georgahti kirjoitti:anteeksi tyhmä kysymykseni, mutta miten kitkakertoimen mukaan määritetään Nm maksimi moottorilta? vai meneekö se sittenkin kW:ien puolelle???
olen tosi apina ja ymmärrän vain kiihtyvyyskäyrän seuraavan vääntökäyrää, mutta tehokäyränkin on meikäläisen mukaan jotenkin vaikutettava tulokseen (vai onko taas kyseessä tulo väännöstä ja nopeudesta ( plus massa, ilmanvastus, jne ) ?? ) ?
hieman OT, mutta luulenpa muutamankin (vähäjärkisemmän) täällä pohtivan samaa asiaa (noin suunnilleen...).....
Vaihdelaatikko kertoo kok.välityksen arvolla sinne tungetun momentin, muttei tehoa ja kun hv=Nm*rpm/7121 on sama kumman tehon vai väännön suhteen asioita haluaa mittieä. Momentti passaa itselle paremmin.
Jos lontoo taippu niin tässä reilu vuoden taikainen löpinä aiheesta
Often when one reads an internet discussion forums cars have a tendency to be rated by wheel power, or more like the peak wheel power figure which is then used to benchmark drivability. Also person who have limited experience of powerful FWD cars often shout out that a FWD with more than 200whp does nothing else than spins wheel etc.
To rate cars by their peak "whp" would of course not be a problem, if the power band for a motor would be "fixed" to a certain shape. Then the peak WHP value would just scale the curve up or down, but as we know in real this is not the case and the following tries to explains in more detail why and also how the whp, tq, gearing etc. link together.
Lets us first look at a bone stock Viggen which will roughly produce the following figures when put into a dyno (blue curves)
http://genuinesaab.com/gallery/albums/9 ... .sized.gif
and with stage III kit the power output is normally percentually lifted through out the rpm registry and resembles the red curves in the same picture.
The plain curves themselves may not open up to all, how the link to performance and traction and a good known approach is look into the calculated acceleration curves in various gears, since the limit of traction can be expressed as a function of acceleration [G's], normally around 0.5G for FWD cars.
For the bone stock Viggen the calculated acceleration curves are shown in the picture below as a function of speed [km/h]. The "height" difference in curves for different gears are due to gearbox, which multiplies the crank shaft Tq with the total gear ration (drive shaft Tq curves
www.stcf.net/slip/slip1.gif).
http://www.stcf.net/slip/slip2.gif
From the chart we can note the following.
1) acceleration in any given gear is the highest at peak tq rpm/speed, not at peak hp
2) tq from the bone stock motor is enough to spin wheels in 1st but in 2nd requires one to pop the clutch, a bump in the road etc. to get the wheel spinning, since steady state acceleration falls shy from the traction limit.
Lets us now add the stage III acceleration curves to the same plot and we get
http://www.stcf.net/slip/slip3.gif
And we can note that 2nd gear acceleration also exceed the traction limit and driving WOT in this gear will result to wheel spin on steady state. From the curves we can also see that for instance in 3rd gear the acceleration begins to fall quit heavily after 110km/h mainly due to std turbo which is beginning to run out of breath and by rev limit the reduction in acceleration is around 50%. It should be remembered that in modern turbo cars the turbo is mainly used to up the low/mid rpm torque and not the peak whp. This is easy to understand when its known that an N/A engine can produce up to 100Nm/liter, 100bhp a liter, meaning that if the Viggen would be without tbo figures would read 230Nm/230hp at the best. Also turbos have quit a narrow operation range, and if the unit has been chosen to kick in around 2000rpm it will not carry effectively past 5k rpm. Anyhow there isn't much that can be done to raise the Tq curve and higher rpm's without modifying the Hw, but if wanted more "grunt" can be taken into use in the are where the stage III tq curve is "flat". Personally drove around in the early days with a "balls-out" stage IIIx and its curves print out in the same plot as follow
http://www.stcf.net/slip/slip4.gif
from the curves we can note that the lower rpm grunt was increased over a "normal" stage III and 3rd gear pushed closer to the traction limit. This type of tune creates the feeling that the car has lots of power, but when run up the gears one does not use the rpms where the extra Tq was obtained, so no improvement in that type of go.
At this point based on the curves we do see that 2nd gear traction has already been lost with the raised tq but 3rd gear there is plenty of marginal to work with until you begin to spin the wheels on steady state acceleration. So lets swap some HW and move on to a 350+whp set-up (my ex. 3071 with std cams etc, dynoed to 412hp/527Nm)
http://www.stcf.net/slip/slip5.gif
Thus the whp increased by 100whp or so it did change much in terms of traction since the Tq did not exceed the tq max. obtained with the stage IIIx set-up. From the graph we can however note that acceleration when running up the gears was greatly improved by moving the rpm registry upwards, but since tuning is a newer ending process the request was for more.
Often when you move forward from this type of bhp level the restriction in the engine HW will begin to pop up (cams, tbo etc) and if not taken care of the breathing at higher rpms will be limited and will set the roof how high the whp can raise. Of course if the tbo is of good side and you just keep upping the boost you can get the "big" peak numbers like in this manner
http://genuinesaab.com/gallery/albums/E ... n9_001.gif
but drivability due to high tq will not be the greatest not the running up the gear performance since the higher rpm grunt is missing.
Next up are the curves in the same plot form my 500bhp set-up and they print out as follow against the 412hp curves. Tq in this set-up was mapped against traction limit in 3rd gear
http://www.stcf.net/slip/slip6.gif
So with bhp once more lifted by nearly 100whp the 3rd acceleration curves remain beneath the traction limit, but instead of just "touching" the limit at 100km/h the remain close to it for a much broader rpm/speed range, but as we can note there still is margin to go at higher rpm's where the GT3071 was inadequate to pump enough air anymore. So Hw swap once more to current Holset Hx40 set-up and those curves plotted in same graph.
http://www.stcf.net/slip/slip7.gif
And with this set-up so far the tq in the mid range has been limited to same figures as before, but up at higher rpms raised and from the curves we can see that the acceleration lies at traction limit from 100km/h to 150km/h J and the aim is to have it carry on all the way to 170km/h (7k rpm).
Comparison of the current to std Viggen
http://www.stcf.net/slip/slip8.gif
and we do note that the all day drivability on WOT has not suffered that much, thus more than double whp. In first the Holset set-up provides more tq to drive shaft from 30km/h, and in second 55km/h, in 3rd 85km/h and in 4th 110km/h .
All torque curves and rpm vs. speed for all of the set-ups
http://www.stcf.net/slip/slip9.gif