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Stop-start + skip-fire

by Steven St. Laurent on

FCA has been looking into increasing efficiency by having “multiple displacement” and stop-start systems work with each other

Stop-start shuts the engine while at a temporary stop; FCA also has a “DECEL” system which cuts power to the engine while coasting, under some conditions. Skip fire activates some cylinders but not others, potentially in a more flexible manner than the current “MDS” which cuts half the cylinders in a Hemi V8 when they aren’t needed.

Potentially, the engine could increase fuel efficiency by up to 20%, and take better advantage of hybrid setups.

A recent patent application describes a variety of ways to implement stop-start with skip fire engines.  References go back to 1959, but work truly intensified starting in 2003, with a variety of people working on the problem. The current application is a joint project with Tula Technology and FCA as co-owners.

Several methods are basic variations on starting out with the engine off (through the stop-start system), and operating in skip-fire mode until a certain engine speed and/or load is reached (in skip-fire mode, at least one cylinder is firing and at least one has no air or fuel entering).  The target engine speed could be an idle speed, and the system could be set to prevent overshoot of the target engine speed. Manifold operating pressure can be a factor, and different engine-restart profiles can be programmed — say, based on pedal position. The target speed or skip behavior can be adjusted, too.

It’s a promising technology.


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