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I think it is safe to say that coasting could be used if it was part of the design of a vehicle and had appropriate sensing to engage control if a runaway condition was detected. Traditionally it is not only frowned on but illegal not to have the motion under governed control, but how many accidents have there been when somebody has let an automatic run away with them - even though the motion is under the governed control of the engine? Banning coasting is not a panacea.

Agreed, there should not be any restitution of forward motion unless the brake pedal is depressed, and then it is fair game to harvest the energy instead of wasting it heating up the discs.

I too use my brakes very little compared with other vehicles/drivers (and I achieve high MPG figures as a result), although some of that will be down to automatics needing to be braked more often than manual transmissions. I was in a traffic jam some years ago, and while we were stationary the woman behind came to tell me my brake lights were not working. None of them? No. Must be the switch then, thanks. When I checked later, at the next service station, they were working fine (but then, I don't sit on my foot brake either; people seem to forget the handbrake until they find they need it for starting uphill - and I saw a police car do that too).
 
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There is always a slight retardation when you lift your foot off the gas pedal. The gasses are being compressed by the engine and as the subsequent decompression return of energy cannot be 100% efficient thus causing engine braking. In fact some large engines use a different form of engine braking by using the compression stroke to compress the air and then decompressing the cylinder with a dump valve that opens at the top of the compression stroke so that the energy used to compress the air is not returned to the system by driving the piston back down.
 
Since the removal of the post time limit of 20 seconds, I have had several double posts to delete. (As I predicted in another thread)
 
Trev said:
There is always a slight retardation when you lift your foot off the gas pedal.
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Of course there is, but af was reporting that his car has excess retardation compared with "normal" cars.

There's not much point talking about the compression/expansion providing less than 100% return on investment - the losses will be overwhelmingly due to friction, not non-linearity in Boyle's law.
 
Our hybrid switches regularly to electric power when on flat roads and the accelerator pedal is barely depressed. I guess the reasoning is that the petrol engine is switched off because its efficiency is so low compared with an electric motor?

If you force it to drive off in electric mode, though, you have to accelerate gently and the electric power cuts out at 20mph no matter how hard you try to be gentle.

Does Trev have a hydrogen powered car?:laugh:
 
Black Hole said:
not non-linearity in Boyle's law.
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I was not aware that implied this, just a loss of efficiency however caused. You forgot to mention the losses due to the engine cooling system cooling the compressed gasses before they re-expand making the system non-adiabatic anyway. (but I grant you that friction is likely to cause, by far, the biggest loss of return energy.)
Mike0001 said:
Does Trev have a hydrogen powered car?
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Nar. It's got a nuclear reactor.:)
 
Mike0001 said:
Also, most of the time, your battery is already going to be charged, so what happens then?
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It doesn't seem to be. Mind you, it's a large battery in the boot; maybe I need to brake more?
c8c4b6e573bd0b5b5defaffbaf04e775.jpg

Deliberately dipped my clutch while rolling this morning and got this helpful message.

01752ac716320cb991324a47ec23b9b2.jpg
 
Black Hole said:
... but how many accidents have there been when somebody has let an automatic run away with them - even though the motion is under the governed control of the engine?
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I used to have about 50 lock-up garages next to my house. Some idiot managed to park up to open his garage door, only to demolish the back wall because he forgot to put it in park and apply the handbrake.

Black Hole said:
.... the woman behind came to tell me my brake lights were not working. ... they were working fine (but then, I don't sit on my foot brake either; people seem to forget the handbrake until they find they need it for starting uphill - and I saw a police car do that too).
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There is no need to do this. The only time I would do it is if I was the last in a queue of traffic, just to make certain the next person to join the queue knows we've stopped. Don't get me started on police drivers and the bad examples they set.
 
EEPhil said:
There is no need to do this. The only time I would do it is if I was the last in a queue of traffic, just to make certain the next person to join the queue knows we've stopped. Don't get me started on police drivers and the bad examples they set.
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Sometimes I can press hard on the footbrake, then take my foot off, and the car stays on a hill without moving. I am not all that keen, as I then spend time worrying about whether the car is slipping backwards.
 
Some team a couple of years back sequenced a tardigrade and found a high proportion of alien DNA. It was mostly bacterial DNA, which regularly gets incorporated into eukaryonic DNA anyway, such as ours.

Then it turned out that the team had sequenced a dirty sample. They had sequenced tardigrade + bacteria.

Ah well.
 
Mike0001 said:
alien DNA
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:eek:

Better keep a Predator handy.

Mike0001 said:
Sometimes I can press hard on the footbrake, then take my foot off, and the car stays on a hill without moving.
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That's a bad case of sticking brakes! Do you get a decent MPG?

I once parked up at work, and a couple of hours later Security told me my car had rolled across the car park and bumped another car (no damage, must have been a crash in slow motion). That was due to the very slight slope and the handbrake releasing as everything cooled down.
 
Mike0001 said:
It's by design, so you can jump from brake to accelerator without rolling backwards.
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...for lazy sods, one-handed drivers, and Americans. I assumed you meant the brakes stick, not that it was supposed to do that.

I thought assisted hill start was a toothless ratchet mechanism that only prevents rolling backwards (not forwards)? That may have been in the non-electronic days, I suppose it's easy enough now to program the brakes to do that.
 
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Black Hole said:
I thought assisted hill start was a toothless ratchet mechanism that only prevents rolling backwards (not forwards)? That may have been in the non-electronic days, I suppose it's easy enough now to program the brakes to do that.
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Yeah, these days the brakes are kept on by the ABS pump.
 
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