GB2363831A

GB2363831A - A drive transmission device

Info

Publication number: GB2363831A
Application number: GB0015451A
Authority: GB
Inventors: Nigel Stephen Woodford
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-06-24
Filing date: 2000-06-24
Publication date: 2002-01-09
Also published as: GB0015451D0

Abstract

A drive transmission device 1, preferably for a bicycle chain or other endless flexible member, comprises: a plurality of transmission member engaging elements 40a-d for engaging the transmission member (not shown); means for constraining the engaging elements to move in a substantially circular orbit about a common axis, in engagement with a transmission member over part of the orbit; and selector means 85 for varying the radial position of the engagement elements 40a-d to vary the diameter of the orbit whereby to vary the transmission ratio of the drive element. The transmission ratio may be variable in discreet steps, or infinitely variable (figs 11 and 12).

Description

2363831 A DRIVE TRANSMISSION DEVICE The present invention relates

generally to a drive transmission device and particularly to such a device for a chain or other endless flexible transmission member drive mechanism.

The present invention is concerned particularly, but not exclusively, with a chain drive transmission mechanism for a bicycle As with other chain driven mechanisms the chain of a bicycle serves to transmit force from one place to another, in this case from a pedal sprocket to a rear driving wheel A gear changing mechanism is usually included on bicycles and is present, as is the case with other gear mechanisms, to change one rate of rotation to another For example, effort applied to the pedals can be geared up for high-speed travel or geared down for hill climbing power In the higher gears the rear wheel turns many times for each turn of the pedals, whilst in the lower gears the wheel turns fewer times in relation to the pedal and in this way speed is traded for ease of pedalling.

In a bicycle, the pedals have at least one associated chain wheel and the rear wheel has at least one sprocket wheel, around which the chain is positioned If the size of the sprocket wheels which engage the chain are varied then the chain drive ratio can be altered The most common form of gear changing mechanisms for bicycles is the derailleur gear system In a derailleur system either or both of the rear wheel and the pedal arrangement have a plurality of associated sprocket wheels of varying diameters which are arranged along a common axis of rotation Hinged levers, called derailleurs, shift the chain from one sprocket wheel to another, and a spring-operated jockey pulley or tension pulley is used to take up or let out the slack in the chain, in this way various gear ratios can be selected.

The derailleur system relies on, and is ultimately limited by, the provision of a plurality of differently sized sprocket wheels which must be laterally mutually spaced to allow introduction of the chain As the number of sprocket wheels increases, to allow for more gear ratios, the amount of space that the arrangement takes up, its weight, and its complexity are all increased In addition a gear change mechanism which requires the chain to be continually removed and replaced on different sprockets is inherently more likely to fail than a single sprocket.

The derailleur system must have multiple sprocket wheels because the chain-engaging teeth of the sprocket wheels are fixed in their radial position An alternative gear change mechanism, the so-called hub gear, has a plurality of planetary gears operated by a single sprocket wheel Hub gears, however, have limitations in that it is difficult to engineer more than five different transmission ratios and the apparatus is usually relatively heavy.

According to the present invention there is provided a drive transmission device for a chain or other endless flexible transmission member drive mechanism, comprising a plurality of trnmission member engagement elements for engaging a trnmission member, means for constraining the engagement elements to move in a substantially circular orbit about a common axis in engagement with a transmission member over a part of the orbit, and selector means for varying the radial position of the engagement elements to vary the diameter of the orbit whereby to vary the transmission ratio of the drive mechanism.

In this way the equivalent of a single sprocket wheel, the circumference of which is variable, can replace multiple sprocket wheels and retain the ability to vary a transmission ratio It is noted that if a gear selecting device as defined above is used, the radial positioning of chain engaging elements of which is variable, then there will be no need for multiple sprocket wheels or for a derailleur gear system in order to achieve variation of the transmission ration of the chain drive mechanism.

The device is particularly suitable for use in conjunction with a single sprocket wheel or a hub gear arrangement because the entire mechanism is in the same plane and does not require any lateral shifting of the chain.

Such a transmission device could be used, for example, in place of the pedal or driven chain wheel and/or rear wheel sprocket/s of a bicycle.

In a preferred embodiment the endless flexible transmission member is a chain comprising a flexibly connected series of links or rings, in which case each transmission member engagement element is provided with at least one tooth for engaging a link of the chain In other embodiments, however, the transmission member may be a belt or the like, in which case each transmission member engagement element may be provided with a suitable engagement portion such as a friction pad for a belt or a V-shape notch or projection for a V-belt arrangement.

