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Technical Paper

2,000,000 Miles of Fluid Evaluation in City Bus Automatic Transmissions

In certain types of city bus service some automatic transmission fluids can fail in less than 10,000 miles. In order to provide satisfactory transmission performance for longer mileage, improved fluids are required. An investigation was undertaken to obtain improved fluids. Fifteen different fluid formulations were evaluated in 30 city buses operated in normal service for more than 2,000,000 miles. It was determined that fluids fail because of frictional deterioration and oxidation. Based on these evaluations, only two fluids were found to be satisfactory for more than 40,000 miles; one additional fluid was satisfactory for more than 30,000 miles. The remaining 12 fluids failed in less than 20,000 miles.
Technical Paper

A Rotary Engine Test to Evaluate Lubricants for Control of Rotor Deposits

During development of the General Motors rotary engine, the lubricant was recognized as important to its success because certain lubricants produced deposits which tended to stick both side and apex seals. Consequently, it was decided to develop a rotary engine-dynamometer test, using a Mazda engine, which could be used for lubricant evaluation. In an investigation using an SE engine oil with which there was rotary engine experience, engine operating variables and engine modifications were studied until the greatest amount of deposits were obtained in 100 h of testing. The most significant engine modifications were: omission of inner side seals, plugging of half the rotor bearing holes, pinning of oil seals, grinding of end and intermediate housings, and using a separate oil reservoir for the metering pump. Using this 100 h test procedure, three engine oils and five automatic transmission fluids were evaluated.
Technical Paper

Correlation of Physical Properties with Performance of Polyacrylate Radial Lip Seals at -30F

This paper evaluates the tendency of lip seals to fracture in a test apparatus in which dynamic runout is 0.010 in and the temperature is cycled between -30 and 0 F. Seals made of eight different polyacrylate polymers were soap-sulfur cured with various types and amounts of carbon black. Physical tests included room-temperature flexibility defined by Young's modulus at small strains, standard tensile tests at room temperature, flexibility at sub-zero temperatures determined by a Gehman test, and sub-zero starting torques of the seals. Primary determinant of successful fracture resistance is a low starting torque resulting from good low-temperature flexibility. The effect of adding graphite to some of these formulations is described and some current commercially available seals are evaluated.
Technical Paper


EXTENSIVE TESTING by GM Research Laboratories has screened five promising transaxle fluids out of 32 mineral-oil-base fluids, 10 synthetic-base fluids, and numerous additive-base stock combination fluids. This paper discusses the findings of the testing and the continuing program on the five fluids. Transaxle fluids have a number of properties affecting performance, including: High-temperature viscosity. Low-temperature fluidity. Shear resistance. Friction properties. Oxidation resistance. Antifoam quality. Effect on seals. Fluid-clutch plate compatibility. Antiwear quality. Extreme-pressure quality. Antirust and anticorrosion qualities.*
Technical Paper

Designing to Resist Fatigue - Examples of Component Design

This paper illustrates by way of two practical examples, namely, transmission gears and crankshafts, how the automotive industry applies basic approaches and methods for achieving fatigue resistant design. Analytic, laboratory, and field studies necessary in the development of these components are briefly outlined.
Technical Paper

Effects of Engine Oil Composition on the Activity of Exhaust Emissions Oxidation Catalysts

Platinum, palladium, and copper-chromium oxidation catalysts for exhaust emission control were exposed to exhaust gases from a steady-state engine dynamometer test in which the amount of oil consumed per unit volume of catalyst was high. When unleaded gasoline (0.004 Pb g/gal, 0.004 P g/gal) was used, conventional SE oil caused somewhat greater loss of catalyst activity than an ashless and phosphorus-free (“clean”) oil. Chemical analysis of the catalyst indicated that phosphorus from the conventional oil was probably responsible for the difference. However, a test run with low-lead (0.5 Pb g/gal, 0.004 P g/gal) gasoline and “clean” oil caused much greater catalyst activity deterioration than either of the tests with unleaded gasoline.
Technical Paper

Engine Oil MS Test Sequences IIA and IIIA

Engine oil test Sequences IIA and IIIA have been developed to replace Sequences I, II, and III. These new sequences are designed to evaluate lubricants for use in current passenger car engines under severe (MS) service conditions. Lubricant performance is evaluated with respect to scuffing wear, rust, corrosion, deposits, and rumble. The Sequence IIA and IIIA test procedure involves major changes which affect the evaluation of engine rusting and provides improved correlation between test results and short-trip service. Average engine rust ratings correlate with service data within ±0.5 numbers. The new test also provides better repeatability and reproducibility in a significantly shorter schedule. The rust repeatability and reproducibility is less than ±0.2 and ±0.6 numbers, respectively. Test time has been reduced 52%.
Technical Paper

