FR3027270A1 - RAILWAY BRAKING SYSTEM FOR A RAILWAY VEHICLE AND METHOD OF BRAKING A RAILWAY VEHICLE COMPRISING SUCH A SYSTEM - Google Patents

Abstract

The invention relates to a rail braking system comprising a service brake (6) comprising a movable main piston (10) delimiting with a body (2) of the system a main pressure chamber (11) fed by a main source for putting said main piston in a first position, an intermediate piston (20), fixedly secured to said main piston (10), movable and delimiting with said body an intermediate pressure chamber (21), distinct from said main chamber, supplied by an intermediate source for putting said intermediate piston in a second position; said system being configured so that, when said main piston is in its first position, said intermediate chamber is supplied by said intermediate source to move said intermediate piston and said main piston in said second position to apply a braking force on a wheelhouse of the system, more important than the force applied when said main piston is in said first position.

Description

FIELD OF THE INVENTION The invention relates to the field of braking of railway vehicles and more particularly rail braking systems for rail vehicles provided with a service brake, or even a parking brake, configured to act on a braking linkage.

It also relates to braking processes of railway vehicles comprising such braking systems. BACKGROUND ART Rail vehicles are generally equipped with service brake cylinders comprising a movable piston under the effect of a fluid under pressure, the displacement of this piston causing a braking action such as the tightening of a brake disc. between two packings, or the direct pressure of a sole against a wheel of the vehicle. These brake cylinders also generally comprise a parking or emergency actuator which is activated in the event of pressure loss of the pressurized fluid and / or in case of voluntary emptying or leakage of the pneumatic system. This actuator, also called parking brake, provides braking through the force of a spring replacing the force of the fluid. Once this parking brake is activated, the brake remains permanently tight. European patent application EP 2 154 040 discloses a rail braking system provided with a rail service brake cylinder coupled to a parking brake actuator. This brake cylinder comprises a body and a piston movable relative to the body to act on the braking linkage via a push rod.

The brake cylinder also includes a pressure chamber defined by the piston and the body and which is connected by a conduit to a source of pneumatic pressure medium to put the piston into a service braking position. In order to actuate the service brake, the service brake pressure chamber is supplied with pneumatic pressure medium via the corresponding source so as to move the piston in the body. The force exerted by the piston is here directly function in particular of the piston section. The parking brake has a body which is distinct from the body of the brake cylinder. The body of the parking brake has an opening opposite the piston of the service brake cylinder, which opening slidably receives a thrust sleeve fitting in this opening in a sealed manner. The parking brake also comprises a piston movably mounted in a cylinder integral with the body and delimiting with the body a parking brake pressure chamber. This parking brake pressure chamber is connected to another source of pneumatic pressure medium via a conduit. The piston has in its center an orifice through which the thrust sleeve passes. The parking brake further comprises springs which constantly urge the piston of the parking brake to a so-called low position where the parking brake is considered to be in a working configuration. To actuate the parking brake when the piston of the service brake cylinder is in the service braking position, the pressure chamber of the parking brake (previously filled with the pneumatic pressure agent) is drained and the brake springs of parking then act on the piston of the parking brake, which drives the sleeve until the latter bears against the piston of the service brake cylinder. The pressure chamber of the service brake cylinder can then be drained since the parking brake is actuated.

The force applied by the parking brake on the service brake piston is directly a function of the force developed by the springs. This force is of course a function of the stiffness and elongation of these springs. With this braking system, the force applied by the service brake cylinder piston when the parking brake is actuated and the service brake cylinder is drained on the brake linkage is often less than the force applied by that brake system. same piston when in service braking position. OBJECT OF THE INVENTION The invention relates to a braking system for a railway vehicle, having improved performance compared with the braking systems of the prior art mentioned above, while being simple, convenient and economical. The invention thus has, in a first aspect, a rail braking system for a railway vehicle with brakes with at least one lining or at least one sole, comprising: - a body; - A braking linkage configured to act on at least one said brake at least one pad or at least one sole; and a service brake comprising a main brake piston movable relative to said body to act on said braking linkage and delimiting with said body a main service brake pressure chamber configured to be powered by a main source of braking agent; pneumatic pressure for putting said main brake piston in a first service braking position; said rail braking system being characterized in that said service brake further comprises an intermediate braking piston fixedly secured to said main braking piston, movable relative to said body to act on said braking linkage and delimiting with said body an intermediate chamber operating brake pressure device, separate from said main service brake pressure chamber, and configured to be powered by an intermediate source of pneumatic pressure medium to put said intermediate brake piston into a second service brake position; with said rail braking system which is configured so that when said main braking piston is in its first service braking position, said intermediate service brake pressure chamber is supplied by said intermediate source of pneumatic pressure medium so as to move both said intermediate brake piston and said main brake piston into said second service brake position; in order to apply a braking force on said linkage greater than the braking force applied when said main brake piston is in said first service braking position. Due to its configuration, the braking system according to the invention makes it possible selectively to supply, for example only momentarily or at least each time it is necessary, one or the other or both of the intermediate chamber. and the main service brake pressure chamber with at least one source of pneumatic pressure medium to increase the braking force applied to the brake linkage by the main service brake piston and inherently by the intermediate piston.

The system according to the invention thus makes it possible to obtain higher service brake braking forces than those obtained with the above-mentioned braking systems of the prior art, in a simple, convenient and economical manner. According to preferred, simple, convenient and economical characteristics of the system according to the invention: said intermediate service brake pressure chamber is adjacent to said main service brake pressure chamber and separated from the latter by a partition wall arranged in said body, said main braking piston has a first side configured to act on said brake linkage and a second side opposite said first side and facing said main service brake pressure chamber and said intermediate brake pressure chamber on duty ; and said intermediate piston has a first side which extends an extension fixedly secured to said main brake piston so as to act on the latter and a second side opposite to said first side and facing said intermediate brake pressure chamber. service; Said primary and intermediate pneumatic pressure agent sources are formed by a single first source of pneumatic pressure agent configured to supply said main and intermediate service brake pressure chambers with a plurality of main portions of conduits; predetermined; and / or the system comprises at least a first pneumatic distribution device configured to be supplied by said pneumatic pressure medium intermediate source and to be connected to said intermediate service brake pressure chamber in order to put said intermediate piston in its second service braking position when it is powered by said intermediate source of pneumatic pressure medium. According to other preferred, simple, convenient and economical features, the system according to the invention further comprises a parking brake configured to act on at least one of said main braking piston and said intermediate braking piston of said service brake and admitting a working configuration and a rest configuration; said parking brake comprising: - a movable locking device with respect to said body and admitting a first position and a second position in which said blocking device is configured to immobilize at least one of said main braking piston and said intermediate braking piston in the service braking position, said parking brake then being in working configuration; and a movable control device with respect to said body, defining therewith a parking brake pressure chamber configured to be fed by a second source of pneumatic pressure medium, and having a stable position in which said The control is configured to maintain said locking device in its second position; with said rail braking system which is configured so that when said control device is in its stable position, said intermediate service brake pressure chamber is supplied by said intermediate source of pneumatic pressure medium, in order to apply when said parking brake is in working configuration, a braking force greater than the braking force applied when said main brake piston is in its first service braking position and said parking brake is in its position. rest configuration. In the braking system according to the invention, the braking piston is immobilized in the service braking position by the parking brake and in particular by its locking device. This means that the brake piston can be immobilized in any position, which position is related to the stroke that the piston has traveled and this stroke depends on the force applied during the service braking phase. The term immobilize means that the force applied by the brake piston on the braking linkage in the working configuration of the parking brake does not decrease, or almost no. There is, however, some loss associated with the recoil of the brake piston, in particular the slight displacement of the piston with respect to the locking device, at the moment when the service brake pressure chamber is drained. This loss is controlled and is defined by a very slight decrease in the applied force which is due in particular to the manufacturing tolerances of both the locking device and the intermediate piston and the brake piston. This reduction in the force applied on the braking linkage is here called loss at the recoil. An acceptable value of these losses at the recoil is at most of the order of 10% of the force applied by the service brake at the instant when the parking brake is actuated to be in working configuration. Thanks to the configuration of the braking piston, the intermediate piston and the parking brake, the springs of the known braking systems described in the part above reflecting the prior art, which springs make it possible to apply the parking brake force on the braking linkage via the pistons of the service brake cylinder. Thus, for the same force applied to the braking linkage when the parking brake is in working configuration, the braking system according to the invention is more compact than the prior art braking systems mentioned above, despite the presence of the intermediate braking chamber; and also lighter in addition to allowing to apply a much higher effort. Note that the braking linkage advantageously has deformable arms whose elasticity can be substituted for the springs of known braking systems described above. It will also be noted that the configuration of the parking brake is chosen so that the force applied directly by the locking device to immobilize the brake piston and the intermediate piston is not greater than the force applied by the springs on the piston. braking braking systems of the prior art mentioned above; whereas the force applied to the braking linkage when the parking brake of the system according to the invention is in the working configuration is at least equal and possibly much greater than that provided by the brake systems of the aforementioned prior art. The system according to the invention thus makes it possible to obtain parking brake and parking brake forces greater than those obtained with the above-mentioned braking systems of the prior art, in a simple, convenient and economical manner.

