Thursday, August 22, 2013

What is DVVT?

The variable valve timing mechanism is called Dynamic Variable Valve Timing (DVVT) and it varies the opening/closing times of the eight intake valves. The system is electronically-controlled and makes variations almost instantaneously in a seamless manner, optimizing the flow of the air-fuel mixture into the combustion chambers. To determine when and what variations are need, the engine management system gets data from at least five sensors (one of which also monitors the temperature of the engine coolant). It then analyses this data and chooses the right opening/closing time for the given driving condition – all within milliseconds.

The system is similar to that used on the Toyota Corolla Altis and Camry (in fact, it comes from Denso, the same supplier as well) and can also be found in the Mitsubishi MIVEC engine, Volvo S60/S80, BMW VANOS engines and the Honda i-VTEC engines.

How effective is DVVT? Very – as the power and torque increases show. Power output is now 63 kW (85.7 bhp) at 6000 rpm, 3.3% more than before and close to the figure for the Honda City’s 1.5-litre engine (88 bhp). Torque is up by an impressive 14.3% to 105 Nm and it peaks at just 3200 rpm which is 1900 rpm lower than before. This latter point demonstrates the value of a variable mechanism because in the past, the engineers had to decide on just one state of tune and practical reasons dictated a higher torque figure. Now they can have the torque peak lower down where it is useful and still have a good spread over almost the entire rev range. Incidentally, the compression ratio is also boosted to 10:1 and this makes combustion more efficient.

Other features of the engine include a resin uniform-length intake manifold for smoother flow and an offset steel crankshaft (reduces friction). There are two drive belts, one to power the air-conditioner compressor, alternator and waterpump, and the other just for the power steering energizer. There is now one ignition coil per spark plug, whereas the old model had one coil for all four spark plugs, and the coils are directly managed by the ECU so there is no distributor needed.

A major benefit from DVVT is that toxic emissions in the exhaust gases are lowered a great deal and with the 3-way catalytic converter, pollution is almost nil. The very poisonous oxides of nitrogen, in particular, are lowered by 40% and all this is due to the much better and more complete combustion.

The complete combustion also enhances fuel economy although in driving terms, the lower fuel consumption also comes from having a better weight-to-power ratio. Perodua’s testing in Malaysia shows that the Kembara with DVVT and manual transmission is 12.02% more economical (12.58 kms/litre) while the automatic is 14.8% more economical (11.02 kms/litre). This testing was done on routes of between 270 kms and 300 kms with a mix of highway, country and urban driving conditions.

As for straightline performance, it would be expected that the new engine will give better figures than before. Factory claims for 0 – 100 km/h are 13.49 (MT) and 13.6 seconds (AT) which are 0.8 and 2.0 seconds better, respectively. Top-end performance also shows improvements of 7.3 km/h (AT) and 4 km/h (MT) with the manual version able to get up to 155.9 km/h while the automatic should hit 151 km/h.

There’s another aspect of the new engine which is also noteworthy and addresses one of the issues which owners had – noise levels. A lot of effort with into bringing this down and apart from engine features like an aluminium oil pan, there are also other parts of the car where noise suppression measures have been taken.

See how DVVT works:


Credit to: autoworld & youtube


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