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In hydraulic servo systems, a pilot stage is often used to reduce the influence of Bernoulli's forces and frictional forces when trying to accurately position a spool. A unique pilot controlled valve (defined as a two dimensional or ''2D'' flow control valve), which utilizes both rotary and linear motions of a single spool, is presented. The rotary motion uses a spiral groove in the sleeve combined with high and low pressure holes on the spool land to control the pressure in the spool chamber, while the linear motion of the spool is actuated by a hydrostatic force. Both linear theory and numerical simulation are adopted in the investigation of the characteristics of the valve. A criterion for stability is established from a linearized model of the valve. The analysis establishes the effects that certain structural parameters have on the valve's static and dynamic characteristics. Special experimental procedures were designed to obtain properties such as mechanical stiffness, leakage flow rate, and dynamic response under different structural parameters and system pressure. It was shown that the leakage through the spool-sleeve clearance had a favorable effect on the valve stability. Theoretical and experimental results show that it is necessary to establish a balance between the static and dynamic performance in establishing appropriate structural parameters. It is also shown that the 2D flow control valve can demonstrate a high speed of response, while maintaining the pilot flow rate at a low level.

This paper first introduces the structure and working principle of a 2D piston pump invented by the research team that the authors are involved with. Afterward, the mechanism of the churning losses caused by the pump's moving parts, which are rotating in oil, is carefully studied by building up mathematical models and using CFD simulations. A test rig is set up to estimate the churning losses of the moving parts by monitoring the torque at different rotational speeds. The analytical results indicated that the torque of the churning losses increased with the increase of the rotational speed. In addition, the experimental data of the churning losses were consistent with the solutions from both the conducted mathematical models and CFD simulations before the rotational speed reached 8000 rpm. However, when the rotational speed exceeded 8000 rpm, the experimental data showed an apparent difference from the calculated ones. Based on the changes in the oil temperature and noise, this difference might be due to cavitation or turbulence. As a result, the churning losses that took place in the 2D high-speed piston pump need to be further studied, especially when the pump is driven by a high-speed motor.

A scheme for an electrohydraulic vibrator excited by a two-dimensional valve is proposed, which significantly extends the frequency range compared to that of vibrators excited by conventional servo valves. In the two-dimensional valve, the rotary motion of the spool coordinates the relative motion of the grooves on the spools area with respect to the windows on the sleeve which in turn, alternates the oil flowrate into and out of the chambers of the hydraulic cylinder (motor) and subsequently excites the piston (rotor) to vibrate. The linear motion of the two-dimensional valve spool is used to vary the peak flowrate and thus the amplitude of the output vibration. The frequency of the vibration excited by the two-dimensional valve is related to the rotary speed of the spool and the number of the grooves on the spool area (windows on the sleeve). This configuration extends the frequency of the hydraulic vibrator by increasing the number of the grooves on the spool area (windows on the sleeve) and the rotary speed of the spool which are in the perfect lubrication of oil. A model of the two-dimensional vibrator is developed and compared to its experimental counterpart. The vibration excited by the two-dimensional valve is influenced by pressure saturation, the elastic force, and the hydraulic resonance. There is a critical valve linear opening, beyond which the output force (torque) reaches a saturation value in both a positive and negative sense. Both simulation and experimental results show that at lower frequencies the ascent and descent slopes of the output force show some inconsistency which becomes more significant above the critical valve linear opening but drops off with a reduction in the valve linear opening. In a higher frequency range, the vibration excited by the two-dimensional valve is mainly influenced by hydraulic resonance. As the input frequency approaches the hydraulic resonant frequency, the output excited vibration essentially becomes the hydraulic resonance. Therefore, the effective frequency range of the hydraulic vibration is not only decided by the frequency bandwidth of the two-dimensional valve, but is influenced by the hydraulic resonance. Nevertheless, the study does provide an access to the high-frequency excitation of the hydraulic vibration.

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Since many studies on axial piston pumps aim at enhancing their high power-weight ratio, many researchers have focused on the generated mechanical losses by the three friction pairs in such pumps and attempted to diminish them through abundant and new structural designs of the pump’s components. In this paper, a high-speed 2D piston pump is introduced and its architecture is specifically described. Afterward, a mathematical model is established to study the pump’s mechanical efficiency, including the mechanical losses caused by the viscosity and stirring oil. Additionally, in this study the influences of the rotational speed, the different load pressures, and the rolling friction coefficient between the cone roller and the guiding rail are considered and discussed. By building a test rig, a series of experiments were carried out to prove that the mechanical efficiency was accurately predicted by this model at low load pressures. However, there was an increasing difference between the test results and the analytical outcomes at high pressures. Nevertheless, it is still reasonable to conclude that the rolling friction coefficient changes as the load pressure increases, which leads to a major decrease in the mechanical efficiency in experiments.

Development of thermally robust palladium-based catalysts for (co)polymerizations of ethylene and polar monomers with high activities is a continuing challenge. Combined hydrogen bonding interactions with steric and electronic modifications, dibenzobarrelene...

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