Many OEMs have engines in their portfolios that use the Atkinson cycle, as the nature of the system allows for increased efficiency of the combustion process. However, these engines lack a “simple mechanism capable of fully producing the Atkinson cycle,” according to Lugo Developments Inc.
The Lugo mechanism
The Lugo mechanism, previously called the Lugo engine, is an enabling component for the introduction of the Atkinson cycle, as well as other engine technologies. Simon Perez, President, Lugo Developments Inc. notes, “Interaction with our peers at the SAE 2015 World Congress and Exhibition resulted in a change to our terminology, from engine to asymmetric crank mechanism.”
The mechanism consists of a pinion gear and a cam mounted onto a crown gear. “You require one pinion and one crown cam per cylinder for inline engines, and a pinion gear and a double cam crown cam per two cylinders for V engines. The pinion gears mount onto the block concentric with the crank axis, and the crown cam mounts onto the crank pin and rotates about this pin,” he explains.
Perez and his team have not designed a new engine in its entirety, but rather a small mechanism that can be implemented into existing engines. He believes that the Lugo mechanism could provide a number of benefits that would be extremely positive to the automotive industry and the future of powertrain technology.
Powertrains using the mechanism will “receive the benefits of a true Atkinson Cycle” – which are increased efficiency of the combustion process. This occurs through an enlarged power stroke compared to that of the compression stroke, which maximises energy output. It is complimented by the bonuses of variable compression ratio (VCR), as the engine can change compression ratio depending on the power and performance needs – again enhancing efficiency.
The mechanism also enables the engine to obtain “15 degrees of positive torque before Top Dead Centre (TDC),” which “opens up solutions to implementing Homogeneous Charge Compression Ignition (HCCI) and Gasoline Direct Injection Compressed Ignition (GDCI). You are giving the design engineer a football field to implement combustion strategies compared to existing engines.”
TDC is the description used for when the piston is at the farthest or nearest position in relation to the crankshaft. By controlling the amount of torque before this event, Perez believes that the engine can save a significant amount of fuel.
Finally, because of the simple design, “the engine essentially remains the same, so engines don’t have big concept changes that mean retooling and relearning.”
Key breakthroughs
Of the benefits described above, Perez believes that there is one that stands out from the rest. He says that the “most important feature is that the mechanism gives the engineer an unprecedented positive torque beginning at 15 degrees before the piston reaches TDC.”
It is during this process that fuel savings through the use of the mechanism are most prominent. Uncontrolled combustion before TDC is highly counter-productive for the engine, explains Perez.
That said, he also believes that the “true mechanical Atkinson cycle with expansion volume and intake volume of 1.3 to 1.8,” whilst enabling “VCR that can be designed with variations from as low as 8:1 to over 22:1” are also extremely positive features when considering the future of the powertrain.
Validate and alleviate
The next step for Perez and his company is to bring the Lugo mechanism into production. “The biggest challenge facing the technology is validation. We have started conversations with the makers of test engines to make the Lugo mechanism available for academic and industry researchers, and we need to convince a powertrain manufacturer to put Lugo into one of their engines,” he says.
Toyota is well known for using Atkinson cycle engines. The company’s new redesigned Tacoma 2016 comes in the form of either a 2.7-litre or 3.5-litre Atkinson cycle engine.
Perez is certain that the demand for the Lugo mechanism is “evident.” He is confident that the industry will start reaping the benefits of the mechanism shortly, and points to the “long future ahead of gasoline and diesel-based engines,” suggesting that the Atkinson cycle will become an “increasingly vital” way of meeting legislation and requirements.
Michael Nash
