Abstract:
An electro-pneumatic braking system including a pneumatic pressure supply pipe, a generator for generating a vehicle load signal, a weighting system designed to supply a weighted pressure which defines a maximum braking pressure, limited as a function of the load signal, and braking control units connected to the weighting system and having a relay valve connected between the pipe and at least one brake cylinder, to cause the application to this cylinder of a controllable braking pressure, equal to or less than the weighted pressure. The weighting system includes an electro-pneumatic drive assembly, interposed between the pipe and the drive inlet of the relay valve and is connected to the pipe through a pressure limiter, and an electronic weighting control unit which controls this drive assembly as a function of the load signal, so as to modulate in predetermined ways the pressure at the drive inlet of the relay valve.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Field of the Invention 
         [0002]    The present invention relates to an electro-pneumatic braking system for a railway vehicle. 
         [0003]    Background 
         [0004]    More specifically, the present invention relates to an electro-pneumatic braking system comprising
       a pneumatic pressure supply pipe,   generator means for generating vehicle load or weight signals,   weighting means designed to supply a weighted pneumatic pressure which defines a maximum braking pressure, limited as a function of the load signals, and   braking control means connected to the weighting means and comprising a relay valve connected between said pipe and (at least) one brake cylinder, to cause the application to said cylinder of a controllable braking pressure, equal to or less than said weighted pressure.       
 
         [0009]    Electro-pneumatic braking systems of this type are well known, and are described, for example, in patent applications EP 0 958 980 A and WO 2013/144543 A. 
         [0010]    There is a general and constant tendency towards the reduction of the size and overall dimensions of these braking systems. 
         [0011]    In particular, there is a tendency to construct these systems in the form of line replaceable units (LRU) to allow fast and simple maintenance. 
         [0012]    These objectives imply an increased use of electronic and electro-pneumatic systems, in place of the conventional pneumatic componentry which was rather heavy and bulky. 
         [0013]    In an electro-pneumatic braking system of the aforesaid type, load signals are generated, indicating the load or weight of the whole vehicle or a part thereof, for example according to whether the braking system is intended to apply the brakes on a vehicle-by-vehicle basis, or on a bogie-by-bogie basis. 
         [0014]    In addition to the weighting means and the service braking control means, an electro-pneumatic braking system of this type usually comprises means for controlling the anti-wheel-slip function, designed to block and then reduce the fluid pressure, and subsequently reapply it to the brake cylinders as a function of information supplied by speed sensors associated with the wheels, to resolve situations of wheel locking and slippage. 
         [0015]    In some cases, the braking control means and the anti-wheel-slip control means are implemented in a single electronic control unit. 
       SUMMARY OF THE INVENTION 
       [0016]    An object of the present invention is to provide an electro-pneumatic braking system for a railway vehicle, the system being characterized by its drastically reduced size, weight and overall dimensions, highly reliable operation and low cost. 
         [0017]    These and other objects are achieved according to the invention with an electro-pneumatic braking system whose principal characteristics are disclosed and claimed herein. 
         [0018]    In a braking system according to the present invention, the weighting means comprise
       an electro-pneumatic drive assembly which is interposed between the pressure supply pipe and the drive inlet of the aforesaid relay valve, and which is connected to this pipe via a pressure and power limiter, and   an electronic weighting control unit which controls this drive assembly as a function of the aforesaid load signal, so as to modulate in predetermined ways the pressure at the drive inlet of this relay valve.       
 
         [0021]    As a result of these characteristics, the weighting means operate on a low-power “pneumatic signal”, which can be “processed” by means of pneumatic devices (solenoid valves) having small passage cross sections. These pneumatic devices can therefore be made with markedly smaller sizes and weights than those of the prior art solutions. 
         [0022]    In a braking system according to the invention, the aforesaid braking control means comprise
       an electro-pneumatic control assembly, interposed between the electro-pneumatic drive assembly of the relay valve and the drive inlet of said relay valve, and   an electronic braking control unit, designed to drive this electro-pneumatic control assembly as a function of service or safety braking request signals.       
