GB2169363A

GB2169363A - Alternative bicycle etc. wheel drive mechanisms

Info

Publication number: GB2169363A
Application number: GB08432331A
Authority: GB
Inventors: Paul Antony Fletcher
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-12-21
Filing date: 1984-12-21
Publication date: 1986-07-09
Also published as: GB2169363B; GB8432331D0

Abstract

A chain sprocket 3 is mounted by a freewheel unit 4 to a wheel hub 1. A slide plate 11 can be moved by a fork plate received in a groove 14 coaxially towards the sprocket 3 so that drive pins 10 sliding within a drive plate 7 fixed to the wheel hub 1 will enter passageways 6 in a drive ring 5 fixed to the sprocket 3. This locks the sprocket 3 to the wheel hub 1 to effect a change to a fixed wheel unit. The slide plate 11 is spring biased in the direction to disengage the drive pins 10 from the passageways 6 in the drive ring 5. <IMAGE>

Description

SPECIFICATION Improvements relating to wheel drive mechanisms This invention is concerned with a unit for enabling a freewheel unit on a bicycle to be changed to a fixed wheel at will.

A freewheeled unit only works when the pedals are pushed down by alternate feet. In contrast a fixed wheel is in constant drive and therefore helps to turn and lift the legs after a pedal has been pushed down. The effect is similar to that of a flywheel and keeps the legs in constant rhythm. A stronger leg will then prevent a weaker leg from becoming overtired. Other advantages of a fixed wheel drive are improved speeds and hill climbing ability, more control in slow traffic, and less fatigue when pedalling with one leg. However, there are disadvantages to a fixed wheel drive, the main one being that the legs are forced to rotate when cycling downhill when effort is not in fact required. Another disadvantage is that the rotating pedal may strike the ground when sharp corners are being turned.Also the rotation of the pedals from a fixed wheel is awkward when the bicycle is being pushed.

It is an object of this invention to provide means whereby a freewheel unit on a bicycle may readily be changed to a fixed wheel drive, and vice versa.

Accordingly this invention provides a freewheel to fixed wheel change unit comprising first and second drive rings for securing respectively to the chain sprocket plate of a freewheel unit of a wheel and to the hub of the wheel, one drive ring carrying drive pins and having a drive mechanism whereby the drive pins may be moved into or out of a position wherein the drive pins engage within openings in the other drive ring so as to interengage the two drive rings.

When changing to the fixed wheel mode the drive pins are moved across into engagement with the other drive ring and will then slot into the openings in that drive ring as these openings pass the ends of the pins. The chain sprocket plate will then be directly linked to the wheel hub, thus creating a fixed wheel drive. When the drive pins are pulled out from the openings the freewheel drive is restored.

The number of drive pins used may vary as required depending upon the type of bicycle to which the unit is to be applied. For stunt bikes substantial drive forces on to the back wheel are required and so several drive pins will be employed. However for a touring bicycle sudden changes in drive force would not be expected and so the unit could be operated, for example, by a single large drive pin.

It is preferred that one drive ring should carry a mounting for attachment within the hub of a wheel, so as to make the unit as compact as possible. Ideally the securing means for the two drive rings will comprise screw-threaded parts for securing to the chain sprocket plate and wheel hub respectively.

These screw-threaded parts should be oppositely handed so that when they are interengaged with one another there will be no tendency for either to become unscrewed.

In the preferred arrangement the drive pins are fixed to a slide plate and pass slidably through passageways in the one drive ring, the drive mechanism being arranged to act on the slide plate to move the slide plate towards or away from the one drive ring. Movement of the slide plate in the disengaging direction is ideally limited by a flange on a spacer bush fitted within the slide plate. Movement of the slide plate may readily be controlled by a cable operated guide fork positioned in a circumferential groove of the slide plate. It is greatly preferred that the drive mechanism should be biased into the disengaging position of the drive pins so that the unit will return automatically to the freewheel condition should any parts of the unit break.

Thus, for example, the guide fork may be mounted on spring loaded pins which bias the guide fork into the disengaging position.

The invention may be performed in various ways and a preferred embodiment thereof will now be described with reference to the accompanying drawings, in which: Figure 1 is a cross-section through a wheel hub to which a freewheel to fixed wheel change unit of this invention has been attached; Figure 2 illustrates three drive parts of the unit of Figure 1; Figure 3 is an end view of a drive mechanism for the unit shown in Figure 1; Figure 4 is a plan view of part of the drive mechanism shown in Figure 3; and Figure 5 illustrates a guide fork interconnecting the drive mechanism with the unit shown in Figure 1.

In Figure 1 there is illustrated a wheel hub 1 carried by a spindle 2. To one side of the wheel hub 1 there is fitted a chain sprocket 3 mounted about a freewheel unit 4. The ball race and ratchet details of the freewheel unit are not illustrated. Secured to the chain sprocket 3 is a drive ring 5 (see also Figure 2) provided with twelve evenly spaced through passageways 6. A drive plate 7 has a collar 8 which is screw-threadedly engaged within the wheel hub 1. The screw-thread of the collar 8 is oppositely handed to the screw-thread by which the drive ring 5 is mounted on the chain sprocket 3. As can be seen from Figure 2, the drive plate 6 incorporates six evenly spaced through passageways 9 which receive an identical number of drive pins 10 carried by a slide plate 11. As shown in Figure 2 the slide plate 11 may incorporate cutaway parts IIA for weight reduction.The slide plate 11 is positioned about a spacer bush 12 provided with a flange 13 which limits the extent to which the slide plate 11 may move away from the drive plate 7.

