The Design of Rolling Bearing Mountings

55 Bevel gear transmission for city trainsWith a so-called two-axled longitudinal drive in undergroundand metropolitan vehicles the traction motor(usually direct current motor) is arranged in the bogiein the direction of travel. A bevel gear transmission isflanged onto both sides of the motor's face. The driveunit firmly attached to the bogie frame is elasticallysupported by the wheel sets. The drive power is transmittedfrom the pinion shaft to the hollow ring gearshaft and then via rubber couplings to the drivingwheel shaft. This drive design leads to good runningbehaviour and moderate stressing for the traction motor,transmission and track superstructure.Machining tolerancesCylindrical roller bearing: Shaft m6, housing M6Tapered roller bearing/motor end:Shaft m6, sleeve M6Tapered roller bearingwith mantle ring: Shaft m6, ring R6 (S7)Tapered roller bearingof ring gear shaft: Shaft n6 – p6housing K6 – M6The axial clearance of the tapered roller bearing pairdepends on gearing and the operating conditions.Dimensioning, bearing selectionMean torques and speeds (hourly torque, hourlyspeed) are calculated from the tractive force – surfacespeed diagram and the time shares for the various runningconditions. By means of the gearing data thetooth loads of the hypoid bevel gear step are calculatedand, depending on the lever arms, are distributed tothe bearing locations.A life of 20,000 to 30,000 hours is assumed for bearingdimensioning. Assuming an average travel speed thiscorresponds to 1.2 – 1.3 million kilometers.To check the static safety of the bearings the maximumtorque (slippage torque) is taken as a basis.LubricationOil sump lubrication provides the transmission bearingswith lubricant. The flinger oil is conveyed via thering gear from the oil sump and fed directly to thetransmission bearings via oil collecting bowls and supplyducts. The special driving conditions for city trainsdemand highly doped oils which are resistant to heatand corrosion.Pinion shaftA single-row cylindrical roller bearing FAGNJ2224E.M1A.C3 (120 x 215 x 58 mm) is mountedas a floating bearing at the pinion end. It accommodatesthe high radial loads. The machined cage of thebearing is guided at the outer ring. The bearing has theincreased radial clearance C3 since the bearing ringshave a tight fit on the shaft and in the housing. Two taperedroller bearings FAG 31316 (80 x 170 x 42.5mm) are used as locating bearings. They are mounted inpairs in O arrangement. The bearing at the motor endaccommodates the radial loads as well as the axial loadsfrom the gearing; the other tapered roller bearing onlyaccommodates the axial loads arising during a changein direction of rotation. A minimum bearing load is arequirement in order to avoid harmful sliding motion(slippage) and premature wear. The cups of thetapered roller bearings are therefore preloaded withsprings.Ring gear shaftThere is a tapered roller bearing with the dimensions210 x 300 x 54.5 mm at each side of the ring gear.Both bearings are adjusted in X arrangement.55: Bevel gear transmission for city trainsFAG 78