WO2015112174A1

WO2015112174A1 - Improved multistage pantograph retraction apparatus and related method

Info

Publication number: WO2015112174A1
Application number: PCT/US2014/013143
Authority: WO
Inventors: Luiz Antônio Silva ABREU; Renato NOAL; Michel NUNES
Original assignee: Norgren, Inc.
Priority date: 2014-01-27
Filing date: 2014-01-27
Publication date: 2015-07-30

Abstract

A valve provided according to an embodiment comprises a first chamber with first and second fluid ports. A second chamber having an exhaust port is in fluid communication with the first chamber. A first seal with the first chamber is configured to open and close on a first valve seat, the first seal biased in the closed position. A passage connects the first fluid port and the second fluid port so that the first fluid port is in communication with the second fluid port when the first seal is in the closed position. The passage allows equilibrium between the first fluid port and the second fluid port. A second seal is biased in a closed position, adapted to fluidly connect the first valve chamber with the exhaust port when a positive fluid flow from the first chamber biases the second seal in an open position.

Description

IMPROVED MULTISTAGE PANTOGRAPH RETRACTION

APPARATUS AND RELATED METHOD

TECHNICAL FIELD

The embodiments described below relate to the field of pantographs, and more particularly, to an improved apparatus and method for retracting a pantograph.

BACKGROUND

Pantographs are electromechanical apparatuses commonly positioned on the roofs of electric vehicles, such as trains, trams, and busses to maintain electrical contact between such vehicles and overhanging catenary electrical wires. Catenary systems are common means for providing electricity to pantograph-equipped vehicles, in a primary catenary wire is situated above the motion path or track of the vehicle, and one or more current-carrying contact wires are suspended therefrom. The pantograph biases a conductor, or contact shoe, against the underside of the contact wire, thus providing an electrical path between the pantograph and the contact wire for the purpose of supplying power to the vehicle. As the vehicle travels at speed, the contact shoe slides along the contact wire to maintain electrical contact.

One prevalent pantograph design is the half-pantograph or 'Z'-shaped style, which has a number of articulating arms that project from the roof of the vehicle towards the contact wire. The traditional method for forcing the contact shoe against the contact wire is by simply spring-loading the arms of the pantograph. Pneumatic systems with the pantograph are also used to raise the arms and hold the contact shoe against the conductor, but even pneumatic systems are often assisted with springs. It should be noted that springs can be used to either bias pantograph arms upwards or downwards, each style of system typically being opposed to a pneumatic cylinder drive.

Contact shoes typically have carbon sliding strips installed that mediate the contact between the contact wire and the vehicle. These strips provide low sliding resistance between the pantograph and contact wire while also providing good electrical conductivity. However, like carbon motor brushes, sliding strips are consumable items. When a sliding strip wears through to expose the support structure below, a dangerous situation occurs due to friction, heat, and the risk of catching a support wire on a portion of the pantograph not designed for either mechanical or electrical contact with the wire. Other dangerous situations can occur when physical impediments with the conducting wires or environment overload the mechanical limits of the pantograph. Such events can cause damage to pantographs, the vehicle itself, electrical infrastructure, and even to bystanders.

Prior art attempts have sought to minimize or prevent such damage by using pneumatic quick release valves or shear bolts that, when actuated or broken, respectively, allow the pantograph to quickly retract in case of an emergency. Quick release valves rapidly purge the pressure of pneumatic systems, allowing the pantograph arms to safely retract. For example, U.S. Pat. No. 3,444,338 discloses fracturing members that break upon exposure to excessive force that might occur upon impact with a catenary wire. This results in the collapse of the pantograph assembly. In another example, U.S. Pat. No. 4,034,832 teaches horn-mounted levers that activate a pneumatic jack to quickly lower a pantograph of the end of the pantograph contacts a wire.

However, it is a problem to apply quick-release valves or shear bolts to spring- loaded pantographs. Quick release valves yield a pressure purge having such a rapid rate that the weight of the pantograph overcomes the countervailing bias forces of the pantograph assembly virtually immediately, resulting in the pantograph rapidly crashing downward, often causing damage to the pantograph and even the host vehicle.

Although prior art attempts have been made to provide a means for rapidly retracting pantographs, the practical applications of these attempts are relatively limited. What is needed, therefore, is an improved quick-release valve system that allows a pantograph to rapidly retract, yet prevents damage due to excessive retraction speeds and forces. This is particularly necessary for spring loaded pantographs. In addition, a system that can be retro-fitted onto existing spring-loaded pantographs is needed. The embodiments described below overcome these and other problems and an advance in the art is achieved. The embodiments described below provide a multi-stage pressure relief valve assembly coupled with a pantograph. By initially rapidly releasing full operating pressure during a first stage, the pantograph initially lowers rapidly, and is thus expediently able to clear potential hazards. However, at least a second stage prevents a full system pressure purge, and provides a buffered landing, slowing the retraction of the pantograph and providing a soft and safe rate of retraction to a resting state.

