Do cruise controls ever control speed on a downhill gradient?

[NY]

My understanding was that cruise controls only control the throttle position
and so a car that is set to (for example) 70 mph may exceed this speed going
down a hill if it is so steep than the car would speed up if CC was turned
off and you lifted right off the throttle. There are plenty of threads on
forums about "why does my car speed up going downhill with the CC turned on"
which explain this.

But are there any cars whose CC can also apply the brakes slightly to
maintain a constant speed downhill if closing the throttle is not, on its
own, enough to keep the vehicle in check? I know some cars have systems
which apply the brakes slightly if they sense that you are gaining on the
car in front and are getting very close; could those cars also use the same
"apply the brakes slightly" technology in conjunction with the CC?

I'm just curious. I'd never rely entirely on CC to stop me speeding up going
down a steep hill. Indeed my experience of using CC on a motorway is that it
is rare to be able to set it to 70 and leave it there because you encounter
a car in front going slower but there's a car on your right preventing you
from pulling out so you need to ease off the speed until it has gone past
and you can pull out - as with non-CC driving where you do this adjustment
subconsciously all the time. So even with CC, it's not a case of "turn on CC
and turn off brain" :-)


Another question: why is it that on a lot of cars with CC, the CC will not
work below about 30 mph, so if you want to maintain a constant 20 in a 20
limit, you can't. I'm assuming that you're in the correct gear for that
speed so it's not that the CC would make the engine labour in too high a
gear at 20. I'm not sure whether the same applies to the speed limiter
functionality of a car's CC - the last time I drove a car with CC I meant to
check this but forgot :-(

[spud-u-d...@potato.field]

On Fri, 5 Jun 2015 13:03:44 +0100
"NY" <m...@privacy.net> wrote:
>But are there any cars whose CC can also apply the brakes slightly to

Cue John Pillockson telling you just to google it.

>maintain a constant speed downhill if closing the throttle is not, on its
>own, enough to keep the vehicle in check? I know some cars have systems

With adaptive cruise control it has to have control over the braking otherwise
it could well hit the car its trying to match speed with. On standard cruise
control I doubt it does - probably would cost too much for the benefit.

However there have been CCs for a while that will force a downward gear
change - on an automatic obviously - when going downhill to slow the vehicle.

>Another question: why is it that on a lot of cars with CC, the CC will not
>work below about 30 mph, so if you want to maintain a constant 20 in a 20

Don't know. Probably engine labouring as you say but there's no reason not to
have it on autos. Most them also won't go above 100mph but the reasoning there
is more obvious.

--
Spud

[John Williamson]

On 05/06/2015 13:40, spud-u-d...@potato.field wrote:
> On Fri, 5 Jun 2015 13:03:44 +0100
> "NY" <m...@privacy.net> wrote:
>> But are there any cars whose CC can also apply the brakes slightly to
>
> Cue John Pillockson telling you just to google it.
>

If I told you the answer, you'd only argue the toss.

--
Tciao for Now!

John.

[John Kenyon]

On 05/06/2015 13:40, spud-u-d...@potato.field wrote:

> On Fri, 5 Jun 2015 13:03:44 +0100
> "NY" <m...@privacy.net> wrote:
>> But are there any cars whose CC can also apply the brakes slightly to
>
> Cue John Pillockson telling you just to google it.

Does your character always change when you leave uk.r and move on uk.t?

[spud-u-d...@potato.field]

I'm supposed to just put up with someone calling me an idiot simply for
posting a relevant question for the group am I? On your bike pal.

--
Spud

[John Kenyon]

Never called you an idiot, but if the cap fits.

[Nightjar .me.uk>]

On 05/06/2015 13:03, NY wrote:
> My understanding was that cruise controls only control the throttle
> position and so a car that is set to (for example) 70 mph may exceed
> this speed going down a hill if it is so steep than the car would speed
> up if CC was turned off and you lifted right off the throttle. There are
> plenty of threads on forums about "why does my car speed up going
> downhill with the CC turned on" which explain this.

True of the cruise control I fitted to my father's car in the 1960s, as
he had to do a lot of motorway driving. It used a magnetic clutch and a
bit of chain attached to the throttle linkage. Accelerating would simply
make the chain go slack, returning to the set position when you lifted
off. Braking would disengage the clutch. I would be surprised if cruise
controls on modern cars were quite that primitive. On my car, pressing
the throttle down sends a signal to the engine management computer, with
no mechanical linkage to the engine.

> But are there any cars whose CC can also apply the brakes slightly to
> maintain a constant speed downhill if closing the throttle is not, on
> its own, enough to keep the vehicle in check? I know some cars have
> systems which apply the brakes slightly if they sense that you are
> gaining on the car in front and are getting very close; could those cars
> also use the same "apply the brakes slightly" technology in conjunction
> with the CC?

I routinely use the speed limiter function on my cruise control to
control the car's speed down a steep hill. On one I often use, I start
out at 45mph, increase to the 50mph limit around the first bend, slow to
35mph for the next bend, then progressively move up to 50mph as the hill
flattens out around the last bend. The car simply keeps to the speeds I
set, slowing as necessary.

> I'm just curious. I'd never rely entirely on CC to stop me speeding up
> going down a steep hill. Indeed my experience of using CC on a motorway
> is that it is rare to be able to set it to 70 and leave it there because
> you encounter a car in front going slower but there's a car on your
> right preventing you from pulling out so you need to ease off the speed
> until it has gone past and you can pull out - as with non-CC driving
> where you do this adjustment subconsciously all the time. So even with
> CC, it's not a case of "turn on CC and turn off brain" :-)

On continental motorways, I just turn on cruise control and the car's
radar slows me down if I am catching up with a vehicle in front and
don't pull out. British motorways are usually too congested for it to
work; even on minimum distance setting, the radar wants a larger space
in front than most British drivers like to see empty.

