Abstract:
A controller for a spring wing on a frog that utilizes a floating piston rod carrying a fixed piston valve and a free-moving piston head is provided. When the piston rod is actuated by the opening movement of the spring wing, the piston valve separates from the piston head briefly, allowing oil to flow through the piston head in a relatively unrestricted manner. The piston head is spring biased towards the piston valve; upon contact between the piston head and the piston valve, the oil flow through the piston head stops, helping to hold the spring wing in the open position. When the spring wing begins to close, the adjustable oil flow through the controller allows the piston rod to move at a controlled rate, thereby controlling the closure rate of the spring wing.

Description:
FIELD OF THE INVENTION 
     This invention relates to a device to control the movement of a spring wing. In particular, this invention relates to a device comprising a hydraulic system to control the movement of a spring wing on a frog. 
     BACKGROUND OF THE INVENTION 
     A frog is used in a railway where two rails cross over each other, to provide support for the wheels as they pass over the intersection. A spring wing or spring rail frog has a movable wing rail that is connected only at one end, such that it moves laterally away from the frog to provide a flangeway when a wheel of a passing car engages the spring wing rail. Examples of basic spring wing frogs are described in U.S. Pat. Nos. 4,624,428 and 4,637,578, both to Frank. 
     A common problem with spring wing frogs is that if the spring wing closes quickly, as compared to the speed of the passing train, it may close after each wheel or between cars, and then be forced open again for the next wheel. In this case, the spring wing is subjected to a greater number of cycles in a given time frame, and is therefore susceptible to failure more rapidly. It is therefore preferable to provide a system in which the rate of closure can be controlled, so that a certain amount of time can be expected to elapse after each car wheel passes, before a spring wing is completely closed. In this manner, a spring wing may be expected to stay open until an entire train has passed, rather than constantly opening and closing as the train passes. 
     U.S. Pat. Nos. 6,158,697 and 5,806,810, both to Young et al., disclose latch holdback mechanisms (either physical or magnetic) designed to hold the spring wing in an open position for a given length of time. Hydraulic fluid is pumped through the system to engage the latch mechanism and hold the spring wing open each time car wheels pass, and bleeds off gradually to release the latch once the wheels have ceased passing. U.S. Pat. No. 2,405,407 to Conley discloses a piston rod within an oil-filled cylinder and a spring connecting the piston and the cylinder. The movement of the piston rod upon opening the spring wing compresses the spring. Movement of the piston further opens a valve on the piston, allowing oil to pass through the valves and hold the piston in an open position. A slow oil leak through a small hole in the valve allows gradual pressure equalization within the cylinder so that the piston and spring wing return to the closed position some time after the last car wheel has passed. PCT Publication No. WO 01/85524 to Moscato et al. discloses a more complex system having three fluid chambers and four fluid flow regulators, in which a hydraulic timing device or similar controller uses a restrictor valve to move the controller at a linearly varying rate depending on the position of the spring wing rail. That is, when the rail is open, the rate of closure is relatively slow, which prevents the rail from closing before the next set of car wheels passes. To avoid excessively slow closure, a relief port is provided, which circumvents the restrictor valve and allows the spring wing to close at a faster rate once it nears its home position. A high pressure relief valve is also provided to protect the timing device from excessively high pressures within the chambers. 
     However, a further consideration is that once the spring wing is released by the passing car wheel, it is biased to return to its original position and can do so very quickly, slamming against the side of the frog and causing noise and damage or wear to the spring wing and the frog. It is therefore preferable to provide a system that retards the movement of the spring wing, so that it closes more gently against the side of the frog, minimizing the chances that the frog or spring wing will be damaged by the impact. U.S. Pat. No. 2,036,198 to Cooper discloses a dash pot arrangement to automatically control the spring wing movement and allow it to return to a closed position in a gentler manner. 
     Hydraulic cylinders have been seen as a good way to deal with both controlling the speed and timing of the spring wing closure. In most systems, the piston rod is connected to the spring wing and moves the piston in the cylinder as the spring wing opens, which causes a pressure change within the cylinder. Similar to Conley, U.S. Pat. No. 1,689,841 to Powell provides a by-pass groove in the cylinder wall to allow graduated oil flow during the piston stroke, to control the movement of switch points. In U.S. Pat. No. 2,686,668 to Bettison, a sliding valve is free to move a short distance along the piston rod between the piston head and a shoulder on the piston rod. Movement of the valve covers and uncovers openings in the piston head, such that oil flows to the correct side of the cylinder to control movement of the piston rod and spring wing. Other earlier systems use a similar mechanism, wherein the pressure change causes a check valve to open, which allows fluid to transit from the pressurized side of the piston to the slightly lower pressure rod side of the piston. The volume of the fluid transiting the piston requires more space than the space created by the piston movement and a compressible gas, typically nitrogen, is provided in cylinder to compensate for the difference in volume between the two sides of the cylinder for a given movement of the piston. Once the piston is fully displaced and starts to return to its original position, the pressurization reverses and the fluid on the rod side of the piston increases, closing the check valve. The hydraulic fluid is then slowly bled from the rod side to the non-rod side of the cylinder, for example with a metering jet or other orifice, allowing the spring wing to close in a controlled manner. 
