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 (J35A7 Engine ('07 model))

The i-VTEC (intelligent variable valve timing and lift electric control system) adopts a cylinder pause VTEC (variable cylinder system). The cylinder pause VTEC system pauses the intake and exhaust valves on the rear bank under certain conditions such as cruise and fuel cut (see illustration below). Since the valves on the rear bank are closed, the frictional losses from valve spring compression and pumping are reduced because no air is compressed in the rear bank. This reduces engine drag.






VCM System Operation (J35A7 Engine ('07 model))

During 6 Cylinder Mode (Intake valve side)

With the rocker arm oil control solenoid off, the rocker arm oil control valve directs oil pressure. Oil pressure then enters secondary rocker arm from the oil passage in the intake rocker shaft, and it moves the VTEC switching piston in the rocker arm. This causes the VTEC switching piston to slide into primary rocker arm and mid rocker arm, locking the rocker arms together. Primary rocker arm and secondary rocker arm are then actuated by the mid rocker arm.






During 6 Cylinder Mode (exhaust valve side)

With the rocker arm oil control solenoid off, the rocker arm oil control valve directs oil pressure. Oil pressure then enters secondary rocker arms A and B from the oil passage in the exhaust rocker shaft, and it moves the VTEC switching piston in the rocker arm. This causes the VTEC switching piston to slide into primary rocker arms A and B, locking primary rocker arms A and B to the secondary rocker arms A and B. Secondary rocker arms A and B are then actuated by the primary rocker arm.





When the engine is off, the VTEC switching piston is held in the engaged position by the return spring. This allows the rocker arms to operate when oil pressure is low during cranking.

VCM System Operation (cont'd) (J35A7 Engine ('07 model))

During Cylinder Pause Mode (intake valve side)

With the rocker arm oil control solenoid energized by the PCM, the rocker arm oil control valve switches oil pressure. Oil pressure then enters primary rocker arm from the oil passage in the intake rocker shaft. This forces the VTEC switching piston into the secondary rocker arm and against the return spring, and disengages the primary rocker arm and secondary rocker arm from the mid arm to stop valve actuation. The mid rocker arm uses a lost motion spring to maintain tension.






During Cylinder Pause Mode (exhaust valve side)

With the rocker arm oil control solenoid energized by the PCM, the rocker arm oil control valve switches oil pressure. Oil pressure then enters primary rocker arms A and B from the oil passage in the exhaust rocker shaft. This forces the VTEC switching piston into secondary rocker arms A and B and against the return spring, and disengages the secondary rocker arms from the primary arms to stop valve actuation. The primary rocker arm uses a lost motion spring to maintain tension.






Variable Cylinder Management (VCM) System (J35A7 engine ('08-10 models))

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 cylinder), 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 (J35A7 engine ('08-10 models))

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 secondary rocker arm from the oil passage in the rocker shaft, and it moves the VTEC switching piston, sliding it into the primary 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 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 primary rocker arm from the oil passage in the rocker shaft, causing the VTEC switching piston to slide into the secondary rocker arm and against the return spring. This disengages the primary rocker arm from the secondary 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.






VCM System Operation (J35A7 engine ('08-10 models)) (cont'd)

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 primary rocker arm from the oil passage in the rocker shaft, causing the VTEC switching piston to slide into the secondary rocker arm and against the return spring. This disengages the primary rocker arm from the secondary 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.