The analysis focuses on the use of a CVT alone, without regenerative braking. This computer study and literature survey considers several examples of CVTs in buses, both with and without flywheel energy storage, and finds a predicted energy savings of 10 to 32 percent. It has been suggested that such transmissions may be of interest for two reasons: (1) simple substitution of a CVT in the place of a conventional transmission may offer fuel savings by allowing the engine to operate at its most efficient speed, and (2) the combination of a CVT and a flywheel allows regenerative braking, in which the vehicle kinetic energy during deceleration is captured for later re-use. ![]() This computer study and literature review is intended to provide insight into the potential applicability of CVTs to buses. However, a CVT can provide some fuel economy benefit with or without an energy-storing flywheel, which is the focus of this report. Flywheel systems require a continuously variable transmission (CVT) of some type to transmit power between the flywheel and the drive wheels. motorcycles), a centrifugal clutch is added to facilitate a "neutral" stance, which is useful when idling or manually reversing into a parking space.Numerous studies have been conducted on the concept of flywheel energy storage for buses. A CVT does not strictly require the presence of a clutch. This is typically higher than the RPM that achieves peak efficiency. ![]() When power is more important than economy, the ratio of the CVT can be changed to allow the engine to turn at the RPM at which it produces greatest power. A belt-driven design offers approximately 88% efficiency, which, while lower than that of a manual transmission, can be offset by lower production cost and by enabling the engine to run at its most efficient speed for a range of output speeds. ![]() The flexibility of a CVT allows the input shaft to maintain a constant angular velocity. This contrasts with other mechanical transmissions that offer a finite number of gear ratios. The underlying theories and mechanisms are also discussed.Ī continuously variable transmission (CVT) (also known as a single-speed transmission, stepless transmission, variable pulley transmission, or, in case of motorcycles, a twist-and-go) is an automatic transmission that can change seamlessly through a continuous range of effective gear ratios. This project report evaluates the current state of CVTs and upcoming research and development, set in the context of past development and problems traditionally associated with CVTs. For internal combustion engines this would be 36 percent, while for diesel engines it is 45 percent. This allows the engine to operate at or near its best brake specific fuel consumption rate, which means that the engine is operating at its highest average adiabatic efficiencies. Using a CVT-configured power train, the engine operates at or near maximum load conditions. The operational philosophy of conventional power trains makes it difficult to reach maximum engine fuel efficiency because the opportunities for operating at the lowest fuel consumption or best "brake specific fuel consumption" are restricted and generally do not agree with the torque and speed conditions imposed on the engine by the vehicle. Conventional power train configurations consist of an internal combustion engine operating across a wide range of torque and speed conditions and a transmission that has, by comparison, only a few discrete gear ratios. To achieve gains in this area, we have challenged the conventional thinking associated with power train functions and designs. This stems from the fact that transmissions operate over a range of power conditions, such as low speed-high torque to high speed-low torque, as well as through a variety of gear ratios. To achieve additional fuel economy improvements, we have begun to focus on increasing efficiency in areas where improvements are much more difficult and costly to achieve-largely on power train components such as the transmission. Unfortunately, improving the variables in that equation is becoming increasingly difficult. One hardly needs to be an automotive engineer to understand that the less fuel an engine consumes, the fewer pollutants produced, and the cleaner the air we breathe.
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