The property of belt friction in an over-wrapped condition was studied. A fractional expression with respect to the ratio of belt tensions was derived by this study. The Euler's belt formula was included as a special case in the equation derived. The equation is a function of the contact angle θ and two kinds of the coefficient of friction µ and µ b , where θ is wrapping angle of a belt around a cylinder, µ is the coefficient of friction between the belt and the cylinder and µ b is the coefficient of friction between the belt and belt respectively. As the equation signifies the possibility of self-locking, the self-locking mechanism was investigated theoretically by the equation. It occurs when the discriminant of self-locking condition became 0 or negative. The necessary conditions for self-locking are µ b <µ and a sufficient over-wrapping angle of the belt. Providing the coefficient of friction µ and the ratio of the coefficients of friction κ=µ b /µ, some critical over-wrapping angles for self-locking were calculated numerically. Experiments were carried out to confirm the occurrence of self-locking predicted by the equation by using a polyethylene film to reduce friction between the belt. Self-locking occurred in the experiment with the polyethylene film wrapped around the belt. But it never occurred without the polyethylene film as predicted by the equation.

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By utilizing the self-locking property of belt, a novel one-way clutch was developed. This device uses a steel belt. It can transmit torque even under off-centered conditions. Some experiments were carried out under several off-centered conditions. The relation between the angular velocities ratio [Formula: see text] and the magnitude of off-centered distance δ was investigated. Here, the subscripts i and P denote the inner shaft and the power ring, respectively. The angular velocities obtained from the experiments were compared with the theoretical values. The experimental results almost corresponded to the theoretical calculations. When there is a parallel misalignment between input and output shafts, the belt is automatically coiled or uncoiled around the shaft with rotation. Some endurance tests on the clutch were also carried out by changing the magnitude of off-centered distance δ under a constant brake torque. The fatigue life of the belt was shortened by an increment of the off-centered distance.