kr79:
Nothing scientific but I’ve been on the same job all afternoon using the p mode it chose the same gears but ran the revs up to 1900 before changing. Slightly quicker to 50 than economy mode. Tried changing manually using all gears at about 1300 rpm. Remember I shift is lightning fast quicker than any driver on a fuller and won’t miss a cog and all I did was make noise and not a lot of progress I was doing just over 30 where I was doing 50 driving normaly.
I have a feeling carryfasts way is how a diesel engine works on paper and would be fine in a peice of static machinery or a boat but in real life on the road where lots of other factors come in to play its not quite the same.
This is superb stuff, kr! One minute we’re arguing the theory, the next we have the results of a practical set of tests. Brilliant!Any chance of measuring fuel consumption and journey time (for the same route, ideally, but any information is good)?
I assume, when using Economy mode, you are accelerating with the accelerator fully depressed?
I would be interested to see what happens if, when accelerating from rest (or a low speed), using
Manual, you take it to 1900rpm, then change into the highest gear you would consider using- say, the one that gives around 900-1000rpm. In other words, accelerating using full “throttle” (they don’t have throttles, but what do you say? Full rack? Full pump? Full welly? ), but using the minimum number of gearchanges you can get away with.
I normally do the same run first thing every morning from hackney to Romford tip then down to barking empty I fueled up tonight and can refuel in our other yard at barking and was planing on trying one day using economy as normal one day on power and one day carry fasts theory of peak tourqe and change up. It’s a good route as it takes in some a roads and urban driving too.
I don’t know if you are familiar with I shift but if you aint there’s an arrow display telling you how many gears you can change up or down at a time. I do use the manual off road and ocasionly on road to hold a gear or the odd change but il try what you say and let you know how it performs.
kr79:
Nothing scientific but I’ve been on the same job all afternoon using the p mode it chose the same gears but ran the revs up to 1900 before changing. Slightly quicker to 50 than economy mode. Tried changing manually using all gears at about 1300 rpm. Remember I shift is lightning fast quicker than any driver on a fuller and won’t miss a cog and all I did was make noise and not a lot of progress I was doing just over 30 where I was doing 50 driving normaly.
I have a feeling carryfasts way is how a diesel engine works on paper and would be fine in a peice of static machinery or a boat but in real life on the road where lots of other factors come in to play its not quite the same.
This is superb stuff, kr! One minute we’re arguing the theory, the next we have the results of a practical set of tests. Brilliant!Any chance of measuring fuel consumption and journey time (for the same route, ideally, but any information is good)?
I assume, when using Economy mode, you are accelerating with the accelerator fully depressed?
I would be interested to see what happens if, when accelerating from rest (or a low speed), using Manual, you take it to 1900rpm, then change into the highest gear you would consider using- say, the one that gives around 900-1000rpm. In other words, accelerating using full “throttle” (they don’t have throttles, but what do you say? Full rack? Full pump? Full welly? ), but using the minimum number of gearchanges you can get away with.
I tried flooring the accelerator on the MAN auto i had on hire ,that was after trying to get the thing to go with gentle acceleration all that happened was it revved round the clock and i ended up changing up manually ,only thing i was thinking was how much fuel i was wasting , it wasnt something i tried again
kr79:
I normally do the same run first thing every morning from hackney to Romford tip then down to barking empty I fueled up tonight and can refuel in our other yard at barking and was planing on trying one day using economy as normal one day on power and one day carry fasts theory of peak tourqe and change up. It’s a good route as it takes in some a roads and urban driving too.
I don’t know if you are familiar with I shift but if you aint there’s an arrow display telling you how many gears you can change up or down at a time. I do use the manual off road and ocasionly on road to hold a gear or the odd change but il try what you say and let you know how it performs.
Your idea of testing Power versus Economy modes, on two separate full days’ work, seems the best test to try. My suggestion of using the fewest gearchanges possible, with the maximum use of the useable revs, is an extreme test. The same applies to the “use every gear and keep it in the middle of the green” method. It will be really interesting, to see what you find. Who needs the roadtests in the comics- we can do it ourselves!
