Abstract:
A vehicular propeller shaft having a hollow shaft, a bellows section integrally connected with said hollow pipe and a universal joint, the bellows section comprises a small diameter section, a large diameter section whose diameter is larger than the small diameter section, a plurality of swelling sections partially, outwardly swelled, having an enlarged diameter and a trapezoid cross section, annularly shaped around the hollow pipe, and consecutively disposed between said small diameter section and said large diameter section and a valley section having a reduced diameter, annularly shaped and disposed between two adjacent swelling sections.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a propeller shaft for a vehicle, more particularly, to a vehicular propeller shaft capable of absorbing an impact by being deformed axially when an impact load is applied in the longitudinal direction of the vehicle. 
     2. Prior Art 
     Generally, a vehicle is constituted so as to transmit engine power from a transmission to a differential through a propeller shaft and from the differential to wheels. 
     However, the propeller shaft is disposed in the transversal center of the vehicle in the longitudinal direction thereof and therefore, for example, in an event of collision, when a large impact is exerted in the lengthwise direction of the vehicle, the deformation of the vehicle body is blocked by a “lengthwise resistance” of the propeller shaft and as a result a still larger impact is caused in the vehicle. 
     In order to solve this problem, Japanese Patent Application Laid-open No. Toku-Kai-Hei 5-178105 discloses a technique in which a propeller shaft is shaped into a hollow pipe to raise a torsional rigidity per weight. Also, the propeller shaft has a swelling portion annually formed in the radial direction thereof. When an excessively large impact load is applied to the vehicle, the swelling portion is deformed so that the propeller shaft is released from a state of lengthwise resistance. 
     As shown in FIG. 8, List of Unpatentable Examples of Automobile Technologies No. 95202 published by the Committee of Intellectual Properties of Japan Automobile Manufactures Association, discloses a propeller shaft  100  comprising a hollow propeller shaft  101 , a center support bearing  102  provided at the rear end of the propeller shaft  100  and a bellows pipe  103  connected in the front thereof with the hollow propeller shaft  101  and connected in the rear thereof with the center support bearing  102 . When an axial load is applied to the propeller shaft  100 , the bellows pipe  103  is deformed so that the propeller shaft  100  can be released from the state of lengthwise resistance. 
     Further, FIG. 9 a  shows a propeller shaft  111  disclosed by Japanese Patent Application Laid-open No. Toku-Kai-Hei 8-226454. The propeller shaft  111  comprises a female member  112  and a male member  113  spline-fitted to the female member  112 . The female member  112  comprises a small diameter portion  112   a  and a large diameter portion  112   b  and the small diameter portion  112   a  is spline-fitted over the male member  113 . Therefore, a step portion  112   c  is formed on the propeller shaft  111  between the small diameter portion  112   a  and the large diameter portion  112   b.    
     When an impact load is applied to thus formed propeller shaft  111  in the longitudinal direction, as shown in FIG. 9 b,  the step portion  112   c  is deformed or broken in the axial direction so as to absorb the impact load. 
     According to the propeller shaft disclosed in the Patent Application No. Toku-Kai-Hei 5-178105, when a large impact load is applied in the longitudinal direction, first the swelling portion must be deformed in the axial direction. However, the deformation of the swelling portion needs a large initial load and therefore the impact can not be absorbed in a proper and effective way. Further, there occurs so called “collision phenomenon” in which both ends of the swelling portion abut against each other and as a result the propeller shaft can not have an adequate crash stroke. On the other hand, the formation of a plurality of swelling portions leads to a fear of reduced critical speed of the propeller shaft. 
     In case of the propeller shaft  100  disclosed in List of Unpatentable Examples of Automobile Technologies No. 95202, when an axial load is exerted on the hollow propeller shaft  101 , the bellows pipe  103  is deformed to reduce the lengthwise resistance of the propeller shaft  100 . 
