VTEC

[hondatu]

Din arhiva, deci prafuit si de demult, dar interesant:

http://www.autoshow.ro/autoshow/arti...article_id=310

Semper Fi - Honda i-VTEC
Florin Oprea
7 Mai 2002

Prezenta la monovolumul Stream, dar si la modelul Civic Type-R generatia de motoare i-VTEC (intelligent Variable Timing and lift Electronic Control) are calitati ce demonstreaza ca tehnologia Honda este intotdeauna pe val.
Doua dispozitive noi fac parte din sistemul i-VTEC. Deschiderea variabila a supapei este facuta de doi culbutori si prin folosirea unui arbore cu came cu profil schimbat. Al doilea dispozitiv controlat de computer variaza pozitia arborelui cu came al admisiei cu peste 50¡ relativ la unghiul arborelui cotit. Un element important al motorului ce completeaza i-VTEC este colectorul de admisie cu lungime variabila controlat de un distribuitor rotativ. La sarcina joasa lungimea se mareste atingand 540 mm cu scopul cresterii vitezei de curgere a aerului creand turbulente ce asigura un amestec omogen si o buna umplere a cilindrilor. La sarcini mari lungimea colectorului scade atingand 270 mm ce asigura un volum sporit de aer aspirat cu rezultat in cresterea puterii motorului.

Schimbarea pozitiei arborelui cu came fata de arborele cotit se face hidraulic cu ajutorul unei mici pompe rotative situata la capatul arborelui cu came al admisiei. Computerul variaza presiunea uleiului modificand rotatia arborelui si implicit a lantului de distributie. Astfel se modifica suprapunerea timpilor supapelor. Acest timp este momentul in care supapa de admisie si cea de evacuare sunt deschise. Intarziind rotatia arborelui cu came scade timpul de suprapunere in timp ce accelerand rotatia timpul creste. Fenomenul de suprapunere al deschiderii supapelor joaca un rol important in functionarea motorului. Un timp scurt da motorului un relanti uniform si un cuplu bun la sarcini mici, dar penalizeaza performantele acestuia la sarcini mari. Un timp de suprapunere mare permite o respiratie excelenta la sarcini mari insa obtinem rezultate slabe la sarcini mici. Prin varierea rotatiei arborelui cu came si a timpului de suprapunere, Honda a obtinut performante excelente atat la regimuri joase cat si la cele mari.

Inaltimea variabila de deschidere a supapei este realizata de doi culbutori diferiti si de camele de pe arbore. In trecut, Honda opera pe motoarele VTEC cu trei culbutori: doi pentru deschiderea a doua supape de admisie, iar celalalt pentru blocarea celorlalti doi si fortarea acestora sa urmeze un profil al camei separat de cel initial. Cu noul dispozitiv de doi culbutori, numai o singura supapa este deschisa la sarcini joase. Acest fapt asigura o buna turbionare a amestecului carburant in cilindru optimizand arderea la regimul de mai sus. La o valoare a turatiei programata in computerul motorului presiune uleiului este folosita pentru blocarea celor doi culbutori. La aceasta turatie se vor deschide ambele supape de admisie, iar culbutorii vor urma profilul camei mai inalte urmarit pana atunci doar de culbutorul secund. Beneficile maxime ale puterii si cuplului se obtin cand sistemul i-VTEC opreaza atat pe supapele de admisie cat si pe cele de evacuare. Imbunatatirea performantelor este doar unul dintre avantajele sistemului i-VTEC. Eficacitatea sistemului este reliefata de curba de cuplu aproape aplatizata. Astfel pentru motorul de 2.0 litri al Hondei Stream, daca valoarea momentului maxim este de 192 Nm la o turatie de 4000 rot/min, cuplul de 184 Nm (96% din valoarea maxima) este disponibil inca de la 3000 de rot/min. Ajutat de o cutie performanta acest motor face minuni.

