節(jié)能車車架設計與優(yōu)化,節(jié)能,車車,架設,優(yōu)化 畢 業(yè) 設 計（論 文）外 文 參 考 資 料 及 譯 文 譯文題目： Design and Finite Element Analysis of an Automotive Clutch Assembly 汽車離合器總成的設計與有限元分析 學生姓名： 專　　業(yè)： 所在學院： 指導教師： 職　　稱： Design and Finite Element Analysis of an Automotive Clutch Assembly Abstract The purpose of a clutch is to initiate motion or increase the velocity of a body generally by transferring kinetic energy from another moving body. The mass being accelerated is generally a rotating inertial body. The present paper deals with designing a friction clutch assembly using Solid Works Office Premium software. The assembly comprises of the clutch plate, the pressure plate and a diaphragm spring. Static structural analysis was done using ANSYS software. The plots for equivalent stress, total deformation and factor of safety were obtained and the design was continuously optimized till a safe design was obtained. Uniform wear theory was used for the analysis. The material assignment is as follows: clutch plate- structural steel, pressure plate- cast iron GS-70-02 and diaphragm spring- spring steel. The friction material assumed is molded asbestos opposing cast iron/ steel surface. Keywords: Design, Finite Element Analysis, Clutch assembly. 1. Introduction The finite element analysis is the most widely accepted computational tool in engineering analysis. Through solid modeling, the component is described to the computer and this description affords sufficient geometric data for construction of mesh for finite element modeling.The main clutch of heavy vehicles is the basic execution component,which realizes the vehicle to start,shift,move and stop.Separating the main clutch will prevent the transmission device and the engine from being damaged by too heavy load during the violent change of the load over the heavy vehicle. 1.1 Clutch A Clutch is a machine member used to connect the driving shaft to a driven shaft, so that the driven shaft may be started or stopped at any time, without stopping the driving shaft. A clutch thus provides an interruptible connection between two rotating shafts. Clutches allow a high inertia load to be started with a small power. Clutches are also used extensively in production machinery of all types. 1.2 Pressure Plate Pressure plate is a cast iron plate that provides a pivot fulcrum for the diaphragm spring, a friction surface for the disc and a mounting surface for the drive straps. Pressure plates are round, metallic devices containing springs and fingers, or levers and controlled by the release fork connected to the shifter. All of the clutch components are enclosed in the bell housing of the transmission, between the rear of the engine and the front of the gearbox. The pressure plate pushes the clutch disc against the constantly spinning engine flywheel. The clutch disc, therefore, is either stationary or rotating at the same speed as the flywheel. Friction material, similar to that found on brake pads and brake drums, causes the clutch disc to spin at the same speed as the engine flywheel. It is this friction between clutch disc and flywheel that allows the engine torque to drive the wheels. 