Abstract:
A drive shaft for transmitting an engine revolution to a rear axle of a motor vehicle comprises, a first shaft comprising a first yoke fixed to an end of the first shaft, a second shaft comprising a second yoke fixed to an end of the second shaft. The second yoke being made of a metal plate by press-forming. A coupling is provided between the first yoke and the second yoke, the coupling having a high-rigidity in a rotating direction of the drive shaft and having an elasticity in an axial direction of the drive shaft.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to a drive shaft for a motor vehicle, especially plural shafts are connected together by a coupling that absorbs an oscillation of the drive shaft in an axial direction of the drive shaft. Since the drive shaft frequently receives an oscillation in the axial direction, the coupling is provided between the shafts in order to absorb the oscillation that would cause a vibration of a motor vehicle.  
           [0002]    This type of drive shaft generally is known. For example, relevant related art is disclosed in Japan Utility model publication (koukai) No. 63-178632. This publication discloses an output shaft, an input shaft and a coupling. One end of the output shaft is connected to a transmission of a motor vehicle and one end of the input shaft is connected to a rear axle of the motor vehicle. The other end of the output shaft and the other end of the input shaft are connected together through the coupling. According to this publication, the coupling is made of rubber material.  
           [0003]    As shown in FIGS. 10 and 11 illustrating a relevant related art, a coupling comprises a main body  1  made of rubber material and formed in an annular shape. Six bushings  2  are provided on an outer periphery of the main body  1  so that all of the bushings are provided in the same interval in a circumferential direction. Every mutually adjoining two bushings  2  are connected together by a wire  8  made from a material that has a high-rigidity, for example, glass fiber. A first yoke  5  that has three arm portions  5   a  is fixed to an end of an output shaft  3 . A second yoke  6  that has three arm portions  6   a  is fixed to an end of an input shaft  4 . The yokes  5  and  6  are formed by forging. The arm portions  5   a  and  6   a  are fixed to the bushings  2  by bolts  12  so that the bushings  2  are fixed alternately to the arm portions  5   a  and  6   a  in the circumferential direction. The end of the output shaft  3  extends through a center of the main body  1  and is supported by supporting rubber  7  provided on the yoke  6  so that an axis of the output shaft  3  and an axis of the input shaft  4  coincide.  
           [0004]    According to this type of coupling, every mutually adjoining two bushings  2  are connected together by the wire  8  and the main body  1  is made of rubber material. Hence, a relative displacement between the output shaft  3  and the input shaft  4  in an axial direction of the input shaft  4  is permitted by the main body  1  while a revolution of the output shaft  3  is transmitted to the input shaft  4  without losing power by virtue of the tension of the wire  8 .  
           [0005]    However, since a structure of this type of coupling tends to be complicated, and thus, a size of this type of coupling become large, another type of coupling that has an annular plate instead of the rubber material as the main body has been provided. This type of coupling is disclosed in, for example, Japan Utility model publication (koukai) No. 60-189620. The annular plate of this type of coupling is also shown in FIG. 12 of the present invention.  
           [0006]    As shown in FIG. 12, an annular plate  9  has six hole portions  10 . The hole portions  10  are provided in an outer periphery of the annular plate  9  so that all of the hole portions are provided in the same interval in a circumferential direction of the annular plate  9 . Three arm portions  12  of a first yoke (not shown) are provided on an output shaft (not shown) and three arm portions  13  of a second yoke (not shown) are provided on an input shaft (not shown). The arm portions  12  and  13  are fixed to the annular plate  9  by bolts (not shown) so that each arm portion  12  and  13  is fixed alternately to the annular plate  9  in the circumferential direction of the annular plate  9 . The annular plate  9  is made of metal that has a rigidity and is formed so that a thickness in an axial direction of the annular plate  9  is equal at all portions. There are provided washers  11  on the hole portions  10 .  
           [0007]    Assuming that a portion connecting every mutually adjoining two holes  10  is called connecting arm portions  9   a , the connecting arm portions  9   a  absorb oscillation that occurs in an axial direction of the output shaft and transmit a revolution of the output shaft to the input shaft without losing power. Further, since the annular plate  9  is made of material that has a rigidity, the output shaft and the input shaft are connected so that both axes of the output shaft and the input shaft coincide without adding any means for arranging the axis of one of the output shaft and the input shaft to the axis of the other of the output shaft and the input shaft.  
