GB2109752A

GB2109752A - Wheel assemblies for vehicles

Info

Publication number: GB2109752A
Application number: GB08231964A
Authority: GB
Inventors: Sydney Jones
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-11-10
Filing date: 1982-11-09
Publication date: 1983-06-08
Also published as: GB2109752B

Abstract

A wheel assembly for a vehicle comprises a wheel 10 with a rotatable hub 11, a flexible wheel rim 12, and radially deformable means, such as leaf springs 13, connecting the hub and rim so that the rim may deform radially with respect to the hub, and one or more deflectors, e.g. rollers 14-16 engageable with the wheel rim at locations away from the ground-engaging portion of the rim 12, so as to limit the radial deformation of the rim at said locations and control the shape of the rim. Means may be provided to vary the distance between the deflector(s) and the wheel axis, and the deflector(s) may be driven to drive the wheel. The wheel may comprise a layer of elastomeric material covering the rim and leaf springs. <IMAGE>

Description

SPECIFICATION Improvements in or relating to groundengaging wheels for vehicles The invention relates to ground-engaging wheels for vehicles and sets out to provide a wheel which is particularly suitable for direct drive and for use on uneven and/or soft ground to give improved adhesion between the wheel and the ground. The invention provides developments of and modifications to the ground-engaging comformable wheel described and claimed in Co- pending Patent Application No. 8030983.

In the prior application there is described and claimed a ground-engaging wheel for a vehicle comprising a hub, a flexible wheel rim encircling the hub and spaced therefrom, radially deformable means connected between the hub and the wheel rim and means for controlling the radial deformation of said means. In use of the wheel on a vehicle, the hub is rotatably mounted on an axle which is fixed, or, in the case of a steerable wheel, is mounted for steering movement. Under the weight of the vehicle, the lower part of the flexible wheel rim conforms to the contour of the ground and thus deforms towards the hub, causing corresponding deformation of the deformable means connecting the hub to the wheel rim.This controlled deformation of the deformable means contributes to, or constitutes, the spring suspension of the vehicle, and the conventional spring suspension between the mounting for the wheel and the body of the vehicle may not be necessary. The arrangement reduces the power required to surmount obstacles during forward progress of the wheel, when compared with a conventional wheel, since as an obstacle is surmounted the accompanying deformation of the flexible wheel rim results in the wheel axle, and hence the centre of gravity of the vehicle, rising along a more gradual slope than is the case with a conventional rigid wheel.

Conformability of the wheel to the contour of the ground requires that the wheel stores considerable energy by elastic deformation as it rides over road obstacles and it arises from three features of the wheel: (a) The high degree of radial elasticity which in turn depends on a low elastic modulus of the material and a high ultimate strength, together with the geometry of the structure which should make maximum advantage of these material properties.

(b) The inextensible but very flexible nature of the wheel rim.

(c) The flexible movement of the deformable means is confined to the plane of the wheel so that radial deflection of the rim at any point leads to compensatory radial deflection at other points.

This is not true for example of a pneumatic tyre wheel.

The prior specification describes various arrangements for controlling deformation of the radially deformable means. For example, where the radially deformable means comprise leaf springs connected between the hub and the wheel rim, their radial deformation is controlled, at least in part, by the resilience thereof. The present invention provides further arrangements for controlling the deformation of the radially deformable means, and hence the contour of the wheel.

According to the invention, a ground-engaging wheel for a vehicle comprises a rotatable hub, a flexible wheel rim encircling the hub and spaced therefrom, radially deformable means connected between the hub and the wheel rim so that the wheel rim may deform radially with respect to the hub, and at least one deflector engageable with the wheel rim at a location away from the ground-engaging portion of the rim, so as to control the radial deformation of the rim at said location.

The deflector may be engageable with a radially outer surface of the flexible rim or with a radially inner surface thereof.