> Another question: why is it that on a lot of cars with CC, the CC will
> not work below about 30 mph, so if you want to maintain a constant 20 in
> a 20 limit, you can't. I'm assuming that you're in the correct gear for
> that speed so it's not that the CC would make the engine labour in too
> high a gear at 20. I'm not sure whether the same applies to the speed
> limiter functionality of a car's CC - the last time I drove a car with
> CC I meant to check this but forgot :-(

No idea. Mine, both cruise control and speed limiter, start at 20mph or
30kph, depending upon the country settings.


--
Colin Bignell

[spud-u-d...@potato.field]

On Fri, 05 Jun 2015 16:36:39 +0100

John Kenyon <etl...@gmx.net> wrote:
>On 05/06/2015 16:11, spud-u-d...@potato.field wrote:
>> On Fri, 05 Jun 2015 15:22:02 +0100
>> John Kenyon <etl...@gmx.net> wrote:
>>> On 05/06/2015 13:40, spud-u-d...@potato.field wrote:
>>>> On Fri, 5 Jun 2015 13:03:44 +0100
>>>> "NY" <m...@privacy.net> wrote:
>>>>> But are there any cars whose CC can also apply the brakes slightly to
>>>>
>>>> Cue John Pillockson telling you just to google it.
>>>
>>> Does your character always change when you leave uk.r and move on uk.t?
>>
>> I'm supposed to just put up with someone calling me an idiot simply for
>> posting a relevant question for the group am I? On your bike pal.
>>
>> --
>> Spud
>>
>
>Never called you an idiot, but if the cap fits.

I wasn't referring to you. Do try and keep up.

--
Spud

[Scott M]

Nightjar <cpb@ wrote:

>> Another question: why is it that on a lot of cars with CC, the CC will
>> not work below about 30 mph, so if you want to maintain a constant 20 in
>> a 20 limit, you can't. I'm assuming that you're in the correct gear for
>> that speed so it's not that the CC would make the engine labour in too
>> high a gear at 20. I'm not sure whether the same applies to the speed
>> limiter functionality of a car's CC - the last time I drove a car with
>> CC I meant to check this but forgot :-(
>
> No idea. Mine, both cruise control and speed limiter, start at 20mph or
> 30kph, depending upon the country settings.

Drove a GM Saab yesterday and that didn't want to play below 30mph. My
BM one is 20-odd mph. The first time I ever played with CC (90s Rover
420) it would do it at any speed, which worked well crawling along.

The answer of course comes down to the designer's fear of
H&S/What-if/"There has to be a limit" as it really makes little odds to
anything at what speeds you can/can't engage it.

If they wanted to put a limit on anything, the difference between
current speed and resume speed would be more important. Had a friend
with a Rover 827 auto. Apparently it was something to behold if he set
cruise to, say, 70 on the m'way and then hit resume after coming to a rest.

--
Scott

Where are we going and why am I in this handbasket?

[NY]

"Scott M" <no_one@no_where.net> wrote in message
news:mku9f4$26k$1...@speranza.aioe.org...

> Nightjar <cpb@ wrote:
>
>>> Another question: why is it that on a lot of cars with CC, the CC will
>>> not work below about 30 mph, so if you want to maintain a constant 20 in
>>> a 20 limit, you can't. I'm assuming that you're in the correct gear for
>>> that speed so it's not that the CC would make the engine labour in too
>>> high a gear at 20. I'm not sure whether the same applies to the speed
>>> limiter functionality of a car's CC - the last time I drove a car with
>>> CC I meant to check this but forgot :-(
>>
>> No idea. Mine, both cruise control and speed limiter, start at 20mph or
>> 30kph, depending upon the country settings.
>
> Drove a GM Saab yesterday and that didn't want to play below 30mph. My BM
> one is 20-odd mph. The first time I ever played with CC (90s Rover 420) it
> would do it at any speed, which worked well crawling along.

The only car with CC that I drove recently was a new Peugeot 208. If you
drove below 20 and hit "Set" it flashed an error message. If you set it 30
and then tried to reduce below this speed with the down arrow, it gave the
same message at some point (I forget exactly what the lowest speed was). I
should have tried setting a speed limit rather than a constant speed to be
maintained, to see whether it would allow that. Setting a limit of 20 is
sufficient to prevent your speed accidentally creeping over on a road where
20 feels abnormally slow for the conditions (unlike some 20 or 30 limits
where you might out of choice drive lower than that anyway).

> If they wanted to put a limit on anything, the difference between current
> speed and resume speed would be more important. Had a friend with a Rover
> 827 auto. Apparently it was something to behold if he set cruise to, say,
> 70 on the m'way and then hit resume after coming to a rest.

I found it difficult to gauge the correct amount of accelerator pressure to
apply when unsetting the CC. Once you've set it you release the accelerator
pedal, but how much pressure to you apply so that when you unset the CC,
there isn't a lurch - either as the engine loses power if you've not applied
enough throttle or as it surges forward if you've applied too much. I'm sure
you get used to judging the correct amount after a while - better for the
car to slow down slightly than to surge forward!

