The hydraulic transmission technology has a history of two or three hundred years since Britain made the first hydraulic press in the world at the end of the 18th century. However, it was not really popularized until the 1930s.
In 1650, Pascal proposed Static pressure transmission principle In 1850, Britain would pascal's principle It was successively used in hydraulic cranes and presses. In 1795, Joseph Braman of England used water in London as the working medium and applied it to industry in the form of a hydraulic press, giving birth to the world's first hydraulic press; In 1905, the working medium was changed from water to oil, which further improved the hydraulic transmission effect. the Second World War During this period, hydraulic transmission and control devices with high power, quick response and accurate action were used on some weapons, which greatly improved the performance of weapons and promoted the development of hydraulic technology. After the war, hydraulic technology quickly turned to civilian use. With the continuous development and improvement of various standards, the standardization, normalization and serialization of various components were popularized in machinery manufacturing, engineering machinery, agricultural machinery, automobile manufacturing and other industries. After the 1960s, atomic energy technology, space technology computer technology The development of microelectronics technology has pushed the hydraulic technology forward again, making it applied in all aspects of the national economy, and has become one of the essential means to realize the automation of production process and improve labor productivity. China's hydraulic industry began in the 1950s, and its products were initially only used for machine tools and forging equipment, and later used for tractors and construction machinery. Since 1964, when some production technologies of hydraulic components were introduced from abroad and hydraulic products were designed by ourselves, hydraulic components in China have been widely used in various mechanical equipment. Since the 1980s, it has accelerated the planned introduction, digestion, absorption and localization of advanced hydraulic products and technologies to ensure that China's hydraulic technology can catch up with the world level in all aspects of product quality, economic benefits, research and development.
At present, the hydraulic technology has made great progress in achieving various requirements such as high pressure, high speed, high power, high efficiency, low noise, durability, and high integration. There are also many new achievements in improving proportional control, servo control, digital control and other technologies. In addition, it has increasingly shown significant advantages in such development work as computer-aided design, computer simulation and optimization, and microcomputer control of hydraulic components and systems. [2]
Hydraulic transmission system It mainly consists of five parts. 1. Power element
The power element is Prime mover An energy conversion device that converts the input mechanical energy into oil pressure energy. Its function is to provide pressure oil for the hydraulic system. The power components are various hydraulic pumps. 2. Actuator
The actuating element is an energy conversion device that converts the pressure energy of oil into mechanical energy. Its function is to output force and speed (linear motion), or torque and speed (rotary motion) under the push of pressure oil. Such components include various types Hydraulic cylinder and Hydraulic motor 。 3. Control regulating element
The control regulating element is used to control or adjust the pressure, flow and direction of the oil in the hydraulic system to ensure that the actuator can complete the expected work. Such components mainly include various Relief valve 、 throttle valve as well as Reversing valve Etc. Different combinations of these elements form different functional Hydraulic transmission system 。 4. Auxiliary components
Auxiliary components refer to oil tank, oil pipe, oil pipe joint Accumulator 、 Oil filter 、 Pressure gauge 、 Flow meter And various sealing elements. These elements play the roles of heat dissipation and oil storage, oil transportation, connection, energy storage, filtering, pressure measurement, flow measurement and sealing to ensure the normal operation of the system. They are indispensable components of the hydraulic system. 5. Working medium
The working medium plays the role of transmitting motion, power and signal in hydraulic transmission and control. T as the medium is hydraulic oil or other synthetic liquid. [3]
And mechanical drive By comparison, hydraulic transmission has the following main advantages: (1) Since oil is generally used as the transmission medium, the hydraulic components have good lubrication conditions; The working fluid can be transported to any position by pipeline, allowing the hydraulic actuator to keep a certain distance from the hydraulic pump; The hydraulic transmission energy can easily change the rotating motion of the prime mover into linear motion. These characteristics are very suitable for the needs of various engineering machinery and mining equipment, and their typical application examples are those used underground in coal mines Single hydraulic prop and hydraulic support 。 (2) It can realize a wide range of Stepless speed regulation , which transmission ratio It can be up to 1:1 000, and the speed regulation performance is not limited by the power. (3) It is easy to realize load control, speed control and direction control, and can carry out centralized control, remote control and automatic control.
