Patent Publication Number: US-10780873-B2

Title: Rail vehicle braking system and braking method for a rail vehicle comprising such a system

Description:
FIELD OF THE INVENTION 
     The invention concerns the field of rail vehicle brakes. 
     It more particularly concerns the rail vehicle braking systems provided with a service brake and with a parking brake configured to act on a braking linkage. 
     It also concerns the braking methods for rail vehicles comprising such braking systems. 
     TECHNOLOGICAL BACKGROUND 
     Rail vehicles are generally equipped with service brake cylinders comprising a piston movable under the effect of a fluid under pressure, the movement of that piston driving a braking action such as the clamping of a disk brake between two linings, or the direct pressure of a block against a vehicle wheel. 
     These brake cylinders also generally comprise a parking or emergency actuator which is actuated in case of pressure loss of the fluid under pressure and/or in case of intentional venting (or draining) or leakage of the pneumatic system. This actuator, also termed parking brake, makes it possible to provide braking by virtue of the load of one or more springs substituting for the load of the fluid. Once this parking brake has been activated, the brake remains continuously engaged. 
     A rail vehicle braking system is known from European patent application EP 2 154 040 which is provided with a parking brake actuator coupled to a rail service brake cylinder. This brake cylinder comprises a body and a piston which is movable relative to the body to act on the braking linkage via a thrust rod. 
     The brake cylinder also comprises a pressure chamber delimited by the piston and by the body and which is connected by a pipe to a source of pneumatic pressure agent to put the piston into a service braking position. 
     The parking brake comprises a body which is distinct from the brake cylinder body. The body of the parking brake has an opening facing the piston of the service brake cylinder, which opening slidingly receives a thrust sleeve fitting into that opening in a fluid-tight manner. 
     The parking brake also comprises a piston movably mounted in a cylinder attached to the body and delimiting with that body a parking brake pressure chamber. This parking brake pressure chamber is connected to another source of pneumatic pressure agent via a pipe. The piston comprises at its center an aperture passed through by the thrust sleeve. 
     The parking brake further comprises one or more springs which continuously bias the piston of that parking brake towards a position referred to as low in which the parking brake is considered as being in a working configuration. 
     To actuate the parking brake when the piston of the service brake cylinder is in service braking position, the pressure chamber of the parking brake (filled in advance with the pneumatic pressure agent) is vented and the spring or springs of the parking brake then act on the piston of the parking brake, which drives the sleeve until the latter comes to bear against the piston of the service brake cylinder. 
     The pressure chamber of the service brake cylinder may then be vented since the parking brake has been actuated. 
     The load applied by the parking brake on the service brake piston is directly related to the load produced by the springs. This load naturally depends on the stiffness and the extension of those springs. 
     With this braking system, the force applied on the braking linkage by the piston of the service brake cylinder when the parking brake has been actuated and the service brake cylinder has been vented is often less than the force applied by that same piston when it is in service braking position. 
     SUBJECT OF THE INVENTION 
     The invention concerns a rail vehicle braking system, having improved performance relative to the braking systems of the above-mentioned prior art, while being simple, convenient and economic. 
     According to a first aspect, the invention is thus directed to a rail vehicle braking system having brakes with at least one lining or at least one block, comprising a body, a braking linkage configured to act on at least one said brake, a service brake comprising a braking piston movable relative to said body to act on said braking linkage and delimiting with said body a service brake pressure chamber configured to be supplied by a first source of pneumatic pressure agent to place said braking piston in a service braking position, as well as a parking brake configured to act on said braking piston of said service brake and having a working configuration and a resting configuration;
     said parking brake comprising a blocking device movable relative to said body to act on said braking piston and having a first position and a second position in which said blocking device is configured to immobilize said braking piston in service braking position, said parking brake then being in working configuration, and a control device movable relative to said body and having a locking position in which said control device is configured to hold said blocking device in its second position;   said rail vehicle braking system being configured to supply the service brake pressure chamber with another pneumatic pressure agent of which the pressure is determined, so as to apply a determined braking force when said parking brake is in working configuration; and   said rail vehicle braking system further comprising a detection and memorization device configured to receive a first information item representing the position of the blocking device, receive a second information item representing the supply of the service brake pressure chamber by the other pneumatic pressure agent, deduce from said first and second information items representing an information item representing the application of the parking brake, and memorize said deduced representing information item; whereby said information item representing the application of the parking brake is kept even if the service brake pressure chamber is no longer supplied by the other pneumatic pressure agent.   

     In the braking system according to the invention, the braking piston is immobilized in service braking position by the parking brake and in particular by its blocking device. This means that the braking piston may be immobilized in any position, which position is linked to the travel which that piston has travelled and that travel depends on the force applied in the service braking phase. 
     By the term immobilize is meant the fact that the force applied by the braking piston on the braking linkage in the working configuration of the parking brake does not reduce, or almost not. 
     A certain loss is however accepted linked to the retraction of the braking piston, in particular on the slight movement of the piston relative to the blocking device, at the time the service brake pressure chamber is vented. This loss is controlled and is defined by a very slight reduction in the force applied which is due in particular to the manufacturing tolerances both of the blocking device and of the braking piston. This reduction in the force applied on the braking linkage is here called losses on retraction. An acceptable value for these losses on retraction is at maximum of the order of 10% to 15% of the force applied by the service brake at the time the parking brake is actuated to be in working configuration. 
     The configuration of the braking piston and of the parking brake makes it possible in particular to dispense with the spring or springs of the known braking systems described above which make it possible to apply the parking brake force on the braking linkage via the service brake cylinder piston. Thus, for the same force applied on the braking linkage when the parking brake is in working configuration, the braking system according to the invention is more compact than the aforementioned braking systems of the prior art, and also lighter. 
     It should be noted that the braking linkage advantageously has deformable arms of which the elasticity may substitute for that of the springs of the known braking systems described above. 
     It should be noted that the configuration of the parking brake is chosen such that the load applied directly by the blocking device to immobilize the braking piston is not generally greater than the load applied by the springs on the piston of the aforementioned braking systems of the prior art; while the force applied on the braking linkage when the parking brake of the system according to the invention is in working configuration is preferably at least equal to or even greater than that procured by the aforementioned braking systems of the prior art. 
     The braking system according to the invention may furthermore make it possible to momentarily supply the service brake pressure chamber with the other pneumatic pressure agent in order to increase the braking force applied to the braking linkage by the service brake piston. The braking force applied to the braking linkage when the parking brake is in its working configuration is therefore increased further by it. 
     The system according to the invention may thus make it possible to obtain braking forces in particular parking brake braking forces greater than those obtained with the aforementioned braking systems of the prior art, simply, conveniently and economically, while affording particularly good safety provision. 
     What is more, detecting the position of the blocking finger makes it possible to give an information item relative to the state of immobilization or non-immobilization of the service braking piston; whereas detecting a pressure value in the service brake pressure chamber arising from the other pressure agent (below called third pneumatic pressure agent), which differs from the first pressure agent, makes it possible to know that service braking has not been applied. 
     The correlation between the representing information items detected makes it possible to deduce simply and conveniently the state of the parking brake and in particular to ensure that the parking brake is applied at a time t. 
     The memorization of the deduced representing information item furthermore makes it possible to ensure, at a time t+1, that the parking brake has indeed been applied at the time t. 
     This memorization function is particularly convenient for example when the user (driver) of the rail vehicle takes this again several hours or days after its immobilization. The natural leakages of the system do not enable it to be ensured that the service brake pressure chamber remains supplied by the other pressure agent and that chamber may even be vented (without deliberate action). That being the case, the information item representing the supply of this chamber may have disappeared. The memorization of the information item deduced as to the fact that the parking brake has indeed been applied makes it possible to supply a reliable indication to the user. 
