GM's new diesel opens up, loses weight

Automotive News reports on a new diesel engine from GM.

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Automotive News

DETROIT -- Henry Ford once said the best engineering is to "simplicate and add lightness."

Charlie Freese and Gary Arvan don't work for Ford Motor Co. But the new diesel V-8 they designed for General Motors is simple and light. On paper, at least, it has the potential to be the first great engine of GM's second century.

GM plans to install the new Duramax 4.5 in its Chevrolet Silverado and GMC Sierra light-duty pickups and several SUVs next fall.

Last year, GM revealed the innovative top half of the new engine, with its turbocharger nestled between the cylinder heads where the intake manifold normally would be.

Now, GM is showing the bottom half of the engine. The innovations there are just as extensive.

Mass death spiral

Arvan is chief engineer for GM's Duramax diesel engines. Freese, GM's executive director of diesel engineering, said reducing the weight of the engine was one of the design team's top goals. Another was to make the diesel indistinguishable from the gasoline engine it will replace.

"If I add mass that I don't need, I need bigger mounts to mate the engine to the vehicle. Now I need bigger springs to suspend the truck. The brakes need to be bigger," he said.

"So a little increase in the power train means big increases in the rest of the vehicle. As I increase the mass to deal with it, now I have to go back to the power train and make sure the power train is sized big enough to move all that mass. It's a death spiral."

Open up the bottom half of the Duramax 4.5 and you'll see things GM has never done in the crankcase of a regular production engine.

Start with the crank journals, the center section of the engine block that holds the crankshaft. They are cast into the block, but not in the usual way. GM used the same type of process, fracture splitting, for the main journal bearing caps that it uses on its connecting rods.

The result is greater precision, higher strength and lower costs on two fronts. The process needs less of the expensive compact graphite iron material for the block and bearing caps. Machining costs drop because the engine uses two bolts per bearing cap, not four.

It's a novel design for a diesel engine. A diesel's high compression ratio puts the crankshaft and bearings under tremendous stress and strain. Most diesels have heavily cast crankshaft bearing journals. GM's may be the lightest ever, with open spaces where you'd normally see thick metal.

Open air

The design of the crankcase also led to better circulation of air between the banks of cylinders. Because the sides of the bearing journals are not cast into the wall of the cylinder block, air can circulate freely as the pistons move. That reduces what engineers call pumping losses that sap performance as the engine turns over.

"One of the big issues for these modern diesels is the ability to handle the exchange of pressures through the crankcase itself," Freese said.

Because GM has not built a gasoline or diesel engine with a similar design, Freese declined to say how much weight or machining costs the new engine saves. But he said it was substantial and that some of the 4.5-liter engine's features likely would be used in future gasoline and diesel engines.

The lower engine's design helps meet two other design goals: Deliver at least a 25 percent fuel economy gain over a similar-size gasoline engine, and meet the toughest emissions standards on the books. GM plans to build the engine tuned just one way, with one emissions system, and offer it in all 50 states.

Some other unique features of the engine include:

-- A hollow balance shaft with a gear-driven center section that transfers internal noise to the rear of the engine near where the transmission is mounted. The noise is muffled by the heavy transmission housing.

-- An aluminum cradle or upper oil pan that mounts between the engine block and the lower oil pan that stiffens the engine block. Said Freese: "We get a 30 percent stiffness improvement compared with any other benchmark design."

(Source: Automotive News)

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