“Most powertrain engineers have a conventional understanding of how to achieve fuel efficiency,” says Scott Bailey, CEO of Tula Technology (tula-tech.com). He does. He spent most of his career at Delphi Powertrain Systems, where he focused on the mechanical side of developing engines that burn less fuel. Now with Tula, Bailey says his approach is no longer conventional. Why? Because Tula also focuses on software, on the integration of advanced signal processing with powertrain controls to help the mechanisms achieve fuel savings and, Bailey says, cost savings for automakers without requiring radical changes in engine design.
So, what’s Tula’s secret and why is no one else doing it?
The strategy is called “dynamic skip fire.” Tula software uses control algorithms to operate the engine at its “fuel-efficient sweet spot” by firing only the required cylinders to meet the torque demanded by the driver’s foot on the acceleration pedal, thereby minimizing pump losses that hinder fuel economy. Bailey says the technology saves 15 to 20% more fuel than existing engines without cylinder deactivation.
Bailey argues the reason Tula is the only company doing this goes back to the “conventional” mindset of powertrain engineers. And Tula has 10 patents and more than 40 others pending pertinent to the technology.
The company is co-located in San Jose, CA, and Plymouth, MI, to leverage the strong engineering base in both locations. In fact, Tula’s technology takes an old engine energy management concept (think: Detroit ingenuity) and couples it with leading software control (think: Silicon Valley computing power).
The skip firing concept dates back to the late 1800s, when engine load control on farm tractors was managed by a governor that cut off cylinders to limit speed. Fast forward a century and some modern production engines still use the concept, albeit with greater complexity. Selective-firing engines by Chrysler, General Motors, Honda, Mercedes-Benz, and VW/Audi deactivate specific cylinders under certain conditions in a fixed pattern.
The difference with the Tula technology is it doesn’t fix patterns; instead it varies the firings and skips cylinders as determined by the engine-control software. The processing also avoids firings that would negatively impact noise and vibration, Bailey says.
“Tula takes the software approach to variable displacement,” he explains.
To develop and demonstrate the capability, Tula engineers modified a 2010 GMC Yukon Denali SUV with GM’s Active Fuel Management system, which deactivates valves on four (1, 4, 6 and 7) of the eight cylinders under specific conditions. They added deactivating lifters to the remaining valves (2, 3, 5 and 8), modified the engine block to incorporate additional galleries to direct oil pressure to the lifters, and fabricated a new lifter oil manifold assembly with 16 solenoid valves to direct oil pressure to the galleries. These types of modifications are “relatively straightforward,” Bailey says.
With a manual transmission, the Tula engine improved fuel economy by 21% over the GM V8 in U.S. federal test procedure and highway fuel economy test cycles, according to Tula. An automatic transmission showed a 17% fuel economy boost with the new technology.
The dynamic skip fire strategy doesn’t just save fuel, it offers monetary savings as well, Bailey says.
Tula claims a cost of $30 per each percent of fuel economy improvement for its technology, compared to a $70 to $100 cost per percent of fuel savings improvement for the turbocharged, downsized engines in production today. The company based these figures on National Academy of Sciences data.
Considering the fuel/cost savings and that the technology is (relatively) easy to integrate, what’s holding up widespread acceptance?
“We are seeing pretty good acceptance. We have no pure invention yet to do, but we have continuous calibration adjustments, and with the length of powertrain development cycles we remain years away from actual production,” says Bailey.
Currently, Tula has three active development projects with global OEMs.—ZP