In article ,
Thomas Prufer wrote:
On Tue, 24 Jul 2018 12:48:25 +0100, TMS320 wrote:

That is why you would press ~hard~ and sustain.

Reminded me, there's something called the "Power Braking Test" or "Stall
Speed Test": Rev up on full throttle against a full brake (only works on
an automatic), note steady-state rpm. Stop after a few seconds lest the
torque converter overheats.

The TC itself limits the speed the engine can get to. And usually well
below the full engine torque.

This puts all the mechanical energy output in the torque converter --
another place to dump the energy when braking a fast-moving car with
engine on full throttle.

I've lost you there.


Thomas Prufer

--
*If I worked as much as others, I would do as little as they *

Dave Plowman London SW
To e-mail, change noise into sound.

"dennis@home" wrote in message
...
On 24/07/2018 12:40, NY wrote:
"Tim Streater" wrote in message
.. .
If the alternator is capable of starting the car why don't they just
remove
the starter motor and save the cost and weight?

Which is what our Auris hybrid does.

Ah I didn't realise the Auris uses the alternator to start the car from
cold. I presume if the fan belt breaks you are utterly buggered because
you can't restart the engine (if it's stopped) to be able to drive (with
the engine using on battery rather than alternator power for its spark)
to a safe place to wait for Mr RAC or Ms AA to tow you to a garage.

Its worse than that on a smart car..
the same belt drives the water pump.
You may start the car and have the belt break and you will only get down
the road before you have to turn the engine off to stop it overheating.
Then you can't restart it.


I think a lot of cars that had the fan driven by the belt also had the water
pump driven by belt. I seem to remember one of my dad's cars which had two
belts driven from different pulleys on the engine: one for fan and the other
for alternator and water pump; or maybe I'm imagining that.

On Mon, 23 Jul 2018 20:26:27 +0100
TMS320 wrote:

An engine is nowhere near powerful enough to overcome the brakes; it
would be just a matter of pressing the pedal harder than the foot is
normally calibrated to do. People don't routinely dial in more than
about a quarter g.

I wonder how much ABS conspires against stopping the engine with the
brakes.

"Rob Morley" wrote in message
news:20180724190048.000ce24c@Mars...
On Mon, 23 Jul 2018 20:26:27 +0100
TMS320 wrote:

An engine is nowhere near powerful enough to overcome the brakes; it
would be just a matter of pressing the pedal harder than the foot is
normally calibrated to do. People don't routinely dial in more than
about a quarter g.

I wonder how much ABS conspires against stopping the engine with the
brakes.

That's an interesting point. I presume it doesn't make any difference as
long as all the wheels carry on turning at the same speed as each other,
which they will as long as none of the wheels skid. However there will come
a point at which the same braking force (subject to the normal front/back
balance) will be enough to stop the undriven wheels, but not to stop the
driven ones which the engine will be struggling to keep turning. At that
point, all the wheels will be braked intermittently.

I suppose it depends on the algorithm used. I can imagine it being more of a
problem if two wheels on the same axle are braked differently, because that
would make the car veer to one side. But if both wheels on one axle are
braked more than both wheels on the other, that wouldn't necessarily make
the car swerve and perhaps ABS is more tolerant of that.

"TMS320" wrote in message
news
On 24/07/18 09:44, Dave Liquorice wrote:
On Tue, 24 Jul 2018 00:14:28 +0100, Dave Plowman (News) wrote:

But why would you bother when it's simple to just turn off the
ignition?

'cause a diesel, burning it's own oil, will just carry on switched off or
not... B-)

Surely the important thing is to get the car to a standstill as
safely as possible?

So just use the foot brake a bit harder than normal to bring both
car and engine to a safe and controlled standstill.

Some people talk or behave as though the foot brake is some incredibly
delicate system that will break if the pedal is pressed down hard.

The orginal start of this thread was based in the US. They mostly drive
automatics over there so the pigging thing will change down to counter
act the braking. Selecting N still doesn't strike me as "right" though,
selecting the highest fixed drive and braking ought to work. Assuming the
auto box and/or computers will allow that change to happen with the
engine under full throttle.

Given that the accelerator pedal now only operates a potentiometer and
autos don't bring mechanical connections to the driver, there is no easy
way of knowing what a "stuck throttle" fault is and how things are going
to respond to the driver's random fiddling. The foot brake is a known
quantity and the only system with sufficient independence.

Thats not true of the ignition.

"NY" wrote in message
o.uk...
"Dave Plowman (News)" wrote in message
...
In article ,
Andy Burns wrote:
They don't have Otto cycle engine, instead Atkinson cycle engine, which
is more efficient though less powerful.

It's an interesting one. Like most hybrids, the IC engine does all the
work when at speed on a long journey. And an Atkinson cycle type is best
at a constant speed. Efficiency takes a dive outside this. Very
noticeable
on early Prius which were very heavy on fuel when cruised at speed.