Tehnologia i-VTEC asigura o mare flexibilitate pentru ca ea permite motorului sa se "exprime" la plina sa valoare in toate cazurile. In plus ea gestioneaza in asa fel motorul obtinandu-se o crestere a puterii acestuia cu 20% si a cuplului, la regimuri joase si medii, cu 10% in timp ce reduce consumul de combustibil cu aproape 20%. Multumita constructiei compacte a rezultat si o scadere a greutatii propulsorului cu 10%.

[Marius -Iulian]

Originally Posted by hondatu

:roll: Marius, NSXul nu are i-VTEC, ci simplu DOHC VTEC!

mea culpa... nu m-am uitat sa verific... inseamna ca tipul cu articolul respectiv nu stia ce vorbea... da' si voi amestecarati VTEC-ul cu VTC-ul (VVT)...

asadar care a fost primul iVTEC?

[hondatu]

Primul i-VTEC a fost asta:

http://www.hondafan.ro/modele.php?id=209

Vezi mai atent spre al 2lea paragraf!

[Marius -Iulian]

asa de tarziu? iVTEC-ul de 2,0l de 160CP nu are VTEC si/sau VTC decat pe admisie...

Vin cu niste mici articole interesante despre VTEC:

VTEC - Variable valve Timing and lift Electronic Control. At low RPM, a VTEC engine uses a normal cam profile to retain a smooth idle, good fuel economy, and good low-end power delivery. The VTEC mechanism engages a high-lift, long-duration “race” cam profile at a set RPM value (i.e., ~5500RPM on the B16A) to increase high-end power delivery.

VTEC-E - Variable valve Timing and lift Electronic Control for Efficiency. This system isn’t really VTEC as we know it. At low RPM, the VTEC-E mechanism effectively forces the engine to operate as a 12-valve engine - one of the intake valves does not open fully, thus decreasing fuel consumption. At a set RPM value (i.e., ~2500RPM in the D16Y5), the VTEC-E mechanism engages the 2nd intake valve, effectively resuming operation as a normal 16-valve engine. Note: in a VTEC-E engine, there are no high-RPM performance cam profiles; this engine is supposed to be tuned for fuel economy, right?

VTC - Variable Timing Control. This is a mechanism attached to the end of the intake camshaft only which acts as a continuously variable cam gear - it automatically adjusts the overlap between the intake and exhaust cams, effectively allowing the engine to have the most ideal amount of valve overlap in all RPM ranges. VTC is active at all RPMs.

i-VTEC - intelligent Variable valve Timing and lift Electronic Control. This is a combination of both the VTEC and the VTC technologies - in other words, i-VTEC = VTEC + VTC. Currently, the only engines that use the i-VTEC system are the DOHC K-series engines.

Now this is where things get tricky - Honda uses the term “DOHC i-VTEC” for two different systems: The first system is used in the K20A2 engine of the RSX Type-S. The second system is used in the K20A3 engine of the Civic Si.

The First System (K20A2):

This system is pretty close to the older DOHC VTEC engines. At low RPM, the K20A2 uses a normal cam profile to retain a smooth idle, good fuel economy, and good low-end power delivery. At 5800RPM, its VTEC mechanism engages a high-lift, long-duration “race” cam profile to increase high-end power delivery. The only difference between this i-VTEC engine and the older VTEC engines is the addition of the VTC system. The intake camshaft has the automatic self-adjusting cam gear which continuously optimizes valve overlap for all RPM ranges.

Here we see an image of the intake cam lobes of the K20A2. Notice there are 3 lobes; the two side lobes are the low-RPM profiles, and the center lobe is the high-lift, long-duration profile which engages at 5800RPM. Basically the same setup as the old VTEC engines we are familiar with.

Now here we see the VTC mechanism - the gear on the end of the intake cam that adjusts valve timing (overlap) automatically on the fly.

This system is used in engines powering the JDM Honda Integra Type-R, Civic Type-R, Accord Euro-R, and the USDM Acura RSX Type-S and TSX.

