Engines with Small, Individual Turbos for Each Cylinder Could Revolutionize Downsizing ""

By | October 18, 2017

Engines with Small, Individual Turbos for Each Cylinder Could Revolutionize Downsizing

From the October 2017 issue

Downsized turbocharged engines have become a cornerstone in the car industry’s effort to increase fuel economy. And as CAFE stand­ards push us toward a 54.5-mpg fleet average, engines are bound to get even smaller and turbo boost even higher. Such radically downsized engines can be strong at full throttle but tend to be sluggish from a stop.

Automakers are exploring plenty of solutions to this problem, including staged turbos, variable-geometry turbines, and electrically driven compressors. Jim Clarke has a more radical idea. Thus far, it’s all theory—no prototype has been built or tested—but it’s a theory with 27 claims covered by a patent and with a weighty résumé behind it. Over the course of a long career at Ford, Clarke was responsible for the modular V-8 and the Duratec V-6, including the Yamaha-built V-8 and Aston Martin V-12 variants. He was also engineering vice president at Navistar, the heavy-truck manufacturer that owns International Trucks, and he headed up special projects for Kohler Engines. His technical partner, Dick Fotsch, is a past president of engine divisions at Navistar and Kohler. Combined, the two have some 60 years of executive-level engineering and management experience. (Full disclosure: Clarke was this author’s manager decades ago at Ford.)

Engines with Small, Individual Turbos for Each Cylinder Could Revolutionize Downsizing

The first element of the design, which they call “synergistic induction and turbocharging,” is to place individual throttles—two per cylinder, one for each intake port—right next to the cylinder head. “Between the throttle and the intake valves, the typical engine has an intake-manifold volume roughly equivalent to the engine displacement,” Clarke says. “That takes time to fill when you open the throttle.” His configuration allows the cylinders to fill much more quickly, rapidly generating full torque and a maximum dose of high-energy exhaust gas. Exploiting that exhaust is the next key idea.

“The closer you put a turbocharger to the exhaust valve, the more energy reaches the turbine to accelerate it,” explains Clarke. Therefore, the synergistic engine has an individual turbo for each cylinder placed as close as possible to the exhaust valves. These turbos can be smaller than they’d be on a single-turbo engine—20 percent smaller in size (50 percent less flow) on a three-cylinder. Smaller turbos mean less rotational inertia, allowing these tiny blowers to spool up more quickly than most current setups. Clarke estimates that his synergistic engine concept could eliminate perceptible turbo lag altogether.

The theory seems promising, but the system requires considerable parts multiplication. On the three-cylinder example, there would be three turbos and six throttles, instead of one each, as well as additional plumbing to interconnect the individual intake and exhaust passages. Three small turbos, of course, might only cost 50 percent more than one large one, and few of the other components are particularly complex or exotic. The question is how well the concept’s performance and cost compare with other lag-mitigating techniques—which are not inexpensive, either. But innovation is rarely cheap.

Remember the ’80s?

Clarke clearly recalls the instant response of a BMW M6 he drove in the 1980s. He attributes that characteristic to its engine having an individual throttle for each cylinder, an arrangement that reduced the amount of air between the throttle and the intake valve. This engine concept takes that premise a step further.

Remember the ’80s?

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