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外文翻譯
畢業(yè)設(shè)計題目：液體動壓滑動軸承試驗臺
原文1：Research on the reliability of sliding bearing support in a swash-plate type axial piston water hydraulic pump
譯文1：研究的可靠性,滑動軸承支撐斜盤式軸向柱塞泵型水液壓
原文2：Application of computational fluid dynamic to model the hydraulic performance of subsurface flow wetlands
譯文2：應(yīng)用計算流體動力學(xué)模型來模擬地下水流水力性能的濕地
Research on the reliability of sliding bearing support in a swash-plate type axial piston water hydraulic pump
Yin F.L., Nie S.L.
College of Mechanical Engineering and Applied
ElectronicsTechnology
Ruan J.
Logistics department of the 92962th army
People's Liberation Army of China
Beijing University of Technology
Beijing 100124, China
yinfanglong89@163.com
Ruan J.
Logistics department of the 92962th army
People's Liberation Army of China
Beijing University of Technology
Beijing 100124, China
yinfanglong89@163.com
Guangzhou 510700, China
hlrj84@163.com
Abstract—In this paper, two kinds of different sliding bearing support structure including a traditional cross-shaft and a semi-shaft are designed for a water hydraulic pump.The characteristics of the two sliding bearings in each structure are calculated. By comparison, it is found that the working conditions of the two sliding bearings, especially the pv value, in the semi-shaft support structure are near to be identical in the cross-shaft one, which will be helpful to prolong their service life. Based on the Stress-strength interference theory, a reliability calculation model of the friction pair between the shaft and sliding bearings is proposed. The analysis results indicate that the semi-shaft sliding bearing support is beneficial to largely raise the inherent reliability of the water hydraulic pump as well as the service life of the pump.
Keywords—water hydraulic pump; sliding bearing; pv value;Reliability
Ⅰ.Introduction
Water hydraulic system is operated with raw water(pure tap water) substituting for mineral oil. Such systems are becoming more and more popular, especially in the fields of steel and glass production, nuclear power generation, coal and gold mining, food and medicine processing, ocean exploration, and underwater robotics.Compared with conventional mineral oil, raw water that acts as hydraulic fluid has several inherent advantages,including low operating cost, sound environmental compatibility, non-flammability, and low pollution potential to products [1-2].
Water hydraulic axial piston pump (WHAP) is one of key power components in water hydraulic systems. There are several challenging issues associated with the pump,such as conflicts between lubrication and wear, and between sealing and leakage. Especially, shaft and bearings form key friction pairs, which will result in significant influences on the pump’s performance.Generally, the hydrodynamic sliding bearing is extensively used for supporting the water hydraulic pump’s shaft. Therefore, in order to improve the pump’s efficiency and reliability, it is crucial to study the force distribution of sliding bearings thoroughly. According to hydrodynamic lubrication theory, the critical points,which satisfies the wear resistance for sliding bearing and shaft of WHAP includes: (1) An optimal load distributed strategy should be used to determine optimal dimensions for achieving the even distributing of the load. (2) Several suitable materials should be selected to meet the water lubrication working conditions and to ensure a long life with lower friction losses [3].
The concepts of both stress and strength relating to reliability design are generalized. In this paper, thereliability of sliding bearing support will be investigated using Stress-strength interference model to calculate the reliability value of the sliding bearings, which will include the effect of the flow fluctuation in WHAP.
II. Description of sliding bearing support
Figure (a) shows a schematic of a typical cross-shaft supporting structure. The cylinder block is supported on the shaft. Two sliding bearings are located on the cylinder’s left and right ends to support the shaft. Figure (b) shows a schematic of a novel design, where a semi-shaft supporting structure is employed. The front sliding bearing is used to support the input shaft (spline shaft). And the rear sliding bearing inside the cylinder is used to support the cylinder block. In the semi-shaft support structure, the spline shaft and cylinder are interference fit, and they are combined by a spline.During pump running, the motor drives input shaft rotating, bringing along the rotation of the cylinder.Because of the presence of the angle of swash plate, the whirling motion of the cylinder is translated into straight reciprocating motion of the pistons. When the cylinder rotated a period, the pistons reciprocate a round-trip to complete a process of suction and discharge of the pump.