1.3 Diaphragm Spring Bhandari (2008) explained in his experiment that Diaphragm spring is a flat, spring-steel disc compressed between the cover and pressure plate that, when pushed by the release bearing, engages and disengages the clutch. The diaphragm spring is a single thin sheet of metal which yields when pressure is applied to it. When pressure is removed the metal springs back to its original shape. The centre portion of the diaphragm spring is slit into numerous fingers that act as release levers. When the clutch assembly rotates with the engine these weights are flung outwards by centrifugal forces and cause the levers to press against the pressure plate. During disengagement of the clutch the fingers are moved forward by the release bearing. The spring pivots over the fulcrum ring and its outer rim moves away from the flywheel. The retracting spring pulls the pressure plate away from the clutch plate thus disengaging the clutch. When the driver steps on the clutch pedal, a number of springs in the pressure plate are compressed by multiple (most often three) fingers. This compression of the spring(s) pulls the pressure plate and the clutch disc away from the flywheel and thus prevents the clutch disc from rotating. When the clutch disc is stationary, the driver can shift into the proper gear and release the clutch pedal. When the pedal is let up, the fingers in the pressure plate release their grip and the spring(s) expand to push the pressure plate into the clutch disc, there by engaging the flywheel. This release process is often called the “clamp load”.It shall be noted that in Diaphragm Springs, Residual stress occurs in either front or rear surface, or both surfaces used for automobile clutches due to shot peening. Studies reveal that the residual stress remarkably affects the load– deflection (P–δ) curve of diaphragm springs. 2. Static Structural Analysis 2.1 Equivalent Stress (Von Mises Stress) While the Equivalent Stress at a point does not uniquely define the state of stress at that point, it provides adequate information to assess the safety of the design for many ductile materials. Unlike stress components, the Equivalent Stress has no direction. It is fully defined by magnitude with stress units. To calculate the factors of safety at different points, the Von Mises Yield Criterion is used, which states that a material starts to yield at a point when the Equivalent Stress reaches the yield strength of the material. Equivalent stress is related to the principal stresses by the equation: (S1-S2)2 + (S2-S3)2 + (S3-S1)2 = 2Se2 (1) Equivalent stress is often used in design work because it allows any arbitrary three -dimensional stress state to be represented as a single positive stress value. Equivalent stress is part of the maximum equivalent stress failure theory used to predict yielding in a ductile material. 2.2 Total Deformation Physical Deformations can be calculated on and inside a part or an assembly. Fixed supports prevent Deformation; locations without a fixed support usually experience deformation relative to the original location. Deformation is calculated relative to the part or assembly in world coordinate system. U2 = (Ux2 + Uy 2 + Uz2) (2) Ux, Uy and Uz are the three components of Deformation. 