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The propeller shaft comprises a transmission shaft 10 consisting of a hollow metal tube 11 with excellent torque transmissibility and a composite material prepregs 12 having higher specific stiffness than a metal material and stacked to the inner surface of the metal tube, and metal yokes 40 mounted

The propeller shaft comprises a transmission shaft 10 consisting of a hollow metal tube 11 with excellent torque transmissibility and a composite material prepregs 12 having higher specific stiffness than a metal material and stacked to the inner surface of the metal tube, and metal yokes 40 mounted on both ends of the transmission shaft and assembled with other devices. The composite material prepregs is co-cure bonded while applying an axial compressive preload to the transmission shaft and creating a vacuum in a space between a vacuum bag inserted in the transmission shaft and the composite material prepregs of the transmission shaft. Teeth 43 or embossments 44, and adhesive-retaining grooves 45 are formed on inner surfaces of the metal yokes, so the transmission shaft is desirably compression-fitted into the metal yokes. Accordingly, the propeller shaft has advantages of securing improved impact, abrasion, and water resistance.

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1. A method of manufacturing a propeller shaft, which includes a transmission shaft having a metal tube and a high specific modulus composite material prepregs stacked to an inner surface of the metal tube, and yokes mounted on both ends of the transmission shaft, comprising the steps of:stacking th

1. A method of manufacturing a propeller shaft, which includes a transmission shaft having a metal tube and a high specific modulus composite material prepregs stacked to an inner surface of the metal tube, and yokes mounted on both ends of the transmission shaft, comprising the steps of:stacking the composite material prepregs to the inner surface of the metal tube; co-cure bonding the composite material prepregs stacked to the inner surface of the metal tube while applying pressure to the surface of the composite material prepregs; and mounting the yokes on both ends of the transmission shaft; wherein the stacking step comprises a first step of preparing composite material prepregs; a second step of wrapping the composite material prepregs around a mandrel; a third step of inserting the mandrel wrapped with the composite material prepregs into the metal tube; and a fourth step of stacking the composite material prepregs wrapped around the mandrel to the inner surface of the metal tube; and wherein a protective layer is stacked to the composite material prepregs so as to improve a damping capacity of the propeller shaft, and the composite material prepregs is wrapped around the mandrel in such a way that the protective layer is placed between the composite material prepregs and the mandrel in the second step. 2. The method as set forth in claim 1, wherein the co-cure bonding step comprises a first step of fitting caps to both ends of the transmission shaft; a second step of sequentially inserting the vacuum bag and an pre-compression shaft through central holes of the caps into the transmission shaft; a third step of rotatably fitting a jig, rotatably assembled with one of the caps, around the pre-compression shaft; and a fourth step of rotating the jig to apply a pre-compression to both sides of the metal tube while creating vacuum in a space between the vacuum tube and the composite material prepregs.3. The method as set forth in claim 2, wherein rings or rubber plates are provided between the caps and end portions of the metal tube so as to airtightly close the space between the vacuum bag and the composite material prepregs.4. The method as set forth in claim 3, wherein a vent is formed in a lateral part of each of the caps to evacuate air from the space between the vacuum tube and the composite material prepregs.5. The method as set forth in claim 2, wherein dummy plugs are assembled with the caps and fitted around the pre-compression shaft to airtightly seal intervals between the pre-compression shaft and the central holes of the caps in the second step.6. The method as set forth in claim 2, wherein a thrust bearing is assembled with any one of the caps and the jig in such a way that the thrust bearing is located between them to reduce torque caused by rotation of the jig in the third step.7. The method as set forth in claim 1, wherein the metal tube is pre-heated to facilitating the stacking of the composite material prepreg to the inner surface of the metal tube before the fourth step.8. The method as set forth in claim 1, wherein, in the fourth step, the mandrel rolls along the inner surface of the metal tube while the metal tube being immobilized.9. The method as set forth in claim 1, wherein, in the fourth step, the mandrel is immobilized and the metal tube rotates about an axis eccentric to an axis of the mandrel.10. The method as set forth in claim 1, wherein the yokes are compression-fitted around the both ends of the transmission shaft while teeth or embossments formed on inner surfaces of the yokes bite an outer surface of the metal tube.11. The method as set forth in claim 10, wherein the yokes are heated before being fitted around the both ends of the metal tube.12. The method as set forth in claim 10, wherein an adhesive is pasted on inner surfaces of the yokes or around outer surfaces of the both ends of the metal tube before the yokes are fitted around the metal tube.13. The method as set forth in claim 10, wherein rubber packings are inserted to inner surfaces of the yokes to prevent moisture or impurities from infiltrating into the yokes when the yokes are fitted around the both ends of the metal tube.14. The method as set forth in claim 10, wherein inserts having an outer diameter almost the same as an inner diameter of the metal tube are inserted into the metal tube before the yokes are fitted around the both ends of the metal tube.15. A method of manufacturing a propeller shaft, which includes a transmission shaft having a metal tube and a high specific modulus composite material prepregs stacked to an inner surface of the metal tube, and yokes mounted on both ends of the transmission shaft, comprising the steps of:stacking the composite material prepregs to the inner surface of the metal tube; co-cure bonding the composite material prepregs stacked to the inner surface of the metal tube while applying pressure to the surface of the composite material prepregs; and mounting the yokes on both ends of the transmission shaft; wherein the stacking step comprises the steps of inserting a hollow mandrel into the vacuum bag; wrapping the composite material prepregs around the vacuum bag, said composite material prepregs wrapped around the vacuum bag having an outer diameter almost the same as or slightly smaller than an inner diameter of the metal tube; and inserting the hollow mandrel wrapped with the composite material prepregs into the metal tube. 16. The method as set forth in claim 15, wherein the co-cure bonding step comprises a first step of fitting caps around both ends of the metal tube; a second step of inserting a pre-compression shaft into the hollow mandrel in such a way that the pre-compression shaft is inserted through central holes of the caps; a third step of rotatably fitting a jig, rotatably assembled with any one of the caps, around the pre-compression shaft; and a fourth step of rotating the jig to apply the pre-compression load to both sides of the metal tube while creating vacuum in a space between the vacuum bag and the composite material prepregs.