     It will moreover be noted that the first pneumatic pressure agent generally makes it possible to supply the service brake pressure chamber when the parking brake is not in working configuration, to apply a service braking force, in accordance with a service brake setting. This same first pneumatic pressure agent may also make it possible to supply the service brake pressure chamber when the parking brake is not in working configuration, to apply an emergency braking force rather than a service braking force, in accordance with an emergency brake setting. It may be considered here that the emergency brake force is a service brake force which is modified by an emergency parameter. 
     According to preferred, simple, convenient and economical features of the system according to the invention:
         said control device delimits with said body a parking brake pressure chamber configured to be supplied by a second pneumatic pressure agent, and having a locking position in which said control device is configured to keep said blocking device in its second position; and said first representing information item is a pressure value of said second pneumatic pressure agent taken in a parking brake pipe supplying said parking brake pressure chamber;   said rail vehicle braking system comprises a dedicated first pneumatic distribution device connected to a source of supply of pneumatic pressure agents and connected to said parking brake pressure chamber in order to supply it with said second pneumatic pressure agent or vent it to place said parking brake respectively in its resting and working configurations, as well as a dedicated second pneumatic distribution device connected to said source of supply of pneumatic pressure agents and connected to said service brake pressure chamber in order to supply it with the other, referred to as third, pneumatic pressure agent of which the pressure value is determined, so as to apply a determined braking force when said parking brake is in working configuration; said first and dedicated second pneumatic distribution devices being configured to be controlled by at least one control signal.   said detection and memorization device comprises a body, a detection piston movably mounted in the body and defining with that latter a first detection chamber and a second detection chamber distinct from the first detection chamber, an elastic return member disposed in the second detection chamber and configured to act on the detection piston, what is referred to as a memory member moveably mounted also in the body, defining with the latter a locking chamber in fluidic communication with the second detection chamber, and being configured to act on the detection piston via a return spring, so as to keep that detection piston in a predetermined position;   the body comprises a first detection aperture opening into the first detection chamber and communicating with a first detection pipe connected to a pipe supplying the service brake pressure chamber; the first detection chamber being configured to be supplied, via the first detection pipe, by the other, referred to as third, pneumatic pressure agent when it supplies the service brake pressure chamber and to be vented when it does not supply the service brake pressure chamber;   the body comprises a second detection aperture opening into the second detection chamber and communicating with a second detection pipe connected to a pipe supplying the parking brake pressure chamber; the second detection chamber being configured to be supplied, via the second detection pipe, by second pneumatic pressure agent when it supplies the parking brake pressure chamber and to be vented when it does not supply the parking brake pressure chamber;   said detection and memorization device further comprises an indication unit with several indicator lights and having a supply signal, a switch and a return spring cooperating with the switch; and said detection and memorization device is configured such that the movement of the memory member in the body makes it possible to act on the switch against the return spring to supply one of the indicator lights;   said detection and memorization device is configured such that, when the parking brake pressure chamber is vented, the second detection chamber and the locking chamber are not supplied, the detection piston is acted upon by the elastic return member, the memory member is acted upon by the return spring, as regards the first detection chamber, this is supplied by the other, so-called third, pneumatic pressure agent and acts upon the detection piston against the return member; so as to place the detection piston in a first state in which the memory member comes to hold it in position;   said detection and memorization device is configured such that, when the parking brake pressure chamber is supplied, the second detection chamber and the locking chamber are supplied, the detection piston is acted upon by the elastic return member and also by the second pneumatic pressure agent, the memory member is moved against the return spring, as regards the first detection chamber, this is not supplied by the third pneumatic pressure agent; such that the detection piston is therefore in a second state in which the memory member does not act on the latter;   the detection piston has a groove formed on the periphery of the detection piston, located towards the second detection chamber, and the memory member is housed in a cavity of the body and is provided with an end head configured to come into engagement in the groove provided on the detection piston when the latter is in a first state in which the memory member comes to keep it in position;   the detection piston furthermore has a rib formed on the periphery of the detection piston, located towards the second detection chamber, and the body is provided with a shoulder against which said rib is configured to come into engagement, when the detection piston is in a second state in which the memory member does not act on the latter;   the detection piston is brought into its second state by a first force equal to the sum of the loads applied by the second pressure agent and by the return member; i.e. respectively approximately the parking brake pressure value multiplied by the surface area of the detection piston on which acts that parking brake pressure, added to the load applied by the return member;   the detection piston is brought into its first state by a second force equal here to approximately the pressure value of the other, referred to as third, pneumatic pressure agent, multiplied by the surface area of the detection piston on which that other agent acts, at the location of a free end of the detection piston;   the second force is greater than the load applied by the return member such that, in the first state of the detection piston, its rib is at a distance from the shoulder of the body and its groove is aligned with and facing the end head of the memory member;   the detection piston is subjected, at a free end, to the second force and remotely opposite its free end, to the first force; and the detection and memorization device is configured here such that the first force is greater than the second force;   said detection and memorization device comprises a first controller configured to receive said first representing information item and a second controller configured to receive said second representing information item;   said detection and memorization device further comprises two conditional management members each provided with a switch, with a return member cooperating with the respective switch and each receiving a supply signal, a first of the two conditional management members being connected by a first section of pipe to a pipe supplying the parking brake pressure chamber, and is also connected by a second section of pipe to both the first controller and to the second controller, and a second of the two conditional management members is connected by a third section of pipe to a pipe supplying the service brake pressure chamber and is also connected by a fourth section of pipe to the second controller.   said actuator is configured to receive a setting for parking brake application by a dedicated first control line; whereas the actuator is configured to receive a parking brake application setting by a dedicated second control line; the first controller is configured to electrically supply or not supply an indicator light by virtue of an electricity supply source, and the second controller is interposed on the first control line, configured to cause the parking brake application setting to be conveyed or not conveyed to the actuator, and configured to electrically supply or not supply an indicator light by virtue of an electricity supply source;   the first controller comprises a first electric coil connected to the second section of pipe, a first switch configured to be actuated to a working position by the first electric coil when it is powered, and a return spring configured to return the switch to a resting position when the first electric coil is not powered; and the second controller comprising a second electric coil connected to the fourth section of pipe, a third electric coil connected to the second section of pipe, as well as a second switch and a third switch mechanically connected to the second switch by an interface; the second and third switches being configured to be actuated together to a working position by the second electric coil when it is powered and the third electric coil is not powered, and to a resting position by the third electric coil when it is powered and the second electric coil is not powered;   the first distribution device is controlled to enable the parking brake pressure chamber to be vented, the switch of the first of the two conditional management members does not establish an electrical path between the supply and the second section of pipe and does not power the first and third electric coils, the first switch of the first controller is not acted upon by the first coil and does not establish an electrical path between the supply and the indicator light which is off, the second distribution device enables the service brake pressure chamber to be supplied with the third pneumatic pressure agent, the switch of the second of the two conditional management members establishes an electrical path between the supply and the fourth section of pipe and powers the second electric coil, the second and third switches are actuated into their working position by the second coil, thus establishing an electrical path between the supply and the indicator light which is on; so as to indicate that the parking brake is applied; and/or   the first distribution device is controlled to enable the parking brake pressure chamber to be supplied, the switch of the first of the two conditional management members establishes an electrical path between the supply and the second section of pipe and powers the first and third electric coils, the first switch is acted upon by the first coil and establishes an electrical path between the supply and the indicator light which is on, the switch of the second of the two conditional management members does not establish an electrical path between the supply and the fourth section of pipe and thus does not power the second electric coil, the second and third switches are actuated into their resting position by the third coil, cutting the electrical path between the supply and the indicator light which is off and authorizing the parking brake signal to pass to the actuator of the second distribution device.       