2.3 Stress Tool (Factor of Safety) The following stress tools are available in the solution object: 1) Maximum Equivalent Stress Safety Tool 2) Maximum Shear Stress Safety Tool 3) Mohr-Coulomb Stress Safety Tool 4) Maximum Tensile Stress Safety Tool In the present analysis Maximum Equivalent Stress Safety Tool has been used. The Maximum Equivalent Stress Safety tool is based on the maximum equivalent stress failure theory for ductile materials, also referred to as the Von Mises theory, octahedral shear stress theory, or maximum distortion (or shear strain) energy theory. Out of the four failure theories supported by Simulation, this theory is generally considered as the most appropriate for ductile materials such as aluminum, brass and steel. The theory states that a particular combination of principal stresses cause failure if the maximum equivalent stress in a structure equals or exceeds a specific stress limit:Se ≥ Slimit. Expressing the theory as a design goal:Se / Slimit < 1 If failure is defined by material yielding, it follows that the design goal is to limit the maximum equivalent stress to be less than the yield strength of the material:Se / Sy < 1 An alternate but less common definition states that fracturing occurs when the maximum equivalent stress reaches or exceeds the ultimate strength of the material:Se / Su < 1 Safety Factor:Fs = Slimit / Se. Using the Equivalent Stress (Von Mises Stress), the Total Deformation and the Stress Tools; it was determined whether the parts would yield under loading conditions or not. The design was continuously optimized during the process. 2.4 Design Considerations A clutch of good design must have adequate torque capacity, ability to withstand and dissipate heat and should have a long life. The clutch must have positive release, smooth engagement, low operating force and ease of repair. To permit easy engagement and to prevent excessive wear during the engagement period the facing should be flexible and the largest possible area should be in contact during engagement. To overcome the inertia of the driven parts, when starting, clutches should be designed for overload capacities of 75 to 100 percent. 3. Finite Element Analysis of Clutch Assembly The finite element analysis of clutch assembly was carried out in the following steps: 1) Calculation of the dimensions of the clutch assembly 2) Material selection for the clutch plate, pressure plate and diaphragm spring 3) Creating a three-dimensional model of clutch assembly (clutch plate, pressure plate and diaphragm spring) in Solid Works Office Premium Software 4) Exporting the model to ANSYS for simulation and dividing it into small elements 5) Defining the material property and geometry data 6) Defining the Environment (a combination of loads and supports) 7)Submitting the Model to the ANSYS solver; Obtaining Solution (Equivalent stress, Total Deformation and Stress Tool) and evaluation of the results 3.1Calculation of the dimensions of clutch assembly First of all the values of coefficient of friction and pressure for clutch were selected from Table 1. It shall be noted that for a friction clutch, during its life time, changes in the friction materials’ topography occur. that these changes will influence the friction characteristics of the clutch, and therefore affect the performance of the