WO2001068426A1

WO2001068426A1 - Brake cylinder empty/load equipment

Info

Publication number: WO2001068426A1
Application number: PCT/US2000/006366
Authority: WO
Inventors: James Hart
Original assignee: Westinghouse Air Brake Technologies Corporation
Priority date: 2000-03-10
Filing date: 2000-03-10
Publication date: 2001-09-20
Also published as: JP3742011B2; AU2000237380A1; JP2004501016A

Abstract

A system compensates for the weight borne by a railcar in determining the force with which the brakes shall apply. The system includes a brake cylinder (6a) and a valve assembly (20). The brake cylinder features a sealed chamber (74) behind its piston (61). During a brake application when the railcar is empty in which the brake cylinder pressure (BCP) exceeds a changeover level, the valve assembly allows back pressure to build behind the piston. This produces a counterforce to partially offset the force produced by the BCP acting on the front of the piston. During a brake application when the railcar is loaded, the valve assembly allows the chamber to exhaust. The system enables the force with which the brakes apply when the railcar is empty to be a fraction of that when the railcar is loaded, with the fraction lowering as the BCP above the changeover level continues to increase.

Description

BRAKE CYLINDER EMPTY/LOAD EQUIPMENT

FIELD OF THE INVENTION

The invention generally relates to a system for controlling the brakes of a railcar. More particularly, the invention pertains to brake equipment that compensates for the weight of the load borne by a railcar truck in formulating the braking effort to be applied to the wheels of the truck.

BACKGROUND OF THE INVENTION The following background information is provided to assist the reader to understand not only the invention disclosed in this document but also the environment in which the invention will most likely be used. The terms used herein are not intended to be limited to any particular narrow interpretation unless specifically stated otherwise in this document. A freight train includes one or more locomotives, a plurality of railcars and a pneumatic trainline referred to as the brake pipe. The brake pipe is essentially one long continuous tube that runs from the lead locomotive to the last railcar in the train. The brake pipe is actually composed of a series of interconnected pipe lengths, with one pipe length la secured to the underside of each railcar, as shown in Figure 1. The brake pipe of the train is thus formed by connecting the pipe length la on each railcar via a glad hand (i.e., a coupler) 2 to the pipe length ,1a on each adjacent railcar. The brake pipe is the means by which service and emergency bra^'ke commands are conveyed from the brake control system in the lead locomotive to each of the vehicles in the train. It is to the brake pipe that the pneumatic bra e equipment on each railcar connects via a branch pipe 3. The pneumatic brake equipment on each railcar typically includes two storage reservoirs 4 & 5, one or more brake cylinders 6 and at least one brake control valve 7 such as an ADB, ABDX or ABDW type valve made by the estinghouse Air Brake Company (WABCO) . Under conditions known in the brake control art, the brake control valve 7 charges the two reservoirs 4 & 5 with the pressurized air it receives from the brake pipe la. It is the pressure level within the brake pipe la that determines whether the brake control valve 7 will indeed charge these two reservoirs, or deliver pressurized air previously stored in one or both of these reservoirs 4/5 to the brake cylinders 6 to apply the brakes.

There are many different types of brake cylinders in use in the railroad industry. As -shown in Figure 2, a brake cylinder typically includes a piston and rod assembly 60, a return spring 65, and a housing 70 in which these parts are enclosed. The housing defines at one end an inlet port 71 and at its opposite end an aperture 72 from which an end of the rod assembly 60 protrudes. The rod assembly 60 features at its head end a piston head 61. In brake cylinders made by WABCO, the piston head 61 usually has a packing cup 62 that securely snaps on its front side, i.e., the side facing inlet port 71. Concentric to the rod assembly 60, the return spring 65 lies compressed between the back side of the piston head 61 and an annular spring seat 79 located about the aperture 72. Spring 65 serves to bias rod assembly 60 to its release position wherein packing cup 62 lies adjacent to the inlet port 71. From the aperture 72 protrudes the other end of rod assembly 60. By this protruding end 69, the rod assembly 60 links to the brake rigging (not shown) . The brake rigging, in turn, links to the brake shoes (not shown) .

When air from the brake control valve 7 enters the inlet port 71, pressure builds against and forcibly acts upon the surface area of packing cup 62. When the force acting on the front side of packing cup 62 exceeds the force exerted by return spring 65 on the back side of piston head 61, the piston head moves against and further compresses spring 65. This forces the protruding end 69 of rod assembly 60 to extend from the aperture 72 of brake cylinder 6. The mechanical force generated by such movement of rod assembly 60 is transmitted by the brake rigging to the brake shoes, and from the brake shoes it is used to forcibly slow, and/or stop, the rotation of the wheels. The magnitude of the braking force applied to the wheels and/or disc brakes of the railcar is directly proportional to the pressure built up against the inlet facing side of packing cup 62. Ultimately, of course, it is the pressure level within the brake pipe la that determines whether, and to what extent, the brakes will apply on the railcar.

One type of brake control system used in the railroad industry is the 26-L Locomotive Air Brake Control System manufactured by WABCO. This brake control system has two handles referred to as the automatic and independent brake handles. By placing these handles into the appropriate positions, a train operator in the locomotive can control how the brakes on the locomotive (s) and railcars operate. Using these handles, the train operator can control how much pressure will be developed in the brake pipe as well as in other important pipes of the train.

By moving the independent brake handle, the train operator can only direct the brake control system to apply or release the brakes on the locomotive (s) . In contrast, by moving the automatic brake handle, the operator can direct the brake control system to apply or release the brakes on both the locomotive (s) and railcars in the train. The level to which the system reduces pressure within the brake pipe la, and thus the amount of braking power exerted by the train brakes, ultimately corresponds to the position of the automatic brake handle. This brake handle can be moved from and in between a release position at one extreme (in which brake pipe pressure is maximum and the brakes are completely released) to an emergency position at the other extreme (in which brake pipe pressure is zero and the brakes are fully applied) . Movement of the automatic brake handle affects the pressure in the brake pipe la and thus how the pneumatic brake equipment on each railcar operates . Moving the automatic brake handle, for example, from the minimum service position towards the full service positions causes the brake pipe pressure to reduce. Exactly how much it reduces depends on how far towards the full service position the brake handle is moved. It is this reduction in pressure that signals the brake control valve (s) 7 on each railcar to supply pressurized air from one or both storage reservoirs 4/5 to the brake cylinders 6 so as to apply the brakes . The amount of pressure built up in the brake cylinders 6, and thus the magnitude of the braking force applied to the wheels, is generally proportional to the amount by which the pressure in the brake pipe la has been reduced.

Especially in the freight train industry, it is desirable to compensate for the load borne by a railcar in determining the force with which its brakes should be applied. On a freight train whose railcars employ load compensation techniques, the problems typically associated with wide variances in weight, such as elevated buff (compressive) and draft (tensive) forces among railcars, are reduced considerably. For each railcar on which load compensation techniques are employed, the pneumatic brake equipment includes empty and load brake equipment.

WABCO manufactures several types of empty and load brake equipment. One such configuration, the SC-1 type shown in Figure 1, employs a P-1 load proportional valve 8 and an S-1 load sensor valve 9, hereafter referred to as the P-1 load valve and S-1 load sensor, respectively. The objective of this equipment is to reduce the force with which the brakes apply when the railcar is empty, yet still permit strong braking on the railcar when it is loaded. Without such equipment, the wheels on an empty railcar tend to slide on the rails during such strong braking and thus sustain damage. On a train with railcars equipped with empty and load brake equipment, the braking is more uniformly applied throughout the train in accordance with the load borne by the individual railcars. This equipment reduces the coupler forces between adjacent railcars and improves overall handling of the train.

Each railcar typically has two trucks (not shown) , one at each end. Each truck includes the wheels, axles, suspension springs, side frames and other parts that together form the structure that supports the body of the railcar. The suspension springs dampen the impacts and vibrations that would otherwise be transmitted from the wheels to the railcar body, and that could otherwise cause damage to the railcar body and/or to the cargo it carries. The springs deflect or compress to an extent proportional to the weight of the load carried by the railcar.

Typically mounted to the underside of the railcar body above each truck, the S-1 load sensor 9 has a sensor arm 90. The load sensor 9 automatically senses whether the railcar is loaded or empty by using its sensor arm 90 to measure the distance between the railcar body and the top of the side frame 100 on the truck. When loaded, the railcar body further compresses the suspension springs thereby reducing the distance between the railcar body and the side frame 100. The distance that the sensor arm 90 can travel is therefore more limited when the railcar is loaded. Conversely, when the railcar is empty, the suspension springs are less compressed thereby maximizing the distance between the railcar body and the side frame. The distance the sensor arm 90 can travel is then at its maximum. Figure 1 illustrates the pneumatic brake equipment in the state it would exist when the brakes are completely released, regardless of whether the railcar is bearing a load. Specifically, with the brakes completely released, the brake pipe la would have to be pressurized to its normal operating pressure. Connected to brake pipe la via branch pipe 3, the brake control valve 7 would have responded to that level of brake pipe pressure by venting the air via pipe 10 from chamber 80 underneath piston 81 of P-1 load valve 8. Because chamber 80 is also connected to first pipe network 11, brake control valve 7 would also have vented air from chamber 91 next to piston assembly 92 of load sensor 9. Anytime the pressure in chamber 91 falls below a preset changeover value (typically 13-15 psi) , spring 93 moves piston assembly 92 back to its exhaust position wherein spool 94 is shifted to the point shown in Figure 1. In this exhaust position, the S-1 load sensor 9 allows diaphragm chamber 82 above piston 81 to exhaust via second pipe network 12 (and equalizing volume 13) to atmosphere via exhaust port 99. The load sensor also keeps its chamber 91 connected to pipe network 11. The force of spring 84 and the extant brake cylinder pressure (BCP) that together compel the check valve of piston 81 off seat 83, coupled with the venting of pressure from diaphragm chamber 82 atop piston 81, enable brake control valve 7 to exhaust the pressure in brake cylinder 6 to atmosphere via pipe network 11, chamber 80 and pipe 10. During a brake application, the pressure in the brake pipe la will reduce to the extent dictated by the magnitude of the brake application being sought. The brake control valve 7 responds to this reduction in brake pipe pressure by supplying pressurized air from the appropriate reservoir (s) 4/5 via pipe 10 to chamber 80 underneath piston 81. Being connected to chamber 80, pipe network 11 communicates this pressurized air to both the brake cylinder 6 and the chamber 91 next to piston assembly 92. The constant of spring 93 is chosen so that piston assembly 92 will be kept in the exhaust position until the BCP in chamber 91 exceeds the changeover value. Consequently, for a light application of the brakes, all of the pressurized air from brake control valve 7 will be directed to brake cylinder 6 whether the railcar is empty or loaded. Only when the BCP in chamber 91 exceeds the changeover value will piston assembly 92 be able to move rightwardly and affect the internal porting of load sensor 9.

