Rail brake

An extended range, consistent force rail brake comprising an adjustable wedge assembly operatively situated between the main power spring(s) and the brake shoe(s) for selectively taking up the vertical distance that the brake shoe is required to travel between the brake release position and an initial railhead contact position. The adjustable wedge assembly is thus selectively expandable in the vertical orientation, and may comprise: an upper block that is operatively connected, either directly or indirectly, to the power spring; a lower wedge rigidly affixed to a replaceable brake shoe; and an intermediate wedge that is located by suitable bearings and/or linkages for transverse, generally horizontal slidable engagement between the upper block and the lower wedge. Each of the upper block and lower wedge elements of the wedge assembly are, respectively, located by suitable bearings and/or linkages for generally vertical translational motion (but very little, if any, lateral or longitudinal horizontal motion) within upper and lower guides provided on a frame of the rail brake.

TECHNICAL FIELD

In embodiments of the presently disclosed subject matter, there is provided a rail brake for braking or anchoring a rail-mounted machine such as a crane.

BACKGROUND

Hydraulically releasable spring-set rail brakes for braking or anchoring rail mounted equipment by pressing a hardened steel brake shoe onto the top surface of a rail (i.e. onto the railhead) under spring force are generally known. In a typical arrangement, when the rail brake is in a release position, a brake shoe is held at a selected vertical distance above the railhead to provide sufficient clearance for track run-out, debris and the like, and at least one associated main power spring is correspondingly held in compression by hydraulic force acting on a piston within a cylinder. As the hydraulic pressure within the cylinder is reduced under control of an operator to a value that is below the restorative spring force of the main power springs, the springs relax, causing the rail brake to advance into a brake set position, in which the piston retreats into the cylinder and the brake shoe correspondingly advances vertically downward into contact with and is pressed onto the railhead.

However, since the restorative spring force of the power springs is highest when the springs are at maximum compression (i.e. in the brake release position) and decreases throughout the stroke of the springs as they relax into the brake set position, a relatively large component of the stored potential energy of the power springs may effectively be wasted during the initial advancement of the brake shoe into contact with the railhead (for which only a comparatively small force is normally required), leaving a relatively small component of the restorative spring force available to press the shoe onto the railhead and do the actual braking. This function of reducing spring force throughout the relaxation stroke of the power springs also limits the vertical distance through which the brake shoe of known rail brakes may be displaced before meeting (and/or deflecting) the railhead, whilst still being capable of providing adequate braking capacity.

SUMMARY

In embodiments of the presently disclosed subject matter, there is accordingly provided an extended range, consistent force rail brake comprising an adjustable wedge assembly operatively situated between the main power spring(s) and the brake shoe(s) for selectively taking up the vertical distance that the brake shoe is required to travel between the brake release position and an initial railhead contact position, before the application of main spring force presses the brake shoe onto the railhead (i.e. fully into the brake set position). The adjustable wedge assembly is thus selectively expandable in the vertical orientation, and may comprise: an upper block that is operatively connected, either directly or indirectly, to the power spring; a lower wedge rigidly affixed to a preferably replaceable brake shoe; and an intermediate wedge that is located by suitable bearings and/or linkages for transverse, generally horizontal slidable engagement between the upper block and the lower wedge. Each of the upper block and lower wedge elements of the wedge assembly are, respectively, located by suitable bearings and/or linkages for generally vertical translational motion (but very little, if any, lateral or longitudinal horizontal motion) within upper and lower guides provided on a frame of the rail brake. In some embodiments, such as those illustrated herein, the transverse vertical cross-section of the lower wedge may comprise a right trapezoid. Other embodiments in which the orientation of the block and wedge elements is essentially inverted (i.e. wherein an intermediate wedge is slidably engaged between an upper wedge and a lower block) are also contemplated and within the scope of the present disclosure.

The engagement surfaces between the upper block, intermediate wedge and lower wedge are selected for relatively high coefficients of static friction, and the wedge angle of the intermediate wedge (and, of course, the corresponding contact angle of the lower wedge) is selected such that, in combination, the transverse, horizontal component of the downwards vertical force exerted on the assembly by relaxation of the main power spring (between at least the railhead contact and brake set positions of the rail brake) is substantially less than the force that would be required to overcome the horizontal component of the frictional force between the engagement surfaces and to drive the intermediate wedge out from between the upper block and lower wedge. In other words, the engagement surfaces and wedge angle are selected such that the resistance to expulsion of intermediate wedge is correspondingly high under large vertically applied loads, thereby providing an acceptable margin of operational safety.