(a) cross-shaft support
(b) semi-shaft support
Fig. 1 Schematic diagram of sliding bearing support
III. Theoretical analyses
A. Load characteristics of the bearings.As shown in Figure 1, the reaction component force that act on a single slipper along X-axis and Z-axis can be respectively described as follows:
In terms of the axial piston pump, the hydraulic pressure in each piston hole can be represented as:
Then the radial resultant force is located in point O (as shown in Figure 1), and the radial resultant force can be expressed as:
Furthermore, with the radial force equilibrium along the X-axis of the supporting structure, we have:
The torque equilibrium along the X-axis can be written as:
Through solving Eqs. (4) – (6), the supporting force of the front and rear bearings can be obtained, respectively:
B. PV value of the bearings
For the valve plate distribution of axial piston pump,the number of pistons within the discharge pressure area (Zg) during one operating period is variably along with the reciprocating motion of the pistons. Ignoring the influence of the pressure pulsation in the pre-loading and pre-unloading areas, and the cylinder weight, affected by the alternative vibration of the number of piston in the discharge pressure area, the sliding bearing is subjected to periodic unstable loads. Water is characterized by very low dynamical viscosity, which is regarded as poor lubricating properties affecting the performance of sliding and rolling contacts [4]. Here it appears that it is impossible to obtain an acceptable film thickness in water lubricated sliding bearings. Consequently, in practical work, the sliding bearings in WHAP are usually working under the condition of an incomplete liquid lubrication. Especially, at the points of turn on / off, the direct contacts between the matching pairs of the shaft and sliding bearings may take place. Moreover, since it is necessary for the sliding bearings the surface hardness should be as high as possible in order to sustain contacting pressure, and thus, the abrasion between the shaft and bearings would be as low as possible in order to improve the sliding bearings’ reliability.
It is essential to select several suitable materials and matching pair. The siding bearings in this paper are made of WR525, which is a thermoplastic composite consisting of carbon fiber in a PEEK matrix. Due to its unique thermal expansion properties, WR525 is ideal for use as impeller wear rings, bushings and case wear rings.WR525 allows the pump user to increase pump efficiency by running tighter wear ring clearances, while decreasing potential pump damage when pumps are cavitated or experience down-line bearing failures. WR525 bearings are specified as standard material on all HGM/HGM-RO boiler feed pumps.
As it is known, the critical pv value is a very important parameter for polymers or their composites in tribological applications, and has been widely used in investigation of ploymers’ sliding wear behaviors. Besides, pv limits are affected by variations in temperature, speed,loading,lubrication and surface finish. Exceeding pv limits will result in accelerated wear and premature bearing failure, where p is the intensity of pressure applied to a bearing surface and v is the relative velocity [5]. Furthermore, the pv value is proportional to bearing’s wear, friction power loss and friction heat [6]. Wear, friction power loss and temperature conditions are the three key index of the service life of the bearings. Therefore, the pv value can be used to preliminarily evaluate the sliding bearings’working life in a WHAP. Generally speaking, in order to guarantee the boundary lubricated bearing running reliably, it is necessary to meet the following three conditions [7]:
Bearing’s average working specific pressure is:
Substituting Eqs. (7) and (8) into Eq. (10), average working specific pressure of the front bearing can be obtained as:
And average working specific pressure of the rear bearing can be represented as:
Radial circumferential velocity of the shaft is:
The friction specific work rate of sliding bearing can be expressed as
Substituting Eqs. (11) – (13) into Eq. (14), the friction specific work rate of the front bearing can be obtained as follows:
And the friction specific work rate of the rear bearing is calculated as follows:
Based on the structure parameters of the WHAP, taking the peak number of pistons in the discharge pressure area (Zg), the working conditions of the bearings under the two different structures are calculated in Table1.
