In-depth analysis of pneumatic transmission, hydraulic transmission and hydraulic transmission

First, the pneumatic transmission articles

Pneumatic transmission uses compressed gas as the working medium, and the fluid transmission of power or information by the pressure of the gas. The system that transmits power is to transfer compressed gas to the pneumatic actuator through the pipeline and Control Valve, and convert the pressure energy of the compressed gas into mechanical energy to work; the system that transmits information uses the pneumatic logic component or the fluidic component to realize the logic operation and the like. , also known as pneumatic control system.

1, the characteristics of pneumatic transmission

The working pressure is low, generally 0.3~0.8 MPa, the gas viscosity is small, the pipeline resistance loss is small, it is convenient for centralized gas supply and medium distance transportation, safe to use, no explosion and electric shock hazard, overload protection ability; but the pneumatic transmission speed is low, Need a gas source.

2. Composition of pneumatic transmission

The pneumatic transmission consists of a gas source, pneumatic actuators, pneumatic control valves and pneumatic accessories. The gas source is typically supplied by a compressor. Pneumatic actuators convert the pressure energy of the compressed gas into mechanical energy for driving the working components, including the cylinder and the air motor. Pneumatic control valves are used to regulate the direction, pressure and flow of the airflow and are divided into directional control valves, pressure control valves and flow control valves. Pneumatic accessories include: water filter for purifying air, oil mist for improving air lubrication performance, muffler for eliminating noise, pipe couplings, etc. There are also pneumatic sensors for sensing and transmitting various information in the pneumatic transmission.

3, the advantages of pneumatic transmission

Using air as the medium, it is inexhaustible, the source is convenient, it is directly discharged after use, it does not pollute the environment, and there is no need to return the gas pipeline, so the pipeline is not complicated;

The air viscosity is small, the flow energy loss of the pipeline is small, and it is suitable for centralized gas supply for long distance transportation;

It is safe and reliable, does not require fire and explosion protection, and can work in high temperature, radiation, humidity, dust and other environments;

The pneumatic transmission reacts quickly;

The air pressure component has a simple structure, is easy to process, has a long service life, is convenient to maintain, the pipeline is not easy to be blocked, and the medium does not have problems such as deterioration and replacement;

4, the disadvantages of pneumatic transmission

The air compressibility is large, so the pneumatic system has poor stability of operation, and the load has a great influence on the working speed;

Pneumatic system has low pressure and is not easy to make large output strength and torque;

The air control signal transmission speed is slower than the electron and light speed, and is not suitable for high speed complex transmission systems;

Exhaust noise is high;

Second, hydraulic transmission articles

Hydraulic transmission is a transmission method that uses liquid as a working medium to transfer energy and control.

1. The basic principle of hydraulic transmission

The Hydraulic Pump is used to convert the mechanical energy of the prime mover into the pressure energy of the liquid, and the energy is transmitted through the change of the liquid pressure energy. Through the transmission of various control valves and pipelines, the liquid pressure is controlled by the hydraulic actuator (Hydraulic Cylinder or motor). It can be converted into mechanical energy to drive the working mechanism and realize linear reciprocating motion and rotary motion. The liquid is called the working medium, generally mineral oil, and its function is similar to the transmission elements such as belts, chains and gears in mechanical transmission.

2, hydraulic transmission system

Hydraulic system consisting of hydraulic pumps, hydraulic control valves, hydraulic actuators (hydraulic cylinders and hydraulic motors, etc.) and hydraulic accessories (pipes and accumulators, etc.).

3, hydraulic transmission system components

The power component, that is, the hydraulic pump, functions to convert the mechanical energy of the prime mover into the pressure kinetic energy of the liquid (expressed as pressure and flow), and its function is to provide pressure oil to the hydraulic system, which is the power source of the system;

The actuator is a hydraulic cylinder or a hydraulic motor. Its function is to convert hydraulic energy into mechanical energy and perform external work. The hydraulic cylinder can drive the working mechanism to realize reciprocating linear motion (or swing), and the hydraulic motor can complete the rotary motion;

Control elements, which are used by various valves to control and regulate the pressure, flow and direction of the liquid in the hydraulic system to ensure that the actuators can operate as expected;

Auxiliary components, including fuel tanks, oil filters, piping and fittings, coolers, pressure gauges, etc. Their role is to provide the necessary conditions for the system to work properly and to facilitate monitoring and control;

The working medium, the transmission liquid, is usually called hydraulic oil. The hydraulic system realizes the movement and power transmission through the working medium, and the hydraulic oil can also lubricate the moving parts in the Hydraulic Components.

