Torque Converter, Single Clutch Auto, and CVT: How Do They Differ?

Technical

Jul 07th, 2021

Torque Converter, Single Clutch Auto, and CVT: How Do They Differ?

Automotive jargon can sometimes be confusing for the average person. Yet, as a car user, you need to familiarise yourself with a few of those terminologies. And that's what this post is about—providing you with the meanings of the terms torque converter, single-clutch auto, and CVT.

If you've owned a car long enough, you'd probably know that there are two main types of transmission: manual and automatic transmission. What you’re less likely to know is this— there are various categories of automatic transmissions. 

This post focuses on three common categories of automatic transmissions: torque converter, single (and dual) clutch auto and CVT. I'll highlight their merits, demerits, and everything else in between, so you don’t get confused the next time you hear these phrases thrown around.

The World of Automatic Transmissions

All automatic transmissions have unique working mechanisms. Nonetheless, they have two common characteristics. 

One, auto transmission vehicles have only two pedals: the accelerator and brake. Second, they take the burden of gear shifting off the driver. This is true whether you’re driving a car with a torque converter transmission, single-clutch transmission, or any other type of automatic transmission. 

Torque Converter vs Single or Dual-Clutch vs CVT

Now, let’s consider the underlying mechanics of a torque converter, CVT, and single-clutch auto transmissions.

Torque Converter 

Torque converter automatic is possibly the most common of all automatic options. You’ll find it used in both budget and luxury cars like the Hyundai Creta and Rolls-Royce, respectively. If a clutch is to a manual transmission vehicle, then a torque converter is to an automatic transmission vehicle. 

It separates the engine from the load and keeps the engine running when the vehicle stops at, say, a stoplight.

Torque converter transmission vehicles offer smooth gearshifts and acceleration from low speeds. However, when pitted against the manual version of the same car, they are slower and less fuel-efficient. Torque converter transmissions also tend to perform better than other types of automatics in heavy-duty situations, thus, they’re more commonly used in four-wheelers and for towing trucks.

This gearbox type has been around since the ‘50s and is also called the classic or traditional automatic transmission.

Single Clutch Auto

Single clutch transmissions (SCT) and its close counterpart, the double-clutch auto (DCT), are essentially like manual transmissions in that they use a clutch to disengage the engine between shifts. The difference? Instead of shifting the gear manually, the car does it by itself, using a sophisticated electronic and hydraulics system. As such, vehicles with single or double-clutch auto don’t have a clutch pedal. They have only the accelerator and brake pedal, as in traditional automatic vehicles. 

During their first decade of existence, most manufacturers struggled to make single-clutch transmissions work correctly. They were sluggish and jerky during gear shifts. For the best experience, drivers had to treat their vehicles like manuals, usually lifting their foot off the gas pedal when shifting—just like you would in a manual car. Because of its unreliability, single-clutch autos were eventually overtaken by dual-clutch autos.

Dual Clutch Auto

If the name didn't give it away already, the dual-clutch transmission (DCT) uses two clutch systems—one for the odd-numbered gears and the other for even-numbered gears. As a result, this gearbox can pre-select the next gear before the shift happens. Consequently, the transitions are faster than with single-clutch gearboxes. When compared with other gearboxes, the shifts are also smoother and can even be undetectable. 

The DCT offers better fuel economy and is far smoother to drive, but it’s got a few cons too. It is expensive to manufacture and repair because of its complex mechanical structure. Also, while changing from a lower gear to a higher gear is often seamless, the same cannot be said about switching from higher to lower.

When you're changing from a, say 4 to 3, it can take some time to deselect gear 5 and select gear 3. That can be a disadvantage when you're trying to overtake another vehicle quickly. 

DCT is called direct shift gearbox (DSG) in the Volkswagen Group cars (Volkswagen, Skoda, and SEAT), Porsche calls it the PDK, and Audi calls it the S-Tronic. All these terms mean the same thing, so don't let marketing jargon confuse you.

Both SCT and DCT are manual transmissions with an automatically controlled clutch. That explains why they are also referred to as Automated Manual (AMT), Semi-Automatic Transmission (SAT), or “Clutchless” Manual Transmission (CMT). 

CVT

Continuously Variable Transmissions are an automatic transmission type that’s been rapidly gaining popularity in recent years. Unlike a traditional automatic transmission, CVT doesn’t use any gears or swap through a set of pre-determined speeds. 

Instead, it uses two pulleys connected by a belt to transfer power from the engine to the wheels. This configuration allows it to constantly vary the drive ratio infinitely and produce the most efficient driving speed at every point in time. Hence, the engine runs more efficiently.

CVT is the most fuel-efficient of the three automatic types we've reviewed. It is popularly used in many Toyota, Honda, Nissan, and Mitsubishi models. That said, let's wrap things up by considering one commonly asked question.

What is the difference between CVT and automatic transmission?

First, it's important to remember that CVT is a type of automatic transmission. Put your gear in "D" position, hit your pedals, and you're good to go. But as a rule, whenever you hear the terms "automatic transmission" or "traditional automatic transmission,” it usually refers to vehicles with torque converter transmission. This implies that we can rephrase our focus question as “torque converter vs CVT."

Compared with traditional auto vehicles, CVTs offer superior fuel economy and smoother acceleration—qualities any driver would love. CVTs also win with manufacturers because they consist of fewer components and are consequently cheaper to manufacture. On the other hand, traditional automatics are far more serviceable and less expensive to maintain than CVTs. 

Wrap Up

Historically, torque converter transmissions are the most popularly used type in production vehicles. However, CVT seems to be taking over these days. If you're not an early adopter and you're considering buying a car with a CVT, then it's better to take your vehicle for a thorough test drive and be sure it's what you want.

For more helpful car tips, jump on our blog at Carpart.com.au


By Damilare Olasinde