JPH0137620B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a skip prevention device for a toothed belt for a bicycle or the like.

(Prior Art) Examples of methods for applying tension to a power transmission belt are as follows.

() This will be explained based on FIGS. 6 and 7. In this example, an arm 54 is attached to a tensioner 53 and a spring 55 is used to apply tension to a belt 52 hung on pulleys 50 and 51.
4 (see Figure 6) or spring 56.
The tensioner 53 is pressed against the belt 52 (see FIG. 7).

However, with this type of movable tensioner, the pressing force is applied taking into account the elongation of the belt, and by applying more tension than necessary at the initial stage, it shortens the belt life and causes an increase in the axial load. bearing part,
Shaft damage occurs. Therefore, it is generally not used for toothed belts.

() Typical toothed belts employ a method in which a tensioner is fixed while applying a constant tension to the belt. In this method, it is necessary to constantly apply a large tension to the belt in order to prevent skips (a phenomenon in which the teeth of the pulley and the belt do not mesh and the teeth of the belt ride on the teeth of the pulley).

For this reason, when used on a bicycle, () a large pedal force is required during general riding, making the pedals feel heavy, which impedes the comfort required of a bicycle () a large force is applied to the crankshaft, so the crankshaft There was a problem that the shaft was easily damaged.

An example of using a toothed belt instead of a chain on a bicycle is shown on page 48 of the February 1980 issue of Science (Publisher: Nihon Keizai Shimbun). In this example, there is no tensioner, and instead a large unfixed pulley (eccentric pulley) is placed over the drive gear connected to the pedal via the crankshaft, thereby solving the skip problem.

However, since the eccentric pulley moves in the width direction, it is necessary to seal the meshing portion between the drive gear and the eccentric gear, and there are also problems in that meshing noise is generated.

(Object of the Invention) The present invention has been made in view of the above-mentioned conventional problems.The present invention improves transmission efficiency by requiring less tension to be constantly applied to the toothed belt. To provide a skip prevention device that applies large tension to a toothed belt and does not use gears.

In other words, when a toothed belt is used on a bicycle, it reduces the pedal force required during general riding to enable comfortable riding of the bicycle, prevents damage to the shaft, and reliably prevents skipping. However, it is an object of the present invention to provide a skip prevention device that does not generate meshing noise.

(Structure of the Invention) In order to achieve the above object, the toothed belt skip prevention device according to the present invention has two pulleys in contact with the back surface of the toothed belt, and the first pulley is on the driving pulley or on the driven pulley. A second pulley contacts the toothed belt between the pulley spans, and connects the rotating shafts of the two pulleys by an arm, with the arm at the intermediate portion thereof. The second pulley is rotatable about a provided spindle, and the second pulley is rotatable on the arm, and the rotation axis of the second pulley is located on the opposite side of the spindle from the first pulley with respect to the spindle. The distance between the rotating shaft of the first pulley and the supporting shaft is longer than the distance between the rotating shaft of the first pulley and the supporting shaft.

Therefore, when the belt teeth try to ride on the pulley teeth, the second pulley is pressed against the toothed belt, increasing the tension applied to the toothed belt and preventing the belt from skipping.

(Example) An example in which the present invention is applied to a bicycle will be described based on the drawings.

As shown in FIG. 1, the force applied to the pedal 1 is transmitted to the driven pulley 4 via the crankshaft 1a, the drive pulley 2, and the toothed belt 3. 1st
In the figure, the left side of the figure corresponds to the front of the bicycle, and when the pedal 1 is depressed, both the pulleys 2 and 4 rotate counterclockwise. Both the drive pulley 2 and the driven pulley 4 are toothed pulleys, and the drive pulley 2 has a larger diameter.

The skip prevention device 5 for the toothed belt 3 is constructed as follows.

Two flat pulleys are in contact with the back surface of the toothed belt 3. The first pulley 6 is in contact with the toothed belt 3 on the driven pulley 4. Further, the second pulley 7 is in contact with the toothed belt 3 between the pulley spans. The second pulley 7 has a larger diameter than the first pulley 6.

The rotation axis of the first pulley 6 is located at one end of the arm 8, and the rotation axis of the second pulley 7 is located at one end of the arm 8.
are connected to the other end of each. Arm 8
is rotatable around a support shaft 9 provided at its intermediate portion.

On the arm 8, the rotation axis 7a of the second pulley 7 is located on the opposite side of the rotation axis 6a of the first pulley 6 with respect to the support shaft 9. The distance l ₁ between the rotation axis of the second pulley 7 and the support shaft 9 is set longer than the distance l ₂ between the rotation axis of the first pulley 6 and the support shaft 9.

Next, the operation of the skip prevention device 5 will be explained.