     According to a second aspect, the invention also relates to a method of braking a rail vehicle, comprising a rail vehicle braking system as described above, comprising:
         the step of receiving an information item representing the position of the blocking finger;   the step of receiving an information item representing the supply by another pneumatic pressure agent of the service brake pressure chamber;   the step of deducing said received representing information items, an information item representing the application of the parking brake; and   the step of memorizing said deduced representing information item.       

     The method according to the invention is particularly simple and convenient to implement, while also being particularly safe. 
     According to preferred, simple, convenient and economical features of the method according to the invention, it comprises in advance, simultaneously or successively whatever the order is, the steps of controlling the movement of the blocking finger into its second position so as to place the parking brake in its working configuration and to control the supply of the service brake pressure chamber with the other pneumatic pressure agent so as to apply a determined braking force. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure of the invention will now be continued with the description of embodiments, given below by way of non-limiting illustration, with reference to the accompanying drawings, in which: 
         FIG. 1  diagrammatically and partially illustrates a rail vehicle braking system in accordance with a first embodiment of the invention, which system is provided in particular with a service brake, with a parking brake and with a control and actuation unit; 
         FIG. 2  diagrammatically represents in more detail the control and actuation unit illustrated in  FIG. 1  and a conveyance network of pipes of the system which is connected to that unit, which unit is in particular provided with first and second pneumatic distribution devices connected to the parking brake and with a device for detection and memorization of the application of the parking brake; 
         FIGS. 3 and 4  are similar to  FIG. 2 , the device for detection and memorization of the application of the parking brake being shown diagrammatically and in accordance with a first embodiment, respectively in a first state and in a second state; 
         FIGS. 5 to 8  represent in more detail the detection and memorization device illustrated in  FIGS. 3 and 4 , in different configurations according to a first operating sequence; 
         FIGS. 9 and 10  represent variants of configurations replacing the configurations of  FIGS. 6 and 7 , to illustrate a second operating sequence of the detection and memorization device illustrated in  FIGS. 3 and 4 ; 
         FIGS. 11 and 12  represent a first variant embodiment of the detection and memorization device illustrated in  FIGS. 3 and 4 ; 
         FIGS. 13 and 14  represent a second variant embodiment of the detection and memorization device illustrated in  FIGS. 3 and 4 ; and 
         FIGS. 15 and 16  are similar views to those of  FIGS. 3 and 4 , showing a device for detection and memorization of the application of the parking brake in accordance with a second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF AN EMBODIMENT 
       FIG. 1  diagrammatically represents a rail vehicle braking system  1  for a rail vehicle with a brake having linings or blocks. 
     The rail vehicle braking system  1  comprises a body  2  here forming a cylinder of a service brake  6  and a parking brake  7 , a control and actuation unit  3  configured to manage the operation of the service brake  6  and of the parking brake  7 , a conveyance network of pneumatic pipes that is connected to the body  2  and to the control and actuation unit  3 , a braking linkage  4  mechanically linked to the body  2  as well as a brake  5  with linings on which the braking linkage  4  is configured to act. 
     The body  2  here has the form of a generally closed envelope. 
     The service brake  6  comprises a service brake piston  8  movable relative to the body  2  in a first axial direction, and a thrust rod  9  also movable relative to the body  2  in a second axial direction perpendicular to the first axial direction. 
     Together with the body  2  the braking piston  8  delimits a service brake pressure chamber  13 . 
     The braking piston  8  has two sides respectively a first side  17  configured to act on the braking linkage  4  via the thrust rod  9  and a second side  18  which is an opposite side to the first side  17  and which is turned towards the service brake pressure chamber  13 . 
     The service brake  6  further comprises a notched rod  21  fastened to the second side  18  of the braking piston  8 . This notched rod  21  extends longitudinally in the first axial direction. 
     The braking piston  8  is configured to move in the body  2  while maintaining the service brake pressure chamber  13  relatively fluid-tight thanks to a membrane  14 , for example formed by a seal, disposed between that braking piston  8  and inside edges of the body  2 . 
     The service brake  6  further comprises a wedge part  10  fastened to the first side  17  of the braking piston  8 . 
     This wedge part  10  has a triangular section and is configured to cooperate with a set of rolling bearing stops  11 , of which one of the rolling bearing stops is linked to the body  2  while the other of the rolling bearing stops is linked to the thrust rod  9 . 
     This thrust rod  9  is provided with a wear adjuster configured to compensate for the wear of the linings of the brake  5  in order to avoid reduction of the braking force by excessive play (further to wear of the linings). 
     The service brake  6  further comprises a spring  12  here disposed around the thrust rod  9 , between the rolling bearing stop which is linked to the latter and an inside edge of the body  2 . This spring  12  is configured to return the stop which is linked to the thrust rod  9  against the wedge part  10 . 
     The service brake  6  further comprises a first aperture  15  formed in the body  2  and configured to enable the movement of the thrust rod  9  through that first aperture  15 . 
     The service brake  6  further comprises a second aperture  16  formed in the body  2  and opening into the service brake pressure chamber  13 . 
     The service brake pressure chamber  13  is connected here by a first supply pipe  72  of the conveyance network of pneumatic pipes, more generally called brake pipe, connected at the location of that second aperture  16 , to a source of supply of pneumatic pressure agents  73  (visible in  FIG. 2 ). 
     The body  2  comprises a cavity  27  situated against the service brake pressure chamber  13  and in which is disposed the parking brake  7 . 
     The parking brake  7  comprises a blocking device here formed by a blocking finger  20  movable relative to the body  2  and extending in the second axial direction. 
     The parking brake  7  further comprises here a holding piston  23  movable relative to the body  2  and with the latter delimiting a parking brake pressure chamber  25 . 
     This holding piston  23  has two sides, respectively a first side  31  on which is attached the blocking finger  20  and which is turned towards the parking brake pressure chamber  25 , and a second side  32  which is an opposite side to the first side. 
     The parking brake  7  further comprises here a spring member  24  disposed between the body  2  and the second side  32  of the holding piston  23 . This spring member  24  is configured to act on that holding piston  23  and therefore on the blocking finger  20 . 
     It should be noted that the holding piston  23  and the spring member  24  here form a movable actuating device of the parking brake  7 . 
     The holding piston  23  is configured to move in the body  2  while maintaining the parking brake pressure chamber  25  relatively fluid-tight thanks to a membrane (not referenced) disposed between that holding piston  23  and the inside edges of the body  2 . 
     The parking brake  7  comprises a third aperture (not shown) formed in the body  2  and opening both into the parking brake pressure chamber  25  and into the service brake pressure chamber  13 , which third aperture is configured to enable the movement of the blocking finger  20  through that third aperture. 
     It should be noted that the relative sealing between the parking brake pressure chamber  25  and the service brake pressure chamber  13  is ensured by the presence of a seal  33  disposed at the interface between that third aperture and the blocking finger  20 . 
     The parking brake  7  further comprises a fourth aperture  28  formed in the body  2  and opening into the parking brake pressure chamber  25 . 
     This parking brake pressure chamber  25  is connected here by a second supply pipe  71  of the conveyance network of pneumatic pipes, also called parking brake pipe, which is connected at the location of that fourth aperture  28 , to the source of supply of pneumatic pressure agents  73  (visible in  FIG. 2 ) via the unit  3 . 
