Chose your automatic transmission fluid with care!

Japanese and Korean vehicle manufacturers demand special ATFs

Everyone who paid attention during their vocational training knows at least roughly how an automatic transmission works. The major advantage compared to its manual counterpart is that the annoying clutch is no longer necessary. For automatic transmissions a torque converter is used instead. In addition, the change of the gear or rather drive position is effected autonomously.

The requirements placed on oils for this kind of transmission – so-called Automatic Transmission Fluids (ATF) – are high. For the use in European and American vehicles they must meet the respective specifications according to standards of TASA, Dexron or Mercon and the individual requirements of the vehicle manufacturers.

Generally, ATF ought to be resistant to ageing and compatible with sealings. Moreover, they need to master a number of different tasks:
- lubrication of sliding/rolling friction parts
- cooling of the transmission
- protection against wear, corrosion, deposits and foam formation
- displaying optimum viscosity at cold starts and high temperatures
- transfer of forces
- ensuring shift comfort by specific friction behaviour.

Transmissions with slip control (see additional info), in particular, need specifically designed ATF. The well-known Japanese components supplier Aisin employs this technology as do many others. Aisin automatic transmissions are mainly used in Japanese and Korean models but also by European manufacturers as for instance VW, Audi and Porsche. The Japanese manufacturers demand fluids meeting the respective standard for the use in their products.

Pre-information necessary
Workshops must take this into consideration when fixing a vehicle or changing ATF and filters in order to guarantee the functioning of the transmission in the long run and without any difficulties. Moreover, the workshop is safe from complaints and subsequent repairs. After all, an unsuitable ATF can impair the sensitive torque converter clutches considerably leading to reduced comfort and unwanted influence on consumption.

With their ATF XN the ADDINOL Lube Oil GmbH offers an automatic transmission fluid not only meeting but outperforming the current performance requirements of Aisin as well as the US-American and European manufacturers of passenger cars and commercial vehicles. The lubricant manufacturer of long-standing tradition recommends ATF XN with its special demands on vibration dampening for passenger cars and light-duty commercial vehicles of the following manufacturers: Mitsubishi (SP III), Nissan (Matic), Toyota (T-IV), Subaru (ATF), Isuzu (Besco ATF-III), Mazda, Daihatsu, Hyundai, Honda and Kia. In addition, ATF XN meets the specifications ZF TE-ML 14A, GM Dexron III and Ford Mercon. Thus it can be applied universally.

Modern torque converters
The closed casing filled with automatic transmission fluid (ATF) – the torque converter – contains a pump, a guide and a turbine wheel in the form of curved paddles. The crankshaft of the engine transmits the high input speed with a low torque directly to the pump wheel. By the help of the ATF and the paddles of the single wheels the high torque is transmitted to the turbine wheel of lower speed and from there to the transmission connected downstream.
The speed of pump and turbine wheel becomes more and more equal. Taking into consideration the functioning of the guide wheel the continuously variable transmission decreases. If this is nearly equal further performance losses in the converter are prevented by a converter lockup clutch. This in turn has positive effects on fuel consumption and thus exhaust emissions but can cause reduced comfort at the same time.

The wanted vibration dampening effect is partly achieved by the automatic transmission fluid used. A controlled slip ratio depending on load and speed with an incomplete power transmission of the converter lockup clutch supports this effect. Here we have the situation of controlled slip.

German article published in kfz-betrieb 40/2010 (view article here)

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