I was surprised at how little battery storage the Auris has (and this may
be
true of other hybrids too), so it only uses the motor for a small amount
of
the duty cycle - maybe a little bit more for lower speeds that you'd find
in
town, so it would keep the towns cleaner at the expense of more pollution
in
the countryside or on longer, faster journeys when the IUC engine also
charges the battery.

It sounds a good idea: design an engine that is as efficient as possible
at
one speed, and then develop transmission that tries to maintain this
engine
speed for a wide range of road speeds.

Are there any hybrids which are purely IC-electric (like diesel-electric
trains) where there is no mechanical connection between IC and wheels,
just a generator and electric motors.

Havent noticed any. It works for the massive stuff like train engines
and haulpaks etc but isnt even seen with truck prime movers.

This would allow all the smoothness of acceleration that you get with an
electric motor, because the ratio between motor and wheels is fixed (maybe
1:1), so there are no losses in a fluid flywheel or in the belts of a
CVT. On the other hand, petrol-electric-kinetic is more energy conversions
so there may be extra losses in that.

At first, I assumed that a petrol/diesel-electric hybrid was like this: no
mechanical connection, only an electric one.

wrote
NY wrote

Are there any hybrids which are purely IC-electric (like diesel-electric
trains) where there is no mechanical connection between IC and wheels,
just

Chrevrolet Volt IIRC.

That’s a plug in hybrid, not a petrol electric. The difference is that most
of the electric comes from the plug in charging, not from the engine.

Diesel electric train engines and haulpaks get all their power from the
engine.

"Rob Morley" wrote in message
news:20180724190048.000ce24c@Mars...
On Mon, 23 Jul 2018 20:26:27 +0100
TMS320 wrote:

An engine is nowhere near powerful enough to overcome the brakes; it
would be just a matter of pressing the pedal harder than the foot is
normally calibrated to do. People don't routinely dial in more than
about a quarter g.

I wonder how much ABS conspires against stopping the engine with the
brakes.

Cant see that it would. That detects the wheel slipping on the ground
and just toggles the brakes so they do the best braking possible.

"NY" wrote in message
o.uk...
"Rob Morley" wrote in message
news:20180724190048.000ce24c@Mars...
On Mon, 23 Jul 2018 20:26:27 +0100
TMS320 wrote:

An engine is nowhere near powerful enough to overcome the brakes; it
would be just a matter of pressing the pedal harder than the foot is
normally calibrated to do. People don't routinely dial in more than
about a quarter g.

I wonder how much ABS conspires against stopping the engine with the
brakes.

That's an interesting point. I presume it doesn't make any difference as
long as all the wheels carry on turning at the same speed as each other,
which they will as long as none of the wheels skid. However there will
come a point at which the same braking force (subject to the normal
front/back balance) will be enough to stop the undriven wheels, but not to
stop the driven ones which the engine will be struggling to keep turning.
At that point, all the wheels will be braked intermittently.

I suppose it depends on the algorithm used. I can imagine it being more of
a problem if two wheels on the same axle are braked differently, because
that would make the car veer to one side. But if both wheels on one axle
are braked more than both wheels on the other, that wouldn't necessarily
make the car swerve and perhaps ABS is more tolerant of that.

I have occasionally had mine trigger, usually when I do a crash stop
at an intersection when someone does something stupid and doesn't
give way and the intersection has loose gravel on it or is very wet.

Don't get any swerve effect at all and the very distinctive sound sounds
like its just the front brakes being pulsed, not the back wheels, in a FWD
car.

On 24/07/2018 18:49, NY wrote:
"dennis@home" wrote in message
...
On 24/07/2018 12:40, NY wrote:
"Tim Streater" wrote in message
.. .
If the alternator is capable of starting the car why don't they
just remove
the starter motor and save the cost and weight?

Which is what our Auris hybrid does.

Ah I didn't realise the Auris uses the alternator to start the car
from cold. I presume if the fan belt breaks you are utterly buggered
because you can't restart the engine (if it's stopped) to be able to
drive (with the engine using on battery rather than alternator power
for its spark) to a safe place to wait for Mr RAC or Ms AA to tow you
to a garage.

Its worse than that on a smart car..
the same belt drives the water pump.
You may start the car and have the belt break and you will only get
down the road before you have to turn the engine off to stop it
overheating.
Then you can't restart it.


I think a lot of cars that had the fan driven by the belt also had the
water pump driven by belt. I seem to remember one of my dad's cars which
had two belts driven from different pulleys on the engine: one for fan
and the other for alternator and water pump; or maybe I'm imagining that.

Unfortunately a number have/had the water pump driven by the timing belt
- if the pump fails and seizes, it strips the timing belt and promptly
wrecks the engine.

SteveW

On 23/07/2018 22:22, NY wrote:
"Nick Finnigan" wrote in message
news
Â*Well it's an auto, so you'll be left foot braking, and not think about
the accelerator in an emergency.

Which bozo thought that it was sensible to operate the brake in an
automatic with your left foot, just because you won't need that foot for
the clutch? It means learning a whole new muscle memory, so as not to press
the brake as hard and as far as you would with the clutch, only to have to
unlearn this if you ever have to drive a manual.


