DESCRIPTION OF THE PATENT FOR THE INDUSTRIAL INVENTION TITLED: METHOD AND CONTROL SYSTEM OF THE SPEED OF A RAILWAY VEHICLE

TECHNICAL FIELD

The present invention relates to a method and a control system of the speed of a railway vehicle.

The present .invention finds an advantageous application in the control of the speed of a train, to which the following description is specifically referred, without losing its general character. PRIOR ART

For the control of trains, automatic control systems are broadly used, in order to assist (semi-automatic control) or completely replace (automatic controls) the train drivers. An example of such automatic systems are electronic anti-derailment devices, which intervene automatically with an emergency braking of the train, when a potential derailment is detected.

To permit the driving in normal conditions of a railway car, the flange at the end of every wheel must not come in contact with the lateral profile of the track. When unnatural conditions begin to occur regarding the dynamics of the vehicle, as for instance too high a speed in a bend, the wheel flange can come into contact with the profile, and the wheel can be raised up to a limit condition, in which the wheel flange is not any more able to have a high contact with the profile of the track; in such conditions, the tapering of the opposite wheel makes immediately the axle exit from its seat, with the beginning of

the derailment.

A known electronic anti-derailment device comprises at least a measuring device mounted on a bushing of a wheel of the railway train, in order to measure instantly the real value of the height of the wheel from the rolling plane of a corresponding track upon which the wheel rolls; if the real value of the height is greater than a safety predetermined value (i.e. if the wheel loses its contact with the rolling plane), an emergency breaking is automatically activated for the railway train.

Known electronic anti-derailment devices measure the height of the wheel of the railway vehicle from the rolling plane of the track, with the only aim of identifying when derailment conditions of the train are presently verified or foreseen. In any case, such electronic anti-derailment devices are of no use in the normal driving of a railway train, wherein the railway train is far from the derailment conditions.

In the semi-automatic or automatic driving of a railway train, the need arises for a control system which permits to control the speed of the railway train, particularly in a bend, in order to combine in an optimal way two conflicting needs: to guarantee the greatest driving safety (which need would lead to minimizing the speed) and to reach the greatest possible performances (which need would bring to maximize the speed) . In other words, it is extremely complicated to obtain in safety conditions the maximum possible performances, particularly when the parameters which influence the performances are varying (for

instance, the effective mass of the railway train) and therefore it is not possible to establish in advance which could be the greatest possible safety conditions. For this reason, in the actual semi-automatic or automatic conditions of a railway vehicle, performance limits are prudentially established (i.e. in order to guarantee the safety in every possible situation) , which in any case do penalize the performances, being always lower (and also very much) than the maximum performances which could be possible, but remaining in any case- in safety conditions.

DESCRIPTION OF THE INVENTION

The aim of the present invention is to provide a method and a control system of the speed of a railway vehicle, such method and system being freed from the above mentioned drawbacks, being easily and economically realised and in particular, permitting the obtaining in safety conditions the maximum possible performances.

According to the invention, a method and a control system of the speed of a railway vehicle are provided, as claimed in the annexed claims .

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the annexed drawings, which illustrate a non-limitative application example, wherein:

Figure 1 is a schematic view of a train equipped with a control system of its speed, according to the present invention;

Figure 2 is a schematic view of the control systems;

Figure 3 is an enlarged view of a wheel of the train of Figure 1, according to a measuring device of the control system;

Figure 4 is a perspective view of a support flange of the measuring device of Figure 3; and

Figures 5-8 are schematic views of four possible contact conditions between the wheel of the train of Figure 1 and a track.

PREFERRED EMBODIMENTS QF THE INVENTION

In the annexed Figure, reference 1 is globally a control system of the speed of a railway vehicle 2. The vehicle 2 has a plurality of wheels 3, which roll upon two tracks 4 (just one of which is shown in Figure 1) .

The control system 1 comprises a control unit 5, which is connected with the power system (not shown) of the vehicle 2, in order to control the speed of the vehicle 2, and a measuring device 6, which is connected to the control unit 5 and can measure the real value of the height of at least one wheel 3 of the vehicle 2, from the rolling plane of a corresponding track 4 onto which the wheel 3 rolls.

