Method of manufacturing of a drive shaft made of fiber reinforced composite material

Abstract: Disclosed is a shaft having a body section (2) and a yoke section (3) formed with at least one end of the body section (2). A hole is formed in the yoke section (3). The body section (2) and yoke section (3) are integrally made of a fiber reinforced composite material including a filament (F) and a plastic adhered to the filament. The shaft comprises a plurality of shaft fiber layers forming the body section (2). Each shaft fiber layer includes a plurality of shaft fiber elements being arranged at predetermined intervals. A plurality of yoke fiber layers form the yoke section (3). Each yoke fiber layer includes a plurality of yoke fiber elements. Each yoke fiber element has ends connected to each shaft fiber element. Each yoke fiber element has either a closed loop arrangement (CLA) or an open loop arrangement (OLA). The CLA is defined by the yoke fiber elements forming closed loops around the hole. The OLA is defined by the yoke fiber elements forming open loops around the hole.

Description: The present invention relates to a method for manufacturing a shaft, in particular a drive shaft made of a fiber reinforced composite material suitable for the propeller shaft of a vehicle. The output of a transmission in an automobile is transmitted via a propeller shaft to a differential gear. The propeller shaft has yokes at both end portions which are coupled via universal joints (mainly spider joints) to the transmission and differential gear, respectively. To enhance the twisting and bending durabilities and reduce the weight of the propeller shaft, yokes are generally welded to the respective ends of its body section, which is made of a metal pipe. Even the light propeller shaft of a metal-pipe, if long, should be divided by two (three joint system) or by three (four joint systems) in consideration of the critical speed. In this case, the number of joints increases, and the number of parts and the number of assembling steps increase, resulting in a higher cost. Further, the number of parts which are to be assembled to the body of a vehicle and the number of assembling steps also increase. As a solution to the above shortcoming, a propeller shaft having a body section formed of fiber reinforced plastics (FRP) has been proposed. This material reduces the overall weight and a shaft made of this material does not need to be divided even if it is long. For example, documents JP-A-05193381 US-A-4,380,443, US-A-4,421,497 and US-A-4,681,556 disclose such shafts. Those propeller shafts comprise an FRP body section and metal yokes secured to both ends of the body section. In the propeller shaft described in document JP-A-05193381, after the FRP body section is formed, the metal yokes are fitted over the end portions of the body section and are secured there by an adhesive. The propeller shafts described in documents US-A-4,380,443 and US-A-4,421,497 have metal rings securely fitted in the end portions of the FRP body section. The end portions of the metal yokes are fitted in and welded to the metal rings. In document US-A-4,380,443, multiple pins penetrating through the body section and protruding therefrom are fixed to the metal rings to prevent the relative movement of the body section to the metal rings. In document US-A-4,421,497, roulettes are formed on the outer surfaces of the metal rings to prevent the relative movement of the body section to the metal rings. In document US-A-4,681,556, metal yoke members 52 are provided at both ends (only one shown) of a propeller shaft 50 as shown in Fig. 15. Each yoke member 52 comprises a hollow spigot portion 52a extending in the same axial direction as a body section 51 and a pair of ring-shaped transverse tubular portions 52b integrally formed at the tip of the spigot portion 52a. The method for manufacturing the shaft according to document US-A-4681556 comprises the steps of placing the metal yoke member on a mandrel and winding filaments, impregnated with a suitable resin, on the yoke member and the mandrel to form the body section of the shaft and secure the yoke member therein. Subsequent to curing of the resin, the mandrel is removed. It is a primary object of the present invention to provide an improved method for manufacturing a shaft such that the manufactured shaft has a higher durability and reliability. This object is achieved by the method according to claim 1. Further developments of this method are defined in the dependent claims. The invention, together with objects and advantages thereof, may best be understood when refering to the following description of the presently preferred embodiments together with the accompanying drawings in which: Fig. 1A is a schematic side view and Fig.1B is a schematic plan view, both showing a first embodiment of a propeller shaft of a vehicle manufactured according to the present invention; Fig. 2A is a partial schematic development view showing a filament layer in an open loop arrangement; Fig. 2B is a partial schematic development view showing a filament layer in a closed loop arrangement; Fig. 2C is a partial schematic development view showing the open and closed loop arrangements overlapping each other; Fig. 3 is a schematic perspective view showing a mandrel used in manufacturing a propeller shaft; Fig. 4 is a graph showing the relation between the ratio of the closed loop arrangement to the open loop arrangement and the torsional strength of the propeller shaft; Figs. 5A, 5B and 5C are partial schematic development views similar to those