GB2324507A - Bob sled - Google Patents

Abstract

A sled runner assembly has a pair of runners 14 pivotally connected to allow independent rotation about an axis 24 perpendicular to the sled runner's length, but held substantially parallel by links 26. Steering of the sled is by shifting of the body weight of the rider, which affects the contact patch of each runner, but without causing the undesirable "snow-plough" braking effect if the runners were allowed to depart from parallel. It is preferred that the axis 24 is arranged forward of the middle of the sled in the intended direction of travel.

Description

IMPROVEMENTS IN BOB SLED DESIGN This invention relates to the field of bob sled design, with particular reference to improvements in the chassis and runner assembly of such a sled.

In the field of Winter sports perhaps the fastest and potentially most dangerous activity is that of bob sledding.

There are a number of disciplines that are recognised at Olympic status within the sport of bob sled, namely two/four-man bob, the luge and the one-man sled, the latter being more commonly known as the skeleton bob.

In the particular case of the skeleton bob, it has long been appreciated that a vital component of its performance is its ability to flex along its total length. This longitudinal flexure enables a rider to redistribute his or her bodyweight along the length of the two surfaces in contact with the ice (commonly referred to as sled runners) thereby allowing the sled rider an 'element' of steering control. Additionally, it has been found to be important to both the speed and smooth passage of the sled that the runners are able to move independently, thereby allowing the sled to "mould" itself to the contours of the track.

Ensuring that the runners remain in contact with the ice at all times gives a smooth and thereby quick run time.

Current skeleton bob designs achieve their complex longitudinal flexure based control by the utilisation of metal or plastic belly pans on which the rider lays. As the sled and rider descend down an ice track the motion and distribution of the rider's weight causes the flexible belly pan to distort thereby causing the chassis to twist giving the required element of steering control. The "chassis twisting" element of the total sled flexure however causes the sled runners to bow along their length and as such the runners do not remain substantially parallel at all times during the sled's motion. This independent bowing movement of the sled runners causes an effect similar to that of "snow ploughing n experienced more commonly on normal downhill skis, whereby increased ice friction is created by the non-parallel sled runners motion against the ice leading to a less effective and consequently slower skeleton bob.

The two sled runners of the skeleton bob are commonly round in cross section, with knife blades cut in to the rear portion to give lateral stability. Each of the runners are bowed along their length, so that when a rider mounts the sled, there exists a contact patch between the runner and ice. As the bow is increased by means of an adjusting screw, the contact patch decreases accordingly. The more bow, the less 'knife' in contact with ice giving greater speed but less stability. As a rider's confidence with the sled and/or track increases he/she will progressively increase the bow until a point of instability is reached, where the rider is using the minimum amount of knife to control the sled.

Steering is effected by the rider shifting their body weight, applying pressure on opposite shoulder and knee.

This causes the runner contact patches to shift in opposite directions, giving a dissimilar amount of knife on each runner allowing a turning force to be induced in the sled. A rider will need to make up to one hundred of these steering movements during a typical run to ensure competitive descent time.

Our invention enables the sled runners of a bob sled to both move independently of each other and yet to remain substantially parallel at all times thereby substantially eliminating the snow plough effect and the possibility of a bowing element along the length of each runner.

Accordingly there is provided a sled runner assembly comprising a pair of runners, said pair of runners consisting of a blade means and an associated runner beam, said pair of runners being connected and maintained in a substantially parallel relationship by a pivot means, said pivot means allowing for independent rotation of each of said runners about an axis substantially perpendicular to said runners' length.

A specific embodiment of the invention will now be described by way of example only with reference to the following drawings: Figure 1 shows a diagrammatic representation of a current state of the art skeleton bob sled, Figure 2 shows a diagrammatic representation of a current state of the art skeleton bob sled undergoing flexure due to use, Figure 3 shows a diagrammatic representation of a skeleton bob sled pivotal runner assembly in accordance with the invention, Figure 4 shows an exploded diagram of a bob sled in accordance with the invention and Figure 5 shows a diagrammatic side view of a skeleton bob showing the contact position between the runners and the ice In Figure 1 a one-man skeleton bob sled is shown 2 having a pair of sled runners 6 connected to a metal belly pan 4 by four runner blocks 8. In use, a rider lies on the metal belly pan 4 and whilst holding two grip handles (not shown) and steers the skeleton bob 2 down an ice run by moving and distributing his or her bodyweight along the length and width of the sled 2.

