GB2042674A

GB2042674A - A Friction Drive Wheel

Info

Publication number: GB2042674A
Application number: GB7905774A
Authority: GB
Original assignee: British Gas Corp
Current assignee: British Gas Corp
Priority date: 1979-02-19
Filing date: 1979-02-19
Publication date: 1980-09-24
Also published as: GB2042674B; CA1128782A

Abstract

A friction drive wheel suitable for high impressed loads has a central hub (1) in which are mounted a plurality of resilient spokes (3). The spokes over at least a portion of their length exhibit curvature in a plane normal to the axis of the wheel and may be tapered towards their free end to modify the stress/strain relationship. A suitable tyre for the wheel has stepped projections (10) which engage the ends of the spokes. <IMAGE>

Description

SPECIFICATION Friction Drive Wheels This invention relates to friction drive wheels and, in particular, to wheels suitable for deriving motive power from translational movement to drive high pressure hydraulic pumps, electrical generators and like potential energy sources.

Friction drive wheels are known in many applications for the conversion of translation movement into other forms of energy and vice versa. For example, a knurled wheel which presses against the pneumatic tyre is employed to drive the lighting dynamo of a pedal cycle. In our co-pending application No. 31507/77 we describe a hydraulic braking system for a pipeline inspection pig which employs a friction wheel bearing against the wall of a pipeline. The wheel rotates as the pig traverses the pipeline and drives a high pressure hydraulic pump which, in turn, actuates a servo-controlled braking system to limit the speed at which the pig travels.

Particularly in applications such as the latter, it is necessary to apply a large force to urge the friction wheel towards the pipeline wall to prevent the occurrence of slipping. If a conventional solid wheel with an elastomeric tyre were employed, there would be a substantial deformation of the tyres and hence high losses due to hysteris. This would create high heat dissipation and would result in rapid degradation of the elastomeric wheel.

In order to overcome this difficulty, a wheel structure has been devised in which a relatively thin elastomeric tyre is mounted on spokes having a curved section so that radial deformation causes flexure of the spokes. The inherent elasticity of the spokes gives rise to a force normal to the driven surface of the wheel.

Accordingly, the present invention provides a friction drive wheel comprising a central hub having mounted thereon the inner ends of a plurality of flexible spokes, the outer ends of which are adapted to receive a resilient tyre, wherein at least a portion of each of said spokes exhibits curvature in a plane normal to the axis of the wheel.

An embodiment of the invention will now be described by way of exampie with reference to the accompanying drawings in which: Figure 1 shows in partial section a side-view of a friction drive wheel and tyre, Figure 2 shows a cross-section along the line X-X of Figure 1, and Figure 3 shows an enlarged side view of a spoke taken from the wheel shown in Figure 1.

Referring now to the drawings, a friction drive wheel has a central hub 1. Mounted in slots 2 in the hub are twenty four spokes 3. The ends of the spokes have a groove 4 in each of the outer edges. Mounted on the hub by means of bolts 5 are two flanges 6 which have inward facing projections 7 which engage the complementary grooves on the spokes and act as retaining members.

The spoked wheel is provided with an elastomeric tyre 8 which is fabricated from a resilient polymeric material such as polyurethane or nitrile rubber. It may be moulded using a split outer mould with a solid inner core, and needs no fabric reinforcement, although this may be provided to enhance the strength and durability.

The tread of the tyre has sipes 9 to improve the grip on the surface of the pipeline. On the inner surface of the tyre carcase is a series of inward projecting steps 10 which cooperate with the ends 11 of the spokes to improve traction.

The design of the spokes is shown in elevation in greater detail in Figure 3. Indicated on the drawing are the dimensions in millimetres of a spoke suitable for a friction drive wheel for use with an hydraulic pump to be mounted on an inspection pig for gas pipelines.

The spoke has a straight, relatively thick root end section 12, which locates in the grooves of the hub. This straight section, when mounted, projects in a radial direction for a short distance and then bends at an angle of approximately sixty degrees (58.70 in the embodiment). Over the remainder of its length, the spoke exhibits a curvature in a plane normal to the axis of the wheel. The radius of curvature is approximately two-thirds of the radius of the wheel. Over the curved portion, the spoke section tapers gradually, the free end being approximately 0.4 times the thickness of the root end. The free end is rounded to reduce wear on the inner surface of the tyre.

In operation the load is carried on three of the twenty four spokes. The spokes carry a tangential load as well as the normal load. An important factor of the shape is that, since the spokes are interleaved in a spiral arrangement, a large proportion of the volume of the wheel is occupied, thus improving the performance.

A friction wheel such as has been described is particularly suitable for driving a high-pressure pump for a servo-controlled braking system for an insepection pig used in gas pipelines. The form of construction is, however, of more general application and may be used in other situations where a high stress is to be applied normal to the bearing surface. It may also be used where some form of springing is to be applied to the impressed load and even for simple traction applications.

Claims

1. A friction drive wheel having mounted thereon the inner ends of a plurality of flexible spokes, the outer ends of which are adapted to receive a resilient tyre, wherein at least a portion of each of said spokes exhibits curvature in a plane normal to the axis of the wheel.

2. A friction drive wheel as claimed in Claim 1, wherein said spokes are demountable.

3. A friction drive wheel as claimed in Claim 2 having a central hub provided with slots or grooves for the reception of spokes.

