Audi Reportedly Rethinks 4-Cylinder, Turbo Designs
|   Monday, August 25, 2014
Audi has been busy behind the scenes reportedly working on major changes to its four-cylinder powerplant to take the vibrations and noise out of the engine and make it run more like a standard six or an eight.

Fox News and Autocar reported Sunday that a working design sketch of proposed major changes to the four-piston engine that the automaker uses to power the A4/S4 and any other version of its vehicles ordered with a four that shows an offset bank of pistons to the side of the of the crankshaft.


Normally pistons are located in the top of a cylinder and they are enclosed with a head cover and gasket to provide the proper pressure for operation. Under the head cover itself are the valves and overhead camshaft that drives the valves to open. The camshaft takes its power from a serpentine belt at the front of the engine.

In the new design, the pistons would be moved from the top position to what appears, in the design sketch, to be the driver's side of the engine. Today, the average car engine has on the order of 15,000 moving parts and it looks like the added connecting rods and counterweights would add to that number.

In other words, though the engine would run more smoothly, it would be more complex to repair. For example, the actual cylinders would have to be moved, as well and the engine size would grow sideways and would not necessarily be shortened, as the new pistons would be parallel to the crankshaft. They would use standard piston connector shafts and wrist pins.

However, the pistons, would, instead of driving the crankshaft directly, drive offset rocker arms that would link the piston to a counterweight and the connector arms used to drive the crankshaft. The same wrist pins could be used. The pistons would be in the same position they now occupy but would be moved to the left so that they would appear to be above the connector arms and counterweights.

Interestingly, the Fox/Autocar report, showing the design changes does make a lot of sense and is in the patent stage. Autocar, Fox noted, found the sketch in a patent filing for the changes.

If you think about how a four operates, it is not really an inherently stable engine as it goes through the four-stage power cycle at exactly 90-degree intervals. Inline fours tend to vibrate and generate noise in such a configuration.

Many automakers have used separate vibration-damping camshafts within the engine to cancel out the inherent roughness of the four, but the cost comes in an even more complex engine as the compensating camshafts or anti-vibration shafts, if you will, add more hardware to the engines. If one of those extra shafts fails, the engine will fail.

This change will allow the automaker to shape the weighting and rotational forces more exactly by the placement of the major weight of the counterweight at the right points for smoothness and it would eliminate the need for added shafts.

The patent, Autocar/Fox notes, also goes on to say that it might also allow the pistons to be used with variable openings thereby increasing the efficiency of the engine and keep it within the bounds of the tightening mileage standards. It is an interesting concept.

Meantime, Fox News also reported from sources, that Audi is considering using an electric start for its turbocharger system. Normally, unequal length manifold runners and extra cooling is used along the turbocharging system to keep the air-fuel charge from dissipating its energy as it travels from the exhaust manifold to the intake side. This has been the major cause of turbo-lag and all sorts of plumbing changes have been tried since turbocharging gained credibility in the 70s and 80s when it was adopted by the auto industry as a way to small engines think they were larger than they actually were.

The beauty of turbocharging is that it uses the waste energy left in the exhaust manifold to drive the compressor impeller of the system that increases engine pressure. Correctly called turbo-supercharging, the system's main drawback was the distance the increased power flow had to run. By the time it reached full power, there could have been a delay of a second or more and the power levels provided might have dropped due to the dispersion and heating caused by the trip.

Turbocharging is best done, experts report, by a dense fuel/air charge at the impeller. If Audi is going to use an electric switch to start the impeller spinning, instead of relying on plumbing turbo-lag will be a thing of the past.
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