Over the years, carmakers have tried to come up with transmissions that can offer the perfect blend of performance and fuel economy. One such gearbox is known as the continuously variable transmission. But in fact, it doesn’t have any gears at all. Instead it relies on a very sophisticated pulley and drive belt arrangement that can provide a nearly endless number of gear ratios. So let’s take a closer look and answer the question, what is a continuously variable transmission?
What Transmission Do I Have?
CVT 101: What is a CVT transmission?
The term CVT stands for continuously variable transmission. That means this transmission can continuously vary the gear ratio to keep the engine in its most efficient state, given the driving situation. This is accomplished using a V-shaped belt that is suspended between two pulleys that have cone-shaped halves. One pulley is connected to the engine, and the other is connected to the output shaft going to the drive wheels.
On a traditional automatic transmission, there will be a set number of gears/ratios that can be used during the driving cycle. If you are driving down the road and need to pass somebody, the computer will tell the transmission to downshift to a lower gear to maximize the use of engine power so that you can accelerate. Once you pass that slow moving Toyota Prius, the transmission will then upshift to a higher gear, which allows the engine RPMs to reduce so you get better fuel economy. None of this applies in a CVT.
A CVT transmission has no gears, just those two pulleys and belt. This means you’re not limited to five, six, eight forward gear ratios. Instead, the vehicle has a near infinite number of gear ratios that will allow the engine to provide peak performance or economy, given the situation. If you need to pass someone, the conical halves of the pulley coming from the engine will squeeze together causing the belt to ride up, while at the same time the conical halves of the pulley going to the drive wheels will spread apart causing that end of the belt to sink down into the now smaller diameter pulley. This creates a lower gear ratio, similar to the chain on a bicycle.
The computer can precisely adjust the separation of each pulley, based on a number of parameters including engine RPM, vehicle speed, road conditions and how hard you’re pushing on the gas pedal. This can yield a different gear ratio every time, but it will always result in the engine being kept at the perfect RPM for the situation.
Differences between a CVT and a traditional automatic transmission
Even though the engine will be kept at the right RPM, you not going to get the sensation of the transmission shifting gears. The only thing you’ll notice is an audible difference in the engine RPMs. In most situations, the engine will be really loud, then it will be really quiet. It may feel like the transmission is stuck in a gear and won’t shift, which may be weird for some people. It can also take a couple of tics for the transmission to lower or raise the gear ratio, which means you may have to be rather deliberate in the way you drive, depending on how much power your engine makes.
What Transmission Do I Have?
In order to give the CVT a broader appeal, many automakers include a feature that gives the CVT synthetic shift points. Although there are no actual gears to work through, the computer manipulates the way the pulleys separate, which gives drivers the feeling of a traditional gear change. There is no point to this, but it does help to sell cars.
