Development and Control System Design of an Electro-Pneumatic Variable Valve Actuator to be Retrofitted to an SI Engine

In a conventional cam-based valve actuation system, the valve events are tied up with the rotation of the crankshaft. In contrast, the electronic variable valve actuation system enables flexible control of valve events independent of the crankshaft rotation. The present article discusses the development and control system design of a single-acting electro-pneumatic variable valve actuation (EPVVA) system that can be retrofitted to a conventional SI engine. The EPVVA system utilizes fast switching solenoid valves which modulate the flow of pressurized air in and out of a pneumatic chamber. The control system design is conducted in MATLAB Simulink platform using model-based approach. The valve actuator model is formulated such that it simulates the trajectory of the motion of the engine valve by numerically integrating a set of coupled differential equations that govern the thermo-fluid-dynamics and applied mechanics aspects of the valve actuation of the EPVVA system. The timings of the valve actuation events are synchronized with the required timings derived from the operation of an engine valve train model that runs in tandem with the valve actuator model. The durations of the electrical pulses sent to the various solenoid valves are controlled to achieve the desirable valve lift profile. The delays in valve actuation are determined in closed loops and are compensated in the next cycle by adjusting the switching-on and switching-off instants of the electrical pulses. The control of the load without a throttle valve is achieved by appropriately altering the area under the valve lift profile, which involves the changing of the maximum lift, with the help of a PID control strategy. The predictions of the mathematical theory and the experimentally measured valve lift profiles show that the desired control of valve events and load can be achieved across a wide range of engine speeds.