GB2104013A

GB2104013A - Motorcycle front wheel suspensions

Info

Publication number: GB2104013A
Application number: GB08215590A
Authority: GB
Inventors: Shinichi Miyakoshi; Tokio Isono
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 1981-05-28
Filing date: 1982-05-27
Publication date: 1983-03-02
Also published as: GB2104013B; DE3220053A1; JPS57198183A; FR2506711A1

Abstract

A motorcycle front wheel suspension includes an upper fork (11) supported by a frame of the motorcycle and a lower fork (12) supporting the front wheel. A rotary lever shock absorber (20) operatively coupled to the lower fork is disposed between opposed side members (11a, 11b) constituting the upper fork, thus reducing unspring weight. <IMAGE>

Description

SPECIFICATION Motorcycle front wheel suspensions This invention relates to motorcycle front wheel suspensions and, more particularly, to a front wheel suspension of linkage formation.

It is known to provide motorocycles with a front wheel suspension including an upper fork rotatably mounted on the head pipe secured to the front end of a frame, and a lower fork supporting the front wheel and directly or indirectly coupled to a lower portion of the upper fork so that vertical displacement of the front wheel following irregular road surfaces is allowed by up-and-down swinging of the lower fork. A cylinder type shock absorber is provided between the upper and lower forks, and the up-and-down displacement of the front wheel is damped by damping force provided by this shock absorber which elongates and contracts with the swinging motion of the lower fork. The shock absorber has to have a length corresponding at least to the swing stroke of the lower fork. That is, the length of the shock absorber has to be set according to the swing stroke.In addition, substantially one half of the weight of the shock absorber acts upon the front wheel and lower fork. Therefore, it is difficult to reduce the so-called upsprung weight, reduction of which is effective for improving the capability of the motorcycle to follow ground contours, and for improving riding comfort. Furthermore, oil seal members in the shock absorber must be pressurebearing seal members so that they can seal with respect to operating fluid which is pressurized to a high pressure inside the shock absorber when damping force is generated. Therefore, the seal force of the pressure-bearing seal members constitutes a resistance against the operation of the shock absorber as it elongates and contracts, thus adversely affecting the damping force characteristics.

According to the present invention there is provided a motorcycle front wheel suspension comprising a fork rotatably supported in a frame of the motorcycle and consisting of a pair of side members, a front wheel support member supporting the front wheel of the motorcycle at one end and coupled at the other end to the fork, the front wheel support member being capable of swinging up and down to allow up-and-down displacement of the front wheel for following irregular road surfaces, and a shock absorber of rotary lever form operatively coupled to the front wheel support for damping the swinging motion thereof, this shock absorber being disposed between said side members. In this suspension the unsprung weight is kept to a minimum and the shock absorber does not require any pressure bearing member such as an oil seal.Furthermore the weight of the shock absorber can be located at the centre or nearly the centre in the lateral direction of the motorcycle body frame so that satisfactory weight balance can be obtained and the shock absorber can be positioned so as to be protected by opposite side members of the fork.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Fig. 1 is a side view of a motorcycle provided with a front wheel suspension of linkage formation; Fig. 2 is a perspective view of the front wheel suspension of Fig. 1; Fig. 3 is a plan view of a detail of a modified form of suspension; Fig. 4 is a fragmentary side view of a shock absorber case which also serves as a bottom bridge; Fig. 5 is a perspective view of the case of Fig. 4; Fig. 6 is a plan view, partly in section, illustrating the coupling between the case and side members of an upper fork; Fig. 7 is a sectional view showing the internal construction of the case;; Fig. 8 is a fragmentary front view showing the disposition of a torsion bar; Fig. 9 is a fragmentary sectional view showing the disposition of a torsion bar in a further embodiment; Fig. 10 is a fragmentary sectional view showing the embodiment of Fig. 9; Fig. 11 is a perspective view showing a further embodiment, in which a torsion bar and a shock absorber are coupled to each other in a different way; Fig. 12 is a perspective view showing a further embodiment, in which a bottom bridge and shock absorber case are provided as separate members; Fig. 13 is a side view showing a motorcycle using a coil spring instead of the torsion bar; Fig. 14 is a fragmentary side view showing a leading link front wheel suspension; and Fig. 1 5 is a fragmentary side view showing a trailing link front wheel suspension.

