How does the mhev work on my car ?

[Chris haworth]

Just bought a 2018 a6 avant c8 40tdi sport mhev , some reviews are saying that my car has intelligent coasting but I’ve never felt it do it can anyone confirm cheers Chris 

[jammy]

On 6/16/2023 at 7:57 PM, Chris haworth said:

Just bought a 2018 a6 avant c8 40tdi sport mhev , some reviews are saying that my car has intelligent coasting but I’ve never felt it do it can anyone confirm cheers Chris 

 

On 6/16/2023 at 7:57 PM, Chris haworth said:

Just bought a 2018 a6 avant c8 40tdi sport mhev , some reviews are saying that my car has intelligent coasting but I’ve never felt it do it can anyone confirm cheers Chris 

Yes it has intelligent coasting, depending on certain conditions and engine parameters it will coast either on idle or with engine cut off completely.

For the latter I have found having the air conditioning on prevents it.

[Chris haworth]

Thanks for reply mate is there any actual proof as Audi Blackburn are saying it only got it on petrol versions it’s unbelievable 

[jammy]

Ah! I didn’t spot that, mine is a petrol and has the coasting. So can’t comment on the diesel. Sorry 😔

[Jim70]

Hi Gary, I have the diesel model and it does have the mhev.

It will carry out the intelligent coasting if you have the air con off and will only cut the engine when the start/stop is turned off also.

You'll only notice it by the rev counter going down to "ready" then if you press the accelerator the engine will restart and return to normal running.

Hope this clears up your query 😀

[jammy]

On 6/22/2023 at 9:59 PM, Jim70 said:

will only cut the engine when the start/stop is turned off also.

Not sure that is correct. As stated I have the petrol, but I never disengage the stop/start and it still coasts with the engine off.

However, gearbox in Sport mode will also prevent coasting / engine off.

[K200CWC]

My  55TDi has it.  Does it irrespective of the Start/Stop setting and the Aircon can be on, however I generally have my Aircon on Eco mode not full mode and most of the time I drive in Economy mode.

Little battery symbol on the end of the MPG display needs to be green.

I've noticed it mostly on the motorway when cruise control is on and the RPM drops to zero and the car speed can drop by up to 2MPH before it restarts the engine.  It will also kick in  if going down a hill on the m-way.

If not on cruise then you need to be off the throttle for a few seconds for it to kick in, again normally happens going down hill.

Maybe it's a 4pot / 6pot difference??

[Optimus]

Your notice a green pedal symbol which indicates it’s active. 
 

either the engine will switch off or it will idle. In order for it to ‘coast’ in gear it needs to be on a slight decline and straightish’ road.

if the decline is steep or the road is quite bendy and the centre of gravity of the car is not stable. I have found it won’t work and likely to ensure the you the driver is in control and the car has all means of stability.

[K200CWC]

I'm under the impression that the green pedal symbol comes on when the car thinks you can come off the gas and it will coast up to a junction without issue.

I get a squiggly parallel line symbol when the cruise is backing off to keep the car stable round the twisty bits.  Very clever and don't know if it uses the cameras, the GPS maps or both to make the decisions.

It's easy for the car to make driving numb but it is safe.

My other car doesn't have traction control, ABS or power steering so I use this to have fun and let the S6 oil burner eat miles in comfort, albeit with the ability to deal with the majority of the people that think there car is an F1 car and think they can drive🙃

[Optimus]

From experience this is what i recall the system in its wider form allowing the following:

- coasting (in gear) engine switched off/ idle RPM when braking coming to a stop or slight decline straight road.

- allows for more frequent use of start/stop technology allowing greater battery usage.

- allows energy recovery for the use of the system by breaking (for example).

- supports electric hybrid turbo technology (spooling turbo by electronic means).

the electrical storage system is designed to support auxiliary systems when the engine is off or reducing electrical load capacity for all of the above.

You’d like to think it would have a massive effect on your MPG in a positive way but I think it equates to an additional 3mpg-7mpg subject to road conditions and driving style all around.

In truth the funny thing about emission control is that it hurts the economy of the vehicle. The science behind it diminishes performance and reliability as well as hampering economic power delivery. 
 

if you were to take this engine and remove/modify all the ‘emission’ related components you’d actually likely get up to 30% noticeable gains in fuel economy and performance. 
 

Adblue is a huge contributing factor impacting poor fuel efficiency. They say Adblue doesn’t affect fuel efficiency, but in order to have the system it requires the exhaust to be hotter. How do you think they do that?

