Rail vehicle emergency braking system

Abstract: A rail vehicle braking system comprises a brake (4) mounted on a rail vehicle by mounting apparatus, the mounting apparatus providing for movement of the brake between a first position, in which the brake is a desired distance above a rail on which the said vehicle is mounted, and a second position, in which the brake engages with the rail to generate a braking force. Movement of the brake from the first to the second position is caused by electromagnetic attraction between the brake and the rail. The mounting apparatus comprises a piston and cylinder arrangement (11, 13, 18, 19, 24) secured between the vehicle and the brake, the piston and cylinder arrangement comprising biasing means (22) to lift the brake into the said first position and supply means (31-33) to introduce hydraulic fluid into the cylinder or to remove hydraulic fluid from the cylinder, whereby the first position of the brake may be adjusted.

Description: Field of the Invention This invention relates to an electro-magnetically operated emergency braking system for rail vehicles of the type where the brake acts directly on the rail. Background to the Invention In addition to braking systems which act on the wheels of railed vehicles, such as locomotives and carriages, these vehicles often comprise an emergency braking system comprising a brake pad which is mounted on the locomotive or carriage. The mounting apparatus comprises a pivotable arm which is itself attached to the bogey of the locomotive ore carriage ahead of the brake pad, and a spring arrangement mounted above the brake pad which serves to hold the brake pad off the rail. The spring arrangement comprises a spring which holds the brake pad off the track. The brake is electro-magnetically actuated, the brake pad being attracted to the rail when an electric current is passed through an electromagnet therein. For the passing of an electric current through the electromagnet in the brake pad to result in effective braking, the distance between the braking surface of the brake pad and the rail is critical. If the distance is too great then the brake will not operate. Although the brakes are known as emergency brakes, they are used relatively frequently, for example for testing purposes, and as such they are subject to wear. Furthermore, the wheels of the railed vehides wear and as a result the distance between the brake and the rail changes. It is therefore necessary that the arrangement for mounting the brake pad provides for adjustment of the distance between the braking surface of the brake pad and the rail. In known braking systems complex mechanical arrangements are used to adjust the position of the brake pad. These arrangements require disassembly for their adjustment. This is a time-consuming task, and is made more arduous by the location of the brake behind the wheels of the vehicle. Additionally, the need for a technician to crawl under the vehicle, or to insert his arm between the wheels of the vehicle to carry out the necessary work has safety implications. A vehicle brake, in which the brakes are actuated hydraulically against spring force, is known from DE 19518893. Summary of the Invention The invention provides a rail vehicle braking system comprising a brake mounted on a rail vehicle by mounting apparatus, the mounting apparatus providing for movement of the brake between a first position, in which the brake is a desired distance above a rail on which the said vehicle is mounted, and a second position, in which the brake engages with the rail to generate a braking force, movement of the brake from the first to the second position being caused by electromagnetic attraction between the brake and the rail, wherein the mounting apparatus comprises a piston and cylinder arrangement secured between the vehide and the brake, the piston and cylinder arrangement comprising biasing means to lift the brake into the said first position, characterised by supply means to introduce hydraulic fluid into the cylinder or to remove hydraulic fluid from the cylinder, whereby the first position of the brake may be adjusted Preferably, the brake is carried by an arm, which is suitably a lever arm, the opposite ends thereof being pivotally attached to the vehide and brake respectively. Preferably, the biasing means comprises at least one spring, which may be a coil spring. The spring may be mounted around the piston rod, and may be mounted in a casing, and the casing may form part of the piston, thereby permitting the piston rod to slide within the said piston. Advantageously, the piston rod end of the cylinder is closed by a cap through which the piston rod may slide. A spring may be provided between the piston