Figure 3 illustrates how the S-1 load sensor 9 would react during an application of the brakes on a railcar that is loaded. The suspension springs on each truck would, of course, be compressed to the extent dictated by the load that the railcar bears. The distance between the railcar body and the side frames of each truck would therefore be reduced. As the BCP supplied by brake control valve 7 to chamber 91 exceeds the changeover value, piston assembly 92 moves against spring 93, with its rightmost end forcibly moving sensor arm 90. With the railcar bearing a load, the sensor arm eventually contacts the top of the side frame 100. The side frame precludes further movement of sensor arm 90 and thereby prevents piston assembly 92 from moving spool 94 to the point at which it would interconnect pipe networks 11 and 12. As long as the pipe networks are cutoff from each other, the brake control valve 7 is cutoff from the P-1 load valve 8. Air from the brake control valve will be able to flow only to brake cylinder 6 via pipe 10, chamber 80 and pipe network 11. The resulting braking force applied to the wheels would then be directly proportional to the amount by which the pressure in the brake pipe la reduced, and would not be diminished by the P-1 load valve 8.

Figure 4 illustrates how the S-1 load sensor 9 would react on a railcar that is empty during an application of the brakes. Absent any load, the suspension springs on each truck will be compressed only to the extent determined by the weight of the empty railcar body. The sensor arm 90 would thus be able to travel to its fullest extent, limited only by the internal structure of the S-1 load sensor 9. (Typically, a load sensor is configured so that a railcar will be considered empty if its springs do not compress more than 20% of their total range of motion.) Consequently, as the BCP supplied by brake control valve 7 to chamber 91 exceeds the changeover value, piston assembly 92 moves against spring 93, with its rightmost end forcibly pushing the sensor arm 90. With the railcar bearing no load and sensor arm 90 thus free to be moved downwardly without contacting the side frame 100, the build up of pressure in chamber 91 moves piston assembly 92 rightwardly far enough to carry spool 94 to the point shown in Figure 4. In this position, spool 94 aligns passages 97 and 98 and, in doing so, connects pipe networks 11 and 12. Pressurized air thus flows from the brake control valve 7 through pipe networks 11 and 12 (and equalizing reservoir 13) into the diaphragm chamber 82 of P-1 load valve 8. The internal structure of the P-1 load valve 8 determines what fraction of the pressure existing in pipe 10, courtesy of brake control valve 7, will be developed in the brake cylinder 6. In the freight train industry, this fraction is typically fixed at 50-60% or some other preset percentage. This percentage is governed by spring 84 and by piston 81, in particular by the relationship of the effective area of its underside to the effective area of the topside of its diaphragm.

(Multiplying the effective area of a side of a piston by the pressure impinging on it gives the force acting on that side of the piston.) With the railcar empty, pressurized air from the brake control valve 7 flows not only to the underside of piston 81 via pipe 10 but also to the topside of piston 81 (i.e., into diaphragm chamber 82) via pipe networks 11 and 12. Whenever the pressure in diaphragm chamber 82 reaches the preset percentage of that in pipe 10, the force acting on the topside of piston 81 is sufficient to overcome the sum of the forces exerted on the underside of piston 81 by spring 84 and the pressure conveyed by pipe 10. Simply stated, whenever the BCP reaches the preset percentage of that provided to pipe 10 by brake control valve 7, the check valve of piston 81 will close against seat 83 and thereby cutoff the flow of air from brake control valve 7 to the brake cylinder 6. On a railcar equipped with empty and load brake equipment, the force with which the brakes would apply on that railcar when empty would be the preset percentage (e.g., 50-60%) of that with which they would apply on that railcar if it were loaded. The relationship between the force output by the brakes on the railcar when empty and the force output by the brakes on the railcar when loaded is referred to as the empty- to-loaded force ratio. The S-1 load sensor 9 thus serves to regulate the flow of air to the P-1 load valve 8. No air is directed to the diaphragm chamber 82 of P-1 load valve 8 on a loaded railcar. On an empty railcar, however, air from the brake control valve 7 will be directed to the diaphragm chamber 82 as long as the BCP it supplies via pipe network 11 to chamber 91 is above the changeover value. During brake applications, the equalizing volume 13 is used to maintain a satisfactory relationship between pressure in the empty and load brake equipment and that in the brake control valve 7 and its reservoirs 4/5 when the railcar is empty. It is the P-1 load valve 8, however, that actually controls the flow of air to the brake cylinder 6 on an empty _, railcar . Specifically, the pressure that the P-1 load valve 8 allows to be built up in the brake cylinder 6 when the railcar is empty is usually 50-60% of what is developed in the brake cylinder 6 when the railcar is loaded for all BCPs above the changeover value (i.e., for all brake applications above a minimum application) .

Another type of empty and load brake equipment, the ELX type, which performs the functions of the S-1 load sensor 9 and P-1 load valve 8 within a single unit, is described in U.S. Patents 5,005,915 and 5,100,207. These patents are assigned to the assignee of the invention disclosed below, and their teachings are incorporated into this document by reference. The load valve and equalizing volume add considerable weight to the empty and load equipment described above. They also occupy space and, especially for the SC-1 type, can complicate the installation of the equipment. Although this prior art empty and load equipment allows the brakes to be applied on an empty railcar with a force that is a fraction of that on a loaded railcar, it does not allow the empty-to-loaded force ratio to be reduced as the BCP rises. The fraction and ratio are generally fixed, no matter how high the BCPs rises above the changeover value. OBJECTIVES OF THE INVENTION

It is, therefore, an objective of the invention to provide a load compensation system that reduces the empty-to- loaded force ratio as the BCP rises beyond a changeover value. Another objective is to provide a load compensation system that does not require a load valve or an equalizing volume, thus making the system simpler, lighter in weight and smaller in size than ^'prior art empty and load equipment.

In addition to the objectives and advantages listed above, various other objectives and advantages of the invention will become more readily apparent to persons skilled in the relevant art from a reading of the detailed description section of this document. The other objectives and advantages will become particularly apparent when the detailed description is considered along with the drawings and claims presented herein. ^■

SUMMARY OF THE INVENTION The foregoing advantages and objectives are attained by the various embodiments of the invention summarized below.

In a first preferred embodiment, the invention provides a system for compensating for the weight of a load borne by at least one truck of a railcar in determining the force with which the brakes a e to be applied on the truck (s) . Each truck typically has a brake control valve and a load sensor interconnected via a first pipe network. When front pressure developed in the first pipe network by the brake control valve is greater than a preset amount and the railcar is empty, the load sensor interconnects a second pipe network to the first pipe network. When the front pressure is lower than the preset amount, regardless of whether the railcar is empty or loaded, the load sensor disconnects the pipe networks from each other and interconnects the second pipe network to atmosphere . The system includes a brake cylinder and a valve assembly. The brake cylinder has a rod assembly normally biased to a release position. The rod assembly has a protruding end to link to the brakes and a head end formed as a piston. The brake cylinder defines an inlet port for receiving fluid from the brake control valve to allow front pressure to build via a first pipe network against a front side of the piston. The build up of such pressure moves the rod assembly from the release position to an applied position. Inside the brake cylinder is a seal to form a compensating chamber concentric to the rod assembly adjacent to a back side of the piston. The valve assembly defines (i) an output port connected to atmosphere, (ii) a release passage connected to the first pipe network, (iii) a back passage network connected to the compensating chamber, and (iv) a front passage network connected to the load sensor through the second pipe network. The valve assembly includes a displacement valve, a release valve and a differential valve. The displacement valve has a normally open position wherein the output port communicates with the back passage network thereby connecting the compensating chamber to atmosphere. In its closed position, it cuts the back passage network off from the output port thereby disconnecting the compensating chamber from atmosphere. The displacement valve adopts the closed position when the front pressure exceeds a predetermined value and the load sensor senses the railcar is empty. The release valve has a normally closed position wherein the back passage network is cutoff from the release passage. The release valve assumes an open position when the front pressure in the release passage falls a minimal amount lower than back pressure existing in the compensating chamber. This allows the back pressure to exhaust, until the displacement valve opens, through the release valve and the release passage to atmosphere along with the front pressure via the first pipe network and the brake control valve. The differential valve has a normally closed position wherein the front passage network is cutoff from the back passage network. The differential valve adopts an open position when the front pressure exceeds a changeover amount more than the back pressure. When it opens, fluid flows from the brake control valve to the compensating chamber through the first and second pipe networks via the load sensor and through the front and back passage networks. As the front pressure increases, the back pressure also increases. The back pressure, however, remains lower than the front pressure by the changeover amount, as dictated by the differential valve. As back pressure builds against the back side of the piston, it produces a counterforce to partially offset the force produced by the front pressure acting on the front side of the piston. This enables the force with which the brakes apply when the railcar is empty to be a fraction of the force with which the brakes apply when the railcar is loaded, with the fraction lowering as the front pressure is increased.

