JP2761022B2 - Belt transmission with automatic tension adjustment mechanism - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a belt transmission that automatically adjusts the tension of a toothed belt in accordance with a driving force and suppresses the skipping phenomenon. is there.

(Prior Art) Conventionally, as a belt transmission device mounted on a bicycle, as shown in FIG. 7, a large-diameter toothed drive pulley b mounted on a crankshaft a and a rear wheel shaft c are mounted. Some are constituted by a toothed driven pulley d having a small diameter and a toothed belt e wound around both pulleys b and d. In this transmission, the toothed belt e is pulled
In order to prevent the belts e from coming off from b and d or slipping, a tension mechanism for applying tension to the belt e by pressing the belt spans in directions approaching each other by the idlers f and f is adopted. However, in this structure, the belt e travels at the pressing position of the idlers f, f while being bent in a direction opposite to the normal direction, so that the damage is large and the belt e needs to be replaced in a relatively short time.

On the other hand, examples of other belt transmission device, as shown in FIG. 8, a floating car having a drive gear b ₁ which is attached to the drive pulley b crankshaft a, the internal teeth meshing with the drive gear b ₁ b composed of _two, obtained by so wrapped around the toothed belt e floating car b ₂ outer periphery are known (JP-b-58-4759
No. 2).

(Problem to be Solved by the Invention) In the latter case, the problem which has been a problem in the former case does not occur. However, on the other hand, the floating vehicle b ₂ is the driving gear
Since the drive reduction by b _1, in order to keep the optimum range the rotational speed of the driven pulley d, these drive gears b ₁ and a floating wheel
it is necessary to increase the diameter of b _2, due to the larger diameter, is inevitably the weight of the bicycle increases.

Further, since the amount of eccentricity relative to the drive gear b ₁ Floating Car b ₂ is not constant, when the stepped strongly pedals for acceleration, A point near in FIG floating car b _2, i.e. after the crank shaft a or disengaged from the inner teeth drive gear b ₁ near the point of tight side of the belt e on a line perpendicular to the straight line connecting the axial center of the wheel axis c, and or engagement becomes inaccurate, these teeth damage There is also a risk of doing so.

Further, as a belt transmission device other than the above, a device in which a small-diameter drive gear is disposed in a drum attached to a crankshaft and having internal teeth so as to obtain a large rotation speed by meshing both gears has also been proposed. However, since the diameter difference between the drum and the drive gear is large, there is a disadvantage that noise at the time of meshing is increased.

The present invention has been made in view of the above points, and an object of the present invention is to suppress the occurrence of damage to a toothed belt and the like and to increase the weight in a belt transmission having an automatic tensioning function as described above. Therefore, the rotation speed of the driven side can be increased more than that of the drive side, so that the transmission is reduced in weight and size, and the noise is reduced.

(Means for Solving the Problems) In order to achieve this object, a solution of the present invention is characterized in that the drive pulley has a configuration having a transmission portion formed of a cycloidal wavy curve.

Specifically, according to the invention described in claim (1), a pair of rotating shafts parallel to each other, a driving and driven pulley including toothed pulleys respectively supported on the rotating shafts, and a winding between the two pulleys. The driving pulley and the toothed belt are configured as follows in a belt transmission device having a toothed belt that is hung to transmit power between both rotation shafts.

That is, a crank plate made of a disk having a corrugated portion formed by an epitrochoid curve on the outer circumference, which is attached concentrically to the rotation shaft and integrally rotatably mounted thereon, and eccentrically disposed on the outer circumference of the crank plate. An eccentric wheel having a tooth portion that meshes with the toothed belt, and a disk having a center hole that is concentrically and rotatably mounted on both sides of the eccentric ring on the outer periphery and that is rotatable with the rotating shaft. A pair of side plates,
A plurality of pins are disposed at equal intervals in the circumferential direction of the side plate, and both ends are supported by both side plates, respectively, and a plurality of pins that are one more than the wave number of the waveform portion on the outer periphery of the crank plate, and are rotatably supported by the pins. And a roller that rolls on a corrugated portion on the outer periphery of the crank plate, and a driving pulley is constituted by these elements. The epitrochoid curve refers to a locus drawn by a fixed point on the circumference of the small circle when the small diameter circle rolls in a circumscribed state along the large diameter fixed circle.

