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New power-dense 2.0L GDI turbo with twin-scroll turbocharger and new combustion system offered in 2013 Chevrolet Malibu
20 September 2012
|New Ecotec 2.0L turbo. Click to enlarge.|
A new, gasoline direct-injected (GDI) Ecotec 2.0L turbocharged engine is available in the 2013 Chevrolet Malibu. It is rated at 259 hp (193 kW), making it one of the most power-dense automotive engines in the industry, GM notes.
A twin-scroll turbocharger generates up to 20 pounds of boost, helping the engine optimize power delivery across the rpm band. It also produces a broad and robust torque curve, delivering 90% of the peak 260 lb-ft of torque (353 N·m) from 1,500 rpm to 5,800 rpm. This added performance comes with greater refinement, as the enhanced torque reduces downshifts and helps quiet the buzz sometimes found in four-cylinder engines.
The Malibu turbo can accelerate from 0 to 60 mph in 6.3 seconds and achieves a top speed of 155 mph (249 km/h). The Malibu turbo has an EPA-estimated fuel economy of 21 city (11.2 l/100 km) and 30 mpg (7.9 l/100 km) highway.
The 2.0T is based on the all-new Ecotec engine family—including the new 2.5L engine that also is new in the 2013 Malibu—and builds on previous GM turbo engines with features that enhance efficiency, durability and refinement. Increased efficiency in all of the new Ecotec engines is achieved in part through lower engine friction, which was reduced by up to 16% using new technologies such as a variable-displacement oil pump.
GM proprietary computational fluid dynamics (CFD) analysis techniques were used to develop an all-new combustion system with a higher compression ratio, which also helped boost efficiency. Electronically controlled supporting components, including the wastegate and bypass, also help optimize performance and efficiency.
The new 2.0T engine features durability and technological features familiar in premium engines, including low-friction hydraulic roller-finger valve operation and an electronic throttle. A hydraulic tensioner keeps the timing chain adjusted for life, and extended-life spark plugs deliver 100,000 miles (160,000 km) of service. Additional engine features include:
- A precision sand-cast engine block with cast-in-place iron liners
- Forged steel crankshaft
- Pistons with jet-spray cooling
- Modular balance shaft system in the oil pan
- Inverted-tooth chain drive systems
- Rotocast aluminum cylinder head with sodium-filled exhaust valves
- Dual Overhead Camshaft (DOHC) with continuously variable valve timing
- Direct injection with cam-driven high-pressure fuel pump
- Two-stage variable-displacement oil pump
- Air-to-air intercooling system.
Engine block and rotating assembly. The sand-cast cylinder block provides structural support and incorporates structural changes shared among the new Ecotec family that enable greater control of noise and vibration. Iron main bearing cap inserts are used on the block to locate the steel crankshaft with reduced noise and vibration. Refinements to the oil-distribution system enable improved oil flow throughout the engine, as well.
The forged steel crankshaft supports the high load of a turbocharged engine while also contributing to high-rpm smoothness. It is complemented by strong connecting rods and aluminum pistons that are designed for the performance parameters of turbocharging. Piston jet-spray cooling reduces engine temperatures and friction by drenching the bottoms of the pistons with engine oil at higher engine speeds.
Greater engine smoothness comes from the modular balance shaft system, which is mounted in the oil pan. The design, which is part of the design changes with the new Ecotec family, minimizes the drive chain length and “buries” the system deep inside the engine to help reduce noise.
Inverted-tooth chain drives. The balance shaft and camshaft drive systems use a premium, inverted-tooth design that is significantly quieter than a roller-type chain. As its name implies, an inverted-tooth chain has teeth on its links—two-pin rolling pivot joints—that essentially wrap around the gear sprocket to take up virtually all the tension. This allows for smoother meshing of the chain links to the sprocket teeth, which is the cause of most noise in chain drive systems. The chain-to-sprocket tooth impact is greatly reduced with the inverted-tooth design (also known as a silent chain drive), which virtually eliminates noise and enhances durability.
