Whilst the invention is according to one embodiment directed towards and primarily described with reference towards automated guideway rapid transit systems, the invention is suitable for use with other forms of rail or track guided vehicle systems used for transporting passengers, freight or for use in materials handling.

Background An automated guideway system utilising vehicles which each accommodate, for example, between eight and twenty-four passengers would typically operate on guideways separated from other vehicular traffic and pedestrians. Due to economic considerations, the installation of automated guideway systems in the suburbs or central business districts of cities will necessitate that the guideway track be elevated above street level rather than underground and will generally be carried on a structure comprising concrete or steel pillars.

In order for such systems to be easily accessible to users, the elevated guideways must be able to descend and ascend on ramps, so that vehicles can be accessed from street level when necessary. In addition, the vehicles must also have adequate acceleration and braking capability and be capable of very short stopping distances which are necessary if they are to operate at high speeds and at close intervals or short headways safely.

Some problems exist with utilising either rigid or pneumatic tyred driven wheels which are detrimental to the operation of known prior art transit systems. One problem is that such vehicles are prone to slippage during braking, during grade descents and particularly during wet or icy conditions. This problem is serious when considering the operation of vehicles on an automated guideway system as their use requires them to be

insensitive to weather conditions. It is important that the vehicles are always able to decelerate or stop quickly, especially in emergencies.

Summary of Invention In one aspect of the present invention there is a brake means for a vehicle adapted to travel along a track, the track consisting of two sets of running faces laterally spaced apart about a longitudinal axis, each set having a primary running face and a secondary running face, said primary running faces on the upper face thereof and the secondary running faces on the lower faces thereof immediately juxtaposed said primary running faces, the vehicle having at least a first set of wheels journaled thereon and engaged with said primary running faces, and a second set of grip wheels journaled thereof and adapted to be moved into engagement with said secondary running faces by an actuating mechanism, characterised in that said brake means is adapted to engage at least one of said grip wheels at two opposed locations on said wheel.

Preferably, in a first embodiment, the at least one grip wheel has an inner cylindrical surface which acts as a braking surface, and at least one brake shoe of generally circular loop form adapted to engage said inner cylindrical surface of said grip wheel.

Preferably, in a second embodiment, a plurality of brake shoes is adapted to engage the inner cylindrical surface of the grip wheel.

Preferably, the axes of rotation of the first set of wheels and the primary running faces are inclined downwardly toward the guideway centreline.

Description of Drawings FIG. 1 depicts a perspective view of a portion of a track including a boarding station and vehicles traveling along it.

FIG. 2 depicts a vehicle traveling along a segment of track.

FIG. 3 is an enlarged side view of a wheel set showing the arrangement of the wheels and the track.

FIG. 4 is an enlarged cross section of a grip wheel and its brake shoe, a portion of track and the lower segment of one of the first set of wheels.

FIG. 5 is an enlarged view of a secondary wheel showing the brake shoe in the non- engaged position.

FIG. 6 is an enlarged side view of a secondary wheel showing the brake shoe in the engaged position.

Mode of Carrying out the Invention Figs. 1 and 2 show vehicles 1 running along a track 2 as in prior art.

In Fig. 1 vehicles 1 traverse a segment of track 2 along an elevated guideway 2, at a station or boarding area 3 and on ramps 4. Vehicles 1 are required to maintain short headways with close intervals between each other to maximise system capacity and meet demand. In order to do this safely each vehicle 1 must be able to decelerate rapidly in the event of the vehicle 1 ahead stopping or an obstruction being present on the track 2.

Fig. 2 shows a vehicle 1 running on a segment of elevated guideway 2 supported by a column 5. Vehicle 1 has a first set of wheels 6 and a second set of grip wheels 7, mounted on bogies attached to the vehicle 1. Wheels 6 run along the upper surfaces of track 2 and grip wheels 7 are adapted to be urged into engagement with the lower surface of the track 2 as described in U. S. Patent No. 5,657,699.

An enlarged view of the arrangement of the wheels on the track 2 is shown in Fig. 3.

Fig. 3 shows one of wheels 6 that run along one of the upper surfaces 8 of the track 9.

One of the grip wheels 7 is shown and is movably engageable with a lower surface 10 of track 9. When wheels 6 are about to lose adhesion with track 9 or when the vehicle is required to decelerate rapidly grip wheels 7 are urged into contact with lower surface 10 of track 9. For this purpose each of grip wheels 7 is rotatably mounted to one end of actuating lever 11 pivotally connected to the vehicle and having its other end connected to power actuator 12.

Braking of the vehicle is achieved by retarding wheels 6 either by wheel brakes or by means of the drive motor. When the vehicles is required to decelerate more abruptly grip wheels 7 are urged against track 9. The adhesion between wheels 6 and upper surfaces 8 of the track 9 is thereby increased allowing greater brake forces to be achieved. Additional drag from grip wheels 7 contributes further retardation. For maximum braking effort, such as in an emergency, grip wheels 7 are braked by engaging brake shoe assembly 16 with inner cylindrical surface 17 of grip wheels 7. This allows the maximum braking forces and maximum retardation to be achieved by utilising the traction of both sets of wheels 6,7. In order to efficiently brake grip wheel 7, the brake shoe assembly 16 should engage the inner cylindrical surface on at least two opposed locations of the grip wheel 7.

Fig. 4 shows one of grip wheels 7 engaged with a lower surface 10 of track 9, rotatably mounted on bearings 14 about a spindle 15 rigidly attached to actuating lever 11. Brake shoe 16 is shown in an engaged position, in contact with inner cylindrical surface 17 of grip wheel 7.

Fig. 5 shows a brake shoe assembly of generally circular loop form 18 nested within grip wheel 7 in an unengaged position not in contact with the inner cylindrical surface 17.

When the brake shoe assembly is unengaged grip wheel 7 can rotate freely along the lower surface 10 of track 9.

Fig. 6 shows brake shoe assembly of generally loop form 18 in engagement with inner cylindrical surface 17 of grip wheel 7, providing a retardation force when grip wheel 7 is in contact with lower surface 10 of track 9.

Fig. 7 shows an alternative embodiment with a plurality of brake shoes.