JP2005239052A - Motorcycle front fork - Google Patents

Abstract

PROBLEM TO BE SOLVED: To strengthen welding attachment to a bottom bridge of a front fork for suspending a front wheel of a motorcycle, and improve shock absorption and vehicle ride comfort by a damper elastic member.
A bottom bridge 27 attached to the lower end of a steering shaft 26 is provided with a notch 27f, and the upper end of a support cylinder shaft 50 of a fork pipe is applied to the bottom bridge 27 and welded to the bottom bridge 27 through a notch 27f, thereby providing a sufficient welding range. By securing, the attachment strength between the bottom bridge 27 and the fork pipe is improved. Furthermore, a damper elastic member 53 is provided inside only the support cylinder shaft 50 of any one of the fork pipes, and the movable cylinder shaft 51 on the side where the damper elastic member is not provided is lengthened to be movable with the support cylinder shaft 50. The fitting length with the cylinder shaft 51 was made longer, the strength rigidity of the front fork was further increased, and smooth sliding of the movable cylinder shaft 51 was realized.
[Selection] Figure 2

Description

  The present invention relates to a front fork that suspends a front wheel of a motorcycle, and more particularly, to a technique that can enhance welding attachment of the front fork and improve riding comfort of a vehicle.

The motorcycle is provided with a front fork for suspending the front wheel. The front fork has a structure in which a pair of fork pipes is attached to the lower end of a steering shaft provided at the front end of the body frame so as to be rotatable about the axis via a bottom bridge, and the front wheels can freely rotate between the lower ends of these fork pipes. And a handlebar is attached to the upper end of the steering shaft to constitute a steering system for the front wheels by operating the handlebar.
The front fork also constitutes a cushion system for the front wheels, and a pair of fork pipes are fitted to the support cylinder shafts welded to the bottom bridge, respectively, so that the movable cylinder shaft is slidable in the axial direction. As a structure in which a cushion spring is interposed between the movable cylinder shaft and the movable cylinder shaft, the front wheel supported in a freely rotatable manner between the lower end portions of the movable cylinder shaft is allowed to be buffered.

As mentioned above, the front fork supports the front wheels of the motorcycle, so it is necessary to ensure sufficient strength and rigidity. Also, by ensuring sufficient strength and rigidity, the front fork can be used when traveling or braking. Riding comfort can be improved.
For this reason, the bottom bridge constituting the front fork and the pair of fork pipes have been attached by a structure as shown in FIGS. 11 is a front view of a mounting portion between the bottom bridge and the pair of fork pipes, and FIG. 12 is a cross-sectional view taken along line AA in FIG.

The bottom bridge 1 has a shape in which a steel plate is bent into a U shape, and an upper plate portion 1a and a lower plate portion 1b are connected by a vertical plate portion 1c. A steering shaft 2 is inserted into the center of the bottom bridge 1 from above. The steering shaft 2 is welded to the upper plate portion 1a via the bracket 3 (welded portion 4a) and welded to the lower plate portion 1b ( Welded part 4b).
Also, fork pipe support cylinder shafts 5 are inserted from below at symmetrical positions around the steering shaft 2 of the bottom bridge 1, and these support cylinder shafts 5 have their upper ends on the lower surface of the upper plate portion 1a. It is applied and welded (welded portion 6a) and welded (welded portion 6b) to the lower plate portion 1b.

In this way, the steering shaft 2 and the fork pipe (support cylinder shaft 5) are connected to each other by inserting the steering shaft 2 and the support cylinder shaft 5 into the bottom bridge 1 and welding the two locations to each other. Strength and rigidity are ensured.
In addition, with respect to the cushion system structure of the front fork, damper elastic members are provided in both support cylinder shafts attached to the bottom bridge, and the sliding of the movable cylinder shaft fitted to the support cylinder shaft from below is made damper. A technique of buffering with an elastic member is known, and further, the shock absorber characteristics are changed by making the heights of these two damper elastic members different or making the height of the two damper elastic members contacting the bottom bridge different. There is known a technique for providing (see Patent Document 1).
Japanese Patent Publication No. 6-41276