Hydrodynamic Sealing with Radial Lip Seals

Conventional radial lip oil seals can be made more effective by utilizing helical grooving beneath the contact lip surface. Miniature hydrodynamic pumps so formed aid the radial lip seal in containing the oil by generating fluid forces opposite in direction to the leakage flow forces. This seal-shaft combination has been termed the Hydroseal. Four factorial experiments were conducted to evaluate the effect of helix angle, groove depth, groove width, and number of grooves on sealing performance. The criterion used as a basis for selecting the optimum design were leakage, wear, hardening of the sealing surface, and pumping capacity. These data indicated that the best hydroseal design was one with three grooves, 0.0003 in. deep, 0.014 in. wide, having a helix angle of 45 deg.
Technical Paper

Projected Lubricant Requirements of Engines Operating with Lead-Free Gasoline

Future low emissions engines will burn unleaded gasoline. Compared with engines of 1970, future engines will have lower concentrations of NOx in the blowby gases, and lower blowby flow-rates; however, oil temperatures will probably be unchanged. The consequences of these conditions for engines using high quality (SE) oils at current drain intervals are: virtual elimination of rust, reduction of sludge, no effect on wear and oil thickening, and possible worsening of varnish. Therefore, extension of the drain interval with SE engine oils in the future may be possible, but final decisions will depend on the findings of research in the areas of engine wear and varnish, and oil thickening.
Technical Paper

Real-Time Measurement of Camshaft Wear in an Automotive Engine - a Radiometric Method

A radiometric method has been developed for the determination of camshaft wear during engine operation. After a radioactive tracer is induced at the tips of one or more cam lobes by the technique of surface layer activation, calibration procedure are performed to determine the amount of radioactive material remaining versus the depth worn. The decrease in γ-ray intensity measured external to the engine is then directly related to cam lobe wear. By incorporating a high-resolution detector and an internal radioactive standard,measurement accuracy better than ±0.2 μm at 95% confidence has been achieved. Without the requirement of engine disassembly, this method has provided unique measurements of break-in wear and wear as a function of operating conditions. Because this approach requires only low levels of radiation, it has significant potential applications in wear control.
Technical Paper

Transmission Air Breathing Suppressor (TABS) Valve - A Device for Improving Automatic Transmission Fluid Life

Automatic transmission fluids can oxidize with use, causing marginal transmission performance and eventual transmission malfunction. Periodic fluid changes are presently recommended to alleviate this problem. Fluid oxidation is promoted in current transmissions because they breathe air freely through a vent tube. To reduce fluid oxidation, and thereby improve fluid and transmission durability, a one-way check valve, called the Transmission Air Breathing Suppressor (TABS), was designed to restrict the intake of air into the transmission and to replace the conventional vent tube. The effectiveness of the TABS valve in reducing fluid oxidation was determined in high temperature transmission cycling tests and in taxicab tests. Fluid oxidation results with the TABS valve-equipped transmissions were compared to those with normally-vented transmissions. By reducing the amount of oxygen in the transmission gas, the TABS valve nearly eliminated fluid oxidation.
Technical Paper

V. I. Improvers and Engine Performance

The use of multigrade (V.I. improved) oils in automotive engines has increased significantly in recent years. However, the performance of these oils in terms of factors such as oil economy, wear, and noise, is not always equal to that of single grade oils. Although the initial viscosity of multigrade oils is related to both the base oil and the V.I. improver, the viscosity decreases with use, with the primary factors determining the magnitude of the change being the degree of shear and the characteristics and concentration of the V.I. improver used. This decrease in viscosity has been assumed to be the cause of the decreases in oil economy that may occur with oil use. However, viscosity changes are not believed to be the primary factor responsible since similar oil economy changes have also been observed for single grade oils. Nevertheless, the characteristics and concentration of the V.I. improver used can be a significant factor influencing oil economy.
Technical Paper

Vehicle Evaluation of Synthetic and Conventional Engine Oils

A five-vehicle, 64 000-km test with 7.45 litre V-8 engines was conducted to determine if synthetic engine oils provided performance sufficiently superior to that of conventional engine oils to permit longer oil change intervals. The results show better performance in two areas of deposit control; inferior performance with respect to wear protection; and essentially equivalent performance in the areas of fuel and oil economies. Based on these data, it was concluded that synthetic engine oils do not provide the necessary performance required to safely recommend their use for extended oil change intervals. In addition, a cost analysis shows that the use of synthetic engine oils, even at a change interval of 32 000 km, will essentially double the customers' cost compared with conventional engine oils at GM's current 12 000-km change interval.