VVT-i - VARIABLE VALVE TIMING INTELLIGENT SYSTEM

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WHAT IS VVT ?

• Variable Valve Timing (VVT) is a generic term for an automobile piston engine technology that adjusts the timing of the opening and closing of the engine's intake and exhaust valves, thereby optimizing performance, fuel efficiency, and emissions.
• VVT allows the lift or duration or timing (some or all) of the intake or exhaust valves (or both) to be changed while the engine is in operation, optimizing performance, efficiency, and emissions under varying driving conditions.

•Two stroke engines use a power valve system to get similar results to VVT.

WHAT IS VVT-i ?

• The VVT-i system is designed to control the intake camshaft with in a range of 50°(of Crankshaft Angle ) to provide valve timing i.e. optimally suited to the engine condition .This improves the torque in all the speed ranges as well as fuel economy ,and reducing exhaust emissions.
• This system controls the intake camshaft valve timing so as to obtain balance between the engine output, fuel consumption & emission control performance. The actual intake side valve timing is feed back by means of the camshaft position sensor for constant control to the target valve timing.

CONSTRUCTION

The Variable Valve Timing (VVT) system includes:
 ECM
 OCV
 VVT controller

•The ECM sends a target duty-cycle control signal to the OCV. This control signal regulates the oil pressure supplied to the VVT controller. Camshaft timing control is performed according to engine operating conditions such as the intake air volume, throttle valve position and engine coolant temperature.
•The ECM uses sensor signals to control the intake valve timing through the VVT controller, improving engine performance, fuel efficiency, and reducing emissions. It verifies and adjusts the intake valve timing based on data from camshaft and crankshaft sensors.
•The ECM uses the VVT system to adjust the intake camshaft timing. It sends a control signal to the OCV, which regulates oil pressure for the VVT controller to change the camshaft position.

1- VVT-i CONTROLLER

•It consist of the housing driven from the timing chain & the vane coupled with the intake camshaft.
The oil pressure sent from the advance or retard side path at the intake camshaft causes rotation in the VVT-i controller vane circumferential direction to vary the intake valve timing continuously.
•When the engine is stopped the intake camshaft will be in the most retard state to ensure start ability.
•When hydraulic pressure is not applied to the VVT-i controller immediately after the engine has been started, the lock pin locks the movement of the VVT-i controller to prevent a knocking noise.

2- CAMSHAFT TIMING OIL CONTROL VALVE

•The camshaft timing oil control valve controls the spool valve position in accordance with the duty-cycle control from the ECM.
•This allows the hydraulic pressure to be applied to the VVT-i controller, enabling adjustment of the camshaft's advance or retard position.

OPERATION

•The camshaft timing oil control valve selects the path according to the advance, retard or hold signal from the ECM.
The VVT-i controller rotates the intake camshaft in the timing advance or retard position or holds it according to the position where the oil pressure is applied.

	OPERATION	CAMSHAFT TIMING OIL CONTROL VALVE DRIVE SIGNAL	DESCRIPTION
ADVANCE		Advance Signal Duty Ratio	When the camshaft timing oil control valve is positioned as illustrated by the advance signal from the ECM, the resultant oil pressure is applied to the timing advance side vane chamber to rotate the camshaft in the timing advance direction.
RETARD		Retard Signal Duty Ratio	When the camshaft timing oil control valve is positioned as illustrated by the retard signal from the ECM, the resultant oil pressure is applied to the timing retard side vane chamber to rotate the camshaft in the timing retard direction.
HOLD		Hold Signal Duty Ratio	The ECM calculates the target timing angle according to the traveling state to perform control as described above. After setting at the target timing, the valve timing is held by keeping the camshaft timing oil control valve in the neutral position unless the traveling state changes. This adjusts the valve timing at the desired target position and prevents the engine oil from running out when it is unnecessary.

•The ECM adjusts valve timing based on engine speed, air volume, throttle position, and water temperature, using the camshaft and crankshaft position sensors for continuous control to achieve the desired valve timing.

*Operation during various driving condition ( Concept Diagram )*






ADVANTAGES OF VVT-i

•Improved torque & output

•Battery & fuel economy

•Reduced nitrogen oxide & hydrocarbon emissions

APPLICATIONS OF VVT-i

•VVT - Toyota 4A-GE 20-Valve engine introduced VVT in the 1992 Corolla GT-versions.
•VVT-i - Continuously varies the timing of the intake camshaft, or both the intake and exhaust camshafts (depending on application).
•VVTL-i - or Variable Valve Timing and Lift with Intelligence, continuously varies the timing of the intake valves. It varies the duration, timing, and lift of the intake and exhaust valves by switching between two different sets of cam lobes, optimizing engine performance across a wide range of operating conditions for enhanced power and efficiency.