I have been following this thread with great interest and I feel I may be able to contribute something on the matter of fuel economy.
As stated earlier I have driven an auto for sometime ,mainly the I-shift but also the MAN Tipmatic. In both cases when the trucks arrived, factory trained drivers came to give us the gen on how to get the best from them, and in both cases a light foot was stressed and also to use the terrain so that you could either run in a higher gear ( which it chose itself )or let it run in Eco-Roll , this facility isn’t available , or wasn’t ,on the MAN’s(Paddies Overdrive to us older drivers, but controlled by electronics. Get the right roads e.g. Windy Hill going over the M62 and you can roll for miles on tickover). If you use more throttle it will hold the gear longer and use revs which may not be necessary.Sometimes, using their methods, progress can be a bit pedestrian. but they are preaching fuel economy , not race track driving.
One big factor that they preached ,and any one of us older generation who has served time on Gardners will be familiar with , is forward observation, keep it rolling because you use the most fuel and energy to set off and get back up to speed. I must admit that I had a slight resentment at being told how to drive after all the years I’ve been at it, but listen and learn and after a while I found myself using a lot of what they had told me. With a bit of mix and match you can still achieve good times with good fuel economy.
ramone:
I tried flooring the accelerator on the MAN auto i had on hire ,that was after trying to get the thing to go with gentle acceleration all that happened was it revved round the clock and i ended up changing up manually ,only thing i was thinking was how much fuel i was wasting , it wasnt something i tried again
I am wondering whether these automatic things have some sort of “kick-down” feature built into the pedal travel, which allows you to get full load/torque without fully depressing it, then flooring it simply raises the point at which it changes up a gear. What happens, when accelerating between 1000 and 1500rpm, when you floor it, and then repeat the exercise using, say, three-quarters “throttle”? Is there a point in the pedal travel, where more travel has no effect on the discernable grunt of the engine? Can you feel any sort of “detent point” in the pedal?
ramone:
I tried flooring the accelerator on the MAN auto i had on hire ,that was after trying to get the thing to go with gentle acceleration all that happened was it revved round the clock and i ended up changing up manually ,only thing i was thinking was how much fuel i was wasting , it wasnt something i tried again
I am wondering whether these automatic things have some sort of “kick-down” feature built into the pedal travel, which allows you to get full load/torque without fully depressing it, then flooring it simply raises the point at which it changes up a gear. What happens, when accelerating between 1000 and 1500rpm, when you floor it, and then repeat the exercise using, say, three-quarters “throttle”? Is there a point in the pedal travel, where more travel has no effect on the discernable grunt of the engine? Can you feel any sort of “detent point” in the pedal?
There`s a kick down feature on the Scanias because we had ours disconnected ,1 driver came in 1 afternoon and announced that those new Scanias were crap because they kept changing between 11th and 12th when flat out ,i think the Dafs and MANs have kickdown too .I mentioned earlier that i had tried different styles of driving the Dafs and MANs ,i tried feathering the accelerator and sometimes they would skip through the box ,but the next time i would end up either changing up manually ,or have to press the accelerator hard which achieved high revs and eventually a higher gear ,very frustrating
newmercman:
I have done a test of sorts on one particular climb that some of you may know, it’s heading north from Baker (home of the Worls’s largest thermometer) on I-15 in California towards Las Vegas. The climb is one of 16 miles and it starts out as a bit of a drag, then gets steeper and steeper all the way to the summit. Driving up there downshifting at 1100rpm and splitting gears I end up in 6lo, so that’s five gearshifts, but as the gradient changes there’s a bit of tooing and froing between 6hi and lo along the way, my fan kicks in after the shift down into 7hi and my EGT (Exhaust Gas Temperature) climbs from 600c to 1000c, the truck has worked very hard pulling this hill and the turbos are pushing over 60psi of boost. The other method, and the one I use everytime now, is to split down to 8lo immediately before the climb, then as soon as the rpms drop below 1400 I change down to 7lo and keep my foot flat to the floor, the turbos fluctuate between 30 and 60psi, the EGT never climbs above 800c and I’m 10mph quicker at the top. MY indash instant mpg readout drops to 3.1mpg against the 2.6mpg minimum when doing it the other way and with just a flick of a switch and a single gearshift, it’s a ■■■■ sight easier on the driver
From this account, it sounds like your engine has a definite “lousy spot” below 1400rpm, where it is less efficient than at higher engine speeds. On a hill like that, wind resistance is only a small part of the total drag and, since energy=force x distance and the rolling and climbing forces are constant with respect to speed, speed is relatively unimportant, as regards MPG. Your method of getting up as quickly as possible seems to benefit fuel use and journey speed.
