Abstract:
A hydraulic stabilizer for a railway freight car truck, the truck having a bolster and side frames each respectively supporting at least one railway axle/wheel set. The hydraulic stabilizer being contained within the area of the spring set between the bolster and the side frame, and having a working cylinder and piston contained within a housing. The device having a rod seal affixed intermediate said cylinder and said piston; and an oil seal affixed intermediate said cylinder and said piston. The oil seal having at least two lip profiles extending radially inward to said cylinder.

Description:
[0001]    Rail vehicles typically use a truck having at least two pairs of wheels mounted on live axles. The truck contains a suspension system having springs on either side of the truck generally above to the rail. The common truck approved by the Association of American Railroads (AAR) is known as a three piece truck; having a bolster and two side frames. The wheels are mounted in the side frames and the bolster is suspended on a set of springs on either lateral side between the bolster and the end frame. Many types of dynamic balance and stability devices are used including friction snubbers, resilient friction wedges and side bearings. 
         [0002]    Because the three piece truck is not rigid, it permits a certain amount of flex that can be desirable in certain railcar applications. However, from the same perspective, the three piece truck can be subject to dynamic instability such as truck hunting, yaw, and other dynamic conditions. Many instability conditions occur at specific speeds, either high or low, and may also be effected by car loading. Hydraulic stabilizers have been utilized to control railcar oscillations including controlling resident rocking of high center of gravity cars. Such hydraulic stabilizers can be installed in the spring group of three piece trucks. Such stabilizers are shown in U.S. Pat. Nos. 4,936,226, 3,626,864, 4,077,096, 3,837,292, 3,995,720 and 3,831,529 which are incorporated herein. Generally, these stabilizers all utilize a piston which is supported in a working cylinder and permitted to travel in a generally vertical manner. Often the piston is mounted at the center of a coil spring in the spring group. In addition to the cylinder, a casing provides a hydraulic reservoir for fluid and a control valve. In a railway truck, the spring sets on either side of the truck provide for lateral movements and displacements as well as supporting the vehicle load. However, the hydraulic stabilizer provides dampening by dissipating energy that the springs would merely return to the overall rail truck system. The dampening is created through energy being dissipated by hydraulic fluid as it moves through a restricting valve. The stabilizers generally have a hydraulic reservoir which provides for thermal expansion and contraction of the hydraulic fluid, cooling, and make up hydraulic fluid or oil as needed resulting from system leaks. Generally, it is highly desirable that railway freight vehicles operate over long periods of time, distance and environmental changes without extensive inspection or maintenance. The reservoir provides for make up of leaked fluid so that dampening can be maintained over the periods between scheduled maintenance. 
         [0003]    While there are a number of places in the hydraulic stabilizer which are candidates for nuisance leakage, one of the critical areas is between the piston and the casing portion which forms the cylinder. Leakage at this point can result in hydraulic fluid being removed from the overall system and requires the make up hydraulic fluid be added from the reservoir. The leakage is usually the result of the relative movement between the piston and the casing and/or its respective seal. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1  shows a side view of a typical three piece truck having two axles per truck and utilizing a hydraulic stabilizer  130  with a spring set. 
           [0005]      FIG. 2  is shows a representation of the device  130  from  FIG. 1 . 
           [0006]      FIG. 3  is a cross section of a typical design of the device  130  from  FIG. 1  such as that shown in U.S. Pat. No. 4,936,226. 
           [0007]      FIG. 4  shows a cross sectional area of a hydraulic stabilizer such as  130 . 
           [0008]      FIG. 5  is a diagrammatic representation a piston for an embodiment of a hydraulic stabilizer. 
           [0009]      FIG. 6  is a cross sectional representation of a rod wiper seal. 
           [0010]      FIG. 7  is a cross sectional view of a twin lip oil seal. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0011]    The hydraulic stabilizer of this invention includes seals, wipers and finishes that enhance the retention of fluids within the hydraulic stabilizer to ensure longer service and can reduce leakage. These changes also reduce the unsightly effects of fluid loss and relates to the perception of quality and integrity of the units throughout their operational service life. The improved sealing permits higher dampening life and reduces the potential for operation at low oil levels. 
         [0012]    The oil seal is a high performance polyether based urethane. Polyether based seals provide superior resistance to chemicals, moisture and better performance and lower temperatures such as, for example, −50° F. and maintain higher levels of flexibility at such lower temperatures. In addition, the seal performs better than typical polyester seals at elevated temperatures, such as, for example, +230° F. 
