Heavier duty for General Motors pickup

  • 03-Mar-2010 09:45 EST
2011 HD.jpg
The 2011 Chevrolet Silverado HD can be fitted with a Duramax diesel engine and Allison six-speed automatic transmission, or a Vortec 6.0-L V8 (L96) and Hydra-Matic six-speed RWD/AWD automatic transmission 6L90 (MYD).

A full-width chrome steel front bumper, new grille, and restyled hood are main cosmetic changes on the 2011 Chervolet Silverado 2500HD and 3500HD, but what's under the skin reflects a substantial reworking of the heavy-duty truck. Making its world debut at the 2010 Chicago Auto Show, the 2011 Silverado HD rides on an all-new, fully boxed frame.

"The predecessor's front frame section was fully boxed, but rearward of the front-frame bay section it was a C-channel, ladder-type design. And the predecessor's crossmembers were bolted on, whereas on the new chassis the crossmembers are welded into place," explained Jeffrey Luke, Global Vehicle Chief Engineer for Full-Size Trucks at General Motors.

Compared to the prior model, Silverado HD is 92% stiffer in bending mode, 20% stiffer in beaming mode, and the front frame structure is 125% stiffer. For 2010, the lineup encompasses 11 different 2500HD models and eight single- and dual-rear-wheel 3500HD models.

The truck's short-long arm/torsion bar front suspension—now with forged-steel upper control arms and cast-iron lower control arms—has a front-axle weight rating of 6000 lb (2720 kg), enabling snow-plow capability on 4WD cab configurations. The Silverado HD's front suspension uses dual urethane jounce bumpers vs. the previous singles, and the shock mount is a two-bolt attachment to the frame rather than the predecessor's single-bolt design.

Silverado HD's asymmetrical rear suspension has 3 in (76 mm) wide leaf springs, which are 20% wider than the previous model's. The leaf-spring design helps support increased rear gross axle weight ratings. On the 2500HD model, the rating is 6200 lb (2820 kg), an increase from the previous 6085 lb (2765 kg). The 3500HD model's numbers are 7050 lb (3205 kg) for single-rear-wheel models and 9375 lb (4260 kg) on dual-rear-wheel models.

"This new foundation provides all of the capability that supports best-in-class towing, best-in-class payload, and best-in-class ride and handling," said Luke. The 3500HD crew cab/long box will have an up to 20,000-lb (9070-kg) towing capacity with a fifth-wheel hitch. Maximum payload capability for the 3500HD is 6335 lb (2870 kg).

The fourth-generation 6.6-L Duramax turbodiesel V8 engine is expected to have greater power and torque than for the 2010 model year, although numbers were not released. Highway fuel economy for the 2011 Silverado HD is projected to increase by 11%.

According to Gary Arvan, Chief Engineer of the Duramax diesel for GM Powertrain, the 2011 diesel engine's piston and rod assembly was redesigned. "The pin end width of the connecting rod was reduced to increase the bearing area between the piston pin and provide a more favorable load path in the piston structure," said Arvan, further noting that the changes enabled the elimination of the bronze bushings (previously on both sides of the piston pin axis) as well as a reciprocating mass reduction of about 9%.

Elimination of the piston-pin bushings within the piston was an engineering priority "as it allows for both reciprocating mass reduction as well as rotating mass reduction while improving piston strength. This is because the dimension between the piston pin centerline and the bottom of the piston below the pin is reduced, allowing for a larger crankshaft counterweight radius," explained Arvan.

The rotating component mass (crankshaft, damper pulley, and flywheel) was reduced 10% on the 2011 engine vs. the 2010 Duramax diesel engine, according to Arvan. "This is due to the increased counterweight radius of 4 mm allowed by the piston changes and movement of external balance masses to the crankshaft," explained Arvan.

Compared to the 2010 model, NOx emissions will be reduced approximately 63%.

"We've chosen a selective catalytic aftertreatment NOx reduction system (using diesel exhaust fluid injection). It frees up some of the constraints we have in developing the engine in terms of engine-out emissions because we can take care of that downstream," explained Arvan.

A new 30,000-psi (2070-bar) piezo-actuated fuel-injection system also helps with emissions performance, and the system is capable of operating on ASTM grade B20 biodiesel. "We've stepped up the capability from the current vehicle's B5 biofuel," said Arvan.

Among the enhancements to the Allison 1000 six-speed automatic transmission are new, low-drag clutch packs and improved lube distribution to help minimize spin loss, according to Timothy Cooney, Assistant Chief Engineer for the Allison 1000 at GM Powertrain. "The lube path—meaning every hole, every slot, and every inlet and outlet—that the oil goes through to lubricate and cool the transmission is a completely new design," said Cooney.

The Silverado HD is the first GM vehicle to employ an exhaust brake. The system uses turbine control of the variable geometry turbocharger and engine compression power to generate backpressure and slow the vehicle without applying the brakes.

According to Jim Mikulec, Lead Development Engineer on the 2011 Silverado HD, the system works by varying the vane positions within the turbocharger and, if necessary, using transmission downshifts. "The intervention is very gradual," said Mikulec, noting the system can function in normal driving, tow-haul as well as cruise on/off modes, to improve upon the existing grade and cruise-grade braking features.

The body-on-frame Silverado HD's standard 36-gal (136-L) fuel tank replaces the prior model's 26- and 34-gal (98- and 129-L) offerings. Fuel range on a single tank is now estimated to be up to 680 mi (1090 km).

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