PSI - Issue 57

Dr.-Ing. D. Jbily et al. / Procedia Structural Integrity 57 (2024) 199–216 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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= , ≥ ,

(1) , = min ( , ) the minimum specific lubricant film thickness in the contact area , the local specific lubricant film thickness the permissible specific lubricant film thickness , minimum required safety factor ISO/TS 6336-22 does not give advice on the value of the minimum safety factor to be respected to avoid the risk of micropitting. Instead, it provides a guidance for the selection of its value depending on the qualitative reliability of the assumptions on which the calculations are based and according to the reliability requirements. The local specific thickness of the lubricant film is dimensionless parameter defined by ISO 6336-22 as the ratio between the thickness ( h Y ) of the lubricant film and the average roughness of the surfaces in contact. = ℎ (8) With: = 0.5 ∗ ( 1 + 2 ) (9) Where: ℎ is the local thickness of the lubricant film is the arithmetic mean effective roughness value 1 is the arithmetic mean roughness of the pinion 2 is the arithmetic mean roughness of the gear wheel The local lubricant film thickness, h Y , is calculated according to the approach of Dowson/Higginson. ℎ = 1600 ∙ , ∙ 0.6 ∙ 0.7 ∙ −0.13 ∙ , 0.22 (10) Where: ρ n,Y is the normal radius of relative curvature at point Y G M is the material parameter U Y is the local velocity parameter W Y is the local load parameter S GF,Y is the local sliding parameter The technical specification ISO/TS 6336-22 defines two methods A and B to determine the local specific lubricant film thickness: • For method A, the local specific lubricant film thickness can be determined in the complete contact area by any appropriate gear computing program. • Method B is simplified method based on the assumption that the determinant local specific lubricant film thickness occurs on the tooth flank in the area of negative sliding. The calculation of the local specific lubricant film thickness is limited to certain points on the path of contact. To determine the permissible specific lubricant film thickness, λ GFP , two methods may also be applied according to ISO 6336-22 : • For Method A, the value of λ GFP is determined based on experimental investigations or service experience relating to micropitting real gears. Such experimental investigations can be performed on