CN1279640A - bicycle crank - Google Patents

Abstract

A bicycle crank comprises at least one chain wheel (1) rotatably mounted about a central axis (2), and two pedal arms (3, 3') each restrictedly rotatably mounted at an eccentric rotation hinge (6,6) of the chain wheel. Two spring devices (8,8 ') are each coupled at its eccentric first spring coupling (11, 11') within the sprocket wheel and draw the pedal arm towards the central axis (2). The pedal arms (3, 3') are rotatable between an inner position, in which they are rotated towards the central axis (2), and an outer position, in which they project substantially radially outwards from the central axis. The angle (V2) formed by a line between the first spring attachment (11,11 ') and the central axis (2) and a line between the central axis and the swivel hinge (6, 6') is between 30 ° and 150 °.

Description

bicycle crank

The present invention relates to bicycle cranks, comprising

at least one sprocket rotatably mounted about a central axis,

Two pedal arms, each pedal arm mounted at a first end in a limited rotatable manner at its rotary hinge fixed relative to the sprocket and eccentrically arranged on each side of the sprocket, and at the second ends are respectively rotatably connected to their pedals to facilitate the application of force by the cyclist, and

two spring means, each spring means being joined at a first end to its first spring link fixed relative to the sprocket and eccentrically disposed on each side of the sprocket, and at a second end Linked to each pedal arm of the second spring link, the second spring link is spaced from the first end of the pedal arm to draw the second end of the pedal arm with the pedal towards the central axis, and when on the pedal The second end of the pedal arm carrying the pedal is allowed to rotate away from the central axis as the applied force increases.

The bicycle crank transfers motion and force from the bicycle pedals to one or more eccentric sprockets for further transfer of motion and force to the rear wheel via a chain.

During the pedaling action of the cyclist, the force is greatest during the downward portion of motion and is slight or non-existent during the remaining portion of motion. In order to increase the energy transferred from the cyclist to the bicycle, several devices have been proposed which extend the distance from the pedal to the center of the crank during the downward pedaling action, thereby giving the force on the pedal a longer turn. moment arm.

FR2062858 describes a bicycle crank in which an inner pedal arm and an outer pedal arm are connected at a spring-loaded hinge. The hinge is pressed by a leaf spring into a position in which the two pedal arms form an angle of approximately 90°. When force is applied to the pedal during the downward pedaling action, the hinge is straightened so that the pedal arm lengthens and the force on the pedal acquires a longer moment arm.

DE858648 describes a bicycle crank with a similar pedal arm, but with the difference that coil springs are used instead of laminated springs.

NO80229 describes a bicycle crank with a sprung curved pedal arm that is forced out to a generally straight position when force is applied to the pedal arm during the downward pedaling action, This increases the distance from the pedals to the center of the bike's crank.

US2316530 describes a bicycle crank in which the pedal arm is rotatably coupled to the sprocket eccentrically, close to the engagement radius of the chain. A spring means in the form of a compression spring extends from the eccentric link of the sprocket to a link on the pedal arm, wherein the spring means has a fully threaded pull rod which urges the compression spring to act as a tension spring and thus to the sprocket Pull the pedal arm. The eccentric rotational linkage of the spring is located on the diametrically opposite side of the eccentric linkage of the pedal arm, and the spring linkage within the pedal arm is located closer to the pedal than the rotational linkage of the pedal arm. An adjustment nut on the tie rod provides a stop that limits the movement of the spring, allowing the pedal arm to move between the inside and outside positions.

Other bicycle cranks with adjustable or movable pedals are described in DE2509021, DE3813953, FR2388713, SE419960, SE446846 and DK162083.

None of the bicycle cranks described above are in widespread use. Presumably this is mainly due to the fact that the pedals yield too easily, with the result that the cyclist loses the feel of control over the bike. Another reason may be that no elongation of the pedal arm occurs at the point of pedaling action desired by the cyclist.

It is an object of the present invention to provide a bicycle crank in which energy is partially stored during the pedaling action when the force on the pedal is maximum and released as a driving force during the subsequent pedaling action. Another object is for the cyclist to experience the motion of the foot and the forces on the foot as a steady motion or force during the storage and release of energy. A further object is that during the lower part of the pedaling action, the pedal does not move closer to the ground than is the case with known bicycle cranks that do not store energy, in order to avoid scratching the ground. It is also an object that a bicycle crank according to the present invention will provide vibration and jolt cushioning of the bicycle to the rider. It is a further object that the moment arm of the pedal force will extend during the downward pedaling action. A still further object is that the invention can be realized by exchanging or adding elements to known types of bicycle cranks in which the pedals are fixed relative to the sprocket.

