The Hindu Business Line : Varying the engine performance

Essentially, variable valve timing technology controls the amount of air that enters the engine under various operating conditions, optimising it based on the kind of demand placed on the engine.

Car manufacturers that have a global presence and have to sell the same car in different markets have to do a fine balancing act. The model that is sold in the US and Europe will be popular only with a bigger, more powerful engine, but will still have to meet the stringent emission norms. The same car model when sold in Asia, including India, may only be preferred with a smaller, more fuel-efficient engine that meets the local emission regulations.

Street-legal vs race-cars

Therefore, in a manner of speaking, street-legal cars have to have a combination of characteristics borrowed from race-cars and technology demonstrators. So, unlike race-cars that are focused on performance, streetcars are more complex and have to be multi-talented. Race-cars have a different set of regulations to deal with in terms of size and accessories used, but are not required to meet the kind of norms that streetcars have to especially on such parameters as emissions, fuel efficiency and drivability in differing conditions.

So, while popular streetcars may need the power and performance of a race-car on the highway or for an overtaking manoeuvre, the same car would also be expected to comfortably handle crawling city traffic without compromising much in terms of emissions and fuel-efficiency.

A popular technology

One of the petrol engine technologies that helps improve the car's drivability, without increasing emissions or compromising fuel efficiency, is `variable valve timing'. This is one automotive jargon that many of us may have heard of; after all, quite a few multinational carmakers are already offering this technology in their vehicles here.

Variable valve timing has been around for sometime now. The first cars with this technology started to appear in the early 1990s. It has since gained popularity around the world and most big names have all adopted this technology and it is not restricted only to the mass-market models.

Variable valve timing is also called variable valve actuation or variable cam timing and various car manufacturers have different abbreviations for their versions. Toyota calls it VVT-i and offers it in the Corolla and the Camry models; Honda calls it i-VTEC, which is featured in the compact sports utility CR-V and the Civic sedan; Hyundai's new Verna has a VTVT system; and BMW's nomenclature for this technology is VANOS.

Compared to their diesel-driven counterparts, the biggest weakness of petrol engines is their inability to generate as much torque as the former. If this performance weakness of petrol engines is addressed, the efficiency of the car automatically receives a boost.

Variable valve timing and related technologies help petrol engines achieve performance goals largely by boosting torque available during varying operating conditions. At times when the driver wants a boost of power, this technology also ensures that the peak power of the engine is immediately made available.

In a camshaft- or cam-driven petrol engine, during the combustion cycle, fresh air intake and spent air exhaust from the pistons are controlled by poppet valves.

Depending on the manufacturer and its own version of variable valve timing system, the technology uses electronic sensors and sub-systems for three valve control parameters — the timing or the duration or the amount of lift of the engine's poppet valves. While some only control one of these parameters, a few high-end systems manipulates all of them to optimise performance. Also, while some systems only control the air intake valves, others also regulate the air exhaust valves for increased efficiency.

Air control

Essentially, the variable valve timing technology controls the amount of air that enters the engine under various operating conditions, optimising it based on the kind of demand placed on the engine. Air intake should neither be continuously high (as in a race-car, which is focused solely on peak power) nor continuously low if optimum performance, better fuel efficiency and low emissions are to be achieved.

But in the absence of variable valve timing the engine's valves may be tuned for a fixed opening and closing cycle that will dampen peak engine performance by choking air intake early, or by feeding too much air at low engine rpm levels leading to a lot of un-burnt fuel being wasted away.

Variable valve timing controls the engine valves' lift (for increased air flow) and/or the duration (longer for high power and shorter for low speeds) and/or the timing (for coming up with the correct response for the driver's demands).

Support technologies

Engines that feature the variable valve timing technology have to use sensors and other related technologies such as a throttle position sensor, engine rpm sensor, drive-by-wire throttle and variable length intake manifold to enable precise electronic control over the engine valves.

The engine load is detected from the engine revolution, vehicle speed and throttle opening and the intake valve timing is switched to the high output pattern or the fuel saving pattern depending on the data fed into the microprocessor. When the load is small, the intake valve close timing is delayed to substantially reduce the amount of intake. At the same time, pumping loss (excess fuel) is reduced with the help of the drive-by-wire throttle to optimise fuel consumption.

Standalone, the variable valve timing technology is said to provide a benefit of 5-8 per cent. But married with other engine technologies it can boost performance. And in an era of high oil prices, it can make a world of difference to the car you drive.

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