Description
Exhaust emissions (CO, HC, NOx) are controlled by a combination of engine modifications and the addition of special control components.
Modifications to the combustion chamber, intake manifold, camshaft and ignition system form the basic control system.
These items have been integrated into a highly effective system which controls exhaust emissions while maintaining good driveability and fuel economy.
The catalytic converter of the gasoline engine is a three way catalyst. It oxidizes carbon monoxide and hydrocarbons (HC), and separates oxygen from the oxides of nitrogen (NOx).
There are two types of three-way catalyst; Palette type and Monolith type.
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Scheme 21
Continuous Variable Valve Timing (CVVT) system advances or retards the valve timing of the intake and exhaust valve in accordance with the ECM control signal which is calculated by the engine speed and load.
By controlling CVVT, the valve over-lap or under-lap occurs, which makes better fuel economy and reduces exhaust gases (NOx, HC). CVVT improves engine performance through reduction of pump loss, internal EGR effect, improvement of combustion stability, improvement of volumetric efficiency, and increase of expansion work.
This system consist of
- the CVVT Oil Control Valve (OCV) which supplies the engine oil to the cam phaser or runs out the engine oil from the cam phaser in accordance with the ECM PWM (Pulse With Modulation) control signal
- the CVVT Oil Temperature Sensor (OTS) which measures the engine oil temperature
- and the Cam Phaser which varies the cam phase by using the hydraulic force of the engine oil.
The engine oil getting out of the CVVT oil control valve varies the cam phase in the direction (Intake Advance/Exhaust Retard) or opposite direction (Intake Retard/Exhaust Advance) of the engine rotation by rotating the rotor connected with the camshaft inside the cam phaser.
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Operation Principle
The CVVT has the mechanism rotating the rotor vane with hydraulic force generated by the engine oil supplied to the advance or retard chamber in accordance with the CVVT oil control valve control.
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Scheme 24
![Scheme 24: [CVVT System Mode]](https://i.diagnostdata.com/repair/66/661084569adc5bdfe55f4fe743fb9dd8033834f9a79b084937c54e88526306a4.webp)
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| Driving Condition | Exhaust Valve | Intake Valve | ||
|---|---|---|---|---|
| Valve Timing | Effect | Valve Timing | Effect | |
| (1) Low Speed/Low Load | Completely Advance | * Valve Under-lap * Improvement of combustion stability | Completely Retard | * Valve Under-lap * Improvement of combustion stability |
| (2) Part Load | Retard | * Increase of expansion work * Reduction of pumping loss * Reduction of HC | Retard | * Reduction of pumping loss |
| (3) Low Speed/High Load | Retard | * Increase of expansion work | Advance | * Prevention of intake back flow (Improvement of volumetric efficiency) |
| (4) High Speed/High Load | Advance | * Reduction of pumping loss | Retard | * Improvement of volumetric efficiency |