VTEC/Variable Cylinder Management (VCM) System Description

Construction

The VTEC on this vehicle is used for switching intake valve lift between low lift and high lift, depending on engine speed and vehiclespeed; it uses a variable cylinder management (VCM) system that switches the operating cylinder. Depending on the drivingconditions, the VCM system switches between 6 cylinder operation and 3 cylinder operation. This mechanism allows driving torque toincrease at the time of low speed and low load, improved fuel consumption, exhaust gas reduction, and higher engine performance athigh speed and high load. The VTEC installed for each bank stops opening and closing the intake and exhaust valves on the rearbank when the 3 cylinder mode is activated. Not opening and closing the valves eliminates the drive resistance (valve springcompression resistance) for valve opening, closing and the suction air resistance (pumping loss), which leads to a reduction of enginerotation resistance.

VTEC Camshaft

The front bank camshaft has intake side high lift cams, intake side low lift cams, and exhaust cams installed. The rear bank camshaft has intake side high lift cams, intake side low lift cams, intake side cylinder stop cams (no lift), and exhaustcams installed.

VTEC Rocker ArmRear bank intake rocker arm

The intake rocker arms on the rear bank are divided into intake primary rocker arms, intake secondary H rocker arms, and intakesecondary L rocker arms; stopper piston A, synchronizing piston B, stopper piston C, synchronizing piston D, and the return spring areinstalled in the hole on the rocker arm.

Rear bank exhaust rocker arm

The exhaust rocker arms on the rear bank are divided into exhaust primary rocker arms and exhaust secondary rocker arms; theexhaust synchronizing piston, synchronizing piston B, and the return spring are installed in the hole on the rocker arm.

Front bank intake rocker arm

The intake rocker arms on the front bank are divided into intake primary rocker arms and intake secondary H rocker arms; the rockerarm piston and the return spring are installed in the hole on the rocker arm.

Rocker Arm Oil Control ValveRear rocker arm oil control valve

Rocker arm oil control solenoid A (bank 1), solenoid B (bank 1), and the VTEC spool valve are integrated and installed on the rearrocker arm oil control valve. The solenoids are switched to ON and OFF by signals from the powertrain control module (PCM), and thedirection of the hydraulic pressure acting onto the spool valve is changed accordingly. By doing this, the direction of the hydraulicpressure acting onto the VTEC switching pistons in the intake and exhaust rocker arms of each cylinder at the rear bank is alsochanged, and low lift, high lift, and cylinder stop are activated alternately.

Front rocker arm oil control valve

Rocker arm oil control solenoid A (bank 2) and the VTEC spool valve are integrated and installed on the front rocker arm oil controlvalve. The solenoids are switched to ON and OFF by signals from the PCM, and the direction of the hydraulic pressure acting onto thespool valve is changed. By doing this, the direction of the hydraulic pressure acting onto the VTEC switching pistons in the intakerocker arms of each cylinder of the front bank is changed, and low lift and high lift are reversed.

Rocker arm oil pressure switch A (bank 1), switch B (bank 1), switch A (bank 2)

Each rocker arm oil pressure switch is attached each rocker arm oil control valve. The switch monitors the hydraulic pressurecondition, and the statuses of the rocker arm oil control solenoid valve and rocker arm oil control valve. Rocker arm oil pressure switchA (bank 1) and rocker arm oil pressure switch A (bank 2) are normally closed, rocker arm oil pressure switch B (bank 1) is normallyopen.

Rocker arm oil pressure switch A (bank 1), Rocker arm oil pressure switch A (bank 2)

Rocker arm oil pressure switch B (bank 1)

Control

Based on engine speed, vehicle speed, engine load, throttle position, and the engine coolant temperature signal sent from varioussensors, the powertrain control module (PCM) determines the ON/OFF of each of the rocker arm oil control solenoids.

The PCM switches low lift, high lift, and 3 cylinder operation by controlling the respective solenoid valves. Hydraulic pressure switchesare installed in each solenoid circuit for monitoring system malfunction.