and the cap to provide a counter to the force generate on the opposite face of the piston by the hydraulic fluid. In one embodiment of the invention the cylinder is in fluid connection with a hydraulic circuit which preferably comprises a coupling which provides for hydraulic fluid to be introduced into the cylinder. The coupling may be a quick release coupling. Advantageously, the hydraulic circuit comprises a release valve which permits hydraulic fluid to be released from the cylinder. Preferably, the hydraulic circuit comprises an accumulator. The provision of an accumulator in the hydraulic circuit allows the brake to move upwards if it encounters an obstacle on the track, thereby reducing the risk of damage to the brake and the brake mounting apparatus. The system preferably comprises a mounting member to mount the piston and cylinder arrangement on the vehicle, advantageously a chassis member thereof. The mounting member may comprise a collar which fits around the cylinder, and onto the vehicle. Any suitable means, for example bolting, may be used to attach the collar to the cylinder and/or the vehicle. The piston rod is preferably pivotally attached to the brake. The brake may comprise a brake block having a braking surface. The said braking surface may comprise a brake pad which may be releasably attachable to the brake block. In a rail vehide braking system according to the invention, the method of adjusting the distance between the brake and the rail when the brake is in the first position requires the technician to add or remove hydraulic fluid from the cylinder. This is a very simple operation, which is also safe because the task can be completed from the side of the vehicle, rather than from the underneath. In practice, although the braking system is for emergency use, these systems are used relatively frequently, and therefore it is often necessary to adjust the distance between the brake and the rail in the first position due to brake wear. The device of the invention will therefore save rail vehide operators considerable time when making these adjustments. Brief Description of the Drawings In the drawings, which illustrate an exemplary embodiment of the emergency braking system according to the invention: Figure 1 is a cross-sectional side view of a brake pad mounting arrangement according to the invention; Figure 2 is a cross-sectional side view of the adjuster component of the invention; and Figure 3 is a schematic representation of the braking system of the invention. Detailed Description of Preferred Embodiments Referring now to Figure 1, a braking system 1 comprises a brake pad mounting member 3 having a brake pad 4 attached thereto. The mounting member 3 is pivotally attached to one end of a lever 6 by means of a pin 7, the other end thereof being attached to an attachment member 5 which is itself attached to a part of the chassis (not shown) by means of bolts 8. The upper surface of the brake pad mounting member 3 has a bracket 9 attached thereto. As can be seen from Figure 2, a link 34 is provided to attach the bifurcated end 25 of the piston rod 24 to the bracket 9. Pins (not shown) are passed through the apertures 10 and 26 and the apertures in the link 34 to attach the piston rod to the brake mounting block 3. The purpose of the link 34 is to permit the piston to slide vertically, while the lever 6 moves in an arc. A collar 12 is attached, for example by bolting, to the chassis member 2, a piston and cylinder arrangement being mounted in the said collar. The piston and cylinder arrangement comprises a cylinder 11 and a piston rod 24, the lower end 25 of which is bifurcated. The upper end of the cylinder 11 is dosed by cap 14 having apertures 15 therein. A first piston member 13 is slidably mounted in the cylinder 11. It can be seen that grooves, in which seals may be placed, are provided around the circumference of the piston. A second piston member 18 is slidably mounted in the cylinder 11 below the first piston member 13. The second piston member 18 has a downwardly extending cylindrical portion 19 in which is mounted the piston rod 24. A coil spring 22 is mounted between the cylindrical portion 19 and the rod 24. A fitting 16 having a threaded portion 17 is mounted in the upper end 18a of the second piston member 18. It can be seen that the fitting has a hexagonal portion which can be adjusted using a suitable spanner. The first piston member 13 abuts the upper surface of the fitting 16, but is not physically attached thereto. The upper end of the piston rod 24 is attached to a sleeve 21, the spring 22 acting thereon to bias the piston rod 24 in the direction Y, thereby ensuring that the brake pad 4 is not in contact with the rail 29 in normal