Used primarily in passenger cars, the dual clutch transmission is in effect two gearboxes operating in parallel, each with its own clutch, according to Lubrizols web site, www.dctfacts.com. While the drive is going through one half of the gearbox, the other half of the box preselects the next expected ratio, ready for the first clutch to disengage and the second to engage in a precisely-timed sequence.

Proponents say DCTs combine fuel economy with smoothness and driving refinement to match the best automatic transmissions, while also providing the shifting response demanded by sporting drivers.

Efficiency
Getrag Ford Transmissions is a joint venture formed in 2001 for development and manufacture of transmissions in Europe. Ingo Steinberg, the companys chief engineer of central engineering, noted how the technology combines the best from manual and automatic transmissions. “If you would consider the current level of development, the DCT technology provides much better fuel economy than corresponding vehicles with automatic torque-converter transmissions, he said.

Tsunlock Andy Yu, BorgWarner Drivetrain Systems Groups vice president of engineering, said customer data over the last decade illustrates DCTs fuel efficiency benefits.

Weve seen up to 15 percent fuel efficiency improvement depending on the baseline that is used, also depending on the cycle that is used to measure the fuel efficiencies, he said. That said, there has been a lot of advancement since the DCT was first introduced, and advancements are primarily in areas of reducing oil usage. Most automatic transmission engineers would tell you pump [efficiency] loss is one of the significant areas of focus when it comes to improving transmission driveline efficiencies.

To boost pump efficiency, BorgWarner is looking at a couple of enablers. One is use of high energy friction material that can reduce the lube usage, therefore allowing the pump size to decrease, he continued. Additionally, with low-leak solenoids, that also allows for resizing of the pump so that you could look for efficiency improvements in that way.

Growth
Dave Morl, global business manager for Lubrizols Driveline Additives Group, said that in addition to likely future growth in Europe and China, Lubrizol also expects the DCT market to expand into North America and Japan.

From our experience and our market studies, we think globally growth to about 10 percent of the transmission requirements by around about 2015 will be DCT transmissions, he stated.

From our market research, we also expect future growth to occur not only geographically but into different applications like, say, commercial vehicles, he continued. Were very confident that vehicle designers and consumers alike will appreciate the easily understood benefits of DCTs, thus we expect adoption to be more expansive and at a faster rate than rival transmission types.

Getrag Ford Transmissions Steinberg expects dual clutch transmission technology to be introduced into North America and to China as well. Chinas government clearly support the introduction of dual clutch transmission technology as an enabler of CO2 emissions reduction, he explained. Regarding A and B class – smaller vehicles – the older force-feed torque-converter transmissions will be replaced by modern dual clutch transmission technology, leading to higher efficiency.

He noted that China has a manual transmission infrastructure, which lends itself perfectly for moving into the DCT arena. Additionally, Chinese OEMs and also Chinese end customers are very mindful of getting state of the art technologies, and DCT is the perfect match for that. Additionally, there is a lot of government regulation to push fuel efficiency up, and thats going to help DCT growth in China.

DCT Fluid Design
Morl emphasized that as early as possible is the ideal stage for the lubricant additive industry to be involved in development of a new transmission design. He noted that new transmission designs for DCTs focus on factors such as shudder, durability and fuel economy.

The impact in demand on the lubricant is considerable, Morl continued. From an additive development perspective, understanding the interactions between hardware and the many, many additive components really enables us to achieve the optimal balance in the DCT fluid.

He emphasized that the DCT additive technology is currently designed to have superior load-carrying capabilities, optimized friction performance, and greatly expanded protection for bearings. Its also important to maintain fuel economy and durability that the OEMs need, Morl added. Incorporating this technology effectively will help ensure the effective launch of DCTs by OEMs, he said, especially in emerging markets that are going to judge the new technology critically from a performance standpoint.

As DCTs become more sophisticated, Morl explained, the trend is towards higher energy densities. And theres more stress on the DCT fluid in areas like anti-shudder performance, friction durability, efficiency and load carrying.

So as a result, newer DCT fluids are specifically formulated for the transmission design, really with a focus on thermal durability, shear and oxidative stability, recompactability with the specific friction materials, and balancing this with base oil compatibility as well, he continued.

Synthetics Not Required
Panelists agreed that synthetic fluids arent required for DCTs.

From our experience in terms of testing and developing additives and lubricants, it is not absolutely required that a synthetic base fluid is needed in development of DCT fluids, Morl said.

BorgWarners Yu said that while the company has launched products with synthetic fluids, moving forward, many of its programs do not use a synthetic fluid.

I think there is some confusion out there relative as to what synthetics actually offer, he noted. And today I would say in most cases you could use a normally processed fluid and still be able to get the life performance, and also the low-temperature viscosity characteristic that works for the product.