EP2648957A1

EP2648957A1 - Improvements relating to trams

Info

Publication number: EP2648957A1
Application number: EP11808691.7A
Authority: EP
Inventors: Lewis Lesley
Original assignee: Tram Research Ltd
Current assignee: Tram Research Ltd
Priority date: 2010-12-10
Filing date: 2011-12-08
Publication date: 2013-10-16
Also published as: GB2486272A; WO2012076893A1; GB201020990D0

Abstract

A train section (20) for use in a rail or tram network which has two sets of steerable wheels. The wheel direction is determined by the angle between the tram section and a leading or following tram section, engine or other rolling stock.

Description

IMPROVEMENTS RELATING TO TRAMS

The present invention is concerned with trams. A design issue relevant to most rail vehicles can be understood with reference to Figure 1 , which shows a curved section of rail track and a carriage 12 moving along it, the carriage having fixed (non-steerable) wheel pairs 14, 16 fore-and-aft. It can be seen that due to the curvature of the rails 18, the wheels are non-parallel to the rails. This is undesirable, potentially creating additional wheel/rail friction, and resultant wear and noise, and other damage through fatigue failure of axles or wheels.

One solution to the problem is found in GB 2 280 160A, Tram Research Ltd. This describes a tram with front and rear carriages connected by an "articulation" - a coupling which allows an angle between the two carriages to vary according to the curvature of the track. The front of the front carriage and the rear of the rear carriage are supported by respective bogies which are pivotally coupled to the carriages, enabling them to turn as required to align themselves with the track. In the middle of the tram, beneath the articulation, is a pair of wheels which can be steered to follow the track. Specifically, Figure 12 of GB 2 280 160A shows an arrangement in which each of a pair of wheels is able to be steered about a respective vertical axis by a respective crank arm. A track rod links the two crank arms, keeping the wheels parallel to one another. The wheels are mounted on one of the tram carriages but their steering angle is controlled by a mechanical linkage, formed as a pushrod, which is coupled to the other carriage. While the point is not explicitly made in GB 2 280 160A, it is believed that the wheels are thereby steered such that their axes of rotation bisect the angle between the two carriages. It might be thought that the centre section wheels could instead be allowed to steer themselves in the manner of castors, but such arrangements prove to be unstable (prone to oscillation). While successful, the layout described in GB 2 280 160A has certain limitations. The carriage weight needs to be borne principally by the bogies located fore-and- aft, rather than by the single pair of wheels supporting the tram's centre portion, which dictates the location of heavy parts of the drive train. Also it would for some purposes be desirable to provide a three-section tram, having a middle carriage with articulated couplings at its front and rear to front and rear carriages, but the middle carriage requires the support of more than one pai of wheels. According to the present invention, there is a tram section having front and rear coupling arrangements for forming articulated connections to neighbouring tram sections in front and behind, and front and rear wheel arrangements both comprising: a pair of wheels for engaging respective rails of a tramway, each wheel being mounted on a respective stub axle and each stub axle being pivotable about a respective upright axis to change a steering angle of the wheel; and

a steering mechanism for controlling the steering angles of the pair of wheels.

By way of example only, specific embodiments of the present invention will now be described, with reference to the accompanying drawings, in which :-

Figure 1 is a plan view of a carriage with non-steerable wheels on a curved section of track;

Figure 2 is a plan view of a tram section according to an embodiment of the present invention on a curved section of track; Figure 3 is a side view of a tram section according to an embodiment of the present invention; Figure 4 is a plan view of a tram section according to another embodiment of the present invention; and

Figure 5 is a plan view of a tram section according to another embodiment of the present invention.

Figure 2 shows a tram section 20 which embodies the present invention, having a front wheel arrangement 22 and a rear wheel arrangement 24. The front wheel arrangement 22 comprises a pair of front wheels 26, 28 which are laterally separated from one another to engage with respective rails 30, 32 of a tramway. Each wheel is mounted for rotation upon a respective stub axle 34. Note that the term "axle" in this context merely refers to some rotatable part which carries the wheel, which may for example take the form of a hub to which the wheel is secured. The stub axle is mounted on the tram section thr ugh a wheel bearing (not seen) and a pivot 36 which defines a generally upright axis, normal to the plane of the paper in Figure 2, about which the stub axle 34 and its wheel 26 can turn, enabling the wheel to be steered to keep it roughly parallel to the rail 30, 32 despite the rail's curvature.

A mechanism is provided to control this steering action of the tram wheels. In Figure 2 the mechanism includes a respective control arm 38, 40 for each of the wheels 26,28 the control arm being coupled to the wheel mountings so that turning the arm changes the wheel's steering angle. In the illustrated embodiment a track rod 42 couples the two steering arms 38, 40 of the front wheels 26, 28 so that the wheels steer together. As is well known, such an arrangement can be designed such that the wheel at the inside of the curve has a larger steering angle than the wheel at the outside of the curve, as it should since the curvature of the inside rail 32 is higher than that of the outside rail 30. This is often referred to as "Ackermann" steering geometry. The rear wheel arrangement comprises rear wheels 50, 52 which are mounted and steered in the same manner as the front wheels 26, 28.

