GB2099943A - Load-responsive brake in brake trolley for track system - Google Patents

Abstract

To take account of weight and track inclination variations, a brake trolley (1) has a longitudinally extending tie rod (11) which is movable by coupling forces applied thereto to cause working surfaces (16) of the tie rod (11) to act on projections (17) of brake cylinders (8a) to move the cylinders (8a) against the force of further springs (18) to supplement the brake applying force applied by springs (9) so that the braking force is related to the coupling forces applied to the tie rod (11). The trolley brakes are spring loaded brakes normally held off by pressure medium in chambers (8d) of piston/cylinder arrangements (8). Upon a determined speed being exceeded, the pressure of the pressure medium in the chambers (8a) is relieved to allow the stored force in the springs (9) to move levers (6) to apply the brakes. <IMAGE>

Description

SPECIFICATION Brake trolleys for track systems The invention relates to brake trolleys for positively guiding rail track systems.

In such brake trolleys, a safety braking system can be provided having at least one brake shoe which is actuated by a piston/cylinder arrangement wherein the piston is connected to the brake shoe, is loaded in the braking direction by a biased spring and in the brake releasing direction by the pressure of a pressure medium which can overcome the bias of the spring so that if a pressure chamber of the piston/cylinder arrangement is relieved abruptly of the pressure of the pressure medium, in case of emergency, the brakes are applied.

Brake trolleys of this kind are used e.g. in trains of cable drawn monorail overhead trolleys and in trains running on tracks fixed to the floor in underground mining. They act as a safety braking system in the event of a traction cable being severed or a tie rod of the train being broken on a steep length of track. The safety braking system is generally put into action by a centrifugal governor, which causes the piston/cylinder arrangement to be relieved of pressure when an admissible maximum speed is exceeded.

The braking force exerted by the brake trolley must naturally be sufficient to bring a fully loaded train to a standstill within a determined braking distance on a length of line with maximum inclination.

For this reason the biasing force of the spring acting on the brake shoe must be correspondingly strong.

This has disadvantages since trains are not always fully loaded and lengths of line are not always of maximum inclination, so that the biasing force of the spring, set to the maximum train weight and the maximum line inclination, can be too great under some circumstances resulting in a train being decelerated too abruptly, with consequent risk of damage to the rails or their mountings. In addition, trains on an overhead track in particular can be set swinging violently by such abrupt braking, and this may endanger miners working along the line or travelling in passenger carriages of the train.

According to the invention, there is provided a brake trolley for positively guided rail track systems, the brake trolley having a safety brake system including at least one brake shoe which can be acted on by a piston/cylinder arrangement, the piston of which is loaded in the braking direction by a biased spring and in the brake releasing direction by a pressure medium which can overcome the bias of the spring, wherein a pressure chamber of the piston/cylinder arrangement can be rapidly relieved of the pressure of the pressure medium in an emergency and wherein the cylinder of the piston/cylinder arrangement can be displaced, so as to increase the applied braking force, by a displaceable tie rod of the brake trolley, the displacement of which is related to the coupling force acting on the tie rod.

With the brake trolley according to the invention, the force of the spring acting on the brake shoe increases as the coupling force acting on the tie rod increases, so that for a light train the braking action is minimised, whereas for heavier trains the braking action is automatically increased.

In a preferred embodiment of the invention, the tie rod of the brake trolley is mounted in the brake trolley so that it can slide longitudinally against the action of a further spring, and has a working surface inclined to the longitudinal direction, against which working surface the cylinder of the piston/cylinder arrangement bears, the cylinder being slidable transversely to the longitudinal direction. Such an arrangement can operate purely mechanically, be simple and strong in construction, and to this extent is appropriate for rough operating conditions underground.

As a means of generating progressively stronger braking forces as the load on the train increases, the inclination of the working surface can vary along the displacement path, in particular so as to increase as the displacement path becomes longer.

In order that the brake trolley will come into action with either a pulling or a pushing coupling force applied to the tie rod, the further spring can preferably yield to pulling and pushing forces and, when the tie rod is relieved of such forces, returns the tie rod to a middle position, and the tie rod has two oppositely inclined working surfaces rising on both sides from the middle position.

In order to ensure that the tie rod returns safely to the middle position and to prevent the displacement means from responding when only weak tensile or compressive coupling forces are acting on the tie rod, the further spring can be biased both in the pushing and the compressing direction and is not deformed until a determined pulling or pushing force is exceeded.

To provide a secure guide for the cylinder and also to ensure that it returns to the starting position after shifting, the cylinder is desirably mounted displaceably in a guide bush and supported against the bush by a return spring.

A brake trolley according to the invention preferably has a plurality of brake shoes disposed in pairs, each pair being actuated by respective piston/cylinder arrangements, working in opposite directions, with associated displacement means. The construction of the displacement means explained above is particularly suitable for actuating brake shoes in pairs.

The invention is diagrammatically illustrated by way of example with reference to the accompanying drawings, in which: Figure 1 is a side elevation of a brake trolley according to the invention; and Figure 2 is a sectional view taken on line ll-ll of Figure 1.

Referring to the drawings, a brake trolley has a base frame 1, which is suspended by wheels 2 from a rail 3 of l-profile. The wheels 2 roll on the lower flange of the rail 3. A friction wheel 4 is disposed between them and can be pressed against the web of the rail 3. The friction wheel 4 drives a centrifugal governor which will not be described in detail. If a specified travelling speed is exceeded the governor triggers a safety braking system which will be further explained below.