     The parking brake  7  further comprises an unlocking part  29  attached to the second side  32  of the holding piston  23  and opening outside the body  2  through a fifth aperture (not shown) formed in that body  2  and opening into the cavity  27 ; such that this unlocking part  29  is accessible to be manipulated from outside the body  2 , if required. 
     It will be noted that this unlocking part  29  may comprise a visual indicator, for example a colored bellows, so as to visibly indicate the state of this part  29 . 
     As a variant, the unlocking part  29  may be coupled to a visual indication system provided with a switch mechanically connected to that part  29  and having a first position and a second position (see below with reference to  FIGS. 3, 4 and 13 to 16 ). 
     The service brake  6  is disposed in the body  2  and is configured to act on the brake  5  via the braking linkage  4 . 
     This brake  5  comprises a brake disk  35  (here viewed from above) mounted for example on a rail vehicle axle  36 , or directly on the wheel to brake. 
     This brake  5  further comprises two shoes  37  each provided with a lining  38  configured to be applied in contact with the disk  35  to reduce its rotational speed and therefore that of the wheel to brake, as well as a fastening eye  39  provided at the remote opposite location to the surface of the lining  38  that is configured to be applied to the disk brake  35 . 
     The braking linkage  4  comprises two or four deformable levers  40  each provided with an upper portion and a lower portion which are attached to each other. Only two levers are illustrated here and, in the case of the linkage having four levers, they may be attached in pairs or as a variant be independent from each other. 
     Each portion of the levers  40  is jointed to a central connector  41  via two pivots  42 . 
     The lower portion of each deformable lever  40  is linked to one of the shoes  37  via its fastening eye  39 . 
     The upper portion of each deformable lever  40  is linked to a respective joint  44 ,  45 . 
     The braking linkage  4  receives the body  2  between the upper portions of the deformable levers  40 , at the location of the joints  44  and  45 . 
     The body  2  is rotatably mounted on the joint  44  which is attached to an end of the thrust rod  9  whereas it has a fixed mounting to the joint  45 , which is directly attached to that body  2 . 
     The braking linkage  4  also comprises a fastening lug  43  joined to the central connector  41  for the mounting of that braking linkage  4  on the rail vehicle; in order for the brake shoes  37  to be situated on respective opposite sides of the brake disk  35  (or of the wheel of the rail vehicle). 
     It should be noted that the coming towards each other of the joints  44  and  45  enables the shoes  37  to move apart from each other and that conversely, the separation of those joints  44  and  45  enables the shoes  37  to be to clamped onto the brake disk  35  (or onto the rail vehicle wheel). 
     The control and actuation unit  3  is connected to the service brake pressure chamber  13  via the first supply pipe  72  to which it is connected; while that unit  3  is also connected here to the parking brake pressure chamber  25  via the second supply pipe  71  to which it is connected. Furthermore, this unit  3  is supplied with pneumatic agents by a main pipe  70  which passes generally along the rail vehicle. 
     The control and actuation unit  3  comprises system members (not shown) which are configured to receive and process representational information relative to operational settings of the rail vehicle, by a first electrical and/or pneumatic and/or manual type channel, denoted  50  in  FIG. 1 . 
     These system members are furthermore configured to receive and process representational information relative to parameters of use of the rail vehicle, by a second channel of electrical and/or pneumatic and/or manual type, which is denoted  60  in  FIG. 1 . 
     These system members may for example be formed by pneumatic relays and/or solenoids and/or pressure switches and/or sensors and/or pressure reducing valves and/or electrical relays and/or electronic cards and/or central processing units or microprocessors, and/or random access memory components comprising registers adapted to record variables of the parameters created and modified during the execution of programs, and/or communication interfaces configured to send and receive data, and/or internal storage members, such as hard disks, able in particular to store the executable code of programs enabling the management of the service and parking brakes  6  and  7 . 
     It will be noted that in  FIG. 1 , the control and actuation unit  3  is associated with a braking linkage and with a single brake  5  of the rail vehicle. As a variant, such a control and actuation unit may be associated with an axle (not shown) of the rail vehicle, provided with a plurality of brakes  5 , or with a bogie (not shown) of the rail vehicle, provided with two axles, or for instance with a wagon (not shown) of the rail vehicle, provided with two bogies, or it is possible for the rail vehicle to comprise only one such control and actuation unit. 
       FIG. 2  diagrammatically represents in more detail the conveyance network of pneumatic pipes and the control and actuation unit  3 . 
     The main pipe  70  forms the channel for conveyance of a pneumatic agent distributed in the conveyance network of pneumatic pipes. The agent in this main pipe  70  is for example at a pressure value of approximately 9 bars. 
     The network may comprise what is referred to as a general pipe (not shown), distinct from the main pipe  70 , and generally extending in parallel thereto. The general pipe also enables pneumatic continuity to be ensured along the rail vehicle and may authorize the service braking of the vehicle, by directly using the fluid passing through the general pipe. As regards the main pipe  70 , this enables equipment particularly for example of the rail vehicle braking system to be supplied, and in particular the source of supply of pneumatic pressure agents  73  here formed by what is referred to as an auxiliary reservoir. 
     This network further comprises, as described in more detail below, a filling and distribution pipe  74  which is tapped onto (that is to say directly connected to) the main pipe  70 , a service brake pipe  75  connected by a tapping  81  onto the filling and distribution pipe  74 , an emergency brake pipe  76  tapped onto the service brake pipe  75  by a tapping  82 , as well as a control pipe  78  connected by a tapping  83  also onto the filling and distribution pipe  74 . 
     The control pipe  78  is subdivided into two pipes at the location of a branch tapping  84 , respectively into the parking brake pipe  71  directly communicating with the parking brake pressure chamber  25  and into an oversupply pipe, referred to hereinafter as preset pipe  79 . 
     Each service brake pipe  75 , emergency brake pipe  76  and preset pipe  79 , joins the brake pipe  72  which directly communicates with the service brake pressure chamber  13 . 
     The filling and distribution pipe  74  has a first filling section extending between the tapping (not shown) onto the main pipe  70  and the auxiliary reservoir  73 , as well as a second distribution section extending from a tapping  80  onto the first section. 
     The control and actuation unit  3  here comprises a one-way valve  85  disposed on the first section of the filling and distribution pipe  74  near the tapping of the latter onto the main pipe  70 , as well as an isolation tap  86  also disposed on that first section. 
     The non-return valve  85  enables the filling of the auxiliary reservoir  73  by the pneumatic pressure agent coming from the main pipe  70  and prohibits the venting of the reservoir  73  into the main pipe  70  if the pressure in the latter becomes less than that in the auxiliary reservoir  73 . 
     The control and actuation unit  3  further comprises here a relay device  93 , or pneumatic relay, supplied by the second distribution section of the filling and distribution pipe  74  and connected to the brake pipe  72 . 
     This relay device  93  is configured to generate, from that second distribution section and from template values of pressure, a pressure of use at a determined throughput for the filling of the service brake pressure chamber  13 . 
     These template values of pressure correspond here to service brake and emergency brake pressure settings and preset, respectively coming from the service brake pipe  75 , the emergency brake pipe  76  and from the preset pipe  79 . 
     The control and actuation unit  3  here further comprises, on the service brake pipe  75 , a pressure reducing valve  87  configured to limit the pressure value for example here to approximately 4 bars as well as a distribution device  88  here formed by a monostable solenoid valve and configured to receive a control signal corresponding to a service brake setting CFS. 