You should also be used to fine movements with the clutch pedal,
especially as you live in a hilly area. Using my left foot for both clutch
and brake is quite easy.

On 24/07/2018 10:12, NY wrote:

Braking the engine when it is transmitting power to the wheels will lead to
a "fight" between brakes and engine, with the risk that the energy that the
engine is generating will heat up brakes too much. If you have an engine
generating maybe 100 hp, you've got to dissipate that sort of energy in the
brakes. What is the effect of the discs heating up dramatically: can it
cause loss of braking force?

Brakes routinely handle far more than 100hp. It takes a long time driving
with the brakes applied before you get any noticeable brake fade.

On 23/07/2018 08:34, NY wrote:

And the strands of the cable had frayed close to that carburettor linkage
so that only about half of them were pulling the linkage; the other half
were jamming the cable against its sheath. No amount of pulling or pushing
would move the cable in the sheath: it was buggered.

My dad drove home very slowly: he jammed the throttle slightly open and
then varied the speed by varying how far he pulled the choke out, using the
slow-running control of carburettor choke mechanisms.

With a dodgy cable, I adjusted the idle setting on the carb to allow a
reasonable speed, and switched off the engine when waiting at junctions.

On 23/07/2018 09:04, Bob Eager wrote:
On Mon, 23 Jul 2018 08:44:27 +0100, NY wrote:

There's a bit of difference between trying to set off from rest (when I
agree most handbrakes will make a big difference and the car may just
squat) and applying it when the car is already moving at high speed.
Handbrakes are usually pretty good at holding the car, even on a hill,
when they are stationary, but very poor at slowing down a moving car. I

They won't pass the MoT if they are VERY poor.

tend to leave my car in first/reverse gear if I'm parking on a very
steep hill, as an added safeguard - the equivalent of leaving an
automatic in Park.

I wouldn't dare to apply the handbrake on my old Land Rover. Transmission
brake!

Not a problem. Your MoT tester will have used it during the test drive.

"Steve Walker" wrote in message
news
I think a lot of cars that had the fan driven by the belt also had the
water pump driven by belt. I seem to remember one of my dad's cars which
had two belts driven from different pulleys on the engine: one for fan
and the other for alternator and water pump; or maybe I'm imagining that.

Unfortunately a number have/had the water pump driven by the timing belt -
if the pump fails and seizes, it strips the timing belt and promptly
wrecks the engine.

Yes my Peugeot is like that. When I had the cambelt routinely replaced at
120,000 miles (or whatever) I was advised to have the water pump replaced
while they had the engine out, even though it seemed to be fine, just in
case it were to fail at some unspecified time in the future and strip the
cambelt. For an extra £30, it was probably money well spent, given that the
pump was fairly old. The garage said they always recommended replacement, to
avoid a second labour cost of getting at the cambelt/water pump area.

On 24/07/18 19:30, Rod Speed wrote:
"TMS320" wrote in message

The foot brake is a known
quantity and the only system with sufficient independence.

Thats not true of the ignition.

A lot of the system has permanent live as well as switched live. The
radio on my car has an occasional fault where to all outward appearances
the ignition has turned it off but it still draws an amp. It only resets
by disconnecting the battery.

"TMS320" wrote in message
news
On 24/07/18 19:30, Rod Speed wrote:
"TMS320" wrote in message

The foot brake is a known
quantity and the only system with sufficient independence.

Thats not true of the ignition.

A lot of the system has permanent live as well as switched live. The radio
on my car has an occasional fault where to all outward appearances the
ignition has turned it off but it still draws an amp. It only resets by
disconnecting the battery.

Doesnt happen like that with an engine with a stuck throttle.

On 25/07/18 10:10, NY wrote:
"Steve Walker" wrote in message
news
I think a lot of cars that had the fan driven by the belt also had
the water pump driven by belt. I seem to remember one of my dad's
cars which had two belts driven from different pulleys on the engine:
one for fan and the other for alternator and water pump; or maybe I'm
imagining that.

Unfortunately a number have/had the water pump driven by the timing
belt - if the pump fails and seizes, it strips the timing belt and
promptly wrecks the engine.

Yes my Peugeot is like that. When I had the cambelt routinely replaced
at 120,000 miles (or whatever) I was advised to have the water pump
replaced while they had the engine out, even though it seemed to be
fine, just in case it were to fail at some unspecified time in the
future and strip the cambelt. For an extra £30, it was probably money
well spent, given that the pump was fairly old. The garage said they
always recommended replacement, to avoid a second labour cost of getting
at the cambelt/water pump area.

A Jagiar XF needs all that and two more belts changed if they are
getting on in age or miles.

As the garage said 'by the time you have taken off the whole front of
the car plus radiators, A/C condensers and oil coooler, a few belts and
a pump wont dent the budget'


--
€œProgress is precisely that which rules and regulations did not foresee,€�

€“ Ludwig von Mises

On 25/07/18 10:55, Rod Speed wrote:
"TMS320" wrote in message
news
On 24/07/18 19:30, Rod Speed wrote:
"TMS320" wrote in message

The foot brake is a known
quantity and the only system with sufficient independence.

