TECHNICAL FIELD OF THE INVENTION THIS INVENTION relates to a retractable ramp assembly and in particular but not limited to a ramp assembly for a bus, train or the like to extend out to and seat on a kerb or other suitable platform.

BACKGROUND OF THE INVENTION

Present retractable ramp assemblies for buses suffer from a number of disadvantages. One major disadvantage is that the assemblies are relatively deep in profile and as a consequence have to be used at the mid door of the bus rather than the front door due to insufficient clearance. This is inconvenient as the driver must move to the mid door if he is to assist a disabled person using the platform. In addition use of the platform with the mid door is potentially dangerous as the driver cannot readily observe its operation. It would be more desirable to have the ramp assembly located at the front door. Present efforts to provide a ramp assembly at the front door have been commercially unsuccessful due to the high maintenance cost associated with existing assemblies. For instance, existing ramp assemblies are prone to wear and include rather complex mechanics prone to fail. While the ramp assembly can be fairly easily repaired the high cost arises due to vehicle downtime. That is, a perfectly good operating vehicle is sidelined while the ramp is being repaired.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a robust, low maintenance ramp assembly suited particularly but not limited to operation in environments where space is at a premium. It is a further object of the present invention to provide a novel method of fitting a ramp assembly to a vehicle.

In one broad form there is provided a vehicle comprising a vehicle body carried on a supporting frame and a retractable ramp assembly mounted co¬ extensive with the supporting frame, the supporting frame having a ramp assembly mounting and the retractable ramp assembly being formed in a sub-frame structure including mounting means for securing the retractable ramp assembly in the ramp assembly mounting on the frame.

In a preferred embodimemnt the invention resides in a vehicle having a door opening and a floor within the vehicle opposite said opening, a vehicle frame and ramp assembly underlying said floor, the vehicle frame comprising spaced longitudinal frame members, there being provided a sub-frame comprising transverse frame members adjacent to the door opening and providing a receiver within the vehicle frame and holding the ramp assembly, the ramp assembly being fastened to the sub-frame, the ramp assembly having a cover plate co¬ extensive with the floor of the vehicle and a ramp member moveable through said opening from a stowed position within the vehicle to an extended position laterally of said vehicle.

In another preferred embodiment the invention resides in a vehicle having a door opening and a floor within the vehicle opposite said opening, a ramp assembly underlying said floor, and having a ramp member moveable through said opening from a stowed position within the vehicle to an extended position laterally of said vehicle, the ramp assembly including spaced guideways and guides travelling in the guideways, the guides being coupled to the ramp member, the guideways and guides comprising high lubricity self lubricating materials in sliding contact and permitting sliding longitudinal movement there between as the ramp travels between the stowed and extended positions. Preferably the ramp assembly includes a screw drive and a drive nut travelling on the screw drive, the drive nut being coupled indirectly to the ramp member by a drive nut release means, the release means being adapted for manual release of the ramp from the drive so that the ramp member can be manually returned to the stowed position. Preferably the drive nut release means comprises a first coupling block rigidly coupled to the frame member and a second coupling block holding the drive nut, the first coupling block having a bracket attached ;o the second coupling block by a frangible connection that can be released to separate the blocks and thereby release the ramp member from the drive. Preferably the cover plate comprises a rear section co-extensive with the floor and a forward section proximate the opening, the forward section being

hinged to the rear section and being adapted to pivot downwardly when the ramp member is in the extended position.

Preferably the ramp member includes a leading edge adapted to extend from the vehicle and encounter obstacles, the leading edge having a sensor means to direct the ramp to stop, the sensor means comprising a multi-directional transducer adapted to detect obstacles encountered from above, below and the side of the transducer.

Preferably the transducer comprises a pneumatic sensor including a channel extending along the leading edge, the channel having a deformable tube fitted in the channel and being displaced laterally below the line of the ramp member, the tube communicating with a pressure sensor to sense a predetermined amount of deformation of the tube and thereby stop the ramp member.

In another embodiment the transducer comprises a mechanical sensor rail extending along the leading edge and being moveable against biasing means in response to the sensor encountering an obstacle, the sensor rail being slidably disposed and constrained in a guide, the guide transforming multi-directional contact of the sensor rail to linear movement thereof activating switch means to stop the ramp. Preferably the ramp member comprises a leading edge and a rear marginal edge section, leaf springs adapted to project through the opening and impinge upon the rear marginal edge section of the ramp assembly to bias the ramp member into a horizontal position and subsequently release the ramp member when it reaches the extended position. Preferably the ramp assembly includes a flap biased to a closed position when the ramp member is in the stowed position, the ramp member pushing the flap to an open position as the ramp member moves to the extended position. Preferably the retractable ramp assembly is mounted as a drop-in unit insertable into a mounting in the floor of the vehicle so that an upper surface of the ramp assembly is co-extensive with the floor of the vehicle.