According to still other preferred, simple, convenient and economical features of the system according to the invention: the system comprises at least a second pneumatic distribution device configured to be powered by said second source of pneumatic pressure agent and to be connected at said parking brake pressure chamber to put said parking brake respectively in its rest configuration when powered by said second source of pneumatic pressure agent and in its working configuration when not powered by said second source of pneumatic pressure agent; said at least one first pneumatic dispensing device comprises an actuator configured to be pneumatically controlled by at least a pipe portion of said system connected at the output of said at least one second pneumatic dispensing device; said at least one first pneumatic dispensing device and / or said at least one second pneumatic dispensing device are formed by a dispenser provided with three orifices and a two-position slide; said two-position slide of said at least one first pneumatic distribution device has, in a first position, a first blocked main inlet configured to be connected to said intermediate source of pneumatic pressure medium via a third portion main driving portion and a first main driving portion, a first service brake output configured to be connected to said intermediate service brake pressure chamber through a fourth main driving portion and a first output main exhaust in fluid communication with said first service brake output and opening into the atmosphere; and in a second position, a first main supply inlet configured to be connected to said pneumatic pressure medium intermediate source through said first and third main pipe portions, a second service brake output in fluid communication with said first main power input and configured to be connected to said fourth main driving portion and a second main entrance blocked; said two-position slide of said at least one second pneumatic distribution device has, in a first position, a first secondary supply inlet configured to be connected to said second source of pneumatic pressure medium via a a third secondary conduit portion, a pressure regulator and a second conduit secondary portion, a first parking brake output in fluid communication with said first secondary supply inlet and configured to be connected to said pressure chamber; parking brake via a fourth secondary driving portion and a sixth secondary driving portion and a second blocked secondary entrance; and in a second position, a second parking brake output configured to be connected to said parking brake pressure chamber through said fourth and sixth pipe minor portions, a first exhaust secondary outlet in fluid communication with said second parking brake output and venting to the atmosphere and a third blocked secondary inlet configured to be connected to said second source of pneumatic pressure medium via a third secondary conduit portion, a regulator pressure and a second secondary portion of driving; and / or - the system comprises a toothed rod projecting from said second side of said intermediate braking piston, said parking brake is disposed in said body, said locking device is formed by a locking pin and said control device is formed by a holding piston movable relative to said body and defining with said body said parking brake pressure chamber and a spring element disposed in said body and configured to act on said holding piston; with said holding plunger being configured to maintain said latch finger in its first position when said parking brake pressure chamber is energized and under pressure, first position wherein said latch finger is spaced from said latched rod; and with said spring member being configured to hold said locking finger in its second position when said parking brake pressure chamber is drained, second position wherein said locking pin immobilizes said piston rod. The invention also relates, in a second aspect, to a method of braking a railway vehicle, comprising a rail braking system as described above, comprising: - the step of supplying the main pressure chamber service brake of said system with a first source of pneumatic pressure medium to move the main service brake piston to a first service brake position so as to apply a first braking force to a braking linkage of said system ; the step of supplying the service brake pressure intermediate chamber of said system with said first source of pneumatic pressure medium to move the intermediate service brake piston into a second service braking position so as to apply on said braking linkage of said system a second braking force greater than said first braking force. The method according to the invention is particularly simple and convenient to implement. According to preferred, simple and economical characteristics of the method according to the invention: said rail braking system comprises a parking brake as described above and said method comprises, before said step of feeding the main chamber of brake pressure in service, the step of supplying the parking brake pressure chamber of said system with a second source of pneumatic pressure medium to move the control device of said system to act on the locking device of said system until the latter leaves at least one free of said main braking piston and said intermediate braking piston of said system, the parking brake of said system then being in the rest configuration; after said step of supplying the main service brake pressure chamber and before said step of supplying the intermediate service brake pressure chamber, the method comprises the step of controlling the emptying of the brake pressure chamber; parking device for moving said blocking device until the latter comes to immobilize at least one of said main braking piston and said intermediate braking piston in a service braking position, said parking brake then being in working configuration; and / or after said step of supplying the intermediate service brake pressure chamber, the method comprises the step of controlling the emptying of said main and intermediate service brake pressure chambers and, optionally, the step unlocking said locking pin of said parking brake so as to leave at least one free of said main braking piston and said intermediate braking piston. BRIEF DESCRIPTION OF THE DRAWINGS The description will now be continued of the invention by the description of exemplary embodiments, given below by way of illustration and without limitation, with reference to the appended drawings in which: FIGS. 1 to 6 illustrate schematically the operation of a rail braking system according to the invention, which system is provided with pneumatic distributors connected to at least one source of pneumatic pressure agent of the vehicle, this system being respectively in different configurations; and FIGS. 7 to 9 show schematically an alternative embodiment of the system visible in FIGS. 1 to 6. DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT FIG. 1 schematically represents a rail braking system 1 for a railway vehicle with brake linings or soles. The rail braking system 1 comprises a body 2 forming here a cylinder of both service brake 6 and parking brake 7, a pneumatic pipe routing network 3 connected to the body 2, a braking linkage 4 mechanically connected to the body 2 and a brake 5 to fittings on which the brake linkage 4 is configured to act. The body 2 here has the shape of a generally closed envelope. The service brake 6 comprises a main service brake piston 10 movable relative to the body 2 in a first axial direction, an intermediate service brake piston 20 movable relative to the body 2 in the first axial direction and mechanically connected to the piston main service brake 8, and a thrust rod 30 mounted at least partially movable in and relative to the body 2 in a second axial direction perpendicular to the first axial direction. The main braking piston 10 delimits with the body 2 a main service brake pressure chamber 11, while the intermediate braking piston 20 delimits with the body 2 an intermediate service brake pressure chamber 21, here adjacent to the main service brake pressure chamber 11. The body 2 is provided with a partition wall 27 separating the intermediate service brake pressure chamber 21 from the main service brake pressure chamber 11. The main brake piston 10 has two sides respectively a first side 12 configured to act on the brake linkage 4 via the push rod 30 and a second side 13 opposite the first side 12 and facing the main chamber of service brake pressure 11 and to the intermediate chamber of service brake pressure 21. The intermediate braking piston 20 also has two sides respectively one pr first side 22 configured to act on the main brake piston 10 and a second side 23 opposite the first side 12 and facing the intermediate chamber of service brake pressure 21 and the parking brake 7. The service brake 6 comprises furthermore, a notched rod 31 fixed on the second side 23 of the intermediate braking piston 20 and mechanically secured to the main braking piston 10, by its second side 13, via the intermediate braking piston 20. This notched pin 31 s extends longitudinally along the first axial direction. Here, in the example illustrated schematically, the intermediate braking piston 20 is thus provided with an extension protruding from its first side 22 and secured integrally to the main braking piston 10.