Thats not true of the ignition.

A lot of the system has permanent live as well as switched live. The
radio on my car has an occasional fault where to all outward
appearances the ignition has turned it off but it still draws an amp.
It only resets by disconnecting the battery.

Doesnt happen like that with an engine with a stuck throttle.

So long as it is stuck from a mechanical cause.

In article ,
The Natural Philosopher wrote:
A Jagiar XF needs all that and two more belts changed if they are
getting on in age or miles.

As the garage said 'by the time you have taken off the whole front of
the car plus radiators, A/C condensers and oil coooler, a few belts and
a pump wont dent the budget'

Hence sensible makers like BMW sticking to chains.

--
*Stable Relationships Are For Horses. *

Dave Plowman London SW
To e-mail, change noise into sound.

TMS320 wrote
Rod Speed wrote
TMS320 wrote
Rod Speed wrote
TMS320 wrote

The foot brake is a known quantity and the only system with sufficient
independence.

Thats not true of the ignition.

A lot of the system has permanent live as well as switched live. The
radio on my car has an occasional fault where to all outward appearances
the ignition has turned it off but it still draws an amp. It only resets
by disconnecting the battery.

Doesnt happen like that with an engine with a stuck throttle.

So long as it is stuck from a mechanical cause.

But if the ecm is having a brain fart, turning the ignition off will still
stop the engine.

And if the brain fart is so massive that it ignores the ignition
switch or the engine start/stop button with a keyless car, the
brakes will stop the car from moving and you are free to stall
a manual that way. And with an automatic, wait for the fuel
to run out or the torque converter to go up in flames and
toast some marshmallows on it before the fuel runs out.

On 25/07/2018 15:39, Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
A Jagiar XF needs all that and two more belts changed if they are
getting on in age or miles.

As the garage said 'by the time you have taken off the whole front of
the car plus radiators, A/C condensers and oil coooler, a few belts and
a pump wont dent the budget'

Hence sensible makers like BMW sticking to chains.

A friend of mine had the chain tensioner wear, allowing slack in the
chain ... it wore through the alloy timing chain cover!

If belts are going to be used, just keep the timing on the timing belt
and everything else on auxiliary belts.

SteveW

"Steve Walker" wrote in message
news
If belts are going to be used, just keep the timing on the timing belt and
everything else on auxiliary belts.

Yes. On the basis that hopefully the camshaft and the valve mechanisms will
never seize up, causing the timing belt to snap. Put everything that could
conceivably seize (water pump, alternator, oil pump) on other drive
mechanisms such as belts or direct gear, so that if they seize, they won't
wreck the cambelt and cause the dreaded meeting of the valves and pistons.

I presume toothed belts are used in preference to chains for the timing to
reduce the noise of a timing chain and the friction of a chain tensioner. I
presume gears would be even more noisy.


When I had the timing belt replaced on my previous car, it took the garage 5
days to get the engine running again because a position sensor broke as they
were removing the old belt and the replacement wouldn't quite fit due to a
change in design. I happened to be cycling past the garage when they were
still working on it one evening, and there was the standard noise of a
cranking but never firing engine. Suddenly it fired and there was a shout of
delight from the workshop (as if England had scored the winning goal in the
World Cup final). For some reason that I didn't follow, as soon as the
engine had fired once, they know it would work forever after - ie it wasn't
a fluke.

Thankfully the garage charged me the standard rate for the job, assuming
everything had gone smoothly, rather than all the extra faffing about time.

This was a little local garage in the village. Up until then they had done a
perfectly good job of servicing my car and repairing normal consumables like
brake pads/discs. This time things didn't go according to plan. I wish I'd
not used them again, because the next job they did on my car was to replace
the "fan belt" (alternator, PAS and aircon) which had failed - fortunately
close enough to home for the RAC to tow me home. The garage seemed to
replace the belt OK, but it turned out they hadn't noticed that the flanges
of the pulley on the crankshaft were bent (*) so the new belt only lasted a
couple of thousand miles. The main dealer where I had the second belt fitted
spotted the bent flanges and replaced the pulley as well. The second belt
lasted for ages. Sadly the village garage refused to accept that the bent
flanges had been there before, so I never got any money back to compensate
for the belt that only lasted a few thousand miles. *That* was the trigger
for me to stop using the local garage ;-(


(*) Which may have been the cause of the first belt failing.

Rod Speed wrote:
- yank on the handbrake
- put the car in neutral
- turn off the ignition

The "correct" answer was to put the car in neutral.

It isnt just one of those, no reason why you cant do
both but dont turn the ignition off. And it isnt just the
handbrake either, the normal brakes should be used too.

You never "yank" on the hand brake, in the absence of foot
brakes the hand brake can be used for the same purpose as
the foot brake, and used in the same way - gentle application
to control the speed.