When the pedal 1 is strongly depressed with an appropriate tension applied to the toothed belt 3 in advance, the upper side of the toothed belt 3 becomes the tension side and the lower side becomes the slack side. Therefore, on the slack side, especially on the driven pulley 4 side, the second
As shown in the figure, the belt teeth 3a ride on the pulley teeth 4a, and a skip is likely to occur. That is, assuming that the height of the pulley teeth 4a is δ, the toothed belt 3 tries to push up the first pulley 6 by δ, giving a clockwise rotational moment to the arm 8. Therefore, as shown in FIG. 3, the second pulley 7 moves toward the toothed belt 3 and is pressed against it, increasing the tension of the belt 3. In this way, skips are prevented from occurring.

Here, the amount of movement of the second pulley 7 is δ×l ₁ /
l becomes ₂ . Therefore, the larger l ₁ is than l ₂ ,
Since the pulley 7 is strongly pressed against the toothed belt 3, it is highly effective in preventing skips.

Further, as can be seen from FIG. 3, the larger the diameter of the second pulley 7, the longer the contact portion between the toothed belt 3 and the pulley 7, and therefore the greater the tension applied to the toothed belt 3.

In this manner, when a skip is about to occur, the tension in the toothed belt 3 is reliably increased, so that the tension constantly applied to the toothed belt 3 can be reduced. Therefore, the pedal 1 requires only a small pressing force during normal riding, allowing the bicycle to be driven comfortably, and furthermore, since the force applied to the crankshaft 1a is small, damage to the crankshaft 1a is prevented. Also, since no gears are used, the noise is low.

The skip prevention device of the present invention is applicable not only to bicycles, but also to general mesh transmissions where there is a sudden change in load. An example of this is load variations due to switching on and off of the clutch.

Next, the outline and results of the skip torque measurement test conducted by the inventor will be shown.

The configuration of the test apparatus shown in FIG. 4 is basically the same as the embodiment shown in FIG. 1, and the same members will be described with the same reference numerals. The difference from the example is that in this experimental device, the pedal and crankshaft are not connected to the drive pulley 2, and the drive pulley 2 is located on the right side of the drawing, the driven pulley 4 is located on the left side, and the drive pulley 2 is located on the opposite side. The skip prevention device 5 is provided above the driven pulley 4 in consideration of the fact that the upper side of the toothed belt 3 is on the slack side since it rotates clockwise. More specific experimental conditions are as follows.

Number of teeth on driving pulley: 44 Number of teeth on driven pulley: 24 Belt width: 10mm Bell length: 848mm STPD tooth profile of belt: S8M Diameter of first pulley: 20mm Diameter of second pulley: 60mm l ₁ = The results of investigating the relationship between the initial tension of the toothed belt 3 and the skip torque under conditions such as 100 mm: l ₂ 20 mm or more are summarized in the fifth section.
This is indicated by solid line A in the figure. The solid line B in FIG. 5 shows the results of examining a similar relationship with the skip prevention device 5 removed and other conditions being the same.

As is clear from FIG. 5, when the skip prevention device 5 is provided, the decrease in skip torque becomes gradual when the initial tension is low. Initial tension is 10Kg
Taking the case of f as an example, by providing the skip prevention device 5, the skip torque can be increased by 50% or more compared to the case where the skip prevention device 5 is not provided.

(Effects) According to the toothed belt skip prevention device of the present invention, (a) Only a small amount of tension is constantly applied to the toothed belt, so transmission efficiency is improved.

(b) When there is a sudden load change, a large tension is applied to the toothed belt, so skips are reliably prevented.

(c) Since gears are not used, an excellent effect of low noise can be obtained.

[Brief explanation of drawings]

Fig. 1 is a front view showing an embodiment of the skip prevention device for a toothed belt according to the present invention, Figs. 2 and 3 are explanatory diagrams of the operation of the same embodiment, and Fig. 4 shows an outline of the skip torque measurement test device. Figure 5 is a characteristic diagram showing the relationship between initial tension and skip torque.
6 and 7 are front views showing a conventional tensioner. 2... Drive pulley, 3... Toothed belt, 4...
Driven pulley, 5... Skip prevention device, 6... First pulley, 7... Second pulley, 8... Arm, 9... Support shaft.

Claims (1)

[Claims] 1. Two pulleys are brought into contact with the back surface of the toothed belt, the first pulley is in contact with the toothed belt on the driving pulley or the driven pulley, and the second pulley is in contact with the toothed belt between the pulley spans. At the same time, the rotation shafts of the two pulleys are connected by an arm, and the arm is rotatable about a support shaft provided in the middle thereof, and the rotation shaft of the second pulley is connected on the arm. is located on the opposite side of the rotation axis of the first pulley with respect to the support shaft, and further, the distance between the rotation axis of the second pulley and the support shaft is set such that the distance between the rotation axis of the first pulley and the support shaft is A toothed belt skip prevention device characterized by being longer than the shaft distance.