           [0008]    However, since both yokes are formed by forging, each yoke tends to be heavy and some after-processes, such as a drilling process for making the hole portions  10  and a cutting process for providing a flat surface at which the yoke is connected to the coupling, are necessary. As a consequence, a drive shaft tends to be heavy and expensive.  
         SUMMARY OF THE INVENTION  
         [0009]    Accordingly, in view of above-described problems encountered in the related art, a principal object of the present invention is to provide a drive shaft that has a lightweight yoke.  
           [0010]    Another object of the present invention is to provide a drive shaft that has an easily assembled yoke and coupling.  
           [0011]    Still another object of the present invention is to provide an inexpensive drive shaft that has durability.  
           [0012]    In order to achieve these and the other objects, there is provided a drive shaft that comprises a first shaft comprising a first yoke fixed to an end of the first shaft, a second shaft comprising a second yoke fixed to an end of the second shaft. The second yoke being made of a metal plate by press-forming. A coupling is provided between the first yoke and the second yoke. The coupling has a high-rigidity in a rotating direction of the drive shaft and has an elasticity in an axial direction of the drive shaft. 
       
    
    
       [0013]    Other aspects and advantages of the invention will become apparent from following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principle of the invention.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a vertical sectional drawing, showing a coupling which is connected to a yoke of a drive shaft according to the first embodiment of the present invention.  
         [0015]    [0015]FIG. 2 is a side view of an annular plate as a coupling of FIG. 1.  
         [0016]    [0016]FIG. 3 is a side view of a yoke, taken from arrow A of FIG. 1.  
         [0017]    [0017]FIG. 4 is a vertical sectional drawing, showing a coupling which is connected to a yoke of a drive shaft according to the second embodiment of the present invention.  
         [0018]    [0018]FIG. 5 is a vertical sectional drawing, showing a yoke and a coupling according to an example of the third embodiment of the present invention.  
         [0019]    [0019]FIG. 6 is a side view of an annular plate, taken from arrow B of FIG. 5.  
         [0020]    [0020]FIG. 7 is a vertical sectional drawing, showing a yoke and a coupling according to an another example of the third embodiment of the present invention.  
         [0021]    [0021]FIG. 8 is a vertical sectional drawing, showing a yoke and a coupling according to the fourth embodiment of the present invention.  
         [0022]    [0022]FIG. 9 is a vertical sectional drawing, showing a yoke and a coupling according to the fifth embodiment of the present invention.  
         [0023]    [0023]FIG. 10 is a vertical sectional drawing, showing a coupling which is connected to a yoke of a drive shaft of a related art.  
         [0024]    [0024]FIG. 11 is a side view of a coupling, taken from arrow C of FIG. 10.  
         [0025]    [0025]FIG. 12 is a side view of an annular plate of an another related art. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]    A drive shaft according to a preferred embodiment of the present invention will now be described with reference to the drawings.  
         [0027]    As shown in FIG. 1, a first yoke  22  is provided on an end of an output shaft  20  of a transmission (not shown), and a second yoke  23  is provided on an end of a main shaft  21 . The first yoke  22  is formed by forging and is fixed to the end of the output shaft  20 . The second yoke  23  is formed by press-forming and is fixed to the end of the main shaft  21  by welding. Each yoke  22  and  23  has radially extending three arm portions  22   a  and  23   a . The arm portions  22   a  are provided so that each arm portion  22   a  is placed in the same interval, and the arm portions  23   a  are provided so that each arm portion  23   a  is placed in the same interval. There are provided plural annular plates  24 , which constitute a coupling that absorbs oscillation that occurs in an axial direction of the main shaft  21 , between the first yoke  22  and the second yoke  23 , and the first yoke  22  and the second yoke  23  are connected through the annular plates  24 .  
         [0028]    As shown in FIGS. 1 and 2, each annular plate  24  has six holes  25  in the same interval of a circumferential direction of the annular plate  24 . The arm portions  22   a  are placed on the holes  25  of one side of the annular plate  24 , and the arm portions  23   a  are placed on the holes  25  of the other side of the annular plate  24 , in order that the arm portions  22   a  and the arm portions  23   a  are placed alternately on the holes  25 . There are provided washers  28  on each bole  25  so that the annular plates  24  are pinched between the washers  28  in the axial direction of the main shaft  21 . Each arm portion  22   a  and  23   a  is fixed to the annular plate  24  by a bolt  26  and a nut  27  through the hole  25 .  