[Newsworthy]

My 2011 Mercedes E250 does indeed keep to the set speed even downhill, not
sure if it is brakeing though (feels like it) other automatics I have
driven will romp away down hills if you don't hit the brakes.
Also the E250 can be set at 20 mph.

[Scott M]

NY wrote:

> I found it difficult to gauge the correct amount of accelerator pressure
> to apply when unsetting the CC. Once you've set it you release the
> accelerator pedal, but how much pressure to you apply so that when you
> unset the CC, there isn't a lurch - either as the engine loses power if
> you've not applied enough throttle or as it surges forward if you've
> applied too much. I'm sure you get used to judging the correct amount
> after a while - better for the car to slow down slightly than to surge
> forward!

It's no different to taking your foot straight off the gas so should
only be notable jerky if at high revs or in a low gear. And you can't
apply too much throttle as it would already be responding to it and
accelerating.

I use cruise a lot at all speeds and don't think I've ever readied my
right foot to take over the gas. If anything it'd be hovering on the brake.

[Recliner]

Touching the brake pedal releases the cc anyway, so it's the way I normally
disengage mine.

[John Kenyon]

On a manual, touching the clutch does the same thing, with the advantage
of no brake light flash (unavoidable on an auto I know)

[Recliner]

The brake light flash is probably a good thing if I'm disengaging the cc in
order to slow down, particularly if someone is following too closely.

[NY]

"John Kenyon" <etl...@gmx.net> wrote in message
news:ml6a4u$8j6$1...@ID-103048.news.dfncis.de...

On all the cars I've driven with CC, I've tended to use the set/resume
button on the steering wheel to temporarily turn off the CC. This has the
advantage of not flashing the brake lights or (slightly) applying the brake
or of interrupting the flow of power. Obviously the brake pedal is the last
resort if you need to reduce speed rapidly and in a hurry, and be sure that
the CC is no longer fighting the brakes.

But I always cover the accelerator pedal and try to anticipate roughly how
far it would be pressed in manual mode, to avoid the sudden loss of power
when you turn off the CC - it's the equivalent of driving at 70 mph with the
engine providing sufficient power to maintain that speed, and then taking
you foot right off the accelerator and then re-applying it: the car will
coast but it will slow down due to air resistance etc. One car I drove (I
think it make have been the Peugeot 208 loan car that I borrowed) seemed to
cut the fuel off instantaneously when the CC turned off and reapplied it
instantaneously when it was resumed, rather than changing the fuel flow
gradually over a fraction of a second, and it always caused a noticeable
lurch.

[NY]

"Recliner" <recli...@btinternet.com> wrote in message
news:1639440199455534634.490244...@news.eternal-september.org...

> The brake light flash is probably a good thing if I'm disengaging the cc
> in
> order to slow down, particularly if someone is following too closely.

If you are slowing down reasonably quickly with the footbrake, yes it is a
good thing. If the brake lights flash every time you switch it off because
you need to lose a couple of mph to match the speed of the car they you are
coming up behind (in a situation where you'd just lift off the accelerator
pedal slightly without CC) there there's a danger of "crying wolf". Some
people seem to be "congenital brakers" who flash their brake lights every
time they come off the power even slightly, and following someone like that
is very tiring because you start to ignore most of the flashes of brake
lights as being false alarms, only to find that occasionally he really *is*
braking and I need to do likewise and not just tweak my speed a smidgen.

Mind you, I remember when I was learning to drive I actually asked the
instructor, in all innocence, whether it was legal to slow down simply by
lifting off the power, because this would not put the brake lights on to
warn the driver behind.

[Recliner]

"NY" <m...@privacy.net> wrote:
> "Recliner" <recli...@btinternet.com> wrote in message
> news:1639440199455534634.490244...@news.eternal-september.org...
>> The brake light flash is probably a good thing if I'm disengaging the cc > in
>> order to slow down, particularly if someone is following too closely.
>
> If you are slowing down reasonably quickly with the footbrake, yes it is
> a good thing. If the brake lights flash every time you switch it off
> because you need to lose a couple of mph to match the speed of the car
> they you are coming up behind (in a situation where you'd just lift off
> the accelerator pedal slightly without CC) there there's a danger of "crying wolf".

I don't have to do anything in that situation, as my car has an adaptive
cruise control -- it automatically slows or speeds up to match the car
ahead. And even if I need to adjust the cruising speed (eg, if the speed
limit changes), I do it with the buttons on the wheel -- each touch changes
the target speed by 1mph, which is displayed in the panel).

> Some people seem to be "congenital brakers" who flash their brake lights
> every time they come off the power even slightly, and following someone
> like that is very tiring because you start to ignore most of the flashes
> of brake lights as being false alarms, only to find that occasionally he
> really *is* braking and I need to do likewise and not just tweak my speed a smidgen.

I let my adaptive cc handle all that. Its radar doesn't care about whether
the car in front's brake lights flash.

[John Kenyon]

IMHO, If someone's following you too closely, an earlier, lighter but
longer touch on the brake pedal is required. A brief flash of brake
light isn't guaranteed to get them back from la-la land...

[NY]

"John Kenyon" <etl...@gmx.net> wrote in message

news:ml6e4p$fq7$1...@ID-103048.news.dfncis.de...

> IMHO, If someone's following you too closely, an earlier, lighter but
> longer touch on the brake pedal is required. A brief flash of brake
> light isn't guaranteed to get them back from la-la land...

Going off topic slightly, onto the subject of being followed by a muppet,
how about this experience I had the other day...

