GB2153761A - Pedal cycle - Google Patents

Abstract

A pedal cycle is driven by means of two pedals 32 carried by respective crank arms 27 which are oscillatable about a common horizontal axis, and a primary sprocket wheel 22 coupled by a chain 40 to a hub 16 of a rear wheel 11, each crank arm being coupled to the primary sprocket wheel via a ratchet and being arranged to drive the primary sprocket wheel by making alternately a working stroke forwards and downwards and an idle return stroke back again, the end of the working stroke of each crank arm being limited by a stop 37. <IMAGE>

Description

SPECIFICATION Pedal cycle In a conventional pedal cycle, the pedals are car ried by crank arms from a central shaft which is fixed to a primary sprocket wheel, the primary sprocket wheel being coupled by a chain to a secondary sprocket wheel connected to the hub of the rear wheel. When the cycle is being ridden, the pe dals and primary sprocket wheel continually rotate through successive revolutions about the axis of the sprocket wheel.As the pedals revolve, with the rider's feet continually in contact one with each pedal, the rider is only able to apply an efficient working force to each pedal as the pedal moves downwards through an angle of between 60 & BR< 900. The driving force is thus applied to the rear wheel intermittently as a working force is applied first to one pedal and then to the other with an intervening period during which the pedals are mov ing past top and bottom dead centre where no effective working force can be applied. This is inefficient and leads to jerky movement, particularly when the rider is straining to pedal uphill.

Since the pedals of a conventional cycle revolve continually through 360 , and this circular movement is necessarily followed by the rider's feet, the rider's knee joints are continually subject to bend ing and straightening. This is uncomfortable, particularly for elderly riders, and not helpful in driving the cycle as each of the rider's legs is bent to the maximum extent during idle upward movement of the pedal, The bending of the knee is exacerbated by the fact that the crank arm carrying each pedal in a conventional cycle projects radially beyond the periphery of the primary sprocket wheel and consequently the sprocket wheel has to be positioned an appreciable distance above the ground to provide adequate clearance between a pedal at bottom dead centre and the ground, particularly when the cycle is tilted sideways upon negotiating a corner.

In accordance with the present invention, a pedal cycle is driven by means of two pedals carried by respective crank arms which are oscillatable about a common horizontal axis, and a primary sprocket wheel located adjacent to the crank arms and coupled by a chain to a secondary sprocket wheel which is connected to the hub of the rear wheel, each crank arm being coupled to the primary sprocket wheel via a one way drive mechanism and being arranged to drive the primary sprocket wheel by making alternately a working stroke forwards and downwards and an idle return stroke back again, the end of the working stroke of each crank arm preferably being limited by a stop. The stop may be rigidly fixed to the frame or may be resilient, e.g. in the form of a tension spring interconnecting the frame with the crank arm.

With this arrangement the cycle will be driven by the rider applying foot pressure alternately to the two pedals so that one makes a working stroke while the other makes a return idle stroke, preferably through an angle of between 50 & 900, corre sponding to the angle through which efficient working pressure can be applied to a pedal. While the working stroke is applied to one pedal, the other pedal makes a full return idle stroke and is immediately ready to receive full working pressure.

Efficient working force can thus be applied to drive the rear wheel smoothly and substantially continu ously. Since the movement of each pedal is through an arc of up to say 90" commencing adjacent, and preferably just forwards of, the top dead centre position, excessive bending of the rider's legs is avoided, because the crank arms do not move backwards and upwards from bottom dead centre. Also, if the pedals are positioned on the crank arms closer to the axis of the crank arms, e.g. between 100 and 140 mm, preferably 120 mm, instead of the conventional 200 mm, from the axis, the displacement of the feet and legs during riding is reduced further. Less bending of the rider's legs, than in the case of a conventional cycle, also arises because it is intended that the primary sprocket wheel will be positioned nearer the ground, e.g.

with a clearance of between 50 and 100 mm above level ground, than in a conventional cycle. This is possible because the crank arms and pedals should never reach bottom dead centre, or indeed project below the lowest point of the primary sprocket wheel, and require additional clearance from the ground. This is the purpose of the stop, when provided, at the end of the working stroke. A similar stop could also be provided to prevent each crank arm and pedal from rotating beyond the normal idle return stroke backwards and downwards past the top dead centre position, for the same reason. Most conveniently, this second stop limits the return idle stroke of the crank arm at a position corresponding to the beginning of the working stroke.However, it is possible that at least one of the crank arms may be swingable backwards and downwards past its top dead centre position to operate a pedal brake. The stop or stops for each crank arm may consist of simple abutments projecting from the cycle frame and engageable by a part of the respective pedal or crank arm.

