Description
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) and improves engine performance through reduction of pumping 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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(1) Low Speed/Low Load (2) Part Load (3) Low Speed/High Load (4) High Speed/High Load
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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 |
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- Remove the cylinder head cover. (Refer to «REMOVAL»(ref-675074-S07246743682014120400000)
- Set No. 1 cylinder to TDC/compression. Turn the crankshaft pulley and align its groove with the timing mark "T" of the lower timing chain cover. Check that the mark (A) of the CVVT sprockets are in straight line on the cylinder head surface as shown in the illustration. If not, turn the crankshaft one revolution (360°)
- Remove the bolt (A) from the service hole in the timing chain cover. It might be required to run a M8X1.25 tap in the hole to clean out the lock-tight (sealer) on the threads. CAUTION: Ensure that debris does not enter into the engine through the open bolt hole.
- Pull and turn the loop (A) on the SST 09240-2G000 to allow the spring loaded shaft (B) to be pulled (locked) against the spring. Add a small amount of light lubricant to the threads of the tool and then thread it into the hole in the timing cover until you can feel it hit the tensioner. Then thread the tool back out about one turn.
- Turn the loop to unlock the tool.
- Slowly turn the tool counterclockwise. Depending on where the pin on the tool is located, a few clicks may be heard as the pin moves over the pawl and shaft. As you turn, you should be able to feel the spring loaded pawl being lifted. Once lifting the pawl, tighten the lock nut (A) and lift the chain and cam gear onto the cam.
- Remove the camshaft. Remove the front camshaft bearing cap (A) with the upper bearing (B). Remove the camshaft bearing cap (A) in the sequence shown in illustration. Remove the camshafts (A).
- Disconnect the intake CVVT assembly (A) and exhaust CVVT assembly (B) from camshaft (C).
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Note. When removing the CVVT assembly bolt, prevent the camshaft from rotating by using a wrench at position D.
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- Install the intake CVVT assembly (A), exhaust CVVT assembly (B) and camshaft (C). Tightening torque: 53.9 ~ 63.7 N.m (5.5 ~ 6.5 kgf.m, 39.7 ~ 47.0 lb-ft) NOTE: When installing the CVVT assembly bolt, fix the camshaft by wrench at position D.
- Install the camshafts. NOTE: Apply a light coat of engine oil on camshaft journals. Install the exhaust camshaft lower bearing (A). Install the camshafts (A). Install the timing chain Check that the mark (A) of the CVVT sprockets are in straight line on the cylinder head surface as shown in the illustration. Install the exhaust camshaft upper bearing (A) to the front bearing cap.
- Install camshaft bearing caps (A) in their proper locations. Tightening order Group A --> Group B --> Group C. Tightening torque: Step 1 M6: 5.9 N.m (0.6 kgf.m, 4.3 lb-ft) M8: 14.7 N.m (1.5 kgf.m, 10.8 lb-ft) Step 2 M6: 10.8 ~ 12.7 N.m (1.1 ~ 1.3 kgf.m, 8.0 ~ 9.4 lb-ft) M8: 27.5 ~ 31.4 N.m (2.8 ~ 3.2 kgf.m, 20.3 ~ 23.1 lb-ft)
- Disconnect the SST (A) (09240-2G000).
- Install the service hole bolt of the timing chain cover. Tightening torque: 11.7 ~ 14.7 N.m (1.2 ~ 1.5 kgf.m, 8.6 ~ 10.8 lb-ft) CAUTION: The bolt must not be reused once it has been assembled.
- Install the cylinder head cover.
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See also:
• INTAKE & EXHAUST SYSTEM - OPTIMA HEV