Rear wheel suspension system in vehicle

Abstract: In a rear wheel suspension system (30) in a four-wheeled vehicle (10) wherein a joint member (31) is mounted in a rear portion of a vehicle body (11) with a pair of left and right front wheels (13,14) secured thereto, the joint member (31) comprising a roll shaft (41) extending substantially in the longitudinal direction of the vehicle body and a vertical swing shaft (36) extending in the transverse direction of the vehicle body, and a power unit (32) which supports 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, the roll shaft (41) is mounted so that a front end portion (41a) thereof is positioned lower than a rear end portion (41b) thereof. It is possible to easily attain the reduction in weight of the vehicle, set a weight distribution of the vehicle freely, and improve the vehicular design freedom. Besides, such rear wheel steering rods and rod connecting members as in the prior art are not needed and therefore it is possible to decrease the number of components used in the rear wheel suspension system.

Description: The present invention relates to a vehicle with a rear wheel suspension system suitable for attaining the reduction in weight of a vehicle and for increasing the degree of freedom in design and simple in construction. 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." In Figs. 10(A) to 10(C) of the above publication there is illustrated 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. 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. 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. It is an object of the present invention to provide a rear wheel suspension system in a vehicle capable of attaining the reduction of weight easily, increasing the degree of freedom in vehicle design and attaining a simple construction. For achieving the above-mentioned object, according to claim 1 there is provided a vehicle with a rear wheel suspension system wherein a joint member is mounted in a rear portion of a vehicle body with a pair of right and rear wheels secured thereto, the joint member comprising a roll shaft extending substantially in the longitudinal direction of the vehicle body and a 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, characterized in that the roll shaft is mounted so that a front end portion thereof is positioned lower than its rear end portion. Since it is not necessary to mount a heavy object on a rear portion of the vehicle body, it is possible to easily attain the reduction in weight of the vehicle; besides, a vehicular weight distribution can be set freely and it is possible to improve the degree of freedom in vehicle design. Further, such rods for steering rear wheels and rod connecting members as in the prior art are no longer required and it is possible to attain a simple construction of a rear wheel suspension system and hence possible to reduce the number of components used in the suspension system and reduce the vehicular manufacturing cost. In claim 2, 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, whereby the vehicle drivability is improved. In claim 3, the rear wheel support member is a drive source using a rear wheel axle as an output shaft. It is possible for a drive source such as an engine or an electric motor to serve also as a rear swing arm, whereby it is possible to reduce the number of components used and reduce the vehicle manufacturing cost. Embodiments of the present invention will be described hereinunder with reference to the accompanying drawings. The drawings should be seen in the directions of reference numerals. Fig. 1 is a side view of a vehicle equipped with a rear wheel suspension system embodying the present invention. Fig. 2 is a side view of the rear wheel suspension system. Fig. 3 is a sectional view of a joint member used in the rear wheel suspension system. Fig. 4 is a plan view of the joint member. Fig. 5 is a schematic diagram showing a vehicle related to the present invention. Fig. 6 is a first operation diagram for explaining the operation of the rear wheel suspension system. Fig. 7 is a second operation diagram for explaining the operation of the rear wheel suspension system. Fig. 8 is a sectional view of a joint member in a rear wheel suspension system according to another embodiment of the present invention. Fig. 9 is a plan view of a joint member in a four-wheeled vehicle according to a further embodiment of the present invention. Fig. 10 is a sectional view taken on line 10-10 in Fig. 9. 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. Numeral 16 denotes a floor step for a driver of the vehicle to put his or her feet thereon, numeral 17 denotes a seat, numeral 18 denotes a windscreen, numeral 21 denotes a roof, and numeral 22 denotes a luggage box. 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 which constitutes the vehicle body 11, a power unit 32 as a rear wheel support member connected to a rear end of the joint member 31 vertically swingably, the power unit comprising an engine and a power transfer unit, and rear cushion units 33 and 34 (the inner-side reference numeral 33 is not shown) mounted between the power unit 32 and the vehicle body 11 (more specifically a pole 25 secured to the body frame 24). Numeral 36 denotes a vertical swing shaft of the power unit 32. 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). 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 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 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) secured to the outer case 46. The numerals 41a and 41b denote a front end portion and a rear end portion, respectively, of the roll shaft 46. Numeral 49 denotes an oil seal. Numeral 50 denotes an axis of 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 41a of the roll shaft 41 is tilted lower than the rear end portion 41b. 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. 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. 