Abstract:
A rear wheel suspension system for a four-wheeled vehicle suitable for attaining vehicle weight reduction, setting weight distribution of the vehicle, improving vehicle design freedom, and decreasing the number of components as compared to conventional rear wheel suspension systems. The system includes a joint member mounted in a rear portion of a vehicle body with a pair of left and right front wheels secured thereto, the joint member including a roll shaft extending substantially in the longitudinal direction of the vehicle body, and connecting to a vertical swing shaft extending in the transverse direction of the vehicle body. In addition, a power unit for supporting the two rear wheels is connected to a rear portion of the joint member by means of the vertical swing shaft, thereby allowing the power unit to be secured to the vehicle body rollably and swingably.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a rear wheel suspension system in a vehicle suitable for attaining a reduction in weight of the vehicle and for increasing the degree of freedom in design and simplicity in construction.  
           [0003]    2. Description of Background Art  
           [0004]    As a rear wheel suspension system in a vehicle wherein a rear wheel axle side is secured to a rear portion of a vehicle body rollably through a roll shaft extending in the longitudinal direction of a vehicle body and vertically swingably through a swing shaft extending in the transverse direction of the vehicle body, and rear wheels are secured to a rear wheel axle, there is known, for example, a suspension system disclosed in Japanese Patent Laid-open No. Hei 5-39073 entitled “Swing Type Vehicle.” 
           [0005]    FIGS. 10(A) to 10(C) of the above publication illustrate a swing type vehicle wherein a pair of right and left front wheels Wf, which are steered with a bar handle 2, are secured to a front portion of a body frame 1, a swing shaft 4 extending substantially horizontally in the longitudinal direction of the vehicle body is provided in a rear portion of the body frame 1, a battery supporting frame 9 is coupled to a second swing shaft 75 which is coaxial with the swing shaft 4, a power unit P is connected to the swing shaft 4 through a swing joint 6, rear wheels Wr are secured to both ends of an output shaft of the power unit P, and a rear end of the battery supporting frame 9 and both right and left ends of the power unit P are connected together using two restriction rods 74R and 74L.  
           [0006]    When the vehicle turns during high-speed travel, a large centrifugal force acts on the battery supporting frame 9 outwards with respect to the turning direction, so that with this centrifugal force the battery supporting frame 9 tilts outwards with respect to the turning direction, centered at the second swing shaft 75. With this tilting motion, a rear portion of the power unit P moves into the same direction as the direction where the centrifugal force acts, i.e., moves outwards with respect to the turning direction by the restriction rods 74R and 74L. Consequently, the power unit P tilts outwards with respect to the turning direction, centered at the swing joint 6, and the rear wheels Wr are steered inwards with respect to the turning direction, i.e., in the same direction as the front wheels Wf.  
           [0007]    According to the above technique, the rear wheels are steered in the same direction as the turning direction (steering direction of the front wheels) with the centrifugal force acting on the battery supporting frame 9, a heavy object, with a battery 10 mounted thereon. Due to the necessity of mounting the heavy object on the rear portion of the vehicle body, it is difficult to attain the reduction in weight of the vehicle body and the degree of freedom in weight distribution is limited. Further, it is necessary to use the restriction rods 74R, 74L and connecting members such as ball joints attached to end portions of those restriction rods, resulting in that the number of components used increases and the manufacturing cost becomes high.  
         SUMMARY AND OBJECTS OF THE INVENTION  
         [0008]    It is an object of the present invention to provide a rear wheel suspension system in a vehicle capable of reducing vehicle weight easily, increasing the freedom of vehicle design, and simplifying vehicle construction.  
           [0009]    For achieving the above-mentioned object a vehicle with a pair of front and rear wheels is provided with a rear wheel suspension system connected to a joint member mounted in a rear portion of the vehicle body. The joint member includes a roll shaft extending substantially in the longitudinal direction of the vehicle body. The roll shaft is mounted so that a front end portion thereof is positioned lower than its rear end portion. Also provided is a vertical swing shaft extending in the transverse direction of the vehicle body, and a rear wheel support member for supporting rear wheels is connected to a rear portion of the joint member, thereby allowing the rear wheel support member to be secured to the vehicle body rollably and swingably.  
