| Fluid power offers the benefits of high power density, high force potential, and high-speed precision control. To achieve variable power demand, systems often implement metering control, which results in heat dissipation and low overall efficiency. Improved efficiency can be obtained with the use of a variable displacement pump, adding cost, complexity, and size compared to a fixed displacement pump. Switch-mode hydraulic circuits, analogous to switch-mode power electronics, provide alternative control topologies that rely on switching between efficient on and off states. A challenge in realizing these circuits is the need for a high-speed valve with a demanding set of requirements. These requirements include fast transition time, high frequency switching, high flow rates, low energy losses, and a variable duty cycle. The work presented includes the design and modeling of valve that meets these requirements, experimental testing of the valve prototype, and experimental demonstration of the prototype in a pressure boost converter. The valve architecture consists of a dual spool design actuated from a common crank-shaft by two 4-bar crank-slider mechanisms. The valve completes two switching cycles per crank-shaft revolution and the variable duty cycle is achieved by phase shifting one crank arm relative to the other. The valve design constraints included a switching frequency up to 120 Hz, a transition ratio of 5% of the cycle period, and a flow rate of 22.8 lpm at a 0.6 MPa pressure drop. The experimental validation of the valve consisted of two quasi-static tests and one transient test. The first test determined the valve effective area as a function of crank-shaft position. The experimental results agreed well with the model resulting in a 3% variation in transition time and a 13.3% variation in valve overlap. The second test measured the valve leakage which matched the model in shape and order of magnitude. The third test measured the input torque. At low speeds, due to binding forces in the revolute joints the model showed poor agreement, however at higher speeds, where inertial forces dominate, agreement improved significantly. The valve prototype was further validated with experimental demonstration in a pressure boost converter. The converter utilized a rigid tube as the inductive element and transient testing was completed at six different duty cycles, ranging from 0.2--0.9. The system demonstrated boost ratio capabilities of 1.08--2.06 with a general trend of higher boost ratios at lower duty cycles. The system efficiencies ranged from 19--62% with decreasing efficiencies at lower duty cycles. Overall, the valve performed well in the system and successfully demonstrated a boost ratio over two. This high-speed valve enables switch-mode circuit studies that can improve efficiency in future work, allowing switch-mode circuits to be a viable control method for hydraulic systems. |
