Fork shaft, telescopic fork, and motorcycle

Abstract

The invention relates to a fork shaft for a telescopic fork, comprising a tubular main part which extends along a longitudinal axis, wherein the main part has an upper bearing region and a lower bearing region, and the main part is designed such that the area moment of inertia thereof in the travel direction differs at least in some regions from the area moment of inertia transversely thereto. Each of the area moments of inertia has a minimum in the central region of the fork shaft, and the main part has at least one weakened region in which the wall thickness of the main part is reduced in order to adjust the area moments of inertia.

Description

[0001] Fork shaft, telescopic fork and motorcycle

[0002] The present invention relates to a fork shaft for a fork of a motorcycle, in particular a motorcycle, a telescopic fork and a motorcycle.

[0003] Fork stems of two-wheelers, such as bicycles or motorcycles, are typically cylindrical tubes with a circular outer cross-section. It is also known to design the outer cross-section to be non-circular, which can provide different mechanical properties in different spatial directions (see, for example, BE 1027 93 7 A1). However, it has been shown that such an approach, especially with double-crown forks, is not sufficient to enable targeted control of the deformation of the lower to the upper fork crown, nor to allow targeted deformation of the fork legs.

[0004] It is therefore an object of the present invention to provide a fork stem for the fork of a two-wheeler, a telescopic fork and a motorcycle, wherein the fork stem is intended in particular to enable a targeted influencing of the deformation of the lower to the upper fork bridge and also a targeted deformation of the fork legs.

[0005] This object is achieved by a steering wheel according to claim 1, a telescopic fork according to claim 13, and a motorcycle according to claim 14. Further advantages and features emerge from the subclaims as well as the description and the accompanying figures.

[0006] According to the invention, a fork stem for a telescopic fork comprises a tubular base body extending along a longitudinal axis, the base body having an upper bearing region and a lower bearing region, and the base body being designed such that its area moment of inertia in the direction of travel differs at least in some regions from its area moment of inertia transverse thereto, the area moments of inertia each having their minimum in a central region of the fork stem, and the base body having at least one weakened region for adjusting the area moments of inertia, in which a wall thickness of the base body is reduced. The weakened region is a region or section of the fork stem or its base body in which its wall thickness is deliberately and partially reduced. This allows for a targeted and needs-based influencing or adjustment of the area moments of inertia.It has surprisingly been shown that this allows a targeted influence on the deformation of the lower to the upper fork bridge and also a targeted deformation of the fork legs, which are attached to the fork bridges.

[0007] It has been found that the area moment of inertia of the fork stem, particularly in the central region, is advantageously greater in the direction of travel than the area moment of inertia perpendicular to it. "In the direction of travel" refers to the area moment of inertia about the y-axis, while "perpendicular to it" refers to the area moment of inertia about the x-axis, with the x-axis oriented along the direction of travel, the z-axis along the longitudinal axis of the fork stem, and the y-axis perpendicular to it. According to one embodiment, the above applies over the entire length or essentially over the entire length of the fork stem (between the bearing areas).

[0008] The bearing areas serve, on the one hand, to support the fork stem within the respective vehicle's frame. The fork bridges are also attached there. Typically, the bearing areas have a round, especially circular, outer cross-section.

[0009] According to one embodiment, the fork tube is designed such that the area moments of inertia decrease toward the center region of the fork tube. Accordingly, according to one embodiment, they are at their minimum there. The center region is the area or section of the fork tube that is positioned centrally or essentially centrally between the bearing areas. There, the area moment of inertia is expediently minimal both in the direction of travel and transversely to it.

[0010] According to a preferred embodiment, the at least one weakened area is formed or arranged centrally or substantially centrally between the bearing areas. According to one embodiment, multiple weakened areas can also be deliberately introduced. According to one embodiment, multiple weakened areas are formed or provided in the circumferential direction and / or along the longitudinal axis. Their effects on the mechanical properties of the fork tube or on the deformation behavior of the entire front wheel guide assembly can be determined, for example, by means of simulation or by testing in real-life driving conditions.

[0011] The fork steerer tube has a front wall section oriented in the direction of travel, an opposite rear wall section, and two side sections which connect the front wall section and the rear wall section in the circumferential direction. According to a preferred embodiment, a weakened region is formed in each of the side sections and in the front and / or rear wall section. Preferably, a weakened region is formed in both the front wall section and the rear wall section. According to a preferred embodiment, these are geometrically identical. The same applies to the weakened regions formed on the side sections, which are also preferably identical to one another. Preferably, all weakened regions are arranged centrally or substantially centrally between the bearing regions.The aforementioned design enables a targeted, graduated stiffness of the fork stem along its longitudinal axis, as well as varying stiffness in the individual spatial directions. Stiffness here primarily refers to flexural rigidity. By introducing the weakened areas, the area moment of inertia of the fork stem along the longitudinal axis is individually and as needed adjusted to achieve the desired deformation of the fork bridges or fork legs, which in turn can specifically influence the handling of the respective vehicle.