 
         [0025]    The electro-pneumatic braking control assembly conveniently comprises a first solenoid valve, or inlet valve, which controls the connection between the electro-pneumatic drive assembly and the drive inlet of the relay valve, and a second solenoid valve, or outlet valve, which controls a discharge connection between the drive inlet of this relay valve and the atmosphere, and a third solenoid valve, for the remotely controlled braking release, connected to the inlet of the relay valve and interposed between said first and second solenoid valves. 
         [0026]    Regarding the last-mentioned solution, although in the attached claims it is shown as being subject to the presence of the characteristics defined in the claims, it will be evident to those skilled in the art that this solution may conveniently be applied even in the absence of the characteristics defined in the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    Other characteristics and advantages of the invention will be apparent from the following detailed description, which is given purely by way of non-limiting example, with reference to the attached drawings, in which: 
           [0028]      FIG. 1  is an electro-pneumatic diagram, partially in block form, of an electro-pneumatic braking system for a railway vehicle according to the present invention; 
           [0029]      FIG. 2  is a partial electro-pneumatic diagram, similar to that shown in  FIG. 1 , and shows a first variant embodiment; and 
           [0030]      FIG. 3  is an electro-pneumatic diagram, similar to those shown in the preceding figures, and shows a further variant embodiment of the electro-pneumatic braking system according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]    In the drawings, the number  1  indicates the whole of an electro-pneumatic braking system according to the present invention, for a railway vehicle of a known type. 
         [0032]    In the illustrated embodiment, the braking system  1  comprises a plurality of brake cylinders BC 1 , . . . BCN, associated with corresponding wheels or axles of the railway vehicle. 
         [0033]    Each brake cylinder BC 1 , . . . BCN is associated with a respective braking control apparatus BCA 1 , . . . BCAN. 
         [0034]    The braking control apparatus BCA 1 , . . . BCAN are associated with a weighting apparatus indicated as a whole by WA. 
         [0035]    The weighting apparatus WA comprises an electronic weighting control unit WCU, which controls an electro-pneumatic drive assembly indicated as a whole by EPDA. 
         [0036]    Each braking control apparatus BCA 1 , . . . BCAN comprises a respective electronic unit BCU which controls an associated electro-pneumatic control assembly EPCA. 
         [0037]    The number  2  in  FIG. 1  indicates a device for generating signals indicative of the load or weight of the vehicle (or of a part thereof, such as a bogie), connected to the electronic unit WCU of the weighting apparatus WA, and to the electronic units BCU of the braking control apparatus BCA 1 , . . . BCAN. 
         [0038]    The electronic units WCU and BCU may be made in the form of free-standing electronic units, or may if necessary be integrated with one another in a single electronic control unit. 
         [0039]    The symbol MBP indicates a main pneumatic pressure supply pipe (known as the “main brake pipe”). 
         [0040]    In each electro-pneumatic control assembly EPCA, the pneumatic pipe MBP is connected to the inlet of a relay valve RV, the outlet of which is connected to the associated brake cylinder BC 1 , . . . BCN. 
         [0041]    The relay valves RV are “power” valves. 
         [0042]    The electro-pneumatic weighting assembly EPDA is pneumatically interposed between the pressure supply pipe MBP and a pneumatic “signal” inlet, indicated by i, of each of the electro-pneumatic control assemblies EPCA. 
         [0043]    As will be evident from the following description, the weighting apparatus WA is designed to supply a pneumatic pressure “signal” to the drive inlets d of the relay valves RV of the braking control apparatus BCA 1 , . . . BCAN, this signal consisting of a “weighted” pneumatic pressure defining the maximum braking pressure, limited as a function of the load signal supplied by the sensor  2 , and applicable to the brake cylinders BC 1 , . . . BCN. 
         [0044]    On the other hand, each braking control apparatus BCA 1 , . . . BCAN is designed to cause the application, to at least one brake cylinder BC 1 , . . . BCN associated with this apparatus, of a braking pressure which does not exceed said weighted pressure, and is, in general, variable as a function of the level of service braking requested, or of the safety braking request, which reach the respective electronic unit BCU at its inputs indicated by a and b respectively. 
         [0045]    Conveniently, the unit BCU of each braking control apparatus BCA 1 , . . . BCAN is also designed to drive the relay valve RV of the associated electro-pneumatic assembly EPCA in such a way as to provide an anti-wheel-slip action when wheel rotation speed signals, supplied to its inputs indicated cumulatively by c, enable a locked condition of these wheels to be detected. 