4. A friction drive wheel as claimed in any one of the preceding claims and having spokes with a

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Friction Drive Wheels This invention relates to friction drive wheels and, in particular, to wheels suitable for deriving motive power from translational movement to drive high pressure hydraulic pumps, electrical generators and like potential energy sources. Friction drive wheels are known in many applications for the conversion of translation movement into other forms of energy and vice versa. For example, a knurled wheel which presses against the pneumatic tyre is employed to drive the lighting dynamo of a pedal cycle. In our co-pending application No. 31507/77 we describe a hydraulic braking system for a pipeline inspection pig which employs a friction wheel bearing against the wall of a pipeline. The wheel rotates as the pig traverses the pipeline and drives a high pressure hydraulic pump which, in turn, actuates a servo-controlled braking system to limit the speed at which the pig travels. Particularly in applications such as the latter, it is necessary to apply a large force to urge the friction wheel towards the pipeline wall to prevent the occurrence of slipping. If a conventional solid wheel with an elastomeric tyre were employed, there would be a substantial deformation of the tyres and hence high losses due to hysteris. This would create high heat dissipation and would result in rapid degradation of the elastomeric wheel. In order to overcome this difficulty, a wheel structure has been devised in which a relatively thin elastomeric tyre is mounted on spokes having a curved section so that radial deformation causes flexure of the spokes. The inherent elasticity of the spokes gives rise to a force normal to the driven surface of the wheel. Accordingly, the present invention provides a friction drive wheel comprising a central hub having mounted thereon the inner ends of a plurality of flexible spokes, the outer ends of which are adapted to receive a resilient tyre, wherein at least a portion of each of said spokes exhibits curvature in a plane normal to the axis of the wheel. An embodiment of the invention will now be described by way of exampie with reference to the accompanying drawings in which: Figure 1 shows in partial section a side-view of a friction drive wheel and tyre, Figure 2 shows a cross-section along the line X-X of Figure 1, and Figure 3 shows an enlarged side view of a spoke taken from the wheel shown in Figure 1. Referring now to the drawings, a friction drive wheel has a central hub 1. Mounted in slots 2 in the hub are twenty four spokes 3. The ends of the spokes have a groove 4 in each of the outer edges. Mounted on the hub by means of bolts 5 are two flanges 6 which have inward facing projections 7 which engage the complementary grooves on the spokes and act as retaining members. The spoked wheel is provided with an elastomeric tyre 8 which is fabricated from a resilient polymeric material such as polyurethane or nitrile rubber. It may be moulded using a split outer mould with a solid inner core, and needs no fabric reinforcement, although this may be provided to enhance the strength and durability. The tread of the tyre has sipes 9 to improve the grip on the surface of the pipeline. On the inner surface of the tyre carcase is a series of inward projecting steps 10 which cooperate with the ends 11 of the spokes to improve traction. The design of the spokes is shown in elevation in greater detail in Figure 3. Indicated on the drawing are the dimensions in millimetres of a spoke suitable for a friction drive wheel for use with an hydraulic pump to be mounted on an inspection pig for gas pipelines. The spoke has a straight, relatively thick root end section 12, which locates in the grooves of the hub. This straight section, when mounted, projects in a radial direction for a short distance and then bends at an angle of approximately sixty degrees (58.70 in the embodiment). Over the remainder of its length, the spoke exhibits a curvature in a plane normal to the axis of the wheel. The radius of curvature is approximately two-thirds of the radius of the wheel. Over the curved portion, the spoke section tapers gradually, the free end being approximately 0.4 times the thickness of the root end. The free end is rounded to reduce wear on the inner surface of the tyre. In operation the load is carried on three of the twenty four spokes. The spokes carry a tangential load as well as the normal load. An important factor of the shape is that, since the spokes are interleaved in a spiral arrangement, a large proportion of the volume of the wheel is occupied, thus improving the performance. A friction wheel such as has been described is particularly suitable for driving a high-pressure pump for a servo-controlled braking system for an insepection pig used in gas pipelines. The form of construction is, however, of more general application and may be used in other situations where a high stress is to be applied normal to the bearing surface. It may also be used where some form of springing is to be applied to the impressed load and even for simple traction applications. Claims

4. A friction drive wheel as claimed in any one of the preceding claims and having spokes with a substantially straight end portion for mounting on a hub.

5. A friction drive wheel as claimed in Claim 4, wherein the curved portion of each of said spokes is bent at an angle to the straight end portion.

6. A friction drive wheel as claimed in Claim 7, wherein the curved portion of each of said spokes is bent at an angle of approximately sixty degrees to the straight end portion.

7. A friction drive wheel as claimed in any one of the preceding Claims, wherein the curved end portion of the spokes is tapered from a relatively thick mounting or root end to a relatively thin free end.

8. A friction drive wheel as claimed in Claim 7, wherein the root end is approximately 2.5 times as thick as the free end.

9. A friction drive wheel as claimed in any one of the preceding claims wherein the radius of curvature of the curved portion of the spokes is approximately two thirds of the radius of the wheel.

1 0. A friction drive wheel as claimed in any one of the preceding Claims, wherein the free ends of the spokes are curved to reduce wear on the inner surface of the tyre.

11. A tyre for a friction drive wheel as claimed in any one of the preceding Claims, having a series of step-like projections on its inner surface to co-operate with the free ends of the spokes.

12. A tyre for a friction drive wheel as claimed in Claim 11, having sipes in its tread to improve traction.

1 3. A friction drive wheel incorporating a tyre as claimed in Claim 11 or Claim 12.