Audi selects Altera SoC FPGAs for production zFAS piloted-driving systems
BMW i ChargeForward Program to demo contribution of intelligent EV charging to grid efficiency

New GM/Tula DSF cylinder deactivation technology could boost fuel efficiency in engines by up to 15%

Comparison of DSF fuel economy gains and costs with competing technologies, from Tula’s 2013 SAE paper. Wilcutts et al. Click to enlarge.

GM is working closely with Tula Technology, a Silicon Valley-based supplier of Dynamic Skip Fire (DSF)—a software-enabled powertrain technology that integrates advanced digital signal processing with advanced powertrain controls to create a variable displacement engine. In 2012, GM Ventures made an equity investment in Tula; in 2013, Tula engineers presented a paper on their technology at the 2013 SAE World Congress.

Independent testing commissioned by Tula finds that the application of DSF technology can improve fuel efficiency in a multi-cylinder engine (4/6/8 cylinders) by as much as 15% when compared to a vehicle equipped with an engine that does not have cylinder deactivation.

Selective firing of engine cylinders has been used for load control going back at least to the late 19th century in agricultural engines common at the time regulated by a governor which cut off cylinders to maintain constant speed. In automotive applications, engine torque production is demanded by the vehicle driver in an often highly transient manner. The basic concept of Dynamic Skip Fire technology is to manage torque production in response to the driver command via selectively engaging or disengaging torque production from engine cylinders rather than by throttling. The operation of each firing cylinder can be optimized for best thermal efficiency, subject to possible constraints such as air-fuel mixture ratio, peak pressures or temperatures (durability), and other factors.

—Wilcutts et al.

Instead of relying on fixed cylinder deactivation or switching between fixed patterns as in current multi-cylinder engines, Tula’s DSF technology continuously makes dynamic firing decisions on an individual cylinder basis to deliver the required engine torque for all vehicle speeds and loads.

In their 2013 SAE paper, the Tula engineers described two primary benefits from dynamic skip fire technology:

  1. Fuel economy improvement via removal of pumping losses and optimization of combustion. For each engine speed, a sweet-spot of thermal efficiency for operating cylinders exists which is at high load for throttled engines due to minimized pumping loss. With combustion occurring preferentially in this regime, the engine combustion system can potentially be optimized to match this operating area. With intake or exhaust (or both) valve deactivation in place, inactive cylinders are prevented from pumping air through the engine, which enables effective use of three-way catalyst technology.

  2. Wide authority over generation of vibrational and acoustic excitations. In normal throttled operation of an engine, excitation spectra are tied to the engine speed, and magnitude is determined by the level of throttling. With dynamic skip fire technology, the spectra are additionally controlled by the number and sequence of firing cylinders. Full dynamic control of firings and non-firings of engine cylinders means that noise, vibration and harshness (NVH) can be dealt with algorithmically, in a flexible and systematic way.

DSF operation tracking engine torque demand. Click to enlarge.   Active NVH management algorithm. Click to enlarge.

Tula’s DSF technology does not rely on fixed cylinder deactivation as in current-production systems, or on switching between fixed patterns (as earlier patented by Daimler-Benz). Rather, it varies the firings and skips continuously with load demand.

Tula licenses its control algorithms to customers via a co-processor solution.

This technology holds the potential to improve fuel economy on select GM vehicles without degrading power capability when it’s required. This joint effort combines software expertise from Silicon Valley with powertrain expertise from General Motors.

—Jon Lauckner, GM chief technology officer, vice president of Global R&D and president of GM Ventures

In addition to the ongoing partnership between the two companies, Ron Yuille, Tula’s Vice President of Powertrain Engineering and Business Development, had held various executive positions within GM, including vice president of powertrain engineering for GM International Operations, vice president of powertrain operations for GM Daewoo and president and CEO of GM Isuzu Diesel Engines Limited.

Since its founding in mid-2010, GM Ventures’ international portfolio includes investments in more than 20 startup companies.


  • Wilcutts, M., Switkes, J., Shost, M., and Tripathi, A. (2013) “Design and Benefits of Dynamic Skip Fire Strategies for Cylinder Deactivated Engines,” SAE Int. J. Engines 6(1):278-288 doi: 10.4271/2013-01-0359



That is really clever.
If it works, it will be a great deal.
I had no idea how large pumping losses were.
Nice to see what happens when you apply some blue sky thinking and s/w to ICEs.


The basic problem for IC still exists: Burning hydrocarbons in the atmosphere and killing people with the exhaust gasses; Nevertheless, this is an advancement of an old idea that has not worked to expectation as yet.


One of the advantages of fuel cell vehicles is they emit no smog producing NOx nor unburned hydrocarbons, but still have range and quick refilling.

I think the solution may be FCVs that have adequate batteries for short trips, a PHEV with a fuel cell range extender. Now get the hydrogen from reforming cellulose ethanol on the car to get closer to "sustainable mobility".

Dr. Strange Love

I am not a big fan of these cylinder deactivation schemes. Unloaded piston rings and net-negative cylinder pressures (relative to the crankcase) result in excessive oil accumulation in those inactive cylinders. Oil loss is a big problem with this.

Honda claims 1 QT per 1000 miles for their VCM-2 V6 engines is acceptacle. This is rubish. (see the most recent class action lawsuit -- customers with fouling SPs on VCM cyl. and possible ring jobs).




The algorithms to prevent the NVH which should automatically follow cylinder deactivation, seems the most clever aspect of this. But as Mahonj says, "Great if it works".


The graphic shows the DSF system at work on an 8 cylinder engine. Funny, I thought the preference was for 6 cylinders, going down to 3. Is this system really for an 18 wheeler?

The comments to this entry are closed.