SUMMARY OF THE INVENTION

A valve according to an embodiment comprises a first chamber. A first fluid port is in fluid communication with the first chamber, and a second fluid port is in fluid communication with the first chamber. A second chamber is in fluid communication with the first chamber. An exhaust port is in fluid communication with the second chamber. A first seal with the first chamber is configured to reciprocate between an open position and a closed position. The first seal is biased in the closed position, and the first fluid port is adapted to be in fluid communication with the second valve chamber when the first seal is in the open position. A passage connects the first fluid port and the second fluid port so that the first fluid port is in fluid communication with the second fluid port when the first seal is in the closed position. A second seal with the second chamber is biased in a closed position, and the second seal is adapted to fluidly connect the first valve chamber with the exhaust port when a positive fluid flow from the first chamber biases the second seal in an open position.

A multistage pantograph retraction apparatus is provided according to an embodiment. The multistage pantograph retraction apparatus comprises a pantograph arm and a pneumatic cylinder configured to retract the pantograph arm at at least two rates.

A method of retracting a pantograph is provided according to an embodiment. The method comprises the step of signaling a need to retract the pantograph. The method further comprises the steps of retracting the pantograph at an initial rate and retracting the pantograph at a subsequent rate.

A method of retracting a pantograph is provided according to an embodiment. The method comprises the steps of connecting at least one pantograph arm to a pneumatic cylinder that is configured to actuate the pantograph arm and connecting the pneumatic cylinder to a multi-stage valve in fluid communication with a signal line. The method further comprises approximately equalizing a working pressure between the pneumatic cylinder and the signal line. Additionally, the method comprises lowering a pressure of the signal line, initially exhausting the pneumatic cylinder through an exhaust port of the multi-stage valve until the pressure of the pneumatic cylinder is approximately 2 bar, and subsequently exhausting the pneumatic cylinder through a bleed orifice of the multi-stage valve until the pressure of the pneumatic cylinder is approximately 0 bar.

ASPECTS

According to an aspect a valve comprises:

a first chamber;

a first fluid port in fluid communication with the first chamber;

a second fluid port in fluid communication with the first chamber;

a second chamber in fluid communication with the first chamber;

an exhaust port in fluid communication with the second chamber;

a first seal with the first chamber, wherein the first seal is configured to reciprocate between an open position and a closed position, wherein the first seal is biased in the closed position, and wherein the first fluid port is adapted to be in fluid communication with the second chamber when the first seal is in the open position; a passage connecting the first fluid port and the second fluid port, wherein the first fluid port is in fluid communication with the second fluid port when the first seal is in the closed position; and

a second seal with the second chamber biased in a closed position, wherein the second seal is adapted to fluidly connect the first chamber with the exhaust port when a positive fluid flow from the first chamber biases the second seal to an open position.

Preferably, the valve further comprises a first biasing member adapted to bias the first seal in a closed position when the first fluid port and the second fluid port are in substantial pressure equilibrium, wherein the first biasing member is adapted to open the first seal when a positive fluid flow of the first fluid port exceeds a pressure threshold of the first biasing member.

Preferably, the pressure threshold of the first biasing member is approximately 0.5 bar. Preferably, the valve further comprises a second biasing member adapted to bias the second seal in a closed position, wherein the second biasing member is adapted to open the second seal when a positive fluid flow of the first chamber exceeds a pressure threshold of the second biasing member.

Preferably, the pressure threshold of the second biasing member is approximately

2 bar.

Preferably, the first chamber is defined by a valve body.

Preferably, the second chamber is defined by a valve body.

Preferably, the valve further comprises a first valve seat with the first chamber wherein the first valve seat sealedly engages the first seal in the closed position.

Preferably, the passage is adapted to allow a pressure equilibrium between the first fluid port and the second fluid port.

Preferably, the first seal is a diaphragm.

Preferably, the second seal is a diaphragm.

Preferably, the passage is an orifice defined by the first seal

Preferably, the valve further comprises a bleed orifice disposed between the first seal and the second seal, wherein the bleed orifice is adapted to fluidly connect the first chamber to an exterior of the valve, so that positive fluid pressure from the first chamber exhausts through the bleed orifice when the second seal is in the closed position.

Preferably, the bleed orifice is approximately 2mm in diameter.

Preferably, the valve further comprises a pneumatic cylinder in fluid communication with the first fluid port.

Preferably, the valve further comprises a signal line in fluid communication with the second fluid port, wherein a pressure loss of the signal line triggers the first seal to open.

According to another aspect, a multistage pantograph retraction apparatus comprises:

a pantograph arm; and

a pneumatic cylinder configured to retract the pantograph arm at at least two rates. Preferably, the pneumatic cylinder further comprises a multi-stage valve configured to retract the pantograph arm at an initial rate by reducing a pressure of the pneumatic cylinder from a working pressure to a first pressure followed by retracting the pantograph arm at a subsequent rate by reducing the first pressure to a second pressure.