of Figs. 2A, 2B and 2C and illustrate a second embodiment; Figs. 6A, 6B and 6C are partial schematic development views similar to those of Figs. 2A, 2B and 2C and illustrate a third embodiment; Figs. 7A, 7B and 7C are partial schematic development views similar to those of Figs. 2A, 2B and 2C and illustrate a fourth embodiment; Figs. 8A, 8B and 8C are partial schematic development views similar to those of Figs. 2A, 2B and 2C and illustrate a fifth embodiment; Figs. 9A, 9B and 9C are partial schematic development views similar to those of Figs. 2A, 2B and 2C and illustrate a sixth embodiment; Figs. 10A, 10B and 10C are partial schematic development views similar to those of Figs. 2A, 2B and 2C and illustrate a seventh embodiment; Fig. 11 is a partial schematic view showing an eighth embodiment; Figs. 12A and 12B illustrate a ninth embodiment, Fig. 12A being a partial schematic development view showing filaments in an open loop arrangement while Fig. 12B is a partial schematic development view showing filaments in a closed loop arrangement; Fig. 13A is a partial cross-sectional view of a propeller shaft according to a still further modification, and Fig. 13B is a front view of the propeller shaft; Fig. 14 is a partial schematic view showing an open loop arrangement according to a still further modification; and Fig. 15 is a partial cross-sectional view showing a propeller shaft manufactured according to prior art. First Embodiment A first embodiment of a propeller shaft manufactured according to the present invention will be described with reference to Figs. 1 through 4. As shown in Fig. 1, a propeller shaft 1 of a vehicle has a cylindrical body section 2 and a pair of yoke sections 3, one formed on each end of the body section 2. The body section 2 and the yoke sections 3 are integrally formed of fiber reinforced plastics (FRP). Each yoke section 3 has a pair of support pieces 3a with a hole 4 formed in each support piece 3a. The axis of each hole 4 is perpendicular to the axis of the body section 2. A metal bushing 5 is securely fitted in each hole 4. The propeller shaft 1 of this embodiment is formed by folding a single filament F at the yoke sections 3 in such a way that a plurality of filament layers are formed at the yoke sections 3 and the body section 2. The filament F need not be a continuous single filament, but a plurality of filaments may be used. Each yoke section 3 is constructed of a plurality of fiber elements Fy of a single filament F, while the body section 2 is constructed of a plurality of fiber elements Fs. Hoops 6 are formed on the outer surfaces of the body section 2 at its ends. A heat-shrinkable film (e.g., polyester film) is wound on the outermost surface of the body section 2. In place of the film, a heat-shrinkable tape or a heat-shrinkable fiber may be wound on the body section 2 in a layered form. In folding the filament F at the yoke sections 3, there are two types of arrangements for the individual fiber elements Fs and Fy in the individual filament layers. In one arrangement, after the fiber element Fy is folded at each yoke section 3, the fiber element Fy does not intersect a plane P containing the center of the hole 4 and the axis of the body section 2 above a line L as shown in Fig. 2A. This arrangement is called a U-shaped arrangement or an open loop arrangement (hereinafter abbreviated as "OLA"). In the other arrangement, after the filament F is folded at each yoke section 3, the filament F intersects the plane P above the line L as shown in Fig. 2B. This arrangement is called an X loop arrangement or a closed loop arrangement (hereinafter abbreviated as "CLA"). Figs. 2A through 2C are schematic development views showing the arrangements of the filament F on nearly the left half of the propeller shaft 1 as viewed in Fig. 1B. Fig. 2A shows the OLA, Fig. 2B shows the CLA, and Fig. 2C shows both the OLA and CLA overlapping each other. The actual number of fiber elements arranged is considerably larger than the illustrated one, but the fiber elements are partially omitted in the illustrations for the sake of diagrammatic convenience. In the diagrams, the portion above the line L corresponds to the yoke section 3 and the portion below the line L corresponds to the body section 2. (Similar illustrations will be given for the other embodiments.) The plane P is perpendicular to each drawing sheet. In each diagram, the left-hand side of a line C shows the propeller shaft 1 developed over a half circumference, and the right-hand side of the line C shows the propeller shaft 1 developed over the remaining half circumference. The fiber elements Fs forming the same layer in the body section 2 are arranged obliquely at predetermined pitches so that the angles  1 between the fiber elements Fs and the axis of the body section 2 become nearly equal to one another. The angle  1 is set to a predetermined value which satisfies the characteristics such as bending, torsion, and vibration, which are required for a particular application. In this embodiment, the angle  1 is set to around ±10 degrees. In other words, assuming that the fiber elements Fs in the filament layer having the OLA shown in Fig. 2A and the CLA shown in Fig. 2B have the angle  1 of +10 degrees, then there are fiber elements Fs which have an angle of -10 degrees. Therefore, when filament layers having different arrangement angles are sequentially overlapped, the arrangement shown in Fig. 2C can be attained. A carbon fiber, glass fiber, aramid fiber and the like may be used as the filament F used in the FRP. A thermosetting resin, such