GB2346854A - Manually operated power transmission system - Google Patents

Abstract

The system comprises one or two pedal operated reciprocatory levers 204 acting on respective pinions during respective downward power strokes via racks 203 to rotate a chainwheel 209, to drive e.g. a bicycle rear wheel 206. Each power stroke, in a two pedal system, acts on the other lever via a lever gear assembly to return it. Unidirectional clutch disengages the respective levers from the final drive during the return strokes. For a single pedal a four-linkage system with two racks provides engaged downward power and automatic return of the pedal.

Description

MANUALLY OPERATED POWER TRANSMISSION SYSTEMS The present invention relates to manually operated power transmission systems and specifically to transmission systems for velocipedes, that is to say, vehicles propelled solely by the physical actions of their riders, or pedal-operated machinery.

Originally velocipedes were propelled by a rider sitting on a saddle position at a height such that the rider's feet were in contact with the ground and the velocipedes were propelled by a walking action on the part of the rider. Later devices employed a pair of swinging arms which were attached to a crank shaft which drove one wheel of the velocipede. With the advent of the so-called safety bicycle came the two-pedal crank and chain drive to the rear wheel which still is the accepted norm.

A disadvantage of the basic two-pedal mechanism is that the useful power delivered to the crank varies from virtually zero at top and bottom dead centre to a maximum when the downward force is being applied tangentially to the circular path followed by each pedal. Skilled riders alleviate this problem to some extent by rotating their ankles during each cycle of pedal movement, dropping their heels at the top of each cycle of pedal so that there is a forward component of thrust at this point. As each pedal cycle continues the rider's heel is raised until the foot is horizontal at the point where the pedal arm is horizontal. As the rotation of the pedal continues, so is that of the rider's heel so that during the second quarter of each cycle of pedal movement, and particularly at the bottom dead centre of the pedal motion, there is a rearward component of thrust. However, this action requires a degree of skill to perfect and may not be available to people with a limited facility for moving their ankles. Also, attempts have been made mechanically to compensate for the differing power delivery during a cycle of pedal movement by using non-circular chain wheels so that the effective lever arm varies during a cycle of pedal motion. Such chain wheels can only be used with a mechanism for compensating for the resultant changes in the distance between the part of the chainwheel engaged with the chain and the centre of the rear sprocket.

Further disadvantages of the existing mechanism are that the rider of a bicycle or tricycle needs full effective motion in the hip joints and that unbalanced forces make the present mechanism impracticable for a onelegged rider unless a fixed rear sprocket is used or the foot of the rider is secured to the pedal.

It is an object of the present invention to provide a drive mechanism for a velocipede which has a higher overall mechanical efficiency than existing pedal operated drive mechanisms and which, in particular, can be operated by a person who does not have the full use of their knee and hip joints, or even has only one leg.

According to the present invention there is provided a manually operated power transmission system comprising, a rotatable primary drive means connected to a driven member, a reciprocating member adapted to engage with the primary drive means and apply a force tangentially thereto throughout a power stroke of the reciprocating member, means for ret. urning the reciprocating member to a starting position at the end of each power stroke and means for isolating the reciprocating member from the driven member during the motion of the reciprocating member to its starting position.

Preferably there are two reciprocating members associated with the primary drive means, the two reciprocating members being adapted to operate in anti-phase, so as to provide for the substantially constant application of force to the primary drive means.

Preferably the primary drive means includes a pinion and coupled chainwheel, and the reciprocating member includes a rack adapted to engage with the pinion at least during each power stroke. If two reciprocating racks are used, then either they can engage with diametrically opposite sides of the pinion, or individual pinions can be used coupled to a single chainwheel.

If a single reciprocating member is used, then the action to return the reciprocating member to its starting position can be derived from a linkage connecting the reciprocating member to the driven member.

If two reciprocating members are used, the motion of one during a power stroke can be used to return the other to its starting position.

There may also be provided also means for allowing the driven member to free-wheel in relation to the primary drive means.

In a particular aspect of the invention the manually operated power transmission system is used to propel a velocipede.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which, Figure 1 is a schematic side view of a conventional bicycle, and shows the position of a rider's foot in three stages of a cycle of rotation of the chain wheel of such a bicycle, Figures 2 and 3 illustrate the principle of the present invention, Figure 4 is a cross-section of a component of an embodiment of the invention, Figure 5 illustrates a second mechanism embodying the invention, fitted to a bicycle, and Figure 6 is a part-cross section of a"free-wheel"mechanism for use with the embodiment of Figure 1.

Referring to Figure 1, a conventional bicycle 100 has a triangulated frame 101, made of metal tubing, which incorporates a pair of front forks 102, only part of which is shown, which can be rotated by a pair of handlebars (not shown) to steer the bicycle. Mounted in the front forks 102 is a front wheel 103. The rear part of the frame 101 of the bicycle 100 is bifurcated to form rear forks 104, in which is mounted a rear wheel 105. Mounted at the base of the frame 101 of the bicycle 100 is a crank-operated chainwheel 106 which drives the rear wheel 105 of the bicycle 100 via a continuous chain 107 and sprocket 108. A rider of the bicycle 100 sits upon a saddle 109 mounted above and to the rear of the chainwheel 106.

