Fuel And Emissions System Description - Variable Cylinder Management (VCM) System

Fuel and Emissions System Description - Variable Cylinder Management (VCM) System

Variable Cylinder Management (VCM) System

The VCM system activates the cylinders based on the driving condition. The system has three modes: 6 cylinder (all cylinder activation), 4 cylinder (pauses the No. 3 and No. 4 cylinders), and 3 cylinder (pauses the rear bank of cylinders). On paused cylinders, the intake and exhaust valves are kept closed. Since the valves are closed, the frictional losses from the valve spring compression and pumping are reduced because no air is compressed in the cylinder. This reduces engine drag.






VCM System Operation

During 6 Cylinder Mode

With the rocker arm oil control solenoids A (Bank 1), B (Bank 1), and A (Bank 2) OFF, the rocker arm oil control valves direct oil pressure. Oil pressure enters the primary rocker arm from the oil passage in the rocker shaft, and it moves the VTEC switching piston, sliding it into the secondary rocker arm and locking primary rocker arm and secondary rocker arms together. The rocker arms are lifted by the camshaft, and all cylinders are active.






During 4 Cylinder Mode

When rocker arm oil control solenoids B (Bank 1) and A (Bank 2) are turned on by the PCM, the front and rear rocker arm oil control valves switch the oil pressure. Oil pressure then enters the No. 3 and No. 4 cylinder's secondary rocker arm from the oil passage in the rocker shaft, causing the VTEC switching piston to slide into the primary rocker arm and against the return spring. This disengages the secondary rocker arm from the primary rocker arm to stop valve activation. The No. 3 and No. 4 cylinder's rocker arms do not move, and the No. 3 and No. 4 cylinders are paused. In the other four cylinders, oil pressure from the front and rear rocker arm oil control valves lock the primary and secondary rocker arms together. The rocker arms are moved by the camshaft, and the four cylinders are active.






During 3 Cylinder Mode

When rocker arm oil control solenoid A (Bank 1) is turned on by the PCM, the rear rocker arm oil control valve switches the oil pressure. Oil pressure then enters the rear bank cylinder's secondary rocker arm from the oil passage in the rocker shaft, causing the VTEC switching piston to slide into the primary rocker arm and against the return spring. This disengages the secondary rocker arm from the primary rocker arm to stop valve activation. The rear bank cylinder's rocker arms do not move, and the rear bank cylinders are paused. At the front bank, oil pressure from the front rocker arm oil control valve locks the No. 4 cylinder's primary and secondary rocker arms together. The No. 4 cylinder's rocker arms are moved by the camshaft, and all front bank cylinders are active.