     However, when the propeller shaft  100  is deformed and shortened, respective tops of the bellows pipe  103  abut against neighboring tops and respective valleys thereof abut against neighboring valleys, that is, “collision phenomenon” is generated. This prevents the propeller shaft  100  from having an adequate crash stroke. On the other hand, an increased number of tops and valleys of the bellow pipe  103  has an adverse effect on the critical speed of the propeller shaft  100 . 
     According to the propeller shaft  111  disclosed in Toku-Kai-Hei 8-226454, the problem is that since the deformation or breakage in the axial direction requires a large impact load, especially, a large impact load at the initial stage, the propeller shaft  111  still has a difficulty in alleviating the impact effectively. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a vehicular propeller shaft having an adequate crash stroke without decreasing critical speed thereof, this preventing the propeller shaft from having a lengthwise resistance, thereby an effective alleviation of impact can be achieved. 
     To attain the object, the propeller shaft has a hollow pipe and a bellows section which comprises a small diameter section, a large diameter section whose diameter is larger than the small diameter section, a plurality of swelling sections partially, outwardly swelled, having an enlarged diameter, annularly shaped around the hollow pipe, and consecutively disposed between the small diameter section and the large diameter section and a valley section having a reduced diameter, annularly shaped and disposed between two adjacent swelling sections. The swelling section has a trapezoid cross section constituted by an up-grade surface, a down-grade surface and a top surface provided between said up-grade surface and said down-grade surface. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a cross sectional view showing a propeller shaft according to a first embodiment of the present invention; 
     FIG. 2 is a partially expanded view of a propeller shaft of FIG. 1; 
     FIG. 3 is a partially expanded view of a portion “A” of FIG. 2; 
     FIGS. 4 a  through  4   e  are explanatory views showing processes of deformation of a bellows section; 
     FIG. 5 is a diagram showing a relationship between a displacement and a load when a bellows section is deformed by the load; 
     FIG. 6 is a cross sectional view showing a bellows section according to a second embodiment; 
     FIG. 7 is a cross sectional view showing a mode of deformation of a bellows section of FIG. 6; 
     FIG. 8 is a schematic cross sectional view of a propeller shaft according to prior art; and 
     FIGS. 9 a  and  9   b  are partially cross sectional views of a propeller shaft according to prior art. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to FIG. 1, a propeller shaft  1  comprises a first propeller shaft  10  which is connected at the front end thereof with a main shaft (not shown) of a transmission (not shown) via a universal joint  21  and which is rotatably supported at the rear end thereof by a center bearing  22  and a second propeller shaft  30  which is connected at the front end thereof with the first propeller shaft  10  via a universal joint  24  and which connected at the rear end thereof with a rear differential (not shown) via a universal joint  23 . 
     The first propeller shaft  10  is shaped into a hollow configuration to enhance the rigidity per weight, as shown in FIG.  2 . The first propeller shaft  10  is connected at the front end thereof with a joint yoke  21   a  and connected at the rear end thereof with a spline shaft  24   a  of the universal joint  24  which is rotatably supported by the center bearing  22 . 
     A bellows section  11  is formed near the front end of the first propeller shaft  10 . As an enlarged sectional view of the portion “A” in FIG. 2 is shown in FIG. 3, the portion “A” is integrally connected on the front side thereof with a small diameter section  12  and is integrally connected on the rear side thereof with a large diameter section  13 . Three consecutive swelling sections  14 ,  15  and  16  have a trapezoid cross section respectively and are annularly provided between the small diameter section  12  and the large diameter section  13  of the bellows section  11 . A first swelling section  14  has a trapezoid cross section constituted by an annular first up-grade surface  14 A, an annular first top surface  14 B and an annular first down-grade  14 C, a second swelling section  15  has a trapezoid cross section constituted by an annular second up-grade surface  15 A, an annular second top surface  15 B and an annular second down-grade surface  15 C, and a third swelling section  16  has a trapezoid cross section constituted by an annular third up-grade surface  16 A, an annular third top surface  16 B and an annular third down-grade surface  16 C. 
