Delphi has made a minority investment in Tula Technology, the developer of Dynamic Skip Fire cylinder deactivation technology. (Earlier post.) The software-enabled powertrain technology integrates advanced digital signal processing with advanced powertrain controls to create a variable displacement engine.
DSF allows the engine’s cylinders to fire or skip (deactivate) on a continuously variable basis. In independent tests, DSF has improved fuel efficiency by up to 17% as measured on a CAFE basis when compared to a vehicle (V8 engine) that does not have cylinder deactivation. GM Ventures made an equity investment in Tula in 2012.
|Comparison of DSF fuel economy gains and costs with competing technologies. Wilcutts et al. (2013) Click to enlarge.|
The significance of this new relationship goes beyond the investment itself. Delphi’s strong expertise in engine management systems and valvetrain components will help us to further optimize the overall performance of DSF and accelerate the deployment of our unique technology for three, four, six and eight-cylinder engines.—R. Scott Bailey, president and CEO, Tula Technology
Tula’s control approach integrates advanced digital signal processing, culled from consumer electronics technology, with powertrain controls. DSF technology does not rely on fixed cylinder deactivation or switching between fixed patterns. Rather, it incorporates any-time, any-cylinder deactivation and can continuously vary the number of cylinders firing, along with cylinder load.
In a 2013 SAE paper, the Tula engineers described two primary benefits from dynamic skip fire technology:
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.
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. Operating the engine in a dynamic skip fire manner alters the torque excitations on the vehicle powertrain, which could lead to unacceptable noise, vibration and harshness (NVH) characteristics.
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.
|An example of a firing sequence that fires one cylinder followed by two skipped cylinders. The pattern will repeat after three engine cycles for an 8-cylinder engine. Serrano et al. (2014)|
Chien, L., Younkins, M., and Wilcutts, M. (2015) “Modeling and Simulation of Airflow Dynamics in a Dynamic Skip Fire Engine,” SAE Technical Paper 2015-01-1717 doi: 10.4271/2015-01-1717
Chen, S., Chien, L., Nagashima, M., Van Ess, J. et al. (2015) “Misfire Detection in a Dynamic Skip Fire Engine,” SAE Int. J. Engines 8(2):389-398 doi: 10.4271/2015-01-0210
Serrano, J., Routledge, G., Lo, N., Shost, M. et al. (2014)“Methods of Evaluating and Mitigating NVH when Operating an Engine in Dynamic Skip Fire,” SAE Int. J. Engines 7(3):1489-1501, doi: 10.4271/2014-01-1675
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