Fig. 1 is a side view, partly diagrammatic, of a notorcycle. The motorcycle frame generally designated by 1 comprises a main portion 2, a downwardly oblique tube portion 3 and a rear frame portion 4. A rear wheel 5 is supported by the rear end of a rear fork 6 which has its front end pivoted by a pivot shaft 7 to the motorcycle frame 1 and can swing up and down about the pivot shaft. Vertical displacement of the rear wheel 5 causing the swinging of the rear fork 6 is damped by a shock absorber or damper 8 which has its upper and lower ends connected to a rear upper portion of the motorcycle frame 1 and the rear fork respectively. A head pipe 9 is secured to the front end of the motorcycle frame 1. A front wheel suspension 10 is supported on the head pipe 9 such that it can be rotated to the left and right.

The front wheel suspension 10 includes an upper fork 11, a lower fork 12 and front and rear arms 13 and 14 connected at the upper and lower ends thereof by pins 1 3a, 1 3b, 1 4a and 1 4b to the upper and lower forks 11 and 12, i.e. connecting both the forks 11 and 12. The axle 1 5a of the front wheel 1 5 is supported by the front end of the lower fork 12. A stem shaft penetrates through top and bottom bridges 1 6 and 17 which connect left and right members of the upper fork 11. The head pipe 9 is thus rotatable to the left and right.

A handle bar 1 8 mounted on the top bridge 1 6 is operable for steering the front wheel suspension 1 0. The front wheel suspension 10 is constructed as a linkage with the lower fork 12 and arms 1 3 and 14 as movable links. As shown in Fig. 2, the front and rear arms 13 and 14 are provided for the left and right side members 11 a, 11 b, 1 2a and 1 2b of the upper and lower forks 11 and 12, that is, the linkage 1 9 is found on the opposite sides of the front wheel 1 5.

The vertical displacement of the front wheel 1 5 following irregular road surfaces takes place with corresponding deformation of the linkage 1 9 caused with rotation of the arms 1 3 and 14 about the pins 1 3a and 14a. As the linkage is deformed, the lower fork 1 2 which is coupled to a lower portion of the upper fork 11 via the arms 1 3 and 14 swings up and down with vertical displacement of the front wheel 1 5. The lower fork 12 thus serves as a swingable front wheel support. If the inclination angles of the arms 1 3 and 14 are set such that their extensions intersect at a point A in Fig. 1, the low fork 12 swings about the point A as an instantaneous centre of swing.

The front wheel axle 1 5a can thus be displaced up and down substantially along a straight orbit B which is substantially parallel with the axis C of the head pipe 9, constituting the axis of steering of the front wheel suspension 1 0.

The vertical displacement of the front wheel 1 5 is damped by a rotary lever type shock absorber or damper 20. In this embodiment, a case 21 of the damper 20 constitutes the bottom bridge 17 connecting the side members 11 a and 1 b of the upper fork 11. In other words, a damper mechanism is accommodated in the interior of the bottom bridge 1 7. This construction has various advantages in addition to being able to reduce component parts in number by using common parts. More particularly, since the damper 20 is provided between the side members 11 a and 11 b, its weight is located at the centre of the motorcycle body in the lateral direction thereof. Thus, satisfactory weight balance can be obtained. Also the damper 20 is protected by the side members 11 a and 11 b.Further, since the damper 20 is mounted in the upper fork 11 which is held stationary with respect to the vertical displacement of the front wheel, the unsprung weight on the side of the lower fork 12 can be reduced. Further, as the bottom bridge 17 has to be formed with high rigidity sufficient to connect the side members 11 a and 11 b it is thus suitable to be the case of the damper 20 in which the operating fluid is pressurized to high pressure when damping force is generated. Further, heat generated as the operating fluid is pressurized can be radiated from the side members 11 a and 11 b which have large surface areas, that is, the side members 11 a and 11 b can be utilized as heat radiators.

