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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > NA Engine (non-turbo) / Drivetrain / Exhaust Modifications > 7 series engine



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      12-27-2005, 02:26 PM   #1
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7 series engine

UNDER THE HOOD: A BRAND-NEW ENGINE WITH UNIQUE, PATENTED TECHNOLOGY

The new 7 doesn’t merely look new; it is new, through and through. Under the long aluminum hood, for example, is a brand-new engine. While its bore, stroke and displacement are unchanged from the previous (and much praised) M62 unit, the new engine --- designated N62, N for “new” --- makes dramatic strides in torque, power, accelerator response and efficiency. There are detail refinements throughout, but two major new technologies are the main driving force behind the engine’s dramatically improved capabilities.

Both of the initial U.S. models are powered by the entirely new 4.4-liter V- 8 engine that produces almost exactly the same power as the current 750iL V- 12 engine, or 325 horsepower; this is a good 15% more than the predecessor V- 8. Equally remarkably, fuel economy is expected to be maintained at about the same level as that of the 2001 740i/iL engine. And response to the accelerator pedal --- one can no longer say “throttle” --- is markedly livelier more spontaneous.

VALVETRONIC: REVOLUTIONARY NEW ‘‘BREATHING’’ CONCEPT

Many contemporary automotive engines have variable valve timing, including all of BMW’s. BMW achieves variable valve timing by rotating the camshafts relative to their driving sprockets. Some manufacturers also have systems that vary valve lift, or the distance the valves open.

BMW’s new Valvetronic system also varies lift --- but to a far greater, and more fundamental, degree than existing systems. Indeed, Valvetronic varies intake-valve lift to such an extent that it assumes the function of the traditional engine throttle; engine breathing is thus controlled entirely by the valves, and the traditional throttle simply goes away. Thus we can no longer call that righthand pedal on the floor a ‘‘throttle pedal.’’ We might as well go back to the old term ‘‘accelerator pedal.’’

The Valvetronic mechanism sits atop the intake valves on each of the new V-8’s two cylinder banks. Each of the engine’s 32 valves (4 valves per cylinder) is actuated as the camshaft lobe deflects a finger-type rocker arm with hydraulic clearance adjustment. On the intake side, however, there is an additional element between the cam lobe and rocker arm, called an intermediate follower.

Intake valves assume function of throttle. The Valvetronic mechanism varies valve lift in a major way: from 0.3 mm to 9.7 mm. Engine breathing --- air intake --- is controlled by varying this lift. The driver’s foot gives the commands; the eccentric shaft turns to control the intermediate follower’s pivot point; valve lift varies accordingly. At minimum lift, the engine is idling or decelerating; at maximum lift, it is producing full power.

Greater efficiency. It may seem surprising that so fundamental an engine component as a throttle (in BMW M engines, throttles) has a fundamental drawback. But it does: As a throttle closes, it imposes a restriction that incoming air has to snake around. This causes so-called “pumping losses,” which take an increasing portion of engine power as the engine is more and more lightly loaded. Thus elimination of the throttle offers the opportunity to increase engine efficiency at ‘‘low-load” operation, i.e. when driving gently. At full power, a throttle is fully open and pumping losses are minimal. By eliminating the throttle(s) 3 and letting the valves control the breathing, Valvetronic essentially eliminates pumping losses. (Diesel engines do not have throttles; this is one of the reasons why they achieve relatively high fuel efficiency.)

More spontaneous engine response. In BMW M engines, an individual throttle for each cylinder, positioned very close to the cylinder, improves engine response by bringing atmospheric pressure right up to the cylinder. Valvetronic goes a step further. When one drives the new 7, one is going to be struck by how spontaneously and quickly the engine responds to the accelerator pedal.

More power. High valve lift contributes to high power output; yet in a traditional engine one cannot simply increase valve lift, as too-high lift would detract from efficient and responsive operation at low speeds and light loads.

Refined engine operation. In light-load driving, operation is especially smooth because of the relatively small valve lift of 0.5 to 2 millimeters. Customers may notice this especially in the engine’s ultra-smooth idling.

Excellent cold starting. The small valve opening promotes highly effective vaporization of fuel, even when the engine is started from cold.

No mechanical throttle linkage. Current BMW engines have electronically controlled throttles, so-called “drive-by-wire.” With Valvetronic, the driver’s call for power is transmitted electronically to the eccentric shaft’s electric servo motor.

Stepless variation of valve lift. Valve lift is varied continuously and smoothly all the way from minimum to maximum lift.

Lighting-fast system response. Clearly, variation of valve lift is fundamental to the performance of a Valvetronic engine. The system can vary lift all the way from minimum to maximum is just 300 milliseconds, or 0.3 sec. To achieve this lightning-fast system response, BMW developed a dedicated Valvetronic microprocessor, which networks with the 40-megahertz/32-bit primary engine computer.

Low friction, precision components. Every ‘‘rubbing point’’ in the Valvetronic mechanism is not a rubbing (friction) point at all. Instead, a low-friction roller transmits the motion: from cam lobe to intermediate follower, from intermediate follower to rocker arm, from eccentric shaft to intermediate follower. The follower itself is manufactured to an extremely high degree of precision: a precision casting in the first place, machined to virtual perfection. Its ‘‘boomerang’’ contour --- the working surface that actuates the rocker arm --- is machined to a tolerance of 8/1000ths of a millimeter. To ensure quiet operation, zero valve clearance is maintained by a hydraulically adjusted pedestal on which the rocker arm pivots; this feature is known from the existing BMW V-12 engine.

DOUBLE VANOS: BMW’S VARIABLE VALVE TIMING MAKES ITS CONTRIBUTION TOO

In recent years, BMW engines have benefited from VANOS --- Variable NOckenwellen Steuerung, German for variable camshaft control or variable valve timing. Where the predecessor engine had VANOS steplessly variable intake-valve timing, the new one incorporates Double VANOS, affecting the intake and exhaust valves. In response to operating conditions and the driver’s demands for power, Double VANOS rotates the intake and exhaust camshafts steplessly between ‘‘earliest’’ and ‘‘latest’’ valve timing. (These extremes of the timing adjust are 40o apart for the intake camshafts, 25 deg apart for the exhaust camshafts.)

As in other BMW engines, Double VANOS enhances the engine’s torque, efficiency and emission control. In the new N62 engine, it operates in combination with Valvetronic to help achieve heretofore unknown levels of performance, efficiency and general operational excellence.

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      12-27-2005, 03:04 PM   #2
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4.4L?

this must be old article, its a 4.8 L now with 360HP.

and that pic looks like a 745i
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      12-28-2005, 05:38 AM   #3
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Look at the end of that article, it was written in 2001


The new 4.8l N62B48TU engine has replaced that one
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      12-28-2005, 08:22 AM   #4
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      12-28-2005, 12:02 PM   #5
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