The first side 22 of the intermediate braking piston 20 is configured to act on the main braking piston 10 via this toothed rod 31.

The main braking piston 10 and the intermediate braking piston 20 are each configured to move in the body 2 while maintaining respectively the main and intermediate service brake pressure chambers 11 and 21 relatively sealed by means of membranes 14 respectively. and 24, disposed between these braking pistons 10 and 20 and the inner edges of the body 2. The service brake 6 further comprises a corner piece 15 fixed on the first side 11 of the main brake piston 10. The corner piece 15 has a triangular section and is configured to cooperate with a set of thrust bearings 16, one of the bearing stops is connected to the body 2 while the other bearing stops is connected to the push rod 30. The push rod 30 is provided with a wear regulator configured to compensate for the wear of the brake linings 5 in order to prevent excessive play (as a result of the wear of s seals) will reduce braking effort. The service brake 6 further comprises a spring 17 here arranged around the thrust rod 30, between the bearing stop which is connected to the latter and the inner edge of the body 2. This spring 17 is configured to recall the stop which is connected to the push rod 30 against the corner piece 15. The service brake 6 further comprises a first orifice 18 formed in the body 2 and configured to allow the displacement of the push rod 30 through the first orifice 18 and thus through the body 2. The service brake 6 further comprises a second orifice 19 formed in the body 2 and opening into the main chamber of service brake pressure 11; as well as a third orifice 25 formed in the body 2 and opening into the intermediate service brake pressure chamber 21. The main service brake pressure chamber 11 is connected by a service brake line portion 53 connected to the level of this second port 19 to a source of pressurized fluid such as, for example, a pneumatic circuit; while the intermediate service brake pressure chamber 21 is connected by a service brake line portion 55 connected at this third port 25 to a source of pressurized fluid such as, for example, a pneumatic circuit. The body 2 comprises a cavity 26 contiguous to the intermediate service brake pressure chamber 21 and in which is disposed the parking brake 7. The parking brake 7 comprises a locking device formed here by a locking pin 42 movable by relative to the body 2 and extending in the second axial direction.

The parking brake 7 further comprises a holding piston 43 movable relative to the body 2 and delimits therewith a parking brake pressure chamber 44. This holding piston 43 has two sides, respectively a first side 45 on which the locking finger 42 is attached and a second opposite side 46 to the first side 45 and facing the parking brake pressure chamber 44. The parking brake 7 further comprises a spring element 47 disposed between the body 2 and the parking brake chamber 44. second side 46 of the holding piston 43. This spring element 47 is configured to act on this holding piston 43 and consequently on the locking pin 42. It will be noted that the holding piston 43 and the spring element 47 form a movable parking brake control device 7. The holding piston 43 is configured to move in the body 2 while maintaining the parking brake pressure chamber 44 relatively tight thanks to a diaphragm (not shown) disposed between this holding piston 43 and the inner edges of the body 2. The parking brake 7 comprises a fourth orifice (not shown) formed in the body 2 and opening into both the pressure chamber of parking brake 44 and in the intermediate service brake pressure chamber 21, which fourth port is configured to allow movement of the blocking finger 42 through this third port.

It will be noted that the relative sealing between the parking brake pressure chamber 44 and the intermediate service brake pressure chamber 21 is ensured by the presence of a seal 48 disposed at the interface between this fourth orifice and the locking finger 42.

The parking brake 7 further comprises a fifth orifice 49 formed in the body 2 and opening into the parking brake pressure chamber 44. It will be noted moreover that this parking brake pressure chamber 44 is connected by a pipe parking brake 61 connected at this fifth port 49 to a source of pressurized fluid, such as for example a pneumatic circuit. The parking brake 7 further comprises an unlocking part 8 attached to the second side 46 of the holding piston 43 and opening outwardly of the body 2 through a sixth orifice (not shown) formed in this body 2 and opening into the cavity 26; so that this unlocking part 8 is accessible to be handled from outside the body 2. The service brake 6 is disposed in the body 2 and is configured to act on the brake 5 via the brake linkage. 4.

This brake 5 comprises a brake disc 31 (here seen from above) mounted for example on a rail vehicle axle 32, or directly on the wheel to be braked. This brake 5 further comprises two pads 33 each provided with a lining 34 configured to be applied in contact with the disc 31 to reduce its rotational speed and consequently that of the wheel to be braked, as well as a fixing eye 35. arranged opposite the surface of the packing 34 configured to be applied on the brake disc 31. The brake linkage 4 comprises two deformable levers 36 each provided with an upper arm and a lower arm which are solidarity.

Each arm of the levers 36 is articulated on a central connector 37 via two pivots 38.

The lower arm of each deformable lever 36 is connected to one of the pads 33 via its fixing eyelet 35. The upper arm of each deformable lever 36 is connected to a respective articulation 39, 40.