In a second preferred embodiment, the system includes a brake cylinder, a load sensor and a valve assembly. The brake cylinder is the same as that summarized for the first embodiment. The load sensor is interconnected to the brake control valve and the inlet port via the first pipe network. It is also connected to a second pipe network. Upon sensing the railcar is loaded or while the front pressure is lower than a preset amount when the railcar is empty, the load sensor assumes an exhaust position in which the pipe networks are disconnected from each other and the second pipe network is interconnected to atmosphere. Upon sensing the railcar is empty while the front pressure is greater than the preset amount, the load sensor shifts to a transfer position in which the first and second pipe networks are interconnected. The load sensor is configured so that the preset pressure it requires to shift to the transfer position exceeds the front pressure required to move the rod assembly to the point at which the brakes begin to apply. The valve assembly includes a release valve and a differential valve whose tops communicate with the compensating chamber and whose bottoms communicate with the load sensor through the second pipe network. The release valve has a normally closed position wherein the compensating chamber is cutoff from the second pipe network. When pressure in the second pipe network falls a minimal amount lower than back pressure existing in the compensating chamber, the release valve assumes an open position thereby allowing the compensating chamber to exhaust via the second pipe network. The differential valve has a normally closed position wherein the second pipe network is cutoff from the compensating chamber. When the front pressure conveyed by the load sensor to the second pipe network exceeds a changeover amount more than the back pressure, the differential valve adopts an open position thereby allowing fluid from the brake control valve to be admitted to the compensating chamber through the first and second pipe networks via the load sensor. As the front pressure increases, the back pressure also increases. The back pressure, however, remains lower than the front pressure by the changeover amount, as dictated by the differential valve. As back pressure builds against the back side of the piston, it produces a counterforce to partially offset the force produced by the front pressure acting on the front side of the piston. This enables the force with which the brakes apply when the railcar is empty to be a fraction of the force with which the brakes apply when the railcar is loaded, with the fraction lowering as the front pressure is increased.

In a third preferred embodiment, the system includes a brake cylinder and a load sensor. The brake cylinder and load sensor are the same as those summarized for the previous embodiment. The compensating chamber of the brake cylinder communicates with a second pipe network. The load sensor is interconnected to the brake control valve and the inlet port via the first pipe network. It is also interconnected to the compensating chamber via the second pipe network. Upon sensing the railcar is loaded or while the front pressure is lower than a preset amount when the railcar is empty, the load sensor assumes the exhaust position in which the first pipe network is disconnected from the second pipe network and the second pipe network is interconnected to atmosphere to vent the compensating chamber. Upon sensing the railcar is empty while the front pressure is greater than the preset amount, the load sensor shifts to the transfer position in which the first and second pipe networks are interconnected thereby allowing back pressure equal to the front pressure to build in the compensating chamber. This produces a counterforce against the back side of the piston that partially offsets the force produced by the front pressure acting on the front side of the piston. This enables the force with which the brakes apply when the railcar is empty to be a fraction of the force with which the brakes apply when the railcar is loaded, whenever the front pressure exceeds the preset amount.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic of the pneumatic brake equipment for a typical railcar of a freight train, showing the internal states that the S-1 load sensor and the P-1 load proportional valves would assume when the brakes are completely released.

Figure 2 is a cross-sectional view of a brake cylinder . Figure 3 shows the S-1 load sensor as it would react on a loaded railcar during an application of the brakes.

Figure 4 shows the S-1 load sensor as it would react on an empty railcar during an application of the brakes.

Figure 5 is depicts the invention in a first embodiment.

Figure 6 is depicts the invention in a second embodiment .

Figure 7 is depicts the invention in a third embodiment . DETAILED DESCRIPTION OF THE INVENTION

Before describing the invention in detail, the reader is advised that identical components having identical functions have been marked, where possible, with the same reference numerals in each of the Figures provided in this document. This has been done for the sake of clarity and to improve understanding of the invention. The invention is an improved empty and load apparatus .

Figures 5-7 depict three separate embodiments of the invention. In each embodiment, the invention is designed to operate with a load sensor and a brake control valve, such as the brake control valve 7 and the S-1 load sensor 9 described above. The invention is described below as if configured to operate on a per truck basis, as would be the case on multi- platform intermodal railcars as they use one load sensor for each truck. Nevertheless, it should be apparent from a reading of this document that the invention may be implemented on a per railcar basis, as would be the case with conventional two-truck railcars as they use a single load sensor to affect the braking on both trucks . Figure 5 illustrates the essential details of a first embodiment of the invention. In this embodiment, the invention

^*■' includes a revised brake cylinder 6a and a valve assembly 20.

The brake cylinder 6a may be manifested as a modification of any one of the many brake cylinders currently in use in the railroad industry. One type of brake cylinder on which the revised brake cylinder 6a may be based is the ABU type brake cylinder produced by WABCO. The modification entails the use of a seal 73 inside the brake cylinder. The seal 73 may take the form of an o-ring, a cup, or any other type of slidable seal, and may be carried within the cylinder or by piston head 61 or both. Deployed concentric to rod assembly 60 adjacent to the back side of piston head 61, the seal 73 forms an airtight chamber, hereafter referred to as compensating chamber 74. Before my invention, the space now designated as compensating chamber 74 was typically left open to atmosphere.

The valve assembly 20 defines two passage networks. The back passage network 75 communicates with the compensating chamber 74 within the brake cylinder 6a. The front passage network 76 communicates with the load sensor via pipe network 12. The valve assembly 20 also has an output passage 77 open to atmosphere, and a release passage 78 that is connected to brake control valve 7 and the load sensor 9 via pipe network 11.

The valve assembly 20 features three check valves, namely, displacement valve 3O, differential valve 40 and release valve 50. Each of these check valves is housed in its own valve housing, as is also shown in Figure 5. Displacement valve 30 has a two-part valve housing 39, whereas check valves 40 and 50 have one-part valve housings 49 and 59, respectively. The release valve 50 is oriented upside down with respect to the displacement and differential valves 30 and 40. With due regard to the orientation of the valves, the bottom of each valve communicates directly with the back passage network 75 and therethrough with the compensating chamber 74 in the revised brake cylinder 6a. The valve housing 39 for displacement valve 30 is composed of two parts 39A and 39B. The lower part 39A contains valve member 31 and main spring 32. The upper part 39B houses a spring-biased piston assembly. Just above valve member 31, the valve housing 39 communicates with output passage 77. Compressed between lower spring seat 32a at the base of housing 39 and upper spring seat 32b on the underside of valve member 31, main spring 32 serves to bias valve member 31 upwardly against a valve seat 33 formed in housing 39 below output passage 77. In the upper part 39B of housing 39, the piston assembly includes piston 34 and counter spring 35. Piston 34 features a disc portion 34b and a protuberant portion 34a, with the protuberant portion 34a having upper and lower sections of preferably different diameters. The disc portion 34b and the upper section of the protuberant portion 34a have their respective diameters preferably matched to fit snugly within the bore of housing 39. Moreover, the perimeter of disc portion 34b preferably defines a groove to accommodate a sealing ring 36b. The upper section of protuberant portion 34a likewise preferably defines a groove in which to secure a second sealing ring 36a. The sealing rings are intended to provide an air-tight barrier, yet allow the piston 34 to be moved within its bore. The lower section of protuberant portion 34a has a diameter narrower than the bore in which it is located, and the area in which it operates is located in proximity to output passage 77. Figure 5 also shows that protuberant portion 34a is situated so that its lower tip contacts the topside of valve member 31.

Piston 34 also defines an equalizing channel 38. This channel extends from the lower section of protuberant portion 34a to the top of disc portion 34b. It permits air to flow between output passage 77 and the upper part 39B of valve housing 39. The equalizing channel 38 assures that the operation of displacement valve 30 will not be impeded by differences in pressure that could otherwise develop at opposite ends of piston 34. Housing 39 also accommodates a piston stop 37 in its upper part 39B. This piston stop 37 communicates directly with the front passage network 76 and indirectly therethrough with the load sensor 9 via pipe network 12. Counter spring 35 lies in compression between the top of housing 39 and the topside of piston 34. Its constant is chosen so that it normally holds piston 34 downwardly against the opposing force exerted by main spring 32 on valve member 31. The piston 34 thus has its disc portion 34b normally seated against piston stop 37, with the lower tip of its protuberant portion 34a holding valve member 31 off valve seat 33. Being normally biased in this open position, displacement valve 30 allows air to escape from compensating chamber 74 through back passage network 75 and lower housing 39A past valve member 31 and out output passage 77. As explained in detail below, only when the pressure on the underside of disc portion 34b exceeds a predetermined value will the combined forces exerted by such pressure and main spring 32 be sufficient to overcome counter spring 35 and close valve member 31 on valve seat 33. When compelled to assume this closed position, displacement valve 30 prevents air within the compensating chamber 74 from escaping to atmosphere via output passage 77. Differential valve 40 features valve member 41 and biasing spring 42 within valve housing 49. Spring 42 lies in compression between lower spring seat 42a at the base of housing 49 and upper spring seat 42b on the underside of valve member 41. The bottom of valve 40 communicates with compensating chamber 74 through back passage network 75. The top of differential valve 40 communicates with load sensor 9 via front passage network 76 and pipe network 12. Spring 42 biases valve member 41 in the closed position against a valve seat 43 formed in housing 49. As explained below, the constant of spring 42 plays a major role in determining how much force is output by the brake cylinder 6a to the brakes when the railcar is empty.

Release valve 50 features valve member 51 and biasing spring 52 within valve housing 59. Spring 52 lies in compression between upper spring seat 52a at the top of housing 59 and lower spring seat 52b on the topside of valve member 51. The bottom of valve 50 communicates with compensating chamber 74 through back passage network 75. The top of release valve 50 communicates with brake control valve 7 and load sensor 9 via release passage 78 and pipe network 11. Spring 52 biases valve member 51 downwardly in the closed position against a valve seat 53 formed in valve housing 59. The constant of spring 52 is preferably quite small.

Being normally biased in the closed position, release valve 50 only opens whenever the BCP or front pressure acting on the front side of brake cylinder 6a is a minimal amount lower than that acting on its back side, i.e., in compensating chamber 74. The exact value selected for the minimal amount will be relatively low given the purpose of the release valve. More specifically, only when the pressure on the underside of valve member 51 is sufficient to overcome the combined forces exerted on the topside of valve member 51 by the BCP and spring 52 will release valve 50 open. This occurs when brake control valve 7 reacts to a release brake command by venting to atmosphere the pressure on the front side of brake cylinder 6a via inlet port 71 and pipe network 11. As long as release valve 50 is open, the pressure in compensating chamber 74 exhausts to atmosphere along with the pressure from the front side of the brake cylinder 6a. I. OPERATION OF FIRST EMBODIMENT OF INVENTION

Figure 5 indicates how the first embodiment of the invention operates with brake control valve 7 and load sensor 9. The invention allows the load borne by the truck (s) to be taken into account in determining the force with which the brakes will be applied. More important, however, is that it enables the empty-to-loaded force ratio of the brake cylinder 6a to be reduced as the BCP rises beyond a changeover value, as explained below.

