Wet Clutch Materials Screening
Clutch Friction Material Screening Using UMT TriboLab
Smooth clutch operation in automatic transmissions is strongly tied to the velocity dependence of the coefficient of friction (COF). Full-scale clutch tests, such as the JASO M348 or any other OEM-specific test protocol run on the SAE No. 2 Friction Test Machine, are typically used to obtain friction data, but these tests are both expensive and time consuming. Further, the evaluation of each new friction material recipe or process change requires the fabrication and assembly of full-scale clutch components. Significant savings in development time and cost can be realized by screening friction materials in the laboratory prior to full scale clutch tests.
Proving Clutch Performance
自动变速箱离合器（也称为湿离合器）的需求越来越高，对减小尺寸时的特异性扭矩容量更高。为了满足竞争性商业环境中的需求，材料设计师和离合器设计工程师可以通过使用分析模型来减少产品开发时间。必威手机客户端使用这样的模型，可以探索大量的设计和材料更改，并可以评估它们对系统性能的影响。离合器和制动器中的关键性能特征被称为其苛刻，振动和噪声（HVN）响应。HVN与COF的滑动速度依赖性密切相关。希望COF随着滑动速度的增加以及在广泛的接触压力范围内表现出稳定或略有增加的值。众所周知，摩擦是系统属性，而不是物质属性。因此，在设计工作中使用分析模型的便利性是通过验证模型的需求，尤其是新离合器材料的摩擦行为来调节的。必威手机客户端此外，与全尺度设备或系统相比，台式测试必须满足随后的性能证明负担。
Assessment of the COF Behavior
As described above, to minimize HVN and assure smooth clutch performance, it is desired that the COF exhibit a steady or slightly increasing value as the sliding velocity increases. A decrease in the COF with increasing velocity can lead to clutch shudder or judder. While there are analytical models that incorporate clutch-system stiffness, material pairs, rotor/stator contact pressure, temperature, sliding velocity, and COF, experimental data are still a required input for the COF, particularly as a function of the other variables. Full-scale tests, such as the JASO M348-2012 or any other OEM-specific test protocol run on the SAE No. 2 Friction Test Machine, are typically used to obtain such data. However, these tests can be expensive and time consuming, and they require the fabrication and assembly of full-scale clutch components.
It would be expected that savings in both cost and time during the material development period can be achieved if a simple benchtop screening test could be used to rank materials prior to their selection for fabrication into parts and implementation in a full-scale test. This includes the clutch material itself, the reaction plate, as well as the fluid in which the clutch operates, in this case referred to as automated transmission fluid (ATF). The purpose of this research and development effort was to devise a benchtop material screening test and protocol that could be used to pre-screen materials prior to moving ahead with fullscale testing. The success of the effort was measured by the ability of the benchtop test to rank materials in the same order as that of the full-scale tests. It was not the aim to exactly replicate the full-scale test protocol, which consists of more than 275 separate conditions of speed, contact pressure and temperature, but rather to develop a simplified subset of test sequences on the benchtop tester from which the same relative ranking of materials could be determined, including the velocity dependence over a wide velocity range.
Size Effects in Simulation
While the contact pressure, sliding speed and temperature are obvious choices for proper simulation, a minimum contact size is also important in benchtop friction material testing. This is because of the non-homogeneous nature of clutch materials, and the need to include all constituents as well as the reservoir and channeling effect of the surface roughness and porosity. Such variation in surface texture is shown in the images to the right, via 3D topographic images obtained using a Bruker white light interferometer (WLI). If the contact is made too small, the effect of both the inhomogeneous composition and the surface roughness on the friction can be lost, and the benchtop test will not properly simulate the actual tribosystem.
完成模拟
The following additional full-scale parameters were deemed to be important to the simulation in the benchtop test:
- The duration of clutch material engagement at a given speed
- The rate of application of the full contact pressure
- 测试条件之间的停留时间
- Recirculation and filtering of the ATF between clutch material changes
台式测试系统，一个UMT TriboLab配备一个扶轮drive, heating chamber and liquid pumping system, along with a close-up example ofa sub-scale clutch test sample, are shown in the image to the left.
Results of Screening Tests
右侧的图像显示了在UMT Tribolab台式系统和全尺度测试钻机上在120°C进行的级速离合器材料测试的COF结果。该一致性在相对排名，曲线形状与速度的函数以及每种材料的COF幅度非常好。
对于材料B，可以看到COF与速度曲线的正斜率，使其成为离合器设计建模的可行选择。其他亚尺度测试序列（包括脱离COF和速度坡道）也显示出与全尺度测试的数据有很好的相关性。
Benchtop Screening Tool
通过正确应用等效的接触应力，加速度，滑动速度，流体条件和温度，在全尺寸离合器测试钻机中使用，UMT Tribolab用作出色的台式筛选工具，可以为建模工作以及加速度提供输入决策时间并降低材料下降的成本，以在全尺寸离合器钻机测试中进行最终证明。必威手机客户端
