Que es el VTEC de Honda?

[Rod GTI]

VTEC son las siglas en inglés de Variable valve Timing and Electronic lift Control. En castellano significa apertura de válvulas variable, electrónicamente controlado.
Honda fue pionero en la década de los 80 en usar este sistema, primero equipando los modelos deportivos de los Civic y CRX además del NSX, para luego ser un Standard en todos los modelos de la marca.

Básicamente consiste en concentrar en un árbol de levas 2 tipos de levas diferentes, las primeras funcionan a bajas revoluciones y tienen poca apertura de válvulas para un menor consumo y un andar mas dócil, y las otras que se activan a altas revoluciones, tienen un diseño mucho mas agresivo, con una apertura de levas mas pronunciada y un avance distinto, para un comportamiento mas deportivo. Este sistema permite mejorar muchísimo el pico de potencia en el auto (aprox. 30HP en un motor de 4 cilindros) ya que permite al motor girar hasta 8000 rpm sin problemas (o hasta 9000 RPM en el S2000!!)

Sistema VTEC
http://img.photobucket.com/albums/v235/rod111/Vtec1.jpg

3 Etapas del VTEC
http://img.photobucket.com/albums/v235/rod111/Vtec2.jpg

Existen 2 tipos de configuraciones:

-SOHC VTEC (Simple Over Head Cam): Arbol de levas simple a la cabeza. Esta configuracion tiene un arbol de levas a la cabeza que comanda tanto las valvulas de admision como las de escape. Se aplica el sistema VTEC solo para las valvulas de admision, por lo tanto en un mismo arbol tiene un juego de levas para la admision a bajas revoluciones, otro para la admision a altas revoluciones y otro mas para las valvulas de escape.

-DOHC VTEC (Double Over Head Camshaft): Doble arbol de levas a la cabeza. Este sistema es mas eficiente ya que se emplea un arbol de levas para la admision y otro para las valvulas de escape, cada uno de ellos con levas de bajas revoluciones y levas VTEC.


Arboles de Levas DOHC
http://img.photobucket.com/albums/v235/rod111/Vtec3.jpg

Por qué los autos no tienen arboles de levas agresivos durante toda la curva de potencia?

Porque si así fuera, el auto no regularía bien en marcha lenta, y tendría un comportamiento muy nervioso, ademas tendria un consumo mucho mas elevado de combustible. Los autos de carrera si usan esta configuración ya que el consumo y el andar no tienen importancia en este tipo de aplicaciones.

En el presente otras automotrices han adoptado sistemas similares en algunos de sus modelos. Ejemplos de ellos son el sistema VVL de Nissan, Double Vanos de BMW, Mivec de Mitsubishi, VVT-i de Toyota y el VVC de Rover. No todos los sistemas son iguales, pero el concepto es similar en todos los casos.

http://img.photobucket.com/albums/v235/rod111/Vtec4.jpg

[HUX]

Que no eran unas estampas bien chidas que se le ponen a cualquier nave??


NTC, es un super sistema, el concepto es tener lo mejor de dos mundos, un perfil mas sedado para mejorar la suavidad y el consumo y otro muy agresivo para el desmpeño..., un día se lo traté de explicar a un amigo de mi papá que le encanta su Camaro Yenko -que se hace como licuadora en los semaforos- y nomas no me lo creía...

[jorge_DOHC]

[Por qué los autos no tienen arboles de levas agresivos durante toda la curva de potencia?

Porque si así fuera, el auto no regularía bien en marcha lenta, y tendría un comportamiento muy nervioso, ademas tendria un consumo mucho mas elevado de combustible. Los autos de carrera si usan esta configuración ya que el consumo y el andar no tienen importancia en este tipo de aplicaciones.

No nada mas eso, también es porque un arbol muy "caliente", como se le llama a los arboles que abren mucho la valvula o de mayor levante, dan mas pontencia y torque en altas RPM y los sacrifican en bajas RPM. Como dices, esto no importa en motores de carreras, porque siempre los traen en altas RPM, pero en aplicaciones "de calle" es mejor tener un poco mas de torque en bajas RPM.

Por esta misma razón no se recomiendan escapes demasiado liberados en autos de calle (Hablo de NA, los turbos son otra historia).

