GB2152172A

GB2152172A - Variable-throw crank

Info

Publication number: GB2152172A
Application number: GB08334388A
Authority: GB
Inventors: Ching-Jong Wu
Original assignee: WU CHING JONG
Current assignee: WU CHING JONG
Priority date: 1983-12-23
Filing date: 1983-12-23
Publication date: 1985-07-31
Also published as: GB8334388D0

Abstract

A cyclically variable-throw crank lever/arm arrangement for a bicycle comprises a crank pedal, on an arm 51, which is constrained by a chain/sprocket 33, 42 connection to move in a circle the axis of which is offset forwardly of the crank-shaft 20, the pedal arm 51 being maintained in substantially parallel (horizontal) planes irrespective of the angular displacement of the crank lever 4, the arrangement automatically increasing the applied force on the forward movement of the pedal. <IMAGE>

Description

SPECIFICATION A bicycle driven mechanism which can automatically increase moment of force when the pedal is pedalled upon forward This invention relates to a drive mechanism.

The drive mechanism according to the invention is particularly suitable for use with a wheeled vehicle such as a bicycle or tricycle.

Although throughout the remainder of this specification specific reference will be made to the application of the drive mechanism to a bicycle, the drive mechanism per se may also be used for driving a capstan or other winch.

BACKGROUND OF THE INVENTION The bicycle is one of the earliest forms of transport used by mankind and is greatly used as a relatively cheap means of transport, as well as for pleasure and competitive racing. It is well known that a bicycle is driven by the rotation of pedal arms and the forces applied to the pedal arms by a rider are transmitted by way of chains and sprockets to produce rotation of a driven bicycle wheel, normally the rear wheel.

Present day bicycles suffer from certain specific short comings, including: 1. fixed pedal arm length; 2. when a pedal arm is in the vertical position the moment of the force is zero, and 3. it is hard to apply a force to the pedals when a rider wishes to start from a stationary position on an incline.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an energy-saving drive mechanism which overcomes, or at least reduces, the problems associated with the shortcomings stated above.

According to the present invention, there is provided a drive mechanism comprising a primary drive shaft mounted for rotation about its longitudinal axis, means for transferring drive imparted to the primary drive shaft to a driven member, a secondary drive shaft spaced apart from and disposed substantially parallel to the primary drive shaft and mounted for rotation about its longitudinal axis, an auxiliary connecting rod drivingly connecting the primary and secondary drive shafts and mounted for rotation with the primary drive shaft and for relative rotation with the secondary shaft, and a lever arm carried by the secondary shaft for rotation therewith whereby application of a force to the lever arm causes (a) angular displacement thereof about the longitudinal axis of the primary drive shaft, (b) the auxiliary connecting rod and the secondary shaft to follow a circular path relative to the longitudinal axis of the primary drive shaft and (c) the lever arm to lie in substantially parallel planes irrespective of the angular displacement of the auxiliary connecting rod so that the effective moment arm of the lever relative to the primary shaft varies between the length of the auxiliary connecting rod and between the combined length of the auxiliary connecting rod and the length of the lever arm. Preferably, the drive mechanism includes two auxiliary connecting rods, each having an associated secondary drive shaft and lever arm with the auxiliary connecting rods mounted in diametrical opposition on the primary drive shaft. Conveniently, the length of the or each auxiliary connecting rod is adjustable.Preferably, the driving connection between the auxiliary connecting rod and the primary and secondary shafts comprises a sprocket mounted on each shaft and an interconnecting driving chain.

In one specific form of the present invention, each lever arm is a bicycle pedal. Where the drive mechanism, according to the invention is applied to a bicycle, it will be appreciated that the pedal arms are always horizontal during rotational motion of the auxiliary connecting rods and that the moment of force increases from a minimum, where the effective lever arm is the length of the auxiliary rod to a maximum, where the effective lever arm is the total length of the auxiliary connecting rod and the pedal arm.

In contrast with conventional drive mechanisms used for a bicycle, it will be appreciated that irrespective of the angular position of the auxiliary connecting rod, that a positive moment of force is applied to the primary drive shaft and hence to the rear driving wheel.