         [0029]    The annular plate  24  is formed so that a width A of connecting arm portions  24   a , which are provided between mutually adjoining holes  25 , is shorter than a width A′ of hole portions at which the holes  25  are provided. Also, an inner diameter of the annular plate  24  at the hole portion is made shorter than an inner diameter at the connecting arm portion  24   a , while the same outer diameter is provided at a whole portion of the annular plate  24 . Thereby, a center line q of the connecting arm portion  24   a  is placed outside of an imaginary line p, which connects two centers of the holes  25  that are adjoining each other. That is, the width A of the connecting arm portion  24   a  is made shorter than the width A′ of the hole portion  25 , and a length of the connecting arm portion  24   a  is made longer than a length of the imaginary line p and a circumference of a pitch circle running through centers of the holes  25 . Consequently, a rigidity of the annular plate  24  in the axial direction of the main shaft  21  is decreased, and thus the annular plate  24  absorbs the oscillation that occurs in the axial direction of the main shaft  21 . Although a rigidity of the annular plate  24  in a circumferential direction of the annular plate  24  is decreased for the similar reason, a decrease of the rigidity in the circumferential direction can be realized increasing the number of the annular plates  24 .  
         [0030]    As shown in FIGS. 1 and 3, a hole  29  into which the bolt  26  is inserted is provided on each arm portion  23   a . A rib portion  30  is provided on the second yoke  23  so that the rib portion  30  is formed along a side of the arm portion  23   a  and connects the rib portion  30 , which is provided on an adjoining another arm portion  23   a , at a root portion of the arm portion  23   a . The rib portion  30  is constituted by a curving portion that is curved toward an opposite direction to the annular plate  24 . Thereby, touches between the second yoke  23  and the annular plate  24  that would cause an age degradation of both the second yoke  23  and the annular plate  24  are prevented even if the annular plate  24  is deformed by flexure that might be caused by a displacement between the output shaft  20  and the main shaft  21 . Therefore, the annular plates  24  are able to have a stable oscillation absorbing performance. The rib portion  30  is placed so that a flat surface is provided at the each hole  29 .  
         [0031]    As shown in FIG. 1, the second yoke  23  is fixed to the main shaft  21  by welding so that a fixing portion W of the second yoke  23  at which the second yoke  23  is fixed to the main shaft  21  and a surface  23   b  at which a head of the bolt  26  is placed are provided on the same surface. That is, the surface  23   b  and the fixing portion W are on the same surface S of the second yoke  23 .  
         [0032]    Both the surface  23   b  and the fixing portion W are on the surface S that is vertical to an axial line O of the main shaft  21 . Thereby, torque transmitted to the second yoke  23  via the bolts  26  and the annular plates  24  is transmitted to the main shaft  21  without affecting a torsional deformation to the second yoke  23 . Although the second yoke  23  is made of a metal plate by press-forming, the second yoke  23  transmits torque to the main shaft  21  without deforming undesirably. Therefore, an age degradation caused by the torsional deformation can be prevented.  
         [0033]    The rib portion  30  is formed on an outside of the fixing portion W in a radial direction of the second yoke  23  in order that a flat surface is provided at the hole  29 . That is, the rib portion  30  is provided on a portion of the second yoke  23  other than the fixing portion W and the holes  29 . Thereby, a rigidity of the second yoke  23  is increased, whereas a decrease of weld strength between the second yoke  23  and the main shaft  21 , a decrease of fixing strength between the second yoke  23  and the annular plates  24 , and a decrease of a reinforcing effect of the rib portion  30  is prevented.  
         [0034]    There is provided a cylindrical portion  31 , which is formed integrally with the second yoke  23 , at a center of the second yoke  23 . The cylindrical member  31  has a bottom surface and an opening  32 , which opens toward the annular plate  24 , and is placed so that the cylindrical member  31  is accommodated in the main shaft  21 . Thereby, an intrusion of foreign matter, such as mud and water, into an inside of the main shaft  21  is prevented.  
         [0035]    According to the first embodiment of the present invention, a rib portion  33  is provided on an outer periphery of the opening  32 . The rib portion  33  is constituted by a convex portion protruding from the surface facing to the annular plate  24 . An inner surface of the cylindrical portion  31  is provided with a tapered surface so that a diameter of the inner surface decreases toward the bottom surface. Thereby, the foreign matter entered into an inside of the cylindrical portion  31  is discharged along the tapered surface without accumulating, and thus, a degradation of the main shaft  21  caused by the foreign matter can be prevented.  
