Continuously Variable Transmissions (CVT) have two major types: one does not use a belt to transmit power, such as Toyota's Hybrid Synergy Drive, which uses mechanical gears; another type of CVT uses belts connecting two pulleys. The first type has the advantage of real mechanical hard connections, high efficiency and high capacity (can handle large torque), but one limitation is that the Toyota Hybrid Synergy Drive, its mechanical structure can only be used in hybrid powertrains, that transmission will not work in a traditional internal combustion engine powered car.
For the belt type CVT, it can be used in all cars with different
types of power sources, and it has unlimited gear ratios; but since it
depends on the friction between the belt and the pulley to delivery
energy, its ability to transmit torque is limited; and its efficiency
under high load is not as good as other traditional automatic
transmissions. Recently, VIT Automobile Science and Technology Ltd, a
company specialized in transmission technology, based in Beijing, China,
released some information about their latest product: moveable teeth
CVT (they called it €HN-CVT€). Below is one of its production units. The
HN-CVT combines the benefits of the above two mentioned CVTs. According
to VIT, they already has one model of the HN-CVT that with torque
rating of 738 lb-ft (1000Nm). What's more, the HN-CVT has an astonishing
high efficiency ratio of 96% (it only loses 4% of the energy coming
from the engine flywheel, before putting the power to the car's wheels).
For comparison, traditional automatic transmissions usually have an
efficiency ratio between 80% - 90%.
The principle of the HN-CVT (moveable teeth CVT) is based on the
fundamental of how a car transmission works. Regardless what type of a
transmission is, they all work in this way: the input side is paired to a
gear with a certain amount of teeth, and the output side is paired to
another gear with another amount of teeth. If the tooth amount of the
two gears are different, the input side and the output side will rotate
at a different speed. For the HN-CVT, it still has a belt. But different
from other CVTs, the belt has fixed teeth on it. The HN-CVT also has a
pulley, but it is a special pulley: it has many small steel sheets
packed on its surfaces.
Those small sheets can go up and down
individually (controlled by the transmission ECU). If some sheets goes
up at the same time, then the convex shape it formed becomes one tooth.
For all the steel sheets on the pulley, the transmission ECU can control
their action to form multiple convex shapes, therefore it essentially
becomes a gear. The key point is: by controlling the combination of
up-down shape of the steel sheets, it can become a gear with any tooth
amount it wants. So the fixed-amount-tooth belt meets the
variable-amount-tooth pulley, and different transmission ratio can be
realized. Because it is tooth-to-tooth contact, this transmission can
handle large amount of forces without causing sliding and frictional
VIT has very ambitious business and marketing plans for the HN-CVT.
According to the company, they have patents in US, Canada, Europe Union
(including 13 countries), Japan, Korea, Australia and India, covering
80% of the world's automobile industry sharing. The HN-CVT has
unmatchable mechanical performance, and also cost advantage. VIT said
its HN-CVT costs 20% - 50% less than other comparable transmission
Because of such advantages, according to our insider information, one
US major automobile company is already cooperating with VIT to develop
dedicated products with this technology. Since there are only three
major car company in the states, the one who is working with VIT must be
GM, or Ford, or Chrysler. From the source, we know we will see the
HN-CVT in some production passenger car in 2017 - 2018, and some luxury
cars may also use this transmission as early as 2020.
If this transmission can reach the mass production stage, I am sure
this will be a big milestone in the auto industry. what do you think?
Source : http://goarticles.com/article/Continuously-Variable-Transmission-A-Revolutionary-Design/10050341/