Adaptive cruise control speed limit

[Stu-perb]

After a couple of weeks of getting acquainted with ACC, the jury is still out for me.

 

On the plus side, it's very intelligent in how it deals with faster moving cars pulling back in too soon after overtaking (i.e. it doesn't react unnecessarily). It's great in the roadworks as we all bimble along on our best behaviour, under the watchful eye of SPECS.

 

The biggest downside, in my opinion, is how it overreacts when a car pulls out into your safe gap (which, let's face it, happens a LOT). Instead of calmly lifting or tickling the brakes in a rational manner, it applies them heavily, resulting in overcompensation and wasted fuel used in coming back up to speed. This needs constant supervision and driver intervention in order to make smooth progress in busy periods (ok, ok, I shouldn't be cruising in this situation, but I could get away with it more with the traditional system).

 

The other failing that I've noticed is that every now and again, it will have a complete brain fart and slam on the anchors as you try to overtake a wagon that's minding its own business in the adjacent left lane. Because this happens very rarely, it's bloody annoying and also a little bit frightening when it does, because it happens for no apparent reason and therefore can't be anticipated!

 

It's a good, but imperfect, system and I feel it's a crying shame that they haven't made it selectable alongside old school cruise control.

 

[DBT85]

On 02/12/2018 at 12:49, freelunch said:

The thing about ACC (which I love) is that it only "sees" what's right in front of it. A careful driver can watch traffic several cars ahead and anticipate much better than ACC. In dense UK traffic, I tend to leave it off and drive the car myself. It's brilliant in roadworks traffic, where all you care about is the car right in front of you. The first time I came to a complete stop, then the car took off on its own again, I was astounded. I still tend to hover my foot near the brake pedal, waiting for the inevitable computer fail.

Exactly the same for me. I'm looking at the brake lights 3 or 4 in front so if I see them I ease off the throttle. ACC would just keep pootling along until the car right in front of me brakes. 

 

It has its uses, but I do find myself toggling it on and off quite a lot when I'm on the motorway.

[DBT85]

On 02/12/2018 at 23:24, Stu-perb said:

It's a good, but imperfect, system and I feel it's a crying shame that they haven't made it selectable alongside old school cruise control.

 

This I can most definitly agree with also. When my car needed recalibration after a windscreen change, I had no cruise at all. Fine, don't be smart and adaptive but at least let me do it the old way. Had a 300 mile trip to take and no cruise was not fun.

[Fatso]

I use ACC (with a DSG) in rush hour traffic most days, it works a treat.

 

On my UK registered MY2018 car the ACC can only be set up to 100mph/160kph, which is a bit of a nuisance on the German autobahn, where the Superb cruises nicely at 110mph.

[RickW]

Just toured Shropshire using ACC  and found it excellent as I got more used to it.

I had a couple of scares at roundabouts where traffic was coming to a sudden halt but it did work very well.

I've learned to control it rather than rely on it and let it control me,if that makes sense.

I'm glad I bought it as an extra as it's enhanced my driving experience. 

[freelunch]

5 hours ago, RickW said:

I've learned to control it rather than rely on it and let it control me, if that makes sense.

 

Yes, exactly.  +1

[penguin17]

8 hours ago, freelunch said:

 

Yes, exactly.  +1

+1.  It’s a driver aid, not a replacement. 

[Mph25]

Does anyone know what distances from the car in front are equivalent to the markings - or is it speed dependent.  And what do most people select (I like to maintain big gaps!)

[GAG]

I find the the second bar gives me a comfortable distance for my style of driving but you would be best to just try it out on each setting until you find the one you are comfortable with.

[BriskodaJeff]

2 hours ago, Mph25 said:

Does anyone know what distances from the car in front are equivalent to the markings - or is it speed dependent.  And what do most people select (I like to maintain big gaps!)

It is speed-dependant, with larger gaps at higher speeds. For motorway driving I use the closest setting, toggling it to one bar around town and two bars in jams or start-stop traffic. 

[Bud]

There are two control loops one for speed ie when there is no target vehicle and one for time when the system maintains the time gap see: 

 

ACC active state – the ACC system is in active control of the vehicle's speed.

ACC speed control state – a substate of 'ACC active' state in which no forward vehicles are present such that the ACC system is controlling vehicle speed to the 'set speed' as is typical with conventional cruise control systems.  Operation during this mode is equivalent to that of conventional speed control. If no forward vehicle is present within the Time Gap or clearance of the system, the vehicle's speed is maintained at the target speed. The engine control system controls the engine output via throttle control to maintain the vehicle speed at the target speed.

ACC time gap control state – a substate of 'ACC active' state in which time gap, or headway, between the ACC vehicle and the target vehicle is being controlled. The ACC system enters follow mode or 'ACC time gap control' if the radar detects a forward vehicle at or within the clearance distance. During this mode of operation, the ACC system sends a target speed to the Engine Control Module and deceleration commands to the Brake Control module to maintain the set time gap between the vehicles.

