A question about cruise control that's been puzzling me for some time...
On my Rover75 2.5, I can set the cruise control for 70mph on a nice flat motorway or good A-road, & the engine will quite happily sit for hours at 2,800rpm.
If I go up a very steep, long hill (eg. Lindale hill on the A590 for any fellow Cumbrians), you would think the engine would have to work a lot harder to maintain the same speed.
So, my question is this - why does the rpm not increase at all??
I'm sure it's a really obvious answer!
Neil.
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Because if it did then your speed would increase rather than stay at a constant 70.
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In a manual gearbox with a fully engaged clutch, or an automatic gearbox with a locked torque converter (as many now have) engine speed is directly proportional to road speed.
When you get to a hill, the throttle will open further, and the engine will consume more fuel and air, but the engine revs will stay the same for the speed in question. When the point is reached that the engine cannot produce enough power to maintain the speed you have set (ie the throttle is fully open), the car will then start to slow down. Again though, revs and road speed will fall together.
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In a manual gearbox with a fully engaged clutch, or an automatic gearbox with a locked torque converter (as many now have) engine speed is directly proportional to road speed. When you get to a hill, the throttle will open further, and the engine will consume more fuel and air, but the engine revs will stay the same for the speed in question. When the point is reached that the engine cannot produce enough power to maintain the speed you have set (ie the throttle is fully open), the car will then start to slow down. Again though, revs and road speed will fall together.
Perfectly put!
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On turbo charged vehicles with cruise control and a boost guage you can see this happening...
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On turbo charged vehicles with cruise control and a boost guage you can see this happening...
And likewise for any car with an instantaneous fuel consumption readout.
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Perfectly put!
Thank you.
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And if you have neither a boost gauge nor a fuel consumtion readout you can actually feel/see the accelerator pedal moving.
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And if you have neither a boost gauge nor a fuel consumtion readout you can actually feel/see the accelerator pedal moving.
The pedal does not move on my Mondeo.
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I just knew that after pressing enter on that post there would be cars out there with pedals that don't move. 8-) Drive by wire throttle?.
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Drive by wire throttle?
Yup, like my V70, and an increasing number of other cars. The pedal stays put, and ECU reactions and response are so rapid that to all intents and purposes, the speed stays totally constant.
This is unlike the V40 2.0T pool car that I sometimes drive when at our Swedish HQ. This car has a conventional throttle setup, and as well as the pedal moving exactly as would happen if controlled by driver's foot, the speed wanders around too when the road is anything except dead level, on a still day.
I find the only downside of drive by wire to be absolute fine motor control when crawling gently in stop start traffic, or performing a tricky manoeuvre in snow or on ice. In this context, you still can't beat a throttle cable and counterloaded spring.
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Ahh, but your V70 and Cheddars Mondeo Ghia have instantaneous fuel consumption readouts and my post clearly stated that in cars that *do not* have these, the pedal can be seen to move. 8-)
I gave up too easily before.
Yes I am that pathetic. 8-)
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Use to muse this in the 330, I'd watch the econometer swing violently to cope with hills and that but revs and speed would stay relentlessly the same. (but no doubt some lane hogging no brainer would spoil my fun)
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I've tried looking at the pedal to see it move on my Mondeo but I can assure you this is very dangerous as you seem to head for the offside ditches!! Needs practise first!
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I once got my foot trapped under the pedal in my previous car - that was scary!
--
\"Nothing less than 8 cylinders will do\"
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Ahh, but your V70 and Cheddars Mondeo Ghia have instantaneous fuel consumption readouts and my post clearly stated that in cars that *do not* have these, the pedal can be seen to move. 8-) I gave up too easily before. Yes I am that pathetic. 8-)
No the Mondeo does not have an instant readout, just an average.
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No the Mondeo does not have an instant readout, just an average.
Hmmm, any Mondeo new or old with a trip computer will have instant mpg readout as well as average, worth checking again..
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Hmmm, any Mondeo new or old with a trip computer will have instant mpg readout as well as average, worth checking again..
I can assure you it doesn't the functions are outside temp/ ave mpg / ave speed / range. All can be changed to metric. I had a Vectra that had the addition of instant mpg, useful to try to drive economically, needed it with 2.5 V6.
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No the Mondeo does not have an instant readout, just an average.
Seems like it might be different with the diesels then - my petrol Mondeo certainly does have an instant readout. Horrible thing it is, especially when it shows single figure MPG :D
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>> And if you have neither a boost gauge nor a fuel >> consumtion readout you can actually feel/see the accelerator pedal moving. >> The pedal does not move on my Mondeo.
Which Mondeo do you have? The pedal certainly moves on my Mondeo, a Mk2 Ghia X. It's a tad disconcerting at first!
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>> >> And if you have neither a boost gauge nor a >> fuel >> >> consumtion readout you can actually feel/see the accelerator pedal moving. >> >> >> >> >> The pedal does not move on my Mondeo. Which Mondeo do you have? The pedal certainly moves on my Mondeo, a Mk2 Ghia X. It's a tad disconcerting at first!
'02 Ghia X TDCi
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>> And if you have neither a boost gauge nor a fuel >> consumtion readout you can actually feel/see the accelerator pedal moving. >> The pedal does not move on my Mondeo.
It does on my V6 Mondeo (cable operated throttle).
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What year is your mondeo? I had a hire one 2004 and it's pedal moved.
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In a manual gearbox with a fully engaged clutch, or an automatic gearbox with a locked torque converter (as many now have) engine speed is directly proportional to road speed. When you get to a hill, the throttle will open further, and the engine will consume more fuel and air, but the engine revs will stay the same for the speed in question. When the point is reached that the engine cannot produce enough power to maintain the speed you have set (ie the throttle is fully open), the car will then start to slow down. Again though, revs and road speed will fall together.
With an auto box the revs will indeed rise if it changes down to maintain the chosen speed. The box will only stay locked if it can maintain the speed in top.
--
\"Nothing less than 8 cylinders will do\"
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My car has cruise control - SWMBO cries "You're going too fast!"
I also have DNOINS (DO not overtake its not safe) Fortunately, for this I have an over-ride button.
I also have TINWYWGITPS! (Something to do with parking.)
I always win.
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I also have TINWYWGITPS! (Something to do with parking.)
T?
I?
N?
Why you won't get into that parking space?
Any good?
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Espada III - well if you have a family and need a Lamborghini, what else do you drive?
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There is no way you'll get into that parking space!!
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#2 - there is no way that you will get into that parking space
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The first one is right, Humpy, 'cos it includes the exclamation mark.
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