     The first swelling section  14  is integrally connected at the front end thereof with the small diameter section  12  via a first bend portion  17 , the second swelling section  15  is integrally connected at the front end thereof with the rear end of the first swelling section  14  via a valley portion  18 , the third swelling section  16  is integrally connected at the front end thereof with the rear end of the second swelling section  15  and it is integrally connected at the rear end thereof with the large diameter section  13  via a second bend portion  20 . 
     Diameters dl, d 2 , d 3  and d 4  of the small diameter section  12 , the first valley  18 , the second valley  19  and the large diameter section  20 , respectively are established to be d 1 &lt;d 2 &lt;d 3 &lt;d 4 . 
     Further, when θ 1  represents an angle at which the first up-grade surface  14 A meets a plane perpendicular to an axis a of the first propeller shaft  10 , θ 2  an angle at which the first down-grade surface  14 C meets that plane, θ 3  an angle at which the second up-grade surface  15 A meets the plane, θ 4  an angle at which the second down-grade surface  15 C meets that plane, θ 5  an angle at which the third up-grade surface  16 A meets the plane and θ 6  an angle at which the third down-grade surface  16 C meets the plane, these angles are established to be θ 1 &lt;θ 2 , θ 3 &gt;θ 4  and θ 5 &gt;θ 6 . 
     Next, FIGS. 4 a  through  4   e  show deformation modes of the bellows section  11  of thus formed propeller shaft  1 , when an impact load P larger than a certain value is applied to the propeller shaft  1  in the lengthwise direction. Starting with an initial mode (not yet deformed) of the bellows section shown in FIG. 4 a,  FIGS. 4 b,    4   c,    4   d  and  4   e  show changes of deformation mode in this order, respectively. Further, FIG. 5 is a graph showing a relationship between load and displacement and symbols b, c, d and e correspond to modes of deformation of the propeller shaft  1  in FIGS. 4 b,    4   c,    4   d  and  4   e  respectively. 
     When the impact load P which is larger than a certain value is applied to the propeller shaft  1 , stress is concentrated on the first bend  17  between the small diameter section  12  and the first up-grade surface  14 A and also concentrated on the first corner  14   a  between the first up-grade surface  14 A and the first top surface  14 B. As a result of this, as shown in FIG. 4 b,  these stress-concentrated portions absorb the impact energy and the bellows section  11  is reduced in the lengthwise size. 
     Accompanied by the size reduction of the bellows section  11 , the bend portion  17  comes close to the first valley portion  18 . Then, the top surface  14 B is deformed and at the same time the second corner  14   b  bends. As shown in FIG. 4 c,  since the inclination θ 1  of the first up-grade surface  14 A is smaller than the inclination θ 2 , the first up-grade surface  14 A submerges under the first top surface  14 B and the first up-grade surface  14 A and the first top surface  14 B are crushed toward the first down-grade surface  14 C in such a way that the first bend portion  17  abuts against the first valley portion  18 . Thus, during this deformation process of the first swelling section  14 , the impact energy up to the portion “c” of FIG. 5 is absorbed. 
     Next, since the diameter d 2  of the first valley portion  18  is formed so as to be larger than the diameter d 1  of the small diameter section  12  and smaller than the diameter d 4  of the large diameter section  13  and the inclination angle θ 3  of the second up-grade surface  15 A is larger than the inclination angle θ 4  of the second down-grade surface  15 C, the second top surface  15 B and the second valley portion  19  are mainly bent and the second swelling section  15 , as shown in FIG. 4 d,  is crashed in such a way that the second up-grade surface  15 A comes close to the second down-grade surface  15 C. Thus, the impact energy up to the portion “d” of FIG. 5 is absorbed. 
     Further, since the large diameter section  13  is relatively large and the inclination angle θ 5  of the third up-grade surface  16 A is larger than the inclination angle θ 6  of the third down-grade surface  16 C, the third top surface  16 B and the second bend portion  20  are mainly bent due to the concentration of stress, the third swelling section  16  is crushed, as shown in FIG. 4 e,  such that the third up-grade surface  16 A covers the third down-grade surface  16 C from above, thus the bellows section  11  is deformed and the impact energy up to the portion “e” of FIG. 5 is absorbed. 
