GM 3.6L DOHC V-6 Harbinger of Future Powertrain Strategy

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Story Behind 10 Best Engines

The Ward’s 10 Best Engines competition has recognized outstanding powertrain development for 15 years. In this latest installment of the 2009 series, Ward’s looks at the future of General Motors Corp.’s 3.6L DOHC V-6. How many engines perform as well in hot sports cars as they do in luxury sedans and large 3-row cross/utility vehicles? There are some, but not many will do so as affordably, or as well, as General Motors Corp.’s 3.6L DOHC V-6.

And it burns regular-grade gasoline, to boot.

The 304-hp, 273-lb.-ft. (370 Nm) direct-injected version of GM’s already excellent 3.6L DOHC “High-Feature” V-6 made its widely acclaimed debut in the rear-wheel-drive ’08 Cadillac CTS, then proliferated to the front-wheel-drive ’09 Chevrolet Traverse CUV and its Saturn, GMC and Buick siblings.

For the next model year, use expands to the ’10 CTS Sport Wagon and new Chevy Camaro, as the base engine.

Before the 3.6L V-6, GM started its DI journey with the 200-hp 2.0L Ecotec I-4 that powers high-performance versions of the Pontiac Solstice and Saturn Sky roadsters (now being phased out as part of the GM restructuring), as well as the Chevy HHR SS.

Next to come are a new 2.4L DI Ecotec 4-cyl. and 3.0L DI version of the HF V-6. The former is standard, the latter optional in the new ’10 Chevy Equinox and GMC Terrain compact CUVs.

The 3.0L DI V-6 will power the ’10 Buick LaCrosse sedan and Cadillac’s new SRX CUV, replacing the port-injected 3.6L V-6 as the standard engine in the ’10 CTS.

3.6L to power many luxury and mainstream GM vehicles in future.

Robert Bosch GmbH supplies the direct-injection system for the 2.0L turbo 4-cyl. and the 3.6L V-6, while Hitachi Ltd. is the DI supplier for the new 2.4L I-4 and 3.0L V-6.

But can GM, currently reorganizing under Chapter 11 bankruptcy proceedings, afford to continue proliferating expensive DI technology at a rapid rate?

“I’m not sure we can afford not to put it on most of the engine portfolio going forward,” says Sam Winegarden, executive director-global engine engineering, GM Powertrain. “That is what you will see in the coming years.” He adds GM’s HF V-6s will be more than 90% DI by 2010 and 100% by 2012.

DI’s benefits clearly outweigh its added cost, Winegarden says. “This is one of the few technologies we’ve found that gives us several benefits.”

“Because of the effect of the (fuel) charge cooling, you can pump up the compression ratio, which gives you torque and power. It also gives you thermal efficiency, which turns into fuel economy. And you also get emissions benefits.”

A strategy that uses multiple injections per combustion event substantially eases emissions compliance. On the federal test procedure, Winegarden says, nearly all harmful emissions are generated in the first 20 seconds after start. “After that, with the catalyst running at over 99% efficiency, virtually nothing is coming out of the tailpipe.” The trick is how quickly the catalyst can be brought up to temperature.

“In a normal port-injected system, you inject the fuel once per combustion cycle. With DI, you have the opportunity to inject more than once per cycle, much like diesels do. That lets us deliver fuel both early and late in the cycle, and the late delivery puts fuel in the exhaust stream to create heat to light the catalyst.”

All of GM’s DI engines run quite happily (and generate their published SAE-certified power and torque ratings) on regular unleaded gas. They also operate more quietly than most, thanks to isolated injectors and other noise-reducing measures. Two other important competitive advantages, Winegarden asserts, are low cost and mass.

With Ford promoting and rolling out its DI and turbocharging combo as EcoBoost, will GM be combining those two technologies more often going forward?

Cadillac CTS premium sedan burns regular.

Yes, Winegarden confirms, because a major component of GM’s fuel-efficiency strategy is “making small engines look big and big engines look small.”

The former is a “downsize and boost” strategy that will see turbocharged Ecotec fours replacing naturally aspirated V-6s and turbo V-6s replacing V-8s in the future. The latter is a tactic that stresses the use of active fuel management cylinder deactivation on V-8s.

Hybridization is another big piece of the GM powertrain strategy.

“As you watch our Advanced Propulsion Plan go through the electrification of the vehicle, you’ll see almost every engine in our portfolio – fours, sixes and eights – a t some point get mated to a hybrid configuration,” Winegarden says.

A Ward’s 10 Best Engines winner for its second straight year, editors have praised GM’s 3.6L DI V-6 (as tested in the ’09 CTS) for its dazzling throttle response, competitive fuel economy, laudable low-end torque, impressive specific output (84 hp/L) and effortless power delivery. Not to mention its quiet idle and smooth everyday cruising, throaty exhaust note and neck-snapping torque at just about any engine speed. Given all that excellence, is there room for improvement?

“There are several things we will look at which will play out across the whole gas portfolio,” Winegarden says. “One of the next things will be variable-valve-lift technology, 2-step or continuously variable, over and above the cam phasing (VVT) we have on it today.”

Another element is friction reduction. “These engines are pretty good from a friction perspective, but we’re always looking for bearing and ring technologies to further reduce it. We have several programs working on advanced materials or structures that would help there.”

One other technology that may emerge is something Winegarden calls “fluid flow on demand.” GM uses variable-displacement oil pumps in transmissions, so why not in engines?

“When the demand for oil is low,” he explains, “you run low pressure and flow. But when you’re going full-throttle, you drive the pump at higher pressure and load. With fuel economy getting more and more important, putting some additional cost into oil-pump technology starts making cost-effective sense, same thing on the cooling side.”

Ameer Haider, assistant chief engineer-GM High-Feature V-6 engines, adds that a lot of opportunity remains for improvement to the combustion system.

“Given the potential of DI,” he says, “we are continuing to investigate how we can get even more efficiency out of it. We are still in the infancy of learning its true potential in improving basic combustion efficiency, in the design of the chamber, how we use the injection and the particle size of the fuel.”

Winegarden contends the computational fluid dynamics work GM is doing today is leading-edge. “As we develop our analytical tools to get better and better,” he says, “it is giving us interesting insights into what’s really going on in the chamber and suggesting opportunities where we may be able to make some advancements.”

Center for Automotive Research Chairman David E. Cole has said GM and Toyota, alone, enjoy the substantial competitive advantage of developing and owning their own powertrain control systems and software.

“That clearly gives us an advantage,” Winegarden says. “If we learn things about how we want to do these controls, it gives us the capability to implement that pretty quickly at a reasonable cost. We are not constrained to a supplier’s standard suite of software or a very expensive bill if we want to do something unique.”

Where will DI go next? It will roll out in the future on the entire gas-engine portfolio, including V-8s, Winegarden says.

“You’ll see it show up on other engine families, and you’ll continue to see the DI percentage of our portfolio increase year by year. That is a huge play in corporate average fuel economy and carbon dioxide, and this is one case where we have the technology developed nicely in time to help support the legislative requirement coming forward.”