           [0010]    Since it is not necessary to mount a heavy object on a rear portion of the vehicle body, it is possible to easily reduce the weight of the vehicle. In addition, the vehicle weight distribution can be set freely, and the degree of freedom for vehicle design can be improved. Further, rods for steering rear wheels and rod connecting members, as in the prior art, are no longer required. Thus, it is possible to simplify the construction of the rear wheel suspension system and to reduce the number of components used therein.  
           [0011]    The joint member is provided with a bearing for supporting the roll shaft, and a damper is disposed between the roll shaft and the bearing. Since a damper is disposed between the roll shaft and the bearing, it is possible to easily adjust the rolling rigidity of the vehicle body and rear wheel steering characteristic, thus improving vehicle drivability.  
           [0012]    The rear wheel support member can be combined with the vehicle drive source using the rear wheel axle as an output shaft. Further, the vehicle drive source, such as an engine or an electric motor, can also be combined with the rear swing arm, making it possible to reduce the number of components used and reduce the vehicle manufacturing cost.  
           [0013]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:  
         [0015]    [0015]FIG. 1 is a side view of a vehicle equipped with a rear wheel suspension system embodying the present invention;  
         [0016]    [0016]FIG. 2 is a side view of the rear wheel suspension system;  
         [0017]    [0017]FIG. 3 is a sectional view of a joint member used in the rear wheel suspension system;  
         [0018]    [0018]FIG. 4 is a plan view of the joint member;  
         [0019]    [0019]FIG. 5 is a schematic diagram showing a vehicle related to the present invention;  
         [0020]    [0020]FIG. 6 is a first operation diagram for explaining the operation of the rear wheel suspension system;  
         [0021]    [0021]FIG. 7 is a second operation diagram for explaining the operation of the rear wheel suspension system;  
         [0022]    [0022]FIG. 8 is a sectional view of a joint member in a rear wheel suspension system according to another embodiment of the present invention;  
         [0023]    [0023]FIG. 9 is a plan view of a joint member in a four-wheeled vehicle according to a further embodiment of the present invention;  
         [0024]    [0024]FIG. 10 is a sectional view taken on line  10 - 10  in FIG. 9. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    [0025]FIG. 1 is a side view of a vehicle equipped with a rear wheel suspension system embodying the present invention. The vehicle is a four-wheeled vehicle, indicated at  10 . In the four-wheeled vehicle  10 , a pair of left and right front wheels  13 ,  14  (the inner-side numeral  13  is not shown) to be steered with a bar handle  12  are secured rotatably to a front portion of a vehicle body  11 , while a rear suspension system  30  embodying the present invention is mounted to a rear portion of the vehicle body  11 . Other elements include floor step  16  for a driver of the vehicle to put his or her feet thereon, a seat  17 , a windscreen  18 , a roof  21 , and luggage box  22 .  
         [0026]    [0026]FIG. 2 is a side view of the rear wheel suspension system according to the present invention. The rear wheel suspension system  30  comprises a joint member  31  attached to a rear portion of a body frame  24  of the vehicle body  11  and a power unit  32  including an engine and a power transfer unit combined with the rear wheel support member, the combined unit being connected to a rear end of the joint member  31  vertically swingably. Two rear shock absorbers units  33  and  34  (the inner-side reference numeral  33  is not shown) are mounted between the power unit  32  and the vehicle body  11  (more specifically a pole  25  secured to the body frame  24 ). A vertical swing shaft  36  extends in the transverse direction of the body vehicle, the vertical swing shaft enabling the power unit  32  to swing vertically. The power unit  32  has an output shaft  37  on which are mounted a pair of left and right rear wheels  26 ,  27  (the inner-side numeral  26  is not shown).  
