WO2000071413A1

WO2000071413A1 - A crank having a variable lever arm

Info

Publication number: WO2000071413A1
Application number: PCT/IT2000/000207
Authority: WO
Inventors: Giambattista Apolloni; Giancarlo Brun
Original assignee: Tecnologia S.A.S Di Valentino Brazzale & C.
Priority date: 1999-05-24
Filing date: 2000-05-22
Publication date: 2000-11-30
Also published as: ITBO990282A1; ITBO990282A0; IT1309263B1; AU5101000A

Abstract

A crank or pedal crank having a variable lever arm comprises an arm member (2) and a crankpin (3) which is slidable relative to the arm member (2) from a position of maximum lever arm to a position of minimum lever arm. Synchronisation means (7) are coupled to the arm member (2) and to the crankpin (3) in order to bring about the alternating movement of the crankpin (3) from the maximum position to the minimum position and vice versa, in synchronisation with the rotational motion of the crank or pedal crank

Description

A crank having a variable lever arm

The present invention relates to the field of cranks, and more especially to a crank which has a variable lever arm and which is operated by a pedal .

In general, a crank comprises an arm member perpendicular to the axis of rotation and a crankpin which constitutes the pin for articulation to the operating member.

A bicycle, for example, comprises a pedal unit, enabling it to move, which comprises a shaft keyed to the arm members of two respective cranks having pedals, for the sake of brevity referred to hereinafter as pedal cranks, to the end of each of which, at the location of the pedal crankpin, is connected a shaft for supporting a pedal. One of the two pedal cranks, generally the one arranged on the right-hand side relative to the direction of travel of the vehicle, is connected to a toothed wheel for transmitting the motion, by means of a chain, to a pinion secured to the rear wheel.

The bicycle is operated by the thrust force exerted on the two pedal cranks in accordance with an alternating circular advance in such a manner that the phase of thrust exerted on a pedal crank corresponds to a return phase of the other pedal crank. Therefore, the moment of rotation imparted to the pinion of the wheel over a complete 360° arc is due to the movement of the pedal connected to a pedal crank for an arc equal to 180° from its position of maximum distance from the ground towards the direction of travel of the bicycle, and for the remaining arc, it is due to the other pedal crank, according to a similar circular motion.

An increase in the length of the arm member of a pedal crank brings about an increase in the lever arm and consequently an increase in the moment of rotation and in the power deliverable, for the same force imparted to the pedal of the pedal crank. However, that increase also increases the amplitude of the circular movement of the pedals and consequently the total effort expended.

The object of the present invention is to avoid the above- mentioned disadvantage by producing a device which enables the power delivered by the pedal unit to be increased for the same force applied and which enables the amplitude of the circular movement of the pedals to be kept constant .

A further object of the present invention is to produce a device which, overall, has increased strength, is reliable over time and is simple and economical to manufacture.

In order to achieve the objects indicated above, the invention relates to a crank or pedal crank having a variable lever arm, comprising an arm member and a crankpin, characterised in that the crankpin is slidable relative to the arm member from a position of maximum lever arm to a position of minimum lever arm, synchronisation means being coupled to the arm member and to the crankpin in order to bring about the alternating movement of the crankpin from the maximum position to the minimum position and vice versa, in synchro- nisation with the rotational motion of the crank or pedal crank.

One advantage of the present invention resides in increasing the lever arm of a crank up to a maximum point during the phases of greatest thrust on the part of a user (referred to hereinafter as active phases) , and in decreasing that arm to the minimum position in the phases of least or zero thrust (referred to hereinafter as passive phases) , so that the amplitude of the movement of the pedals is equal to the amplitude of the movement of the pedals of a crank having a constant lever arm.