I was turning right at a cross-roads (signposted with a standard
cross-in-a-triangle warning sign) which is immediately before the
single-carriageway road becomes dual-carriageway, with all the "dual
carriageway ahead" signs. There is a marked centre lane for right-turning
traffic to move into so it can wait for a gap in the oncoming traffic.

I indicated a good 200 yards before the start of this lane, moved into it as
it started at the end of the hatching, and began to brake to a halt, waiting
till it was safe to turn right. I saw a car follow me into this lane and I
presumed he also was turning right. At the last minute he gave me a loud
blast on the horn, flashed his lights and swerved to my left. I can only
think he totally misread the signs and lane markings, and thought I was
moving out to overtake another car at the start of the two-lane section -
and then discovered the hard way that I wasn't. I braced myself in case he
ran into the back of me, glad that I hadn't already started to turn
otherwise I'd have been catapulted into the oncoming traffic. Luckily he
managed to swerve round me without clipping my car. His skid marks are still
there!

[Scott M]

NY wrote:

> Some people seem to be "congenital brakers" who flash
> their brake lights every time they come off the power even slightly,

I suspect a lot of people believe you have to have the right foot on one
pedal or the other otherwise the magic will stop. I knew a bloke who
bought an automatic who behaved like that. Watching him in the works'
carpark was always amusing as he wouldn't let it creep and all manoevers
were all or nothing lurches.

[NY]

"Scott M" <no_one@no_where.net> wrote in message

news:ml6m90$6ip$1...@speranza.aioe.org...

> NY wrote:
>
>> Some people seem to be "congenital brakers" who flash their brake lights
>> every time they come off the power even slightly,
>
> I suspect a lot of people believe you have to have the right foot on one
> pedal or the other otherwise the magic will stop. I knew a bloke who
> bought an automatic who behaved like that. Watching him in the works'
> carpark was always amusing as he wouldn't let it creep and all manoevers
> were all or nothing lurches.

My dad used to be like that when he first started driving automatic cars -
his right foot was permanently on one pedal or the other. Then he went on an
Advanced Driving course organised by work (he had a company car) and they
made "certain comments" and he got a lot better after that. Even *I* knew
(and I was much too young to drive at the time) that he tended to lurch
rather a lot and that maybe the car would coast without his foot on a pedal.

I drove an automatic petrol car the other day (a loan car while mine was
being serviced) and it was weird to have a petrol car which would crawl
forwards (a bit faster than I'd have liked!) when you released the footbrake
without pressing the accelerator. Setting off smoothly from rest took a few
moments practice when I'd been used to using the clutch pedal to do a lot of
the fine adjustment of acceleration from rest in my manual and so had *two*
means of controlling speed, used in conjunction.

The funniest thing is to watch and listen in any supermarket car park when
there are elderly drivers parking and leaving. A lot seem to employ the
engine-racing-and-clutch-slipping technique for manoevring: they wind the
engine up to about 2000 rpm and let the clutch plates barely kiss; in an
automatic they get the engine racing and control the speed on the brake.
Either way you get a distinctive smell of hot clutch or hot transmission
fluid.

One old guy got himself into a spot of bother next to me and after he'd gone
backwards and forwards several times and come perilously close to denting my
doors, I offered my help to reverse him out of what was admittedly a tight
space. He sat in the passenger seat while I reversed his car out and he sat
there gobsmacked as I kept the engine revs barely above idling (it was a
diesel so I knew it wouldn't stall), used a bit of clutch to get the car
rolling and then covered the brake to slow down as I started to turn. "But
how did you do that without pressing the accelerator?" he asked in
amazement.

I can't help wondering if the car-shoots-through-supermarket-window
accidents that occasionally get reported are caused by elderly people with
automatic transmissions applying way too much power and then letting their
foot slip off the brake. If I had my way I'd make sure the footbrake pedal
in an automatic was the same width as in a manual and close enough to the
accelerator that you couldn't get your left foot onto the brake while
pressing the throttle - then you'd have to press one pedal *or* the other,
not both at the same time.

[Nick Finnigan]

On 09/06/2015 13:57, NY wrote:
>
> I drove an automatic petrol car the other day (a loan car while mine was
> being serviced) and it was weird to have a petrol car which would crawl
> forwards (a bit faster than I'd have liked!) when you released the
> footbrake without pressing the accelerator.

It is quite normal to have a petrol car which will crawl forwards without
pressing the accelerator. I stalled a common rail diesel twice on a test
drive because the I pulled off as usual without using the accelerator but
the clutch biting point was more sudden than I'm used to.

[NY]

"Nick Finnigan" <N...@genie.co.uk> wrote in message
news:mlaa6d$lo5$1...@speranza.aioe.org...

The only diesel car that I have frequently stalled is a VW Golf with the
older Pump Duse (as opposed to common rail) engine. It seemed as if when the
engine revs got too low, the engine management cut off the fuel rather than
striving to keep the engine going, even if it chugged a bit. It's the only
diesel I've ever stalled repeatedly, as opposed to the occasional "oops, not
enough power / let the clutch in too quickly". Looking on forums, this
engine seems notorious for stalling with too little power, more like a
petrol than a diesel.

[spud-u-d...@potato.field]

On Thu, 11 Jun 2015 19:10:15 +0100
"NY" <m...@privacy.net> wrote:
>The only diesel car that I have frequently stalled is a VW Golf with the
>older Pump Duse (as opposed to common rail) engine. It seemed as if when the
>engine revs got too low, the engine management cut off the fuel rather than
>striving to keep the engine going, even if it chugged a bit. It's the only
>diesel I've ever stalled repeatedly, as opposed to the occasional "oops, not
>enough power / let the clutch in too quickly". Looking on forums, this
>engine seems notorious for stalling with too little power, more like a
>petrol than a diesel.