         [0027]    [0027]FIG. 3 is a sectional view of the joint member used in the rear suspension system according to the present invention. The joint member  31  comprises a roll shaft  41  shown in FIG. 3 extending substantially in the longitudinal direction of the vehicle body for mounting the power unit  32  and the rear wheels  26 ,  27  rollably to the vehicle body  11  shown in FIG. 2. Flanges  42  and  43  are attached to a front end portion of the roll shaft  41  to attach the joint member  31  to the body frame  24  (see FIG. 2). An outer case  46  is provided as a bearing which supports the roll shaft  41  rotatably through bushings  44  and  45 , and arms  47  and  48  (the numeral  48  is not shown) are secured to the outer case  46 . A front end portion  41   a  and a rear end portion  41   b  are provided on roll shaft  46 , with an oil seal  49  disposed there between.  
         [0028]    An axis  50  is provided for the roll shaft  41 . The present invention is characterized in that the roll shaft  41  is secured to the vehicle body  11  (see FIG. 2) through flanges  42  and  43  in such a manner that the front end portion  41   a  of the roll shaft  41  is tilted lower than the rear end portion  41   b . In FIG. 2, the angle between a horizontal line HL and the axis  50 , i.e., an inclination angle of the axis  50 , is assumed to be α.  
         [0029]    In the roll shaft  41 , a washer  52  is abutted against an end face of the bushing  45 , one end of a collar  53  is abutted against the washer  52 , and a nut  55  is disposed at the opposite end of the collar  53  through a washer  54 . The nut  55  is threadedly engaged with the end portion of the roll shaft  41  to prevent dislodgment of the roll shaft  41  from the outer case  46 . A lid  56  is fixed to the outer case  46  with bolts  57  and nuts  58 .  
         [0030]    [0030]FIG. 4 is a plan view of the joint member according to the present invention. Arms  47  and  48  extend sideways and backwards from an outer surface of the outer case  46  of the joint member  31  and brackets  61  for mounting the power unit  32  (see FIG. 2) are attached to rear ends of the arms  47  and  48 , respectively.  
         [0031]    As described above in connection with FIG. 2, the rear wheel support member is combined with the power unit  32  which uses the axle of the rear wheels  26  and  27  as the output shaft  37 . The power unit  32  is also combined with a rear swing arm, making it possible to reduce the number of components and hence reduce manufacturing cost.  
         [0032]    FIGS.  5 ( a ) to  5 ( c ) are schematic diagrams illustrating the vehicle related to the present invention. In FIG. 5( a ), which schematically illustrates a side face of the four-wheeled vehicle  10 , the front wheels  13  and  14  are secured to the vehicle body  11 , and the flanges  42  and  43  of the joint member  31  are secured to the rear portion of the vehicle body  11 . The roll shaft  41  is secured to the flanges  42  and  43  in such a manner that its front end portion  41   a  is positioned lower than its rear end portion  41   b . The roll shaft  41  is supported rotatably by the outer case  46 , the arms  47  and  48  are attached to the outer case  46 , the power unit  32  is mounted to the arms  47  and  48  swingably. The rear wheels  26  and  27  are mounted on the output shaft  37  of the power unit  32 . FIG. 5( b ) is a sectional view taken on line b-b in FIG. 5( a ) and FIG. 5( c ) is a plan view of FIG. 5( a ).  
         [0033]    Next, the operation of the rear wheel suspension system  30  constructed as above will be described. FIGS.  6 ( a ) and  6 ( b ) are diagrams explaining the operation of the rear wheel suspension system according to the present invention. FIG. 6( a ) shows the four-wheeled vehicle running at high speed, with the bar handle turned left causing the front wheels  13  and  14  to steer to the left. In FIG. 6( b ), as the front wheels  13  and  14  are steered to the left, the vehicle body  11  rolls at a rolling angle of β clockwise as indicated with arrow. This causes the roll shaft  41 , the outer case  46  and the flanges  42  and  43  to tilt to the right, opposite to the steered direction of the front wheels  13  and  14 .  