These objects are achieved according to the invention with a bicycle crank of the type mentioned in the introduction plus the features stated in the claims.

Below in conjunction with the description to specific embodiment, compare with the known bicycle crank of the type described in US2316530, and with reference to accompanying drawing, describe the present invention in more detail, in the figure:

1 is a front view of a bicycle crank according to the present invention viewed from the side of the sprocket of the bicycle,

Figure 2 is a front view of the bicycle crank of Figure 1 viewed from the opposite side,

Figure 3 is an exploded perspective view of a rotary hinge used in the present invention,

Fig. 4 is a schematic diagram of a bicycle according to the present invention,

Figures 5a-e show a bicycle crank according to the invention during a downward pedaling action,

Figures 6a-e show a bicycle crank of the type described in US2316530 during the downward pedaling action.

Throughout the figures, the same reference numerals have been used for corresponding parts.

Figures 1 and 2 show a bicycle crank according to the invention as viewed from the sprocket side and the opposite side of the bicycle, respectively. Unmarked references designate the front pedal arm, ie the pedal arm in the downward pedaling action, and corresponding elements and parts. A marked reference designates the pedal arm in upward return motion.

In a known manner, the bicycle crank comprises at least one sprocket 1 , mounted rotatably about a central axis 2 , operating a chain through an external toothed ring of radius R1 . Furthermore, the two pedal arms 3, 3' are respectively mounted at their first ends 4, 4' in a restricted rotatable manner at their swivel hinges 6, 6', wherein the swivel hinges are arranged eccentrically on each side of the sprocket 1 And relatively fixed on it. A fixed connection between the swivel hinge and the sprocket is obtained on the sprocket side by arranging the swivel hinge 6 at one end of the bracket 17, which is firmly connected to the sprocket 1 and functionally constitutes a part of the sprocket. Reinforcement. On the opposite side, the rotary hinge 6' is arranged on a bracket 17' which is firmly connected to the sprocket via a rotatable hub 16. The rotatable hub 16 is of the same type as known bicycle cranks which do not store energy and are therefore not further described.

Each pedal arm is rotatably connected to its pedal 7, 7' at a second end 5, 5' by a rotatable link 15, 15' for exertion by the rider. Two spring means in the form of tension springs 8, 8' are attached at first ends 9, 9' to their first spring links 11, 11', respectively, said links being fixed and eccentric with respect to the sprocket Placed on each side of the sprocket. This fixed connection is obtained by means of a spring coupling 11 which is part of the sprocket on the sprocket side and a spring coupling 11' which is part of the bracket 17' on the opposite side of the sprocket.

Tension springs 8, 8' are attached to each pedal arm 3, 3' at a second spring attachment 12, 12' at a second end 10, 10' which is spaced from the first end 4, 3' of the pedal arm. 4' a certain distance. In the described embodiment, the second spring link 12, 12' is located at the second end 5, 5' of the pedal arm, close to the link 15, 15' of the pedal and further away from the rotary hinge than the link of the pedal. 6, 6' is slightly far away. The second spring link can also be identical to the link 15, 15' of the pedal.

When an increased downward force acts on the pedal, the tension spring 8, 8' draws the second end 5, 5' of the 'pedal arm' with the pedal 7, 7 towards the central axis 2, so that the pedal with the pedal The second end of the arm is pivoted away from the central axis in the direction indicated by arrow P2.

Fig. 3 is an exploded perspective view of the rotary hinge 6, 6'. A stop 13, 13', firmly connected to the bracket 17, 17', cooperates with a stop 14, 14' at the first end 4, 4' of the pedal arm 3, 3'. These two sets of stops together result in a restricted rotatability within the swivel hinge 6, 6'.

According to the invention, the stops 13, 14, 13', 14' are adapted to allow the pedal arm 3, 3' to rotate between an inner position and an outer position, wherein in the inner position the pedal arm is connected to the central axis 2 and the pivoting hinge The line between 6, 6' forms an obtuse angle V1, whereas in the outer position the pedal arms 3, 3' protrude (point) substantially radially outwards from the central axis 2. This is shown very clearly in FIG. 4 , which is a schematic diagram of a bicycle crank according to the invention, showing the pedal arm in an inner position. The outer position is shown in Figure 1, where the front pedal arm 5 is in the outer position.