     When the setting value CFS is null, the distribution device  88  is configured to interrupt the service brake pipe  75 ; and when the setting value CFS is not null, the device  88  is configured to authorize the passage of a pneumatic pressure agent, called first pressure agent, to the relay device  93  which receives a service brake pressure template value and which generates a service brake pressure to supply the service brake pressure chamber  13  for the braking of the vehicle. 
     The control and actuation unit  3  further comprises a pressure sensor  90  connected to a tapping  89  onto the service brake pipe  75  and which makes it possible to control the service brake pressure template value. 
     The control and actuation unit  3  further comprises a venting solenoid valve  91  connected by the tapping  89  onto the service brake pipe  75  and which makes it possible to vent that pipe via a venting aperture  92  on that solenoid valve  91 . 
     The solenoid valve  91  is monostable and configured to receive a control signal corresponding to a work setting CT and to operate in reverse. 
     When the setting value CT is not null, the solenoid valve  91  is configured to interrupt the communication of the service brake pipe  75  with the venting aperture  92 ; and when the setting value CT is null, that solenoid valve  91  is configured to allow the communication of that pipe  75  with that venting aperture  92 . 
     The control and actuation unit  3  further comprises here, on the emergency brake pipe  76 , a distribution device  96  formed here by a monostable solenoid valve operating in reverse and configured to receive a control signal corresponding to an emergency brake setting CFU. 
     When the setting value CFU is not null, the distribution device  96  is configured to interrupt the emergency brake pipe  76 ; and when the setting value CFU is null, the device  96  is configured to authorize the passage of a pneumatic pressure agent to the relay device  93  which receives an emergency brake pressure template value and which generates an emergency brake pressure to supply the service brake pressure chamber  13  for the braking of the vehicle. 
     The control and actuation unit  3  further comprises a pressure limiter  95  (or pressure reducing valve) on the emergency brake pipe  76  upstream of the distribution device  96 , which limiter  95  is controlled according to a load parameter param_C of the vehicle received via a load pipe  77  connected to the limiter  95 ; and a pressure sensor  94  tapped onto the load pipe  77 . 
     The load parameter param_C is an information item representing the vehicle load and may for example concern a single wagon, or several successive wagons or the entirety of the rail vehicle. This depends on the number of braking systems in accordance with the invention and the strategy of brake actuation. 
     It will furthermore be noted that certain parameters of operation of certain rail vehicles may naturally (or initially) be dependent on the vehicle load for example to manage the service brake whereas others are not dependent on the vehicle load. 
     The control and actuation unit  3  comprises on the brake pipe  72 , a pressure switch  97  downstream of the relay device  93  and configured to check whether or not a pneumatic pressure agent, has a pressure value at least greater than a predetermined threshold value, in the brake pipe  72  and therefore whether there is a pressure in the service brake pressure chamber  13 . 
     The control and actuation unit  3  further comprises on the brake pipe  72  an anti-wheel-slide device  98  here formed by a monostable solenoid valve and configured to receive control signals which correspond to anti-wheel-slide parameters Param_AE of the vehicle; so as to ensure the effectiveness of the rail vehicle braking. 
     These anti-wheel-slide parameters Param_AE are information items representing the anti-wheel-slide or the wheel-slide of the vehicle and may for example correspond to the load of the vehicle, to its speed of locomotion as well as to the service and/or emergency brake template values. 
     The control and actuation unit  3  comprises on its control pipe  78  a pressure reducing valve  99  configured to limit the pressure value for example here to approximately 6 bars. 
     The control and actuation unit  3  comprises a dedicated first pneumatic distribution device  51  on its parking brake pipe  71  and a dedicated second pneumatic distribution device  61  on its preset pipe  79 . 
     The first pneumatic distribution device  51  is formed by a first distributor  52 , here monostable, also called solenoid valve, provided with a movable slide  53  with two positions, with a single inlet aperture  54  (denoted  54   a  or  54   b  in the drawings) connected to the control pipe  78 , with a single outlet aperture  55  (denoted  55   a  or  55   b  in the drawings) connected to the parking brake pipe  71 , and with an aperture  56  (denoted  56   a  or  56   b  in the drawings) opening into the atmosphere. 
     The first distributor  52  is furthermore provided with an actuator  57  configured to move the slide  53  from its first position to its second position according to a control signal received by that actuator  57 , and with a return member  58  configured to bring the respective slide  53  back from its second position to its first position without being acted upon by the actuator  57 . 
     The second pneumatic distribution device  61  is formed by a second distributor  62  which is monostable here, or solenoid valve, provided with a movable slide  63  which has two positions, with a single inlet aperture  64  (denoted  64   a  or  64   b  in the drawings) connected to the control pipe  78  via the preset pipe  79 , with a single outlet aperture  65  (denoted  65   a  or  65   b  in the drawings) connected to the brake pipe  72  via the preset pipe  79  and the relay device  93 , and with an aperture  66  (denoted  66   a  or  66   b  in the drawings) opening into the atmosphere. 
     The second distributor  62  is furthermore provided with an actuator  67  configured to move the slide  63  from its first position to its second position according to a control signal received by that actuator  67 , and with a return member  68  configured to bring the respective slide  63  back from its second position to its first position without being acted upon by the actuator  67 . 
     The control and actuation unit  3  further comprises a dedicated control device configured to control the first and second pneumatic distribution devices  51  and  61 . 
     This control device of the first and second pneumatic distribution devices here comprises a control line  46  directly linked to the actuators  57  and  67  of the first and second pneumatic distribution devices  51  and  61  and configured to convey a parking brake application setting CFP. 
     When the parking brake application setting CFP is null, this means that the parking brake  7  must be applied here ( FIGS. 2 and 3 ). This is what is referred to as a security application. 
     According to requirement, the first distributor  52  has a first so-called safety position by default in which its single outlet aperture  55   a  connected to the parking brake pressure chamber  25  via the parking brake pipe  71  communicates with its aperture opening into the atmosphere  56   a , whereas its single inlet aperture  54   a  connected to the auxiliary reservoir  73  via the control pipe  78  and the supply and distribution pipe  74  is obturated ( FIGS. 2 and 3 ). 
     The parking brake pressure chamber  25  is then vented and the blocking finger  20  comes to immobilize the rod  21  of the piston  8 . The parking brake is applied. 
     As regards the second distributor  62 , this has a first position by default which is also referred to as a safety position, in which its single outlet aperture  65   a  connected to the service brake pressure chamber  13  via the brake pipe  72  communicates with its single inlet aperture  64   a  connected to the auxiliary reservoir  73  via the control pipe  78  and the supply and distribution pipe  74 , whereas its aperture  66   a  to the atmosphere is obturated ( FIGS. 2 and 3 ). 
     The second distributor  62  thus authorizes the passage of a pneumatic pressure agent, referred to as third pressure agent, to the relay device  93  which receives a preset pressure template value and which generates a preset pressure to supply the service brake pressure chamber  13 . 
     To remove the application of the parking brake  7  ( FIG. 4 ), a non-null setting for application of the parking brake CFP passes in the control line  46  to the actuators  57  and  67  which move the slides  53  and  63  of the first and second distributors  52  d  62  against the return members  58  and  68 . 
     If required, the first distributor  52  has a second position in which its single outlet aperture  55   b  connected to the parking brake pressure chamber  25  via the parking brake pipe  71  communicates with its single inlet aperture  54   b  connected to the auxiliary reservoir  73  via the control pipe  78  and the supply and distribution pipe  74 , whereas its aperture opening into the atmosphere  56   b  is obturated ( FIG. 4 ). 