         [0034]    FIGS.  7 ( a ) to  7 ( c ) are additional diagrams explaining the operation of the rear wheel suspension system according to the present invention. FIG. 7( a ) is a plan view, FIG. 7( b ) is a view as seen in the direction of arrow b, and FIG. 7( c ) is an enlarged view of a principal portion (with flanges  42  and  43  added) of FIG. 7( b ). In FIG. 7( a ), as the roll shaft  41  tilts to the right, with inclination angle α (see FIG. 2), the rear end portion  41   b  of the roll shaft  41  moves to the right, opposite to the steering direction.  
         [0035]    As a result, the roll shaft  41 , as well as the outer case  46  and the arms  47  and  48 , rotate relatively with respect to each other (actually, as will be described below in connection with FIGS.  7 ( b ) and  7 ( c ), the rotation of the outer case  46  and the arms  47 ,  48  is less than the rotation of the roll shaft  41 ). The rightward movement of the rear end portion  41   b  of the roll shaft  41 , causes the rear portions of the arms  47  and  48  attached to the outer case  46  move rightwards, which in turn causes the rear portion of the power unit  32  and rear portions of the rear wheels  26  and  27  to move rightwards as indicated with arrow {circle over ( 1 )}. Thus, the rear wheels  26  and  27  can be steered leftwards, that is, in the same direction as that of the front wheels  13  and  14 .  
         [0036]    In FIG. 7( b ), since the rear wheels  26  and  27  are mounted directly on the output shaft of the power unit  32 , the power unit only rolls by a small amount even if the front wheels are steered and turned. Thus the outer case  46  and the arms  47 ,  48  only rotate a small amount also.  
         [0037]    In FIG. 7( c ), since the roll shaft  41  rotates with rolling of the vehicle body  11 , while the outer case  46  rotates a smaller amount, there is a relative rotation between the roll shaft  41  and the outer case  46 . Further, since the rear end portion of  41   b  of the roll shaft  41  descends with rotation of the roll shaft  41 , the rear portions of the arms  47  and  48  connected to the outer case  46  also descend, as indicated by the arrows in FIG. 7( c ).  
         [0038]    Thus, in FIG. 7( a ), the vehicle body  11  advances in the direction of arrow {circle over ( 2 )} and is steered by the front wheels  13  and  14 . The rolling that occurs at the time of turning is diminished. Thus, the stability and posture of the vehicle body  11  are more easily controlled. Also, when the front wheels  13  and  14  are steered for example to the right, the rear wheels  26  and  27  steer in the same direction as that of the front wheels, that is, to the right.  
         [0039]    As described above in connection with FIGS. 2, 3, and  5 ( c ), the power unit  32  which support the rear wheels  26  and  27  is connected to a rear portion of the joint member  31 , thereby allowing the power unit  32  to be secured to the vehicle body  11  rollably and swingably. Again, the roll shaft  41  is mounted in a tilted state wherein the front end portion  41   a  of the roll shaft  41  is lower than the rear end portion  41   b  of the roll shaft.  
         [0040]    According to the above construction, since it is not necessary to mount a heavy object on the rear portion of the vehicle body, it is possible to reduce the vehicle weight, it is possible to freely distribute the weight of the vehicle, and hence possible to improve the design freedom of the vehicle. Moreover, restriction rods for steering the rear wheels and connecting members for the restriction rods, as in the prior art, are no longer necessary. Thus the construction of the rear wheel suspension system is simple, the number of components thereof is decreased, which in turn decreases the manufacturing cost of the vehicle.  
         [0041]    Further, without relying on a centrifugal force acting on a heavy object and  27  can be steered in accordance with a rolling angle of the vehicle body  11 . Since the rear wheels  26  and  27  can be steered in the same direction as a steered direction of the front wheels  13  and  14 , it is possible to improve the steering stability and maintain proper posture of the vehicle body while traveling at high speeds.  
