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Design of an Electric Variable CAM Phaser Controller
Abstract:
As the emissions and fuel economy standards for internal combustion engines become ever more stringent, a variety of valvetrain control methods have been developed to improve engine performance. One of these is camshaft (CAM) phasing, which controls the angular position of the CAM relative to the crankshaft allowing changes to the timing of valve lift events. This method has demonstrated advantages including broadening the engine torque curve, increasing peak power at higher RPM, reducing hydrocarbon and NOx emissions, and improving fuel economy. In addition, external EGR systems can be eliminated because internal cylinder dilution control can be achieved by varying CAM timing.
Current implementations of CAM phasing use oil-pressure-based electro-mechanical systems. While these systems are relatively low cost and have proven to be robust, they have disadvantages at low oil temperatures and pressures (such as during cranking events). To overcome performance issues of oil based systems, Delphi has created a CAM phasing system using a brushless DC (BLDC) motor to drive the phasing mechanism. This approach provides full control independent of oil conditions and demonstrates increased phasing authority.
This paper will describe the electronics and algorithms required to control the three-phase BLDC motor which is part of the electric variable CAM phasing (eVCP) system. This controller takes desired CAM phase angle as an input, calculates the phase angle error, and closes the loop on the resultant motor current command. The electronics are packaged in a production-style case suitable for use in customer development applications.
From a software perspective, this paper will discuss architecture considerations, including provisions for model-based rapid algorithm development and low-level motor control functions. Hardware component selection criteria and electromagnetic compatibility (EMC) design considerations will also be included. Finally, motor performance test data will be presented.