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Eaton optimized TVS scavenging pump managing precision airflow for CARB-sponsored, Achates opposed-piston engine

Eaton will supply a TVS (Twin Vortices Series) air pump to manage airflow in the demonstration of the Achates Power two-stroke opposed-piston engine (OP Engine) at the upcoming Internal Combustion Engine Fall Technical Conference in San Diego.

The Eaton device for the opposed piston two-stroke device is a scavenging pump, not an EGR pump, notes Mihai Dorobantu, director, Technology Planning and Government Affairs, Eaton Vehicle Group. However, the TVS scavenging pump is conceptually very similar to the TVS EGR pump Eaton recently showcased at IAA.

Eaton EGR Image

Eaton TVS EGR pump.

Eaton’s TVS air pumps currently supply airflow to several Achates OP Engine prototypes; these will gradually transition to a new Eaton TVS air pump currently under development. Fundamental to the OP cycle is the air pump, which is the key air management technology and an enabler of the engine’s outstanding performance.

The current opposed piston engine device is a modified TVS supercharger that was available when the design of that engine started, Dorobantu said. Eaton is working with Achates to understand the best timing to switch to a prototype TVS air pump. This is a complex decision, Dorobantu said, as there are many “moving parts” with both engine, truck and air pump.

We moved the maximum efficiency of the device to suit the opposed-piston specific gas exchange needs, while minimizing the power draw. We also made the intake compatible with the engine architecture, i.e., the pump intake is now at boosted pressure. Because of the higher pressure and temperature conditions, we are lubricating the pump with engine oil and have a novel sealing strategy. We modified the lobe geometry and developed a new coating to eliminate the impact of EGR. Finally, we reduced the operating speed to promote the longer life needs of commercial vehicles.

—Mihai Dorobantu

The on-road demonstration project is funded by a $9-million grant from the California Air Resources Board (CARB) to CALSTART, an organization supporting clean transportation that is overseeing the project. (Earlier post.)

The OP Engine will power the CALSTART Class 8 commercial truck, which is expected by CALSTART to achieve a 90% reduction in NOx and a 15–20% fuel efficiency improvement.

Eaton is pleased to contribute to this promising project that has the potential to dramatically reduce emissions and increase fuel economy in diesel engines. Eaton’s TVS air pump, with its ability to produce a precise, controllable airflow, is the ideal solution for the OP Engine.

—Mihai Dorobantu



The growth in engine complexity is one more indication that we may be reaching "peak engine." With each passing month, more and more of the public become aware of the electric option. We just need to see cost reductions to see the market change.


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