BRIEF DESCRIPTION OF THE DRAWINGS One form of drive mechanism in accordance with the present invention will now be described by way of example with reference to the accompanying drawings in which Fig. 1 is a plan view of the drive mechanism: Fig. 2 is a section taken through important integers of the drive mechanism; Fig. 3 is a schematic drawing showing the loci of certain members of the drive mechanism; Fig. 4 is a section showing details of a drive mechanism between primary and secondary drive shafts; Fig. 5 is an exploded view of the primary drive shaft and associated components; Fig. 6 is an exploded view of an auxiliary connecting rod, secondary drive shaft and lever arm, and Fig. 7 shows diagrammatically the application of the drive mechanism to a bicycle.

Referring to Figs. 1 and 2, the drive mechanism shown includes a primary or main drive shaft 20, an auxiliary connecting rod 36, a lever or support arm 51, which, when the unit is applied to a bicycle is constituted by a pedal arm, and a chain driven sprocket unit.

Referring to Figs. 2 and 5 a hub 1, comprises a thick walled tube forming what is .conventionally called the bottom bracket of a bicycle. As shown in Fig. 2 the bottom bracket or thick walled tube is brazed to rear forks RF which support a rear bicycle wheel RW. A fixed sleeve shaft 21 is mounted within the hub 1 and includes stepped threads at either end thereof, which project axially beyond the ends of the hub 1.

Threaded locating rings 21 2 secure the fixed sleeve shaft 21 to the hub 1. Certain of the stepped threads are relatively fine and serve to hold a lower coupling ring 31 within the fixed sleeve shaft 21. Two locating ball bearing retainers 213 are used to retain the ball bearing rings 202 between the inner side of the fixed sleeve shaft 21 and the outer retaining ring 201 which is carried on the main shaft 20.

The fine stepped threads 211 on each end of the fixed sleeve shaft 21 are used to carry a fixed sprocket 33 and a locating ring 212 positions the auxiliary fixed sprocket 33. On the axis of the fixed sleeve shaft 21 there is a main shaft 20. At the end of the main shaft 20 there is a pentagonal neck 205 which is used to drive the drive sleeve shaft 30. When assembled, the pentagonal neck fits into a pentagonal opening 301 and is locked with a nut 203. The drive sleeve shaft 30 is of cup shape with the skirt secured to upper coupling ring 35, and in turn to a sprocket 34.

The cup-shaped surface of the drive sleeve shaft 30 includes two openings through which a small chain 60 passes. Attached or integral with the cup is an auxiliary connecting rod 36. An arcuately shaped inner ring 31 retains a ball bearing ring 301 between the upper coupling ring 35 and the lower coupling ring 31.

As shown in Figs. 1, 2 and 6, the crossshaped auxiliary connecting rod 36 is a part of the above sleeve shaft 30. In addition to threaded portion 361, the rod 36 has four milled rebates to form a rod of cruciform section. When the support arm 4 and a coil spring 38 are assembled and the small chain 60 assembled, tension in the chain 60 may be altered by adjusting the nut 37 forward or backwards. The cruciform section rod 36 slides within a cruciform shaped socket in the support arm 4 and serves to both locate and prevent bending. The head of the support arm 4 is cup-shaped and a fixed slide ring 43 is provided on the inner side. The attachment of the fixed side ring 43 to the head of the support arm 4 is through threads on both parts on the inner wall. Near the opening of the head part of the support arm 4 there is a locating ball bearing ring retainer 412.

The auxiliary sprocket unit consists of an auxiliary sprocket 42, a coupling shaft 41 and two ball bearing rings, all of which are installed inside the head of the support arm 4.

The auxiliary sprocket 42 is of annular form having a chain retaining wall disposed on either side of a ring of gear teeth and an axial hole of pentagonal shape. The auxiliary sprocket 42, with the inner pentagonal socket is connected to the pentagonal neck of the coupling shaft 41 and a nut 411 secures the two parts together. Furthermore, the auxiliary sprocket 42 and the two ball bearing rings 422, are installed inside the head of the support arm 4 by the fixed ring 43 which, when tightened, will properly seat the ball bearing rings 422, the ball bearing ring retainers on both sides of the head of the support arm 4, and the fixed side ring 43.

The other end of the coupling shaft 41 is fixed onto a pedal arm 51 by a grub screw 52.

The pedal support assembly has a traditional pedal support arm and pedal.

The above description explains the mechanism and there now follows a description of the motional status, relative positions, and specific features of each sub-assembly of the drive mechanism of the invention.

