GM Powertrain engineers have revealed technical and development details of their company's all-new Modular Ecotec family of long-stroke 1.0- to 1.5-L three- and four-cylinder gasoline engines that the company expects will eventually power about 25% of the automaker’s global vehicle production in the A through C/D segments.
The new Ecotec range replaces three incumbent engine families. The 11 variants, all configured for 12 V stop-start, share a 74-mm (2.91-in) cylinder bore and 81-mm (3.19 in) bore centers. Displacements are established by number of cylinders and six available crankshafts offering a selection of three different strokes—77.4, 81.3, and 86.6 mm (3.05, 3.20, and 3.41 in).
Depending on market and vehicle application, the engines will use port fuel injection (naturally aspirated) or direct injection with turbocharging, and they will be calibrated for gasoline, E100, CNG, or bi-fuel LPG, according to Steve Keifer, Vice President of Global Powertrain Engineering.
All were developed to achieve class-leading NVH, fuel efficiency, mass per displacement, and specific hp and torque ratings, as benchmarked against what Global Chief Engineer Tom Sutter considers to be the core competitive set: Volkswagen’s new EA211 family and Ford’s global Ecoboost engines of similar displacement. SAE-rated horsepower and torque will range from 75 to 165 hp (56 to 123 kW) and 70 to 184 lb·ft (95 to 250 N·m), respectively.
Mass reduction was a major design goal, according to Sutter. He said the new 1.4-L turbo four-cylinder, fully dressed, is 44 lb (20 kg) lighter than its counterpart in the current Chevrolet Cruze, and 8 lb (3.6 kg) lighter than VW's EA211-based 1.4 turbo.
The new family also achieves “significant” manufacturing commonality benefits and reductions in GM’s powertrain bill-of-material, Keifer noted. The engines will be in 27 GM models by the 2017 model year, he said. First to deploy is the 1.0-L turbo triple in the recently introduced 2014 Opel Adam minicar. It will be followed by 1.4-L turbo and 1.5-L naturally aspirated four-cylinder units for the redesigned 2015 Chevrolet Cruze in China.
Total global production for the new modular family will take place in five GM Powertrain plants including the all-new facility in Shenyang, China. Annual volumes are expected to reach over 2.5 million units, at a production rate that GM estimates could reach 10,000 units per day. The program, begun in early 2011, represents a significant chunk of the $1 billion GM Powertrain is investing in new product and development resources “in the next several years,” Kiefer said.
HCCI program learnings
The Modular Ecotec family is a clean-sheet design, with more than 300 engineers involved with its development, Sutter said. Pontiac, MI, and Russelsheim, Germany were the lead technical facilities for the base architecture, with GM Powertrain Shanghai, Bangalore, and Seoul contributing significant systems work including control software and the PFI systems development and integration. The turbocharger systems partner is Mitsubishi Heavy Industries (MHI), and Continental led development of the fuel system.
Sutter, whose experience includes GM’s Atlas family of modular inline four-, five-, and six-cylinder light truck engines, noted that extensive combustion-system development enabled his team to achieve substantial gains in BSFC with commensurate reductions in intake, injection, and combustion noise. “We challenged the team to meet PFI levels of NVH with a 2900-psi (20-MPa) DI system,” he said. “Not easy to do, but they hit the targets.”
GM released some brake-specific fuel consumption (BSFC) data for the turbocharged variants. The 1.0-L triple achieves 369 g/kW·h, while BSFC of the 1.4 L and 1.5 L four-cylinder versions are 361 and 351 g/kW·h, respectively. (See accompanying graph by clicking the arrow near the top of this article.) Sutter said the new 1.4-L DI turbo engine delivers 5% better BSFC than GM’s current 1.4-L turbo as used in the 2014 Chevrolet Malibu.
The combustion chambers and the full induction tracts (including the composite intake manifold) are configured to induce high airflow and aggressive charge “tumble” to ensure no wetting of the intake valves and spark plugs. Compression ratios range from 10:1 to 12.5:1, depending on engine and fuel system. The turbocharged triples will run 10.5:1 and are calibrated for “regular” octane gasoline. In developing the combustion strategies, GM leveraged its decade of HCCI (homogeneous charge compression-ignition) development.