     However, hydraulic cylinders are susceptible to several potential problems. Any small openings through which fluid is expected to pass may be subject to erosion and plugging due to contaminants in the fluid. Components such as the metering jet are not replaceable, and may fail. Further, such components, or any grooves or other orifices within the hydraulic cylinder, are not adjustable, so the closure speed and timing cannot be changed, for example for different train speed limits mandated by different locations. 
     Another potential drawback is hydraulic fluid leakage—if the fluid within the cylinder leaks, the cylinder will eventually have insufficient fluid and will not operate properly. The hydraulic retarder disclosed in U.S. Pat. No. 2,686,668 to Bettison includes a pathway between an oil reservoir and the likeliest area of the cylinder to leak, such that any leakage is pulled back into the reservoir and can be returned to the cylinder. 
     Even if there is sufficient fluid within the cylinder, hydraulic cylinders may still be susceptible to hydrolocking. The piston will always try to travel its full stroke through a cylinder, but if the spring wing moves very quickly, it forces the piston rod to likewise move very quickly. If the hydraulic fluid is unable to transit quickly enough through the check valve or any other openings, which tend to be relatively small and restrictive, the non-rod side of the cylinder will be too full of incompressible fluid, which prevents the rod from travelling far enough and causes it to buckle. The resulting piston rod distortion results in misalignment of the check valves and causes a functional failure, if not a complete structural failure. 
     It is therefore an object of this invention to provide a mechanism to control the movement of the spring wing on a frog that overcomes some or all of the foregoing difficulties. 
     It is a further object of the invention to provide a spring wing controller that can respond quickly to the movement of the spring wing, with reduced chance of failure due to the rapid movement of the spring wing. 
     It is a further object of the invention to provide a control mechanism for a spring wing that is adjustable for various operating conditions. 
     These and other objects of the invention will be better understood by reference to the detailed description of the preferred embodiment which follows. Note that the objects referred to above are statements of what motivated the invention rather than promises. Not all of the objects are necessarily met by all embodiments of the invention described below or by the invention defined by each of the claims. 
     SUMMARY 
     In one aspect, the invention comprises a controller for a spring wing that utilizes a floating piston rod carrying a fixed piston valve, and a free-moving piston head. The piston head is spring biased towards the valve. When the piston rod is actuated by the opening movement of the spring wing, the piston valve separates from the piston head briefly, allowing oil to flow in a relatively unrestricted manner and minimizing pressure spikes and oil cavitation within the controller. The spring movement urges the piston towards the valve, stopping the oil flow and helping to hold the spring wing in place. When the spring wing closes, the oil flow through the controller, which is adjustably set, allows the piston rod to move at a controlled rate, thereby controlling the closure rate of the spring wing. 
     In one aspect, the invention comprises a controller for a spring wing on a frog, comprising a casing comprising a body having front and rear end caps to define a piston chamber; a piston rod operatively connected to and actuated by the spring wing, the piston rod passing through openings in the front and rear end caps; a floating piston head having a central opening through which the piston rod passes; and a piston valve operatively attached to the piston rod and adapted to close the central opening. 
     In a further aspect, the controller may also comprise a fluid reservoir in fluid communication with the piston chamber, and a metering device to control fluid flow between the piston chamber and the fluid reservoir. A filter may be provided between the fluid reservoir and the piston chamber and/or within the fluid reservoir. The fluid reservoir may also be provided with a removable cover for external access. The metering device is preferably adjustable. 
     In yet a further aspect, one or both of the openings in the end caps may comprise one or more of a rod wiper to clean the piston rod, a seal to prevent contaminants from entering the piston chamber or to prevent fluid from exiting the piston chamber and/or a support to support the piston rod. 
     In yet further aspects, the controller may comprise a spring mounted on the front end cap to bias the piston head away from the front end cap. The rear end cap may comprise a connector to connect the casing in a switch. 
     In another aspect, the invention comprises a method of controlling a spring wing on a frog, comprising the steps of providing a controller comprising a body having front and rear end caps to define a piston chamber, and a piston rod passing through the front and rear end caps; actuating the piston rod and a piston valve operatively connected to the piston rod toward the rear end cap, by movement of the spring wing to an open position, thereby separating the piston valve from contact with a floating piston head, exposing a central opening in the piston head and allowing hydraulic fluid within the piston chamber to pass through the central opening; moving the floating piston head toward the rear end cap into contact with the piston valve, thereby closing the central opening; and actuating the piston rod, the piston valve and the piston head toward the front end cap, by movement of the spring wing to a closed position. The floating piston head may be moved toward the piston valve by releasing a spring mounted between the front end cap and the piston head. 