A. OPERATION DURING A RELEASE OF BRAKES According to known practice, the brake pipe is pressurized to its normal operating pressure when the train operator moves the automatic brake handle to the release position. In the configuration shown in Figure 5, the brake control valve 7 will respond to the resulting increase in brake pipe pressure by venting air from the front side of brake cylinder 6a via inlet port 71 and pipe network 11. Because pipe network 11 is also connected to load sensor 9 and release passage 78, the brake control valve 7 also vents air from chamber 91 of load sensor 9 and from the top of release valve 50. As explained earlier, anytime the pressure within chamber

91 falls below the preset value, spring 93 moves piston assembly

92 leftwardly, carrying spool 94 to the exhaust position. In its exhaust position, load sensor 9 allows both the underside of disc portion 34b of displacement valve 30 and the top of differential valve 40 to exhaust to atmosphere via pipe network 12 and exhaust port 99.

Assume it is an empty railcar on which the brakes are being released, thus meaning that pressure has previously been built within compensating chamber 74. As brake control valve 7 exhausts air from pipe network 11, release valve 50 is the first valve in valve assembly 20 to react to the drop in BCP. Specifically, a small pressure differential soon develops across release valve 50. Once this pressure differential reaches the point at which spring 52 can no longer hold valve member 51 on seat 53, release valve 50 opens. The air under pressure in compensating chamber 74 then exhausts through release valve 50 and release passage 78 and, along with the air from the front side of brake cylinder 6a, through pipe network 11 to atmosphere via brake control valve 7. With load sensor 9 in the exhaust position, pressure is also being simultaneously removed from the topside of valve member 41 and from the underside of disc portion 34b. The force exerted on the underside of valve member 41, primarily by spring 42 and to a lesser degree by the extant pressure in compensating chamber 74, keeps differential valve 40 closed as the brakes are releasing.

Displacement valve 30 will eventually open, however, when the pressure on the underside of disc portion 34b drops to or below the predetermined value. Specifically, as the pressure drops below this threshold level, the force exerted by counter spring 35 on piston 34 overcomes the opposing forces exerted on valve member 31 by main spring 32 and the extant pressure in compensating chamber 74. Piston 34 moves downwardly, with disc portion 34b stopping on stop 37 and the lower tip of protuberant portion 34a pushing valve member 31 off seat 33. Consequently, whenever the BCP (in front passage network 76) falls below the threshold value, displacement valve 30 allows air to escape from compensating chamber 74 through back passage network 75 and lower housing 39A past valve member 31 and out output passage 77 to atmosphere. The pressure in compensating chamber 74 now rapidly drops, causing the force acting on the underside of valve member 51 to fall quickly below that required to keep release valve 50 open. With the pressure differential across valve 50 now changed in favor of the topside of valve member 51, release valve 50 closes. Compensating chamber 74, however, remains open to atmosphere via displacement valve 30. The revised brake cylinder 6a reacts to the evacuation of pipe network 11 by retracting its piston and rod assembly 60 inwardly into housing 70. More specifically, with the^' pressure dropping on the front side of piston head 61, return spring 65 (aided minimally by the extant pressure in compensating chamber 74) expands against the back side of piston head 61. Rod assembly 60 is thereby retracted to its release position wherein packing cup 62 on piston head 61 sits adjacent to inlet port 71 of housing 70, as shown in Figure 5. The protruding end 69 of rod assembly is what is physically attached to the brake rigging on the truck. ^' The retraction of rod assembly 60 therefore releases the brakes.

B. OPERATION DURING AN APPLICATION OF BRAKES

During a brake application, the pressure in the brake pipe reduces to the extent dictated by the magnitude of the brake application being sought. In the configuration shown in Figure 5, the brake control valve 7 will respond to the resulting decrease in brake pipe pressure by supplying pressurized air from the appropriate reservoir (s) 4/5 to the front side of brake cylinder^' 6a via inlet port 71 and pipe network 11. Because pipe network 11 is also connected to release passage 78 and¹ load sensor 9, brake control valve 7 also supplies air to the top of release valve 50 and to chamber 91 next to the piston assembly 92 of load sensor 9. Little or no pressure initially exists within compensating chamber 74 when the brakes are first being compelled to apply. Consequently, the force of biasing spring 52, coupled with that from the rise in BCP in pipe network 11, will hold valve member 51 on seat 53, thereby keeping release valve 50 closed. As noted earlier in regards to load sensor 9, spring

93 has its constant chosen so that piston assembly 92 is kept in the exhaust position until the BCP in chamber 91 exceeds the preset value. Consequently, for any application of the brakes lighter than or equal to a preset magnitude, all of the pressurized air from brake control valve 7 will be directed to brake cylinder 6a whether the railcar is empty or loaded. Only when the pressure in chamber 91 exceeds the preset value will piston assembly 92 be able to move rightwardly and affect the internal porting of the load sensor 9. Employed as shown in Figure 5, load sensor 9 connects the BCP to valve assembly 20 when the railcar is empty as explained below and disconnects it when the railcar bears a load.

1. APPLICATION OF BRAKES ON A LOADED RAILCAR

On a loaded railcar, the suspension springs on each truck compress to the extent dictated by the weight of the railcar body and the load it carries. The distance between the railcar body and the side frame 100 of each truck would therefore be shorter than it would be on an empty railcar. When the pressure supplied by brake control valve 7 to chamber 91 exceeds the preset value, piston assembly 92 moves against spring 93, with its rightmost end forcibly moving the sensor arm 90. Because the railcar is loaded during this brake application, the sensor arm 90 soon contacts the top of side frame 100. The side frame 100 precludes further movement of sensor arm 90, thus preventing piston assembly 92 from moving spool 94 to the point at which it would interconnect pipe networks 11 and 12. (See Figure 3) As long as load sensor 9 keeps pipe networks 11 and 12 disconnected from each other, brake control valve 7 is cutoff from front passage network 76. Displacement valve 30, therefore, remains open and differential valve 40 remains closed. This leaves compensating chamber 74 open to atmosphere, and prevents pressure from building up on the back side of piston head 61 of brake cylinder 6a.

Even for a brake application greater than the preset magnitude, the brake control valve 7 on a loaded railcar will only be able to supply air to release passage 78 and the front side of brake cylinder 6a via pipe network 11. The pressure building in release passage 78 contributes to the force exerted by spring 52 on the topside of valve member 51 to keep release valve 50 closed. Meanwhile, the air flowing into inlet port 71 soon generates a force on the front side of piston head 61 that exceeds the opposing force exerted by return spring 65 on its back side. From the perspective of Figure 5, this force moves piston head 61 leftwardly causing it to further compress return spring 65 and forcing the protruding end 69 of rod assembly 60 to extend outwardly from the aperture 72 of brake cylinder 6a. The extension of rod assembly 60 forces the brake rigging to apply the brakes. Because the invention and load sensor 9 prevented pressure from building up on the back side of piston head 61, the magnitude with which the brakes apply is directly proportional to the pressure built up against the front side of piston head 61.

2. APPLICATION OF BRAKES ON AN EMPTY RAILCAR

On an empty railcar, the suspension springs on each truck compress only to the extent dictated by the weight of the railcar body. The distance between the railcar body and the side frame 100 of each truck would therefore be at its maximum. When the pressure supplied by brake control valve 7 to chamber 91 exceeds the preset value, piston assembly 92 is pushed rightwardly against the opposing force of spring 93. Because the railcar is empty during this brake application, the sensor arm 90 is pushed downwardly to its fullest extent, without contacting the side frame 100 of the truck. The resulting build-up of pressure in chamber 91 moves piston assembly 92 rightwardly far enough to carry spool 94 to the point at which it interconnects pipe networks 11 and 12. (See Figure 4) Consequently, in addition to supplying release passage 78 and inlet port 71 through pipe network 11, brake control valve 7 is now allowed by load sensor 9 to supply air to check valves 30 and 40 via front passage network 76 and pipe networks 11 and 12.

Valve assembly 20 responds to the brake application as follows when the railcar is empty. Release valve 50 stays closed because the pressure building in release passage 78 contributes to the force exerted by spring 52 to keep valve member 51 seated on seat 53. Displacement valve 30 remains open until the pressure in front_, passage network 76 exceeds the predetermined value. Differential valve 40 remains closed until the pressure in front passage network 76 exceeds a changeover level. Air from brake control valve 7 therefore acts upon the front side of piston head 61 via inlet port 71 before any air is admitted to compensating chamber 74. By remaining open until the BCP rises to the predetermined level, displacement valve 30 keeps compensating chamber 74 vented to atmosphere and thereby allows the piston and rod assembly 60 to be moved easily from the release position towards the applied position. The movement of rod assembly 60, of course, effectively reduces the volume of compensating chamber 74 and displaces the atmospheric pressure it contains, as such pressure is vented to atmosphere via displacement valve 30 and output passage 77. The predetermined level is preferably set between a minimum of 7 psi and a maximum of 35 psi, the exact value being lower than the changeover pressure dictated by differential valve 40. Displacement valve 30 thus prevents compensating chamber 74 from acting as a closed chamber, i.e., as an air-tight chamber that would impede the initial movement of the rod assembly 60 towards the applied positio .

Displacement valve 30 closes as soon as the BCP in front passage network 76 exceeds the predetermined value. Specifically, the force that such pressure develops on the underside of disc portion 34b, when combined with the force exerted by main spring 32 on the underside of valve member 31, is sufficient to overcome counter spring 35 and close valve member 31 on valve seat 33. When closed, displacement valve 30 prevents the extant air in compensating chamber 74 from escaping to atmosphere via output passage 77. Until the BCP in front passage network 76 rises beyond the changeover level, compensating chamber 74 will also remain closed to the influx of air from brake control valve 7.

Differential valve 40 initially opens when the pressure in front passage network 76 exceeds the changeover level. Specifically, pressure in excess of the changeover level will forcibly move valve member 41 off seat 43 against the opposing force of spring 42. When opened, differential valve 40 allows air from brake control valve 7 into compensating chamber 74 via front passage network 76 and pipe networks 11 and 12. It also maintains a generally fixed pressure differential across valve member 41. Due to this incoming_, air, "back pressure" builds in compensating chamber 74 and forcibly acts on the back side of piston head 61. On an empty railcar when the brake command requires

BCP to be greater than the changeover amount, the invention thus allows brake control valve 7 to supply air to both the front and back sides of piston head 61. The air flowing into inlet port 71 generates a force on the front side of the piston head that will exceed the opposing forces exerted (by return spring 65 and the back pressure) on its back side. Under these conditions, the pressure on the front side of piston head 61 will always be higher than the back pressure by the fixed differential, with the front pressure acting on a larger effective area. A net or "effective" ^' force is thus output by brake cylinder 6a to the braking rigging, and this force increases as both the front and back pressures are increased. The effective force owes its origins to what can be referred to as the "effective BCP," i.e., a pressure equivalent to that which would be necessary, absent back pressure, to apply against the front side of piston head 61 to produce a force of the same magnitude.

