SAFETY DEVICE FOR PNEUMATIC BRAKING CYLINDERS WITH PARKING-BRAKE SECTIONS, FOR RAILWAY AND TRAMWAY VEHICLES

Abstract: Safety device for pneumatic braking cylinders (10) for railway and tramway vehicles, particularly for underground trains, having a service-brake section (10a) connected to the pneumatic line and a parking-brake section (10b) connected to a pressurised air supply (12) and operable to ensure the vehicle remains stationary. The device includes a cut-off valve (20) interposed be­ tween the pressurised air supply (12) and the parking-break section (10b) of the cylinder (10) and arranged to break their communication, exhaust the said section, and then enable its operation, in such a manner as to avoid any untimely opera­ tion tending to cause undue braking of the vehicle in service.

Description: Safety device for pneumatic braking cylinders with parking-brake sections, for railway and tramway vehicles The present invention relates generally to braking systems for railway and tramway vehicles, particularly for underground trains. In particular, the invention relates to braking systems which use pneumatic cylinders having a service-brake section connected to a pneumatic line and a parking-brake section connected to a pressurised air supply and arranged to operate as a result of the interruption of the connection and the exhaustion of the parking-brake section in order to ensure that the vehicle remains stationary. In braking systems of this type, communication between the parking-brake section of the cylinder, normally constituted by a simple spring actuator, and its pressurised air supply is controlled by a solenoid valve movable between an energised open position and a de-energised, closed, exhaust position. In practice, therefore, the operation of the parking-brake section is controlled by this solenoid valve independently of the service-brake circuit: consequently, any malfunctions of the solenoid valve or, as occurs more frequently, interruptions of the electrical supply may cause untimely braking with consequent danger, particularly for underground trains in the event of unwanted stoppages in tunnels. The object of the present invention is to solve this problem by means of a safety device for avoiding untimely braking caused by the operation of the parking-brake section. In order to achieve this object, the invention provides a safety device characterised in that it includes a cut-off valve interposed between the pressurised air supply and the parking-brake section of the cylinder and arranged to keep their communication open, even in the event of breakdown or electrical interruption, and to allow this communication to be broken, and hence the parking-brake section to operate,only in the event of breakdown or electrical interruption with simultaneous activation of the service-brake section of the cylinder. Thus, in practice, the device according to the invention allows the parking-brake section to operate only if both the following conditions are satisfied: - full application of the service brake, - subsequent electrical command by the conductor. According to the invention, this cut-off valve includes: - a two-position directional shuttle valve respectively for opening communication between the pressurised air supply and the parking-brake section of the cylinder and for closing this communication and exhausting the parking-brake section, - first electro-pneumatic actuator means for keeping the directional valve in the open position in normal conditions of electrical supply and for allowing the directional valve to move into the closed exhaust position in the absence of an electrical supply, and - second actuator means for controlling the movement of the directional valve into the closed exhaust position in the absence of an electrical supply upon operation of the service brake. According to another aspect of the invention, a one-way flow valve is connected between the cut-off valve and the pressurised air supply so as to prevent the parking-brake section from exhausting with the directional valve in the open position in the event of a breakage of the connection between the safety device and the pressurised air supply. According to another characteristic of the invention, the safety device further includes retaining means for locking the directional valve in the open position, the retaining means being disengageable as a result of the operation of the second actuator means and also acting as stop means for locking the directional valve in the closed exhaust position following its movement into this position. According to a preferred embodiment of the invention, the first actuator means include a first pneumatic cylinder supplied through a two-position directional solenoid valve having a respective open position corresponding to its normal energised condition, in which it keeps the pneumatic