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Detroit Expands DT12 Transmission Lineup, Re-engineers DD15 Engine for Better Fuel Economy


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Heavy Duty Trucking (HDT)  /  May 26, 2020

Enhancements to the Detroit DD15 engine, combined with an expanded lineup of the DT12 automated manual transmission, have resulted in improved fuel economy, performance and durability, according to the company.   

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: the DT12-HE, DT12-H, and DT12-HL. The DD15 Gen 5 engine has also been updated and engineered to improve efficiency for the Freightliner Cascadia, and it will be available for January 2021 truck builds.

The new DT12 Transmission Lineup

The all-new DT12-HE transmission option offers higher overall ratios for improved downspeeding and an improved oil system design, both contributing to increased efficiency. It will debut with Cascadia production beginning in early 2021, with additional model applications to be announced soon.

The DT12-HL is a lightweight carry-over option intended for weight-sensitive applications. The DT12-H is a revised designation that retains the same characteristics of the previous DT12. Both the DT12-H and DT12-HL are currently available for order in Cascadia builds.

The Detroit DD15 Generation 5 engine

The new DD15 Gen 5 engine includes increased downspeeding, improved combustion, and a new swirl piston design. A combination of almost 50% new componentry and fine-tuning by Detroit’s engineers results in up to a 3% improvement in fuel efficiency from propulsion alone, according to the company.

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 now reached at 1,500 rpm versus the prior generation’s 1,625 rpm, and peak torque is achieved at 900 rpm versus 1,075 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 makes combustion cleaner and more efficient than the previous generation of the DD15.

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 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. To accomplish this, ThermoCoasting will engage engine brakes when necessary between 900 and 1,500 rpm while the engine mimics coasting by maintaining zero torque at the flywheel to balance power delivery.

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