The safety braking system has brake shoes 5, each of which is arranged axially displaceably in the hub of the wheels 2 and can be pressed against the web of the rail 3. The shoes 5 are actuated by two-armed levers 6. Each lever 6 is fixed to the base frame 1 of the trolley, so that it can pivot about a horizontal axis 7, and each can be acted on by a respective piston/cylinder arrangement 8. Pairs of opposing shoes 5 are disposed one on each side of the rail 3, and are pressed against the web of the rail like tongs by the associated levers 6.

As will be seen from Figure 2, each lever 6 is associated with a respective piston/cylinder arrangement 8. Each arrangement 8 has a cylinder 8a, a piston 8b and a piston rod 8c, the piston rod 8c bearing against the lower end of the respective lever 6. Each piston 8b is loaded in the braking direction by a compressed spring 9 and in the brake releasing direction by a pressure medium filling a pressure chamber 8d within the cylinder8a. Adjoining the pressure chamber 8d is a relief valve (not shown) which can open rapidly and which is released by the already-mentioned centrifugal governor (not shown).When the pressure chamber 8d is relieved, the compressed spring 9 in each -piston/cylinder arrangement 8 is relieved abruptly and pushes the associated piston 8b and piston rod 8c outwards to push the associated end of the lever 6 outwards, so that the associated brake shoe 5 is pressed against the web ofthe rail 3.

The cylinder 8a of the piston/cylinder arrange ments 8 are mounted in pairs in respective guide bushes 10, so that they can slide in the direction in which the spring 9 is relieved, i.e. outwards. Displacement means described below is used to slide the cylinders 8a outwards.

The displacement means comprises a tie rod 11 which projects from the base frame 1 at each end thereof and is provided with coupling members 12 for connecting the brake trolley to other trucks or carriages of an overhead trolley train. The tie rod 11 is mounted in the base frame 1 so that it can slide longitudinally ofthe brake trolley to a limited extent.

It is supported in the base frame by means of a further spring 13 in the form of a set of plate springs.

The set of plate springs are compressed within a receiving casing 14 which is mounted on the base frame 1 and through which the tie rod 11 passes.

Each end of the further spring 13 is associated with a respective sleeve-like pressure member 15 provided at opposite ends of the casing 14. The pressure members 15 are mounted so that they are nondisplaceable relative to the tie rod 11 in the direction in which the further spring 13 is compressed, but displaceable overthetie rod 11 in the opposite direc- tion. In this way the tie rod 11 can be shifted in either direction so as to compress the further spring 13, and the tie rod is biased to a middle position by the further spring 13. Thus the tie rod will move lon gitudinally of the brake trolley only when a given pulling or pushing coupling force is exceeded.

The tie rod 11 extends through the guide bushes 10 of piston/cylinder arrangements 8 at its ends and is provided in these regions with working surfaces 16, inclined to its longitudinal direction. The piston/cylinder arrangements 8 which are displaceable in the guide bushes 10 bear against the respective wo-rking surfaces 16 by means of pressure members 17. The working surfaces 16 rise to both sides from the middle position illustrated in the drawing, in such a way that when the tie rod 11 is shifted the cylinders 8a are displaced outwardly against the bias of still further springs 18. As illustrated in the drawing, the inclined working surfaces 16 may be curved, so that when the tie rod 11 is shifted longitudinally there is a gradual increase in the brake applying force.

Claims (8)

1. A brake trolley for positively guided rail track systems, the brake trolley having a safety brake system including at least one brake shoe which can be acted on by a piston/cylinder arrangement, the piston of which is loaded in the braking direction by a biased spring and in the brake releasing direction by a pressure medium which can overcome the bias of the spring, wherein a pressure chamber of the piston/cylinder arrangement can be rapidly relieved of the pressure ofthe pressure medium in an emergency and wherein the cylinder of the piston/cylinder arrangement can be displaced, so as to increase the applied braking force, by a displaceable tie rod of the brake trolley, the displacement of which is related to the coupling force acting on the tie rod.

2. A brake trolley according to claim 1, in which the tie rod of the brake trolley is mounted in the brake trolley so that it can slide longitudinally against the action of a further spring and is provided with a working surface inclined to the direction of displacement, on which working surface bears the cylinder of the piston/cylinder arrangement, which cylinder can slide transversely to the longitudinal axis of the tie rod.

3. A brake trolley according to claim 2, in which the inclination of the working surface varies over the displacement path, and in particular increases as the displacement path grows longer.

4. A brake trolley according to claims 2 or claim 3, in which the further spring is disposed between the tie rod and the brake trolley, can yield to pulling and pushing forces and, when the tie rod is relieved of such forces, returnsthetie rod to a middle position, and the tie rod has two oppositely inclined working surfaces for the cylinder of the piston/cylinder arrangement, rising on both sides from the middle position.

5. A brake trolley according to claim 4, in which the further spring is biased both in the pulling and pushing direction, and is deformed only when a determined pulling or pushing force is exceeded.

6. A brake trolley according to any one of claims 1 to 5, in which the cylinder of the piston/cylinder arrangement is mounted displaceably in a guide bush and is supported against the guide bush by a return spring.

7. A brake trolley according to any one of claims 1 to 6, in which a plurality of the brake shoes are disposed in pairs, each pair being actuated by respective piston/cylinder arrangements, working in opposite directions, with a respective displaceable tie rod.

8. A brake trolley for positively guided rail track systems substantiaily as hereinbefore described and illustrated with reference to the accompanying drawings.