JPS6127230B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a mounting structure for fixing a steering shaft to a steering head pipe (hereinafter abbreviated as head pipe) in a motorcycle.

When attaching a steering shaft connected to a front fork to a head pipe on the vehicle body, conventionally, bearings were provided at the upper and lower opening ends of the head pipe, and the steering shaft with an under bracket fixed to it was inserted into the head pipe so as to be rotatable. In addition, a means is employed in which a nut is screwed onto the upper end of the steering shaft protruding from the head pipe, and the steering shaft is tightened in the axial direction between the nut and the under bracket.

However, in the past, a male threaded portion to be screwed into the nut was carved from the upper end of the steering shaft to the upper edge of the upper bearing, so this male threaded portion substantially reduced the wall thickness of the steering shaft, and The end of the cut in the external threaded part was located exactly at the part led out from the head pipe of the steering shaft, and as a result, a notch effect occurred at the end of the cut in the externally threaded part, causing stress concentration. In the case of the above configuration, bending stress is applied to the steering shaft through the attenuation bracket, and since the force applied from the front fork is particularly large in motorcycles for motocross racing, the bending stress is also large. There was a risk that the steering shaft would break at the end of the male thread.

This invention was made based on the above circumstances, and an object thereof is to provide a mounting structure for a steering shaft in a motorcycle, which can improve the strength of the steering shaft without increasing its size, and can prevent breakage of the steering shaft. It is something.

That is, in order to achieve the above object, the present invention provides an upper bearing and a lower bearing in the upper and lower openings of a steering head pipe, rotatably inserts the steering shaft into the steering head pipe, and inserts a steering shaft into the lower end of the steering shaft. Assuming a motorcycle in which an under bracket is attached and an upper bracket is attached to the upper end, and the upper part of the front fork is bridged between these two brackets, a cylindrical tightening fitting is fitted to the upper end of the steering shaft, A flange portion is formed on this tightening fitting to press the upper bearing and tighten the steering shaft between it and the under bracket, and a flange portion is formed on the inner peripheral surface of this tightening fitting at a distance from the upper bearing in the axial direction of the steering shaft. A female threaded portion is formed at the position, and the boss portion of the above-mentioned fastening bracket is fitted onto the outer periphery of this tightening metal fitting, while the above-mentioned fastening bracket is held on the inner circumferential surface of the upper end opening of the above-mentioned steering shaft so as not to come off from the steering shaft. Screw in the bolt that is attached to the upper end of the steering shaft, which is surrounded by the boss of the upper bracket, and screw it into the female threaded part of the tightening fitting at a distance from the upper bearing in the axial direction of the steering shaft. It is characterized by forming a male threaded portion.

An embodiment of the present invention will be described below based on the drawings.

In the figure, reference numeral 1 indicates a frame, and this frame 1 has a main pipe 3 and a down tube 4 welded to a head pipe 2, a seat pillar tube 5 and a seat rail 6 are joined to the main pipe 3 and down tube 4, and the seat rail 6
A back stay 7 is welded between the down tube 4 and the down tube 4. An engine 8 is mounted on this frame 1 via brackets 9...
And a fuel tank 10 straddles the main pipe 3,
Further, seats 11 are provided on the seat rails 6, respectively. Further, at the rear of the frame 1, the lower front end of a rear arm 13 that pivotally supports the rear wheel 12 is pivotally supported via a pivot shaft 14, so that it can swing freely.
The upper front end of this rear arm 13 and the main pipe 3
A suspension device 17 consisting of a shock absorber 15 and a coil spring 16 is installed between the two. Therefore, this motorcycle has a monocross suspension type frame.