In my experience its only fuel injected petrol engines that are easily stalled.
Old carbouretter ones generally had more torque at idle rpm and so you could
be a bit more casual with the clutch and rpm when pulling away.

--
Spud

[space...@gmail.com]

On Friday, June 5, 2015 at 8:03:15 AM UTC-4, NY wrote:
> My understanding was that cruise controls only control the throttle position
> and so a car that is set to (for example) 70 mph may exceed this speed going
> down a hill if it is so steep than the car would speed up if CC was turned
> off and you lifted right off the throttle. There are plenty of threads on
> forums about "why does my car speed up going downhill with the CC turned on"
> which explain this.
>
> But are there any cars whose CC can also apply the brakes slightly to
> maintain a constant speed downhill if closing the throttle is not, on its
> own, enough to keep the vehicle in check? I know some cars have systems
> which apply the brakes slightly if they sense that you are gaining on the
> car in front and are getting very close; could those cars also use the same
> "apply the brakes slightly" technology in conjunction with the CC?
>

The 2008 BMW 335i I had would apply the brakes to keep your speed. Same with the 2016 Mercedes E350 I'm in now. VERY nice feature. I have had others , Honda that would downshift going downhill but that wasn't very good.

> I'm just curious. I'd never rely entirely on CC to stop me speeding up going
> down a steep hill. Indeed my experience of using CC on a motorway is that it
> is rare to be able to set it to 70 and leave it there because you encounter
> a car in front going slower but there's a car on your right preventing you
> from pulling out so you need to ease off the speed until it has gone past
> and you can pull out - as with non-CC driving where you do this adjustment
> subconsciously all the time. So even with CC, it's not a case of "turn on CC
> and turn off brain" :-)
>
>
> Another question: why is it that on a lot of cars with CC, the CC will not
> work below about 30 mph, so if you want to maintain a constant 20 in a 20
> limit, you can't. I'm assuming that you're in the correct gear for that
> speed so it's not that the CC would make the engine labour in too high a
> gear at 20. I'm not sure whether the same applies to the speed limiter
> functionality of a car's CC - the last time I drove a car with CC I meant to
> check this but forgot :-(

Mercedes will set as low as 20mph.

[pat.thetrut...@gmail.com]

Yes..some MERCEDES Benz does

[NY]

<pat.thetrut...@gmail.com> wrote in message
news:3d7efd6c-973f-4881...@googlegroups.com...
> Yes..some MERCEDES Benz does

Does it do this just by applying the brakes if shutting off the fuel isn't
enough to keep the speed constant, or does it also (for an automatic car)
change down for added engine braking?

Given that most cars have ABS nowadays, you'd think that it would be more
common than it is for cruise control to apply the brakes if necessary, given
that ABS has the technology to apply the brake without the driver pressing
the pedal.

[Recliner]

ABS only works when you're pressing the brake pedal. What it does is to
*reduce* the brake pressure on any slipping (ie, stopped) wheel(s).

I think you're confusing ABS with traction control and Electronic stability
control.

[TMS320]

On 05/10/18 10:29, NY wrote:
> <pat.thetrut...@gmail.com> wrote in message
> news:3d7efd6c-973f-4881...@googlegroups.com...
>> Yes..some MERCEDES Benz does
>
> Does it do this just by applying the brakes if shutting off the fuel
> isn't enough to keep the speed constant, or does it also (for an
> automatic car) change down for added engine braking?

Autos i nmy experience change down.

However, the results can be variable. I hired a car in the US with an 8
speed box which would go down the first 2 or 3 gears as expected but if
that wasn't sufficient it would go down the next gear and, inexplicably,
apply power and increase speed.

It is inevitable that a stepped box cannot be precise - if one gear is
not enough, the next might be too much unless a modicum of power is put
in - but to speed so much up was strange. Hard to know whether the
behaviour was deliberate (it's possible to speculate reasons) or a bug.

Contrast to a CVT transmission which is bound to do the right thing
unless it needs to push the engine beyond 6000rpm.

[NY]

"TMS320" <dr6...@gmail.com> wrote in message
news:ppagmt$b3a$1...@dont-email.me...

> Contrast to a CVT transmission which is bound to do the right thing unless
> it needs to push the engine beyond 6000rpm.

My experience of CVTs, as a passenger in a DAF and a Volvo, is that they
choose a very low ratio and rev the engine very high, long after a
conventional automatic or a competent manual driver would have changed up
progressively through the gears.

[TMS320]

If your experience of CVT is from a Daf, things have moved on somewhat.
Even though the principle is the same, the mechanical implementation is
totally different and the ratio is electronically determined.

Performance and economy are better than from a competent manual driver
and there is no hesitation and lurching on undulating roads, as with a
stepped auto. Some people just don't like the way the the revs are
adjusted to driver power demand (lowest to meet demand), rather than
being linked to road speed.

[Arthur Conan Doyle]

TMS320 <dr6...@gmail.com> wrote:

>Performance and economy are better than from a competent manual driver
>and there is no hesitation and lurching on undulating roads, as with a
>stepped auto. Some people just don't like the way the the revs are
>adjusted to driver power demand (lowest to meet demand), rather than
>being linked to road speed.

I need to drive a CVT again and see how they perform. I did not like the early
implementation for the reason you cited - the disconnect from road speed. That
said, my regular commute has me turn off a flat road, decellerating from 50mph
and on to accellerating S turns up a rather steep incline. My current 6 speed
has a very hard time with downshifts followed by almost immediate upshifts.

