Cosby
05-18-2005, 03:44 PM
http://www.jaai.com/sateidojo/check-sheet/lesson02/image/03-cvt.jpg
The continuously variable transmission, or C.V.T., is both the oldest and newest thing going in cars.
The oldest because Leonardo da Vinci conceived the idea five centuries ago.
The newest because Chrysler and Mercedes-Benz are developing the transmissions for introduction later in this decade.
Manufacturers that have offered C.V.T.'s in past or present cars include Audi, Ford, Honda, Mini, Nissan, Saturn, Subaru and Toyota.
The Ford Five Hundred has a C.V.T. when equipped with all-wheel drive; front-drive models offer a choice of C.V.T. or six-speed automatic.
As its name suggests, a continuously variable transmission eliminates the fixed ratios (gears) of conventional automatic and stick-shift transmissions. This provides two advantages:
Press the accelerator and the sensation is like riding an escalator instead of climbing the stairs.
The second gain is better mileage - 2 m.p.g. or so better, about the same benefit you'd get by trading your automatic for a stick shift. The standard sales pitch is that a C.V.T. has the smoothness of an automatic with the efficiency of a manual.
Engineers skin the C.V.T. cat three ways. Ford and Toyota use a complex system of planetary gears and an electronically regulated motor-generator - an electric machine that can act as either a motor or a generator - to achieve step-free propulsion in hybrid vehicles.
Other C.V.T.'s sold in this country are propelled by metal belts or chains wrapped around two V-shaped pulleys. Computer-controlled actuators squeeze the adjustable pulleys tightly against the belt or chain and vary the size of the pulleys to change the transmission ratio. When the drive pulley is small and the driven pulley is large, you get a low ratio for accelerating from a stop; swapping pulley sizes provides an appropriate cruising ratio.
The C.V.T.'s efficiency advantage comes from its wide range of available ratios. With four-speed automatics, the difference between first and fourth gears is typically a factor of 4 to 1. C.V.T.'s typically achieve a 6-to-1 spread for lower cruising r.p.m., and therefore better mileage.
So why aren't C.V.T.'s the universal choice for harnessing engines to drive wheels? For one thing, it is hard to engineer belts, chains and pulleys that are strong enough to propel a large, heavy American car. C.V.T.'s make the most sense in Japan, where minicars are the norm. If you are attracted to the technology but concerned about reliability, your best bet is to choose a C.V.T. from a Japanese automaker; they have the most experience with them.
Also, although C.V.T.'s are usually smaller, lighter and contain fewer parts than conventional automatics, they are more expensive to make.
The toughest challenge for engineers is making C.V.T.'s durable and competitive with alternatives in terms of mileage and acceleration. It took Ford two years longer than expected to ready its C.V.T.'s for sale.
Faced with a $100 million bill to fix slipping belts, General Motors recently decided to replace the C.V.T.'s in its Saturn Vue and Ion with new six-speed automatics. The next-generation Mini Cooper is also expected to switch from a C.V.T. to a conventional automatic.
In addition to cost, durability and performance issues, C.V.T.'s have new competition. Conventional automatics now have as many as seven speeds, and some new transmissions use two computer-controlled clutches to improve mileage. In the car world, a better mousetrap is always just down the road.
http://www.baileycar.com/CVT.jpeg
I believe this is the new CVT at UC Davis that weighs 150lbs and has a 98% drivetrain efficiency.
The continuously variable transmission, or C.V.T., is both the oldest and newest thing going in cars.
The oldest because Leonardo da Vinci conceived the idea five centuries ago.
The newest because Chrysler and Mercedes-Benz are developing the transmissions for introduction later in this decade.
Manufacturers that have offered C.V.T.'s in past or present cars include Audi, Ford, Honda, Mini, Nissan, Saturn, Subaru and Toyota.
The Ford Five Hundred has a C.V.T. when equipped with all-wheel drive; front-drive models offer a choice of C.V.T. or six-speed automatic.
As its name suggests, a continuously variable transmission eliminates the fixed ratios (gears) of conventional automatic and stick-shift transmissions. This provides two advantages:
Press the accelerator and the sensation is like riding an escalator instead of climbing the stairs.
The second gain is better mileage - 2 m.p.g. or so better, about the same benefit you'd get by trading your automatic for a stick shift. The standard sales pitch is that a C.V.T. has the smoothness of an automatic with the efficiency of a manual.
Engineers skin the C.V.T. cat three ways. Ford and Toyota use a complex system of planetary gears and an electronically regulated motor-generator - an electric machine that can act as either a motor or a generator - to achieve step-free propulsion in hybrid vehicles.
Other C.V.T.'s sold in this country are propelled by metal belts or chains wrapped around two V-shaped pulleys. Computer-controlled actuators squeeze the adjustable pulleys tightly against the belt or chain and vary the size of the pulleys to change the transmission ratio. When the drive pulley is small and the driven pulley is large, you get a low ratio for accelerating from a stop; swapping pulley sizes provides an appropriate cruising ratio.
The C.V.T.'s efficiency advantage comes from its wide range of available ratios. With four-speed automatics, the difference between first and fourth gears is typically a factor of 4 to 1. C.V.T.'s typically achieve a 6-to-1 spread for lower cruising r.p.m., and therefore better mileage.
So why aren't C.V.T.'s the universal choice for harnessing engines to drive wheels? For one thing, it is hard to engineer belts, chains and pulleys that are strong enough to propel a large, heavy American car. C.V.T.'s make the most sense in Japan, where minicars are the norm. If you are attracted to the technology but concerned about reliability, your best bet is to choose a C.V.T. from a Japanese automaker; they have the most experience with them.
Also, although C.V.T.'s are usually smaller, lighter and contain fewer parts than conventional automatics, they are more expensive to make.
The toughest challenge for engineers is making C.V.T.'s durable and competitive with alternatives in terms of mileage and acceleration. It took Ford two years longer than expected to ready its C.V.T.'s for sale.
Faced with a $100 million bill to fix slipping belts, General Motors recently decided to replace the C.V.T.'s in its Saturn Vue and Ion with new six-speed automatics. The next-generation Mini Cooper is also expected to switch from a C.V.T. to a conventional automatic.
In addition to cost, durability and performance issues, C.V.T.'s have new competition. Conventional automatics now have as many as seven speeds, and some new transmissions use two computer-controlled clutches to improve mileage. In the car world, a better mousetrap is always just down the road.
http://www.baileycar.com/CVT.jpeg
I believe this is the new CVT at UC Davis that weighs 150lbs and has a 98% drivetrain efficiency.