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. As described above in connection with Fig. 2, the present invention is characterized in that the rear wheel support member is the power unit 32 which uses the axle of the rear wheels 26 and 27 as the output shaft 37. The power unit 32 can also serve as a rear swing arm, so that it is possible to reduce the number of components and hence reduce the manufacturing cost of the four-wheeled vehicle 10 (see Fig. 1). 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, 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 41a is positioned lower than its rear end portion 41b, 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, and 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). The following description is now provided about the operation of the rear wheel suspension system 30 constructed as above. Figs. 6(a) and 6(b) are a first operation diagram for explaining the operation of the rear wheel suspension system according to the present invention. In Fig. 6(a), while the four-wheeled vehicle is running at high speed, the bar handle is, for example, turned left to steer the front wheels 13 and 14 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, so that the roll shaft 41 and the outer case 46 tilt to the right reverse to the steered direction of the front wheels 13 and 14 together with the flanges 42 and 43. Figs. 7(a) to 7(c) are a second operation diagram for explaining the operation of the rear wheel suspension system according to the present invention, of which 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, since it has the inclination angle α (see Fig. 2), the rear end portion 41b of the roll shaft 41 moves to the right reverse to the steering direction. 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 outer case 46 and the arms 47, 48 rotate little, but the roll shaft 41 rotates). Further, with the rightward movement of the rear end portion 41b of the roll shaft 41, rear portions of the arms 47 and 48 attached to the outer case 46 move rightwards, causing a rear portion of the power unit 32 and rear portions of the rear wheels 26 and 27 to move rightwards as indicated with arrow 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. 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 rolls little even if the front wheels are steered and turned, so that the outer case 46 and the arms 47, 48 rotate little. In Fig. 7(c), since the roll shaft 41 rotates with rolling of the vehicle body 11, while the outer case 46 rotates little, there occurs a relative rotation between the roll shaft 41 and the outer case 46. Further, since the rear end portion of 41b 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, that is, the arms 47 and 48 swing downward as indicated with arrows. Thus, in Fig. 7(a), the vehicle body 11 advances in the direction of arrow 2 ○ which is the steered direction of the front wheels 13 and 14, so that rolling at the time of wheel turn is diminished, whereby it is possible to enhance the stability of the vehicle body 11 and control the posture of the vehicle body easily. Also when the front wheels 13 and 14 are steered to the right, the rear wheels 26 and 27 can be steered in the same direction as that of the front wheels, that is, to the right. As described above in connection with Figs. 2, 3 and 5(c), in the rear wheel suspension system 30 in the four-wheeled vehicle 10 wherein the joint member 31 provided with the roll shaft 41 extending substantially in the longitudinal direction of the vehicle body and the vertical swing shaft 36 extending in the transverse direction of the vehicle body is attached to the rear portion of the vehicle body 11 with a pair of left and right front wheels 13, 14 secured thereto, and 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, the present invention is characterized in that the roll shaft 41 is mounted in a tilted state so as to position the front end portion 41a of the roll shaft 41 lower than the rear end portion 41b of the roll shaft. 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 easily attain the reduction in weight of the four-wheeled vehicle 10; besides, it is possible to set a weight distribution of the four-wheeled vehicle 10 freely and hence possible to improve the design freedom of the vehicle. Moreover, such restriction rods for steering the rear wheels and connecting members for the restriction rods as in the prior art are no longer necessary, so that the rear wheel suspension system 30 can be constructed simply and the number of components thereof can be decreased. Therefore, it is possible to decrease the manufacturing cost of the four-wheeled vehicle 10. Further, without relying on a centrifugal force acting on a heavy object mounted to the rear portion of the vehicle body as in the prior art, the rear wheels 26 and 27 can be steered in accordance with a rolling angle of the vehicle body 11; besides, 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 in high-speed travel. Consequently, it is possible to easily control the posture of the vehicle body 11. In the rear wheel steering structure according to the present invention, moreover, 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. Further, if the inclination angle α is made negative (that is, if the front end portion 41a of the roll shaft 41 is raised higher than the rear end portion 41b 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 in accordance with a rolling angle of the vehicle body 11. Thus, the rear wheel steering structure is a simple mechanical structure and it is possible to reduce the manufacturing cost in comparison with that of a complicated electronically controlled type. Fig. 8 is a sectional view of a rear suspension system using a joint member according to another embodiment of the present invention. As to the same components as in the previous embodiment described in connection with Fig. 3, they will be identified by the same reference numerals as in the previous embodiment and 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, the flanges 42 and 43 secured to a front portion of the roll shaft 68, a damper 71 interposed between the case body 65 and the roll shaft 68, and a roll locking mechanism 72 which will be described in detail later. Numeral 73 denotes a nut for preventing dislodgment of the roll shaft 68. 