Preferably the ramp assembly comprises a body and a ramp comprising a front ramp section, a rear ramp section and an intermediate ramp section, the

front ramp section being adapted to extend and retract relative to the intermediate and rear ramp sections, the intermediate ramp section being biased against the front ramp section and being hinged to the rear ramp section, the rear ramp section being hinged to the ramp assembly body, the arrangement being that a wheel chair or the like travelling over the front ramp section engages the intermediate ramp section at a first relatively shallow inclination and then engages the rear ramp section at a further relatively shallow inclination, the combination providing a generally contiguous ramp over the front ramp section, the intermediate section and the rear section. Preferably, the ramp is adapted to extend from the body in a generally horizontal orientation and at the end of its travel have its leadirg edge swing downward to provide an inclined ramp, the ramp assembly including biasing means opposite the leading edge of the ramp biasing the ramp towards its horizontal orientation in order to assist retraction of the ramp into the body. BRIEF DESCRIPTION OF THE DRAWINGS

In order that the present inventions can be more readily understood and be put into practical effect, reference will now be made to the accompanying drawings which illustrate preferred embodiments and wherein:-

Figure 1 is a perspective drawing which illustrates a vehicle having a ramp assembly according to the present invention;

Figure 2 is an exploded perspective drawing illustrating how the ramp assembly is fitted into the vehicle;

Figures 3A to 3D are side views with side panel removed exposing the interior of the assembly and illustrating operation of a ramp assembly according to the present invention;

Figure 4 is a part perspective drawing illustrating a guide and guideway suitable for a ramp assembly according to the present invention;

Figures 5 and 6 are respective perspective views illustrating a preferred drive nut assembly for use with a ramp assembly according to the present invention;

Figure 7 is a cross-section drawing illustrating a leading edge sensor suitable for use in a ramp assembly according to the teachings of the present invention;

Figure 8 is a cross-section drawing illustrating an alternative leading edge sensor according to the teachings of the present invention; and

Figure 9 is a circuit schematic diagram suitable for controlling operation of the ramp assembly.

Referring to the drawings there is illustrated in Figure 1 a vehicle 10, in this case a bus, having a ramp 1 1 shown projecting off onto a kerb 12. The ramp 1 1 is housed in a ramp body which, as will be described below has an upper surface 1 3 co-extensive with the floor 14 of the bus. The ramp 1 1 is retractable into the vehicle to a stowed position below the upper surface 13.

Generally speaking the floor 14 of the bus illustrated in Figure 1 is mounted on a support frame that allows for a low profile vehicle providing a relatively low step from kerbside into the vehicle. In the main this makes it very difficult to fit a ramp assembly below the floor and the present invention in one preferred embodiment embodies removing part of the vehicle frame adding a sub- frame and building a supporting and structural frame into the ramp assembly and then fitting this into the sub-frame of the vehicle. This is illustrated in Figure 2 whereby the vehicle frame members are illustrated at 1 5 and 16 and as can be seen a box like sub-frame 1 8 is fitted, the vehicle having been modified to accommodate the sub-frame 18. The sub-frame 18 is the outer structural frame for the ramp assembly and has a pan 1 7 fitted to form a base and protect the ramp assembly from below. In this sense and as shown in Figure 2 the ramp assembly is "a drop-in unit" cartridge type unit that is placed into position from above making it a simple matter and easy to insert into the sub-frame of the vehicle. Structural integrity of the vehicle is not interfered with, the frame 18 is designed to ensure structural integrity. The ramp assembly also has a cross-frame member 19 employed between the angles 20 and 21 . The angles 20 and 21 simply screw to the frame members 22 and 23 using fasteners. A cover plate 13 is screwed into position and this cover can be simply

removed should the mechanics of the retractable ramp assembly which are housed beneath it require service.

It will be appreciated that as the ramp is fitted into the frame of the vehicle that the cover plate 1 3 can be mounted contiguous with the floor 14 of the bus. This means the ramp 1 1 actually projects out from a position just below the floor. A cover flap 24 closes behind the ramp when it is stowed and can be set at fairly low inclination and therefore provide for low impact of the cover flap 24 upon a wheelchair or the like moving into the vehicle.

Referring now to Figures 3 A to 3D there is shown preferred ramp assembly employing a front ramp section 1 1 , an intermediate ramp section 24 that also serves as a cover flap and a rear ramp section (not shown). The intermediate section 24, flap and the rear ramp section 25 are fixed but pivot relative to each other while the front ramp section 1 1 is the retractable portion of the ramp. As can be seen in Figure 3D the front section 1 1 extends generally horizontally and at the end of its travel swings down to the position illustrated. The ramp 1 1 travels over plastics support blocks 26 at each side of the assembly and at the extended position rests on rollers 27. As it reaches the end of its travel the ramp is supported by the bias of a pair of spaced leaf springs one of which can be seen at 28, the leaf springs biasing the ramp up into the horizontal position to aid in retraction of the ramp in the sense that the screw drive shown at 29 does not have to overcome as much inertia as it is assisted by the biasing of the leaf springs to retract the ramp. The leaf springs release the ramp at the end of its travel onto the rollers 27. The downward motion of the ramp is illustrated in phantom in Figures 3C and 3D The ramp section 24 is hinged along hinge 30 while the ramp section 25 is hinged to the frame member 19 at 31. This means when the ramp is in the position illustrated in Figure 3D the ramp section 24 which is biased down and also serves as a cover flap for the fully retracted ramp is inclined over its distance about the thickness of the ramp itself. The ramp section 26 is also slightly inclined thereby providing effectively a first, intermediate and rear ramp, each of slightly differing inclination that have to be traversed by a wheelchair travelling up onto the section 1 3. The section 13 is at floor level.

