I. Preface

    Hydraulic and control technology is an extremely widely used basic technology, which has been widely used in various fields of national economy. China's hydraulic and control technology has long lagged behind foreign countries, which has seriously restricted the improvement of China's host level and the realization of industrial automation, so it is of great economic and practical significance to rapidly improve the level of hydraulic technology and control technology in China.

    In the traditional hydraulic transmission, is through a variety of hydraulic valves to control the direction of motion, speed and position of ordinary cylinders. In order to meet various requirements, hydraulic pioneers, after nearly a century of continuous efforts, invented and produced hundreds of specifications of hydraulic components and products. However, in order to obtain precise control, ordinary hydraulic components no longer meet the requirements. Since the 1970s, with the booming development of high-tech clusters such as microelectronics-led information technology, biotechnology, new materials technology, new energy technology, space technology and marine development technology, the world has gradually seen the emergence of high-technology such as mechanical and electronic industries, optoelectronic industries, office automation equipment, information processing systems, electronic medical equipment, modern biological products, new materials and new energy industries. Fluid drive and control technology is one of the key technology areas that play an important role in the mechanical and electronic technology industry. Fluid transmission and control includes two aspects: hydraulic transmission and control and gas transmission and control. Hydraulic drive and control technology used in production began in the seventeenth century, after more than two hundred years of wandering, until the 1940s, only into the rapid development of the period. Although pneumatic technology has a long history of application, it was really applied to production in the eighteenth century, and its application and research only began to be taken seriously in the 1950s. The emergence of cybernetics, especially the development of automatic control theory and technology, so that fluid transmission and control technology has made rapid progress. At present, fluid transmission and control technology has been widely used in metallurgy, coal, petroleum, chemical, energy, aviation, aerospace, national defense and other fields, becoming an indispensable support technology in the development of the national economy.

Second, the development of hydraulic technology

    Hydraulic technology is a liquid (mainly mineral oil) as the working medium to achieve energy transfer, conversion, distribution and control of a technology. The development of hydraulic technology is always closely integrated with the contemporary high technology. The birth of cybernetics in the 1940s has greatly contributed to the rapid development of hydraulic technology, which has gradually expanded its scope of application, not only in the field of national defence with an irreplaceable position, but also has penetrated into various sectors of the national economy, the degree of development and application of hydraulic technology has become an important symbol of the level of industrial development of a country. In recent years, the combination of hydraulic technology and microelectronics, computer technology, sensor technology, etc., has produced another leap forward. The current development of hydraulic technology is mainly focused on the following aspects:

    (1) the development of integrated, interlocking, miniaturised and lightweight hydraulic components. With the increase in the complexity of hydraulic systems, hydraulic components are required to have high reliability, reduce piping, save installation space, easy maintenance and other characteristics, and must develop the above types of hydraulic components. Following the integrated block type, stacked valve type, cartridge valve type, in recent years there will be control elements attached to the power components of the integrated composite hydraulic device.

    (2) Development of high-performance hydraulic control components. Adapt to the needs of the development of mechatronics host. Such as the development of low control power valve, the development of electro-hydraulic proportional valve to adapt to field conditions, high response frequency electro-hydraulic servo valve, low-cost proportional valve and does not require A/D and D / A conversion, can be directly interfaced with the computer digital valve.

    (3) Green development research aimed at environmental protection, safety and meeting sustainable development. Such as pollution-free pure water hydraulic technology and related new materials, development and application research of new processes, application research to reduce component and system noise, reduce leakage and improve sealing performance.

    (4) Improving the reliability of components and systems. In addition to scientific design, advanced materials and perfect technology, attention should also be paid to the reliability of application and maintenance, system condition monitoring, fault diagnosis and reducing the sensitivity of components to pollution. Strengthening pollution control and the application research of new engineering materials are of great significance to improve the reliability of components and systems.

    (5) to improve efficiency, reduce energy consumption as the goal of the system matching design theory, methods and computer research on hydraulic systems for automatic adaptation control means.

