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Discussion Starter #1
I have been using the cruise control (the standard one, not the adaptive) quite a bit recently, and it made me curious -- how does the cruise control lower the speed?

I use this functionality quite often -- when you are driving along on a road and the speed limit goes from for example 110 to 70 km/h, you can just hold the cruise control lever down for a few seconds and the car will quite swiftly lower the speed. It is also useful when passing a speed camera zone.

I have a manual gear box, and the cruise control definitely lowers the speed more quickly than just lifting the throttle, more similar to a down-shift. But given the car is a manual, of course it can't be doing that.

So does anyone know? Does it apply the breaks? Does it engage the generator harder? Magic?
 

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I think that the system use brakes to lower speed. You can see that especially at night when the rear brake lights goes on when lowering the speed through cruise control. And something else.I believe that the benefit from using cruise control is the fuel economy when driving long distances.
 

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Discussion Starter #3
Interesting -- I have to try reducing speed at night to see if it lights up the brake light. Thanks!
 

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As the throttle control is electronic, ie no physical connection to the accelerator pedal, all the cruise module does is tell the throttle to close, thus slowing you down.
 

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The Audi cruise control differs slightly from others in that instead of holding the lever to progressively speed up or slow down, moving the lever pre-sets the desired speed on the DIS. If you're cruiseing at 70 and hold the lever down long enough to cause the pre-set speed to drop to, say, 10 the car will apply the brakes rather firmly to get you there.

This was a point of discussion on here a couple of years ago when some of us thought our cars were having 'HAL' moments.
 

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Discussion Starter #6
speary said:
As the throttle control is electronic, ie no physical connection to the accelerator pedal, all the cruise module does is tell the throttle to close, thus slowing you down.
If you're cruiseing at 70 and hold the lever down long enough to cause the pre-set speed to drop to, say, 10 the car will apply the brakes rather firmly to get you there.
Thanks all for the input. This is actually a bit contradictory -- does it apply the brakes or just close the throttle? I guess reducing speed in the dark and watching for the brake light will be the answer...

In general I do like the behavior, and imagine it would help reduce fuel consumption if indeed it does close the throttle.
 

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Thanks all for the input. This is actually a bit contradictory -- does it apply the brakes or just close the throttle? I guess reducing speed in the dark and watching for the brake light will be the answer...

In general I do like the behavior, and imagine it would help reduce fuel consumption if indeed it does close the throttle.
It uses both the brakes and closing of the throttle.
 
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