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The torque controlled full toroidal IVT (Infinitely Variable Transmission) provides significant fuel economy benefit over conventional stepped ratio transmissions. This is achieved, in part, by using high overdrive ratios. This benefit must be provided alongside good driveability, which requires the system to have a fast response while being well damped. This paper gives a theoretical overview of the dynamic response of the IVT focusing on different interactions between the full toroidal variator and hydraulic control circuits. The concept of system stability is applied to sub-systems and their interactions to indicate design requirements of this torque controlled transmission.

The present IVT (Infinitely Variable Transmission) is built around a full toroidal variator where high forces acting on low inertia characterize it as a smooth and responsive system. Because of the complex and frequent motions of the rollers, the variator dynamics plays a key role in the transmission. Furthermore, the IVT requires detailed description of the interactions between variator, driveline and hydraulic for an optimum control development. Accurate variator dynamic investigation is therefore a vital element of the modeling requirement. A complete one-roller model of a full toroidal variator including mechanic and hydraulic parts is presented in this paper. The roller movement is described in response to a torque and a speed ratio change. A six-roller model is then introduced to highlight the difference between the rollers behavior.

A full-toroidal CVT has been expected as a new generation of transmission. However, high contact pressure is needed to generate traction force and temperature due to shear in contact areas becomes very high. Therefore, the fatigue life of variator is insufficient. This paper describes the application of developed bearing steel to improve the fatigue life of the varitator. Failure due to pitting depends on a film parameter Λ so that the limitation of Λ to prevent failure has been determined by a two roller test machine. Durability test of the variator made of developed bearing steel with the larger Λ than the limitation has been carried out to confirm the prevention of pitting by a dual-cavity full-toroidal CVT's variator test rig. The thickness of EHD (Elastohydrodynamic) fluid film has also been calculated by isothermal Newtonian EHD analysis with spin motion to confirm whether adequate film thickness is provided to avoid failure.

Many types of variable speed accessory drive systems have been researched and developed, but none have been adopted in a production car1,2. There has been an increasing demand on the accessory drive system due to the adoption of new accessories in passenger cars. Along with the increasing demand on the system, nothing can be done which would decrease fuel economy. So, the efficiency of the system must be improved. This has caused renewed interest in variable speed accessory drives. A compact V-ribbed (serpentine) belt CVT system for accessory drive (called CVAD: Continuously Variable Accessory Drive System) has been developed3. By applying the CVAD for the accessory belt drive system, fuel savings, increased vehicle performance in acceleration, noise reduction, increased life of accessories and V-ribbed belts, and a reduction in the size of accessories are possible. The performance of a prototype variator, the principal component of the CVAD, has been evaluated.