You may think that the pistons in your car’s engine slide in and out of the cylinder bore holes smooth as silk, but according to researchers from Germany’s Fraunhofer Institute for Machine Tools and Forming Technology, the process could be smoother. If it was, your car would burn less gasoline, and require less oil for lubrication. Well, those researchers have developed an engine-building tool, designed to minimize engine cylinder friction.
There are two types of bore hole distortion that lead to the friction – static and thermal. Static distortion occurs when the engine is being assembled, with mechanical stress from activities such as the tightening-down of screws causing the bore holes to subtly change their shape. Thermal distortion occurs once the engine is running, as heat causes the bore holes to warp. In either case, the result is that the pistons rub against the inside of the bore holes, in the places where they’re distorted.
The researchers start by removing the cylinder head from a sample engine, to see what static distortions have been caused by the assembly process. They then simulate the operating temperature of the engine by heating it to 90º C (194º F), then measuring what thermal distortions have occurred. Their tool comes into play next.
It’s a cylindrical honing tool, used to carve out the inside of the bore holes. Due to integrated piezo actuators, however, it can expand or contract its diameter as required. When the dimensions of the distortions are fed into the system, the tool can be inserted into a bore hole, then take on the required shape as it’s turning, grinding the distortions away.
A prototype of the tool is now being tested with auto manufacturers. The Fraunhofer team believes that it could result in fuel savings of two to three percent, along with less oil consumption and longer engine life.
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