         [0036]    A shape of the second yoke  23 , the holes  29 , the cylindrical portion  31  and the rib portions  30  and  33  are formed by press forming. Therefore, the weight of the second yoke  31  can be decreased compared to a yoke formed by forging, and some after-processes, such as a drilling process for making the hole portions and a cutting process for providing a flat surface at which the yoke is connected to the coupling, are not necessary. As a consequence, an inexpensive drive shaft can be provided.  
         [0037]    A rod portion  34  is provided on the output shaft  20 . The rod portion  34  protrudes from an end of the output shaft  20  and penetrates through a center of the annular plate  24 . An end of the rod portion  34  is accommodated in the cylindrical portion  31  so that a length L of the rod portion  24  in the cylindrical portion  31  is longer than an axial maximum displacement between the output shaft  20  and the main shaft  21  caused by an axial oscillation of the main shaft  21 .  
         [0038]    A gap D is provided between an inner surface of the cylindrical portion  31  and an outer surface of the rod portion  34  in order to avoid touching of the rod portion  34  to the inner surface of the cylindrical portion  31  even when one of the output shaft  20  and the main shaft  21  relatively moves with respect to the other of the output shaft  20  and the main shaft  21  in the axial direction of the main shaft  21 . Accordingly, a sliding resistance caused by a relative movement between the output shaft  20  and the main shaft  21  in the axial direction of the main shaft  21  can be prevented. Further, a degradation of an oscillation absorbing performance can be prevented. Consequently, a torque of the output shaft  20  is transmitted to the main shaft  21  via the first yoke  22 , the annular plate  24  and the second yoke  23  without loss, while the axial oscillation is absorbed by an axial elasticity of the annular plate  24 .  
         [0039]    Next, the drive shaft according to the second embodiment of the present invention will be described, referring FIG. 4. Parts of this embodiment are given the same reference characters to corresponding parts of the first embodiment, and only differences from the first embodiment will be described.  
         [0040]    In this embodiment, as shown in FIG. 4, there is provided a cylindrical portion  131 , which is provided separately with the second yoke  123 , at a center of the second yoke  123 . An opening  132  whose periphery is curved cylindrically in the axial direction of the main shaft  21  and protruding toward the output shaft  20  is provided at a center of the second yoke  123 . The cylindrical portion  131  is made of a metal plate by press-forming. The cylindrical portion  131  has a bottom surface.  
         [0041]    An inner surface of the cylindrical portion  131  is provided with a tapered surface in order that a diameter of the cylindrical portion  131  decreases toward the bottom surface. A flange portion  131   a , which is curved in a radial direction of the cylindrical portion  131 , is provided on an end of the cylindrical portion  131 . The second yoke  123  has a hole at the center of the second yoke  123 , and the cylindrical portion  131  is inserted into the hole from the bottom surface of the cylindrical portion  131  by press-fitting so that the cylindrical portion  131  is accommodated in the main shaft  21 . That is, an outer surface of the cylindrical portion  131  touches an inner surface of the peripheral portion of the opening  132 , while an end of the outer periphery of the opening  132  and the flange portion  131   a  are fixed together by welding.  
         [0042]    Since the cylindrical portion  131  is provided separately with the second yoke  123 , the cylindrical portion  131  can be made of a thinner metal plate than a metal plate of the second yoke  123 . Thereby, a decrease of a weight of the second yoke  123  can be provided. Further, an easy processing of the cylindrical portion  131  can also be provided. Moreover, since the cylindrical portion  131  is formed separately with the second yoke  123 , the cylindrical portion  131  that has an accurate size can be formed.  
         [0043]    According to the second embodiment of the present invention, while the cylindrical portion  131  is fixed to the second yoke  123  by both press-fitting and welding, the cylindrical portion  131  may also be fixed to the second yoke  123  by only press-fitting.  
         [0044]    Next, the drive shaft according to the third embodiment of the present invention will be described, referring FIGS. 5 and 6. Parts of this embodiment are given the same reference characters to corresponding parts of the first and the second embodiments, and only differences from the first and the second embodiments will be described.  
         [0045]    In this embodiment, as shown in FIG. 5, a large diameter portion  221   d  is provided on an end of a main shaft  221  at which the second yoke  123  is fixed to the main shaft  221  by welding. A diameter d 2  of the large diameter portion  221   d  is being larger than a diameter d 1  of an other portion  221   c  of the main shaft  221 . The large diameter portion  221   d  is formed by plasticity-forming.  
