Fuel and Emissions System Description - VTEC System

Fuel and Emissions System Description - VTEC System

VTEC

- The VTEC system changes the cam profile to correspond to engine speed. It maximizes torque at low engine speed and output at high engine speed. The low lift cam is used at low engine speeds, and the high lift cam is used at high engine speeds.
- Both the intake valve side and the exhaust valve side have primary and secondary rocker arms. These rocker arms are locked and separated to change the cam profile by switching the oil passages. Roller rockers are used to minimize mechanical friction.





- The VTEC system oil pressure switched by the rocker arm oil control valve changing the hydraulic circuit. The rocker arm oil control valve is controlled by the rocker arm oil control solenoid. The rocker arm oil pressure switch detects VTEC system oil pressure and sends this information to the PCM.





VTEC System Operation

At low engine speed

At low engine speed, the rocker arm oil control solenoid is turned off by the PCM. Oil pressure from the rocker arm oil control valve does not enter the rocker shaft. The primary and secondary rocker arms are separated by a return spring and the intake and the exhaust secondary rocker arms are lifted by the low lift cam lobe.






VTEC System Operation

At high engine speed

At high engine speed, the rocker arm oil control solenoid is turned on by the PCM. Oil pressure from the rocker arm control solenoid enters the intake secondary rocker arm and the exhaust primary rocker arm via the rocker shaft, and it moves the VTEC switching piston into the intake primary rocker arm and the exhaust secondary rocker arm. This causes the VTEC switching pistons to lock both rocker arms (primary and secondary) together. Both rocker arms are then lifted by the high lift cam lobe.