[0012] Regarding the beneficial effects on the motorcycle's handling, it should be noted that this depends heavily on the individual case. Such a fork stem can have a beneficial effect on the response of the spring / damper elements. Such a fork stem can have a beneficial effect on smoothness. Such a fork stem can have a beneficial effect on steering behavior. Such a fork stem can have a beneficial effect on driving stability, etc.

[0013] The weakened area is preferably formed or shaped by removing material from the wall of the fork stem. This material removal can be planned for during the manufacture of the base body. Alternatively, the material removal can also be introduced subsequently, for example, through a separating manufacturing process.

[0014] Preferred materials for the fork steerer tube are metallic materials such as aluminum or steel. In particular, it may be appropriate to subsequently introduce at least one weakened area mechanically, for example, by grinding, milling, or similar processes. However, materials such as reinforced plastics, particularly CFRP (carbon fiber reinforced plastic), can also be used, particularly in the bicycle sector. Here, the weakened areas can be at least partially incorporated or incorporated during production. This does not preclude the possibility of at least partially mechanically reworking the weakened areas, which are at least preformed in this way.

[0015] According to a preferred embodiment, the material removal is designed as a pocket with an approximately triangular cross-section. Such a "triangle" is preferably formed as an isosceles triangle. The angle between the sides is, for example, between 90 and 179°, particularly preferably between 130 and 175°, and further preferably between 150 and 172°.

[0016] According to a preferred embodiment, the weakened area formed in the front and / or rear wall section comprises a complete removal of material. The pocket is therefore expediently designed such that the material for the wall of the fork shaft is perforated. The weakened area forms a hole or opening. A continuously closed cross-section is therefore no longer present. This allows for targeted intervention in the deformation behavior of the entire front wheel guide assembly of the respective vehicle.

[0017] According to a preferred embodiment, the complete material removal is designed as an elliptical opening, the main axis of which preferably extends along the longitudinal axis. As already mentioned, according to a preferred embodiment, weakened areas of this type are formed in both the front wall section and the rear wall section.

[0018] According to a preferred embodiment, the lateral weakened regions are longer than the weakened regions in the front and / or rear wall sections. According to a preferred embodiment, the weakened regions in the lateral wall sections each have an angle between the legs of 160 to 178°, while the weakened regions in the front wall section and the rear wall section are preferably designed such that the triangular pockets formed there have an angle of approximately 120 to 160° between the legs.

[0019] Preferably, the weakened areas are formed on the outside of the fork stem. This means that the material removal is or has been carried out on the outside of the base body. The inner wall of the fork stem is expediently round in cross-section, particularly circular and constant along the longitudinal axis. Alternatively, the weakened areas can also be formed on the inside of the fork stem, or the material removal can take place on the inside of the fork stem. However, this can be more complex from a manufacturing perspective.

[0020] The fork stem is specifically designed for use in a telescopic fork, such as those found in motorcycles. Such motorcycles can be single- or multi-track, such as trikes or LMW (Leaning Multi Wheel) vehicles. However, such a fork stem can also be used in bicycles. These, too, increasingly feature telescopic forks or double-crown forks. Bicycles of the type in question can incorporate an auxiliary motor, for example, an electric one, or be powered purely by muscle power.

[0021] The invention also relates to a telescopic fork or a double-crown fork comprising a fork stem according to the invention. The telescopic fork comprises two fork crowns and two fork legs or fork tubes. The two fork legs usually consist of a stanchion and a fork tube. The fork crowns are connected by the fork stem. The geometry of the fork stem can advantageously influence the deformation behavior of the entire telescopic fork.

[0022] The invention also relates to a motor cycle, in particular a motorcycle, comprising a telescopic fork according to the invention. The fork shaft enables different deformations in the individual spatial directions of the front wheel guide system, whereby the vehicle's dynamic driving characteristics can be specifically modified. Certain independently adjustable deformations can thus be conveniently implemented in a targeted manner. Further advantages and features will become apparent from the following description of an embodiment of a fork shaft with reference to the accompanying figures.

[0023] They show:

[0024] Fig. 1 : a sketch of an embodiment of a fork stem;

[0025] Fig. 2: the fork tube known from Fig. 1 rotated by 90°.

