VARIABLE VALVE TIMING MECHANISM CONSTRUCTION/OPERATION[L3 Turbo]

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Component and Function

Variable valve timing actuator
•  Continuously modifies the phases of the intake camshaft and crankshaft at the forward end of the intake camshaft using hydraulic pressure from the oil control valve (OCV).
OCV
•  Operated by current (duty signal) from the PCM. Switches the hydraulic oil passages to the variable valve timing actuator.
CKP sensor
•  Input the engine revolution signal to the PCM.
CMP sensor
•  Inputs the cylinder identification signal to the PCM.
PCM
•  Controls the OCV so that optimum valve timing is obtained according to engine operation conditions.


Operation outline

•  The variable valve timing actuator has two hydraulic chambers: a valve timing advance chamber and a valve timing retard chamber. They are located between the integrated housing of the camshaft sprocket and the camshaft integrated rotor. The oil pump supplies engine oil to each chamber. Hydraulic pressure applied to each chamber is controlled by the OCV, and the relative phases of the camshaft sprocket and the camshaft are modified to obtain optimum valve timing according to engine operation conditions.
At engine start
•  When the stopper pin in the variable valve timing actuator engages with the rotor, which is at the position of maximum valve timing retard due to spring force, the camshaft sprocket and the camshaft rotate as one unit. When the oil pump pressure rises and the stopper pin is disengaged, it becomes possible to modify the relative angles of the camshaft sprocket and the camshaft.
Advancing valve timing
•  When the spool valve in the OCV moves to the left according to the PCM signal, hydraulic pressure, from the oil pump, feeds into the valve timing advance passage and finally to the valve timing advance chamber in the variable valve timing actuator. Then, the rotor integrated with the camshaft rotates in the valve timing advance direction, against the housing driven by the crankshaft, and the valve timing is advanced.
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1
Hydraulic pressure flow
2
Oil pump
3
Housing
4
Case
5
Oil pan
6
To valve timing advance chamber
7
Rotor
8
Valve timing advance chamber
9
Variable valve timing actuator
10
Spool valve
11
From valve timing retard chamber
12
Camshaft

Retarding valve timing
•  When the spool valve in the OCV moves to the right according to the PCM signal, hydraulic pressure, from the oil pump, feeds into the valve timing retard passage and finally to the valve timing retard chamber in the variable valve timing actuator. Then, the rotor integrated with the camshaft rotates in the valve timing retard direction, against the housing driven by the crankshaft, and valve timing is retarded.
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1
Hydraulic pressure flow
2
Oil pump
3
Oil pan
4
Housing
5
Case
6
From valve timing advance chamber
7
Valve timing retard chamber
8
Rotor
9
Variable valve timing actuator
10
Spool valve
11
To valve timing retard chamber
12
Camshaft

Maintaining intermediate valve timing
•  The spool valve in the OCV is located near the middle of the valve timing advance and retard positions. Because of this, hydraulic pressures are maintained in both valve timing advance and retard chambers of the variable valve timing actuator. At the same time, relative angles of the rotor and the housing are fixed and maintained, resulting in fixed valve timing.
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1
Oil pump
2
To valve timing advance chamber
3
To valve timing retard chamber