C. Scale factor
Actually, analyzing Eqs. (10), (11), (14) and (15), it is found that the dz, B andinfluence the match of the two bearings’ working conditions. Define the bearings’linear velocity ratio asaverage specific work rate ratio asThen we have:
The three parameters mentioned above can be calculated (as shown in Table 2).
D. Reliability model and evaluation
In terms of a WHAP, design of the sliding bearing is an important part for raising its reliability. In this paper, the pv value is defined as the stress between the sliding bearing friction pair-Y, and it is a random variable. The allowable pv value [pv] can be defined as the strength-X.
Generally speaking, the contact stress p between the friction pair and the relative linear velocity v are mutually independent random variables, and they are all distributed normally, so the product pv is also distributed normally.Thus, according to the formula when the stress and strength are all distributed normally, the reliability coefficientcan be determined by means of the equation:
In fact, the pv or allowable pv value can be expressed by the two random variables Pd and ：
K is constant coefficient. Pd is the working pressure of the pump and ω is the relative angular velocity. Based on probability theory, the average value and the standard deviation can be obtained, respectively:
Through solving Eqs. (22) and (23), we have:
The rated pressure of the WHAP can be allowed for fluctuating within ±5%. According to the definition of mean value and the principle of3σ , we have:
The allowable pv value [pv] of WR 525 is 8.89MPam/s, and its standard deviation [ pv] s is 0.315.Substituting Eqs. (24) – (28) and their corresponding data into Eq. (20), the reliability coefficient R u of the two kinds of structure can be calculated respectively. Hence, the corresponding reliability R for each structure can be obtained, as listed in Table 3.
IV. Discussion
In terms of the WHAP, the failure of any sliding bearing could destroy the pump’s supporting and balance to cause severe noise and vibration. It also could lead to the invalidation of the flow distribution and make the volumetric efficiency decrease sharply. Thus, service life of WHAP is determined by the bearing which has the severe working condition.
Table 1 presents the calculated results of the key parameters in two different sliding bearings distribution structure. It indicates that the working conditions of the sliding bearings in each distribution structure are different.Firstly, the center distance L2 in the semi-shaft structure is smaller than the cross-shaft one. This means that the rear bearing in the semi-shaft structure is closer to the center point of the resultant force, and the distance between the front and bearing is also smaller. Thus it is favorable to balance the torque of F1 and F2 so that making the sliding bearings work smoothly. Secondly, the loads on the sliding bearings in each structure are different. In the cross-shaft structure, the loads on the front bearing are much larger than on the rear one. However, in the semi-shaft structure, the loads on the front bearing reduced, while the loads on the rear bearing increased, so as to make the bearings’ supported load condition in the front and rear location closely and their loads distributed evenly. Additionally, the front bearing’s average working specific pressure (pz) and its pv value in the cross-shaft structure, are much larger than the rear one. However, in the semi-shaft structure, the front bearing’s pz and pv value reduced slightly, for which the rear bearing increases a little. Comparing the results listed in Table 2, it can be seen that thevalue of the semi-shaft structure are smaller than which are in the cross-shaft structure. Moreover, these values are close to 1. It is revealed that in the semi-shaft structure, the working conditions of the two sliding bearings are near to be identical.
From Table 3, the reliability value of the siding bearings support in the semi-shaft structure are higher. It is indicated that the sliding bearings of the semi-shaft have longer service life than those in the cross-shaft.Consequently, it can be concluded that the distribution of sliding bearings in the semi-shaft structure is beneficial to make the bearings’ working conditions equilibrium and to improve the reliability of the pump.
V. Conclusion
In this research, two sliding bearings of the WHAP which have the same size work in the same water medium in same time. So the change law of loads on the bearings similar. Besides, they are made of the same material:
WR525. Hence, the life of the two sliding bearing support structure depends on the bearing which has higher working conditions especially the pv value. So it is important to design a rational structure arrangement to make the two bearings’ working conditions as equal as possible. Consequently, for the sake of raising the sliding bearing’s life in the WHAP, the scale factorsmust be close to 1. Additionally, the degree of reliability is a main indicator for the reliability of the sliding bearing support structure. So the reliability value of the sliding bearing support structure should be as large as possible for improving the WHAP’s reliability.