ramone:
There`s a kick down feature on the Scanias because we had ours disconnected ,1 driver came in 1 afternoon and announced that those new Scanias were crap because they kept changing between 11th and 12th when flat out ,i think the Dafs and MANs have kickdown too .I mentioned earlier that i had tried different styles of driving the Dafs and MANs ,i tried feathering the accelerator and sometimes they would skip through the box ,but the next time i would end up either changing up manually ,or have to press the accelerator hard which achieved high revs and eventually a higher gear ,very frustrating
Sounds like these vehicles change their gearchange “regime” according to the position of the pedal, which means you have to memorise how hard to press, if you want it to perform consistently. This may be a compromise to account for the practices of rotten drivers. I guess the only solution is to floor it and change up manually, when accelerating. At least then, you can choose the change-up point, and how many gears you want to skip.
There is no flat spot below 1400rpm, it will hold on down there very well, it will pull down to about 900rpm where the instant mpg reading climbs up into the low 4s, but the EGT goes through the roof and she starts to cough black smoke (unburnt fuel) out of the chimneys, so I don’t often go down that far. The reason I change down at 1400rpm is to get the revs up to 1800rpm so I can power up the climb with 800rpms of torque rise to help me out
The art of getting good journey times and good economy is really very simple…momentum
This is why, as Bassman said, the quality of a driver’s skills can make a difference, you don’t need to concentrate on getting the maximum from every last drop of fuel, just keep her rolling and the rest looks after itself, this way is also much kinder to tyres and the driveline and is nowhere near as tiring for the driver
On the subject of change up points, the AMTs will change gear according to engine load, so if you’re feathering the throttle it knows that you’re not demanding full load, so will change up early, which demonstrates that even the gearbox knows that if you require full ‘throttle’ you want to get down the road quickly, in that case it hangs out the gearchanges, so that blows Carryfast’s theory completely out of the water, after all, the primary objective of the AMT is to maximise efficiency
kr79:
Nothing scientific but I’ve been on the same job all afternoon using the p mode it chose the same gears but ran the revs up to 1900 before changing. Slightly quicker to 50 than economy mode. Tried changing manually using all gears at about 1300 rpm. Remember I shift is lightning fast quicker than any driver on a fuller and won’t miss a cog and all I did was make noise and not a lot of progress I was doing just over 30 where I was doing 50 driving normaly.
I have a feeling carryfasts way is how a diesel engine works on paper and would be fine in a peice of static machinery or a boat but in real life on the road where lots of other factors come in to play its not quite the same.
Unless you’re driving a Scania 730 upshifting at less than 1,400 isn’t exactly what I’ve been saying and even 1,400 would probably only apply in the case of something like a 620.The shift point isn’t ‘peak torque’ either it’s all about extracting as much work as possible from the ‘top part’ of the torque ‘curve’ (more like plateau in the case of the 730 etc) which usually means a bit more than just taking it up to 1,300 rpm.But I wouldn’t like to be paying for the fuel if you follow ZB’s idea and/or that 1,900 rpm upshift point regularly.