Deceleration control – The ACC system decelerates the vehicle by lowering the target speed sent to the Engine Control Module and sending a brake deceleration command to the Brake Control Module. The maximum allowed braking effort of the system is 0.2 [g]. During brake deceleration events, the Brake Control Module activates the brake lights.

Acceleration control – The ACC system accelerates the vehicle by increasing the target speed sent to the Engine Control Module. The Engine Control Module tries to maintain the target speed and can accelerate the vehicle at a rate of up to 0.2 [g] of acceleration.

 

Transitioning Between Speed Control and Follow Modes

The ACC system automatically transitions between Speed Control and Time Gap (Follow) Modes. The mode of operation is determined by the lower of the set speed for Speed Control Mode and the target speed to maintain the gap between the ACC vehicle and a forward vehicle. Basically, if no vehicle is present within the clearance distance, the system will operate in Speed Control mode, else, it will operate in Time Gap mode.

 

All from http://sunnyday.mit.edu/safety-club/workshop5/Adaptive_Cruise_Control_Sys_Overview.pdf

 

[Bud]

All of the above said you can change the gaps as you have recognised and also set the acceleration response when using driving mode "Individual".

[Mph25]

1 hour ago, Bud said:

There are two control loops one for speed ie when there is no target vehicle and one for time when the system maintains the time gap see: 

 

(Snipped)

 

All from http://sunnyday.mit.edu/safety-club/workshop5/Adaptive_Cruise_Control_Sys_Overview.pdf

 

 

 

Interesting.

 

Although from that

A Note to the Reader
This document was developed for use in a workshop on software system safety. There are known deficiencies in both this document and the system described by this document. It is not intended to represent an existing or future production intent system implementation.

[Bud]

I take that as meaning it could not be built just like that, they would need to introduce further safeguards to ensure the overall system safety.  

 

It's a generic starting point that system designers and SW developers could use and tailor for vehicle specific installations.  Those other system elements and interfaces including the system variables, thresholds and safe guards would be considered as intellectual property 

[penguin17]

Even the 'Very Close' setting leaves quite a good gap at NSL, IMO.  Maybe there's an Audi setting which can be enabled with VCDS so you can get within 6 inches of the car in front? 

[Fantantonio]

So the ACC has to be enabled whilst over 20mph in order to continue working in stop start traffic? Or you can just enable it while stopped in traffic and it will continue to stop/start based on the car in front?

[facet edge]

6 minutes ago, Fantantonio said:

So the ACC has to be enabled whilst over 20mph in order to continue working in stop start traffic? Or you can just enable it while stopped in traffic and it will continue to stop/start based on the car in front?

You can enable it when you are stopped. It will not go any faster than 20mph. If the traffic stops for any length of time you will have to flick the ACC lever to start moving again, although the start stop will start the engine when the car in front moves.

[BriskodaJeff]

10 minutes ago, facet edge said:

You can enable it when you are stopped. It will not go any faster than 20mph. If the traffic stops for any length of time you will have to flick the ACC lever to start moving again, although the start stop will start the engine when the car in front moves.

Though IIRC you can't enable it while the footbrake is depressed. I enable mine as I pull away. You can set the speed limit required before you enable it by the way. If you don't do that, it will default to the current speed (if doing over 20mph) or 20mph if you aren't. 

[mdpslm]

ACC on my Superb in Switzerland has a top limit of 160KMH, motorway top speed is 120KMH.

I find that the slow down/braking & acceleration rates when in fast moving traffic is much smoother in comfort mode also aided by use of a longer distance setting from the car in front also allows the ACC algorithm to use engine braking more effectively before the need for it to use the brakes.

[drewellis]

On 06/12/2018 at 03:15, DBT85 said:

This I can most definitly agree with also. When my car needed recalibration after a windscreen change, I had no cruise at all. Fine, don't be smart and adaptive but at least let me do it the old way. Had a 300 mile trip to take and no cruise was not fun.

+1

In the recent bad weather, a few times the radar has been covered up by snow. It would have been nice to be able to use "dumb" cruise control at these times as I was traveling quite a distance on the motorway...

[RedBaron1916]

Just in case anyone has missed it (and I had) .... if the ACC disengages ... (say because you have been stationary longer than the preset period), use the stalk to reactivate it (just a quick flick towards you) and your car will smoothly move away when the car in front moves.  For some reason, it does it a lot smoother than pressing the throttle .... took me ages to find that. Just keep an eye on the brake lights in front then give it a quick flick when they go out 

 

[JR RS]

+1 for using the stalk to resume.

 

I find it much more easier and convenient.

[milanj]

+1 also here, for using the stalk to resume.

 

Makes morning drive to work thru traffic so much better!

[Steviedakota]

A bit off topic, but what does the button at the end of the ACC stalk do?

[xman]

1 minute ago, Steviedakota said:

A bit off topic, but what does the button at the end of the ACC stalk do?

 

Whatever you do, do not press this button