Preferably, the multi-stage valve further comprises:

a first chamber;

a first fluid port in fluid communication with the first chamber and the pneumatic cylinder;

a second fluid port in fluid communication with the first chamber;

a second chamber in fluid communication with the first chamber;

an exhaust port in fluid communication with the second chamber;

a first seal with the first chamber, wherein the first seal is configured to reciprocate between an open position and a closed position, wherein the first seal is biased in the closed position, and wherein the first fluid port is adapted to be in fluid communication with the second chamber when the first seal is in the open position; a passage connecting the first fluid port and the second fluid port wherein the first fluid port is in fluid communication with the second fluid port when the first seal is in the closed position; and

a second seal with the second chamber biased in a closed position, wherein the second seal is adapted to fluidly connect the first chamber with the exhaust port when a positive fluid flow from the first chamber biases the second seal in an open position.

Preferably, the multi-stage valve further comprises a bleed orifice disposed between the first seal and the second seal, wherein the bleed orifice is adapted to fluidly connect the first chamber to an exterior of the valve so that positive fluid pressure from the first chamber exhausts through the bleed orifice when the second seal is in the closed position.

Preferably, the bleed orifice is approximately 2mm in diameter.

Preferably, the multistage pantograph retraction apparatus further comprises a signal line in fluid communication with the multi-stage valve, wherein a pressure loss of the signal line triggers the pantograph arm to retract. Preferably, the signal line comprises a tube configured to rupture upon receiving a rupturing force.

Preferably, the multistage pantograph retraction apparatus further comprises a sliding strip configured to contact a contact wire, wherein the tube is configured to rupture when the sliding strip is damaged.

According to another aspect, a method of retracting a pantograph comprises the steps of:

signaling a need to retract the pantograph;

retracting the pantograph at an initial rate; and

retracting the pantograph at a subsequent rate.

Preferably, the step of signaling a need to retract the pantograph comprises the step of reducing a pressure of a signal line.

Preferably, the signal line is connected to a monitoring tube, wherein the monitoring tube is configured to rupture upon receiving a rupturing force.

Preferably, the step of retracting the pantograph at an initial rate further comprises the step of reducing a pressure of a cylinder with the pantograph from a working pressure to a first pressure.

Preferably, the step of reducing a pressure of a cylinder with the pantograph from a working pressure to a first pressure further comprises the step of exhausting a fluid with the cylinder through an exhaust port of a multi-stage valve.

Preferably, the step of retracting the pantograph at a subsequent rate further comprises the step of reducing a pressure of a cylinder with the pantograph from a first pressure to a second pressure.

Preferably, the step of reducing a pressure of a cylinder with the pantograph from a first pressure to a second pressure further comprises the step of exhausting a fluid with the cylinder through a bleed orifice of a multi-stage valve.

Preferably, the working pressure of the cylinder with the pantograph is between approximately 11 bar and approximately 5 bar.

Preferably, the first pressure of the cylinder with the pantograph is between approximately 2.5 bar and approximately 1.5 bar.

Preferably, the second pressure of the cylinder with the pantograph is between approximately 0.5 bar and approximately 0 bar. Preferably, the method of retracting the pantograph of Claim 27, further comprises the step of equalizing a pressure of a signal line with a pressure of a cylinder with the pantograph.

According to another aspect, a method of retracting a pantograph, comprises the steps of:

connecting at least one pantograph arm to a pneumatic cylinder that is configured to actuate the pantograph arm;

connecting the pneumatic cylinder to a multi-stage valve in fluid communication with a signal line;

approximately equalizing a working pressure between the pneumatic cylinder and the signal line;

lowering a pressure of the signal line;

initially exhausting the pneumatic cylinder through an exhaust port of the multistage valve until the pressure of the pneumatic cylinder is approximately 2 bar; and subsequently exhausting the pneumatic cylinder through a bleed orifice of the multi-stage valve until the pressure of the pneumatic cylinder is approximately 0 bar.

Preferably, the at least one pantograph arm is biased with at least one spring. Preferably, the signal line is connected to a monitoring tube configured to rupture upon receiving a rupturing force.

Preferably, a sliding strip is configured to prevent the monitoring tube from rupturing when the sliding strip is undamaged. BRIEF DESCRIPTION OF THE DRAWINGS

The same reference number represents the same element on all drawings. It should be understood that the drawings are not necessarily to scale.

FIG. 1 illustrates a prior art vehicle with a pantograph;

FIG. 2 illustrates a prior art pantograph;

FIG. 3 illustrates a pantograph according an embodiment;

FIG. 4 illustrates a pantograph according an embodiment;

FIG. 5 is a graph illustrating pantograph travel over time; FIG. 6 is an illustrative example of an isometric representation of an embodiment; FIG. 7 is an illustrative example of an isometric representation of the embodiment of FIG. 6;

FIG. 8 illustrates a side view of an embodiment;

FIG. 9 illustrates a front view of the embodiment of FIG. 8; and

FIG. 10 illustrates a cross sectional side view of the embodiments of FIGS. 8 and

9.

