| 摘要: | 大型旋轉軸承多為直徑一米以上之軸承，因其能承受高負載低轉速的特性，常與齒輪做結合以做為驅動機構之功能，其中四點接觸旋轉軸承，因可同時承受軸向力、徑向力及傾覆力矩，且為滾珠設計，使啟動力矩較小，大多應用在風力發電機、挖掘機、吊車轉塔或軍用砲塔座等之旋轉機構。
旋轉軸承最容易破壞的地方之一為滾珠，因此研究上大多以滾珠受力情形為主；但大型旋轉齒輪軸承為了要輕量化，多會將軸承環部之壁厚減少，如此雖可減輕重量但也增加了環部破壞的風險。因此本篇論文分析軸承在受到靜態及動態負載後，對壁厚的影響為何。另一方面，除了一般的負載，螺絲的預力也會影響到軸承的應變情況，在分析上也納入考量。
本論文針對某具有轉塔之車輛的旋轉齒輪軸承為分析目標。整體結構係由軸承內環、外環、與內環連接之轉塔，以及與外環連接之車體組成，軸承環部與轉塔及車體接合方式為螺絲，總共178顆滾珠及36顆螺絲。
在靜態負載分析方面使用MSC.Marc分析軸承之結構強度。有限元素建模中，將滾珠以承受壓力之彈簧代替，其剛度曲線由KISSsoft根據ISO/TS16281計算而得，螺絲則用樑元素代替；如此可大幅減少分析時間，並且不影響分析結果。而在一般的分析上，不論是利用受載接觸分析模型或是使用有限元素分析FEM，均是以靜態負載為主，但旋轉軸承受到動態負載作用影響卻是不可忽略。因此本論文除了分析靜態負載以外，也使用MSC.CoSim結合MSC.Adams的動態負載分析與MSC.Marc的有限元素分析，以符合真實的情況模擬滾珠與結構在動態下之受力情形。
旋轉軸承在承受動態負載條件共分成平地及坡地狀態承受動態衝擊負載，以及在平地運輸時，受到地面起伏振動等兩種情況。論文中以協同模擬分析旋轉軸承在這些情況下，確認滾珠負載是否在安全範圍內，軸承環部結構強度是否可承受動態衝擊以及螺栓在鎖緊狀態下負載變化狀況。
另一方面，由與旋轉軸承連接的介面板在加工時仍具有一定程度的平面度誤差，軸承環部在螺絲鎖緊下會產生變形，因此必須要能確保在最差的誤差情況下，軸承環部、滾珠與滾道可符合強度要求，以及軸承不會因軸承環部變形使運轉不順暢。
在靜態分析結果中，當軸承僅受螺絲預力，會使軸承變形造成與螺絲接近之滾珠產生更多的負載；平地與坡地受到負載時，徑向力與偏心重量造成負載由一號滾珠漸增到89號滾珠；薄壁應力及螺絲受力受螺絲預力影響較大，負載條件影響較小；軸承間隙會使滾珠負載分配區間變小；當介面板平面度在規範最大值下，對滾珠造成的負載約在5400 N，仍在安全範圍內，造成之啟動力矩約為900 N-m，為介面板無變形情況下之兩倍。
而在動態分析結果方面，軸承受到衝擊負載時，因為衝擊方向朝向一號滾珠及軸承重心偏向89號滾珠影響，因此負載會由1號滾珠漸增到89號滾珠，而滾珠負載值最大時間點在平地衝擊時，會與衝擊最大值時間點一致，坡地衝擊則是在衝擊最大時間點過後，因傾覆力矩在衝擊過後造成更大的負載；平地運輸振動則是在接觸對I上分佈差不多，接觸對II則因為傾覆力矩在89號滾珠會有最大值，時間點上滾珠負載最大值會與振動最大值的時間點一致，從負載對應到的應力值來看，並不會對滾珠及軸承造成破壞。從結果也可以看出螺絲對軸承的影響，軸承在螺絲鎖固點附近的位置會因預力變形關係而有較大的應力，進而影響到滾珠及環部薄壁動態受力。而螺絲本身因預力關係，在動態負載作用下，負載並無太大的變化
;Slewing bearings are mostly the bearings with a diameter more than one meter. Because of their ability to bear high loads under low speeds, they are often combined with gears to serve as a driving mechanism. Among them, the four-point contact bearing can bear axial force, radial force and tilting moment at the same time, and can transmit a small starting torque due to ball design. Most of them are used in rotation mechanisms such as wind turbines, excavators, crane turrets or military turrets, etc.