[Lucky Luciano]

Nissan NVCS and "Cam-Phasing" vs Honda VTEC

Nissan chose to focus their NVCS system mainly at low and medium speed torque production because the vast majority of the time, engine RPMs will not be at extremely high speeds. The NVCS system can produce both a smooth idle, and high amounts of low and medium speed torque. Although it can help a little at the top-end also, the main focus of the system is low and medium range torque production.

We all know how Honda's VTEC system works, but here is where it runs into trouble. Since it only has one profile with fixed phasing for low-RPM's (cannot advance or retard valve opening/closure), the low-RPM profile must be able to produce a smooth idle and stable running at light loads. This means retarded intake valve opening. At low and medium revs but high load, the intake valves cannot advance on the low-RPM profile like they could on Nissan's NVCS, so volumetric efficency is possibly lost, and torque production cannot be optimized in this range. Finally at the top-end, a higher lift and duration cam profile is used and the system drastically improves top-end torque production (peak horsepower), but it is never able to optimize torque in the low-end or mid-range.

So the NVCS system and in general cam phasing technology helps significantly in the low-end and mid-range with torque production, but really not that much at the top-end. Honda's VTEC helps significantly at the top-end (peak horsepower), but not at all in the low-end and mid-range.

[Lucky Luciano]

Cam-Changing Systems

- Honda VTEC
- Mitsubishi MIVEC
- Nissan Neo VVL (not used in US market)

Cam-Phasing Systems

- Audi 2.0-litre - continous inlet
- Audi 3.0 V6 - continous inlet, 2-stage exhaust
- Audi V8 - inlet, 2-stage discrete
- BMW Double Vanos - inlet and exhaust, continuous
- Ferrari 360 Modena - exhaust, 2-stage discrete
- Fiat (Alfa) SUPER FIRE - inlet, 2-stage discrete
- Ford Puma 1.7 Zetec SE - inlet, 2-stage discrete
- Ford Falcon XR6's VCT - inlet, 2-stage discrete
- Jaguar AJ-V6 and updated AJ-V8 - inlet, continuous
- Lamborghini Diablo V12 since SV - inlet, 2-stage discrete
- Mazda MX-5's S-VT - continous inlet
- Mercedes V6 and V8 - inlet, 2-stage ?
- Nissan QR four-pot and V8 - continuous inlet
- Nissan NVCS - late-80's, early-90's cars (added by SteVTEC)
- Nissan VQ V6 CVTC- inlet, continuous ?
- Nissan VQ V6 CVTC since Skyline V35 - inlet, electromagnetic
- Porsche Variocam - inlet, 3-stage discrete
- PSA / Renault 3.0 V6 - inlet, 2-stage
- Renault 2.0-litre - inlet, 2-stage discrete
- Subaru AVCS - inlet, 2-stage ?
- Toyota VVT-i - continuous, mostly inlet but some also exhaust
- Volvo 4 / 5 / 6-cylinder modular engines - inlet, continuous
- Volkswagen VR6 - inlet, continuous ?
- Volkswagen (Audi) W8 and W12 - continuous inlet, 2-stage exhaust

Cam-Changing *and* Phasing Systems

- Toyota VVTL-i
- Honda i-VTEC
- Porsche VarioCam Plus


The number of cam-phasing systems in use is far more than cam-changing systems.

[Lucky Luciano]

La fuente es un amigo de otro foro Maximaorg que se llama stevetec.

Me acuerdo que alguna ves Roberto Chamorro puso en el foro rpm una explicación que se me hizo muy buena, que por cierto nadie lo peló por estar ocupados contando chistes pero el tema era excelente, a ver si nos ayuda con el tema.

[Lucky Luciano]

VANOS is a combined hydraulic and mechanical camshaft control device managed by the car's DME (http://www.bmwworld.com/technology/dme.htm) engine management system.
The VANOS system is based on an adjustment mechanism that can modify the position of the intake camshaft versus the crankshaft. Double-VANOS adds an adjustment of the intake and outlet camshafts.