         [0013]    An additional feature is the superior performance of the twin lift profile of sealing on the reciprocating piston rod. Such twin lift profile permits dry rod sealing with the double lift seal as opposed to the prior art single lift design. Twin sealing lifts are energized by a profiled NDR insert designed to ensure complete actuation of the twin sealing lifts under pressure conditions found within the hydraulic stabilizer. The insert permits complete actuation at both low temperatures and high temperatures. 
         [0014]    The NDR (acrylonitrile-butadiene) nitro rubber expander gives high levels of elasticity and resistance to compression set to assure better sealing throughout the hydraulic stabilizer&#39;s normal service life. 
         [0015]    The hydraulic stabilizer is also equipped with a polyacetal anti-extrusion to keep the oil seal stable under pressure conditions. 
         [0016]    The rod wiper is a metal cased element securely bonded to urethane with the metal being treated with a rust inhibitor. The urethane has a precision trimmed wiping lip capable of operating in conditions of dirt and grit. 
         [0017]    This precision seal keeps dirt and foreign debris from entering the stabilizers which might cause premature wear of all of the sealing elements. This wiper rod seal precludes oil whether it has escaped from the hydraulic stabilizer or other source from reentering the unit. Oil entering the unit can carry dirt and grit which has an abrasive effect on the life of the stabilizer and its seals. 
         [0018]    The piston rod has been modified from the prior art to improve surface finish (No. 2 and No. 3 RMS) allowing for superior “dry seal” characteristics in the hydraulic stabilizer. 
         [0019]      FIG. 1  shows a typical three piece truck the operations and details are similar to that described in more detail in U.S. Pat. No. 4,936,226 (incorporated herein) except using improved stabilizer device  130 . As can be seen two railway freight wheels  26  and  26 ″ engage a rail  28  and are connected to a side frame  24 . The bolster  20  is fitted through a window in the side frame  24  and a set of one or more springs, usually coil springs, which support the bolster within the side frame conform a railway truck. Typically springs  22  can be clusters having a central secondary coil spring nestled within the outer spring. Any number of springs can be used in support of the bolster. Also shown in  FIG. 1  is the improved hydraulic device as shown fits in a slot that would typically be utilized for an additional spring. However, the improved device  130  can also be inserted any place between the bolster  20  and the side frame  24  that provides a stabilization or dampening of forces resulting from relative movement between 20 and 24. It will normally be desirable to place the device  130  in the position of one or more of the normal coiled springs. While shown in  FIG. 1  on a lateral side of the spring clusters, the hydraulic stabilizer  130  could equally be placed in a central or other location within the spring set. 
         [0020]      FIG. 2  shows improved stabilizer  130  with a concentric spring as used in  FIG. 1 .  FIG. 2  shows an improved stabilizer device  130  having a body portion  60  that includes a sight glass  61 . The sight glass permits visual inspection of the fluid level in the body portion. An integral spring  62  is mounted around and generally concentric with the upwardly extending piston. The unitized spring and hydraulic dampening of the stabilizer  130  provide both additional support and dynamic dampening of relative movement between the bolster and the side frame. In some embodiments, the integral spring may not be used and a larger piston can then be utilized in the body portion. However, it is presently preferred that the unit contain an integral spring as it permits additional spring support in a set of springs in any given bolster. 
         [0021]      FIG. 3  is a device similar to that in U.S. Pat. No. 4,936,226 with similar reference numbers. The details of these parts are as described in such patent and incorporated herein. The piston rod  33 , seal  48  and wiper  39  of  FIG. 3  have similar function but differ from those in the prior art patent.  FIG. 3  shows a hydraulic stabilizer similar to that in the prior art but including the improvements of this invention. A body  30  includes a reservoir portion  42 . In the upper part of the body is a piston rod  33  which extends upward out of the casing. This is the rod which would bear upon a mechanical connection or a direct connection to the bolster. As the bolster moves up and down, rod  33  respectively would move up and down. Also housed within the body or casing  30  is a piston  44  which moves vertically up and down during operation of the dampener. The casing  38  includes a wiper  39  which contacts piston rod  33  to remove any oil or grease contained therein. Piston  44  which moves within the inner surface of sleeve  34  of the dampener has typical hydraulic interconnection as does the piston rod  33  for providing hydraulic metering or dampening. Such metering and dampening hydraulics are well known in the industry and shown in the patents incorporated herein by reference. The piston  33  moves up and down within an upper casing opening  43 . The bore  46  is sealed by the piston and the upper seal  48 . The upper seal  48  and the wiper  39  work in conjunction to provide the improved dampening device of the present invention. 