By comparing the working conditions of the sliding bearings in each structure, it is found that the pv value of the two sliding bearings in the semi-shaft structure are closer than in the cross-shaft one. And the scale factorof the semi-shaft structure are closer to 1, compared to the cross-shaft one. Additionally, the reliability value of the sliding bearings in the semi-shaft structure is higher than which in the cross-shaft one.Obviously, all the comparisons mentioned above show that the arrangement of sliding bearings in the semi-shaft structure does a better job in achieve the purpose of distributing the load averagely and raising the service life of the sliding bearings in the water hydraulic piston pump as well as improving the reliability of WHAP.
ACKNOWLEDGMENT
This research was funded by Natural Science Foundations of China (№s 50675074 and 51075007), NCET of State Education Ministry (№ NCET-07-0330), and PHR (IHLB) 20090203.
REFERENCES
Nomenclature
The author;Yin F.L. Nie S.L. Ruan J.
Nationality:China
Source:The 2011 International Conference on Fluid Power and Mechatronics, Beijing, August 16-17, 2011, 282-286.
研究的可靠性,滑動軸承支撐斜盤式軸向柱塞泵型水液壓
Yin F.L., Nie S.L.
大學(xué)的機械工程和應(yīng)用ElectronicsTechnology
Ruan J.
中國 北京 北京科技大學(xué) 中國人民解放軍 物流部門的92962部隊 100124
Yinfanglong89@163.com
中國 廣州 hlrj84@163.com 510700
文摘-在本文中,兩種不同的滑動軸承支撐結(jié)構(gòu)包括一個傳統(tǒng)的十字軸和半軸,被設(shè)計為--水液壓泵?；瑒虞S承在每個結(jié)構(gòu)計算。相比之下,特別是兩個根據(jù)應(yīng)力-強度干涉理論,一個可靠性計算模型之間的摩擦副軸和提出了滑動軸承。分析結(jié)果表明,半軸滑動軸承的支持是有益的,很大程度上提高固有可靠性的水液壓泵以及泵的使用壽命。
滑動軸承pv值,在半軸支撐結(jié)構(gòu)都是相同的附近的十字軸,這將有助于延長其使用壽命。
關(guān)鍵詞—水液壓泵;滑動軸承;pv值;可靠性
Ⅰ介紹
