razlikovati moras CAM CHANGING in CAM PHASING.
VTEC je cam changing. saj ima razlicne profile na odmicih gredeh. Tako lahko sportni profil "Vtec powa" odpre ventile dlje in globlje. Valvetronic nima razlicnih profilov pac pa eno posebno gred ki celo vrsto ventilov potiska globlje, regulira pa jo ta elektromotor. Naloga je ista. le da odira globoko glede na potrebe. Pri VTEcu lahko moc narasca vse do 8500rpm. Podobni sistemi so le mitsubishijev Mivec in nisanov NeoVVL.
VVTi od toyote je cam phasing. torej samo zamika odpiranje venitlov. Ali bo odprl odtenek prej ali kasneje. To omogoca boljse zracenje zgorevalnega prostora. V nasprotju z vtec-om ki zaradi podalsanja odpiranja ventilov omogoci konkretno vec zraka v valj in lahko explozija zgodi se mocnejsa. To je tudi dosti cenejsi in preprostejsi sistem, saj temelji le na variatorju na jermenici. to je vsa ometnost. Zelo poceni zadeva, uporablja jo tudi ford, mazda, po novem renault, celo alfa itd. Res pa da je VVTi neodcisen od obratov, zamika glede na zahtevnost voznje: Variable Valve Timing with INTELIGENCE!
hondin tristopenjski vtec ki omogoca da do 2500rpm motor dela le z 4 sesalnimi ventili. Pri 4500-5500 rpm se ventili odpirajo globlje in tudi dlje.
VVTi cam phasing - prekrivanje ventilov:
Basically, it varies the valve timing by shifting the phase angle of camshafts. For example, at high speed, the inlet camshaft will be rotated in advance by 30° so to enable earlier intake. This movement is controlled by engine management system according to need, and actuated by hydraulic valve gears.
variator faze zamika:
Valvetronic:
Valvetronic is essentially a variable valve lift system acting on intake valves. Compare with conventional twin-cam engines with finger followers, it employs an additional eccentric shaft, an electric motor and several (one per valve) intermediate rocker arms (see picture). The motor control the angle of eccentric shaft, which rotate the angle hence depth of the intermediate rocker arms acting on finger followers, which in turn activate opening and closing of valves. If the rocker arms push deeper towards finger followers, the intake valves will have higher lift, vice-versa.
Now you might think about Honda's VTEC. Can Valvetronic use its variable lift to increase power like VTEC ? Sadly, Valvetronic is actually less efficient at high rev than conventional engines, let alone VTEC. As you can see, the camshaft drives the long intermediate rocker arms, in turn drive finger followers, this generates quite a lot of friction. Therefore the efficiency and refinement of Valvetronic engines drop rapidly at over 6,000 rpm. No wonder in the foreseeing future BMW will not equip its M-power engines with Valvetronic.
Edited by - petronas on 04/08/2003 14:48:17