         [0022]      FIG. 4  shows a cross-section of an embodiment ( 130 ) of a stabilizer of the invention.  FIG. 4 , as previously described and known from the prior art, piston rod  8  moves up and down within bore  5  with corresponding movements of the bolster. Sleeve  21  forms a lower cavity in casing  1  sealed to the wear plate at  4 . The piston  22  moves within the sleeve and is sealed at  17 . The piston  8  includes both an oil seal  2  and a rod wiper  3 . More details of the seal and rod wiper are shown in  FIGS. 6 and 7 . 
         [0023]      FIG. 5  shows the piston rod  8  from  FIG. 4  in more detail. The piston rod  8  itself has been modified to a much improved surface finish (#2-#3 RMS) allowing for superior “dry seal” characteristics in the new hydraulic stabilizer design. This new improved design requires little or no lubrication for an extended service life, with no weeping or oil loss. The piston rod  8  works in conjunction with the improved seal  2  and wiper  3  shown in  FIG. 4 .  FIGS. 5   c  and  5   b  show enlarged views of respective upper portions of the piston rod  8  and the lower interior edge. The upper shoulder area shows a slope angle of approximately 10°. Shown in  FIG. 5   b  is a double angled chamfer having an interior of 15° and a larger exterior extending angle of 30°. These angles can in some embodiments improve the installation, wear and sealing characteristics of the device. 
         [0024]      FIG. 6  shows in detail a cross-section of an improved rod wiper  3  having a metal or other material for reinforcement. The rod wiper can be a metal cased element securely bonded to urethane. The metal portion can be treated with a rust inhibitor. The urethane interior portion can have a precision trimmed wiping lip  101  capable of operating in dirty conditions. This precision lip keeps any dirt or foreign debris from entering the stabilizer which might cause premature wear of other of the sealing elements. 
         [0025]    The rod wiper  3  is inserted into the mating bore with the piston  8 . The wiper  3  is usually located at an upper portion of the mating bore and above the oil seal  2 . It will be understood that the rod wiper is generally a cylindrical device which is pressed into the mating bore of the piston  8 . As such, the outer peripheral surface of the outer rod can have at least a portion made of a metallic or other hard reinforcing material. As can be seen in  FIG. 6 , the reinforcing element  102  is made of a metal or hard plastic. Metal is generally preferred. As shown, it can be made in a J form having an outer circumferential upright portion which is generally fit circumferentially into the bore. The hook of the J portion then extends into the bolded elastomeric portion which forms the lip  101 . This J portion permits easy insertion of the rod wiper into the piston bore and it maintains a structural rigidity for the elastomeric molded portion which forms a lip. In some embodiments it will be desirable to have a valley formed between the upper portion of the J reinforcing ring  102  and the lip  101 . This will permit the lip  101  to deform while maintaining a wiping contact with the piston  8 . 
         [0026]      FIG. 7  shows detail of the improved oil seal  2 . An additional feature giving superior performance is the twin lip profile of sealing on the reciprocating piston  8  for “dry rod sealing” with this new oil seal versus previous single lip design. These twin sealing lips  105 ,  107  are energized by a unique profiled NBR insert designed to ensure complete actuation of the twin sealing lips under various pressure conditions throughout both low temperature as well as high temperature use. The NBR (acrylonitrile-butadiene) nitrile rubber expander gives much more elasticity and resistance to compression set to assure better sealing throughout the useful service life. The oil seal can also be equipped with a polyacetal anti-extrusion ring  104  to keep the oil seal stable under pressure. 
         [0027]    The annular inset expander  107  causes the lower lips  106  and  108  to maintain contact with their respective sealing surfaces such as, for example, the outer surface of piston  8  and the inner surface on the casing which holds the oil seal  2 . The lip  108  can be a static seal with the casing. The interior lip  106  which seals against the piston can be a dynamic seal. In some instances, the lip  108  may not be necessary. However, even if lip  108  is not utilized, the expander  107  can be utilized in these applications. As such, there are two dynamic seals  105  and  106  which seal against the outer surface of piston  8 . In addition, the anti-extrusion ring  104  is contained on the interior circumferential of the oil seal. The anti-extrusion ring may be made of a number of materials including a polyacetal. One of the functions of the ring  104  is to prevent deformation or extrusion of the lip  105 . Ring  104  acts as protection to assure a high quality condition of the lip during dynamic conditions between the piston  8  and the oil seal  2 . 
         [0028]    While some of the embodiments of the present invention have been shown in detail in this specification, it is understood that other embodiments of the invention may be practiced which are included within the scope of the claims.