Views: 0 Author: Site Editor Publish Time: 2024-10-22 Origin: Site
The problem of strain and wear of refrigerator compressor is prominent due to poor crankshaft lubrication in use, and the power of the compressor lubrication system comes from the crankshaft, so the optimal design of the crankshaft is very important. By studying the geometric factors affecting the oil loading of the crankshaft of a compressor, the influence of the parameter of the distance between the upper oil outlet of the spiral viscous pump and the intersection point of the distribution pump and the wall surface of the spiral viscous pump on the oil volume of the crankshaft is calculated. The calculations show that the smaller this distance, the higher the amount of oil applied to the crankshaft. The experimental results are verified, and the calculation results are in good agreement with the experimental results, which provides guidance and reference for the analysis and optimization of the oiling capacity of the crankshaft.
In this paper, the oiling capacity of the crankshaft of a refrigerator refrigeration compressor is numerically calculated and tested by a combination of experiments and calculations, which provides technical support for the optimization of a new high-efficiency compressor.
1. Numerical simulation model
With the rotation of the crankshaft, the lubricating oil gradually rises along the suction pipe, and the rising process of the lubricating oil is a two-phase mixing process of oil and gas. In this paper, the VOF model is used to simulate the change process of oil and gas two-phase liquid level.
The crankshaft studied in this paper is a crankshaft applied to a new energy-efficient refrigerator compressor with R600a working fluid, using 10# lubricating oil. Affected by the processing technology and machining accuracy, the distance between the upper oil outlet of the crankshaft spiral viscous pump and the intersection point of the distribution pump and the wall surface of the screw pump is the distance between the oil hole and the crankshaft oil hole. Considering the dimensional tolerance deviation in crankshaft machining, in order to avoid the phenomenon of opening up with the retract groove, the distance between the intersection point of the oil hole and the distribution pump and the outer wall of the crankshaft is between 1.5 mm ~ 2.5 mm, as shown in Figure 1 H value.
Fig.1. The distance between the intersection of the upper outlet and the dispensing pump
of the spiral viscous pump and the wall of the spiral viscous pump
In this paper, the distance between the intersection point of the upper oil outlet hole and the distribution pump and the outer wall of the crankshaft in case 1 is 1.6 mm, the distance between the intersection point of the upper oil outlet hole and the separator pump and the outer wall of the crankshaft in case 2 is 1.8 mm, and the distance between the intersection point of the upper oil outlet hole and the separation pump and the outer wall of the crankshaft in case 3 is 2.4 mm.
As shown in Figure 2, the oil flow channel diagram is given, and in order to verify the advantages and disadvantages of these three crankshafts, the performance of these three crankshafts will be compared and analyzed.
Fig.2. Oil flow channel on crankshaft and different oil hole offsets
The internal channel of the crankshaft can be divided into three parts: the lower section of the suction pipe with blades is a centrifugal pump, which agitates the lubricating oil through the blades, so that the lubricating oil climbs along the wall surface of the suction pipe under the action of centrifugal force; The middle section is a spiral viscous pump, and the lubricating oil moves to the upper end under the action of viscous force, providing lubrication for the bearings and flanges in the process; The upper section is the distribution pump, which lubricates moving parts such as pistons, connecting rods and piston pins. This study is the influence of the cross position between the viscous pump to the upper distribution pump on the crankshaft oil volume and internal oil pressure, the upper oil outlet of the crankshaft spiral viscous pump and the intersection point of the distribution pump and the distance from the wall of the spiral viscous pump, the oil delivered to the viscous pump is squeezed into the upper distribution pump by oil pressure.
2. Model simplification
Because the calculation model of oil on the crankshaft is complex, the geometry and calculation of this model are simplified and assumed as follows:
（1）.The lubricating oil does not contain refrigerant, and the top of the oil pool contains vapor phase refrigerant;
（2）. the flow is isotherm;
（3）. The physical properties of lubricating oil and refrigerant are constant and do not change with changes in temperature and pressure;
（4）. The acceleration of the motor when starting is infinite;
（5）. The outer surface of the viscous pump in the middle section is matched with the rotor of the compressor to form a cylindrical gap with a thickness of 0.2 mm, and the influence of this gap is considered in the calculation process;
（6）.The effect of interference between the crankshaft and the rotor is not considered.
Fig.3 Boundary condition settings for the calculation
3. Calculations and analysis of results
A slip mesh is used to simulate the rotational motion of the crankshaft, and the motion of the crankshaft is realized using a motion reference system (MRF). In this calculation, the rotational speed is set to 3000 r/min, the suction pipe is inserted into the lubricating oil pool, and the insertion depth is set to 12 mm. The upper surface of the oil pool is the pressure inlet, and the volume fraction of the oil is set to 1; The oil outlet and air outlet at the top end of the crankshaft are pressure outlets, and the return volume fraction of the oil is set to 0; The internal areas and walls of the entire crankshaft section are set to a rotating grid; Because of the assumption that there is no slip wall, the main bearing section is set to a stationary wall.
The 10# lubricating oil commonly used in refrigerator compressors is used, and at the same time, it is unified for theoretical calculation, experimental verification and practical use. The density ρ = 875 kg/m3 of 10# lubricating oil, the dynamic viscosity is calculated by the empirical formula, the viscosity coefficient of lubricating oil is μ=0.0034 Pa·s, and the surface tension is 0.2 N/m. Figure 4 shows the setting of the liquid lubricant and gas phase refrigerant and the depth of the crankshaft insertion into the model.