newmercman:
Carryfast it’s simple to understand No really it is
Now, go back and look at the SFC graph posted by [ZB] who does get it
From 1050-1500 rpms the torque is high and the fuel consumption is good, that gives you a 450rpm window, which will allow a full gear shift, so shortshifting will achieve nothing except one thing…
It will use more fuel
If you draw a graph to show the time taken for a lorry to reach cruising speed from rest it will not be a linear line, but will have a saw tooth effect, this will come from changing gear, the lorry stops gaining forward motion and slows down. Are you with me so far
Put simply you will lose 3mph of speed for each gearchange, this speed has to be recovered in order to reach cruising speed, the way a lorry does this is by using more fuel and taking more time
If you change gear 8 times on the way up to speed by using full gearshifts you lose 24mph If you change gear 16 times on the way up to speed by using splitshifts you lose 48mph which must be recovered to reach cruising speed
So, in your infinite wisdom, please tell me how throwing 48mph away is going to be more efficient
Firstly I don’t think that I’ve said use 16 upshifts to even get a 2800 up to 60 mph maybe because it only had 12 of which around just 10, at most,were enough to get the job done.
If it’s dropping 3 mph over the time it takes to upshift a decent box then who needs brakes just declutch the thing and let it roll to a stop. It might not sound much but I certainly don’t remember losing 3 mph over the time it took to declutch any box although the 16 speed synchros probably came closest to it.
But.That’s not the same thing as starting off from rest on a long incline at 36-44 t gross,maybe more in some circumstances,when you’re going to burn more fuel and lose more momentum by running the thing up to peak power at each upshift and then waiting for the revs to drop down low enough to make use of the torque before you can put it into the next gear up using that whole gears only idea.But if I read it right ZB didn’t say anything about upshifting at 1,500 unless that’s where ‘peak power’ is on the truck he’s referring to in his theory.In which case it’s going to need to be something ( a lot) better than a Scania 730 which would still need around 1,900 rpm to reach that and it’ll be running at a lot more than 56-65 mph when it reaches top gear at those revs.Just don’t look at the fuel gauge after it’s done that a few times.
The “normal” method- 2,4,6,8,10,12. Five gearchanges (1700rpm drops it back to around 1040rpm).
The “reduced gearchanges” method- 2,5,8,11,12. Four gearchanges (2000rpm drops it back to around 960rpm).
The “reduced gearchanges, careful with the clutch” method- 3,6,9,12. Three gearchanges as in 2. above.
The “reduced performance, waste fuel, accelerated gear linkage wear” method. Use every gear. (1500, 1170rpm).
Of course, any combination of these is possible. These US spec sheets recommend a cruising engine speed of 1350rpm.
The “normal” method- 2,4,6,8,10,12. Five gearchanges (1700rpm drops it back to around 1040rpm).
The “reduced gearchanges” method- 2,5,8,11,12. Four gearchanges (2000rpm drops it back to around 960rpm).
The “reduced gearchanges, careful with the clutch” method- 3,6,9,12. Three gearchanges as in 2. above.
The “reduced performance, waste fuel, accelerated gear linkage wear” method. Use every gear. (1500, 1170rpm).
Of course, any combination of these is possible. These US spec sheets recommend a cruising engine speed of 1350rpm.
So you’re saying that 2. reduced gearchanges,let alone 3. reduced gearchanges careful with the clutch,is going to be the most economical .
Or 5. just leave it in manual and use it like a 13 speed Fuller and upshift it at around 1,500 rpm max ( in which case they could have just fitted the Fuller and kept it simple ) but there’s no harm in that case in putting some extra gears in the Fuller box for when you might need them But there’s no way that taking it up to 1,700 let alone 2,000 rpm at each upshift is going to save fuel whichever choice is used.Although it wouldn’t be hanging around if anyone did decide to considering the power output.
Carryfast:
So you’re saying that 2. reduced gearchanges,let alone 3. reduced gearchanges careful with the clutch,is going to be the most economical .
Or 5. just leave it in manual and use it like a 13 speed Fuller and upshift it at around 1,500 rpm max ( in which case they could have just fitted the Fuller and kept it simple ) but there’s no harm in that case in putting some extra gears in the Fuller box for when you might need them But there’s no way that taking it up to 1,700 let alone 2,000 rpm at each upshift is going to save fuel whichever choice is used.Although it wouldn’t be hanging around if anyone did decide to considering the power output.
