New technology including coasting and variable compression ratios to lead a surge in petrol engine efficiency for the VW Group

The Volkswagen Group is preparing a revolution in petrol engine efficiency, according 
to hints from Audi technical chief Ulrich Hackenberg.

Speaking at Audi’s recent annual conference, he said engines with “electro-mechanical assistance for forced induction” and “variable compression ratios” were in development. 

Hackenberg also said coasting would become an important fuel-saving technology over the next few years. A coasting function - where the transmission disengages from the engine on the overrun - is already built into some VW Group models equipped with dual-clutch automatic gearboxes. 

Hackenberg gave no details on how Audi will introduce variable compression ratio technology, but the principle has long been something of a Holy Grail for engine designers. Being able to vary an engine’s compression ratio depending on the immediate demands being placed on it should lead to significant advances in efficiency. 

In 2000, Saab demonstrated its experimental supercharged and turbocharged SVC engine, which used a tilting block to change the volume of the combustion chamber and, therefore, the compression ratio. More recent designs have altered compression ratios by changing the throw of the crankshaft or through the manipulation of conrods.

Audi demonstrated electrically assisted forced-induction technology in the summer of 2012 as part of an experimental twin-turbo V6 engine. It used an electrically driven turbo which was spun up to high speed by a motor and used to force air into the engine at low speeds — something a normal turbo cannot do until the engine is running at higher revs.

This technology not only allows turbocharged engines to perform effectively from a standstill, but is also very effective for downsized two and three-cylinder engines.

Hackenberg said coasting technology - which has significant fuel-saving potential - would arrive in four stages. The first level already features on some dual-clutch ’boxes, with the next version expected to function when the car is travelling below 4mph. The ultimate version will see the transmission decoupling and the engine shutting down when cruising at speed, travelling downhill or approaching traffic lights that are about to turn red. 

Electric turbochargers, variable compression ratios, cylinder deactivation and coasting combined have the potential to hugely improve the real-world economy of future petrol engines.

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36

28 March 2014

I have always used coasting to improve mpg, even though you are told these days not to, because you are "not in control" of the vehicle. I always coast when travelling downhill or decelerating, but I have my feet hovering over the clutch and brake pedals. Maybe that would fail me a driving test but you don't need to be engine braking to be in control of a car going downhill, in my opinion, I am still perfectly in control of my vehicle. Now that coasting is making a return, why not reintroduce freewheeling hubs, as used by Saabs many years ago. Very simple idea but could improve real world mpg, so why not.

currently a happy owner of a Mitsubishi Shogun Pinin :)

28 March 2014

Roverfan, I'm afraid you've got it all wrong. If you take your foot off the accelerator while the car is still in gear, fuel flow is shut off. If you take the car out of gear, then fuel is required to keep the engine idling. What you're doing is actually using more fuel.

29 March 2014
Cardinal Fang wrote:

Roverfan, I'm afraid you've got it all wrong. If you take your foot off the accelerator while the car is still in gear, fuel flow is shut off. If you take the car out of gear, then fuel is required to keep the engine idling. What you're doing is actually using more fuel.

There is a long downhill road where I live followed by a long straight. I go into neutral at the top of the hill and dont need to engage gear again for a good 5 minutes. If I stay in gear the car slows down and I have to tap the accelerator every now and then to maintain momentum. Maybe different cars are different, but in my own personal experience I get better mpg (I work it out on every refuel, sad as that may sound) when I use frequent coasting. As I say, for your car what you are saying may be true, I am not saying you are wrong. But coasting works for me.

currently a happy owner of a Mitsubishi Shogun Pinin :)

30 March 2014

At 30mph in gear foot off throttle down hill my instant MPG reading is -_ _ . _ _.
At 30 MPH coasting with the engine idling my MPG is 134.

 

 

28 March 2014

I can't wait for these improvements so that we can finally confine diesel to boats, where it belongs. I had a Rover 75 (from the late 1950s) when I was young and poor and it had a freewheel. I must say I didn't use it very often but that was probably in part because it was a very pleasant old duffer of a car but not one you would want to start running away from you.

31 March 2014

I too had a 1950s Rover 75 when I was an impecunious university student, and it's true that the combination of freewheel with a one-and-a-half tonne car with drum brakes all round and no servo assistance meant that stopping required some forward planning. The sensation of this stately old bus gathering speed noiselessly as the speedo needle crept past 70 on a long downhill stretch was a memorable experience!
Of course, with modern brakes, there's no reason not to use coasting as a technique to save both fuel and driveline wear. To do so is simply to replicate the function of automatic transmission.

28 March 2014

I hate cars that coast. My wife's Jeep Liberty with the V6 and automatic runs away down hill so one has to keep braking to stay at the posted speed limit. Half the new cars I rent on my travels do the same thing. This is why driving on wet roads at night is horrible. All you can see are bright red brake lights! Both my Land Rover Discovery and my Nissan Frontier pickup are terrific. I can set the cruise control and without touching the brake so I can be sure my speed is constant without having to touch the brakes both up and down hill.

Coasting transmissions will just transfer the cost of petrol to the cost of brake discs and pads while blinding the drivers behind at night. That's no improvement. I believe coasting transmissions should be banned as dangerous.

28 March 2014

I hate cars that coast. My wife's Jeep Liberty with the V6 and automatic runs away down hill so one has to keep braking to stay at the posted speed limit. Half the new cars I rent on my travels do the same thing. This is why driving on wet roads at night is horrible. All you can see are bright red brake lights! Both my Land Rover Discovery and my Nissan Frontier pickup are terrific. I can set the cruise control and without touching the brake so I can be sure my speed is constant without having to touch the brakes both up and down hill.

Coasting transmissions will just transfer the cost of petrol to the cost of brake discs and pads while blinding the drivers behind at night. That's no improvement. I believe coasting transmissions should be banned as dangerous.

28 March 2014

are the three words in one sentence that startled me into writing this comment so early in the morning. All the technologies hinted at in this article have been tried and in most cases failed to catch on. It's gonna be a slow news day and perhaps full of regurgitated press statements.

28 March 2014

Surely coasting costs you fuel? Then engine is still consuming fuel to keep itself running. Modern injection engines don't consume any fuel if you lift off the accelerator whilst in gear - the forward movement of the car via the gearbox keeps the engine spinning. The VW examples seem to go further, if you can remove the frictional losses of the drivetrain and turn off the engine, mpg gains seems possible.

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