     The first distributor  52  thus authorizes the passage of a pneumatic pressure agent, referred to as second pressure agent, directly to the parking brake pressure chamber  25  via the parking brake pipe  71 . The blocking finger  20  is then withdrawn into that chamber and releases the rod  21  of the piston  8 . 
     As regards the second distributor  62 , this has a second position in which its single outlet aperture  65   b  is connected to its aperture  66   b  open to the atmosphere, whereas its single inlet aperture  64   b  connected to the auxiliary reservoir  73  via the control pipe  78  and the supply and distribution pipe  74  is obturated ( FIG. 4 ). 
     The second distributor  62  thus prohibits the passage of the third pneumatic pressure agent to the relay device  93  which thus does not receive the preset pressure template value and which vents the preset pressure if required. 
     The control and actuation unit  3  further comprises a dedicated detection and memorization device  100  configured for detecting the application of the parking brake  7  and for memorizing the information that the parking brake is applied, even when the brake pipe  72  and/or the preset pipe  79  no longer conveys a pneumatic pressure agent for example on account of natural leakages of the system  1 . 
     This detection and memorization device  100  for the application of the parking brake  7  is configured to receive an information item representing the supply of the service brake pressure chamber  13  by the third pneumatic pressure agent via the second distributor  62 , and to receive an information item representing the venting of the parking brake pressure chamber  25  via the first distributor  52 . 
     This detection and memorization device  100  may be configured to retrieve these information items directly from the parking brake pipe  71  and/or from the preset pipe  79 , after the second distributor  62 , and/or from the brake pipe  72 , between the service brake pressure chamber  13  and the anti-wheel-slide device  98  or between the latter and the relay device  93  (dashed lines in  FIG. 2 ). 
       FIGS. 3 and 4  represent in more detail the detection and memorization device  100 , according to a first embodiment. To simplify the drawings, the conveying and system members described hereinabove with reference to  FIG. 2 , in particular concerning the service brake, the emergency brake, the venting, the relaying and the anti-wheel-slide, are grouped together here in a sub-unit referenced  48  (this will also be the case in  FIGS. 11 and 16 ). 
     This detection and memorization device  100  comprises a body  102 , a detection piston  103  movably mounted in the body  102  and defining with the latter a first detection chamber  104  and a second detection chamber  106  distinct from the first detection chamber  104  and an elastic return member  105  disposed in the second detection chamber  106  and configured to act on the detection piston  103 . 
     The detection and memorization device  100  further comprises what is referred to as a memory member  112  movably mounted also in the body  102 , defining with the latter a locking chamber  114  (visible in  FIGS. 5 and 8 ) and being configured to act on the detection piston  103 , via a return spring  113 , so as to maintain that piston  103  in a predetermined position. 
     The locking chamber  114  is in fluidic communication with the second detection chamber  106 . 
     The body  102  comprises a first detection aperture  108  opening into the first detection chamber  104  and communicating with a first detection pipe  107  which is connected by a tapping  109  to the preset pipe  79 , here between the second distributor  62  and the relay device  93 . 
     The first detection chamber  104  is configured to be supplied, via the first detection pipe  107 , by the third pneumatic pressure agent passing in the preset pipe  79  when the second distributor  62  authorizes the passage of that pressure agent ( FIG. 3 ); whereas that chamber  104  is vented when the single outlet aperture  65   b  of the second distributor  62  communicates with its aperture  66   b  opening into the atmosphere ( FIG. 4 ). 
     The body  102  further comprises a second detection aperture  111  opening into the second detection chamber  106  and communicating with a second detection pipe  110  which is connected by a tapping  112  to the parking brake pipe  71 . 
     The second detection chamber  106  is configured to be supplied, via the second detection pipe  110 , by the second pneumatic pressure agent passing in the parking brake pipe  71  when the first distributor  52  authorizes the passage of that pressure agent ( FIG. 4 ); whereas that chamber  106  is vented when the single outlet aperture  55   b  of the first distributor  52  communicates with its aperture  56   b  opening into the atmosphere ( FIG. 3 ). 
     The detection and memorization device  100  further comprises an indication unit  116  having a supply signal  117 , a switch  118  and a return spring  121  cooperating with the switch  118 . This indication unit  116  is connected here to two indicator lights  119  and  120 , which are distinct. 
     The detection and memorization device  100  is configured such that the movement of the memory member  112  in the body makes it possible to act on the switch  118  against the return spring  121  to supply the indicator light  120 , which is thus on. Without the switch being acted upon, it is the indicator light  119  which is supplied and thus on. 
     In  FIG. 3 , the parking brake pressure chamber  25  is vented such that the parking brake  7  is applied. The second detection chamber  106  and the locking chamber  114  are not supplied such that the detection piston  103  is acted upon by the elastic return member  105  and the memory member  112  is acted upon by the return spring  113 . As regards the first detection chamber  104 , this is supplied by the third pneumatic pressure agent and acts on the detection piston  103  against the return member  105 ; so as to place the detection piston  103  in a first state in which the memory member  112  comes to hold it in position. The memory member  112  is then in a first position in which it does not act on the switch  118  and it is thus the indicator light  119  which is supplied and on; to indicate that the parking brake  7  is applied. 
     Holding the detection piston  103  in its first state makes it possible to memorize the information that the parking brake is applied, even when the brake pipe  72  and/or the preset pipe  79  no longer convey a pneumatic pressure agent for example on account of natural leakages of the system  1 . 
     In  FIG. 4 , the parking brake pressure chamber  25  is supplied such that the parking brake  7  is not applied. The second detection chamber  106  and the locking chamber  114  are supplied such that the detection piston  103  is acted upon by the elastic return member  105  and also by the second pneumatic pressure agent, and the memory member  112  is moved against the return spring  113 . As regards the first detection chamber  104 , this is not supplied by the third pneumatic pressure agent. The detection piston  103  is thus in a second state in which the memory member  112  does not act on the latter. The memory member  112  is in a second position in which it acts on the switch  118  and it is thus the indicator light  120  which is supplied and on; to indicate that the parking brake  7  is not applied. 
     It will be noted that the unlocking part  29  of the parking brake  7  is coupled here to the visual indication system provided with a switch  34  mechanically connected to that part  29 , with an electricity supply line (not shown) connected to the switch  34 , with an elastic return member (not shown) actuating the switch  34  into a first position, and with a transfer line  59  connected to the switch  34  and extending to a visual indicator such as an indicator light  69 . 
     For example, when the unlocking part  29  is not acted upon, the switch  34  is actuated by the return member into its first position in which no electrical path is established between the electricity supply line and the transfer line  59 , such that the indicator light  69  is not supplied and is thus off; whereas when the unlocking part  29  is acted upon, the switch  34  is moved against the return member from its first position to a second position, in which an electrical path is established between the electricity supply line and the transfer line  59 , such that the indicator light  69  is supplied and is thus on to indicate that the braking piston  8  is not held in position. Of course, the inverse operation is possible (the light would be on when the braking piston is held). 
       FIGS. 5 to 8  illustrate a first sequence making it possible to detect and memorize that the parking brake  7  has been applied. 
     In  FIGS. 5 to 8 , the memory member  112  and the indication unit  116  are housed in a cavity  190  of the body  102 . 
     The memory member  112  is provided with a seal  194  on a periphery to delimit with the body  102  the locking chamber  114  and with an end head  115  configured to come into engagement against the detection piston  103 . 
     The detection piston  103  has a seal  191  on a periphery to delimit, with the body, both the first detection chamber  104  and the second detection chamber  106 . 