Fig. 5 shows the appearance of the damper case 21. The case 21 may be fabricated by casting, forging or die-casting. The side members 11 a and 11 b are secured to the case 21 by bolts 22 screwed into threaded holes 21 a formed in the opposite side walls of the case 21, as shown in Fig. 4. The case 21 is formed in its rear portion with a vertical hole 21 b penetrating it. The stem shaft 23 mentioned above extends through the hole 21 b. The case 21 has a vertically raised front portion 21 c, the interior of which constitutes a chamber filled with the operating fluid.

The internal construction of the chamber is shown in Fig. 7. A lateral wall member 24 divides the chamber to define upper and lower chambers S, and S2 in which respective pistons 25 and 26 are slidably fitted. The pistons 25 and 26 are coupled to the opposite ends of a piston arm 27a coupled to an operating shaft 27 via connecting rods 28 and 29. A damping force generating chamber S3 is formed on one side of the chambers S1 and S2 such that it communicates with the chambers S1 and 53 through passages 30,31,32 and 33. The passages 31 and 32 are opened and closed by respective valve members 34a and 34b of a valve 34.In the damping force generating chamber S3, upper and lower damping force generating means of the same construction are assembled. These means respectively comprise covers 36 and 37 secured to the case 21, cylindrical members 38 and 39 integral with the respective covers 36 and 37, plate valves 42 and 43 including disc-like members 40 and 41 fitted on the outer periphery of the cylindrical members 38 and 39 and sets of plate springs, collars 44 and 45 urging the plate valves 42 and 43 against the disc-like members 40 and 41, orifices 46 and 47 formed in the disc-like members 40 and 41 and closed by the plate valves 42 and 43, caps 50 and 51 secured to the tip of the cylindrical members 38 and 39 and formed with the orifices 48 and 49, and threaded needle valves 54 and 55 extending in inner passages 52 and 53 of the cylindrical members 38 and 39 and having tapered end portions 54a and 55a adapted to occupy the orifices, 48 and 49.

The operating shaft 27, as shown in Fig. 6, projects from the front wail of the case 21.

Coupled to the projecting end 27b of the shaft is a stem portion of a lever arm 56 extending laterally with respect to the motorcycle body. As shown in Fig. 2, the free end of the lever arm 56 is coupled to the upper end of a rod 57 by means of a bolted joint 57a. The lower end of rod 57 is coupled by a pin 57b to an end portion 1 3c of one arm 1 3 extending above the portion thereof coupled by the pin 1 3a to the upper fork 11. The rod 57 and arm 13 form a linkage 58 coupling the front wheel support lower fork 1 2 and the rotary sever type damper 20. A torsion bar 59 is disposed on the outer side of one side member 11 a of the upper fork 11. The torsion bar 59 is rotatably supported in a bearing 60. Its upper end is secured by serration coupling to a mounting member 61, that is, the upper end is a secured end. The lower end of the torsion bar 59 is serration coupled to the inner end of a link arm 62, which has its outer end coupled by a rod 63 to the end portion 1 3c of the arm 13. The coupling of the link arm 62 and rod 63 and the coupling of the arm end portion 1 3c and rod 63 are by bolted joints 63a and 63b. The link arm 52, rod 63 and arm 13 form a linkage 64 coupling the lower fork 12 and torsion bar 59.While only a single torsion bar is shown, it is possible to provide two tdrsion bars 59 on the opposite side members 11 a and 11 b by providing the other arm 1 3 with an end portion 13c' as shown by broken lines in Fig. 2, while providing two dampers 20 in the bottom bridge 17, thus coupling the individual arms 13 to the respective torsion bars and dampers.

When the front wheel 1 5 is upwardly displaced, the rod 57 is raised with rotation of the arm 1 3 in the counterclockwise direction about the pin 13a.

