菱錐式無級變速器的結構設計【P=1.5KW n=1500rpm R=8】

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LETTER Improving the fatigue strength of the elements of a steel belt for CVT by cavitation shotless peening Hitoshi Soyama ? Masanori Shimizu ? Yuji Hattori ? Yuji Nagasawa Received: 9 May 2008 / Accepted: 19 May 2008 / Published online: 6 June 2008 C211 Springer Science+Business Media, LLC 2008 The elements of steel belts used for continuously variable transmission (CVT) are subjected to a bending load during operation. The weakest portion of the elements is at the root of the ‘‘neck’’ which works into metallic rings. In order to reduce the stress concentration, the root of the neck is rounded and the shape of element is optimized. Nevertheless, if the fatigue strength of the elements can be improved, the steel belt can be applied to larger engines. Although conventional shot peening is one way of enhancing the fatigue strength, it is very difficult for shot to reach into deep and narrow regions. Recently, a peening method using the impact produced as cavitation bubbles collapse has been developed [1–9]. This method is called ‘‘cavitation shotless peening (CSP)’’, as shot are not required [3–6, 8]. CSP can peen the surface even through deep narrow cavities, as the bubbles can reach these parts and collapse where peening is required. In the present article, improvement of the fatigue strength of the elements of a CVT metallic belt by CSP was demonstrated experimentally. Elements were treated with different processing times and evaluated by a fatigue test to find the optimum processing time. In order to evaluate the peening effect by CSP, the residual stress was measured. Note that this is the first report published on the improvement made in the fatigue strength of a part with regions that cannot be hit directly by shot. Cavitation shotless peening was applied to the element using cavitating jet apparatus, the details of which can be found in references [3–6, 8]. The jet was injected into the neck region through grooves in the elements, which were stacked and held together, and scanned perpendicularly over the elements, as shown in Fig. 1. The processing time per unit length, t p , is defined by the number of scans n and the scanning speed v; t p ? n v e1T The cavitation number,r, a key parameter for cavitating jets, is defined by the injection pressure, p 1 , the tank pressure, p 2 , and the saturated vapor pressure, p v ,as follows; r ? p 2 C0 p v p 1 C0 p 2 ? p 2 p 1 e2T r can be simplified as indicated in Eq. 2 because p 1 C29 p 2 C29 p v . Absolute pressure values were used to determine the cavitation number. Considering the results from previous work [3–6, 8], the CSP conditions shown in Table 1 were selected. The shape of the element tested was identical to actual elements used in steel belts for CVT. The element was made of Japanese Industrial Standards JIS SK5 and was heat treated in the same way as actual elements. In order to examine the improvements made in the fatigue strength, the residual stress of the elements at position A in Fig. 2 was measured using X-ray diffraction with a