sub.2 to the benefit of the third axle A.sub.3 based on a first adhesion value μ.sub.2 between the wheels of said second axle A.sub.2 and the rail and a second adhesion value μ.sub.3 between the wheels of said third axle A.sub.3 and the rail.

(31) The aforesaid step of determining the effectiveness of the cleaning of the rail may comprise the steps of: measuring the first adhesion value μ.sub.2 and the second adhesion value μ.sub.3; and determining the effectiveness of the cleaning by performing a subtraction operation between the second adhesion value μ.sub.3 and the first adhesion value μ.sub.2.

(32) In the following is reported by way of example, an illustrative case wherein the total number of axles of the railway vehicle is four.

(33) Considering FIG. 7, it is possible to assess the adhesion engaged by the four axles making up the railway vehicle.

(34) The adhesion μ.sub.1 available for the first axle δ.sub.1 is not influenced by the cleaning, such axle being the first to encounter the rail. The adhesion μ.sub.1 depends only on the conditions of the rail, i.e. the ambient/contaminant conditions that will be indicated in the following with “amb”.

(35) The adhesion μ.sub.1 engaged by the first axle is a function of the local sliding δ.sub.1 of the first axle on the rail:
μ.sub.1=f(μ.sub.max,δ.sub.1)=f(amb,δ.sub.1)

(36) Conversely, the adhesion μ.sub.2 available for the second axle depends on the cleaning produced by the previous first axle (Δμ.sub.12).
μ.sub.2,max=μ.sub.max+Δμ.sub.12

(37) The cleaning produced by the first axle in favor of the second axle Δμ.sub.12 is a function of the sliding δ.sub.1 of the first axle on the rail, as well as of the cleaning characteristics typical of the contaminant (contaminant more or less easy to remove with the same sliding), which are indicated hereinafter with the term “cleaning”.
μ.sub.2,max=μ.sub.max+f(clean,δ.sub.1)

(38) The adhesion μ.sub.2 engaged by the second axle is a function of the local sliding δ.sub.2 of the second axle on the rail.
μ.sub.2=f(μ.sub.2,max,δ.sub.2)=f(amb,δ.sub.1,cleaning,δ.sub.2)

(39) Likewise, the adhesion μ.sub.3 engaged by the at least one third axle depends on the local sliding δ.sub.3 and on the cleaning produced by the previous axles, hence by δ.sub.1, δ.sub.2 and by cleaning.

(40) Likewise, the adhesion μ.sub.4 engaged by the fourth axle depends on the local sliding δ.sub.4 and on the cleaning produced by the previous axles, hence by δ.sub.1, δ.sub.2, δ.sub.3 and by the cleaning.

(41) According to these considerations:
μ.sub.average=¼*(f(amb,δ.sub.1)+f(amb,δ.sub.1,δ.sub.2,cleaning)+f(amb,δ.sub.1,δ.sub.2,δ.sub.3,cleaning)+f(amb,δ.sub.1,δ.sub.2,δ.sub.3,δ.sub.4,cleaning))

(42) In the case of an adhesion curve such as the one illustrated in FIG. 5, and in the case wherein a sliding corresponding to the adhesion peak μ.sub.p is imposed on all the axles, assuming (see FIG. 8) control of all axles on the adhesion peak μ.sub.p, that is, at small slides around δ.sub.p, no rail cleaning is produced.
Δμ.sub.12=Δμ.sub.23=Δμ.sub.34=0
and therefore
μ.sub.2,max=μ.sub.3,max=μ.sub.4,max=μ.sub.1,max

(43) All the axles thus find the same adhesion as the head axle finds (first axle in the direction of travel), as no axle cleans the rail.

(44) Thus:
μ.sub.average=μ.sub.1,max

(45) In the case of an adhesion curve such as that of FIG. 5, wherein on all the axles a slide of δ>>δp is imposed, it is possible to obtain a cleaning effect (this effect is certainly not a priori but rather depends on the effectiveness of the cleaning on the contaminant in question: parameter previously defined as cleaning).

