tailieunhanh - Engineering Tribology 2E Episode 5

Tham khảo tài liệu 'engineering tribology 2e episode 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 156 Engineering Tribology Eccentricity Figure Relationship between Petroff multiplier and eccentricity ratio for infinitely long 360 bearings 8 . eccentricity ratio until an eccentricity ratio of about is reached. Although the operation of bearings at the highest possible levels of Sommerfeld number and eccentricity ratio will allow minimum bearing dimensions and oil consumption the optimum value of the eccentricity ratio as already mentioned is approximately . Interestingly the optimal ratio of maximum to minimum film thickness for journal bearings is much higher than for pad bearings as is shown below at 0 0 where film thickness is a maximum h1 c 1 and at 0 n where film thickness is a minimum h0 c 1 - so that the optimal inlet outlet film thickness ratio for journal bearings is 1 1 0 7 . This ratio is higher than for linear pad bearings for which it is ho 1 - 1 - g ap g equal to . There is a noticeable discrepancy in optimum ratios of maximum to minimum film thickness but strictly speaking these two ratios are not comparable. in the case of linear pad bearings classical theory predicts a maximum load capacity while for journal bearings there is no maximum theoretical capacity instead a limit is imposed by theoretical considerations. When cavitation effects are ignored the friction coefficient for a bearing with the Half-Sommerfeld condition is _ 8Rc 1 -- 2 1 5 g L2 2 1 0 5 Lubricant Flow Rate For narrow bearings the flow equation is simplified since dp dx 0 and is expressed in the form Hydrodynamic Lubrication 157 Uh qx 2 and the lubricant flow in the bearing is c Ld c U UhL Qx Jo dy 2 Substituting for h from gives the flow in the bearing Qx ULc 1 e cos 0 in order to prevent the depletion of lubricant inside the bearing the lubricant lost due to side leakage must be compensated for. The rate of lubricant supply can be calculated by applying the boundary inlet-outlet conditions to equation . .