Furthermore, according to the invention, when the pedal arm is in its inner position, the first spring 11, 11' should lie between the line between the central axis 2 and the swivel hinge 6, 6' and the second end 5, 5' of the pedal arm. same side. Referring to Figure 4, this means that the first spring coupling 11 should lie on the line between the central axis 2 and the swivel hinges 6, 6'. Furthermore, the position of the first spring link will be determined by an angle V2 formed by the line between the first spring link 11, 11' and the central axis 2 and between the central axis 2 and the rotary hinge 6, 6' The line is formed, which should be between 30° and 150°.

Figures 5a-e show a bicycle crank according to the invention during a downward pedaling action, where the pedal is acted upon by a force F and the sprocket moves in the direction indicated by the arrow P1. Here it can be seen how the spring stretches and thus stores energy when the pedal arm is moved from the inner position (see FIG. 5b ) to the outer position (see FIG. 5c ). As the pedal arm moves further down, near the bottom of the pedaling action, the spring contracts (see Figure 5d), releasing the stored energy as the driving force that drives the sprocket while the pedal arm moves back to the inner position .

Tests have shown that during the movement of the pedal arm from the inner position to the outer position and back to the inner position, the movement and counter pressure of the pedal on the cyclist's foot is experienced as a steady motion or force.

Tests have also shown that during the lower part of pedaling, the pedals do not move substantially closer to the ground than known bicycle cranks that do not store energy.

The bicycle crank according to the present invention also provides dampening of vibrations and jolts from the bicycle to the rider. This cushioning effect is especially pronounced when a mountain bike is being ridden down a rough incline while the cyclist is standing on the frame, where the road surface may include, for example, tree roots or stones, which create severe vibrations and bumps in the bike . In this situation, the bicycle's speed is maintained by gravity and the rider is almost standing on the pedals, which extend forwards and backwards, as shown in Figure 5c. Since the cyclist distributes his weight on the two pedals, and assuming that the various dimensions of the bicycle crank and the tension of the springs are appropriate for the cyclist's weight, the front pedal will exhibit a springy swing between the inner and outer positions. centre position. Due to the rotation of the rear wheel and the freewheel linkage between the sprocket and the rear wheel, the elastic motion of the front pedal will be transferred to the rear pedal and not to the rear wheel. This provides a spring damping effect of both pedals.

With the bicycle crank according to the invention, its further object can be achieved, that is, the torque arm (moment arm) of the pedal force, that is, the torque arm of the force exerted on the pedal by the cyclist during the downward pedaling action. has been extended. The extension of the torque arm of the pedal force helps to increase the energy transferred from the cyclist to the sprocket, but since this effect is also accomplished in several known bicycle cranks mentioned at the outset, this feature cannot by itself Said to constitute the core of the present invention.

The invention can be realized by mounting the bracket 17 on a sprocket and a corresponding hub of standard known type in which the pedal is fixed relative to the sprocket. Similarly, bracket 17' may be mounted on the opposite side of the hub to the sprocket. The first spring link 11 can be realized through an existing or new hole in the sprocket. The invention can thus be realized by retro-fitting elements in the crank of a bicycle of the type where the pedal is fixed relative to the chain wheel.

The exact relationship between the design of a bicycle crank according to the present invention and how it is experienced by the user is complex, depending on the user's weight, the way the bicycle is used, and the rider's personal preferences. Therefore, it is not possible to specify an exact, universal optimum dimension for the different distances of the spring arrangement and the bicycle crank.

However, tests have shown that the stops 13, 14, 13', 14' in the swivel hinge 6, 6' and in the first end 4, 4' of the pedal arm should be designed such that the angle V1 is between 110° and 160°, more preferably Preferably between 130° and 150°, and preferably around 145° as shown in FIG. 4 .

It has also been proven that the first spring couplings 11, 11' should be arranged in such a way that the angle V2 is between 60° and 120°, preferably between 75° and 105°, and preferably as shown in 4 shows approximately 90°.

In addition, the distance between the central axis 2 and the rotating hinges 6, 6' should be 0.6 to 1.4 times the engagement radius R1 of the chain, preferably 0.8 to 1.2 times, and most preferably About 1.0 times, as shown in Figure 4.

The distance between the first spring connector 11, 11' and the central axis 2 should be 0.3 to 1.0 times the distance between the central axis 2 and the rotary hinge 6, 6', preferably 0.3 to 1.0 times. 5 to 0.8 times, and preferably about 0.65 times.