(46) With reference to FIG. 9:
Δμ.sub.12=Δμ.sub.23=Δμ.sub.34=Δμ.sub.clean
Therefore:
μ.sub.2,max=μ.sub.1,max=Δμ.sub.clean
μ.sub.3,max=μ.sub.2,max=Δμ.sub.clean=μ.sub.1,max=2*Δμ.sub.clean
μ.sub.4,max=μ.sub.3,max=Δμ.sub.clean=μ.sub.1,max=3*Δμ.sub.clean

(47) At the same time, each axle, sliding at a δ far from the peak value δ.sub.p, will not exploit all the locally available adhesion μ.

(48) With reference to FIG. 9:
μ.sub.1=μ.sub.1,max−Δμ.sub.slide
μ.sub.2=μ.sub.2,max−μΔ.sub.slide=μ.sub.1,max+Δμ.sub.clean−Δμ.sub.slide
μ.sub.3=μ.sub.3,max−μΔ.sub.slide=μ.sub.1,max+2*Δμ.sub.clean−Δμ.sub.slide
μ.sub.4=μ.sub.4,max−μΔ.sub.slide=μ.sub.1,max+3*Δμ.sub.clean−Δμ.sub.slide

(49) Calculating the average adhesion of the vehicle:
μ.sub.average=μ.sub.1,max+3/2*Δμ.sub.clean−Δμ.sub.slide

(50) Comparing the average adhesion obtained in the case of an adhesion curve such as the one illustrated in FIG. 5, in the case wherein on all the axles a slide corresponding to the adhesion peak is imposed, and in the case wherein on all the axles a slide of δ>>δ.sub.p is imposed, one notes that: If Δμ.sub.clean>⅔*Δμ.sub.slide, it is appropriate to control the axles in large slides of δ>>δ.sub.p, i.e. with a slide greater than the second predetermined threshold t.sub.2. If Δμ.sub.clean>⅔*Δμ.sub.slide, it is appropriate to control the axles with reduced sliding δ=δ.sub.p, i.e. with a slide less than the first predetermined threshold t.sub.1.

(51) In the examples given above, the adaptive factor is equal to ⅔. For example, in the case of five axles, the adaptive factor is equal to ½.

(52) In the case of adhesion curves such as those of FIG. 6, regardless of the effectiveness of cleaning, the most appropriate choice is to bring all the axles into large slides, that is, with a slide greater than the second predetermined threshold t.sub.2 (δ≈20%≈δ.sub.p) consequently maximizing both the local adhesion and the possible cleaning effect.

(53) According to such management of the sliding points we have (see FIG. 10):
μ.sub.1=μ.sub.1,max
μ.sub.2=μ.sub.1,max+Δμ.sub.clean
μ.sub.3=μ.sub.1,max+2*Δμ.sub.clean
μ.sub.4=μ.sub.1,max+3*Δμ.sub.clean

(54) Thus, the average vehicle-level adhesion is:
μ.sub.average=μ.sub.1,max+3/2*Δμ.sub.clean

(55) From the analysis of the preceding cases, (case of an adhesion curve such as the one illustrated in FIG. 5 and wherein on all the axles a slide is imposed corresponding to the adhesion peak, the case of an adhesion curve such as the one of FIG. 5 wherein on all the axles a slide of δ<<δ.sub.p is imposed, and the case of adhesion curves such as those in FIG. 6), it may be noted that the choice of the optimal sliding point (the one that maximizes the average adhesion of the vehicle) must pass through the assessment of three main factors:

(56) FACTOR 1: Type of adhesion curve: i.e. if the adhesion peak is obtained for small sliding values (FIG. 5), i.e. for a slide less than the first predetermined threshold t.sub.1, or for large sliding values (FIG. 6), i.e. for a slide greater than the second predetermined threshold t.sub.2, close to δ.sub.limit;

(57) FACTOR 2: Δμ.sub.slide (parameter defined only for the curve illustrated in FIG. 5), i.e. difference in adhesion between the peak of the curve and the adhesion engaged with a slide close to the limit slide (see FIG. 9).

