What ever happened to CVT?

Nissan is using them in several of their models and I think Saturn has them too. Not sure about Toyota.

Audi, as well.

Continuously variable transmissions are transmission that allow any gear ratio to be used (within reason). With CVTs, the computer that controls it can keep it so that the engine is always running at the speed for best efficiency.

They have nothing to do with flywheels storing kinetic energy (although they can be used that way.

Jeff

Toyota uses one in its hybrids. Ford uses them on the Taurus and 500 and Sable.

But, they don't use a flywheel to store kinetic energy.

Jeff

For fuel efficiency improvements, the effort goes into reducing the weight of vhicles. Heavy flywheels add to the energy needed to accellerate and climb hill - even though they give energy back when they decellerate and descend hills.

Isn't the 2008 Corolla going to have one?

Actually Toyotas Hybrid Synergy Drive system doesn't use a CVT. The "power split device" is more like a standard differential as both electric motors and the engine are constantly engaged in a planetary setup. A traditional transmission-like setup isn't needed in the HSD system due to the massive amounts of torque put out by the motors; there is no need to multiply torque.

With the flywheels too?

As far as electric motors, do they set them up so that they can generate electricity back into the system when decelerating or going downhill?

Try again:

The idea of the CVT is just to generate torque, but do so with the best possible gear ratio, which the hybrid synergy drive does.

Jeff

Alright, I'll give it to you that the Synergy drive and traditional CVTs are both designed to accomplish same purpose, but the design is completely different. From your linked wiki article:

"When required to classify the transmission type of an HSD vehicle (such as in standard specification lists or for regulatory purposes), Toyota describes HSD-equipped vehicles as having E-CVT (Electronically-controlled Continuously Variable Transmission)."

Toyota simply refers to it as a CVT because nothing else on the market resembles the internals of their Power Split device. Traditional CVTs have two "gears", one drive and one driven, and the ability to change the drive ratio by mechanically changing the size of the "gears" and running a chain between the two. Toyota's power split device involving two motors and an internal combustion engine doesn't even begin to resemble this setup. We took one apart in one of Toyota's Hybrid classes.

Yeah, they do. One of the two electric motors has the ability to change from a motor to a generator during braking. The mechanical brakes in the Prius aren't activated until about 50% pedal travel. I worked at a dealer up until early last year, and up until then we still didn't have one repair order involving brake pad replacement on ANY Pruis, and the 1st gen was out in '01. I've had a Prius on the lift with well over 100k, and the pads still had more than half of their meat left!

Toyota refers to it as a CVT because the effective gear ratio is continuously variable.

It does work very differntly than traditional CVTs, of course.

That's not the only way to do it.

Toyota's power split device involving two motors and an

Your right, the method I described is just the classical design of a CVT. However, Toyotas Hybrid system does not use anything resembling any CVT out on the market. Like I said before, there isn't the same need to multiply torque in the HSD system, and that is the primary function of all other transmissions out there. Here's another snip from your Wiki articles:

"The continuously variable transmission should not be confused with the power split transmission (PST), as used in the Toyota Prius and other hybrid vehicles that use two or more inputs with one output, despite some similarities in their function."

At this point I think we're getting into a debate as to what does and what doesn't constitute a CVT. I've just been told through all the Hybrid classes I've been sent to that though HSD can produce infinitely variable ratios, it's not a CVT. On a cooler, more interesting note, one of the coolest things I remember from those classes was a video from Japan of software engineers tweeking the complicated traction control system needed to get the near-300 lbft of torque produced by the motor at zero rpm to the pavement through the tiny little economy tires standard on the Pruis. At one point they turned the system off completely and spent a few minutes smoking the parking lot up by barely breathing on the accelerator. No matter how far up you go, guys still like lay patches on pavement, I guess. Even if they do wear lab coats.

As for when the brakes are used, that depends on the model of the Prius, as well as the requested braking force. (If ABS/traction control is activated, you'll have full mechanical/hydraulic braking, for example, and mostly mechanical/hydraulic in a panic stop as well.)

The NHW10 Prius was available only in Japan starting in 1997, available in the 1998-2000 model years. Some of these are now being seen grey market in UK, New Zealand, and Australia...

The NHW11 Prius was introduced in 2000 (2001 model year) to many countries worldwide, such as the US, Canada, UK, Australia, much of Europe... and sold through 2003 (often referred to as the Classic Prius). So, depending on your viewpoint, it may have been the 1st generation Prius, but it was first available for purchase in the summer/fall of 2000.

The NHW20 Prius was introduced in 2003 (2004 model year) in yet even more countries, and is the current generation (hatchback) Prius.

Exactly.

Sorry, I don't own the wikipedia.

This means that it is a different type of transmission than the traditional transmission. It doesn't meant that it is not a type of transmission.

Actually, you do need to change the gear ratio. Otherwise, the speed of the vehicle would be directly proportional to the speed of the engine or the engine won't drive the vehicle.

One major function of the HSD is allow the engine to spin at the best speed for the task at hand. The best speed can be the most efficient speed or the speed that will allow the most power get to the wheels. These functions require changing the effective gear ratio.

So you do need to multiple the engine torque, which is what the HSD does. We can argue all we want whether or not it is a transmission (it is).

Wow, that's awesome!

The gear ratio in the PSD is fixed, its just a planetary gear set. There isn't any need for torque multiplication because the primary electric motor, or MG2, or "tractive" motor, produces enough torque on its own to get the vehicle up to speed without having to change ratios. It's essentially a "1 speed", as the output shaft of the HSD is directly connected to MG2. As the torque curve of any electric motor quickly falls off as rpm increases, the engine is used to assist the motor with extra torque needed to keep the vehicle cruising. The engine's output has absolutely no direct effect on wheel speed.