Detroit releases DT12 transmission series, redesigned DD15 engine
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Detroit releases DT12 transmission series, redesigned DD15 engine


David Sickels is the Senior Editor of Fleet Equipment. He has a history of working in the media, marketing and automotive industries in both print and online.

Detroit has enhanced its DD15 engine and has expanded the lineup of its DT12 automated manual transmission.

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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 of which are now available to order, Detroit says. Engineered with fuel efficiency and performance in mind, the new DT12-HE debuts with enhanced features and capability, the company adds.

The Detroit DT12-HE transmission is a new DT12 option which Detroit says boasts higher overall ratios for improved downspeeding and an improved oil system design, both contributing to increased efficiency. The DT12-HE debuts with Freightliner Cascadia production beginning in early 2021 and additional model applications will be announced soon.


Also included in the DT12 On-Highway Series is the DT12-HL transmission, a lightweight carry-over option offering comparable efficiency and durability to the rest of the portfolio and intended for weight-sensitive applications. Lastly, Detroit says the DT12-H retains the same characteristics of the DT12. Both the DT12-H and DT12-HL are currently available for order in Cascadia builds.

The DD15 Gen 5 engine has been completely updated and will be available with January 2021 truck builds. The Gen 5 advances Detroit’s heavy-duty engine platform (HDEP).

The new DD15 Gen 5 brings enhanced performance, durability and fuel economy for the Cascadia, Detroit says. The company says the complete rethink of the DD15 includes increased downspeeding, better combustion and a new swirl piston design. With the nearly 50% new componentry, the DD15 Gen 5 brings up to a 3% improvement in fuel efficiency from propulsion alone, and the engine also stands to reduce carbon dioxide emissions, the company says.


The company says 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.

Detroit says a new EPA GHG21-compliant aftertreatment system for the DD15 Gen 5 debuts a smaller unit design to reduce weight by more than 60 lbs. while increasing nitrous oxide conversion and, dependent on duty cycle, allowing increased diesel particulate filter service intervals.

The DD15 Gen 5 also debuts ThermoCoasting, a new feature that prevents aftertreatment cool down during a driving regen to keep the keep the system at the optimum temperature, Detroit says. 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, the company says. The DD15 Gen 5 also includes improved cooling circuitry and temperature distribution across cylinder heads.

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