as an epoxy resin, vinyl ester resin, unsaturated polyester resin or phenol resin, may be used as the matrix in the FRP. Those fibers and resins are properly combined to satisfy the demanded characteristics. Of the mentioned fibers, the carbon fiber is the best choice in view of the strength and weight reduction, and the glass fiber is the second best choice. As the matrix, the epoxy resin is the best choice with respect to heat resistance and moisture resistance. In this embodiment, the combination of the carbon fiber and epoxy resin is employed. A spider joint is rotatably attached via a bearing to the bushing 5 of each yoke section 3. Since the body section 2 and the yoke sections 3 are formed integrally, the propeller shaft 2 and the yoke sections 3 deform in nearly the same way when the propeller shaft 1 expands or shrinks in accordance with a change in temperature. Unlike the prior art shaft where the body section 2 and the yoke sections 3 are made of different materials, the fatigue properties of the present propeller shaft 1 are improved thus extending its service life. Further, the propeller shaft 1 can be made lighter than the conventional FRP propeller shaft. The general shape of the yoke section 3 is determined by the filament layer in the OLA shown in Fig. 2A. It has been proven that the mechanical strengths, such as torsional strength and torsional rigidity, demanded for the propeller shaft 1 are satisfied even where the propeller shaft 1 is constructed of only the filament layers in the OLA. With the use of only the filament layers in the OLA, however, there remains a gap 7 between the bushing 5 and the body section 2 which has an undesirable shape. The filament layers in the CLA are arranged to close the gap 7 as shown in Fig. 2B. The filament layers in the CLA contribute to the torsional strength more than the filament layers in the OLA. If the number of the filament layers in the CLA increases too much, the space between the bushing 5 and the body section 2 expands outward deteriorating the appearance. By combining the filament layers in the OLA and filament layers in the CLA, the propeller shaft 1, which is satisfactory in shape and material, can be obtained. The number of the filament layers constituting the body section 2, which is normally about four to twenty, is determined by the productivity and material requirements. The torsional strength, the torsional rigidity, and the shape of the propeller shaft 1 were evaluated while changing the proportion of the filament layers in the OLA to the filament layers in the CLA. The torsional strength was evaluated for the CLA proportion of 0%, 25%, 50%, 75% and 100%, and the torsional rigidity was evaluated only for those CLA proportions for which the torsional strength reached the target value. The shape evaluation was conducted also for CLA proportions other than those mentioned above. The results are shown in Fig. 4. In Fig. 4, the four evaluation marks indicate the following. X: defect Δ: normal ○: good o ○: excellent The torsional strength exceeded the target value in every case except for the case where the CLA proportion is 100%. The torsional strength tended to increase with an increase in the CLA proportion until the CLA proportion became 75%. Accordingly, the combination of the OLA proportion of 20 to 100% and the CLA proportion of 80 to 0% is preferable. The combination of the OLA proportion of 55 to 70% and the CLA proportion of 45 to 30% is more preferable, and the combination of the OLA proportion of 60 to 65% and the CLA proportion of 40 to 35% is the most preferable. In any case, the total of the OLA proportion and CLA proportion comes to 100%. A method of manufacturing the propeller shaft 1 will now be described. The propeller shaft 1 is produced by a filament winding method. As shown in Fig. 3, a mandrel 8 has a cylindrical metal body 80 with support pins 9 detachably inserted in both ends. The support pins 9 serve to form the holes 4 of the associated yoke sections 3 of the propeller shaft 1. Multiple protruding pins 10 are radially arranged in a detachable manner on the mandrel body 80 at predetermined intervals in the circumferential direction at positions corresponding to the boundaries between the body section 2 and the yoke sections 3. The bushing 5 is fitted over each support pin 9 of the mandrel 8, and a bushing cover (not shown) is attached to the outer surface of the bushing 5. At this time, a clearance is formed between the end face of the cover and the mandrel 8. Then, the mandrel 8 is set to a filament winding machine (not shown) which can undergo multi-axis control. The filament winding machine should control the mandrel 8 in at least the rotational direction and the axial direction. However, a preferable filament winding machine is of a three-axes control type which can control the mandrel 8 in a direction perpendicular to the axial direction in addition to the rotational and axial directions. Next, the filament winding machine is activated to control the rotation of the mandrel 8 and the movement of the thread guide section of the winding machine, so that the filament F is wound on the mandrel 8 while being impregnated with a thermosetting resin. In winding the filament F, first, the filament F is wound on the mandrel body 80 corresponding to the body section 2 at a predetermined angle. Then, the filament F is folded back along the circumferential direction of the bushing 5 to change the direction of the arrangement. The filament wound around the bushing 5 is located between the mandrel 8 and the bushing cover. The filament