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SIMPLIFIED CONTROL OF THE MOTOR CAR has occupied the minds of designers ever since the earliest days of the industry. In the many attempts to make driving a car easier for the man‐in‐the‐street, steam was one of the forms of propulsion used until the early ‘thirties’ but when the internal combustion engine finally won the day, efforts were concentrated on finding something better than the friction clutch and manually operated gearbox for use in conjunction with this type of engine. Before World War II several fully automatic transmissions for passenger cars had already been developed, especially in the U.S.A., and it was during this war that these transmissions found application in fighting vehicles. With the return of peace, motor manufacturers turned to fully automatic transmissions in a big way. It is hardly surprising, considering the generally advanced state of mechanisation in that country, that in the volume production of this type of transmission the U.S. again took the lead. Also, the large output of the domestic motor industry offered the best chances for a favourable return on the considerable capital investments inherent to volume production of complex transmission designs.

LUBRICATION of automatic transmissions provides the oil marketers and additive suppliers with a major challenge in terms of fluid development to satisfy the diverse requirements of such units. Fluid development is further complicated by the large number of non‐automotive applications for which automatic transmission fluids (ATFs) are being used.

The single recent event that has most significantly changed the way in which automotive transmission fluids are defined took place in 1990 when General Motors published its Dexron HE specification. This represented the first major modification of General Motors' Automatic Transmission Fluid (ATF) specifications since July 1978. (The original Dexron II specification was first published in 1973.) The driving force behind the timing for the introduction of this specification was the launch, in 1991, of the Buick Park Avenue with a newly redesigned, electronically‐controlled version of the older Hydramatic 440‐T4 Front‐Wheel‐Drive (FWD) automatic transaxle. This unit was designated the 4T‐60E. The majority of designers of computer‐controlled transmissions use electro‐hydraulic solenoid valves to open and close hydraulic circuits to make the transmission shift. For this reason, many of the new transmission designs require ATFs to have superior low‐temperature fluidity properties. Dexron IIE calls for fluids having a −40°C Brookfield viscosity of less than 20,000 cP, compared with the 50,000 cP requirement of the Dexron II. Only fluids approved to the new specification will be officially endorsed by GM from January 1993.

ALMOST EVERY MOTOR CAR manufactured in the U.S.A. is fitted with one form or other of automatic transmission system. Such transmission systems are quite complex and the fluid used must meet exacting specifications, which, incidentally, are not all exactly similar for all systems. There is little doubt that we are approaching the same stage in our own car manufacture because, even if we ourselves do not consider it worth paying the extra cost of these refinements, if our overseas customers demand them, we shall have to supply, and indeed are supplying.

TWO interesting papers concerned with Automatic Transmission Fluids were presented at the SAE National Meeting at Chicago in October, 1959. The first of these, dealing with Oxidation Stability, Shear Stability and Rubber Swell Properties, was given by H. E. Deen and C. M. Stendahl of Enjay Laboratories. These authors developed a new test, the Enjay Bench Oxidation Test, for studying automatic transmission fluids and found that this showed excellent correlation with the Powerglide L 39 transmission test. The object was to provide a screening test for an expected future transmission test.

IT HAS FREQUENTLY BEEN OBSERVED that the average domestic motorist is apt to take the lubrication of his car for granted and pay less attention to the quality of the oil and drainage periods than the lubricant supplier would desire. Insofar as this criticism may be justified the motorist is undoubtedly influenced by the efficiency of the lubrication system of the modern automobile, its mechanical perfection and robustness, the dependable quality of the lubricants available and, at least with regard to the engine, the simplicity of oil prescription. This latter advantage is duo to the modern, additive treated, all seasons motor oil.

IT is not without interest in Britain to observe the trend to over 15 million passenger cars fitted with an automatic transmission in service in the United States of America. Without doubt, the rapid increase in numbers from around 2 millions in 1949 has been due to the growing demand from motorists for the easier and less tiring method of car driving. The conventional system of clutch and gearbox operation is fast dying out in American car production.

In 1959, more than 75% of cars produced in the U.S.A. were fitted with automatic transmissions, and the Hydra‐Matic system is in wide use. In the case of this transmission, smoothness of operation is particularly important with respect to the 2–3 shift, which is the only forward shift that is accomplished by engagement of clutch plates. In a paper to the Society of Automobile Engineers, at the Summer Meeting in June, John J. Rodgers and Merrill L. Haviland, of the General Motors Research Laboratories, presented the results of investigations aimed at clarifying the manner in which additives modify the friction characteristics of automatic transmission fluids, as well as the effect of an inert atmosphere on transmission shift performance.

The purpose of this paper is to discuss a method that can evaluate the friction durability of automatic transmission fluid.

A small clutch was used to test the friction durability. The method adopts a similar sequence to that of SAE No. 2. Three commercial oils were studied. One of them meets the specification of the GM's DEXRONIIE and the others meet the DEXRONIII.

The results showed that two commercial oils have different friction durability. Two further samples were blended in the lab and friction durability was researched by this method.

The results showed that the samples have a good durability. The research indicates that the method is quite capable of distinguishing between some samples. The results also indicate the difference between the DEXRON specifications at friction durability.