     The detection piston  103  furthermore has a groove  193  as well as a rib  192  here adjacent to the groove  193  and each formed on the periphery of the detection piston  103 , located towards the second detection chamber  106 . 
     The groove  193  is configured to receive, in engagement therewith, the end head  115  of the memory member  112  when the latter is in its first position and the detection piston  103  is in its first state. 
     As regards the rib  192 , this is configured to come into engagement against a shoulder  196  provided in the body  102 , when the detection piston  103  is in its second state. 
     In  FIG. 5 , the second detection chamber  106  and the locking chamber  114  are supplied such that the detection piston  103  is acted upon both by the elastic return member  105  and also by the second pneumatic pressure agent, and the memory member  112  is moved against the return spring  113 . 
     As in  FIG. 4 , this means that the parking brake pressure chamber  25  is supplied. 
     As regards the first detection chamber  104 , this is on the contrary not supplied by the third pneumatic pressure agent. 
     The detection piston  103  is thus brought into its second state by a first force equal to the sum of the loads applied by the second pressure agent and by the return member  105 ; i.e. respectively approximately the parking brake pressure value multiplied by the surface area of the detection piston  103  on which acts that parking brake pressure, added to the load applied by the return member  105 . 
     In this second state of the piston  103 , the rib  192  of the piston is in engagement against the shoulder  196  of the body  102 , the end head  115  of the memory member  112  is at a distance from the piston  103  and this memory member  112  is in its second position in which it acts on the switch  118  of the indication unit  116 ; so as to indicate that the parking brake  7  is not applied. 
     In  FIG. 6 , the second detection chamber  106  and the locking chamber  114  are vented by the actuation of the first distributor  52 . 
     The detection piston  103  is solely acted upon under the load applied by the return member  105  and remains in its second state. 
     As regards the memory member  112 , this is acted upon by the return spring  113  and its end head  115  comes to be applied, in an intermediate position, on the periphery of the detection piston  103 . 
     In the second state of the detection piston  103 , its groove  193  is offset relative to the end head  115  of the memory member  112  and is not opposite thereto, such that the latter does not hold the detection piston  103  in position. 
     What is more, in the intermediate position of the memory member  112 , the latter continues to act on the switch  118  of the indication unit  116  to indicate that the parking brake  7  is not applied. 
     In  FIG. 7 , the first detection chamber  104  is supplied by the third pneumatic pressure agent by the actuation of the second distributor  62  and the detection piston  103  is acted on against the return member  105 . 
     As in  FIG. 3 , this means that the service brake pressure chamber  13  is supplied by the third pneumatic pressure agent. 
     On the contrary, the second detection chamber  106  and the locking chamber  114  remain vented. 
     The detection piston  103  is thus brought into its first state by a second force here equal to approximately the preset pressure value multiplied by the surface area of the piston  103  on which that preset pressure acts. 
     This second force is greater than the load applied by the return member  105  such that, in this first state of the piston  103 , its rib  192  is at a distance from the shoulder  196  of the body  102  and its groove  193  is aligned with and facing the end head  115  of the memory member  112 . 
     The memory member  112  is actuated by the return spring  113  into its first position, in which its end head  115  comes into engagement in the groove  193  of the piston  103  in order to keep the latter in position, in its first state. 
     In the first position of the memory member  112 , the latter no longer acts on the switch  118  of the indication unit  116 , which is moved to change the supply of the indicator light, in order to indicate that the parking brake  7  is henceforth applied. 
     In  FIG. 8 , the first detection chamber  104  is no longer supplied by the third pneumatic pressure agent, for example on account of natural leakages from the system  1  and here from the preset pipe  79 . 
     The detection piston  103  has been slightly moved under the action of the elastic return member  105  but remains held in its first state by the cooperation between the end head  115  of the memory member  112  and the groove  193  of the piston  103 . 
     The indication that the parking brake  7  is applied thus remains memorized. 
       FIGS. 9 and 10 , associated with  FIGS. 5 and 8 , illustrate a second sequence making it possible to detect and memorize that the parking brake  7  has been applied.  FIG. 9  replaces  FIG. 6  and  FIG. 10  replaces  FIG. 7 . The configurations of  FIGS. 5 and 8  are not repeated. 
     In  FIG. 9 , the second detection chamber  106  and the locking chamber  114  are still supplied by the second pneumatic pressure agent via the parking brake pipe  71 ; whereas the first detection chamber  104  is also supplied by the third pneumatic pressure agent by virtue of the actuation of the second distributor  62 . 
     The detection piston  103  is subjected, at its free end  197 , to the second force here equal approximately to the preset pressure value multiplied by the surface area of the piston  103  on which that preset pressure acts; and the piston  103  is also subjected, remotely opposite its free end  197 , to the first force equal to the sum of the loads applied by the second pressure agent and by the return member  105 . 
     The detection and memorization device  100  is configured here such that the first force is greater than the second force in order for the detection piston  103  to remain in its second state. 
     The memory member  112  is in its second position in which it acts on the switch  118  of the indication unit  116  so as to indicate that the parking brake  7  is not applied. 
     In  FIG. 10 , the second detection chamber  106  and the locking chamber  114  are vented by the actuation of the first distributor  52 . 
     The detection piston  103  is still subjected, at its free end  197 , to the second force but is now only subjected, remotely opposite its free end  197 , to the force applied by the return member  105 . 
     As the second force is greater than the load applied by the return member  105 , the detection piston  103  is thus brought into its first state in which its rib  192  is at a distance from the shoulder  196  of the body  102  and its groove  193  is aligned with and facing the end head  115  of the memory member  112 . 
     The memory member  112  is actuated by the return spring  113  into its first position, in which its end head  115  comes into engagement in the groove  193  of the piston  103  in order to keep the latter in position, in its first state. 
     In the first position of the memory member  112 , the latter no longer acts on the switch  118  of the indication unit  116 , which is moved to change the supply of the indicator light, in order to indicate that the parking brake  7  is henceforth applied. 
     In  FIGS. 11 and 12 , which are similar to  FIGS. 3 and 4 , the indication unit of the detection and memorization device is formed by a distributor  125  of the monostable pneumatic valve type, having a movable slide with two positions controlled by an actuator  126  itself controlled by the memory member  112  described above, and by a return member  127 . 
     In a second position ( FIG. 11 ), this distributor  125  has an inlet aperture  135   a  which is obturated and connected to a management pipe  128  which is connected by the tapping  84  to the control pipe  78 , an outlet aperture  136   a  connected to a visual indicator  131  having two positions and a return spring  132 , as well as an aperture  137   a  opening into the atmosphere and communicating with the outlet aperture  136   a.    
     The distributor  125  is here in its first position when the memory member  112  does not act on the actuator  126  and the parking brake  7  is applied. 
     In a second position ( FIG. 12 ), this distributor  125  has an inlet aperture  135   b  communicating with the outlet aperture  136   b  and supplying by a pneumatic pressure agent the visual indicator  131  which passes from one position to the other against the spring  132 ; whereas the aperture  137   b  is obturated. 
     The distributor  125  is here in its second position when the memory member  112  acts on the actuator  126  and the parking brake  7  is not applied. 
     Optionally, the indication unit of the detection and memorization device is also provided with an indicator having a cross  133  which has a return spring  134  and is also connected to the control pipe  78  via an auxiliary pipe  129  itself connected by a tapping  130  to the management pipe  128 . 
       FIGS. 13 and 14  are identified in  FIGS. 3 and 4 , with the exception of the fact that the detection and memorization device  100  is configured here such that the first detection pipe  107  is directly connected to the brake pipe  72  (that is to say after the relay device, and before or after the anti-wheel-slide) rather than to the preset pipe  79 . The operation of this device can be deduced from the description given above. 
