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Sažetak Nove kategorije ulja za osobna vozila, koje propisuje American Petroleum Institute (API) usmjeravaju primjenska svojstva ulja na poboljšanje ekonomičnosti potrošnje goriva i smanjenje emisije. Taj trend je rezultirao povećanom ponudom motornih ulja, koja pogoduju uštedi goriva što se postiže smanjenjem viskoznosti i dodatkom modifikatora trenja. Smanjenje emisije je postignuto smanjenjem količine fosfora (% P) u motornim uljima, jer je nađeno da je fosfor otrov za katalizator u katalitičkim konverterima. Kada su u formulacije ulja uvedeni modifikatori trenja, istraživači četiriju japanskih proizvođača motorkotača su objavili rezultate svojih studija (SAE 961217), koji pokazuju da ulja sa smanjenim trenjem mogu uzrokovati preveliko proklizavanje spojke startera, limited-slip spojke i višelamelne spojke. U spomenutom članku su autori izvijestili, da su konstruktori motora, koji kod razvojnih ispitivanja koriste motorno ulje gradacije SAE 10W-30, opazili pojavu pittinga, ako se koristi ulje niže viskoznosti od gradacije SAE 10W-30. Nakon te studije količina fosfora je smanjena u API specifikacijama od SG (bez ograničenja sadržaja fosfora) preko SH (0,12 % P) i SJ/SL (0,10 % P) do SM (0,08 % P). Poznato je, da fosfor iz Zn-ditiofosfata tvori zaštitni sloj između metalnih površina čime štiti zupčanike od trošenja i pittinga kada uljni film postane pretanak. Tijekom razvoja motornog ulja 10W-30 API SJ za motorkotače opažena je pojava pittniga kod testova na motoru CBR600. Kako je % P bio ograničen specifikacijom API SJ, a debljina uljnog filma određena viskoznošću SAE gradacije 10W-30, rješenje je nađeno u uporabi vrlo smično stabilnog poboljšivača indeksa viskoznosti, koji nije tipičan za motorna ulja osobnih vozila, te je zbog minimalnog pada viskoznosti ulja ostvarena potrebna debljina uljnog sloja u motoru motorkotača. Uporaba ekstremno smično stabilnog poboljšivača indeksa viskoznosti omogućit će, da se u uvjetima povećanog smicanja u motorima motorkotača kor, The new American Petroleum Institute (API) categories for passenger car motor oils have focused on improving fuel economy and reducing emissions. This has resulted in more fuel efficient oils being developed by lowering the viscometrics and by adding friction modifiers. The emissions reductions have resulted from lowering the percent phosphorus (% P) in the engine oils because phosphorus has been found to poison the catalyst in the catalytic converter. When friction modifiers were introduced, researchers from four Japanese motorcycle manufacturers published the results of their studies (SAE 961217) which indicated that low friction oil cn cause too much slippage in starter motor clutches, one-way limited slip clutches, and wet multi-plate clutches. In that same study they reported that engine manufacturers use 10W-30 grade oil to develop new engine technology, and gear pitting was observed with oils of viscosity grades lower than 10W-30 in all four manufacturers’ motorcycle engines. Since that study, the % P has been lowered in engine oils as the API categories have evolved from SG (no % P limit) to SH (0.12% P) to SJ/SL (0.10% P) to SM (0.08% P). The phosphorus from zinc dithiophosphate is known to form a protective film between metal parts which provides protection against wear and gear pitting if the oil film becomes too thin. During the development of a 10W-30 API SJ motorcycle oil, gear pitting was observed when testing was conducted in a CBR600 engine. Since the % P was limited by the API SJ category and the oil film thickness was limited by the 10W-30 viscosity grade, the solution was to use an extremely shear stable viscosity modifier, not typically used in passenger car applications, to ensure minimum shearing, therefore maintaining the oil film thickness in this motorcycle engine. The use of this extremely shear stable viscosity modifier technology therefore will enable lower % P 10W-30 oils, formulated to meet API SJ or higher categories for pass