Variable Valve Timing (VVT) is nothing but the alteration of process for the time valve lift event, and its frequently used to improve fuel economy, engine performance. Honda was amongst the first to introduce this technology to the world with its VTEC engines in 1980's.
VTEC (Variable Valve Timing and Lift Electronic Control) is an combination of electronic and mechanical system that allows the engine to have multiple camshafts.
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VTEC engines have an extra intake cam with its own rocker, which follows this cam. The profile on this cam keeps the intake valve open longer than the other cam profile. At low engine speeds, this rocker is not connected to any valves. At high engine speeds, a piston locks the extra rocker to the two rockers that control the two intake valves.
Modern variable valve timing VVT- systems uses a cam phaser that rotates the position of each cam shafts relative to timing chain. The cam phaser consists of two basic components, an outer sprocket connected to the timing chain and an inner rotor to the camshaft, that varies the valve timing by adjusting the rotation angel of the cam. The inner rotor has a set of lobes, and oil fills the space between the outer housing and lobes.
Left one, the rotor will simply spin at the same rate as the outer housing.
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The majority of these VVT systems use oil pressure to push the rotor back and forth, oil-pressure-actuated systems require an upsize oil pump to produce the extra pressure that's required to work cam phaser, which reduce the some of the fuel economy gains of VVT.
With Variable Valve Timings, power and torque can be optimized across a wide rpm band, with the most noticeable results as:
1. Engine can rev higher, thus raises the peak power.
2. Low - speed torque increases, thus improves drivability.
Valve lifts can also be varied according to engine speed. At high speed, higher lift quickens air intake and exhaust, thus further optimised the breathing. Hence according to engine speed the lifts can arranged as,
- Cam-Changing VVT
- Cam-Phasing VVT
- Cam-Changing + Cam-Phasing VVT
- Rover's unique VVC systems
Exhaust gas recirculation is a commonly adopted technique to reduce emission and improve fuel efficiency. In general maximum overlap is necessary between intake valves and exhaust valves opening whenever the engine is running at high speed. However, when the car is running at a medium speed in highway, maximum overlapping may be useful as a mean to reduce fuel consumption and emission. Since the exhaust valve do not close until the intake valves have been open for a while, some of the exhaust gases are recirculated back into the cylinder at the same time as the new fuel or air mix is injected. As a part of the fuel or air mix is replaced by exhausted gases, less fuel is needed. As the exhaust gas contains of non combustible gas, such as CO2, the engine runs properly at the leaner fuel or air mixture without failing to combust.
Market Analysis for Variable Valve Timing
As the automobile industry is growing rapidly in a past few years, with various advance technologies evolved in various parts of manufacturing and various new innovations by automotive makers attracts buyers towards this new innovations.
If we look up to variable valve timing market, as the system has universally accepted all over the world due to low cost of cam phasing units. And as the technology is upgrading in every parts of manufacturing of automotive consumers also looks positives while approaching this new technologies.
Asia Pacific is the largest automobile producing region in the world hence it is the region where the technology's penetration is low but due to larger size of the target industry in the region it emerges as the market driver. Hence this VVT systems has huge demands for this region in the upcoming future.
The other Regions like Europe and America has a also the huge demand due to VVTs Popularity. Car makers like Ford and Toyota are also realizing on the use of these technologies in their engines to keep up with the tightening emission norms.
As per the market research analysis "the combined market for variable valve timing market and start stop systems is expected to be worth 88.8 million units and $9.8 billion by year 2018.
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