DETAILED DESCRIPTION OF THE INVENTION FIGS. 1-10 and the following description depict specific examples to teach those skilled in the art how to make and use the best mode of embodiments of a valve and related apparatus for retracting a pantograph and related methods. For the purpose of teaching inventive principles, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate variations from these examples that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific examples described below, but only by the claims and their equivalents.

Referring initially to FIG. 1 as a prior art reference, a vehicle 10 that derives electricity from at least one external source is positioned below a catenary system 12. A primary catenary line 14 suspends at least one contact wire 16 therefrom. The contact wire 16 carries an electrical current for supply to a vehicle 10 below. A pantograph 18 attached to the vehicle 10 is biased vertically to make contact with the contact wire 16 to create an electrical path between the contact wire 16 and the pantograph 18 for the purpose of supplying power to the vehicle 10 while the vehicle is stationary or in motion. A contact shoe 20 having sliding strips 22 (see FIGS. 2-4) slidingly engages the contact wire 16 to maintain electrical continuity between the catenary system 12 and the vehicle 10. In most embodiments, the system is grounded through vehicle tracks 24. Though a train is illustrated, the vehicle 10 is not limited to trains, and may be any vehicle, tracked or non-tracked, that derives at least some electricity from an overhead source. FIG. 2 illustrates, by way of example, a pantograph 18, which is of a type well known in the art. A frame 26 provides the support for the pantograph 18 and also supports feet 28 utilized in mounting the frame 26 to the roof of a vehicle 10. The contact shoe 20 is pivotingly attached to at least one upper arm 30 that is in turn pivotingly attached to at least one lower arm 32 at an arm joint 34. The lower arm 32 is pivotingly attached to a central axis 38. When the central axis 38 rotates, the lower arm 32 either raises or lowers, thus causing the upper arm 30 and contact shoe 20 to also raise or lower, respectively. At least one spring 36 is attached to the central axis 38, which typically assists the pantograph 18 in maintaining a raised position, and also serves to provide a level of shock absorption for the pantograph 18. A pneumatic cylinder 40 is also attached, via a piston 42, to the central axis 38. By actuating the piston 42 towards the central axis 38 (i.e. extending the piston 42), the pantograph 18 is lowered, and by retracting the piston 42, the pantograph 18 is raised. Therefore, with the pantograph 18 in the raised position, and the piston 42 being in a retracted orientation, should the pressure in the pneumatic cylinder 40 be rapidly purged, the pantograph 18 will violently collapse due to the weight of the pantograph 18, which easily overcomes the upward force exerted by the by the spring 36. Those skilled in the art will readily recognize mechanical variations that provide a pantograph that operates in a similar, or in the same, manner.

FIG. 3 shows a pantograph 18 according an embodiment. The pantograph 18 comprises a pantograph controller 44 in fluid communication with the pneumatic cylinder 40 by a cylinder line 46. In one embodiment, the fluid is air. In an alternate embodiment, the fluid is a hydraulic fluid, and the pneumatic cylinder 40 is a hydraulic cylinder 40a (not shown). The pantograph controller 44 comprises valves, switches, compressors, tanks, electronics, etc. necessary to control the pneumatic cylinder 40 so to raise and lower the pantograph as part of normal pantograph operation. In particular, the pantograph controller 44 pressurizes the pneumatic cylinder 40 with, for example, approximately 5 to 11 bar of working pressure to retract the piston 42 so to maintain the pantograph in a raised position. A multi-stage valve (MSV) 48 is in fluid communication with the cylinder line 46 and also a signal line 50. The signal line 50 is maintained in substantial pressure equilibrium with the working pressure of the pneumatic cylinder 40. If a drop in pressure of the signal line 50 occurs, this triggers an immediate and rapid evacuation of the pneumatic cylinder 40 through the MSV 48. However, to prevent the violent collapse of the pantograph 18 typical of the prior art, the MSV 48, when triggered by the signal line 50, rapidly reduces the pressure of the pneumatic cylinder 40 from the working pressure to a first pressure of approximately 1-3 bar, and preferably to between approximately 1.5-2.5 bar, and even more preferably to approximately 2 bar, by venting through an exhaust port 54. This, referred to as the initial stage of evacuation, results in an immediate and rapid evacuation of the pneumatic cylinder 40 and concomitant retraction of the pantograph 18, but only to a certain point. The subsequent stage of evacuation— mediated by the MSV 48— causes the pneumatic cylinder 40 to slowly evacuate between the first pressure of approximately 2 bar to a second pressure of approximately 0 bar by bleeding pressure through a bleeding orifice 52 of the MSV 48. This results in a slow descent of the pantograph 18 as the pantograph 18 reaches a fully retracted and resting position, thus avoiding the damage to the pantograph 18 or vehicle 10 that typically occurs due to rapid retraction. FIG. 4 is an illustrative example of an embodiment of a pantograph 18 having a diagrammatic representation of the MSV 48.