By way of example, a wedge assembly comprising a wedge angle of 14°, engagement surfaces of the upper block and lower wedge formed of mild steel, and engagement surfaces of the intermediate wedge formed of 6061 T6 aluminum alloy, have empirically been shown to remain self-locking under application of a vertical load of at least as much as 440,000 N. Some or all of the engagement surfaces may alternately or in addition be textured or serrated, and/or comprise combinations of known brake-type friction materials and steels (e.g. sintered metallic/mild steel). Many suitable combinations are possible, as would be apparent to those of skill in the art having regard to the foregoing principles.

In some embodiments, a wedge spring biases the intermediate wedge into engagement between the upper block and lower wedge, and a wedge retracting linkage is provided for withdrawing the intermediate wedge from engagement between the upper block and lower wedge in a direction that is opposite to the biasing force supplied by the wedge spring.

When the rail brake transitions from the brake release position to the railhead contact position, the lower wedge is released and permitted to advance vertically downward until the brake shoe makes contact with the railhead. At the same time, the biasing force of the wedge spring draws the intermediate wedge horizontally deeper into engagement between the upper block and lower wedge, such that any slack created by the downward translational movement of the lower wedge is filled. In other words, the overall vertical height of adjustable wedge assembly is expanded.

Once the vertical height of the wedge assembly has been expanded as above, main spring force presses the brake shoe onto the railhead, bringing the brake fully into the brake set position. Since little or no relaxation of the main power spring is required to advance the brake shoe into contact with the railhead, essentially the full restorative spring force (and stroke) of the power spring is available for pressing the brake shoe onto the railhead, thereby increasing the consistency of braking force applied (by reducing dependence on height, and by accommodating deflection of the rail under pressure from the brake), and extending the effective operational range of the rail brake.

When the rail brake is released, and the main power spring is once again compressed by increasing hydraulic force acting on a piston within a cylinder. In embodiments that include a wedge retracting linkage, this movement of the piston brings it into direct or indirect contact with the retracting linkage and acts upon the retracting linkage so as to cause the withdrawal of the intermediate wedge from engagement between the upper block and lower wedge in a direction that is opposite to the biasing force of the wedge spring. In some embodiments, the retracting linkage is configured for a 5:1 lever ratio, such that the intermediate wedge is moved 5 units of length for each one unit of length that the piston acts on the retracting linkage.

In the specific embodiments illustrated herein below, the main power spring comprises a single helical (i.e. coil) spring. However, various alternative biasing means, such as disc springs, self-locking cams, and the like may also be employed for the provision of sufficient suitable braking force, as would be apparent to those of skill in the art.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

The following description of specific embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. The rail brake of the present invention may take form in a number of different embodiments depending upon the particular requirements of the use, such as the nature, size and weight of the rail-mounted equipment to be anchored.

With reference first toFIGS. 5 and 6, there is illustrated an adjustable wedge assembly100for a rail brake10in accordance with one embodiment of the presently described subject matter. The wedge assembly100is selectively expandable in the vertical orientation, and as will be described further below in relation to the specific embodiment ofFIGS. 1-4, is operatively situated between a main power spring18(seeFIGS. 1-4) and a replaceable brake shoe102for selectively taking up the vertical distance that the brake shoe102is required to travel between a brake release position (as seen inFIG. 5) and an initial railhead contact position in which the brake shoe102is in contact with a railhead101. Once the vertical height of the wedge assembly100has thus been expanded to fill this slack distance between the brake release and railhead contact positions of the rail brake, the full restorative force of power spring18is released, causing the rail brake to enter into a brake set position (seeFIG. 6), wherein the brake shoe102is pressed vertically downward onto the railhead101.

Wedge assembly100comprises an upper block104that is operatively connected, either directly or indirectly (such as by a power wedge cam14and rollers16a,16b, as is further described below), to a main power spring18; a lower wedge106rigidly affixed to brake shoe102; and an intermediate wedge108that is located by suitable bearings and/or linkages (not shown) for transverse, generally horizontal slidable engagement between the upper block104and the lower wedge106. Each of the upper block104and lower wedge106elements of wedge assembly100are, respectively, located by suitable bearings and/or linkages (not shown) for generally free vertical translational motion, but limited or no lateral or longitudinal horizontal translational motion, within opposing upper guides110and opposing lower guides112provided, respectively, on a frame12of the rail brake10. In the illustrated embodiment, the transverse vertical cross-section of lower wedge106is right trapezoidal.

