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