GB2573555A

GB2573555A - Steering centralisation device

Info

Publication number: GB2573555A
Application number: GB1807603.4A
Authority: GB
Inventors: William Griffin Robert
Original assignee: TOMCAT SPECIAL NEEDS INNOVATION Ltd
Current assignee: TOMCAT SPECIAL NEEDS INNOVATION Ltd
Priority date: 2018-05-10
Filing date: 2018-05-10
Publication date: 2019-11-13
Anticipated expiration: 2038-05-10
Also published as: GB201807603D0; GB2573555B

Abstract

A steering centralisation device 110 comprises a housing 116 for fixing to the frame (14, figure 1) of a tricycle, a force transfer element 128 for fixing to the forks 130 of the tricycle, the force transfer element 128 being rotatable relative to the housing 116, first and second compression springs 146 connected to opposing sides of the force transfer element 128, the first and second springs 146 both being tensioned to hold the force transfer element 128 in an equilibrium position relative to the housing 116. Spring housings 136 may comprise seals 158, 160 and an orifice 162 for trapped air to escape, thereby providing a damping effect on the steering. The force transfer element 158 may also be connected to a remote steering controller.

Description

STEERING CENTRALISATION DEVICE

The present invention relates to a steering centralisation device and particularly to a steering centralisation device which can be used to self-centralise the steering of the front wheel of a tricycle.

BACKGROUND TO THE INVENTION

When designing a tricycle, it is a well-known problem that in order to provide handle bars at the right height for the user and to avoid the front wheel colliding with the pedal movement, the front wheel has to be position a long way forward of the seat.

This design problem is exacerbated in low sitting, semi-recumbent, trikes, which are highly suited to disabled individuals. This is because the seat is typically arranged at a height corresponding to wheelchair height. This is necessary to facilitate straightforward mounting and transfer, whether from a standing or sitting position. The riding position demands that the front wheel, when clear of the pedals and pedalling feet, is considerably further forward from the rider sitting position than would be the case on a bicycle, for example.

If then, the handlebars are arranged in a suitable position, the axis of the front fork and handlebar stem is at a more acute angle to the road surface than the fork/handlebar axis of a bicycle. When using conventional bicycle forks, this factor may cause the axis of the forks to meet the road surface ahead of the point of contact between the tyre and road surface, instead of behind it, as is ideally the case. This geometry causes a natural tendency for the wheel to flop sideways with potential danger to the rider. In other words, the natural tendency of the steering is not to self-centralise as with a bicycle or car, but to naturally veer sideways.

This problem can be solved geometrically by building the forks in such a way that the pivotal axis of the fork, when extended in an imaginary line to the road, makes contact with the road at a point on, or slightly behind the point of contact of the tyre with the road, in other words behind the vertical plane that cuts through the front wheel axle. However, when this geometric solution is used, the necessary offset between the steering pivot axis and the wheel axis can be so great that standard proprietary bicycle forks cannot be used as their offset (usually in the region of 46 to 50mm) is insufficient and specialised forks of high cost and unconventional appearance must be specially constructed. It is undesirable to use unconventional designs for use by disabled people, because it can unnecessarily draw attention to their disability.

Another way of overcoming this problem when using conventional cycle components is to provide a single tension spring, anchored at one end to a fixed point on the frame and at the other, to a crank arm, attached to, and extending backwards from the head of the forks. When the fork is turned, the crank arm describes an arc about the axis of the fork. The shortest distance between the spring attachment point of the crank arm and the spring attachment point of the frame is central (or straight ahead for the vehicle), thus any disturbance of the steering forks to navigate the vehicle, causes tension in the spring resulting in a force that works to pull the forks back toward a central line. The disadvantage of this method is that it has a crude bulky appearance and is prone to wander. It also requires that the user has to act against the spring, when turning in one direction only, which can lead to further instability of the tricycle and rider.

It is an object of the present invention to provide a steering centralisation device, which reduces or substantially mitigates these problems.

STATEMENT OF INVENTION

According to the present invention, there is provided a steering centralisation device comprising a housing for fixing to the frame of a tricycle, a force transfer element for fixing to the forks of the tricycle, the force transfer element being rotatable relative to the housing, first and second compression springs connected to opposing sides of the force transfer element, the first and second springs both being tensioned to hold the force transfer element in an equilibrium position relative to the housing.

Advantageously, the device of invention can be utilised to act against the upsetting forces caused by the geometric design of a tricycle. Furthermore, the centralising device can very accurately and precisely return the steering to an equilibrium, or default position, which is particularly useful in a disabled environment where the users judgement or motor function may be impaired by disability.

