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VTEC System Description
Overview
This system improves fuel efficiency and reduces exhaust emissions at all engine speeds, vehicle speeds, and engine loads. The powertrain control module (PCM) switches the low and high lift cam depending on the engine speed and load in order to optimize the fuel efficiency and the engine output. The rocker arm oil control solenoid switches the intake valve side of the VTEC system on and off; the solenoid is controlled by the PCM. Valve Timing Operation Image
Construction
VTEC is composed of the VTEC camshaft, the VTEC rocker arm, and the rocker arm oil control valve. VTEC Camshaft
The front and rear bank camshafts have intake side high lift cams, intake side low lift cams, and exhaust cams installed. VTEC Rocker Arm
The intake rocker arms are divided into intake primary rocker arms and intake secondary H rocker arms; the rocker arm pistons and the return spring are installed in the hole on the rocker arm. Rocker Arm Oil Control Valve
The rocker arm oil control solenoid A and the VTEC spool valve are integrated and installed on the cylinder head. The solenoids are switched ON and OFF by signals from the PCM, and the direction of the hydraulic pressure acting onto the spool valve is changed. By doing this, the direction of the hydraulic pressure acting onto the VTEC switching pistons in the intake rocker arms of each cylinder is changed, and low lift and high lift are reversed. Rocker Arm Oil Pressure Switch
The rocker arm oil pressure switch is attached to the rocker arm oil control valve. It monitors the hydraulic pressure condition, and the statuses of the rocker arm oil control solenoid and the rocker arm oil control valve. Control
Based on the vehicle speed signal, engine speed signal, engine load signal, and engine coolant signal sent from various sensors, the PCM determines what the lift amount should be and controls the ON/OFF of the rocker arm oil control solenoid. Operation
At low engine speed
At low engine speed, the rocker arm oil control solenoid is turned off by the PCM. Oil pressure from the rocker arm oil control valve does not enter the intake rocker shaft. The primary and the secondary intake rocker arms are lifted by the low lift cam lobe. Rocker Arm Oil Control Solenoid OFF
At high engine speed/high load operation
At high engine speed, the rocker arm oil control solenoid is turned on by the PCM. Oil pressure from the rocker arm oil control solenoid enters the intake secondary rocker arm via the intake rocker shaft, and it moves the VTEC switching piston in the rocker arm. This causes the VTEC switching piston to slide into the intake primary rocker arm, locking the intake secondary and primary rocker arms together. Both intake rocker arms are lifted by the high lift cam lobe. Rocker Arm Oil Control Solenoid ON
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