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      06-14-2012, 07:16 PM   #1
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BMW Valvetronic and TwinPower Turbo Overview

BMW Valvetronic and TwinPower Turbo Overview

As announced yesterday, BMW's N20, N54, S65, N18 engines have each picked a best engine award at the 2012 International Engine of the Year Awards [Full Award Results].

Here's a brief overview of two of the technologies featured in many of the BMW engines available today - TwinPower Turbo and VALVETRONIC (variable valve lift) technology. Valvetronic was first introduced by BMW on the 316ti compact in 2001, and has since often been coupled with BMW's double-VANOS.

Until 2012, no M model used Valvetronic, but instead continued to feature multiple throttle-bodied designs. The 2012 F10 M5 with its S63Tu engine (more details 1, details 2) is the first M model engine to utilize Valvetronic technology in lieu of the individual throttles found on its equivalents in the BMW X5 M and X6 M. The 2013 BMW 650i Gran Coupe's updated N63Tu engine (good for a +45hp bump over the N63 engine) will also add Valvetronic technology. See the text below for more Valvetronic information.

More Valvetronic Details:
It typically works in conjunction with the independent Double VANOS system that continuously varies the timing (on both intake and exhaust camshafts). Valvetronic-equipped engines rely on the amount of valve lift for load control, rather than a butterfly valve in the intake tract. In other words, in normal driving, the "gas pedal" controls the Valvetronic hardware rather than the throttle plate.

Cylinder heads with Valvetronic use an extra set of rocker arms, called intermediate arms (lift scaler), positioned between the valve stem and the camshaft. These intermediate arms are able to pivot on a central point, by means of an extra, electronically actuated camshaft. This movement alone, without any movement of the intake camshaft, can vary the intake valves' lift from fully open, or maximum power, to almost closed, or idle.

Because the intake valves lift now have the ability to move from almost closed to fully open positions, and everywhere in between, the primary means of controlling engine output is transferred from the throttle plate to the intake valvetrain. By shortening the duration of the intake instead of throttling, pumping losses are reduced and fuel economy is improved. By reducing the valve lift, asymmetrically on 4-valve engines, swirl is generated in the cylinder, leading to a better air/fuel mixture. By avoiding a large air reservoir between the throttle and the engine responsiveness can be improved, though it depends on the speed of the electric motor actuating the second camshaft.

However, the throttle plate is not removed, but rather defaults to a fully open position once the engine is running. The throttle will partially close when the engine is first started, to create the initial vacuum needed for certain engine functions, such as emissions control. Once the engine reaches operating speed, a vacuum pump run off the passenger side exhaust camshaft (on the N62 V8, exhaust cam on the N52/K) provides a vacuum source, much as a diesel engine would, and the throttle plate once again goes to the fully open position.

The throttle plate also doubles as an emergency backup, should the Valvetronic system fail. In this case, the engine would enter a "limp home" program, and engine speed would once again be controlled by the throttle plate.

Animations Featuring BMW TwinPower Turbo 6, 4, 3-cylinder Motors

BMW N20 Turbo 4 Cylinder Engine