As can be seen the whole body of the ramp assembly in this case is approximately 75 millimetres deep and the drive is provided by a screw driver

29 driven by a drive assembly. The drive assembly can employ a gear box as shown or a belt drive extending transversely of the assembly can extend to a motor on the side.

The ramp 1 1 is pivotal ly mounted on a carriage 32 arranged on opposite sides to travel in guides, the guides being precision engineered to eliminate as much vibration as possible.

Referring to Figure 4 part of the ramp assembly has been removed to illustrate a ramp guide 33 travelling in a guideway 34. The guide 33 is fastened to the carriage as shown. A similar guide and guideway is employed on the other side of the assembly. The guide 33 is formed from a waxed high lubricity nylon while the guideway 34 is aluminium rail graphite impregnated using a molybonding process. The combined effect is to provide a precision guide and guideway that does not require lubrication and due to its simplicity and constrained relationship to intimate longitudinal sliding contact is free from the effects of vibration not having parts prone to fail such as rollers present in the prior art.

A suitable guide can be made from Cadco Nylon 6GPE available in stock from Cadillac Plastics Australia, corner Newstead Terrace and Evelyn Street, Newstead, Queensland, 4006, Australia.

This particular nylon has polyethylene-wax as lubricant, which will not spin, dry, drain or machine out so the guide can be formed by any usual manufacturing process. The Nylon 6GPE is self lubricating with a 50% lower coefficient of friction than conventional types but still has all the well known reliability of standard cast nylon.

The guideway rail is aluminium treated using a molybonding process providing excellent dry film lubrication. The rails can be coated by arrangement at "Molybond" Protection Custom Coatings at 106 Woodpark Road, Smithfield, Sydney, New South Wales, 2146, Australia.

Referring to Figures 5 and 6 there is illustrated a drive nut assembly 35, in Figure 5 an acetal drive nut 36 is in its operative driving position indirectly

coupled to the carriage 32 via a coupling block 37. The coupling block 37 is welded to the carriage 32 while a U-shaped bracket 38 couples the coupling block 37 to the drive nut at 39. In the event the platform fails to operate and is left projecting from the vehicle, a special tool 38 can be inserted as shown in Figure 5 in phantom to lever the bracket away to the position shown in Figure 6 to release the ramp from the drive. The ramp can then simply be pushed back into the stowed position.

Referring now to Figure 7 there is illustrated the detail of a. ramp leading edge which comprises a channel 40 having a downwardly projecting neck 41 the whole channel being filled with a resilient fitting 42 having a flexible tip 43 projecting slightly below the level of the ramp 24. The tip 43 has a longitudinally extending hollow 44 which communicates through a tube 45 ultimately with a pressure sensor 46 to detect changes in pressure within the hollow 44. It will be appreciated that as shown in phantom in Figure 7 the downward movement of the leading edge into engagement with a kerb as shown will be sensed and this can be used to cease extension of the ramp.

Figure 8 illustrates an alternative, in this case a mechanical sensor employing limit switches. In this case the ramp section includes a dovetail slot 48 which slidably receives a smaller dovetail projection 49 biased away from spaced limit switches by a rubber ring 50. The leading edge is therefore multi¬ directional touch sensitive in its sensing and will activate the limit switches at various contact angles. Screws pass through the edge at 51 and engage the limit switches. The screws are used to adjust sensitivity. Typically three limit switches are employed spaced across the leading edge. These are illustrated at 52, 53 and 54 in Figure 9 and so open circuit when an obstacle is encountered.

Referring now to Figure 9 there is illustrated a circuit schematic and as can be seen limit switches 52, 53, 54 are shown providing input to a PLC on the bus. The PLC is responsive to a number of conditions including but not limited to checking that the brakes of the vehicle have been applied, that the vehicle has "kneeled" in the sense of its air bag suspension having dropped and that the bus doors are open prior to providing a signal to initiate extension of the platform which in turns provides power to the motor 57 via the relay bank corresponding

to switches illustrated at 59 to reverse current through the motor. The switches 52, 53, 54 stop the motor by the leading edge sensing an obstacle. Switches 60 and 61 are end of ramp travel limit switches for full extension and full retraction respectively. Switches 62 and 63 respond to a PLC command to extend and retract the ramp respectively causing current flow through the appropriate relays. Whilst the above has been given by way of illustrative example of the present invention many variations and modifications thereto will be apparent to those skilled in the art without departing from the broad ambit and scope of the invention as set forth in the appended claims.