Search Results

The General Motors Dexron-II automatic transmission fluid specification, issued in August 1973, defines physical, chemical, and performance requirements of a new class of fluids developed to meet increasingly severe service in passenger car and commercial automatic transmissions. Four new tests for determining fluid performance and durability have been developed for the specification. Results from these tests with Dexron-II prototype fluids are compared to those with Dexron fluids. It was found that the prototype fluids are much more oxidation-resistant than typical fluids in the Turbo Hydra-matic oxidation test; a 60% improvement in fluid durability has been realized in the Turbo Hydra-matic transmission cycling test; and Dexron-II prototype fluid friction and wear characteristics are about equivalent to those for Dexron fluids in the high energy, friction characteristics and durability test, and the wear test.

Exhaust emission tests run on an engine dynamometer are compared with those run on a chassis dynamometer. The worst case average difference between the chassis and engine dynamometer mass emissions, obtained over a period of 6 months, was less than 7%. The elimination of the driver, vehicle, and chassis dynamometer yielded significant improvement in test reproducibility with respect to carbon monoxide and oxides of nitrogen. A digital computer was used to control speed and throttle position of the engine dynamometer experiments. No transmission was used. The computer and engine dynamometer duplicated transient effects of transmission, vehicle, and chassis dynamometer.

Concern over exhaust emissions has revived interest in the gas turbine as a powerplant for passenger cars, and concern over cost has stimulated interest in the single-shaft version of this engine. A novel transmission is needed to compensate for the inherently poor output characteristics of the single-shaft engine. The rated power and response time of the engine and the efficiency and power split of the transmission are shown to be the primary parameters influencing vehicle acceleration. Some factors affecting engine response time are reviewed. Transmission parameters are studied by considering standing-start accelerations of an automobile powered by a fixed-geometry single-shaft engine using versions of three of the many types of possible transmissions. For the combinations considered, the fixed-geometry single-shaft engine cannot easily provide vehicle performance matching that of the traditional two-shaft turbine engine, if both start with the compressor idling at half rated speed.

Performance-based test techniques were developed to determine high- and low-temperature automatic transmission fluid viscosity requirements. High-temperature fluid viscosity requirements were determined using engine-transmission-dynamometer tests. Low-temperature fluid viscosity requirements were established with a motor-driven 3-speed transmission apparatus. It is concluded that the current used-fluid Dexron viscosity limit of 5.5 cs minimum at 210 F provides a good safety factor for preventing excessive internal leakage at high temperatures. Since some Dexron fluids have -40 F viscosities approaching the 55,000 cp specification limit, lowering it will be considered in future specifications.

The General Motors Research Laboratories has installed a data acquisition and control computer to be time-shared with a variety of test programs. These include vehicle emissions evaluations, safety studies, transmission investigations, metallurgical processes and materials developments. Many special interface systems have been designed to enhance the computer's compatibility with a variety of test requirements. Expandable remote scanning systems have been developed and manual input and computer display systems were designed to minimize the engineer-computer communication problem. Special vehicle emissions programs were developed utilizing the basic hardware and software systems projected for the overall Research Laboratories operation.

Engine oil and automatic transmission fluid viscosities are major factors in assuring good starting and running performance in cold weather. To determine the contributions of the engine and transmission to the cranking and running effort, instantaneous torque and power, obtained with an instrumented engine-transmission apparatus, were determined for five engine oils ranging in viscosity from 4 to 184 poise (SAE 5W to SAE 20W) and for four transmission fluids ranging in viscosity from 3200 to 83,000 cp at -20 F. Specific engine and transmission cranking variables - engine friction, compression and expansion, engine rotational inertia, and transmission friction and rotational inertia - were analyzed in detail. The engine required most of the cranking effort, which increased with increasing engine oil viscosity. Increasing engine oil viscosity increased engine friction torque but decreased engine friction power because of decreased cranking speed.