4. Working principle of hydraulic transmission system

The following figure shows a simple grinding machine as an example. The electric motor drives the hydraulic pump to suck oil from the fuel tank, and the hydraulic pump converts the mechanical energy of the electric motor into the pressure energy of the liquid. The hydraulic medium enters the left chamber of the hydraulic cylinder through the pipeline through the throttle valve and the reversing valve, and pushes the piston to move the work table to the right. The hydraulic medium discharged from the right chamber of the hydraulic cylinder flows back to the oil tank through the reversing valve. After the reversing valve is reversing, the hydraulic medium enters the right chamber of the hydraulic cylinder, causing the piston to move to the left to push the table to move in the opposite direction. Changing the opening of the throttle valve adjusts the speed of movement of the hydraulic cylinder. The pressure in the hydraulic system can be adjusted via the relief valve. When drawing a hydraulic system diagram, the hydraulic symbols are represented by prescribed symbols for the sake of simplicity. This symbol is called a functional symbol.

5, the basic circuit

A typical oil circuit consisting of hydraulic components used to perform a specific function. Any hydraulic drive system consists of several basic circuits, each with a certain control function. Several basic circuits are combined to control the moving direction, working pressure and moving speed of the actuator according to certain requirements. According to different control functions, the basic circuit is divided into a pressure control circuit, a speed control circuit and a direction control circuit.

1 pressure control loop

Pressure control valves are used to control the entire system or local range of pressure circuits. According to different functions, the pressure control circuit can be divided into four circuits: voltage regulation, voltage transformation, pressure relief and voltage regulation.

2 speed control loop

A loop that controls the speed of movement of the actuator by controlling the flow of the medium. According to the function, it is divided into speed control loop and synchronous loop.

3 direction control loop

A circuit that controls the direction of flow of the hydraulic medium. A circuit that uses a directional control valve to control the direction of motion of a single actuator so that it can move or stop in the forward and reverse directions is called a commutation loop. When the actuator is stopped, a circuit that prevents the actuator from moving due to leakage due to external factors such as a load is called a lock circuit.

Third, hydraulic transmission articles

A fluid-driven medium that uses liquid kinetic energy to transfer energy. The impeller converts the rotational speed and torque input by the power machine (internal combustion engine, electric motor, turbine, etc.), and drives the working part of the machine through the output shaft. The liquid interacts with the impellers mounted on the input shaft, the output shaft, and the housing to generate a change in momentum moment, thereby achieving the purpose of transferring energy.

Hydraulic transmissions and hydraulic transmissions that transfer energy by liquid pressure can vary greatly in principle, structure, and performance. The input shaft and the output shaft of the hydraulic transmission are only connected to the working medium by liquid, and the components are not in direct contact, which is a non-rigid transmission.

1. Characteristics of hydraulic transmission

Automatic adaptability. The output torque of the torque converter can be automatically increased or decreased as the external load increases or decreases, and the rotational speed can be automatically reduced or increased correspondingly, and the stepless speed regulation can be realized in a large range;

Anti-vibration and vibration isolation performance. Because the working medium between the impellers is liquid, the connection between them is non-rigid, so it can absorb the impact and vibration from the engine and the external load, so that the machine starts smoothly, accelerates evenly, and prolongs the life of the parts;

Through-through performance. Refers to the degree of torque change of the input shaft (ie pump wheel or engine shaft) when the load changes without changing the pump wheel speed. Due to the different types of hydraulic components, they have different penetrability, which can be reasonably matched with the engine according to the different requirements of the working machine, so as to improve the power and economic performance of the machine;

2, the basic principle of hydraulic transmission

The prime mover (internal combustion engine, electric motor, etc.) drives the pump wheel to rotate, increasing the speed and pressure of the working fluid. This process realizes the conversion of mechanical energy to liquid kinetic energy; then the working fluid with kinetic energy then impacts the turbine, at which time the liquid releases energy to The turbine rotates the turbine to output power for energy transfer.

3, hydraulic transmission

The device uses liquid as the working medium to realize energy transfer by the kinetic energy of the liquid. Commonly, there are hydraulic couplers, hydraulic torque converters and hydraulic mechanical components.

1 fluid coupling

Also known as a hydraulic coupling, it is a mechanical device used to connect a power source (usually an engine or a motor) to a working machine to transmit rotational power. The automatic transmission that was once used in automobiles has a wide range of applications in maritime and heavy industry.

2 Hydraulic torque converter

A hydraulic component consisting of a pump wheel, a turbine, and a guide wheel. Installed between the engine and the transmission, hydraulic oil is used as the working medium to transmit torque, torque, shift and clutch.

4, the application of hydraulic transmission

Hydraulic transmission used in modern machines began in the early 20th century. It was first used as the transmission mechanism between the ship's power plant and the propeller to solve the problem of high-power, high-speed gas turbines and the reduction gear between the propellers whose speed was limited by "cavitation". . Hydraulic transmission has been widely used in automobiles, tractors, construction machinery, construction machinery, railway locomotives, tank and armored vehicles, oil drilling machinery, lifting and transportation machinery, fans, pumps and other products.