1 Force analysis of known gear parameters: modulus mn=2.5, pressure angle=20, helix angle=20 (right-handed), number of teeth Z=46. Sliding bearing condition: speed n=2600r/min, maximum transmission torque T =130Nm, the transmission diagram and the force diagram are shown in the following 1.
d=mnZ/cos=122.38mmFt=2000T/d=2124.5NFr1=Fttann/cos=823NFa=Fttan=773.3N Additional torque is: T=Fa d=94.64Nm Additional radial force is: Fr=T/B=94.64 /0.036=2629N Since the gear is an intermediate gear, the angle between the driving wheel and the driven wheel on the radial force of the gear is 67.2, so the radial force is Fr=2Fr1cos Fr=4000N=F
2 Wear check calculation According to the literature [1], the average pressure, pv value and sliding speed of the bearing are checked.
Pm=FBD=42000.03 0.045=3111111Papm=25MPapv=Fn19100B=3.1111112600191000.03=19750000Pam/spv=30MPam/sv=Dn60 1000=3.14 45 2600601000=6.123m/sv=12m/s
3 Minimum oil film thickness check For sliding bearings with large load and high rotational speed, in order to make it work normally, the minimum oil film thickness condition must be met to form elastohydrodynamic lubrication, that is to say, the eccentricity can not be too large. The eccentricity is calculated to perform a minimum oil film thickness check.
3.1 The relative clearance between the shaft and the bearing is calculated according to the tolerance of the shaft and the bearing: 0.0350.1mm, according to the relative clearance formula: = D can be obtained for the gap range: 0.0007780.002222.
3.2 Calculating the bearing capacity of dimension 1 The lubricating oil used for this bearing is 15W40CF14 and the oil of 15W/40 is close to the engine oil. At 100°, the viscosity of the oil is 12.516.3mm2/s (0.0120.0163PaS), and the working temperature is 80. According to the linear relationship in the literature [2], the viscosity can be found as: 18mm2 / s (0.018PaS). According to the dimension [1] in the literature [3], the calculation formula of the bearing capacity: F = pm2n (the unit of n is r/s) can calculate the bearing capacity of bearing capacity class 1.
3.3 Eccentricity The diameter of the gap is 0.005mm, and the corresponding bearing capacity F of 1 can be calculated. The corresponding eccentricity can be obtained by looking up the map. According to the literature [1], the formula and conditions for meeting the minimum oil film thickness necessary for elastohydrodynamic lubrication are determined by surface roughness, shaft radius, eccentricity and safety factor:
Hmin=r(1-)hminS(Rz1 Rz2) can be obtained by r(1-) S(Rz1 Rz2) so that the allowable eccentricity value when the minimum oil film thickness condition is satisfied can be derived, and the calculation result is listed in 1.
1-S(Rz1 Rz2)r
1 Calculation result and corresponding value of 3.4 analysis 1) It can be seen from 1 that as the diameter gap increases, the allowable bias rate also increases, but the relative gap and the bearing capacity and eccentricity of dimension 1 increase accordingly. . At the maximum power, the eccentricity of the actual working condition is greater than the allowable eccentricity, that is to say, when the requirements of the drawings are met, the minimum oil film thickness between the shaft and the bearing cannot be guaranteed to fully meet the requirements for forming the elastohydrodynamic lubrication, thus making it possible Causes direct contact between the shaft and the bearing, causing wear and even burning.
2) From the calculation formula of the allowable minimum eccentricity, it can be known that if the accuracy of the surface geometry error of the part is improved, the deformation of the part is small, the installation error is small, and the surface roughness of the part is good, the bearing is likely to work normally.
3) The bearing capacity of the bearing can be improved by improving the shaft or bearing structure, such as not opening the circumferential oil groove, but opening the axial oil groove on the non-load bearing area on the shaft (for the shaft, its radial load in the circumferential direction) The direction is basically unchanged), the bearing capacity of the bearing is greatly improved, and the principle is as shown in 2.
4) According to the non-dimensional bearing capacity and allowable eccentricity relationship curve, and placed in the bearing capacity diagram of the pressure supply radial bearing, as shown in the following 3 curve.
The relationship curve in the bearing capacity diagram of the circular bearing is known from 3, the working area of ​​the bearing is in the narrow area enclosed by the left or upper side of the red (thick solid line) curve and the thick black line. This is because: when the working area When it is located below or to the right of the curve, the minimum oil film limit is not satisfied, so that the bearing cannot form elastohydrodynamic lubrication, resulting in poor lubrication, resulting in direct contact between the shaft and the bearing. It can be seen from the figure that part of the red (thick solid line) curve is in zone 1 of the figure, and in these areas, the edge contact between the bearing and the shaft is severe, which is easy to cause bearing and shaft burning, in fact due to its The working area is narrow. When the load has impact, the gap is too large or the viscosity of the lubricating oil is lowered, the red (thick solid line) curve will move up or to the left, causing serious contact between the shaft and the bearing, causing the bearing and the shaft. Burnt. When the bearing surface geometry error, part deformation and installation error, load is stable, the viscosity of the lubricating oil is improved, etc., the red (thick solid line) curve will shift to the right, and the working area of ​​the bearing will expand. The performance will be improved, and the bearing may work properly.
4 Conclusions 1) When the full-power output of this type of automobile engine fan output gear sliding bearing can not fully meet the minimum oil film thickness requirement for elastohydrodynamic lubrication, it may cause direct contact between the shaft and the bearing, resulting in severe wear and even burning of the bearing. damage.
2) For the bearing to work properly, it is necessary to improve the structure of the bearing and improve its manufacturing precision to increase its load carrying capacity or reduce its output power to reduce its load.
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