The Design of Rolling Bearing Mountings

116 Axial piston machineCylinder block A accommodates a number of pistonsB symmetrically arranged about the rotational axis.Piston rods C transmit the rotation of drive shaft D tothe cylinder block. They also produce the reciprocatingmotion of the pistons, provided that the rotationalaxis of cylinder block and drive shaft are at an angle toeach other.Fluid intake and discharge are controlled via two kidney-shapedopenings E in pump housing F. Bore G establishesconnection from each cylinder to openings E.During one rotation of the cylinder block, each boresweeps once over the intake (suction) and discharge(pressure) openings. The discharge opening is subjectedto high pressure. Consequently, the pistons are actedupon by a force. This force is carried by the pistonrods to the drive shaft and from there to the drive shaftbearings.D C B A GFEBearing selectionAt relatively high speeds, bearings H and J have toaccommodate the reactions from the calculated resultantload. The bearing mounting should be simple andcompact.These requirements are met by deep groove ball bearingsand angular contact ball bearings. Bearing locationH features a deep groove ball bearing FAG 6208,bearing location J two universal angular contact ballbearings FAG 7209B.TVP.UA in tandem arrangement.Suffix UA indicates that the bearings can be universallymounted in tandem, O or X arrangement.HJIn axial piston machines only some of the pistons arepressurized (normally half of all pistons). The individualforces of the loaded pistons are combined to give aresultant load which acts eccentrically on the swashplate and/or drive flange.Operating dataRated pressure p = 100 bar = 10 N/mm 2 ; max. speedn max = 3,000 min –1 , operating speed n nom =1,800 min –1 ; piston diameter d K = 20 mm, pistonpitch circle = 59 mm, angle of inclination = 25°,number of pistons z = 7; distance between load lineand rotational axis e = 19.3 mm.eBearing dimensioningAssuming that half of the pistons are loaded, pistonloadF K = z/2 · p · d K2 . π/4 = 3.5 · 10 · 400 · 3.14/4 == 11,000 N = 11 kNFor determination of the bearing loads the piston loadF K is resolved into tangential component F Kt andthrust load component F Ka :F Kt = F K · sin = 11 · 0.4226 = 4.65 kNF Ka = F K · cos = 11 · 0.906 = 9.97 kNThe two components of the piston load produce radialloads normal to each other at the bearing locations.The following bearing loads can be calculated bymeans of the load diagram:Bearing location JF Jx = F Ka · e/l = 9.97 · 19.3/90 = 2.14 kNF Jy = F Kt · (l + t)/l = 4.65 · (90 + 10)/90 = 5.17 kNF rJ = √ F Jx2 + F Jy2 = √ 4.58 + 26.73 = 5.59 kNFAG 166