In the area of engine boosting, the name Eaton is synonymous with supercharging. Company engineers are hard at work designing them so they perform better while limiting their cost.
Mike Froehlich, Manager, Advanced Engineering, Vehicle Group, Supercharger division, Eaton, on April 17 presented a paper at the SAE 2013 World Congress in Detroit and also sat for a video-interview with AEI. He discussed a number of matters in both, including the trend of compound boosting as a way to meet the growing demand of customers for better fuel economy (in addition to, or as opposed to, enhanced engine output).
In the interview he was asked to describe the relative advantages of superchargers and turbochargers. "Both devices have their advantages," he said. "The supercharger really offers good instantaneous boost response. Just putting a supercharger on an engine won’t necessarily give you better fuel economy. It’s gotta be a complete system design, with the OEM; they have to design their engine, their transmission, their drive ratios to really offer the best potential benefit that you can get in terms of fuel economy. I think you're going to see more in the future the true optimum solution is a combination of the two, such as Volkswagen Twincharger."
In his paper co-authored by his Eaton colleague Nathan Stewart, he wrote: "Continued advancement in combustion has reduced knock limitations, enabling higher brake mean effective pressure levels at lower engine speeds and making compound boost systems more attractive."
Froehlich and Stewart's paper (2013-01-0919) details how improvements have been incorporated into Eaton's TVS V-Series (TVS=twin Vortices Series; V=Volumetric Series) superchargers. Development of the V-Series focused on rotor length, diameter, and helix angle, as well as inlet and outlet port geometry, optimized for performance and NVH characteristics.
The "final output of this optimization," they write, is the V250. The combination of smaller rotor L/d ratio (see figure) and three lobes per rotor reduces the length of the rotor tips and flanks by approximately 28% over a TVS R-series model of comparable displacement … The optimized design parameters developed for the V250 were then used to create a model displacing 400cc per revolution, the V400. The reduced rotor tip length multiplied by fewer rotor lobes, combined with other minor differences in geometry, results in approximately 32% less leakage cross sectional area per unit displacement in the V-Series designs than TVS R-Series units of similar displacement.
The goals of improving low-speed volumetric and thermal efficiencies were achieved, the authors say. Volumetric efficiency is improved across virtually all of the operating range, while isentropic efficiency is better than R-Series at low speeds but not as good as R-Series at higher speeds and pressure ratios.
The improved low-speed volumetric efficiency of the V250 and V400 offer the ability to reduce the minimum engine peak torque speed or meet low speed engine torque targets with a drive ratio lower than that which would be required of an R-Series unit of similar displacement. Achieving peak torque with a lower drive ratio results in less air that must be bypassed at higher speeds, thus increasing overall engine efficiency.
Both TVS R-Series and TVS V-Series models are targeted for two-, three-, and four-cylinder gasoline and diesel engines ranging from 0.5 L to 2.0 L of displacement, as a single boost device or as part of a compound boost system. Eaton has also developed an R570 and is working on a V600, along with other sizes.