FIG. 5 is a graph illustrating the drop of a pantograph 18 with and without the MSV 48 installed. Without an MSV 48, when the pneumatic cylinder 40 is rapidly evacuated, such as through a quick release valve well known in the art, the pressure leaves the cylinder 40 as rapidly as the valve will allow. Since the size of the exhaust port of a quick release valve is determinative of the rate of cylinder evacuation, a pantograph 28 utilizing such a valve will be set so that either the retraction rate is relatively slow through the entire descent or alternatively relatively fast through the entire descent. If the valve is set so purging occurs too slowly through the use of a small exhaust port, the pantograph 18 will not retract at a rate deemed expedient enough for emergency situations. If, on the other hand, a large exhaust port is utilized, as is shown in FIG. 4, then the pantograph 18 falls relatively freely and rapidly throughout the duration of retraction, which may result in damage. However, by using an embodiment of the multi-stage valve 48, the initial retraction rate during a first stage is as fast as though using a standard quick release having a relatively large exhaust port 54, but once a first pressure is reached, pressure reduction slows by evacuating cylinder fluid instead through a bleeding orifice 52 during the subsequent stage of pantograph 18 retraction.

FIGS. 6-10 illustrate an embodiment of an MSV 48. FIGS. 6 and 7 are illustrative examples of a 3D representation of an exterior of an embodiment. The MSV 48 has a valve body 56, first fluid port 58, second fluid port 60, a spring housing 68, and may also have a silencer 62 over the exhaust port 54. FIG. 8 illustrates a side view of an embodiment of an MSV 48, and FIG. 9 illustrates a front view of an embodiment of an MSV 48.

FIG. 10 illustrates a cross sectional side view of an embodiment of an MSV 48. The first fluid port 58 is coupled to the first chamber 68, and the second fluid port 60 is also coupled to the first chamber 68. The first chamber 68 is connected to a second chamber 70, and the second camber is connected to the exhaust port 54. A first seal 72 is disposed in the first chamber 68, and configured to reciprocate between an open and closed position. When in the closed position (as illustrated), the first seal 72 sealedly rests against a first valve seat 74. The first seal 72 may be a diaphragm, disc, poppet, or any other valve seal known in the art. A first biasing member 76 biases the first seal 72 in a closed position. When the first seal 72 is in an open position, maximum fluid communication occurs between the first fluid port 58 and second chamber 70, through the first chamber 68. Conversely, when the first seal 72 is in a closed position, no fluid communication occurs between the first fluid port 58 and second chamber 70. At least one passage 78 connects the first fluid port 58 with the second fluid port 60 to provide minimal fluid communication. In one embodiment the passage 78 is defined by the body 56. In a related embodiment, the passage 78 is defined by the first seal 72. In one embodiment, the passage 78 provides minimal fluid communication between the first fluid port 58 and the second fluid port 60 when the first seal 72 is in either the open or closed position, while in another embodiment the passage 78 provides minimal fluid communication between the first fluid port 58 and the second fluid port 60 only when the first seal 72 is in the closed position.

Fluid pressure introduced into the first fluid port 58 at a rate that does not exceed the biasing force of the first biasing member 76 flows through the passage 78 and into the second fluid port 60. In this case, when the second fluid port 60 is attached to a closed vessel, the fluid pressure of the first fluid port 58 will equilibrate with the fluid pressure of the second fluid port 60. In this state of equilibrium, the biasing force exerted upon the first seal 72 by the first biasing member 76 will maintain the first seal 72 in a closed position. However, if the fluid pressure of the second fluid port 60 is suddenly decreased, the relatively increased pressure of the first fluid port 58 over the second fluid port 60 will overcome the force exerted by the first biasing member 76, thus causing the first seal 72 to move to the open position and fluidly connecting the first fluid port 58 with the second chamber 70. In this case, if the second chamber 70 were in fluid communication with the exhaust port 54, fluid under pressure with the first fluid port 58 would rapidly exhaust to the atmosphere, as in prior art quick release valves.

However, in an embodiment of the MSV 48, a second seal 80 with the second chamber 70 is biased in a closed position by a second biasing member 84, which is illustrated in FIG. 10 by a spring, though any biasing means known in the art is contemplated. The second seal 80 may be a diaphragm, disc, poppet, or any other valve seal known in the art. When in a closed position, the second seal 80 contacts a second valve seat 82. While the second seal 80 is in a closed position, there is substantially no fluid communication between the second chamber 70 and the exhaust port 54. Thus, if the first seal 72 is open and the second seal 80 is open, there is fluid communication between the first fluid port 58 and the exhaust port 54.