         [0042]    In the rear wheel steering structure according to the present invention, the steering angle of the rear wheels  26  and  27  can be changed by changing the inclination angle α (see FIG. 2) of the roll shaft  41 . Thus, if the inclination angle α is made negative (that is, if the front end portion  41  a of the roll shaft  41  is raised higher than the rear end portion  41   b  to tilt the roll shaft  41 ), the rear wheels  26  and  27  can be steered in a direction opposite to a steered direction of the front wheels  13  and  14 . Thus, the rear wheel steering structure is a simple mechanical structure, making it possible to reduce the manufacturing cost in comparison with that of a complicated electronically controlled type structure.  
         [0043]    [0043]FIG. 8 is a sectional view of a rear suspension system using a joint member according to another embodiment of the present invention. As in the previous embodiment described in FIG. 3, components will be identified by the same reference numerals, and thus explanations thereof will be omitted. A joint member  64  comprises a case body  65 , a roll shaft  68  inserted into the case body  65  rotatably through a pair of bearings  66  and a bearing  67 . Flanges  42  and  43  are secured to a front portion of the roll shaft  68 . A damper  71  is interposed between the case body  65  and the roll shaft  68 . A roll locking mechanism  72  is provided which will be described in detail later. A nut  73  is provided for preventing dislodgment of the roll shaft  68 .  
         [0044]    The case body  65  supports the roll shaft  68  through the bearings  66  and  67 , and it is a bearing in a broad sense. (If the case body  65  bears the roll shaft  68  directly without using the bearings  66  and  67 , the case body  65  is an intrinsic bearing (sliding bearing)).  
         [0045]    The front portion of the roll shaft  68  is formed with flange mounting surfaces  75  and  76 , and flanges  42  and  43  are mounted to the flange mounting surfaces  75  and  76  respectively, with bolts  77  and nuts  78 . In the roll locking mechanism  72 , a sideways projecting member  79  having a sectorial portion which projects sideways of the roll shaft  68  is serrated (or splined) to the roll shaft  68 . A collar  81  is interposed between the bearings  66  and the sideways projecting member  79 .  
         [0046]    [0046]FIG. 9 is a plan view of a joint member in the four-wheeled vehicle according to a further embodiment of the present invention, in which a lid provided on top of the joint member  64  is removed. End portions of arms  47  and  43  of the joint member  64  are provided with flanges  47   a  and  48   a , the flanges being secured to side faces of a case body  65  with bolts  82 .  
         [0047]    A roll locking mechanism  72 , which is for locking a relative rotation between a roll shaft  68  and the case body  65 , comprises a sideways projecting member  79  secured to the roll shaft  68 , a first arm-like member  83  secured to the case body  65  swingably so as to lock the rotation of the sideways projecting member  79 . A second arm-like member  84  is secured to the case body  65  swingably so as to push the first arm-like member  83  against the sidewavs projecting member  79 . A link member  85  is interposed between the first and second arm-like members  83 ,  84 .  
         [0048]    The sideways projecting member  79  is formed with a groove  87 , while the first arm-like member  83  is provided at a front end thereof with a pawl portion  88  for engagement with the groove  87  of the sideways projecting member  79 . The second arm-like member is provided at an end portion thereof with a cable mounting portion  93  for mounting an inner cable  92  which constitutes a roll locking cable  91 .  
         [0049]    The roll locking cable  91  functions as follows to restrict rolling of the vehicle body  11  of the four-wheeled vehicle (see FIG. 1). When the inner cable  92  is pulled by operating an operating lever disposed near the bar handle  12  (see FIG. 1), the pawl portion  88  of the first arm-like member  83  is caught in the groove  87  of the sideways projecting member  79  to lock the rotation of the roll shaft  68  with respect to the case body  65 .  