Until the brakes are released, the back pressure will always be the sum of the brake cylinder (i.e., "front") pressure acting on the front side of piston head 61 minus the changeover amount. For example, if the differential is set at 30 psi, the pressure in chamber 74 will always be 30 psi less than the pressure acting against the front side of piston head 61. This differential, or changeover pressure, is governed primarily by the constant of spring 42 and by valve member 41, in particular by its mass and the effective area of its top and undersides. The back pressure in compensating chamber 74 serves to reduce the overall force output by brake cylinder 6a when the railcar is empty. The effective force that the brake cylinder 6a outputs to the brakes is reduced by an increasing amount, relative to the force output when the railcar is loaded, as the BCP rises beyond the changeover value. The effective brake force output under these conditions is, of course, dependent on many factors. The factors include (a) the effective areas of the front and back sides of piston head 61, (b) the magnitude of the front and back pressures acting on those surfaces, and (c) the constant of return spring 65.

Furthermore, the ratio of the effective force output by brake cylinder 6a when the railcar is empty to the force that it outputs when the railcar is loaded is also dependent on the cited factors . Also important are the characteristics of differential valve 40 (e.g., the constant of spring 42 and the mass and surface areas of valve member 41).

The ratio of empty-to-loaded output forces is thus related to the effective BCP. The higher that the BCP is on the railcar when loaded during a service or emergency brake application, the greater will be the percent reduction in the force output by brake cylinder 6a when the railcar is empty.

Empty-to-loaded force ratios have been derived empirically for several brake cylinders 6a of varying design. For each brake cylinder, these ratios and the relevant design factors corresponding thereto are listed in the following tables. Each table assumes that displacement valve 30 opens below approximately 12 psi, meaning that the back pressure in compensating chamber 74 was vented to atmosphere when the front pressure in the front passage network 76 fell below 12 psi-

Referring to the column headings used in each table, BACK DIAMETER represents the size of seal 73 against the back side of the piston head; C.V. DIFFERENTIAL represents the differential across check valve 40; B. VOL represents the volume of the compensating chamber, applied; REDUCTION represents the reduction achieved in the force output by the brake cylinder when the railcar is empty; STD BCP represents the BCP that would be derived from the given reduction on a loaded railcar; EMPTY B represents the front pressure on an empty railcar; BACK BC represents the back pressure; F-LOADED represents the force output by the brake cylinder when the railcar is loaded for the given reduction; F-EMPTY represents the force output by the brake cylinder when the railcar is empty; and E-L FORCE RATIO represents the ratio of empty-to-loaded output forces.

Back Diameter: 6.5 C.V. Differential: 10

Both the prior art apparatus and the invention allow the brakes on an empty railcar to be applied with a fraction of the force that the brakes apply with on the railcar when it is loaded. In doing so, the prior art apparatus uses a load sensor and a proportioning valve merely to lower the pressure directed against the front side of the brake cylinder piston. In that arrangement, the force output by a brake cylinder 6 is reduced on an empty railcar only by a generally fixed ratio (e.g., between 50-60%), for all BCPs above the preset amount. The invention, however, employs valve assembly 20 and compensating chamber 74 to exert pressure on the back side of' the brake cylinder piston. It also enables the brakes on an empty railcar to apply with a force that is lower than that with which they would apply on that railcar if it were loaded. How much lower depends, however, on how high the BCPs rises above the changeover value. The tables show that the empty-to-loaded force ratios vary depending on the magnitude of the BCP. For BCPs lower than the changeover amount, however, the force output by the brake cylinder 6a will not be reduced.

This has the advantage of allowing relatively higher braking forces on empty railcars than prior art systems when that is advantageous and at the same time to further reduce the braking force when it- is most needed to prevent the wheels from sliding. When empty and loaded railcars are operated in the same train, it is helpful to allow the empty railcars to produce relatively high retarding forces during braking, particularly when descending grades. This allows the wheels on the empty railcars to share" more equally with the wheels on the loaded railcars in dissipating the heat created in retarding the entire train. Therefore, where wheel sliding is not a significant risk during relatively lighter brake applications, it is advantageous to allow a higher percentage of the normal braking force to be applied on empty railcars. For heavier brake applications, however, it is necessary to reduce the braking forces on the empty railcars to a greater degree, to minimize the likelihood that the wheels will slide.

II. OPERATION OF SECOND EMBODIMENT OF INVENTION

Figure 6 suggests how the second embodiment of the invention operates. In this embodiment, the invention includes differential valve 40, release valve 50, the revised brake cylinder 6a and a modified load sensor 9a. Differential valve 40 is oriented upside down with respect to release valve 50. With due regard to the orientation of the valves, the top of each valve communicates with the compensating chamber 74 of revised brake cylinder 6a. The bottom of each valve communicates with load sensor 9a via pipe network 12. The modification of the load sensor entails changing the force required to move piston assembly 92 against spring 93. As described operationally below, the pressure required to move piston assembly 92 from the exhaust position must now exceed that required to move the piston and rod assembly 60 of brake cylinder 6a to the point at which brake shoes contact the wheels of the truck (s) .

A. OPERATION DURING AN APPLICATION OF BRAKES

During a brake application, the pressure in the brake pipe reduces to the extent dictated by the magnitude of the brake application being sought. In the configuration shown in Figure 6, the brake control valve 7 will respond to the resulting decrease in brake pipe pressure by supplying pressurized air from the appropriate reservoir (s) 4/5 to the front side of brake cylinder 6a via inlet port 71 and pipe network 11. Simultaneously, brake control valve 7 also supplies air to chamber 91 next to piston assembly 92 of load sensor 9a.

Spring 93 keeps piston assembly 92 in the leftmost position until the BCP in chamber 91 exceeds this new preset value. Consequently, for any brake application lighter than or equal to a preset magnitude, all of the pressurized air from brake control valve 7 will be directed to the inlet port 71 of brake cylinder 6a whether the railcar is empty or loaded. Only when the front pressure in chamber 91 exceeds the preset value when the railcar is empty will the internal porting of load sensor 9a be affected. Employed as shown in Figure 6, load sensor 9a essentially serves to connect the BCP to valves 40 and 50 when the railcar is empty and to disconnect it when the railcar bears a load. 1. APPLICATION OF BRAKES ON A LOADED RAILCAR

On a loaded railcar, the distance between the railcar body and the side frame 100 of' each truck is reduced to the extent dictated by the weight borne by the railcar. Only when the pressure supplied by brake control valve 7 to chamber 91 exceeds the preset value will piston assembly 92 move against spring 93 and forcibly push the sensor arm 90 downwardly. The sensor arm 90, however, will soon contact the top of side frame

100 thereby preventing piston assembly 92 from moving spool 94a to the transfer position, i.e., to the point at which it would interconnect pipe networks 11 and 12. Because pipe networks 11 and 12 remain disconnected from each other when the railcar is loaded, brake control valve 7 will remain cutoff from the undersides of differential valve 40 and release valve 50. Meanwhile, as the pressure builds against the front side of piston head 61, piston and rod assembly 60 begins moving towards the applied position. Such movement of piston head 61 reduces the volume of, and thus increases the back pressure within, compensating chamber 74. Release valve 50 opens once the pressure differential across it reaches the point at which spring 52 can no longer hold valve member 51 on seat 53. The air under pressure in chamber 74 thus exhausts through release valve 50, pipe network 12 and exhaust port 99 to atmosphere. Differential valve 40 stays closed, however, because the force of spring 42, coupled with that from the extant pressure in compensating chamber 74, holds valve member 41 on seat 43.

During an application of the brakes when the railcar is loaded,

^• release valve 50 thus prevents the build up of pressure in compensating chamber 74. This allows the brake cylinder piston 60 to move unimpeded towards the applied position.

The brake control valve 7 on a loaded railcar will therefore only be able to supply air to the front side of brake cylinder 6a via pipe network 11. Air flowing into inlet port 71 soon generates a force on the front side of piston head 61 that exceeds the opposing force exerted by return spring 65 on its back side. From the perspective of Figure 6, this force moves piston head 61 rightwardly causing it to further compress return spring 65 and forcing the protruding end 69 of rod assembly 60 to extend outwardly from the aperture 72 of brake cylinder 6a. The extension of rod assembly 60 forces the brake rigging to apply the brakes. Because the invention and load sensor 9a prevented pressure from building up on the back side of piston head 61, the magnitude with which the brakes apply is directly proportional to the pressure built up against the front side of piston head 61.

2. APPLICATION OF BRAKES ON AN EMPTY RAILCAR On an empty railcar, the distance between the railcar body and the side frame 100 of each truck would be at its maximum. As brake control valve 7 supplies air to inlet port 71 and chamber 91, pressure begins to build against the front side of piston head 61 and against piston assembly 92 of load sensor 9a. Eventually overcoming the opposing force exerted by return spring 65, this front pressure soon moves the brake cylinder piston 60 to the applied position, thereby reducing the volume of compensating chamber 74. Until the BCP exceeds the preset value, however, spring 93 holds piston assembly 92, and spool 94a therewith, in the exhaust position. Consequently, as the brake cylinder piston 60 moves towards the applied position, release valve 50 is forcibly opened due to the ensuing build up of pressure in compensating chamber 74. Air under pressure in compensating chamber 74 exhausts through release valve 50, pipe network 12 and exhaust port 99 to atmosphere. Differential valve 40 initially stays closed due to the force of spring 42 and the extant pressure in compensating chamber 74. As the pressure supplied by brake control valve 7 to chamber 91 exceeds the preset value, the resulting force moves piston assembly 92 rightwardly far enough to carry spool 94a to the transfer position. Because the railcar is empty during this brake application, the sensor arm 90 can be pushed downwardly to its fullest extent, without contacting the side frame 100. In addition to supplying inlet port 71, brake control valve 7 is now allowed by load sensor 9a to supply air to the undersides of check valves 40 and 50 via pipe networks 11 and 12.

