Hydraulic transmission and pneumatic transmission are called fluid transmissions. It is an emerging technology developed according to the hydrostatic pressure transmission principle proposed by Pascal in the 17th century. It is a widely used technology in industrial and agricultural production. Today, the level of fluid drive technology has become an important indicator of the level of industrial development in a country.

 

Automotive Automatic Transmission Research Center:

 

Early use of hydraulic transmission

 

In 1795, the British Joseph Braman (1749-1814) used water as a working medium in London, applied it to the industry in the form of a hydraulic press, and created the world's first hydraulic press. In 1905, working medium water was changed to oil and further improved.

 

After World War I (1914-1918) hydraulic transmission was widely used, especially after 1920, it developed more rapidly. Hydraulic components did not begin to enter the formal industrial production stage until about 20 years after the end of the 19th century and the beginning of the 20th century. In 1925, F.Vikers invented the pressure balanced vane pump, which laid the foundation for the gradual establishment of industrial or hydraulic transmission of hydraulic components. G.Constantimsco's theoretical and practical research on the transmission of energy fluctuations at the beginning of the 20th century; his contribution to hydraulic transmissions (hydraulic couplings, torque converters, etc.) in 1910, Both fields have been developed.

 

During the Second World War (1941-1945), 30% of the US machine tools used hydraulic transmissions. It should be pointed out that the development of hydraulic transmission in Japan is more than 20 years behind the development of countries such as Europe and the United States. Around 1955, Japan quickly developed hydraulic transmissions and in 1956 the "Hydraulic Industry Conference" was established. In the past 20-30 years, Japan's hydraulic transmission has developed rapidly and it has taken a leading position in the world.

 

Basic principle of hydraulic drive application

 

Hydraulic transmission has many outstanding advantages, so its application is very extensive, such as general work. Industrial plastics processing machinery, pressure machinery, machine tools, etc.; construction machinery, construction machinery, agricultural machinery, automobiles, etc. in walking machinery; metallurgical machinery, lifting devices, roll adjustment devices for the iron and steel industry, etc.; flood control for civil engineering and water conservancy projects Gates and dams, river bed lifts, bridge control mechanisms, etc.; power plant turbine speed control devices, nuclear power plants, etc.; ship deck cranes (deck winches), bow gates, bulkhead valves, stern thrusters, etc.; Giant antenna control devices for special technologies, measurement buoys, lifting and revolving stages, etc.; gun control devices for military industry, ship anti-roll devices, aircraft simulations, retractable devices for landing gear, and rudder control devices.

 

The basic principle of hydraulic transmission is to use a pressurized fluid as a working medium to achieve energy conversion and transfer of power in a closed container. The liquid is called a working medium and is generally a mineral oil. Its function is similar to that of a transmission element such as a belt, a chain, and a gear in a mechanical transmission.

 

In hydraulic transmission, the hydraulic cylinder is the simplest and relatively complete hydraulic transmission system. Analyzing its working process can clearly understand the basic principles of hydraulic transmission.

 

Composition of hydraulic transmission system

 

The hydraulic system is mainly composed of five parts: power element (oil pump), actuator (cylinder or hydraulic motor), control element (various valves), auxiliary components and working medium.

 

1. Power element (oil pump) Its role is to convert the liquid using the mechanical energy of the prime mover into hydraulic pressure energy; it is the power part in the hydraulic transmission.

 

2. Actuator (cylinder, hydraulic motor) It converts the hydraulic energy of the liquid into mechanical energy. Among them, the cylinder moves in a straight line and the motor rotates.

 

3, control components Including pressure valves, flow valves and directional valves. Their role is to adjust the speed of the hydraulic motor steplessly as needed, and to regulate and control the pressure, flow and flow of the working fluid in the hydraulic system.

 

4, auxiliary components In addition to the above three components, including pressure gauges, oil filters, energy storage devices, coolers, fittings and fuel tanks, etc., they are also very important.

 

5. Working medium Working medium refers to hydraulic oil or emulsion in various types of hydraulic transmission. It achieves energy conversion through oil pump and hydraulic motor.

 

Advantages and disadvantages of hydraulic transmission

 

1, the advantages of hydraulic transmission

 

(1) Small size and light weight, for example, the same power hydraulic motor has only 10% to 20% of the motor weight. As a result, the inertial force is small, and when a sudden overload or stoppage occurs, a large impact does not occur;

 

(2) It can automatically adjust the traction speed within a given range, and can realize stepless speed regulation, and the maximum speed range can reach 1:2000 (usually 1:100).

 

(3) The commutation is easy, and without changing the rotation direction of the motor, the rotation of the working mechanism and the conversion of the linear reciprocating motion can be realized more conveniently;

 

(4) The hydraulic pump and the hydraulic motor are connected by oil pipes, which are not strictly limited to each other in the space arrangement;

 

(5) Due to the use of oil as the working medium, the relative motion of the components can be self-lubricated with little wear and long service life.

 

(6) The control is simple and the degree of automation is high;

 

(7) Easy to implement overload protection.

 

(8) Hydraulic components are standardized, serialized, universalized, easy to design, manufacture and use.

 

2, the disadvantages of hydraulic transmission

 

(1) The use of hydraulic transmission requires high maintenance, and the working oil should always be kept clean;

 

(2) High requirements for the manufacturing precision of hydraulic components, complicated process, and high cost;

 

(3) Maintenance of hydraulic components is more complicated and requires a higher level of technology;

 

(4) Hydraulic transmission is sensitive to changes in oil temperature, which will affect its working stability. Therefore, hydraulic transmission should not work at very high or low temperatures.

 

The general working temperature is in the range of -15°C~60°C.

 

(5) Hydraulic transmission In the process of energy conversion, especially in the throttling speed control system, the pressure is large and the flow loss is large, so the system efficiency is low.