Synchronized phase shifting of multiple variable cam actuators

Modern automotive engines often employ additional devices or systems, such as variable cam timing (VCT), that improve fuel economy, emissions, and/or peak torque and power. Every additional degree of freedom introduced by a new actuator increases mapping, calibration, and control design complexity. In addition, in VCT engine configurations with two banks of cylinders such as "V" engines or horizontally opposed engines, VCT creates control issues that arise due to requirements that multiple VCT devices shift synchronously. Non-synchronous VCT actuator movement may be caused by oil pressure differences between the banks (asymmetric oil supply), actuator sticking (cold starts), other mechanical imbalances, or improperly calibrated actuator control loops. Forcing the actuators to move together provides sufficient mitigation so that emission control and torque response are not compromised due to incorrect airflow estimation or spark timing. There are several approaches one can take to synchronize actuators. In this paper, we describe a system that modifies the reference cam phase command sent to the local VCT control loops in the two banks in order to slow down the faster actuator to match the response rate of the slower one. In this way we can prevent the difference between the banks from exceeding a set of threshold. The control algorithm accomplishes this without a-priori knowledge of which is the slow actuator and at what rate it is moving. The system automatically adjusts if actuators characteristics alter further, which may happen due to ageing or other factors.