The second biasing member 84 exerts a biasing force against the second seal 80 to maintain the second seal 80 in a closed position, however, positive fluid pressure in the second chamber 70, if greater than the pressure exerted by the second biasing member 84, will cause the second seal 80 to move into an open position. In one embodiment, the force exerted by the second biasing member 84 is adjustable, so the threshold pressure required to open the second seal 80 is changed according to the adjustment. In a preferred embodiment, the force exerted by the second biasing member 84 requires approximately 2 bar of opposing fluid pressure on the second seal 80 to open the second seal 80.

The bleeding orifice 52 is disposed between the first seal 72 and the second seal 80, being in fluid communication with fluid therebetween. The bleeding orifice 52 exhausts fluid to the outside of the valve body 56 at a relatively slow rate that is determined by the size of the bleeding orifice 52. In one example the diameter of the bleeding orifice 52 is approximately 2mm, but the diameter may be configured according to the application. Additionally, an adjustable bleeding orifice 52a (not shown) is also contemplated. In such an embodiment, a needle valve or similar means can be used to adjust the volume of fluid that can pass through the adjustable bleeding orifice 52a.

By way of example the MSV 48 may be installed on a pantograph 18 to facilitate a rapid descent when triggered to descend, followed by a soft landing to prevent damage to the pantograph 18 or vehicle 10. Returning particularly to FIGS. 3 and 10, the pantograph controller 44 effectuates the pressurization of the pneumatic cylinder 40 through cylinder lines 46. This pressurization, to typically a working pressure of between approximately 5 bar and 11 bar, raises the pantograph 18. The cylinder line 46 is in fluid communication with the first fluid port 58, and the signal line 50 is in fluid communication with the second fluid port 60. Due to the passage 78 connecting the first and second fluid ports 58, 60, the second fluid port 60, and therefore the signal line 50 also, are pressurized to the working pressure. In this state, both the first and second seals 72, 80 are in the closed positions and the pantograph 18 may undergo normal operation without actuating the MSV 48. However, if the signal line 50 loses pressure, this signals a need for the pantograph 18 to retract, and the retraction of the pantograph 18 is initiated. When the signal line 50 loses an amount of pressure whereby the pressure on the first fluid port 58, and a related pressure against the first seal 72, exceeds the biasing force of the first biasing member 76, the first seal 72 opens to allow fluid flow into the second chamber 70. Since the working pressure of the pneumatic cylinder 40 is higher than the threshold pressure set by the second biasing member 84, the second seal opens, thus providing fluid communication from the pneumatic cylinder 40 to the exhaust port 54. The pneumatic cylinder 40 therefore rapidly exhausts, lowering the pressure from the working pressure to a first pressure that is dictated by the second biasing member. In one embodiment, the first pressure is 2 bar. Once the pressure in the pneumatic cylinder 40 is less than 2 bar, the second biasing member 84 forces the second seal 80 into the closed position. When this occurs, fluid is forced out of the MSV 48 through the bleeding orifice 52. Thus, from the first pressure to a second pressure— a subsequent retraction phase from approximately 2 bar to approximately 0 bar in an embodiment— the fluid of the pneumatic cylinder 40 is slowly bled from the MSV 48, which slows and cushions the landing of the pantograph. The initial phase, from the working pressure to the first pressure is characterized by a rapid retraction of the pantograph 18, followed by the gentle subsequent phase wherein the pantograph 18 safely lands in a resting position.

With continued reference to FIGS. 3 and 4, in an embodiment, the signal line 50 is connected to a monitoring tube 86. The monitoring tube 86 is preferably protected from damaging forces by the sliding strip 22. When the sliding strip 22 is damaged or worn through, the monitoring tube 86 is exposed. In the case of a contact wire 16 wearing through a sliding strip 22, the monitoring tube 86 is subjected to friction against the contact wire 16, causing the monitoring tube 86 to rupture. Once the monitoring tube 86 ruptures, pressure of the signal line 50 is released through the breach, thus generating a signal for the pantograph 18 to retract. Similarly, if the contact shoe 20 is damaged, the monitoring tube 86 or signal line 50 may rupture. The monitoring tube 86 is made from a material strong enough to maintain the working pressure of the signal line 50, yet fragile enough to quickly rupture when in contact with the contact wire 16. In one embodiment, the sliding strip 22 comprises a hollow cavity, and further comprises the monitoring tube 86. In one embodiment, the signal line 50 is attached to a switch that is actuatable to release pressure from the signal line 50.

It should be appreciated that the MSV 48 is contemplated as a stand-alone multi- stage pressure release valve, and nothing noted herein serves to limit embodiments thereof to only pantograph-related uses, as these serve as illustrative examples. By adjusting the size of the exhaust port 54 and/or the bleeding orifice 52, the rate of pressure release in the first and second stages may be tailored to alternate applications.