         [0050]    The roll locking cable  91 , includes an outer tube  95 . A swing shaft  96  of the first arm-like member, a swing shaft  97  of the second arm-like member, and a pair of nuts  98  are provided for mounting the roll locking cable  91  to the case body  65 .  
         [0051]    [0051]FIG. 10 is a sectional view taken on line  10 - 10  in FIG. 9. As illustrated in Fig. 10, a damper  71  used as a component of the joint member  64  comprises an elastic member receiving chamber  101  formed within the case body  65 . Elastic members  102  are disposed at four corners of the elastic member receiving chamber  101  (for example, rubber or a soft resin is suitable as the elastic members). A pressing member  103  is disposed inside the elastic members  102  and splined to the roll shaft  68 . The damper  71  is what is called a “Neidhart damper” in which as the pressing member  103  rotates together with the roll shaft  68 , the pressing member  103  compresses the elastic members  102 , thereby giving rise to a damper action.  
         [0052]    As described above in connection with FIGS. 8 and 10, the joint member  64  of the present invention is provided with the case body which supports the roll shaft  68  and a damper  71  disposed between the roll shaft  68  and the case body  65 . Since the damper  71  is thus disposed between the roll shaft  68  and the case body  65 , it is possible to easily adjust the rolling rigidity and rear wheel steering characteristic of the vehicle body  11  (see FIG. 1), whereby the drivability of the four-wheeled vehicle  10  can be improved. Further, since rolling can be locked, when it is not necessary to steer the rear wheels in phase with the front wheels, it is possible to cancel steering of the rear wheels, making it possible to ensure a small turning radius.  
         [0053]    The rear wheel suspension system according to the present invention may be of a structure wherein the roll shaft inclination angle a is changed in accordance with the vehicle speed. More specifically, the vehicle speed can be detected by a vehicle speed sensor, and the roll shaft can be tilted by an actuator in accordance with a signal provided from the vehicle speed sensor.  
         [0054]    Alternatively, the inclination angle α can be changed in accordance with a steering angle of the front wheels. More specifically, the rotation of the bar handle which steers the front wheels can be transmitted backward by means of a rod through a gear, and change the inclination angle α of the roll shaft by means of a cam attached to a rear end of the rod. Another alternative is for the steering angle of the front wheels to be detected by means of a sensor then tilting the roll shaft by an actuator based on a signal provided from the sensor.  
         [0055]    The damper used in the present invention is not limited to a rubber damper which utilizes rubber, but it may be a damper which utilizes fluid such as air or oil. The vehicle to which the invention is applied is not limited to a four-wheeled vehicle, but may be a three-wheeled vehicle comprising two front wheels and one rear wheel. Further, the drive source used as the rear wheel support member in the present invention is not limited to a power unit provided with an engine, but may be an electric motor.  
         [0056]    According to the present invention constructed as above there are attained the following effects. According to the rear wheel suspension system in a vehicle of the present invention, since the roll shaft is mounted so that its front end portion is positioned lower than its rear end portion, it is not necessary to mount a heavy object on the rear portion of the vehicle body. This makes it possible to reduce the vehicle weight, distribute the vehicle weight freely, and improve the freedom of vehicle design. Moreover, rear wheel steering rods and rod connecting members, as in the prior art, are not needed. Thus, construction of the rear wheel suspension system is simple, number of components used is reduced, and the vehicle manufacturing cost decreased.  
         [0057]    According to the rear wheel suspension system in a vehicle of the present invention, since the joint member is provided with a bearing for supporting the roll shaft and a damper is disposed between the roll shaft and the bearing, it is possible to adjust the rolling rigidity and rear wheel steering characteristic of the vehicle body easily, whereby the vehicle drivability is improved.  
         [0058]    According to the rear wheel suspension system in a vehicle of the present invention, since the rear wheel support member is a drive source which uses the rear wheel axles as an output shaft, it is possible to let such a drive source as an engine or an electric motor serve also as a rear swing arm and hence it is possible to reduce the of components used and reduce the vehicle manufacturing cost.  
         [0059]    The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.