The Second System (K20A3):

This system does not really conform to the “DOHC i-VTEC” nomenclature, as Honda would like us to believe. As I mentioned in my previous post, it actually should be called “i-VTEC-E,” because it uses a VTEC-E mechanism rather than a standard VTEC mechanism. At low RPM, the VTEC-E system effectively forces the engine to operate as a 12-valve engine - one of the intake valves does not open fully, thus decreasing fuel consumption. At 2200RPM, the VTEC-E system engages the 2nd intake valve, effectively resuming operation as a normal 16-valve engine. There are no high-RPM performance cam profiles; this engine is tuned to balance fuel economy and power, rather than provide pure performance. On the intake cam, there is the VTC mechanism which basically is an automatic self-adjusting cam gear used to continuously optimize the valve overlap for all RPM ranges. This being a VTEC-E system - and not a true DOHC VTEC system - is the reason the K20A3 redlines at a measly 6800RPM, while the K20A2 is able to rev all the way to 7900RPM.

Here we see an image of the intake cam lobes of the K20A3. Notice there are only 2 lobes - there is a nearly round one used only for the low-RPM disabled intake valve, and then there is the regular lobe used by the other valve at low-RPM and by both valves at high-RPM:

This system is used in engines powering the USDM Acura RSX base, Honda Civic Si, Accord 4-cylinder, CRV, and Element.

Special note: The K20A3 engine used in the Acura RSX base has a slightly different intake manifold design from the K20A3 engine used in the Civic Si. The RSX engine uses a dual-stage manifold, similar in concept to the manifold of the B18C1 in the old Integra GSR. It uses long intake runners at low-RPM to retain low end power, and switches at 4700RPM to a set of shorter intake runners to enhance high-end torque. This accounts for the extra 9 ft-lb of torque in the RSX (141 ft-lb, vs. 132 ft-lb in the Civic Si).

Myths:

1. The i-VTEC engine engages VTEC gradually, and not suddenly like in the old VTEC engines.

Wrong. The i-VTEC engine “engages VTEC” at a single set RPM, like always. Read the definitions above.

2. VTC engages at a set RPM.

Wrong. VTC is always activated. Read under “VTC” above.

3. The K20A3 engages VTEC at 5000+ RPM.

Wrong. Technically, there is no “VTEC” (as we think of it) in the K20A3 engine - it uses a VTEC-E technology, which engages at 2200RPM. Read under “The Second Sytem” above.

[Marius -Iulian]

excelente precizari. clar de unde vine diferenta dintre variantele de 160 si 200-210CP ale motorului de 2.0l. vad ca VTC (=VVT) este pe toate numai pe camele valvelor de admisie nu si pe cele de evacuare.

Uite de aici:

Technically, there is no “VTEC” (as we think of it) in the K20A3 engine - it uses a VTEC-E technology, which engages at 2200RPM. Read under “The Second Sytem” above.

Deci practic pe Si nu exista VTEC-ul asa cum exista pe RSX Type S sau Civic Type R, cu acel lift brusc la 5900. Lui K20A3 i "se taie" la 6800 de tot.

[hondatu]

Bune infourile astea, o sa mai am/avem nevoie de ele!
Am si eu ceva, nu sant insa sigur daca le ai de aici:

http://world.honda.com/history/chall...989vtecengine/

[Marius -Iulian]

super link!

[hondatu]

Dar pe NSX alaturi de VTEC mai exista si VVIS care daca nu ma insel a existat si pe Prelude. Asta ce-ar mai fi?

Fuel and Induction System:

Programmed Fuel Injection (PGM-FI) with Variable Volume Induction System (VVIS)

Cumva asa ceva?
Avand avantajul noului sistem Honda de inductie fortata a aerului si debitul precis al benzinei furnizat de sistemul de injectie electronic PGM-Fi, acest sistem incorporeaza senzori de oxigen si un convertizor catalitic cu trei cai pentru a mentine un optim al eficientei combustiei odata cu un nivel al noxelor cu mult sub ceea ce prevad asteptatele regulamente Europene si asigurand astfel fiabilitatea pe termen lung.

sursa: http://www.honda-bikes.ro/inov/low_emissions.php