It has also been confirmed that the distance between the rotary hinges 6, 6' and the connecting parts 15, 15' of the pedals should be 0.5 to 1.2 times the distance between the central axis 2 and the rotary hinges 6, 6', preferably Preferably, it is 0.7 to 1.0 times, and preferably about 0.8 times.

The spring means 8, 8' should be pre-tensioned so that a certain amount of tension is required to give it an initial stretch. This object is achieved by the fact that the cyclist must exert a certain amount of minimum force on the pedals in order to move the pedal arms from the inner position to the outer position. When the spring constant and pretension are selected correctly for the spring, the pedal arm will only appear in the outer position in the area of the downward pedaling action, where the pedal force is maximum, which means that the pedal is now in the position shown in Figure 5b-d location shown.

In a preferred embodiment, as shown in Figures 1 and 2, the outer diameter of the sprocket is 220mm, the angle V1 is 145°, the angle V2 is 90°, and the distance between the central axis 2 and the rotating hinge 6, 6' is 100mm, the distance between the first spring link 11, 11' and the central axis 2 is 65mm, the distance between the rotary hinge 6, 6' and the pedal link 15, 15' is 80mm, and the rotary hinge 6, 6' The distance from the second spring connecting member 12, 12' is 97mm. The spring arrangement consisted of a linear extension spring pretensioned to an initial stretch at a tension of 1.3 kN.

In order to further clarify how the invention differs from known bicycle cranks, the invention is explained below by comparison with a bicycle crank of the type described in US2316530 shown in FIG. 6a.

The bicycle crank shown in Fig. 6a comprises a sprocket 101, a pedal arm 104 and a spring device 108, wherein the pedal arm is connected to the sprocket 101 with an eccentric rotary hinge 106 at one end and a pedal 107 at the other end. , the spring device 108 is connected at one end to the sprocket 101 of the first spring link 111 and at the other end is connected to the pedal arm 104 at a position closer to the pedal 107 than the rotary hinge 106 . The use of stop means in the form of nuts within the spring means 108 ensures that the pedal arm 104 can move between an inner position as shown in FIG. 6a and an outer position as shown in FIG. 6c. The stop arrangement also provides pretension to the spring arrangement 108 . The spring attachment 111 is located diametrically opposite to the rotary hinge 106, which is a fundamental difference with respect to the bicycle crank according to the invention. Furthermore, the pedal arm 104 moves over an area closer to the center of the crank compared to the pedal arm in the bicycle crank according to the invention.

Figures 5a-e show a bicycle crank according to the invention during a downward pedaling action, while Figures 6a-e show a bicycle crank of the type described in US2316530 during a corresponding downward pedaling action, Figure 5a corresponding to Figure 6a, Figure 5b corresponds to Figure 6b, and so on.

The difference between these two types of bicycle cranks is explained below by considering theoretical mechanics. The dynamical relationship related to the mass of the bicycle crank element is not important for the mode of operation of the bicycle crank and can therefore be ignored.

According to the principles of mechanics, an object will begin to rotate when it is subjected to a moment, defined by the product of a force and its moment arm. In the case of both bicycle cranks, when the moment from the pedal force exceeds the moment from the spring tension (hereinafter referred to as the spring force), the pedal arm 4, 104 will start to turn and move from the inner position to the outer position, wherein the moment is about Rotate the hinge 6, 106 calculated. Expressing in mathematical terms the initial rotation of the pedal arm of the bicycle crank according to the present invention is the following moment equation:

F _p ^* a _p = F _s ^* a _s ,

Where F _p is the pedal force, a _p is the moment arm of the pedal force, F _s is the spring force and a _s is the moment arm of the spring force.

Similarly, the initial rotation of the pedal arm of a bicycle crank of the type described in US2316530 is given by the following moment equation:

F' _p ^* a' _p = F' _s ^* a' _s ,

The corresponding reference symbols are used here.

This moment equation is maintained as long as the rotary joint 6 , 106 is not subjected to any moment, ie during the entire movement of the pedal arm to the outer position. Thus, the position of the pedal arm is determined by the pedal force, its moment arm, and the spring force and its moment arm, where these parameters are variables. Thus, a complete comparison of the pedal arm position during the pedaling action can be understood very clearly for both bicycle cranks.

To simplify the description and comparison of the modes of operation of the bicycle crank, it is assumed that the pedal force is directed vertically downward and has a constant magnitude during the down pedaling action, ie F _p =F' _p =F.