Further, the toothed belt has a length at which a slight slack occurs when the driving pulley is not loaded.

On the other hand, in the invention described in claim (2), the drive pulley has the following configuration.

That is, the drive pulley is composed of a crank plate made of a disk that is rotatably and integrally mounted on the rotating shaft and a disk that is concentrically and rotatably mounted on both sides of the crank plate on the inner periphery. A pair of side plates, a plurality of pins disposed at equal circumferential positions on the outer periphery of the side plates, and both ends of which are supported by both side plates, and a roller rotatably supported by each of the pins, It is arranged eccentrically with respect to the crank plate between both side plates, has teeth on the outer periphery that mesh with the toothed belt, and is formed on the inner periphery by a hypotrochoid curve having a wave number one greater than the number of pins, and And an eccentric wheel having a corrugated portion for rolling the roller. The epitrochoid curve is a locus drawn by a fixed point on the circumference of the small circle when the small diameter circle rolls in an inscribed state along the large diameter fixed circle.

(Operation) According to the above configuration, in the invention according to claim (1), when a driving force is applied to the rotating shaft on the driving pulley side, the crank plate rotates, and the driving force is transmitted from the corrugated portion on the outer periphery of the crank plate. The power is transmitted to the eccentric wheel via a roller on a pin engaging with the corrugated portion and the side plate, and further transmitted to the driven pulley via a toothed belt meshed with the outer periphery of the eccentric wheel. At that time, with the application of the driving force to the crank plate, the contact position between the plurality of rollers and the corrugated portion on the outer periphery of the crank plate changes continuously, and the center of the eccentric wheel is the axis of the crank plate (rotating shaft). It moves so as to rotate around the center while maintaining a predetermined amount of eccentricity with respect to the center. By this movement, the pitch circumference of the toothed belt is increased, and the slack is eliminated, so that an appropriate tension can be applied to the belt.

Power transmission from the crank plate to the eccentric wheel is performed by rolling the roller on the eccentric wheel side on a waveform portion formed of an epitrochoid curve on the outer periphery of the crank plate, and the number of rollers is larger than the wave number of the waveform portion. since one more, if the number of rollers (pin) a, the rotational speed of the crank plate (rotation axis) and N _a, the rotational speed N _B of the eccentric _{wheel, N B = {a / (} a + 1)} · N _A … For this reason, the eccentric wheel can be rotationally driven at substantially the same speed although the speed is reduced by the crank plate, without increasing the diameter of the drive pulley, so that the drive pulley can be reduced in weight and size.

In addition, since power is transmitted while all the rollers are in contact with the corrugated portion, in theory, half of the rollers contribute to the transmission of the driving force, so that even when a large driving force is applied, it is transmitted to each roller. It is possible to share the transmission and prevent damage to the rollers and the like.

Further, since the power is transmitted while each roller rolls with respect to the corrugated portion, the amount of eccentricity between the crank plate and the eccentric wheel is kept constant, and the engagement between each roller and the corrugated portion is not released, Both are always in a stable contact state, so that generation of noise can be prevented.

In the invention according to claim (2), unlike the above, the driving force applied to the crank plate is transmitted from the side plate on the outer periphery of the crank plate to the eccentric wheel via the pin, the roller, and the corrugated portion engaging with the roller. , And further transmitted to a driven pulley via a toothed belt. According to the present invention, the power transmission from the crank plate to the eccentric wheel is performed by the rollers on the crank plate side rolling on a waveform portion formed of a hypotrochoid curve on the inner periphery of the eccentric wheel. Since this number of rollers is one less than the number of waves of the waveform portion, the rotational speed N _B of the eccentric wheel the wave number of the corrugations a
Is given by the above equation. For this reason, the eccentric wheel can be driven to rotate at substantially the same speed by the crank plate without increasing the diameter of the drive pulley, and the weight and size of the drive pulley can be reduced. In addition, other functions are the same as those of the invention described in claim (1), and it is possible to prevent damage to the rollers and the like, reduce noise, and the like.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