The lowering of the primary sprocket wheel, and hence of the pedals, may also allow a lowering of the cycle saddle, thereby reducing the rider's elevation and wind resistance. However, further ergonomic efficiency may be achieved if the horizontal distance between the saddle and the pedals is increased, by comparison to a conventional cycle. This may be achieved by moving the saddle backwards, although still in front of the axis of the rear wheel or wheels. The rider may then be able to ride with his legs substantially straight at all times, commensurate with knee bending sufficient to push the pedals through a working stroke upon final straightening of the legs.The legs will be working in a more horizontal attitude than in a conventional cycle and the necessary reaction may be obtained by forming the seat as a bucket seat against the back of which the small of the rider's back will press. A bucket seat has the additional advantage that it does not chafe the inside of the rider's thighs as much as a conventional pointed saddle, and a pointed saddle is no longer necessary as the rider's thighs do not have to bend so far downwards to operate the pedals of the new cycle.

Each crank arm and pedal may make a working stroke against the action of a return spring which is responsible for pivoting it back through the idle stroke when the rider's foot pressure is released, and the other pedal is making a working stroke. Alternatively, each crank arm could be connected to the other so that the working stroke of one carries the other back through an idle stroke provided that the foot pressure on the other pedal is released.

Preferably, however, each pedal incorporates means for engagement with the rider's shoe so that the idle stroke is effected by the rider drawing the respective foot backwards. The engagement means might comprise a toe strap or cup but this may impede the rider from immediately taking his feet from the pedals and placing them on the ground in the case of an emergency stop. This would seriously reduce the advantage of lowering the pedals and seat, as,, compared with the layout of the conventional cycle, of enabling a rider to place both feet on the ground whilst sitting on the seat. Preferably, therefore, the engagement means comprises an upstanding part, which may be slightly curved, to engage the rear of the rider's shoe. This is also the most convenient position for receiving a reaction from the rider's shoe to draw the pedal back through the idle stroke.Engagement between the rider's shoe and the pedal may be provided by a toe shroud at the front of the pedal. The rest of the pedal may then comprise a, preferably roughened, plate or other comparatively flat support from which the rider may slide his foot off outwardly quickly in case of emergency. This may be further facilitated if the support is inclined slightly downwardly and outwardly, up to an angle of 10 to the horizontal. Each pedal is preferably pivotally mounted on top of the respective crank arm.Each pedal will then be operated by being tilted by the rider's foot so that the working pressure is applied substantially normally to the plane of the support, and then tilted backwards at the end of the working stroke so that the rider's shoe heel applies a pressure substantially normally to the upstanding rear part of the pedal to draw the pedal back through the idle stroke.

In the most convenient and compact construction, the common oscillatory axis of the crank arms is the same as the axis of the primary sprocket wheel. The one way drive mechanism between the crank arms and the sprocket wheel may take any conventional form. However, in one arrangement, each crank arm carries a pawl which cooperates with a respective ratchet wheel fixed coaxially on a shaft which carries the primary sprocket wheel.

The invention is applicable not only to conventional bicycles but also to tandem cycles, and to tricycles or even cycles with four wheels in which case the secondary sprocket will be connected to the hub of one or both of the rear wheels.

One example of a unisex bicycle constructed in accordance with the present invention is illustrated diagrammatically in the accompanying drawings, in which: Figure I is a side elevation; Figure 2 is a perspective view of parts adjacent to the primary sprocket wheel; Figure 3 is a horizontal section through the axis of the primary sprocket wheel; and, Figure 4 is a part section taken on the line IV-IV in Figure 3.

As shown in Figure 1, the bicycle has a frame consisting of an upper bar 5, a lower bar 6, a seat bar 7, a rear upper fork 8, a rear lower fork 9, and a front wheel fork 10. The rear forks and the front fork are supported on rear and front nominally 650 mm rear and front wheels 11 and 12 respectively.

The front fork 10 is fitted with a T-shaped handlebar 13, which is telescopically adjustable upwards and downwards in conventional fashion. The seat bar 7 carries, via a strut 14, which is telescopically adjustable longitudinally of the bar 7, a moulded plastics bucket seat 15. The seat preferably has a height greater than 220 mm and a width of at least 290 mm. The illustrated seat has sides but this is unnecessary.

