Rocker Arm Oil Control System
The high output 1.8L (RPO-LNK) engine has a high speed cam system that increases engine output between 6000-8200 RPM. The increase in power is possible because valve lift is significantly increased at engine speeds above 6000 RPM. A second camshaft lobe with a high lift profile is cast into each camshaft, alongside the low/medium speed lobes. In order to use the high speed cam only when desired, the engine utilizes a rocker arm oil control system. The system uses unique rocker arms that are hydraulically operated and electronically controlled. See Fig 1 .
The rocker arms ride on rocker arm shafts that supply engine oil, that is under pressure, to the rocker arms. The flow of engine oil to the rocker arms and shafts is controlled by the rocker arm oil control solenoid valve. A rocker arm oil pressure switch signals the Powertrain Control Module (PCM) when oil pressure is detected. A screen type oil filter is located in the oil supply passage to the rocker arm shafts. The rocker arm oil control solenoid and the oil pressure switch are located in the oil control housing.
During engine operation below 6000 RPM, the rocker arms follow the low/medium speed cam lobes. When engine oil is allowed to flow unobstructed to the rocker arms, the arms follow the high speed cam lobes, increasing valve lift. The flow of engine oil to the rocker arms is controlled by the rocker arm oil control solenoid valve. The solenoid is Pulse Width Modulated (PWM) by the PCM. The rocker arm oil pressure switch detects oil pressure when the rocker arm oil control solenoid is ON. The oil pressure switch input enables the PCM to monitor the operation of the rocker arm oil control solenoid. The rocker arm oil filter removes dirt and debris from the supply of engine oil to the rocker arm shafts.
The rocker arm oil control solenoid is commanded OFF by the PCM at engine speeds below 6000 RPM. With the solenoid OFF, oil that flows into the oil supply passage easily flows out thorough the solenoid and the return oil passage. See Fig 2 . There is adequate oil for lubrication of the rocker arms and shafts, but because the flow is unrestricted there is no increase in oil pressure. Without significant oil pressure in the rocker arms the low/medium speed cam followers operate the valve train. The rocker arm oil pressure switch is closed.
The rocker arm oil control solenoid is commanded ON by the PCM at engine speeds above 6000 RPM. With the solenoid ON, oil that flows into the oil supply passage is blocked by the solenoid from the return oil passage. See Fig 3 . This creates significant oil flow to the rocker shafts and the rocker arms. Oil pressure increases in the rocker arms and the high speed cam followers operate the valve train. The rocker arm oil pressure switch is open.