The brake linkage 4 receives the body 2 between the upper arms of the deformable levers 36, at the joints 39 and 40. In other words, the body 2 is mounted on the braking linkage 4 via the joints 39 and 40. More specifically, the body 2 is rotatably mounted on the hinge 40 which is secured to one end of the push rod 30 while it is fixedly mounted on the hinge 39, which is directly integral with this 2. The braking linkage 4 also comprises a fastening lug 41 secured to the central connector 37 for mounting this braking linkage 4 on the railway vehicle; so that the braking pads 33 are located on either side of the brake disc 31 (or the wheel of the railway vehicle). Note that the approximation of the joints 39 and 40 allows to move the pads 33 away from each other and that, conversely, the distance of these joints 39 and 40 makes it possible to tighten the pads 33 on the disk brake 31 (or on the wheel of the railway vehicle). The air pipe routing network 3 here comprises a main pneumatic circuit formed of a main pipe 50 which is for example configured to run along the railway vehicle. The main line 50 is configured to convey a fluid 25 at a first predetermined pressure, for example substantially equal to about 3.8 bar. It should be noted that the network may comprise a general pipe (not shown) configured to convey a fluid under a predetermined initial pressure, for example approximately equal to approximately 5.5 bar, as well as a pressure regulator (for example an expander, not shown) disposed on or upstream of the general pipe, which regulator is configured to limit the pressure of the fluid flowing in this main pipe to the predetermined pressure. The network 3 here comprises a first branch point 51 connected to the main pipe 50 and, at the outlet of this first branch point 51, two separate pneumatic circuits also called the first source of pneumatic pressure agent and the second source of the agent. pneumatic pressure. The first source of pneumatic pressure agent is here configured to supply the service brake 6 while the second source of pneumatic pressure agent is here configured to supply the parking brake 7. The first source of pneumatic pressure agent here there is a first main pipe portion 52 connected at a first end to the first branch point 51 and extending to a second branch point 67 of the network 3, the second point to which it is also connected by a second end opposite to its first end. The network 3 comprises, at the output of this second branch point 67, a first main sub-circuit (also called main source of pressure agent) configured to supply the main service brake pressure chamber 11 and a second sub-circuit. main circuit (also called intermediate pressure agent source) distinct from the first main sub-circuit and configured to supply the intermediate service brake pressure chamber 21. The first main sub-circuit has a second main driving portion 53 connected by a first end to the second branch point 67 and a second end opposite its first end, to the second port 19 of the service brake 6. The second main portion of line 53 thus opens into the main chamber of brake pressure 11 to pneumatically supply the latter. The second main sub-circuit has a third main portion of pipe 54 connected by a first end to the second branch point 67 and a second end opposite its first end, to a distributor 65 of the network 3, here three ports and two positions, and monostable. The second main sub-circuit further has a fourth main pipe portion 55 connected by a first end to the distributor 65 and a second end opposite its first end, to the third port 25 of the service brake 6. The fourth main portion of pipe 55 thus opens into the intermediate chamber of service brake pressure 21 to pneumatically supply the latter.

The distributor 65 is here more generally disposed in the first source of pneumatic pressure agent and interposed between the main brake pipe 50 and the intermediate service brake pressure chamber 21. The distributor 65 comprises a movable slide 80 and an actuator 81 which is configured to move this drawer 80.

The actuator 81 is configured to receive a pneumatic control signal here (see below). The dispenser 65 has a return spring 84 configured to move the slide 80 from a first position to a second position. In Figures 1 and 2, the dispenser 65 is shown in its first position, which first position is not its default position. In other words, the actuator 81 of the distributor 65 is configured to receive a non-zero pneumatic signal or at least sufficient to move the slide 80 between its second position (the default position also called "normally closed" illustrated in Figures 3 to 5) and its first position (illustrated in Figures 1 and 2). The slide 80 includes a first chamber 82 provided with three inputs / outputs 82a, 82b and 82c and a second chamber 83 also provided with three inputs / outputs 83a, 83b and 83c. In each of the first and second positions of the spool 80, the third main pipe portion 54 and the fourth main pipe portion 55 are each connected to one of the three inlets / outlets 82a-c and 83a-c.

The second source of pneumatic pressure agent here has a first secondary portion of line 56 connected by a first end to the first branch point 51. The network 3 further comprises an auxiliary reservoir 62 connected to the main line 50 via a second end the first secondary portion of pipe 56, opposite its first end. Such an auxiliary reservoir 62 is generally present on each bogie of the railway vehicle. The auxiliary reservoir 51 therefore comprises a fluid at such a first predetermined pressure.

The network 3 comprises, at the outlet of the auxiliary reservoir 62 (the first secondary portion of pipe 56 being connected at the inlet of this auxiliary reservoir 62), a pressure regulator 63 (here an expander) connected to the auxiliary reservoir 62 via a second secondary portion of line 57 of the second source of pneumatic pressure agent. The second secondary portion of pipe 57 is thus connected both to the auxiliary reservoir 62 at one end and to the pressure regulator 63 at a second end opposite its first end. This pressure regulator 63 is configured to limit the pressure of the fluid flowing in this second source of pneumatic pressure agent at a determined second pressure, for example substantially equal to about 3 bars. The second source of pneumatic pressure agent has a third secondary portion of line 58 connected by a first end to the pressure regulator 63, at the outlet of the latter and, by a second end opposite its first end, to a distributor 64 of the network 3, here with three orifices and two positions, and monostable (also called second distribution device). The second source of pneumatic pressure agent has a fourth conduit secondary portion 59 connected by a first end to the distributor 64 and a second end opposite its first end to a third branch point 68 of the network 3.

At the outlet of this third branch point 68, the second source of pneumatic pressure agent has a fifth secondary portion of pipe 60 connected by a first end to this third branch point 68 and by a second end opposite its first end, to the actuator 81 of the distributor 65 (also called the first dispensing device). It is therefore through the fifth secondary portion of pipe 60 that the pneumatic control signal of this actuator 81 and thus of the distributor 65 passes through. At the outlet of this third branch point 68, the second source of pneumatic pressure medium present in in addition to a sixth secondary portion of line 61 connected by a first end to this third branch point 68 and by a second end opposite its first end, to the fifth orifice 49 of the parking brake 7. The sixth secondary portion of conduit 61 thus opens in the parking brake pressure chamber 44 for pneumatically supplying the latter. The distributor 64 is here more generally disposed in the second source of pneumatic pressure agent and interposed between the auxiliary reservoir 62 and the parking brake pressure chamber 44. The distributor 64 comprises a movable slide 70 and an actuator 71 which is configured to move this drawer 70. The actuator 71 is configured to receive a control signal 66, for example pneumatic. The dispenser 64 has a return spring 74 configured to move the spool 70 from a first position to a second position. In Figures 1 and 2, the dispenser 64 is shown in its first position, which first position is not its default position. In other words, the actuator 71 of the dispenser 64 is configured to receive a non-zero or at least sufficient pneumatic signal to move the spool 70 between its second position (the default position also referred to as "normally closed" shown in FIGS. ) and its first position (illustrated in Figures 1 and 2).

The drawer 70 has a first chamber 72 provided with three inputs / outputs 72a, 72b and 72c and a second chamber 73 also provided with three inputs / outputs 73a, 73b and 73c. In each of the first and second positions of the spool 70, the third minor portion of the line 58 and the fourth minor portion of the line 59 are each connected to one of the three inputs / outputs 72a-b and 73a-c. We will now describe the operation of the rail braking system 1 with reference to Figures 1 to 6, which schematically illustrate different configurations of this system 1. In Figure 1, the rail braking system 1 is in a reset configuration. In this reset configuration, the main and intermediate service brake pressure chambers 11 and 21 are not powered (they are drained) so that the main brake piston 10 and the intermediate braking piston 20 are each in a position resting, in which they do not apply braking force on the push rod 30. Therefore, the joints 39 and 40 of the brake linkage 4 are at a distance from each other which allows keep away the pads 33 of the brake disk 31. The parking brake pressure chamber 44 is supplied by the sixth secondary pipe portion 61, which extends the fourth secondary pipe portion 59, which is connected via the distributor 64 to the auxiliary reservoir 62, through the third secondary portion of pipe 58, the pressure regulator 63 and the second secondary portion of pipe 57. The parking brake pressure 44 is thus under pressure so that the holding piston 43 is in a first position in which the spring member 47 is compressed and the locking pin 42 is in a first position away from the notched pin 31 of the service brake 6.