Figures 3 and 4 illustrate a further tram section 100 embodying the present invention. Parts which have already been described with reference to Figure 2, including the front and rear wheels 26, 28, 50, 52, their control arms 38, 40 and the track rods 42, are given the same reference numerals in Figures 3 and 4 that were used in Figure 2, and will not be described again. The tram section 100 is intended to form a middle section of a tram. That is, it will be coupled at its front end to a front tram section (not shown) and at its rear end to a rear tram section (not shown). A three section tram is envisaged but trams with four or more sections, with multiple middle sections 100, are possible. The tram section 100 has front and rear coupling arrangements 102, 104 for forming articulated couplings to the front and rear tram sections.

Some means is required for controlling the steering angles of the tram wheels to keep them roughly parallel to the rails. While alternative approaches are possible, in Figure 4 this is achieved by controlling the wheel's steering angles in dependence upon the angle formed at the articulated coupling between the tram section 100 and the neighbouring front or rear sections. This is achieved through a mechanical coupling, as will now be explained.

Looking at the front wheel arrangement 22, a control lever 106 is coupled to the front tram section (not shown), so that as the first section turns relative to the middle section 100, the control lever 106 turns about its fulcrum 102. The control lever 106 in its turn acts on a connecting lever 108 having a fulcrum 110. At its end remote from the control lever 106, the connecting lever 108 couples to a push rod 1 12 which actuates the track rod 42 and so steers the tram wheels. Note that the provision of the connecting lever 108 provides a reversal of direction in the mechanism needed to ensure that the wheels steer in the correct sense - i.e. the steer to the left as the track curves to the left. The device used to steer the tram wheels need not be purely mechanical. Figure 5 illustrates an alternative arrangement in which the control lever 106 acts upon a position sensor 1 14 whose output is supplied to control electronics 1 16 which in turn control a servo mechanism 118, which may be of electrical, hydraulic or other type and which moves the push rod 1 12 to steer the wheels.

Note also that in Figures 4 and 5 the wheels are seen to be mounted on wishbones 120 which are part of a sprung suspension system of a type which is in itself known in the art.

The wheels 26, 28, 50, 52 may be driven. In Figure 4 each wheel is provided with a respective drive motor, schematically represented as 122.

The tram section 20 may be provided with its own braking system. This can take any suitable form including disc, dram, shoe-on-tyre etc. It may be provided with its own power system and this can take any suitable form including hub motors, separate motor with drive shaft, electric, hydraulic, mechanical. The steering of the wheels on the centre tram section improves ride comfort for passengers and lengthens the potential life of the vehicle. Steering into and out of curves, keeping the wheels generally parallel to the curves, improves rail life by reducing sidewear. The tram section 20 can provide a wide low floor space for disabled access and safe passenger circulation through the tram. It can improve flexibility for passengers accommodation and facilities including exterior door locations. It provides, potentially, a consent floor height throughout the tram, making boarding and alighting safer for all passengers. It must be understood that the aforegoing embodiments serve only as examples of ways in which the present invention can be implemented, the scope of the invention being determined by the appended claims. Numerous variations are possible. For example, while in the embodiments above the wheels arc steered according to an angle between adjacent sections of the tram, an alternative would be to directly sense (e.g. by use of some form of follower engaging with the track) the angle between the track and the tram section, and to steer the wheels accordingly either through a mechanical coupling or by means of an electronic sensor/servo arrangement.

Claims

1. A tram section having front and rear coupling arrangements for forming articulated connections to neighbouring tram sections in front and behind, and front and rear wheel arrangements both comprising:

a pair of wheels for engaging respective rails of a tramway, each wheel being mounted on a respective stub axle and each stub axle being pivotabie about a respective upright axis to change a steering angle of the wheel; and

a steering mechanism for controlling the steering angles of the pair of wheels.

2. A tram section as claimed in claim 1 in which each steering mechanism is adapted to control the steering angles of its pair of wheels as functions of an angle between the tram section and a neighbouring tram section.

3. A tram section as claimed in claim 1 in which the steering mechanism of the front wheel arrangement is adapted to control the steering angles of the front wheels as functions of an angle between the tram section and the neighbouring tram section in front, and the steering mechanism of the rear wheel arrangement is adapted to control the steering angles of the rear wheels as functions of an angle between the tram section and the neighbouring tram section behind.

4. A tram section as claimed in any preceding claim in which the or each steering mechanism comprises a mechanical linkage configured to be coupled to a neighbouring tram section and to control the steering angles of the associated wheels.

5. A tram section as claimed in claim 4 in which the mechanical linkage comprises a control lever.

6. A tram section as claimed in claim 5 in which the control lever is coupled to a connecting lever which is in turn coupled to a control arm arranged to steer at least one of the wheels.

7. A tram section as claimed in any of claims 1 to 3 in which each steering mechanism comprises at least one servo mechanism arranged to control wheel steering angles.

8. A tram section as claimed in any preceding claim in which each wheel is provided with a respective steering arm whose angular position controls the steering angle of the wheel.

9. A tram section as claimed in claim 8 in which the steering arms of each pair of wheels are coupled by a track rod so that the paired wheels steer together.

10. A tram section as claimed in any preceding claim in which at least one of the wheels is driven by a respective drive motor.

1 1. A tram comprising a tram section as claimed in any preceding claim coupled to a front tram section at its front and to a rear tram section at its rear.