Variator from A to Z

A CVT-type transmission from the passenger compartment of a stationary car is practically indistinguishable from a familiar automatic machine. Here you can see the selector lever and the familiar letters PNDR, there is no clutch pedal. How does a continuously variable CVT transmission work in modern cars? What is the difference between a toroidal and a V-belt variator? This will be discussed in the following article.

CVT - continuously variable transmission

Among the varieties of transmissions, a stepless variator stands out, which is responsible for transmitting torque. First, a little historical background.

CVT history

When it comes to the background of the variator device, the personality of Leonardo da Vinci (1452-1519) is mentioned. In the works of the Italian artist and scientist, one can find the first descriptions of a continuously variable transmission that has seriously changed by the XNUMXst century. The millers of the Middle Ages also knew the principle underlying the device. Using a belt drive and cones, millers manually acted on the millstones and changed the speed of their rotation.

Almost 400 years passed before the appearance of the first patent for an invention. We are talking about a toroidal variator patented in 1886 in Europe. The successful use of CVT transmissions on racing motorcycles led to the fact that at the beginning of the XNUMXth century a ban on the participation of equipment equipped with CVTs was introduced in the competition. To maintain healthy competition, such prohibitions made themselves felt throughout the last century.

The first use of an automobile variator dates back to 1928. Then, thanks to the efforts of the developers of the British company Clyno Engineering, a car with a CVT-type transmission was obtained. Due to the underdevelopment of technology, the machine was not distinguished by reliability and high efficiency.

A new round of history took place in Holland. The owner of the DAF concern, Van Dorn, developed and implemented the Variomatic design. The plant's products are the first variant of mass application.

Today, world-famous companies from Japan, the USA, Germany are actively practicing the installation of continuously variable transmissions on cars. To meet the conditions of the time, the device is constantly being improved.

What is CVT

CVT stands for Continuous Variable Transmission. Translated from English, this means "continuously changing transmission." In fact, continuity is manifested by the fact that the change in gear ratio is not felt by the driver in any way (there are no characteristic shocks). The transmission of torque from the motor to the drive wheels is realized without the use of a limited number of steps, so the transmission is called continuously variable. If the designation CVT is found in the marking of the car configuration, then we are talking about the fact that a variator is used.

Types of variators

The structural element responsible for transmitting torque from the drive shaft to the driven shaft can be a V-belt, chain or roller. If the specified design feature is chosen as the basis for classification, then the following CVT options will be obtained:

• V-belt;
• cuneiform;
• toroidal.

These types of transmissions are used mainly in the automotive industry, although there are much more options for devices responsible for a smooth change in gear ratio.

Why stepless transmission is needed

Thanks to the stepless transmission, the internal combustion engine will transmit torque without delay at any time of its operation. Such delays occur when the gear ratio changes. For example, when the driver shifts the manual transmission lever to another position or the automatic transmission does its job. Due to the continuous transmission, the car smoothly picks up speed, the efficiency of the motor increases, and a certain fuel economy is achieved.

The device and principle of operation of the variator

Questions about what the device of the variator is and what the principle of its operation will be discussed in more detail. But first you need to identify what are the main structural elements.

Main Components

The CVT transmission includes a driving and driven pulleys, a belt (chain or roller) connecting them, and a control system. The pulleys are located on the shafts and look like two halves of a conical shape, facing each other with the tops of the cones. The peculiarity of the cones is that they can converge and diverge in a given range. More precisely, one cone moves, while the other remains motionless. The movement of the pulleys on the shafts is controlled by a control system that receives data from the vehicle's on-board computer.

Also the main components of CVT are:

• torque converter (responsible for transmitting torque from the engine to the input shaft of the transmission);
• valve body (supplies oil to rotating pulleys);
• filters to protect against the production of metal and deposits;
• radiators (remove heat from the box);
• planetary mechanism that provides reverse movement of the car.

V-belt variator

The V-belt variator is represented by two sliding and expanding pulleys connected by a metal belt. By reducing the diameter of the drive pulley, a simultaneous increase in the diameter of the driven pulley occurs, which indicates a reduction gear. Increasing the diameter of the drive pulley gives an overdrive.

Changing the pressure of the working fluid affects the movement of the cone of the drive pulley. The driven pulley changes its diameter thanks to a tensioned belt and a return spring. Even a slight change in pressure in the transmission affects the gear ratio.