1 to 4 show a first embodiment in which the present invention is applied to a drive system of a bicycle. 1 to 3, reference numeral 1 denotes a crankshaft as one rotating shaft rotatably supported by a bicycle frame (not shown), and 2 denotes a crankshaft arranged in parallel with the crankshaft 1 and rotates on the frame. A rear wheel axle, which is the other rotating shaft freely supported, supports the rear wheel (not shown) of the bicycle. As shown in enlarged detail in FIG. 1, a pair of crank arms 3 and 3 (only one is shown) are integrally mounted on the crankshaft 1 for rotation, and a pedal (not shown) is provided at an end thereof. The crankshaft 1 is rotationally driven by alternately depressing the pedals of the two crank arms 3,3. The mounting structure of each crank arm 3 will be described. The tip of the crankshaft 1 is formed with a tapered tapered portion 1a, and the tip of the crankshaft 1 is formed with a male thread.
1b is provided. On the other hand, the crank arm 3 has a boss portion 3a and a tapered hole 3b through which the tapered portion 1a can be inserted, and a nut fitting hole 3c that is continuous with the small-diameter side end thereof is formed concentrically. The tapered portion 1a of the crankshaft 1 is inserted through the tapered hole 3b of the crank arm 3, and the crank nut 4 is inserted into the male screw portion 1b protruding from the nut fitting hole 3c.
Are screwed and fastened, whereby the crank arm 3 is rotationally fixed to the crankshaft 1.

A toothed drive pulley 5 is attached to the crankshaft 1 so as to rotate integrally therewith. A driven pulley 14 having a diameter smaller than that of the driving pulley 5 and having a tooth portion 14a
The driven pulley 14 and the rear wheel are integrally connected to each other only in the driving rotation direction (counterclockwise direction in both figures) by a one-way clutch mechanism (not shown). This is between the two pulleys 5 and 14 and is wound around the toothed belt B having a tooth portion B ₁ in the bottom surface (inner circumferential surface), so as to transmit power to the rear wheel shaft 2 from the crank shaft 1 by the belt B Has been made.

The drive pulley 5 is provided with a boss 3a of the crank arm 3.
(Crankshaft 1) has a substantially disk-shaped crank plate 6 rotatably supported integrally. A waveform portion 7 formed by an epitrochoid curve is provided on the outer periphery of the crank plate 6, and the wave number of the waveform portion 7 is eight.

An eccentric wheel 8 slightly thicker than the crank plate 6 is disposed on the outer periphery of the crank plate 6 so as to be eccentric with respect to the axis O ₁ of the crank plate 6.
Teeth 8a which mesh with teeth B ₁ is formed.

On both sides of the eccentric ring 8, a pair of side plates 9, 9 each made of a disk are concentrically rotated by a bolt 10 penetrating the side plates 9, 9 and the eccentric ring 8 and a nut 11 fastened thereto. They are attached together. These side plates 9, 9 are fixed to the eccentric ring 8 at substantially their outer peripheral portions, and their outer peripheral edges slightly protrude radially outward from the outer peripheral surface of the eccentric ring 8, and the outer peripheral teeth 8a of the eccentric ring 8 are A pulley groove is formed, and the pulley groove regulates the movement of the toothed belt B in the width direction. Each side plate 9 has a center hole 9a at its center.
The center hole 9a has a diameter larger than the outer diameter of the boss 3a of the crank arm 3, and the crank arm boss 3a and the crank shaft 1 are loosely fitted in the center hole 9a,
The eccentric wheel 8 is made eccentric with respect to the crank plate 6.

Nine pins 12, 12,... Which are one more than the wave number (eight) of the corrugated portion 7 on the outer periphery of the crank plate 6 are provided near the inner periphery of the eccentric wheel 8 between the two side plates 9, 9. I have. These pins 1
Are arranged at equal intervals (40 °) in the circumferential direction of the side plate 9, and both ends of each of the two side plates 9, 9.
It is supported by. Each of the pins 12 is fitted into a bottomed hole 9b, 9b drilled in the facing surface of the side plate 9, 9, and the bolt 1
The side plate 9 and the eccentric ring 8 are integrally fixedly supported by the 0 and the nut 11 at the same time. Each of the pins 12 has a roller 13 that rolls on the corrugated portion 7 on the outer periphery of the crank plate 6.
Are rotatably supported by an oil-impregnated bearing or the like. Thus the center of the eccentric wheel 8 (side plate) is decentered with respect to the center O ₁ of the crank plate 6 (crankshaft 1) is adapted to rotate in its eccentric state.

