New “Skip Fire” Cylinder Deactivation Could Launch by 2020

A next-generation cylinder deactivation system being developed by Tula Technology Inc. could arrive in a production vehicle by 2020, company officials say. The system, dubbed dynamic skip fire, promises to hike the fuel efficiency of large SUVs by as much as 21%.

General Motors Co. touted the DSF system in January as being able to improve the fuel economy of 4-, 6- and 8-cylinder engines about 15%.

Tula and Delphi Automotive plc demonstrated the latest iteration of the technology last week near Detroit in a GMC Yukon Denali with a 6.2-liter V-8 engine. Delphi and GM are investors in Tula and are working with the Silicon Valley-based startup to commercialize the system. GM is expected to be the first carmaker to use DSF.

Tula says tests of a V-8-powered fullsize SUV equipped with the system have shown as much as a 21% improvement in fuel efficiency. The company estimates it would cost carmakers $300-$600 per engine to add the technology to existing powerplants.

As with current cylinder deactivation systems, DSF switches off two or more cylinders under low-load conditions. Until now, such systems have been fixed firing patterns with only half of an engine's valves equipped with the technology.

DSF is active on all cylinders and makes continuous decisions about how many and which cylinders should fire. Another difference: The throttle flap is kept almost fully open to improve airflow efficiency.

In last week's test in the Denali, all but two of the V-8 engine's cylinders were turned off while the vehicle cruised at highway speeds conditions in which the vehicle requires only about 30 hp to maintain speed, Delphi notes. Additional cylinders were activated immediately as needed during acceleration.