A hollow steering shaft 18 is rotatably inserted into the head pipe 2, and an upper bracket 19 (also referred to as a handle crown) and an under bracket 20 are fixed to the upper and lower insertion ends of the steering shaft 18. . Between the upper bracket 19 and the under bracket 20, there are front forks 21 and 2.
1, and a front wheel 22 is pivotally supported at the lower ends of these front forks 21, 21. Further, a steering handle 23 is attached to the attachment bracket 19. Therefore, when the handle 23 is rotated, the upper bracket 19, under bracket 20, front forks 21, 21, and front wheel 22 are rotated integrally around the steering shaft 18.

Next, a structure for attaching the steering shaft 18 to the head pipe 2 will be explained with reference to FIGS. 3 and 4.

An upper bearing 24 and a lower bearing 25 are fitted inside the upper and lower opening ends of the head pipe 2.
The steering shaft 18 has these two bearings 2.
4 and 25, and passes through the head pipe 2. The under bracket 20 is welded to the lower end of the steering shaft 18. Further, a male threaded portion 26 is carved at the upper end of the steering shaft 18, and this male threaded portion 26
The end of the cut is located at a distance from the upper bearing 24 in the axial direction. This male threaded portion 26
A nut 27 as a tightening fitting is screwed onto the cylindrical portion 28 which is fitted around the upper end of the steering shaft 18, and this cylindrical portion as shown in FIG. It is integrally provided with a seat portion 29 projecting like a flange from the outer peripheral edge of the lower end of the seat portion 28 . The inner surface of the upper end of this cylindrical portion 28, that is, the upper bearing,
A female threaded portion 30 is formed at a distance in the axial direction upper side of the seat portion 29, and a female threaded portion 30 is formed on the outer periphery of the seat portion 29 to be engaged with a tightening tool. It is formed. When such a nut 27 is fitted onto the upper end of the steering shaft 18 and tightened, the seat 29 presses against the upper bearing 24, and the head pipe 2 side is tightened between the nut 27 and the under bracket 20. Both bearings 24 and 25 are inserted in the axial direction to hold the steering shaft 18 so that it can rotate relative to the head pipe 2 and not come off.

Note that between the nut 27 and the upper bearing 24,
A bearing cover 32 is held in place, and a seal 33 that slides into contact with the outer periphery of the head pipe 2 is provided at the opening of the bearing cover 32.

On the other hand, an attenuator bracket 19 is fitted into the cylindrical portion 28 of the nut 27. A boss portion 34 is formed in this portion of the atsupah bracket 19, and the outer periphery of the cylindrical portion 28 is loosely fitted into a fitting hole 34a formed in the boss portion 34, and is secured in the axial direction by a clamp bolt (not shown). They are attached in orthogonal directions. In addition, the steering shaft 18
A female threaded portion 35 is formed on the inner peripheral surface of the upper end opening,
The steering shaft 18 is attached to this female threaded portion 35.
A bolt 36 is screwed in from the upper end side. This bolt 36 is attached to the boss portion 34 of the atsupah bracket 19.
is held between the seat part 29 of the nut 27,
Attach bracket 19 to steering shaft 1
8, it is held in place to prevent it from coming off. Therefore, the steering shaft 18 assembled in this way
In this case, the male threaded portion 26 is formed within a range surrounded by the boss portion 34 and the cylindrical portion 28 of the upper bracket 19.

The operation of the embodiment having such a configuration will be explained.

When the front wheels 22 follow the unevenness of the road surface and move up and down while driving, this vibration is transmitted to the front forks 21 and 2.
1 to the upper bracket 19 and the under bracket 20. The atsupah bracket 19 is connected to the nut 2 via its boss portion 34.
The nut 27 transmits the vibration to the steering shaft 18. In this case, since the steering shaft 18 is supported at both ends by the head pipe 2 via the upper bearing 24 and the lower bearing 25, the vibration is transmitted to the upper part of the steering shaft 18 which protrudes above the head pipe 2, and to the upper part of the upper bearing 24. This acts as a bending stress centered on the edge (indicated by line LL in FIG. 3).