水液壓系統(tǒng)的原始水(純自來水)取代了礦物油。這種系統(tǒng)正變得越來越流行,尤其是在田野的鋼鐵和玻璃生產(chǎn)、核電、煤炭、黃金礦業(yè)、食品和醫(yī)藥處理、海洋探險,水下機器人。與傳統(tǒng)的礦物油,原水,充當液壓流體有幾個固有優(yōu)勢,包括更低的運營成本、合理的環(huán)境兼容性、耐燃性、低污染潛力產(chǎn)品[1-2]。
水液壓軸向柱塞泵(重擊)是一個關(guān)鍵的動力組件在水液壓系統(tǒng)。有幾個挑戰(zhàn)性問題相關(guān)的泵,如沖突之間,潤滑和穿密封和泄漏。特別是,軸和軸承形式主要摩擦副,這將導(dǎo)致顯著影響泵性能。通常,水動力滑動軸承是廣泛用于支持水液壓泵的軸。因此,為了提高泵的效率和可靠性,這是至關(guān)重要的,研究了滑動軸承力分布的徹底。根據(jù)流體動力潤滑理論,關(guān)鍵的點,這滿足了耐磨性的滑動軸承和軸的重擊包括:(1)一個最佳負載分布策略應(yīng)該用于確定最優(yōu)尺寸對實現(xiàn)甚至分發(fā)的負載。(2)幾個應(yīng)該選擇合適的材料,以滿足水潤滑的工作條件,確保一個長壽命和低摩擦損失[3]。
二者的概念的應(yīng)力和強度可靠性設(shè)計有關(guān)的推廣。在本文中,可信度的滑動軸承的支持將被采用了應(yīng)力-強度干涉模型來計算可靠性價值的滑動軸承,這將包括流動的影響波動。
Ⅱ描述的滑動軸承的支持
圖(a)展示了一個示意性的一個典型的十字軸支承結(jié)構(gòu)。缸體的軸上的支持。兩個滑動軸承位于汽缸的左和右端支持軸。圖(b)顯示了一個新穎的設(shè)計原理,在那里一個半軸支承結(jié)構(gòu)采用。前面的滑動軸承是用來支持輸入軸(花鍵軸)。和后方滑動軸承在氣缸內(nèi)用于支持缸體。在半軸支撐結(jié)構(gòu)、花鍵軸和圓柱干涉配合,他們結(jié)合的花鍵。在泵運行時,馬達驅(qū)動器輸入軸旋轉(zhuǎn),帶上的旋轉(zhuǎn)圓筒。因為存在的防波板的角度,旋轉(zhuǎn)運動的缸是翻譯成直線往復(fù)運動的活塞。當缸旋轉(zhuǎn)一個時期,活塞往復(fù)運動的往返來完成一個過程的入口及出口的泵。
（a） 十字軸的支持
（b）半軸的支持
圖1示意圖的滑動軸承的支持
Ⅲ理論分析
a的負荷特性軸承。如圖1所示,反應(yīng)分力,作用于一個滑塊沿著x軸和z軸可以分別描述如下:
在術(shù)語的軸向柱塞泵、液壓在每個活塞孔可以表示為:
然后徑向合力位于點O(如圖1),和徑向合力可以表述為:
此外,由于徑向力平衡沿著x軸的支承結(jié)構(gòu),我們有:
沿著x軸的扭矩平衡可以寫成:
通過求解方程式。(4)-(6),支持力量的前后軸承可以分別獲得:
B PV值的軸承
對于閥板分布的軸向柱塞泵,活塞的數(shù)量在放電壓力區(qū)(Zg)在一個操作周期是不定地隨著活塞的往復(fù)運動。忽略壓力脈動的影響在預(yù)加載和pre卸貨區(qū),汽缸重量,受替代振動的數(shù)量活塞在放電壓力區(qū),滑動軸承受到周期性不穩(wěn)定的負載。水具有非常低的動力粘度,它被認為是貧窮的潤滑性能影響性能的滑動和滾動接觸[4]。這里似乎是不可能獲得一個可接受的膜厚度在水潤滑滑動軸承。因此,在實際工作,滑動軸承在打敗通常工作條件下的一個不完整的液體潤滑。特別是,在點開/關(guān),直接接觸摩擦副之間的滑動軸承的軸和可能發(fā)生。此外,因為它是必要的滑動軸承表面硬度應(yīng)該盡可能高的為了維持接觸壓力,因此,磨損的軸和軸承之間會盡可能低為了提高滑動軸承的可靠性。
它是必要的選擇幾個合適的材料和匹配的一對。外墻軸承在本文是由WR525,這是一種熱塑性復(fù)合構(gòu)成的碳纖維在PEEK矩陣。由于其獨特的熱膨脹性能,非常適合用作WR525葉輪磨損環(huán)、襯套和案例穿環(huán)。WR525允許泵用戶增加泵效率進行更嚴格的穿環(huán)間隙,同時減少潛在的泵損壞當泵cavitated或經(jīng)驗的下線軸承故障。WR525軸承被指定為標準物質(zhì)在所有HGM / HGM-RO鍋爐給水泵。
