• Apr 10, 2010

A variety of continuously variable transmissions types are already on the market, including the well-known variable pulley-and-belt type used by companies like Honda, Suzuki and Subaru. Australian Steve Durnin thinks he has a better idea, however. He's developed a CVT featuring no belts or pulleys, and all the gears are continuously engaged.

A short video on Australian TV doesn't really offer much insight into the workings of the device, but like others it is intended to keep an engine operating at its most efficient speed regardless of vehicle speed. We've looked over the patent application and the typically dense language did little bit to enlighten us. Nonetheless, we'll try to explain what we think might be happening.

The system consists of a pair of ring gears and parallel transmission shafts. Each of the shafts have a modulator mechanism that can rotate the shafts, thereby adjusting the effective input-to-output ratio. As near as we can tell, it uses something similar to a mechanism that makes a differential work to adjust the relative rotational speeds of the two shafts. It's difficult to tell from the sole illustration just how everything moves around. Durnin claims the transmission can provide a 20 percent improvement in efficiency. However, the modulator mechanism will require some energy input to work. Whether that's factored into the savings is presently unknown. Hopefully, we'll see more of this and learn precisely how it works.

[Source: Bayside Bulletin, WIPO, Australian Broadcasting Corp.]


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  • 15 Comments
      • 4 Years Ago
      This sounds promising, but there are many developments that sound promising and then you never hear of them again.
      • 4 Years Ago
      Go Aussie.
      • 4 Years Ago
      This is the first time that I've heard of this, though it seems that there is nothing new under the sun. It is a very interesting concept. The video on the jump is worth watching. It should be an advantage over the standard CVT and their fragile belts.
      • 4 Years Ago
      will this be as fragile as a conventional CVT? i know my car has a CVT and the transmission manufacturer told me that anything more than about 129 lb-ft of torque would trash the transmission.
        • 4 Years Ago
        those CVTs are purpose built for their respective cars, and take up much more space than the CVT in my car. small car CVTs are, as they stand right now, really impractical because they're as fragile as glass when there's a decent amount of torque.
        • 4 Years Ago
        AFAIR the CVTs used in Hybrids (say, Prius, Lexus RX) are not comparable to those used on IC Engines. The IC Engined CVTs usually use some kind of "belt drive" (very simply spoken) which have a lower max. torque because the belt will start to slip and klill itself if you overload it.
        The CVTs in Hybrids are a combination of planetary gearsets that work by running the various elements (sun, planets, ring gear) at variable speeds, driven by the electric motor(s). Therefore, consisting of "normal" gears they can be made to accept any torque.
        • 4 Years Ago
        If I'm not mistaken the newer maxima's use cvt's. they have about 260 ft lbs of torque. The new lexus RX hybrid also has a cvt with plenty of torque.

        Regardless, I would not buy a vehicle that had a cvt. What's the expected life of cvt belts anyways?
        • 4 Years Ago
        CVTs can handle much more torque, considering all of the torquey hybrids (RX, Highlander) and Nissan 3.5L VQs that use the transmission.
        • 4 Years Ago
        as i said in my last comment, airchompers, CVTs purpose-built for torquier engines are not as fragile as the CVT in my car. but it should be noted that a belt CVT built to fit into a smaller car can't possibly withstand a lot of torque. in the case of my car, the transmission manufacturer (ZF) says that 129 is the magic number, and the belt is liable to snap anywhere higher than that. on CVTs in nissan and audi sedans, as well as in the hybrids so often mentioned, the components can take up more space, and so are bigger and more durable. i know that one CVT can't speak for all of them, i was trying to say that the way they're built now is not good for small cars, because in order to make everything small enough, they can't be built to be very sturdy.
      • 4 Years Ago
      A Canadian company currently holds patents on a co-planer gear set infinitly variable transmission that work exactly the same way.

      The main issue is that you need to take energy out of the system to shift the phase angle between the gear sets. Its this Phasing that changes the output gear ratio. currently this is often done with hydraulics.
        • 4 Years Ago
        Idea and patents are one thing but making the damned thing work for 250,000 miles without breaking down is another.
        • 4 Years Ago
        To me, it seem this is just another take on the planetary gears CVT, which is already in widespread use, e.g. in the Prius.
        Only that this one seems more complicated and fragile.
        What he IMHO fails to see ist that you need to support the torque transmittet through the engine, which you have to do on the parts that are made like "handles" on his model. This is where, on a hybrid, the strong e-motors make it work, and strong the need to be.
        There is a nice app online that illustrates the workings of such a gearset:
        http://www.wind.sannet.ne.jp/m_matsu/prius/ThsSimu/index_i18n.html
      • 4 Years Ago
      How about inventing a CVT that doesn't make me feel like I'm driving a Hoover?
      • 4 Years Ago
      The GM two mode transmission is a CVT with 4 ranges. That beats anything that's out there.
      • 4 Years Ago
      I can't stand these transmissions! I was in the market for a Maxima until I saw they were only available with CVT. Now I have no idea what to get.
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