Thus, the operating shaft 27 of the rotary lever type damper 20 is rotated clockwise by the lever 56. This rotation causes advancement of the piston 26 shown in Fig. 7, thus forcing out the operating fluid in the section S2 through the passage 32 opened by the valve member 34b, orifice 48, passage 52 and passage 30 into the chamber S1. At this time, the orifice 48 provides a throttling action for its aperture is reduced by the tapered portion 54a of the needle valve 54 occupying the aperture. Thus, the damper 20 generates damping force with respect to the upward displacement of the front wheel 1 5. The needle valve 54 is of the threaded type to permit adjustment of the aperture of the orifice for adjusting the damping force.When the front wheel 1 5 is displaced at a high speed, the operating fluid in the chamber S2 is highly pressurized. Thus, with oil hydraulic pressure acting through the orifice 46, the plate valve 46 is flexed and opened. In other words, when the front wheel 1 5 is displaced at a high speed, the operating fluid passes through the orifices 48 and 46. The damping force is thus generated according to the speed of displacement of the front wheel 1 5.

Meanwhile, with the rotation of the arm 13 in the counterclockwise direction, the torsion bar 59 is twisted via the rod 63 and link arm 62. Thus, the force which is necessary for twisting the torsion bar 59 which can provide spring force, constitutes a damping force when the front wheel 1 5 is upwardly displaced.

When the front wheel 1 5 is downwardly displaced, the arm 1 3 is rotated in the clockwise direction so that the rod 57, lever 56 and operating shaft 27 of the damper 20 execute in the converse manner to the operation described above. Again in this case, damping force is generated by the throttling action of the orifice, the aperture of which is reduced by the tapered portion 55a of the needle valve 55. The damping force is adjusted by the thread type needle valve 55. When the front wheel 1 5 is downwardly displaced at a high speed, the plate valve 43 is opened so that the operating fluid passes through the orifices 49 and 47.Thus, the damping force is generated according to the displacement speed of the front wheel 1 5. The torsion bar 59 also releases torsional energy stored with previous upward displacement of the front wheel. Further, when the torsion bar 59 is twisted beyond the neutral position, it generates a damping force with respect to the downward displacement of the front wheel 1 5.

In the damper 20 which operates as described above, pressure-bearing seal members 65, as shown in Fig. 6, may be provided in bearing portions of the operating shaft 27. The seal force of the seal members 65 thus does not affect damping force of the damper so much compared to the case of a cylinder type damper.

If the rod 57 of the linkage 58 coupling the lower fork 12 and damper 20 is a turn buckle capable of length adjustment, height adjustment of the motorcycle can be obtained. If the rod 63 in the linkage 64 coupling the lower fork 12 and torsion bar 59 is a turn buckle, it is possible to make adjustment of the pre-load of the spring force of the torsion bar 59. Further, the angle of the link arm 62 with respect to the torsion bar 59 may be suitably set such that the twist angle of the torsion bar 59 with unit displacement of the front wheel 1 5 is small, i.e., the spring force of the torsion bar 59 is low, while the displacement of the torsion bar 59 is small and the twist angle is increased, i.e., the spring force of the torsion bar 59 is increased, with increasing displacement of the front wheel 1 5.Thus, the damping characteristics of the torsion bar 59 can be set as a progressive characteristic.

Fig. 3 shows a different embodiment, in which the pre-load of the torsion bar is adjustable. Here, a serrated end 79a of a torsion bar 79 is insertedly coupled to the stem of an adjustment arm 81. A mounting boss portion 71 a of the upper fork 71 is pivotally coupled by a pin 83 to one end of a threaded rod 82 extending in the lateral direction of the motorcycle body. The tip of the adjustment arm 81 is loosely fitted on the other end of the threaded rod 82. The arm 81 and threaded rod 82 are coupled together by lock nuts 84 and 85. The arm 81 may be rotated with respect to the threaded rod 82 in the direction of insertion or removal after loosening the lock nuts 84 and 85.

The pre-load of the torsion bar 79 is adjusted by an amount corresponding to the rotation of the arm 81. After adjustment, the arm 81 is locked to the threaded rod 82 by tightening the lock nuts 84 and 85.

In the embodiment of Figs. 1 and 2, the torsion bar 59 is disposed on the outer side of the side member 11 a of the upper fork 11. If the side member 11 a is hollow, the torsion bar 89 may be disposed in the interior of the side member 11 a.

Doing so improves the appearance.

