Variable Compression Ratio: An Old Technology Renewed

Gone are the days when we had to manage our vehicle with a constant compression ratio. Surprised? This sentence appears as though written by a technology geek. I have seen some of my friends modifying their bikes in the college years. The end product being worst than previous! The main problem associated with these vehicles today being the internal combustion engine.  No doubt that many of us want to get rid of it.

Confused? OK let us make our facts clear. A normal gasoline engine of a bike works with a compression ratio of about 10:1-10.5:1. While that for a diesel engine is about 22:1-25:1.While we can seldom guarantee that we will be able to drive in an ideal environment. Because sometimes we apply brakes while sometimes we accelerate our vehicle. When we accelerate our vehicle, the engine has to produce higher power with same compression ratio. If we could somehow decrease this Compression Ratio we can drastically boost the performance of engine.

Well, you will now be happy to know that the important drawback has been overcome due to the technology developed by ‘Svenska Aeroplan AktieBolaget’ commonly known as ‘Saab’ which is a Dutch owned Swedish car manufacturer. The technology which they used had existed in laboratory for years but was not used practically on road. It was only in the year 2000 that Saab took effort to use it during the period when GM took over. The technique is to modify the compression ratio as per our requirement which is otherwise constant. The engine by Saab was a 1.6 liter turbocharged engine and was able to vary compression ratio from 8 to a maximum of 14. It was also provided with a pivoting head which could adjust the slope of its upper surface in relation to lower part of engine hence the result was the change in volume.

A similar technology was also developed by Nissan. They developed what is called as VCR-Piston crank system. In this technology Compression ratio is modified by using a multi-link mechanism. Nissan replaced the connecting rod by a multi-link mechanism. In this mechanism the upper link is engaged with piston pin. The control shaft and control link are connected through what is called a control link. The control shaft has an eccentrically connected bearing. The lower link is kept as a free link. By activating this mechanism through this control shaft, the piston is moved from top dead center position to bottom dead center position.  As described earlier when we say that we are changing the upper plane of piston, we are actually controlling the angle of control shaft.

The fuel economy of a non-turbo engine and the power output of a turbocharged engine can be achieved in one engine. It also means that we can achieve the present efficiency and power with one third the engine space. The multi-link mechanism is also controls engine vibration it amounts to a great reduction of space and is also effective from environment point of view.

However this technique is highly effective in 2 stroke engine due to simplicity of design, while it can also be used for a 4 stroke engine only with some difficulty.

The same technology is also called developed by a France. They call it MCE5-VCRi engine. With simple changes the technology is similar.  So all in all, this is a simple one but still not much thought about concepts. Even being old this concept has not been applied much. But one thing is for sure, we will use it someday or another because we are in a need to safe our fuel and increase the efficiency of our machines.

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