     According to the propeller shaft  1  having thus formed bellows section  11 , since the diameter d 1  of the small diameter section  12  is established to be smaller than the diameter d 2  of the first valley portion  18  and the inclination angle θ 1  of the first up-grade surface  14 A is established to be smaller than the inclination angle θ 2  of the first down-grade surface  14 C, when the impact load is applied to the bellows section  11  in the axial direction, the bend portion  17  submerges under the first valley portion  18 . At this moment, when the impact load is furthermore applied to the bellows section  11 , the bend portion  17  slides under the first valley portion  18  and it never abuts against the first valley portion  18 . Thus, at the initial stage of impact, the bellows section  11  is easily deformed with a small impact load. Further, since the diameter d 2  of the first valley section  18  is established to be equal to or smaller than the diameter d 3  of the second valley section  19  and the inclination θ 3  of the second up-grade surface  15 A is established to be larger than the inclination θ 4  of the second down-grade surface  15 C, the second swelling section  15  is crashed such that the second up-grade surface  15  comes close to the second down-grade surface  15 C, the impact energy is absorbed. Further, since the diameter d 3  of the second valley portion  19  is established to be smaller than the diameter d 4  of the large diameter section  13  and the inclination angle θ 5  of the third up-grade surface  16 A is established to be larger than the inclination angle θ 6  of the third down-grade surface  16 C, when the impact load is applied to the bellows section  11  in the axial direction, the second valley portion  19  submerges under the second bend portion  20 . At this moment, when the impact load is furthermore applied to the bellows section  11 , the second valley portion  19  slides under the second bend portion  20  and it never abuts against the second bend portion  20 . Thus, since the first bend portion  17 , the first valley portion  18 , the second valley portion  19  and the second bend portion  20  are deformed respectively in such a way that the first bend portion  17  and the second bend portion  20  submerge under the bellows section  11  without abutting between these portions  17 ,  18 ,  19  and  20 . As a result, the propeller shaft  1  secures an adequate crush stroke and can be relieved from lengthwise resistance of the propeller shaft. 
     Further, since the bellows section  11  is constituted by small numbers of swelling sections, the first swelling section  14 , the second swelling section  15  and the third swelling section  16 , the vehicle safety can be secured without reducing critical speed of the propeller shaft. 
     Further, since the bellows section  11  is formed only at the front portion of the first propeller shaft  1 , the components after the center bearing  22  can be used as they are in the prior art. 
     Next, a propeller shaft according to a second embodiment of the present invention will be described by reference to FIGS. 6 and 7. The components of the propeller shaft which are identical in both embodiments are denoted by identical reference numbers and are not described in detail. 
     FIG. 6 is an enlarged sectional view of a bellows section  11  which corresponds to FIG. 3 according to the first embodiment. In the second embodiment, the second swelling section  15  is deleted from the bellows section  11  of the first embodiment. The bellows section  11  has a small diameter section  12  and a large diameter section  13 , and a first swelling section  14  and a third swelling section  16  are annularly formed consecutively between the small diameter section  12  and the large diameter section  13  of the bellows section  11 . 
     These small diameter section  12 , first swelling section  14 , third swelling section  16  and large diameter section  13  are formed consecutively via a first bend portion  17 , a first valley portion  18  and a second bend portion  20 . Here, reference numerals d 1 , d 2  and d 4  denote the diameters of the small diameter section  12 , the first valley portion  18  and the large diameter section  13 , respectively and the diameters d 1 , d 2  and d 4  are established so as to be d 1 &lt;d 2 &lt;d 4 . 
     Further, reference numerals θ 1 , θ 2 , θ 5  and θ 6  denote angles at which a plane perpendicular to the axis a of the propeller shaft  10  meets a first up-grade surface  14 A, a first down-grade surface  14 C, a third up-grade surface  16 A and a third down-grade surface  16 C, respectively and these angles are established to be θ 1 &lt;θ 2  and θ 5 &gt;θ 6 . 