Further, as shown in Fig. 9, a torsion bar 99 may be disposed between the side members of the upper fork 91, adjacent the inner side of one, that is the side member 91 a as shown in Fig. 9.

In this case, an arm 93 which is coupled by a pin 93a to the lower end of the upper fork 91, is disposed on the outer side of the side member 91 a. The side member 91 a is formed with a seethrough hole 92 extending in the lateral direction of the motorcycle body. A link arm 94 which has its inner end coupled to the lower end of the torsion bar 99 is inserted in the hole 92. A ball 94a is mounted in the outer end of the link arm 93. As shown in Fig. 10, the arm 93 has an integral bent end portion 93a extending substantially parallel to the side member 91 a from the pin 93a. A ball 94a is received in a notch 93d formed in the end portion 93c. As the arm 93 is rotated about the pin 93a for vertical displacement of the front wheel, the torsion bar 99 is twisted via the link arm 94 like the previous embodiment.In this embodiment, only the link arm 94 may be provided between the arm 93 and torsion bar 99, and the rod 63 of the linkage 64 mentioned above may be omitted.

Fig. 11 shows a further embodiment, in which rods 1 23 and 127 respectively coupled to a torsion bar 129 and a rotary lever type shock absorber or damper 120, are independently coupled to respective opposite sides arms 11 3-1 and 113-2 connecting the upper fork 111 and lower fork 112. In this embodiment, the linkage 124 coupling the lower fork 112 and torsion bar 129 and the linkage coupling the lower fork 112 and the damper 1 20 individually use their own arms 113-1 and 113-2. Thus, the driving force for twisting the torsion bar 1 29 by operating the damper 120 generating the damping force can be shared by the arms 113-1 and 113-2.

Fig. 12 shows a further embodiment, in which a rotary lever type shock absorber or damper 140 is provided separately of top and bottom bridges 136 and 1 37 connecting opposite side members 131a and 131bofthe upperfork 1 31 . In this embodiment the damper 140 is again disposed between the side members 131 a and 131 b, thus providing for satisfactory weight balance and protection of the damper 140 by the side members 131 a and 131 b.Further, it is possible to provide two dampers 1 40 and dispose two torsion bars 139 on the left and right side members 131 a and 131 b such that these dampers and torsion bars are independently coupled to the respective left and right arms 133 by forming the arms 133 with end portions 1 33c and 133c'. Indeed in any of the embodiments described above the damper can be provided separately of top and bottom bridges connecting the opposite side members of the upper fork.

Fig. 13 shows a further embodiment, in which a coil spring is used instead of the torsion bar. The coil spring 1 50 is provided between a stationary link and movable link of a linkage 159, namely between the upper fork 151 and front arms 153.

In this embodiment, damping with respect to the vertical displacement of the front wheel 1 55 may be obtained with the combination of the rotary lever type shock absorber or damper 1 60 and coil spring 1 50.

In the above embodiments, the lower end portion of the upper fork and the lower fork, which is a front wheel support member, are coupled together by arms. Figs. 14 and 1 5 show further embodiments, in which a pivotal front wheel support member 1 72 or 1 82 is directly coupled to the lower end of a fork 1 71 or 181 rotatably mounted on the head pipe 1 69 or 1 99 at the front end of the motorcycle frame 161 or 191. In the embodiment of Fig. 14, the pivotal members 172, which supports the front wheel 1 75 with its front end, is linked by a pin 1 72a to the lower end of the form 1 71. The front wheel suspension of this embodiment is thus of a leading link type. In the embodiment of Fig.15, the pivotal member 182, which supports the front wheel 1 85 with its rear end, is linked by a pin 1 82a to the lower end of the fork 1 81. The front wheel suspension of this embodiment is thus of a trailing link type. In either of the embodiments of Figs. 14 and 15, the rotary lever type shock absorber or damper 1 70 or 1 80 is disposed between the opposite side members of the fork 171 or 181 either with its case forming a bridge between the side members of the fork (as illustrated), or separately of upper and lower bridges of the fork. The damper 1 70 or 1 80 is coupled to the pivotal member 1 72 or 182 via a rod 177 or 187.

