Phrase Of The Day: "Torsional Excitations"

Edward Niedermeyer
by Edward Niedermeyer

What keeps powertrain engineers up at night? C’mon, get your mind out of the gutter. The move towards downsized, turbocharged engines is creating a number of new engineering challenges, and “torsional excitations” grabbed the spotlight at this year’s Society of Automotive Engineers Congress. Steven Thomas, manager of Ford’s global transmission and driveline, research and advanced engineering, illuminated the issue [via Wards].

As we reduce the engine torque, particularly just off idle prior to the boost coming on, we’re going to adversely impact the ability to accelerate the vehicle. I would challenge you all to think about new ways of dealing with this. We could really use new designs to deal with these challenges to optimize the fuel economy, but at the same time deal with (noise, vibration and harshness) and performance issues presented by these new engines.

The problem: the increased inertia of forced-induction engines. The practical example: a turbocharged Fiesta. A worthy adversary, a worthy cause. Let’s do this.

Inertia is already a challenge for the Fiesta, as Thomas reveals that

Ford’s new DCT, which also appears this year in the ’12 Focus, is “great for CO2 reductions and fuel economy, but I have to tell you one of its challenges is the amount of inertia in a dual dry-clutch assembly.”

Add a downsized, forced induction engine, which the Fiesta was not designed for, and the potential for “torsional excitation” rises. One possible solution, the use of dual-mass flywheels, is being tested by Ford for use in a possible turbocharged Fiesta, but initial results show it could actually increase engine friction by as much as 15%. If “DMF”s don’t work, the options become somewhat more limited:

Pendulum dampers are being considered to address the problem. And with automatic transmissions, torque converters incorporating improved dampers can quell some of the vibrations, but more work is necessary.

And, says Thomas, three-cylinders are even tougher to keep smooth, as their uneven firing pattern works with torsional excitations to create severe NVH conditions. The future of engines may be downsized and turbocharged, but it’s still got a few bad vibrations to work out.

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  • DasFast DasFast on Apr 17, 2011

    I think the perfect solution is already here from the combined efforts of Rotrex and Torotrak. They're joined in a venture called (obviously enough) Rotrak. The best supercharger made meets a small CVT drive. This setup could accomodate multiple power/boost profiles depending on what the situation calls for, including a torque mode that would keep the compressor spinning at decent speed just off of idle. From what I understand making it more affordable is where the rest of their efforts lie.

  • Davekaybsc Davekaybsc on Apr 17, 2011

    Audi seems to have it right with their 2.0T. The A4 is generally faster than the 328i off the line, and is also faster 30-50 and 50-70. It does definitely lose in smoothness though, the turbo 4 is definitely nowhere near as smooth in operation as the straight 6.

    • See 1 previous
    • Diesel Fuel Only Diesel Fuel Only on Apr 17, 2011

      Lorenzo: Not to mention that once you go to a V-8, or even a V-6, you have double the number of heads, twice the head gaskets (in theory), the crank now needs counterweights and balance shafts, double the number of cams, two timing belts/chains, all unnecessary moving parts and unnecessary weight compared to a Straight-6. That weight so far forward also ruins your handling. Agreed that the slant-six was a great engine. The cars were economical on fuel and had good mechanical reliability at a time when so many four-cyl. engines, even years later, were downright crude. Aside: many European commercial engines are also I-6 diesels.

  • MRF 95 T-Bird Back when the Corolla consisted of a wide range of body styles. This wagon, both four door and two door sedans, a shooting brake like three door hatch as well as a sports coupe hatchback. All of which were on the popular cars on the road where I resided.
  • Wjtinfwb Jeez... I've got 3 Ford's and have been a defender due to my overall good experiences but this is getting hard to defend. Thinking the product durability testing that used to take months to rack up 100k miles or more is being replaced with computer simulations that just aren't causing these real-world issues to pop up. More time at the proving ground please...
  • Wjtinfwb Looks like Mazda put more effort into sprucing up a moribund product than Chevy did with the soon to be euthanized '24 Camaro.
  • Wjtinfwb I've seen worse on the highways around Atlanta, usually with a refrigerator or washer wedged into the trunk and secured with recycled twine...
  • Wjtinfwb Surprising EB Flex hasn't weighed in yet on it being the subject of a recall...