When learning to drive I discussed with my instructor the
cut brake line movie trope. Use gears and hand brake to
slow down, when as slow as possible swiftly clutch to
disenage engine, hand brake to stop, key off to kill engine.

I'd never thought about accelerator stuck on, but a
similar procedure would work: use the other controls
to slow the car and engine, getting to a safe enough
speed to stop/stall/kill the engine in a controlled
manner.

Amazingly, I had this happen to me half a year ago - press
foot brake, nothing happens. Woah! Gently pull hand brake,
yes that's working, carefully get off motorway and limp
the couple of miles home. Foot brake worked about one in
four times. Garage diagnosed "bubbles in brake fluid"
whatever that is. Replacing the brake fluid fixed everything.

wrote
Rod Speed wrote

- yank on the handbrake
- put the car in neutral
- turn off the ignition

The "correct" answer was to put the car in neutral.

It isnt just one of those, no reason why you cant do
both but dont turn the ignition off. And it isnt just the
handbrake either, the normal brakes should be used too.

You never "yank" on the hand brake,

You can do with a handbrake turn.

in the absence of foot brakes the hand brake can be used
for the same purpose as the foot brake, and used in the
same way - gentle application to control the speed.

Depends on how close you are to what you dont want to run into.

When learning to drive I discussed with my instructor
the cut brake line movie trope. Use gears and hand brake
to slow down, when as slow as possible swiftly clutch to
disenage engine, hand brake to stop, key off to kill engine.

I'd never thought about accelerator stuck on, but a
similar procedure would work: use the other controls
to slow the car and engine, getting to a safe enough
speed to stop/stall/kill the engine in a controlled manner.

Makes more sense to turn the engine off
and use the foot brake to stop the car.

Amazingly, I had this happen to me half a year ago - press
foot brake, nothing happens. Woah! Gently pull hand brake,
yes that's working, carefully get off motorway and limp
the couple of miles home. Foot brake worked about one
in four times. Garage diagnosed "bubbles in brake fluid"
whatever that is. Replacing the brake fluid fixed everything.

I had complete brake failure in a series 1 landrover, work
vehicle with a ton of soil samples on board, in the steepest
area in the country. No big deal, just use the gears.

On 25/07/18 15:39, Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
A Jagiar XF needs all that and two more belts changed if they are
getting on in age or miles.

As the garage said 'by the time you have taken off the whole front of
the car plus radiators, A/C condensers and oil coooler, a few belts and
a pump wont dent the budget'

Hence sensible makers like BMW sticking to chains.


https://www.youtube.com/watch?v=HQpQIi7gI_U

On Tue, 24 Jul 2018 19:13:19 +0100, NY wrote:

I wonder how much ABS conspires against stopping the engine with
the
brakes.

That's an interesting point. I presume it doesn't make any difference as
long as all the wheels carry on turning at the same speed as each other,

The wheels are rarely all turning at the same speed, differences in
rolling radius and very rarely going in a dead straight line... B-)

ABS doesn't kick in until a wheel has, or is very close to, locking
up. You're not likely to be braking (as in rate of slowing vehicle
down) that hard. You might be braking hard but that to is counter the
torque coming from the engine not from the tyre/road.

--
Cheers
Dave.

"Dave Liquorice" wrote in message
idual.net...
On Tue, 24 Jul 2018 19:13:19 +0100, NY wrote:

I wonder how much ABS conspires against stopping the engine with
the
brakes.

That's an interesting point. I presume it doesn't make any difference as
long as all the wheels carry on turning at the same speed as each other,

The wheels are rarely all turning at the same speed, differences in
rolling radius and very rarely going in a dead straight line... B-)

ABS doesn't kick in until a wheel has, or is very close to, locking
up. You're not likely to be braking (as in rate of slowing vehicle
down) that hard. You might be braking hard but that to is counter the
torque coming from the engine not from the tyre/road.

Yes but the force needed to stop a wheel that is being rotated by the engine
will be greater then the force needed to stop a wheel in normal
circumstances - won't it? So won't there be a tendency for both the undriven
(eg rear) wheels to lock up while the driven wheels (front) are still able
to overcome that braking force. There will be some discrepancy due to the
normal difference between the balance of the front and rear brakes.

On Thu, 26 Jul 2018 09:05:16 +0100 (BST)
"Dave Liquorice" wrote:
On Tue, 24 Jul 2018 19:13:19 +0100, NY wrote:

I wonder how much ABS conspires against stopping the engine with
the
brakes.

That's an interesting point. I presume it doesn't make any difference as
long as all the wheels carry on turning at the same speed as each other,

The wheels are rarely all turning at the same speed, differences in
rolling radius and very rarely going in a dead straight line... B-)

ABS doesn't kick in until a wheel has, or is very close to, locking

It has to lock up or at least considerably slow down first, the ABS isn't
psychic. I imagine the algorithm simply takes the average of the wheel speeds
and then operates on any wheel going much slower or much faster. Of course that
has a number of potential issues, eg on snow or ice the ABS has no way of
knowing if the car is skidding or parked, if 1 wheel is going much faster
than the other 3 is that wheel spinning or are the others skidding etc.
I'm sure car manufacturers have written some clever algorithms that remember
the speed up until now and cross check against engine rpm and gear but there's
only so much it can do.