cylinder pressurised, and an exhaust position corresponding to its de-energised condition, in which it exhausts the pneumatic cylinder to allow the movement of the directional valve from the open position to the closed exhaust position, and in that the second actuator means comprise a second pneumatic cylinder disposed on that side of the directional valve opposite the first pneumatic cylinder and having a piston connected to the shuttle of the directional valve, the second pneumatic cylinder being supplied in the braking phase by the service-brake circuit so as to move the piston towards the directional valve to place the shuttle thereof in its closed exhaust position. Further characteristics of the invention will become apparent from the detailed description which follows with reference to the appended drawings, provided purely by way of non-limiting example, in which: Figure 1 illustrates schematically a pneumatic braking cylinder for railway and tramway vehicles, provided with a safety device according to the invention, Figure 2 is a schematic diagram illustrating the safety device, and Figure 3 is a variant of Figure 2. With reference initially to Figure l, a pneumatic braking cylinder for railway and tramway vehicles is generally and schematically indicated 10. The cylinder 10 is of generally known type and therefore will not be described in detail For the purpose of the present invention, it suffices to say that it has within it a service-brake section 10a and a parking-brake section lOb normally constituted by a simple actuator held in a rest position against the action of resilient biasing means by pressurised air. The pressurised air is supplied to the parking-brake section lOb through a line 12 connected to the main line of the braking system of the vehicle or an auxiliary reservoir, and including a flexible portion 14. The service-brake section 10a is connected by a line 16 including a flexible pipe 18 to a pneumatic or electro-pneumatic braking circuit of known type, through a conventional distributor. According to the invention, a safety device 20 is attached to the outside of the cylinder 10 and is connected between the line 12 (or the flexible pipe 14) and the parking-brake section lOb so as to avoid untimely operation of this section lOb. As illustrated in greater detail in Figure 2, the safety device includes a two-position, two-way directional valve 60 the input of which is connected through a passage 61 to the line 12 (or the flexible tube 14) through a one-way flow valve 63, and the output of which is connected to the parking-brake section lOb through a passage 65. The valve 60 is movable from the open position illustrated in Figure 2, in which communication between the pipe 12 and the parking-brake section lOb is open, to a closed position in which this communication is closed and the section lOb is exhausted, thus actuating the parking brake. Under normal operational conditions of the braking circuit, the valve 60 is held in its open position by the action of a pneumatic cylinder 62 the pressure chamber of which is supplied from a duct 64 branching from the passage 61 downstream of the one-way flow valve 63, through a two-position, two-way directional solenoid valve 66. In its energised condition, the solenoid valve 66 is normally in the open position illustrated in Figure 2, so as to keep communication between the tube 12 and the pressure chamber of the pneumatic cylinder 62 open and to retain the valve 60 in its open position. When de-energised, the solenoid valve 66 is moved into its closed position, exhausting the pressure chamber of the pneumatic cylinder 62 and allowing the valve 60 to move into its closed, exhaust position. An actuator 68 is associated with a latch member 70 movable between a withdrawn rest position and an advanced operative position in which it cooperates with a catch notch 72 of the slide of the valve 60 when the latter is in its closed exhaust position as well as with a catch notch 82 when the slide is in its open position, in the event of a breakdown of the solenoid valve 66, in the manner explained below. The operation of the latch member 70 is obviously that of locking and retaining the valve 60 in its open position or in its closed exhaust position, as will be specified below. In the case of Figure 2, the actuator 68 is of the pneumatic type and is connected in the manner illustrated to the output of the solenoid valve 66. Hence, when the solenoid valve 66 is in its energised open condition, the latch member 70 is located in its withdrawn rest position against the action of a biasing spring 71. When the solenoid valve 66 is de-energised and is in the closed position, however, the pneumatic actuator 68 is moved into its exhaust position and the spring 71 urges the latch member 70 into its advanced operative position to cooperate with the notch 82 or the