Figure 2 shows a similar one-man bob sled 2 but shown undergoing the exaggerated effects of the flexing of the flat metal belly pan 4 to a complex flexed state 10. The otherwise parallel runners 6 are shown in a correspondingly flexed position 12 resulting in the otherwise substantially straight runners 6 bowing along their length. The action of this flexure thereby leads to a friction inducing snow plough effect.

Figure 3 shows a one-man skeleton bob sled in accordance with the invention having a pair of parallel sled runners 14 connected to two longitudinal runner beams 16 at runner block connection points 18. The runner beams 16 are maintained in the longitudinal parallel relationship by two cross bars 26 connected at the runner block locations 18. An I-section bearing assembly 20 having a central pivot position 22 is releasably connected to both runner beams 16 at connection points 24. The connection of the pivotal I-beam assembly 20 to both runner bars 16 enables both runners 14 and their corresponding runner beams 16 to rotate relative to each other about an axis substantially perpendicular to the normal orientation of the runners 14. This free relative rotational movement of each independent runner is mechanically limited by the whole assembly being connected to a flexible belly pan (not shown) and the mechanical restriction provided by the two cross bar and rose bearing assemblies 26 located in a position substantially parallel to the rotational central axis of the I-beam assembly 20.

In use, a belly pan 4 (as shown in Figure 1) is fastened over the total assembly shown in Figure 3, and steering handles 28 are mounted through a form of saddle plate 30 on to the said belly pan thereby allowing the rider to secure themselves to the sled. Due to the independent free relative rotational movement of each of the runners, the problem of belly plan flexing and the associated bowing of the runners 12 is substantially removed, and the action of said runners is constrained to a parallel motion by the restraining force of the cross bars 26. The independent movement available to the two runners allows the sled to remain in contact with the ice for a greater proportion of time thereby providing more controllable steering and reducing the frictional force with the ice normally associated with the snow ploughing effect prevalent with the older type of design sled.

The pivotal I beam assembly 20 is shown having its rotation axis 34 positioned at the lateral centre line of the sled 38. The contact patch 40 between the runner 14 and the ice 36 is shown at a position at the centre line of the sled 38. Due to the fact that the steering is effected by the rider shifting body weight, this action causes the runner contact patches 40 to move forward in the direction of travel. When entering a corner, the rider exerts forward pressure on the sled 2 giving a resultant force to the runners 14 at a position forward of the contact patch 40 centre line 38 at a new position 32. When the pivotal I beam assembly 20 is used on a bob sled, the shift of this resultant force to a new position R, 32 gives a turning moment of (R multiplied by the distance X] which is introduced into the bob sled chassis leading to an exaggerated steering effect. The steering control of a bob sled fitted with our I beam pivot assembly 20 invention can therefore be further improved over the state of the art flexible belly pan sleds by moving the position of the I beam pivot assembly 20 forward of the centre line of the sled 38.

This embodiment of the invention has been illustrated in respect of a one-man skeleton bob sled, but it will be recognised that the concept of free relative rotational movement between runner assemblies could be applied to all of the bob track disciplines, including without limitation the two/four-man bob and the luge.

Additionally the application of a pivotal chassis assembly could be applied to any form of transport which requires parallel and free relative rotational movement along any blade runner or means runner comprising a connected series of wheels or tracks, e.g. motorised sleds, trailers, transport vehicles and the like.

Claims (4)

1. A sled runner assembly comprising a pair of runners, said pair of runners consisting of a blade means and an associated runner beam, said pair of runners being connected and maintained in a substantially parallel relationship by a pivot means, said pivot means allowing for independent rotation of each of said runners about an axis substantially perpendicular to said runners' length.

2. A sled runner assembly as described in claim 1 wherein said pivot means is connected to each of said runners at a position forward of the central lateral axis of each of the runner blades in their intended direction of travel.

3. A bob sled comprising a runner assembly as described in claim 1 or claim 2.

4. A sled runner assembly substantially as herein before described with reference to the accompanying drawings.