In article ,
NY wrote:
Yes but the force needed to stop a wheel that is being rotated by the
engine will be greater then the force needed to stop a wheel in normal
circumstances - won't it? So won't there be a tendency for both the
undriven (eg rear) wheels to lock up while the driven wheels (front)
are still able to overcome that braking force. There will be some
discrepancy due to the normal difference between the balance of the
front and rear brakes.

Very much so. The braking effort needed to 'beat' the engine on full belt
will be considerable. And on a FWD very likely to get the rear brakes to
the point of locking - especially on a wet surface.

Which goes back to the only sensible way. Switch off the engine but leave
the car in gear. You'll still have servo assistance to the brakes while
the engine turns. Maybe not power steering if electric, but it will still
be possible to steer the car to a halt.

--
*The only difference between a rut and a grave is the depth.

Dave Plowman London SW
To e-mail, change noise into sound.

On 26/07/18 09:38, wrote:

It has to lock up or at least considerably slow down first, the ABS isn't
psychic. I imagine the algorithm simply takes the average of the wheel speeds
and then operates on any wheel going much slower or much faster. Of course that
has a number of potential issues, eg on snow or ice the ABS has no way of
knowing if the car is skidding or parked, if 1 wheel is going much faster
than the other 3 is that wheel spinning or are the others skidding etc.
I'm sure car manufacturers have written some clever algorithms that remember
the speed up until now and cross check against engine rpm and gear but there's
only so much it can do.

This was discussed in control theory at university. Part of the
algorithm is double or triple differentiation of rotation speed. In the
days before cheap microprocessors easy to do with phase lock loops.

I guess they have put many more deductions in modern systems. Clever
people have been working on it for 40 years and no doubt they have
covered any eventuality people on news groups can imagine.

"NY" wrote in message
o.uk...
"Dave Liquorice" wrote in message
idual.net...
On Tue, 24 Jul 2018 19:13:19 +0100, NY wrote:

I wonder how much ABS conspires against stopping the engine with
the
brakes.

That's an interesting point. I presume it doesn't make any difference as
long as all the wheels carry on turning at the same speed as each other,

The wheels are rarely all turning at the same speed, differences in
rolling radius and very rarely going in a dead straight line... B-)

ABS doesn't kick in until a wheel has, or is very close to, locking
up. You're not likely to be braking (as in rate of slowing vehicle
down) that hard. You might be braking hard but that to is counter the
torque coming from the engine not from the tyre/road.

Yes but the force needed to stop a wheel that is being rotated by the
engine will be greater then the force needed to stop a wheel in normal
circumstances - won't it?

Yes.

So won't there be a tendency for both the undriven (eg rear) wheels to
lock up while the driven wheels (front) are still able to overcome that
braking force.

I don't get that with a crash stop, its audibly the front brakes
doing the ABS pulsing, not the back ones with a FWD.

There will be some discrepancy due to the normal difference between the
balance of the front and rear brakes.

Sure, but the ABS handles that fine.

On 25/07/18 18:56, Rod Speed wrote:
TMS320 wrote
Rod Speed wrote

Doesnt happen like that with an engine with a stuck throttle.

So long as it is stuck from a mechanical cause.

But if the ecm is having a brain fart, turning the ignition off will
still stop the engine.

And if the brain fart is so massive
...
with an automatic, wait for the fuel to run out or the torque
converter to go up in flames and toast some marshmallows on it before
the fuel runs out.

Indeed. The mechanically inclined might be able to find a connector or
fuse to pull. But at least you would be stationary before it
went up rather having to make a decision between using the back of a
lorry or tree/wall/ditch as a buffer.

Although the thread started with a basic all mechanical car It has to be
remembered that a lot of alleged (*) run away cases have
been on drive by wire vehicles.

(*) Emphasis alleged. I believe analysis of the infamous Toyota problem
found a genuine issue of the pedal being sticky (ie, did not release
properly when the driver lifted) but the complaints of "unintended
acceleration" (ie, the car suddenly did its own thing) this brought on
happened mainly at low speeds amongst drivers in the higher age group.

That reminds me, there was that case the other day when someone crashed
a Ferrari and claimed it was the car's fault. He had the book thrown at him.

On 26/07/2018 09:09, NY wrote:
"Dave Liquorice" wrote in message
idual.net...
On Tue, 24 Jul 2018 19:13:19 +0100, NY wrote:

I wonder how much ABS conspires against stopping the engine with
the
brakes.

That's an interesting point. I presume it doesn't make any difference as
long as all the wheels carry on turning at the same speed as each other,

The wheels are rarely all turning at the same speed, differences in
rolling radius andÂ* very rarely going in a dead straight line...Â* B-)

ABS doesn't kick in until a wheel has, or is very close to, locking
up. You're not likely to be braking (as in rate of slowing vehicle
down) that hard. You might be braking hard but that to is counter the
torque coming from the engine not from the tyre/road.