The deflector preferably comprises a rotatable auxiliary wheel or roller, the periphery of which is engageable with the flexible wheel rim so as to rotate as the wheel rim rotates. There may be provided two or more deflectors engageable with the wheel rim.

The provision of one or more such deflectors can achieve any or several of the following objects: (a) In the case where the deflector is a rotatable auxiliary wheel or roller the wheel or roller may be driven to transmit a drive to the conformable wheel.

(b) Part of the wheel load may be transferred from the axle to the deflector or deflectors, so stiffening the resilient characteristics of the wheel.

(c) The length of the flexible rim which is in contact with the ground is increased or decreased.

(d) The shape of the wheel profile may be altered to reduce the intrusion of the wheel into the vehicle load space in a variety of ways, for example, by allowing a lower load platform or, in the case of a wheelchair, by shaping the wheel profile to adapt to the shape of an occupant of the chair.

(e) The deflector or deflectors may provide a pitch stabilising force so that it is possible to support a vehicle on a single pair of large wheels on a common axis. This may be of advantage, for example, in enabling a vehicle, such as a wheelchair, to negotiate steps.

In any of the above arrangements means may be provided for varying the distance between the deflector and the axis of rotation of the wheel. For example, the wheel may be rotatable about a fixed axis, the distance of the deflector from that axis being variable. Thus, the deflector may have a mounting which is pivotable or slidable with respect to the axis of rotation of the wheel.

Alternatively the deflector may be fixedly located, the wheel being rotatable about an axis which is movable in a manner to vary the distance between the axis and the deflector.

By mounting the deflector on a spring loaded arm incorporating energy-absorbing means, unwanted oscillation of the vehicle may be damped out without increasing the rolling resistance of the wheel.

The following is a more detailed description of embodiments of the invention, reference being made to the accompanying drawings in which Figures 1 to 6 are diagrammatic representations of a wheel according to the invention, and Figure 7 is a section through the wheel of Figure 6.

Referring to Figure 1 , the ground-engaging wheel 10 comprises a rotatable hub 1 a flexible wheel rim 12, encircling the hub and spaced therefrom, and a plurality of leaf springs 13 connected between the hub and the wheel rim.

The ends of the leaf springs may be rigidly connected to the hub and wheel rim where the flexibility of each leaf spring permits adequate angular movement between it and the rim in the plane of the wheel. For example, the inner ends of the springs may be secured to the hub by rivets or sectured in slots in the hub, and the outer ends of the springs may be riveted to the wheel rim.

Alternatively, however, the springs may be connected to the hub and/or to the wheel rim by pivotal connections, the axes of the connections extending parallel to the axis of rotation of the wheel.

Engaging the outer periphery of the wheel rim 12 is a rotatable roller 14 which is rotatable on a fixed axis disposed above the axis of rotation of the hub 11, but closer thereto than the radius of the wheel when undeformed. The roller 14 therefore deforms the wheel 10 as shown. This increases the length of the flexible rim 12 which engages the ground, as well as stiffening the wheel 10 and providing a fore and aft stabilising force. Additional rollers 1 5 and 1 6 may be provided fore-and-aft of the roller 14 to increase the stabilising force. The auxiliary rollers 14, 15, 1 6 may be conventional rigid or resilient rollers, or may be small conformable rollers, having flexible rims, similar in construction to the main wheel 10.

In the arrangement of Figure 2 an auxiliary roller 1 7 is located, with or without an optional further roller 1 8, to shape the periphery of the wheel to a form suitable for use on a wheelchair and to provide a stable base in the case where the wheelchair has only two wheels on a single axle. A further optional roller 1 9 may be provided, the roller 10 being rotatably mounted on a springloaded arm 20, energy-absorbing means being connected between the spring-loaded arm and the body of the vehicle.

In the modified arrangement of Figure 3 there are provided additional pairs of subsidiary rollers 21 and 22 engaging the inner surface of the wheel rim 12.