notch 72. In the case of the variant illustrated in Figure 3, however, in which parts identical or similar to those described above are indicated by the same reference numerals, the actuator 68 is of the electromagnetic type and is connected electrically to the energisation circuit of the solenoid valve 66. The operation of the latch member 70 in this case is exactly the same as that described above. In order to achieve the movement of the valve 60 from the open position to the closed exhaust position, a pneumatic cylinder 73 is provided and is located on the opposite side of the valve 60 from the pneumatic cylinder 62. A piston 75 is sealingly slidable in the cylinder 73 and defines a pressure chamber 76 on the side opposite the valve 60. This pressure chamber 76 is connected to the pipe 16, and hence to the servicebrake circuit, through a passage 77. The piston 75 is fixed to an axial rod 80 connected to the slide of the valve 60. When there is no pressure in the thrust chamber 76 and hence in the pipe 16, the piston 75 is disposed in its withdrawn position illustrated in Figures 2 and 3. When there is pressure in the chamber 76, that is, when the pipe 16 is supplied by the electro-pneumatic service-brake circuit, the piston 75 moves to the right as shown in the drawings, moving the slide of the valve 60 correspondingly with the effects which will be clarified below. Operation a) Conditions of movement (vehicle unbraked). The service-brake section lOa of the cylinder is not supplied. The air pressure in the line 12 reaches the parking-brake section lOb of the cylinder through the one-way flow valve 63, the duct 61, the valve 60, and the duct 65, so as to annul the action of the resilient elements of this section. Simultaneously, the air in the duct 61 reaches the solenoid valve 66 through the duct 64, the solenoid valve 66 being energised and hence allowing the supply of the chamber 62 which keeps the shuttle in the open position and inhibits the action of the escapement 68. b) Service braking The duct 16 of the brake supplies the section lOa of the cylinder, applying the service brake. The pressurised air reaches the chamber 73 of the shuttle valve through the duct 77 without causing its movement in that this is prevented by the greater pressure present in the chamber 62; consequently, the spring section lOb of the cylinder behaves as it does under the conditions of movement. c) Application of the parking brake In order to operate the parking brake, it is necessary to act as follows: - to operate the service brake fully, thus restoring the conditions of point (b), - to de-energise the solenoid valve 66. Thus, the duct 64 is cut off and the chamber 62 and the device 68 are exhausted. The shuttle of the valve 60 moves as a result of the thrust exerted by the pressure present in the chamber 73 which is no longer opposed by that in the chamber 62 and this means that the spring section lOb of the cylinder is exhausted to allow the application of the parking brake. Switching having been effected, the escapement 70, under the action of the spring 71, locks the shuttle in its new position to ensure that the parking brake is kept on whether or not the service brake is on. d) Release of the parking brake By energising the solenoid valve 66, one restores the conditions of movement in that there are re-supplied the escapement 68 which is released and the chamber 62 which cause the translational movement of the shuttle, even when the service brake is on, since the pressure in the duct 12 is always greater than that in the duct 16. As a result of the translational movement of the shuttle, communication between the pressurised air supply 12 and the section lOb of the cylinder is restored, annulling the action of the resilient members of the parking brake. Safety a) Accidental interruption of the electrical supply to the solenoid valve during movement If the electrical supply to the solenoid valve 66 is interrupted, the chamber 62 is exhausted and the shuttle does not move since the chamber 73 is not supplied in the absence of service braking. Furthermore, the chamber of the escapement 68 is exhausted, allowing the movement of the shuttle to be blocked and ensuring communication between the pressurised duct 12 and the section lOb of the spring cylinder. Any subsequent service braking does not cause movement of the shuttle due to the action of the escapement 68 and the parking brake cannot operate. b) Breakage of the flexible pipe 14 (Figure 1) Should the flexible pipe 14 break, the one-way flow valve 63 prevents exhaustion of the pressure in the section lOb of the cylinder and thus prevents the parking brake from operating. Naturally the constructional details and forms of embodiment may be varied widely with respect to that described and illustrated, without thereby departing from the scope of the present invention

