Current Phase using VTB
Hybrid Systems - Component Level Model Development:
Mathematical models of hybrid actuation systems are being developed at the component level. These component models are based on the most fundamental physical parameters, which are, in-turn, user controlled parameters. Such models are transferred from their native language, typically C++ or Matlab/Simulink, into a format suitable for the Virtual Test Bed (VTB) environment.
Using VTB, the user can manipulate both the fundamental parameters of the components and the assembly of various components to build an entire actuation system (inclusive of variable loading scenarios). This allows for highly variable simulations and component/system optimization within the virtual environment. Ultimately, the virtual environment will become a powerful design tool with the ability to perform a nearly infinite number of "What-if?" scenarios for hybrid actuator development.
Models currently being developed include...
1) Piezoelectric stacks
2) Spool valves
3) Variable spool orifice geometries and flow paths
4) Hydraulic amplifier pistons
Future Integration of VTB and Prototype Hardware
Development of a Hardware-in-the-Loop Simulation:
A hardware-in-the-loop (HIL) simulation will be developed based on the use of the Virtual Test Bed (VTB), a computer simulation environment developed at the University of South Carolina. Within VTB, an internal combustion engine will be modeled. The engine model will provide output data such as piston position and user commanded engine speed. This output will dictate the position of the engine valve, and in-turn, the position of the actuator controlling the engine valve.
The hardware portion of the HIL will be composed of the piezoelectric/hydraulic hybrid actuator and its closed loop control system. The actual position of the actuator will be monitored and provided to the VTB as a command position for the virtual engine valve. Within the virtual engine, the valve will be seen to displace as the hardware actuator displaces.
The actuator displacement will primarily depend upon the position of the virtual piston. Every two cycles of the piston will require the valve to open once. Therefore, the timing of the actuator is not a simple sinusoidal input, as was the case during previous development. Instead, an equivalent frequency must be established for each potential engine velocity. (Please see the mathematical derivation section for an explanation of equivalent frequency.)
Engine rotational velocity will be dictated by the user through a virtual throttle. The virtual throttle will be the user’s interface with the HIL and will be a slider switch to determine the engine’s velocity. This engine velocity dictates the timing and position of the piston, and as stated, the piston position will dictate the actuator’s commanded position.
This exercise will result in both a working HIL for camless engine actuators as-well-as a specification for future actuator development. The functional HIL will provide a test bed for the optimization of actuator hardware and control algorithms. The specification will outline both the physical and signal connections, providing an outline for future hardware designs. The benefit of creating such a system and matching specification is that future camless engine actuator designers will have the opportunity to test and optimize their systems in an established and consistent virtual environment. This will allow for significant savings, both time and money, as designers will not need an engine and engine valve interface produced. Testing of actuator designs will be available in the virtual engine environment for developers both within the university and around the world.
The development of a hardware-in-the-loop simulation will provide a test bed for both current and future camless engine actuator designs. The ability to test prototype actuators without needing to design and construct the linkages and engine interface allows for a greater focus on the development of advanced actuators. Prototypes will be able to be compared within an identical environment. Furthermore, testing actuators on a virtual engine has less of an impact if errors occur. This is of great benefit during the development stage, especially when designing alternative timing and control scenarios.
The established interface can be supplied as a specification to other researchers. This interface, along with the VTB environment, which is provided at no charge, will allow for all researchers to conduct identical experiments with their actuator prototypes. Furthermore, once a system is established, it can easily be expanded to other HIL actuator experiments.