Further, in order to allow the belt B to be hung between the pulleys 5 and 14 in a no-load state, and to tension the belt B in a load state to enable transmission, the toothed belt B is used.
Is a length at which a slight slack occurs when the drive pulley 5 is not loaded, and the axis O ₁ , O _{3 of the} crankshaft 1 and the rear wheel axle 2 are set.
And the straight line l _A connecting together, orthogonal and the straight line l loose side eccentric zone Z that is defined by a _B passing through the axis O ₁ of the crank shaft 1 to the straight line l _A, the axis O of the eccentric wheel 8 _The length is set so that ₂ is positioned eccentrically by a predetermined amount. Incidentally, the belt length is specifically in a range represented by the following equation. That is, between axes of the pitch circumferential length of the belt B Lp, the pitch diameter of the drive pulley 5 Dp, the pitch diameter of the driven pulley 14 dp, the axis O ₁ and the axis O ₃ of the rear wheel axis 2 of the crank shaft 1 Assuming that the distance is C and the amount of eccentricity between the axis O 1 of the crankshaft ₁ and the rotation center O ₂ of the eccentric wheel 8 is X, Lp> 2 (C−X) + π (Dp + dp) / 2 + (Dp−dp) ² / {4 (C−X)}... And Lp <2 (C + X) + π (Dp + dp) / 2 + (Dp−dp) ² / {4 (C + X)}.

In addition, the wave number and pin
Of course, the number of the rollers 12, 12,... (Rollers 13, 13,...) Can be increased or decreased to a plurality other than the illustrated example.

Next, the operation of the above embodiment will be described. Double pulley
In a no-load state in which power is not transmitted between the drive pulleys 5 and 14, the rollers 13, 13,... On the other hand, the eccentric wheel 8 is most deeply connected at the tension side (upper left side in the figure) of the straight line connecting the axis O ₁ and O _{2 of} the crankshaft 1 and the eccentric wheel 8. Is eccentric toward the belt B loose side (lower right in the figure) on the straight line.

When the crankshaft 1 rotates due to the stepping operation of the pedal from this state, the crank plate 6 integrated therewith rotates,
At this time, the eccentric wheel 8 does not rotate due to the regulation by the belt B. That is, although the corrugated portion 7 of the crank plate 6 rotates in the counterclockwise direction in the figure, the plurality of rollers 13 do not rotate around the axis O ₂ of the eccentric wheel 8. For this reason, each roller 13 moves in the clockwise direction relative to the waveform portion 7 in the clockwise direction.
Rolling on the upper part, the part where the rollers 13, 13,... Are most deeply connected to the corrugated part 7 moves from the upper left to the upper right through the upper part in the above-mentioned figure. Accordingly, the eccentric wheel 8 moves eccentrically from the lower right direction to the lower left direction through the lower direction in the figure while maintaining a predetermined eccentric amount with respect to the crankshaft 1. As a result, the eccentric wheel 8 moves in the direction of increasing the pitch circumference of the belt B, so that the belt B absorbs the slack and is given tension.

In a driving state in which the bicycle is running with the pedal fully depressed, the eccentric wheel 8 is positioned in the lower left direction with respect to the crankshaft 1 as shown by the solid line in FIGS. Is provided with tension. Therefore, at this time, the eccentric movement of the eccentric wheel 8 is restricted by the toothed belt B and stops. This regulation, the eccentric 8 to rotate its axis O ₂ around at that position, the power to the belt B traveling is transmitted to the driven pulley 14 by this rotation.

Therefore, in this embodiment, tension is applied to the belt B by the eccentric movement of the eccentric wheel 8 with respect to the crankshaft 1 in the drive pulley 5, so that the belt B is automatically tensioned without bending in the opposite direction to the normal direction. Can be
Even if the belt B is used for a long time, the damage can be suppressed.

The speed ratio from the crankshaft 1 to the eccentric wheel 8 is a roller.
Since the difference between the number of 13, 13,... And the wave number of the waveform portion 7 is one, it becomes 9: 8, and the rotation is reduced. However, the deceleration is extremely smaller than the conventional transmission structure in which the driving wheel and the floating wheel are engaged with each other, and can be regarded as substantially constant speed. Therefore, the driven pulley can be driven without increasing the outer diameter of the driving pulley 5 so much.
14 can be driven, and the transmission can be made lightweight and compact.

