How Does a CVT Work? AutoGuide com News

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How Does a CVT Work?

Automatic are HUGELY popular in North Europe is still a strong for the manual gearbox but on this of the Atlantic self-shifters account for at 90 percent of new-vehicle sales; the trans lost the market-share decades ago and in spectacular fashion.

their dominance the automatic is not a adversary, a single threat. are several major kinds ranging from the traditional stepped-ratio unit, to dual-clutch to the controversial CVT, which of is shorthand for continuously variable

And that final option is the one raises the ire of true automotive like nothing else side of hybrids. If these don’t have three and a mechanical ratio-selector to play they just aren’t

CVTs are a relatively new trend on the they promise better economy and smoother driving, but how do actually work?  How can change ratios without gears? Is this automotive or just common-sense engineering?

A INSIDE

Surprisingly there is a variety of different CVT designs out but for automotive applications many of just aren’t practical. Loing, vice president of advanced planning and strategy at North America said us there is basically one system, we use in different sizes and executions… for mounted applications.”

Of all the automakers in North America has probably been the most in pushing CVTs. The technology has throughout their lineup in years and you can get one in vehicles ranging the tiny Versa Note all the way up to the hefty Pathfinder crossover.

The used by Nissan and other consists of a few major components a pair of variable-diameter pulleys as a special belt that them. Jim Paris, director of development, Continental business transmissions NAFTA region things up succinctly. He said “By their dimensions the belt rides higher or lower on the and changes the ratio between the and the driven pulley.”

In short one gets bigger and the other This movement changes the between the two; it’s a simple and effective idea always provides the driver the proper “gear.”

Curiously a tire-one supplier company, actually build any CVTs. they focus on controllers. said “We’re actually the maker of transmission electronics on the This includes things sensors, actuators and mechatronic

They work intimately OEMs on all kinds of automatic from conventional planetary to dual-clutch units to CVTs and

Now, one of the most complicated of a CVT is actually the belt, probably appropriately referred to as a chain. said “The belts have a lot of work to do, transferring a of engine torque through the He also touched on their and complexity, noting that difficult to build and require tight manufacturing tolerances, that makes them expensive.


These belts are constructed of a series of metallic joined together by metal This design allows the to flex yet still transfer without ripping apart. other CVT designs use chains consist of innumerable metal to form a sturdy yet flexible Keeping things simple, CVTs push while pull.

In addition to automobiles are used in all kinds of applications snowmobiles to stationary machinery. In lighter-duty applications the transmissions feature rubber belts of chains or bands.

Beyond the pulley style, Nissan experimented with another CVT The toroidal design is completely and has no belts. Instead it features and disks that vary the between input and output.

said “Nissan looked at technical challenge,” building one in the He noted that “it was an exceptional comparing it to an expensive watch, that was its Achilles’ heel; it was too costly for mass-market vehicles.

A third option is called the a design used in the popular Prius and its Hybrid Synergy system. This setup a planetary gearset like a automatic transmission but with a literally. “Suns, planets and are each attached to a torque-producing Paris said. “They two electric machines and the engine” he Varying the torque applied to parts of the gearset changes the just like a variable-diameter CVT.

BENEFITS

CVTs to gain more and more in the marketplace. Nissan and to a lesser Audi were pretty on the forefront of this movement but automakers are jumping on the “belt-wagon” so to Loing said that their latest models and Honda [are] coming to CVT as

There are a couple reasons for “shift” (no pun intended) in transmission Loing said “the one is fuel economy, the other one is With no preset ratios a typical planetary-gear automatic he “[there’s] no torque cut” the power flows in one steady as you accelerate – it doesn’t get interrupted by changes.

“I think in general the is valued” Loing noted, not by all drivers. “[Some] customers to like to have some of torque cuts.” In response can actually simulate traditional in several of its new CVTs to make mimic a conventional automatic

Loing said the reason a CVT is efficient than a conventional is because “it has the engine operate the maximum torque and maximum By doing this the engine operates in the optimal RPM zone.”

Paris said that to a typical planetary-gearset transmission number of mechanical parts is lower.” He also said odd, in a way CVTs are a less design than other types.” According to Paris have “higher internal but since they “allow the to operate in a narrower rev band” more efficient overall.

said that friction is companies like Jatco, a in the CVT market one of Nissan’s major have been ruthlessly to reduce. According to Jatco new CVT 8 model features a best-in-class spread and significantly lower compared to previous CVT models.

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Of course everything has its advantages and CVTs are no exception. One of the biggest has to do with how much torque can handle. Loing said typically limited to between 300 and 350 meters of twist.

In ‘Murican that works out to between 220 and 260 lb-ft of torque.

However, in recent years have been able to how much CVTs can handle. improvement of the belt has made torque increase possible” said.

Another potential is mass. Even though have fewer internal Paris said “CVTs to be the heaviest of the transmission types.” He said that due to low adoption in the past “[They’ve] been expensive to replace.”

But what reliability? Do CVTs have issues than conventional transmissions? Paris said yes, noting that have been a number of lawsuits associated with units.

But automakers have made strides in improving over the years. In fact said drivers shouldn’t any issues with CVTs, that Nissan backs up with the same warranty get with a conventional automatic “There’s no reason why it should be he said.

Another downside to has to do with NVH, that’s vibration and harshness. Due to their torque capacity they’re paired with small, engines. During acceleration will typically hold a at a specific RPM, which can a droning sound and lots of irritation.

THE FUTURE

Going CVTs are practically guaranteed to gaining traction in markets the world as automakers work to fuel efficiency. Japanese led by Nissan are really pushing Loing said “It’s our selling transmission in North noting that “It’s that’s here to stay us.”

Nissan is even starting to its CVT offerings in the Old World, a market still dominated by manual “We see now even in Europe CVTs in the Nissan lineup and associated diesel” Loing said, that the new generation of the company’s compact crossover features an paired with a CVT.

One of future improvement could be the of dry clutches instead of torque Paris said “That take some money out of which according to him tend to be

As it stands today continuously transmissions will probably their growth in the marketplace. them for efficiency and smoothness or them because of droning NVH and durability issues they’re not anywhere.

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