One of the most easily damaged parts of the slewing bearing is the rolling element, so most of the research focus on the acting force of rollers or balls. However, in order to reduce the weight of large slewing gear bearings, the wall thickness of the bearing ring is often reduced. Although the weight can be reduced, it also increases the risk of damage to the ring structure. Therefore, this paper analyzes the impact of the bearing loads on the wall thickness under static and dynamic loads. On the other hand, in addition to the general working loads, the pre-load of the screws will also affect the deformation of the bearing, which is considered in the analysis.
The objective of this paper is to analyze the slewing gear bearing of a vehicle with a turret. The structure is composed of an inner ring, an outer ring, 178balls, a turret and a vehicle body. 36 screws are used for connection between the bearing ring and the turret and the vehicle respectively.
In the static load analysis, MSC.Marc is used to analyze the structural strength of the bearing. In the element modeling, the ball is replaced by a spring element, the stiffness curve is calculated by KISSsoft according to ISO/TS16281. The screw is replaced by a beam element. This modeling can greatly reduce the analysis time without affecting the analysis results for the bearing structure. In general, either the load contact analysis model or the Finite Element Method_(FEM) is based on the static load analysis. However, the effect of the dynamic load on the slewing bearing cannot be ignored. Therefore, in addition to the static load analysis, MSC.CoSim combined with MSC.Adams_(dynamic analysis) and MSC.Marc_(FEM) to simulate the dynamic force on the balls and the bearing structure in accordance with the real situation.
Slewing bearing under dynamic loading is divided into two types of conditions: impact loading on the bearing in the case of flat and sloping field, and transport vibrations in the case of flat field. MSC.CoSim is used to analyze the slewing bearing under these conditions to confirm whether the ball load can be within the safe range, the structural strength of the bearing ring can bear dynamic impact, and the load variation of the bolts in locked state.
On the other hand, the interface plate connected with the slewing bearing has a certain degree of flatness error. The bearing ring will be deformed when the screws locked. Therefore, it must be able to ensure that the rings, balls and raceways of the bearing under the worst tolerance condition, can meet the strength requirements, and the deformation of the raceway will not cause uneven running of the bearing.
In the static analysis results, the bearing preload of the screws will cause the deformation of bearing ring and also more load on the balls which are close to the screws. When the bearing is under working loads, the radial force and the eccentric weight cause the shared load of the individual ball increase from ball 1 to ball 89. The thin-wall stress and screw load are greatly affected by the screw preload, less by the working loads. The bearing clearance will lead to a smaller distribution interval. When the flatness of the interface plate is the maximum value of the specification, 0.4 mm, the maximum bearing load is about 5400 N, which is within a safety range. In this case, the starting torque is increased to 900 N-m, the value is about twice to the normal interface.
In terms of dynamic analysis results of the bearing under the impact load, the shared load of the individual ball increases from the 1st ball to the 89th ball, because the impact direction is toward the 1st roller and the center of gravity of the bearing is near to the 89th roller. The time point of the maximum ball load value will be consistent with the time point of the maximum value of the impact in case of flat field. And in case of the slope condition, the maximum ball load value occurs after the time point of the maximum impact value, due to an increased load caused by the tilting moment after the impact. The bearing loads due to transportation vibration are more evenly distributed on the balls with the contact pair I than contact pair II, because the tilting moment will make the maximum value at the 89th ball. The maximum ball load occurring at the time point will be the same as the time point for the maximum vibration amplitude. From the point of view of the stress value corresponding to the load. The condition will not cause the balls and bearing ring walls damage. The effect of the screws on the bearing can also be seen from the results, the bearing will be deformed mainly due to the screws preload. As consequence the stress on the balls and the thin wall of the bearing rings near the screws is enlarged. |
