上田 博之

Synchronous belt drives are widely used in various machines in order to transmit rotation accurately and synchronously. In these machines, idlers are commonly used to increase the angle of contact on the pulley and to avoid obstacles. However the generating source of the transmission error under a transmission force with an idler remains unclear In the present study, transmission error over a period of one pitch of the pulley was investigated both theoretically and experimentally for a synchronous belt drive attached an idler when a transmission force acted on the belt span. The experimental results agree closely with the computed results. The transmission error is greatly affected by change in the meshing state in the incomplete meshing sections. The idler position at which the transmission error is reduced exists even if the transmission torque increases. In addition, transmission error is reduced when the helix angle is increased.

はすば歯付ベルトの伝達トルク作用時の片寄りについて、原動プーリ上と従動プーリ上におけるベルトの軸方向移動のつりあいから理論解析を行い、計算結果と実験結果を比較検討した。その結果、走行中のベルトにおいて原動プーリ上と従動プーリ上との間にオフセットを生じる。ベルトの片寄りは、このオフセットと両プーリにおけるかみあい始めのベルト歯のせん断ひずみにより生じることがわかった。ベルトの片寄り量は、伝達トルクの増加とともに増加するが、伝達トルクが一定ならば、取付張力を低く設定することによって低減できる。

Helical timing belts have been developed in order to reduce the noise that occurs when conventional timing belts are driven. Helical timing belts are characterized by synchronous rotation. Although several studies have been performed to clarify the noise characteristics and belt life of helical timing belts, the transmission error of these belts remains unclear. In the present study, the transmission error having a period of one pitch of the pulley was investigated both theoretically and experimentally for helical timing belt drives. Experimental conditions were such that the transmission force acts on the helical timing belts under quasi-static conditions and the belt incurs belt climbing at the beginning of meshing and at the end of meshing. Experimental results obtained for the transmission error agreed closely with the computed results. The computed results revealed that helical timing belts can be analyzed as a set of very narrow belts for which the helix angle is zero. The transmission error was found to decrease when the helix angle or the belt width increase within a range defined such that the face advance is less than one belt pitch. In addition, there exists an appropriate installation tension that reduces the transmission error.

Idlers are widely used in synchronous belt drives in order to adjust the center distance and in order to increase the angle of contact. A meshing phase angle occurs when an idler is attached and this is thought to generate a transmission error. In the present study, a transmission error having a period of one pitch of the pulley was investigated both theoretically and experimentally for synchronous belt drives with an idler attached on the belt span. The experimental conditions were such that the speed ratio was one under a quasi-static condition and no load. The experimentally obtained transmission error that occurs due to the idler agrees closely with the computed result. In addition, changes in tooth load and frictional force have a greater influence than change in meshing phase angle on the magnitude of the transmission error. The magnitude of the transmission error is affected when the idler is moved in the direction normal to the bearing stand, and is unaffected when the idler is moved in the direction parallel to the bearing stand. Furthermore, when the diameter of the idler increases, the transmission error remains constant. However, when the diameter of the idler decreases, the transmission error increases.

A new helical timing belt has been developed to reduce noise. lit the present study, three belts, each having a curvilinear tooth profile and helix angles of 3 deg, 5 deg and 10 deg, respectively, were designed. The noise and life of the helical timing belt under a constant transmission force are compared with those of a conventional timing belt, in which the helix angle is zero. The noise level of the new helical belts having helix angles of 5 deg or 10 deg was found to be around 5 dB(A) lower than the conventional belt. The belt life was found to be almost identical for each type when the installation tension was set while the slack side tension for the transmission force was lowest. The results of the present study showed that helical belts should be selected for applications in which noise is a crucial factor.

Belt side tracking caused by the helix angle of the tooth trace of a helical synchronous belt under no load was investigated in the present study. Belt side tracking is an important problem because it influences the transmission characteristics, belt life and noise characteristics. Experimental results of belt side tracking were correlated the force on the belt tooth when the belt tooth began to mesh with the pulley tooth. It was confirmed that the amount of belt side tracking is proportional to the magnitude of the installation tension and the helix angle, and is inversely proportional to the belt width.

A new helical synchronous belt has been developed to reduce noise. However, in addition to the noise characteristics, the transmission characteristics must be considered. The present study examines experimentally the transmission error in a helical synchronous belt drive caused by side tracking of the belt due to the helix angle of the tooth trace. Experiments were performed under quasi-static conditions and no load. Experimental results suggested that the transmission error that occurs over the course of one belt revolution was caused by the change in the belt pitch when belt zigzagging was limited by optimization of the flanged pulley because of the axial force of the belt. These results are in good agreement with computed results that considered the change in the belt pitch. Thus, the side face of the belt should be processed appropriately, because belt zigzagging is introduced under normal conditions when the cylindrical belt has been cut to a constant width. When the installation tension is decreased and the distance between the driving and the driven shafts is shortened, this transmission error can be reduced.

騒音対策用に試作した円弧歯形のはすば歯付ベルトと従来のすぐば歯付ベルトの騒音と寿命について比較検討した。その結果，はすばベルトはかみ合い衝撃音が低下し、騒音低減効果が大であることが確認できた。その結果はねじれ書くが１０°が最も大きくすぐばベルトよりも騒音レベルは5db（A)程度低くなる。また、取付張力を適切に設定することにより、すぐばとはすばベルトの寿命は同程度にすることができる。

騒音低減を目的とした円弧歯形で、歯すじのねじれ角を3°、5°、10°のはすば歯付ベルトを試作し、通常の歯付ベルトと騒音を比較した。その結果、ねじれ角が大きくなるほど、騒音低減効果は大きく、ねじれ角が10°の場合、歯付ベルト特有のかみ合い衝撃音が発生していないことを確認した。また、その騒音レベルは、通常の歯付ベルトと比較して５～１０ｄｂ（A)程度低下しており、十分な騒音低減効果が得られることがわかった。

ねじれ角を５°と１０°傾けた騒音対策用のはすば歯付ベルトを試作し、負荷時における走行疲労実験を行い、耐久性の視点から実用化の可能性を検討した。その結果、いずれのねじれ角においても、寿命までの繰り返し数は、取付張力を伝達トルクに対してゆるみ側張力が最も低くなるように設定すれば、すぐば歯付ベルト（ねじれ角が0°）と同程度となった。このことにより、騒音低減が必要とされる場合、はすば歯付ベルトを使用すれば、寿命にしても問題ないことがわかった。

Using helical teeth for synchronous belt drives is very effective in reducing noise. However, it is necessary to find out how durable such belts are. In this study, running fatigue tests on both helical and conventional synchronous belts, used generally in industry and in vehicle engines, were carried out under a constant transmission force. The helix angles of the helical belts were 5゜and l0゜. Other dimensions were the same as those of conventional belts. The life of the helical belts was compared with that of the conventional belts. It was found that the belt life was almost the same for each type and was longest for both when installation tension set up as the slack side tension for the transmission force was the lowest. The results proved that when noise is a crucial factor, helical belts should be used.