Further, since the power transmission is performed while all the rollers 13, 13,... Always roll on the corrugated portion 7, the eccentric wheel 8 moves to the equilibrium position at the time of driving while keeping the eccentric amount constant. In addition, the rollers 13 do not come off from the corrugated portion 7, so that they can always be kept in a stable contact state, and the generation of noise can be reduced.

In addition, in the transmission state of the driving force, since the plurality of rollers 13, 13,... Of the driving pulley 5 and half of the corrugated portion 7 share and transmit the driving force, even when the driving force is large, the rollers 13 Can be effectively prevented.

In addition, the eccentric range of the eccentric wheel 8 is extremely large in a range of approximately 180 ° on the side where the belt B is loosened, so that the pedal operation can be performed smoothly. Moreover, since the tension is gradually applied to the belt B during driving, the risk of damage is further reduced.

Further, since the amount of eccentricity of the eccentric wheel 8 is large, it is not necessary to make the accuracy of the length of the belt B strict when setting the length of the belt B, and the belt B can be easily wound around both the pulleys 5 and 14. Further, even if the belt B is stretched due to long-term use, the eccentric wheel 8 automatically moves so as to compensate for the stretch, and the belt B is stably tensioned. It can be used for a long time and its life can be extended.

5 and 6 show a second embodiment of the present invention.
1 and 3 are denoted by the same reference numerals, and detailed description thereof is omitted.)
(The roller 13) is replaced between the crank plate 6 'and the eccentric wheel 8'.

In this embodiment, a pair of side plates is provided on both sides of the crank plate 6 '.
The side plates 9, 9 are arranged concentrically and rotatably with respect to the crank plate 6 'at the inner periphery thereof by bolts 10 and nuts 11 penetrating through the crank plate 6' and the eccentric wheel 8 '. They are attached together. Nine pins 12, 12,... Are provided at equal angular intervals in the circumferential direction between the outer peripheral portions of the both side plates 9, 9 near the outer periphery of the crank plate 6 ', and a roller 13 is mounted on each of the pins 12. Rollably supported. In addition, each of the above pins
An eccentric ring 8 'is inserted between the side plates 9, 9 on the outer peripheral side from the position 12 so as to be eccentric to the crank plate 6', and the pins 12, 12,... One more than the number (9)
A corrugated portion 7 'formed by a hypotrochoid curve having a wave number of 10 and rolling each roller is provided.
Other configurations are the same as those of the first embodiment.

Therefore, in this embodiment, the driving force applied to the crank plate 6 'is applied to the pins 12, 1 from the side plate on the outer periphery of the crank plate 6'.
, The rollers 13, 13, ... and the corrugated portion 7 'engaged with the rollers 13, 13, ... are transmitted to the eccentric wheel 8', and the power from the crank plate 6 'to the eccentric wheel 8' is transmitted. The transmission is performed by rolling the rollers 13, 13,... On the crank plate 6 'side on a corrugated portion 7' formed of a hypotrochoid curve on the inner periphery of the eccentric wheel 8 '. Since the number of the rollers 13, 13,... Is one less than the wave number of the waveform portion 7 ', the eccentric wheel 8' is rotated by the crank plate 6 'at a substantially constant speed without increasing the diameter of the driving pulley 5'. The drive pulley 5 'can be driven, so that the weight and size of the drive pulley 5' can be reduced. The other operations are the same as those in the first embodiment, and it is possible to prevent the roller 13 and the like from being damaged and to reduce noise.

In each of the above embodiments, the present invention is applied to a drive system of a bicycle. However, the present invention can be applied to various belt transmissions requiring high durability.

