What is the principle of hydraulic transmission?

Hydraulic transmission is a kind of hydraulic transmission which mainly uses liquid pressure energy.

Hydraulic transmission and pneumatic transmission, called fluid transmission, are new technologies developed according to the hydrostatic transmission principle put forward by Pascal in the17th century, which are widely used in industrial and agricultural production. Nowadays, the level of fluid transmission technology has become an important symbol of a country's industrial development level.

Early application of hydraulic transmission

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1795, Joseph Braman of England (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. At the beginning of the 20th century, G. Neusk made 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.

Basic principles of application scope of hydraulic transmission

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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.

The basic principle of hydraulic transmission is to realize energy conversion and power transmission in a closed container with pressure oil as working medium. Liquid is called working medium, generally mineral oil, and its function is similar to that of belt, chain, gear and other transmission elements in mechanical transmission.

In hydraulic transmission, hydraulic cylinder is the simplest and relatively complete hydraulic transmission system. By analyzing its working process, we can clearly understand the basic principle of hydraulic transmission.

Composition of hydraulic transmission system

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

1, power component (oil pump) whose function is to use the mechanical energy of the prime mover to convert liquid into hydraulic energy; It is the power part of hydraulic transmission.

2. Actuator (oil cylinder, hydraulic motor) It converts the hydraulic energy of liquid into mechanical energy. Among them, the oil cylinder moves linearly and the motor rotates.

3. Control elements include pressure valve, flow valve and directional valve. Their function is to adjust the rotating speed of the hydraulic motor steplessly as needed, and to adjust and control the pressure, flow and flow direction of the working liquid in the hydraulic system.

4. Auxiliary components Besides the above three components, other components, including pressure gauge, oil filter, energy storage device, cooler, pipe fittings and oil tank, are also very important.

5. Working medium Working medium refers to hydraulic oil or emulsion that realizes energy conversion through oil pump and hydraulic motor in various hydraulic transmissions.

Advantages and disadvantages of hydraulic transmission

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1, the advantages of hydraulic transmission

(1) is small and light. For example, the weight of a hydraulic motor with the same power is only 10% ~ 20% of that of the motor. Therefore, the inertia force is small, and when suddenly overloaded or stopped, there will be no big impact;

(2) The traction speed can be automatically adjusted within a given range to realize stepless speed regulation, and the maximum speed regulation range can reach 1: 2000 (generally 1: 100).

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

(4) The hydraulic pump and the hydraulic motor are connected by oil pipes, and there is no strict mutual restriction on the spatial arrangement;

(5) Because the oil is used as the working medium, the relative moving surfaces of the parts can be lubricated by themselves, with little wear and long service life;

(6) simple operation and control, high degree of automation;

(7) It is easy to realize overload protection.

(8) Hydraulic components are standardized, serialized and generalized, which is convenient for design, manufacture and use.

2, the shortcomings of hydraulic transmission

(1) Hydraulic transmission requires high maintenance, and the working oil should always be kept clean;

(2) The manufacturing precision of hydraulic components is high, the process is complex and the cost is high;

(3) The maintenance of hydraulic components is complicated and requires high technical level;

(4) Hydraulic transmission is very sensitive to the change of oil temperature, which will affect its working stability. Therefore, hydraulic transmission cannot work at very high or low temperature.

The general working temperature is-15℃~60℃.

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

Classification of hydraulic components

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Power components-gear pump, vane pump, plunger pump and screw pump

Actuator-hydraulic cylinder: piston hydraulic cylinder, plunger hydraulic cylinder, swing hydraulic cylinder and combined hydraulic cylinder.

Hydraulic motors: gear hydraulic motors, vane hydraulic motors and plunger hydraulic motors.

Control element-directional control valve: one-way valve, reversing valve.

Pressure control valve: overflow valve, pressure reducing valve, sequence valve, pressure relay, etc.

Flow control valve: throttle valve, speed regulating valve and diverter valve.

Auxiliary components-accumulator, filter, cooler, heater, oil pipe, pipe joint, oil tank, pressure gauge, flowmeter, sealing device, etc.

If you think this entry needs improvement, adding new content or modifying wrong content, please edit it.

References:

1. Hydraulic and pneumatic technology

2. Hydraulic and Pneumatic Transmission, Huazhong University of Science and Technology Press, edited by He Cunxing.

Contributors (9 persons in total)

Omomi 12, Mystery of Modena, iamchenzetian, Autumn Cold in Shui Mu, sfrh, Clear Dew Without Leaving a Trace, happywolf2007, Goodbye Seattle, Shao Hao was sentenced to no wife.

This entry is mentioned in the following entries:

Automobile Transmission Department of Mechanical and Electrical Engineering College of Shandong Agricultural University

Interpretation of "hydraulic transmission" in Chinese-English dictionary (source: Baidu dictionary);

hydraulic transmission