Yes but the force needed to stop a wheel that is being rotated by the
engine will be greater then the force needed to stop a wheel in normal
circumstances - won't it? So won't there be a tendency for both the
undriven (eg rear) wheels to lock up while the driven wheels (front) are
still able to overcome that braking force. There will be some
discrepancy due to the normal difference between the balance of the
front and rear brakes.

It might be more likely at lower speeds. If so, ABS stops operating
below a threshold limit.

SteveW

On 26/07/2018 11:49, Rod Speed wrote:


"NY" wrote in message
o.uk...
"Dave Liquorice" wrote in message
idual.net...
On Tue, 24 Jul 2018 19:13:19 +0100, NY wrote:

I wonder how much ABS conspires against stopping the engine with
the
brakes.

That's an interesting point. I presume it doesn't make any
difference as
long as all the wheels carry on turning at the same speed as each
other,

The wheels are rarely all turning at the same speed, differences in
rolling radius andÂ* very rarely going in a dead straight line...Â* B-)

ABS doesn't kick in until a wheel has, or is very close to, locking
up. You're not likely to be braking (as in rate of slowing vehicle
down) that hard. You might be braking hard but that to is counter the
torque coming from the engine not from the tyre/road.

Yes but the force needed to stop a wheel that is being rotated by the
engineÂ* will be greater then the force needed to stop a wheel in
normal circumstances - won't it?

Yes.

So won't there be a tendency for both the undriven (eg rear) wheels to
lock up while the driven wheels (front) are still able to overcome
that braking force.

I don't get that with a crash stop, its audibly the front brakes
doing the ABS pulsing, not the back ones with a FWD.

That's because the combination of heavy braking and engine braking (the
latter will be true if you are doing an emergency stop properly), the
weight transfers forward and the front brakes do most of the work -
which is why cars have large disks on the front, while having much
smaller disks or even small drums on the rear.

There will be some discrepancy due to the normal difference between
the balance of the front and rear brakes.

Sure, but the ABS handles that fine.

The brakes are designed to be much more powerful on the front than the
back, as the front does most of the braking. Some also have mechanical
valves that limit the rear braking pressure. If you build your own car
in the UK, one of the tests is of the relative power of front and rear
brakes and that the fronts lock before the rears.

Obviously if the engine is still driving, this will affect things, but
at a guess, with heavy braking, but slow decelleration (lots of the
braking simply counteracting the engine) there is a good chance that the
reduced weight transfer will keep the rears turning until below the ABS
cut-off speed.

SteveW

"TMS320" wrote in message
news
On 25/07/18 18:56, Rod Speed wrote:
TMS320 wrote
Rod Speed wrote

Doesnt happen like that with an engine with a stuck throttle.

So long as it is stuck from a mechanical cause.

But if the ecm is having a brain fart, turning the ignition off will
still stop the engine.

And if the brain fart is so massive
...
with an automatic, wait for the fuel to run out or the torque converter
to go up in flames and toast some marshmallows on it before
the fuel runs out.

Indeed. The mechanically inclined might be able to find a connector or
fuse to pull. But at least you would be stationary before it
went up rather having to make a decision between using the back of a
lorry or tree/wall/ditch as a buffer.

Although the thread started with a basic all mechanical car It has to be
remembered that a lot of alleged (*) run away cases have
been on drive by wire vehicles.

(*) Emphasis alleged. I believe analysis of the infamous Toyota problem
found a genuine issue of the pedal being sticky (ie, did not release
properly when the driver lifted)

Yeah, forgot about those.

but the complaints of "unintended acceleration" (ie, the car suddenly did
its own thing) this brought on happened mainly at low speeds amongst
drivers in the higher age group.

I thought that was mostly just some senile old fool shoving the accelerator
instead of the brake and the car doing what it was told to do.

Corse without a data recorder, its hard to be sure what happened.

That reminds me, there was that case the other day when someone crashed
a Ferrari and claimed it was the car's fault. He had the book thrown at
him.

But that might well just be the usual line of a bull**** or the court
deciding that.

On 26/07/18 19:35, Rod Speed wrote:
"TMS320" wrote in message

but the complaints of "unintended acceleration" (ie, the car
suddenly did its own thing) this brought on happened mainly at low
speeds amongst drivers in the higher age group.

I thought that was mostly just some senile old fool shoving the
accelerator instead of the brake and the car doing what it was told
to do.

Indeed.

Corse without a data recorder, its hard to be sure what happened.

Cars do record some things.

"Steve Walker" wrote in message
news
On 26/07/2018 11:49, Rod Speed wrote:


"NY" wrote in message
o.uk...
"Dave Liquorice" wrote in message
idual.net...
On Tue, 24 Jul 2018 19:13:19 +0100, NY wrote:

I wonder how much ABS conspires against stopping the engine with
the
brakes.

