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Are CVTs The Fuel-Efficient Transmission Of The Future?

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Xtronic CVT, 6th generation  -  for 2013 Nissan Altima

Xtronic CVT, 6th generation - for 2013 Nissan Altima

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If you've driven a Toyota, Lexus or Honda hybrid, or any recent Nissan automatic, you'll be familiar with continuously-variable transmissions (CVT).

You'll be familiar with the smoothness, the quiet running at low speeds, and the way the revs soar when you ask for a bit more power. But with CVT becoming more popular, is public perception of noisy, slow CVT cars slowly changing?

For customers used to regular torque-converter automatics with distinct steps in power and torque delivery, CVTs can feel unnatural and even annoying. Planting your foot to the carpet sends the engine revs upwards for the most power, but also the most noise. In a vehicle with a small engine, it can feel like a lot of work for very little progress.

But, as Automotive News reports, CVTs have gone from 1 percent market share in 2005, to 7 percent in 2010. By 2015, that figure could more than double to 16 percent.

CVTs are increasingly used for efficiency reasons. By continually altering the relationship between engine speed and power transmitted to the wheels, a CVT can ensure that no more fuel is used than is needed at any point.

This means, when cruising around town or even staying at a steady speed on the freeway, the revs can remain low, saving fuel. But ask for more power, and the engine spins faster and stays there, supplying as much power as it can muster, rather than having to switch between ratios like a regular gearbox.

Nissan Motor Co uses CVTs in several vehicles, and has found that, once used to the transmission, drivers don't mind the different characteristics.

Chris Martin, spokesman for Honda, concurs, adding that drivers are more interested in the end result (economy) than the means by which it reaches that end.

"Nobody's coming into our dealerships and asking us for CVTs, but they are coming in and asking for fuel economy. And if you look at the government efficiency requirements for the next few years, a CVT provides the fuel efficiency we want in both highway and city driving."

Honda is set to launch an Accord with CVT in the fall, and Toyota--already well used to CVTs in all Toyota and Lexus hybrids--may give next year's Corolla a CVT too.

Perception of the transmission is tainted by those who consider CVT-equipped cars unenjoyable to drive, or feel that they're indicative of vehicles with low performance, but that's certainly not the case in some high-end hybrids, like the 340-horsepower 2013 Lexus GS 450h.

Others aren't quite so fun--the Toyota Prius uses CVT to good effect in terms of efficiency, but the drone of its four-cylinder under full throttle could never be considered musical, nor could several other small, four-cylinder vehicles with CVT.

However, whether consumers like them or not, CVT could well be the best route to better fuel efficiency from vehicles in the future. And as the technology improves, drivers will quickly get used to their new, stepless transmissions.

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Comments (26)
  1. Much ado about nothing. I drive both a stick shift and a Prius with hybrid synergy drive (still not sure it is a CVT). Both allow you to accelerate and both make more noise when doing so.

    Most importantly, both sound pretty ridiculous to anyone that has ever driven a Nissan LEAF.
     
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  2. It's like Antony says: "whether consumers like them or not, CVT could well be the best route to better fuel efficiency".

    The trend is clear: ever more compromised ICE vehicles compete with ever less compromised EVs.
     
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  3. Well, said Chris
     
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  4. Yes your Prius has a cvt trans. Believe me I had an '08. and I bet that you probably drive a 1st. gen. Honda Insight with the only man. trans. on any hybrid gas/electric veh. mass produced in considerably small numbers.Yes none of them probably has the silence or electric torque of a pure electric but wouldn't it be gret if they made an electric simulated trans. where it would help slow down your veh. or is that what regen. brakes are for?!
     
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  5. @John, @TakWang: While the output of the Prius transmission is continuously variable, it is NOT a mechanically variable model like those that Antony is writing about, which use belts on pulleys of variable diameter to vary the ratio of engine speed to output torque continuously.

    The Prius has what we call an "eCVT," or electronic continuously variable transmission, which uses a planetary gearset to blend torque in continuously variable ratios from the combustion engine and to AND FROM the two motor-generators.

    Same effect, entirely different mechanism, and too few media outlets adequately explain the difference (IMHO). Hope this helps.
     
