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Discussion Starter #1
so whenever im regen braking down a mountain and it eventually maxes out my battery chrage, the car says its still in EV mode, but the engine kicks on when im still braking downhill and full battery. if i look at the energy flow chart, it shows the tires sending arrows to the engine. why does this happen? it makes no sense to waste gas when braking down a hill. might as well switch to neutral on large decents?
 

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It also makes no sense for the software to startup the petrol engine when the battery is showing over 75% full and you have just pressed the start button first thing in the morning.

You would think it would run on electric until the car got moving to perhaps 30 mph and the battery had at least dropped down to 30% ......... especially in warm weather. :(:unsure:
 

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Because it cannot use regen anymore as the battery is full. So it turns on the engine to provide compression braking. Virtually no fuel is needed for this, in fact I believe most modern cars, not just hybrids, turn off fuel delivery with zero power needed. If you coast down in neutral, your speed will increase and you will have to use the physical brakes.
 

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I agree with @yticolev, it's likely just using the engine for braking and using no fuel while doing it. If you flip the dash display to show fuel consumption the next time this happens I'll bet that it shows none.
 
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Discussion Starter #5
Because it cannot use regen anymore as the battery is full. So it turns on the engine to provide compression braking. Virtually no fuel is needed for this, in fact I believe most modern cars, not just hybrids, turn off fuel delivery with zero power needed. If you coast down in neutral, your speed will increase and you will have to use the physical brakes.
Compression braking versus physical braking? What’s the diff? I figured it just used physical brakes after regen is done
 

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Compression braking is done by the engine. Physical brakes use rotors and disks. Both slow the car, but using compression braking reduces brake wear. Someone posted recently that modern cars on cruise control actually activate brakes to keep speed steady down hill. I've never experienced that as I've never had a fully charged battery and I haven't met a hill yet that regen braking didn't hold the set speed (as far as I know). So I don't even know that activating the physical brakes on CC is a thing for our cars or any EVs.
 

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It would be unwise to ever shift to neutral while the vehicle is moving.
 
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In the UK it’s illegal to coast in neutral, probably dates back to the time when they had cable operated brakes, My Dad had an old Rover16 1946 that had Freewheel that allowed the car to coast when you took your foot off the accelerator to improve economy,
On later models it was discontinued,
 

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It would be unwise to ever shift to neutral while the vehicle is moving.
Why exactly? Best way to clean rusty brake rotors, most efficient way to come to a stop. Transmission will still shift into the correct gear at all times should you shift back into drive. That's my experience anyway coasting up to a stop light that changes to green.
 

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UK Highway Code (the short answer)

Rule 122
Coasting. This term describes a vehicle travelling in neutral or with the clutch pressed down. It can reduce driver control because
  • engine braking is eliminated
  • vehicle speed downhill will increase quickly
  • increased use of the footbrake can reduce its effectiveness
  • steering response will be affected, particularly on bends and corners
  • it may be more difficult to select the appropriate gear when needed.

and an article based on the Rule giving a fuller explanation


Coasting down a hill might feel fine, but there are plenty of people who seem to have that nagging sense of doubt that maybe it’s not quite the best way to drive. It’s fine though, right? You’re still in control and you must be saving fuel? Unfortunately not – Coasting can be dangerous and coasting doesn’t save fuel.
Here’s why it’s a bad technique…
If you’re new to driving and are reading this, coasting is when you drive along with the clutch pushed in, or have the gear stick in neutral – or both. This disengages the engine from the wheels. This naturally happens every time you switch gear for a fraction of a second, but coasting is where you do this for a prolonged period using the car’s momentum and gravity to keep going.
Why coasting is a bad technique…


When coasting downhill, gravity and momentum combine so you rapidly gain speed. You might go faster but you’re far less in control…
  • Without the engine connected to the wheels, you can’t use the engine’s gears to slow down (known as “engine braking”) – giving you less control
  • To make up for the lack of engine braking, you have to press harder on the main brakes, wearing them out more quickly
  • It’s more difficult to take a steady, safe line through a corner, which can mean potentially crossing into the path of oncoming hazards
  • If you need to rapidly react to something, putting the car back in gear takes crucial seconds that affects your response time.
You can find the official Highway Code guidelines on coasting here (Rule 122).
Is coasting when driving illegal?
No. There isn’t any UK law specifically prohibiting someone from coasting downhill. However, if you were to be involved in an accident that was influenced by coasting, the argument could be made that the driver did not have control of the vehicle – which would be an offence.
Coasting & fuel consumption
With the technology in modern cars, it’s now an old misconception that coasting actually saves fuel. If anything, coasting could actually increase your fuel consumption. Here’s what happens in 2 different scenarios…
Driving down a hill normally –
  • You’re at the right speed so you take your foot off the accelerator
  • Your engine’s Electronic Control Unit (ECU) detects that the accelerator isn’t engaged and automatically cuts fuel from going into the fuel injectors because you’re at the right speed
  • The wheels continue to spin and, because they’re still connected to the engine via the gearbox, they keep the engine turning
  • This means you use very little or potentially no fuel at all when driving down a hill in gear
Coasting down a hill in neutral –
  • You’re at the right speed so you put the car in neutral which disconnects the engine from the wheels
  • You also take your foot off the accelerator
  • The engine still needs to keep turning but, because the engine and wheels are disconnected, the car can’t get the rotational power it needs from the wheels. Instead, it needs to send a small amount of fuel into the engine to keep it powered (known as “idling”) instead of drawing that power directly from the wheels.
“Older cars had fuel injected into the engine by a carburettor, which was a mechanical device, with no intelligent control electronics. These days, cars have electronic fuel injection, powered by an intelligent electronic control unit (ECU). This means that modern cars have been able, for many years now, to do clever things like shut off all fuel to the engine if no power input is required to the wheels – e.g. when driving down a hill at a constant speed. So, the next time someone says you can save fuel by taking your car out of gear going down a hill, you can put them straight!” – Dan Regan, Head of Innovation at Lightfoot
So all in all, coasting – downhill or in any other circumstances – can be potentially dangerous and doesn’t save you any fuel along the way.
 

