Development of a closed loop control system:
Closed loop control will be designed to monitor the engine valve position and compare that position to the desired input position. Unlike solenoid based camless engine systems, the closed loop control of a piezoelectric piloted system provides significantly greater opportunity for fine control. This improvement is due to the unlimited positioning of the piezoelectric stacks as opposed to the on/off, binary position available for solenoids. By developing a closed loop feedback controller, the variable positioning of the piezoelectric stacks can be exploited. This will allow for greater direct control of hydraulic orifice cross-sectional area, thereby indirectly controlling fluid flow rates, engine valve displacement, velocity, and acceleration.
Fully closed loop control will be facilitated by a dSPACE DS1102 controller unit. The output of the controller will be a voltage signal provided to the high voltage amplifier and ultimately the piezoelectric stack. Input to the controller will consist of voltages associated with the engine valve displacement, the spool valve displacement, or both. Other input to the control system will include timing algorithms and demanded engine speed.
Closed loop control for piezoelectric piloted actuators represents an advance for engine valve timing due to the piezoelectric stack’s variable position. Unlike earlier camless engine control systems that relied on the control of binary position solenoids, closed loop control of the piezoelectric stacks allows for any arbitrary stack displacement. This, in conjunction with a spool valve for control of hydraulic fluid, provides for a greater level of engine valve control. Such a control system will allow researchers, and ultimately manufacturers, to control engine valve timing, displacement, and seating velocity with considerably greater precision, reliability, and repeatability. The improvement to the control of various engine valve parameters will lead to greater control over engine performance, fuel efficiency, and reduced emissions. These improvements to consumer automobile technologies are significant.