(58) FACTOR 3: Δμ.sub.clean, i.e. the effectiveness of the cleaning effect from which the axle (n+1) benefits when the axle n is made to slide with a slide greater than the second predetermined threshold t.sub.2, close to δ.sub.limit.

(59) In the case of a railway vehicle moving on rails, the assessment of these three factors and the consequent choice of the sliding point, according to the criteria described above, must take place in real time during the braking of the vehicle in order to maximize the average adhesion engaged by the vehicle, thereby maximizing the deceleration of the vehicle and thereby minimizing the stopping distance of the vehicle.

(60) To assess the effectiveness of cleaning (FACTOR 3) it is therefore necessary to impose a significant slide, i.e. a slide greater than the second predetermined threshold t.sub.2 (δ≈δ.sub.limit) on the axle n and to verify the potential gain of adhesion on the axle (n+1).

(61) At the same time, by sliding the axle with a slide greater than the second predetermined threshold t.sub.2, close to δ.sub.limit, the rail conditions are modified for the following axles and it becomes impossible to assess the adhesion value relative to small slides, i.e. with a slide less than the first predetermined threshold t.sub.1 (δ<5%). Therefore, factors 1 and 2 cannot be assessed.

(62) The object of the invention is to manage the sliding of the vehicle axles as follows: FIRST AXLE: δ1≈1-2% SECOND AXLE: δ2≈20% THIRD AXLE: δ3=δ2≈20% FOURTH AXLE: optional

(63) The first axle, the head axle, is controlled in a small slide. In this way, by measuring the adhesion engaged by the first axle, the adhesion value relative to small slides is obtained
μ.sub.1=(1−2%)
without producing cleaning, i.e. without changing the characteristics of the rail for following axles.

(64) The second axle, on the other hand, is controlled in a significant slide, i.e. greater than the second predetermined threshold t.sub.2. In this way, by measuring the adhesion engaged by the second axle, the adhesion value relative to large slides is obtained
μ.sub.2=μ(20%)
producing a possible cleaning for the following axle, cleaning that will depend on the characteristics of the contaminant (cleaning factor 3).

(65) The third axle is controlled at the same sliding value imposed for the second axle.

(66) In this way, by measuring the adhesion engaged by the third axle, it is possible to assess the effectiveness of the cleaning by calculating the cleaning factor:
Δμ.sub.clean=μ.sub.3−μ.sub.2

(67) Moreover, by comparing the measured adhesion for the first and second axles, the type of adhesion curve may be determined (FACTOR 1) and possibly Δμ.sub.slide (FACTOR 2) may calculated.

(68) If (μ.sub.2>μ.sub.1), it is a case of an adhesion curve of the type illustrated in FIG. 6.

(69) The most appropriate choice is therefore that of bringing all the axles into large slides, that is to say, a sliding greater than the second predetermined threshold t.sub.2 (δ≈20%≈δ.sub.limit);

(70) If (μ.sub.2>μ.sub.1), it is a case of an adhesion curve of the type illustrated in FIG. 5) and one may calculate:
Δμ.sub.slide=μ.sub.1−μ.sub.2

(71) At this point, noting all the factors, one may choose the optimal sliding point:
If (Δμ.sub.clean>⅔*Δμ.sub.slide)
the most appropriate choice is therefore that of bringing all the axles into large slides, that is to say, a slide greater than the second predetermined threshold t.sub.2 (δ≈20%≈δ.sub.limit);
if (Δμ.sub.clean<⅔*Δμ.sub.slide):
the most appropriate choice is to control the axles on the adhesion peak, i.e. with a slide less than the first predetermined threshold t.sub.1 (δ<5%).

(72) The principle of the invention remaining the same, embodiments and details of construction may be varied with respect to those described by way of non-limiting example, without thereby departing from the scope of the invention as described and claimed herein. It is understood, moreover, that each embodiment may be combined with any other embodiment.