VANOS operates on the intake camshaft in accordance with engine speed and accelerator pedal position. At the lower end of the engine-speed scale, the intake valves are opened later, which improves idling quality and smoothness. At moderate engine speeds, the intake valves open much earlier, which boosts torque and permits exhaust gas re-circulation inside the combustion chambers, reducing fuel consumption and exhaust emissions. Finally, at high engine speeds, intake valve opening is once again delayed, so that full power can be developed.
VANOS significantly enhances emission management, increases output and torque, and offers better idling quality and fuel economy. The latest version of VANOS is double-VANOS, used in the new M3 (http://www.bmwworld.com/models/m3a.htm).
VANOS was first introduced in 1992 on the BMW M50 engine used in the 5 Series (http://www.bmwworld.com/models/5_series.htm).


http://www.bmwworld.com/images/gears.gif
Here's how it works:
In overhead cam engines, the cams are connected to the crankshaft by either a belt or chain and gears. In BMW VANOS motors there is a chain and some sprockets.
The crankshaft drives a sprocket on the exhaust cam, and the exhaust cam sprocket is bolted to the exhaust cam. A second set of teeth moves a second chain that goes across to the intake cam. The big sprocket on the intake cam is not bolted to the cam, for it has a big hole in the middle. Inside the hole is a helical set of teeth. On the end of the cam is a gear that is also helical on the outside, but it's too small to connect to the teeth on the inside of the big sprocket. There is a little cup of metal with helical teeth to match the cam on the inside and to match the sprocket on the outside. The V (Variable) in VANOS is due to the helical nature of the teeth. The cup gear is moved by a hydraulic mechanism that works on oil pressure controlled by the DME (http://www.bmwworld.com/technology/dme.htm).

http://www.bmwworld.com/technology/vanos_cutaway.jpg
At idle, the cam timing is retarded. Just off idle, the DME energizes a solenoid which allows oil pressure to move that cup gear to advance the cam 12.5 degrees at midrange, and then at about 5000 rpm, it allows it to come back to the original position. The greater advance causes better cylinder fill at mid rpms for better torque. The noise some people hear is the result of tolerances that make the sprocket wiggle a bit as the cup gear is moved in or out.
Double VANOS
Double-VANOS (double-variable camshaft control) significantly improves torque since valve timing on both the intake and outlet camshafts are adjusted to the power required from the engine as a function of gas pedal position and engine speed.

http://www.bmwworld.com/technology/vanos.gif
On most BMW engines that use a single VANOS, the timing of the intake cam is only changed at two distinct rpm points, while on the double-VANOS system, the timing of the intake and exhaust cams are continuously variable throughout the majority of the rpm range.

With double-VANOS, the opening period of the intake valves are extended by 12 degrees with an increase in valve lift by 0.9 mm.
Double-VANOS requires very high oil pressure in order to adjust the camshafts very quickly and accurately, ensuring better torque at low engine speeds and better power at high speeds. With the amount of un-burnt residual gases being reduced, engine idle is improved. Special engine management control maps for the warm-up phase help the catalytic converter reach operating temperature sooner.

Double-VANOS improves low rpm power, flattens the torque curve, and widens the powerband for a given set of camshafts. The double-VANOS engine has a 450 rpm lower torque peak and a 200 rpm higher horsepower peak than single-VANOS, and the torque curve is improved between 1500 - 3800 rpm. At the same time, the torque does not fall off as fast past the horsepower peak.
The advantage of double-VANOS is that the system controls the flow of hot exhaust gases into the intake manifold individually for all operating conditions. This is referred to as "internal" exhaust gas re-circulation, allowing very fine dosage of the amount of exhaust gas recycled.

While the engine is warming up, VANOS improves the fuel/air mixture and helps to quickly warm up the catalytic converter to its normal operating temperature. When the engine is idling, the system keeps idle speeds smooth and consistent thanks to the reduction of exhaust gas re-circulation to a minimum. Under part load, exhaust gas re-circulation is increased to a much higher level, allowing the engine to run on a wider opening angle of the throttle butterfly in the interest of greater fuel economy. Under full load, the system switches back to a low re-circulation volume providing the cylinders with as much oxygen as possible.

[Lucky Luciano]

Fuente: http://www.bmwworld.com/technology/vanos.htm

[Lucky Luciano]

Chequen lo que hace Renault, la verdad muy simple y eficiente, mis respetos:

F1 Engines _ Valve technology
All F1 engines have used pneumatic valves for some time, first introduced by Renault on the late versions of the their V6 turbo engine.


Wire spring valve
http://scarbsf1.com/valves/ilmor_std_valve.jpg
Previously wire valve springs have been used, they use a coil spring (13) to return the valve (1) to a closed position after the cam has retarded. They required huge amounts of the detail development on their shape and material to reach the rev limits of around 15k RPM. The pressure to deliver power from 3.5l and later 3.0l engines required ever higher rev ceilings and metal springs could not longer be developed at the same rate as the rest of the engine.