[TMS320]

I rather like the disconnect. Noise is an indication of power instead. I
think the aim is keep the engine in a high torque mode for efficiency -
perhaps fully open throttle with stratification - and map the revs
(power) to accelerator position. When hiring in NZ recently I drove both
types. Even though the CVT was in a cheaper car with less underlying
refinement and performance, it showed up the inevitable hesitation in a
stepper.

[NY]

"TMS320" <dr6...@gmail.com> wrote in message

news:ppf8fb$fbv$1...@dont-email.me...

The ultimate aim of any transmission is that the position of the accelerator
is directly proportional either to car acceleration or speed, without the
intervening uncertainty of variable (continuous or stepped) gear ratios. In
a manual, you control when the gear change will occur so can compensate for
this in that you learn how much to increase or decrease the accelerator
position as you change gear, both to account for the different engine speed
required in the new gear and the greater acceleration in a lower gear as the
mechanical load on the engine is lower.

I find that I press the accelerator to a certain position to get a desired
acceleration in the gear that I'm in, and auto transmissions foul this up by
changing down at some unspecified point during the acceleration, requiring
me to back off the power to avoid unexpected surge in acceleration.

I suppose in a manual I'm used to choosing a gear that will give me
reasonable acceleration so I can go from the minimum speed that I've gone
down to on a roundabout to the point at which I plant to level out my speed.
It may take more that one gear to cover that range, but I will level out the
acceleration briefly either side of the gear change so I'm not changing
*during * acceleration - one of the things that they don't teach but which
gives smoother driving.

I'd love to drive an electric car which has just one fixed ratio and a motor
which can give constant acceleration over a wide range of road speeds
(subject to an artificially-limited maximum as you are setting off from rest
to avoid wheelspin), and maybe subject to a controlled reduction as you come
off the power rather than a very sudden transition from positive
acceleration to no acceleration (and in fact slight deceleration due to
friction and air resitance).

[NY]

"TMS320" <dr6...@gmail.com> wrote in message

news:ppf8fb$fbv$1...@dont-email.me...

>> My experience of CVTs, as a passenger in a DAF and a Volvo, is that they
>> choose a very low ratio and rev the engine very high, long after a
>> conventional automatic or a competent manual driver would have changed up
>> progressively through the gears.
>
> If your experience of CVT is from a Daf, things have moved on somewhat.
> Even though the principle is the same, the mechanical implementation is
> totally different and the ratio is electronically determined.

Yes, my knowledge is from the early 80s. I used to get a lift to the place I
was working in my year off before university in a Volvo 340 (IIRC) which had
Variomatic. And when I was at university I knew someone who had a Daf 33
which was much older. I'm not sure whether Volvo did any development from
the transmission technology that they bought the rights to use, but it
didn't show. Setting off from rest in both cars was very sluggish, with the
engine racing in a low ratio for a long time (equivalent to staying in first
gear until you were doing about 20), then the engine note fell but the car
stayed at a constant speed (ie ratio increased at exactly same rate as
engine speed decreased) and then the car began to pick up more speed, maybe
with the transmission finally giving a constant ratio. I'd expect the engine
to rise to an optimum-torque speed and then the ration to increase so as to
speed the car up, but that doesn't explain the initial acceleration, then
the long period of constant speed but varying ratio, and then the continued
acceleration.


(I once drove a Ford Focus with ordinary stepped auto which had a similar
reciprocal ration between engine speed and gear ratio, but that was a fault.
It was very tiring trying the accelerate up to motorway speed, because once
I got up to about 40, it changed down progressively as soon as I applied
more power, so I could do 50 in any of the gears - all that changed was the
engine note. It would get up to 70 eventually, but it took a long time and a
lot of very gentle acceleration not to trigger it to change down. I'm afraid
I was a bit of a middle lane hogger on that trip (a site visit from work)
because once I'd got up to 70 I wasn't going to risk changing back to Lane 1
and then have to accelerate (even slightly) to get up to the same speed as
the traffic that I was joining in Lane 2.

When I got to the site I rang the hire company the following morning and
reported the fault (it was after hours the previous night when I picked up
the car), and to give them credit they had a replacement ready by the time I
was going home that evening. They brought it on a breakdown truck, so
evidently they decided that the fault sounded so bad that they weren't going
to risk driving the original car back to base.

Since that is the last auto car I've driven, apart from a loan car from a
garage which was just a mile or so from garage to home and back, it's easy
to remember that bad experience. I have to keep reminding me that it was a
freak and that not *all* autos are like that :-) But they do tend to be too
sensitive to slight throttle increase triggering an downchange, in a
situation where in a manual I'd hold onto the present gear and simply apply
more power, rather than changing down half-way through the acceleration. I
suppose if you drive a car enough you get used to its quirks and manage to
make sure the downchanges occur before or after acceleration, and never
during.

[Nick Finnigan]

On 09/10/2018 18:58, NY wrote:
> I'd love to drive an electric car which has just one fixed ratio and a
> motor which can give constant acceleration over a wide range of road speeds
> (subject to an artificially-limited maximum as you are setting off from
> rest to avoid wheelspin), and maybe subject to a controlled reduction as
> you come off the power rather than a very sudden transition from positive
> acceleration to no acceleration (and in fact slight deceleration due to
> friction and air resitance).