That's an interesting point. I presume it doesn't make any difference
as
long as all the wheels carry on turning at the same speed as each
other,

The wheels are rarely all turning at the same speed, differences in
rolling radius and very rarely going in a dead straight line... B-)

ABS doesn't kick in until a wheel has, or is very close to, locking
up. You're not likely to be braking (as in rate of slowing vehicle
down) that hard. You might be braking hard but that to is counter the
torque coming from the engine not from the tyre/road.

Yes but the force needed to stop a wheel that is being rotated by the
engine will be greater then the force needed to stop a wheel in normal
circumstances - won't it?

Yes.

So won't there be a tendency for both the undriven (eg rear) wheels to
lock up while the driven wheels (front) are still able to overcome that
braking force.

I don't get that with a crash stop, its audibly the front brakes
doing the ABS pulsing, not the back ones with a FWD.

That's because the combination of heavy braking and engine braking (the
latter will be true if you are doing an emergency stop properly),

No it isnt. I do those crash stops when some fool fails to give
way usually at an intersection or roundabout and there is
never enough time to do any engine braking in that situation.

the weight transfers forward and the front brakes do most of the work -
which is why cars have large disks on the front, while having much smaller
disks or even small drums on the rear.

Thats just the reason you only get ABS pulsing on the front brakes.
You dont see the rear wheels slipping much with a FWD and a
crash stop. In other words you dont usually see a 4 wheel skid.

Least I dont because we dont get black ice or snow here.

There will be some discrepancy due to the normal difference between the
balance of the front and rear brakes.

Sure, but the ABS handles that fine.

The brakes are designed to be much more powerful on the front than the
back, as the front does most of the braking. Some also have mechanical
valves that limit the rear braking pressure. If you build your own car in
the UK, one of the tests is of the relative power of front and rear brakes
and that the fronts lock before the rears.

Obviously if the engine is still driving, this will affect things, but at
a guess, with heavy braking, but slow decelleration (lots of the braking
simply counteracting the engine) there is a good chance that the reduced
weight transfer will keep the rears turning until below the ABS cut-off
speed.

On Tue, 24 Jul 2018 23:48:08 +0100, Nick Finnigan wrote:

Braking the engine when it is transmitting power to the wheels
will
lead to a "fight" between brakes and engine,

The brakes will win, provided the car is in a high gear. Even in 1st
I reckon the brakes will still win, just need a bit more effort.

with the risk that the energy that the engine is generating will
heat
up brakes too much. If you have an engine generating maybe 100 hp,

you've got to dissipate that sort of energy in the brakes.

Which they are designed to do, how much energy do you think they have
to take in an emergency stop from 70 mph? 1000 kg car doing 70 mph
has around 500,000 J of kinetic energy. Stop it in say 5 seconds(*)
that 100,000 J/s or 100 kW. 100 bhp is 75 kW.

(*) A modern car can proably stop a fair bit faster than that with
the aid of ABS working overtime.

What is the effect of the discs heating up dramatically: can it
cause
loss of braking force?

Yes, "brake fade". Conversely if a brake is binding the disc can glow
cherry red and still not lose braking. I've had both.

Brakes routinely handle far more than 100hp. It takes a long time
driving with the brakes applied before you get any noticeable brake
fade.

About 5 mins in a "spirted" 1000' ish foot decent using, the brakes
rather more than the gears, down a rather good driving road, B-)
Slightly alarming when you start to brake as a corner approaches
rather too quickly, just slam it down another gear to make it round.
Once faded they'd come back quite quickly but would also fade again
quite quickly... It was several minutes of driving with no braking
before they came back reliably.

--
Cheers
Dave.

On Thu, 26 Jul 2018 11:29:14 +0100
TMS320 wrote:
On 26/07/18 09:38, wrote:

It has to lock up or at least considerably slow down first, the ABS isn't
psychic. I imagine the algorithm simply takes the average of the wheel speeds

and then operates on any wheel going much slower or much faster. Of course
that
has a number of potential issues, eg on snow or ice the ABS has no way of
knowing if the car is skidding or parked, if 1 wheel is going much faster
than the other 3 is that wheel spinning or are the others skidding etc.
I'm sure car manufacturers have written some clever algorithms that remember
the speed up until now and cross check against engine rpm and gear but
there's
only so much it can do.

This was discussed in control theory at university. Part of the
algorithm is double or triple differentiation of rotation speed. In the
days before cheap microprocessors easy to do with phase lock loops.

I assumed ABS systems had always been microcontroller controlled, didn't
realise there were analogue versions. Interesting to know.

I guess they have put many more deductions in modern systems. Clever
people have been working on it for 40 years and no doubt they have
covered any eventuality people on news groups can imagine.

No doubt, but the more complex ian algorithm becomes the more likely it is
that there's some nasty undisovered edge cases lurking in there either due to
the implementation or the algorithm itself which might cause serious problems.
In aviation they do formal proof checking, multiple implementations of the same
algorithm by different teams and god knows what else to mitigate this, but I
doubt the automotive industry is quite so thorough simply due to cost.