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MOTOREX Magazine 2004 72 EN

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MOTOREX_Magazine_2004_72_en

Transmission fluids

Transmission fluids Photo: RohMax GmbH Transmission fluids 4 ... 3 ... 2 ... 1 ... ZF presented its pre-selector transmission at the 1921 Berlin Motor Show. The transmission failed to make a major impact because of the relatively high production costs. Photo: ZF kick-down and go! An increasing number of drivers in western Europe and Switzerland are opting for the simplicity and convenience of automatic transmissions (ATs) when they come to buy a new car. Gone are the days of manual shifting: just kick-down and go. The car takes care of shifting, all the way up to 5th, 6th or even 7th. Planetary transmissions the key The beginning was inauspicious. The Frenchman Didier designed the first planetary transmission as far back as 1906. This ingenious invention, which is still one of the major components of automatic transmissions, provided the foundation for the design’s breakthrough. Zahnradfabrik Friedrichshafen, or ZF, produced the first four-speed pre-selector transmission with no shift lever in 1921. A clever gear selector mounted on the steering wheel or dashboard let drivers preselect gears. A spring then automatically shifted the transmission to the appropriate gear when the driver pressed the clutch pedal. General Motors (GM) commenced series production of automatic transmissions in 1932 and, by 1939, was manufacturing a four-speed AT with reverse and Hydramat hydraulic clutch. In those days, of course, there were no special automatic transmission fluids (ATFs) to lubricate the gears. Any oil that was good enough for the engine was good enough for the transmission, regardless of its viscosity. 7G-TRONIC from Mercedes-Benz: The world’s first seven-speed automatic transmission Slip-controlled torque converter lock-up clutch with damping elements Input end – transferring engine torque to the transmission Hydrodynamic torque converter Oil pump controlling hydraulic supply pressure High-speed solenoid valves for controlling the shift actuators The first specification for automatic transmission fluids – Type A – did not appear until 1949 and, while automatic transmissions quickly became a huge success in the United States, they have always lagged behind manual transmissions in Europe. New specifications in 1957 A new ATF specification – Type A, Suffix A, or TASA – was issued in 1957, and ZF started series production of its hugely popular 3HP12 3-speed transmission for 1.5 to 2.2-liter engines in the year 1965. This masterpiece of engineering featured a mechanical planetary transmission with three forwards gears mounted behind its hydraulic torque converter. The layout of three forwards and one reverse gear remained unchanged for almost two decades. It was not until the 1973 oil crisis that car manufacturers were compelled to seriously reexamine a longstanding weakness of automatic transmissions – they are more expensive and less fuelefficient than their manual counterparts. There are no loopholes in physics: Shift actuators with multiplate clutches and planetary gear assemblies Electronics for demanddependent control of shifting action Control unit comprising solenoid valves, electronics and sensors built in to the sump 8 9 Output end – transferring engine torque to the drive axle Parking lock Mechanical connection to the selector lever Photo: Presse MB the only way of staying in the most economical engine speed range for longer is to increase the number of gears. Electronics and “intelligent” transmissions In 1982/83 ZF set new standards by launching the first four-speed automatic car transmission with “intelligent” control: for the first time the engine electronics were networked with the transmission’s control system. As a result, the number of gears was increased from five to six or today even seven. However, precision mechanics and transmission management can only work together effectively if the fluids make their own substantial contribution to maximum performance. Just as an automatic transmission needs intelligent electronics, so it needs the right ATF to ensure perfect function. Our chemists and engineers have taken up this challenge. MOTOREX produces a full range of ATFs, from a simple Type A to its state of the art Dexron III H or its ATF for the latest generation of 7-speed transmissions. Photo: Presse MB Photo: ZF In the torque convertor the ATF transmits the engine torque to the automatic transmission. 28% of Swiss cars have today an automatic transmission, making Switzerland Europe’s leader. It still lags far behind the United States 85% though!

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