         [0046]    As shown in FIG. 6, an annular plate  224  has connecting arm portions  224   a  and  224   b  provided between mutually adjoining holes  225 . The connecting arm portion  224   a  is being placed an outside of an imaginary line p, which connects two centers of the holes  225  that are adjoining each other, in a radial direction of the annular plate  224 . The connecting arm portion  224   b  is placed an inside of the imaginary line p in the radial direction of the annular plate  224 . The connecting arm portion  224   a  and the connecting arm portion  224   b  are symmetrical at the imaginary line p.  
         [0047]    According to the third embodiment of the present invention, since the main shaft  221  and the second yoke  123  are fixed together at the large diameter portion  221   d  of the main shaft  221 , a large welding area can be provided, and thus, the strength of the welding between the main shaft  221  and the second yoke  123  can be increased. Further, since the other portion  221   c  of the main shaft  221  is provided with a diameter d 1 , which is smaller than a diameter d 2  of the large diameter portion  221   d,  an increase of a weight of the main shaft  221  can be avoided obtaining the same strength of the welding between a main shaft which has the diameter d 2  at all portions of the main shaft and the second yoke  123 .  
         [0048]    While the third embodiment of the present invention shows that the main shaft  221  has two diameter portions d 1  and d 2 , the drive shaft may also have plural diameter portions. In this case, as shown in FIG. 7, the large diameter portion  221 d comprises from a first large diameter portion  222  and a second large diameter portion  223 . A diameter d 2  of the first large diameter portion  222  is larger than a diameter d 1  of the other portion  221   c  of the main shaft  221  and smaller than a diameter d 3  of the second large diameter potion  223 .  
         [0049]    According to the another example of the third embodiment, since the large diameter portion  221   d  is provided with two large diameter portions  222  and  223  in order that a diameter of the main shaft  221  increases toward an end of the main shaft  221  at which the second yoke  123  is fixed to the main shaft  221 , a thin thickness portion of the main shaft  221  can be prevented from locally making at a root portion of the large diameter portion  221   d,  and thus, an even thickness of the main shaft  221  can easily provide on whole portions of the main shaft  221 , when the large diameter portion  221   d  is formed.  
         [0050]    Next, the drive shaft according to the fourth embodiment of the present invention will be described, referring FIG. 8. Parts of this embodiment are given the same reference characters to corresponding parts of the first, second and third embodiments, and only differences from the first, second and third embodiments will be described.  
         [0051]    In this embodiment, as shown in FIG. 8, a convex portion  321   e  is provided between a large diameter portion  321   d  and an other portion  321   c  of the main shaft  321 . The convex portion  321   e  is formed so that a diameter of the convex portion  321   e  is larger than the diameter d 2  of the large diameter portion  321   d.  The convex portion  321   e  is provided with a surface that runs smoothly between the large diameter portion  321   d  and the other portion  321   c  of the main shaft  321 .  
         [0052]    According to the fourth embodiment of the present invention, although the convex portion  321   e  retains its shape under a normal operation, the convex portion  321   e  is deformed, as shown a broken line in FIG. 8, when the main shaft  321  receives an extreme shock in an axial direction of the main shaft  321 . Thereby, the extreme shock is effectively absorbed by a deformation of the convex portion  321   e.  Further, since the second yoke  123  is fixed to the large diameter portion  321   d  of the main shaft  321 , a large welding area W can be provided, and thus, the strength of welding between the main shaft  321  and the second yoke  123  can be increased.  
         [0053]    Next, the drive shaft according to the fifth embodiment of the present invention will be described, referring FIG. 9. Parts of this embodiment are given the same reference characters to corresponding parts of the first, second, third and fourth embodiments, and only differences from the first, second, third and fourth embodiments will be described.  
         [0054]    In this embodiment, as shown in FIG. 9, a second rib portion  40  is provided outside of the first rib portion  30  in a radial direction of a second yoke  423 . The second rib portion  40  constitutes a curved portion of the second yoke  423  that is parallel curved to the first rib portion  30  in an axial direction of the main shaft  121 . Thereby, the rigidity of the second yoke  421  can be increased.  
         [0055]    The present 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.  
         [0056]    While the present invention is disclosed on the basis of certain preferred embodiments, it in not limited thereto, but is defined by the appended claims as interpreted in accordance with applicable law.  
         [0057]    This application relates to and incorporates herein by reference Japanese Patent application No. 2000-171048 filed on Jun. 7, 2000 and Japanese Patent application No. 2000-310060 filed on Oct. 11, 2000, from which priority is claimed.