JPH04169390A - Continuously variable transmission system for bicycle - Google Patents

Abstract

PURPOSE:To obtain the shift ratio suitable for the transmission efficiency of the pedal depression force and reduce the fatigue of a rider by eccentrically supporting a pair of driving sprocket wheels on a crank shaft, pivotally fitting support arms connected to the driving sprocket wheels on a crank, and arranging an eccentric quantity adjusting system between the crank and the support arms. CONSTITUTION:An endless chain 6 is wound between a pair of sprocket wheels 16 provided at both end sections of the hub 15 of a rear wheel via a one-way clutch 19 and a pair of driving sprocket wheels 8 eccentrically supported on a support crank shaft 10 respectively, and an eccentric quantity adjusting system is arranged between a crank 5 and the driving sprocket wheels 8. A support arm 4 is pivotally supported on a shaft 3, an eccentric spring 7 is inserted between the end section of the support arm 4 and the crank 5, and a disk-shaped driving sprocket wheels 8 are connected to the end section of the support arm 4 crossing with the crank 5 with bolts 23. When the depression force of a pedal 2 is applied to the shaft 3 to rotate the driving sprocket wheel 8, the load of the rear wheel is increased, when the tensile force of the endless chain 6 is increased, the driving sprocket wheel 8 is pushed toward the crankshaft 10 against the force of the eccentric spring 7, the eccentric quantity (e) of the driving sprocket wheel 8 against the crankshaft 10 is decreased, and the shift ratio is decreased.

Description

[Detailed Description of the Invention] □Field of Industrial Application] The present invention relates to a continuously variable transmission mechanism for bicycles that changes the gear ratio steplessly by eccentrically displacing a pair of drive chain wheels with respect to the crankshaft. It is.

[Prior Art] Conventional continuously variable transmission mechanisms for bicycles select chain wheels with different numbers of teeth depending on the load to lighten the pedal operation burden, but power transmission is interrupted during gear changes. There are problems such as the endless chain easily coming off, and the number of parts is large, resulting in high costs.

The continuously variable transmission mechanism for a bicycle disclosed in JP-A-59-102680 changes the gear ratio by making the drive chain wheel eccentric with respect to the crankshaft. Even if the amount of eccentricity is constant, the gear ratio varies greatly depending on the rotation angle of the crank.

In particular, since the variation period of the gear ratio repeats maximum and minimum every one revolution of the crank, it does not match the change in pedal effort every half revolution of the crank, making it extremely difficult for the driver to drive.

In addition, when the drive chain wheel is eccentric, the pin of the crank slides relative to the slit of the drive chain wheel while transmitting power, resulting in large frictional resistance and low transmission efficiency. There is a problem that it is easy to wear out.

[Problems to be Solved by the Invention] In view of the above-mentioned problems, an object of the present invention is to provide a continuously variable transmission mechanism for a bicycle that allows smooth transmission of power and is free from wear due to sliding.

[Means for Solving the Problem] In order to achieve the above object, the present invention has a configuration including a pair of left and right drive chain wheels driven by a crank and a pair of left and right drive chain wheels supported by a rear wheel hub via a one-way clutch. A pair of drive chain wheels is supported eccentrically with respect to the crankshaft by passing an endless chain between the drive chain wheels and the drive chain wheels, and the support arm connected to each drive chain wheel is swingably connected to the crank by the shaft. However, an eccentricity adjustment mechanism is provided between the crank and the support arm.

[Function] According to the present invention, the pair of drive chain wheels is connected to the crankshaft,
The rotation of a pair of drive chain wheels, which are eccentrically arranged in opposite phases, is alternately transmitted every half rotation to a pair of chain wheels on the rear wheels by separate endless chains. By adjusting the eccentricity of the drive chain wheel relative to the crankshaft, the gear ratio (transmission ratio) changes steplessly without changing the endless chain.

By appropriately setting the characteristics of the eccentric spring that biases the drive chain wheel in the direction of increasing the amount of eccentricity, the optimum gear ratio can be automatically obtained for load fluctuations such as on slopes.

