This paper introduced the characteristics of flat and V-shaped belt which were driven through the frictional force determined by the aspect of tribology for mechanical designs. Basic properties of the frictional belts were shown, at first, to design the transmitting belt systems, and then classical theory describing the critical state of frictional forces and tensions of the belt was also explained for mechanical designs, while practical theory was also introduced to determine the actual properties of the belt in driven state. Some principal benefits of CVT (Continuously Variable Transmission) driven by frictional belt were also shown introducing the behavior of the belt due to the tilting of the pulley on the sliding shaft, as an example of determined features of the frictional V-belt type CVT.

Passenger vehicles which are equipped with metal-push belt type continuously variable transmissions (B-CVTs) are increasing in the world. Lubricant fluids for belt CVTs (B-CVTFs) must be able to produce a higher metal friction coefficient in order to improve the transmittable torque capacity between the belt and pulley in the CVT. Lubrication condition between the metals is known to be in boundary lubrication, which implies that lubricant additives would give a great impact on the metal friction characteristics. This review focuses how lubricants applied to B-CVTFs could control friction properties and how tribofilm properties link to a macro scale friction obtained by tribometers.

Flat-belt drives show lower bending loss and friction loss, and give higher transmission power compared to V-belt drives. However, control of meandering flat-belts has been the most concerned issue in practical use. Conventionally, flange pulleys and crown pulleys have been used to prevent belts from meandering. But, with these methods, it has been difficult to sufficiently demonstrate the performance of flat-belts and to avoid decreasing lifetime or transmission capability of belts. In this report, we introduce a new simple mechanism that doesn’t need external force such as electrical control and doesn’t have flange pulleys and crown pulleys. Also this mechanism offers autonomous control of meandering belts by tension of themselves. Finally, the abilities of flat-belts are fully demonstrated and that gives more energy-saving transmission system.

The fatigue failure mechanism was discussed caring out some observations of damaged rubber belts, especially CVT rubber belt and V-ribbed belt. Then, the life estimation and long-life strategy of them were developed basing on the discussions. There were three fatigue failure modes in CVT rubber belt, namely interface de-bonding at the inside of the belt by dishing deformation,shearing crack initiation at the side surface by the friction force and cog-bottom failure by belt-bending around pulleys. The fatigue life estimation was then performed for each failure mode. In V-ribbed belt, there were two failure modes for rib-top crack initiation. One was the friction failure at the side surface of the rib. The second one was the crack initiation at the inside of the rib near the rib-top. The crack initiation of the rib-inside failure was relatively important to strengthen the V-ribbed belt under commercial driving conditions.

Euler’s belt formula was reconsidered and expanded so as to apply it to multilayered wrapping conditions. A calculation method of tension, normal force and friction of a belt wrapped around a drum of any contour is explained. The frictional force of belt is enhanced by double-layered wrapping. Belt buckle uses this property to fix a belt by means of friction. It uses two axes to make double-layered condition and obtain self-locking state. A self-locking of belt can also be generated even on an axis by multilayered wrapping. The necessary conditions for a belt to become a self-locking state by multilayered wrapping on an axis is µ > µ_b, where μis the coefficient of friction between an axis and belt and µ_b is the coefficient of friction between belts. By using the property of self-locking, a belt-type one-way clutch was devised. This clutch can transmit rotational torque even in some off-centered conditions. However, angular velocity fluctuates according to the magnitude of off-centered distance. In order to decrease angular velocity fluctuation, a looped belt type one-way clutch was devised. The mechanism of this clutch is illustrated.

Two-cylinder type rolling contact fatigue (RCF) testing under an insufficient lubricating condition was conducted to investigate the mechanism of peeling, in which many small cracks were observed at RCF surfaces. The effect of black oxide treatment on the suppression of peeling was also investigated. Surface roughness of two-cylinder sets made of JIS-SUJ2 were adjusted to bring about peeling on the driven cylinder surface, which had a lower surface roughness. Measurement of surface roughness and observation of surface texture were carried out by using a laser microscope and a field emission scanning electron microscope (FE-SEM), respectively. The results showed that the initial cracks of peeling were formed by plastic deformation, which occurred due to the severe contacts of surface roughness asperities. When the black oxide treatment was applied to the driving cylinder, a reduction of driving cylinder’s surface roughness during rolling contact, i.e., “running-in”, was significantly promoted. This significant promotion of running-in leads to a reduction of the severity for asperity contact, and therefore results in the suppression of peeling.

This paper presents a study of the environmental performance impact of a comprehensive set of conventional viscosity lubricants and latest low viscosity lubricants, considering the use for average fuel economy passenger vehicle (118.1g-CO₂/km in 2016). The vehicle was assumed to be equipped with either automatic transmission (AT) or contentiously variable transmission (CVT) with a lifetime mileage of 150 000km. Engine oil, transmission fluid as well as oil filter were identified as requiring servicing (replacement) in the maintenance phase. It was found that the analyzed engine oil, AT fluid and CVT fluid with different formulations show almost identical CO₂ emissions per weight from the lubricants production, and the contribution of the oil filters and the transmission fluids to CO₂ emissions in the maintenance phase accounts for over 20%. The latest low viscosity lubricants improved vehicle fuel economy by up to 4.0% compared to conventional viscosity lubricants. As a consequence, latest lubricants have the potential to save the vehicle life cycle CO₂ emissions by up to 630kg-CO₂ even when subtracting the produced CO₂ emissions in the maintenance phase, with comparison of conventional viscosity lubricants.