Structural design analysis of small linear refrigeration compressor

Structural design analysis of small linear refrigeration compressor Core Tip: Household refrigerators, freezers and other small refrigeration devices are large energy consumers in the civil field. Most of the energy is consumed in refrigeration compressors. Therefore, improving compressor efficiency is the main technical means to achieve energy saving in small refrigeration devices. Linear compressors have high efficiency, small size, compact structure, Household refrigerators, freezers and other small refrigeration devices are large energy consumers in the civil field. Most of the energy is consumed in refrigeration compressors. Therefore, improving the efficiency of compressors is the most important technical means to achieve energy saving in small refrigeration devices. Linear compressors are considered to be one of the main development directions of energy-saving technologies for small refrigeration compressors due to their high efficiency, small size, compact structure, and convenient control. For the specific use environment of small refrigeration equipment, the applicable linear compressor should have the characteristics of small size, simple structure, high efficiency, high reliability, easy installation, convenient control and low cost. Based on these requirements, this paper compares and analyzes the structural design of small linear refrigeration compressors. 1 Analysis of linear motor driver Linear motor driver is the most important part of linear compressor. In theory, any kind of linear motor can be the driver of a linear compressor. The characteristics of various linear motors are different, so you need to choose the type that best suits the refrigerator. Linear motors can be divided into two major categories of linear motors and linear drives from the working principle and use angle, see. Among them, the linear synchronous oscillator motor can automatically generate high-frequency reciprocating linear motion using the principle of electromagnetic force and spring resonance, which can directly drive the reciprocating motion of the mover, with large output, low loss, and high efficiency, which is most in line with the use requirements of linear compressor drivers. The name and working principle of the linear synchronous oscillator motor are similar to the common linear synchronous motor, but the structure is simpler than the linear synchronous motor, which has the performance advantages of the linear synchronous motor and avoids fund projects. The shortcomings of the complicated structure of the linear synchronous motor, and the displacement can be easily adjusted by adjusting the motor terminal voltage during the operation process, which is convenient for control. In summary, in response to the working requirements of the driver for small linear refrigeration compressors, it is ideal to use a linear synchronous oscillation motor as the driver of the linear compressor. According to the type of movable body, linear synchronous oscillation motor can be divided into three types, namely moving iron type, moving coil type and moving magnet type, or can be divided into moving iron type, moving coil type, moving magnet type and moving magnet type Four types. Is a schematic diagram of the structure of four types of motors. Moving iron linear motor uses iron core material, and the magnetic field is generated by the excitation coil. This type of motor can produce a large driving force and compression ratio, but it must use a multi-phase winding to generate a reciprocating linear motion, which is large in size, and the movement of the mover in the air gap is unstable. The moving coil type, that is, the mover is composed of a coil, while another coil provides excitation, or is provided by a fixed permanent magnet component. The advantage of this type of motor is that the piston stroke is easier to control, there is no radial force and torque on the mover, no axial force when there is no load, and no hysteresis loss. But the driving force is relatively small, and the lead problem is not easy to solve. The moving magnet type mover is composed of permanent magnet material, and the excitation is completed by the coil. Studies have shown that the utilization rate and the reduced mass of the mover are conducive to the design of the corresponding resonant spring, with greater thrust and higher efficiency; but the principle is relatively complicated, and the system design needs to consider the nonlinear magnetic permeability, hysteresis loss, Influence of eddy current loss and other factors. The main difference between the moving magnet type and the moving magnet type is that the former mover is a simple permanent magnet or a permanent magnet plus a non-conductive bracket, the latter mover is a permanent magnet plus a mover core, but the basic working principle is the same, so sometimes in The two structures are classified as one. A common feature of the moving coil type and moving magnet type is that its winding coil only needs a single phase to achieve the purpose of driving the reciprocating oscillation of the mover, so it can be greatly reduced in size. Since the moving magnet type has a central axis of magnetic permeability, it must also use a multi-phase winding to function. From this point of view, it is similar to the moving iron type. (C) Moving magnet type (d) Moving magnet type structure diagram of four synchronous linear oscillation motors In different working environments, you can choose the appropriate motor form according to your needs. Therefore, according to the application requirements of small refrigeration equipment and the advantages and disadvantages of the above four linear synchronous oscillation motors, the dynamic magnetic linear oscillation motor is selected as the driver. 2 Piston layout structure analysis Due to the inherent characteristics of the linear compressor linear drive, that is, the reciprocating oscillation motion in the linear direction, and the motion state on both sides are completely symmetrical, it is easy for the linear compressor to achieve dual cylinder opposed, dual side piston compression. Therefore, the choice of single-sided piston compression or double-sided piston compression is a problem to be considered in the design of linear compressors. The comparison of the two layout methods is shown as follows. The advantage of single-sided compression is that the structure is simpler, while double-sided compression requires a larger size, which is not conducive to installation in a narrow space, and the intake and exhaust systems are correspondingly more complicated. However, the double-sided piston runs more smoothly because if it is compressed on one side, it will be affected by the gas force half the time during the full stroke and the other half will not be affected by the gas force, which will affect the stability of the vibration. The structure of the layout can eliminate this adverse effect, and it has a very obvious effect on reducing the instability and noise caused by vibration (see). In addition, the frequency of double-sided compression can be lower under the requirement of the same displacement, and because the length of the mover is relatively long, it is also easier to use the bearing to locate the mover. The choice of layout is closely related to the type of linear actuator used. In the above analysis of various linear oscillation drives, it is mentioned that the design scheme of some drives uses a moving iron type or moving magnet type design scheme. In this case, the compressor has a solid shaft, and it is more suitable to use double-sided Layout; if the meter uses a moving coil or moving magnet single-phase linear oscillation motor solution, coupled with a double-sided layout will completely offset the advantages of single-phase motors in size and structure, so the single-sided layout is used at this time More optimized. The above theoretically compared the advantages and disadvantages of single and double compression. However, if the compressor power is small, and there is no particularly strict restriction on the installation space, the difference between the single and double-sided layout on the performance of the whole machine is not particularly obvious. Therefore, the scheme of making two structures at the same time is adopted, and a comparative study is conducted. 