In the mounting structure of the bottom bridge 1 and the support cylinder shaft (fork pipe) 5 as described above, as shown in detail in FIG. 12, the welding of the portion applied to the upper plate portion 1a of the support cylinder shaft 5 is performed. However, the range of the welded portion 6a is limited although it is desirable that welding is performed over substantially the entire circumference of the support cylinder shaft 5. The reason why the welding range is limited in this way is that the portion that cannot be welded is in a narrow space sandwiched between the upper plate portion 1a and the lower plate portion 1b, and the position where the vertical plate portion 1c and the steering shaft 2 interfere. This is because it is extremely difficult to perform welding work by inserting a welding rod into the part.
Note that the upper end opening of the support cylinder shaft 5 closes the upper end opening by applying the upper end of the support cylinder shaft 5 to the upper plate portion 1a as described above in order to prevent intrusion of rainwater and dust.

  As for the structure of the cushion system of the front fork, it is preferable to provide a damper elastic member in the support cylinder shaft to buffer the sliding of the movable cylinder shaft. On the other hand, by providing the damper elastic member, the movable cylinder shaft is provided. Therefore, in order to secure the necessary slidable length, the length of the movable cylinder shaft must be shortened. The fitting length was shortened. The fitting length between the support cylinder shaft and the movable cylinder shaft contributes to the strength and rigidity of the fork pipe as a whole, and is an important factor for smoothly sliding the movable cylinder shaft. There was room for improvement in improving the performance.

The present invention has been made in view of the above-described conventional circumstances, and an object thereof is to realize a reasonably strengthened weld attachment structure for a front fork.
Another object of the present invention is to improve the riding comfort of a motorcycle by improving the front fork.

The present invention provides a motorcycle in which a notch is provided at a portion where a fork pipe (that is, a support cylinder shaft) of a bottom bridge is attached, and an upper end surface of the support cylinder shaft is applied to the fork pipe attachment portion and welded to the bottom bridge through the notch. The front fork.
Therefore, there is no need to insert a welding rod into the narrow space sandwiched between the bottom bridge plates as in the conventional case, and the upper end of the support cylinder shaft is easily welded to the bottom bridge by welding through a notch. can do. In addition, since the support cylinder shaft attachment part of the bottom bridge remains without dropping because it is a notch, the part closes the upper end opening of the support cylinder axis to prevent rainwater and dust from entering the fork pipe.
That is, for example, by providing a notch that is continuous or intermittent over substantially the entire circumference of the support cylinder shaft, the support cylinder axis can be welded to the bottom bridge over substantially the entire circumference.

Furthermore, the present invention provides a damper elastic member for buffering the sliding of the movable cylinder shaft inside the support cylinder shaft of one of the fork pipes, and the length of the movable cylinder shaft of the other fork pipe without the damper elastic member. This is a front fork of a motorcycle in which the length of the one movable cylinder shaft is made longer than that of the other fork pipe, and the fitting length between the support cylinder shaft and the movable cylinder shaft in the other fork pipe is made longer than that of the one fork pipe.
Therefore, while realizing the buffering of the movable cylindrical shaft by the damper elastic member, the fitting length between the supporting cylindrical shaft and the movable cylindrical shaft is sufficiently secured to increase the strength and rigidity as the fork pipe and to smoothly move the movable cylindrical shaft. Smooth sliding and improving the riding comfort of the vehicle.

According to the present invention, since the upper end surface of the support cylinder shaft applied to the bottom bridge is welded through the notch provided in the bottom bridge, the support cylinder shaft has a structure in which the upper end opening of the support cylinder shaft is closed. It can be welded over substantially the entire circumference, and the strength and rigidity as a fork pipe can be increased.
Further, according to the present invention, a damper elastic member for buffering sliding of the movable cylinder shaft is provided inside the support cylinder shaft of one of the fork pipes, and the length of the movable cylinder shaft of the other fork pipe without the damper elastic member. Since the length is increased, the fitting length between the support cylinder shaft and the movable cylinder shaft in the fork pipe can be sufficiently secured, and the buffering by the damper elastic member and the smooth sliding of the movable cylinder shaft can be realized.