The check valves respond to the air frorn brake control valve 7 as follows when the railcar is empty. Release valve 50 quickly closes because the pressure building in pipe network 12 adds to the force exerted by spring 52 to seat valve member 51. Differential valve 40 remains closed, however, until the pressure in pipe network 12 exceeds the changeover level. Air from brake control valve 7 thus acts upon the front side of piston head 61 via inlet port 71 before pressure is allowed to build in compensating chamber 74. By staying closed until the front pressure rises to the changeover level, differential valve 40 keeps the back pressure in chamber 74 relatively low. At least initially, this allows the brake cylinder piston 60 to be moved easily towards the applied position.

Differential valve 40 opens once the pressure in pipe network 12 exceeds the changeover level. Front pressure in excess of the changeover level will forcibly move valve member 41 off seat 43 against the opposing force of spring 42. When opened, differential valve 40 allows air from brake control valve 7 into compensating chamber 74 via pipe networks 11 and 12. Due to this incoming air, back pressure builds in compensating chamber 74 and forcibly acts on the back side of piston head 61. The air flowing into inlet port 71, however, generates a force on the front side of the piston head that will exceed the opposing forces exerted (by return spring 65 and the back pressure) on the back side of the piston head. The effective force output by brake cylinder 6a is conveyed through the braking rigging to the brakes.

Until the brakes are released, differential valve 40 will operate to keep the back pressure in compensating chamber 74 the sum of the BCP acting on the front side of piston head 61 minus the changeover amount. The back pressure reduces the overall force output by brake cylinder 6a when the railcar is empty. For all BCPs above the changeover value, the invention determines what fraction of the force normally output by brake cylinder 6a when the railcar is loaded will be output by brake cylinder 6a when the railcar is empty. Moreover, the foregoing tables show that the empty-to-loaded force ratios for those brake cylinders vary depending on the magnitude of the BCP. For BCPs lower than the changeover value, however, the force output by the brake cylinder 6a will not be reduced. B. OPERATION DURING A RELEASE OF BRAKES During a release of the brakes, the brake control valve 7 responds to the resulting increase in brake pipe pressure by venting air from the front side of brake cylinder 6a via inlet port 71 and pipe network 11. The brake control valve 7 also vents air from chamber 91 of load sensor 9a due to the connection it shares with pipe network 11. As the brake control valve 7 initially begins to exhaust air from pipe network 11, it is also exhausting air from pipe network 12 and the undersides of valves 40 and 50. Because the pressure in pipe network 12 quickly falls below the differential set by valve 40, differential valve 40 will be closed and remains closed thereafter. As air continues to exhaust from pipe network 12, the pressure on the underside of valve member 51 soon falls below the back pressure in compensating chamber 74. Once this pressure differential reaches the point at which spring 52 can no longer by itself hold valve member 51 on seat 53, release valve 50 opens. The air under pressure in compensating chamber 74 then also starts to exhaust via release valve 50 and pipe networks 11 and 12.

When the pressure in chamber 91 falls below the preset value, spring 93 moves piston assembly 92 leftwardly, carrying spool 94a to the exhaust position. The undersides of valves 40 and 50 will then be connected by load sensor 9a to exhaust port 99. The pressure in compensating chamber 74 will thus continue to drop, causing the force acting on the topside of valve member 51 to fall quickly below that required to keep release valve 50 open. Meanwhile, the evacuation of pipe network 11 is causing brake cylinder piston 60 to retract into housing 70. This expands the size of compensating chamber 74 and further reduces the pressure contained within it. With the pressure differential across valve 50 now changed in favor of the underside of valve member 51, release valve 50 closes. Any pressure, if any, remaining in compensating chamber 74 is of no consequence. Retracted to its release position, brake cylinder piston 60 has pulled its protruding end 69 inwardly and thereby released the brakes.

The operation of the second embodiment during a release of the brakes on a loaded railcar is now described. The brake control valve 7 will be able to exhaust air only from pipe network 11, not pipe network 12. This is due to the state that load sensor 9a was forced to assume by the loaded railcar. Specifically, load sensor 9a was prevented from interconnecting pipe networks 11 and 12 on the loaded railcar because movement of piston assembly 92 was greatly limited by the contact that sensor arm 90 had with the top of side frame 100. Piston assembly 92 and its spool 94a were thus not completely moved out of the exhaust position, and the undersides of valves 40 and 50 were left vented to atmosphere via exhaust port 99.

Consequently, as the front pressure in pipe network 11 and chamber 91 now falls below the preset value, spring 93 merely moves piston assembly 92 to its leftmost position, with spool 94a still within the exhaust position. Because back pressure was not allowed to build in compensating chamber 74 when the brakes were being applied, compensating chamber 74 contains no pressure to vent as the brakes are being released. The evacuation of pipe network 11 merely causes brake cylinder piston 60 to retract into housing 70. As it retracts, brake cylinder piston 60 pulls its protruding end 69 inwardly and thereby releases the brakes. III. OPERATION OF THIRD EMBODIMENT OF INVENTION

Figure 7 suggests how the third embodiment of the invention operates. This embodiment employs the revised brake cylinder 6a and the modified load sensor valve 9a. The differential valve 40 and release valve 50 are not used. The compensating chamber 74 is merely connected directly to the load sensor 9a via pipe network 12 and passage 97.

A. OPERATION DURING AN APPLICATION OF BRAKES

In the configuration shown in Figure 7, the brake control valve 7 will respond to a decrease in brake pipe pressure by supplying pressurized air via pipe network 11 to both the front side of brake cylinder 6a and chamber 91 of load sensor 9a. Spring 93 keeps piston assembly 92 in the leftmost position until the BCP in chamber 91 exceeds the preset value. For any brake application lighter than or equal to a preset magnitude, all of the pressurized air from brake control valve 7 will therefore be directed to brake cylinder 6a whether the railcar is empty or loaded. Only when the pressure in chamber 91 exceeds the preset value when the railcar is empty will piston assembly 92 be able to be moved rightwardly and affect the internal porting of the load sensor 9a. Employed as shown in Figure 7, load sensor 9a is used to connect the BCP to the compensating chamber 74 when the railcar is empty and to disconnect it when the railcar is loaded. 1. APPLICATION OF BRAKES ON A LOADED RAILCAR

On a loaded railcar, load sensor 9a generally operates in the same manner as that described for the second embodiment. When the pressure supplied by brake control valve 7 to chamber 91 exceeds the preset value, sensor arm 90 soon contacts the top of side frame 100. This prevents piston assembly 92 and its spool 94a from being moved completely out of the exhaust position. The pipe networks 11 and 12 thus remain disconnected from each other, leaving brake control valve 7 cutoff from compensating chamber 74. Meanwhile, as the front pressure builds against the front side of piston' head 61, the brake cylinder piston 60 begins moving towards the applied position. This reduces the volume of compensating chamber 74, causing the air contained within it to exhaust to atmosphere via pipe network 12, passage 97 and exhaust port 99. The invention thus prevents back pressure from building in compensating chamber 74 when the brakes are being applied. This allows the brake cylinder piston 60 to move unimpeded towards the applied position during an application of the brakes when the railcar is loaded. The brakes therefore apply with a magnitude that is directly proportional to the front pressure built up against the front side of piston head 61.

2. APPLICATION OF BRAKES ON AN EMPTY RAILCAR On an empty railcar, load sensor 9a also basically operates in the same manner as that described for the second embodiment. As brake control valve 7 supplies air to inlet port 71 and chamber 91, pressure begins to build against the front side of piston head 61 and against piston assembly 92 of load sensor 9a. Eventually overcoming the opposing force exerted by return spring 65, this pressure soon moves the brake cylinder piston 60 to the applied position, thereby reducing the volume of compensating chamber 74. Until the front pressure exceeds the preset value, however, spring 93 holds piston assembly 92 and its spool 94a in its leftmost, exhaust position. Therefore, as the brake cylinder piston 60 moves towards the applied position, the air in compensating chamber 74 will exhaust to atmosphere through pipe network 12 and exhaust port 99.

As the front pressure supplied by brake control valve 7 to chamber 91 exceeds the preset value, the resulting force moves piston assembly 92 rightwardly far enough to carry spool 94a out of the exhaust position and to the transfer position. Because the railcar is empty during this brake application, the piston assembly 92 can push sensor arm 90 downwardly to its fullest extent, without contacting the side frame 100. In addition to supplying inlet port 71, brake control valve 7 is now allowed by load sensor 9a to supply air directly to compensating chamber 74 via passage 97 and pipe network 12.

During an application of the brakes on an empty railcar, back pressure only builds in compensating chamber 74 when the BCP exceeds the preset value. Moreover, in this third embodiment of the invention, the back pressure equals the front pressure. The front , pressure, however, generates a force on the front side of piston head 61, that exceeds the opposing forces exerted (by return spring 65 and the back pressure) on the back side of piston^' head 61. The effective force output by brake cylinder 6a is conveyed through the braking rigging to the brakes . The effective force is dependent on the effective areas of the front and back sides of piston head 61, the magnitude of the front and back pressures acting on those surfaces, and the constant of return spring 65.

For four different designs of brake cylinder 6a, the empty-to-loaded force ratios have been derived and are listed in the following tables. Each table assumes a C.V. DIFFERENTIAL of zero. These tables show that, regardless of the BCP, the empty- to-loaded force ratios are essentially constant. For any given brake cylinder, the empty-to-loaded force ratio will be dependent on the diameter of the seal 73 employed against the back side of the piston head 61. Unlike the other embodiments of the invention, this embodiment causes the force with which the brakes apply on an empty railcar to be a nearly fixed fraction of that with which they would apply on the railcar if loaded, for all BCPs above the preset value. For BCPs lower than the preset amount, the force output by the brake cylinder 6a will not be reduced.

Back Diameter: 6.6 CN. Differential: 0

44.3 90Em 78.0 72.8 72.8 6126 2492 0.407

44.3 l lOEm 96.0 89.8 89.8 7540 3073 0.408

Back Diameter: 7.5 CN. Differential: 0

Back Diameter: 7.9 CN. Differential: 0

B. OPERATION DURING A RELEASE OF BRAKES

The operation of the third embodiment during a release of the brakes on an empty railcar is now described. The brake control valve 7 responds to the resulting increase in brake pipe pressure by venting air from the front side of brake cylinder 6a and from chamber 91 of load sensor 9a. As the brake control valve 7 begins to exhausts air from pipe network 11, it is also exhausting air from compensating chamber 74 via pipe network 12.

