Nonlinear Compensation using Bypassed Delta-Sigma Modulation for Variable Valve Actuation

This paper discusses the first introduction of delta-sigma modulation (DSM) as a method to compensate for nonlinearity. DSM is used as the compression method for audio and visual data, but has never been used as a method to compensate for nonlinearity. Increasing robustness has conventionally been used to compensate for nonlinearity, but the use of DSM enables direct compensation. In addition, DSM differs from standard methods of impressing high-frequency components in enabling highly accurate modulation of the control input calculated by the controller, and therefore entails no loss of control performance. The research discussed a modified form of DSM that has been termed "bypassed DSM," which resolves the accuracy deterioration of modulation when the reference signal with large amplitude is inputted to DSM. Bypassed DSM was applied in the lift control of inlet valves in an engine using a continuously variable valve timing and lift system (CVTL), and its effectiveness was verified in actual operation. The use of bypassed DSM resulted in a dramatic improvement in holding performance of valve lift to set point and in transient control performance during vehicle operation.