GENERAL MOTORS 1.6L
The Inside Scoop on GM’S Baby Diesel
We Get Gory Details About GM’S Latest North American Diesel Engine
We weren’t expecting a diesel announcement from GM when invited to the press launch of the new GMC Terrain, but there it was—a new 1.6-liter, state-of-art diesel four-cylinder. With some quick footwork we were able to spend time with Mike Siegrist, Assistant Chief Engineer for North American diesel passenger cars at General Motors. You may remember him from our Cruze diesel story a couple of years ago. When it deals with small diesels at GM, the buck stops at Mike’s desk.
Of course, we normally are not all that excited about small engines, but this pocket rocket packs a serious punch for a lightweight with an Sae-certified 137 horsepower and 240 lb-ft of torque while passing stringent new U.S. environmental standards. It was also recently announced that when coupled with the 6-speed manual transmission in the Cruze Diesel Sedan that it features an Epa-estimated 52 mpg highway fuel economy rating, or 47 mpg when coupled with the new 9-speed automatic (see sidebar below).
Since we had less than an hour our questions were a bit rushed, and we may have missed some details, but we now know a lot more about GM’S new “Whisper Diesel” than we did before. We are working on bringing you a full review of the new Cruze Diesel Sedan as soon as we can; until then here’s a slightly edited transcript of our exclusive interview.
UDBG: Mike, is this engine going into all three vehicles, Terrain and its sibling Chevrolet Equinox as well as Cruze? Mike Siegrist: The engine that goes into Cruze is very similar. The last generation had a 2.0-liter. The engine we’re talking about now is a 1.6-liter that goes into Cruze, Equinox, and Terrain. The 2.0-liter engine in Cruze was only on sale for model years 2014 and 2015. It served its purpose. It labeled at 46 mpg, better than any non-hybrid in all North America.
UDBG: Pretend we're completely ignorant; tell us everything about this motor, one we’ll be able to buy later this year. MS: Would you like to talk Tech first? This is a complex engineering project to put into production. Our (General Motors) center of expertise for small diesel engines is in Torino, Italy. They do all the engine hardware as well as the (engine) controller and software. Then we bring that engine from Europe‚ and it is in a bunch of European applications I can share with you‚ and develop the product for North America here in Michigan.
UDBG: What does that mean, what sauce do you add to the meat? MS: It means dynamometer development, durability development on dynamometers, calibration and drivability engineering, and finally integration into the vehicles together with our vehicle colleagues. We do all that development here in North America. It’s a partnership with the guys that are in Europe. The chief engineer for this project resided in Torino, Italy.
UDBG: Why do it that way, why add the additional geographical complexity? MS: We do it because we in North America are very well versed in requirements for North America. We took an engine that exists as a product for Astra, Insignia, Zafira, Meriva, Mokka (all Opel vehicles), and in Korea Chevrolet Orlando and Trax. So this same basic engine is in production in those regions. We take the base engine and develop it here, as the base requirements are different.
There are three basic standards we have to meet in North America that are different. One is our emissions standards are different, and tougher. The cycles are a lot tougher. Second, we have the most extensive diagnostic rules in the world, dictated by the California Air Resources Board. So diagnostics are considerably different from those of any other country or region.
Third, and the most important to the customer, is the environment the product operates in. In North America we have roads that are higher; I’ve driven many times to the top of Mt. Evans in Colorado’s Rocky Mountains at 14,300 feet. We drive at 130° F down into Death Valley and need to properly drive the vehicle out! We also get colder than elsewhere and the engine has to start properly; it’s all those environmental conditions that
we have to meet while meeting strict emissions standards. They’re the most important to our customers.
UDBG: So let’s do a walk around the engine! MS: The engine is a brand-new engine family. We designed it at our Torino facility from the ground up to be the latest in diesel technology starting about seven years ago. It’s been in production for about three years prior to its North American introduction. It’s not a legacy from anything. Our development focused on three things; one, great fuel economy; two, very high power density‚ being powerful for a 1.6-liter motor; third, of utmost importance was its noise and vibration characteristics. From the beginning, NVH was a focus.
UDBG: Mike, doesn’t this engine have a solid reputation in Europe? MS: The European press has named this the “flustern” diesel, the whisper diesel, because it is the benchmark for noise and vibration characteristics for a small diesel engine. (That’s versus Volkswagen, Audi, Peugeot, Ford, Fiat and others.) When you drive this in a Cruze, Terrain, or Equinox it is transparent to the vehicle, you almost cannot detect that it is a diesel. Other than the fun part, the torque. The engine is SAE certified at 137 hp, 230 lb-ft, and the torque bandwidth is the fun part. It makes 219 lb-ft from 1,500-3,250 rpm, a large-big-wide torque band.