In this reset configuration of the system 1, the parking brake 7 is in a reset configuration while the service brake 6 is in a rest configuration. In this configuration, the drawer 70 of the dispenser 64 is in its first position which indicates that the actuator 71 has received a control signal 66 (non-zero) and therefore that the drawer 70 has been moved from its second position (position by defect) at its first position against the return spring 74 which is compressed. In this first position of the slide 70, the first chamber 72 has a first secondary supply inlet 72b connected to the auxiliary reservoir 62 via the third secondary portion of the pipe 58, the pressure regulator 63 and the second secondary portion. 57, a first parking brake output 72c in fluid communication with the first secondary supply inlet 72b and connected to the parking brake pressure chamber 44 via the fourth secondary driving portion 59 which is extended by the sixth secondary portion of conduit 61 at the third branch point 68 of the network 3. The first chamber 72 of the slide 70 also has a second blocked secondary entrance 72a.

None of the inputs and outputs of the second chamber 73 of the drawer 70 is connected. In addition, in this configuration, the spool 80 of the dispenser 65 is in its first position which indicates that the actuator 81 has received a control signal (non-zero) and thus the spool 80 has been moved from its second position ( default position) at its first position against the return spring 84 which is compressed. The control signal is here a pneumatic signal supplied by the fifth secondary portion of line 60 which extends, at the third branch point 68 of the network 3, the fourth secondary portion of line 59. In this first position of the slide 80, the first chamber 82 has a first blocked main inlet 82b connected to the main pipe 50 via the third main pipe portion 54 and the first main pipe portion 52, a first service brake outlet 82c connected to the chamber service brake pressure intermediate 21 through the fourth main pipe portion 55 and a first main exhaust outlet 82a in fluid communication with the first service brake outlet 82c and opening into the atmosphere. None of the inputs and outputs of the second chamber 83 of the drawer 80 is connected.

The parking brake 7 and the distributor 65 are here dimensioned and configured so that the respectively rearming pressure of the parking brake 7 and for the passage from the second position to the first position of the slide 80 is relatively small, for example the order of 2 bar at 6 bar and preferably here at about 3 bar.

In FIG. 2, the rail braking system 1 is shown in an application configuration of the service brake 6. In this application configuration of the service brake 6, the main service brake pressure chamber 11 is powered by the main brake pipe 50 via the first and second main pipe portions 52 and 53. The main service brake pressure chamber 11 is thus under pressure and the main brake piston 10 has been moved in the first direction axial from its first position to a second position in which the wedge piece 15 has spaced the set of bearing stops 16, thereby displacing the push rod 30 and the hinge 39. Therefore, the hinges 39 and 40 move away. one of the other and cause the approach of the pads 33 and thus the application of the pads 34 against the brake disk 31. In the application configuration of the brake of Service 6 of the system 1, the levers 36 are deformed (elastically). The axial displacement of the main braking piston 10 causes the axial displacement of the extension of the intermediate braking piston 20, which also drives the toothed rod 31 axially, while the intermediate service brake pressure chamber 21 is not energized. . The intermediate braking piston 20 has been moved in the first axial direction from its first position to a second position.

In this configuration illustrated in FIG. 2, the parking brake pressure chamber 44 is still under pressure as mentioned with reference to FIG. 1. In this application configuration of the service brake 6 of the system 1, the parking brake 7 is still in its reset configuration while the service brake 6 is in a working configuration. The position of the spool 70 of the dispenser 64 and the position of the spool 80 of the dispenser 65 are therefore similar to those illustrated in FIG. 1. In the configuration illustrated in FIG. 2, the first predetermined pressure, here equal to approximately 3.8 bars. , fluid injected into the service brake pressure chamber 11 moves the main braking piston 10 and therefore the intermediate braking piston 20 each of a same predetermined stroke in order to act on the braking linkage 4 with a first predetermined force and therefore apply a first predetermined force on the brake disc 31. This first predetermined force is for example between about 30 kN and 50 kN and preferably here about 38 kN. In FIG. 3, the rail braking system 2 is shown in a locking configuration in which the main braking piston 10 and the intermediate braking piston 20 of the service brake 6 are immobilized in their respective second position illustrated in FIG. The brake linkage 4 is here in the same position as that illustrated in Figure 2 and the force exerted on the disc 31 does not decrease, or almost no. The main service brake pressure chamber 11 is still under pressure (but not powered), the intermediate service brake pressure chamber 21 is not powered, while the parking brake pressure chamber 44 is drained.

The emptying of the parking pressure chamber 44 frees the spring element 47, which moves the holding piston 43 from its first position to a second position called the stable position and thus moves the locking finger 42 from its first position to a second position. position in which it comes to immobilize the toothed rod 31 by engrainement of the distal end of the locking pin 42 with notches provided on the toothed rod 31. To empty the parking brake pressure chamber 44, the actuator 71 of the distributor 64 has received a different control signal 66, here for example zero, so that the slide 70 has moved from its first position to its second position under the action of the return spring 74. In this second position of the 70, the second chamber 73 of this drawer 70 has a second parking brake output 73c connected to the parking brake pressure chamber 44 via the fourth and sixth minor portions of line 59 and 61; and a first secondary exhaust outlet 73a in fluid communication with the second parking brake output 73c and opening into the atmosphere. The second chamber 73 of this slide 70 also has a third blocked secondary entrance 73b to which is connected the auxiliary reservoir 62, via the third secondary portion of the pipe 58, the pressure regulator 63 and the second secondary portion. 57. None of the inlets and outlets of the first chamber 72 of the drawer 70 is connected. In this locking configuration, no fluid under pressure travels in the fourth secondary portion of line 59 and therefore in the fifth secondary portion of line 60; and the control signal supplied to the actuator 81 of the distributor 65 becomes therefore almost zero. The distributor 65 therefore passes, under the action of the spring 84, its second position in its first position. In this second position, the spool 80 has a first main supply inlet 83b connected to the main line 50 via the first and third main line portions 52 and 54, a second service brake output 83c in fluid communication with the first main supply inlet 83b and connected to the fourth main duct portion 55. The second chamber 83 of the drawer 80 also has a second blocked main entrance 83a. None of the inputs and outputs of the second chamber 83 of the drawer 80 is connected. In FIG. 3, no pressurized fluid travels in the first, third and fourth main pipe portions 52, 54 and 55; so that the intermediate service brake pressure chamber 21 is not energized. FIG. 4 illustrates the rail braking system 2 in a so-called supercharging configuration of the service brake 6. The distributors 64 and 65 are each in their first position as detailed with reference to FIG. 3 and the main line 50 supplies each of the first, second, third and fourth main pipe portions 52 to 55 so as to supply the main and intermediate service brake pressure chambers 11 and 21; respectively directly and via the second chamber 83 of the spool 80 of the distributor 65. The fluid under the first predetermined pressure and conveyed to the main chambers and intermediate service brake pressure 11 and 21, can supercharge the brake 6. The supply of the main and auxiliary service brake pressure chambers 11 and 21 respectively makes it possible to move the main piston and the intermediate braking piston 10 and 20 respectively, to further discard the bearing thrust bearing 16 and so on. further away the joints 39 and 40 of the brake linkage 4. This distance is representative of a predetermined force applied by the main brake piston 10 on the stop 30, which force generates a second predetermined force greater than the first predetermined force on the brake disc 31 via the pads 33.

This second predetermined force is here a function of the section of each of the braking pistons 10 and 20 and the pressure of the injected fluid while the first force previously applied (FIG. 2) depends solely on the section of the main braking piston 10. This second predetermined force is for example between about 60 kN and 90 kN and preferably here about 73 kN, for a first predetermined pressure equal to about 3.8 bars. The toothed rod 31 and the locking pin 42 are here configured to allow such displacement of the brake pistons 10 and 20 while the locking pin 42 immobilizes this toothed rod 31. For example, the toothed rod 31 has a predetermined toothing and the distal end of the locking pin 42 also has a predetermined toothing complementary to the predetermined toothing of the toothed rod 31.