Third, the impact of modern technology on traditional hydraulic technology

       With the progress of science and technology, not only the connotation of hydraulic technology itself has included many high-tech content, but also its application has been throughout the various fields of high-tech, especially in many products of electromechanical integration. The influence of high technology on modern hydraulic technology is mainly reflected in electronics and information technology, village material science and modern manufacturing technology. They have both brought new opportunities for the further development of hydraulic technology and also played a role as a challenge and competitor in some respects.

3.1 The influence of electronics and information technology

    Hydraulic technology is often divided into two areas: "hydraulic drives" (hydraulic drives) and "hydraulic control". Conventional hydraulic control systems commonly use a number of fixed and variable throttle elements to measure, identify and regulate system flow by means of differential pressure. Such complex hydraulic network systems consisting of several "hydraulic resistances" have been developed to a very high level. In the 1970s, for example, devices were available to regulate the displacement of pumps and motors in a purely hydraulic manner according to certain established rules (constant power, constant torque, load-sensitive, speed feedback-sensitive, etc.), but in the same period electronic control technology was rapidly emerging. The development of electronic proportional and pulse width control technology has led to the variable system of hydraulic variable pumps and motors only needing to retain the function of pushing the outer disc or cylinder deflection and a common set of electro-hydraulic interface devices, while leaving the processing of the regulation signal to the electronic system to complete. The introduction of electronic regulation technology at a deeper level, particularly digital bus technology, has enabled the development from discrete control of individual components to comprehensive real-time optimised control of the entire system from the prime mover, the transmission machine to the working machine. In contrast to purely hydraulic controls, which require precision machining, electronic controls offer significant advantages not only in terms of functionality and control accuracy, but also in terms of size, energy efficiency, compatibility and development and manufacturing costs. In view of this, the role of hydraulic controls will increasingly be taken over by electronic devices, while the tasks of hydraulic devices are gradually concentrated on the power transmission aspects of energy conversion, power flow switching and overload protection of the main system. However, even hydraulic drives are facing challenges from electric drive technology. In recent years, based on the progress of microelectronics and magnetic materials technology, with excellent stepless speed control performance of AC frequency conversion electric drive has become an important competitor of hydraulic pump a motor drive device.

3.2 The impact of materials science and advanced manufacturing technology

    The basic principles of hydraulic technology is easy to understand, but to successfully achieve its function but depends on the progress of materials science and manufacturing technology. Some data show that the development of hydraulic technology in the last 20 years has come from the scientific research results of its own structural improvement of only about 20, while relying on materials, surface technology, processing technology and other aspects of research results accounted for 30%. Of course, this phenomenon does not only occur in the field of hydraulic technology, no discipline or industry can close its doors and develop itself. The interplay of disciplines, learning from each other and the transplantation of results is the trend in science and technology today and in the future. Science and technology are in a spiral. The structure of various hydraulic components has undergone a repeated cycle from simple to complex and then to simple again, from once to several times. The performance of the components has been qualitatively improved after each cycle, and this has been largely due to advances in materials and manufacturing technology over the same period. The original hydraulic components were simple in construction, for example an iron cylinder with a solid return body made up the hydraulic cylinder. Later on, people began to break down a simple component into a combination of "specialised" parts, such as those dedicated to changing the direction of motion, anti-wear, load-bearing and sealing, depending on the function required. The result is an increase in the performance of the component, but also in its complexity. As soon as new materials with a certain combination of properties and new machining methods to create complex surfaces became available, attempts were made to regroup multiple functions into a single part. For example, in the early days of the internal curve motor, the plunger was widely used to seal the oil, the crossbar (or connecting rod) transmitted the force, and then the roller with needle bearings was converted to torque. With the advent of new materials and manufacturing techniques with good overall performance, the new motors have been able to combine the functions of oil sealing, force transmission and roller support in a specially shaped plunger, and to replace pairs of radial thrust bearings with a single "four-point contact" bearing, even with the inner and outer rings of the bearing also The inner and outer rings have even been "integrated" into the raceway spool and output shaft. These measures have drastically reduced the radial dimensions of the motors, more than doubling their power density over the years, while significantly reducing their price. The significance of materials science and new manufacturing technologies for the technological advancement of hydraulic components is thus evident.