Claims: CLAIMS 1. Safety device for pneumatic braking cylinders for railway and tramway vehicles, particularly underground trains, having a service-brake section connected to a pneumatic or electro-pneumatic service-brake circuit and a parking-brake section connected to a pressurised air supply and arranged to operate as a result of the interruption of this connection and the exhaustion of the parking-brake section, characterised in that it includes a cut-off valve (20) interposed between the pressurised air supply (12) and the parking-brake section (lOb) of the cylinder (10) and arranged to keep their communication open, even in the event of breakdown or electrical interruption, and to allow this communication to be broken, and hence the parking brake-section (lOb) to operate, only in the event of breakdown or electrical interruption with simultaneous activation of the service-brake section (lOa) of the cylinder. 2. Device according to Claim 1, characterised in that a one-way flow valve (63) is interposed between the pressurised air supply (12) and the cut-off valve (20) and is arranged to prevent the exhaustion of the parking-brake section (lOb) with the cut-off valve (20) in the open position in event of breakage of the connection between this cut-off valve (20) and the pressurised air supply (12). 3. Device according to Claim 1 or Claim 2, characterised in that the cut-off valve (20) includes: - a two-position directional shuttle valve (60) respectively for opening communication between the pressurised air supply (12) and the parking-brake section (lOb) of the cylinder (10) and for closing this communication and exhausting the parking-brake section (lOb), - first electro-pneumatic actuator means (62, 66) for keeping the directional valve (60) in the open position in the normal conditions of electrical supply and for allowing the directional valve (60) to move into the closed exhaust position in the absence of an electrical supply, and - second actuator means (73) for controlling the movement of the directional valve (60) into the closed exhaust position in the absence of an electrical supply upon operation of the service brake. 4. Device according to Claim 3, characterised in that the second actuator means (73) are piloted by the pressure in the service-brake circuit (16). 5. Device according to Claim 3 or Claim 4, characterised in that it further includes retaining means (70, 82) for locking the directional valve (60) in the open position, the retaining means (70, 82) being disengageable as a result of the operation of the second actuator means (73). 6. Device according to Claim 5, characterised in that the retaining means also act as stop means (70, 72) for holding the directional valve (60) in the closed exhaust position following its movement into this position. 7. Device according to any one of Claims 3 to 6, characterised in that the first actuator means include a first pneumatic cylinder (62) supplied through a two-position directional solenoid valve (66) having a respective open position corresponding to its normal energised condition, in which it keeps the pneumatic cylinder (62) pressurised, and a discharge position corresponding to its de-energised condition, in which it exhausts the pneumatic cylinder (62) to allow the movement of the directional valve (60) from the open position to the closed exhaust position, and in that the second actuator means comprise a second pneumatic cylinder (73) disposed on that side of the directional valve (60) opposite the first pneumatic cylinder (62) and having a piston (75) connected to the shuttle of the directional valve (60), the second pneumatic cylinder (73) being supplied by the service brake circuit so as to move the piston (74) towards the directional valve (60) to place the shuttle thereof in its closed exhaust position. 8. Device according to Claims 5 and 6, characterised in that the stop means include a latch member (70) movable between a rest position and an operative position to cooperate with complementary catch means (82, 72) of the directional valve (60), the latch member (70) being operated by means of an actuator (68) operatively associated with the directional solenoid valve (66) so that, in the energised condition and the de-energised condition of the latter, there is a corresponding rest position and operative position of the latch member (70), respectively. 9. Device according to Claim 8, characterised in that the actuator (68) is of the pneumatic type and is supplied through the directional solenoid valve (66). 10. Device according to Claim 8, characterised in that the actuator (68) is of the electromagnetic type and is connected electrically to the directional solenoid valve (66).

Inventors: RESTORI, ETTORE
Applicants: WABCO WESTINGHOUSE COMPAGNIA FRENI S.P.A.
Application year: 1986
Main classification: B60T13
IPC codes: B60T17, B60T13