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  6. Just a note: The "CVT" in the Toyota hybrids is not a belt-and-pulley CVT like those in gasoline-only cars, but a planetary gearset that is more properly called a Power Split Device. That's an important distinction from a maintenance point of view.

    Belt-and-pulley CVTs need to have that special sticky transmission fluid changed every 30,000 miles, while Toyota recommends the PSD's fluid never be changed (though experienced Prius owners on PriusChat recommends a WS fluid drain-and-refill every 60,000 miles).

    PSD is also mechanically much simpler (and consequently more reliable) than a belt-and-pulley CVT-- The Prius power split device has just 27 moving parts. There is no gear-shifting or belt-and-pulley wear-and-tear.
     
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  7. Thanks for your note Forest, you're entirely right. I should really have clarified that in the article. They're different, but have the very similar characteristics while driving :)
     
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  8. Glad you mentioned this Forest and good to see someone else appreciates the internals of the Prius drive train. I have a theory the Volt uses three clutches to avoid paying Toyota royalties on the HSD which is a more elegant solution.
     
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  9. Volt design is also different b/c its main drive is electric, where Prius's main drive is gas engine and electric motor is feeding the power into the planetary gearsets...
     
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  10. Not really. The MG2 main electric traction motor in the Prius is directly geared to the front wheels as well as the PSD ring gear-- i.e. the gear ratio between MG2 and the front drive wheels are fixed.

    That's why the Prius can move under electric power alone up to 41mph. Above 41mph, the gasoline engine has to kick in to rotate the planetary carrier gears to protect the small MG1 starter/counterbalancing/generator from overrevving (software limited to 6000RPM).

    The Prius PSD can be made to behave like the Voltec system if MG2 is made much bigger (also need bigger HV battery) *and* MG1 is redesigned to withstand higher RPMs or geared at a lower ratio so the gas engine does not have to spin to limit MG1 revs.
     
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  11. Volt's traction motor is connected to the sun gear, its generator is connected to the planet gears and its ICE is driving the ring gears. When the Volt is in EV mode, ring gears stay fixed without any input from the Gas engine. As the sun gear spins up to high speed, its efficiency drops, so the generator gets turn on and start to spin the planet gears to slow down the sun gear in the process. Once the battery is depleted. ICE is turned on at high speed (> 70mph) to spin the ring gear... Each of them are driven seperately by a clutch. YOu can search for technical overview video on Youtubes if you want.

    That sounds different from Toyota's Synergy drive to me...
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  12. Different in that the sun, planetary and ring gears are connected to different power sources (MGs and ICEs), but fact remains that the Prius MG2 is DIRECTLY geared to the drive wheels. The MG2 electric motor in the Prius DIRECTLY drives the wheels to move the car. YOu can search for technical overview video on Youtubes if you want.

    You are thinking of the Honda IMA system when you say "the main drive is the gas engine and the electric motor is feeding power to the planetary gearsets (like on the Accord Hybrid with its 6-speed auto trans).
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  13. "In the Volt, the electric motor can drive the car to all speed and condition."

    That's incorrect. At higher speed, TWO electric motors are used.

    Prius at high speed uses both electric motors and gas engine. ICE can come on at higher speed to lower MG1 speed. The same concept was deployed in Volt to lower MGb speed by spinning MGa.

    Since Volt has 3 clutches to switch operation modes, the lag can take a few seconds. None of that exists in HSD.

    Volt in CS mode (with ICE on) provides more power at speed above 35 MPH. The battery and electric motors cannot provide full power at all speeds and conditions. See the graph below:

    http://www.motortrend.com/roadtests/alternative/1010_2011_chevrolet_volt_test/photo_43.html
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  14. "main drive" means that the electric motor alone can't drive the car in all speed and condition but the ICE can...

    In the Volt, the electric motor can drive the car to all speed and condition.
     