     Next, in thus formed propeller shaft  1 , an operation of the propeller shaft, when a longitudinal impact load larger than a certain value is applied, will be described by reference to FIGS. 6 and 7. 
     When an impact load P which is larger than a certain value is applied to the propeller shaft  1 , stress is concentrated on a first bend portion  17  where the small diameter section  12  turns abruptly to the first up-grade surface  14 A and on a first corner  14   a  where the first up-grade surface  14 A turns abruptly to the top surface  14 B. As a result, the first bend portion  17  and the first corner  14   a  are deformed to absorb impact energy and the bellows section  11  is reduced in size. 
     Accompanied by the reduction of the bellows section  11 , the first bend portion  17  comes close to the first valley portion  18  and a second corner  14   b  where the first top surface  14 B turns to the first down-grade surface  14 C is bent outwardly. Further, since the inclination angle θ 1  of the first up-grade surface  14 A is established to be smaller than the inclination angle θ 2  of the first down-grade surface  14 C, the first up-grade surface  14 A slidably submerges under the first down-grade  14 C, while the first bend portion  17  and the first valley portion  18  are crushed. Thus, impact energy is absorbed by the size reduction of the bellows section  11 . 
     Next, the first valley portion  18  whose diameter is formed so as to be larger than the small diameter section  12  and smaller than the large diameter section  13 , is deformed and the third up-grade surface  16 A is crushed by the up-coming first down-grade surface  14 C to absorb impact energy. 
     As a result of this, stress is concentrated on a second bend portion  20  where the third down-grade surface  16 C turns to the large diameter section  13  and the second bend portion  20  and the third top surface  16 B are mainly deformed. Thus, the third swelling section  16  is crushed and the first bend portion  17  and the first valley portion  18  submerge under the large diameter section  13 , as shown in FIG.  7 . Thus, impact energy is absorbed by the size reduction of the bellows section  11 . 
     According to the propeller shaft  1  having thus constituted bellows section  11 , since the diameters d 1 , d 2  , d 4  of the small diameter section  12 , the first valley portion  18  and the large diameter section  13  respectively are established to be d 1 &lt;d 2 &lt;d 4 , in the same manner as the first embodiment, the first bend portion  17  which is formed at the end of the small diameter section  12  having a small diameter, the first valley portion  18  and the second bend portion  20 , are deformed in this order. Further, since the inclination angles θ 1 , θ 2  of the first up-grade surface  14 A and the first down-grade surface  14 C respectively are established to be θ 1 &lt;θ 2  and the inclination angles θ 5 , θ 6  of the third up-grade surface  16 A and the third down-grade surface  16 C respectively are established to be θ 5 &gt;θ 6 , the time difference is generated between the first swelling section  14  and the second swelling section  16  when these sections are deformed. Accordingly, the bellows section  11  can be deformed with a relatively small impact load and the initial load is properly controlled to alleviate impact effectively. Further, since the first bend portion  17  and the first valley portion  18  submerge under the large diameter section  13 , while they are deformed, without collisions between the first bend portion  17 , the first valley portion  18  and the second bend portion  20 , an adequate crash stroke can be secured and the lengthwise resistance of the propeller shaft  11  can be avoided when an impact is applied thereto. 
     Further, due to still smaller number of the swelling sections than the first embodiment, the reduction of the critical speed can be avoided more surely. 
     In this embodiment, the bellows section  11  is formed at the front portion of the first propeller shaft  10 , however, it is possible to dispose the bellows section  11  in the vicinity of the rear portion of the first propeller shaft  10 . Further, the number of swelling sections is not limited to two or three and it is possible to increase the number of swelling sections of the bellows section within an allowable range of the reduction in critical speed of the propeller shaft  11 . 
     While the presently preferred embodiments of the present invention have been shown and described, it is to be understood that these disclosures are for the purpose of illustration and that various changes and modifications may be made without departing from the scope of the invention as set forth in the appended claims.