The present invention will be specifically described based on an embodiment.
First, as shown in FIG. 8, in the motorcycle of this example, the skeleton of the vehicle body is constituted by a frame 20, a leg shield 21 and a low floor step floor 22 are provided at the front of the frame 20, and the rear of the frame 20 is provided. A scooter type in which a rear body 23 is provided and a seat 24 is provided on the rear body 23.
A steering shaft 26 having a handlebar 25 at its upper end is provided at the front end of the frame 20 so as to be rotatable about the shaft, and a bottom bridge 27 is welded to the lower end of the steering shaft 26. A front fork 28 is welded to the bottom bridge 27, and a front wheel 29 is rotatably provided at the lower end of the front fork 28.

  A power unit 33 is configured by integrating the engine 31 and a belt-type continuously variable transmission 32 that transmits engine output. The power unit 33 swings up and down via a link mechanism 35 on a bracket 34 provided on the frame 20. The power unit 33 is supported by a cushion unit 40 between the power unit 33 and the frame 20. The engine output is transmitted to the rear wheel 36 supported by the power unit 33 via the belt type continuously variable transmission 32, and the rear wheel 36 is driven to rotate.

  A mechanical drum brake device 42 is provided on each of the front wheel 29 and the rear wheel 36, and these brake devices 42 brake the rotation of the wheels by pulling the brake arm 43 by the brake operation force transmission member 44. That is, the brake operation force that the driver holds the brake lever 45 provided on the handlebar 25 is transmitted through the brake operation force transmission member 44, and the brake arm 43 is rotated to brake the wheel rotation.

9 and 10 show details of the front side portion of the motorcycle.
The front fork 28 has a structure in which a pair of fork pipes are attached to the bottom bridge 27, and each fork pipe is a cushion in which a movable cylinder shaft 51 is slidably accommodated in a support cylinder shaft 50 via a coil spring 52. In the structure, the upper end portion of each support cylinder shaft 50 is fixed by welding to the bottom bridge 27 and is steered together with the steering shaft 26.
A damper elastic member 53 made of an elastic material such as rubber is provided in one support cylinder shaft 50. When the movable cylinder shaft 51 slides greatly, such as when a motorcycle gets over an obstacle, the A damper elastic member 53 abuts between the upper end of the movable cylinder shaft 51 and the bottom surface side (bottom bridge 27) of the support cylinder shaft 50 to buffer the sliding.

An axle 55 is supported between the lower ends of the movable cylinder shaft 51, and a wheel 56 of the front wheel 29 is rotatably supported on the axle 55 via a bearing. A hub portion 57 formed in a drum shape in the center of the wheel 56 also serves as a brake drum of the drum brake device 42, and a pair of semicircular brake shoes are provided in the hub portion 57, as is well known. A mechanical drum brake device is provided that spreads by rotating and is brought into pressure contact with the inner peripheral surface of the brake drum 57 to brake the rotation of the brake drum 57 (that is, the front wheel 29).
A brake operation force transmission wire 44 is connected to the brake arm 43, and the arm 43 and the wire 44 are connected by a brake joint 60. In addition, 59 shown in FIG. 9 is a speedometer cable which transmits the rotation speed of the front wheel 29. FIG.

The attachment structure of the support cylinder shaft 50 (fork pipe) and the steering shaft 26 to the bottom bridge 27 will be described in detail with reference to FIGS.
1 is a front view of a mounting portion between a bottom bridge and a pair of fork pipes, FIG. 2 is a plan view seen from above in FIG. 1, FIG. 3 is a cross-sectional view taken along the line BB in FIG. It is a top view which shows the state before attaching the support cylinder shaft 50 with the same eyes | visual_axis as FIG.
The mounting structure of this example is the same as the structure shown in FIGS. 11 and 12 in the approximate structure of the bottom bridge 27 and the mounting structure of the support cylinder shaft 50 and the steering shaft 26. The bent bottom bridge 27 has a structure in which the steering shaft 26 and a pair of front fork support cylinder shafts 50 are welded, and a welded structure in which the support cylinder shaft 50 and the bottom bridge 27 are notched as described below is characteristic. It is an important part.