         [0046]    With reference to  FIG. 1 , the electro-pneumatic drive assembly EPDA is connected to the pneumatic pressure supply pipe MBP through a pneumatic pressure limiter valve  3 , the outlet of which is connected to the supply inlet of a relay valve  4 , of the type having an opposing spring, and to the inlet of a solenoid inlet valve  5  driven, in operation, by the weighting control unit WCU. 
         [0047]    The solenoid valve  5  has its outlet connected to a small reservoir  6 , as well as to the drive inlet of the relay valve  4  and to the inlet of a solenoid outlet valve  7  which, in operation, is also driven by the weighting control unit WCU. 
         [0048]    In the illustrated embodiment, the solenoid valves  5  and  7  are three-way two-position valves which are normally closed. 
         [0049]    The outlet of the relay valve  4  is connected to the inlet i of the electro-pneumatic control assembly EPCA of the braking control apparatus BCA 1 , . . . BCAN through a respective constriction  8 . 
         [0050]    The electro-pneumatic drive assembly EPDA of the weighting apparatus WA further comprises an electric pressure sensor or transducer  9 , connected to the pipe which links the outlet of the relay valve  4  to the inlet i of the electro-pneumatic braking control assemblies EPCA. The electrical output of this sensor or transducer  9  is connected to a corresponding input of the weighting control unit WCU, to indicate to the latter, in operation, the pressure at the outlet of the relay valve  4 . 
         [0051]    The reservoir  6  acts as a “pneumatic storage unit” in which, in operation, a pressure corresponding to the weight of a vehicle, or of a part thereof, is stored. 
         [0052]    With reference to  FIGS. 1 to 3 , in the illustrated embodiment each electro-pneumatic braking control assembly EPCA comprises a solenoid inlet valve  10 , driven, in operation, by the corresponding braking control unit BCU. 
         [0053]    The solenoid valve  10  in the illustrated embodiment is of the three-way, two-position, normally open type, and has its outlet connected to the inlet of a further solenoid valve  20 , the outlet of which is connected to the drive inlet d of the relay valve RV. 
         [0054]    The outlet of the solenoid valve  20  is also connected to a small reservoir  11  and to the inlet of a solenoid outlet or discharge valve  12 , also controlled in operation by the electronic braking control unit BCU. 
         [0055]    The solenoid valve  20  is of the three-way, two-position, normally open type, while the solenoid valve  12  is of the three-way, two-position, normally closed type. 
         [0056]    As will be more clearly apparent from the following text, the solenoid valve  20  is intended to cause, when energized, the release of the braking by the associated brake cylinder BC 1 , . . . BCN. 
         [0057]    A pressure sensor or transducer  13  is connected pneumatically between the outlet of the relay valve RV and the associated brake cylinder BC 1 , . . . BCN, in order to supply, in operation, an electrical signal indicative of the pressure at the outlet of said relay valve RV to the corresponding electronic braking control unit BCU. 
         [0058]    The electro-pneumatic braking system described above with reference to  FIG. 1  operates essentially in the following way. 
         [0059]    The electronic weighting control unit WCU receives from the device  2  a signal indicative of the weight of the railway vehicle or of a part thereof, such as a bogie, according to whether the braking system  1  is designed to provide “vehicle-by-vehicle” braking or “bogie-by-bogie” braking. 
         [0060]    The weighting control unit WCU controls the solenoid inlet valve  5  and the associated solenoid outlet valve  7  in such a way that, when these solenoid valves are de-energized, the first valve ( 5 ) disconnects the reservoir  6  from the outlet of the pressure regulator  3 , and the second valve ( 7 ) prevents the reservoir  6  from discharging into the atmosphere. 
         [0061]    The reservoir  6  conveniently has a capacity essentially corresponding to the volume of the drive chamber of the relay valve  4  and of the piping connecting the solenoid valves  5  and  7  to this relay valve. 
         [0062]    When the solenoid inlet valve  5  is energized, it connects the reservoir  6  to the outlet of the pressure limiter  3 . 
