“New” Transmissions Help Boost Fuel Economy

CVTs and DCTs are gaining popularity, but they require unique fluids for best performance.
Matt Erickson | VICE PRESIDENT, PRODUCT DEVELOPMENT

Devices we can loosely call “transmissions” have been around for more than 100 years. One of the earliest units was developed in 1904 and contained two gears automatically selected based on engine speed.

Owing to the relentless pursuit of increased fuel economy, today’s automatic transmissions contain up to 10 forward gears. More gears mean the engine runs at optimum efficiency more often, boosting fuel economy. Engineers have also used lightweight materials and low-viscosity fluid – and less of it – to further increase efficiency.

Continuously variable transmissions (CVT) and dual-clutch transmissions (DCT) present the latest developments in automotive transmissions. These technologies have been around for decades, but they’ve only recently caught on in mass-produced vehicles. Today, I want to talk about these “new” transmission designs and explain their lubrication needs.

The Shift to CVTs

CVTs continuously and smoothly select the optimum gear ratio as operating conditions change, meaning the engine is always running at its ideal rpm for maximum efficiency. In a CVT equipped vehicle, the driver doesn’t feel gear changes like he or she does in a vehicle using a traditional stepped automatic transmission because, in essence, the transmission doesn’t “shift” gears. Some manufacturers program simulated shift points to create the illusion that the transmission is actually shifting. In reality, however, it uses a pair of pulleys that vary their diameters to adjust the effective gear ratio, similar to the CVT shown from a UTV.

The computer varies the pulley diameters so the engine can move the car as efficiently as possible, which improves fuel economy. Honda,* for example, says CVTs can increase fuel economy by 5 percent.

There are challenges, however. Most CVTs use a metal chain or belt to transfer torque between the drive pulley and driven pulley. A fluid with incorrect frictional properties can allow the belt or chain to slip. This not only leads to a bad driving experience, it can cause the belt/chain and pulleys to wear out, leading to expensive repairs.

DCTs Continue to Grow

While you’ll most likely find a CVT in a smaller sedan, DCTs are often used in sports cars and supercars.

Essentially, a DCT is an automatic transmission based on the architecture of a manual transmission. It consists of two manual clutches in the same housing. Most rely on computer-controlled, wet multi-plate clutches and do not require torque converters. By losing the torque converter and its inertia, DCTs gain energy efficiency. They provide more efficient shifts than traditional automatics because as one clutch engages, the other readies the next gear, reducing the time spent shifting and increasing the time spent putting power to the ground, improving efficiency. Properly maintained and lubricated, the system delivers smooth, split-second shifts – the perfect complement to a powerful, high-performance engine.

While DCTs are capable of seamless shifts, they can shudder or lurch at slow speeds. Transmission fluid with specific frictional properties is required to prevent shudder. DCT fluid must also have excellent film strength to provide protection during the high-heat operation native to high-performance sports sedans and supercars.

While automatic transmissions still dominate the market, CVT and DCT use has grown steadily for years and is expected to continue as automakers look for all the fuel-economy gains they can find.

It would be convenient if formulators could make a single lubricant for Automatics, CVTs and DCTs. But it’s impossible given their unique needs. That’s why we design 100% Synthetic CVT Fluid (CVT) and 100% Synthetic DCT Fluid (DCT) to round out our transmission fluid line. Each lubricant is specifically formulated to target the performance areas critical for its unique application.

This gives you a complete line of solutions no matter what you drive.

*All trademarked names and images are the property of their respective owners and may be registered marks in some countries. No affiliation or endorsement claim, express or implied, is made by their use. All products advertised here are developed by AMSOIL for the use in the application shown.

Reproduced With The Permission Of AMSOIL INC. All Rights Reserved.

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