Suspension for a Rail Vehicle

Abstract

A suspension for a rail vehicle includes at least one spring (18) carrying a wedge element (20) constrained to move in a vertical direction and a load application member (24) for engaging the wedge (20) to transmit the load to the wedge (20) along a direction. The damping ration of the suspension is variable by altering the engagement between the load application member (24) and the wedge (20) and hence the direction.

Description

This invention relates to a suspension for a rail vehicle.

It is known in suspensions for rail vehicles for the main body of the vehicle to be suspended on a multi-axle bogie or a single axle bogie using suspensions which include a top pedestal supported by suspension springs which are in turn supported by an axle box attached to a wheel set by a bearing. Typically, as in the Barber Easy Ride Suspension, these include multiple long travel springs and have so called floating wedge friction damping. In this arrangement the friction damping is brought about by a fixed plate transmitting load to an inclined face of the wedge such that the vertical face of the wedge, having a composite liner, is forced against a respective vertical face of the axle box or saddle, on either side of the wheel/bearing centre line. This action results in a horizontal damping force acting towards the centre line, which produces resistive forces against lateral and vertical acceleration of the wheel set in the Y and Z planes respectively due to the frictional engagement of the vertical faces. This damping force is load dependent, increasing with increasing load on the vertical wedge support springs from tare to laden. In known arrangements the damping ratio, which is the ratio of the horizontal force at the wedge vertical face to the vertical force applied by the spring to the wedge, is fixed and constant.

Under current arrangements instability can occur during high speed tare running of rail vehicles. This is particularly true for freight vehicles, which tend to be either run in their tare or fully laden states.

The present invention consists in a suspension for a rail vehicle including at least one spring carrying a wedge constrained to move in the vertical direction and a load application member for engaging the wedge to transmit load to the wedge along a direction characterised in that the damping ratio of the suspension is variable by altering the engagement between the member and the wedge and hence the direction.

In one embodiment one of the member or wedge may have a generally flat engagement face and the other may have a non-planar face whereby the flat face can pivot on the non-planar face to alter the direction.

It will be appreciated that by altering the direction the size of the horizontal damping force component is varied non-linearly and hence non-linear variations of the damping ratio can be achieved.

In a particularly preferred embodiment the member is pivotally mounted and further includes a resilient element for urging the member against the wedge. Preferably the resilient element is rated to be fully compressed at the design maximum load of the vehicle. For freight vehicles, it would normally be desired that the resilient member is sufficiently strong to maintain the plate in a first pivoted position, when the vehicle is unladen or at tare weight, and to be fully compressed when the vehicle is in at least a substantially loaded state. In this way the suspension can provide a first damping ratio which is suitable for tare running and a second damping ratio which is suitable for laden running, but more sophisticated arrangements can be envisaged, for example the resilient element could be replaced by an hydraulic ram, which altered the angle of the plate either under manual control or automatically in response to a detected load in the vehicle.

For freight vehicles it is particularly preferred that in one state the direction is substantially 30° to horizontal and in another state the direction is substantially at 40° to the horizontal.

Although the invention has been defined above it is td be understood that it includes any inventive combination of the features set out above or in the following description.

The invention may be performed in various ways and a specific embodiment will now be described, by way of example, with reference to the accompanying drawings in which:

FIG. 1 a is a vertical view of a bogie set for tare running; and

FIG. 1 b is the equivalent view of the left hand side of the bogie of FIG. 1a in its fully laden condition.

A bogie 10 includes a top pedestal 11, that supports the body, for example, of a railway wagon (not shown), an axle box 12 which is attached to a wheel set 13 by a bearing 14, and a suspension system, generally indicated at 15 acting between the pedestal 11 and the axle box 12.

The suspension 15 includes two upper load bearing springs 16 mounted on respective sides of a centre line 17 and a pair of damping spring sets 18, which are also mounted on respective sides of the centre line 17.

Each spring sets 18 includes coaxial springs 19 which together support a wedge element 20 that is constrained to travel vertically by the engagement of its face 21 with the vertical face 22 on the axle box 12. Up to this point the design is entirely conventional.

However, instead of the pedestal 11 having a fixed inclined face for engaging the upper surface 23 of the wedge element 20, a pivoted plate 24 is provided. As will be seen in FIG. 1a the plate 24 can pivot towards and away from the pedestal 11. It will also be seen that the face 23 is domed, rather than flat as in the conventional design, so that as the plate 24 pivots, it can be readily aligned on the surface 23 to vary the line of action of the force transmitted through the plate 24 into the wedge element 20. It will be understood that by changing the angle of that line of action, the magnitude of the horizontal component of that force is also changed with the result that the friction or damping force generated between the faces 21 and 22 is altered. As this force is one of the components of the damping ratio, the net result is to change the damping ratio.

It will be specifically noted that it the design of the embodiment a further spring 25 is provided to act between the pedestal 11 and the plate 24 in a sense to urge the plate away from the pedestal 11 and against the wedge 20. By choosing a suitable spring 25 it is possible to arrange for it to be in its extended position as show in FIG. 1A when the respective vehicle is in its tare condition, but the spring 25 is fully compressed (see FIG. 1b) in the laden condition of the vehicle. As will be noted this changes the angle of the face of the plate 24 from 40° in the tare condition to 30° in the laden position. The line of action or direction of transmitted load is therefore varied between 10° to the horizontal and 60° to the horizontal, with the resultant change on the resolved components of the applied load, as mentioned above.

This construction provides a particularly suitable arrangement for freight vehicles in that it acts essentially in a flip flop manner with the plate either being in its FIG. 1a or FIG. 1b condition. For vehicles which have more variable loads, such as passenger vehicles, the spring may be chosen for progressive compression, or a combination of springs may be used or, as is mentioned above, some positive actuator, such as a hydraulic ram could be used, but obviously that would be a more expensive approach.

Claims

1. A suspension for a rail vehicle comprising at least one spring carrying a wedge constrained to move in a vertical direction and a load application member for engaging the edge to transmit load to the wedge along a direction such that the damping ratio of the suspension is variable by altering the engagement between the member and the wedge and hence the direction.

2. The suspension as claimed in claim 1 wherein one of the member or wedge has a generally flat engagement face and the other has a non-planar face whereby the flat face can pivot on the non-planar face to alter the direction.

3. The suspension as claimed in claim 2 wherein the member is pivotally mounted and further including a resilient element for urging the member against the wedge.

4. The suspension as claimed in claim 3 wherein the resilient element is rated to be fully compresses at the design maximum load.

5. The suspension as claimed in claim 1 wherein the member is a flat plate.

6. The suspension as claimed in claim 1 wherein one direction is substantially 50° to the vertical.

7. The suspension as claimed in claim 6 wherein another direction is at substantially 60° to the vertical.