Hello, 

 

could somebody please explain to me what "regenerative breaking" does?

 

Under equipment there is "Start/stop system with regenerative braking". 

 

Thanks!

Have a read here.

 

http://www.volkswagen.co.uk/technology/glossary/brake-energy-regeneration

OK thanks. 

 

1. so when the engine is automatically turned off (at red light) then at start up is uses less fuel because it gets power from regenerative breaking?

 

2. if I disable star/stop system - does this also affect/disable regenerative braking?

Simply put, and shorn of corporate speak, "regenerative braking" is the capture and storage of a vehicle's kinetic energy when slowing, and its subsequent use to charge a storage device which will then be used to supply some of the energy required to accelerate the vehicle and/or run its electrical and/or hydraulic and/or compressed air systems.

 

A "stop/start system" should turn the engine off when it would otherwise be idling for more than a few seconds at a time, and it should be independant of a true regenerative braking system (well except that the stored energy can be used to restart the engine).

OK thanks. 

1. so when the engine is automatically turned off (at red light) then at start up is uses less fuel because it gets power from regenerative breaking?

2. if I disable star/stop system - does this also affect/disable regenerative braking?

 

For current VAG cars "Regenerative Braking" means that when the car is decelerating or braking the alternator load is increased to harvest some of the kinetic energy & charge up the battery.

It is not connected with Stop/Start.

When "restarting" the system uses the normal starter motor (the same as the driver would when starting manually).

 

It is a very basic system & I would suggest a bit of a "sale & marketting" feature.

As far as I'm aware you cannot disable it, its active all the time.

Peugeot have some very nice (in-production and concept) systems for regenerative braking.

In production they use an integrated starter/generator which is capable of accelerating the engine to idle-speed during restarting (reducing the fuel required to start the engine e.g. in Stop/Start conditions).

At this years motor shows they also showed a compressed air energy recovery system which compresses air in a cylinder during deceleration & then uses this air to start the vehicle moving from stationary.

 

I'm sure other OEMs also have varying types of energy recovery system as well.

It does mean you have a very big battery, I was stunned at the size of mine on a 1.4 petrol.  I don't think however cold it gets I'm ever gonna have a problem starting the car on a winter's morning.

It does mean you have a very big battery, I was stunned at the size of mine on a 1.4 petrol.  I don't think however cold it gets I'm ever gonna have a problem starting the car on a winter's morning.

Batteries aren't a light bit of kit either, so in some ways the extra weight of the battery may negate some or all of the benefits of regenerative braking.

Batteries aren't a light bit of kit either, so in some ways the extra weight of the battery may negate some or all of the benefits of regenerative braking.

The physical size of the battery is no different on my mkIII as it was on my mkII.

It does mean you have a very big battery, I was stunned at the size of mine on a 1.4 petrol.  I don't think however cold it gets I'm ever gonna have a problem starting the car on a winter's morning.

 

The physical size of the battery is no different on my mkIII as it was on my mkII.

 

The size of the battery may be the same but the density could have increased? I'm not sure if there are any long term consequences of raising the voltage used to charge the battery from brake regeneration, so it'll be interesting to see. I'm guessing at battery replacement time you won't be able to slot in any old 12V battery, it'll have to be a special one suitable for re-gen braking.

Some manufacturers relocate batteries to the boot to aid weight distribution, such is their weight (as is the case with our A6 and BMW's as well). 

The thing is... If your battery is fully charged then it cannot store any more energy so regenerative braking will not do anything.  Same applies if the battery is hardly charged at all, it would just get a bit of an overcharge for a few seconds.

 

I thought the whole point was that when you pulled away after braking the alternator was disconnected from the charging system which puts less load on the engine and the battery supplies all the power, this reduces fuel consumption (albeit only by an absolutely tiny amount but enough for marketting to get all shouty about it and people to believe it actually does something).

 

It's as laughable as the cylinder on demand fuel savings on the 1.4 engine.... look at the 'normal' 1.4 Vs the one which turns off 2 cylinders (Surely that would be a 50% saving?).  I can't see any real life difference to mpg.

