CVVT and Camshaft

Description and Operation

Description

The Continuously Variable Valve Timing (CVVT) system advances or retards the intake and exhaust valve timing according to the ECM control signal, which is calculated from engine speed and load. Controlling CVVT provides valve overlap or underlap, which results in better fuel economy, reduced exhaust emissions (NOx, HC), and improved engine performance by reducing pumping losses, the internal EGR effect, improving combustion stability and volumetric efficiency, and increasing expansion work. This system consists of

• The CVVT oil control valve (OCV) supplies engine oil to the cam phaser or drains engine oil from the cam phaser according to the ECM PWM (Pulse Width Modulation) control signal.
• CVVT oil temperature sensor (OTS), which measures the engine oil temperature.
• and Cam Phaser, which changes the camshaft phase using hydraulic pressure from the engine oil.

engine oil flowing from the CVVT oil control valve changes the camshaft phase in the advance direction (Intake Advance / Exhaust Retard) or the opposite direction (Intake Retard / Exhaust Advance) by rotating the rotor connected to the camshaft inside the cam phaser.

Operating Principle

The CVVT has a mechanism that rotates the rotor vane by hydraulic force. The force is generated by engine oil supplied to the advance or retard chamber according to the control of the CVVT oil control valve.

[CVVT System Mode]

(1) Low Speed/Low Load	(2) Partial Load
(3) Low Speed/High Load	(4) High Speed/High Load

Driving Condition	Exhaust Valve		Intake Valve
	Valve Timing	Effect	Valve Timing	Effect
(1) Low Speed /Low Load	Fully Advance	* Lower valve overlap * Improved combustion stability	Fully Retard	* Lower valve overlap * Improved combustion stability
(2) Partial Load	Retard	* Increased expansion work * Reduced pumping losses * Reduced HC	Retard	* Reduced pumping losses
(3) Low Speed /High Load	Retard	* Increased expansion work	Advance	* Prevents intake backflow (improves volumetric efficiency)
(4) High Speed /High Load	Advance	* Reduced pumping losses	Retard	* Improved volumetric efficiency

Repair Procedures

Removal

1. 1
   Remove the cylinder head cover. (Refer to Cylinder Head Assembly - Cylinder Head Cover)
2. 2
   Remove the vacuum pump. (Refer to Cylinder Head Assembly - "Vacuum Pump")
3. 3
   Remove the timing chain. (Refer to Valve Timing System - Timing Chain)
4. 4
   Remove the intake CVVT assembly (A) and the exhaust CVVT assembly (B).

   

5. 5
   Remove the front camshaft bearing cap (A), center camshaft bearing cap (B), and rear camshaft bearing cap (C) in the order shown.

   

   

6. 6
   Remove the camshafts (A).

   

Inspection

Camshaft

1. 1
   Inspect the camshaft lobes. Using a micrometer, measure the cam lobe height. Cam Lobe Height: Intake: 41.79824 mm (1.6456 in) Exhaust: 41.57000 mm (1.6366 in)

   

   If the cam lobe height is less than the standard value, replace the camshaft.
2. 2
   Inspect the camshaft journal oil clearance.

   1. Clean the camshaft bearing caps and journals.
   2. Install the camshafts on the cylinder head.
   3. Place a strip of Plastigage on each camshaft journal.

      

   4. Install the front camshaft bearing cap (A), center camshaft bearing cap (B), and rear camshaft bearing cap (C) in the following sequence, tightening to the specified torque. Tightening Torque: Step 1: A: 9.8 N·m B: 5.9 N·m Step 2: A: 18.6 - 23 N·m B: 11.8 - 13.7 N·m C: 11.8 - 13.7 N·m

      

      

   5. Remove the bearing caps.
   6. Measure the plastigage at the widest point. Camshaft Bearing Oil Clearance: Intake: 0.027 - 0.057 mm (0.0010 - 0.0022 in) Exhaust: 0.027 - 0.057 mm (0.0010 - 0.0022 in)

      

      If the oil clearance is greater than the maximum, replace the camshaft. If necessary, replace the cylinder head.
   7. Completely remove the plastigage.
   8. Remove the camshaft.
3. 3
   Inspect the camshaft end play.

   1. Install the camshaft (A).

      

   2. Install the front camshaft bearing cap (A), center camshaft bearing cap (B), and rear camshaft bearing cap (C) in the following sequence, tightening to the specified torque. Tightening Torque: Step 1: A: 9.8 N·m B: 5.9 N·m Step 2: A: 18.6 - 23 N·m B: 11.8 - 13.7 N·m C: 11.8 - 13.7 N·m

      

      

   3. Using a dial indicator, measure the camshaft end play while moving the camshaft back and forth. Camshaft End Play: Intake: 0.1 - 0.2 mm (0.0039 - 0.0078 in) Exhaust: 0.1 - 0.2 mm (0.0039 - 0.0078 in)

      

      If the end play exceeds the limit, replace the camshaft. If necessary, replace the cylinder head.
   4. Remove the camshafts.
4. 4
   Inspect the CVVT assembly.

   1. Clamp the camshaft in a vise. Be careful not to damage the cam lobes and journals in the vise.
   2. Make sure the CVVT is locked by turning it clockwise or counterclockwise. It should not rotate.
   3. Intake CVVT: Seal one of the two advance holes in the camshaft journal with tape. Exhaust CVVT: Seal one of the two retard holes in the camshaft journal with tape. [Intake]

      

      [Exhaust]

      

   4. Intake CVVT: Apply approx. 150 kPa (1.5 kgf/cm², 21 psi) of compressed air to the unsealed supply port to release the lock. Exhaust CVVT: Apply approx. 150 kPa (1.5 kgf/cm², 21 psi) of compressed air to the unsealed retard port to release the lock.
   5. Intake CVVT: With compressed air applied, rotate the CVVT in the advance direction (counterclockwise) within its phase range, and check that the CVVT rotates smoothly. Exhaust CVVT: With compressed air applied, rotate the CVVT in the retard direction (clockwise), and check that the CVVT rotates smoothly.

      

      CVVT Phase Range: Intake: 25° (from the most retarded position to the most advanced position) Exhaust: 20° (from the most advanced position to the most retarded position)
   6. Intake CVVT: Rotate the CVVT to the most retarded position (clockwise), then make sure the CVVT is locked. Exhaust CVVT: Rotate the CVVT to the most advanced position (counterclockwise), then make sure the CVVT is locked.

CVVT (Continuously Variable Valve Timing) Assembly

Installation

1. 1
   Install the camshafts (A).

   

2. 2
   Install the front camshaft bearing cap (A), center camshaft bearing cap (B), and rear camshaft bearing cap (C) in the order shown. Tightening Torque: Step 1: A: 9.8 N·m B: 5.9 N·m Step 2: A: 18.6 - 23 N·m B: 11.8 - 13.7 N·m C: 11.8 - 13.7 N·m

   

   

3. 3
   Install the intake CVVT assembly (A) and exhaust CVVT assembly (B).

   Tightening torque: 63.7–74 N·m

   

4. 4
   Install the remaining parts in the reverse order of removal.