Page 16 - E BOOK ENGINE MECHANICAL M2

2. MIVEC ENGINES

3. SWITCHING VALVE TIMING & LIFT MIVEC ENGINE
The switching valve timing & lift MIVEC system uses a mechanism that switches the intake valve
timing and the amount of its valve lift. The intake camshaft is configured with low speed cam profile
and high speed cam profile. According to engine speed, the rocker arms may ride on either one of
these.
This MIVEC system also has an additional operating cam switching mechanism to the conventional
SOHC 4 valve engine. The switching mechanism operates the changeover by alternating between a
low lift cam used for low engine speed mode, and a high lift cam used for high engine speed mode.
In the low speed mode, the intake flow into the combustion chamber is enhanced by the small
amount of valve lift due to the low lift cam. The combustion is stabilized achieving fuel economy, low
harmful exhaust gas emission and high engine torque output.
In the high speed mode, longer intake valves opening period in conjunction with a larger amount of
valve lift due to the high lift cam lobe, increases intake air volume, and the high engine output could
be obtained.

Switching piston
T-lever

Intake rocker arm

Intake high lift cam

Intake rocker arm

Camshaft Intake low lift cam

Fig. 2-7

Fig. 2-8

Pub. No. PTAE1225 2 - 4