During the driving of the vehicle 2, particularly in a bend, the unit 5 controls the speed of the vehicle 2 as a function of the real value of the height of at least one wheel 3 from the rolling plane. In particular, the control unit 5 has a memory 7 (shown in Figure 2) in which an optimum range of the value of the height is stored, with both a lower and an upper limit value; the unit 5 controls the speed of the vehicle 2, in order to maintain the real value of the height within the optimum range. The unit 5 controls preferably in feedback the speed of the vehicle 2, in order to maintain the real value of the height within the optimum range, and utilizing as a feedback variable the real value of the height.

In other words, the control unit 5 increases the speed of the vehicle 2, if the real value of the height is smaller than the lower limit value of the optimum range, and reduces the

speed of the vehicle 2 if the real value of the height is greater than the upper limit value of the optimum range. Furthermore, the control unit 5 provides an emergency braking of the vehicle 2, if the real value of the height is greater than the upper limit value of the optimum range, by a quantity greater than a safety predetermined threshold (i.e. if the vehicle 2 dangerously approaches itself to a condition of potential derailment) .

In Figure 2 a basic diagram of the control system 1 is shown, underlining how the unit 5 controls in feedback the speed of the vehicle 2, utilising as a feedback variable the real value of the height. In particular, the control unit 5 comprises, in addition to the memory 7 into which the optimum range for the value of the height is stored, a block 8 which compares the real value of the height given by the measuring device β with the optimum range given by the memory 7 to determine an error value, and a regulation block 9, which receives the error value from the comparison block 8 and consequently drives the vehicle 2. Typically, the regulation block 9 comprises a regulator PID (Proportional, Integral, Derivative) of known kind.

According to Figure 3, the measuring device β comprises a pair of proximity switches 10, each of them is mounted in a fixed position on a bushing of the wheel 3, to measure directly a value of the height, and an accelerometer 11 mounted in a fixed position onto the bushing of the wheel 3, to measure a value of the transversal acceleration acting on the wheel 3. The

measuring device 6 estimates the real value of the height as a function of the value of the height, measured by the proximity switches 10, and according to the value of the transversal acceleration measured by the accelerometer 11.

The two proximity switches 10 are reciprocally redundant, and are mutually mounted at a distance in the direction of advance of the vehicle 2; in this way, the evaluation of the height is always guaranteed with continuity, even when one of the two proximity switches 10 is located upon a junction of the track 4. According to a different embodiment not shown, the measuring device 6 comprises a single proximity switch 10.

According to the embodiment shown in Figures 3 and 4, the measuring device 6 has a support flange 12 with a central body 13, which has the form of an inverted "V", with two central inclined segments 14, and is fixed to a bushing of the wheel 3, and with two lateral segments 15, each of which is horizontal starting from a central segment 14, and supports a proximity switch 10.

According to a preferred embodiment, in order to measure the real value of the height of at least one wheel 3 from the rolling plane, it is foreseen to measure directly a value of the height by means of the proximity switches 10 (normally an average value is made between the two measurements of the two proximity switches 10) , to measure a value of the transversal acceleration acting on the wheel 3 by means of the accelerometer, and to estimate the real value of the height as a function of the height measured by the proximity switches 10,

and as a function of the value of the transversal acceleration, measured by the accelerometer 11.

For example, the value of the transversal acceleration measured by the accelerometer 11 could be integrated twice in the time, in order to obtain a corresponding value of the transversal position of the wheel 3 with reference to the track 4, and therefore • the value of the transversal position could be converted in a corresponding value of the vertical position, by means of a biunique conversion law; the value of the vertical position could be compared with the value of the height measured by the proximity switches 10, in order to confirm or correct the value of the height measured by the proximity switches 10.

It is important to note that having every wheel 3 a tapered shape, a biunique relation exists between the height of the wheel 3 from the rolling plane of the track 4 and the transversal position of the wheel 3 with reference to the track 4; consequently, the biunique conversion law which matches a transversal position value to a corresponding vertical position value, is a function of the tapered profile of the wheel 3, and is determined in an initial step of design and calibration of the control system 1.