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)). 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. Numeral 81 denotes a collar interposed between the bearings 66 and the sideways projecting member 79. 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 48 of the joint member 64 are provided with flanges 47a and 48a, which flanges are secured to side faces of a case body 65 with bolts 82. 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 secured to the case body 65 swingably so as to push the first arm-like member 83 against the sideways projecting member 79, and a link member 85 interposed between the first and second arm-like members 83, 84. 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. 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. The numeral 95 denotes an outer tube as a constituent of the roll locking cable 91, numeral 96 denotes a swing shaft of the first arm-like member, numeral 97 denotes a swing shaft of the second arm-like member, and a pair of components indicated at 98 are nuts for mounting the roll locking cable 91 to the case body 65. Fig. 10 is a sectional view taken on line 10-10 in Fig. 9. In the same figure, 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 disposed at four corners of the elastic member receiving chamber 101 (for example, rubber or a soft resin is suitable as the elastic members), and a pressing member 103 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. As described above in connection with Figs. 8 and 10, the present invention is characterized in that the joint member 64 is provided with the case body which supports the roll shaft 68 and that the damper 71 is 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 is locked, when it is not necessary to steer the rear wheels in phase with the front wheels, it is possible to cancel steering the rear wheels and hence possible to ensure a small-turn performance. The rear wheel suspension system according to the present invention may be of a structure wherein the roll shaft inclination angle α is changed in accordance with the vehicle speed (more specifically, the vehicle speed is detected by a vehicle speed sensor and the roll shaft is tilted by an actuator in accordance with a signal provided from the vehicle speed sensor) or of a structure wherein the inclination angle α is changed in accordance with a steering angle of the front wheels (more specifically, the rotation of the bar handle which steers the front wheels is transmitted backward by means of a rod through a gear and the inclination angle α of the roll shaft is changed by means of a cam attached to a rear end of the rod, or a steering angle of the front wheels is detected by means of a sensor and the roll shaft is tilted by an actuator in accordance with a signal provided from the sensor). 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. In a rear wheel suspension system 30 in a four-wheeled vehicle 10 wherein a joint member 31 is mounted in a rear portion of a vehicle body 11 with a pair of left and right front wheels 13, 14 secured thereto, the joint member 31 comprising a roll shaft 41 extending substantially in the longitudinal direction of the vehicle body and a vertical swing shaft 36 extending in the transverse direction of the vehicle body, and a power unit 32 which supports 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, the roll shaft 41 is mounted so that a front end portion 41a thereof is positioned lower than a rear end portion 41b thereof. It is possible to easily attain the reduction in weight of the vehicle, set a weight distribution of the vehicle freely; and improve the vehicular design freedom. Besides, such rear wheel steering rods and rod connecting members as in the prior art are not needed and therefore it is possible to decrease the number of components used in the rear wheel suspension system.

Claims: Vehicle (10) with a rear wheel suspension system (30) wherein a joint member (31; 64) is mounted in a rear portion of a vehicle body (11) with a pair of right and left front wheels (13, 14) secured thereto, said joint member (31; 64) comprising a roll shaft (41; 68) extending substantially in the longitudinal direction of the vehicle body (11) and a swing shaft (36) extending in the transverse direction of the vehicle body (11), and a rear wheel support member (32) for supporting rear wheels (26, 27) is connected to a rear portion of said joint member (31; 64), thereby allowing said rear wheel support member (32) to be secured to the vehicle body (11) rollably and swingably, characterized in that said roll shaft (41; 68) is mounted so that a front end portion (41a) thereof is positioned lower than a rear end portion (41 b) thereof. Vehicle (10) with a rear wheel suspension system according to claim 1, wherein said joint member (64) is provided with a bearing (65) for supporting said roll shaft (68), and a damper (71) is disposed between said roll shaft (68) and said bearing (65). Vehicle (10) with a rear wheel suspension system according to claim 1 or claim 2, wherein said rear wheel support member (32) is a drive source using a rear wheel axle as an outputshaft (37).

Inventors: FURUTA SHINJI, KOBAYASHI HIROYOSHI, OZEKI TAKASHI, TAGAMI TAKUYA, TAKAMOTO HIROSI, TAKAYANAGI SHINJI, FURUTA, SHINJI, KOBAYASHI, HIROYOSHI, OZEKI, TAKASHI, TAGAMI, TAKUYA, TAKAMOTO, HIROSI, TAKAYANAGI, SHINJI, Furuta, Shinji, c/o K.K. Honda Gijutsu Kenkyusho, Kobayashi, Hiroyoshi, K.K. Honda Gijutsu Kenkyusho, Ozeki, Takashi, c/o K.K. Honda Gijutsu Kenkyusho, Tagami, Takuya, c/o K.K. Honda Gijutsu Kenkyusho, Takamoto, Hirosi, c/o K.K. Honda Gijutsu Kenkyusho, Takayanagi, Shinji, K.K. Honda Gijutsu Kenkyusho
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 2001
Main classification: B62K5
IPC codes: B60G9, B62K5, B62K25