       FIGS. 15 and 16  represent a system provided with a detection and memorization device  100  in accordance with a second embodiment. 
     Here, the actuator  67  of the second distributor  62  is configured to receive a parking brake application setting CFP 1  by a dedicated first control line  46 ; whereas the actuator  57  of the first distributor  52  is configured to receive a parking brake application setting CFP 2  by a dedicated second control line  47 . 
     The device  100  comprises a first controller  160  configured to electrically supply or not supply an indicator light  120  by virtue of an electricity supply source  189 . 
     The device  100  further comprises a second controller  150  interposed on the first control line  46  and configured to configured to cause the parking brake application setting CFP 1  to be conveyed or not conveyed to the actuator  67  of the second distributor  62 , and furthermore configured to electrically supply or not supply an indicator light  119  by virtue of an electricity supply source  185 . 
     The device  100  further comprises two conditional management members  170  each provided with a switch  178 , with a return member  172  cooperating with the respective switch  178  and each receiving a supply signal  171 . 
     A first of the two conditional management members  170  is connected by a first section of pipe  176  to the parking brake pipe  71  via a tapping  175 , and is also connected by a second section of pipe  177  both to the first controller  160  and to the second controller  150 . 
     A second of the two conditional management members  170  is connected by a third section of pipe  173  to the sub-unit  48  and in particular to the brake pipe  72 , between the relay device  93  and the anti-wheel-slide device  98 , and also connected by a fourth section of pipe  174  to the second controller  150 . 
     The first controller  160  comprises a first electric coil  186  connected to the second section of pipe  177 , a first switch  188  configured to be actuated to a working position by the first electric coil  186  when it is powered, and a return spring  187  configured to return the switch  188  to a resting position when the first electric coil  186  is not powered. 
     The second controller  150  comprises a second electric coil  180  connected to the fourth section of pipe  174 , a third electric coil  181  connected to the second section of pipe  177 , as well as a second switch  182  and a third switch  183  mechanically connected to the second switch  182  by an interface  184 ; the second and third switches  182  and  183  being configured to be actuated together to a working position by the second electric coil  180  when it is powered and the third electric coil  181  is not powered, and to a resting position by the third electric coil  181  when it is powered and the second electric coil  180  is not powered. 
     In  FIG. 15 , by the CFP 2  control, the first distributor  52  is in its first position with its single outlet aperture  55   a  connected to its aperture  56   a  opening into the atmosphere; so as to enable the venting of the parking brake pressure chamber  25 . 
     If required, the switch  178  of the first of the two conditional management members  170  does not establish an electrical path between the supply  171  and the second section of pipe  177  and does not power the first and third electric coils  186  and  181 . 
     Thus, the first switch  188  is not acted upon by the first coil  186  and does not establish an electrical path either, between the supply  189  and the indicator light  120 , which is thus off. 
     The second distributor  62  is in its first position, in which its single inlet aperture  64   a  and its single outlet aperture  65   a  communicate, to supply the service brake pressure chamber  13  with the third pneumatic pressure agent. 
     The switch  178  of the second of the two conditional management members  170  establishes an electrical path between the supply  171  and the fourth section of pipe  174  and thus powers the second electric coil  180 . 
     The second and third switches  182  and  183  are then actuated into their working position by the second coil  180 , thereby establishing an electrical path between the supply  185  and the indicator light  119  which is thus on. 
     This indicator  119  thus makes it possible to indicate that the parking brake  7  is applied. 
     It will be noted that this indication is memorized and kept even if the pressure value in the brake pipe  72  reduces or cancels out (for example due to leakages), since the second controller  150  has no return spring for the second and third switches  182  and  183 , which therefore remain in their working position. 
     In  FIG. 16 , by the CFP 2  control, the first distributor  52  is in its second position with its single inlet aperture  54   b  communicating with its single outlet aperture  55   b  to supply the parking brake pressure chamber  25 . 
     If required, the switch  178  of the first of the two conditional management members  170  establishes an electrical path between the supply  171  and the second section of pipe  177  and powers the first and third electric coils  186  and  181 . 
     Thus, the first switch  188  is acted upon by the first coil  186  and establishes an electrical path between the supply  189  and the indicator light  120 , which is thus on. 
     This indicator  120  thus makes it possible to indicate that the parking brake  7  is not applied. 
     The pressure value in the brake pipe  72  is such that the switch  178  of the second of the two conditional management members  170  does not establish an electrical path between the supply  171  and the fourth section of pipe  174  and thus does not power the second electric coil  180 . 
     The second and third switches  182  and  183  are thus actuated into their resting position by the third coil  181 , thus cutting the electrical path between the supply  185  and the indicator light  119  which is thus off and furthermore authorizing the control CFP 1  to pass to the actuator  67  of the second distributor. 
     The second distributor  62  is in its second position in which its single outlet aperture  65   b  communicates with its aperture  66   b  opening into the atmosphere. 
     In a variant not illustrated, the distributors  52  and  62  are doubled by other first and second distributors disposed in series with the first and second distributors. 
     In a variant not illustrated, the unit may comprise a parking brake test device provided with test lines connected to the actuators of the distributors. 
     In a variant embodiment not illustrated, the distributors  52  and  62  are configured such that the parking brake  7  must not be applied when the application setting of the parking brake CFP is null. This is what is referred to as an availability application. 
     The difference relative to the distributors illustrated in  FIGS. 2 to 4  lies in the fact that the first and second respective positions are swapped. 
     In other words, when the application setting of the parking brake CPF is null, the first distributor  52  has a first position by default referred to as an availability position in which its single outlet aperture  55   a  connected to the parking brake pipe  71  communicates with its single inlet aperture  54   a  connected to the control pipe  78 , whereas its aperture opening into the atmosphere  56   a  is obturated. 
     As regards the second distributor  62 , this has a first position by default also referred to as an availability position in which its single outlet aperture  65   a  communicates with its aperture  66   a  open to the atmosphere, whereas its single inlet aperture  64   a  connected to the control pipe  78  is obturated. 
     On the contrary, when the application setting of the parking brake CPF is not zero, the first distributor  52  has a second position in which its single outlet aperture  55   b  communicates with its aperture opening into the atmosphere  56   b , whereas its single inlet aperture  54   b  is obturated; and as regards the second distributor  62 , this has a second position in which its single outlet aperture  65   b  communicates with its single inlet aperture  64   b , whereas its aperture  66   b  open to the atmosphere is obturated. 
     In variants that are not illustrated:
         the distributors are bistable rather than monostable, they each comprise two actuators and the unit is provided with two control lines each connected to an actuator on each distributor;   the rail vehicle braking system may comprise a service brake lacking a wedge part attached to the braking piston, such that this piston acts directly on the thrust rod, which acts on the deformable levers; and in that case, the braking piston together with its notched rod and the thrust rod are movable in the second axial direction whereas the parking brake is configured such that the blocking finger and the holding piston are movable in the first axial direction;   the rail vehicle braking system has a braking linkage different from that illustrated in the Figures, in particular the braking linkage comprises a block configured to act directly on a wheel of the rail vehicle, that block being directly jointed by a pivot type joint fastened to the thrust rod, a rigid lever fastened to the body of the system as well as a deformable lever fastened both to the rigid lever and to the joint on the block; and/or   the rail vehicle braking system comprises a braking linkage configured to act on a brake having blocks as described above and is provided with a service brake with or without a wedge part attached to the braking piston.       

     It should be noted more generally that the invention is not limited to the examples described and represented.