How to choose gear box: advantages and disadvantages of CVT

About variators say a lot, some praise, others criticize. We would like to understand the advantages and disadvantages of automotive CVTs.

2015-11-14 11:52:34 311

speedspeed rotationcheeks pulleyaccelerator pedaladvantages disadvantagesautomatic transmission

Device and principle of operation of the variator

To understand the principle of operation of this mechanism, it is necessary to consider the device a V-belt variator. It consists of two pulleys connected by a V-belt. The pulleys are assembled from conical disks, which are able to shift and move apart, thus changing the diameter of the pulleys. To move the vehicle to its wheels it is necessary to make a considerable effort, the speed of rotation of the drive wheels of the machine should be small, and the torque is maximum. All of the above fully applies to the driven shaft of the gearbox, because the force to the wheels of the car passed from him. After you start the engine and turn the transmission, the rotational motion from the crankshaft through a clutch or torque Converter is transmitted to the driving shaft of the variator. At this point only the drive shaft begins to spin, the distance between the cheeks of the pulley is a maximum, the radius of the pulley is minimal. In the slave drive, everything is exactly the opposite: the distance between the cheeks of the pulley is minimum and the radius of the pulley is possible. Driven shaft will have a maximum torque and to rotate at low speed. The driver continues to press the accelerator pedal, the engine speed grow and the speed of rotation of the drive shaft of the variator increases. The cheeks of the pulley under the influence of centrifugal force is compressed, pushing the belt in the direction opposite from the city centre. The cheeks of the driven pulleys, on the contrary, unclenched, allowing the belt to move closer to the center. So, with increasing engine speed and increasing the speed of rotation of the driving pulley, its diameter increases and the diameter of the driven pulley decreases. As a result, the torque transmitted to the driven disk (and therefore to the wheels) is reduced, and the speed of its rotation increases. In addition there is a V-belt variator CVT toroidal: it is the change in torque and the gear ratio between the disks occurs by changing the position of the rollers.

Advantages of CVT

Due to the lack of a rigid connection between the engine and the wheels, in a car with a CVT there is no moment of release when changing gear, so the connection between the engine and the wheels there constantly, and the craving grows and shrinks smoothly, which is very beneficial to stability and drivability, especially in adverse weather, ice or heavy rain. A car equipped with CVT, has excellent dynamics, if necessary he is able to quickly accelerate and effectively slow down the speed of their movement. It never stalls at traffic lights during the starting and on the rise is not rolled back. Due to the infinite number of speeds of the variator, the engine of this car operates in the optimal mode with rated power, saving the resources of their mechanisms and consumes significantly less fuel than the same motors with mechanical or automatic transmissions. The level of harmful substances in exhaust gases of cars with the CVT is significantly lower than that of similar models with the "mechanics" or "automatic", and the level of noise of the engine, below half.


The use of the variator is limited by the power of the engine, engines with power of over 220 horsepower, these devices are not installed. Repair variator – quite complex and expensive. Each model of transmission requires the use of a certain type of gear oil. Using the wrong type of oil can cause gearbox failure. For movement on the vehicle equipped with the CVT have to make adjustments in his riding style: pull away with spinning the wheels will not succeed, and to perform complex maneuvers of the call type of entry or speed exit of the turn press on the accelerator pedal should be somewhat earlier than in cars with manual or automatic transmission. Good luck to you! No nail, no wand!

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