Variable Valve Timing Explained

MIVEC

MIVEC Stand’s for Mitsubishi Innovative Valve timing Electronic Control system and as it says it’s owned by Mitsubishi. It’s similar to that of Honda’s VTEC which was normally used to vary the Inlet valve timing and lift depending upon the engine load.

Why it’s needed?

            By adopting technologies like this manufacturers are able to attain more power, better efficiency and most importantly they were also able prepare themselves for the emission requirements. Sometimes they also help in the branding strategies of the companies.

How does it work?

            It alters the cam profile depending upon the drivers demand. There are two different kinds of cam lobe in each cylinder one called low lift lobe and other is called as medium lift lobe and there is one more lobe called high lift mode which is centrally located between the both. They are connected to one special kind of T-shaped lever which actuates the high lift profile when needed. They get connected to one special piston which works on hydraulic pressure difference.

            During low revs the T- shaped lever (Contains a piston) revolves without connecting them to the other cam lobes. At this time only, the low lift and the medium lift lobes work continuously. When the engine reaches a pre-determined rpm due to hydraulic pressure difference the piston moves up and gets engaged to the high lift cam and thus the high lift cam is engaged to the system. The switching over rpm is said to be around 3500rpm in all MIVEC engines.

            Due to MIVEC smaller valve overlap @ low engine rpm’s result in reducing the amount of fresh charge sent back to the manifold due to long overlap etc.

Structure of MIVEC system        

 

                       

When MIVEC is disengaged @ Low rev’s the system is like below,       

Take a closer look in the piston position

                                                                                                         

When MIVEC kicks in after 3500RPM the piston position changes like below,




Take a closer look  of the piston position



Advantages:

¶      Better power out of a smaller displacement engine.

¶      More efficiency.

¶      Emission requirements are attained easily.

Different manufacturers have different name for it few of them are listed below,

BMW	Vanos
Honda	VTEC(Variable Valve Timing and Lift Electronic Control),I-VTEC(Intelligent Variable Valve Timing and Lift Electronic Control)
Hyundai	CVVT - Continuous Variable Valve Timing
Ford	VCT-Variable Cam Timing, TiVCT-Twin Independent Variable Cam Timing
Toyota	VVT- Variable Valve Timing, VVT-I Varies both inlet and exhaust cam shaft independently

You can also refer this video from Youtube for better comparison of the systems,