transmission system. Table 1: The values of different parameters for Moulded Asbestos on Cast Iron or Steel Contact Surfaces Coefficient of friction Max Temp, Bearing Pressure Comment μ °C N Wearing surface Opposing surface Wet Dry Molded Asbestos Cast Iron or Steel 0.08-0.12 0.2-0.5 260 0.34-0.98 Wide field of applications Selecting, Coefficient of friction μ = 0.2857 and Bearing Pressure F = 0.7 N Take: Do =180 (Keeping Do constant and calculating the values of other dimensions) The ratio of inner to outer diameter for maximum torque transmission: X= (Di/Do) = 0.48; for Pressure= constant. X= (Di/Do) = 0.577; for Pressure= constant. Where: Di = Inner diameter Do = Outer diameter Assuming uniform wear theory: Therefore; Di=Do*0.577 Di=180*0.577 Di=103.86 Fa= π*F*Di*(Do-Di)/2 Fa=3.14*0.7*103.86*(180-103.86)/2 Fa=8695.190 N Mt=n*μ*Fa*(Dm)/2 Mt= 2*0.2857 *8695.190*((180+103.86)/2)/2 Mt = 352600 N-mm d= ((16*Mt)/ (pi*td)) 1/3 d = ((16*352600)/(3.14*40))1/3 d = 35.54 mm Where： Fa = Normal Force Mt = Torque Transmitted 3.2 Material Selection The following materials were selected for finite element analysis: 1）Clutch Plate: Structural Steel. 2）Pressure Plate: Cast Iron GS-70-02. 3）Diaphragm Spring: Spring Steel. The table 2 shows the mechanical properties of the above three selected materials. Table 2: The mechanical properties of the three selected materials S. No. Material Elastic Modulus (Pa) Poisson Ratio Coefficien of Thermal Expansion Density kg/m3 1. Structural Steel 2.0x1011 1.3 1.20x10-5/C 7850 2. Cast Iron GS-70-02 1.8 x1011 0.28 1.229 x 10-4/°C 7400 3. Spring Steel 2.1 x1011 0.3 3.26 x 10-6/ °C 7850 3.3 Development of 3-D model for clutch assembly in Solid Works Software 3.3.1. Clutch Plate It is an assembly formed from: a Plate, Friction Lining and a Splined Hub. 1) Plate: The features used in Solid Works are Extrude, Cut-Extrude, Circular Pattern and Fillets. 2) Friction lining: The features used in Solid Works are Extrude, Cut-Extrude. 3) Splined Hub: The features used in Solid Works are Extrude, Circular Pattern. Clutch Plate Assembly: Mate feature in Solid Works was used to join the three components. 3.3.2. Pressure Plate It is mated with friction lining and the features used in Solid Works are Assembly Mates, Loft (extending over 4 planes), Cut-Loft (extending over 3 planes) Cut-Extrude. 3.3.3. Diaphragm Spring The features used in Solid Works are Loft (extending over 6 planes), Shell, Cut-Extrude, Circular pattern, Extrude. The figure 1 shows the finite element model of the clutch assembly (Exploded View): Fig. 1. The finite element model of the clutch assembly 3.4 Finite element analysis of each part of clutch assembly using ANSYS software 3.4.1 Clutch Plate A Mesh was created (Dividing the model into small elements). Material property and geometry data were defined (as per the section 3.1 and 3.2). The Environment (a combination of loads and supports) was defined is follows: Loads: Moment: 176.3 N-m (each side); Pressure: 0.7 MPa. The Model was submitted to the ANSYS solver and the solutions for the Equivalent von mises stress, Total Deformation and Stress Tool were obtained. The figure 2 shows the distribution of equivalent von-mises stress over the clutch plate. The figure 3. shows the