two-dimensional position sensitive proportional counter (2D PSPC) using the 2D method [10]. After CSP, part of the element was cut off and put into the X-ray H. Soyama (&) Tohoku University, 6-6-01 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan e-mail: soyama@mm.mech.tohoku.ac.jp M. Shimizu C1 Y. Hattori Toyota Motor Corporation, 1200 Mishuku, Susono 410-1193, Japan Y. Nagasawa Toyota Central R&D Labs. Inc, 41-1 Yokomichi, Nagakute 480-1192, Japan 123 J Mater Sci (2008) 43:5028–5030 DOI 10.1007/s10853-008-2743-6 apparatus to detect diffractive X-rays, as shown in Fig. 2. A Cr tube operated at 35 kV and 40 mA was used. The diameter of the collimator was 0.1 mm. X-rays were counted for 20 min for each frame. The diffractive plane was the (211) plane of a–Fe, and the diffractive angle, 2h, was about 156 degree. The values used for Young’s modulus and the Poisson ratio were 210 GPa and 0.28, respectively. The residual stress in the longitudinal direc- tion of the element was obtained from 13 frames using the 2D method. In order to evaluate the fatigue strength of the element, a bending fatigue test was carried out on the element, as shown in Fig. 3. As shown in the figure, the element was fixed and a load F was applied perpendicularly. Figure 4 illustrates the relationship between the number of cycles to failure, N, and the normalized amplitude of the bending force, C22 F, used in the fatigue test, for various pro- cessing times per unit length, t p . The amplitude of the bending force was normalized by the fatigue strength of the non-peened specimen, which was obtained by Little’s method [11]. The fatigue tests were terminated at N = 10 6 , as it was confirmed that specimens which survived 10 6 cycles also survived 10 7 cycles. From the figure, it is clear that CSP can extend the lifetime of specimens compared to non-peened specimens. The normalized fatigue strength, C22 F FS , of specimens treated by CSP is 1.22 at t p = 2.5 s/mm, 1.38 at t p = 5 s/mm, 1.48 at t p = 10 s/mm, 1.32 at t p = 20 s/mm, and 1.28 at t p = 40 s/mm, respectively. At t p = 10 s/mm, the fatigue strength of the element has been improved by 48% compared with that of the non-peened element. Figure 5 shows the normalized fatigue strength C22 F FS as a function of CSP processing time per unit length, t p . C22 F FS increases with t p until t p = 10 s/mm and then decreases Table 1 CSP conditions Injection pressure p 1 MPa 30 Tank pressure p 2 Mpa 0.42 Cavitation number r 0.014 Nozzle diameter d mm 2 Standoff distance s mm 80 Fig. 2 Measurement position of the residual stress using X-ray diffraction Fig. 3 Schematic diagram of the bending fatigue test of the element Fig. 4 Improvement of the fatigue strength of the element by CSP Fig. 1 Setup of the elements treated by CSP J Mater Sci (2008) 43:5028–5030 5029 123 slightly. This shows that, as with shot peening, there is an optimum processing time, and that too long processing times cause the fatigue strength to decrease. For the con- ditions applied here, the optimum CSP processing time per unit length was 10 s/mm. Figure 6 shows the variation in the residual stress of