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Why VVTI?
In
contrast to the fixed valve timing of conventional engines, the VVT-I
system is an computer controlled
mechanism
that continually varies the timing for opening and closing the intake
valves in accordance with the vehicle's operating conditions.
By
determining the level of performance that is demanded of the engine at a
given time by way of the driver's accelerator operation and the engine rpm,
the VVT-I enables the overall performance of the engine to be enhanced all
the way from the low to the high rpm range.
Design
VVT-I
is comprised of three major components
1.The electronic control unit(ECU), which calculates optimum intake valve
timing based on engine operating conditions.
2.The oil control valve (OCV), which controls hydraulic pressure under the
ECU's instruction and
3.The VVT pulley, which continuously changes the intake valve timing using
hydraulic pressure.
The VVT-I is an engine control system that has achieved high levels of the
seemingly opposing performances of Higher power out-put, Lower fuel
consumption, Cleaner exhaust gases.
D-4D High technology, clean diesel
Originally introduced in Europe in the top selling Avensis range, D-4D is
widely recognised as one of the most advanced diesel technologies on the
market today. Toyota D-4D engines are available on select models of Yaris,
Yaris Verso, Corolla Verso, Innova, Avensis, Avensis Verso, RAV4, Land
Cruiser and Previa models.
Until recently, diesel engines relied on relatively simple technology with
a low-pressure mechanical injector delivering fuel to a pre-combustion
chamber in the cylinder head, where a single ignition - fired by the intense
heat of high compression - takes place.
The system was reasonably fuel efficient but lacked precision and
refinement, leading to vibration and noise. Fuel combustion can be
incomplete, allowing smoke and other emissions to pass into the exhaust.
D-4D components
Toyota's common rail system makes use of a high pressure pump and
intelligent, computer controlled injectors to deliver precisely the right
amount of fuel, at precisely the right time, directly into the centre of
the combustion chamber.
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