[Embodiments of the Invention] FIG. 2 is a plan sectional view of a continuously variable transmission mechanism for a bicycle according to the present invention, and FIG. 1 is a side view of the same. A crankshaft 10 is rotatably supported at the connection between the front frame 9 and a bifurcated rear fork 13 extending rearward almost horizontally, and left and right cranks 5 extending in front and rear or vertically opposite directions are provided at both ends of the crankshaft 10. be combined. A pedal 2 is supported by a shaft 3 at the end of each crank 5.

A shaft 17 is fixed between the rear forks 13. That is, the end of the shaft 17 is inserted into a hole in the flattened rear end of the rear fork 13, and a nut 18 is screwed onto the end of the shaft 17 to be fastened. A rear wheel hub 15 is rotatably supported on the shaft 17. The rear wheel is constructed by connecting a large number of spokes 14 extending radially from a hub 15 to a rim 12 that supports a tire 12a. A pair of chain wheels 6 are supported at both ends of the hub 15 via one-way clutches called freewheels.

A pair of drive chain wheels 8 eccentrically supported on the crankshaft 10
and a pair of chain wheels 16 on the rear wheels, each with an endless chain 6
is passed over.

According to the present invention, an eccentricity adjustment mechanism is provided between each crank 5 and the drive chain wheel 8. For this reason, the support arm 4 is attached to the shaft 3.
is rotatably supported. The support arm 4 extends towards the crankshaft 10 and is curved at right angles so as to overlap above the crank 5. An eccentric spring 7 is interposed between the end of the support arm 4 and the crank 5. A disc-shaped drive chain wheel 8 is coupled to the end of the support arm 4 intersecting with the crank 5 by a bolt 23 .

As shown in FIG. 1, a pair of left and right drive chain wheels 8 (only the right drive chain wheel 8 is shown in FIG. 1) are independently connected to the crankshaft 1.
It is supported eccentrically with respect to zero. In order to avoid interference with the crankshaft 10, an elongated hole 21 is provided in the drive chain wheel 8, and the crankshaft 10 (actually, the boss portion 5a of the crank 5) passes through the elongated hole 21. In FIG. 1, the position where the eccentricity e of the driving chain wheel 8 with respect to the crankshaft 10 is maximum is shown by a solid line, and the position where the eccentricity is 0 is shown by a chain line. In order to take up slack in the endless chain 6, a tension wheel 20 supported on the rear fork side is engaged with the endless chain 6.

Next, the operation of the continuously variable transmission mechanism for a bicycle according to the present invention will be explained. When the vehicle is stopped, the support arm 4 is biased to rotate counterclockwise about the shaft 3 by the force of the eccentric spring 7 in FIG.

When the force applied to the pedal 2 is applied to the shaft 3, the drive chain wheel 8 rotates around the crankshaft 10. Substantially, the drive chain wheel 8 drives the endless chain 6 as a drive chain wheel with a radius of D+e, and the gear ratio is (D+e)/d (where, D is the radius of the drive chain wheel 8, and d is the radius of the chain wheel 16). radius).

When the load on the rear wheels increases, the tensile force of the endless chain 6 increases, and the endless chain 6 pushes the drive chain wheel 8 toward the crankshaft 10 against the force of the eccentric spring 7. In other words, the eccentricity e of the drive chain wheel 8 with respect to the crankshaft 10 becomes smaller, and the gear ratio becomes smaller. Therefore, the gear ratio changes automatically in accordance with the load, and by simply applying approximately the same amount of force to the pedals 2, the vehicle can easily travel at high speeds on flat roads and at low speeds on uphill roads.

At the top dead center and bottom dead center of the crank 5, the torque exerted by the crank 5 on the drive chain wheel 8 is 0, so the endless chain 6 remains strongly tensioned and the drive chain wheel 8 has an eccentricity of 0. . With half a rotation of the right crank 5 (from top dead center through the state shown in FIG. 1 until reaching bottom dead center), the gear ratio changes as shown by line 30 in FIG. 3. That is, at the top dead center and bottom dead center of the crank 5, the eccentricity of the drive chain wheel 8 becomes 0 (above the line 29), and the gear ratio becomes D/d. At an intermediate point between the top dead center and the bottom dead center of the crank 5, the eccentricity e of the drive chain wheel 8 becomes maximum due to the force of the eccentric spring 7, and the gear ratio becomes (D10e)/d. Then, by turning the left crank 5 half a turn, line 3 appears in Figure 3.
The gear ratio changes as shown by 1.

