AGMA 10FTM12

The lubrication of gears has two major functions: Reducingfriction and wear as well as dissipating heat. The power losses,especially the no-load losses, decrease with decreasing immersiondepth using dip lubrication. The load-dependent gear power lossesare nearly unaffected by minimized lubrication. However, the gearbulk temperatures rise dramatically by using minimized lubricationdue to a lack of heat dissipation. With minimized lubrication thescuffing load carrying capacity decreased by up to morethan60%compared to rich lubrication conditions. The dominatinginfluence of the bulk temperature is therefore very clear. Starvedlubrication leads to more frequent metal – to contact and thegeneration of high local flash temperatures must be considered. Anadditional factor for the scuffing load carrying capacitycalculation in case of minimized lubrication conditions isproposed. Concerning pitting damage test runs showed that bylowering the oil level the load cycles without pitting damagedecreased by approximately 50% up to 75% for minimized lubricationcompared to the results with rich lubrication conditions. Theallowable contact stress is clearly reduced (up to 30%) byminimized lubrication. A reduced oil film thickness as aconsequence of increased bulk temperatures results in more frequentmetal-to-metal contacts causing a higher surface shear stress. Incombination with a decreased material strength due to a possibletempering effect at high bulk temperatures the failure risk ofpitting damage is clearly increased. The common pitting loadcarrying capacity calculation algorithms according to DIN/ISO areonly valid for moderate oil temperatures and rich lubricationconditions. For increased thermal conditions, the reduction of thepitting endurance level at increased gear bulk temperatures can beapproximated with the method of Knauer (FZG TU München, 1988). Anadvanced calculation algorithm for pitting load carrying capacitycalculation at high gear bulk temperatures (valid for high oiltemperatures as well as for minimized lubrication) is proposed. Themicropitting risk was increased by low oil levels, especially athigh loads and during the endurance test. The micropitting damageis caused by poor lubrication conditions which are characterized bya too low relative oil film thickness due to high bulktemperatures. Again, the actual bulk temperatures are of majorsignificance for calculation of the micropitting load carryingcapacity. The wear rate of the gears is almost unaffected by theoil level. Only a slight increase of wear could be observed withminimized lubrication. This increase can be explained by the higherbulk temperature of the gears running under minimized lubricationconditions. The investigations showed that there exists a naturallimitation for lowering the oil quantity in transmissions withoutdetrimental influence on the load carrying capacity. Knowing theselimitations enables the user to determine the possible potentialbenefits of reduced oil lubrication. The correct prediction of theactual gear bulk temperatures is of major importance in thiscontext. A method for the estimation of the gear bulk temperatureat reduced immersion depth respectively poor lubrication conditionsis proposed.

Edition:

10

Published:

10/01/2010

Number of Pages:

15

File Size:

1 file , 900 KB