The means for constraining the engagement elements is typically a spindle having arms on which the engagement elements are carried.

The means for constraining the engagement elements may be a support member rotatably mounted about the said common axis, in which the support member has radial slots in which respective engagement elements are carried, and includes means for securing each chain-engagement element in one of a plurality of selectable positions along a respective slot.

In a chain drive mechanism the selectable positions are constrained to be at fixed intervals which correspond to the length of a chain link in order that the chain can be smoothly engaged and retained by teeth However, where a transmission member without links or other fixed engagement points is used, such as a belt, the selectable positioning of the engagement elements along respective slots may be infinitely variable whereby to provide an infinitely variable gearing mechanism.

The radial positions of the engagement elements may be individually adjustable; where this is the case the radial position of a chain-engagement element may be varied at a region of its orbit at which it is disengaged from the transmission member.

Alternatively the radial positions of the transmission member engagement elements may be collectively adjustable using a suitable linkage mechanism.

The selector means may comprise arcuate abutment surfaces positionable within the orbit and curved so as to contact a part of the chain engagement element whereby to vary its radial position as it orbits.

The present invention also provides a drive mechanism incorporating the drive transmission device as hereinbefore described, and a bicycle incorporating such a drive mechanism.

The size of the device and thus the range of transmission ratios is limited only by other surrounding components In the case of a bicycle there are well- established principles of the effective maximum and minimum sizes of sprocket wheels will be well known to those skilled in the art.

In a particularly useful embodiment the support member also functions as a chain guard.

Various embodiment of the present invention will now be more particularly described by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic side view of a bicycle chain drive mechanism incorporating a device according to the present invention; Figure 2 is a side view of a support member of a first embodiment; Figure 3 is a side view of a transmission member engagement element of a first embodiment; Figure 4 is a section view taken along line IV-IV of Figure 3; Figure 5 is a section view taken along line V-V of Figure 9; Figure 6 is a side view of one side of a slot shown in the region of a radial positioning hole; Figure 7 is a schematic side view of an arrangement used to change the radial position of the engagement element shown in Figure 3 within the support member shown in Figure 2; Figure 8 is a partial perspective view of an arcuate abutment member shown in Figure 7 taken along the line Vi II-VIII of Figure 7.

Figure 9 is a side view of a device of the present invention shown assembled with the components shown in Figure 1 to 4; Figure 10 is a side view of the device of Figure 9; Figure 11 is a diagrammatic plan view of a radial slot of an infinitely variable transmission device according to a second embodiment shown with clutch plates engaging an engagement element; Figure 12 shows the slot of figure 9 with the clutch plates disengaged to allow radial movement of the engagement element; and Figure 13 is a diagrammatic side view of a chain support arrangement.

Figure 1 shows a drive transmission device for a chain drive mechanism shown adapted for use with a bicycle There is shown a device generally indicated 1 which is mounted on a spindle 2 The spindle 2 is driven to rotate by pedals 3, 4 carried by crank arms 5, 6 which are mounted on the spindle 2 A connecting bar 7 fixedly joins the spindle 2 to a rear sprocket wheel 8.

The device 1 has a disc-shape support member 10 which carries four transmission member engagement elements 40 ab,c,d for engaging a chain The device 1 is connected to a handle bar mounted gear selector (not shown) which controls a gear selector lever 90 The radial position of the elements with respect to the member is variable under the control of the lever 90 as described in more detail below The member 10 also acts as a chain guard.

A chain 9 runs around the engagement elements of the device 1 and over the rear sprocket wheel 8, and also engages a known spring-operated jockey pulley system 11 for taking up or letting out slack in the chain 9 as the transmission ratio is changed, as shown by the arrow A.

The device 1 extends into the space between the chain 9, which is normally unused, and does not require any modifications of the bicycle other than replacement of existing sprocket wheels in order to operate.

Referring now to Figures 2 to 8 there are shown the components of the device 1 of Figure 1 prior to assembly for purposes of clarity and explanation.

Figure 2 shows a disc-shape support member generally indicated 10 The support member 10 has a hole 20 for mounting the device on a spindle and defines an axis of rotation about which the support member 10 can rotate Four spokes 21, 22, 23, 24 extend from the spindle 20 and are joined at the circumference of the support member by a rim 25.

Each spoke has a radial slot 30, 31, 32, 33; each slot has four mutually spaced radial positioning holes a, b, c, d which are described in more detail with reference to Figure and 6.

Figure 3 shows a transmission member engagement element 40 a which comprises a generally rectangular body 45 and an arcuate head portion 50 An upstanding ridge 46 runs centrally along the length of the body 45.