However, in reality, when the load on the rear wheels is relatively light and the left and right cranks 5 are rotated continuously, the eccentricity of the drive chain wheel 8 becomes 0 at the top dead center and bottom dead center of the cranks 5. No. The amount of contraction (the amount of eccentricity e) of the eccentric spring 7 changes in accordance with the load at that time, and the gear ratio changes as shown by the line 35 in FIG. 3 with respect to the rotation angle of the left and right cranks 5.

In addition, in the above-mentioned embodiment, the pair of left and right drive chain wheels 8 may be arranged on one side of the vehicle body.

The fulcrum of the support arm 4 is not limited to the pedal shaft 3, but can be selected at any position on the crank 5.

As an eccentricity adjustment mechanism, the mechanical displacement of the gear ratio selection lever disposed on the handle is transmitted to the cam mechanism disposed on the crank 5 via a cable, and the angle between the crank 5 and the support arm 4 (the eccentricity e ), a constant gear ratio corresponding to the driver's leg strength can be obtained. Also,
The support arm 4 is slidably supported in the longitudinal direction of the crank 5,
The gear ratio may be set using a worm, screw, or the like.

If a friction type one-way clutch is used as the one-way clutch that transmits the rotation of the drive chain wheel 8 to the rear wheels, the operation when switching the torque transmission between the left and right drive chain wheels 8 becomes very smooth.

[Effects of the Invention] As described above, the present invention provides an endless chain between a pair of left and right drive chain wheels driven by a crank and a pair of left and right chain wheels supported by a rear wheel hub via a one-sided clutch. A pair of drive chain wheels is supported eccentrically with respect to the crankshaft, and a support arm connected to each drive chain wheel is swingably connected to the crank by a shaft, and between the crank and the support arm. Since an eccentric spring is interposed in the structure, the following effects can be achieved.

(a) In general, when the crank is at top dead center and bottom dead center, the conversion efficiency of the drive torque applied to the crank by pedal force is low. A greater pedal force is required at bottom dead center, which can be tiring for the driver.

However, according to the present invention, if the eccentric direction of the drive chain wheel relative to the crankshaft is set so that the gear ratio is minimized near the top dead center of the crank, a gear ratio suitable for transmission efficiency of pedal depression force can be obtained. , driver fatigue is reduced.

Between the top dead center and bottom dead center of the crank, which has high transmission efficiency,
The large gear ratio reduces driver fatigue and enables efficient high-speed operation.

(b) Since the drive chain wheel is urged in the direction of increasing eccentricity by the eccentric spring, when the load is small (when the tensile force applied to the endless chain is small), the drive chain wheel moves to the maximum eccentric position, You can drive at high speeds easily.

When the load is heavy, such as on a slope, the tensile force applied to the endless chain increases, and the eccentricity of the drive chain wheel decreases.
Large driving torque can be obtained with the same pedal force.

(C) The only thing that makes the drive chain wheel eccentric is the eccentric spring interposed between the crank and the support arm that connects the drive chain wheel, and since there are no sliding parts, the operation is smooth and durable. Excellent.

[Brief explanation of the drawing]

FIG. 1 is a side view of a continuously variable transmission mechanism for a bicycle according to the present invention;
FIG. 2 is a plan view of the same, and FIG. 3 is a diagram showing the speed change characteristics of the continuously variable transmission mechanism. 3: Axis 4: Support arm 5: Crank 6: Endless chain 7: Eccentric spring 8 Two drive chain wheels 1.5: /1 chain 16
:Chain wheel 19-way one-way clutch Patent applicant: Isuzu Motors Co., Ltd. Representative Patent attorney: Toshio Yamamoto Figure 1 Figure 3

Claims (1)

[Claims] An endless chain is passed between a pair of left and right drive chain wheels driven by the crank and a pair of left and right chain wheels supported by the rear wheel hub via a one-way clutch.
A pair of drive chain wheels are eccentrically supported, a support arm connected to each drive chain wheel is swingably connected to a crank via a shaft, and an eccentric amount adjustment mechanism is provided between the crank and the support arm. A continuously variable bicycle transmission mechanism featuring: