Anti-Shudder Properties of ATFs—An Investigation into Friction Modifying Mechanisms Using VSFT and SAE No. 2 Tests

Abstract

In recent years, continuous slip torque converter clutches (CSTCCs) have been widely used in automatic transmissions, mainly to improve fuel efficiency. With the adoption of these devices the problem of shudder vibration has arisen. To help alleviate this problem, better anti-shudder characteristics are desired for automatic transmission fluids (ATFs). Positive µ-v curves are well recognized to correlate to the avoidance of shudder. A variable-speed friction tester (VSFT), which combines a low-velocity friction apparatus (LVFA)-type test with the ability to age an oil in situ, was used to determine friction characteristics of four model ATF formulations in a wet clutch tribosystem. The linear-defined multiple parameter spider chart ATF evaluation (LSAE) method was applied to present the ATF's overall friction results including anti-shudder performance and durability (Zhao, et al. (1)). One modified SAE No. 2 test was also used to test the four oils' friction behavior, to compare with the VSFT results. Similar performance rankings have been obtained from those two tests. Both test results and evaluation parameters will be discussed in this article and the response will be linked to the physical parameters defining the posttest surface. The oil absorption ability of post test friction material is shown to be important to the overall friction performance. The environmental scanning electron microscope (ESEM) images and 3D profiling results showed that some surface topographical parameters, such as V vc (void volume of the core) and V vv (void volume of valleys), can be linked with the friction modifying mechanisms in the ATF tests.

Water contamination effect in wet clutch system

“…There have been several experiments on the development of a wet clutch test rig appropriate for certain applications. [1][2][3][4][5][6][7]9,19,22 The test rig used in this investigation has been designed to investigate the friction characteristics of a single clutch contact. The test parameters of the rig can be controlled in a range described in Table 1.…”

“…18 Paper based friction materials are widely used as commercial friction plate linings because of their suitable frictional characteristics. 22 This friction lining is composed of natural or synthetic (cellulose, aromatic polyamide) fibres, solid lubricants and particulates (like graphite, cashew dust, MoS2, acrylic rubber) impregnated with thermosetting resin binder. In watercontaminated lubricant, the fibres can loosen from the diluted binder, which results in material degradation.…”