When the pressure in chamber 91 falls below the preset value, spring 93 moves piston assembly 92 leftwardly, carrying spool 94a to the exhaust position. The chamber 74 will then be connected by load sensor 9a to atmosphere via passage 97 and exhaust port 99. Meanwhile, the evacuation of pipe network 11 continues, causing the piston 60 to retract inwardly into housing 70 under the force of return spring 65. The protruding end 69 of brake cylinder piston 60 soon reaches the release position at which point the brakes are completely released. The operation of the third embodiment during a release of the brakes on a loaded railcar is now described. The brake control valve 7 will be able to- exhaust air only from pipe network 11, not pipe network 12. This is due to the state that load sensor 9a was forced to assume by the loaded railcar. Specifically, the load sensor 9a was prevented from shifting to the transfer position because movement of piston assembly 92 was greatly limited by the contact that sensor arm 90 had with the top of side frame 100. Piston assembly 92 and its spool 94a were thus not moved out of the exhaust position, and the compensating chamber 74 was left vented to atmosphere via exhaust port 99.

Consequently, as the front pressure in pipe network 11 and chamber 91 now falls below the preset value, spring 93 merely moves piston assembly 92 to its leftmost position, with spool 94a still within the exhaust position. Because back pressure was not allowed to build in compensating chamber 74 when the brakes were being applied, compensating chamber 74 contains no pressure to vent as the brakes are being released. The evacuation of pipe network 11 merely causes brake cylinder piston 60 to retract into housing 70. As it retracts, brake cylinder piston 60 pulls its protruding end 69 inwardly and thereby releases the brakes.

The presently preferred embodiments for carrying out the invention have been set forth in detail according to the Patent Act. Persons of ordinary skill in the art to which this invention pertains may nevertheless recognize various alternative ways of practicing the invention without departing from the spirit and scope of the following claims. Persons who possess such skill will also recognize that the foregoing description is merely illustrative and not intended to limit any of the ensuing claims to any particular narrow interpretation.

Accordingly, to promote the progress of science and the useful arts, I secure for myself by Letters Patent exclusive rights to all subject matter embraced by the following claims for the time prescribed by the Patent Act.

Claims

CLAIMSI claim:

1. A system for compensating for the weight borne by at least one truck of a railcar in determining force with which brakes are to be applied on said truck; said truck having a brake control valve and a load sensor interconnected via a first pipe network; said load sensor (i) interconnecting a second pipe network to said first pipe network when front pressure developed in said first pipe network by said brake control valve is greater than a preset amount and said railcar is empty, (ii) disconnecting said pipe networks from each other and interconnecting said second pipe network to atmosphere when said front pressure is lower than said preset amount regardless of whether said railcar is empty or loaded; said system comprising: (a) a brake cylinder including a rod assembly therein normally biased to a release position, said rod assembly having a protruding end to link to said brakes and a head end formed as a piston, said brake cylinder defining an inlet port for receiving fluid from said brake control valve to build said front pressure via said first pipe network against a front side of said piston to move said rod assembly from said release position to an applied position, said brake cylinder including a seal disposed therein .to form a compensating chamber concentric to said rod assembly adjacent to a back side of said piston; and (b) a valve assembly defining (i) an output port connected to atmosphere, (ii) a release passage connected to said first pipe network, (iii) a back passage network connected to said compensating chamber, and (iv) a front passage network connected to said load sensor through said second pipe network, said valve assembly including a displacement valve, a release valve, and a differential valve such that: (1) said displacement valve has (i) a normally open position wherein said output port communicates with said back passage network thereby connecting said compensating chamber to atmosphere and (ii) a closed position wherein said back passage network is cutoff from said output port, said displacement valve adopting said closed position when said front pressure exceeds a predetermined value and said load sensor senses said railcar is empty;

(2) said release valve has a normally closed position wherein said back passage network is cutoff from said release passage, said release valve assuming an open position when said front pressure in said release passage falls a minimal amount lower than back pressure existing in said compensating chamber thereby allowing said back pressure to exhaust through said release valve and said release passage to atmosphere along with said front pressure via said first pipe network and said brake control valve; and

(3) said differential valve has a normally closed position wherein said front passage network is cutoff from said back passage network, said differential valve adopting an open position when said front pressure reaches a changeover amount more than said back pressure thereby allowing fluid from said brake control valve to be admitted to said compensating chamber through said first and second pipe networks via said load sensor and through said front and back passage networks to build said back pressure against said back side of said piston to produce a counterforce to partially offset the force produced by said front pressure acting on said front side of said piston, with said back pressure remaining said changeover amount lower than said front pressure as said front pressure increases; thereby enabling the force with which said brakes apply when said railcar is empty to be a fraction of the force with which said brakes apply when said railcar is loaded, with said fraction decreasing as said front pressure is increased.

2. The system claimed in claim 1 wherein said displacement valve includes :

(a) a lower assembly housed in a lower housing, said lower assembly having a valve member and a main spring for urging said valve member against a lower valve seat formed in said lower housing just below said output passage, said lower housing being in communication with said back passage network; and

(b) an upper piston assembly housed in an upper housing, said upper piston assembly having a piston and a counter spring, said piston having (i) a disc portion whose underside is in communication with said front passage network and (ii) a protuberant portion whose lower tip contacts a topside of said valve member; said displacement valve normally held in said open position wherein said counter spring holds said piston against an opposing force exerted on an underside of said valve member by said main spring so .that (A) said underside of said disc portion seats against a piston stop formed in said upper housing and (B) said protuberant portion pushes said valve member off said lower valve seat; said displacement valve adopting said closed position when said front pressure in said front passage network exceeds said predetermined value thus causing combined forces of said front pressure acting on said underside of said disc portion and said main spring acting on said underside of said valve member to overcome a force exerted by said counter spring on said piston so as to seat said valve member against said lower valve seat.

3. The system claimed in claim 2 wherein said displacement valve further includes an equalizing channel within said piston, said equalizing channel extending from a lower section of said protuberant portion to a top of said disc portion to allow communication between said output passage and said upper housing above said piston.

4. The system claimed in claim 1 wherein said release valve is defined within a valve housing whose top communicates with said release passage and whose bottom communicates with said first passage network, said release valve including: .

(a) a valve member; and

(b) a' spring for urging said valve member against a valve seat formed in said valve housing to bias said release valve in said closed position, said release valve adopting said open position when said front pressure falls said minimal amount lower than said back pressure thus causing a force of said back pressure acting on an underside of said valve member to overcome combined forces of said front pressure and said spring acting on a topside of said valve member.

5. The system claimed in claim 1 wherein said differential valve is defined within a valve housing whose top communicates with said front passage network and whose bottom communicates with said back passage network, said differential valve including:

(a) a valve member; and

(b) a spring for urging said valve member against a valve seat formed in said valve housing to bias said differential valve in said closed position, said differential valve adopting said open position when said front pressure in said front passage network exceeds said changeover amount more than said back pressure thus causing a force of said front pressure acting on a topside of said valve member to overcome combined forces of said back pressure and said spring acting on an underside of said valve member.

6. The system claimed in claim 1 wherein said brake cylinder exhibits an empty-to-loaded force ratio that varies depending on an .effective pressure acting on said brake cylinder.

7. The system claimed in claim 1 wherein said valve assembly is incorporated within said load sensor.

8. A system for compensating for the weight borne by at least one truck of a railcar in determining force with which brakes are to be applied on said truck, said truck having a brake control valve; said system comprising:

(a) a brake cylinder including a rod assembly therein normally biased to a release position, said rod assembly having a protruding end to link to said brakes and a head end formed as a piston, said brake cylinder defining an inlet port for receiving fluid from said brake control valve to build front pressure .via a first pipe network against a front side of said piston to move said rod assembly from said release position to an applied position, said brake cylinder including a seal disposed therein to form a compensating chamber concentric to said rod assembly adjacent to a back side of said piston;

(b) a load sensor interconnected to said brake control valve and said inlet port via said first pipe network and connected to a second pipe network, said load sensor (i) upon sensing said railcar is loaded or while said front pressure is lower than a preset amount when said railcar is empty, assumes an exhaust position in which said pipe networks are disconnected from each other and said second pipe network is interconnected to atmosphere and (ii) upon sensing said railcar is empty while said front pressure is greater than said preset amount, shifts to a transfer position in which said first and second pipe networks are interconnected, said load sensor set so that said preset amount of pressure exceeds said front pressure required to move said rod assembly to the point at which said brakes begin to apply; and

(c) a valve assembly having a release valve and a differential valve whose tops communicate with said compensating chamber and whose bottoms communicate with said load sensor through said second pipe network such that:

(1) said release valve has a normally closed position wherein said compensating chamber is cutoff from said second pipe network, said release valve assuming an open position when pressure existing in said second pipe network falls a minimal amount lower than back pressure existing in said compensating chamber thereby allowing said compensating chamber to exhaust via said second pipe network; and

(2) said differential valve has a normally closed position wherein said second pipe network is cutoff from said compensating chamber, said differential valve adopting an open position when said front pressure conveyed by said load sensor to said second pipe network reaches a changeover amount more than said back pressure thereby allowing fluid from said brake control valve to be admitted to said compensating chamber through said first and second pipe networks via said load sensor to build said back pressure against said back side of said piston to produce a counterforce to partially offset the force produced by said front pressure acting on said front side of said piston, with said back pressure remaining said changeover amount lower than said front pressure as said front pressure increases; thereby enabling the force with which said brakes apply when said railcar is empty to be a fraction of the force with which said brakes apply when said railcar is loaded, with said^' fraction decreasing as said front pressure is increased.

9. The system claimed in claim 8 wherein said release valve 50 is defined within a housing and includes: .

(a) a valve member; and

(b) a spring for urging said valve member against a valve seat formed in said housing to bias said release valve in said closed position, said release valve adopting said open position when said front pressure falls said minimal amount lower than said back pressure thus causing a force of said back pressure acting on one side of said valve member to overcome combined forces of said front pressure and said spring acting on the other side of said valve member.