(4) The hydraulic transmission can realize the backlash free transmission, so the transmission is stable, the operation is labor-saving, the response is fast, and the high-speed start and frequent reversing can be achieved.
(5) Hydraulic components are standardized, serialized and generalized products, which are easy to design, manufacture and promote application.
And Electric drive In comparison, the main advantages of hydraulic transmission are as follows: (1) Small mass and small volume. This is because the motor is limited by magnetic saturation, and its tangential force per unit area is dozens of times different from the hydraulic pressure that hydraulic machinery can withstand.
(2) The motion inertia is small and the response speed is fast. The torque inertia ratio (i.e. the ratio of driving torque to rotating inertia) of hydraulic motor is much larger than that of motor, so its acceleration performance is good. For example, it usually takes one second to several seconds to accelerate a medium power motor, while the acceleration of the same power motor Hydraulic motor It only takes about 0.1 s. This good dynamic characteristic is beneficial to Hydraulic control system It is even more significant. (3) Low speed hydraulic motor The low speed stability of the motor is much better than that of the motor. (4) The application of hydraulic transmission can simplify the electrical system of machine equipment. This is of great benefit to the underground work of coal mines with explosion risk. [4]
(1) In the transmission process, because the energy needs to be converted twice, there are pressure loss, volume loss and mechanical friction loss, so the total efficiency is usually only 0.75~0.8.
(2) The working performance and efficiency of transmission system are greatly affected by temperature. General hydraulic transmission is difficult to work in high or low temperature environment.
(3) The liquid has certain compressibility, and there is inevitably leakage on the matching surface, so the hydraulic transmission cannot guarantee the strict transmission ratio.
(4) The working fluid is very sensitive to pollution, and the polluted working fluid will do great harm to the hydraulic components, so it is difficult to find the fault of the hydraulic system, and has high requirements for the technical level of the operators and maintenance personnel.
(5) Manufacturing accuracy of hydraulic components Surface roughness The material and heat treatment requirements of the material are relatively high, so the cost is high. In general, the advantages of hydraulic transmission are main. Some of its shortcomings are being gradually overcome with the development of production technology. If we further absorb the advantages of other transmission methods and adopt electrohydraulic, pneumatic, hydraulic and other combined transmission, we can give full play to its characteristics. [4]
The main applications of hydraulic transmission are as follows:
(1) General industrial hydraulic system plastic processing machinery（ injection molding machine ）Pressure machinery（ forging press ）Heavy machinery (scrap steel briquetting machine), machine tools (full-automatic hexagonal lathe Surface grinder ）Etc; (2) Hydraulic system construction machinery for traveling machinery（ excavating machinery ）Hoisting machinery（ Truck crane ）Construction machinery（ Piling machine ）Agricultural machinery（ Combine harvester ）, Automobile（ Steering gear 、 Shock absorber ）Etc; (3) Hydraulic system metallurgical machinery for iron and steel industry（ Rolling mill ）Lifting device（ elevator ）Roll adjustment device, etc; (4) Hydraulic system flood gate and dam device (tide protection baffle), river bed lifting device, bridge operating mechanism and mining machinery (rock drill) for civil engineering;
(5) Hydraulic system turbine (speed governing device) for power plant;
(6) Hydraulic system giant antenna control device, measuring buoy, aircraft landing gear retraction and retraction device, rudder control device, lifting and rotating stage for special technology;
(7) Marine hydraulic system deck lifting appliances（ Winch ）, bow door Bulkhead valve , stern propeller, etc; (8) Gun control device of hydraulic system for military industry, ship anti rolling device, aircraft simulation, etc. [1]