As best seen in Figure 3A, the rollers, such as 21, of each pair may be mounted on a fork 23 which embrace the wheel rim 12, the rollers 21 projecting inwardly from the arms of the fork and engaging the inner surfaces of the wheel rim on either side of the springs 12. The provision of the further rollers 21 and 22 further stabilises the wheel in the fore-and-aft direction.

In the arrangement of Figures 4 and 5 the wheel axle 24 is mounted so as to be movable fore-and-aft on the vehicle. In the arrangement shown the axle is slidable in a fore-and-aft extending slot, but the axle may also be mounted on pivoted arms capable of fore-and-aft swinging movement. During normal forward movement of the wheel, as shown in Figure 4, the axle 24 lies in its forward position at the leading end of the slot 25. However, when an obstruction, such as a step 27, is encountered, as shown in Figure 5, the wheel axle 24 is pushed rearwardly, to the rear end of the slot 25, displacing the wheel 10 rearwardly with respect to the body of the vehicle.

This rearward displacement of the wheel 10 causes the wheel rim 12 to engage an auxiliary roller 26 mounted on the vehicle body, the roller 26 being so located as to deform the periphery of the wheel to such a shape as to stabilise the wheel as it mounts the step 27.

In the arrangements shown the slot 25 is horizontal, but in some configurations it may be preferable for the slot to be arranged at an angle to the horizontal.

In each of the above arrangements, as the wheel moves at constant velocity over the ground the shape of the wheel rim remains unchanged if the load and the nature of the ground do not vary, and in these conditions the angular velocity of the hub and the linear velocity of the wheel rim along its length are both constant, even where in the general case the wheel periphery is not circular.

The pattern of the disposition of the springs remains unchanged in space, closing up at some parts of the wheel (Regime A in Figure 2) and opening out at other parts (Regime B).

Nevertheless, some portions of each spring move at variable velocity as that spring performs a revolution around the hub, moving relatively slowly where the springs are bunched together and relatively fast where they are widely separated. The spatial positions of these two regimes vary with the pressure on the wheel rim exerted by the ground, i.e. the load, the pressure exerted by any auxiliary roller, and the features of the terrain (for example, the forces invoked in the wheel as it mounts a step). Thus an elastic diaphragm stretched tightly between the hub and the wheel rim would change its shape under these varying conditions, the linear velocity of the periphery being a constant v0 and the angular velocity of the hub being a constant cho0. In between the hub and the periphery the individual parts of the diaphragm will change both angular and linear velocities. A roller in contact with the diaphragm will thus have an angular velocity relative to the main wheel depending on the variable conditions applied to the wheel. By suitably selecting the point of contact between the roller and the diaphragm one or other of the variable influences can suitably be enhanced.

Although the invention has been particularly described with respect to arrangements in which the radially deformable means comprise leaf springs or a flexible continuous diaphragm, it will be appreciated that other forms of radially deformable means may be employed, such as longitudinal extensible and retractable radial spokes.

Figures 6 and 7 show an alternative arrangement in which the leaf springs 1 3 and flexible rim 12 are covered with an elastomer 30, which may be of rubber, synthetic rubber or other resiliently flexible plastics material, each as a closed-cell resilient foamed plastics.

The layer of elastomer may, for example, be about 10 mm in thickness on a wheel having a diameter of 400 mm. It is found that the performance of the wheel according to the invention depends to some extent on the relative flexibilities of the springs and the rim, and the provision of an elastomeric covering layer improves the relative flexibilities in the radial direction, in the axial direction and in torsion.

Further, the elastomeric covering layer protects the springs and rim from the environment, and, due to its thickness, also acts as a buffer to limit the relative deflection between the springs and between the springs and rim. This permits the maximum possible deformation of wheel to be limited to an extent whereby the wheel may still function as required.