“With HCCI we have four enabling technologies: precise fuel injection; high-authority cam phasing; continuously variable valvetrain, and cylinder pressure sensing (which we’ve introduced on our diesels). We’re only missing the cylinder-pressure sensing, but all of them provided many learnings for the new engines,” explained Matthias Alt, Lead Engineer on the three-cylinder engines who spent years on GM’s HCCI development.
Alt noted that the new family “has broad cam-phasing authority, 65 degrees total, and a very precise injection system. We use the exact same central injector angle [mounted 6° from vertical] as in the HCCI combustion system. We use the same metering of the small fuel quantities to ensure precise control of the intake and combustion energy based on the quantity of fuel we inject.” Across the family, 90% of peak torque is delivered between 1500-5000 rpm.
CAE (computer-aided engineering) and acoustic analysis led GM engineers to rubber-mount the DI engines’ fuel rail inside the cast-aluminum camshaft cover and encapsulate the injection pump, noted Assistant Chief Engineer Kendell Fulton, who worked on various GM-Fiat diesel programs. He said the PFI engines’ fuel rail (part of a clever new induction module for the CNG/LPG units) is similarly isolated and features an internal device for damping the injection pulses.
The DOHC (double overhead cam) cylinder heads are semi-permanent mold castings in 356-T7 alloy. They feature integrated, liquid-cooled exhaust manifolds which, in conjunction with new switchable electronic coolant pumps aid engine warmup. The 16 valves are actuated via hydraulic roller finger followers, the aluminum cam phasers and hollow “assembled” camshafts being driven by a “silent type” inverted-tooth timing chain.
Unique single-stage/single-scroll MHI turbochargers are specified for three- and four-cylinder variants. The liquid-cooled, low-inertia turbos mount directly to the integral-cast exhaust manifold and feature wastegates controlled by pressure rather than vacuum for faster response, said Fulton. Some naturally aspirated variants employ a two-stage variable intake manifold that switches tract length at 5000 rpm to optimize torque and power.
There are also two exhaust-aftertreatment configurations, depending on engine and global market application. The first setup employs a close-coupled catalyst and an underbody catalyst. The second uses what GM calls SVCC (single-volume close-coupled), which aggregates the engine and underfloor catalytic “bricks” into a single canister fitted directly downstream of the turbocharger.
“This allows us to use smaller bricks for reduced backpressure and lower mass,” Fulton explained, “and it saves cost.”
Balance shaft, lightweight architectures
While Ford chose not to use a balance shaft for its 1.0-L Ecoboost triple, opting instead for a clever unbalanced flywheel-and-pulley on opposite ends of the 120° crankshaft to quell first-order vibration, the GM team engineered in a single balance shaft integrated with the electronically controlled variable displacement oil pump and mounted in the cast-aluminum oil pan. The shaft is driven by a short chain off the crank sprocket and spinning at engine speed.
Besides being inherently balanced rotationally, the triples’ (including a 1.1-L PFI version for regional markets) 120° crankshafts also aid induction efficiency and cylinder scavenging, Alt noted.
Down below, the cylinder block is a high-pressure die casting in A380-T5 alloy. The open-deck design, with wall thickness of 4 mm (0.157 in), has cast-in iron liners and features a cast ADC10-T5 bedplate for additional stiffness. The block’s inter-cylinder bulkheads include cast-in windows to enable bay-to-bay breathing—a key to reduced crankcase windage, the engineers said. The block and head include lubricant galleries to supply the cam phasers.
All turbocharged and naturally aspirated DI versions get crankshafts forged in 1538MV steel alloy, while the PFI variants use nodular-iron cranks with hollow-cast cores for less weight. Conrods are PM steel with “cracked” big ends. The short-skirt pistons use three rings and have semi-machined crowns cooled by dedicated oil jets in the crankcase.
GM Powertrain engineers are proud of the new modular engine family, particularly its NVH attenuation that, they claim, beats VW’s EA211 1.4-L four-cylinder by 50% in noise intensity, based on dyno and road testing, and is to 25% quieter than Ford’s 1.0-L Ecoboost triple.
In addition to the NVH countermeasures noted above, the new engines include a stamped steel sump located at the bottom of the aluminum oil pan, and a direct-mounted front accessory drive including an overriding alternator coupler (to remove the effect of crankshaft oscillations), among other details.Continue reading »