New Generation N62 Engine
Chapter 3 P.36
Course Contents/Background Material
© BMW AG,
Service Training
- Valvetronic
General information
Over its entire speed and load range, the petrol engine needs a
flammable and combustible fuel-air mixture which closely
approximates the
λ
1 ratio (excluding direct injection petrol
engines).
The mixture quantity must be altered to vary the speed and
output. This variation is effected by the throttle valve.
The mixture, which falls within the narrow range of
λ
1, is formed
outside the combustion chamber using the carburettor or fuel
injection systems (external mixture formation).
Mixture control, determined by the throttle valve, is not optimal
in all the different load ranges. This is particularly true of the
idling to part-load ranges, since the throttle valve is only opened
slightly in these ranges.
The throttle valve prevents the engine from aspirating freely. The
consequences are poor cylinder filling, poor torque and
increased fuel consumption.
The technical measures introduced, such as the optimisation of
the gas exchange, the improved valve overlap, the introduction
of DISA, the steady improvement of mixture control and many
other measures concerning the engine, can use the throttle
valve to minimize the disadvantageous tendency of preventing
the engine from aspirating freely, but they cannot prevent it
altogether.
This is where the new, completely unique Valvetronic design
comes in.
The Valvetronic system simultaneously varies the effective valve
opening period, and also the valve opening lift between 0.3 mm
and 9.85 mm, according to speed and load. This means that it
controls the fuel-air mixture volume according to engine require-
ments.
This type of mixture volume control makes the load control
throttle valve unnecessary.
