It consists of two liquid tanks with different sizes, which are filled with water or oil. Water-filled is called "hydraulic press"; Oil-filled ones are called "oil presses". Each of the two hydraulic cylinders has a slidable piston. If a certain pressure is applied to the small piston, according to Pascal's law, the small piston will transfer this pressure to the big piston through the pressure of the liquid and push the big piston upward. Let the cross-sectional area of the small piston be S 1 and the downward pressure on the small piston be F 1. Therefore, the pressure of small piston on liquid is P=F 1/SI, which can be transmitted in all directions by liquid with constant size. "The pressure on the big piston must also be equal to p. If the cross-sectional area of the big piston is S2, the upward pressure F2 generated by the pressure P on the big piston is equal to pXS2, and the cross-sectional area is a multiple of the cross-sectional area of the small piston. As can be seen from the above formula, if a small force is added to the small piston, a large force will be obtained on the large piston. So use hydraulic press to press plywood, squeeze oil, extract heavy objects, forge steel and so on.
[Edit this paragraph] Development history of hydraulic transmission
Hydraulic transmission and pneumatic transmission are collectively called fluid transmission, which is a new technology developed according to the hydrostatic transmission principle put forward by Pascal in17th century. Braman (1749- 18 14) used water as working medium in London and applied it to industry in the form of hydraulic press, thus giving birth to the world's first hydraulic press. 1905, the working fluid water is replaced by oil, which is further improved.
After World War I (1914-1918), hydraulic transmission was widely used, especially after 1920. Hydraulic components began to enter the formal industrial production stage from the end of 19 to the beginning of the 20th century. 1925, F.Vikers invented the pressure balance vane pump, which laid the foundation for the gradual establishment of modern hydraulic component industry or hydraulic transmission. Constantine in the early 20th century? Newcastle (g? Constantimsco) conducted theoretical and practical research on energy fluctuation transmission; 19 10's contribution to hydraulic transmission (hydraulic coupling, hydraulic torque converter, etc. ) these two fields have been developed.
During World War II (194 1- 1945), 30% of machine tools in the United States used hydraulic transmission. It should be pointed out that the development of hydraulic transmission in Japan is nearly 20 years later than that in Europe and America. Around 1955, Japan developed hydraulic transmission rapidly, and 1956 established the "Hydraulic Industry Association". In recent 20~30 years, Japan's hydraulic transmission has developed rapidly and occupied a leading position in the world.
Hydraulic transmission has many outstanding advantages, so it is widely used, such as general industrial plastic processing machinery, pressure machinery, machine tools, etc. Construction machinery, construction machinery, agricultural machinery, automobiles, etc. In mobile machinery; Metallurgical machinery, lifting device, roller adjusting device, etc. Used in steel industry; Flood control dam device, river bed lifting device, bridge control mechanism, etc. Used in civil and hydraulic engineering; Turbine speed regulating devices in power plants and nuclear power plants. Deck crane (winch), bow door, bulkhead valve, stern propeller, etc. For ships; Giant antenna control device for special technology, measuring buoy, lifting turntable, etc. Gun control device for military use, ship anti-rolling device, aircraft simulation, aircraft landing gear retracting device, rudder control device.
Development trend of hydraulic technology
Due to the wide application of high-tech achievements in hydraulic technology, such as automatic control technology, computer technology, microelectronics technology, friction and wear technology, reliability technology, new technology and new materials, the traditional technology has made new development, and the quality and level of hydraulic systems and components have been improved to a certain extent. However, it is impossible for the hydraulic technology facing 2 1 century to make an amazing technological breakthrough. We should mainly rely on the improvement and expansion of the existing technology and constantly expand its application fields to meet the future requirements. Based on the opinions of experts at home and abroad, its main development trend will focus on the following aspects:
1. Reduce energy consumption and make full use of energy.
-Hydraulic technology has made great progress in converting mechanical energy into pressure energy and pressure energy into mechanical energy, but there has always been energy loss, mainly reflected in the volume loss and mechanical loss of the system. If all the pressure energy can be fully utilized, the efficiency of energy conversion process will be significantly improved. In order to reduce the loss of pressure energy, the following problems must be solved:
① Reduce internal pressure loss of components and systems to reduce power loss. The main performance is to improve the pressure loss of the internal flow channel of the component, and the use of integrated circuits and casting flow channels can reduce the pipeline loss and oil leakage loss.
(2) Reduce or eliminate the throttling loss of the system, minimize the overflow of unsafe needs, and avoid using the throttling system to adjust the flow and pressure.
③ Adopting static pressure technology and new sealing materials to reduce friction loss.
④ Develop miniaturization, light weight and compounding, and extensively develop 3-way and 4-way solenoid valves and low-power solenoid valves.
