经典文档下载后可编辑复制湖北文理学院毕业设计(论文)英文翻译题目有限元热分析的陶瓷离合器专业车辆工程班级Xxx姓名Xxxx学号2010138xx指导教师职称Xxx 副教授2014年2月25日Fethermal analysis of a ceramic clutch1. IntroductionAbrasive dry running vehicle clutches are force closure couplings. Torque and speed transmission are ensured by the frictional force generated between two pressed surfaces. Reasons for the application of ceramic as a friction medium include good heat and wear resistance properties, which provide the opportunity to drive higher pressures, and a low density. Thus, an increasing power density is enabled with a parallel minimization of construction space.Measurements with a first prototype of a clutch disk using ceramic facings were performed at Karlsruhe University in a laboratory specialized in passenger car drive system testing. In the course of analysis the finite element (FE) model was to be constructed with the knowledge of measurement data and measurement conditions. Calculations were intended to determine the temperature distribution of the clutch disk and its environment at each moment in time corresponding to measurements. It is essential to be familiar with the temperature range in order to examine the wear characteristics of the system. Thus, important information is derived from measurement data. In critical load cases, the highest expected temperatures must be forecast in space and time in order to protect measuring instruments close to the location of heat generation.The goal of this study is to analyze and modify the clutch system to provide better operating conditions by improving the heat conduction and convection of the system or to increase the amount of the energy converted into frictional heat. Furthermore, it is desired to find better design solutions for more efficient clutch systems.Calculations were performed by the Cosmos Design Star software. During model development, great care had to be taken for proper simplification of geometry, the selection of element sizes, and the correct adjustment of time steps due to the substantial hardware requirements for transient calculations. Changes in thermal parameters such as the surface heat convection coefficient and thermal load had to be taken into consideration on an on-going basis in terms of time and location. The two sides of the analyzed test clutch system can only be managed by two independent models linked by heat partition,according to the hypothesis that the contact temperature must be identical on both sides while there is proper contact between them and its value must be adjusted by iteration. Calculations revealed that the heat partition changed by cycle and it differed along the inner and outer contact rings. As a result of the different cooling characteristics between the ceramic and steel side, a heat flow is launched from the ceramic side to the steel side. This heat flow was also determined by iteration, its value also changes by cycle and differs along the inner and outer contact rings.2. First prototype of a clutch using engineering ceramics as friction materialThe examined clutch disk was developed according to the “specific ceramic” product development process established at the Institute for Product Development (IPEK) at the University of Karlsruhe. This development process already has the possibility for connection to a real transmission shaft; further, it has a cushion spring device for the facings allowing good start behaviour. Abrasive clutches must comply with the following basic requirements:●high torque transmission according to high friction coefficients,●high comfort (no vibrations through self-induced chattering),●homogeneous temperature distribution,●low wear characteristic.A critical element of the switch is the abrasive disk.With regard to the design utmost care must be taken to select the right material. A high and constant friction coefficient,，wear resistance and thermal resistance are desired characteristics. The clutch disk has instead of the generally applied ring-shaped abrasive inlet two rows of SSIC (as sintered) ceramic pellets. These pellets are placed on 6 separate segments. The segments are fixed to the central hub by rivets. Each segment consists of 4 plates, 2 working as facing springs and 2 as carriers.3. MeasurementsMeasurements were performed at the department of power train development of the Institute for Product Development (IPEK) at the Karlsruhe University (TH) ResearchUniversity, where a category IV component test rig is used for tests of new frictional materials and examinations of new materials in real clutch disks. Real conditions are applied by the simulation of driving resistance (e.g. starting in the plane, starting at the hill). It is a component test rig leveled on the fourth position of the tribological testing environment.In order to give an idea of dimensions: the equipment length is about 4-5m. The two electric motors and the axial force are controlled independently by computer; thereby many operational states can be realized. This enables the equipment to complete a myriad of tribological measurements all while properly modeling the operation of a clutch disk in a passenger car. It is also equipped with an automatic IT measurement system. Measurable quantities include the following:●two heavy-duty electric motors (150 KW, Baumuller DS 160L-305),●device suitable for exerting axial force,●torque meter (Manner Sensortelemetrie MF100),●axial force meter,●steel disk in friction,●replaceable head to affix the device to be tested,●temperature along two different radii at 0.4mm below the abrasive surface of the steeldisk (Omega HJMTSS-IM100U-150-2000,J-typeiro-constantan thermocouples),●revolutions per minute for both sides (Polytene LSV 065).The greatest challenge out of these is temperature measurement as we would like to know the