As I understand it, in a normal car, as soon as the engine is running, the alternator starts charging the battery at its maximum rate until the battery is fully charged, then the alternator outputs only as much electricity as needed to run all the car's systems.  This puts a load on the engine, which means it burns more fuel.

 

In a regenerative system, the battery is not fully charged again after starting.  Instead, the car waits until you apply the brakes, then the alternator starts charging the battery.  The energy comes from the car's momentum spinning the wheels/engine/alternator.  When you accelerate again, the alternator stops charging and the battery is used to power accessories.  In this way the battery is rarely "fully" charged, instead maintaining about 50-70% of full charge.  Enough to restart the car several times.  If the charge starts to get too low, then the alternator will use engine load to charge like an old car.

I suppose I should be interested in how it works but in reality I'm not, what I do know is my little 1.4 engine has a 69Ah battery and whilst I appreciate the Elegance spec has a few bits'n'bobs accessories thats a lotta battery and I agree John, could well be expensive to replace fortunately for me both the warranty and PCP expire at the same time.

Battery Managment is very complex on modern cars.

The alternator load can be controlled by the ECU so the load can be ramped in/out & it can be decided when charging is needed.

e.g.

   Reduced at pull-away or at full-load (same as AC compressor loading).

   Increased when the engine is cold to improve warm-up time.

 

The battery charging is controlled to provide regeneration cycles (discharging, slow charging, fast charging) to extended the life of the battery.

Unless you live in an extreme climate or make limited use of the car, modern batteries should last many years without replacement.

 

As Sheldon.Cooper says the fuel savings with this kind of system will be almost nothing.

Providing you use the car a normal amount, the battery should stay at the desired state of charge anyway so the recovery is probably not actually used very often.

Nevertheless, the concept is sound (taking kinetic energy during deceleration which can be used later) even if it wont give you an extra 2mpg per tank.

 

Every manfacturer has it so its not really a unique selling point.

In my eyes, Its nothing more than a marketting gimic on the back of the publicity of KERS from Formula1.

But then again it does make it sound very technological "Stop-Start with Regenerative Braking". 

Edited 21 August, 201411 yr by Gabbo

Also, as far as I am aware, "Regenerative Braking" uses a standard battery so shouldn't increased the price.

 

I would also doubt it is a driver to include a larger battery as better battery management and low power-electronics should drive smaller batteries.

Its more likely complexity, assembly or commerical issues resulting in a standard size battery for several engines.

That's a difficult concept/difference for an old timer to grasp. I thought a voltage regulator would have the same nett result on energy in and out of the battery. I like having a fully charged battery at all times.

That's a difficult concept/difference for an old timer to grasp. I thought a voltage regulator would have the same nett result on energy in and out of the battery. I like having a fully charged battery at all times.

Why?

 

A fully charged 70Ah battery contains the same amount of electricity as a half-charged 140Ah one does. With modern battery technology the bigger one needn't be any heavier than the smaller one was 20 years ago either.

Also, as far as I am aware, "Regenerative Braking" uses a standard battery so shouldn't increased the price.

 

I would also doubt it is a driver to include a larger battery as better battery management and low power-electronics should drive smaller batteries.

Its more likely complexity, assembly or commerical issues resulting in a standard size battery for several engines.

 

Not always the case. Most cars that have RB will have a specific type of battery, and in quite a lot of cases now, the car and battery have to be paired when a new one is fitted, otherwise the ECU sees the symptoms of the old battery, and applies the same parameters to the new one.

Not always the case. Most cars that have RB will have a specific type of battery, and in quite a lot of cases now, the car and battery have to be paired when a new one is fitted, otherwise the ECU sees the symptoms of the old battery, and applies the same parameters to the new one.

The specific type of battery (such as AGM) is required to support the repeated starting loads of a start/stop system not a requirement of regenerative braking. If the battery manager determines the battery is fully charged then regenerative braking doesn't take place.

 

One of the regular complaints about vehicles with regenerative braking is that it is inconsistent, but if the battery is fully charged then there is simply nowhere to "dump" the energy without adding e.g. a passive load to be used in this situation - which adds extra cost that manufacturers simply don't want.

Edited 28 October, 20169 yr by PetrolDave