the element at position A in Fig. 2 with processing time per unit length, t p . In order to evaluate the reproducibility, the residual stress of two elements was measured for each value of t p using the 2D X-ray diffraction method. Standard deviations for each measurement are shown in Fig. 6. Without CSP, the residual stress was -140 ± 50 MPa and after CSP this was greater than -600 MPa. Thus, CSP can introduce compressive residual stress into the surface even where there are deep and narrow cavities. The impact induced by collapsing cavitation bubbles can introduce compressive residual stress into surfaces that cannot be hit directly by shot (see Fig. 1). The residual stress on the surface increased to between -800 MPa and -1,000 MPa for short processing times, t p = 2.5 s/mm, then decreased slightly saturating at about -800 MPa, as shown in Fig. 6. According to a previous report [5], the compressive residual stress of the sub-surface in materials increases after the residual stress on the surface has saturated. Thus the compressive residual stress of the sub-surface would increase for t p C 2.5 s/mm. This is one of the reasons why the optimum processing time for the present conditions was t p = 10 s/mm, even though the compressive residual stress had reached its maximum at t p = 2.5 s/mm. In order to increase the fatigue strength of the elements of a steel belt for CVT, the elements were treated by CSP. The fatigue strength of the element was evaluated and the residual stress was measured by X-ray diffraction using a 2D method with a 2D PSPC. It was revealed that the fatigue strength of the element could be improved by 48% by CSP. It was also shown that CSP can introduce com- pressive residual stress even into the surface of deep and narrow cavities. This work was partly supported by Japan Society for the Promotion of Science under Grant-in-Aid for Scientific Research (A) 20246030. References 1. Soyama H, Park JD, Saka M (2000) Trans ASME J Manuf Sci Eng 122:83. doi:10.1115/1.538911 2. Soyama H, Kusaka T, Saka M (2001) J Mater Sci Lett 20:1263. doi:10.1023/A:1010947528358 3. Soyama H, Saito K, Saka M (2002) Trans ASME J Eng Mater Technol 124:135. doi:10.1115/1.1447926 4. Odhiambo D, Soyama H (2003) Inter J Fatigue 25:1217. doi: 10.1016/S0142-1123(03)00121-X 5. Soyama H, Sasaki K, Odhiambo D, Saka M (2003) JSME Int J 46A:398. doi:10.1299/jsmea.46.398 6. Soyama H, Macodiyo DO, Mall S (2004) Tribol Lett 17:501. doi: 10.1023/B:TRIL.0000044497.45014.f2 7. Soyama H (2004) Trans ASME J Eng Mater Technol 126:123. doi:10.1115/1.1631434 8. Soyama H, Macodiyo DO (2005) Tribol Lett 18:181. doi: 10.1007/s11249-004-1774-7 9. Soyama H (2007) J Mater Sci 42:6638. doi:10.1007/s10853- 007-1535-8 10. He BB (2003) Powder Diffr 18:71. doi:10.1154/1.1577355 11. Little RE (1972) ASTM STP 511:29 Fig. 5 Optimum CSP processing time per unit length Fig. 6 Introduction of compressive residual stress into the element by CSP 5030 J Mater Sci (2008) 43:5028–5030 123 附 錄1：英文文獻翻譯及原文 通過噴丸改善無級變速器鋼帶的疲勞強度 無級變速器（CVT）采用的鋼帶在操作過程中要受到彎曲載荷。元件的最薄弱的部分是在作為金屬環(huán)的“頸部”的根部。為了減少應力集中，頸部的根部做成圓形，并對鋼帶的形狀進行了優(yōu)化。不過，如果該元件可以提高疲勞強度，鋼帶可應用于大引擎。