As shown in Fig. 3 loci of pedal support arms and Fig. 4 rotational loci of this creation, when one auxiliary rod and support arm 4 is pedalled into vertical upward position the other auxiliary rod and support arm 4 must be in vertical downward position. At this time, the pedal support arms 51 are in right angle with respect to auxiliary rod and support arms 4, i.e. in horizontal position, because interactions between pedal support arms 51, fixed sprockets 33, shaped sprockets 42 with same teeth, and small chains 6. When force is applied to pedal, the pedal support arms 51 will generate a rotational moment around coupling shaft 41.Because shaped sprocket 42, coupling shaft 41 and fixed sprocket 33 are connected together through a small chain 6, and fixed sprocket 33 is coupled to fixed sleeve shaft 21 at hub 1, therefore, the rotational moment generated by pedal support arms 51 will act on auxiliary support arm structure to produce a circular motion around main shaft 20.

If we let auxiliary arm structure 4, 36 rotate around main shaft 20 to certain angular position, because pedal support arm 5i is coupled to shaped sprocket 42 and fixed sprocket 33 of same teeth through small chain 6, hence it will rotate around coupling shaft 41 to the same angular position as the auxiliary arm structure does. Suppose now, that auxiliary arm structure 4, 36 is rotated around its main shaft 20 90 clockwise from its upper vertical position, the pedal support arm 51 will be rotated around its coupling shaft 41 counter clockwise 90", at this time, the auxiliary arm structure 4, 36 is in line with pedal.

Support arm 51 at horizontal position, consequently the moment of force is increased, and energy saving purpose is hence served. During this time, when another auxiliary arm structure 4, 36 is rotated 90" clockwise from its lower veritcal position, another pedal support arm 51 will rotate around coupling shaft 41 counter clockwise 90 , at this time, the auxiliary arm structure is in parallel fold position with pedal support arm 51, therefore, its moment of force is smaller than former. When force is continuously applied to pedal, the loci of pedal, pedal support arms 51, and coupling shafts 41 of this creation is shown in Fig. 3. As a summary of above description: the pedal support arms 51 of this creation is always kept in horizontal position during driving.When auxiliary support arm structure 4, 36 is driven clockwise 90 from its vertical position, one pedal support arm 51 will be in line with one auxiliary support arm structure 4, 36 at horizontal position, meanwhile its moment of force is increased twice, and at the same time, the other pedal support arm 51 will be in parallel fold with other support arm structure 4, 36 at horizontal position, hence its moment of force is remained unchanged.

When this creation, bicycle driving mechanism is trying to be installed on bicycle frame, the forward extending effect of pedal support arm 51 when auxiliary arm structure 4, 36 is rotated to horizontal position should be considered, one way or another to solve this problems includes to move hub 1 as backward as possible or to increase the distance between front wheel and back wheel through modification of bicycle framework, both of these measures can serve the purposes of preventing pedal from bumping front wheel, and for the easiness of pedalling.

Various features of the present invention and practical applications thereof includes: (1) A bicycle driving mechanism when it is pedalled forward will automatically increase its moment of force. This driving mechanism consists of the following items: main shaft mechanism: including hub, fixed sleeve shaft, main shaft, fixed sprocket, driven sleeve shaft, upper and lower coupling ring, and locating rings for retaining and locating the whole driven structure.

Auxiliary support arm structure: including cross shaped auxiliary rod, nuts, coil spring, small chain, which is driven by pedal support arms to produce around main shaft circular motion.

Sprocket Unit: including shaped sprocket, ball bearing rings, and coupling shaft, which is coupled to fixed sprocket by small chain.

Pedal Unit: including pedal support arms and pedals.

The special features of this creation is that +shaped sprocket is coupled to fixed sprocket by small chain, therefore, when force is applied on pedal to drive auxiliary support arm to produce around main shaft circular motion, the pedal support arms will always be kept in horizontal up and down motion, and moment of force at one side will be increased twice when auxiliary support arm at this side is driven to horizontal position and in line with pedal support arm, meanwhile, moment of force will be maintained unchanged at other side, because at this time the auxiliary support arm at other side is driven to horizontal parallel fold position with other pedal support arm.

(2) According to feature 1 the shaft mechanism may include: A hub; which is coupled to front support rod upper support rod, and rear wheel support rod and on which its axis is used to mount fixed sleeve shaft for retaining and locating main shaft mechanism.

