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 control signal from the ECM, which is calculated based on engine speed and load.

CVVT control provides valve overlap or underlap, which improves fuel economy, reduces exhaust emissions (NOx, HC), and improves engine performance by reducing pumping losses, improving internal exhaust gas recirculation effect, improving combustion stability, improving volumetric efficiency, and increasing expansion work.

This system consists of the following:

• CVVT Oil Control Valve (OCV), which 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 cam phase by hydraulic force of engine oil.

Engine oil flowing from the CVVT oil control valve changes the camshaft phase in the advance direction (intake advance / exhaust retard) or in the opposite direction (intake retard / exhaust advance) relative to engine rotation, by rotating the rotor connected to the camshaft inside the cam phaser.

Operating Principle

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

1. 1

   CVVT Intake

   

2. 2

   CVVT Exhaust

   

[CVVT System Mode]

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

Repair Procedures

Removal

1. 1

   Remove the timing chain.

   (See Timing System - Timing Chain)

2. 2

   Remove the intake CVVT (A) and exhaust CVVT (B).

   

   [Intake Camshaft]

   

   [Exhaust Camshaft]

   

3. 3

   Remove the front camshaft bearing cap (A) and the camshaft bearing cap (B).

   

4. 4

   Remove the intake camshaft (A) and the exhaust camshaft (B).

   

Inspection

Camshaft

1. 1

   Inspect the camshaft lobes.

   Using a micrometer, measure the cam lobe height.

   Cam Lobe Height

   Intake: 36.4183 mm (1.4337 in.)

   Exhaust: 36.1543 mm (1.4233 in.)

   

   If the cam lobe height is less than the standard value, replace the camshaft.

2. 2

   Inspect the camshaft journal surface for wear.

   If the journal is excessively worn, replace the camshaft.

3. 3

   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) and the camshaft bearing cap (B) in the following manner, with the specified torque.

      Tightening Torque

      Front camshaft bearing cap: 9.8 N·m

      Camshaft bearing cap: 5.9 N·m

      Front camshaft bearing cap: 18.6–23 N·m

      Camshaft bearing cap: 11.8–13.7 N·m

   5. Remove the bearing caps.

   6. Measure the Plastigage at its 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 camshafts.

4. 4

   Inspect the camshaft end play.

   1. Install the camshaft bearing cap.

   2. Using a dial indicator, measure the camshaft end play by moving the camshaft back and forth.

      If the end play is greater than specified, replace the camshaft.

      If necessary, replace the bearing caps and cylinder head as a set.

      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.)

      

   3. Remove the camshafts.

CVVT Exhaust Assembly

1. Inspect the CVVT assembly.

   1. Clamp the exhaust camshaft in a vise. Be careful not to damage the cam lobes and journals in the vise.

   2. Make sure the exhaust CVVT is locked by turning it clockwise or counterclockwise. It must not rotate.

   3. Exhaust CVVT: Seal one of the two holes in the camshaft journal with tape.

      

   4. Exhaust CVVT: Apply approx. 150 kPa (1.5 kgf/cm², 21 psi) compressed air to the unsealed retard hole to release the lock.

   5. Exhaust CVVT: While applying compressed air, turn the CVVT in the retard direction (clockwise), and make sure the CVVT rotates smoothly.

      CVVT phase range

      Exhaust: 20° ± 1° (from most advanced position to most retarded position)

      

   6. Exhaust CVVT: Turn the CVVT to the most advanced position (counterclockwise), then make sure the CVVT is locked.

Installation

1. 1

   Install the intake camshaft (A) and the exhaust camshaft (B).

   

2. 2

   Install the front camshaft bearing cap (A) and the camshaft bearing cap (B) using the following method and specified torque.

   Tightening Torque

   A: 18,6–23 N·m

   B: 11,8–13.7 N·m

   

   

3. 3

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

   Tightening Torque

   Intake:

   85,3–95 N·m

   Exhaust:

   63,7–74 N·m

   

4. 4

   Install in the reverse order of removal.