As shown in Figure 1 the slide plate 11 incorporates a circumferential groove 14 which receives the fork 15 of a fork plate 16 (Figures 3 to 5). This fork plate 16 is bolted onto a pair of bolts 17, 18 which are slidably received within a mounting member 19. Springs 20 on the bolts 17 and 18 bias the fork plate 16 towards the mounting member 19 and thus also bias the slide plate 11 into its outermost position. As can be seen from Figure 3 the mounting member 19 carries a support bar 21 which provides a pivotal support for a lever 22 which can be operated by a cable 23 which passed up through the support bar 21.

The cable 23 will lead forward to an operating member carried on the handlebars of the bicycle. The end of the lever 22 engages within a circumferential notch 24 in the bolt 18. Thus as the cable is moved in the upward direction (as seen in Figure 3) the lever 22 will force the bolt 18 inwardly against the bias of the springs 20 and thus cause the fork plate 16 to move the slide plate 11 closer to the drive plate 7. The drive pins 10 will then be able to engage within the openings 6 in the drive ring 5 thus interconnecting the drive ring 5 and the drive plate 7. By this means the chain sprocket 3 is rigidly interconnected with the wheel hub 1 thus overriding the effect of the freewheel unit 4. The bicycle wheel is then in the fixed wheel mode.When the cable 23 is released the springs 20 will cause the pins 10 to be withdrawn from the openings 6 in the drive ring 5, thus reverting the unit to the freewheel mode. Should any parts of the unit break (for instance the cable 23 might faii) the springs 20 will cause the unit to be moved into the freewheel mode automatically.

The change unit and drive mechanism illustrated in the drawings may readily be detached from the rear fork frame 25 (Figure 4) and the wheel hub of the bicycle if it is desired to revert the bicycle to a standard construction. It will be appreciated that modified forms of drive mechanism may be employed.

Furthermore the change unit itself may be attached to the chain sprocket and wheel hub in ways other than that illustrated in Figure 1.

For example, with a Deraillier multiple gear sprocket it is preferable to fit all the mounting parts of the change unit inside the sprocket unit, so that the drive ring 5 is attached to a part of the chain sprocket, whilst the drive plate is secured to the hub or a part which is to be attached to the hub of a bicycle. This can result in a very compact arrangement.

Figure 6 illustrates a modification of the unit shown in Figure 1. Here the drive ring 5A is bent over the drive plate 7A and it is the downwardly extending portion 26 of the drive ring which receives the drive pins 10 carried by the slide plate 11. The slide plate 11 therefore rotates with the chain sprocket 3 and when the slide plate 11 is moved across the pins 10 will engage within passageways 27 formed in the drive plate 7A. This provides a more compact arrangement which has the added advantage that the passageways within the drive plate 7A are protected by the overlapping drive ring 5A so that there will be a much reduced tendency for the passageways 27 to become clogged, such as by mud thrown up by the wheels.

It will be appreciated that other means of supporting and driving the drive pins 10 into engagement with the drive ring 5 may be employed as desired. Furthermore the number of drive pins 10 and the corresponding passageways (for example passageways 6 and 9 shown in Figure 2) may be varied to suit particular requirements.

Whilst the freewheel to fixed wheel change unit has been described in relation to bicycle wheels it is of course possible for this unit to be employed in other situations, such as the drive parts of engineering machinery.

Claims

1. A freewheel to fixed wheel change unit comprising first and second drive rings for securing respectively to the chain sprocket plate of a freewheel unit of a wheel and to the hub of the wheel, one of the drive rings carrying drive pins and having a drive mechanism whereby the drive pins may be moved into or out of a position wherein the drive pins engage within openings in the other of the drive rings so as to interengage the two drive rings.

2. A unit according to claim 1, wherein one drive ring carries a mounting for attachment within the hub of a wheel.

3. A unit according to claim 1 or claim 2, wherein the two drive rings carry oppositely handed screw-threaded parts for securing to the chain sprocket plate and the wheel hub respectively.

4. A unit according to any one of claims 1 to 3, wherein the drive pins are fixed to a slide plate and pass slidably through passageways in the one drive ring, the drive mechanism being arranged to act on the slide plate to move the slide plate towards or away from the one drive ring.

5. A unit according to claim 4, wherein movement of the slide plate in the disengaging direction is limited by a flange on a spacer bush fitted coaxially within the slide plate.

6. A unit according to claim 4 or claim 5, wherein movement of the slide plate is controlled by a cable operated guide fork positioned in a circumferential groove of the slide plate.

7. A unit according to any one of claims 1 to 6, wherein the drive mechanism is biased into the disengaging position of the drive pins.

8. A unit according to claim 6 and claim 7, wherein the guide fork is mounted on spring loaded pins which bias the guide fork into the disengaging position.

9. A unit according to any one of claims 1 to 8, wherein the parts thereof are designed to fit within the sprocket unit of the wheel.

10. A freewheel to fixed wheel change unit substantially as herein described with refer ence to the accompanying drawings.