The corresponding engagement surfaces114a,114b, respectively, between the upper block104and intermediate wedge108, and the engagement surfaces116a,116b, respectively, between the intermediate wedge108and lower wedge106are selected for relatively high coefficients of static friction, and the wedge angle118of the intermediate wedge108(and, of course, the corresponding contact angle of the lower wedge106) is selected such that, in combination, the transverse, horizontal component of a downwards vertical force acting on the intermediate wedge108of assembly100by relaxation of the main power spring18(during at least the railhead contact and brake set positions of the rail brake10) is substantially less than the force that would be required to overcome the horizontal component of the frictional force between the upper and lower engagement surfaces114,116and to drive the intermediate wedge108horizontally out from between the upper block104and lower wedge106. In other words, the engagement surfaces114,116and wedge angle118are selected such that the resistance to expulsion of intermediate wedge108is correspondingly high under a large vertically applied load, thereby providing an acceptable margin of operational safety. Either or both of engagement surfaces114,116may alternately or in addition comprise textured or serrated surface treatments, and/or comprise combinations of known brake-type friction materials and steels (e.g. sintered metallic/mild steel). In one embodiment, a wedge assembly100comprising a wedge angle of 14°, and in which engagement surfaces of the upper block114aand lower wedge116bformed of mild steel, and the engagement surfaces of the intermediate wedge114b,116aformed of 6061 T6 aluminum alloy, have been shown to remain self-locking under application of a vertical load of at least as much as 440,000 N.

Turning now toFIGS. 1-4, one specific embodiment of a rail brake10is shown. Rail brake10generally comprises a frame12within which a wedge assembly100is supported by suitable bearings and/or linkages (not shown) for generally free vertical translational motion, but limited or no lateral or longitudinal horizontal translational motion, within at least one opposing pair of guides112. A generally frustoconical power wedge cam14is located between upper and lower force generation rollers16a,16b, respectively, within frame12, and is urged in a first, brake set direction by a generally horizontally disposed main power spring18. A hydraulically actuated piston20is operably connected to the cam14, and may be driven under control of an operator by hydraulic pressure in a second, brake release direction opposite to the brake set direction (i.e. against the biasing force of the power spring18) from a hydraulic cylinder22that is formed into or operably connected to the frame12.

In preferred embodiments, in order to enhance efficiency, rollers16aand16bare free rolling in the horizontal orientation (such that the rollers are able to move generally horizontally between the frame12and the wedge assembly100in conjunction with power wedge cam14) and not mounted on axles or pivots. In other embodiments, conventional bearings may be substituted for rollers16a,16b.

In the illustrated embodiment, the frustoconical profile of power wedge cam14is shown as generally linear. However, in preferred embodiments, the profile of power wedge cam14may curve with variable geometry in order to produce linearly increasing mechanical advantage as the power spring18extends, thereby compensating for losses in spring force through extension. Through the selection of suitable cam profiles and dry-running with no lubrication between cam14and rollers16a,16b, the possibility of undesired relative movement of the rollers vis-à-vis the power cam may be minimized.

A wedge spring24biases the intermediate wedge108into engagement between the upper block104and lower wedge106, and a pivotally mounted wedge retracting linkage26is provided for withdrawing the intermediate wedge108from engagement between the upper block104and lower wedge106in a direction that is opposite to the biasing force supplied by the wedge spring24.

When the rail brake10is transitioned from the brake release position to the railhead contact position, the lower wedge106is released and permitted to advance vertically downward until the brake shoe102makes contact with the railhead101. At the same time, the biasing force of the wedge spring24draws the intermediate wedge108horizontally deeper into engagement between the upper block104and lower wedge106, such that any slack created by the downward translational movement of the lower wedge106is filled. In other words, the overall vertical height of adjustable wedge assembly100is expanded.

