| All about variable valve timing
Question : I WILL be in the market for a new
car soon. I have been told that
the latest engines come with
Variable Valve Timing technology
that makes the vehicle more
powerful and saves on fuel.
Please elaborate on what
variable valve timing is and
how it works.
Answer :
VARIABLE Valve Timing (VVT), as
the name suggests, varies the
valve timing of the engine.
There are varying flavours of
WT depending on the vehicle
manufacturer, and they are
known as VTEC, VVTi, VVTi-L,
DVVT, etc, but they all function to
vary the valve timing or valve lift,
or both.
For smooth engine operation at
low speeds, valve overlap must be
kept small and lift low. The opposite is true for high engine speed
operation. The result of using a
large valve overlap and high
valve lift at low speeds is rough
running, and in extreme cases,
backfire through the exhaust.
VVT can be applied to the inlet
valves, exhaust valves or both.
The variation in timing can be
either on-off or progressive, and
can either be mechanical,
hydraulic or electronically controlled.
WT does increase engine output, reduce exhaust emissions
and increase fuel economy. |