First and second spring housings may be attached to the housing and accommodate the respective first and second springs. Advantageously, the device is entirely selfcontained and needs no secondary anchor point to the frame, thus the area where the frame adjoins the fork head tube is clear and unrestricted. Being self-contained, it is better protected from the elements and accidental damage.

Furthermore, the underside of the housing, when in situ, may be open. This allows unimpeded access for servicing.

First and second rods may connect between the force transfer element and the first and second springs.

First and second arcuate slots may be provided on opposing sides of the force transfer element for connection to the respective first and second springs. The arcuate slots allows one of the connection rods to rest in an inoperative position on rotation of the force transfer element. This reduces the space occupied by the steering centralisation device, as the rod would be forced to move by the force transfer element if not accommodated by the respective arcuate slot.

A clevis may be connected to each of the first and second rods and a clevis pin may be engaged in each arcuate slot. The clevis and clevis pin allow for straightforward connection of the connection rods to the force transfer element.

A ball joint may be provided between each spring connection rod and respective clevis. The ball joint has the advantage of allowing the connection rod to travel on a straightline axis in and out of the spring housing. This facilitates sealing for air damping as described further below.

An adjuster nut may be provided for adjusting the tension of each of the first and second compression springs. Advantageously, the turn right - turn left spring force acting to return the forks to a central position can be individually and finely adjusted to suit vehicle and user weight.

A buffer element may be attached to each spring rod. The buffers serve to prevent any backlash and provide for a smoother steering action. In particular, the buffers reduce the sensation of discontinuity which would be felt when turning from left to right or vice versa, as the clevis pins impact the ends of the arcuate slots.

The buffer elements may be made from rubber or may be provided by springs.

Seals may be provided at the respective ends of the spring housings. The seals seal the interior of the housings so that the spring housings may be used as air dampers. This is useful when, for example, steering action becomes lively due to uneven terrain. When a force is applied to disturb the alignment of the fork, for example by encountering a pothole, free movement of the fork is suppressed by the compression of the entrapped air, damping unsafe oscillations in the mechanism that could lead to erratic steering.

An aperture may provided through one of the seals. The aperture allows the spring rod to extend out of the spring housing to engage the force transfer element.

The first and second spring housings may be attached to the housing. This provides a simple and easily adjusted design.

Alternatively, the first and second spring housings may be remote from the housing and cables may connect the force transfer element to the first and second springs. This allows a more compact and elegant design.

The force transfer element may be connected to a remote steering controller. This allows riders with significantly impaired arm or sight function to use the tricycle. This connection may be by cables or alternatively by a hydraulics system.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made by way of example only to the accompanying drawings, in which:

Figure 1 shows the front wheel and downtube of a tricycle with an embodiment of the steering centralisation device fitted;

Figure 2 shows a cross-sectional view from above of the steering centralisation device of Figure 1, with the first and second springs and force transfer element in a neutral or equilibrium position;

Figure 3 shows a cross-sectional view from above of the steering centralisation device of Figure 1, with the first and second springs and force transfer element in a rotated position; and

Figure 4 shows a cross-sectional view from above of a second embodiment of steering centralisation device in a rotated position.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring firstly to Figure 1, a steering centralisation device is indicated generally at

10. The steering centralisation device 10 is attached to a tricycle 12.

Referring now to Figure 2, the steering centralisation device 10 is shown in isolation.

The steering centralisation device 10 includes a bell housing 16. The bell housing 16 has an open underside, a side wall and a top wall. The side wall of the bell housing 16 is substantially D-shaped, having an arcuate section 18 and a flat section 20 joining the ends of the arcuate section. The bell housing 16 is for attachment to the frame 14 of a tricycle, particularly the point on the frame 14 that sheathes the steering column.

The flat portion 20 of the side wall of the housing 16 includes a pair of threaded bores

22. The threaded bores 22 are internally threaded apertures in the side wall communicating with the interior of the housing 16. The threaded bores 22 are located near the ends of the flat portion 20. The threaded bores 22 are angled towards each other in a direction away from the bell housing 16.

Referring once more to Figure 1, the housing is attached to the frame in line with the front wheel forks 24 of the tricycle 12.

The steering centralisation device 10 also includes a force transfer element 28. The force transfer element 28 is a quadrant plate. The quadrant plate 28 is a substantially planar steel member. The quadrant plate 28 includes a central aperture 30 for receiving the steering column 26 of the tricycle.

The quadrant plate 28 includes a pair of arcuate slots 32. Each arcuate slot 32 defines an arc of a circle centred on the central aperture 30.

The quadrant plate 28 is disposed within the interior of the bell housing 16.

The quadrant plate 28 is attached to the forks 24 of the tricycle. The quadrant plate 28 rotates relative to the housing 16 as the wheel forks 24 and steering column 26 rotate relative to the frame 14.