Fig. 4 Calculated initial lubricant, refrigerant and crankshaft conditions
Compared with the average value of the three crankshafts after stabilization, the oil load of the crankshaft with a shift of 2.4 mm is 9.72 L/h, the oil load of the crankshaft with an offset of 1.8 mm is 9.80 L/h, the oil load of the crankshaft with an offset of 1.6 mm is 9.97 L/h, and the oil load of the crankshaft with an offset of 1.6 mm is larger. Fig. 5 b) shows that the oil volume fluctuation of the crankshaft with a deviation of 2.4 mm is significantly larger than that of 1.6 mm, and the oil supply of the 2.4 mm crankshaft is significantly more unstable than that of the 1.6 mm crankshaft, and the minimum oil supply is less than 8 L/h, resulting in the risk of insufficient oil supply affecting the crankshaft lubrication.
Figure 5： Calculation results of the model
The volume distribution of oil is shown in Fig. 6, from which it can be seen that the crankshaft with an offset of 2.4 mm is significantly inferior to the crankshaft with an offset of 1.6 mm, the spiral channel of the crankshaft with an offset of 1.6 mm is filled with oil, and the crankshaft channel with an offset of 2.4 mm is mixed with gas.
Especially for inverter compressors, in the high-speed or low-speed operation of the compressor, such as gas mixed in the crankshaft groove, it will affect the stability of the crankshaft oiling process and destroy the oil film, so that the lubrication state between the crankshaft main shaft and the crankcase shaft hole, the crankshaft auxiliary shaft and the connecting rod bore or the piston pin and the connecting rod bore is converted from hydrodynamic lubrication to boundary lubrication. Cavitation may even occur, resulting in surface strain and wear of the crankshaft. Cavitation is a very important form of abrasion, in which water, mineral oil and other fluids flow through the surface of a metal material, resulting in a change in flow velocity due to a change in local geometry, which in turn changes the internal pressure of the liquid. If the local pressure becomes lower than the vaporization pressure of the liquid, the liquid will boil, quickly produce vapor bubbles, and quickly burst in the higher pressure region, which will cause the metal surface to be subjected to repeated impact forces, and then cavitation will occur .
Fig.6 Volume distribution of oil (red is liquid phase refrigeration oil, blue is gas phase refrigerant, and others are oil and gas mixtures.)
Both the amount of oil applied to the crankshaft and the volume distribution of the oil applied to the crankshaft are better than those with an offset of 2.4 mm.
4. Experimental verification
4.1 Experimental test of oil quantity on crankshaft single product
The crankshaft with the distance of 1.6 mm, 1.8 mm and 2.4 mm from the wall of the screw pump was selected from the upper oil outlet of the screw pump and the intersection point of the distribution pump from the wall surface of the screw pump, and the oil quantity on the crankshaft was tested. The device in the experiment can accurately control the oil temperature, the speed of the crankshaft and the immersion depth of the crankshaft, this experimental equipment is to load the crankshaft that needs to be tested into the shaft sleeve, adjust the level of the lubricating oil surface in the oil pool, according to the set crankshaft suction pipe insertion depth, drive the crankshaft fixed on the pulley to rotate through the servo motor, collect the amount of oil thrown out of the crankshaft crank oil hole with the set speed and running time, and calculate the oil amount of different experimental crankshafts. In the experimental tests, the settings of these parameters are consistent with the calculations. Fig. 7 shows the pump oil test bench for the oil quantity test on the crankshaft. Table 1 shows a comparison of the experimental and numerically calculated values of the oil quantity on the crankshaft.
Fig.7. Crankshaft pump oil test bench
Table 1 Comparison of experimental and calculated values
Due to the simplification and assumptions of the model, there is still a certain gap between the calculated and experimental values, but from the trend point of view, the numerical calculations and the experimental values remain consistent. Experiments also show that the amount of oil on the crankshaft decreases as the oil hole offset increases.
4.2 Reliability verification of the whole compressor machine
In addition, the crankshaft in two states is installed as a compressor for verification, and the other parts are exactly the same, and it is installed on the BCD-546 refrigerator of the United States for the reliability of the whole machine for long-term operation test, and the compressor is anatomically analyzed after the test, and through observation and detection, it is found that the wear near the oil port on the crankshaft has differences, as shown in Figure 8 is the comparison of the wear and tear of the surface of the two crankshafts after the refrigerator is transported for a long time.
Fig.8 Comparison of the wear of the crankshaft after the whole refrigerator is transported for a long time
As can be seen from Table 2, the crankshaft with an oil port offset and a wall thickness of 2.4 mm is worse than the crankshaft with an offset of 1.6 mm.
Table 2 Comparison of the accuracy of crankshafts with different oil hole offsets after long operation
5 . Conclusion
In this paper, the oil loading capacity of the crankshaft of refrigerator compressor is numerically calculated and experimentally tested, and the calculation model of the oil loading capacity of the crankshaft is verified, which provides a quantitative evaluation method for the analysis and optimization of the oil loading capacity of the crankshaft. Based on simulation and experiments, the distance between the intersection point of the upper oil outlet of the screw pump and the distribution pump from the wall surface of the screw viscous pump is an important parameter affecting the oil quantity on the crankshaft, and this offset value should be strictly controlled in the production and processing process.
（1）. The calculation model of the crankshaft was established, and the numerical simulation was carried out based on Fluent, and the influence of the geometric design parameters of the crankshaft on the volume flow rate of the inlet and outlet was studied.
（2）. Using the theoretical model and experimental test verification analysis, it is found that the farther the upper oil outlet of the crankshaft screw pump and the intersection point of the distribution pump are from the center of rotation, the more the influence of centrifugal force can be fully utilized to increase the oil loading, and the higher the oil loading, that is, the smaller the oil hole offset on the crankshaft, the more stable the oil supply and oil supply on the crankshaft, and the better the compressor crankshaft lubrication, reducing wear and product reliability.