The body 45 has a connecting pin 55, shown in more detail in Figure 4, which is used to connect the element 40 a to the support member 10 of Figure 1 The head portion includes a plurality of teeth 60 which are shaped and spaced so as to be engageable with the links of a chain.

In this embodiment the body 45 and head portion 50 are fixedly attached to each other.

In other embodiments the head portion may be detachable to allow for substitution with different head portions which may, for example, have differently sized or spaced teeth or comprise a friction plate for engaging a belt.

Figure 4 is a cross-section of Figure 3 taken along line IV-IV The pin 55 is fixed orthogonally to the body 45 and comprises an elongate body 65 and an enlarged head The body 65 of the pin 55 has a compression spring 71 associated therewith The connecting pin 55 is used to secure the engagement element 40 in a radial position on the support member 10 as described in more detail below.

Figure 5 is a section through line V-V of Figure 10 showing an engagement element secured within a slot 32 of the support member; Figure 6 is a side view of one side of a slot 32 shown in the region of a radial position c Each radial position a, b, c, d comprises a hole within the slot, having a conical portion 200 and a parallel portion 205 The body 65 of the pin 55 can move freely within the parallel portion 200 and hence between positions ab,c,d, however, the head portion 70 cannot move along the slot The head 70 must be raised out of the conical portion 200 before the body can move between holes; it is resiliently biased to the secured position in which the head is retained in the conical portion 200 by the spring 71.

To change the radial position of an engagement element 40 within the member 10 the element must be moved between the radial positions a, b, c, d For this purpose there is provided the components shown in Figure 7 There is shown a rectangular support plate 75 having three longitudinal slots 76, 77, 78 in which are slidably mounted first 80 and second 85 arcuate abutment members.

As shown best in Figure 10, the members 80, 85 are movable along the length of the plate 75 in the slots 76, 77, 78 using a ratio selector lever 90 In this embodiment the members are moved using a common lever 90 so as to move together and to leave a fixed gap indicated by arrow 79 therebetween In other embodiments the members are moved separately.

The lever 90 is in turn connected to a ratio selector (not shown) such as a handle bar mounted gear selector and can be moved only in fixed increments, which correspond to the distance between the radial positions a, b, c, d of the member 10.

To appreciate how the arcuate abutment members 80, 85 causes the engagement elements 40 to move between the holes a, b, c, d of the support member 10 there is shown in Figure 8 a perspective view of a cross-section of the first member 80 of Figure 7 taken along line VIII.

The member 80 comprises a base portion 95 having a concavely curved upstanding wall 100 which extends orthogonally thereto.

To one side of the wall 100 the base portion 95 comprises a ramped face 96 leading to a ledge 97 which extends to a first abutment surface 105 of the wall 100.

To the other side of the wall 100 is an arcuate strengthening plate 101 which adds strength and rigidity to the member 80.

A typical path for an engagement element with respect to the member is represented by a broken line and described in more detail below.

2 0 Figures 9 and 10 show the components of Figures 2 to 8 assembled into a transmission device generally indicated 1 In use, the support member 10 rotates around the spindle 20; for example the spindle 20 may have pedals mounted on it for causing the member to rotate The engagement elements 40 a, b, c, d transmit the movement to a chain (not shown) which is engaged by their teeth 60.

As the engagement element 40 a orbits around the axis, the lower part of the body 65 of the pin 55 can pass freely through the gap 89 between the first 80 and second 85 abutment members The engagement element 40 a is securely retained within the hole c at a set radial position by the resilience of spring 71 and so can resist the radially inward forces placed on it by a chain The ridge 46 is substantially the same width as the body 65 of the pin 55 and so is able to slide within the slot 30 c When the element is secured in a radial position The ridge 46 resists the turning forces applied to the element 40 a by a chain.

When a user selects a new transmission ratio this intention is passed through to the lever 90 which moves, in fixed increments, with respect to the plate 75 This causes movement of the abutment members 80, 85 either towards or away from the rim 25.

If a higher ratio is required the members 80, 85 are moved away from the rim 25 and vice versa.

For example if the members 80, 85 are moved towards the rim 25 by one quantum of movement, that is to change the ratio by one step, then the abutment member 80 will move up and occupy space which was previously occupied by the gap 79 The pin 55 can no longer move freely past the member 80 and will contact the ramp face 96 at an angle dependent on how much of a change of the radial position of the element 40 c is required and hence how much the member 80 has been moved As the element rotates it will move up the face 96 and onto the ledge 97 whereupon it contacts the surface 105.