Claims

1. A motorcycle front wheel suspension comprising a fork rotatably supported in a frame of the motorocycle and consisting of a pair of side members, a front wheel support member supporting the front wheel of the motorcycle at one end and coupled at the other end to the fork, the front wheel support member being capable of swinging up and down to allow up-and-down displacement of the front wheel for following irregular road surfaces, and a shock absorber of rotary lever form operatively coupled to the front wheel support for damping the swinging motion thereof, this shock absorber being disposed between said side members.

2. A front wheel suspension as claimed in claim 1, wherein the shock absorber has a case that is a bottom bridge connecting said side members.

3. A front wheel suspension as claimed in claim 1, wherein the shock absorber is provided separately of top and bottom bridges connecting said side members.

4. A front wheel suspension as claimed in claim 1, 2 or 3, wherein said fork is an upper fork and said front wheel support member is a lower fork to which the shock absorber is coupled via a linkage that includes a lever arm of the shock absorber that is connected to an arm that serves to connect the upper fork to the lower fork, this lastmentioned arm being coupled to one end of a torsion bar that has its other end fast with the upper fork.

5. A front wheel suspension as claimed in claim 4, wherein the lower fork consists of a pair of side members, and wherein there are two shock absorbers respectively coupled to the lower fork side members, and two torsion bars respectively coupled to respective arms serving to connect corresponding upper and lower fork side members.

6. A front wheel suspension as claimed in claim 4 or 5, wherein the (or each) lever arm is connected by a rod to the (or the corresponding) arm connecting the upper and lower forks, this (or each such) arm and rod being constructed as a turn buckle linkage whereby the height of the motorcycle can be adjusted.

7. A front wheel suspension as claimed in claim 4, 5 or 6, wherein the (or each) arm connecting the upper and lower forks is coupled to the (or the corresponding) torsion bar by a turn buckle whereby the pre-load of the spring force of the (or each) torsion bar can be adjusted.

8. A front wheel suspension as claimed in claim 4, 5 or 6, wherein the (or each) torsion bar is fast with the upper fork via an adjustment arm that is locked between the torsion bar and the upper fork in adjustable manner so that the pre-load of the spring force of the (or each) torsion bar can be adjusted.

9. A front wheel suspension as claimed in any one of claims 4 to 8, wherein the (or each) torsion bar is disposed inside the (or the corresponding) upper fork side member.

10. A front wheel suspension as claimed in claim 4, wherein the torsion bar is disposed between said side members and is coupled to the arm connecting the upper and lower forks by a link arm having one end coupled to the torsion bar and its other end entered in a notch in one end of the arm connecting the upper and lower forks.

11 A front wheel suspension as claimed in claim 1, 2 or 3, wherein said fork is an upper fork and said front wheel support member is a lower fork that consists of a pair of side members, the shock absorber being coupled to one of the lower fork side members via a linkage that includes a lever arm of the shock absorber that is connected to an arm that serves to connect this lower fork side member to its corresponding upper fork side member, and wherein an arm that serves to connect the other lower fork side member to its corresponding upper fork side member is coupled to one end of a torsion bar that has its other end fast with this corresponding upper fork side member.

12. A front wheel suspension as claimed in claim 1, 2 or 3, wherein said fork is an upper fork and said front wheel support member is a lower fork to which the shock absorber is coupled via a linkage that includes a lever arm of the shock absorber that is connected to an arm that serves to connect the upper fork to the lower fork, this last-mentioned arm being coupled to one end of a coil spring that has its other end coupled to the upper fork.

13. A front wheel suspension as claimed in claim 1, 2 or 3, wherein the front wheel support member is directly coupled to the fork.

14. A front wheel suspension as claimed in claim 13, wherein the front wheel support member supports the front wheel at its front end and is linked at its rear end to the lower end of the fork.

1 5. A front wheel suspension as claimed in claim 13, wherein the front wheel support member supports the front wheel at its rear end and is linked at its front end to the lower end of the fork.

1 6. A motorcycle front wheel suspension substantially as hereinbefore described with reference to any of the embodiments illustrated in the accompanying drawings.