1 Introduction
Recently, variable valve timing engines have attracted a
lot of attention because of their ability to control valve
events independent of crank shaft rotation, allowing for
reduced pumping loss (work required to draw air into
the cylinder under part-load operation), and increased
torque performance over a wider range than conventional
spark-ignition engine. Variable valve timing also
allows control of internal exhaust gas recirculation (by
control of the valve overlap), allowing for control of
NOx emissions produced during combustion.
Several detailed studies have been performed to show
the benefits of variable valve timing engines. [1] describes
a mechanical variable valve timing system, and
points to the possibility of controlling the air flow into
the engine via the valve openings, thus eliminating the
throttle and reducing pumping losses. In [2] and [3],
varying the intake valve timing was shown to reduce
pumping mean effective pressure while improving fuel
economy and NOx emissions. [4] describes an electrohydraulic
valvetrain based engine and provides a good
summary of the benefits of camless engines. [5] showed
that by optimizing valve events at part-load conditions,
volumetric efficiency, fuel economy, and NOx emissions
0-7803-5519-9100 $10.00 © 2000 AACC
could be improved. More recently, in [6] it was shown
that using the flexibility of an electromechanical valvetrain
to run in 2, 3, and 4 valve modes, as well as
by using cylinder deactivation, fuel economy consumption
could be improved over a wide range of operating
conditions.
More recent attention has focused on the controloriented
modeling and the control of variable valve
timing engines. [7] modeled the cylinder-by-cylinder
breathing dynamics of a careless engine system, including
higher frequency runner dynamics using the forced
oscillator model. The model was then used to obtain a
cycle-averaged model between valve duration and lift
and mean-valued cylinder charge. In the companion
paper, [7], the cycle-averaged model was used with the
cylinder-by-cylinder model to develop and demonstrate
a control approach to estimate cylinder charge online
and use that information to update a feedforward map
between charge demand and valve lift and duration.
However, the model used in [7] and [8] did not include
modeling of the exhaust process and the effects of combustion
on cylinder pressure, and therefore the effects
of combustion on the breathing process and torque produced.
This paper attempts to to demonstrate a more
complete cylinder-by-cylinder model that includes the
exhaust valves, manifold, and breathing process, as
well as the in-cylinder combustion.
2 In-Cylinder Dyanmics
The in-cylinder dynamics consist of the 4 states of
cylinder pressure, temperature, mass, and burned gas
residual fraction, as described in [9]. The cylinder pressure
is obtained from the perfect gas law
Pc~Vcyt =rncytRTcyl (1)
Where Pcyt is the cylinder pressure, Vcul is the cylinder
volume, mcut is the cylinder mass, R is universal gas
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variable valve timing is where the engine changes valve timing based on the driving situation much like ignition timing is changed to meet the needs of the engine in specific situations. in most cars valve timing is static and determined by the timing gear on the camshaft
valve timing diagram of two stroke engine
It is the "Advertised duration", used by the factory. It is the Valve timing from when the valve is .006inches off the valve seat to .006" off the valve seat.
According to Wikipedia, a variable valve timing is a "process of altering the timing of a valve lift event, and is often used to improve performance, fuel economy or emissions".
Valve timing is not adjustable on a stock engine. The timing chain is either installer correctly or not.
Yes accuauly its the cam that does control valve timeing.. on the lobes of the cam .
to inject oil into the valve timing controller assembly
Ignition timing or valve timing?
Ignition timing or valve timing?
bad timing,worn cam,valve adjustment
This component is electrically operated by the engine computer. It (on most vehicles) changes the oil pressure in the variable valve timing system to adjust the valve timing. It is very similar to the solenoids in use inside an automatic transmission.
there are two kinds of timing marks. one is for ignition timing and one for valve timing.