In the Figure, one arm 110 of the crank which drives the chainwheel, an associated pedal I I I and foot 112 of a rider of the bicycle are shown at the start, A, of a cycle of operation of the crank 110, at a quarter of the cycle, B, and at the half-way point, C, of the cycle of movement. It can be seen readily that ; at position A there is no rotational component of thrust from the rider's foot, at position B the rotational component of thrust is a maximum and at position C it has decreased to zero again, becoming negative during the second half of a rotational cycle of the crank arm 110, so that an appreciable part of the effort expended by the rider is wasted so far as propelling the bicycle is concerne.

Referring to Figures 2 and 3, which illustrate an embodiment of the invention fitted to a bicycle similar to that shown in Figure 1, the chainwheel and crank of the bicycle shown in Figure 1 are replaced by a similarly position pinion 2UU which is mounted upon an axle 201 via a unidirectional clutch 202, or another unidirectional drive device. An arcuate rack 203,whichformspart of a triangulated framework 204, which is pivoted about the axle 205 of the rear wheel 206 of the bicyclc, cngages with the pinion 200. A treadle 207 is attached to the rack 203 and enables it to be moved in a downwards direction by a rider of the bicycle, imparting a torque to the pinion 200. The radius of curvature of the arcuate rack 203 is the same as the length of the arms 208 of the framework 204 so that the rack 203 and pinion 200 remain in engagement throughout the motion of the rack 203. The unidirectional clutch 202 enables the rack 203 to be returned to its starting position at the end of each power stroke without effecting the rotation of the axle 201. An identical rack and pinion system is position at the other end of the axle 201, but are not shown in Figure 2. A chainwheel 209 is fixed to one end of the axle 201, so that a downward movement of either of the treadles 206 rotates the chainwheel 209 in the same direction.

The chainwheel 209 is arranged to rotate the rear wheel 206 of the bicycle in the normal way.

Alternatively, the concave rack 203 may be replaced by a convex rack placed behind the pinion 200 and the treadle 207 attached to a projection of the lower arm 208 of the framework 204.

Referring to Figure 4, there is shown a part-longitudinally sectioned view of a mechanism 400 which enables one rack 203 to be returned to its starting position while the other is carrying out its power stroke. Components which correspond to those described with reference to previous Figures have the same reference numerals. Each pinion 200 has an inwardly pointing tubular extension 401 which is journaled on the axle 201 to which the chainwheel 209 is fixed. At the inboard ends of the extensions 401 are respective bevel gears 402 which mesh with another bevel gear 403. Unidirectional clutches 202 are incorporated in housings at the inboard ends of the tubular extensions 401. As one pinion 200 is rotated in its driving direction, the bevel gears 402 and 403 cause the other pinion 200 to rotate in the opposite direction via the action of the associated unidirectior. al clutch 202, so raising its co-operating rack 203. (Neither rack is shown in the Figure).

If a normal free-wheel sprocket is not included in the rear wheel of the bicycle, the unidirectional clutches 202 will provide a free-wheel action. The assembly is mounted to the frame of the bicycle by bearings 404.

Figures 5 and 6 illustrate a bieycle incorporating an embodiment of the invention which utilises only one treadle and so can be used by an individual who has one leg only. Again, those components which correspond with component. previously referred to have the same reference numerals.

In this embodiment of the invention, the pinions 203 are replaced by a single pinion 500 which is fixed to the chainwheel on its outer side.

Although it is not necessarily so, the pinion 500 has a diameter approximately equai to that of the chainwheel. A concave rack 501 is formed on the rear side of a generaily triangula plate 502. A lever 503 which has a pedal extension 503'is pivotally attached to the plate 502. An upper tie rod 504 is pivotally attached to the upper end of the lever 503 and a lower tie rod 505 is attached to the plate 502 at the same position as the pivot pin of the lever 503. The tie rods 504 and 505 are pivotally linked by a lever 506 the length of which is approximately equal to that of the lever 503 so that the tie rods 504, 505 are approximately parallel. Attached to the lower tie road 505 is a convex rack 507. Upper and lower pedal stops 508 and 509, respectively, are attached to the frame 510 of the bicycle.

The mechanism operates as follo-W-s : as a rider pushes downward on the pedal 503'at the start of a power stroke, the lever 503 pulls the tic rod 504 forward. This action causes the lever 506 to pull the tie rod 505 backwards and bring the rack 501 into engagement with the pinion 500. Further downward movement of the pedal extension 503'rotates the pinion 500 and the attached chainwheel, so driving the bicycle forwards. Eventually, the pedal cxtension 503'contacts thc lower stop 209, and the lever 503 rotates anti-clockwise, pushing the upper tie rod 504 backwards. This causes the lever 506 to rotate anti-clockwise pushing the tie rod 505 forward. disengaging the rack 501 from the pinion 500 and causing the rack 607 to engage with the rear of the pinion 500. At this stage, the pinion 500 is being driven by the rear wheel of the bicycle, so that the rack 507 is moved upwards, so lifting the tie rod 505, the plate 502 and the associated pedal extension 503'. This action continues until the pedal extension 503'makes contact with the upper stop 508 when the lever 5Q3 rotates in a clockwise direction causing the tie rod 505 to pull the plate 502 backwards, bringing the rack 501 into engagement with the pinion 500 for another power stroke by the rider.

