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Transmissions and Transmission Fluids
Published in Leslie R. Rudnick, Synthetics, Mineral Oils, and Bio-Based Lubricants, 2020
Scott Halley, Timothy Newcomb, Richard Vickerman
A CVT is a transmission which theoretically has an infinite number of available gear ratios, and the shift steps are imperceptible and unnoticed. The most common CVT relies on a belt or chain looped around two variable diameter pulleys, called variators, as shown here (Figure 34.6).
Automotive Systems/Robotic Vehicles
Published in Shuzhi Sam Ge, Frank L. Lewis, Autonomous Mobile Robots, 2018
Michel R. Parent, Stéphane R. Petti
The engine torque (and furthermore, the torque available at the wheel which controls the vehicle acceleration) is also dependant on the rotation speed of the engine which in turn depends on the gear ratio. This gear ratio can be changed manually through the gear box and through the clutch operated with a pedal. This combination of clutch and gearbox can be replaced by a hydraulic gearbox with mechanical or nowadays electronic selection of the gear. Some vehicles also use continuously changing gear ratios (the CVT or Continuously Variable Transmission) through a system of two variable diameter pulleys and a belt (see Figure 16.9). Modern CVT offer full electronic control of the transmission ratio. Another approach for a fine control of the torque available at the wheel while minimizing the emissions is the “robotized gearbox.” In this approach, an electronic controller (sometimes replaced by buttons or levers operated by the driver as in Formula 1 racing) pilots an actuator which operates the clutch and another actuator which changes the gears.
Vehicle Transmission
Published in Mehrdad Ehsani, Yimin Gao, Stefano Longo, Kambiz M. Ebrahimi, Modern Electric, Hybrid Electric, and Fuel Cell Vehicles, 2018
Mehrdad Ehsani, Yimin Gao, Stefano Longo, Kambiz M. Ebrahimi
A CVT has a gear ratio that can be varied continuously within a certain range, thus providing an infinite number of gears. The continuous variation makes it possible to match virtually any engine speed and torque to any wheel speed and torque. It is, therefore, possible to achieve an ideal torque–speed profile (constant power profile).
Interactive Effect between Organic Friction Modifiers and Additives on Friction at Metal Pushing V-Belt CVT Components
Published in Tribology Transactions, 2018
Yasushi Onumata, Hongyuan Zhao, Chun Wang, Ardian Morina, Anne Neville
The emission of CO2 from automobiles is a global concern; the legislative pressures and environmental demands are annually being increased. In order to comply with the legislation, car manufacturers put their priority on improving fuel efficiency, and some advanced transmission systems, such as metal pushing V-belt continuously variable transmission (CVT) and dual clutch transmission (DCT), have been developed to increase their market share (Murakami (1); Abo and Kobayashi (2); Matthes (3)). The CVT is capable of improving fuel efficiency by continuously changing the gear ratio, which makes it possible to operate the engine under more efficient conditions. This continuous gear shift is achieved by a steel belt–pulley mechanism (Okamura (4)), where a torque input from the engine is transferred through steel–steel contact between the belt and the pulley as shown in Fig. 1. Minor slip generally occurs at the belt–pulley contact as a result of the mechanical configuration (Oshidari (5); Ando, et al. (6)); therefore, the steel–steel contact friction at low sliding speeds should be kept at a sufficient level to reduce the risk of macroscopic slip, leading to damage in the transmission. On the other hand, a paper clutch system is also installed at a torque converter of the CVT. It consists of a paper clutch plate and a counter steel plate, and the clutch engagement should be controlled appropriately to prevent vibration, often referred to as shudder (Yoshimura (7)). It is generally considered that a relationship between the friction coefficient (µ) and the sliding speed (V) of the clutch paper material (µ-V characteristics) is an essential factor, because the theoretical analysis reported by Kugimiya, et al. (8) indicated that a positive µ-V slope is capable of preventing a self-induced vibration. Therefore, it is preferable to manage the friction lower in a low sliding speed region (Zhao, et al. (9)).