e smaller than the cumulative flow cross sections of said ducts 22 and smaller than that of the ducts 31 19 of the pipe 27 and of the recess 25 the flow cross section of the duct 24 is a calibrating flow cross section that is intended for calibrating the pressure of the oil supplying the bearing 14 as the flow cross sections of the ducts 22 and of the ducts 31 19 are larger than that of the duct 24 the oil pressure will barely change while flowing in the ducts 22 and will therefore be substantially the same in the cavities 20 and 23 moreover the cavities 23 and 20 are designed so as to change this pressure as little as possible fig4 shows a variant in which it is the ducts 19 that provide the oil pressure calibration function the flow cross section defined by the ducts 19 cumulative flow cross sections of said ducts 19 is smaller than that of the duct 24 and smaller than that of the ducts 31 22 cumulative flow cross sections of said ducts 31 22 of the pipe 27 and of the recess 25 the flow cross section of the ducts 19 is a calibrating flow cross section that is intended for calibrating the pressure of the oil supplying the bearing 14 the pressure of the oil will therefore be changed while flowing in the ducts 19 and will be higher in the cavity 20 than in the cavity 23 other configurations may result from adding or eliminating parts between the internal part.