Toyota Valvematic

[Motron]

Ciao a tutti, prendo spunto da questo video che molti di voi avranno già visto:

[video=youtube;RHNXbGGvOdc]http://www.youtube.com/watch?v=RHNXbGGvOdc[/video]

Per parlare di questo sistema..
la sua variazione è continua? permette di fare a meno della valvola a farfalla in alcuni punti di funzionamento?

 

[piero7510]

La variazione è continua però la valvola a farfalla è ancora presente ma viene utilizzata ai bassi regimi per ottenere una regolazione molto precisa del flusso d'aria, oltre è completamente spalancata.
L'alzata delle valvole può variare tra un 1mm e 11mm in modo continuo.

Se hai voglia di tradurtelo ti riporto una esauriente relazione tecnica che ho trovato nel web:

2008-08-13 - Toyota announced on occasion of a Technology Seminar in Berlin that the new Avensis will be equipped with the newly developed variable valve timing and lift system called Valvematic. The innovation that further improves both fuel efficiency and performance at the same time is a combination of the already known Variable Valve Timing intelligent (VVT-i) with a new mechanism that continually varies the lift of the inlet valves in order to better control the intake air flow.

The Valvematic is a compact system that minimises energy losses. Its design makes the application in every engine possible. The compactness of the variable arm enables the rocker shaft being placed in the same height with camshafts. Because the height of the camshaft was the same as the height of a conventional one, by introduction of a cam carrier system, the same cylinder head could be used.

The Valvematic system consists of an actuator, which drives the control shaft, the variable valve lift mechanism for each cylinder and the cam phaser VVT-i. The electrically activated system VVT-i varies air induction by automatically adjusting the pipe length according to rpm, thus working at lower rpm and engine temperatures than a conventional hydraulic system. The variable valve lift mechanism consists of four parts: the roller arm transmits the input from the camshaft, two oscillation cams contact the roller rocker arms and the slider, which contains the helical spline, transmits the rotating power of the roller arm to the oscillating cam. The slider is connected to the control shaft and links the movement in the axis direction of the control shaft. The phase of the roller arm and the oscillation cams varies with the action of the helical spline. Because the angle of rotation of the variable arm and cam is always uniform, the range in which the roller rocker arm comes in contact with the oscillation cam changes. The cam surface of the oscillation cam consists of a no lift part and a lift part. It can change the valve lift height from 1 millimetre to 11 millimetres.

Valve lift and valve timing are determined based on best fuel efficiency. The target throttle valve angle is calculated for optimal airflow for high performance. In order to minimise the fluctuation of the intake airflow, the actuators are continuously functioning. Further, a technique to maintain a continuous airflow was developed using modelling of induction system parts including air cleaner, throttle valve, surge tank, intake manifold, and intake valve.

According to a company's spokesman, using Valvematic, the valve lift for best fuel economy and power across each operating range can be chosen. During light load conditions (1 millimetre valve), the intake throttle is used to more precisely control airflow volume. For medium to high loads, the intake throttle is wide open, and airflow volume is controlled by the valve lift. Pumping losses are reduced across entire load range. When combined with variable valve timing, this mechanism allows the valve opening and closing event to be controlled independently. The valve timing mechanism is driven by hydraulic oil pressure, and so exhibits some delayed response compared to the electro-mechanical actuation of valve lift mechanism. While synchronisation between valve lift and valve timing is desired for some valve overlap, delayed timing response can cause too much overlap, which has negative impact on fuel economy and drivability. In such a case, additional throttle angle is used to maintain drivability. And using the output control by the valve lift, good response in transient situation could be given because no intake volume after control mechanism.

When applied to a 2.0-litre straight-four Naturally-Aspirated gasoline engine, Valvematic provides according to a company's spokesman up to 10 percent of fuel consumption reduction, 10 percent power output improvement, enhanced transient response and reduces CO2 emissions. It will be available from the beginning of next year in the 1.8-litre and the 2.0-litre version of the new Avensis.

 

[Waller]

Quattrocerchi dirà che l'hanno copiato dal MultiAir

 

[Motron]

Si è piu o meno come immagino e cioè niente male.

In sostanza ha lo stesso scopo del multiair, eliminare la farfalla, qui viene ottenuto con un sistema più semplice con alcuni pro e contro ma con una efficacia comunque elevata.

Certo diminuire del 10% i consumi ad un ottimo motore come il toyota non è lo stesso che dimininuirli ad uno un pò piu assetato come il Fiat :biggrin2:

 

[piero7510]

Probabilmente hanno dovuto conservare la farfalla ai bassi regimi e con poca richiesta di potenza per ottenere una regolazione molto precisa ed identica del flusso d' aria tra i vari cilindri, cosa che non
sarebbe stato possibile affidando tale funzione unicamente all' alzata delle valvole, considerata la difficoltà ad ottenere esattamente l' identica alzata a causa delle inevitabili tolleranze delle punterie (anche se il recupero del gioco è idraulico).
Se il regime del minimo, per esempio, fosse regolato unicamente dalle valvole, l' alzata sarebbe limitata a solo qualche decimo di mm e penso che sarebbe piuttosto difficile ottenere lo stesso identico valore su tutte le 8 valvole di aspirazione.
Tale differenza diventa naturalmente trascurabile se le alzate divengono importanti.