Tweet
Siccome spesso ricorrono prove al banco e fattori di correzione, facciamo chiarezza una volta per tutte :
Se non volete leggere tutto che oltretutto è in inglese, i fattori più largamente usati sono DIN Ed EC. Sotto c'è un pezzo riassuntivo in italiano.
DIN corregge a 1013 mBar e 20°C (praticamente Al mare nella mezza stagione)
EC corregge a 990 mBar e 25°C (praticamente in collina primavera inoltrata)
************************************************** **
The majority of the charts you see here use certain correction factors to adjust the measured power of the bike on a given day under given atmosphic conditions, and adjust them to what they should be if tested at sea level. There are several horsepower correction factors you may see on these dyno charts. The most recognised are:
• SAE (Society of Automotive Engineers), USA. Power is corrected to reference conditions of 29.23 InHg (99 kPa) of dry air and 77 F (25°C). This SAE standard requires a correction for friction torque. Friction torque can be determined by measurements on special motoring dynamometers (which is only practical in research environments) or can be estimated. When estimates must be used, the SAE standard uses a default Mechanical Efficiency (ME) value of 85%. This is approximately correct at peak torque but not at other engine operating speeds. Some dynamometer systems use the SAE correction factor for atmospheric conditions but do not take mechanical efficiency into consideration at all (i.e. they assume a ME of 100%).
• STD or STP. Another power correction standard determined by the SAE. This standard has been stable for a long time and is widely used in the performance industry. Power is corrected to reference conditions of 29.92 InHg (103.3 kPa) of dry air and 60 F (15.5°C). Because the reference conditions include higher pressure and cooler air than the SAE standard, these corrected power numbers will always be about 4 % higher than the SAE power numbers. Friction torque is handled in the same way as in the SAE standard.
• ECE (European Community), Europe. The ECE standard is based on the European Directives. Power is corrected to reference conditions of 99 kPa (29.23 InHg) of dry air and 25°C (77 F). Friction torque is not taken into consideration at all.
• DIN (Deutsche Industrie Norm), Germany .The DIN standard is determined by the German automotive industry. Power is corrected to reference conditions of 101.3 kPa (29.33 InHg) of dry air and 20°C (68 F). With the advent of European legislation and standards, national standards such as the DIN (formerly widely used) are now less significant.
• Actual You may see this on some charts, especially from Ivan. What this means is this is the actual horsepower achived on the day tested and no correction factor has been applied. One can assume better or worse results with varying weather conditions.
************************************************** ***
Dyno Correction Factors
When you use the Dynojet software to graph dyno runs you get some options as to how you interpret the data. Because atmospheric conditions (ambient air temperature and pressure) affect air density they therefore affect power output. The influence of atmospheric variations needs to be accounted for in some way to make comparing dyno figures achieved under different conditions valid. There are international standards set down by organisations such as the SAE (Society of Automotive Engineers), the European Community and whoever is responsible for the DIN correction system (I’m not sure who that is, TUV maybe?) for this. Exactly how each standard does this is up to the body that puts it forward.
According to Edition 4 (1996) of the Bosch Automotive Handbook (an amazingly fact packed piece of literature) all the standards listed are the same save the DIN standard. The DIN 70 020 system uses a different ambient air pressure and temperature to the other standards – they use 1013mBar and 20 degrees Celsius as the nominal ‘zero correction’ conditions, whereas the SAE J1349, ISO 1585, JIS D1001 and EWG 80/1269 all use 990mBar and 25 degrees Celsius as the nominal conditions. The way the ambient pressure is measured is also different, with the DIN system using ‘absolute’ air pressure and the others using ‘dry’. As far as I can remember, ‘dry’ is ‘absolute’ with the vapour pressure subtracted, which is how relative humidity is accounted for. If I had a thermodynamics book on my bookshelf I’d be able to tell more, but for some reason I only have materials and mechanics/vibration books, which is odd given I majored in Fluid Mechanics and Thermodynamics.
The DIN system also uses a different equation, so it varies quite a bit.
The Dynojet software gives 4 correction options – SAE, STD, EEC and DIN. I haven’t seen the STD or EEC correction formulas, but the EEC gives a very similar result to the SAE system which I usually use. Of the 4, STD gives the highest readings by far with DIN not too far behind. The table below shows power outputs according to the 4 systems and the uncorrected power as measured for one of my ST2 runs.