⑤ In order to improve the performance of hydraulic system, load sensing system, secondary regulation system and accumulator circuit are adopted.
⑥ In order to maintain the hydraulic system in time and prevent pollution from affecting the life and reliability of the system, it is necessary to develop new pollution detection methods, measure pollution online and adjust it in time, and it is not allowed to lag behind to avoid losses caused by untimely treatment.
2. Active maintenance
-The maintenance of hydraulic system has changed from simple troubleshooting to fault prediction, that is, when the first symptom of fault is found, it is repaired in advance to eliminate hidden dangers and avoid the development of equipment malignant accidents.
—— To realize active maintenance technology, we must strengthen the research on fault diagnosis methods of hydraulic system. At present, relying on the feeling and experience of experienced maintenance technicians to judge and find faults by looking, listening, touching and measuring is no longer suitable for the large-scale, continuous and modern development of modern industry. It is necessary to modernize the fault diagnosis of hydraulic system, strengthen the research of expert system, summarize the knowledge of experts and establish a complete expert knowledge base with learning function. According to the input phenomenon and knowledge in the knowledge base, the computer uses the existing reasoning method in the inference engine to calculate the cause of the fault, improve the maintenance scheme and preventive measures. In order to further trigger the general tool software of hydraulic system fault diagnosis expert system, only a few rules need to be modified or added for different hydraulic systems.
-In addition, it is the direction of the hydraulic industry to develop the self-compensation system of the hydraulic system, including self-adjustment, self-lubrication and self-correction, and compensate before faults occur.
3. Electromechanical integration
The combination of electronic technology and hydraulic transmission technology makes the traditional hydraulic communication and control technology more dynamic and expands its application field. Realizing mechatronics can improve the working reliability, realize the flexibility and intelligence of hydraulic system, change the shortcomings of low efficiency, oil leakage and poor maintainability of hydraulic system, and give full play to the advantages of large output, small continuity and fast response of hydraulic transmission. Its main development trends are as follows:
(1) The application of electro-hydraulic servo proportional technology will continue to expand. The hydraulic system will be transformed from electro-hydraulic on-oE system and open-loop proportional control system to closed-loop proportional servo system. In order to adapt to the above development, sensors such as pressure, flow, position, temperature, speed and acceleration should be standardized. Computer interfaces should also be unified and compatible.
(2) Develop solenoid valves with power consumption less than 5mA and high frequency solenoid valves (less than 3mS) for pulse width modulation system.
(3) Automatic measurement and diagnosis of flow, pressure, temperature and oil contamination of hydraulic system. Due to the decrease of computer price, monitoring system will be developed, including centralized monitoring and automatic adjustment system.
(4) Standardization of computer simulation, especially for high-precision and "advanced" systems.
(5) Electronic direct control components will be widely used, such as the electronic direct control of hydraulic pumps, and the adoption of universal control mechanism will also be discussed in the future. Present situation and development of mechatronics of hydraulic products.
Hydraulic industry:
-Hydraulic components will develop in the direction of high performance, high quality, high reliability and complete system; Develop in the direction of low energy consumption, low noise, low vibration, no leakage, pollution control and application of water-based media to meet environmental protection requirements; Develop high integration, high power density, intelligence, electromechanical integration and light and small micro-hydraulic components; Actively adopt new technologies, new materials and high technologies such as electronics and sensors.
-The development of hydraulic coupling to high speed, high power and integrated hydraulic transmission device, the development of hydraulic coupling with water medium speed regulation and the development of automobile application field, and the development of hydraulic reducer to improve product reliability and mean trouble-free working time; Hydraulic torque converter should develop high-power products, improve parts manufacturing technology, improve reliability, popularize computer-aided technology, and develop matching technology between hydraulic torque converter and power shift gearbox; The liquid viscous speed regulating clutch should improve the product quality, form a batch, and develop in the direction of high power and high speed.
Pneumatic industry:
-Products are developing in the direction of small size, light weight, low power consumption and integration, and actuators are developing in the direction of multiple types, compact structure and high positioning accuracy; Pneumatic components are combined with electronic technology to develop in the direction of intelligence; The performance of components is developing towards high speed, high frequency, high response, long life, high temperature resistance and high pressure resistance. Oil-free lubrication has been widely used, and new technologies, new processes and new materials have been applied.
(1) adopts high-pressure hydraulic components, with continuous working pressure of 40Mpa and instantaneous maximum pressure of 48Mpa；;
(2) Diversification of control means;
(3) Further improve the regulation performance and improve the efficiency of the transmission system;
(4) Developing a compound adjusting transmission device combining mechanical, hydraulic and electric transmission;
(5) Developing an efficient system with energy saving and energy storage functions;
(6) further reducing noise;
(7) Adopt hydraulic threaded cartridge valve technology, which has compact structure and reduces oil leakage.