Other features and advantages will emerge from the following detailed description of a preferred embodiment, with reference to the appended drawings of a bicycle pedal, unit which are given purely by way of non-limiting example and in which:

- Figure 1 is a perspective view of a right-hand pedal unit according to the present invention,

- Figure 2 is a sectional top view of the device of Figure 1,

- Figure 3a is a side view of a particular embodiment of the synchronisation means of the present invention,

- Figure 3b is a sectional view along the line X-X of Figure 3a,

- Figure 4a is a front view of a preferred embodiment of the present invention, and

- Figure 4b is a sectional view along the line A-A of Figure 4a. Referring now to Figure 1, a pedal unit 1 comprises an arm member 2 connected to a toothed wheel (not shown) for transmitting movement, and a pedal crankpin 3 to which a pin 4 for a pedal 5 is secured. One end of the arm member 2 comprises a hollow portion the inside of which accommodates, at least partially, a disc 7 which comprises, in its peripheral portion 8 of the two respective faces, a groove 9 and, in its inner portion, the pedal crankpin 3 inside which is inserted the pin 4 which is secured, for example, although this is not to constitute a limitation, by means of a resilient ring inserted in the groove 19. The hollow portion of the arm member 2 comprises in the peripheral walls a series of openings 6 for accommodating the disc 7 and its connections to the respective members of the pedal unit.

The end of the arm member 2 remote from the hollow portion comprises a portion, which, by way of non-limiting example, has a disc 11 in which two pairs of slots 12 are formed for the above-mentioned connection of the arm member 2 to the toothed wheel, and the usefulness of which will become clearer in the course of the description.

Figure 2 is a sectional top view of a right-hand pedal unit comprising the arm member 2 and the pedal 5. One end of the arm member 2 comprises the hollow portion inside which the disc 7 is rotatably housed and the side walls of which comprise the openings 6 permitting the connections to the other members of the pedal unit . The disc 7 is maintained in the housing by means of a pair of ball bearings 20 which are connected to the side walls of the arm member 2 and which are slidable inside the groove 9 of the peripheral portion 8 of the disc 7.

It will be appreciated that the arm member 2 can also be articulated to the disc 7 by methods other than those illustrated in the present embodiment, with the objects and advantages of the present invention remaining the same.

The side wall of the arm member 2 facing the pedal 5 comprises a cover 13 which is secured to the arm member 2, for example, although this is not to constitute a limitation, by means of two screws 14, and which comprises one of the openings 6. The pin 4 is connected to the disc 7 through the two side openings 6 by means of two ball bearings 10 maintained in abutment on the side openings 6 arranged opposite one another. Also secured to the pin 4 is a rocking lever 15 which is maintained at a distance from the ball bearing 10 by means of a shoulder washer 16. The pedal 5 is secured to the pin by means of a pedal-locking bush 17 and a pedal crank- locking bush 18.

Figure 3a is a front view of an embodiment of the disc 7 given purely by way of non-limiting example and Figure 3b is a sectional view along the line X-X of Figure 3a. The disc 7 comprises on each face a groove 9 which is formed in the outer portion 8 and inside which the ball bearing 20 slides. The inner portion of the disc 7 has a "clover-leaf" shape comprising four radial openings 21 defined by the diametral portions 22. Formed between an outer portion 8 and one of the diametral portions 22 is the pedal crankpin 3 comprising a seat 23 which is suitable for the insertion of the pin 4 and whose side wall 24 facing the inside of the disc 7 has a greater thickness in order to offer more resistance to the stresses of the pin 4.

In use, the pressure exerted on the pedal 5 permits a circular movement of the arm member 2 for the transmission of motion to the toothed wheel and therefore to the pinion of the wheel, and at the same time permits rotation, synchronised with the movement of the pedal crank, of the disc 7 inside the hollow portion of the arm member 2 and therefore the sliding of the pin 4 along the openings 6. That movement, which is promoted by the presence of the ball bearings 10 slidable in the openings 6, changes the position of the pin 4, and consequently of the crankpin 3, relative to the arm member 2, thus changing the lever arm of the pedal crank.

In particular, at the start of the active phase of the pedal crank, that is to say, when the pedal 5 is in its position of maximum distance from the ground (at 90° relative to the direction of travel) , the pin 4 is in an intermediate position relative to the extent of the side openings 6. A thrust exerted on the pedal 5, and therefore on the pin 4, forces the disc 7 to rotate relative to the arm member 2, causing the pin 4 to slide at the same time along the side openings 6 as far as a position of the pedal crank parallel to the ground in which the pin 4 abuts the front end of the opening 6, determining the position of maximum lever arm. The subsequent thrust which carries the pedal 5 towards the ground in the final position of the active phase continues the rotation of the disc 7 relative to the arm member 2, gradually returning the pin 4 to the intermediate position relative to the side openings 6.