RPM UNCORR SAE STD DIN EEC
2500 19.5 19.9 20.3 20.2 19.9
3500 39.1 39.8 40.6 40.3 39.8
4500 54.6 55.7 56.8 56.4 55.7
5500 71.8 73.2 74.7 74.1 73.2
6500 85.5 87.1 88.9 88.2 87.2
7500 92.7 94.5 96.5 95.7 94.6
8500 91.4 93.2 95.1 94.4 93.2
9500 83.5 85.2 86.9 86.2 85.2
************************************************** ***
Quando si rileva la potenza di un’automobile si usa solitamente un banco a rulli. I risultati ottenuti sono però influenzati dalle condizioni ambientali. Ecco quali sono i fattori correttivi da utilizzare per riportare i risultati della prova alle condizioni ambientali standard.
Correzione della potenza per prova su banco a rulli
La correzione della potenza rilevata sul banco prova deve essere apportata per tener conto delle reali condizioni ambientali in cui si è svolta la prova. Ricordiamo infatti che la potenza dichiarata dai costruttori è quella rilevata con propulsore montato su banco prova motori e non con vettura su banco a rulli. Tutti i banchi prova a rulli, una volta rilevata la potenza applicano un fattore correttivo a seconda della normativa scelta. Quì di seguito vi forniamo le equazioni utilizzate per effettuare la correzione. Il fattore correttivo k da utilizzarsi è quindi il seguente:
essendo:
Nel caso di normativa DIN bisogna porre:
P = pressione barometrica in hPa
T = temperatura entrata filtro aria
A = 1013
b = 1,0
x = 20
y = 0.5
Nel caso di normativa ECE si ha invece:
P = pressione barometrica in hPa
T = temperatura entrata filtro aria
A = 990
b = 1.2 per motori a benzina
b = 1.0 per motori Diesel
b = 0.7 per motori turbodiesel
x = 25
y = 0.6 per motori a benzina
y = 0.7 per motori diesel
y = 1.5 per motori turbodiesel
Non dimenticate poi che 1CV vale di più di 1hp
Se non volete leggere tutto che oltretutto è in inglese, i fattori più largamente usati sono DIN Ed EC. Sotto c'è un pezzo riassuntivo in italiano.
DIN corregge a 1013 mBar e 20°C (praticamente Al mare nella mezza stagione)
EC corregge a 990 mBar e 25°C (praticamente in collina primavera inoltrata)
************************************************** **
The majority of the charts you see here use certain correction factors to adjust the measured power of the bike on a given day under given atmosphic conditions, and adjust them to what they should be if tested at sea level. There are several horsepower correction factors you may see on these dyno charts. The most recognised are:
• SAE (Society of Automotive Engineers), USA. Power is corrected to reference conditions of 29.23 InHg (99 kPa) of dry air and 77 F (25°C). This SAE standard requires a correction for friction torque. Friction torque can be determined by measurements on special motoring dynamometers (which is only practical in research environments) or can be estimated. When estimates must be used, the SAE standard uses a default Mechanical Efficiency (ME) value of 85%. This is approximately correct at peak torque but not at other engine operating speeds. Some dynamometer systems use the SAE correction factor for atmospheric conditions but do not take mechanical efficiency into consideration at all (i.e. they assume a ME of 100%).
• STD or STP. Another power correction standard determined by the SAE. This standard has been stable for a long time and is widely used in the performance industry. Power is corrected to reference conditions of 29.92 InHg (103.3 kPa) of dry air and 60 F (15.5°C). Because the reference conditions include higher pressure and cooler air than the SAE standard, these corrected power numbers will always be about 4 % higher than the SAE power numbers. Friction torque is handled in the same way as in the SAE standard.
• ECE (European Community), Europe. The ECE standard is based on the European Directives. Power is corrected to reference conditions of 99 kPa (29.23 InHg) of dry air and 25°C (77 F). Friction torque is not taken into consideration at all.
• DIN (Deutsche Industrie Norm), Germany .The DIN standard is determined by the German automotive industry. Power is corrected to reference conditions of 101.3 kPa (29.33 InHg) of dry air and 20°C (68 F). With the advent of European legislation and standards, national standards such as the DIN (formerly widely used) are now less significant.