The locking pin 42 allows the displacement of the toothed rod 31 only in a direction of movement of the brake pistons 10 and 20 to further tighten the brake disc 31. The locking pin 42 again immobilizes the toothed rod 31 as soon as the latter is stopped in the third position of the braking pistons 10 and 20 (FIG. 4). In the lock and boost configurations of the service brake 6 (FIGS. 3 and 4), the parking brake 7 and the service brake 6 are each in a working configuration. In a variant not shown, the system 2 is furthermore provided with a control valve, for example in place of the second branch point 67, which makes it possible to select the supply of one or the other or the two of the main and intermediate service brake chambers 11 and 21. In FIG. 5, the rail braking system 1 is shown in a drain configuration of the service brake 6. The emptying of each of the main and intermediate pressure chambers In other words, neither the main service brake pressure chamber 11, nor the intermediate service brake pressure chamber 21, nor the first, second, third and fourth main driving portions 52 to 55 are not vented directly. The pressurized fluid present in the main and intermediate chambers of the service brake pressure 11 and 21 escapes from the latter, in particular from the main brake pipe 50. In this configuration of the emptying of the service brake 6 of the system 1, the dispenser 65 has its drawer 80 in its first position. Thanks to the parking brake 6 and in particular to the assembly formed by the locking finger 62, the holding piston 43 and the spring element 47, in combination with the toothed rod 42 attached to the braking pistons 10 and 20 (main and intermediate) of the service brake 6, these two brake pistons 10 and 20 remain in their respective third position where they act on the braking linkage 4 to apply the second predetermined force on the brake disc 31 via the pads 33, despite the emptying of each of the main and intermediate service brake pressure chambers 11 and 21. In other words, in this drain configuration of the service brake 6, the parking brake 7 is in a working configuration while the service brake 6 is blocked in its working configuration, despite the emptying of the main and intermediate service brake pressure chambers 11 and 21. The second predetermined force pe can slightly decrease once the rooms 11 and 21 emptied. For example, this second predetermined force can be understood, once the emptying is carried out, between about 50 kN and 85 kN and preferably here equal to about 64 kN. In Figure 6, the rail braking system 1 is shown in an unlocking configuration. In this unlocking configuration, a force has been applied to the unlocking piece 8 of the parking brake 7 so as to pull this unlocking piece 8 towards the outside of the body 2.

The displacement of this unlocking part 8 causes the holding piston 43 and consequently the locking pin 42 against the spring element 47 which is thus compressed. The fact that the blocking finger 42 reaches its second position, the latter does not cooperate with the toothed rod 31, which is free. Therefore, the spring 17 disposed around the push rod 30 and between the inner edge of the body 2 and the thrust bearing fixed on the push rod 30 returns to its initial position. This spring 17 therefore drives the bearing stop 16 disposed between the push rod 30 and the wedge piece 15 in the second axial direction, thereby causing the return of the main braking piston 10 in the first axial direction, to its position. rest, and therefore the toothed rod 31 and the intermediate braking piston 20, also to its rest position.

The joints 39 and 40 of the brake linkage 4 are brought closer to one another so that the deformable levers 36 return to their initial positions illustrated in FIG. 1 and the pads 33 are found at a distance from the brake disc 31, which is thus free to rotate (the brake disc 31 is no longer braked).

In this unlocking configuration, the parking brake 7 is in an unlocking configuration while the service brake 6 is in a rest configuration. In the unlocking configuration of the system 1, the distributors 64 and 65 are for example in the same configurations as those illustrated in FIG. 5, with the main and auxiliary service brake chambers 11 and 21 and the parking brake chamber 44. which are drained. The parking brake 6 is configured so that the force to be applied for unlocking, via the unlocking part 8, is relatively small to be performed manually by a user such as the driver of the railway vehicle. For example this effort is of the order of about 10 to 50 daN.

FIGS. 7 to 9 illustrate an alternative embodiment of the rail braking system illustrated in FIGS. 1 to 6. In general, the same references have been used for similar elements. The system illustrated in FIGS. 7 to 9 is devoid of a parking brake as described above with reference to FIGS. 1 to 6. The body 2 of the system is therefore devoid of a parking brake chamber. This body 2 comprises a main service brake piston 10 defining with the body a main service brake pressure chamber 11; and an intermediate service brake piston 20 defining with the body an intermediate service brake pressure chamber 21. The two service brake pistons 10 and 20 are integrally connected together by an extension of the intermediate piston 20 and a rod 90, which unlike the notched pin 31 of the system shown in Figures 1 to 6, is not serrated, is integrally attached to the second side of the intermediate piston 20. The main piston is configured to act on the braking linkage 4 via the stop, in the same manner as indicated above. The pneumatic conduit routing network is without it distributor 64 and is here illustrated in a simplified manner. The main pipe 50 is directly connected to the branch point 67 and the network comprises, at the outlet of this bypass point 67, a first main sub-circuit configured to supply the main service brake pressure chamber 11 and a second sub-circuit. main circuit separate from the first main sub-circuit and configured to supply the intermediate service brake pressure chamber 21. In FIG. 7, the service brake 6 is in a rest configuration where the main and intermediate pressure chambers of The service brake 11 and 21 are not powered (they are drained) so that the main braking piston 10 and the intermediate braking piston 20 are each in a rest position, in which they do not apply force. braking on the push rod 30.

Consequently, the joints 39 and 40 of the brake linkage 4 are at a distance from one another, which makes it possible to keep the skids 33 of the brake disc 31 at a distance. In this configuration, the spool 80 of the dispenser 65 is in its first position which indicates that the actuator 81 has received a control signal 60 (non-zero) and thus the drawer 80 has been moved from its second position (default position) to its first position. position against the return spring 84 which is compressed. The control signal 60 is here an independent pneumatic signal 10 and therefore not provided by a secondary pipe portion as described above with reference to FIGS. 1 to 6. In this first position of the slide 80, the first chamber 82 presents a first blocked main inlet 82b connected to the main line 50 via the third main line portion 544, a first service brake output 82c connected to the intermediate service brake pressure chamber 21 via the fourth main pipe portion 55 and a first main exhaust outlet 82a in fluid communication with the first service brake outlet 82c and opening into the atmosphere.

None of the inputs and outputs of the second chamber 83 of the drawer 80 is connected. In FIG. 8, the system is shown in an application configuration of the service brake 6 and the latter is thus in a working configuration.