Each area 31 between adjacent elastomercovered springs 13 may be open, or may be filled with a diaphragm of elastomer, as indicated by dotted lines at 32 in Figure 7. For example, where the width of the rim 12 and springs 13 is about 70 mm, the diaphragm between the springs may have a thickness of about 25 mm. In an alternative arrangement, not shown, only the diaphragm 32 of elastomer between the springs 13 is provided, and the springs and the rim themselves are not covered with a layer of elastomer.

The elastomer covering layer and diaphragm may be formed by placing the wheel in a mould and injection moulding the elastomeric material around the wheel.

Claims

1. A ground-engaging wheel for a vehicle comprising a rotatable hub, a flexible wheel rim encircling the hub and spaced therefrom, radially deformable means connected between the hub and the wheel rim so that the wheel rim may deform radially with respect to the hub, and at least one deflector engageable with the wheel at a location away from the ground-engaging portion of the rim, so as to control the radial deformation of the rim at said location.

2. A ground-engaging wheel according to Claim 1, wherein the deflector is engageable with a radially outer surface of the flexible rim.

3. A ground-engaging wheel according to Claim 1, wherein the deflector is engageable with a radially inner surface of the flexible rim.

4. A ground-engaging wheel according to any of Claims 1 to 3, wherein the deflector comprises a rotatable auxiliary wheel or roller, the periphery of which is engageable with the flexible wheel rim so as to rotate as the wheel rim rotates.

5. A ground-engaging wheel according to any of Claims 1 to 4, wherein there are provided two or more deflectors engageable with the wheel rim.

6. A ground-engaging wheel according to Claim 4, wherein the wheel or roller is driven to transmit a drive to the conformable wheel.

7. A ground-engaging wheel according to any of Claims 1 to 7, wherein means are provided for varying the distance between the deflector and the axis of rotation of the wheel.

8. A ground-engaging wheel according to Claim 7, wherein the wheel is rotatable about a fixed axis, the distance of the deflector from that axis being variable.

9. A ground-engaging wheel according to Claim 8, wherein the deflector has a mounting which is pivotable or slidable with respect to the axis of rotation of the wheel.

10. A ground-engaging wheel according to Claim 7, wherein the deflector is fixedly located, the wheel being rotatable about on an axis which is movable in a manner to vary the distance between the axis and the deflector.

11. A ground-engaging wheel according to any of Claims 1 to 10, wherein the deflector is mounted on a spring-loaded arm incorporating energy-absorbing means.

1 2. A ground-engaging wheel according to any of Claims 1 to 11, wherein said radially deformable means comprise leaf springs connected between the hub and the rim.

13. A ground-engaging wheel according to any of Claims 1 to 12, wherein said radially deformable means comprise an elastic diaphragm extending between the hub and the rim.

14. A ground-engaging wheel according to Claims 12 and 13, wherein said leat springs are embedded in the elastic diaphragm.

15. A ground-engaging wheel according to Claim 14, wherein said elastic diaphragm is provided by a body of elastomeric material in which at least the leaf springs and rim of the wheel are embedded.

16. A ground-engaging wheel according to Claim 12, wherein the leaf springs and rim are covered with a layer of elastomeric material.

1 7. A ground-engaging wheel for a vehicle comprising a rotatable hub, a flexible wheel rim encircling the hub and spaced therefrom, and a plurality of leaf springs connected between the hub and the wheel rim and capable of bending resiliently in the general plane of the wheel, the leaf springs and the wheel rim being covered by a layer of elastomeric material.

18. A ground-engaging wheel according to Claim 17, wherein the leaf springs are riveted to the hub and wheel rim respectively.

1 9. A ground-engaging wheel according to Claim 17 or Claim 18, wherein a diaphragm of elastomeric material extends across each area defined by two adjacent leaf springs and the wheel rim.

20. A ground-engaging wheel according to Claim 19, wherein the diaphragm is integral with the layers of elastomeric material covering the leaf springs and wheel rim.

21. A ground-engaging wheel substantially as hereinbefore described with reference to the accompanying drawings.