     In a further aspect the method may comprise the step of controlling fluid flow within the piston chamber to control a rate at which the spring wing moves to the closed position. This may be done by providing a fluid reservoir and a metering device in the controller, and controlling fluid flow may comprise using the metering device to control fluid flow between the piston chamber and the fluid reservoir. The fluid may also be filtered within the fluid reservoir and/or between the fluid reservoir and the piston chamber. Contaminants within the fluid may also be allowed to settle within the fluid reservoir. 
     The foregoing was intended as a summary only and of only some of the aspects of the invention. It was not intended to define the limits or requirements of the invention. Other aspects of the invention will be appreciated by reference to the detailed description of the preferred embodiments. Moreover, this summary should be read as though the claims were incorporated herein for completeness. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described by reference to the detailed description of the preferred embodiment and to the drawings thereof in which: 
         FIG. 1  is a perspective view of the controller of the invention; 
         FIG. 2  is a cross sectional view of the rear end of the controller; 
         FIGS. 3   a - 3   c  are side views of the controller in three positions, with the outer casing removed; 
         FIG. 4  is a longitudinal cross-sectional view of the controller; and 
         FIG. 5  is a lateral cross-sectional view of the controller. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , the controller  10  of the invention comprises a casing  12  having a body  14  capped by front  16  and rear  18  end caps. A rear end cap  18  may be provided with a connecting mechanism  20  of any suitable configuration, to securely attach the controller  10  in place in the switch. In this context, the words “caps” does not necessarily require that the front and rear ends of the body  14  be separate pieces; the body  14  may be formed with integral front and/or rear portions. The body  14  may itself also be formed of one or more pieces. 
     An internal fluid reservoir  22  (shown only in  FIG. 5 ), which is preferably covered by a removable cover  24  and provided with a fill valve  26 , is also provided to hold a hydraulic fluid, such as oil or other suitable incompressible fluid. A fluid flow metering device, which is preferably externally accessible, such as via a cavity  28 , is also provided to allow control and adjustment of the fluid flow through the controller  10 , as will be discussed later. 
     A piston rod  30  is provided that preferably passes through both the front  16  and rear  18  end caps. A clevis  32  or similar attachment mechanism may be provided on the end of the rod nearest the frog, to ensure that movement of the spring wing is accurately translated to the piston rod  20 . 
     Referring now to  FIG. 2 , the internal parts of the controller  10  comprise a piston valve  34 , a piston head  36  and a spring  38 . The piston valve  34  is operatively attached to the piston rod  30 , via suitable means such as one or more retainers  42 ; movement of the piston rod towards either the rear  18  or front  16  (not shown) end cap therefore also moves the piston valve  34  in the same direction and by the same amount. Piston head  36  has a central opening  40  through which piston rod  30  passes. Piston head  36  is floating, not attached to the piston rod  30 , and central opening  40  of the piston head  36  is sized to provide a gap between the inside surface of the central opening  40  and the outside surface of the piston rod  30 . Piston head  36  and piston valve  34  are separable, but able to contact each other such that while the piston valve  34  and piston head  36  are together, the piston valve  34  closes the central opening  40 . Valve  34  may fit snugly within central opening  40  or may extend outside central opening  40 , as long as the central opening  40  is essentially closed, restricting fluid flow through central opening  40  when piston head  36  and piston valve  34  are in contact. Valve  34  may also be provided with one or more seals  44  to ensure that no fluid leakage occurs between it and the piston rod  30  or piston head  36 . 
     Rear end cap  18  may also be provided with appropriate rod wipers  46 , seals  48  and/or supports  50  to ensure that movement of the piston rod  30  does not push fluid out of, or pull contaminants into, the controller  10 , and that the rod  30  is not deformed over time by the weight of the valve  34  or gravitational force. As best shown in  FIG. 4 , front end cap  16  may be similarly provided with appropriate rod wipers  46 , seals  48  and/or supports  50 . 
