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BMW Explains The M550d xDrive’s Three Turbo System: Video 27
Posted by Kurt Ernst in Automotive, BMW, BMW M550d xDrive, Kurt, Technical, Turbocharging, video, Videos on 02 27th, 2012

Forced induction, in the form of supercharging or turbocharging, coaxes more horsepower out of an engine by cramming in more air. Both methods have fans and detractors, and both methods have their strengths and weaknesses. Superchargers are typically belt driven and therefore scavenge a small-but-measurable amount of power from the engine to operate. Turbochargers use spent exhaust gasses to drive a turbine and compressor, and therefore offer essentially free horsepower.

Turbochargers, however, have their limitations as well. Generally speaking, a smaller turbo, with a low-mass impeller, will spool up quickly but can’t produce significant power beyond midrange. Larger turbos take longer to spool up, (thus producing turbo lag), but typically generate more boost and produce a broader range of power. Twin-turbo systems, which have been in use for years, generally employ both small and large turbos to optimize power delivery across the broadest range possible.

If two turbos are better than one, then three turbos, if properly sized and sequenced, are better than two. That’s the thinking behind the TwinPower Turbo system (which, ironically, uses three turbos) that BMW is employing on the new, diesel-powered M550d xDrive sedan. At low engine speeds, a small turbo provides near-instant boost, before handing the force-feeding duties off to a second, slightly larger turbo. At high engine speeds, a third small turbo comes on line, ensuring that the additional power is delivered seamlessly across an engine’s speed range.

If you get the feeling that the system is complex, you’re correct. As the video below, courtesy of BMW Blog, demonstrates, the plumbing linking the turbos to the engine is complex, and the two smaller turbos benefit from variable geometry compressors. When working optimally, the system should produce impressive power and torque, delivered across an engine’s entire speed range. When something breaks out of warranty, however, owners may not have the option of taking the car to a local mechanic for repairs.

It’s a moot point for those of us on this side of the pond, anyway, since BMW isn’t importing any of the three-turbo diesel models to these shores. That’s probably a good thing, since it allows our Euro neighbors to fully de-bug the system before it comes to the United States. If it comes to the United States.

New Cafe Rules Not All Bad: Turbo Usage Expected To Triple 2
Posted by Kurt Ernst in Automotive, Forced Induction, Fuel Economy, Kurt, News, Technical, Turbocharging on 08 2nd, 2011

Turbos awaiting installation at Hyundai's Alabama plant.

If you want to get substantially better fuel economy out of a car or truck, your options for doing so are somewhat limited. You can lighten the vehicle, but doing so is likely to reduce overall strength or substantially increase the price. You can add a hybrid drivetrain, but that adds weight, increases complexity and adds to the price. You can downsize the engine, but few drivers are willing to accept a significant reduction in power just to gain a few more mpgs. There’s another choice, though, and it’s one that’s being rapidly embraced by manufacturers as the best and most cost-effective solution: downsize the engine, and then turbocharge it.

In the old days, turbos had a questionable reputation for reliability. Formula One engines of the 1980’s, for example, were small displacement, turbocharged four-cylinders that ran massive amounts of boost to create power. Calling these engines fragile is an understatement, and spectacular engine failures were common. Even on road cars, turbos often experienced bearing problems related to oil circulation, and engine failure was far more common than on less stressed, normally aspirated cars.

Not so with the new generation of turbocharged cars. Ford’s EcoBoost, for example, runs a modest amount of boost, but pumps the additional air into an engine that already has high compression and gasoline direct injection. High compression and turbocharging used to be a recipe for disaster, but today’s knock-sensing technology makes such a setup possible. The end result is more power, plus better fuel economy, from a smaller displacement engine.

Turbo and component supplier Honeywell sees the writing on the wall. Their vice president of engineering, Steve McKinley, summed it up by saying, “Engine downsizing coupled with turbos is the quickest way to make a significant improvement in the overall fuel efficiency of the U.S. automotive portfolio while maintaining performance levels.” In other words, now would probably be a very good time to invest in Honeywell stock.

GM agrees with this philosophy, too, and offers a 1.4-liter turbo option for their Cruze compact sedan. The upcoming Sonic will have a forced-induction engine choice, too, and don’t be surprised to see turbocharged fours replacing V-6s and I-6s throughout many manufacturer’s product lines.

More power from less gas? What’s not to like about that?

Source: Left Lane News