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In fact, it does take more energy to not coast to a stop in a hybrid. Yes, the momentum that could have been used for extra distance is partially saved by regen, but that is relatively inefficient (on the order of 15%). It also takes more energy to coast to a stop in gear in an ICE vehicle. The extra distance you could have traveled by coasting is now wasted as heat in compression braking.

Coasting or driving in gear is not recommended for idiots. Period. Additionally, I'd point out that a number of BEVs (I think including the latest Ioniq) can be set up for zero regen, in other words, coasting when foot is off accelerator. That's for drivers who like to practice high efficiency.
 

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The Highway Code is a set of information, advice, guides and mandatory rules for road users in the United Kingdom. Its objective is to promote road safety. The Highway Code applies to all road users including pedestrians, horse riders and cyclists, as well as motorcyclists and drivers. It was first published in 1931, with regular updates since, and is the basis of our entire nation's behaviour on the roads.

Coasting while 'in gear' does not go against this advise because the car is ready to respond immediately to the driver's inputs without them having to put it back in Drive first regardless of whether the car is an ICE, Hybrid or BEV.

This is an international forum and we all have to accept that the rules governing some members may an anathema to others, but that doesn't make them right or wrong, they are simply the laws enacted by that state to which its citizens must comply or face the consequences. It's what makes the world such an interesting place :giggle:
 

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Coasting while 'in gear' does not go against this advise because the car is ready to respond immediately to the driver's inputs without them having to put it back in Drive first regardless of whether the car is an ICE, Hybrid or BEV.
So the coasting option that is available on many BEVs doesn't technically break this advice, although completely inadvertently as BEVs were on no one thoughts when such "rules" were made. But the reasons for having it in gear are mostly obliterated by a BEVs coasting function, only maintaining ability to accelerate without touching the shifter for those super rare instances where accelerating will avoid a collision.

Coasting in gear brings up semantics. Yes, some will say that a car is "coasting" if your foot is off all the pedals. However if the engine is engaged in an ICE drivetrain, compression braking is occurring. So in a scientific sense, you are not coasting. As far as I know, the only mainstream ICE cars capable of true coasting when not in neutral or the clutch pedal is depressed are some older SAAB models that freewheeled.

But let me repeat: Coasting or driving in gear is not recommended for idiots. Period. No matter what the bureaucrats say. Coasting is completely safe for good drivers.
 

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I always thought coasting in neutral was dangerous because the hydraulics for brakes require vacuum to operate properly. That vacuum is provided by a turning engine. If the engine dies while in neutral, one or two pumps of the brake pedal makes it hard as rock and baking is dangeroulsy limited. Sit in the driveway with the car off and pump the brake pedal a few times. See what happens.
 

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I always thought coasting in neutral was dangerous because the hydraulics for brakes require vacuum to operate properly.
No vacuum. Electrically boosted hydraulic pressure. That's what you hear when you open the car door in the morning is the brake system pressurizing so brake feel is correct when you start the car. Good thought process though!

Vacuum isn't necessary for brake operation in ordinary cars, but is for the power assist. I drove my last car for a couple months with power brakes. Required a stiff press, but quite manageable around town. Fixed it before I went home, not entirely sure if I could generate enough pressure in an emergency.
 

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I also found out that while going on a long descent with the ICE on providing engine braking and the battery at 100%, and not pressing on the brake pedal, that actually drains power from the battery.
 

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Wise words of warning from the Ionic Manual:
Page 36:
When the engine run with the shift lever in N (Neutral), the hybrid system cannot generate electricity. The hybrid battery cannot recharge with the shift lever in N (Neutral)

Page 364:
Always come to a complete stop before shifting into D (Drive) or R (Reverse).
Do not put the shift lever in N (Neutral) while driving.

Page 367:
WARNING Do not drive with the shift lever in N (Neutral). The engine brake will not work and lead to an accident.

Page 371:
Do not move the shift lever to N (Neutral) when driving. Doing so may result in an accident because of a loss of engine braking and the transmission could be damaged.

I accidentally changed from D to N before completely coming to a halt. There was a mighty clunk from the transmission and the whole car jolted forward. For all these reasons I would not advise anyone to coast in neutral.
 

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I accidentally changed from D to N before completely coming to a halt. There was a mighty clunk from the transmission and the whole car jolted forward. For all these reasons I would not advise anyone to coast in neutral.
Using that logic, I've never experienced that when shifting into neutral. For that reason, I would advise others do the same. Lame. Glad you take your manual literally without thought though. The law is the law. You do know that most of the manual is boilerplate, with "wisdom" just copied and pasted from other manuals, and often local driving ancient and outdated old wive's tales?

But again, idiots shouldn't use neutral (perhaps it should be removed as an unneeded option), or drive.
 

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Discussion Starter #19
honestly i felt no diff between engine and neutral braking. driving down mount hood is quite the drive, and the battery maxes out the charge maybe 1/10th of the way down from regen and then im stuck driving for MILES on a full charge that kicks the engine on, and when the engine comes on when still braking down a hill maxed out, it actually gets pretty loud. the RPMs go higher than highway driving... why would the engine need to be almost redlining with RPMs just for compression braking? makes no sense
 

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If the engine turns over more slowly, less compression braking, and speed increases. Simple.
 
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