I reckon, for the purposes of acceleration, changing up at 1500-1700rpm and skipping one gear will probably be what the I-shift does, automatically, although kr79 et al will know better. I also reckon that, in manual, the reduced gearchanges method will give good fuel consumption and save some time. This is based on the SFC graph for the Scania engine I found. I can’t find a similar graph for the Volvo engine, but they are usually of the same form. Your method is the same as no.4 in my list. It is rubbish.
Carryfast:
So you’re saying that 2. reduced gearchanges,let alone 3. reduced gearchanges careful with the clutch,is going to be the most economical .
Or 5. just leave it in manual and use it like a 13 speed Fuller and upshift it at around 1,500 rpm max ( in which case they could have just fitted the Fuller and kept it simple ) but there’s no harm in that case in putting some extra gears in the Fuller box for when you might need them But there’s no way that taking it up to 1,700 let alone 2,000 rpm at each upshift is going to save fuel whichever choice is used.Although it wouldn’t be hanging around if anyone did decide to considering the power output.
I also reckon that, in manual, the reduced gearchanges method will give good fuel consumption
Carryfast: Trust me it won’t.Especially with that D16 motor.
How do you know? What’s different about the D16?
All the theoretical factors have been discussed at length in the posts above, with manufacturer’s data to back it up. Numerous posts cite practical experience, yet you still ignore it all. Where do you get your information, that nobody else can see? Have a good read of this. It might keep you quiet for a day or two: 130.236.48.54/en/Publications/Li … 924_TS.pdf
For those who are interested, the report is some poor sod’s postgrad thesis on calculating the fuel consumption of a lorry.
On page 27, there is a graph of engine efficiency, similar to the one I posted earlier. It is not as detailed as the other one. I think he’s just nicked it out of the brochure. I think his lorry is a 124-420 Euro 2, but I can’t find anything in the report that mentions it. The photo shows it on five axles. He goes into great detail about his new model of rolling resistance- it’s about 7.3kgf/tonne GVW, with a tiny bit of variation with speed. I checked this against the old adage that it takes about 100bhp to overcome rolling resistance at 60-odd mph on a 40 tonner. Blow me- the result was almost exactly 100bhp!
Page 89 refers to turbo boost pressure during gearchanges.
well then anorak, common sence and teory are going hand in hand,as it should,cheers benkku,now going to change gears as before knowing i,m on right way.of couse visiting the pump has proved it to,
Trip one done. Loaded hackney tipped Romford empty to barking loaded to chingford empty to Hackney using full auto in economy mode got 8.38mpg. About to leave on same trip using power mode.
Those d16 Volvo lumps are not as powerful as you think in American spec, 550hp/2250lb/ft is as big as they get, my CAT will ■■■■ all over them and get better fuel figures in the process. Anyone who has run a 15ltr twin turbo CAT will tell you that economy is not their strong point
They’re also unreliable, mostly from unreliable emissions crap, but they love an injector cup too
I had a 610 FH16 for a couple of months before I came over here, it never impressed me at all, except for the badge and it had one of the worst gearchanges I’ve ever encountered, shift loads were very high and it was notchier than that awful EcoSplit from ZF, most unlike a Volvo gearbox
Carryfast your love of the Fuller does surprise me somewhat You had a 2800 with the ZF constant mesh box and then EPS Mercs, have you ever used a Fuller
Are you aware that the internals of the 13spd Fuller and the Volvo are identical They’re both constant mesh transmissions, one has electronic gubbins on top, one doesn’t, unless it’s the Eaton UltraShift, in which case it is a dreadful thing and is the ultimate boat anchor
), but using the minimum number of gearchanges you can get away with.
It might not sound much but I certainly don’t remember losing 3 mph over the time it took to declutch any box although the 16 speed synchros probably came closest to it.