A pair of spring housings 34 is provided. Each spring housing 34 includes a body portion 36 and a front portion 38.

Each body portion 36 is a hollow cylindrical member, defining a tube.

Each front portion 38 is a cylinder of narrower external diameter than the rest of the housing 34. Each front portion 38 is externally threaded. Each front portion 38 is coaxial with and joined to the respective body portion 36.

Each front portion 38 has an axial bore 40. Each axial bore 40 extends through the front portion 38. The axial bore 40 connects the hollow interior of the body portion to a front surface of the spring housing 34.

A circumferential shoulder 44 is provided on the inner surface of each spring housing 34, between the body portion 36 and the front portion 38.

Spanner flats 42 are provided on the external surface of each body portion 36 adjacent to the front portion 38.

The front portion 38 of each housing 34 is partially or wholly received in one of the threaded bores 22 of the bell housing 16. The spring housings 34 are therefore angled toward each other.

A coil spring 46 is provided in the hollow interior of each body portion 36. Each coil spring 46 rests on the respective shoulder 44.

A pair of spring rods 48 is provided. Each spring rod 48 is a cylindrical rod having a first end and a second end. Each first and second end is externally threaded. Each spring rod 48 is disposed with its first end within the body portion 36 of one of the spring housings 34 and extends through the axial bore 40 into the bell housing 16. Each spring rod 48 extends through one of the coil springs 46.

A pair of clevis devices 50 is provided. Each clevis device 50 includes a body portion and pair of arms joined to and extending from the body portion. A pin extends between the arms. An internally threaded bore extends into each body portion. The bore has the same diameter as the second end of the respective spring rod 48.

Each clevis device is disposed within the interior of the bell housing. The quadrant plate 28 is received between the arms of each clevis device 50. The pin of each clevis device 50 extends through one of the arcuate slots 32. The second end of each spring rod 48 is received in the bore of one of the clevis devices 50.

A nut 52 is provided on the first end of each spring rod 48. The diameter of each nut 52 is greater than that of the springs 46. The springs 46 are held in compression between the nuts 52 and the shoulders 44.

A buffer bush 54 is provided on each spring rod 48. Each buffer bush 54 is situated between the respective clevis device 50 and the front portion 38 of the respective spring housing 34. The buffer bushes 54 are under compression from the springs 46.

In this embodiment, the buffer bushes 54 are rubber and spring buffers. However, in other embodiments, an oil damper could be used in addition to the rubber and spring buffers for improved damping.

The operation of the steering centralisation device 10 will now be described.

When the steering column 26 is turned relative to the frame 14, the quadrant plate 28 rotates relative to the bell housing 16. In Figure 3, the steering column 26 has turned to the right, causing the quadrant plate 28 to rotate to the right.

As the quadrant plate 28 rotates to the right, the end of the left arcuate slot 32 pulls the left clevis pin forward. In turn, this pulls the left spring rod 48 through the left bore 40 into the bell housing 16. The left spring 46 becomes compressed between the nut 52 and the shoulder 44.

The left spring 46 therefore exerts an anticlockwise torque on the steering column 26 to resist the torque causing the initial turn. This has the effect of damping the motion of the steering column 26 and forks 24.

Meanwhile, the right clevis pin travels in the right arcuate slot 32. This allows the right spring rod to remain stationary relative to the bell housing 16.

This reduces the length of the spring housings 36 required. If the right spring rod 48 were to be pushed out of the bell housing 16 upon a rightwards turn, a longer spring housing would be required to accommodate it.

In Figure 2, the steering centralisation device is shown in an equilibrium position. This is the position in which the compression force in each spring is the same.

The equilibrium position is calibrated by rotating the spring housings 34 relative to the bell housing 16, i.e. screwing the front portions 38 in the bores 22. By adjusting the spring housings nearer to, or further from the bell, backlash in the clevis/quadrant mechanism can be precisely eliminated.

In the configuration shown, the equilibrium position corresponds to the steering column 26 and forks 24 pointing ‘straight ahead’. However, the default alignment of the forks 24 can be altered by contra-rotation of the spring housings 34. In other words, if the left housing 34 is screwed into the bell housing 16 by one turn and the right housing 34 is screwed out of the bell housing 16 by one turn, the quadrant will re-align to the right though no backlash will have been introduced.

Tightening the nuts 52 increases the pre-compression of the springs 46. This increases the spring compression required to disturb equilibrium and thus the force exerted by the spring 46 to bring the fork 24 back to its default equilibrium position.

When turning from a rightwards direction as shown in Figure 3 to a leftwards direction, the rear face of the left clevis device 50 would impact the front face of the left spring housing 34, were it not for the left buffer bush 54. This does not halt the motion of the steering centralisation device 10 because the left clevis pin can travel in the left arcuate slot 32 to accommodate further movement, but it would produce a very defined sensation that the central position had been reached. This is not desirable because, at every transition to left and right, the user would feel a check to free and smooth movement. The buffers prevent this.