F is wound on the body 80 such that a predetermined proportion of the OLA to the CLA is obtained at each yoke section 3 thus forming a plurality of filament layers. After the number of filament layers reaches a predetermined value, hooping is carried out inward of each ring of the pins 10 at both ends of the body 80 to complete the winding of the filament F. Next, the pins 10 are detached from the body 80 and a heat-shrinkable film, such as a polyester film, is wound on the outer surfaces of the cylindrical filament layers on the mandrel 8. Then, the mandrel 8 with the filament layers and the film is placed in a curing oven to be cured at a predetermined temperature. The curing temperature, which differs depending on the resin in use, is, for example, about 180°C for an epoxy resin. Finally, the bushing cover and the support pins 9 are removed from the body 80. Then, the body 80 is pulled out of the filament layers to complete the propeller shaft 1. The hoops at both ends of the body section 2 prevent the disturbance of the filament arrangements at the end portions of the body section 2 until the thermosetting of the resin is completed after the removal of the pins 10. The heat-shrinkable film, like the hoops, prevents the disturbance of the filament arrangements and improves the appearance of the propeller shaft 1. The heat-shrinkable film also improves the shock resistance of the propeller shaft 1 when it is in use. If a small stone or the like hits the propeller shaft 1 while the vehicle is running, for example, the propeller shaft 1 can endure the impact due to the heat-shrinkable film wound around its outer surface. A description will now be given of an example of procedures for forming one filament layer of the body section 2 in the OLA. A first arrangement layer A1 shown on the left-hand side in Fig. 2A is produced to form one of the pair of support pieces 3a of the yoke section 3 shown on the left-hand side in Fig. 1A. A second arrangement layer A2 shown on the right-hand side in Fig. 2A is produced to form the other support piece. The formation of the first arrangement layer A1 will be explained in accordance with numerals (1), (2) and (3) in Fig. 2A. The filament F is wound on the body 80 of the mandrel 8 along the leftmost line (1) of the first arrangement layer A1. Next, the filament F is engaged with one pin 10 (not shown in Fig. 2A; see Fig. 3), changing its arrangement direction, and is folded back around the bushing 5. At this time, the filament F is folded back in symmetry to the plane P. Then, the filament F is engaged with another pin 10, again changing its arrangement direction, and is laid out along the rightmost line (2) of the first arrangement layer A1. Thereafter, the filament F is folded back at the yoke section 3 at the opposite end of the shaft (on the right-hand side in Fig. 1A). Then, the filament F is laid out along the line (3) which is located one pitch inward of the line (1). Thereafter, the filament is sequentially shifted inward by one pitch in the same manner, thus forming the first arrangement layer A1. After the formation of the first arrangement layer A1, the second arrangement layer A2 is formed inward line by line in the same way as the first arrangement layer A1. The angles  1 at which the individual fiber elements Fs constituting a single layer on the body section 2 intersect the axis of the body section 2 are nearly the same. Subsequent layers are formed in substantially the same manner as described for the above case. In subsequent layers, the angle  1 may be opposite to that of the previous layer and the arrangement may be OLA or CLA. In folding the filament F back at the yoke section 3, the fiber portion leading into and the fiber portion leading away from the fold need not always be symmetrical to the plane P. In the case where the portion of the fiber element Fy leading into the fold is located outermost on the left-hand side of the yoke section 3 as shown in Fig. 2A, for example, the portion leading away from the fold may be located innermost (near the plane P) on the right-hand side of the yoke section 3. In this case, though not illustrated, the portion leading into the fold is gradually shifted inward on the left-hand side of the yoke section 3 while the folded end (leading away) of the fiber element Fy is gradually shifted outward on the right-hand side of the yoke section 3. Second Embodiment A second embodiment will be described below with reference to Fig. 5. This embodiment differs from the first embodiment in the arrangement of the fiber element Fs on the body section 2 of the propeller shaft 1. The other structures are the same as those of the first embodiment. In the second embodiment, half of the fiber elements Fs constituting the same layer on the body section 2 are inclined symmetrically to the remaining half with respect to the plane P. For a fiber reinforced composite material, generally speaking, the fiber reinforcing effect becomes small at a place where the filaments constituting the composite material are more sharply bent. When the angles  1 between the individual fiber elements Fs constituting the same layer on the body section 2 and the axis of the body section 2 are the same as in the first embodiment, the angle  2 between the fiber element Fs and the fiber element Fy in the CLA is relatively large. In other words, the angle  2 between the fiber element Fs and the fiber element Fy, both located on the right-hand side of the plane P in Fig. 2B, is relatively large and the reinforcing effect by the filaments near the interface portion between