VTEC System Description (KA/KC)

Overview 

This system improves fuel efficiency and reduces exhaust emissions at all levels of engine speed, vehicle speed, and engine load. The VTEC mechanism changes the valve lift and timing by using more than one cam profile. The VTEC system changes the cam profile (angle) at cruising speeds. (Cam angle is changed to obtain the EGR effect and reduce pumping loss.)

Valve Timing Operation Image 

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

Construction 

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

VTEC Camshaft 

The cam shaft is structured so that each cylinder has two height lift cam lobe and a low lift cam lobe.

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

VTEC Rocker Arm 

The rocker arm is divided to the primary rocker arm, the secondary rocker arms A and B. The inner side of the intake secondary rocker arms A and B have two VTEC switching piston and a return spring.

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

Rocker Arm Oil Control Valve 

The rocker arm oil control valve are integrated with the cylinder head. The rocker arm oil control solenoid turns ON or OFF the solenoid depending on a signal from the PCM to switch the hydraulic pressure applied to the valve to subject the valve to an ON/OFF control. By switching the ON/OFF of the valve, the hydraulic pressure applied to the VTEC switching piston in the rocker arm is controlled.

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

Rocker Arm Oil Pressure Switch 

The rocker arm oil pressure switch attached to the rocker arm oil control valve monitors the hydraulic pressure condition and the statuses of the rocker arm oil control spool valve.

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

Control 

Based on the vehicle speed signal, engine speed signal, engine load signal, throttle aperture signal, and engine coolant signal sent from various sensors, the PCM controls the ON/OFF of the rocker arm oil control solenoid.

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

Operation 

At high load 

At high load, the rocker arm oil control solenoid is turned on by the PCM. Oil pressure from the rocker arm oil control solenoid enters into the intake primary 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 secondary rocker arm B, locking the intake secondary arms A and B together. The intake primary rocker arm and the intake secondary rocker arm A are driven by the height lift cam.

Rocker Arm Oil Control Solenoid ON 

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

At engine start, and cruise 

At engine start, and cruise, 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 intake secondary rocker arms A and B are driven by the low lift cam, and the primary rocker arm is driven by the height lift cam.

Rocker Arm Oil Control Solenoid OFF 

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