The bottom bridge 27 has a shape similar to the above-described conventional structure in which a steel plate is bent into a U-shape, and an upper plate portion 27a and a lower plate portion 27b are connected by a vertical plate portion 27c. A steering shaft 26 is inserted into the center of the bottom bridge 27 from above, and the steering shaft 26 is welded to the upper plate portion 27a via the bracket 30 (welded portion 61a) and welded to the lower plate portion 27b ( Welded part 61b).
Further, support cylinder shafts 50 of the fork pipe are inserted from below at symmetrical positions around the steering shaft 26 of the bottom bridge 27, and these support cylinder shafts 50 have their upper ends on the lower surface of the upper plate portion 27a. It is applied by welding (welded portion 62a) and welded to the lower plate portion 1b (welded portion 62b).

A pair of semicircular cutouts 27d are provided in the upper plate portion 27a where the support cylinder shaft 50 is attached in contact with each other, and the semicircular cutouts of the upper plate portion 27a are opposed to each other. Between the notches 27d, a bulging portion 27e bulging upward is provided. The pair of semicircular cutouts 27d are formed in sizes and shapes corresponding to the upper ends of the support cylindrical shafts 50, respectively, and the circular portion of the upper plate portion 27a surrounded by the pair of semicircular cutouts 27d. 27f is connected to the upper plate portion 27a by the bulging portion 27e.
Therefore, when the support cylinder shaft 50 is applied to the lower surface of the upper plate portion 27a, the upper end opening of the support cylinder shaft 50 is closed by the circular portion 27f without requiring a cap member, and the upper end edge of the support cylinder shaft 50 is used. The entire circumference of the support cylinder shaft 50 faces the semicircular cutout 27d. By welding the inside of the semicircular cutout 27d, the upper plate is uniformly spread over the entire circumference with the upper end of the support cylinder shaft 50 closed. It can be welded to the portion 27a, and rain water or the like can be prevented from entering the support cylinder shaft 50, and the support cylinder shaft 50 can be attached to the bottom bridge 27 with sufficient strength and rigidity.

  In order to form the notch 27d as described above in the upper plate portion 27a, for example, as shown in FIG. 5, a cylindrical cutting tool 64 having a diameter spanning a pair of bulging portions 27e is used. This can be easily performed by rotating the shaft and cutting the upper plate portion 27a into an annular shape with the cutting teeth at the tip. That is, when the cutting tool 64 cuts the upper plate portion 27a and stops cutting, the bulging portion 27e remains without being cut out, and thus is surrounded by the pair of semicircular cutouts 27d as described above. A structure in which the circular portion 27f is connected to the upper plate portion 27a by the bulging portion 27e is easily formed.

The formation of the notches 27d can also be performed by various known methods such as press punching.
Further, the bulging portion 27e is extremely useful when performing the above-described cutting process. However, for example, in the case of press punching, the bulging portion 27e can be omitted, and the bulging portion 27e is notched. What is necessary is just to provide according to the processing method of 27d.
Further, in the present invention, the shape of the notch 27d is not limited to a semicircular shape, but the upper end edge of the support cylinder shaft 50 is exposed over a necessary range, such as an intermittent notch that is annular as a whole. It is sufficient if it can be welded. In the present invention, the configuration and shape of the bottom bridge 27 are not limited to the above example. In short, in the mounting structure in which the support cylinder shaft 50 of the fork pipe is abutted against the bottom bridge 27 and welded, A cutout 27 d for welding the upper end of the support cylinder shaft 50 may be provided in the bottom bridge 27.