the yoke section 3 and the body section 2 is relatively weaker because a large angle  2 corresponds to a sharper bend by the fibers at the interface between the body and the yoke. In contrast to the first embodiment, the angle of bend  2 between the fiber element Fs and the fiber element Fy in the CLA shown in Fig. 5B is smaller than the angle of bend  2 shown in Fig. 2B. Therefore, the reinforcing effect by the filaments near the interface portion between the yoke section 3 and the body section 2 is stronger as compared with the propeller shaft 1 of the first embodiment. The other function and advantages of the second embodiment are the same as those of the propeller shaft 1 of the first embodiment. The propeller shaft 1 is manufactured using the same mandrel 8 and method as used in the first embodiment. Third Embodiment A third embodiment will now be discussed with reference to Fig. 6. The propeller shaft 1 of this embodiment is essentially the propeller shaft 1 of the second embodiment where the arrangement of the filament F is partly changed. In the third embodiment, while the arrangement of the fiber element Fs on the body section 2 is the same as that of the second embodiment, a part of the arrangement of the fiber element Fy at the yoke section 3 is different from that of the second embodiment. In the second embodiment, as shown in Figs. 5A and 5B, the fiber elements Fs constituting the same layer on the body section 2 are continuous with fiber elements Fy forming only an OLA or forming only a CLA at the yoke section 3. In the third embodiment, however, some fiber elements Fs constituting the same layer on the body section 2 are continuous with fiber elements Fy arranged in both an OLA and a CLA. More specifically, the outer fiber element Fs in a given filament layer, whose angle of bend  2 becomes relatively large when the CLA is used, is continuous with the fiber element Fy whose arrangement is changed to an OLA as shown in Fig. 6B. As a result, the maximum angle of bend  2 for the whole layer is reduced. As compared with the propeller shaft 1 of the second embodiment, therefore, the reinforcing effect by the filaments near the interface portion between the yoke section 3 and the body section 2 is further improved. The other function and advantages and the method of the third embodiment are the same as those of the second embodiment. Fourth Embodiment A fourth embodiment will now be discussed with reference to Fig. 7. The propeller shaft 1 of this embodiment is essentially the propeller shaft 1 of the first embodiment where the arrangement of the fiber element is partly changed. In the fourth embodiment, while the arrangement of the fiber element Fs on the body section 2 is the same as that of the first embodiment, the arrangement of the fiber element Fy at the yoke section 3 partly differs. In the first embodiment, the fiber elements Fs constituting the same layer on the body section 2 are continuous with fiber elements Fy forming only an OLA or only a CLA at the yoke section 3. In the fourth embodiment, however, the fiber elements Fs constituting the same layer on the body section 2 are continuous with fiber elements Fy arranged in both an OLA and a CLA as shown in Fig. 7A. More specifically, the arrangement of outermost fiber element Fy at the yoke section 3 in the first embodiment when the OLA is used, is changed to the CLA as shown in Fig. 7A. Therefore, the yoke section 3 of the propeller shaft 1 of this embodiment becomes narrower than those in the above-described embodiments. Accordingly, the distance D (Fig. 7C) between the support pieces 3a constituting the yoke section 3 becomes wider. This reduces the possibility of interference of the yoke sections with the mating yokes of a vehicle when the propeller shaft 1 is installed. The other function and advantages and the method are almost the same as those of the first embodiment. Fifth Embodiment A fifth embodiment will now be discussed with reference to Fig. 8. The fiber elements Fs on the body section 2 in this embodiment have straight sections Fss. The fifth embodiment differs significantly from the first embodiment in that there are a plurality of bending points (two in this embodiment) Pb between the fiber element Fs on the body section 2, which has the angle  1 , and the fiber element Fy at the yoke section 3. Therefore, the angle of arrangement  1 of each fiber element at the end of the body section 2 differs from that of the same fiber element at the intermediate portion of the body section 2. As shown in Fig. 8A, the straight sections Fss of each fiber element Fs in the OLA are arranged in parallel to the axis of the body section 2 at the end portion thereof. As shown in Fig. 8B, the individual fiber elements Fs in the CLA are arranged at angles of almost ±45 degrees with respect to the axis of the body section 2 at the end portion thereof. Those fiber elements Fy in the CLA which are located on opposite sides of the plane P at the folding portion, are inclined on the body section 2 in symmetry to the plane P. Further, only those fiber elements Fy in the CLA which are located on the left-hand side of the plane P at the folding portion of the yoke section 3, are arranged to be continuous with one layer of the fiber elements Fs on the body section 2. Therefore, the fiber elements Fy on both sides of the plane P are continuous with two layers of the fiber elements Fs on the body section 2. In this embodiment, the fiber elements Fs at the end portion of the body section 2 are continuous with the fiber elements Fy at the yoke section 3 after its