The detailed descriptions of the above embodiments are not exhaustive descriptions of all embodiments contemplated by the inventors to be within the scope of the invention. Indeed, persons skilled in the art will recognize that certain elements of the above-described embodiments may variously be combined or eliminated to create further embodiments, and such further embodiments fall within the scope and teachings of the invention. It will also be apparent to those of ordinary skill in the art that the above-described embodiments may be combined in whole or in part to create additional embodiments within the scope and teachings of the invention. Thus, although specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. The teachings provided herein can be applied to other devices and method, and not just to the embodiments described above and shown in the accompanying figures. Accordingly, the scope of the invention should be determined from the following claims.

Claims

What is claimed is:

1. A valve (48) comprising:

a first chamber (68);

a first fluid port (58) in fluid communication with the first chamber (68);

a second fluid port (60) in fluid communication with the first chamber (68); a second chamber (70) in fluid communication with the first chamber (68);

an exhaust port (54) in fluid communication with the second chamber (70);

a first seal (72) with the first chamber (68), wherein the first seal (72) is configured to reciprocate between an open position and a closed position, wherein the first seal (72) is biased in the closed position, and wherein the first fluid port (58) is adapted to be in fluid communication with the second chamber (70) when the first seal (72) is in the open position;

a passage (78) connecting the first fluid port (58) and the second fluid port (60), wherein the first fluid port (58) is in fluid communication with the second fluid port (60) when the first seal (72) is in the closed position; and

a second seal (80) with the second chamber (70) biased in a closed position, wherein the second seal (80) is adapted to fluidly connect the first chamber (68) with the exhaust port (54) when a positive fluid flow from the first chamber (68) biases the second seal (80) to an open position.

2. The valve (48) of Claim 1, further comprising a first biasing member (76) adapted to bias the first seal (72) in a closed position when the first fluid port (58) and the second fluid port (60) are in substantial pressure equilibrium, wherein the first biasing member (76) is adapted to open the first seal (72) when a positive fluid flow of the first fluid port (58) exceeds a pressure threshold of the first biasing member (76).

3. The valve (48) of Claim 2, wherein the pressure threshold of the first biasing member (76) is approximately 0.5 bar.

4. The valve (48) of Claim 1, further comprising a second biasing member (84) adapted to bias the second seal (80) in a closed position, wherein the second biasing member (84) is adapted to open the second seal (80) when a positive fluid flow of the first chamber (68) exceeds a pressure threshold of the second biasing member (84).

5. The valve (48) of Claim 4, wherein the pressure threshold of the second biasing member (84) is approximately 2 bar.

6. The valve (48) of Claim 1, wherein the first chamber (68) is defined by a valve body.

7. The valve (48) of Claim 1, wherein the second chamber (70) is defined by a valve body.

8. The valve (48) of Claim 1 further comprising a first valve seat (74) with the first chamber (68) wherein the first valve seat (74) sealedly engages the first seal (72) in the closed position.

9. The valve (48) of Claim 1, wherein the passage (78) is adapted to allow a pressure equilibrium between the first fluid port (58) and the second fluid port (60).

10. The valve (48) of Claim 1, wherein the first seal (72) is a diaphragm.

11. The valve (48) of Claim 1, wherein the second seal (80) is a diaphragm.

12. The valve (48) of Claim 1, wherein the passage (78) is an orifice defined by the first seal (72).

13. The valve (48) of Claim 1, further comprising a bleed orifice (52) disposed between the first seal (72) and the second seal (80), wherein the bleed orifice (52) is adapted to fluidly connect the first chamber (68) to an exterior of the valve (48), so that positive fluid pressure from the first chamber (68) exhausts through the bleed orifice (52) when the second seal (80) is in the closed position.

14. The valve (48) of Claim 13, wherein the bleed orifice (52) is approximately 2mm in diameter.

15. The valve (48) of Claim 1, further comprising a pneumatic cylinder (40) in fluid communication with the first fluid port (58).

16. The valve (48) of Claim 1, further comprising a signal line (50) in fluid communication with the second fluid port (60), wherein a pressure loss of the signal line (50) triggers the first seal (72) to open.

17. The valve (48) of Claim 16, wherein the signal line (50) comprises a tube (86) configured to rupture upon receiving a rupturing force.

18. A multistage pantograph retraction apparatus comprising:

a pantograph arm (30,32); and

a pneumatic cylinder (40) configured to retract the pantograph arm (30,32) at at least two rates.

19. The multistage pantograph retraction apparatus of Claim 18, wherein the pneumatic cylinder (40) further comprises:

a multi-stage valve (48) configured to retract the pantograph arm (30,32) at an initial rate by reducing a pressure of the pneumatic cylinder (40) from a working pressure to a first pressure followed by retracting the pantograph arm (30,32) at a subsequent rate by reducing the first pressure to a second pressure.

