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Reed valves are a type of check valve commonly found in a wide range of applications including air compressors, internal combustion engines, musical instruments, and even the human heart. While reed valves have been studied extensively in these applications, published research on the modeling and application of reed valves in hydraulic systems is sparse. Because the spring and mass components of a reed valve are contained in a single element, it is light and compact compared to traditional disk, poppet, or ball style check valves. These advantages make reed valves promising for use in high-frequency applications such as piston pumps, switch-mode hydraulics, and digital hydraulics. Furthermore, the small size and fast response of reed valves provide an opportunity to design pumps capable of operating at higher speeds and with lower dead volumes, thus increasing efficiency and power density. In this paper, a modeling technique for reed valves is presented and validated in a hydraulic piston pump test bed. Excellent agreement between modeled and experimentally measured reed valve opening is demonstrated. Across the range of experimental conditions, the model predicts the pump delivery with an error typically less than 1% with a maximum error of 2.2%. [ABSTRACT FROM AUTHOR]

Switch-mode hydraulic control is a compact and theoretically efficient alternative to throttling valve control or variable displacement pump control. However, a significant source of energy loss in switch-mode circuits is due to throttling during valve transitions. Hydraulic soft switching was previously proposed as a method of reducing the throttling energy loss, by absorbing, in a small variable volume chamber, the flow that would normally be throttled across the transitioning high-speed valve. An active locking mechanism was previously proposed that overcomes the main challenge with soft switching, which is a lock mechanism that releases quickly and with precise timing. This prior work demonstrated a reduction in energy losses by 66% compared to a control circuit. In this paper, a numerical model is developed for a switch-mode virtually variable displacement pump (VVDP) circuit, utilizing the proposed soft switch. The model is then used as a means of designing a proof of concept prototype to validate the model. The prototype design includes methods for controlling the soft switch spring preload, travel distance, piston displacement required to unlock the soft switch, valve command duty cycle, switching cycle period, and load pressure. Testing demonstrated that the soft switch circuit performed as expected in a baseline condition. The operating region for this prototype was found to be quite narrow. However, the model does a good job of predicting the displacement of the soft switch. [ABSTRACT FROM AUTHOR]

Switched inertance hydraulic systems (SIHS) use inductive, capacitive, and switching elements to boost or "buck" (reduce) a pressure from a source to a load in an ideally lossless manner. Real SIHS circuits suffer a variety of energy losses, with throttling of flow during transitions of the high-speed valve resulting in as much as 44% of overall losses. These throttling energy losses can be mitigated by applying the analog of zero-voltage-switching, a soft switching strategy, adopted from power electronics. In the soft switching circuit, the flow that would otherwise be throttled across the transitioning valve is stored in a capacitive element and bypassed through check valves in parallel with the switching valves. To evaluate the effectiveness of soft switching in a boost converter SIHS, a lumped parameter model was constructed. Simulation demonstrates that soft switching improves the efficiency of the modeled circuit by 42% at peak load power and extends the power delivery capabilities by 77%. [ABSTRACT FROM AUTHOR]

Switch-mode hydraulic circuits are a theoretically efficient, compact, fast responding, and inexpensive control option. Despite the many potential benefits of switch-mode hydraulic circuits, the control method suffers from large energy losses during transitions of the high-speed valve due to throttling and fluid compressibility. Rannow and Li previously proposed utilizing soft switching to minimize the throttling energy loss (Rannow and Li, "Soft Switching Approach to Reducing Transition Losses in On/Off Hydraulic Valve," J. Dyn. Syst., Measure. Control (in press)). A major challenge of this approach is a locking soft switch that releases quickly and with precise timing, while under load. In this paper, a novel soft switch locking mechanism is presented that utilizes the pressure signal in the switched volume to trigger the release. A dynamic model is developed of three unique soft switch circuits and two control circuits that create a virtually variable displacement pump. The model is used to perform a grid search optimization of the soft switch parameters for the three circuits. The three soft switch circuits reduce the throttling and compressibility energy losses between 49% and 66% compared with the control circuit. The simulation results demonstrated that the soft switch circuits perform as expected for duty cycles and pressures below the design conditions. At higher duty cycles and pressures, the short time the circuit is connected to tank prevented the soft switches from resetting between cycles, preventing proper function. This novel lock and release soft switch mechanism enables soft switching in switch-mode hydraulic circuits, which significantly reduces throttling and compressibility energy losses during valve transitions. Lower losses during valve transition allow the use of slower switching valves, lowering energy consumption, and cost. [ABSTRACT FROM AUTHOR]

Fluid compressibility has a major influence on the efficiency of switch-mode hydraulic circuits due to the release of energy stored in fluid compression during each switching cycle and the increased flow rate through the high-speed valve during transition events. Multiple models existing in the literature for fluid bulk modulus, the inverse of the com-pressibility, are reviewed and compared with regards to their applicability to a switch-mode circuit. In this work, a computational model is constructed of the primary energy losses in a generic switch-mode hydraulic circuit with emphasis on losses created by fluid compressibility. The model is used in a computational experiment where the system pres-sure, switched volume, and fraction of air entrained in the hydraulic fluid are varied through multiple levels. The computational experiments resulted in switch-mode circuit volumetric efficiencies that ranged from 51% to 95%. The dominant energy loss is due to throttling through the ports of the high-speed valve during valve transition events. The throttling losses increase with the fraction of entrained air and the volume of fluid experi-encing pressure fluctuations, with a smaller overall influence seen as a result of the sys-tem pressure. The results of the computational experiment indicate that to achieve high efficiency in switch-mode hydraulic circuits, it is critical to minimize both the entrained air in the hydraulic fluid and the fluid volume beh\'een the high-speed valve and the pump, motor, or actuator. These computational results are compared with experimental results in Part II of this two part paper series. [ABSTRACT FROM AUTHOR]

In this article, the author presents experimental work with a generic switch-mode hydraulic circuit. It mentions that the experiment aims to validate a previously presented computational model, emphasizing the energy loss due to fluid compressibility. It includes that calculated volumetric efficiency from experimental works ranged from to 61 percent to 75 percent, with efficiency increasing with decreased levels of entrained air, system pressure, and switched volume.

Hydraulic applications requiring a variation in the speed or torque of actuators have historically used throttling valve control or a variable displacement pump or motor. An alternative method is switch-mode control that uses a high-speed valve to rapidly switch between efficient on and off states, allowing any hydraulic actuator to have virtually variable displacement. An existing barrier to switch-mode control is a fast and efficient high-speed valve. A novel high-speed valve concept is proposed that uses a phase shift between two tiers of continuously rotating valve spools to achieve a pulse-width modulated flow with any desired duty ratio. An analysis of the major forms of energy loss, including throttling, compressibility, viscous friction, and internal leakage, is performed on a disk spool architecture. This analysis also explores the use of a hydrodynamic thrust bearing to maintain valve clearance. A nonoptimized design example of a phase-shift valve operating at 100 Hz switching frequency at 10 l/min demonstrates an efficiency of 73% at a duty ratio of 1 and 64% at 0.75 duty ratio. Numerous opportunities exist for improving this efficiency including design changes and formal optimization. The phase-shift valve has the potential to enable switch-mode hydraulic circuits. The valve has numerous benefits over existing technology yet requires further refinement to realize its full potential. [ABSTRACT FROM AUTHOR]