For the mechanism to operate, the chain cog at the rear wheel must be of the simple, so-called, fixed type. However, Figure 6 is a part longitudinally sectioned view of a mechanism by means of which a free-wheeling action can be achieved if desired. Again, features which are common have the same reference numerals. Referring to Figure 7, the pinion 500 is fixed to a shaft 700, the other end of which terminates in one half 701 of a dog clutch 702.

The chainwheel 209 is integral with a hollow shaft 703 which is journaled upon the shaft 700 by bearings 704, 705. The shaft 703 is rotatably mounted in a bottom bracket (not shown) of a bicycle frame (also not shown) by bearings 706, 707. Attached to the free end of the shaft 703 is-a unidirectional clutch 708 connecting the shafts 700 and 703, which permits the pinion 500 to rotate backwards relative to the chainwheel 209, so permitting the rack plate 502 and rack 501 to be raised at the end of each power stroke. Attached to the casing 709 of the unidirectional clutch 708 is the drive half 710 of the dog clutch 702. The driven half 701 of the dog clutch 702 is moved into, and out of, engagement with the driving part 710 by means of a hardened steel, spring-loaded pin 711 to which it is fixed, or with which it is integral. The pin 711 is operated by a lover 712 which is connected via a Bowden cable 713 to a control (not shown) which is mounted on a convenient part of the bicycle with which the device is being used. If the rider wishes to free-wheel, then the lever 712 is operated to disengage the dog clutch 702 so that the chainwheel 209 and pinion 500 are disconnected, so enabling the rack plate 502 and pedal 503'to remain at their lowest positions. When it is desired to resume"pedalling", the lever 712 is released so enabling the dog clutch 702 to be engaged by the movement of the spring-loaded pin 711.

Although, for convenience, only a simple dog clutch has been described, in practice, to facilitate the engagement of the clutch at speed and to avoid abruptness in the resumption of motion of the mechanism, the dog clutch would include a synchronising mechanism. Alternatively, a cone or a plate clutch could be used.

The rack and pinion drive can be replaced by other forms of reciprocating tangential drive mechanisms such as an endless chain and two sprockets, with a treadle attached to a swinging arm, which is attached to the chain at one end and pivoted at the axle of the rear wheel of the bicycle at the other.

Another possibility is the use of a two-drum rope drive, arranged so that rope is wound off one drum at the same time as it is wound onto the other.

The invention has been described in relation to a bicycle. It is, however, equally applicable to tricycles, other vehicles such as invalid carriages, or pedal-powered generator systems.

Claims (10)

1. CLAIMS 1. A manually operated power transmission system comprising, a rotatable primary drive means connected to a driven member, a reciprocating member adapted to engage with the primary drive means and apply a force tangentially thereto throughout a power stroke of the reciprocating member, means for returning the reciprocating member to a starting position at the end of each power stroke and means for isolating the reciprocating member from the driven member during the motion of the reciprocating member to its starting position.
2. 2. A power transmission system according to claim 1 wherein there are two reciprocating members associated with the primary drive means, the two reciprocating members being adapted to operate in anti-phase, so as to provide for the substantially constant application of force to the primary drive means.
3. 3. A power transmission system according to claim 1 or claim 2 wherein there is included means for returning the, or each, reciprocating member to a starting position at the end of the power delivery stroke.
4. 4. A power transmission system according to claim 3 wherein there is included two reciprocating members and there is included means for utiiising the motion of one reciprocating member during a power deliverystroketoreturntheotherreciprocatingmembertoastarting position for a power delivery stroke.
5. 5. A power transmission system according to claim 3 wherein there is a single reciprocating member and the means for returning the reciprocating member to its starting position for a power delivery stroke comprises a linkage adapted to utilise the motion of the driven member to return the reciprocating member to its starting position for a power delivery stroke.
6. 6. A power transmission system according to any proceeding claim wherein the primary drive means includes a pinion and an associated chainwneel and the reciprocating member includes a rack adapted to engage with the chainwheel during a power delivery stroke.
7. 7. A power transmission system according to claim 6 wherein there is included a unidirectional clutch arranged to permit motion of the pinion in a reverse direction to that of the chainwheel to faciiitate the return of the reciprocating member to its starting position for a power delivery stroke.
8. 8. A power transmission system according to any proceeding claim incorporated into a velocipede.
9. 9. A power transmission system according to claim 8 wherein the velocipede is a bicycle.
10. 10. A manually operated power transmission system substantially as hereinbefore described and with reference to the accompanying drawings.