distribution of total deformation over the clutch plate. The figure 4 shows the distribution of Factor of Safety (Stress Tool) over the clutch plate. The figure 4 shows that the minimum factor of safety for the clutch plate is greater than10. Fig. 2 The equivalent von-Mises stress plot for the clutch plate Fig. 3 The Total Deformation plot for the clutch plate Fig. 4. The Factor of Safety (Stress Tool) plot for the clutch plate 3.4.2 Pressure Plate The model of the pressure plate was meshed. The material property and geometry data were defined as per section 3.1 and 3.2. The Environment (a combination of loads and supports) was defined is follows: Loads: Moment = 356.2 N-m Pressure 1 = 0.7 MPa; Pressure 2 = 0.75 MPa. (Pressure 1 acts on the back surface of the pressure plate; it is the reaction pressure from the clutch plate, and Pressure 2 acts on the front portion of the pressure plate facing the diaphragm spring) The Model was submitted to the ANSYS solver and solutions were obtained (Equivalent von-Mises stress, Total Deformation and Stress Tool). The figure 5 shows the distribution of equivalent von-Mises stress over the entire pressure plate. The figure 6 shows the distribution of total deformation over the entire pressure plate. The figure 7 shows the distribution of factor of safety (Stress Tool) over the entire pressure plate. The figure 7 shows that the minimum factor of safety for the pressure plate is 1.797. Fig. 5. The equivalent von-Mises stress plot for the pressure plate Fig. 6 The total deformation plot for the pressure plate Fig 7. The Factor of Safety (Stress Tool) plot for the pressure plate 3.4.3 Diaphragm Spring The model of diaphragm spring was meshed. The material property and geometry data were defined as per section 3.1 and 3.2. The Environment was defined is follows: Loads: Moment = 356.2 N-m; Force = 10 N. The Model was submitted to the ANSYS solver and Solutions for equivalent von -Mises stress, Total Deformation and Stress Tool were obtained. The figure 8. shows the distribution of equivalent von-Mises stress over the entire diaphragm spring. The figure 9 shows the distribution of total deformation over the entire diaphragm spring. The figure 10 shows the distribution of factor of safety (Stress Tool) over the entire diaphragm spring. The figure 10 shows that the minimum factor of safety for the diaphragm spring is 2.1657. Fig. 8. The equivalent von-Mises stress plot for the diaphragm spring Fig. 9. The total deformation plot for the diaphragm spring Fig. 10. The Factor of Safety (Stress Tool) plot for the diaphragm spring Conclusions In the present work a friction clutch assembly was designed and a model of the same was created in Solid Works Office Premium Software. It consist of three parts viz. clutch plate, pressure plate and diaphragm spring. Finite element analysis was performed in ANSYS software. The finite element analysis was carried out in three steps: Pre-processing, Solving and Post processing. The plots for Equivalent von-Mises stress, total deformation and stress tool (factor of safety) were calculated and analyzed. The finite element analysis showed that the designed friction clutch assembly is safe. 汽車離合器總成的設計與有限元分析 摘要 離合器的作用就是依靠轉移來自另一個運動物體的動能來啟動或加速，離合器的加速通常是慣性旋轉。