Another transmission article on another version of the CVT transmission — the toroidal CVT system — replaces the belts and pulleys with discs and power rollers.
Although such a system seems drastically different, all of the components are analogous to a belt-and-pulley system and lead to the same results — a continuously variable transmission. Here’s how it works:
One disc connects to the engine. This is equivalent to the driving pulley.
Another disc connects to the drive shaft. This is equivalent to the driven pulley.
Rollers, or wheels, located between the discs act like the belt, transmitting power from one disc to the other.
The wheels can rotate along two axes. They spin around the horizontal axis and tilt in or out around the vertical axis, which allows the wheels to touch the discs in different areas. When the wheels are in contact with the driving disc near the center, they must contact the driven disc near the rim, resulting in a reduction in speed and an increase in torque (i.e., low gear). When the wheels touch the driving disc near the rim, they must contact the driven disc near the center, resulting in an increase in speed and a decrease in torque (i.e., overdrive gear). A simple tilt of the wheels, then, incrementally changes the gear ratio, providing for smooth, nearly instantaneous ratio changes.
Both the pulley-and-V-belt CVT and the toroidal CVT are examples of frictional CVTs, which work by varying the radius of the contact point between two rotating objects. There is another type of CVT, known as a hydrostatic CVT, that uses variable-displacement pumps to vary the fluid flow into hydrostatic motors. In this type of transmission, the rotational motion of the engine operates a hydrostatic pump on the driving side. The pump converts rotational motion into fluid flow. Then, with a hydrostatic motor located on the driven side, the fluid flow is converted back into rotational motion.
Often, a hydrostatic transmission is combined with a planetary gearset and clutches to create a hybrid system known as a hydromechanical transmission. Hydro-mechanical transmissions transfer power from the engine to the wheels in three different modes. At a low speed, power is transmitted hydraulically, and at a high speed, power is transmitted mechanically. Between these extremes, the transmission uses both hydraulic and mechanical means to transfer power. Hydro-mechanical transmissions are ideal for heavy-duty applications, which is why they are common in agricultural tractors and all-terrain vehicles.
That being said, you are not likely to find a CVT of this ‘ilk’ in a car or truck. It would not stop me from calling 866-320-1182 to find a good used transmission for a commercial vehicle of some sort. Now, we have concluded our four part series on CVT transmissions, brought ti you by GotTransmissions.com Blog.
