VTEC/VTC System Description

VTEC 

Overview 

VTEC system changes the valve lift timing and lift height depending on the engine speed and load in order to optimize the fuel efficiency and the engine output.

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Construction 

VTEC is composed of the VTEC camshaft, VTEC rocker arm, and rocker arm oil control valve.

Control 

Based on the signals sent from the various sensors, the powertrain control module (PCM) determines the lift amount and controls ON/OFF of the rocker arm oil control solenoid.

The PCM generates and determines the control amount based on signals from various sensors to subject the rocker arm oil control solenoid to a feedback control.

For locations of each component on the vehicle, refer to the Component Location Index

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Operation 

Rocker Arm Oil Control Solenoid 

When the rocker arm oil control solenoid is turned off by the PCM, the spool valve is moved upward in the figure by the spring and the oil pressure from the oil pump enters the upper oil passage in the figure.

When the rocker arm oil control solenoid is turned on, the rocker arm oil control solenoid is moved upward in the figure and the spool valve is moved downward against the spring by the oil pressure, then the oil pressure from the oil pump enters the lower oil passage in the figure.

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VTEC Rocker Arm (LOW Lift) 

Oil pressure from the rocker arm oil control valve enters the primary rocker arm via the oil port. This oil pressure and the return spring tension push the stopper piston and the VTEC switching pistons to the left side in the figure. Thus the primary and the secondary rocker arms are separated from the middle rocker arm, and the primary and the secondary rocker arms are driven by the low lift cam.

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VTEC Rocker Arm (HIGH Lift) 

Oil pressure from the rocker arm oil control valve enters the secondary rocker arm via the oil port. This oil pressure moves the VTEC switching piston in the secondary rocker arm to the right side in the figure. This causes the VTEC switching piston to slide into the middle rocker arm and the primary rocker arm, locking the secondary, middle, and the primary rocker arms. Thus all rocker arms are driven by the high lift cam.

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VTC 

Overview 

The VTC system changes intake valve timing continuously depending on the engine operating conditions.

The electrical VTC is adjusted through electric control and it enables the phase of the intake camshaft to have non-step advances or retards the valve timing.

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Construction 

The VTC consists of the electric VTC motor which is integrated with the control unit, and the VTC actuator. The electric VTC motor drives the VTC actuator, and advances or retards the valve timing by changing the phase.

The VTC motor in the VTC actuator 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.

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Control 

The electric VTC system diagram is as follows.

The motor is controlled through the command from the powertrain control module (PCM). The PCM performs advances or retards the valve timing based on the data from various sensors, and performs feedback-control based on the data from CMP sensor A.

For locations of each component on the vehicle, refer to the Component Location Index

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

Operation 

This VTC system liaises with the VTEC system. 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.