However, the upper part of the steering shaft 18 is not only surrounded by the cylindrical part 28 of the nut 27 and reinforced with mechanical strength, but also the wall thickness of the steering shaft 18 is substantially reduced by the presence of the male threaded part 26. However, since this male threaded portion 26 is formed at a position axially upwardly spaced apart from the upper bearing 24, this male threaded portion 26 and its cut end will not be located on the above-mentioned line L-L. Therefore, the notch effect does not occur at the upper edge of the upper bearing 24, so the mechanical strength of the steering shaft 18 is improved, and there is no possibility that the steering shaft 18 will break at the L-L location. The male threaded portion 26 is substantially connected to the outer bracket 1.
9, the bending stress transmitted from the upper bracket 19 will not occur at the cut end of the male threaded portion 26. Moreover, the stress transmitted from this hot spring bracket 19 is once transferred to the nut 2.
Since the nut 27 has a cylindrical portion 28 that fits into the steering shaft 18, the stress can be dispersed in the axial direction of the steering shaft 18 by the cylindrical portion 28.
This has the advantage of reducing stress concentration.

Even if the nut 27 is accidentally over-tightened during maintenance, since the male threaded portion 26 is formed on the upper edge of the steering shaft 18, local tensile stress will not be generated at the L-L portion. This prevents the mechanical strength of the L portion from decreasing.

According to the present invention described in detail above, thinning of the area corresponding to the upper edge of the upper bearing of the steering shaft is prevented, and the cut end of the external thread is not located at this area, so that unlike the conventional No notch effect occurs and the mechanical strength of the steering shaft is improved. In addition, since the male threaded portion is formed in a position surrounded by the thicker bracket, even if the wall thickness of the steering shaft is reduced due to the presence of the male threaded portion, the reduced strength due to this thinner wall will be compensated for by the thicker bracket. This also improves the mechanical strength of the upper part of the steering shaft. Therefore, even if bending stress is applied through the hot-top bracket, problems such as breakage of the steering shaft are prevented, and the steering shaft has sufficient durability even when large stress is generated on the hot-top bracket, especially when driving on rough terrain. You can get sex. Furthermore, this configuration has the advantage that there is no need to substantially increase the size of the steering shaft.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, in which Fig. 1 is a side view of the motorcycle, Fig. 2 is a front view, Fig. 3 is a sectional view taken along the line - in Fig. 2, and Fig. 4 is a perspective view of the nut. It is a diagram. 2... Steering head pipe, 18... Steering shaft, 19... Hot spring bracket, 20
...Under bracket, 21, 21...Front fork, 24...Upper bearing, 25...Lower bearing, 26...
Male thread part, 27... Tightening fitting (nut), 28...
Cylinder part, 29... Seat part, 30... Female thread part, 34... Boss part, 36... Bolt.

Claims (1)

[Claims] 1. Upper bearings are provided in the upper and lower openings of the steering head pipe, and the steering shaft is rotatably inserted into the steering head pipe,
In a motorcycle in which an under bracket is attached to the lower end of the steering shaft, an under bracket is attached to the upper end, and the upper part of the front fork is bridged between these two brackets, a cylindrical tightening metal fitting is attached to the upper end of the steering shaft. A flange portion is formed on the inner circumferential surface of the tightening fitting to press the upper bearing to the under bracket and tighten the steering shaft between the upper bearing and the under bracket. A female screw portion is formed at a distance apart, and the boss portion of the upper bracket is fitted to the outer periphery of this tightening metal fitting, while the upper bracket is attached to the inner circumferential surface of the upper end opening of the steering shaft relative to the steering shaft. Screw in the bolt that holds the screw in place, and attach the female thread of the tightening fitting to the outer peripheral surface of the upper end of the steering shaft surrounded by the boss part of the upper bracket, at a distance from the upper bearing in the axial direction of the steering shaft. A mounting structure for a steering shaft in a motorcycle, characterized in that a male thread is formed to be screwed into the steering shaft.