EFFICIENT FLUID POWER CONTROL

液压的应用是多种多样的。液压驱动具有功率密度高、响应速度快、可控性好等优点，具有结构紧凑、重量轻等优点。在大多数流体动力液压系统中，负载的速度和力是通过阀门来控制的，以节流和降低液压。这是一种简单但效率极低的方法，因为多余的能量会以热量的形式损失，而且以这种方式浪费超过50%的输入功率是很常见的。另一种方法是使用可变容量的液压泵或马达。这是更有效的，但可变容量泵和电机是昂贵的。拟议的工作研究了两种方法来提高液压系统的效率，同时保持对速度和力的良好控制，而不需要与可变容量泵相关的费用。第一种方法是开关电抗液压变压器(SRHT)，这是一种用于控制液压源流量和压力的新型装置。第二种方法是电液压作动器(EHA)。这两个系统都消除了对控制阀的需要，从而提高了效率。对于这两种应用，可能需要主动的液载噪声衰减技术。开关电抗液压变压器(SRHT)：提出了一种控制液压源流量和压力的新装置。它由一个高速开关阀和一个“惯性管”组成。该装置起到了变压器的作用，能够提高压力或流量。该装置可以被配置为提供可变容量泵、压力溢流阀、压力补偿流量控制阀或比例阀的功能。这些控制模式中的每一种都可以在没有昂贵的可变容量泵的情况下实现，也不需要控制阀固有的低效。以前的工作突出了噪声和寄生功率损耗的问题。如果使用更新的材料和技术并结合仔细的设计来克服这些问题，它可能会提供一种比压力/流量控制阀更具成本效益的高效替代方案。电液压执行机构(EHA)：在EHAS中，变速电动马达驱动固定排量泵，后者将流量直接输送到线性执行机构。从集中式电源转向分布式多泵/执行器系统会降低各个子系统的功率水平。此外，与传统的阀控液压系统相比，无阀电液驱动系统具有效率更高的优点，进一步降低了功率要求。由于泵和执行器之间的紧密耦合，EHA系统可能会受到噪声问题的影响，从而允许直接传输压力脉动。挑战是在获得良好的动态性能的同时，实现更高的效率、低噪声以及降低系统重量和尺寸。主动流体噪声衰减：流体噪声(FBN)是液压系统空气噪声和振动的主要贡献者，并导致系统部件疲劳增加。虽然被动系统降低噪音已被证明是有效的，但它们需要调谐到特定的系统，它们的衰减频率范围有限，而且它们可能很大。此外，基于膨胀室、蓄能器或软管的衰减装置可能不适合EHA或SRHT系统，因为它们增加了系统的合规性，并会损害动态响应。有源设备为流体增加能量以抵消或破坏压力波动，从而降低噪声水平，在更广泛的频率和系统设计范围内都可以有效，而不会影响系统的动态响应。SRHT设备和EHA系统都可能受到噪声问题的影响，因此将受益于有源噪声衰减。

The applications of hydraulics are diverse. Hydraulic actuation offers many benefits including compact and lightweight design due to high power density, fast response and good controllability. In most fluid power hydraulic systems, speed and force of the load are controlled using valves to throttle the flow and reduce the hydraulic pressure. This is a simple but extremely inefficient method as the excess energy is lost as heat, and it is common for more than 50% of the input power to be wasted in this way. An alternative method is to use a variable capacity hydraulic pump or motor. This is more efficient, but variable capacity pumps and motors are expensive.The proposed work investigates two methods of increasing the efficiency of hydraulic systems while maintaining good control of speed and force without the expense associated with variable capacity pumps. The first method is the Switched Reactance Hydraulic Transformer (SRHT), a novel device for controlling the flow and pressure of a hydraulic supply. The second method is the Electro-Hydrostatic Actuator (EHA). Both of these systems increase efficiency by removing the need for control valves. For both applications, active fluid-borne noise attenuation techniques may be necessary.Switched Reactance Hydraulic Transformer (SRHT):A new device for controlling the flow and pressure of a hydraulic supply is proposed. It consists of a high-speed switching valve and an 'inertance tube'. Acting as a transformer, the device is able to boost the pressure or flow. The device could be configured to provide the functionality of a variable capacity pump, a pressure relief valve, a pressure compensated flow control valve or a proportional valve. Each of these control modes can be achieved without an expensive variable capacity pump and without the inefficiency inherent in a control valve. Previous work highlighted problems of noise and parasitic power losses. If these problems can be overcome using more recent materials and techniques combined with careful design, it could provide a more cost-effective efficient alternative to pressure/flow control valves.Electro-hydrostatic Actuation (EHA):In EHAs, a variable speed electric motor drives a fixed displacement pump which delivers flow directly to a linear actuator. Moving from centralised power supplies to distributed multi-pump/actuator systems brings reductions in power levels for individual subsystems. Furthermore, valveless electro-hydrostatic actuation systems provide benefits of greater efficiencies compared to conventional valve-controlled hydraulic systems, further reducing the power requirements. EHA systems can suffer from noise problems because of the close coupling between pump and actuator, allowing direct transmission of pressure pulsation. The challenges are to achieve good dynamic performance while achieving higher efficiency, low noise and reduced system weight and size.Active Fluid Borne Noise Attenuation:Fluid-borne noise (FBN) is a major contributor to air-borne noise and vibration in hydraulic systems as well as leading to increased fatigue in system components. Although passive systems to reduce the noise have been shown to be effective, they require tuning to specific systems, their attenuation frequency range is limited and they may be bulky. Furthermore, attenuation devices based on expansion chambers, accumulators or hoses are likely to be unsuitable for EHA or SRHT systems as they add compliance to the system and would impair the dynamic response. Active devices, which add energy to the fluid to cancel out or destroy the pressure ripple to reduce noise levels, can be effective at a much wider range of frequencies and system designs without affecting the system's dynamic response. Both the SRHT device and EHA system may suffer from noise issues, and as such, will benefit from active noise attenuation.