Snowmobiles perfected the CVT concept many years ago.
I think snowmobiles may have a different standard of “perfection” than automobiles have. How many snowmobiles see more than 50 hours of use per year?
The snowmobile variable pulley system is also used on a lot of scooters. I was kind of considering getting a 250cc size scooter until I researched the gas mileage people get with them, 60 mpg? oh be still my beating heart! I think I’ll just shift gears on a 250cc motorcycle and get 70-80 mpg instead.
Apparently, there’s a lot of friction in a belt drive CVT which offsets the theoretical advantage of stepless shifting.
Manual CVTs have been standard on self propelled combine harvesters almost since they replaced tractor pulled combines. This allows the operator to steplessly change ground speed while keeping the engine at full rpm to drive the threshing machinery.
Manual CVT on heavy equipment as well as garden tractors and larger are quite robust. They are not belt driven but use hydraulics. They could be adapted to car use but are very NOISY and inefficient and as yet, not light and compact enough to even usurp gear drive. Solid gear drive is tough to beat when loads and speeds are constant. Belt driven CVTs are still the way to go for now till a better mouse trap is invented for greater loads. But I remind myself that the big reason electric motors are used as heavy duty drive motrs in ships and locomotives, is to eliminate the transmissions in these monsters. IMHO, CVTs are a stop gap.
If you’re buying new, and the powertrain warranty (usually 100,000 miles for most manufacturers - make sure you check) covers the CVT, I would go for it. If you’re the type of person who buys an extended warranty, you’ve got a lower risk profile, so you might as well get the CVT.
If you’re buying a used car that comes with a short warranty, or no warranty, I might opt for a conventional conventional automatic transmission, especially if it’s one with a lot of gears (at least 5 or 6).
Electric motors are great for cruising, but at low speed when they produce high torque, they also draw high current, which leads to waste heat. Cars that are in stop and go traffic all the time do better with gears than electric motors.
“Toyota is going to a CVT in the Corolla for 2014, but instead of continuous operation, the transmission is programed to change ratios in steps, simulating a conventional transmission. Go figure.”
Toyota is not alone in this simulation.
On Subaru’s CVT models, if the driver puts the trans into “manual mode”, using the paddles causes the CVT to simulate 6 gears. Again…go figure!
@chunkyazian
Theoretically, constant speeds ( especially lower when air resistance is less of a factor) are more efficient for all motors. In hybrids, the best mileage is in stop and go city driving because the electric motor is more efficient then a gas motor with a transmission doing it. Cruising at higher speeds with increased air resistance and loss of regen braking, electric motors have less of an advantage. The mileage then drops as the gas motor is utilized more at constant higher speeds. So, I feel the opposite is true. Hybrids are designed to run in three modes but the electric drive only is common place for all in stop and go driving at low speeds where acceleration and regenerative braking and constant torque electric are taken advantage of.
Too bad. I’ve not read much positive about the Subaru CVTs. Recent comparison of a Forester/CVT with the Mazda CX-5/6sp auto had same mpgs for both, but the CX-5 was MUCH nicer to drive. If there’s no mpg benefit, why bother?
@dagosa
Perhaps I should clarify, from the wheel power to electric power standpoint, electric motors are inefficient at high torque low speed compared to cruising. Even Tesla briefly considered using a 2 speed transmission in its roadsters
Traction motors do have their place in automobiles, between the engine and transmission.
I have driven a Prius, Nissan Altima and Nissan Rogue, all with CVT’s. The one I didn’t like at all was the Rogue. Real struggle to go, the Altima was a rental and I got used to it and after 2 days actually the better handling made up for the CVT (my daily driver being a Camry!). The Prius was just fine.
Perhaps I should clarify, from the wheel power to electric power standpoint, electric motors are inefficient at high torque low speed compared to cruising. Even Tesla briefly considered using a 2 speed transmission in its roadsters
Most of the CVTs I’ve seen are actually used on electric motors in industrial applications where speed adjustment is important.
Although, the invention and perfection or the solid state variable frequency drive is rapidly making CVT’s obsolete.
@chunkyazian
I don’t disagree that electric motors are less efficient when accelerating from low speed when more torque is needed then when cruising. But check your mileage indicator on an internal combustion motor, so aren’t they (all motors). Electrics may be " less" efficient but are still more so then ICE engines which suffer from the same problem to a greater degree.
The large, heavy, power robbing gear transmission needed for an internal combustion engine is what separates the electric motor in low speed stop and go driving with higher torque demands. This disadvantage is somewhat mitigated when weights are low and torque demands are low enough to allow the use of a weaker CVT. We are debating apples and oranges.
The real advantage of electric motors in stop and go is the ability to recover kinetic energy during braking instead of throwing the energy away with brakes and zero standby power consumption while waiting for red lights to turn green.
I read somewhere that standby power consumption accounts for about 15% of the gas consumed by a typical car in urban traffic. A small four will burn about .25 gallons per hour idling, a V-8 as much as .5 gallons per hour. Diesels burn about 1/3 the fuel that a comparable gasoline engine burns during idle.
The big equalizer and why efficient gas motors with CVTs will still have an out, is in northern towns and cities. It will be hard to surplant hybrids and gas with electrics that need to “burn” something to generate enough heat in a mid to large car with lot’s of glass area.
I bought a Nissan Versa with CVT at the end of 2012. It was great for the first year and a half, then last summer started hesitating, with a slight squeal, when I would lightly touch the accelerator to adjust my speed on the interstate. Now, 6 months later, I never know what it’s going to do, especially on freeway onramps. Sometimes it does that surge-hesitate thing, like I’m a novice driving a standard transmission. The first time I took it in to the dealer, they claimed they couldn’t reproduce the problem. I tried to take it to another dealer, but they said they’d need to keep it for at least 2 days.
The upshot is, if you want a safe, reliable car, stick with a regular automatic transmission.