During the passive phase, the pedal crank completes the circular path, passing from a position parallel to the ground, in which the rotation of the disc 7 brings the pin 4 into abutment with the rear end of the opening 6, corresponding to the minimum position of the lever arm, as far as the starting position of the active phase described above.

In this preferred embodiment, during all of the circular movement of the arm member 2, the diametral portion 22 on which the seat 23 is formed inside the disc 7, always maintains the same angular position relative to the ground as the arm member 2.

In use, the presence of the rocking lever 15 increases the surface over which a foot bears on the pedal 5, so that the rotational movement of the disc 7 inside the hollow portion of the arm member 2 is promoted.

As described above, the disc-shaped portion 11 of the arm member 2 comprises two pairs of slots 12 for the connection of the pedal unit to the keyed shaft (not shown) . The slots 12 enable the arm member 2 to be mounted in different positions relative to the keyed shaft in order, during the stage of assembling a pedal unit, to vary the effective distance between the pedal and the keyed shaft and thus to personalise the pedal unit according to a user's requirements. Although the examples described above all relate to particular embodiments of the component parts of a pedal crank, a person skilled in the art would have no difficulty in recognising that it is possible to obtain alternative embodiments of the present invention using equivalent means, the production of a movement of the pedal crankpin 3 relative to the arm member 2 from a position of maximum lever arm to a position of minimum lever arm, in synchronisation with the rotational motion of the pedal crank, remaining the same.

According to another embodiment of the present invention which is illustrated in Figures 4a and 4b, the pin 4 is connected to the side openings 6 by a different method in order to ensure greater slidability of the crankpin 3 relative to the ball bearings 10. In particular, the pin 4 is secured to a guide carriage 25 inserted inside the inner surface 26 of the side opening 6 of the arm member 2. The inner surface 26 and the side surfaces 27 of the guide carriage 25 are slightly spaced from one another in order to permit the insertion of sliding balls 28 and are inclined with opposite inclinations in order to prevent the balls 28 from escaping.

Of course, the principle of the invention remaining the same, the embodiments and the details of construction may be varied widely with respect to those described and illustrated, which have been given purely by way of illustrative example, without thereby departing from the scope of the invention.

Claims

1. A crank or pedal crank having a variable lever arm, comprising an arm member (2) and a crankpin (3) , characterised in that the crankpin (3) is slidable relative to the arm member (2) from a position of maximum lever arm to a position of minimum lever arm, synchronisation means (7) being coupled to the arm member (2) and to the crankpin (3) in order to bring about the alternating movement of the crankpin

(3) from the maximum position to the minimum position and vice versa, in synchronisation with the rotational motion of the crank or pedal crank.

2. A crank or pedal crank according to claim 1, characterised in that the synchronisation means (7) are mounted to be rotatable relative to the arm member (2) .

3. A crank or pedal crank according to claim 2, characterised in that the rotatable synchronisation means comprise at least one disc-shaped member (7) .

4. A crank or pedal crank according to claim 3, characterised in that the crankpin (3) comprises a seat (23) formed on the disc-shaped member (7) , a pin (4) of an operating member being secured in the seat (23) .

5. A crank or pedal crank according to claim 4, characterised in that the arm member (2) comprises, at one of its ends, a hollow portion inside which the disc-shaped member

(7) is accommodated at least partially, two side openings (6) being formed in the arm member (2) on opposite sides relative to the disc-shaped member (7), the pin (4) being inserted in the seat (23) and passing through the openings (6) .

6. A crank or pedal crank according to claim 5, characterised in that the pin (4) secured to the disc (7) is coupled to the arm member (2) by means of a pair of first slide members (10) slidable in the side openings (6) of the arm member (2) .

7. A crank or pedal crank according to claim 6, characterised in that the disc (7) comprises at least one peripheral groove (9) inside which second slide members (20) secured to the arm member (2) engage slidably.

8. A crank or pedal crank according to claim 1,- characterised in that one end of the arm member (2) comprises a plurality of slots (12) .

9. A crank or pedal crank according to claim 1, characterised in that the crankpin (3) is connected to at least one guide carriage (25) which is slidable on sliding balls (28) .

10. A crank or pedal crank according to any one of the preceding claims, characterised in that a pedal (5) is connected to the crankpin (3) .