Pneumatic valve spring
http://scarbsf1.com/valves/renault_pneu_valve_1.jpg
Pneumatic systems use conventional cams operating the valve (4) via a shim\bucket or finger follower, the valve spring pocket is replaced with a chamber (28) pressurised with nitrogen (held within a cylinder in the sidepods) that runs at a constant pressure to return the valve when the cam timing retards. You often see the teams suffer a loss of pressure in the races through leaks in the system, the driver comes in and mechanics re-pressurises the pneumatic circuit, this rarely works for more than few laps. Also when Engines are changed the un-installed engine needs a remote gas cylinder connected in order for the valves not to drop and hit the pistons.


Wire spring vs Pneumatic valve comparision
http://scarbsf1.com/valves/ilmor_pneu-std_valve_comparison.jpg


Renault Electro-Hydraulic (Camless) valve actuation
http://scarbsf1.com/valves/renault_electro-hydraulic_valve_1.jpg
Renault have not planned an Electro-mechanical system, which was commonly believed to use actively controlled magnetic coils to open and close the valves. Clearly the electrical and RPM performance required from the this system were not ready or suitable for a F1 engine.
What Renault have is an Electro-hydraulic system, where two pressurised circuits operate the valve (16). Valve return is still handled by the pneumatic system (52, 20), but the opening of the valves discards cams for a hydraulic circuit (50) controlled by a electronic valve (58). As this system can use high pressure hydraulics already on the car to operate the valve at the required RPM ceiling, the system seems almost too simple..! Infinitely variable valve timing plus the loss of the reciprocating weight of the cams and drive gears makes this an enticing solution. This solution has yet to race or to my knowledge even be tested in a car, Renault have admitted that as a broader automotive organisation, that this systems has been tried.

[Lucky Luciano]

Aunque en el caso de renault la apertura de válvulas variable es indiferente de alguna forma a los lóblos del árbol.

[HUX]

Yo lo veo medio complicado..., y eso de andar presurizando el sistema y que no dure mas de un par de vueltas como que no me convence. Como le hacen los demas? Para muy altas RPM's?

[Lucky Luciano]

BMW utliliza en sus motores 4 cilindros otra tecnología que se llama Valvetronic.


http://www.bmwworld.com/images/gears.gif
Here's how it works:Fuel injection systems monitor the volume of air passing through the throttle butterfly and determine the corresponding amount of fuel required by the engine. The larger the throttle butterfly opening, the more air enters the combustion chamber.

At light throttle, the throttle butterfly partially or even nearly closes. The pistons are still running, taking air from the partially closed intake manifold. The intake manifold between the throttle and the combustion chamber has a partial vacuum, resisting the sucking and pumping action of the pistons, wasting energy. Automotive engineers refer to this phenomenon as "pumping loss". The slower the engine runs, the more the throttle butterfly closes, and the more energy is lost.

http://www.bmwworld.com/technology/vt_schema.gif
Valvetronic minimizes pumping loss by reducing valve lift and the amount of air entering the combustion chambers.

Compared with conventional twin-cam engines with finger followers, Valvetronic employs an additional eccentric shaft, an electric motor and several intermediate rocker arms, which in turn activates the opening and closing of valves. If the rocker arms push deeper, the intake valves will have a higher lift, and vice-versa. Thus, Valvetronic has the ability to get deep, long ventilation (large valve lift) and flat, short ventilation (short valve lift), depending on the demands placed on the engine.

http://www.bmwworld.com/technology/vt_schema1.gif
Operating Parameters:

Valve lift is variable between 0 and 9.7 mm.
Adjustment of the worm gear from one extreme to the other takes 300 milliseconds.
Combined with double-Vanos (http://www.bmwworld.com/technology/vanos.htm) valve timing technology, the camshaft angle relative to the crankshaft can be adjusted by up to 60°.
The intermediate arm is finished to a tolerance of 0.008 mm.
The cams controlling the eccentric shaft are machined to tolerances of a few hundredths of a millimeter. Additional Benefits:

In Valvetronic engines coolant flows across the head, resulting in a temperature reduction of 60%.
The water pump size is cut in half, reducing power consumption by 60%.
The power steering fluid is warmed quickly, reducing the power used by the hydraulic pump.
Mounting the water and power pump on the same shaft and a heat exchanger between coolant and engine oil reduces oil temperature by 30%. The efficiency of Valvetronic engines drop rapidly at over 6,000 rpm since stronger valve springs are required. The stronger springs create higher friction losses. Don't expect to see Valvetronic in the "M" series (http://www.bmwworld.com/models/m_series.htm) engines any time soon.

