Currently reading: Audi plans super-smooth four-cylinder engine
New patent reveals Audi's plans for a new hyper-efficient engine, which is planned to be a smooth as larger six and eight cylinder options
2 mins read
15 August 2014

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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15 August 2014
Variable Compression is the holy grail of current engine design, so if Audi have figured out a way to commercialise the idea it will be a significant step forward.

15 August 2014
Why go to all that added complexity, when a four cylinder engine can be made to run more smoothly using balancer shafts?

16 August 2014
Frightmare - - -

Doesn't work adequately. Look at the 4-cyl in the new BMW 328i. They went all out with counterbalancing, and it does not apply throughout the RPM range, especially just off idle.


15 August 2014
Audi - do you know what else is as smooth as a 6 cylinder engine? A 6 cylinder engine!! So how about designing a new one including all the wonderful new fuel saving measures available (even if they only mostly benefit the lab tests) and I'm sure the final figures will be as good or almost as good as a fancy new 4.

15 August 2014
Once you got to the technicalities you lost me there. All I could work out is that Audi will in future use 2L engines to replace larger capacity engines in its largest cars like A8. Are we talking about petrol or diesel?
At the moment Volkswagen is getting 300bhp out of 2L petrol engine. Is this engine suitable for A8 size car? It doesn't look preposterous on paper but would it be able to haul all that weight in real life without further reliability issues?

15 August 2014
But this does look like a very good way of achieving a variable compression ratio (and better efficiency) and improved smoothness in one go. I guess the downsides are increased size, weight, cost and the potential for more moving parts to wear out - but I'm sure this is a better idea than the Volvo variable compression design which was tried a few years ago.

15 August 2014
Will this really be an Audi engine or a Volkswagen engine used in Audi's?

As long as it is smooth, reliable & powerful enough to pull two tonnes of car around in high altitudes, it will be perfect.

15 August 2014
This design is very interesting, but even though it's probably not to scale it looks to be quite long, tall and wide for four cylinders. Wouldn't it be a lot easier to just build a flat 4 engine to get a smoother feel? It would be a lot shorter and a lot lower, probably not that much wider, and presumably a lot lighter.

15 August 2014
I'm romantic. But nothing replaces a NA 6 pots...
But this is the end of such engines...

15 August 2014
This is just a jointed version to get round Nissan's patented variable compression system. Unfortunately, doubling the joins will double the losses in the crank system, which would make this engine wholly uncompetitive on fuel economy/emissions. Also, half the 'smoothness' of an engine is down to the number of cylinders and the rotational inertia of crankshaft/flywheel assembly. Since it still only has four cylinders, it still won't be as smooth as a six, even if the secondary forces from the conrods are removed. Why to Audi continue to publicise their inadequacy as engineers?


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