JPH0789477A - Driving device for bicycle - Google Patents

Abstract

PURPOSE:To provide a driving device for a bicycle, by which very large rotating torque can be obtained by small stepping force to secure excellent running performance. CONSTITUTION:A crank arm 5 comprises a base part 9 and an expansible part 11 inserted in the base part 9 in such a manner as to slide. A driven pin 21 is provided on the expansible part 11, and the driven pin 21 is fitted in a guide groove 19 of a guide 17 for expansion and contraction. The stepping side of the guide groove 19 is formed like an ellipse elongated toward the front wheel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bicycle drive device for depressing a pedal and rotating a sprocket via a crank arm.

[0002]

2. Description of the Related Art In a bicycle, a pedal is stepped on by a bending motion of a leg to rotate a sprocket via a crank arm. The rotation of the sprocket is transmitted to the wheels via a chain etc. and the bicycle runs, but in order to have excellent running performance, it is necessary to be able to obtain a large turning torque with a small stepping force. Is.

[0003]

In order to obtain a large turning torque with a small stepping force, the crank arm may be made long, but if it is made too long, the bending motion of the leg at the time of returning cannot be smoothly performed. hand,
On the contrary, the running performance is reduced, and the pedal may come into contact with the ground at the lower end position.

Therefore, an object of the present invention is to provide a bicycle drive device capable of obtaining a large rotational torque with a small stepping force, and as a result, excellent traveling performance can be secured.

[0005]

In order to achieve this object, a bicycle drive device of the present invention is provided with a pedal and a retractable crank arm for rotating a sprocket, and a crank arm provided on the crank arm. The driven portion and the extension / contraction guide for guiding the driven portion so that the crank arm is in the extended state only when the pedal is stepped on are provided.

[0006]

When the crank arm is rotationally moved to the stepped-in position, the driven portion is guided by the extension / contraction guide, and the crank arm is extended. When the crank arm rotationally moves to the return position, the driven portion is guided by the expansion / contraction guide, and the crank arm is in the contracted state.

[0007]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a front view of a bicycle drive device according to the present invention, and FIG. 2 is a plan view of the bicycle drive device.

The sprocket 1 is fixed to the base end of a crank arm 5 having a pedal 3 at the tip, and a chain 7 for driving force transmission is hung between the sprocket 1 and a sprocket for a rear wheel (not shown). There is.

As shown in detail in FIG. 3, the crank arm 5 comprises a base portion 9 and a telescopic portion 11 slidably inserted into the base portion 9, and the telescopic portion 1 is provided in the base portion 9.
A compression coil spring 13 that pushes 1 outward is arranged.

Inside the crank arm 5, the frame 1
An expansion / contraction guide 17 supported by 5 is arranged, and a driven pin 21 (driven part) projecting from the expansion / contraction part 11 of the crank arm 5 is fitted into the guide groove 19 of the expansion / contraction guide 17. I'm out. As shown in detail in FIG. 4, the driven pin 21 has a roller 23 at the tip thereof, and the roller 23 extends and contracts according to the rotation of the crank arm 5.
It moves in the guide groove 19 of 7.

The guide groove 19 of the expansion / contraction guide 17 is formed so as to have a semi-circular shape on the return side A, but on the stepping side B, an elliptical shape (accurate to the right) in the front wheel direction (rightward in the figure) It does not have to be oval) and is formed to be drawn. Therefore, when the crank arm 5 rotationally moves to the depression side B, the driven pin 21 moves the extension guide 17.
The guide arm 19 moves in an elliptical manner along the guide groove 19 to move outward, and as a result, the expandable portion 11 moves outward and the crank arm 5 is in an extended state. The crank arm 5 extends most when it is in the horizontal state on the step-in side B (the state shown in FIG. 1), but when it is further rotated from the horizontal state, the expansion / contraction part 11 moves inward by the movement of the driven pin 21 along the guide groove 19. It moves and gradually contracts from the longest time. When the crank arm 5 reaches the return side A, the expansion / contraction part 11 is moving to the innermost side, and the crank arm 5 is in the contracted state (see the phantom line in FIG. 1). After that, the crank arm 5 rotates in the contracted state until it reaches the step-in side B.

A compression coil spring 13 arranged in the base portion 9.
Smoothes the outward movement of the expansion / contraction portion 11 on the stepping side B, and helps reduce the stepping force on the upper side of the stepping side B, which requires the largest stepping force.

[0014]

As described above, when the bicycle drive device of the present invention is used, the crank arm is extended at the stepping position, so that the turning radius becomes long and a large stepping force produces a large turning torque. You can Moreover, since the crank arm is in a contracted state at the return position, it is possible to ensure excellent running performance without hindering the smooth bending motion of the leg or contacting the pedal with the ground. Become.

[Brief description of drawings]

FIG. 1 is a front view of a bicycle drive device according to the present invention.

FIG. 2 is a plan view of a bicycle drive device.

FIG. 3 is a sectional view showing details of a crank arm.

FIG. 4 is a plan view showing details of a driven pin portion.

[Explanation of symbols]

 1 Sprocket 3 Pedal 5 Crank arm 17 Extension guide 21 Driven pin (driven part)

Claims (1)

[Claims] 1. An extendable and retractable crank arm for rotating a sprocket having a pedal, a driven portion provided on the crank arm, and the driven portion so that the crank arm is in an extended state only when the pedal is stepped on. A drive device for a bicycle, comprising: a telescopic guide for guiding the vehicle.