Belt device

The belt-shaped CVT belt consists of metal cables or strips. Their number can reach up to 12 pieces. The strips are located one above the other and fastened together with steel staples. The complex shape of the brackets allows not only to fasten the strips, but also to provide the contact with the pulleys necessary for the operation of the transmission.

Protection against rapid wear is provided by the coating. It also prevents the belt from slipping over the pulleys during operation. In modern cars, it is unprofitable to use leather or silicone belts due to the small resource of the part.

V-chain variator

The V-chain variator is similar to the V-belt, only the chain plays the role of a transmitter between the drive and driven shafts. The end of the chain, which touches the conical surface of the pulleys, is responsible for the transmission of torque.

Due to its greater flexibility, the V-chain version of the CVT is highly efficient.

The principle of its operation is exactly the same as that of a transmission with a belt drive.

Chain device

The chain consists of metal plates, each of which has connecting lugs. Due to the movable connection between the plates in the chain design, they provide flexibility and keep the torque at a given level. Due to the links arranged in a checkerboard pattern, the chain has high strength.

The breaking force of the chain is higher than that of the belt. Lug inserts are made from alloys that resist rapid wear. They are closed with the help of inserts, the shape of which is semi-cylindrical. The design feature of chains is that they can stretch. This fact affects the operation of the continuously variable transmission, therefore, it requires close attention during scheduled maintenance.

Toroidal variator

The toroidal type of CVT gearbox is less common. A notable feature of the device is that instead of a belt or chain, rotating rollers are used here (around its axis, pendulum movements from the drive pulley to the driven one).

The principle of operation is the simultaneous movement of the rollers on the surface of the halves of the pulleys. The surface of the halves have the shape of a toroid, hence the name of the transmission. If the contact with the driving disk is realized on the line of the largest radius, then the point of contact with the driven disk will lie on the line of the smallest radius. This position corresponds to the overdrive mode. When the rollers move towards the driven shaft, the gear is downshifted.

CVT in the automotive industry

Automotive brands are developing their own options for continuously variable transmission. Each concern names the development in its own way:

1. Durashift CVT, Ecotronic - American version from Ford;
2. Multitronic and Autotronic - German CVTs from Audi and Mercedes-Benz;
3. Multidrive (Toyota), Lineartronic (Subaru), X-Tronic and Hyper (Nissan), Multimatic (Honda) - these names can be found among Japanese manufacturers.

Pros and cons of the CVT

Like a manual or automatic transmission, a continuously variable transmission has its pros and cons. The advantages are:

• comfortable movement by car (position “D” on the selector is set before the start of movement, the engine accelerates and slows down the car without jerks characteristic of mechanics and automatic);
• uniform load on the engine, which is combined with the precise operation of the transmission and contributes to fuel economy;
• reduced emissions of harmful substances into the atmosphere;
• dynamic acceleration of the car;
• missing wheel slip, which increases safety (especially when it comes to driving in icy conditions).

Of the minuses of a continuously variable transmission, attention is drawn to themselves:

• a design limitation on the combination of a variator with powerful internal combustion engines (so far we can only talk about a few cars with such a tandem);
• limited resource even with regular maintenance;
• expensive repairs (purchase);
• high risks when buying a used car with CVT (from the “pig in a poke” series, since it is not known for certain how the previous owner operated the car being sold);
• a small number of service centers in which the masters would take up the repair of the device (everyone knows about CVTs);
• restriction on towing and trailer use;
• dependence on monitoring sensors (on-board computer in the event of a malfunction will give incorrect data for operation);
• expensive gear oil and the requirement for constant monitoring of its level.

CVT resource

The nuances of operation (road conditions, driving style) and the frequency of maintenance of a CVT transmission affect the resource of the device.

If the manufacturer's instructions are not followed, if the regular maintenance regulations are violated, it is useless to count on a long service life.

The resource is 150 thousand km, the transmission, as a rule, does not nurse more. There are isolated cases when the CVT was changed as part of the warranty repair on cars that did not pass 30 thousand km. But this is an exception to the rule. The main unit that affects the service life is the belt (chain). The part requires driver's attention, because with heavy wear, the CVT can completely break.

Conclusions

When it comes to cars with continuously variable torque transmission, there is a reason for negative assessments. The reason is that the node requires regular maintenance, and its resource is small. The question of whether to buy a car with CVT, everyone decides on their own. The transmission has advantages and disadvantages. In conclusion, you can give a warning comment - when buying a used car with a CVT, you need to be extremely careful. The owner of a used car can hide the features of operation, and the CVT in this regard is a sensitive option for a mechanical transmission.