Thermal Behaviour of a Slipping Wet Clutch Contact

Abstract

Wet clutches are used in automatic transmissions to enable gear changes and also to reduce energy loss in the torque converter. These friction devices are susceptible to stick-slip effects, which result in the vehicle giving an unsteady ride. Stick-slip effects can be avoided by ensuring the wet clutch and lubricant combination produces a friction coefficient that increases with sliding speed. Although wet clutches have been studied throughout the industry for many decades, the mechanism of the generated friction is still not fully understood. It is known that, because of the fibrous nature and thus very large roughness of friction material, the overall contact between clutch plates actually consists of many small, independent, contact units, which are the sites of the generated friction. Some authors have suggested that a temperature rise due to friction either at these contact units or of the overall clutch plate may be important in controlling friction behaviour. In this study, the flash temperatures at the contact units formed in the wet clutch contact have been measured using an infrared camera. Three friction materials have been tested. It was found that measured flash temperature in a pure sliding system similar to that present in a slipping clutch remain well below 5°C, and are therefore unlikely to play a major role in the observed friction-speed dependency of slipping wet clutches at speeds below 2 m/s.

3D Measurements of Lubricant and Surface Temperatures Within an Elastohydrodynamic Contact

“…3b. The effect of the chromium coating on the measurements was considered minor as, according to the research of Reddyhoff [29] and Jaeger [26], the temperature reduction across the 150 nm thickness coating was only about 10%. As chromium is opaque to infrared, the radiation from oil and ball is fully reflected so that the radiation received by the infrared camera in this case originates only from the lower surface of sapphire disc.…”

“…Reddyhoff and co-workers [14,24,28,29] overcame some of the limitations which Spikes encountered by employing a high spatial resolution (6 µm) and high sensitivity IR microscope lens to improve accuracy and map the contact temperature rises down to 0.01 K. They also validated the method by comparing the shear stress calculated from the temperature with the measured friction. Reddyhoff et al [24] then extended the technique to measure asperity contacts by improving the calibration procedure and using a super-resolution method to further improve spatial resolution down to 1-2 µm [28,30].…”

A theoretical and experimental study of viscoelastic rolling contacts incorporating thermal effects

“…The temperature distribution in the contact was measured using an infrared microscopy technique, developed in previous research [38], [39], [40]. This method uses the same apparatus described above to produce the contact (i.e.…”

“…This is achieved by gradually heating the ball, using cartridge heaters, and measuring the temperature using RTD probes (both located with the PCS EHL rig). Unlike previous research ( [39], [40]), this approach , does not account for the background radiation from the bulk of the sapphire disc. However, it was assumed to be negligible, since the emissivity of sapphire is very low, especially when compared to the high emissivity of the nitrile ball specimen.…”

Study on the High Temperature Friction and Wear Behaviors of Cu-Based Friction Pairs in Wet Clutches by Pin-on-Disc Tests

“…During the engagement of wet clutches, a large quantity of heat is generated intensively in 1 second, and the temperature rises rapidly at the interfaces of friction pairs. Researchers, such as Mansouri et al [5], Jen and Nemecek [6], Ingram et al [7], Seo et al [8], and Wenbin et al [9], investigated the heat transfer, temperature distribution, and thermal stresses of wet clutches by numerical models and experiments. The temperature distribution at the contact surfaces and the thermal stresses in the friction pairs are nonhomogeneous.…”