A fixed sleeve shaft; which is mounted on axis of hub and fastened to hub by locating rings one at each end. On each side of fixed sleeve shaft, there are stepped threads, the small stepped threads are used for installation of fixed sprocket and to be locked-on by small locating ring, the big stepped threads are used to serve both purposes of fixed sleeve shaft to be locked-on hub and lower coupling ring by locating rings respectively. At the inner surface of fixed sleeve shaft, there are two outward protruding locating ball bearing retainers, they are used to locating and retaining main shaft ball bearing rings.

Main Shaft: which is installed in the axis of fixed sleeve shaft. On its surface just opposite to the two locating ball bearing ring retainers on inner surface of fixed sleeve shaft, there are two locating ball bearing ring retainers too, they are used to locate and retain the two main shaft ball bearing rings. At its two ends, there are pentagonal shaped necks, one each on each end, they are used to installing driven sleeve shaft and to by tightened by two nuts.

Driven Sleeve Shaft; which is designed into a ladle shape, its skirt end is inlaid to big sprocket and coupled to upper coupling ring.

It is used to drive big chain through big sprocket.

Fixed Sprocket; which is installed on small stepped threads of fixed sleeve shaft. It is used in corporation with small chain and 9- shaped sprocket to produce up and down motion of pedal support arms.

Upper coupling ring; Its inner surface is curved to retain ball bearing ring between lower coupling ring and its outer surface is fastened to inner part of big sprocket by several screws. It is used to support big sprocket.

(3) According to feature 1, the auxiiiary support arm structure may include: Cross shaped auxiliary rod; which is an integral part of driven sleeve shaft, and threads are provided on rod surface. Furthermore, the rod surface is milled with four troughs, and due to this tact, it is named as cross shaped auxiliary rod. It is used to prevent twist effect of support arm when it is assembled into the cross shaped socket of support arm. The nuts and coil spring attached to it is used to adjusting the tension of small chain.

(4) According to feature; 1 the sprocket unit may comprise: shaped sprocket; which is assembled into the cavity of support arm head by hexagonal neck of coupling shaft, the two ball bearings on outer shoulders of shaped sprocket incorporate with two locating ball bearing retainers one each on support arm head and fixing side ring respectively, are used to seat shaped sprocket into proper position inside support arm head, when fixing side ring is properly tightened. Because number of teeth of shaped sprocket is the same as fixed sprocket, therefore, the angular rotation of pedal support arm and auxiliary support arm are synchronized, which in turn makes pedal support arm always in horizontal up and down motion when pedal is pedalled.

Coupling shaft; the pentagonal neck side of coupling shaft is coupled to shaped sprocket inside support arm head, the other side is fastened to pedal support arm by a screw, which is used to providing driven moment through pedalling of pedal.

Claims

1. A drive mechanism comprising a primary drive shaft mounted for rotation about its longitudinal axis, means for transferring drive imparter to the primary drive shaft to a driven member, a secondary drive shaft spaced apart from and disposed substantially parallel to the primary drive shaft and mounted for rotation about its longitudinal axis, an auxiliary connecting rod drivingly connecting the primary an secondary drive shafts, and mounted for rotation with the primary drive shaft and for relative rotation with the secondary shaft, and a lever arm carried by the secondary shaft for rotation therewith whereby application of a force to the lever arm causes a angular displacement thereof about the longitudinal axis of the primary drive shaft, b the auxilliary connecting rod and the secondary shaft to follow a circular path relative to the longitudinal axis of the primary drive shaft and c the lever arm to lie in substantially parallel planes irrespective of the angular displacement of the auxiliary connecting rod so that the effective moment arm of the lever relative to the primary shaft varies between the length of the auxiliary connecting rod and between the combined length of the auxiliary connecting rod and the length of the lever arm.

2. A mechanism according to Claim 1 including two auxiliary connecting rocks each having an associated secondary drive shaft and lever arm with the auxiliary connecting rods mounted in diametrical opposition on the primary drive shaft.

3. A mechanism according to Claim 1 or Claim 2 wherein the length of the or each auxiliary connecting rod is adjustable.

4. A mechanism according to any preceding claim wherein the driving connection between auxiliary connecting rod and the primary and secondary shafts comprises a sprocket mounted on each shaft and an interconnecting driving chain.

5. A wheeled vehicle including a drive mechanism according to anyone of claims 2 to 4.

6. A bicycle including a drive mechanism according to anyone of claims 2 to 4 wherein each lever arm is a pedal.