temperature of the revolving steel disk. The two thermoelements placed in the steel disk forward data to the computer through a wireless blue tooth system and are placed 0.4mm below the abrasive surface of the steel disk on the two opposite arcs of the clutch disk.3.2. Measurement processDue to component analyses and cost reduction only one side of the clutch disk is mounted with ceramic facings. Thus, the clutch disk and its fitting will be referred to as the ceramic side, and the abrasive steel disk with its environment revolving together will be referred to as the steel side. In the course of measurements, data were collected at a sampling frequency of 100 and 1000HZ. Measurements were conducted according to thetime curves.The measurement starts by increasing the revolutions per minute of the steel side (the driving side) to a specific value (1500 rpm here). Then the ceramic side (the driven side), held at zero rpm, is pushed towards the steel disk and the axial force is applied until a designated value is reached (nominally 4200N here). Upon reaching the designated axial force the ceramic side is released and the two sides start to synchronize. A few seconds after synchronization, the axial load is discontinued and after some time both the steel and the ceramic sides—revolving at the same speed—are slowed down. This is deemed to be one measurement cycle. Ten cycles are completed in the course of a single measurement. During application of the axial force the ceramic side is held at zero rpm until the desired force is reached to ensure synchronization occurs at nearly the same time of each cycle. This is unfavorable from the viewpoint of both measurements and calculations. Measurements are usually conducted by changing only 3 parameters: the speed, the axial load and the inertia. The following figures are applied in various combinations:●speed n: 700, 1100 and 1500 (rpm),●axial force F: 4200, 6400 and 8400 (N) and●inertia I: 1, 1.25 and 1.5 (kgm2).Experimental measurements are launched with approx.10-15 min intervals, during which the system cools down to about 30-40 1C. This makes calculations difficult, as the exact temperature distribution of the system is not known at the commencement of the measurement. However, it can be assumed that a period of 10-15min is sufficient for a nearly homogeneous temperature distribution to be produced. The parameters for the following simulation have been chosen for an intermediate case with a speed n =1500 rpm, an axial force F = 4200 N and an inertia I = 1 kg m2.4. Calculations of heat generationThe mechanical energy consumed during the friction of two bodies is transformed into heat. The generated heat can be calculated by the following simple formula: Q =μ·ν·F [W] .where m is the the frictional coefficient; v is the sliding velocity; F is the force perpendicularly compressing the surfaces. And the heat flux density per surface unit isq=μ·ν·p [Wm2].where p is the the pressure calculated as a ratio of the force and the contacting surface. As the ceramic tablets are placed at two different radii along the clutch disk, the heat generated must be calculated separately for each radii. Sliding can be divided into two sections. In the first section, the ceramic side is kept in a stationary position by braking, meanwhile the axial load is increased; therefore compression changes in the course of time while the speed difference between the two sides is constant. In the second section (at synchronization) the speed difference is equalized while the force value is constant, so velocity changes in time. On the basis thereof, the heat generated is.The nominal contact area is the aggregate of the contacting surfaces of the 24 and 18 ceramic tablets on the given ring. The diameter of ceramic tablets is:.Calculations were performed for the load case to be characterized by the following parameters:.Based on experimental measurements a constant friction coefficient of 0.4 was established..The velocity can be calculated with the knowledge of the radius and the speed..Surface pressure can be calculated as a ratio of the axial force and the contacting surface. This produces the same figure for each ceramic pellet, assuming an even load distribution..Thus, the maximum values of the generated heat are.In the first section of sliding, the generated heat is rising due to the increase of the load force; in the second section, it is decreasing due to the equalization of the speed difference. It is necessary to know the time of each sliding section in order to be able to specify the generated heat time curve. These can be determined from measurement data series. Synchronization time can be easily determined from the speed of the ceramic side. Speed increase is linear. Force increase is non-linear. For the sake of simplicity, force increase was substituted by a straight line in calculations so that the area below the straight line is nearly identical with the area measured below the curve. Thus, the time difference between the two terminal points of the straight line is the time of the first sliding section.The above-mentioned method was applied for each cycle and their average was specified. Based on these results, the following values were determined for sliding times:.Now the time curve of heat generation can be produced. The same curve was used in each cycle as there were no significant differences between parameters in each cycle. The generated heat-calculated this way-will appear as thermal load in the thermal model. It must be distributed appropriately between the contacting surfaces by taking intoconsideration heat partition. Heat partition requires the contact temperatures to be identical at both surfaces. Correct adjustment requires repeated iterations.有限元热分析的陶瓷离合器1 引言磨料空转车辆离合器是力封闭联轴器。