VTEC/VTC System Description - Operation

Rocker Arm Oil Control Valve 

The oil pressure from the oil pump is sent to the rocker arm oil control solenoid and the valve.

The rocker arm oil control solenoid switches ON and OFF depending on a normal/delayed close signal from the PCM.

As a result, the oil pressure applied to the valve is ON/OFF-controlled.

Rocker Arm Oil Control Solenoid Valve OFF (Otto Cycle) 

The rocker arm oil control solenoid is turned off by the PCM. Oil pressure does not press the spool valve and the spool valve is lifted by the spring.

Courtesy of HONDA, U.S.A., INC.

Rocker Arm Oil Control Solenoid Valve ON (Atkinson Cycle) 

The rocker arm oil control solenoid is turned on by the PCM. Oil pressure presses the spool valve down, and the hydraulic circuit is switched.

Courtesy of HONDA, U.S.A., INC.

VTEC Rocker Arm (normal mode) 

During the short duration cam operation, high oil pressure acts on the primary rocker arm, while low oil pressure acts on the secondary rocker arm. The primary, secondary, and mid rocker arms are separated from each other. The primary and secondary rocker arms are driven by the short duration cams.

Courtesy of HONDA, U.S.A., INC.

VTEC Rocker Arm (Atkinson cycle) 

During the operation of the long duration cam, high oil pressure acts on the secondary rocker arm, while low oil pressure acts on the primary rocker arm. Therefore, the VTEC switching piston moves, so that the primary, mid, and secondary rocker arms are connected and move together.

Since the mid rocker arm is driven by the long duration cam, the primary and secondary rocker arms are also driven by the long duration cam.

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VTC Motor/VTC Actuator 

The VTC motor has two gears that change phase. One is the gear assembly that is integrated with the timing sprocket, and the other is the gear that meshes with the planetary gear subassembly that is rotated by eccentricity, and the motor shaft rotated by the motor. The planetary gear subassembly is connected to the intake camshaft.

When the VTC actuator makes one rotation relative to the VTC motor, the planetary gear subassembly also moves by one gear tooth, and advances or retards the valve timing.

Courtesy of HONDA, U.S.A., INC.

VTEC+VTC Operation 

The VTEC + VTC operation uses the long duration cam and the VTC phase control to achieve the fuel-efficient Atkinson cycle for the hybrid drive, which uses both the engine and motor. For cruising, the engine is used directly. At engine start and during acceleration when high torque and high power output are required, the operation is switched to that of the short duration cam.

Courtesy of HONDA, U.S.A., INC.

The basic operation of VTEC and VTC is described below:

Mode	Operation	Additional remarks
Startup	Maximum retarded Courtesy of HONDA, U.S.A., INC.	When starting the engine, it retards the phase of the short duration cam, and retards the timing of the intake valve to close, reducing the engine's actual compression ratio, thereby reducing vibration. When engine speed increases through the cranking by the motor, the angle gradually advances.

Mode	Operation	Additional remarks
Cold engine (during warm-up)	Advance Courtesy of HONDA, U.S.A., INC.	When the engine is cold, advances the phase of the short duration cam, to improve the combustion condition, and warm the engine.
Normal drive (Otto cycle)	Advance/Retard Courtesy of HONDA, U.S.A., INC.	When power is required, the phase of the short duration cam is advanced/retarded. This enables both high power output and high fuel efficiency.
Normal drive (Atkinson cycle)	Advance/Retard Courtesy of HONDA, U.S.A., INC.	When in hybrid drive and overdrive operation, the phase of the long duration cam is advanced/retarded.This enables high fuel efficiency.

Mode	Operation	Additional remarks
Engine stop (idling stop)	Maximum retarded Courtesy of HONDA, U.S.A., INC.	When the engine is stopped, the phase is fully retarded to prepare for re-start.
Fail-safe mode	Maximum retarded Courtesy of HONDA, U.S.A., INC.	When there is a VTC problem, the phase is fully retarded. Cranking for engine start is done by the generator motor. Therefore the cranking speed is high, so that engine start is possible even during a VTC problem.
Vehicle in ON mode/OFF mode	Advance/Retard Courtesy of HONDA, U.S.A., INC.	At power ON, the phase is fully retarded to prepare for start (at normal temperature). At power OFF, the phase is changed to advance for cold start. For this reason, an operation noise is heard when the power switch is turned ON/OFF.