雖然傳統(tǒng)的噴丸是一種提高疲勞強度的方法，但卻很難到達深而窄的區(qū)域。 最近，一種用沖擊產生空化泡爆裂的沖擊法已經開發(fā)出來。這種方法稱為“氣穴噴丸”，因為噴射不是必需的。由于泡沫可以通過深而窄的通道而到達凹面，并在需要的地方爆裂，所以CSP可以到達這些區(qū)域，并對表面進行加工。 在本文中，CSP對無級變速器鋼帶疲勞強度的提高已被實驗證明。元件分別進行了不同時間的處理，并進行了疲勞測試評估，以找出最佳的處理時間。為了評估CSP噴丸的效果，對殘余應力進行了測量。請注意，這是第一篇發(fā)表的關于不直接噴射某一部分而使其疲勞強度提高的報告。 CSP使用空化射流裝置應用于元件，詳情可見參考文獻。氣體通過堆疊的溝槽注入到元件的頸部，垂直地通過元件，如圖1。每單位長度的處理時間tp，由流動數(shù)n和流動速度v定義： 空化射流的關鍵參數(shù)空化數(shù)r，由注射壓力p1定義，罐內壓力p2和飽和蒸氣壓力pv，如下： σ可用式（2）簡化表示，因為p1〉〉p2〉〉pv。絕對壓力值被用來確定空化數(shù)?？紤]到以??往的工作成果，表1中所示的CSP處理條件是進行了篩選的。 測試的元件形狀與無級變速器實際使用的鋼帶元件是一樣的。該元件是根據(jù)日本工業(yè)標準JIS SK5制造的，與實際元件的加熱處理相同。 為了檢測疲勞強度的提高，在圖2的A位置，通過一個二維位置X -射線衍射靈敏正比計數(shù)器，用二維的方法對元件的殘余應力進行測量。CSP后，該元素的一部分被切斷，進入X -射線衍射儀檢測X射線，如圖2所示。鉻管在35千伏電壓和40 毫安電流的條件下使用。準直器直徑為0.1毫米。 X射線計數(shù)每幀為20分鐘。衍射平面是一個α-Fe平面（211），衍射角2θ，約156度。楊氏模量和泊松比使用的值分別為210 GPa和0.28。元件的縱向殘余應力用二維的方法從13個單位獲得。 為了評估元件的疲勞強度，對元件進行了一個彎曲疲勞測試，如圖3所示。正如圖所示，該元件是固定的，負載F為垂直方向。圖4說明了在疲勞測試中用于多種單位長度處理時間tp的循環(huán)失敗次數(shù)N和規(guī)范化的彎曲力振幅之間的關系。受彎力振幅是由非噴丸樣品的疲勞強度規(guī)范，這是用里特的方法得到的。疲勞試驗被終止在N = 106，因為它證實了能承受106次循環(huán)的樣品，也能承受107次。從圖中可明顯看出，相對于非噴丸樣品，CSP可延長樣品的壽命。經CSP處理的樣品的歸一疲勞強度，當tp = 2.5 s/mm時，為1.22，當tp = 5 s/mm時，為1.38，當tp = 10 s/mm時，為1.48，當tp = 20 s/mm時，為1.32，當tp = 40 s/mm時，為1.28。當tp = 10 s/mm時，元件的疲勞強度相對于非噴丸元件提高了48%。 圖5所示為每單位長度的CSP處理時間tp的函數(shù)歸疲勞強度。隨著tp增加而升高，直到tp = 10 s/mm則有所降低。這表明，噴丸存在一個最佳的處理時間，如果處理時間過長會造成疲勞強度降低。對于在這里適用的條件，最佳的CSP每單位長度的處理時間為10 s/mm。圖6顯示的是圖2中的A位置元件的殘余應力在單位長度處理時間tp下的變化情況。為了評估的重復性，分別對兩種元件的殘余應力在單位長度的處理時間下用二維X射線衍射法進行了測試。 每次測量的標準偏差如圖6所示。若不用CSP處理，殘余應力為-140 ± 50 MPa，而用CSP處理后，殘余應力強于-600 MPa。因此，CSP可以對表面有殘余壓應力，即使是深而窄的腔。由空化旗袍爆裂產生的影響可以給表面帶來殘余壓應力，是直接噴射所不能做到的（見圖1）。當tp = 2.5 s/mm時，短時間處理的表面的殘余應力提高到-800 MPa and -1,000 MPa之間，然后略有下降到大約-800 MPa，如圖6所示。根據(jù)先前的一份報告，材料表面的殘余應力飽和后，其次表面的殘余壓應力會增加。因此次表面的殘余壓應力在tp ≥2.5 s/mm時將增加。這就是目前條件下的最佳處理時間為tp = 10 s/mm的原因之一，即使當tp = 2.5 s/mm時殘余壓應力達到了最大值。 為了使無級變速器鋼帶元件的疲勞強度增加，對元件進行了CSP處理。元件的疲勞強度進行了評估，且通過一個二維位置X -射線衍射靈敏正比計數(shù)器，用二維的方法對元件的殘余應力進行了測量。它表明經過CSP處理后元件的疲勞強度可提高48%。也證明了CSP可以對元件表面有殘余壓應力，即使是深而窄的腔。 附 錄2：英文文獻原文 湘潭大學機械工程學院畢業(yè)論文（設計）工作中期檢查表 系 機制系 專業(yè) 機械設計制造及其自動化 班級 07機一 姓 名 姚昊雄 學 號 2007964212 指導教師 聶松輝 指導教師職稱 教授 題目名稱 菱錐式無級變速器結構設計 題目來源 科研 企業(yè) √ 其它 課題名稱 題目性質 工程設計 理論研究 科學實驗 軟件開發(fā) 綜合應用 @ 其它 資料情況 1、選題是否有變化 有 √ 否 2、設計任務書 √ 有 否 3、文獻綜述是否完成 √ 完成 未完成 4、外文翻譯 完成 √ 未完成 由 學 生 填 寫 目前研究設計到何階段、進度狀況： 已經完成了前期資料的查閱，整體方案設計也快完成了。 已經開始計算 校核 由 老 師 填 寫 工作進度預測（按照任務書中時間計劃） 提前完成 按計劃完成 拖后完成 無法完成 工作態(tài)度（學生對畢業(yè)論文的認真程度、紀律及出勤情況）： 認真 較認真 一般 不認真 質量評價（學生前期已完成的工作的質量情況） 優(yōu) 良 中 差 存在的問題與建議： 指導教師（簽名）： 年 月 日 建議檢查結果： 通過 限期整改 緩答辯 系意見： 簽名： 年 月 日 注：1、該表由指導教師和學生填寫。 2、此表作為附件裝入畢業(yè)設計（論文）資料袋存檔。 湘潭大學興湘學院 畢業(yè)論文（設計）任務書 論文（設計）題目： 菱錐式無級變速器結構設計 學號：2007964212 姓名： 姚昊雄 專業(yè)： 機械設計制造及其自動化 指導教師： 聶 松 輝 系主任： 周 友 行 一、主要內容及基本要求 1、鋼錐無級變速器的結構設計； 2、輸入功率P=1.5kw，輸入轉速n=1500rpm，調速范圍R=8； 3、一張裝配圖A0#1張，零件圖總量A0#1張； 4、設計說明書一份； 5、英文文獻一份。 二、重點研究的問題 1、鋼錐無級變速器原理及其結構； 2、變速原理的傳動結構的實現(xiàn)。 三、進度安排 序號 各階段完成的內容 完成時間 1 熟悉課題及基礎資料 第一周 2 調研及收集資料 第二周 3 方案設計與討論 第三～四周 4 無級變速器布局設計 第五周 5 無級變速器總裝配圖設計 第六～九周 6 無級變速器工程圖設計 第十周 7 撰寫說明書 第十一周 8 英文文獻翻譯，答辯 第十二周 四、應收集的資料及主要參考文獻 [1] 阮忠唐. 機械無級變速器[M]. 機械工業(yè)出版社. [2] 阮忠唐.機械無級變速器設計與選用指南[M].化學工業(yè)出版社. [3] 徐灝.機械設計手冊第3卷[M].機械工業(yè)出版社. [4] 毛謙德.袖珍機械設計師手冊第3版[M].機械工業(yè)出版社. [5] 機械設計手冊新版第2卷[M].機械工業(yè)出版社.