As the hydraulic pressure within the cylinder22is reduced under control of an operator to a value that is below the restorative spring force of the main power spring18, the spring relaxes, causing the rail brake10to advance into the brake set position in which piston20retreats into the cylinder22and brake shoe102is correspondingly pressed vertically downward onto railhead101via the vertically expanded wedge assembly100. Since very little relaxation of the main power spring18is required to advance the brake shoe102into contact with the railhead101, essentially the full restorative spring force (and stroke) of the power spring18is available for pressing the brake shoe102onto the railhead101, thereby increasing the consistency of braking force applied (by reducing dependence on height of shoe102vis-à-vis railhead101), and extending the effective operational range of the rail brake.

When rail brake10is released, and the main power spring18is once again compressed by increasing hydraulic force acting on piston20within cylinder22. Movement of piston20in the brake release direction brings piston20into contact (either directly or indirectly) with and acts upon retracting linkage26, which in turn withdraws intermediate wedge108from engagement between the upper block104and lower wedge106in a direction that is opposite to the biasing force of the wedge spring24. In the illustrated embodiment, retracting linkage26communicates with a retraction plate27of the piston20via a cam roller28. In some embodiments, the arms of retracting linkage26are configured for a 5:1 lever ratio, such that pivotal motion of linkage26will cause intermediate wedge108to be moved 5 units of length for each one unit of length that the piston20acts on the retracting linkage26.

InFIG. 1, rail brake10is shown in the fully released position, in which power spring18is fully compressed by hydraulic pressure within cylinder22. Wedge extension spring24is fully extended by operation of retraction plate27of piston20on the roller28of linkage26, and there is maximum distance between the brake shoe102and the rail101. Force generation rollers16a,16bare located in a “home” position.

InFIG. 2, hydraulic pressure within cylinder22and been slightly relieved, allowing the power spring18, cam14and rollers16a,16bto extend a small distance horizontally, and to push piston20deeper into cylinder22. This in turn permits wedge extension spring24to draw intermediate wedge108into further engagement between the upper block104and lower wedge106by virtue of the release of linkage26. The wedge108travels only until all the distance is taken up between the brake shoe102and the top of rail101.

InFIG. 3, the power spring18has been extended somewhat further to allow the intermediate adjusting wedge108to take up the maximum distance between the brake shoe102and the rail101. However, it should be noted that even at this maximum distance, at least 75% of power spring18stored energy remains. During each of the foregoing motions, the rollers16a,16band power wedge cam14are advanced horizontally and produce a small downward movement. The rollers and power wedge cam may be kept loaded and free from slippage by loading springs (not shown), and the upper block104under the lower power roller16bmay be laterally restrained by suitable bearings and/or linkages. These elements are not illustrated in the Figures in order to provide principal clarity.

InFIG. 4, the rail brake10is shown with the wedge at maximum vertical rail deviation with high forces applied. It can be noted that the intermediate adjusting wedge108remains in essentially the same position, as the power wedge cam14has continued to travel and generate increasing forces. The amount of power wedge cam movement and corresponding power spring extension is dependent on the stiffness, or spring rate, of the rail and rail bed, and the machine to which the brake is mounted. The wedge, lever and attached lower link, allow small vertical movements, produced by the power wedge. The rail clamp is now producing high applied forces and capable of high resulting braking forces.

To release rail brake10, hydraulic pressure is increased within hydraulic cylinder22. The power spring is compressed and applied forces are steadily reduced, as the power wedge is retracted. The power wedge retracts until it reaches a point equivalent to about 25% of spring travel. At this point a plate comes in contact with the wedge lever cam rollers, thereby starting retraction of the adjusting wedge. Also, a plate mounted at the end of the power wedge contacts the power rollers, moving them towards their home position. It should be noted that all components are only subject to small forces during these motions. Retraction is now completed with all components returned to their home position with maximum clearance between rail and brake shoe. It should also be noted that the rail brake is also available to produce maximum output force at even minimum retracted clearance between brake shoe and rail. The adjusting wedge would simply move a minimum distance and the power wedge would produce high forces sooner; that is all. The adjusting wedge can take effect at an infinite number of positions.

The present description is of the best presently contemplated mode of carrying out the subject matter disclosed herein. The description is made for the purpose of illustrating the general principles of the subject matter and not to be taken in a limiting sense; the described subject matter can find utility in a variety of implementations without departing from the scope of the invention made, as will be apparent to those of skill in the art from an understanding of the principles that underlie the invention.