Hydraulic transmission:
It takes the hydraulic oil as the working medium, changes the mechanical energy of the prime mover into the pressure energy of the hydraulic oil through the power element (oil pump), then converts the pressure energy into the mechanical energy through the control element, drives the load to realize the straight-line or rotary movement with the help of the actuator element (oil cylinder or oil motor), and adjusts the force and speed of the actuator element through the remote control of the control element and the adjustment of the flow Degree.
When the system is disturbed by the outside world, the output of the actuator generally deviates from the original setting value, resulting in certain error hydraulic control: like hydraulic transmission, the system also includes power components, control components and actuator, and also transmits power through oil.
The difference between the two is that the hydraulic control has a feedback device. The function of the feedback device is to compare the output (displacement, speed, force and other mechanical quantities) of the actuator with the input (which can be variable or constant). The system is controlled by the deviation after comparison, so that the output of the actuator changes or remains constant with the change of the input. It is a closed-loop hydraulic transmission system, also known as hydraulic servo system or hydraulic servo system.
The on-off or logic control elements are used in the hydraulic transmission system. For its control purpose, it is to maintain the stability of the set value or simply change the direction, also known as the set value and sequence control elements.
In the hydraulic control system, the servo control element is used, which has a feedback structure and is controlled by an electrical device. It has a high control accuracy and response speed, and the controlled pressure and flow are constantly changing. The output power can be amplified.
Proportional control is a kind of control between the above two. The proportional control valve is a new type of electro-hydraulic control element developed on the basis of on-off control element and servo control element. It has some characteristics of the above two types of elements. The on-off control for manual adjustment can not meet the requirements, but it does not need the servo valve to be as strict as the hydraulic system Where pollution control is required.
Advantages and disadvantages of hydraulic transmission system
Among the four kinds of transmission modes (mechanical, electrical, hydraulic and pneumatic), none of them is perfect, and hydraulic transmission has the following extremely obvious advantages:
In terms of structure, its output power per unit weight and output power per unit size are of force and force in four kinds of transmission modes, with a large moment inertia ratio. In the case of transmitting the same power, the hydraulic transmission device has small volume, light weight, small inertia, compact structure and flexible layout.
In terms of working performance, speed, torque and power can be adjusted steplessly, with fast action response, quick change of direction and speed, wide range of speed adjustment, and speed range up to 100:l to 2000:1; with good action speed, simple control and adjustment, convenient operation and labor saving, it is convenient to cooperate with electrical control and connect with CPU (computer) for automation.
In terms of use and maintenance, the components have good self lubrication, easy to realize overload protection and pressure maintaining, safe and reliable; the components are easy to realize serialization, standardization and generalization. All the equipment with hydraulic technology is safe and reliable.
From the perspective of economic cost: the plasticity and variability of hydraulic technology are very strong, which can increase the flexibility of flexible production, and it is easy to change and adjust the production process. The manufacturing cost of hydraulic components is relatively low, and the adaptability is relatively strong. It is easy to combine hydraulic pressure with computer control and other new technologies to form the "mechatronics, hydraulics and optics" integration, which has become the trend of world development and is easy to realize digitalization.
Disadvantages of hydraulic transmission:
Everything is in two, and hydraulic transmission is no exception:
Due to the relative movement of the hydraulic transmission surface inevitably exists leakage, at the same time, the oil is not absolutely incompressible, coupled with the elastic deformation of the oil pipe, the hydraulic transmission can not get a strict transmission ratio, so it can not be used in the inline transmission chain of machine tools such as processing screw gear.
In the process of oil flow, there are edge loss, local loss and leakage loss, and the transmission efficiency is low, so it is not suitable for long-distance transmission.
Under the condition of high and low temperature, it is difficult to use hydraulic transmission.
In order to prevent oil leakage and meet some performance requirements, the manufacturing accuracy of hydraulic components is high, which brings some difficulties to use and maintenance.
It is not easy to check if there is a fault, especially in the unit where the hydraulic technology is not very popular. This contradiction often hinders the further promotion and application of the hydraulic technology. Hydraulic equipment maintenance needs to rely on experience, training hydraulic technicians for a long time.