In this application configuration of the service brake 6, the main service brake pressure chamber 11 is supplied by the main brake pipe 50 via the second main pipe portion 53. The main pressure chamber the service brake 11 is therefore under pressure and the main brake piston 10 has been moved in the first axial direction from its first position to a second position in which the corner piece 15 has spaced the set of bearing stops 16, thus displacing the push rod 30 and the hinge 39. Therefore, the joints 39 and 40 move away from each other and bring the pads 33 closer together and thus the application of the pads 34 against the disc of In the application configuration of the service brake 6 of the system 1, the levers 36 are deformed (elastically). The axial displacement of the main braking piston 10 causes the axial displacement of the extension of the intermediate braking piston 20, which also axially drives the rod 90, while the intermediate chamber of service brake pressure 21 is not supplied. The intermediate braking piston 20 has been moved in the first axial direction from its first position to a second position. The position of the spool 80 of the distributor 65 is therefore similar to that illustrated in FIG. 1. In the configuration illustrated in FIG. 8, the first predetermined pressure, here equal to about 3.8 bars, of the fluid injected into the pressure chamber of the service brake 11 moves the main braking piston 10 and consequently the intermediate braking piston 20 each of the same predetermined stroke so as to act on the braking linkage 4 with a first predetermined force and consequently apply a first force predetermined predetermined on the brake disk 31. This first predetermined effort is for example between about 30 kN and 50 kN. FIG. 9 illustrates the system in a so-called supercharging configuration of the service brake 6. The actuator 81 of the distributor 65 receives a different control signal 60, here for example zero, so that the spool 80 moves from its first position to its second position under the action of the return spring 84. In this second position, the slide 80 has a first main supply inlet 83b connected to the main pipe 50 via the third main pipe portion 54, and a second service brake output 83c in fluid communication with the first main supply inlet 83b and connected to the fourth main pipe portion 55. The second chamber 83 of the slide 80 also has a second main inlet blocked 83a. None of the inputs and outputs of the second chamber 83 of the drawer 80 is connected. The main pipe 50 feeds each of the second, third and fourth main pipe portions 53 to 55 so as to supply the main and intermediate service brake pressure chambers 11 and 21; respectively directly and via the second chamber 83 10 of the spool 80 of the distributor 65. The fluid under the first predetermined pressure thus conveyed into the main chambers and intermediate service brake pressure chambers 11 and 21, allows to supercharging the service brake 6. The supply of the main and auxiliary service brake pressure chambers 11 and 21 respectively displaces the main piston and the intermediate brake piston 10 and 20 to further discard the bearing thrust bearing 16 and further away the joints 39 and 40 of the brake linkage 4. This distance is representative of a predetermined force 20 applied by the main brake piston 10 on the stop 30, which force generates a second predetermined force greater than the first effort predetermined on the brake disc 31 via the pads 33. This second predetermined effort Iné is here a function of the section of each of the braking pistons 10 and 20 and the pressure of the injected fluid 25 while the first force previously applied (FIG. 8) depends solely on the section of the main braking piston 10. This second predetermined force is for example between about 60 kN and 90 kN, for a first predetermined pressure equal to about 3.8 bars. In non-illustrated variants: - the intermediate braking piston is integrally mounted around the rod (notched or not toothed), which therefore passes through the intermediate braking piston and extends to the main brake piston, to which it is solidly connected by its second side; the distributors are not controlled pneumatically but rather electrically or hydraulically; - The distributor 64 is here controlled in reverse control, that is to say that in the absence of a signal, the parking brake is triggered (direct control); but it can be controlled in direct control, that is to say that in the presence of a signal, the parking brake is triggered (reverse driving); in the reset configuration of the rail braking system, the resetting operation is performed electrically or mechanically or hydraulically rather than pneumatically; in the unlocking configuration of the rail braking system, the unlocking part is held in an unlocking position of the parking brake by a pneumatic or electric or mechanical lock; - In the release configuration of the rail braking system, the unlocking control is performed manually by the use of at least one cable, or pneumatically or electrically or hydraulically; The unlocking configuration of the rail braking system is obtained by supplying the parking brake pressure chamber, as for the rearming configuration rather than by actuating an unlocking part; at least one of the service brake pressure chambers may be voluntarily drained rather than leaked from the system; the main and intermediate service brake pressure chambers here have similar internal diameters, but the intermediate chamber may have an internal diameter smaller or greater than that of the main chamber, so as to provide different forces at a pressure of 30.degree. similar diet; In the lock configuration, the actuation of the locking device can be effected by an electric actuator rather than by pressurizing a pressure chamber supplied via a distributor; the distributor which is configured to supply the intermediate service brake pressure chamber is not pneumatically controlled by a secondary portion of pipe which extends another secondary portion of pipe connected to the distributor configured to supply the parking brake chamber; but rather by an independent pneumatic pipe; The rail braking system does not have a regulator at the outlet of the auxiliary tank and / or does not have an auxiliary reservoir and / or the first and second sources of pneumatic pressure medium are completely distinct rather than coming from one main pipe; - The rail braking system comprises a service brake without corner piece attached to the main brake piston, so that the main piston acts directly on the push rod, which acts on the deformable levers; and in this case, the main brake piston together with its toothed rod and the thrust rod are movable in the second axial direction while the parking brake is configured so that the locking pin and the holding piston are movable in the first axial direction; the distributor disposed in the pneumatic circuit called the first source of pneumatic pressure agent is not configured to supply, at the outlet of this distributor, the intermediate chamber of service brake pressure, but is rather configured to supply, as output of this distributor, the main service brake pressure chamber; - the wedge piece is not mounted on the first side of the main piston and the rod, notched or not, is not mounted on the second side of the intermediate piston, but the corner piece is mounted on the first side of the intermediate piston and the rod is mounted on the second side of the main piston and, optionally, the locking finger (in the case of a parking brake system as described above) is configured to come blocked the rod in the main service brake pressure chamber; - The rail braking system has a braking linkage different from that illustrated in the figures, in particular, the braking linkage comprises a sole configured to act directly on a wheel of the railway vehicle, this sole being directly articulated by a hinge of the type. pivot fixed to the push rod, a rigid lever fixed to the body of the system and a deformable lever attached to both the rigid lever and the hinge on the sole; and / or - the rail braking system has a brake linkage configured to act on a shoe brake as described above and is provided with a service brake with or without a corner piece attached to the brake piston. It is recalled more generally that the invention is not limited to the examples described and shown.

Claims (15)

