Fuel and Emissions System Description - VTEC/VTC

Fuel and Emissions System Description - VTEC System

VTEC/VTC

- The i-VTEC system has a variable valve timing control (VTC) mechanism on the intake camshaft in addition to the usual VTEC.This system improves fuel efficiency and reduces exhaust emissions at all levels of engine speed, vehicle speed, and engine load.
- The VTEC system changes the intake valve lift and timing by using more than one cam profile.
- PZEV model: The VTEC system pauses one side of the exhaust valves in addition to changing the intake valve lift and timing.
- The VTC system changes the phase of the intake camshaft via oil pressure. It changes the intake valve timing continuously.










VTC System

- The VTC system makes continuous intake valve timing changes based on operating conditions.
- Intake valve timing is optimized to allow the engine to produce maximum power.
- Cam angle is advanced to obtain the EGR effect and reduce pumping loss. The intake valve is closed quickly to reduce the entry of the air/fuel mixture into the intake port and improve the charging effect.
- The system reduces the cam advance at idle, stabilizes combustion, and reduces engine speed.
- If a malfunction occurs, the VTC system control is disabled and the valve timing is fixed at the fully retarded position.





VTC System Diagram

The VTC oil control solenoid valve controls oil pressure to the advance chamber/retard chamber of the VTC actuator according to a signal from the ECM/ PCM. When the VTC actuator vanes rotate to the advance or retard position, the intake camshaft timing is changed.
CMP sensor A detects the intake camshaft angle and sends the information to the ECM/PCM. The ECM/PCM controls the VTC oil control solenoid valve as the intake camshaft angle changes.






VTEC System

Intake valve side (All models)

- 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.
- The rocker arm oil control solenoid (rocker arm oil control solenoid A) switches the intake valve side of the VTEC system on and off; the solenoid is controlled by the ECM/PCM.
- The rocker arm oil pressure switch (rocker arm oil pressure switch A) detects VTEC system oil pressure (intake valve side) and sends this information to the ECM/PCM.

Exhaust valve side (PZEV model)

- The VTEC system switches the operation of one of the exhaust valves to pause and lift the valve.
- At idle and low engine speed, one side of the exhaust valves is paused, and the valve lifts when the engine speed goes up.
- The system reduces hydrocarbons (HC) exhaust emissions at low engine speed.
- Rocker arm oil control solenoid B switches the exhaust valve side of the VTEC system on and off; the solenoid is controlled by the PCM.
- Rocker arm oil pressure switch B detects the VTEC system oil pressure (exhaust valve side), and sends this information to the PCM.

All models except PZEV (Intake valve VTEC)











PZEV model (Intake and exhaust valve VTEC)











VTEC System Operation

Intake valve side

At low engine speed, the rocker arm oil control solenoid (rocker arm oil control solenoid A) is turned off by the ECM/PCM. Oil pressure from the rocker arm oil control valve does not enter the intake rocker shaft. Each intake rocker arm is separated by a return spring and lifted by each low lift cam lobe.





At high engine speed, the rocker arm oil control solenoid (rocker arm oil control solenoid A) is turned on by the ECM/PCM. Oil pressure from the rocker arm control solenoid enters the primary intake rocker arm via the intake rocker shaft, and it moves the VTEC switching piston in the rocker arm.
This causes the VTEC switching piston to slide into the intake mid rocker arm and the intake secondary rocker arm, locking the rocker arms together. Both intake rocker arms are lifted by the high lift cam lobe.






Exhaust valve side (PZEV model)

At idle and low engine speed, rocker arm oil control solenoid B is turned off by the PCM. Oil pressure from the rocker arm oil control valve does not enter the exhaust rocker shaft. Each exhaust rocker arm is separated by a return spring, and lifted by each cam lobe. The exhaust primary rocker arm is moved by the normal lift cam lobe (valve active), and the exhaust secondary rocker arm is moved by the no lift cam lobe (valve pause).





When the engine speed reaches 2,500 rpm or more, rocker arm oil control solenoid B is turned on by the PCM. Oil pressure from the rocker arm oil control solenoid enters the primary exhaust rocker arm via the exhaust rocker shaft, and it moves the VTEC switching piston in the rocker arm. This causes the VTEC switching piston to slide into the exhaust secondary rocker arm, locking the exhaust rocker arms together. Both exhaust rocker arms are moved by the normal lift cam lobe (valve active).