circumstances. The lower end of the cylinder 11 is closed by a plug 27 through which the piston rod 24 passes. A coil spring 23 is mounted in the cylinder 11 between the end portion 18a of the second piston member 18 and the plug 27, thereby biasing the second piston member 18 in the direction Y. The space X between the lower surface of the brake pad 4 and the upper surface of the rail 29 is controlled by introducing hydraulic fluid into the space 30 between the end cap 14 and the first piston member 13. Hydraulic fluid is introduced through the apertures 15 which are connected to an accumulator (shown in greater detail in Figure 3). When the brake pad has worn, hydraulic fluid is introduced into the space 30, thereby increasing the fluid pressure therein. This causes the piston to move in the direction opposite to direction Y against the force generated by the coil spring 23. Alternatively, if adjustment to the spacing X needs to be made due to wheel wear, then hydraulic fluid will be removed from the space 30 so that the piston can move in the direction Y until the spacing X is as required. Clearly when the wheel is fitted with new tyres the space X will again need to be re-set. This will involve introducing fluid into the space 30 so that the piston moves opposite to the direction X. Referring now to Figure 3, a hydraulic accumulator 31 is attached by pipes 32 to the apertures 15. A quick release coupling 33 is provided in one of the pipes 32 in order that additional hydraulic fluid can be fed into the space 30 to adjust the space X between the track 29 and the brake pad 4. The accumulator 31 is preferably provided with a bleed valve to allow hydraulic fluid to be removed from the space 30 when it is necessary to raise the position of the piston rod 24. The reason for providing the hydraulic accumulator 31 is so that if the brake mounting block 3 or the lever arm 6 are hit by an object lying on the line, the apparatus will simply move upwards in the direction Y without being damaged.

Claims: A rail vehicle braking system, comprising a brake (4) mounted on a rail vehicle (2) by mounting apparatus, the mounting apparatus providing for movement of the brake between a first position, in which the brake is a desired distance above a rail (29) on which the said vehicle is mounted, and a second position, in which the brake engages with the rail to generate a braking force, movement of the brake from the first to the second position being caused by electromagnetic attraction between the brake (4) and the rail (29), wherein the mounting apparatus comprises a piston and cylinder arrangement (11, 13, 18, 19, 24) secured between the vehicle and the brake, the piston and cylinder arrangement comprising biasing means (22) to lift the brake into the said first position, characterised by supply means (31-33) to introduce hydraulic fluid into the cylinder (11) or to remove hydraulic fluid from the cylinder, whereby to adjust the first position of the brake. A rail vehicle braking system according to Claim 1, wherein the brake is mounted on an arm (6) which is pivotably attached to the vehicle. A rail vehicle braking system according to Claim 1 or 2, wherein the piston comprises a piston rod (24), the free end of which is attachable to the brake. A rail vehicle braking system according to Claim 1, 2 or 3, wherein the biasing means (22) comprises at least one spring. A rail vehicle braking system according to any preceding claim, wherein the cylinder contains a first piston (13), and a separate second piston (18) located below the first piston (13) and connected to the brake (4) and biased upwardly by biasing means (23), the position of the first piston (13) in the cylinder being adjustable by introducing hydraulic fluid into the cylinder (11) or removing fluid from the cylinder (11), whereby the first piston (13) serves as an adjustable stop limiting upward travel of the second piston (18). A rail vehicle braking system according to Claim 5, wherein the biasing means (23) for the second piston (18) comprises a spring provided within the cylinder to counter the pressure of the hydraulic fluid on the second piston. A rail vehicle braking system according to any preceding claim, wherein the supply means (30-33) comprises an externally-accessible coupling (33) for sealingly introducing fluid and a release valve for selectively allowing the controlled release of fluid. A rail vehicle braking system according to Claim 7, wherein the supply means comprises an accumulator (31).

Inventors: CALLINGHAM DEREK, HODGKINSON PETER LESLEY, CALLINGHAM, DEREK, HODGKINSON, PETER LESLEY
Applicants: FLUID POWER DESIGN LTD, FLUID POWER DESIGN LIMITED
Application year: 1999
Main classification: B61H7
IPC codes: B61H7