• Actual You may see this on some charts, especially from Ivan. What this means is this is the actual horsepower achived on the day tested and no correction factor has been applied. One can assume better or worse results with varying weather conditions.
************************************************** ***
Dyno Correction Factors
When you use the Dynojet software to graph dyno runs you get some options as to how you interpret the data. Because atmospheric conditions (ambient air temperature and pressure) affect air density they therefore affect power output. The influence of atmospheric variations needs to be accounted for in some way to make comparing dyno figures achieved under different conditions valid. There are international standards set down by organisations such as the SAE (Society of Automotive Engineers), the European Community and whoever is responsible for the DIN correction system (I’m not sure who that is, TUV maybe?) for this. Exactly how each standard does this is up to the body that puts it forward.
According to Edition 4 (1996) of the Bosch Automotive Handbook (an amazingly fact packed piece of literature) all the standards listed are the same save the DIN standard. The DIN 70 020 system uses a different ambient air pressure and temperature to the other standards – they use 1013mBar and 20 degrees Celsius as the nominal ‘zero correction’ conditions, whereas the SAE J1349, ISO 1585, JIS D1001 and EWG 80/1269 all use 990mBar and 25 degrees Celsius as the nominal conditions. The way the ambient pressure is measured is also different, with the DIN system using ‘absolute’ air pressure and the others using ‘dry’. As far as I can remember, ‘dry’ is ‘absolute’ with the vapour pressure subtracted, which is how relative humidity is accounted for. If I had a thermodynamics book on my bookshelf I’d be able to tell more, but for some reason I only have materials and mechanics/vibration books, which is odd given I majored in Fluid Mechanics and Thermodynamics.
The DIN system also uses a different equation, so it varies quite a bit.
The Dynojet software gives 4 correction options – SAE, STD, EEC and DIN. I haven’t seen the STD or EEC correction formulas, but the EEC gives a very similar result to the SAE system which I usually use. Of the 4, STD gives the highest readings by far with DIN not too far behind. The table below shows power outputs according to the 4 systems and the uncorrected power as measured for one of my ST2 runs.
RPM UNCORR SAE STD DIN EEC
2500 19.5 19.9 20.3 20.2 19.9
3500 39.1 39.8 40.6 40.3 39.8
4500 54.6 55.7 56.8 56.4 55.7
5500 71.8 73.2 74.7 74.1 73.2
6500 85.5 87.1 88.9 88.2 87.2
7500 92.7 94.5 96.5 95.7 94.6
8500 91.4 93.2 95.1 94.4 93.2
9500 83.5 85.2 86.9 86.2 85.2
************************************************** ***
Quando si rileva la potenza di un’automobile si usa solitamente un banco a rulli. I risultati ottenuti sono però influenzati dalle condizioni ambientali. Ecco quali sono i fattori correttivi da utilizzare per riportare i risultati della prova alle condizioni ambientali standard.
Correzione della potenza per prova su banco a rulli
La correzione della potenza rilevata sul banco prova deve essere apportata per tener conto delle reali condizioni ambientali in cui si è svolta la prova. Ricordiamo infatti che la potenza dichiarata dai costruttori è quella rilevata con propulsore montato su banco prova motori e non con vettura su banco a rulli. Tutti i banchi prova a rulli, una volta rilevata la potenza applicano un fattore correttivo a seconda della normativa scelta. Quì di seguito vi forniamo le equazioni utilizzate per effettuare la correzione. Il fattore correttivo k da utilizzarsi è quindi il seguente:
essendo:
Nel caso di normativa DIN bisogna porre:
P = pressione barometrica in hPa
T = temperatura entrata filtro aria
A = 1013
b = 1,0
x = 20
y = 0.5
Nel caso di normativa ECE si ha invece:
P = pressione barometrica in hPa
T = temperatura entrata filtro aria
A = 990
b = 1.2 per motori a benzina
b = 1.0 per motori Diesel
b = 0.7 per motori turbodiesel
x = 25
y = 0.6 per motori a benzina
y = 0.7 per motori diesel
y = 1.5 per motori turbodiesel
Non dimenticate poi che 1CV vale di più di 1hp
Comment