Mode PCM sends command to the rocker arm oilcontrol solenoid

Rocker arm oil pressure switch (detected oilpressure)

Solenoid A(Bank 1)

Solenoid B(Bank 1)

Solenoid A(Bank 2)

Switch A (Bank 1)

Switch B (Bank 1)

Switch A (Bank 2)

Mode PCM sends command to the rocker arm oilcontrol solenoid

Rocker arm oil pressure switch (detected oilpressure)

Solenoid A(Bank 1)

Solenoid B(Bank 1)

Solenoid A(Bank 2)

Switch A (Bank 1)

Switch B (Bank 1)

Switch A (Bank 2)

6 Cylinder LowLift

OFF OFF OFF ON (Low) OFF (Low) ON (Low)

6 Cylinder HighLift

ON OFF ON OFF (High) OFF (Low) OFF (High)

3 Cylinder OFF ON OFF ON (Low) ON (High) ON (Low)

Operation6 cylinder low lift mode

The powertrain control module (PCM) switches rocker arm oil control solenoid A (bank 1), solenoid B (bank 1), and solenoid A (bank2) to OFF. On the rear bank side, the pressurized oil from the oil pump passes through the VTEC spool valve and flows into the rearrocker arm. On the intake side, the hydraulic pressure acts onto the right side of synchronizing piston B in the figure, and stopperpiston A and synchronizing piston B are moved to the left side in the figure by the spring force and the hydraulic pressure. By doingthis, the intake primary rocker arm and the intake secondary L rocker arm are synchronized and joined. Low lift drive is done by thecams having the small valve lift. On the exhaust side, the hydraulic pressure acts onto the spring side of exhaust synchronizing piston,and by using the spring force and the hydraulic pressure to move synchronizing piston B and exhaust synchronizing piston in thedirection of the arrow in the figure, the exhaust primary rocker arm and the exhaust secondary rocker arm are synchronized, causingthem to move as one. On the front bank side, the hydraulic pressure from the oil pump is not applied to the rocker arm piston becausethe spool valve is pushed up by the spring force. The rocker arm piston is pushed by the spring force to the left side in the figure, theintake primary rocker arm and the intake secondary rocker arm separate, and a low lift movement is done by the cams having thesmall valve lift.

6 cylinder high lift mode

The PCM switches rocker arm oil control solenoid A (bank 1) to ON, solenoid B (bank 1) to OFF, and solenoid A (bank 2) to ON. Onthe rear bank side, the pressurized oil from the oil pump passes through the VTEC spool valve and flows into the rear rocker arm. Onthe intake side, the hydraulic pressure is applied to the right side of synchronizing piston D in the figure, and the hydraulic pressuremoves stopper piston C and synchronizing piston D to the left in the figure. By doing this, the intake primary rocker arm and the intakesecondary H rocker arm are synchronized and joined and high lift drive is done by the cams with large valve lift. On the exhaust side,the hydraulic pressure is applied to the spring side of exhaust synchronizing piston, and by using the spring force and the hydraulicpressure to move synchronizing piston B and exhaust synchronizing piston in the direction of the arrow in the figure, the exhaustprimary rocker arm and the exhaust secondary rocker arm are synchronized, causing them to move as one. On the front bank side,the hydraulic pressure from the oil pump is applied to the left side of the rocker arm piston, as the solenoid is ON and the spool valveis pushed to the lower side by the hydraulic pressure, so that the rocker arm piston is pushed to the right in the figure. The intakeprimary rocker arm and the intake secondary H rocker arm are synchronized and joined, and high lift movement is done by the camswith a large valve lift.

3 cylinder mode

The PCM switches rocker arm oil control solenoid A (bank 1) to OFF, solenoid B (bank 1) to ON, and solenoid A (bank 2) to OFF. Onthe rear bank side, the pressurized oil from the oil pump passes through the VTEC spool valve and flows into the rear rocker arm. Onthe intake side, the hydraulic pressure acts onto the left side of stopper piston A in the figure, and stopper piston A and synchronizingpiston B are moved to the right side in the figure. By doing this, the intake primary rocker arm and the intake secondary L rocker armand the intake secondary H rocker arm are separated and a cylinder stop is done. On the exhaust side, the hydraulic pressure isapplied to synchronizing piston B, and by using hydraulic pressure to move synchronizing piston B and exhaust synchronizing pistonin the direction of the arrow in the figure, the exhaust primary rocker arm and the exhaust secondary rocker arm are separated, and acylinder stop is done. On the front bank side, the hydraulic pressure from the oil pump is not applied to the rocker arm piston becausethe spool valve is pushed up by the spring force. This causes the rocker arm piston to be pushed by the spring force to the left side inthe figure; the intake primary rocker arm and the intake secondary H rocker arm are separated, and a low lift movement is done by thecams having the small valve lift.