Volkswagen's New Engine Cycle - The 'Budack' Cycle

Опубликовано 20 сентября 2017, 14:00

How Does VW's New Budack Engine Cycle Work?
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From the Volkswagen Tiguan Media Kit:
"The all-new 2018 Volkswagen Tiguan arrives in dealerships this summer powered by the most advanced version ever of Volkswagen’s EA888 four-cylinder engine. The updated version of the benchmark EA888 four-cylinder, turbocharged and direct-injection engine uses an innovative modification to the conventional four-stroke cycle to offer an improved combination of power, efficiency and responsiveness.

First introduced in the 2009 CC, the EA888 continued Volkswagen’s move toward smaller, turbocharged engines that offer the fuel economy benefits of downsizing with the power of a larger-displacement unit. Though EPA estimates are not yet available, compared with the 1.8-liter EA888 Gen 3 engine that is fitted in the current Passat, Jetta, Beetle, and Golf family models, the new 2.0-liter EA888 Generation 3B is expected to offer improved fuel efficiency along with a 20 percent boost in maximum torque to 221 pound-feet. The majority of the engine—from the cast-iron block to the aluminum-alloy pistons and cylinder head to the valve springs—has been updated along the way.

During development, engineers focused on making the engine more efficient in the range of driving that most customers use every day, which led to the introduction of a modified Miller combustion cycle that is unique to the Volkswagen Group. Whereas the traditional Miller cycle closes the intake valves just before the end of the intake stroke, the so-called Budack-cycle closes the intake valves much earlier. This results in longer effective combustion as well as faster air flow for the incoming gases, which improves the mixing of the fuel and air. The net effect is lower fuel consumption and more torque than the 2.0-liter EA888 engine fitted in the 2017 Tiguan.

The key feature that enables the new engine to produce better fuel economy, as well as excellent performance, is the variable valve timing system on the intake camshaft. Depending on engine load, it is possible to switch between short and long valve opening. At idling speed and under partial load, the valve opening is shorter. When the engine is placed under greater load, a switch to the camshaft lobe that opens the valve for a longer period is made and the driver can make use of the full power and torque of the engine.

The changes in the new version of the EA888 advance the twin goals of power and efficiency. The peak 184 horsepower (for the Tiguan) kicks in at 4,400 rpm, 400 revs sooner than in the 1.8-liter edition, and maintains its output until 6,000 rpm. Maximum torque of 221 lb-ft is achieved at 1,600 to 3,940 rpm. As in the previous 2.0-liter TSI® engines, the increased displacement comes solely from a longer piston stroke (92.8 mm vs. 84.1 mm in the 1.8 TSI), while the compression ratio rises to 11.7:1 due to a modified piston crown and combustion chamber. New TSI injectors can push fuel into the cylinder at a higher maximum pressure (250 bar or 3,626 psi), with up to three injection sequences per stroke depending on conditions."

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