referring to fig1 and 2 , an embodiment of the present invention will be described . fig1 is an axial sectional view of a liquid cooled a . c . generator and fig2 is a partial cutaway elevational view of fig1 wherein same reference characters designate corresponding component parts of the aforementioned conventional liquid cooled a . c . generator and the description of them will be omitted . in fig1 and 2 , numeral 25 denotes a tube trough to be closed with a bracket cover 17 provided in a rear bracket 12 . one end 25a of the tube trough is connected to an inlet pipe 14 , whereas the other end 25b communicates with the internal space 27 of the rear bracket 12 via a through - hole 26 . further , numeral 28 denotes a through - hole for allowing the internal space 27 to communicate with an outlet pipe 15 , and 29 a good thermoconductive tube forming the cooling - fluid passage , the thermoconductive tube being made of thermoconductive , flame - and heat - resistant silicone rubber . first , the tube 29 is passed through the through - hole 26 of the rear bracket 12 in such a state that the rear bracket 12 is free from the bracket cover 17 before being fitted to the body of a front bracket 8 . the tube 29 projected inside the rear bracket 12 is wound twice in the internal space 27 and then the rear end 29a of the tube 29 is fitted into the outlet pipe 15 via the through - hole 28 . then the tube 29 projected outside the rear bracket 12 is forced through the tube trough 25 and the rear end 29b of the tube 29 is fitted into the inlet pipe 14 . after the rear bracket 12 is fixed to the body , the bracket cover 17 is secured thereto so as to contain the tube 29 in the tube trough 25 and the internal space 27 . when the pressure of the cooling fluid is applied to the tube 29 in this state , it will be inflated and settled in position as shown in fig1 and 2 . seals can thus be dispensed with since the cooling - fluid passage is formed with one tube 29 and the watertightness is improved . the low - temperature cooling fluid introduced from the inlet pipe 14 starts cooling the rectifier 19 , the voltage regulator 21 and the bearing 13 which are giving off low - temperature heat and then flows into the stator coil 7 having high - temperature heat before flowing out of the outlet pipe 15 . therefore , the cooling operation can be performed with efficiency . moreover , a greater cooling effect is achievable as the stator coil 7 that has conventionally been cooled indirectly can be cooled directly by the tube 29 . if the opening formed on the outer periphery of the tube 29 housed in the tube trough 25 and the internal space 27 as shown in fig3 according to the first aspect of the present invention is filled with a thermoconductive filler 30 , not only the pressure resistance but also the thermoconductivity of the tube 29 improves , thus increasing the cooling efficiency further . although the front side is to be air - cooled by the fan 11 according to the first and second aspects of the present invention , the front side like the rear side may be water - cooled by the tube in order to water - cool the whole structure . as set forth above , the cooling - fluid passage formed with one tube according to the present invention has the effect of making such a liquid cooled a . c . generator less costly and also improving its watertight reliability and cooling efficiency .