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The half-toroidal CVT is an innovative transmission that executes
smooth, continuous gear ratio changes by changing the angle of the
power rollers between the input disk and output disk. Toroidal CVT
development began in 1877. One hundred years later, NSK undertook
its development in 1978, spending as much as 21 years to develop a
practical application. Featuring smooth, silent, and continuous gear
ratio changes, as well contributing to conserving energy and further
reduction of CO2 emissions,
the highly efficient half-toroidal CVT POWERTOROS Unit is the desired
transmission that is a result of NSK's advanced technology in tribology.
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•Tribology in Half Toroidal CVT
Power can be transmitted much more smoothly if
the gear teeth that transmit power are made as small as possible.
Although a half-toroidal CVT has not real gear teeth, power is transmitted
by
a mechanism called traction drive. In the half-toroidal CVT, which
achieves a quiet and smooth transmission of great power, is a layer
of oil that is pressurized under an extreme load to approximately
1/1000 mm thick at the point of contact between the disc and power
roller. This special oil has a characteristic of forming into
a glass-like substance under high pressure. Power is transmitted from
the disc to the oil, and then to the power roller. In other words,
since it is in rolling contact under high surface pressure, the durability
of the contact surface becomes an issue. In order to solve this issue,
NSK gathered all of its tribology technology to develop CVT steel,
which is highly purified steel for CVTs where non-metal contaminants
have been removed to the most possible extent. This material achieves
constant rigidity by increasing the amount of austenite composition
in the steel, which helps make foreign substances entering the gear
virtually harmless. We succeeded in developing a material that is
highly reliable with long life while operating under the most severe
conditions of massive loads, high temperatures, and high speeds.
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•Power Split System
The next generation of the half-toroidal CVT is
even more efficient thanks to NSKÕs power-split system. This system
utilizes planetary gears combined with the half-toroidal CVT and
a planetary gear device. This power circulatory speed-changing mechanism
had been conceived in theory before, but had not actually been developed
since the best non-level speed changer had not yet been developed.
By changing two modes, a wide range of speeds and a very highly efficient
form of power conveyance was achieved in our power-split system, which
is the truly ideal speed changer. |
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| Incorporating a planetary gear allows most of the engine power to be transmitted directly to the wheel, bypassing the harf-toroidal CVT. |
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