FIG. 6 is a partial sectional view showing details of the internal structure of the front fork 28. In addition, when distinguishing one from the other about the support cylinder axis | shaft 50, the movable cylinder axis | shaft 51, and the coil spring 52, it describes by attaching | subjecting the identification codes R and L to these codes | symbols, and also in FIG. It is described with a reference sign.
The illustrated front fork 28 is provided with a damper elastic member 53 only inside one support cylinder shaft 50R (in the illustrated example, on the left side as viewed in the drawing), as shown in cross-section. The damper elastic member is not provided inside the other support cylinder shaft 50L.
The front fork 28 is fitted in the support cylinder shaft 50 so that the movable cylinder shaft 51 is slidable in the axial direction from its lower end opening, and is movable with the upper end surface of the support cylinder shaft 50 (that is, the upper plate portion 27a of the bottom bridge). A coil spring 52 is interposed between the upper end of the cylinder shaft 51 and the movable cylinder shaft 51 is slidable in the axial direction against the coil spring 52. The damper elastic member 53 is a support cylinder shaft. It is mounted between the upper end surface of 50R and the upper end of the movable cylinder shaft 51R (that is, inside the coil spring 52R) so as to be movable in the axial direction. In the figure, reference numeral 66 denotes a lid member that closes the upper end opening of the movable cylinder shaft 51R and forms a contact surface of the damper elastic member 53.

That is, when an external force is applied to the front wheel 29 while the motorcycle is running, the movable cylindrical shaft 51 slides upward against the coil spring 52 to buffer it, and when a larger external force is applied, the damper elastic member 53 Is sandwiched between the upper end of the support cylinder shaft 50R and the upper end of the movable cylinder shaft 51R to provide a larger buffering action and restrict further sliding of the movable cylinder shaft 51.
The contact surface of the damper elastic member 53 on the upper end side of the support cylinder shaft 50R is constituted by the circular portion 27f of the bottom bridge upper plate portion 27a. As described above, the circular portion 27f is notched by the notch 27d and the support cylinder shaft is formed. Since the upper end of 50 is welded, the damper elastic member contact surface of the support cylinder shaft 50R is configured with sufficient strength and rigidity.

Here, since it is necessary to secure a stroke considering the contact with the damper elastic member 53 as described above, the fitting length between the support cylinder shaft 50R on the side where the damper elastic member 53 is provided and the movable cylinder shaft 51R is determined. However, the fitting length between the support cylinder shaft 50L on the side where the damper elastic member 53 is not provided and the movable cylinder shaft 51L is not limited as long as the same stroke length can be obtained. Therefore, the length of the movable cylinder shaft 51L on the side where the damper elastic member is not provided is longer (H) than the movable cylinder shaft 51R on the side where the damper elastic member 53 is provided, and the side where the damper elastic member is not provided. The fitting length between the support cylinder shaft 50L and the movable cylinder shaft 51L is longer than the fitting length between the support cylinder shaft 50R on the side where the damper elastic member 53 is provided and the movable cylinder shaft 51R.
Accordingly, the fork pipe on the side where the damper elastic member is not provided secures the fitting length between the support cylinder shaft 50 and the movable cylinder shaft 51 as much as possible to sufficiently satisfy the strength and rigidity required for the fork pipe, and the movable cylinder shaft. The sliding of 51 can be made smooth, and the buffer characteristics can be changed by the fork pipe on the side where the damper elastic member 53 is not provided, and the riding comfort of the vehicle can be improved as a whole.

FIG. 7 shows another example of the internal structure of the front fork 28. In addition, when distinguishing one from the other about the support cylinder axis | shaft 50, the movable cylinder axis | shaft 51, and the coil spring 52, description code | symbol is attached with the identification codes R and L, and also in FIG. It is described with a reference sign.
In the illustrated front fork 28, a damper elastic member 53 is provided only on one fork pipe as in the above example, and the structure of the fork pipe on the side where the damper elastic member 53 is provided is the same as in the above example. is there.
The fork pipe on the side where the damper elastic member 53 is not provided has a longer fitting length (H) between the support cylinder shaft 50L and the movable cylinder shaft 51L than the other, as in the above example, but it has a slightly smaller diameter. The coil spring 52L is held by a spring guide 68 and is supported on the inner side of the movable cylinder shaft 51L.

