Audi is working on a totally new type of four-cylinder engine that is intended to be as smooth running as a six-cylinder or eight-cylinder unit.
The move comes as premium car makers embark on a big reduction in the fuel consumption of larger models - such as the A8 L - by downsizing engines and using hybrid drivetrains.
It’s thought that Audi was awarded a patent for this unusual design last year. The description is for an “internal combustion engine with multi joint crank drive and additional masses on articulated connecting rods for damping free inertia forces.”
In simple terms, this design uses a radically different layout to avoid generating the internal forces that make four-pot engines less smooth.
The pistons and conrods no longer run in line with the crankshaft. Instead, they are offset to one side of the crank and connected to it via a rocker-style link.
The centre of the rocker link is attached to the crank and the other end to a second conrod, which is attached to a fixed shaft and has a counterweight at its head.
The principle seems to be that a four-cylinder engine will run more smoothly without pistons moving on the same axis as the crankshaft, and that a counterweight on the end of the second conrod should further damp out unwanted internal forces.
As configured in the drawing above, the new engine would be as wide a regular ‘V’ engine. Also, if the secondary shaft was lobed like a camshaft and could also be swivelled along its axis, this arrangement might permit variable compression ratios.
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IF 3 CYLINDERS AND 90 DEGREE V6S CAN BE SMOOTHED OUT...
3's different than 4's
Check "The Internal Combustion Engine in Theory and Practice", by Charles Fayette Taylor.
The secondary and tertiary vibration plots tell the whole story. Ironically, it's easier to make a vertical "3" run more smoothly than a vertical "4", --- until now, of course. But how good and durable this Audi engine will be is another story. ----- And, yes, some historic engines, like the 90-degree V-8 or the horizontally opposed flat 6 are inherently very smooth. But I am mystified as to why Audi did not consider a flat 4 like the original "Beetle" engine or the current Subaru BRZ engine. Any ideas? -------
comlicated