20. The multistage pantograph retraction apparatus of Claim 19, wherein the multi- stage valve (48) further comprises:

a first chamber (68); a first fluid port (58) in fluid communication with the first chamber (68) and the pneumatic cylinder (40);

an exhaust port (54) in fluid communication with the second chamber (70);

a passage (78) connecting the first fluid port (58) and the second fluid port (60) wherein the first fluid port (58) is in fluid communication with the second fluid port (60) when the first seal (72) is in the closed position; and

a second seal (80) with the second chamber (70) biased in a closed position, wherein the second seal (80) is adapted to fluidly connect the first chamber (68) with the exhaust port (54) when a positive fluid flow from the first chamber (68) biases the second seal (80) in an open position.

21. The multistage pantograph retraction apparatus of Claim 20, wherein the passage (78) is adapted to allow a pressure equilibrium between the first fluid port (58) and the second fluid port (60).

22. The multistage pantograph retraction apparatus of Claim 20, wherein the multistage valve (48) further comprises a bleed orifice (52) disposed between the first seal (72) and the second seal (80), wherein the bleed orifice (52) is adapted to fluidly connect the first chamber (68) to an exterior of the valve (48) so that positive fluid pressure from the first chamber (68) exhausts through the bleed orifice (52) when the second seal (80) is in the closed position.

23. The multistage pantograph retraction apparatus of Claim 20, wherein the bleed orifice (52) is approximately 2mm in diameter.

24. The multistage pantograph retraction apparatus of Claim 19, further comprising a signal line (50) in fluid communication with the multi-stage valve (48), wherein a pressure loss of the signal line (50) triggers the pantograph arm (30,32) to retract.

25. The multistage pantograph retraction apparatus of Claim 24, wherein the signal line (50) comprises a tube (86) configured to rupture upon receiving a rupturing force.

26. The multistage pantograph retraction apparatus of Claim 25, further comprising a sliding strip (22) configured to contact a contact wire (16), wherein the tube (86) is configured to rupture when the sliding strip (22) is damaged.

27. A method of retracting a pantograph, comprising the steps of:

signaling a need to retract the pantograph;

retracting the pantograph at an initial rate; and

retracting the pantograph at a subsequent rate.

28. The method of retracting the pantograph of Claim 27, wherein the step of signaling a need to retract the pantograph comprises the step of reducing a pressure of a signal line.

29. The method of retracting the pantograph of Claim 28, wherein the signal line is connected to a monitoring tube, wherein the monitoring tube is configured to rupture upon receiving a rupturing force.

30. The method of retracting the pantograph of Claim 27, wherein the step of retracting the pantograph at an initial rate further comprises the step of reducing a pressure of a cylinder with the pantograph from a working pressure to a first pressure.

31. The method of retracting the pantograph of Claim 30 wherein the step of reducing a pressure of a cylinder with the pantograph from a working pressure to a first pressure further comprises the step of exhausting a fluid with the cylinder through an exhaust port of a multi-stage valve.

32. The method of retracting the pantograph of Claim 27, wherein the step of retracting the pantograph at a subsequent rate further comprises the step of reducing a pressure of a cylinder with the pantograph from a first pressure to a second pressure.

33. The method of retracting the pantograph of Claim 32, wherein the step of reducing a pressure of a cylinder with the pantograph from a first pressure to a second pressure further comprises the step of exhausting a fluid with the cylinder through a bleed orifice of a multi-stage valve.

34. The method of retracting a pantograph of Claim 30, wherein the working pressure of the cylinder with the pantograph is between approximately 11 bar and approximately 5 bar.

35. The method of retracting a pantograph of Claim 30, wherein the first pressure of the cylinder with the pantograph is between approximately 2.5 bar and approximately 1.5 bar.

36. The method of retracting a pantograph of Claim 31, wherein the first pressure of the cylinder with the pantograph is between approximately 2.5 bar and approximately

1.5 bar.

37. The method of retracting a pantograph of Claim 31, wherein the second pressure of the cylinder with the pantograph is between approximately 0.5 bar and approximately 0 bar.

38. The method of retracting the pantograph of Claim 27, further comprising the step of equalizing a pressure of a signal line with a pressure of a cylinder with the pantograph.

39. A method of retracting a pantograph, comprising the steps of:

lowering a pressure of the signal line;

initially exhausting the pneumatic cylinder through an exhaust port of the multi- stage valve until the pressure of the pneumatic cylinder is approximately 2 bar; and subsequently exhausting the pneumatic cylinder through a bleed orifice of the multi-stage valve until the pressure of the pneumatic cylinder is approximately 0 bar.

40. The method for retracting a pantograph of Claim 39, wherein the working pressure of the cylinder with the pantograph is between approximately 11 bar and approximately 5 bar.

41. The method for retracting a pantograph of Claim 39, wherein the at least one pantograph arm is biased with at least one spring.

42. The method for retracting a pantograph of Claim 39, wherein the signal line is connected to a monitoring tube configured to rupture upon receiving a rupturing force.

43. The method for retracting a pantograph of Claim 42 wherein a sliding strip is configured to prevent the monitoring tube from rupturing when the sliding strip is undamaged.