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The secret of CVT: Why does this transmission system make the vehicle as smooth as silk?
In modern automotive technology, continuously variable transmission (CVT) is gaining importance as it provides drivers with smooth and seamless power delivery. Unlike traditional fixed gear ratio transmissions, CVTs are able to vary within a continuous gear ratio range, which allows the engine to run at the optimal speed for better fuel efficiency and power performance.
The design principle of CVT is derived from a simplified mechanical structure, usually consisting of two pulleys with variable diameters and a belt or chain.
The working principle of a CVT involves a variable diameter pulley actuated by the engine, allowing for seamless adjustment of gear ratios compared to a traditional transmission's few fixed gear ratios. This means that the driver will not feel any abrupt changes during acceleration or deceleration, and this smooth transition makes the driving experience more pleasant.
Types of CVT
Pulley type CVT
Pulley-type CVTs are by far the most common type, typically using a V-belt running between two pulleys of variable diameter. This design allows the diameter of the pulley to vary with the distance between the pulleys, thereby adjusting the gear ratio. As the former approaches, the latter moves away accordingly to maintain the tension of the belt.
Due to the tight coupling between the pulleys and belt, this type of CVT can operate at up to 88 percent efficiency, which is less efficient than a manual transmission but makes up for it by keeping the engine running at its optimum rpm.
Hydraulic CVT
A hydraulic CVT uses an engine-driven positive displacement pump to send oil pressure to one or more hydraulic motors, which generate torque that is applied to the vehicle's drive wheels. The advantage of hydraulic CVT is its vague speed, which allows the vehicle to run smoothly at low speeds.
Torroidal CVT
The Toroidal CVT is another unique design that consists of a series of discs and rollers, which allows it to withstand higher torque loads than pulley-type CVTs. This design effectively avoids interference from external devices.
The advantage of Toroidal CVT is that it can better control power output under completely stepless transmission.
Other types of CVT
In addition to the CVTs mentioned above, there are also friction disc CVTs and other pinion-based designs, which are usually used in specific applications, such as agricultural machinery or some special vehicles.
Application of CVT in modern automobiles
CVT first appeared on the mass-produced Dutch DAF 600 in 1958, and was subsequently gradually used in a number of new cars. For example, hybrid models such as the Toyota Prius often use CVT systems to improve fuel efficiency and performance.
The successful rollout of these systems demonstrates the growing consumer demand for a smoother driving experience.
With the advancement of technology, this type of transmission is no longer limited to small cars, but is becoming more and more common in high-performance racing cars, showing an important development direction of future automotive technology. However, the CVT design is not without its drawbacks, and many drivers are wary of its performance in high-torque situations, leaving room for drivetrain improvement.
Among many transmission systems, CVT may be the trend of the future. As part of technological progress, it brings an unprecedented driving experience. However, whether such technology can be accepted by consumers in the long run and ensure the reliability of the transmission system is a question we need to think deeply about?