I've followed a couple of Leafs (on NSL single carriageways) and the
drivers showed far more enthusiasm than most drivers on those roads.
The performance was indistinguishable from me staying in second gear with
my foot to the floor (lighter petrol car with similar peak power). And I
already have a controlled reduction as I come off the power.

[TMS320]

On 09/10/18 20:42, NY wrote:

> Since that is the last auto car I've driven, apart from a loan car from
> a garage which was just a mile or so from garage to home and back, it's
> easy to remember that bad experience. I have to keep reminding me that
> it was a freak and that not *all* autos are like that :-)  But they do
> tend to be too sensitive to slight throttle increase triggering an
> downchange,

They are not "too sensitive".

> in a situation where in a manual I'd hold onto the present
> gear and simply apply more power,

If the engine can deliver more power in the current gear, an auto
doesn't shift down. Perhaps you have a lead foot and rely on having the
point in the accelerator travel where the engine limits?

[TMS320]

On 09/10/18 18:58, NY wrote:
> "TMS320" <dr6...@gmail.com> wrote in message
> news:ppf8fb$fbv$1...@dont-email.me...
>> On 06/10/18 18:52, NY wrote:
>>> "TMS320" <dr6...@gmail.com> wrote in message
>>> news:ppagmt$b3a$1...@dont-email.me...
>>>> Contrast to a CVT transmission which is bound to do the right thing
>>>> unless it needs to push the engine beyond 6000rpm.
>>>
>>> My experience of CVTs, as a passenger in a DAF and a Volvo, is that
>>> they choose a very low ratio and rev the engine very high, long after
>>> a conventional automatic or a competent manual driver would have
>>> changed up progressively through the gears.
>>
>> If your experience of CVT is from a Daf, things have moved on
>> somewhat. Even though the principle is the same, the mechanical
>> implementation is totally different and the ratio is electronically
>> determined.
>>
>> Performance and economy are better than from a competent manual driver
>> and there is no hesitation and lurching on undulating roads, as with a
>> stepped auto. Some people just don't like the way the the revs are
>> adjusted to driver power demand (lowest to meet demand), rather than
>> being linked to road speed.
>
> The ultimate aim of any transmission is that the position of the
> accelerator is directly proportional either to car acceleration or
> speed,

Sort of. The accelerator controls power. The transmission is to broaden
the engine's range.

> without the intervening uncertainty of variable (continuous or
> stepped) gear ratios.

Any uncertainty in an auto is down to the parameters the engineers embed
in the shift mapping.

What should happen is that when the engine can deliver the power you
want in the next gear it should change up. When it can't deliver the
power you want in the current gear it should change down. For various
reasons it can't be done perfectly.

> In a manual, you control when the gear change will
> occur so can compensate for this in that you learn how much to increase
> or decrease the accelerator position as you change gear, both to account
> for the different engine speed required in the new gear and the greater
> acceleration in a lower gear as the mechanical load on the engine is lower.
>
> I find that I press the accelerator to a certain position to get a
> desired acceleration in the gear that I'm in, and auto transmissions
> foul this up by changing down at some unspecified point during the
> acceleration, requiring me to back off the power to avoid unexpected
> surge in acceleration.

Yes, that is often the result with a stepped auto due to the mapping
issue above. They work ok if you what a step increase in power but they
don't work satisfactorily when gradually moving the accelerator on
undulating roads.

This is why I find a CVT so much nicer.

> I suppose in a manual I'm used to choosing a gear that will give me
> reasonable acceleration so I can go from the minimum speed that I've
> gone down to on a roundabout to the point at which I plant to level out
> my speed. It may take more that one gear to cover that range, but I will
> level out the acceleration briefly either side of the gear change so I'm
> not changing *during * acceleration - one of the things that they don't
> teach but which gives smoother driving.

Ummm... a manual inherently has an interval without drive for as long as
you keep the clutch disengaged. The revs will rise if you don't lift.

> I'd love to drive an electric car which has just one fixed ratio and a
> motor which can give constant acceleration over a wide range of road

> speeds...

An electric motor is no different in delivery to an ice, clutch, gearbox
combination except for refinement of operation.

[NY]

"TMS320" <dr6...@gmail.com> wrote in message

news:ppjd48$mpt$1...@dont-email.me...

I aim to keep my engine revs in the range 1000-2500 (it's a diesel), and
select an appropriate gear. But I try to make sure that I select the right
gear *before* starting to accelerate, and then change up when I've finished
accelerating, apart from when going directly from 0 - 60 when obviously
several gearchanges are required, but I ease off the power for each
gearchange so I'm changing with the car briefly at a constant speed - makes
for smoother changes. What I try at all costs to avoid (and automatics
don't) is a gearchange half-way through acceleration, because that's when
you notice the change in acceleration if the car changes down unexpectedly
and I have to back off the power to keep the acceleration constant.

I doubt whether I've ever hit the rev limiter - apart from one case when I
pulled out from a side road and a car appeared which I'm sure wasn't there
as I set off - so I used maximum boost to get up to speed as fast as
possible to avoid him having to brake too hard. For a moment, his car
disappeared in a cloud of black smoke from my exhaust :-)

[NY]

"TMS320" <dr6...@gmail.com> wrote in message

news:ppjd49$mpt$2...@dont-email.me...

> Ummm... a manual inherently has an interval without drive for as long as
> you keep the clutch disengaged. The revs will rise if you don't lift.

Yes, I'm assuming that during the gearchange I will lift off the power so
the engine doesn't race under the brief no-load condition and so it will be
at the right speed for the new gear. I'm not perfect at rev-matching, but a
damn sight better than people who release the accelerator totally, let the
clutch up on an idling engine and then accelerate (*).