本論文涉及了利用可靠的高端辦公軟件設計一個摩擦離合器，離合器總成由程度從動盤、壓盤和膜片彈簧組成。靜態(tài)結構分析由ANSYS軟件完成，求出等效應力的劃分、總變形和安全系數(shù)，并且不斷的優(yōu)化直到得到一個安全可靠的設計。均勻磨損理論用于分析，材料使用如下：從動盤——結構鋼、壓盤——鑄鐵、膜片彈簧——彈簧鋼。假設摩擦材質是不同于模制石棉的鑄鐵/鋼表面。 關鍵詞：設計、有限元分析、汽車離合器總成。 1、 介紹 有限元分析是最被廣泛接受的用于工程分析的計算工具。通過給電腦提供實體模型、組件描述，并且此描述為建立有限元模型的網(wǎng)格提供了足夠的幾何數(shù)據(jù)。重型車輛的主離合器的基本執(zhí)行組件是用來實現(xiàn)車輛的啟動、轉變、移動和停止，分離主離合器將防止傳動裝置和負荷劇烈變換期間的發(fā)動機受到重載而損壞。 1.1離合器 離合器是一種用來連接主動軸和從動軸的機械構件，以便從動軸可能隨時啟動或停止，而主動軸沒有停止。因此，離合器提供了一個可中斷的兩個轉動軸之間的連接。離合器允許高慣性負荷始于小功率，離合器也被廣泛用于所有類型的機械生產(chǎn)。 1.2壓盤 壓盤是一個鑄鐵盤，它給膜片彈簧、摩擦片表面和驅動皮帶的安裝提供了一個主支點。壓盤是圓環(huán)形的，金屬設備包含彈簧、指針或杠桿，通過分離叉連接到移動位置。所有的離合器組件都封閉在變速器外殼內，安裝在發(fā)動機后面和變速器前面。壓盤將離合器圓盤推向不斷旋轉的發(fā)動機飛輪，因此，離合器盤不是靜止的就是和飛輪同轉數(shù)旋轉，正是離合器片與飛輪間的摩擦讓發(fā)動機轉矩驅動車輪。 1.3膜片彈簧 班達里（2008）在實驗中解釋到膜片彈簧是平的，當推動分離軸承，離合器就嚙合或分離，在覆蓋面和壓盤之間的膜片彈簧被壓縮。當施加壓力時，膜片彈簧是一層很薄的金屬片；當撤銷壓力后回到原來的形狀。膜片彈簧中部的棘爪裂縫作為分離杠桿。離心力將發(fā)動機的離合器總成的強度往外扔，導致杠桿擠壓壓盤，依靠分離軸承的前移使棘爪脫離。彈簧的軸心在支撐環(huán)之上，它的外輪緣遠離飛輪，回位彈簧拉著壓盤遠離離合器片，從而分離離合器。 當駕駛員踩下離合器踏板，由多個棘爪（最多3個）壓縮壓盤上的若干數(shù)量的彈簧，這種壓縮彈簧將壓盤和離合器片拉離飛輪，從而阻止離合器圓盤的旋轉，當離合器圓盤靜止駕駛員可以切換合適的檔位；而松開離合器踏板，壓盤上的棘爪釋放，彈簧擴大到推動離合器圓盤上的壓盤，以上工作通過飛輪，這種釋放過程通常被稱為“加緊力”。應當注意在彈簧膜片中，殘余應力發(fā)生在前面或者后面，由于噴丸硬化兩者都用于汽車離合器。研究表明，殘余應力顯著影響膜片彈簧的載荷—撓度曲線。 2、 靜態(tài)結構分析 2.1等效應力（馮.米塞斯應力） 在一個點上的等效應力無法唯一定義在這個階段上是應力狀態(tài)，它為許多塑新材料提供了足夠的信息來評估這個設計的安全性。不同于壓力組件，等效應力是沒有方向的，它的壓力大小和單位是充分明確的。材料開始在某一點屈服時，當?shù)刃_到材料的屈服強度時使用馮.米塞斯屈服準則來計算不同點的安全性。 等效應力與主應力的關聯(lián)方程式：（S1-S2)2+（S2-S3)2+（S3-S1)2=2Se2 等效應力通常應用于設計工作，因為它允許將一些任意的三維應力狀態(tài)表現(xiàn)為一個正的壓力值，等效應力是最大等效應力用于預測材料屈服的一部分強度理論。 2.2總變形 在某個部分或一個組件內的物理變形是可以計算的，固定支架可以防止變形，相對于沒有固定支點的原始位置經(jīng)常變形，在坐標系中的部件或組件的變形可以被計算：U2=(Ux2+Uy2+Uz2) Ux、Uy、Uz是變形的三個部分 2.3應力工具（安全系數(shù)） 以下是應力工具可解決的對象： 1) 最大等效應力 2) 最大剪應力 3) 最大拉應力 4) 摩爾—庫侖應力 目前最大等效應力分析工具已被使用。最大等效應力工具是基于塑性材料最大等效應力強度理論的，也參考了等效應力、八面體剪應力理論或最大變形（剪切應力）強度理論。由于這四個強度理論的仿真支持，這個理論被認為是最適合塑性材料的比如鋁、黃銅和鋼鐵。 這個理論表明如果一個構件的最大等效應力等于或大于限制的特定應力就是就是這個主應力失效的原因：Se≥Slimit。 以此作為設計目標的理論：Se/Slimit<1 如果由于材料屈服失敗的話，它遵循了限制最大等效應力小于材料的屈服強度的設計目標：Se/Sy<1。 另一個不太常見的定義指出：出現(xiàn)壓裂時的最大等效應力等于或大于材料的極限強度。 Se/Su<1、Fs=Slimit/Se 使用等效應力（馮.米塞斯應力）、總變形和應力工具，是來確定零件是否會屈于加載條件下。這個設計也是在不斷優(yōu)化的過程。 2.4設計注意事項 一個好的離合器要有足夠的轉矩能力、承載能力和散熱性以及壽命長。離合器要準確脫離、平順嚙合、操作容易和維修方便。嚙合表面應柔韌并且盡可能最大面積的接觸，這樣易于嚙合或防止過度磨損。為了克服驅動部件開始時的慣性，離合器應設計75%~100%的過載容量。 3、 離合器總成的有限元分析 離合器總成的有限元分析分為以下幾個步驟： （1） 計算離合器總成的尺寸 （2） 選擇離合器片、壓盤和膜片彈簧的材料 （3） 用辦公軟件創(chuàng)建一個離合器總成（離合器片、壓盤和膜片彈簧）的三維立體模型 （4） 導出ANSYS軟件里的仿真模型并分成小的要素 （5） 定義材料的屬性和幾何數(shù)據(jù) （6） 定義環(huán)境(總載荷和支承結構) （7） 給ANSYS求解程序提交模型，獲取解決方案（等效應力、總變形和應力工具）和評估結果 3.1離合器總成的尺寸計算 首先從表1選出離合器的摩擦系數(shù)和壓力值。 應當指出的是對于一個摩擦離合器來說，在它的壽命期內，摩擦材料的形狀發(fā)生變化，這些變化將影響離合器的摩擦特性，因而影響傳動系統(tǒng)的性能。 表1.鑄鐵、鋼鐵對應的不同數(shù)值的模壓石棉值 接觸表面 摩擦系數(shù) 最高溫度 支承壓力 評論 μ °C N 磨損面 相反表面 潮濕 干涸 模制石棉 鑄鐵/鋼 0.08-0.12 0.2-0.5 260 0.34-0.98 廣泛應用 選擇摩擦系數(shù)μ=0.2857、軸承壓力F=0.7N. Do=180（定值，計算其他尺寸） 最大傳輸扭矩的內外直徑比：X=(Di/Do)=0.48、X=(Di/Do)=0.577 壓力為常數(shù)（Di:內徑Do:外徑） 假設均勻磨損理論：Di=Do*0.577=180*0.577=103.86 Fa=π * F * Di * (Do-Di)/2 =3.14 *0.7*103.86*(180-103.86)/2 =8695.190N Mt=n * μ * Fa * (Dm)/2 =2*0.2857*8695.17*[(180+103.86)/2]/2 =352600N.mm d= [(16 *Mt)/ (pi *td)] 1/3 =[(16 *352600)/(3.14 *40)]1/3 =35.54mm 當Fa等于法向力，Mt等于扭矩傳輸d等于軸直徑 3.2材料選擇 以下是有限元分析的材料選擇 1） 離合器片——結構鋼 2） 壓盤——鑄鐵 3） 膜片彈簧——彈簧鋼 表2描述了上述三個材料選擇的力學性能 S. No. 材料 彈性模量(Pa) 泊松比 熱膨脹系數(shù) 密度kg/m3 1. 結構鋼 2.0x1011 1.3 1.20x10-5/C 7850 2. 鑄鐵 GS-70-02 1.8 x1011 0.28 1.229x 10-4/°C 7400