Continuously variable transmission

Continuously variable transmissions, as a rule, are classified according to the type of gear providing a stepless change in the gear ratio:

• Electric transmission - the engine rotates the generator, electric motors - wheels ( Belaz cars, DET-250 tractor, ZIS-154 ).
• Hydraulic volumetric transmission - the engine rotates an adjustable hydraulic pump, the oil flow through the tubes is fed to hydraulic motors, rotating wheels ( Don-1500 combine harvesters ).
• Hydrodynamic transmission, or torque converter, is a device made of wheels with blades located respectively, which transfer oil between the wheels. It goes well with the characteristics of the internal combustion engine, automatically changing the gear ratio, but the increase in torque is insignificant (up to 2.5) and requires an additional gearbox (used in most automatic transmissions of cars and buses).
• Variator - a mechanical transmission based on the transmission of rotation (moment) by friction through an intermediate body (belt, roller, ball), which can be transferred to any point of variable radius of the driving and / or driven wheels, receiving a change in the gear ratio. The most widely used is the V-belt variator (it is used in Niva combine harvesters, some models of modern passenger cars, scooters ).
• Combined transmission - the main point is transmitted through conventional mechanical gears, and the smaller part of the moment is stepless, which allows to combine to some extent the advantages of different types of gears.

At the heart of most modern automotive CVTs is a V-belt drive . One or both pulleys (master and slave) are equipped with sliding sidewalls; the gap between the sidewalls of the pulleys in the simplest case is determined by the centrifugal regulator, load couplings can also be used. With increasing engine speed and the drive shaft, the sides of the drive shaft are shifted, thereby the pulley’s bore diameter increases, and the gear ratio decreases.

Belt drive is suitable for mopeds and especially small class cars; for heavier machines, a chain drive is used on the same constructive principle.

It is advisable to use a disco-ball variator with an unlimited range of gear ratio in varioles of cars of small and middle class .

CVT History

The first continuously variable transmission was patented in 1886 . Since the 1950s, continuously variable transmissions have been widely used for airborne aircraft electric generators driven by auxiliary engines.

The first automobile continuously variable transmission with rubber V-belts was used in small-sized Dutch cars DAF ( DAF 600 ), and after the sale of the DAF department for passenger cars, Volvo inherited the patent.

In 1987, wedge CVTs with chain drive were launched into mass production by Ford and FIAT ( Ford Fiesta , FIAT Uno ). At the same time, Subaru started production of its CVT, which it supplied and is supplying to other automakers.

In the late 1990s, CVTs began to be installed on middle-class cars, instead of traditional hydromechanical automatic transmissions .

The CVT installed on the Toyota Prius , the developers called the PSD (Power Split Device, power distribution device, “three-way clutch”). A PSD was built on the basis of a planetary gear , where a generator is connected to the “sun”, a “satellite carrier” is connected to the engine, and a “ring gear” is connected to an electric motor and wheels. Since the ratio of the diameters (number of teeth) of the gears of the planetary gear is constant, the planetary gear divides the torque of the internal combustion engine in a constant ratio. However, the motor generator connected to the “sun” of the planetary gear can be more or less loaded with electric current.

The hybrid car system controller controls this process. The braking moment and, accordingly, the generator speed can vary over a wide range (from −6000 rpm to +6000 rpm), that is, the generator can also work as an electric motor. Therefore, the speed of rotation of the wheels of the car changes smoothly, steplessly. At the same time, the power received by the generator does not disappear - in the form of electrical energy it is supplied to the “traction” electric motor and, combining efforts with the engine torque, sets the car in motion. Such a hybrid drive is generally called a hybrid synergistic drive .

• Electric gear

• Continuously variable two-stream transmission for tractor and special equipment
• The device and features of automotive variators