Electrical transmissions are driven and controlled by electricity. The use of AC motors for transmissions is simple and inexpensive, making them the most widely used and an integral part of all kinds of transmissions. However, AC motors are generally difficult to infinitely variable speed, while DC motors can be realized stepless speed, but the DC power supply is more expensive. At present, thyristor technology to make AC motor stepless speed greatly simplified, but in high-power and low-speed applications such as high-torque yet to be further improved. Electrical control, especially electronic computer control, with the signal change and transmission of convenient, easy to manipulate over long distances and other unique advantages, so in the automation requirements of the high degree of occasions is essential.
Hydraulic transmission is the use of liquid as a medium to transfer energy, hydraulic transmission and other transmission to compare some of the following advantages:
(1) easy to obtain a large force or torque
Hydraulic transmission is the use of liquid pressure to transfer force or torque. Hydraulic pumps can obtain a higher pressure, the current hydraulic pumps up to 35MPa pressure, so the hydraulic cylinder can obtain a large force or moment. For example, a 30cm diameter hydraulic cylinder, when the pressure is 21MPa, you can get 1.48×10^6N thrust, so it is widely used in heavy machinery that requires a lot of force or moment.
(2)Large power-to-weight ratio
The power-to-weight ratio is the ratio of its output power to its weight. Power to weight ratio of equipment that is smaller in weight and volume and can output a larger power. For example, the hydraulic pump on the aircraft, the weight of each kW power is only 0.209kg, while the weight of each kW of the motor will be up to 1.5-2kg. so in the requirements of the transmission of high power and does not allow a larger volume of cases should be used in the hydraulic transmission.
(3) easy to realize the reciprocating motion
Hydraulic face to realize reciprocating motion is the most convenient, while the motor must be through the rack and pinion institutions such as rotary motion into a linear reciprocating motion.
(4) easy to realize a wide range of stepless variable speed
Hydraulic transmission by adjusting the flow of liquid can be easily realized stepless speed, and speed ratio range. For example, with a throttle valve to adjust the flow rate, the flow rate can change from 0.02L/min to 10OL/min speed ratio of up to 5000, other forms of transmission is incomparable to the speed ratio.
(5) Transmission of smooth movement
As the hydraulic fluid control can be very small flow rate is still very uniform, so the movement of the equipment can be very smooth, for example, machine tools can be realized in the following 1mm/min no creep stable feed.
(6) Fast and shock-free speed change and direction change can be realized.
This is due to the large power-to-weight ratio of the hydraulic mechanism, so the inertia of the hydraulic equipment is small, and therefore the reaction speed is fast. For example, the rotary inertia of the hydraulic motor is not more than 10 % of the same power motor, so start the medium-power motor to 1 ~ 2s, while the same power of the hydraulic machinery starting time is not more than O.ls. Therefore, in the high-speed frequent machine tools (such as surface grinders, gantry planers) using hydraulic transmission can make the change of direction impact is greatly reduced.
(7) compared with mechanical transmission is easy to layout and maneuvering
Hydraulic transmission components connected by the pipeline, so there is a great deal of freedom in the installation position, the components can be placed in the position we want. For example, put the pump source does not affect the layout of the machine in the place, the manipulation mechanism in the most convenient place, such as ships on the manipulation mechanism in the front of the cabin on the cockpit, and its rudder is in the stern, which is difficult to achieve with mechanical transmission, while the hydraulic transmission is no difficulty.
(8) Easy prevention of overloading accidents
In hydraulic transmission it is easy to control the pressure of the system by means of pressure valves, thus preventing overloading and avoiding accidents, and it is possible to know the working conditions and the size of the load at various places by means of manometers fitted into the system, whereas it is not easy to observe the size of the load at various places in a mechanical transmission.
(9) automatic lubrication, component life is long
Hydraulic transmission in the use of most of the medium for mineral oil, which produces lubrication of hydraulic components, so the hydraulic components have a self-lubricating effect, its life is longer.
(10) easy to achieve standardization, serialization
Various hydraulic systems are composed of hydraulic components, so the standardization of hydraulic components, serialization, can greatly improve production efficiency, reduce costs and improve product quality.
