Motor termic? Priviti momentul/cuplul! Puterea e irelevanta!

[marius-ciclistu]

Caracteristicile dinamice ale unui motor termic sunt date doar de curba de moment (cuplu).



Puterea este irelevanta pentru ca la valoarea ei maxima, prin formula

W=Nm*rad/s

sau

Cp=Nm*RPM/7021.55

sau

PS=Nm*RPM/7023, etc.

ofera doar o valoare de moment (cuplu) la o turatie ridicata si irelevanta, din cauza ca, la turatia puterii maxime, forta de tractiune este mai mica decat forta de tractiune la turatia momentului maxim.

Astfel, conform Principiului al doilea al mecanicii (Isaac Newton)

F=m*a

F - forta de tractiune
m - masa autovehiculului
a - acceleratia (nu accelerarea !)

rezulta ca si acceleratia este mai mica la turatia puterii maxime in comparatie cu acceleratia de la turatia cuplului maxim.

Exemplu 1: compararea fortelor si acceleratiilor unui motor (turbo-diesel in acest caz).


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Se poate observa ca in treapta intai de viteza, forta este mai mare (decat forta maxima din treapta 2) chiar si peste turatia puterii maxime. Deci, pentru maximizarea performantelor de accelerare, trebuie sa NU schimbam treapta de viteza la turatia puterii maxime(4000 rpm), ci sa folosim plaja de turatie pana la capat. Liniile de culoare aurie trebuie sa fie ~ orizontale pentru performante maxime. Tinand cont de acest lucru se pot interpreta si celelalte curbe de forta si acceleratie in treptele 2,3 si 4.

Exemplu 2: compararea puterilor (a doua motoare aspirate pe benzina)


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Concluzie:

"Puterea este o oglindire denaturata a fortei si acceleratiei in privinta motoarelor termice." Marius Pantea feb.2017


Atentie!

Transmisia si anvelopele au un rol foarte important si pot fi decisive atunci cand comparam doua motoare cu momente apropiate.

Exemplu 3: compararea momentelor (a doua motoare aspirate pe benzina)



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Graficele au fost realizate cu calculatorul si comparatorul de transmisie auto marius-ciclistu http://marius-ciclistu.ro/calculatortransmisieauto.php


Vedeti si Cal putere vs Cal FORTA.

[marius-ciclistu]

Cum sa schimbi vitezele pentru a obtine performante maxime




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Pentru performante maxime, turatia de schimb a treptelor de viteza este dictata de curba de cuplu si de rapoartele de transmitere, NU de turatia puterii maxime!
Graficul este pentru un Ford Focus 1.6 TD 2008 cu graficul de cuplu dat de producator ca si valori de intrare.

107 Cp / 4000 RPM,

240 Nm/ 1750 RPM,

1316 kg.

Calculatorul poate fi folosit aici:

http://marius-ciclistu.ro/calculatortransmisieauto.php


Concluzia este aceeasi pentru orice motor pe benzina sau motorina.

[marius-ciclistu]

The power’s mislead in thermal engine’s regard.pdf

[marius-ciclistu]

Puterea, in fizica, ar trebui redenumita in Rata energiei.

Power, in physics, should be renamed to Energy Rate.

[marius-ciclistu]

So it turns out that in the 1770s the power word was used as "ability to act" or "ability to do" or "potential". https://hsm.stackexchange.com/a/3255/19097 https://hsm.stackexchange.com/questions/3254/etymology-of-power-math

Also Watt is supposed to had defined the power as force * velocity (https://hsm.stackexchange.com/questions/13304/when-was-the-concept-of-power-defined/13309#13309), so saying that a horse's ability to act is equal to force multiplied by velocity makes sense.

In the 1840s, so ~70 years later Joules defines the energy concept. (https://hsm.stackexchange.com/questions/2553/where-did-p-vi-come-from/2554#2554)

So energy rate concept is younger than the watt concept.

[marius-ciclistu]

After 4 years since I introduced the calculation of the average torque of the engine in the car and moto transmission calculators, that I knew is not accurate so I did not include it in the publication about power from january 2020, I've defined the weighted average torque of the engine to have an approximate single characteristic of the engine on all its RPM range that is clearer than maximum power or maximum torque.

The weight of the interval between 2 RPM measure points from the torque graph is equal with the time needed for the engine to accelerate from first point to the second under (any) load, divided with the total time needed to accelerate on all RPM range. This weight is multiplied by the average of the torque values of those 2 points.

I published it for the first time here https://masinamea.4tuning.ro/blog/marius_ciclistu/cuplul-mediu-ponderat-al-motorului-este-o-1335/
and here https://hsm.stackexchange.com/questions/15842/has-the-weighted-average-torque-of-the-engine-been-ever-defined-by-anyone-until
and is also available for calculation in the car https://marius-ciclistu.ro/cartransmissioncalculator.php
and moto https://marius-ciclistu.ro/mototransmissioncalculator.php transmision calculators where also the calculation of the time (used in this definition) is explained.

[marius-ciclistu]

After one month since I defined the weighted average torque, I discovered via manual calculation tries, that there is an even clearer single torque value:

The Equivalent constant engine torque - is the torque with which a car's engine with one gear ratio can accelerate over the same distance in the same time, providing a single value as a characteristic for that engine on all its rpm range.


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I published this here: https://masinamea.4tuning.ro/blog/mariu ... -mai-1390/

[marius-ciclistu]

Thanks to ChickenCoding123 now the equivalent constant engine torque is available (already calculated) in the car and moto transmission calculators.

It can replace the max power of an engine as a technical description because it is more accurate to compare two engines using it that using power.