Tze-Chi Jao

Fundamentals of anti-shudder durability: Part I - Clutch plate study

In automatic transmission technology development the degradation of paper friction plates has often been considered a major failure mechanism by which transmissions lose their anti-shudder characteristics. One of the most common degradation processes for paper friction plates is known as glazing. In this study, we focus on the relationship between friction plate glazing and anti-shudder durability in the Japanese Automobile Standards Organization (JASO) low velocity friction apparatus (LVFA) rig test following the procedure M349-98. We also investigate the impact of used friction plates and used oil on torque capacity durability as measured by an SAE No. 2 machine following the JASO procedure M348-95. We find that friction plate glazing has no correlation with anti-shudder durability. A completely glazed plate can have long anti-shudder durability but a barely glazed plate can have short anti-shudder durability. The basic reason for the lack of correlation is that friction plate glazing does not affect boundary friction coefficients. In almost all the cases studied, changes in fluid properties have a greater influence on boundary friction than does surface glazing.

Friction Reduction of Lubricant Base Oil by Micelles and Crosslinked Micelles of Block Copolymers

Diblock copolymers with one block soluble and the other block insoluble were dispersed in an industrial base oil (BO) to yield spherical micelles (SMs). SMs were also prepared in more manageable solvents that had similar solubility properties as the BO towards the copolymers but had lower viscosities and lower boiling points and absorbed less in the near UV region. The photocrosslinking of the cores of the latter micelles yielded crosslinked micelles or nanospheres. We have tested the lubrication properties of the micelle and nanosphere samples in BO under conditions simulating those found in automobile engines. Solutions of micelles and nanospheres with 2-cinnamoyloxyethyl acrylate units in their cores exhibited a unique friction reduction pattern and had friction coefficients that were significantly lower in the boundary lubrication regime (BLR) than in the mixed lubrication regime. Such particles reduced the friction of the BO by > 70% in the BLR and performed substantially better than the widely used industrial anti-friction agent glyceryl monooleate. The factors affecting this unique friction reduction behavior were investigated and a possible reason for it was proposed.

Enhancement of Engine Oil Wear and Friction Control Performance through Titanium Additive Chemistry

Traditionally, wear protection and friction modification by engine oil is provided by zinc dithiophosphate (ZDDP) or other phosphorus compounds. These additives provide effective wear protection and friction control on engine parts through formation of a glassy polyphosphate antiwear film. However, the deposition of phosphorus species on automotive catalytic converters from lubricants has been known for some time to have a detrimental effect of poisoning the catalysts. To mitigate the situation, the industry has been making every effort to find ZDDP-replacement additives that are friendly to catalysts. Toward this goal we have investigated a titanium additive chemistry as a ZDDP replacement. Fully formulated engine oils incorporating this additive component have been found to be effective in reducing wear and controlling friction in a high-frequency reciprocating rig (HFRR), 4-ball bench wear, Sequence IIIG, and Sequence IVA engine tests. Surface analysis of the tested parts by Auger electron spectroscopy, secondary ion mass spectrometry (SIMS), and X-ray photoelectron spectroscopy (XPS) have shown that Ti species have been incorporated into the wear tracks and can only be found on the wear tracks. We used synchrotron based near edge X-ray absorption fine structure (NEXAFS) to investigate the chemical bonding mechanism of the Ti additive with the metal surface that affects the wear improvement mechanism. We postulate that Ti provides antiwear enhancement through inclusion in the metal/metal oxide structure of the ferrous surface by forming FeTiO3.

ATF Friction Properties and Shift Quality

Multiple plate disk clutches are used extensively for shifting gears in automatic transmissions. In a shift from one gear to another one or more clutches is engaging or disengaging. In these active clutches the automatic transmission fluid (ATF) and friction material experience large changes in pressure P, temperature T, and sliding speed v. The coefficient of friction, μ, of the ATF and friction material depends on v, P and T, and also changes during clutch engagement. Changes in μ can lead to vibration and poor shift quality if the ATF and clutch friction material are improperly selected. An in-depth theoretical understanding of the cause of vibration in shifting clutches is crucial in the development of a suitable ATF to work with a particular friction material. To understand the relationship between ATF friction properties and shifting clutch vibration we present a theoretical model that identifies several possible causes: (1) self-excitation instability, (2) a reduction in friction holding torque during engagement, or (3) resonance caused by periodic pressure oscillations. The ATF and friction material properties that affect these sources of vibration include the friction level, μ, and the friction slopes with respect to sliding speed ∂μ/∂v, pressure ∂μ/∂P, and temperature ∂μ/∂T. These properties must be carefully balanced to ensure that a clutch will deliver good shift quality and high torque capacity with effective vibration suppression.

Characterization of Deposits Formed on Sequence IIIG Pistons

In the latest passenger car motor oil specifications the Sequence IIIG engine test is used to determine the ability of lubricants to control piston deposits. We have analyzed the chemical composition of Sequence IIIG deposits in order to determine the source of the piston deposits and determine if the mechanism for deposit formation in the Sequence IIIG engine test is similar to previously published mechanisms for formation of high temperature engine deposits. These previous mechanisms show that combustion by-products react with lubricant in the piston ring zone. The mixture of combustion by-products and lubricant are oxidized to form deposit precursors which are further oxidized to form deposits. Since the Sequence IIIG engine test uses lead-free fuel it is important to reexamine the nature of piston deposits formed in gasoline engines and in particular in the Sequence IIIG engine test. Using thermogravimetric, infrared and SEM/EDS analyses we discovered that Sequence IIIG deposits contain a significant amount of carbonaceous material. This carbonaceous material appears to be a deposit formed by the Sequence IIIG fuel. In addition, the Sequence IIIG deposits are quite different from Sequence IIIE deposits since they do not appear to be nitrated or contain lead sulfate.

Effect of Detailed Base Oil Structure on Oxidation Performance of Automatic Transmission Fluids

Automatic transmission fluids (ATF) should be oxidatively stable so that their frictional properties are maintained as the fluids are aged. To test the oxidative stability of ATFs, automobile manufacturers have created oxidation tests in which ATFs are aged in operating transmissions. In these tests, the total acid number (TAN) of the oil is measured throughout the test, and at the end of the test the TAN of the oil must be below specified limits. In general, oxidation of oils occurs by formation of free radicals that can react with the oils to form acidic species that are detected by the TAN of the used oils [1, 2]. Peroxides also form when an oil is oxidized and the peroxides can react with the oil to form acids [1,2]. Base oil structure, presence of wear metals, and the amount of oxygen dissolved in the oil can all affect the oxidative stability of oils [1,2]. Therefore, we investigated how each of these three factors affect changes in TAN as oils are aged in the GM cycling and GM oxidation tests (GMOT). Base oil structure is the major factor affecting the oxidative stability of ATFs. In particular, we have found that the cyclo-paraffin concentration in the base oils used to formulate ATFs can be related to oxidative stability. The lower the number of cycloparaffins in the base oil, the better the oxidative stability of the ATF.Copyright