angle of arrangement is changed once so that the maximum value of the angle of bend  2 between the fiber elements Fs and the fiber elements Fy is smaller than that of the first embodiment. Further, the arrangement of the filament F becomes easier. The propeller shaft 1 of the fifth embodiment is manufactured by the filament winding method using the mandrel 8 which has two lines of pins 10 in association with each end portion of the body section 2. When the filament F is wound on the mandrel 8, it engages the individual pins 10 to change the arrangement direction or the angle of arrangement. Sixth Embodiment A sixth embodiment will now be discussed with reference to Fig. 9. The sixth embodiment differs significantly from the above-described embodiments in that the positions of the bending points Pb between the fiber element Fy at the yoke section 3 and the fiber element Fs on the body section 2 in the same layer are shifted in the axial direction of the body section 2. The other structure is fundamentally the same as that of the second embodiment. As shown in Figs. 9A and 9B, the bending points Pb of the filament F in the OLA and CLA are located on the boundary between the yoke section 3 and the body section 2 or are located on the yoke section (3) side with respect to the boundary. The maximum value of the angle of bend  2 of the filament F in the sixth embodiment is also smaller than that of the first embodiment so that this embodiment exhibits the same function and advantages as the second embodiment. As the bending points Pb of the filament F of the propeller shaft 1 according to this embodiment are dispersed, the strengths of the yoke section 3 and the area near the interface portion between the yoke section 3 and the body section 2 are improved. The propeller shaft 1 of this embodiment is manufactured by the filament winding method using the mandrel 8 which has plural lines of pins 10 in association with each end portion of the body section 2. When the filament F is wound on the mandrel 8, the filament F engages the individual pins 10 to change the arrangement direction or the angle of arrangement. Seventh Embodiment A seventh embodiment will now be discussed with reference to Fig. 10. As shown in Fig. 10A, the fiber elements Fs in the OLA are arranged nearly parallel to the axis of the body section 2. As shown in Fig. 10B, the individual fiber elements Fs in the CLA are arranged at angles of almost ±45 degrees with respect to the axis of the body section 2. Further, only those fiber elements Fy in the CLA which are located on the left-hand side of the plane P at the folding portion of the yoke section 3 are arranged to be continuous with one layer of the fiber elements Fs on the body section 2 (as in the fifth embodiment). Therefore, the fiber elements Fy on both sides of the plane P are continuous with two layers of fiber elements Fs on the body section 2. In other words, in this embodiment, the maximum value of the angle of bend  2 between the fiber elements Fs and the fiber elements Fy is smaller than that of the propeller shaft 1 of each embodiment described earlier and the strength of the yoke section 3, particularly the strength to the torsional torque, is further improved. The improved torsional strength permits the body section 2 to be made narrower and thinner. The other function and advantages of this embodiment are the same as those of the first embodiment. The propeller shaft 1 of this embodiment is manufactured using the mandrel 8 of the first embodiment in almost the same manner as the first embodiment. The angle at which the fiber elements Fs in the CLA intersect the axis of the body section 2 may be other than ±45 degrees. Propeller shafts were manufactured with this angle changed to ±60 degrees and ±75 degrees. The breakdown torsional strengths in both cases reached the target value. With the same proportion of the fiber elements Fs in the CLA, the breakdown torsional strength increased as the angle of the fiber element Fs became smaller as follows. torque for ±75° < torque for ±60° < torque for ±45° In each of the cases where the angle at which the fiber elements Fs in the CLA intersect the axis of the body section 2 was set to the aforementioned values, the propeller shaft 1 was manufactured with the proportion of the fiber elements Fs in the CLA changed and the torsional torque, torsional rigidity, and the critical number of rotations were evaluated. The best result was obtained when the proportion of the fiber elements Fs in the CLA was equal to or below approximately 40%. Eighth Embodiment An eighth embodiment will now be discussed with reference to Fig. 11. In this embodiment, those fiber elements Fs on the body section 2 which are continuous with the fiber elements Fy in the CLA at the yoke section 3 are arranged nearly in the circumferential direction at the end portion of the body section 2. That is, the angles of bend  2 between the fiber elements Fy and the fiber elements Fs in the CLA all become smaller. This increases the reinforcing effect of the filament F in the vicinity of the interface portion between the yoke section 3 and the body section 2. In manufacturing the propeller shaft 1 of this embodiment, the filament F is arranged in, for example, the numbered order shown in Fig. 11, and the OLA and the CLA are alternately formed at the yoke section 3. In the case where all the fiber elements in the CLA are arranged as in the eighth embodiment, since the end portion of the yoke section 3 which connects to the body section and the adjoining end portion of the body section 2 expand, it