Rotocast aluminum cylinder head with sodium-filled exhaust valves. The 2.0T’s A356T6 aluminum cylinder head is cast using a Rotocast process—similar to the heads on the supercharged Corvette ZR1’s engine—for high strength, reduced machining and improved port flow. The head is also designed specifically for direct injection, with unique injector mounting locations below the ports and port and combustion chamber designs optimized for direct injection and high boost pressure.
The head uses stainless steel intake valves that are nitrided for improved durability and undercut to improve flow and reduce weight. The exhaust valves have sodium-filled stems that promote valve cooling. At normal engine operating temperatures, the sodium inside the valve stem becomes liquid. The liquid sodium promotes heat transfer away from the valve face and helps maintain a lower, more uniform valve temperature. The result is reduced valve guide seat wear and consistent valve seating.
With performance the priority for this engine, the exhaust manifold is made of cast stainless steel to enable approximately 1,800 °F (980 °C) turbine inlet temperatures with a dual-scroll manifold. It is extremely durable and delivers exceptional airflow.
DOHC with continuously variable valve timing. Continuously variable valve timing optimizes the engine’s turbocharging system by adjusting valve timing at lower rpm for improved turbo response and greater torque delivery.
Cam phasing changes the timing of valve operation as conditions such as engine load and speed vary. It allows a balance of smooth torque delivery over a broad rpm range, high specific output and good specific fuel consumption. Cam phasing also provides another effective tool for controlling exhaust emissions. Because it manages valve overlap at optimum levels, it eliminates the need for a separate exhaust gas recirculation (EGR) system.
Direct injection. Direct injection moves the point where fuel feeds into an engine closer to the point where it ignites, enabling greater combustion control. Because the ports are not used to mix the fuel and air, the airflow is increased, resulting in improved efficiency and power. The evaporation of the fuel in the cylinder cools the air-fuel mixture to a lower temperature than conventional port injection, which allows a compression ratio of 9.5:1. Direct injection also reduces emissions, particularly cold-start emissions, by about 25%.
Cam-driven high-pressure fuel pump. A high-pressure, camshaft-driven pump provides the fuel pressure required for the direct injection system. The engine-mounted fuel pump is augmented by a conventional electrically operated supply pump in the fuel tank. The fuel delivery system features a high-pressure stainless steel feed line and a pressure-regulated fuel rail without a conventional fuel return line from the engine to the tank. Fuel pressure varies from about 750 psi at idle to 2,250 psi at wide-open throttle.
Two-stage variable-displacement oil pump. The variable-flow oiling system contributes to greater fuel efficiency, by matching the oil supply to the engine load. Rather than the speed-dependent output of a conventional, fixed-displacement pump, the engine’s variable-flow pump—which is driven off the balance-shaft module—changes its capacity based on the engine’s demand for oil. This prevents wasting energy to pump oil that is not required for proper engine operation.
Twin-scroll turbocharger and air-to-air intercooling system. The turbocharger system’s twin-scroll design is used to increase power. Each scroll on the turbine is fed by a separate exhaust passage—one from cylinders one and four, the other from cylinders two and three—to virtually eliminate turbo lag at low engine speeds.
Because direct injection cools the intake process compared to port injection, the 2.0T is designed with a relatively higher compression ratio of 9.5:1, compared with a conventional port-injected turbo engine. This enables higher boost for greater power and fuel efficiency.
An intake charge cooler enhances the power-increasing benefits of the turbocharging system. The air-to-air intercooler draws fresh air through a heat exchanger to reduce the temperature of compressed air that’s forced through the intake system by the turbocharger. Inlet temperature is reduced as much as 120 °C (250 °F). Cooler air is denser, which means more oxygen is packed in the cylinders and available to burn fuel, consequently generating greater power.
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