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  15. Xialong Li we have been through this before and it seems to be "your" definition only. We all know the Prius cannot achieve the electric speed of the Volt as it is hampered by battery size and motor size. The point being made it is still electrically driven within the confines of it's battery,motor and software.You seem unwilling to recognise this why? The Prius was marketed as a Hybrid which is capable of low speed limited range EV operation and ICE for performance and longer range.Surely you are intelligent enough to see if it had a battery like the Volt,a larger drive motor and software operating the ICE as a generator only it would work like the Volt.Whats your problem?
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  16. @ Don, we were talking about the difference of the Prius Synergy drive vs. Volt's Voltec system. "Weaker" electric motor is one of the difference. Plus, electric motor don't drive the same gears in the Prius vs. the Volt. So, they are different.

    Don't be so defensive, I am NOT saying which one is better or worse. They are different.
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  17. "where Prius's main drive is gas engine and electric motor is feeding the power into the planetary gearsets..."

    And that's where you are wrong. MG2 in the Prius does not feed power into the planetary gearset except during regenerative braking. When electricity is being applied to MG2 to make it turn as a motor, it TURNS THE WHEELS DIRECTLY.

    MG2 in the Prius is PERMANENTLY, DIRECTLY GEAR-MESHED with the drive wheels. At speeds below 41MPH, the MG2 electric motor IS the "main drive" in the Prius, where the ICE does not necessarily need to run.
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  18. There are more comments in this thread
  19. It is all about fuel economy. Whatever transmission delivers the power needed, at the best cost. Same with fuel. For economy natural gas is best for the largest vehicles, and a contender for all vehicles. It supplies electricity for electric vehicles.
     
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  20. The concept of CVT has been around for almost 100 years now. Tanks used to use it on their transmissions. The major issue is cost and reliability. CVT is efficient but it used to have issue with reliabilities in high torque applications. Nissan's Murano used to 2 gears for low speed start up and then CVT at higher speed to alleviate the problem. Now, as materials improve, it is being used everywhere. CVT is certainly less complex and lighter than a traditional 6-speed or 8-speed transmission. The cost to produce them also has came down a lot which helps to compete against the traditional transmission design.
     
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  21. I have found under aggressive accleration if you back off slightly on the gas as the car is accelerating you will lose the drone.The car will still accelerate as the CVT is changing up while engine revs come down to match car speed. This of course is in passing or filtering situations and not when going from zero to max speed, which is unnecessary in the real world. There is a technique as with any different system and the trick is not to be so ham footed ( if there is such a term) and adapt.
     
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  22. I never understood the droning comments. The more power you request, the faster the engine is going to spin. That's more natural to me.

    That's the same as dropping into low gear and the engine revving fast and loud. The engine revs slower as shifting into higher gear should be unnatural. If I want max power, the engine shouldn't be revving at half the redline RPM.
     
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  23. Torque equals power, an ICE developes max torque within a narrow band (rev range). With fixed ratio transmissions the ICE with an inexperienced driver will rev from below to above this optimum range as it goes "through the gears". This is the sound everyone is used to. A CVT has unlimited ratios between a lower and upper limit. When the pedal is floored it lets the ICE rev to its max torque point and hold there (droning away) and while the car acclerates the ratios creep up the scale until top speed is reached. This is why when accelerating to fifty to seventy there is nothing to be gained by holding the engine at high RPM, you can back off early lowering the revs and the CVT will still change up with the car accelerating.
     
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  24. I practice this technique with a belt CVT city car and also my Prius electronic CVT. My first experience of belt CVT's back in the seventies was the Dutch DAF a forerunner of todays evolutionary design. They responded the same way. Most people think because of the difference in sound to a conventional sys the transmission is slipping or the belts are stretching (rubber bands).This is a naive uneducated observation.
     
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  25. Take a look to this new transmission CVT design by BitRaptor. Is a continuously variable transmission CVT gear only (the only one functional in the world), very compact and lightweight, and which could replace the current systems both for efficiency, simplicity and not least the costs.

    Because this CVT work only with pinions is better the all other systems by efficiency and high torque transmission.

    In the web page you will find more explanations, drawings and a short video of a basic prototype.
    http://www.bitraptor.com/en_edyson_CVT.html

    The first prototype will be ready for tests during this year.
     
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  26. Very interesting concept if they can overcome friction in the sliding mount for the planet gears. There may also be a design limit to the ratios available and no overdrive possibility since only direct drive is produced at the first position shown. I can see this in some installations but not in cars with ICE's.
     
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