is preferable that a part of the CLA in each previously-discussed embodiment be replaced with the arrangement of this embodiment. Ninth Embodiment A ninth embodiment will now be discussed with reference to Fig. 12. While the arrangement of the filament F at the yoke section 3 of the propeller shaft 1 of this embodiment is the same as that of the fourth embodiment shown in Fig. 7, the arrangement of the filament F on the body section 2 differs from that in the fourth embodiment. More specifically, those fiber elements Fs which are located on opposite sides of the plane P and constitute the same layer are symmetrically inclined with respect to the plane P. Accordingly, the filament's reinforcing effect in the vicinity of the interface portion between the yoke section 3 and the body section 2 becomes greater than that of the propeller shaft 1 of the fourth embodiment. The other function and advantages of this embodiment are the same as those of the fourth embodiment. Although only several embodiments of the present invention have been described herein, it should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms, particularly in the following forms, without departing from the scope of the invention. (1) In the above-described embodiments, the support pieces 3a of the yoke section 3 are curved in association with the outer shape of the mandrel 8. As shown in Fig. 13, however, both sides of each support piece 3a of the yoke section 3 may be formed flat. With the yoke section 3 having such a shape, it is easy to attach a snap ring or the like when the spider joint is coupled to the yoke section 3 via a bearing. In forming the support pieces 3a in that shape, a spacer having a flat outer surface is attached to the proximal end of the support pin 9 and the mandrel 8 with the bushing 5 and bushing cover attached outside the spacer is used to manufacture the propeller shaft 1. (2) The bushing 5 is not essential, so that the bearing may be directly fitted in the hole 4 when the bushing 5 is not used. In this case, the propeller shaft 1 is manufactured using the mandrel which has support pins 9 whose outside diameter is equivalent to the outside diameter of the bearing. When the bushing 5 is used, a corrugation, such as a roulette, may be formed on the outer surface of the bushing 5 to improve the adhesive strength between the bushing 5 and the FRP for the purpose of preventing the rotation or the drive-off of the bushing 5. Further, the bushing 5 may have a polygonal outer shape with multiple grooves formed in the outer surface extending in the axial direction. (3) As the combination of the filament and matrix resin which constitute the FRP, a carbon fiber and vinyl ester resin, a carbon fiber and phenol resin, or the like may be used instead of the carbon fiber and epoxy resin. In this case, the costs of the replacement resins are lower than the cost of the epoxy resin thus reducing the overall cost of the propeller shaft. Further, carbon fiber and glass fiber may be mixed, or carbon fiber and aramid fiber may be mixed. As the matrix resin, the thermosetting resin may be replaced with a thermoplastic resin, such as polyether ether ketone (PEEK) or nylon. (4) The present invention may be adapted for other drive shafts than the propeller shaft 1 for a vehicle. When the rotational speed is slow or the required specifications such as torsional strength, heat resistance, and moisture resistance, are low, the glass fiber or aramid fiber may be used alone as the reinforced fiber or a resin other than epoxy resin may be used as the matrix resin. In other words, the epoxy resin (EP), vinyl ester resin (VE), unsaturated polyester resin (UP) and phenol resin as the matrix, and the carbon fiber (CF), glass fiber (GF), and aramid fiber (AF) as the reinforced fiber may be properly combined in accordance with the demanded performances. The combinations include CF-VE, CF-UP, CF-phenol resin, GF-EP, GF-VE, GF-UP, AF-EP, AF-VE, AF-UP, and AF-phenol resin. When high heat resistance and high moisture resistance are not required, it is preferable to use a resin other than epoxy resin. When the required torsional strength is low, it is preferable to use the glass fiber or aramid fiber. The carbon fiber may be mixed with the glass fiber or aramid fiber. Those combinations result in a lower manufacturing cost than the combination of the carbon fiber and epoxy resin. Further, the body section 2 may be formed in a polygonal prism rather than a cylinder. (5) In the seventh embodiment, the filaments Fs parallel to the axis of the body section 2 shown in Fig. 10A may be replaced with fiber elements Fs which are slightly inclined with respect to the axis of the body section 2. (6) At the time the filament is arranged, not all the fiber elements Fs should be folded back around the hole 4 or the bushing 5 to constitute the fiber elements Fy. The fiber elements Fs may be partly folded at the end portion of the body section 2 before reaching the bushing 5. The mandrel 8 may have the shape of a circular column or may be designed to be separable into a plurality of parts. (7) The hoops 6 provided at the end portions of the body section 2 may be properly formed between the filament layers. The provision of the hoops 6 between the filament layers contributes to the stabilization of the filament arrangement at the end portions of the body section 2. (8) As shown in Fig. 14, both ends of the open loop of the fiber element Fy may be arranged eccentrically outside the body section 2. Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope of the appended claims.

