In the automotive industry, quite significant changes are occurring. Every year, they develop the latest devices and systems that facilitate the driving process and improve the quality of car trips. Replaced by more modern solutions and automatic transmissions. Now, along with traditional torque converter automatic transmissions, manufacturers are equipping new models with a variable-speed transmission. Let's see what a CVT is, how it works, what advantages it has.
The advent of CVT
Automakers present the CVT as a novelty, but the stepless CVT was invented and developed many years ago. The first idea came to the talented head of Leonardo da Vinci in 1490.
However, they were able to translate it into reality only in 1950. The first passenger car, equipped with a variator gearbox, is the DAF 600. The transmission itself was called the Variomatik. Then this transmission began to be used in Volvo.
Difference of a variator from other transmissions
In modern manual gearboxes, five or more gears. In torque converter automatic transmissions - six or more. And in the variator there are no familiar steps. But that is not the whole difference. To clarify the situation, you need to consider the principle of the system. So we can understand why CVT transmissions are convenient.
In the usual gearbox with steps, there is one serious minus - these are fixed gear ratios, which sometimes in real conditions are not enough. Even if you move on absolutely even more expensive, the motor overcomes the force of inertia during acceleration. Then, after dialing the ideal ratio of speed and gear ratio, the engine accelerates the car. Next, the selected gear becomes low. To increase it, higher levels are needed, and in traditional gearboxes there is only a certain number of gears. In addition, a jerk is felt when shifting to a higher gear. Therefore, the engineers had a solution - they removed the steps from the transmission system. As a result, managers at car dealerships today offer cars with CVTs. Advertising says that gear changes in CVTs occur without any jerks. And indeed it is.
This mechanism changes the torque gradually on two disks or pulleys - a driven and a leading one. The movement begins smoothly, unlike other types of gearboxes. A car with a CVT feels like a powerful electric car. Speed ​​grows smoothly. There is no extraneous noise. It is believed that a car with a CVT accelerates faster.
In addition, the CVT transmission very, very significantly simplifies management. Even a novice car owner can handle this checkpoint. This type of transmission does not respond to driving style, and the engine will not be able to stall at a traffic light. Even with fast set speeds, the motor runs very quietly. If you press the gas pedal fully, the car will accelerate at lightning speed without the characteristic sounds.
Some drivers feel uncomfortable that the engine is not audible, and the ICE does not manifest itself at all when changing speeds. But this is not a flaw.
Leading auto brands have long established production of cars with CVTs. To distinguish designs from the total mass, each manufacturer dates its own name system. So, the Honda CVT has a name - Autotronic. Toyota calls these mechanisms the Multidrive system. X-Tronic and Hyper are Nissan CVTs.
CVT device
So, this is a mechanical unit, the main task of which is to transmit torque from the engine to the wheels of the car steplessly. In a sense, this is an automatic transmission, but the device is completely different.
The classic CVT has two pulleys. They can be moved apart. The pulleys are interconnected by a V-belt. The CVT in a modern car is a little more complicated, because there is a need for reverse and lower gears. CVT, or CVT transmission, is arranged as follows.
Sliding pulleys are the so-called “cheeks” mounted on one shaft. They are driven by a hydraulic cylinder compressing the discs depending on the speed of the crankshaft or by a signal from the control unit. But the variator and the box - the robot - are still different things.
Varieties of drives
Initially, a rubber belt was used to connect the pulleys. It was characterized by very low durability - its resource was only 50 thousand kilometers. The belt was not enough for efficient operation, low flexibility and a small bend angle. Therefore, the element does not allow you to adjust the engine speed ratio widely. Then they began to use more flexible metal V-belts. Rotation is transmitted by friction.
The wedge-shaped belt is made of metal strips on which steel plates are strung. These elements are located tightly together. The upper part of the plate has a conical shape. At the base there is a groove where metal tapes are installed.
When creating the “Multi-” and “Linetronic” models, the engineers went even further and began to use the chain in the box. These are V-chain variators. The chain is made of plates that are interconnected by axles. The design is more flexible. The moment is transmitted by the end part of the chain in contact with the conical disk.
A torque converter is used to transmit torque from the engine to the transmission. The differential serves to distribute power among the drive wheels. The reverse gear is made in the form of a planetary mechanism. The device also includes a hydraulic pump and a control system.