Figures 5a, 6a show a pedal near the top where the pedal force is directed towards the rotary hinge. The moment arms a _p , a' _p of the pedal force are therefore 0, and the pedal force produces no moment. The spring force has moment arms a _s , a' _s and creates a moment that holds the pedal arm in the inner position.

Figures 5b and 6b show the pedals at positions where the moment arm of the pedal force is equal to the moment arm of the spring force, ie a _p = a _s and a' _p = a' _s . For comparison purposes, assume that the springs in both bicycle cranks are sized in such a way that the tension required to initially stretch the springs is the same as the pedal force, so Figures 5b, 6b show the moment at which the pedal force will exceed the spring force torque and the pedal arm will begin to move out of the inner position.

Figures 5c, 6c show the pedal in a position where the pedal force is perpendicular to the distance from the pedal to the swivel hinge. In this case, the moment arms a _p , a' _p of the pedal force are equal to the distance from the pedal to the swivel joint, whereby their maximum value is obtained, which means that the moment of the pedal force also obtains its maximum value. For both bicycle cranks it can be seen that the moment arms a _p , a' _p of the pedal force are about twice the moment arms a _s , a' _s of the spring force, assuming that the dimensions of the spring in both bicycle cranks are way, that is, the pedal arm is in the outer position.

Figures 5d and 6d show the pedal when the moment arms a _p , a' _p of the pedal force are approximately 1.33 times the moment arms a _s , a' _s of the spring force. Since in this case the pedal arm is in the outer position and the spring is stretched, the spring force is greater than when the pedal arm is in the inner position, for comparison it is assumed that the springs are sized in this way in both bicycle cranks , where the pedal arm begins to move towards the inner position.

Figures 5e, 6e show that the pedal arm is near the bottom and the pedal force is again directed towards the swivel hinge. The moment arms a _p , a' _p of the pedal force are again 0, so the pedal force produces no moment. The moment arms a _s , a' _s of the spring force cause the spring force to generate a moment which holds the pedal arm in the inner position.

The ratio between the moment arm of the pedal force and the moment arm of the spring force is the same for each respective figure 5a-e and 6a-e. By comparing these figures it can be seen that the pedals in Figures 6a-e move farther during pedaling than the pedals in the corresponding Figures 5a-e. This is especially clearly illustrated when comparing Figures 5c and 6c and 5d and 6d, in the region where the pedal arm starts to move back into the inner position. These graphs thus show that in the bicycle crank according to the invention an earlier expansion and retraction of the pedal arms is obtained than in a bicycle crank of the type described in US2316530. Rather this earlier expansion and retraction of the pedal arms benefits the cyclist.

By comparing Figures 5e and 6e, it can further be seen that in the region where the pedal arm moves back to the inner position, the bicycle crank according to the invention enables a rounder and thus smoother pedal than a bicycle crank of the type described in US2316530 effect.

The moment of the pedal force depends on the rotational position of the crank and, as described in connection with Figure 5c, has its maximum value when the pedal force is perpendicular to the distance from the pedal to the rotational hinge. This maximum moment is expected to occur when the pedal is approximately at the level of the central axis, so according to the invention the pedal arm protrudes approximately radially outwards from the central axis when it is in the outer position.

However, the moment arm of the spring force does not depend on the rotational position of the crank. As shown in Figures 5 and 6, the moment arm of the spring force depends on the position of the pedal arm and the position of the first spring link, and it can be seen that for both bicycle cranks, the moment arm of the spring force follows the pedal arm from the inside The position decreases as it moves toward the outer position.

It can be seen from FIG. 5 that the first spring attachment cannot be located on the diametrically opposite side of the rotary hinge in the bicycle crank according to the invention, because this would cause the moment arm of the spring force to tend towards zero when the pedal arm moves towards the outer position. Variation in which the pedal arms project radially outward from the central axis in the outer position. According to the invention this condition is determined by the angle V2 formed by the line between the first spring link and the central axis and the line between the central axis and the rotary hinge, which is at least 30°. The invention is further limited by the fact that the angle V2 should be a maximum of 150°, since a larger angle will produce a smaller extension of the spring during pedal arm movement. However, it should be clear from the above discussion that these limitations are not critical to the actual design of the bicycle crank according to the invention.