Claims: A method for manufacturing a shaft having a body section (2) and a yoke section (3), by using a mandrel (8) including a mandrel body (80), a support pin (9) penetrating the mandrel and a plurality of pins (10) arranged on a periphery of the mandrel body (80) near the support pin (9), and by arranging a filament (F) with a resin in a layered form on the mandrel (8), the method comprising the steps of: a) arranging an end of the filament (F) along the mandrel body (80); b) changing a direction of the arrangement of the filament (F) by engaging the filament (F) with a predetermined one of the pins (10); c) partly forming a yoke filament layer of the yoke section (3) in one of an open loop arrangement (OLA) and a closed loop arrangement (CLA) by bending the filament along the support pin (9); and d) partly forming a shaft filament layer of the body section (2) by arranging the filament (F) along the periphery of the mandrel body (80) after changing again the direction of the arrangement of the filament (F) by engaging the filament with a different pin (10) than the predetermined pin (10). The method according to Claim 1, wherein steps (b) to (d) are repeated while shifting in the peripheral direction of the mandrel body (80) the bending points (Pb) at which the arrangement direction of the filament (F) is changed, thus completing the formation of said yoke filament layer and said shaft filament layer, wherein the yoke filament layer is constructed of a plurality of yoke fiber elements (Fy) each formed by a portion of the filament (F) and wherein the shaft filament layer is constructed of a plurality of shaft fiber elements (Fs) each formed by a portion of the filament (F). The method according to Claim 2, wherein additional yoke filament layers and additional shaft filament layers are formed in the same manner as the first yoke filament layer and the first shaft filament layer. The method according to Claim 2, wherein said shaft fiber elements (Fs) are arranged to incline with respect to the longitudinal axis of the body section (2). The method according to Claim 2, wherein said yoke fiber elements (Fy) of the open loop arrangement (OLA) are arranged to be symmetrical with respect to a plane (P) containing the longitudinal axis of the body section (2). The method according to Claim 3, wherein said shaft filament layers and yoke filament layers are the same in number and the number is within the range of four to twenty. The method according to Claim 2 or 3, wherein said shaft fiber elements (Fs) of a given shaft filament layer are arranged to be symmetrical with respect to a plane (P) containing the longitudinal axis of the body section (2). The method according to Claim 3, wherein a predetermined number of the yoke filament layers include both the open loop arrangement (OLA) and the closed loop arrangement (CLA) within the same yoke filament layer. The method according to Claim 8, wherein the opposite ends of each yoke fiber element (Fy) of the closed loop arrangement (CLA) in the yoke filament layers are connected to the shaft fiber elements (Fs) located to the outside of each shaft filament layer to narrow the width of the yoke section (3). The method according to Claim 4, wherein said shaft fiber elements (Fs) have straight sections (Fss) extending parallel to the longitudinal axis of the body section (2) in order to reduce the angle (O 2 ) of the bend formed by a specific shaft fiber element (Fs) located to the outside of each shaft filament layer and the yoke fiber element (Fy) connected to the specific shaft fiber element. The method according to Claim 2, wherein the bending points(Pb) between said yoke fiber elements (Fy) and shaft fiber elements (Fs) are shifted axially along the body section (2).

Inventors: ANAHARA MEIJI, MITA YASUYA, MIYASHITA YASUKI, YASUI YOSHIHARU, ANAHARA, MEIJI, MITA, YASUYA, MIYASHITA, YASUKI, YASUI, YOSHIHARU, ANAHARA, MEIJI, /O K.K. TOYODA, MITA, YASUYA, /O K.K. TOYODA, MIYASHITA, YASUKI, /O K.K. TOYODA, YASUI, YOSHIHARU, C/O K.K. TOYODA
Applicants: TOYOTA JIDOSHOKKI KK, KABUSHIKI KAISHA TOYOTA JIDOSHOKKI
Application year: 1995
Main classification: F16C3
IPC codes: B60K17, F16C3, B29C70, B29L31, B29K105