Smooth operation, a huge range of gear ratios and the ability to adapt them to the situation are the advantages of stepless CVT cases. There is also the other side of the coin – power losses, performance degradation, increased combustion and limited gear life.
Gearboxes are an essential component in cars with internal combustion engines. They solve the issue of limited range of useful power unit revolutions. The commonly used method of torque transmission and multiplication is not without flaws. Gears must be switched, which means that the transfer of propulsive forces is not continuous, and the rapidly changing speed of the crankshaft means that the engine only works for a short time in the optimal range of rotation.
The shortcomings of classic transmissions have been minimized by increasing the number of gears – 6-speed gearboxes can even be found in segment B cars. In the case of “automatic machines” 7-, 8- and even 9-speed gears are increasingly at stake, which are rapidly changed; in both double clutch gearboxes and gearboxes with a torque converter.
The most precise gear matching to the situation is possible on vehicles with continuously variable CVT (Continuously Variable Transmission) transmissions. The change takes place without jerks and breaks in the supply of driving forces. The controller takes into account, among others the power train load, and the rate and degree of pressure on the accelerator pedal.
If full acceleration is needed, the CVT can constantly maintain high revs (e.g. 5500 rpm) – until the pressure on the accelerator pedal is reduced. The situation is reversed when the driver begins to gently operate the right pedal or travels at a constant speed. Then the engine starts at low speed. At 130 km / h, the Audi tachometer with continuously variable Multitronic transmission indicates 2450 rpm. If the car had a manual 5-speed transmission, the engine would spin at 3200 rpm, burning larger amounts of fuel and making more noise.
Sounds great … Why didn’t CVT cases become popular? The majority of drivers cannot accept maintaining steady turns during acceleration. The scale of the phenomenon has been limited in many models. In sport or manual mode, the CVT transmission begins to work like a classic “automatic”, switching electronically programmed gears.
The owner of a car with a continuously variable transmission should remember that sharp starts, long-term driving at high speed, towing trailers or attempting to drive on deep snow or a pit road are not used for the mechanics of the continuously variable transmission. They get all the bones in the bone, including the belt.
In modern cars, belt transmissions are the most popular. Their heart is a variator – a set of two pairs of conical discs between which a chain is stretched. Gear ratios change simultaneously (from the largest, when starting, to the smallest after stabilizing the speed), thanks to which the chain remains optimally pressed against the discs. The work of modern CVT boxes is controlled by electrohydraulic systems. They ensure not only the variator settings, but also multi-plate clutches, which are responsible for idling creep, starting and reversing.
The gearboxes are designed for a specific torque load. Most manual gearboxes endure power lifting attempts. For stepless chests, the margin is small. For example, developed by Audi Multitronic withstands up to 400 Nm. That’s the 3.0 TDI for the A6 model. In the four-wheel drive version with the S tronic dual clutch transmission, the torque was set at 450 Nm. The release of reserves in the A6 with the Multitronic transmission is possible, but the operation will not work out for good.
Transmission life varies greatly. In aggressively treated cars, the chest can give up a ghost of 100,000 km. If the driver does not regularly press the gas to the floor, he will have to repair the chest after 200-250 thousand. km. The costs of the operation are high – you have to spend from a few to several thousand zlotys. The advent of problems with the CVT gearbox most often heralds metallic noises, jerks, creep in N mode, or no creep or stalling after moving the gearbox selector to position D.
Stepless gears are available under different trade names. Some brands, e.g. Mitsubishi, use the CVT mark. In Audi we will find Multitronic transmissions, in Mercedes (older classes A and B) – Autotronic, in Nissan – X-tronic, Seats (only in Exeo) – Multitronic, in Subaru – Lineartronic, in Toyota – Multidrive S.
The infinitely variable transmission is the fastest to find in a Japanese car – new or used. On the secondary market, you can find “exotic” offers, such as Jeeps Patriot and Compass 2.4 CVT, Fiat Punto II 1.2 Speedgear CVT, Ford C-Max 1.6 TDCi CVT or MG F Stepspeed roadsters. Rare models can be a source of problems – there are no companies that would be able to quickly diagnose cross-sectional issues