         [0063]    When the solenoid outlet or discharge valve  7  is energized, it allows the pressure previously accumulated in the reservoir  6  and in the drive chamber of the relay valve  4  to be discharged into the atmosphere. 
         [0064]    The pressure sensor or transducer  9  supplies an electrical signal indicative of the pressure instantaneously present at the outlet of the relay valve  4  to the electronic weighting control unit WCU. 
         [0065]    On the basis of the signal supplied by the pressure sensor or transducer  9 , and by driving the solenoid inlet valve  5  and the solenoid outlet or discharge valve  7 , the control unit WCU acts in such a way that a weighted pneumatic pressure is present at the outlet of the relay valve  4 , this pressure defining the maximum value of the braking pressure applicable to the brake cylinders BC 1 , . . . BCN. This maximum value of the braking pressure is limited as a function of the load value indicated by the signals supplied by the device  2 . 
         [0066]    The inlet pressure limiter device  3  prevents the pressure at the inlet of the solenoid valve  5  and of the relay valve  4  from exceeding a predetermined maximum value, thereby also fixing the maximum value that the pneumatic pressure can reach at the outlet of the relay valve  4 . 
         [0067]    The pressure at the outlet of the relay valve  4 , that is to say at the outlet of the electro-pneumatic drive assembly EPDA, arrives at the inlets i of the electro-pneumatic braking control assemblies EPCA associated with the various brake cylinders BC 1 , . . . BCN. 
         [0068]    In each electro-pneumatic braking control assembly EPCA, when the solenoid valves  10 ,  20  and  12  are de-energized, that is to say in the condition shown in  FIG. 1 , the pneumatic pressure received from the relay valve  4  reaches the reservoir  11  and the drive chamber of the relay valve RV, through the solenoid valves  10  and  20 . The reservoir  11  and the drive chamber of the relay valve RV are disconnected from the atmosphere, because the solenoid discharge valve  12  is closed. 
         [0069]    The volume of the reservoir  11  corresponds to the overall volume of the drive chamber of the relay valve RV and the volume of the pipes connecting this reservoir to the solenoid valves  20  and  12 , and to the drive inlet d of the relay valve RV. 
         [0070]    In operation, each braking control unit BCU receives the load or weight information from the device  2 , the information element about the pressure at the outlet of the corresponding relay valve RV from the associated sensor or transducer  13 , and the information relating to any service or emergency braking request at its inputs a and b, as well as the information relating to the rotation speed of the wheels of the vehicle, at its inputs c. 
         [0071]    During the normal running of the railway vehicle, each braking control unit BCU controls the value of the pressure at the outlet of the relay valve RV in such a way that this pressure is proportional to the weighted drive pressure sent to its inlet d by the relay valve  4  of the electro-pneumatic drive assembly EPDA, and proportional to the service braking request signal applied to the input a of this unit BCU. 
         [0072]    If there is a safety or emergency braking request which arrives at the input b of the braking control units BCU, these units cause the associated solenoid inlet valves  10  to be deenergized, allowing the relay valve  4  to fill the reservoir  11  with fluid at the outlet pressure of said relay valve  4 , or of the electro-pneumatic drive assembly EPDA of the weighting apparatus WA. The solenoid discharge valve  12  prevents the discharge of the reservoir  11  into the atmosphere. 
         [0073]    Consequently, in the presence of a safety braking request, the relay valve RV supplies to the associated brake cylinder a flow of fluid whose pressure corresponds to the weighted pressure determined by the electro-pneumatic drive assembly EPDA, as described above. 
         [0074]    When a braking control unit BCU, on the basis of the signals relating to the rotation speed of the wheels of the vehicle supplied to its inputs c, detects a wheel slip condition, this causes a reduction of the braking pressure at the associated brake cylinder, by energizing the solenoid inlet valve  10  and de-energizing the solenoid outlet valve  12 , until the slip condition is resolved. 
         [0075]    The solenoid valve  20  can be energized by means of a remote braking release control signal (remote release signal) RR. The energizing of the solenoid valve  20  in one direction prevents the solenoid inlet valve  10  from filling the reservoir  11  with the pressurized fluid received from the relay valve  4 ; instead, it causes this reservoir  11  and the drive chamber of the relay valve RV to discharge into the atmosphere. 
