Detroit’s new transmission series, redesigned engine offer better fuel economy, performance, durability for Freightliner Cascadia drivers

Detroit’s new transmission series, redesigned engine offer better fuel economy, performance, durability for Freightliner Cascadia drivers
Detroit has revamped the DD15 Gen 5 engine and offers three new transmission options designed to enhance Freightliner Cascadia tractors. (Courtesy: Freightliner)

PORTLAND, Ore. ― Enhancements to the Detroit DD15 engine and an expanded lineup of the popular Detroit DT12 automated manual transmission will benefit Freightliner Cascadia customers with better fuel economy, performance and durability.

The DT12 transmission has evolved into the DT12 On-Highway Series to offer three purpose-built options to meet the unique needs of various on-highway applications; all options are now available to order. Engineered with fuel efficiency and performance in mind, the all-new DT12-HE debuts with enhanced features and robust capability, according to a statement released by Freightliner May 26.

The DD15 Gen 5 engine has been completely updated and engineered to deliver the efficiency the market expects and is a perfect complement to the Cascadia tractor. The DD15 Gen 5 engine will be available with January 2021 truck builds. The Gen 5 advances the legacy of Detroit’s heavy-duty engine platform (HDEP), the most popular Class 8 heavy-duty engine platform sold in North America for the past five years, according to data from IHS Markit.

“The addition of the DD15 Gen 5 and DT12 On-Highway Series to the Detroit portfolio is sure to add to the momentum we have built by delivering the most robust and fuel-efficient powertrain on the market,” said Kelly Gedert, vice president of On-Highway market development for DTNA. “With a rich heritage of innovative engineering, world-class manufacturing facilities and access to a global tool kit of cutting-edge technologies, our customers demand Detroit solutions because they are the best in the industry.”

The new family of DT12 transmissions

The DT12 On-Highway Series pioneers new features for the DT12 transmission line.

The trifecta-topping Detroit DT12-HE transmission is an all-new DT12 option that unleashes ultimate performance, capability and efficiency, according to the manufacturer. Customer adoption is growing for downspeeding with faster rear axles ratios to achieve maximum powertrain fuel efficiency. In answer to this increasing demand, the DT12-HE transmission boasts higher overall ratios for improved downspeeding and an improved oil system design, both of which contribute to increased efficiency. The DT12-HE debuts with Cascadia production beginning in early 2021; additional model applications will be announced soon.

Also included in the DT12 On-Highway Series, is the DT12-HL transmission, a lightweight carryover option that offers comparable efficiency and durability to the rest of the portfolio and is intended for weight-sensitive applications. Lastly, the DT12-H, a revised designation for the stalwart of the portfolio, retains the same characteristics that have made the DT12 a favorite of fleets of all sizes. Both the DT12-H and DT12-HL are now available for order in Cascadia builds.

The DD15 Gen 5 Engine

The new DD15 Gen 5 engine advances the legacy of the highly capable, real-world validated DD15 to bring enhanced performance, durability and fuel economy for the Cascadia. A complete rethink of the engine and the application of precision engineering principles combine to provide cutting-edge improvements for 2021, including increased downspeeding, better combustion and a new swirl piston design. With nearly 50% new componentry for the DD15 and fine-tuning by the global team of Detroit engineers, the DD15 Gen 5 brings up to a 3% improvement in fuel efficiency from propulsion alone. As an additional benefit of more efficient operation, the engine stands to reduce carbon dioxide emissions.

A new ball bearing simple geometry turbocharger reduces friction and allows peak power and torque to be reached faster in the Cascadia. Peak horsepower is reached at lower engine RPMs of 1500 RPM versus the prior generation’s 1625 RPM, and peak torque is achieved at 900 RPM versus a previously rated 1075 RPM. Modified inlet ports in engine cylinders and a new piston bowl shape combine to create a swirl effect that creates a fuel-spray pattern for better atomization. Along with an ultra-high compression ratio, the new swirl design piston results in cleaner, more efficient combustion than the previous generation of the DD15.

The durability of many key components is improved thanks to reduced design complexity and increased robustness. A new EPA GHG21-compliant aftertreatment system for the DD15 Gen 5 debuts a smaller unit design to reduce weight by more than 60 pounds while increasing nitrous oxide conversion and, dependent on duty cycle, allowing increased diesel particulate filter service intervals.

The DD15 Gen 5 debuts ThermoCoasting, a new feature that prevents aftertreatment cool-down during a driving regen to keep the keep the system at the optimum temperature. To accomplish this, ThermoCoasting will engage engine brakes when necessary between 900 and 1500 RPM while the engine mimics coasting by maintaining zero torque at the flywheel to balance power delivery. Powertrain noise levels during ThermoCoasting are unobtrusive and parallel the decibel levels observed when in low engine brake setting. ThermoCoasting stands to benefit aftertreatment performance and is just one of many thermal management improvements made to the DD15 Gen 5, which also includes improved cooling circuitry and temperature distribution across cylinder heads.

Equipped with a DT12 transmission and DD15 engine, the Cascadia is a technological powerhouse of the open road, specifically designed, engineered and assembled for optimal efficiency, maximum utilization and lowest real cost of ownership, according to Freightliner.

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Detroit’s new transmission series, redesigned engine offer better fuel economy, performance, durability for Freightliner Cascadia drivers


Dd15 engine the rpm speed ratio is proportion. Like your speed is 80 mph. The rpm 1500 to 1600 the rpm. But if you compared LT A26 engine speed is 80 mph rpm is only 13.5. That a big deference. LT A26 cylinder bore is more bigger than dd15 and a connecting rod is more shorter than dd15. Meaning high speed rotation of every piston. LTA26 455 hp compare to 505 dd15 is more powerful than dd15 dome type of piston.