REVENDICATIONS1. Railway braking system for a rail vehicle with brakes having at least one lining or at least one sole (5), comprising: - a body (2); - A braking link (4) configured to act on at least one said brake to at least one lining or at least one sole (5); and - a service brake (6) comprising a main braking piston (10) movable relative to said body (2) to act on said braking link (4) and delimiting with said body (2) a main pressure chamber a service brake (11) configured to be powered by a main source of pneumatic pressure medium (50, 52, 53) for bringing said main brake piston (10) into a first service braking position; said rail braking system (1) being characterized in that said service brake (6) further comprises an intermediate braking piston (20) fixedly secured to said main braking piston (10) movable relative to said body (2) for acting on said brake linkage (4) and defining with said body (2) an intermediate service brake pressure chamber (21), distinct from said main service brake pressure chamber (11), and configured to be powered by an intermediate source of pneumatic pressure medium (50, 52, 54, 55) for placing said intermediate braking piston (20) in a second service braking position; with said rail braking system (1) being configured so that when said main brake piston (10) is in its first service braking position, said intermediate service brake pressure chamber (21) is powered by said an intermediate source of pneumatic pressure medium (50, 52, 54, 55) for moving both said intermediate brake piston (20) and said main brake piston (10) in said second service brake position; in order to apply a braking force to said wheelhouse (4) greater than the braking force applied when said main brake piston (10) is in said first service braking position. 2. System according to claim 1, characterized in that said intermediate service brake pressure chamber (21) is adjacent to said main service brake pressure chamber (11) and separated from the latter by a separation wall ( 27) formed in said body (2), said main brake piston (10) has a first side (12) configured to act on said brake linkage (4) and a second side (13) opposite said first side (12). and facing said main service brake pressure chamber (11) and said intermediate service brake pressure chamber (21); and said intermediate piston (20) has a first side (22) of which extends an extension fixedly secured to said main brake piston (10) so as to act on the latter and a second side (23) opposite said first side (12) and turned towards said intermediate service brake pressure chamber (21). 3. System according to one of claims 1 and 2, characterized in that said main and intermediate sources of pneumatic pressure agent are formed by a single first source of pneumatic pressure agent configured to supply said main chamber and intermediate service brake pressure (11, 21) by a plurality of predetermined main driving portions (52 to 55). 4. System according to any one of claims 1 to 3, characterized in that it comprises at least a first pneumatic distribution device (65) configured to be powered by said intermediate source of pneumatic pressure agent and to be connected to said intermediate service brake pressure chamber (21) for placing said intermediate braking piston (20) in its second service braking position when powered by said intermediate source of pneumatic pressure medium. 5. System according to any one of claims 1 to 4, characterized in that it further comprises a parking brake (7) configured to act on at least one of said main brake piston (10) and said intermediate braking piston (20) of said service brake (6) and having a working configuration and a rest configuration; said parking brake (7) comprising: - a locking device (42) movable relative to said body (2) and having a first position and a second position in which said blocking device (42) is configured to immobilize at least one of said main braking piston (10) and said intermediate braking piston (20) in the service braking position, said parking brake (7) then being in working configuration; and - a control device (43, 47) movable with respect to said body (2), delimiting therewith a parking brake pressure chamber (44) configured to be fed by a second source of pneumatic pressure medium ( 56, 57, 58, 59, 61), and assuming a stable position in which said controller (43, 47) is configured to maintain said lock (42) in its second position; with said rail braking system (1) which is configured so that when said control device (43, 47) is in its stable position, said intermediate service brake pressure chamber (21) is fed by said intermediate source of pneumatic pressure agent (52, 54, 55), in order to apply, when said parking brake (7) is in working configuration, a greater braking force than the braking force applied when said main piston braking circuit (10) is in its first service braking position and said parking brake (7) is in its rest configuration. 25 6. System according to claim 5, characterized in that it comprises at least a second pneumatic distribution device (64) configured to be fed by said second source of pneumatic pressure agent and to be connected to said pressure chamber of parking brake (44) for placing said parking brake (7) respectively in its rest configuration when powered by said second source of pneumatic pressure medium and in its work configuration when not in use. not powered by said second source of pneumatic pressure agent. 302 72 70 40 7. System according to claims 4 and 6, characterized in that said at least one first pneumatic distribution device (64) comprises an actuator (81) configured to be pneumatically controlled by at least a pipe portion (59, 60) of said system (1) connected at the output of said at least one second pneumatic distribution device (64). 8. System according to one of claims 6 and 7, characterized in that said at least one first pneumatic distribution device (65) and / or said at least one second pneumatic distribution device (64) are formed by a distributor provided three orifices (72a-c, 73a-c, 82a-c, 83a-c) and a two-position slide (70, 80). 9. System according to claim 8, characterized in that said drawer (80) with two positions of said at least one first pneumatic distribution device (65) has, in a first position, a first blocked main entrance (82b) configured to be connected to said pneumatic pressure medium intermediate source via a third main pipe portion (54) and a first main pipe portion (52), a first service brake outlet (82c) configured to be connected to said intermediate service brake pressure chamber (21) via a fourth main pipe portion (55) and a first main exhaust outlet (82a) in fluid communication with said first service brake outlet (82c) opening into the atmosphere; and in a second position, a first main supply inlet (83b) configured to be connected to said pneumatic pressure medium intermediate source through said first and third main pipe portions (52, 54), a second service brake output (83c) in fluid communication with said first main supply inlet (83b) and configured to be connected to said fourth main driving portion (55) and a second main blocked entrance (83a). 30 10. System according to one of claims 8 and 9, characterized in that said slide (70) at two positions of said at least one second pneumatic distribution device (64) has, in a first position, a first secondary supply inlet (72b) configured to be connected to said second source of pneumatic pressure medium through a third pipe sub-portion (58), a pressure regulator (63) and a second secondary portion of conduit (57), a first parking brake output (72c) in fluid communication with said first secondary supply inlet (72b) and configured to be connected to said parking brake pressure chamber (44) via a fourth secondary pipe portion (59) and a sixth pipe minor portion (61) and a second blocked secondary inlet (72a); and in a second position, a second parking brake output (73c) configured to be connected to said parking brake pressure chamber (44) through said fourth and sixth conduit minor portions (59, 61), a first secondary exhaust outlet (73a) in fluid communication with said second parking brake output (73c) and opening into the atmosphere and a third blocked secondary inlet (73b) configured to be connected to said second source of agent pneumatic pressure through a third line portion (58), a pressure regulator (63) and a second line portion (57). 11. System according to claims 2 and 5, characterized in that it comprises a toothed rod (31) projecting from said second side (23) of said intermediate braking piston (20), said parking brake (7) is disposed in said body (2), said locking device is formed by a locking pin (42) and said control device is formed by a holding piston (43) movable relative to said body (2) and delimiting with said body (2 ) said parking brake pressure chamber (44) and a spring element (47) disposed in said body (2) and configured to act on said holding piston (43); with said holding piston (23) being configured to hold said locking pin (42) in its first position when said parking brake pressure chamber (44) is energized and under pressure, first position in which said blocking finger (42) is spaced from said toothed shaft (31); and with said spring member (47) being configured to hold said locking finger (42) in its second position when said parking brake pressure chamber (44) is drained, second position in which said blocking finger (42) immobilizes said piston rod (31). 12. A method of braking a railway vehicle comprising a rail braking system (1) according to any one of claims 1 to 11, comprising: - the step of supplying the main chamber of the service brake pressure (11 ) of said system (1) with a first source of pneumatic pressure medium for moving the main service brake piston (10) into a first service braking position so as to apply to a braking link (4) of said system (1) a first braking force; the step of supplying the intermediate service brake pressure chamber (21) of said system (1) with said first source of pneumatic pressure medium to move the intermediate service brake piston (20) into a second service braking position so as to apply on said braking linkage (4) of said system (1) a second braking force greater than said first braking force. 13. The method of claim 12, characterized in that said rail braking system (1) comprises a parking brake according to claim 5, said method comprising, before said step of supplying the main chamber of service brake pressure ( 11), the step of supplying the parking brake pressure chamber (44) of said system (1) with a second source of pneumatic pressure medium to move the control device (43, 47) of said system (1 ) to act on the locking device (42) of said system (1) until the latter leaves at least one of said main braking piston (10) and said intermediate braking piston (20) of said system (1), the parking brake (7) of said system (1) then being in the rest configuration. 14. The method of claim 13, comprising, after said step of supplying the main service brake pressure chamber (11) and before said step of supplying the intermediate service brake pressure chamber (21), the a step of controlling the emptying of the parking brake pressure chamber (44) to move said locking device (42) until the latter comes to immobilize at least one of said main braking piston (10) and said intermediate piston of braking (20) in a service braking position, said parking brake (7) then being in working configuration. 15. The method of claim 14, comprising, after said step said step of supplying the intermediate chamber of service brake pressure (21), the step of controlling the emptying of said main and intermediate chambers of service brake pressure ( 11, 21) and, optionally, the step of unlocking said locking pin (42) of said parking brake (7) so as to leave at least one of said main braking piston (10) and said intermediate braking piston ( 20).