bjbj BWM Valvetronic Electronic Valve Lift Valvetronic engines use a combination of hardware
and programing to abolish the need for a regular throttle mechanism. Valvetronic varies the
lift of the intake valves. Based on signals formerly taken mechanically from the accelerator
pedal position sensor, the stepper motor changes the phase of the eccentric cam, modifying
the action of the intake valves.This system has a conventional intake cam, but it also
uses a secondary eccentric shaft with a series of levers and cam followers, activated by
an electronic stepper motor. The Valvetronic engine replaces the function of the throttle
body by using infinitely variable intake valve lift. Valvetronic has its own computer housed
in a separate unit away from the engine management system, networked through CAN network with
the digital engine management system incorporating a 40-megahertz, 32 or 64 bit computer. Valvetronic
was introduced on the all-alloy 1.8 liter, 4-cylinder engine for the E46 316 t I BMW,
it is now applied to some eight and 12-cylinder engines. The new HYPERLINK "http://www.usautoparts.net/bmw/models/e65.htm"
E65 7 Series has Valvetronic engines. The entire Valvetronic system is pre-assembled
and inserted as a module into its position in the cylinder head. Valvetronic engines
are built near Coventry, England. Valvetronic reduces maintenance costs, lowers exhaust
emissions, improves cold start behavior, and provides a smoother running engine. It also
does not need specific fuel grades or fuel qualities because of its fine atomization
of fuel. Because Valvetronic allows the engine to breathe unrestricted, fuel consumption
is reduced by 15%. The fuel savings are highest at lower engine revolutions. With fuel injection
systems, at light throttle, the throttle butterfly nearly closes, while the pistons are still
running, taking air from the partially closed intake manifold. The intake manifold between
the throttle and the combustion chamber has a partial vacuum, resisting the sucking and
pumping action of the pistons and wasting energy. Automotive experts refer to this phenomenon
as pumping losses. The slower the engine runs, the more the throttle butterfly closes, and
the more energy is lost. Valvetronic minimizes pumping losses by reducing valve lift and
therefore, the amount of air entering the combustion chambers. This system is now possible
because of advances in technology. Compared with conventional twin-cam engines with cam
followers, Valvetronic employs an additional eccentric shaft, an electric motor and several
intermediate rocker arms, which in turn activates the opening and closing of valves. If the
rocker arms pushes deeper, the intake valves will have a higher lift, and vice-versa. Therefore,
Valvetronic has the ability to get deep, long ventilation or a large valve lift, and flat,
short ventilation or a short valve lift, depending on the demands placed on the engine. The Operating
Parameters of the Valvetronic system are as follows: Valve lift is variable between 0
and 9.7 millimeters. The cams controlling the eccentric shaft are machined to tolerances
of a few hundredths of a millimeter. In Valvetronic engines coolant flows across the head, resulting
in a temperature reduction of 70%. The water pump size is cut in half, reducing power consumption
by 55%. Adjustment of the worm gear from one extreme to the other takes 300 milliseconds.
Combined with HYPERLINK "http://www.usautoparts.net/bmw/technology/vanos.htm" double Vanos valve timing technology, the
camshaft angle relative to the crankshaft can be adjusted by up to 60 degrees. The efficiency
of Valvetronic engines drop rapidly at over 6,500 rpm, since stronger valve springs are
required. The stronger springs creates higher friction losses. So in essence Valvetronic
has its greatest benefit at normal and lower engine revolutions. hCk_ hCk_ gd\a hCk_ hCk_
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