The face 96 pushes the pin 55 up against the action of the spring 71 which releases the head portion 70 from the hole 30 c Radial movement of the element 40 c is now possible because the body 65 of the pin 55 can move between holes whereas the head could not As the element 40 c continues to rotate the pin 55 experiences radially inward forces from the surface 105 When the pin 55 reaches the end of the member it is directly in line with a new hole because of a fixed incremental movement of the abutment member 80, and snaps into place by the action of the spring 71.

Each of the four elements 40 a, b, c, d is moved in this way to maintain a circular path for the chain to engage; if there were differences in the radial positions there would not be a constant transmission ratio.

Referring now to Figures 11 and 12 there is shown an alternative embodiment suitable belt driven device in which the transmission ration is infinitely variable The same principles as for the first embodiment are used, which is engagement elements mounted on a spindle for rotation and the radial position of which is variable.

In this embodiment each engagement element has a friction pad (not shown) in place of teeth, to engage a belt.

The radial slot 130 of a support member 110 is shown, however there are no holes In addition, the pin 155 of an element 140 is not retained in the slot 130 by the resilience of a spring Instead, the pin 155 is retained by frictional forces provided by a clutch mechanism comprising two plates 112, 113 which operates to clamp the pin 155 in place when the device 101 is in gear and to release the pin 155 when a change in transmission ratio is required In this way indexed movement from a selector lever is not required, simply an unconstrained amount of movement which corresponds to the required change to the transmission ratio When the lever is activated the clutch plates 120, 130 are moved apart to allow the pin 155 to move freely within the slot under the influence of abutment surfaces as previously described When the movement is finished the clutch plates 112, 113 re-engage the pin 155 to retain it securely within the slot 130.

In such an embodiment it is preferable for adjustments of the radial position to be done whilst the engagement elements are not engaged with the transmission member to prevent movement of the element due to the forces from the transmission member.

The engagement elements must be spaced sufficiently so as not to overlap in their innermost orbits; when the elements reach their outermost orbits there may therefore be a sizeable gap therebetween in which the chain is unsupported It is preferable for the chain to follow a substantially circular path around the device and the embodiment shown in Figure 13 seeks to overcome this problem.

The elements 40 a, 40 b are connected by a telescopic link arm 210 which may freely change its length and its pivotally connected to each element 40 a, 40 b, at pivot points 220,225 The arm has a curved strip 230 fixedly attached at each end.

As the radial position of the engagement elements 40 a, 40 b is changed the length of the ann 210 is also changed As the length of the arm 210 shortens the curvature of the strip 230 increases and vice versa The strip 230 serves as a support for a chain between the elements.

Claims

1 A drive transmission device for a chain or other endless flexible transmission member drive mechanism, comprising a plurality of transmission member engagement elements for engaging a transmission member, means for constraining the engagement elements to move in a substantially circular orbit about a common axis in engagement with a transmission member over a part of the orbit, and selector means for varying the radial position of the engagement elements to vary the diameter of the orbit whereby to vary the transmission ratio of the drive mechanism.

2 A drive transmission device as claimed in Claim 1, in which the device is for a chain drive mechanism, in which the transmission member engagement element has at least one tooth for engaging a link of the chain.

3 A drive transmission device as claimed in Claim 1 or Claim 2, in which the means for constraining the engagement elements is a support member rotatably mounted about the said common axis, the support member having radial slots in which respective engagement elements are carried, and means for securing each engagement element in one of a plurality of selectable positions along a respective slot.

4 A drive transmission device as claimed in Claim 1 or Claim 2, in which the selectable positioning of the engagement elements along respective slots is infinitely variable whereby to provide an infinitely variable gearing mechanism.

A device transmission device as claimed in any preceding claim, in which the radial positions of the engagement elements are individually adjustable.

6 A drive transmission device as claimed in Claim 4, in which the radial position of a engagement element is varied at a region of its orbit at which it is disengaged from the chain.

7 A drive transmission device as claimed in any of Claims 1 to 3, in which the radial positions of the engagement elements are collectively adjustable.

8 A drive transmission device as claimed in any preceding claim, in which the selector means comprise arcuate abutment surfaces positionable within the said orbit and curved so as to contact a part of the chain engagement element whereby to vary its radial position as it orbits.

9 A chain drive mechanism incorporating the drive transmission device of any preceding claim.

A bicycle incorporating the chain drive mechanism of Claim 8.

11 A drive transmission device substantially as hereinbefore defined with reference to, and as shown in, the accompanying drawings.