籠谷 正則

One of the biggest problem of timing belt drives was its high noise level at high belt speed. For the purpose of noise reduction, the research and development of helical timing belts for automotive engines had been started more than 25 years ago in Japan. But the development failed because of the problem of tooth forms, belt materials, high helix angles etc. Recently the study and the development of helical timing belts with round shape tooth forms has started again. Helical timing belt are being used for medical instruments, office automation equipment, machine tools etc. The authors will describe the present state and the future of this new type helical timing belt currently in Japan.

Idlers are widely used in synchronous belt drives in order to adjust the center distance and increase the angle of contact. The attachment of an idler induces a meshing phase angle, which is thought to generate transmission error In the present study, the transmission error over a period of one pitch of the pulley under no load was investigated both theoretically and experimentally for synchronous belt drives with an idler attached on the belt span. The experimentally-obtained transmission error caused by the installation of the idler agrees closely with the computed results. The magnitude of the transmission error is affected by the position of the idler. In addition, the transmission error varies with idler diameter, becoming constant over a certain diameter. At small idler diameters, the transmission error increases.

One of the biggest problem of timing belt drives was its high noise level at high belt speed. For the purpose of noise reduction, the research and development of helical timing belts for automotive engines had been started more than 25 years ago in Japan. But the development failed because of the problem of tooth forms, belt materials, high helix angles etc. Recently the study and the development of helical timing belts with round shape tooth forms has started again. Helical timing belt are being used for medical instruments, office automation equipment, machine tools etc. The authors will describe the present state and the future of this new type helical timing belt currently in Japan.

Idlers are widely used in synchronous belt drives in order to adjust the center distance and increase the angle of contact. The attachment of an idler induces a meshing phase angle, which is thought to generate transmission error In the present study, the transmission error over a period of one pitch of the pulley under no load was investigated both theoretically and experimentally for synchronous belt drives with an idler attached on the belt span. The experimentally-obtained transmission error caused by the installation of the idler agrees closely with the computed results. The magnitude of the transmission error is affected by the position of the idler. In addition, the transmission error varies with idler diameter, becoming constant over a certain diameter. At small idler diameters, 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.

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.

Experiments on a transmission error caused by production errors in polychloroprene rubber timing belts were performed under a quasistatic condition and an initial tension. The experimental results were compared with the computed results obtained using the measurement results of the production error in the belt. It was confirmed that the transmission error, having a period of one revolution of the belt, was mainly caused by a single pitch error, a change in cross-sectional area of the load carrying cords and a change in modulus of elasticity for one revolution of the belt. As the experimental results coincided quite well with the computed ones, it was concluded that the measurement methods for the single pitch error and the belt elongation factor, and the arrangement methods of these values used to compute the transmission error were valid. Further, it was found that the transmission error due to the production error in the belt lessens when the initial tension becomes smaller.

Experiments on a transmission error caused by production errors in polychloroprene rubber timing belts were performed under a quasistatic condition and an initial tension. The experimental results were compared with the computed results obtained using the measurement results of the production error in the belt. It was confirmed that the transmission error, having a period of one revolution of the belt, was mainly caused by a single pitch error, a change in cross-sectional area of the load carrying cords and a change in modulus of elasticity for one revolution of the belt. As the experimental results coincided quite well with the computed ones, it was concluded that the measurement methods for the single pitch error and the belt elongation factor, and the arrangement methods of these values used to compute the transmission error were valid. Further, it was found that the transmission error due to the production error in the belt lessens when the initial tension becomes smaller.

A theoretical analysis is made for two kinds of noise reduction methods of timing belts. The methods are confirmed experimentally in a companion paper [1]. Modeling the traveling belt as a string with parametric excitation in tension and density, we obtain an approximate solution for the amplitude of the transverse vibration and carry out some numerical computations for the response of the belt. It is shown that the maximum amplitude of the transverse vibration at resonance is reduced by the two kinds of parametric excitation. The method of variable tension suppresses the maximum amplitude almost for all modes of vibration at resonance and that of the variable density is effective for higher modes except the first mode at resonance. © 1990 by ASME.