10. The system claimed in claim 8 wherein said differential valve is defined within a housing and includes: (a) a valve member; and

(b) a spring for urging said valve member against a valve seat formed in said housing to bias said differential valve in said closed position, said differential valve adopting said open position when said front pressure exceeds said changeover amount more than said back pressure thus causing a force of said front pressure acting on one side of said valve member to overcome combined forces of said back pressure and said spring acting on the other side of said valve member.

11. The system claimed in claim 8 wherein said brake cylinder exhibits an empty-to-loaded force ratio that varies depending on an effective pressure acting on said brake cylinder.

12. The system claimed in claim 8 wherein said release valve and said differential valve are incorporated within said load sensor.

13. A system for compensating for the weight borne by. at least one truck of a railcar in determining force with which brakes are to be applied on said truck, said truck having a brake control valve; said system comprising: (a) a brake cylinder including a rod assembly therein normally biased to a release position, said rod assembly having a protruding end to link to said brakes and a head end formed as a piston, said brake cylinder defining an inlet port for receiving fluid from said brake control valve to build front pressure via a first pipe network against a front side of said piston to move said rod assembly from said release position to an applied position, said brake cylinder including a seal disposed therein to form a compensating chamber concentric to said rod assembly adjacent to a back side of said piston, said compensating chamber communicating with a second pipe network; and

(b) a load sensor interconnected to said brake control valve and said inlet port via said first pipe network and interconnected to said compensating chamber via said second pipe network, said load sensor (i) upon sensing said railcar is loaded or while said front pressure is lower than a preset amount when said railcar is empty, assumes an exhaust position in which said first pipe network is disconnected from said second pipe network and said second pipe network is interconnected to atmosphere thereby venting said compensating chamber and (ii) upon sensing said railcar is empty while said front pressure is greater than said preset amount, shifts to a transfer position in which said first and second pipe networks are interconnected thereby allowing back pressure equal to said front pressure to build in said compensating chamber and produce a counterforce against said back side of said piston to partially offset the force produced by said front pressure acting on said front side of said piston, said load sensor set so that said preset amount of pressure exceeds said front pressure required to move said rod assembly to the point at which said brakes begin to apply; thereby enabling the force with which said brakes apply when said railcar is empty to be a fraction of the force with which said brakes apply when said railcar is loaded, whenever said front pressure exceeds said preset amount.

14. The system claimed in claim 13 wherein said brake cylinder exhibits an empty-to-loaded force ratio that is fixed regardless of an effective pressure acting on said brake cylinder.

15 A brake cylinder for a rail vehicle, said brake cylinder comprising:

(a) a housing defining at one end an inlet port for receiving fluid from a source thereof and at an opposite end an aperture;

(b) a rod assembly disposed within said housing, said rod assembly having (i) a protruding end that protrudes out of said aperture and is linkable with brakes of said rail vehicle and (ii) a head end formed as a piston; (c) a spring for biasing said rod assembly to a release position wherein said piston lies adjacent to said inlet port and said protruding end is retracted approximate said aperture; and

(d) a seal disposed in said housing to form a compensating chamber concentric to said rod assembly adjacent to a back side of said piston, said compensating chamber for receiving said fluid from said source thereof; such that said fluid received at said inlet port acts upon a front side of said piston against said spring to move said rod assembly from said release position to an applied position and said fluid received into said compensating chamber acts upon said back side of said piston to produce a counterforce to partially offset the force produced by said fluid acting on said front side of said piston.

16. In a load sensor of the type switchable between (i) an exhaust position wherein a first pipe network along with a brake control valve and a brake cylinder to which said first pipe network communicates is disconnected from a second pipe network and said second pipe network is interconnected to atmosphere when said load sensor senses that (A) said railcar is loaded or (B) said railcar is empty while front pressure in said first pipe network is lower than a preset amount and (ii) a transfer position wherein said first and second pipe networks are interconnected when said load sensor senses that said railcar is empty while said front pressure is greater than said preset amount, an improvement comprising:

(a) a displacement valve having (i) a normally open position wherein an output port thereof open to atmosphere communicates with a compensating chamber in said brake cylinder and (ii) a closed position wherein said compensating chamber is cutoff from said output port, said displacement valve adopting said closed position when said load sensor is in said transfer position and said front pressure in said first and second pipe networks has exceeded a predetermined value;

(b) a release valve having a normally closed position wherein said compensating chamber is cutoff from said first pipe network, said release valve adopting an open position when said front pressure in said first pipe network falls a minimal amount lower than back pressure existing in said compensating chamber thereby allowing said back pressure to exhaust through said release valve and said first pipe network to atmosphere with said front pressure via said first pipe network and said brake control valve; and

(c) a differential valve having a normally closed position wherein said second pipe network is cutoff from said compensating chamber, said differential valve adopting an open position when said load sensor is in said transfer position and said front

_I pressure in said first and second pipe networks reaches a changeover amount more than said back pressure thus allowing fluid to flow from said brake control valve through said first and second pipe networks via said differential valve in said load sensor into said compensating chamber to build said back pressure against a back side of a piston in said brake cylinder to produce a counterforce to partially offset the force produced by said front pressure acting on a front side of said piston, with said back pressure remaining said changeover amount lower than said front pressure as said front pressure increases; and thereby enable said brake cylinder to apply the brakes on said railcar with a force when said railcar is empty that is a fraction of the force with which said brakes apply when said railcar is loaded, with said fraction decreasing as said front pressure is increased.

17. In a load sensor of the type switchable between (i) an exhaust position wherein a first pipe network along with a brake control valve and a brake cylinder to which said first pipe network communicates is disconnected from a second pipe network and said second pipe network is interconnected to atmosphere when said load sensor senses that (A) said railcar is loaded or (B) said railcar is empty while front pressure in said first pipe network is lower than a preset amount and (ii) a transfer position wherein said first and second pipe networks are interconnected when said load sensor senses that said railcar is empty while said front pressure is greater than said preset amount, an improvement comprising:

(a) a release valve having a normally closed position wherein said compensating chamber is cutoff from said second pipe network, said release , valve adopting an open position when pressure existing in said second pipe network falls a minimal amount lower than back pressure existing in said compensating chamber thereby allowing said back pressure to exhaust from said compensating chamber through said release valve and said second pipe network; and

(b) a differential valve having a normally closed position wherein said second pipe network is cutoff from said compensating chamber, said differential valve adopting an open position when said load sensor is in said transfer position and said front pressure in said first and second pipe networks reaches a changeover amount more than said back pressure thus allowing fluid to flow from said brake control valve through said first and second pipe networks via said differential valve in said load sensor into said compensating chamber to build said back pressure against a back side of a piston in said brake cylinder to produce a counterforce to partially offset the force produced by said front pressure acting on a front side of said piston, with said back pressure remaining said changeover amount lower than said front pressure as said front pressure increases; and thereby enable said brake cylinder to apply the brakes on said railcar with a force when said railcar is empty that is a fraction of the force with which said brakes apply when said railcar is loaded, with said fraction decreasing as said front pressure is increased.

18. A valve assembly for use with empty and load brake equipment, said valve assembly comprising:

(a) a body defining (i) a first housing having lower and upper portions thereof, (ii) a second housing, (iii) third housing, (iv) an output port_, connecting said first housing approximate said lower and upper portions thereof to atmosphere,

(v) a front passage network connected to said upper portion of said first housing and a top of said second housing, (vi) a release passage connected to a top of said third housing, and

(vii) a back passage network connected to a bottom of each of said housings;

(b) a displacement valve disposed within said first housing, said displacement valve having (i) a normally open position wherein said back passage network communicates with said output port and therethrough to atmosphere and (ii) a closed position wherein said back passage network is cutoff from said output port, said displacement valve adopting said closed position when a front pressure in said front passage network exceeds a predetermined value;

(c) a differential valve disposed within said second housing, said differential valve having a normally closed position wherein said front passage network is cutoff from said back passage network, said differential valve adopting an open position when said front pressure in said front passage network reaches a changeover amount more than said back pressure in said back passage network; and

(d) a release valve disposed within said third housing, said release valve having a normally closed position wherein said back passage network is cutoff from said release passage, said release valve assuming an open position when said front pressure in said release passage falls, a minimal amount lower than a back pressure in said back passage network.

19. The valve assembly claimed in claim 18 wherein said displacement valve includes: (a) a lower assembly housed in said lower portion, said lower assembly having a valve member and a main spring for urging said valve member against a lower valve seat formed in said lower portion just below said output passage, said bottom of said lower portion being in communication with said back passage network; and

(b) an upper piston assembly housed in said upper portion, said upper piston assembly having a piston and a counter spring, said piston having (i) a disc portion whose underside is in communication with said front passage network and against which said front pressure acts and (ii) a protuberant portion whose lower tip contacts a topside of said valve member; said displacement valve normally held in said open position wherein said counter spring holds said piston against an opposing force exerted on an underside of said valve member by said main spring so that (A) said underside of said disc portion seats against a piston stop formed in said upper portion and (B) said protuberant portion pushes said valve member off said lower valve seat; said displacement valve adopting said closed position when said front pressure in said front passage network exceeds said predetermined value thus causing combined forces of said front pressure acting on said underside of said disc portion and said main spring acting on said underside of said valve member to overcome a force exerted by said counter spring on said piston so as to seat said valve member against said lower valve seat.

20. The valve assembly claimed in claim 19 wherein said displacement valve further includes an equalizing channel within said piston, said equalizing channel extending from a lower section of said protuberant portion to a top of said disc portion to allow communication between said output passage and said upper portion above said piston.

21. The valve assembly claimed in claim 18 wherein said differential valve includes:

(a) a valve member; and (b) a spring for urging said valve member against a valve seat formed in said second housing to bias said valve member in said closed position, said differential valve adopting said open position when said front pressure in said front passage network exceeds said changeover amount more than said back pressure thus causing a force of said front pressure acting on a topside of said valve member to overcome combined forces of said back pressure and said spring acting on an underside of said valve member.

22. The valve assembly claimed in claim 18 wherein said release valve includes:

(a) a valve member; and

(b) a spring for urging said valve member against a valve seat formed in said third housing to bias said valve member in said closed position, said release valve adopting said open position when said front pressure in said release passage falls said minimal amount lower than said back pressure in said back passage network thus causing a force of said back pressure acting on an underside ^"of said valve member to overcome combined forces of said front pressure and said spring acting on a topside of said valve member.