By using more fuel! This system is literally a ‘fix’ to hide real fuel consumption numbers which would harm ratings and sales…

Edited July 4, 2023 by Optimus

[ahin4114]

Most of the MHEV function is limited by the state of charge of the 48v battery and the current draw in the system. 
if the battery is well charged and the draw is low it will coast when the load from the engine is low enough. If you have good charge then you can still have the air con on, but once the charge drops then the engine might stay engaged as there is insufficient power available without the alternator drawing from the engine. 
Same for stop start it traffic lights as the same electrical system is used. 
The little green foot is to tell you you could save fuel, though it may not coast completely. The battery indicator on the consumption gauge is to indicate whether enough energy is being recuperated to add charge to the battery, but it doesn’t show the battery charge level. 
That’s what I gleaned from the manual and research for my Q7. Still seems to behave the same in my C8 RS6. 

[jammy]

17 minutes ago, ahin4114 said:

Most of the MHEV function is limited by the state of charge of the 48v battery and the current draw in the system. 
if the battery is well charged and the draw is low it will coast when the load from the engine is low enough. If you have good charge then you can still have the air con on, but once the charge drops then the engine might stay engaged as there is insufficient power available without the alternator drawing from the engine. 
Same for stop start it traffic lights as the same electrical system is used. 
The little green foot is to tell you you could save fuel, though it may not coast completely. The battery indicator on the consumption gauge is to indicate whether enough energy is being recuperated to add charge to the battery, but it doesn’t show the battery charge level. 
That’s what I gleaned from the manual and research for my Q7. Still seems to behave the same in my C8 RS6. 

The 40Tdi is a 12volt battery, so there are differences in how the system works.

I do agree though, that the state of charge of the battery is key and probably more so in the much smaller 12v system.

I quite often knock the gearbox into S and let the engine do the braking when slowing down on long stretches. It recuperates the kinetic energy and tops up the battery nicely. Since doing this I’ve found the coasting function operates at nearly every opportunity.

 

[A6A6]

Hi guys, I just bought my first Audi A6 and have question for coasting with MHEV 48v battery.

Does your car hold the speed when engine is cut off?

If the battery is charged and car shifts to battery, RPM drops to zero (when start/stop is active) and it starts coasting, but the speed wont hold up.

It is starting to drop immediately. Only when driving down hill, the speed will hold up for a while or even accelerate.

The driving speed is usually about 60-100 kilometers per hour.

Car is A6 3.0 tdi Q mhev.

 

[Optimus]

The battery does not provide any propulsion to the drivetrain what’s so ever.

 

it is in function start stop with additional coasting features where the engine will shut off coming to a stop or during a moderate decline whilst descending down a road.

 I’ll be brutally honest having clocked now over 30k miles in mine. Unless you drive the vehicle in a manner where you are chasing high mpg and progress is not real progress (holding traffic at round abouts) your real world mpg is like mid 40s for a 73 litre tank capacity.

the system is a complete gimmick and I’d rather remove the weight and faff of it all o save a 100+kgs. 

 

[A6A6]

Optimus, thanks for your comment. This explains me much, but I'm also little bit disappointed to Audi's solution for this. Was hoping it would work better. 

Anyway, I have quite optimal route from home to work, and av consumption has been now 4.9 litres per 100km (board computer), but in real life a little bit higher.

If only viewed for individual drive to work, it is around 4.3 litres but this requires very gently pedal and optimizing. And trying not to be an obstacle for other drivers 😁 

 

[ahin4114]

2 hours ago, Optimus said:

the system is a complete gimmick and I’d rather remove the weight and faff of it all o save a 100+kgs. 

 

Given that plug-in hybrids add roughly 100kg of weight, I would hazard that the MHEV is adding significantly less. 
 

Sadly the European regulations mean that unless Audi (and others) add these systems then the cars simply get pulled from sale. 
 

As a biker as well, I lament the day that increased regulations caused Honda to pull great bikes like the Pan European and VFR from sale because it simply wasn’t economically viable to ‘tweak’ the engine to meet regulations. 
 

My RS6 doesn’t feel compromised my the MHEV, and I have done long sections in the south of France coasting on idle because of it. 

[K200CWC]

What's the build up of the 100KG+ for the MHEV as it's not actually propelling the car?

On my 2022 S6 it only appears to be a 48V battery, 48V starter/alternator and a 48V turbo motor??

[Optimus]

Wiring loom, battery bank, additional control units etc. 

I don’t know precise weight but you’d be surprised how heavy wiring looms can be 5kg-45kg

[ahin4114]

Yes - however the delta between the core loom and the additional elements required for the 48v system will be a single digit percentage of that total weight.