According to a preferred embodiment, the measuring device 6 determines a time in which a flange 16 of the wheel 3 comes into contact with the lateral profile of the track 4, when the transversal acceleration value measured by the accelerometer 11 has a discontinuity; in other words, when the flange 16 of the wheel 3 comes into contact with the lateral profile of the track

4, the lateral movement of the wheel 3 is abruptly modified (reduced) and therefore at the time of the contact of the flange 16 with the lateral profile of the track 4, the transversal acceleration value measured by the accelerometer 11 has a clear discontinuity .

With reference to Figures 5-8, the contact between the railway wheel 3. and the corresponding track will now be described in a dynamic range.

It is possible to identify three contact types between the railway wheel 3 and the track 4 (according to different dynamic conditions of the railway car) : normal driving conditions, limit driving conditions, and dangerous driving conditions with the danger of a derailment.

In normal driving conditions (shown in Figures 5 and 6) , ideally a single contact point exists (indicated with A in Figure 5 and with B in Figure 6) between the wheel 3 and the track 4 (in reality, such contact points correspond to an area of reduced dimensions) . Increasing the dynamic stresses applied on the wheel 3 (i.e., in case of an increase of the speed in a bend and/or in case of entering a bend with a lower curvature radius) , the contact points move towards the periphery of the wheel 3 (with a displacement from contact point A to contact point B) . In normal driving conditions, always a single contact point exists between the wheel 3 and the track 4, and such contact point is localized in the tapered part of the wheel 3; in this case, the wheel flange 16 is not taking part to this movement, i.e. it does not contact the track 4. The variation of

the position of the contact point along the tapered profile of the wheel 3 corresponds to safe driving conditions; it is important to note that due to the tapering of the wheel 3, in the passage from contact point A to contact point B the wheel 3 raises from the rolling plane of the track 4.

According to Figure 7, if the dynamic stresses applied to the wheel 3 do heavily increase, the contact point (indicated in Figure 7 with C) between the wheel 3 and the track 4 continues to move along with the tapered profile of the wheel 3, until the contacts is reached between the wheel 3 and the track 4, even in a second localized contact point in the wheel flange 16 (indicated in Figure 7 with D) . When two different contact points exist between the wheel 3 and the track 4, the way of driving passes to limit conditions (illustrated in Figure 7); such a limit driving condition is generally considered acceptable for the driving of the vehicle 2, even if these limit conditions are very near to dangerous conditions.

According to Figure 8, if the dynamic stresses acting on the wheel 3 do reach too high values, the contact point (indicated with E in Figure 8) returns to be just one single point, localized on the wheel flange 16; in this case, there are dangerous driving conditions with an anticipated derailment.

From the above description, it can be inferred that a correspondence (biunique connection) exists between the passage from contact point A (illustrated in Figure 5) to contact point E (illustrated in Figure 8) and the height of the wheel 3 from the rolling plane of the track 4; in other words, a

correspondence exists (biunique connection) between the dynamic stresses acting on the vehicle 2 and on the wheel 3 and the height of the wheel 3 from the rolling plane of the track 4. Consequently, the measurement of the real value of the height of the wheel 3 from the rolling plane of the track 4 is an indication of the quality of the contact conditions between the wheel 3 and the . track 4, and therefore it can be effectively used to control the speed of the vehicle 2.

According to a preferred embodiment, the upper limit value of the height within the optimum range corresponds to a condition in which the wheel 3 has two different contact points with the track 4, in correspondence with the tapered surface and the wheel flange lβ, as indicated in Figure 7.

The method and control system 1 described above have many advantages, as they are easy and economic to produce and above all they permit to obtain in safe conditions the greatest possible performances. In other words, thanks to the method and the control system 1 described above, the vehicle 2 can reach always the greatest possible performances, still remaining in safe conditions.

Due to the many advantages described above, the method and the control system 1 described above can be advantageously applied for the control of the speed of every kind of railway vehicle, different from a train, as for instance, a city car or a subway train for city transport.