Man’s fascination with fast and personal transportation over land, sea and air is evident from the mention of the Flying Chariot or the “Auran Khatola” in the ancient Indian mythology and the famous Magic Carpet in the Arabian Night Tales. The Internal Combustion engine has come a long way since the Wright Brothers used one on their flying contraption, which flew 150 feet, and the day Henry Ford rolled out the first production automobile. Today the Internal Combustion engine stands as a shining example of the evolution of man’s engineering prowess and how he has reached the pinnacle of its design leaving no stone unturned in achieving it. In fact research and development is now more concentrated on the engine head design than anywhere else solely because the other conventional components are more or less reached their optimum designs. All improvised designs primarily aimed at enhancing fuel economy, and to obtain wide-ranging engine performance for both driving pleasure and environmental friendliness. Intake and head design has leapfrogged in the last two decades culminating into what is called Cam Less Valve Actuation. From optimized intake manifold designs and high-pressure injectors, to efficient Intercoolers and variable geometry turbochargers, all have come a long way. Recent advances in Fuel Delivery Systems like the new generation Common Rail Fuel Injection System and the acclaimed Pump Deuse Technology conceived by the Volkswagen group has further catapulted the cause of complete technology overhaul of the various systems of the Engine Head. The radical technology introduced by the Honda Motor Company back in the 80’s revolutionized the entire concept of valve timing. Honda gave the world, what came to be known in the automotive circles as Variable Valve Timing and what they called Variable Valve Timing Electronic Control or VTEC. Frugality and performance are two parameters unheard of on a single platform. In other words, performance demands high capacity engines, and frugality- small efficient engines. So to achieve both on a single platform was impossible using conventional methods. Honda tackled this head on with VTEC. Other automobile companies soon followed suite and gave it their own names. Toyota called it VVTi, Porsche-Vario cam and BMW called it VANOS. But technology to attain this technological marvel was constrained by the Internal Combustion Engines ubiquitous Camshaft because of its function specific design. De facto there is a direct relationship between the shape of the cam lobes and the way the engine performs. An aggressively shaped cam, in other words a cam with a high angle of dwell is good for high RPM performance whereas a cam with a low angle of dwell works very well at lower RPM’s giving the engine exactly what it demands. To infer from this that there are only two power bands would be putting a stop to the true potential of the valve actuation system development. In reality there are several intermediate power bands that even a multiple camshaft equipped engine is robbed off. So it is not entirely untrue to say that Variable Valve Actuation System is on the verge of a complete impasse. Of course, other areas too are being worked upon which can probably compensate, if not make up, the lack of a true Variable Valve Actuation System and so it even seems that this deadlock may not be ever tackled. But Variable Valve Actuation System designers might now have an opportunity to have their cake and eat it too and they owe this to the Cam Less Valve Actuation System. The advent of the Cam Less Valve Actuation system has given the power and ability to challenge and even change the way conventional engines breathe and work. One will not be saddled with just a couple of cam-profiles to work with but perhaps over a hundred! Technology, which could not have been perceived before because of mechanical constraints, has risen like the Phoenix. Cylinder Deactivation or Multi Displacement Technology- the brainchild of a hand full of automobile geniuses is now very much possible and can single handedly address the serious issue of the paucity of fuel. A very valid question would be that if there is indeed a fuel crisis looming over us then why try and develop such advanced and complex technology, spending extravagant sums of money when all of it could be used for power trains of tomorrow. Well, the answer is quite simple- potential power trains of tomorrow like the fuel cell based engine is still years away from mass production. The idea of using hydrogen as a fuel in the Internal Combustion engine is still in its formative years and seems very promising and perhaps even attractive but the problems associated with producing, storing and handling still persist and there shall be considerable time before this is feasible. The bottom line is that we have to devise a way to make the best and the most efficient use of our remaining fuel reserves and the Cam Less Valve Actuation System is the only way out.
Such precision-guided systems also take care of one of our times biggest problems- emission control. To accept this technology
would be prudent, to embrace it- brilliant.
1.The incorporation of VVT TECHNOLOGY in the SAVT
The dynamics of airflow through a combustion chamber change radically between 2,000 rpm and 6,000 rpm. Despite the manufacturer’s best efforts, there was just no way to maximize valve timing for high and low rpm with a simple crankshaft-driven valve train. Instead, engineers had to develop a “compromise” system that would allow an engine to start and run when pulling out of the driveway but also allow for strong acceleration and highway cruising at 140 plus Kmph. Obviously, they were successful. However, because of the “compromise” nature of standard valve train systems, few engines were ever in their “sweet zone,” which resulted in wasted fuel and reduced performance.
The VVT system ensures that the engine always remains in its “sweet zone”. However, this works well only theoretically. The mechanical constraints imposed by a camshaft / camshafts is simply too much to take care of all power bands. Even the best VVT techniques like DOHC VTEC and DOUBLE VANOS fail to satiate the engines incessantly changing appetite, throughout the revolutions.
The SAVT is the true upholder of the engines “sweet zone”. It is capable of continuously varying the valve timing right through each of the power bands. It eradicates the use of Multiple Profile Camshafts as well as all the complexities, which arise with such a setup.
2. The incorporation of Multi Displacement Technology / Cylinder Deactivation.
The simple fact is that when one only needs small amounts of power such as for crawling around the city, what one really needs is a smaller engine. In other words, an engine performs most efficiently when it’s working harder, so making it do work of an engine half it’s size and efficiency suffers. Pumping losses are mostly to blame. When a petrol engine is running with the throttle wide open, pumping losses are minimal. But at part-throttle the engine wastes energy trying to breathe through a restricted airway and the bigger the engine, the bigger the problem.
Thus, deactivating half the cylinders at part load is much like temporarily fitting a smaller engine. If we consider a V6 engine, the MDT is activated at part throttle between 1000rpm and 3000rpm, when the actuators prevent the valves from opening. Hot gases are trapped in 3 of the 6 cylinders, compressing and expanding like giant air springs as the engine turns over and keeping the cylinders warm. But as long as the valves remain closed, only 3 cylinders consume fuel instead of 6. Engine efficiency is also improved because the 3 dormant cylinders are no longer working hard at sucking air into the engine, something that consumes a substantial amount of power.
MDT also opens up new avenues for engineers, such as, the option to employ High Torque D.C Motors, which work in tandem with the firing cylinders while the remaining cylinders remain dormant.