[Rod GTI]

Ohhhh por dios ya se hizo como una controvercia de los sistemas de aperturas de valvulas... bueno ahorita me vengo a checar loq ue puso el buen Luciano... dejen terminar lo de lso turbos

[roberto]

asi es Luciano, de hecho yo me basé en el post original de maximas.org que es el que citas.

Y como aclaracion para Rod JDM, en japoneses fué primero Nissan con su NCVS que era básicamente cam-phasing. Y despues intentaron con el cam-changing. Honda no fue pionero, de hecho cuando ellos apenas estaban sacando el VTEC en el NSX, hasta el pinche Tsuru ya tenía VTC a 5500rpm.

No te vayas a molestar ni a sentir conmigo, yo respeto el trabajo que hace Honda, pero las cosas son como son. Honda es una empresa que empezó fabricando anillos para motores Toyota; vaya! que han crecido bastante.

Alguna vez me preguntaron que por que era mejor el cam-phasing que el cam-changing. El primer post de Luciano lo explica bastante bien. Es la clásica conclusión de "Los HP venden, el torque gana las carreras" y por lo menos Mazda, Nissan y Toyota en los japoneses han apostado por una buena cantidad de HP sin sacrificar torque.

Pero vamos a ilustrarlo mejor... VVT-i y MIVEC en su gran mayoría de presentaciones no son mas que regulaciones de apertura variable en pro de la ecología. Sistemas que evitan que se instale un EGR a un motor, pues recuerda que ese sistema "americano" ensucia en TB y genera mas calor.

Imagina que quieres comer rápidamente, con VTEC es como si cada vez abrieras la boca mas grande para tomar bocados mayores, claro que en cada bocado necesitas cambiar de cuchara por una mas grande. Con CVTC siempre abres la boca del mismo tamaño, pero cada vez vas adelantando la cabeza para atrapar el bocado y mantienes la boca abierta mas tiempo, chance y hasta en cada paso te echas mas de un bocado.

Ya se que tiene muchos bugs esa explicación, pero me gusta porque la mejor moraleja es " Del plato a la boca se cae la sopa, asi que mejor adelanta la cabeza." jejejejejeje

i-VTEC es cam-phasing + cham-changing con 3 cam-profiles.

La cosa es que todo esto tiende a ser irrelevante, porque hoy en día la mayoría de los fabricantes están mas preocupados (y con justa razón) en aprovechar las tecnologias valvulares en hacer motores mas verdes.

[Bytemax]

a ver si mañana lo leo... jejeje

[roberto]

a ver si mañana lo leo... jejeje


imprimelo y leelo en el baño :eructo:bien

[Rodrigo Z.]

La cosa es que todo esto tiende a ser irrelevante, porque hoy en día la mayoría de los fabricantes están mas preocupados (y con justa razón) en aprovechar las tecnologias valvulares en hacer motores mas verdes.

Totalmente de acuerdo. Es claro que en la gran mayoría de los casos, cualquier enfoque de variación de curvas de potencia y torque la hacen hoy en día con enfoques ecológicos y/o de consumo. El mismo enfoque bien se podría adaptar a exprimir al 100% los motores... y como es más complejo que simplemente cmabiar árboles, pues limitan a nuestro honorable mundo del aftermarket para darle el giro más "racing" a los motores.

Mi experinecia personal con VTEC ha sido demasiado extrema, o realmente traes el motor en muy bajas vueltas (muy buen torque citadino entre las 1,300 y 2,500 rpm's) o de plano te la pasas arriba de las 5,000, si no en el inter siento que el motor realmente pierde lógica de consumo vs potencia.

En el caso del VANOS fue otra historia. En micaso específico con el S50B32 (6 cil, 321 hp y 6 gargantas) la entrega de potnecia y torque era tna lineal que se perdía la sensación de aceleración para el piloto, pero de copiloto se sentía un empuje contundente desde las 2,000 hasta las 8,000 vueltas.