>> I'd love to drive an electric car which has just one fixed ratio and a
>> motor which can give constant acceleration over a wide range of road
>> speeds...
>
> An electric motor is no different in delivery to an ice, clutch, gearbox
> combination except for refinement of operation.

Except that with only one ratio, there will be no discontinuities so the
acceleration of the car will be more similar to that of the motor, and with
good control electronics the acceleration of the car should be smooth and
fairly proportional to the accelerator position.


(*) I was once a passenger in a car driven by a woman who had been driving a
while (she was not newly-passed). She couldn't understand why her
gearchanges were so jerky (as if she'd briefly hit the brake), and kept
apologising for her car. I said nothing, though I thought I knew why, but
when she later asked for my advice, I suggested that she might try keeping
the engine revs constant as she pressed the clutch, rather than taking her
foot right off the accelerator, and then either pressed it a bit further
(when changing down) or released it slightly (when changing up) to match the
engine the new gear. I'll never forget her look of delight when she managed
it and the gearchange was smooth. I reckon she'd never been taught properly
(or at least, the instructor had never corrected her habit) and she didn't
know any different.

[TMS320]

On 10/10/18 09:21, NY wrote:
> "TMS320" <dr6...@gmail.com> wrote in message
> news:ppjd48$mpt$1...@dont-email.me...
>> On 09/10/18 20:42, NY wrote:
>>
>>> Since that is the last auto car I've driven, apart from a loan car
>>> from a garage which was just a mile or so from garage to home and
>>> back, it's easy to remember that bad experience. I have to keep
>>> reminding me that it was a freak and that not *all* autos are like
>>> that :-)  But they do tend to be too sensitive to slight throttle
>>> increase triggering an downchange,
>>
>> They are not "too sensitive".
>>
>>> in a situation where in a manual I'd hold onto the present gear and
>>> simply apply more power,
>>
>> If the engine can deliver more power in the current gear, an auto
>> doesn't shift down. Perhaps you have a lead foot and rely on having
>> the point in the accelerator travel where the engine limits?
>
> I aim to keep my engine revs in the range 1000-2500 (it's a diesel), and
> select an appropriate gear. But I try to make sure that I select the
> right gear *before* starting to accelerate, and then change up when I've
> finished accelerating, apart from when going directly from 0 - 60 when
> obviously several gearchanges are required, but I ease off the power for
> each gearchange so I'm changing with the car briefly at a constant speed
> - makes for smoother changes.

Your description of what you do sounds awful.

An up change with an auto is smooth. If you're not going all out all
that happens is that the revs drop but the power remains the same. On
mine, there is a 2:1 rev change between 1st & 2nd and even if I'm going
all out I don't notice the effect of the 40% drop in power.

> What I try at all costs to avoid (and
> automatics don't) is a gearchange half-way through acceleration,

An auto doesn't shift down "half-way through acceleration" unless *you*
press the pedal harder. The ability to do a down shift with the pedal
hard down is a virtue.

> because
> that's when you notice the change in acceleration if the car changes
> down unexpectedly and I have to back off the power to keep the
> acceleration constant.

Acceleration is proportional to power/(speed x mass). The accelerator
pedal controls power.

[Kenji Takemoto]

Em sexta-feira, 5 de junho de 2015 às 09:03:15 UTC-3, NY escreveu:
> My understanding was that cruise controls only control the throttle position
> and so a car that is set to (for example) 70 mph may exceed this speed going
> down a hill if it is so steep than the car would speed up if CC was turned
> off and you lifted right off the throttle. There are plenty of threads on
> forums about "why does my car speed up going downhill with the CC turned on"
> which explain this.
>
> But are there any cars whose CC can also apply the brakes slightly to
> maintain a constant speed downhill if closing the throttle is not, on its
> own, enough to keep the vehicle in check? I know some cars have systems
> which apply the brakes slightly if they sense that you are gaining on the
> car in front and are getting very close; could those cars also use the same
> "apply the brakes slightly" technology in conjunction with the CC?
>

[Kenji Takemoto]

There is a eletric conection betwen cruise control and gear box module, if the speed is over speed automaticly the over drive gear will be disable.

[NY]

"Kenji Takemoto" <kenta...@gmail.com> wrote in message
news:aad9d702-67a1-40f7...@googlegroups.com...

I've not encountered a CC which changes down (disables the overdrive gear)
if the car goes over the speed that it is set at. Maybe that is something
that only happens with automatic - and the only cars I've driven with CC
have all been manuals. Indeed with the Honda CR-V, if you press on the
accelerator you can exceed the speed that is set on CC: useful if you need
to overtake. Once you take your foot off the accelerator, the car returns to
the speed that CC is set to.

In answer to my own earlier question about the speed limiter (but not the
CC) working below 30 mph, I've now found that the answer is "yes". Both a
Peugeot 208 and a Honda CR-V will allow the speed limiter to be set to (for
example) 20 mph and will enforce that speed, but they won't let you set a
cruise speed below 30.

[Recliner]

With my 13-year-old car, the automatic gear box obviously changes up and
down while under cruise control, and the brakes are also applied if the car
in front slows. Basically, you set the adaptive cruise control on entry to
a motorway or continuous A road, and don't touch the pedals until you exit.
You can adjust the target speed with buttons on the steering wheel.

If traffic speeds drop really low (below 20mph), the computer hands back
control (more modern versions will go right down to zero and back up again
when the traffic moves).

[victoria...@gmail.com]

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