In the central position shown in Figure 2, both buffers 54 are in compression. Preferably, the device is calibrated so that the buffers 54 are not near maximum compression in this position. There is thus a smooth translation from left to right and vice versa, as the compressive load reduces on one buffer 54 and increases on the other until full buffer compression has been achieved and spring compression takes over.

In other embodiments, the buffers 54 may be omitted. The clevis devices 50 are then free to move past the point of equilibrium. When all compression in the expanding spring has been released, the clevis comes to rest as the pin is free to move in the arcuate slot 32. This provides a seamless transition from left to right and right to left, while allowing the central position and the spring tension to be adjusted in the manner previously described.

Although in this embodiment, the spring housings 34 are provided adjacent the bell housing 16, in other embodiments they may be distant from the bell housing 16. They may be connected to the bell housing by a cable and pulley system. This may be advantageous where space or neatness of appearance are a consideration.

Referring now to Figure 4, a second embodiment of a steering centralisation device is indicated at 110. The second embodiment 110 is similar to the first embodiment 10, and like features are indicated by numerals stepped by 100.

In the second embodiment 110, the spring housings 144 are constructed to act as air dampers. The clevis devices 150 are coupled to the spring rods 168 by a ball or knuckle joint 156. The knuckle joint 156 allows the spring rods 168 to move parallel with the axes of the spring housings 144.

A seal 158 is provided between the axial bore 160 of each spring housing 144 and the respective spring rod 168. A further seal 160 is provided between each nut 152 and the interior of the respective body portion 146.

The interiors of the spring housings 144 are sealed to airflow except for an orifice 162 and a valve (not shown). The orifice 162 allows metered passage of entrapped air from the spring housing. The orifice is of fixed cross section in this embodiment, but in other embodiments may be of variable cross section.

The valve allows rapid passage of air into the spring housing 144 on the expansion stroke.

This arrangement is useful, when for example, the steering action becomes lively due to uneven terrain. In this embodiment, when a force is applied to disturb the alignment of the fork, for example by encountering a pothole, free movement of the fork is suppressed by the compression of the entrapped air within the spring housing 146 and 5 the metered rate of escape of trapped air from the orifice 162. In this manner, the arrangement acts to dampen unsafe oscillations in the mechanism that could lead to erratic steering.

These embodiments are provided by way of example only, and various changes and 10 modifications will be apparent to persons skilled in the art without departing from the scope of the present invention as defined by the appended claims.

Claims

1. A steering centralisation device comprising a housing for fixing to the frame of a tricycle, a force transfer element for fixing to the forks of the tricycle, the force transfer element being rotatable relative to the housing, first and second compression springs connected to opposing sides of the force transfer element, the first and second springs both being tensioned to hold the force transfer element in an equilibrium position relative to the housing.

2. A steering centralisation device as claimed in claim 1, in which first and second spring housings accommodate the respective first and second springs.

3. A steering centralisation device as claimed in claim 1 or claim 2, in which the housing is open on one side.

4. A steering centralisation device as claimed in any preceding claim, in which first and second arcuate slots are provided on opposing sides of the force transfer element for connection to the respective first and second springs.

5. A steering centralisation device as claimed in claim 4, in which first and second rods connect between the force transfer element and the first and second springs.

6. A steering centralisation device as claimed in claim 5, in which a clevis is connected to each of the first and second rods and a clevis pin is engaged in each arcuate slot.

7. A steering centralisation device as claimed in claim 6, in which a ball joint is provided between each spring rod and respective clevis.

8. A steering centralisation device as claimed in any preceding claim, in which an adjuster nut is provided for adjusting the tension of each of the first and second compression springs.

9. A steering centralisation device as claimed in any preceding claim, in which a buffer element is attached to spring rod.

10. A steering centralisation device as claimed in claim 9, in which the buffer element is made from rubber.

11. A steering centralisation device as claimed in claim 9, in which the buffer element is a spring.

12. A steering centralisation device as claimed in any preceding claim when dependent on claim 2, in which seals are provided at the respective ends of the spring housings.

13. A steering centralisation device as claimed in claim 12, in which an aperture is provided through one of the seals.

14. A steering centralisation device as claimed in any preceding claim, when dependent on claim 2, in which the first and second spring housings are attached to the housing.

15. A steering centralisation device as claimed in any preceding claim, when dependent on claim 2, in which the first and second spring housings are remote from the housing and cables connect the force transfer element to the first and second springs.

16. A steering centralisation device as claimed in claim 1, in which the force transfer element is connected to a remote steering controller.