That is, in the fork pipe on the side where the damper elastic member 53 is not provided, the seat plate 69 of the coil spring is provided inside the movable cylinder shaft 51L, and the folder member 70 having an opening at the upper end of the movable cylinder shaft 51L is provided. ing. The coil spring 52L is held by a cylindrical shaft-shaped spring guide 68 attached at its upper end to the circular portion 27f of the bottom bridge upper plate portion 27a, and the lower end portion of the coil spring 52L is moved from the opening of the folder member 70 into the movable cylindrical shaft 51L. And is supported by a seat plate 69.
According to such a structure, in addition to the fact that the fitting length between the support cylinder shaft 50L and the movable cylinder shaft 51L can be ensured as much as possible by the fork pipe on the side where the damper elastic member is not provided as in the above example, the support is thus supported. Even if the fitting length between the cylinder shaft 50L and the movable cylinder shaft 51L is increased, the coil spring 52L can be elongated according to the mounting position of the seat plate 69. The length of the spring is one important factor in setting the spring characteristics, and the length of the coil spring 52L can be increased to realize a soft cushion feeling.

It is the front view which fractured | ruptured partially the attachment part of the bottom bridge and fork pipe which concern on one Embodiment of this invention. It is the top view which looked at the attaching part of the bottom bridge and fork pipe which concern on one Embodiment of this invention from the upper direction in FIG. FIG. 3 is a cross-sectional view taken along the line BB in FIG. 2. It is a top view which shows the state before attaching the support cylinder shaft of the bottom bridge which concerns on other one Embodiment of this invention with the same eyes | visual_axis as FIG. It is a figure explaining the formation method of a notch concerning one embodiment of the present invention. It is a fragmentary sectional view showing the internal structure of the front fork concerning one embodiment of the present invention. It is a fragmentary sectional view showing other examples of the internal structure of the front fork concerning one embodiment of the present invention. 1 is a side view showing an overall configuration of a motorcycle to which the present invention is applied. 1 is a partial cross-sectional side view showing a front fork portion of a motorcycle to which the present invention is applied. 1 is a partial cross-sectional front view showing a front fork portion of a motorcycle to which the present invention is applied. It is the front view which fractured | ruptured the attachment part of the conventional bottom bridge and a fork pipe partially. It is AA arrow sectional drawing in FIG.

Explanation of symbols

26: Steering shaft, 27: Bottom bridge,
27a: upper plate portion, 27b: lower plate portion,
27c: vertical plate portion, 27d: notch,
27e: bulging portion, 27f: circular portion,
28: Front fork 50, 50R, 50L: Supporting cylinder shaft,
51, 51R, 51L: movable cylinder shaft, 52, 52R, 52L: coil spring,
53: damper elastic member, 62a, 62b: welded part,
H: difference in fitting length,

Claims (2)

In front forks of motorcycles,
The motorcycle has a notch in the bottom bridge fork pipe attachment part attached to the lower end of the steering shaft, the upper end surface of the fork pipe is abutted against the fork pipe attachment part and welded to the bottom bridge through the notch. Front fork. The front fork of the motorcycle according to claim 1,
Each of the pair of fork pipes that support the front wheels has a movable cylindrical shaft slidably fitted to a supporting cylindrical shaft attached to the bottom bridge, and a cushion spring is interposed between the supporting cylindrical shaft and the movable cylindrical shaft. Intervening structure,
Further, a damper elastic member for buffering sliding of the movable cylinder shaft is provided inside the support cylinder shaft of one of the fork pipes, and the length of the movable cylinder shaft of the other fork pipe without the damper elastic member is set to the one of the fork pipes. A motorcycle front fork characterized in that it is longer than the length of the movable cylinder shaft, and the fitting length between the support cylinder shaft and the movable cylinder shaft in the other fork pipe is longer than that of the one fork pipe.

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