VARIABLE VALVE TIMING (VVT)
UEME4363
INTERNAL COMBUSTION ENGINES
ASSIGNMENT: Group T (2a)
What is VVT?
VVT= Variable Valve Timing Enable to have both low-end torque and
high-end power increase fuel efficiency by varying the
duration, timing and lift of the intake and exhaust valves relative to the engine speed.
How VVT helps?
By three main approach: varying the duration of intake valve opens
accordingly;regulating the timing of the intake and
exhaust valves;adjust the valve lift (distance which a valve
opens) depending on the engine speeds.
How VVT helps?
Volumetric Efficiency:ɳv = ma/ρaVd
Where:ma = mass of air into the engine (or cylinder) for one cycleρa = air density evaluated at atmospheric
conditions outside the engineVd = displacement volume
How VVT helps?
In term of duration/timing:At LOW speeds:
○ VVT ensures the intake valves are close as soon as the piston hit the BDC position
At HIGH speeds: ○ VVT allows the intake valves to be held open
earlier or longer to let the air fill up
How VVT helps?
In term of valve lift:At LOW speeds:
○ Small valve lift; low engine speeds generally have low intake manifold pressures
○ high velocity of intake air to create enough pressure different to draw in air into the cylinder
At HIGH speeds: ○ Big valve lift; to take in more air and fuel to
generate more engine power in the higher RPM ranges
How VVT helps?
Variable Valve Timing and Electronic Lift Control(VTEC)
Power modeFuel economy mode
Variable Valve Timing and Electronic Lift Control(VTEC)
i-VTEC, latest from Honda the main disadvantages of the VTEC
system are the weight and complexity of the system itself.
Compare to other VVT like VVT-i, it is more complex as it compromise of both valve timing and valve lift. Hence, this cause the VTEC engine is more expensive to produce.
Variable Valve Timing with Intelligence (VVT-i)
Variable Valve Timing with Intelligence (VVT-i) cannot vary the valve lift; has less top
end power However, VVT-i is the simplest and
cheapest form of VVT when compare to other current available VVT because unlike other systems that employ individual mechanism for every cylinder, each camshaft needs only one hydraulic phasing actuator.
Valvetronic
The most radical feature of this system is: no throttle butterfly is used
varies the amount of intake valve lift to regulate engine speed
Valvetronic
Valvetronic
better fuel economy as sucking air via a partially closed butterfly in the throttle body as power is loss in the process
response faster when throttle is pressed Yet, even more complex which directly
escalate the cost; additional components also cause
additional friction and inertia and do not help in improving top end power