3 Analysis of the gas path structure In the traditional compressor gas path structure, the intake and exhaust valves are located on the same side of the cylinder, and the valve plates of different layers are assembled together to form the intake and exhaust path. However, this design is not suitable for linear compressors, because in this structure, the intake and exhaust valve pieces are hidden inside the entire valve plate, the valve plate itself is not elastic, and the piston stroke of the ordinary rotary compressor Strictly restricted by the transmission mechanism, there will be no collision with the cylinder; the linear compressor's piston stroke is not rigidly limited, so once the piston movement exceeds the expected stroke, the valve plate will have a rigid collision, resulting in strong noise and even zero Damaged parts. In order to avoid the above problems, a solution is to design a disc spring support, an exhaust valve body made of organic material, so that the entire exhaust valve part is elastic, thereby avoiding rigid collisions, and because it has more With a large flow area, this valve can minimize the over-compression loss. In addition, the suction valve is transferred to the top of the hollow piston, so that the suction valve and the suction channel are in the piston, so that the flow resistance and suction heating loss are minimized. This airway layout scheme has certain advantages, but it is only applicable when the structure does not have a solid shaft. Therefore, the spring can be further changed into an elastic hollow element, such as a bellows, etc., and at the same time, the intake and exhaust valve body and the intake and exhaust valve body will not rigidly collide with the piston. This method has applied for a patent for invention. See two suction and exhaust structures. The choice of intake and exhaust structure also depends on the type of linear actuator used. If the moving magnet type is used, it is more difficult to use the hollow piston air intake in the presence of a solid shaft; correspondingly, the moving coil type or the moving magnet type does not have this problem. On the contrary, if the hollow piston air intake is used for the structure Simplification is also more advantageous. It is planned to make these two gas circuit structures at the same time and make a comparative analysis. 4 Sealing and lubricating structure scheme analysis Traditionally, the seal of the piston cavity is sealed by the piston ring and the lubricating oil film. In addition, the part where the outer surface of the piston is in contact with the inner wall of the piston cavity can be coated with a layer of coating material (such as Teflon, etc.). The effect is outstanding, and it is more suitable for the above-mentioned piston head suction air path structure scheme. In addition, a special magnetic fluid substance has also been used to seal the piston chamber of the compressor. From the perspective of gas circuit structure, the coating scheme is more appropriate. Theoretically speaking, the linear compressor driven by a linear motor eliminates the inefficient mechanical transmission mechanism, and there is no direct contact between the mover and the stator, which can completely achieve oil-free lubrication, but this requires extremely high assembly accuracy. Guaranteed, and because more and more permanent magnet components are used in linear motors, the lateral force acting on the mover shaft generally affects the performance of the linear motor. Therefore, at present, small linear compressors still need to use oil lubrication. However, due to the cancellation of the rotary motion mechanism, it is necessary to research and develop a separate oil supply device. The oil supply device has essentially the same function as a small pump, so it can be designed using the principles of various pumps. For example, plunger type oil supply device, or oil supply device using diaphragm pump principle, see. The above two oil supply device schemes will also be verified by experiments. Diaphragm pump type oil supply device structure schematic diagram Resonator analysis The current resonant components in linear compressor linear motor drivers are mainly column springs and leaf springs. In the linear oscillation motor, the resonator is used to limit the displacement of the adjustable mover on the one hand, and adjust the elastic coefficient of the entire vibration system on the other hand. Column springs are easier to design, calculate, and produce than leaf springs, and have a wide range of applications. Therefore, from the perspective of process and cost, the column spring has certain advantages. However, the leaf spring has a small size, and its axial stiffness and radial stiffness are superior to column springs. Studies have shown that the use of leaf springs can greatly improve the performance and stability of the compressor. If you want to use leaf springs, the outstanding problem is that the range of leaf springs is narrow. Different motors have to redesign the shape of the spring, and the design workload is very large. The more prominent contradiction is that as a sensitive technology, developed countries The design method and performance analysis method of the plate type flexible spring mastered by it are strictly technically blocked, so the application is more difficult. Therefore, it is planned to use a suitable column spring as the resonant part of the compressor. 6 Conclusion According to the requirements of refrigerators, after comparing the different schemes of linear compressor linear motor driver and piston layout, gas circuit, sealing, lubrication and resonance components, it is considered that the linear compressor driven by dynamic magnetic linear synchronous oscillation motor is reasonable The design can achieve a more optimal effect between efficiency and size cost. Therefore, this motor is selected as the driver of the linear compressor, and is equipped with a surface-coated piston and a column spring as a resonator. On this basis, the layout of the two sets of pistons, the gas path structure and the lubrication scheme were determined, and experimental studies were conducted separately.

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