(Effects of the Invention) As described above, according to the inventions set forth in claims (1) and (2), the drive pulley that transmits power between the driven pulley and the driven pulley by the toothed belt is rotatably integrated with the rotation shaft thereof. A crank plate supported on the crank plate, and a transmission mechanism including a corrugated portion formed of a cycloidal wavy curve and a plurality of rollers rolling on the corrugated portion provided on the crank plate so as to be eccentric to a predetermined amount. The toothed belt is constituted by an eccentric ring that is meshed with the toothed belt at the outer periphery and meshes with the toothed belt, and the length of the toothed belt is set to a length at which a slight slack occurs when the drive pulley is not loaded. Driving force can be transmitted without bending in the opposite direction to the normal direction, and the size of the driving pulley can be reduced to reduce the weight and size of the entire driving device. Noise can be reduced by the rolling of the rollers on the profile. In addition, by setting the belt length, the eccentric wheel can be eccentric with respect to the crank plate to obtain the belt tension effect while securing the engagement between the roller and the corrugated portion, and to obtain this automatic tension function. Increase the eccentric range and the amount of movement of the eccentric wheel to smooth the rotation of the drive pulley,
Damage to the toothed belt can be reduced, and it is not necessary to set the belt length with high accuracy. Furthermore, the belt can be easily wound around, and even if the belt is stretched, the transmission function can be ensured and the belt can be used continuously for a long period of time. As a result, not only the durability can be improved, but also the pedal operation can be smoothly performed, and this has practically excellent effects.

[Brief description of the drawings]

1 to 4 show a first embodiment of the present invention. FIG. 1 is an enlarged vertical sectional view of a driving pulley, FIG. 2 is a schematic front view showing a belt transmission device in a no-load state, and FIG. FIG. 4 is a schematic front view showing the same load state, and FIG. 4 is a schematic front view of the transmission showing the movement of the eccentric ring. 5 and 6 show the second embodiment. FIG. 5 is a diagram corresponding to FIG. 1, and FIG. 6 is a diagram corresponding to FIG. 7 and 8 are views corresponding to FIG. 3 showing a conventional example. 1 ... Crank shaft (rotating shaft) 2 ... Rear wheel shaft (rotating shaft) 5,5 '... Driving pulley 6,6' ... Crank plate 7,7 '... Corrugated portion 8,8' ... Eccentric wheel 8a, 8a '... tooth 9, 9' ... side plate 9a, 9a '... center hole 12 ... pin 13 ... roller 14 ... driven pulley 14a ... tooth B ... toothed belt O ₁ ... … Crank plate axis O ₂ … Eccentric ring axis O ₃ … Rear wheel axis

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F16H 7/00-7/24 F16H 55/32-55/56 F16H 1/32 B62M 9/00-9/16

Claims (2)

(57) [Claims] 1. A pair of rotating shafts parallel to each other, a driving and driven pulley composed of toothed pulleys respectively supported on the rotating shafts, and a power wound between the two pulleys wound between the two pulleys. A crank plate comprising a disk having a toothed belt for transmitting, the drive pulley being rotatably and integrally mounted concentrically on the rotating shaft, and having a wavy portion formed by an epitrochoid curve on the outer periphery; An eccentric wheel arranged eccentrically on the outer periphery of the crank plate and having teeth on the outer periphery for meshing with the toothed belt; A pair of side plates each formed of a circular plate having a center hole capable of loosely fitting; and a corrugated portion on the outer periphery of the crank plate, which is disposed at equal intervals in the circumferential direction of the side plates and both ends are supported by both side plates. One more than the wave number of And a roller rotatably supported by each of the pins and rolling on a corrugated portion on the outer periphery of the crank plate. The toothed belt has a slight slack when the driving pulley is not loaded. A belt transmission having an automatic tension adjustment mechanism, characterized in that the belt transmission has a length that causes the belt transmission. 2. A pair of rotating shafts parallel to each other, a driving and driven pulley comprising toothed pulleys respectively supported on the rotating shafts, and a power wound between the two pulleys to be wound between the two pulleys. A drive belt, the drive pulley comprising: a crank plate formed of a disk that is rotatably and integrally mounted concentrically on the rotation shaft; and a concentric inner periphery of both side surfaces of the crank plate. And a pair of side plates made of a disk attached to rotate integrally with each other; a plurality of pins arranged at equal circumferential positions on the outer periphery of the side plate, both ends of which are supported by both side plates; A roller rotatably supported, and disposed eccentrically with respect to the crank plate between the two side plates,
An eccentric wheel having a tooth portion meshing with the toothed belt on the outer periphery, and an eccentric wheel formed by a hypotrochoid curve having a wave number greater than the number of the pins by one and having a wave portion for rolling the roller on the inner periphery. A belt transmission having an automatic tension adjusting mechanism, wherein the toothed belt has a length that causes a slight slack when the driving pulley is not loaded.