Although not shown, the cycle will preferably have fixed brakes and a gear change mounted in a hub 16 of the rear wheel 11.

The bars 6 and 7 and the fork 9 carry, at their intersection, a hub 17. A shaft 18 is supported by two ball bearings 19 in the hub 17 and has, at each end, a projecting stub shaft 20. Only one of these stub shafts 20 is visible in Figure 3 and that stub shaft is connected to the shaft 18 via an intermediate stepped shaft portion 21. A primary sprocket wheel 22 is keyed on the shaft portion 21.

Each stub shaft 20 is or square cross section and carries a bushing 23, which is held in position by a retaining washer 24 and bolt 25. The bushing 23 incorporates a ratchet wheel 26. A crank arm 27 is pivotally mounted on each of the bushings 23 by means of a pair of bearings 28. Each crank arm has a hollow portion accommodating a sliding pawl 29, which is urged by a spring 30 into engagement with teeth 31 on the ratchet wheel 26.

A pedal 32 is pivotally mounted at 33 about a transverse horizontal axis on the top of each of the crank arms 27 with an interposed tension spring 34, the pivotal mounting allowing tilting of the pedal to follow the natural angle of the rider's foot, as the crank arm is pressed forwards and downwards. Each pedal comprises a plate having, adjacent to its rear, a transverse step 35 for abutment with the heel of a rider's shoe, and at its front an open sided curved toe shroud 36 for overlying the toe of a rider's shoe.

The forward and downward motion applied via each pedal to the respective crank arm 27 is limited by abutment of the crank arm with a rubber stop 37 fitted on the end of a transverse bar 38, which in turn is carried by two stubs 39 welded to an projecting forwardly and downwardly from the hub 17.

As shown in Figure 1, the primary sprocket wheel 22 is connected by a toothed plastic drive chain 40 to a complementary secondary sprocket wheel mounted around the hub 16. Alternate forward and downward working strokes of the crank arms 27, by rider's foot pressure applied to the pedals 28, causes the shaft 18 and hence the primary sprocket wheel 22 to be driven in the same direction and this drive is transmitted by the chain 26 to the rear wheel 11 to propel the cycle.

The diameter of the sprocket wheel 22 and the radial distance between the axis of the sprocket wheel 22 and the pivotal connection 33, is of the order of 110 to 120 mm. The clearance between the lowest portion of the sprocket wheel 22, which represents the lowest point of the driving mechanism, and the ground 41 is of the order of 75 mm.

Claims (11)

1. A pedal cycle which is driven by means of two pedals carried by respective crank arms which are oscillatable about a common horizontal axis, and a primary sprocket wheel located adjacent to the crank arms and coupled by a chain to a secondary sprocket wheel which is connected to the hub of the rear wheel, each crank arm being coupled to the primary sprocket wheel via a one way drive mechanism and being arranged to drive the primary sprocket wheel by making alternately a working stroke forwards and downwards and an idle return stroke back again.

2. A cycle according to claim 1, wherein a stop is provided for limiting the working stroke of each crank arm.

3. A cycle according to claim 1 or claim 2, in which the pedals are positioned on the crank arms at a distance of between 100 and 140 mm from the axis of the crank arms.

4. A cycle according to any one of the preceding claims, in which the primary sprocket wheel has a clearance of between 50 and 100 mm above level ground on which the cycle is resting.

5. A cycle according to any one of the preceding claims, which is fitted with a bucket seat.

6. A cycle according to any one of the preceding claims, in which each pedal incorporates means for engagement with the rider's shoe so that the idle stroke is effected by the rider drawing the respective foot backwards.

7. A cycle according to claim 6, in which the engagement means comprises an upstanding part to engage the rear of the rider's shoe.

8. A cycle according to any one of the preceding claims, in which each pedal is pivotally mounted to the top of the respective crank arm.

9. A cycle according to any one of the preceding claims, in which the common oscillatory axis of the crank arms is the same as the axis of the primary sprocket wheel.

10. A cycle according to any one of the preceding claims, in which each crank arm carries a pawl cooperating with a respective ratchet wheel fixed coaxially on a shaft which carries the primary sprocket wheel.

11. A pedal cycle substantially as described with reference to the accompanying drawings.