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The Future of Powertrains: What Will We See Under the Hood?

Appears in Print as: 'The Future of Powertrains: Everything but the Kitchen Sink'

The 2016 to 2025 CAFE standards will bring many significant alterations to automotive powertrains, with even more and greater change to follow.
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The accent is unmistakably British, but Dr. David J. Brooks, Product Group Director, Engines at Ricardo, Inc. (ricardo.com), isn’t some U.K. propeller head for whom future powertrains are an intellectual exercise. “When I moved to the States,” he says, “the first thing I bought was a Hemi-engined Dodge Challenger. If I was going to be living here, I had to check that box.” Brooks also understands the differences between driving comparatively short distances in the U.K. (it is only about 320 miles wide) and the U.S., where “you might get in and drive for 24 hours fully laden with kit, a boat, kids and dogs. And the vehicle is expected to do that without any issue.”

What Powertrain Changes Are Coming?

So what does the automotive future look like in light of coming fuel economy and emission standards? According to Brooks, there will be few dramatic changes in powertrains in the next few years as OEMs meet the new CAFE standards with existing technology. Downsizing has begun, the number of boosted engines is increasing almost as quickly as the number of gears in transmissions, and variability is being added to both intake and exhaust cams.

Electric Boosting

Electric boosting—a super capacitor-driven electric turbocharger that fills the torque troughs the larger exhaust-driven turbo can’t meet—will follow. Working in tandem with a belt starter generator, it adds power directly to the crankshaft when not providing boost. Hybrids, driven by CAFE subsidies, will be more common, but still bit players. Reduced weight, improved aerodynamics, decreased friction, and more efficiently sized vehicles will help automakers keep many of their current powertrains, but when standards demand a fleet average of more than 50 mpg, everything changes.

Turbocharger Design

According to Brooks, in 2025 and beyond, “The engine is downsized again and more highly boosted. Expect multi-stage—twin, triple, even quadruple turbine blades—to get low-transient and high-transient performance. Plus, you will have energy recovery with two stages of electric boost, and switch between the two when needed to reduce pumping losses when you don’t need them. The excess then going into the batteries or super capacitors.”

But it doesn’t stop there.

Engine As Generator

“The real pie-in-the-sky stuff,” he continues, “is both using regenerative braking, minimized combustion and split-cycle engines, where the engine is a generator ticking away in the background in conjunction with alternative fuel or battery technology.” Brooks says Ricardo is investigating split-cycle engines powered by cryogenic fuels that cool the combustion chamber down to bring emissions near to zero. There’s even a study of using cryogenic working fluid that expands in the cylinders to provide mechanical energy. Brooks candidly admits: “There’s some interesting stuff going on, but even I can’t say that I understand it all!”

Undoubtedly, a lot of money is going to be thrown at these future powertrains, especially the engine block. High-pressure boosting will require a lot of strength in the bottom end to prevent the block from twisting and chucking pistons out its side. Energy recovery systems will be integrated into the transmission, eliminating today’s parasitic belts and drives, but requiring a complete rethink of the relationship between engine and transmission, with the former possibly becoming part of the latter. Tighter particulate matter standards will eliminate today’s tradeoff between NOx emissions and particulates. With some OEMs going for stoichiometric combustion, others for lean, and still others for HCCI (Homogenous Charge Compression Ignition), the question of aftertreat-ment of these gasoline engines becomes critical. Like a diesel, will they need a three-way catalyst, a particulate filter, SCR (Selective Catalytic Reduction) or a combination of technologies? Probably.

Achieving Torque

As B- and C-segment vehicles move from four- to three- to two-cylinder engines, the question of what happens to light-duty trucks pops up. “I think you could potentially put a 2.5-liter four-cylinder engine with 450 to 500 Nm [330 to 370 lb-ft] of torque in a mid-size pickup without an issue,” says Brooks. “The problem is getting the low-end torque that you need for towing and commercial use. That’s where you struggle.” One solution is to add more speeds to the transmission, dividing the spread up more each time the engine is downsized. Proposals for 10 or more speeds are on the table, and this will allow the engine to run in its most efficient range. “You want to calibrate the powertrain to run as much as possible in that range to get the best BSFC [Brake Specific Fuel Consumption] to hit your economy target in real-world driving and on the test cycle,” he says.

Predictive Software

Predictive software is another area of study that promises to grow exponentially as economy standards tighten. Says Brooks: “There will be a lot more predictive calculations made in parallel to try and mitigate what the driver is doing when he’s driving. I think this idea of a model running in parallel to the actual controller will be huge, and that alone may give us some breathing room in terms of how quickly this onslaught of technology will happen.” In short, with systems becoming more complex and interdependent, the focus will shift from mechanical to computer control, and the code jockeys will rule the world.

However, what will this car of the future look like to the average consumer? Brooks has an idea. “I think you will have a combustion engine in there with a lot less cylinders. There will be a smartly integrated boost system or electrification system, and smaller fuel tank, and the vehicle will be lighter and possibly smaller. Chevy Suburbans will look different. They will be much more aerodynamic, have a smaller, highly boosted combustion engine with electrification on at least some models. The hood will be much smaller, and the power generation and storage systems will be integrated such that the components are placed for optimum weight distribution. Finally,” he posits, “there will be a huge passenger compartment with the running gear hidden away.”