Claims (10)

1. a bicycle crank comprises

At least one sprocket wheel (1), it is rotatably mounted around a central axis (2),

Two pedal arms (3,3 '), each pedal arm is pivotally mounted to its turning joint (6 at first end (4,4 '), 6 ') in, turning joint is fixing and be arranged on each side of sprocket wheel (1) prejudicially with respect to sprocket wheel (1), and connects (15 rotationally respectively at second end (5,5 '), 15 ') to its pedal (7,7 ') on, so that the cyclist uses power, turning joint (6,6 ') and first end (4 of pedal arm, 4 ') be provided with corresponding block (13,14,13 ', 14 '), these stop limits pedal arms (3,3 ') between two exterior points, rotate and

Two spring installations (8,8 '), each spring installation is at first end (9,9 ') be attached to its first spring connecting piece (11,11 ') on, the first spring connecting piece is fixing with respect to sprocket wheel (1), at second end (10,10 ') be attached to the second spring connecting piece (12,12 ') on each pedal arm (3,3 '), the second spring connecting piece is from first end (4 of pedal arm, 4 ') certain distance, to have second end (5,5 ') of the pedal arm of pedal (7,7 ') to central axis (2) traction, and second end that allows to have the pedal arm of pedal on pedal when the power used increases leaves (P2) central axis

It is characterized in that:

Block (13,14,13 ', 14 ') be suitable for allowing pedal arm between an interior location and an external position, to rotate, at interior location, line between pedal arm (3,3 ') and central axis (2) and the turning joint (6,6 ') forms an obtuse angle (V1), and position externally, pedal arm (3,3 ') from central axis (2) roughly radially outward stretch out and

When pedal arm is positioned at its interior location, the first spring connecting piece (11,11 ') be positioned at central axis (2) and turning joint (6,6 ') the same side of line between and pedal arm second end (5,5 ') is by the definite position of angle (V2), this angle is by the first spring connecting piece (11,11 ') and the line between the central axis (2) and formed by the line between central axis (2) and the turning joint (6,6 '), they are between 30 ° and 150 °.

2. bicycle crank as claimed in claim 1 is characterized in that: the second spring connecting piece (12,12 ') is positioned at second end (5,5 ') of pedal arm, and is consistent or contiguous with the connecting piece (15,15 ') of pedal.

3. bicycle crank as claimed in claim 1 or 2, it is characterized in that: at turning joint (6,6 ') and pedal arm first end (4,4 ') internal stop (13,14,13 ', 14 ') be suitable for when pedal arm is positioned at its interior location, at pedal arm (3,3 ') with central axis (2) and turning joint (6,6 ') angle between the line between (V1) is between 110 ° and 160 °, is more preferably between 130 ° and 150 °, and preferably about 145 °.

4. the described bicycle crank of one of claim as described above, it is characterized in that: the first spring connecting piece (11,11 ') position is determined by angle (V2), this angle is by the first spring connecting piece (11,11 ') and the line between the central axis (2) and central axis (2) form with line between the turning joint (6,6 '), they are between 60 ° and 120 °, be more preferably between 75 ° and 105 °, and preferably be approximately 90 °.

5. the described bicycle crank of one of claim as described above, it is characterized in that: central axis (2) and turning joint (6,6 ') distance between is 0.6～1.4 times of chain engages radius (R1), is more preferably 0.8～1.2 times, preferably about 1.0 times.

6. the described bicycle crank of one of claim as described above, it is characterized in that: the first spring connecting piece (11,11 ') and the distance between the central axis (2) be central axis (2) and turning joint (6,6 ') 0.3～1.0 times of the distance between, be more preferably 0.5～0.8 times, and preferably about 0.65 times.

7. the described bicycle crank of one of claim as described above, it is characterized in that: turning joint (6,6 ') with the connecting piece (15 of pedal, 15 ') distance between is central axis (2) and turning joint (6,6 ') between 0.5～1.2 of distance times, more preferably 0.7～1.0 times, and be preferably about 0.8 times.

8. the described bicycle crank of one of claim as described above, it is characterized in that: the second spring connecting piece (12,12 ') is positioned at from turning joint (6,6 ') than the farther position of connecting piece (15,15 ') from pedal.

9. the described bicycle crank of one of claim as described above, it is characterized in that: spring installation (8,8 ') is made up of pre-tensioned extension spring.

10. the described bicycle crank of one of claim as described above, it is characterized in that: sprocket wheel (1) is attached firmly on the rotating propeller boss (16), this propeller boss is attached firmly to carriage (17 in the both sides of sprocket wheel, 17 ') on, and carriage is attached firmly to turning joint (6,6 ') and on the first spring connecting piece (11,11 ').

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