Variable Cam Timing System: Overview: Notes

Variable Cam Timing (VCT) enables rotation of the camshaft(s) relative to the crankshaft (phase-shafting) as a function of engine operating conditions. There are four types of VCT systems.

• Exhaust Phase Shifting (EPS) system - the exhaust cam is the active cam being retarded.
• Intake Phase Shifting (IPS) system - the intake cam is the active cam being advanced.
• Dual Equal Phase Shifting (DEPS) system - both intake and exhaust cams are phase shifted and equally advanced or retarded.
• Dual Independent Phase Shifting (DIPS) system - where both the intake and exhaust cams are shifted independently.

All systems have four operational modes; idle, part throttle, wide open throttle and default mode. At idle and low engine speeds with closed throttle, the phase angle are controlled by air flow, engine oil temperature and engine coolant temperature. At part and wide open throttle the PCM controls cam timing based on engine RPM, load and throttle position. VCT systems provide reduced emissions and enhanced engine power, fuel economy and idle quality. IPS systems also have the added benefit of improve torque. In addition, on some applications a VCT system can eliminated the need for an external Exhaust Gas Recirculation (EGR) system. The elimination of the EGR system is accomplished by controlling the overlap in valve opening between the intake valve opening and exhaust valve closing.

Currently for the 2004 model year, Ford Motor Company uses the IPS and DEPS systems. The IPS system is on Lincoln LS, Thunderbird and Focus SVT and the DEPS system is on the F150 5.4L 3V.