Operating principle
V-belt variator works as follows. The diameter of the pulleys varies depending on the mode in which the engine is running. The pulley diameters are changed by means of a special drive. At the beginning of movement, the driving element has the smallest diameter, and the disks are unclenched as much as possible. In this case, the driven disk has the maximum possible diameter. When the speed starts to increase, the drive pulley will increase the diameter, and the size of the driven shaft will decrease. Accordingly, the gear ratio is also reduced.
When the driver begins to press the accelerator, and the engine will gain momentum, the driving pulley increases in diameter, and the driven pulley decreases. Then, during acceleration, the automatic transmission variator will maintain the optimal engine mode, at which you can realize power and better dynamics.
Toroidal variator
Unlike V-belt and V-chain constructions, this box does not have chains or belts. Drives that are used instead of pulleys move. Work is carried out by means of rollers that create torque between the disks.
Gear ratios change when the rollers adjust position and radii. The rotation is carried out using a separate system. Rollers can change the force of pressing to the discs. Each variator of this type uses its own devices and technologies. A striking representative - the box-variator “Nissan X-Tronic”. Hydraulic roller control is implemented here. Rollers move up and down. I must say that this variator is quite rare. But it is believed that the future lies with these systems.
CVTs Nissan
The lineup of the brand is equipped with three types of CVT transmissions - these are CVT7 and two variants of CVT8. What are their features? Below we consider each of these types of boxes.
CVT7
This is not quite a variator, but a hybrid system. It combines a two-speed classic automatic transmission and a CVT transmission. Due to this symbiosis, it was possible to obtain small overall dimensions and a wide range of gear ratios. This model can be found on various models. This is “Centra”, “Tiida”, “Beetle”. Also installed a variator box on “Qashqai” with an engine of 1.2 liters. The mechanism withstands torque up to 180 Nm.
CVT8
This unit can be manufactured in two versions. The first option is designed for engines with an average volume, with a torque limit of - 250 Nm. This mechanism uses a steel belt. This transmission can be found on cars “Nissan Qashqai”, “X-Trail”, “Beetle”, as well as “Beetle Nismo” with engines of two liters.
For more powerful models, the second version of this variator is presented - it is able to digest a torque of 380 Nm. The model is designed for serious engines from 3 liters or more and diesel engines. A chain is used as a drive mechanism. Only she is able to withstand significant loads from the engine flywheel.
Toyota CVTs
The Toyota CVT has been installing on its cars since 2006. The first models K310 and K311 were equipped with engines of 1.5 and 1.8 liters. Since 2013, the Axio and Fielder models are installed on cars of any trim levels, regardless of the motor. The unit is a classic V-belt variator.
This gearbox (automatic variator) is arranged quite simply. There are two pulleys, a V-belt that connects the pulleys. The belt is metal. A torque converter is used to transmit torque. In general, this cavity is a classic device.
disadvantages
Any invention has various disadvantages. CVTs are no exception. Manufacturers try to eliminate weaknesses, but owners or potential owners should know about them:
- Boxes are not installed on cars with powerful engines, although there are already options that can digest serious torque. In case of breakdowns, the repair will result in a round sum. In addition, such nodes are not being repaired at all stations.
- The operation of the unit depends on many sensors, as it is electronically controlled. If at least one of the sensors fails, this will lead to incorrect operation of the entire system. The device also requires the filling of special liquids and constant level control.
- This transmission during operation experiences quite serious loads. There are restrictions on towing, as well as on movement with trailers. However, reviews about CVT boxes are generally positive.
Benefits
The first and most important is the comfort of car operation. Reviews say that the car moves smoothly - acceleration is fast, without jerking. When braking, there are also no jerks. Performance is stable even with a sufficiently long ride.
Due to more optimal engine loads, as well as well-designed unit operation, fuel can be saved. Reviews are a confirmation of this. The owners also say that the variator provides safety when driving on ice - wheel slippage is excluded. Auto CVT rides quieter than its counterparts with other gearboxes.
Conclusion
So, we found out how this transmission is arranged, what features and advantages it has. In general, reviews about CVT boxes are positive. Cars really smoothly begin to move, there are no problems with them on slippery roads. Beginners quickly learn this box. CVT are reliable enough if you do not violate the rules of operation. There is a myth that acceleration is slower than in automatic transmission. But this is a subjective opinion. In practice, a car with a CVT accelerates as fast as on a manual gearbox.