         [0076]    Consequently, when the solenoid valve  20  is energized, the relay valve  20  reduces the braking pressure at the associated brake cylinder, preventing this cylinder from causing a retarding action. 
         [0077]    The positioning of the solenoid valve  20 , which enables the brake release to be controlled, between the solenoid inlet valve  10  and outlet valve  12  is such that it does not affect the speed of the air flow between the drive chamber of the relay valve RV and the solenoid discharge valve  12 . 
         [0078]    This positioning of the solenoid valve  20  prevents the emptying of the storage chamber of the relay valve RV from being slowed down in the course of anti-wheel-slip braking. 
         [0079]      FIG. 2  is a partial illustration of a first variant embodiment. In this drawing, parts and elements described previously have again been given the same alphanumeric references as those used previously. 
         [0080]    The variant according to  FIG. 2  differs from the braking system according to  FIG. 1  essentially in that the relay valve  4  of the electro-pneumatic drive assembly EPDA of the weighting apparatus WA is of the type having no return spring, and in that a further pressure limiter  14  is interposed between the drive inlet of this relay valve and the outlet of the pressure reducer  3 . 
         [0081]    By its presence, the pressure reducer  14  causes the pressure in the reservoir  6  to have a predetermined minimum value, and therefore stabilizes the minimum value of the pneumatic pressure deliverable at the outlet of the electro-pneumatic drive assembly EPDA.  FIG. 3  is a partial illustration of a further variant embodiment. 
         [0082]    In this drawing also, parts and elements identical to or corresponding to parts and elements described previously have again been given the same alphanumeric references as those used previously. 
         [0083]    By contrast with the variant shown in  FIG. 2 , in the solution according to  FIG. 3  the electro-pneumatic drive assembly EPDA of the weighting apparatus WA no longer has a relay valve. The outlet of this electro-pneumatic assembly EPDA is taken to the reservoir  6 , which acts as a “pneumatic storage” reservoir in which, in operation, a pressure corresponding to the weight of the vehicle is stored, in a similar manner to that of the solution known from European Patent EP  0   958   980  B 1 , which, however, provides for the use of a further relay valve which supplies pressure directly to the brake cylinders. 
         [0084]    In operation, the weighting control unit WCU provides continuous regulation of the pneumatic pressure in the reservoir  6  when pressure variations are present in the drive chambers of the relay valves RV of the electro-pneumatic braking control assemblies EPCA, both in service braking and in emergency anti-wheel-slip braking. 
         [0085]    In the embodiment according to  FIG. 3 , the volume of the reservoir  6  is conveniently at least ten times the sum of the volumes of the drive chambers of the relay valves RV, in order to provide “soft” control. 
         [0086]    The pressure in the reservoir  6  may be controlled on the basis of a predetermined algorithm, for example on the basis of the following expression: 
         [0000]    
       
         
           
             
               
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         [0000]    where
       Po and Vo are the pneumatic pressure and the volume of the reservoir  6 ,   t is time,   P SB  is the applied emergency or safety pressure, and   P i  and V i , where i=1,2, . . . N, are the pressures and volumes of the reservoirs  11  of the electro-pneumatic assemblies EPCA of the braking control apparatus BCA i .       
 
         [0091]    In emergency braking, the control unit WCA “consumes” some of the air stored in the reservoir  6 , but subsequently replaces the consumed amount of air therein by following a predictive algorithm, such as that shown above, on the basis of the (known) volumes of the circuits and the pneumatic components making up these circuits, and on the basis of the instantaneous pneumatic pressures detected by means of the sensors or transducers  9  and  13 . 
         [0092]    In the diagram of  FIG. 3 , the reservoir  11  does not necessarily represent an actual “physical” reservoir, but may simply represent the volume of the drive chamber of the relay valve RV and of the connections between this relay valve and the valves  10 ,  20  and  12 . 
         [0093]    The solution according to  FIG. 3  is notably economical, since it is no longer necessary to use a relay valve in the electro-pneumatic drive assembly EPDA of the weighting apparatus WA. 
         [0094]    Naturally, the principle of the invention remaining the same, the forms of embodiment and the details of construction may be varied widely with respect to those described and illustrated, which have been given purely by way of non-limiting example, without thereby departing from the scope of the invention as defined in the attached claims.