     Referring now to  FIGS. 3   a - 3   c , the operation of the controller  10  is as follows. When the spring wing is in a closed position, it pulls piston rod  30  towards the front end cap  16  of the controller  10 . In this position, the valve  34  contacts piston head  36 , with spring  38  under some compressive pressure between the valve and the front end cap  16  of the controller  10 , as shown in  FIG. 3   a . In the immediate time interval after a train car passes the spring wing and forces it open, the piston rod  30  moves towards the rear end cap  18 , carrying valve  34  in the same direction and separating it from piston head  36 , as shown in  FIG. 3   b . The hydraulic fluid pressure is approximately equal at both the front and rear sides of the piston head  36 , avoiding a situation where movement of the piston rod is hampered by the pressure exerted by the incompressible fluid to the rear of the controller, and possibly retarding the rapid response of the spring wing. The movement of the piston rod  30  and valve  34  uncovers the central opening  40  (not shown), allowing fluid within the controller  10  to flow as necessary to maintain equal pressure on both sides of the piston head  36 . The combined movement of the valve  34  away from piston head  36  and flow of the hydraulic fluid through central opening  40  releases the pressure on spring  38 , allowing spring  38  to expand and push piston head  36  towards the rear end cap  18  until it meets valve  34 , as shown in  FIG. 3   c . This closes central opening  40  (not shown) and prevents further fluid flow directly through piston head  36 . Because there is now more fluid between the piston head  36  and the front end cap  16 , the fluid pressure holds the piston rod  30  towards the rear end cap  18  of the controller  10 , and therefore helps to retain the spring wing in an open position. 
       FIGS. 4 and 5  show the hydraulic fluid flow path during operation of the controller  10 . When valve  34  and piston head  36  are separated by movement of the piston rod  30 , fluid within piston chamber  56  is free to move through central opening  40  in the piston head  36  from the rear side  54  of the piston head  36  to the front side  52 . The size of the central opening  40 , as well as the amount of space around the circumference of the valve  34 , is sufficient that hydraulic fluid presents relatively little resistance to movement of the piston rod  30  and spring wing. This avoids a situation where the piston head  36  is forced to move against high pressure due to the fluid already on the rear side  54  of the chamber  52 , under which the piston rod may be susceptible to buckling and/or failure. 
     Chamber outlet  58  in the front end  52  of the piston chamber  56  passes fluid to a flow metering device  60 , such as a needle valve, timing circuit or other suitable device to control fluid flow out of the piston chamber  56 . Flow metering device  60  may be adjustable, in order to allow the fluid flow rate through the metering device to be adjusted as needed to accommodate operative conditions such as the location of the frog, the size of the frog, and wear as the frog ages. Reservoir inlet  62  passes fluid from the metering device  60  into the internal reservoir  22 . 
     Internal fluid reservoir  22  performs several functions. Because it stores extra hydraulic fluid, it may compensate for fluid volume changes, for example because of temperature changes, and for losses, such as through leakage or seepage. The reservoir  22  also manages unwanted foaming should aeration of the fluid occur. Finally, it acts as a settling tank for contaminates or particles that could collect in the system. Reservoir  22  is preferably provided with removable cover  24  for access to the reservoir for cleaning, refilling or other purposes. 
     Fluid passes from the reservoir  20  to the piston chamber  56  through a reservoir outlet  64 , which is preferably fitted with a filter  66  to prevent contaminants from flowing into the piston chamber  56 . It will be understood that the filter  66  may be provided at any inlet or outlet in the reservoir  22  or piston chamber  56 , or at any point within the fluid flow path. 
     To expand further on the fluid flow mechanisms during operation of the controller  10 , the fluid pressure within piston chamber  56  is approximately equal on either side  52 ,  54  of the piston head  36  when the spring wing is closed, as discussed earlier. The opening of the spring wing and associated piston rod movement separates the valve  34  and the piston head  36 , increasing the pressure on the rear side  54  of the piston head  36 . However, the separation of the valve  34  and piston head  36  exposes central opening  40 , allowing fluid to flow to the front side  52  of the piston head  36 . The removal of pressure exerted by the valve  34 , as well as the decrease in fluid pressure on the rear side  54  of the piston head  36  allows the spring  38  to expand, pushing piston head  36  towards the rear end cap  18  of the controller  10  until it meets valve  34  and again seals central opening  40 . At that point, there is a larger volume of fluid on the front side  52  of piston head  36  than on the rear side  54 . 
     When the train cars have finished passing, and the spring wing tries to resume a closed position, it will exert pressure to pull piston rod  30  towards the front end cap  16 , increasing the pressure in the front end of chamber  56 . Fluid flows out of piston chamber  56  through chamber outlet  58 , at a rate controlled by flow metering device  60 , which decreases the pressure in the front of the chamber  56 . However, the controlled rate of fluid flow means that the movement of the piston rod  30  is also controlled, which in turn controls the rate of closure of the spring wing. 
     Fluid then flows from the metering device  60  into the reservoir  22 , where it may settle and/or be filtered, as described above, before re-entering the piston chamber  56  to equalize the pressure in the front and rear ends of the piston chamber  56 , in preparation for the next spring wing actuation. 
     In the foregoing specification, the invention has been described with reference to specific embodiments thereof. However, the scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.