UDBG: May we have the nitty-gritty details please? MS: The block is aluminum with cast-in iron cylinder liners and an aluminum bedplate. The turbo is a Variable Geometry Turbo-style; the scrolls shape the torque curve. If you were to have a fixed-scroll turbo the torque curve would look considerably different than with VGT. You could shape that curve to focus on torque or horsepower, not both. That’s the advantage we get from the Vgt-style turbo.
We have mechanical solenoid injectors running at 2,000 bar (29,000 psi—ed.). It’s a very sophisticated injection system, and we have a very advanced combustion system.
UDBG: What do you mean by advanced combustion? MS: Our combustion analysis, performed to optimize the burn process between fuel economy, emissions and power was a lot of work. Originally, and from a design standpoint, we wanted an engine that was very well balanced and was optimized for global requirements. To be able to use this engine in Korea, Europe or North America, well, if you start with a poor combustion process it is not possible to meet the emissions requirements we have (in North America) or the fuel economy. It took many computer simulations, many iterations or repetitions in order to achieve this.
That’s a big statement. And of course most of the work was done in mathematical analysis and simulation of combustion. We’re very good; I’d say the guy we have doing this is one of the best in the world, very very good.
UDBG: It’s said getting air in, air out is a key to every engine’s performance. What have you done here? MS: We have an intake manifold with variable swirl. Each cylinder has two ports entering the head, one open and one with a valve in it. We open or close the valve to create or reduce mixture motion. There’s a common open/close shaft used to create the mixture motion and change the combustion process. It looks just like a little throttle valve.
MS: Really, for this engine it’s mostly swirl, not tumble. On a diesel you want great mixture motion since when you inject the fuel, eight to ten times per combustion event, you need the mixture to have lots of motion.
UDBG: 8-10 events? That’s a surprise! So we’re beyond the previous limits of solenoid-driven electro-mechanical injectors at 4-6 events, into the realm of piezoelectric injectors?
MS: Oh yeah! 8-10. This is part of what makes it really quiet, too. That eight, or nine, or ten injections per (combustion) event really have a huge noise benefit. It’s dramatic, and common sense. If you get a big burst of fuel it’s a dramatic event. Spread it out (essentially feeding the fire) and it’s quite different.
UDBG: Wouldn’t the ability to spread out the fuel give you great control over the combustion event, and power? MS: It really does. It helps to shape the torque process, the curve. For all the attributes we’re looking for we get more control.
UDBG: The engine also has a unique feature; where does the timing go? MS: Unlike a small block, its architecture places the timing at the rear, not the front. This makes it much quieter because much of the timing gear is encapsulated by the transmission. It covers and absorbs the noise.
There are lots of other details that make it quiet. For example, the way we isolate the oil separator on top of the cylinder head with little standoffs to create a gap between the head and the separator. We have a molded foam piece that goes over the injectors that really quiets them down‚ since they are a pretty big noise source. All of this leads the engine to be the “whisper diesel.”
Swirl versus tumble is a topic that often comes up when discussing combustion chambers and design. They’re self-descriptive about the fuel-air mixture as it enters the combustion chamber.
UDBG: Any other details we’ve missed? MS: Two other items I’ve not mentioned. Remember the fuel economy? Contributing to that is the engine’s very low friction. Piston rings are designed to minimize tangential loading, yet we still use conventional cylinder honing. And we don’t use polymer-coated bearings. It’s got a two-step variable displacement oil pump. In addition‚ it has oil squirters at the bottom of each piston. We control those when we need them—another friction improvement. They are controlled by a separate solenoid to a galley in the lubrication system that turns them on and off.
UDBG: So, aluminum block, aluminum bedplate, any other exotic details to share? MS: The rest is pretty standard. Alloy pistons, steel rods, steel crankshaft and an 18:1 compression ratio.
UDBG: Why aluminum for the bedplate? Is it robust enough? MS: Oh, it is. Our analytical tools for structural analysis are so capable that we can lighten up the engine significantly and still have the same structural integrity.
UDBG: And for emissions? MS: It uses SCR, of course. DOC/DPF and particulate trap, plus SCR. The refill interval for the sedan urea tank should be about 4,000 miles. Our target for the SUV will be about 7,500 miles as it has larger capacity.
UDBG: Earlier you mentioned GM’S ability to control its own software for engine control hardware. Any details to share? MS: Yes. Another very important component is that our control system (ECU) is done internally. We write all our own software whereas we used to purchase it. So we have great control and it is common among all our engines. Having internal control over software is a huge enabler for developing all the diesel products in our portfolio.
Chevrolet is becoming the biggest diesel engine brand in North America with the Duramax they’ve had for quite a while in the Silverado. Then we came out with the first generation Cruze (2.0-liter), and now the Canyon and Colorado and their 2.8-liter XLDE, and now the second generation Cruze and Equinox and Terrain. When we’re developing these products, to have standard work that we do this with is important to our calibrations. UDBG