眾所周知,關(guān)鍵的pv值是一個非常重要的參數(shù)對聚合物或他們的復(fù)合材料在摩擦學(xué)的應(yīng)用程序,并已廣泛應(yīng)用于調(diào)查ploymers“滑動磨損行為。此外,pv極限溫度變化的影響、速度、加載,潤滑和表面光潔度。超過光伏限制將導(dǎo)致加速磨損和過早軸承故障,p是壓力強度應(yīng)用于軸承表面,v是相對速度[5]。此外,pv值成正比軸承的磨損、摩擦功率損耗和摩擦熱[6]。穿,摩擦功率損耗和溫度條件下的三個關(guān)鍵指標的軸承的使用壽命。因此,pv值可用于初步評估滑動軸承的工作生活在一個重擊。一般來說,為了保證邊界潤滑軸承運行可靠,必須滿足以下三個條件[7]:
軸承的平均工作特定壓力是:
取代方程式。(7)和(8)到Eq。(10),平均單位壓力的工作前軸承可以得到:
和平均單位壓力的工作后軸承可以表示為:
徑向圓周速度的軸是:
具體工作率的摩擦滑動軸承可以表達為
取代方程式。(11)-(13)到Eq。(14),摩擦具體工作率的前軸承可以得到如下:
和摩擦率的具體工作后軸承是計算方式如下:
基于結(jié)構(gòu)參數(shù)的重擊,采取的峰值活塞在放電壓力區(qū)(Zg),工作條件下的軸承的兩個不同的結(jié)構(gòu)計算中。
C 比例因子
實際上,分析方程式。(10),(11),(14)和(15),它是發(fā)現(xiàn)dz,B 和比賽的兩個軸承工作條件。定義軸承'linear速度比特定工作率比我們有:
上面提到的三個參數(shù)可以計算(如表2所示)。
D 可靠性模型和評價
從一個重擊,滑動軸承的設(shè)計是一個重要的部分為提高其可靠性。摘要pv值定義為應(yīng)力之間的滑動軸承摩擦副y,它是一個隨機變量。允許的pv值(pv)可以被定義為強度x。一般來說,接觸應(yīng)力p之間的摩擦副和相對線速度v是相互獨立的隨機變量,并且他們都是正態(tài)分布,所以產(chǎn)品pv也正態(tài)分布。因此,根據(jù)公式當壓力和強度都是分布式通常可靠性系數(shù)可以確定通過方程:
事實上,pv或容許pv值可以表示為兩個隨機變量Pd和:
K是常數(shù)系數(shù)。Pd是工作壓力的泵和角速度ω是相對的?；诟怕世碚?平均值和標準偏差分別可以得到:
通過求解方程式。(22)和(23日),我們有:
額定壓力的重擊可以被允許在±5%的波動。根據(jù)定義的平均值和of3σ原則,我們有:
允許的pv值(pv)的525年是8.89 mpam WR / s,其標準偏差(pv)年代是0.315。取代方程式。(24)-(28)和相應(yīng)的數(shù)據(jù)轉(zhuǎn)換成Eq。(20),可靠性系數(shù)R u的兩種結(jié)構(gòu)可以分別計算。因此,相應(yīng)的可靠性R可以得到每一個結(jié)構(gòu),如表3所示。
Ⅳ討論
在術(shù)語的重擊,任何一個失敗的滑動軸承可以摧毀泵的支持和平衡造成嚴重的噪音和振動。它還可能導(dǎo)致的失效流分布和使容積效率大幅下降。因此,使用壽命的重擊是由軸承具有嚴重的工作條件。
表1給出了計算結(jié)果的關(guān)鍵參數(shù)在兩個不同的滑動軸承分布結(jié)構(gòu)。它表明,滑動軸承的工作條件在每個分布結(jié)構(gòu)是不同的。首先,該中心距離L2在半軸結(jié)構(gòu)是小于十字軸一。這意味著后軸承在半軸結(jié)構(gòu)接近中心點的合力,之間的距離也變小前和軸承。因此它有利于平衡扭矩的F1和F2,以便使滑動軸承工作順利。其次,對滑動軸承載荷在每個結(jié)構(gòu)是不同的。在十字軸結(jié)構(gòu)、負載前軸承是遠遠大于背面的一個。然而,在半軸結(jié)構(gòu)