[0026] Fig. 1 shows a sketch of a fork stem 10 extending along a longitudinal axis L. For orientation, a Cartesian coordinate system is sketched, with its z-axis extending along the longitudinal axis L. Its x-axis extends along a direction of travel F, and the y-axis perpendicular to it. The fork stem 10 has a hollow cylindrical base body, which is deliberately "weakened" along the longitudinal axis L by weakened areas 26. The fork stem 10 comprises an upper bearing area 16 and a lower bearing area 18. The bearing areas 16, 18 serve, on the one hand, to support the fork stem in the frame of the respective vehicle. The fork bridges are also attached there. Typically, the bearing areas 16, 18 have a round, in particular circular, outer cross-section. The fork stem 10 comprises an outer surface 14 and an inner surface 12. In the embodiment sketched here, this is formed constantly along the longitudinal axis L.The fork stem 10 comprises a front wall section 20, lateral side sections 24 and a rear wall section, which is not visible in this view. In the front wall section 20, a weakened area 26 is formed in such a way that an opening or a hole 28 is formed. In other words, the fork stem 10 or its wall is completely open at this point. The weakened areas 26 on the side sections 24 are longer when viewed along the longitudinal axis L, but less deep. The course of the weakened areas 26 can be seen in particular from the cross sections Q1 to Q6. Basically, it can be seen from Fig. 1 and also from Fig. 2 that the weakened areas or the corresponding material removals have an approximately triangular shape.In particular, they are isosceles triangles, with the angle between the sides preferably being relatively large, i.e., significantly greater than 90°, particularly preferably greater than 130°. In the embodiment outlined here, the angle is preferably larger at the side sections 24 than in the front or rear wall sections. Such a geometry can be easily produced using a separating manufacturing process.

[0027] Fig. 2 shows the sketch known from Fig. 1, with the fork stem 10 now rotated by 90°. In this view, the weakened areas 26 in the front wall section 20 and in the rear wall section 22 are particularly visible. These are also designed as triangular pockets. The angle between the legs is provided here with the reference symbol a. It can be seen that the weakened areas 26 on the side sections 24 are significantly longer. In cross-section, these are also designed as triangular pockets, but the angle between the legs is significantly larger here than in the weakened areas 26 in the front wall section 20 or in the rear wall section 22. A fork stem of this type enables a targeted influence on the deformation of the lower to the upper fork bridge and also a targeted deformation of the fork legs.This is achieved through the targeted, graduated (flexural) stiffness of the fork tube along its longitudinal axis, especially between the bearing areas, as well as varying in the individual spatial directions. The resulting varying deformation in the individual spatial directions of the front wheel guide system allows the vehicle's dynamic handling characteristics to be specifically influenced. The effect of certain independently adjustable deformations on driving dynamics can be specifically implemented.

[0028] List of reference symbols

[0029] 10 Fork tube

[0030] 12 inner surface

[0031] 14 Exterior surface

[0032] 16 upper storage area

[0033] 18 lower storage area

[0034] 20 front wall section

[0035] 22 rear wall section

[0036] 24 page section

[0037] 26 weakening area

[0038] 28 opening, hole

[0039] Q1 ...Q6 cross section(s) a angle

[0040] L Longitudinal axis x, y, z Cartesian coordinate system

[0041] F Direction of travel

Claims

Claims 1. Fork shaft (10) for a telescopic fork, comprising a tubular base body which extends along a longitudinal axis (L), wherein the base body has an upper bearing area (16) and a lower bearing area (18), and wherein the base body is designed such that its area moment of inertia in the direction of travel (F) is at least partially different from its area moment of inertia transverse thereto, wherein the area moments of inertia each have their minimum in a central area of ​​the fork shaft (10), and wherein the base body has at least one weakened area (26) for adjusting the area moments of inertia, in which a wall thickness of the base body is reduced.

2. Fork shaft (10) according to claim 1, wherein the base body is designed such that the area moment of inertia in the direction of travel (F), in particular in the central region, is greater than the area moment of inertia transverse thereto.

3. Fork stem (10) according to claim 1 or 2, wherein the base body is designed such that the area moments of inertia decrease towards the central region of the fork stem (10).

4. Fork stem (10) according to one of the preceding claims, wherein the at least one weakened region (26) is arranged substantially centrally between the bearing regions (16, 18).

5. Fork shaft (10) according to one of the preceding claims, wherein a plurality of weakened regions (26) are formed in the circumferential direction and / or along the longitudinal axis (L).

6. Fork stem (10) according to one of the preceding claims, wherein the fork stem (10) has a front wall section (20) oriented in the direction of travel (F), an opposite rear wall section (22) and two side sections (24), and wherein a weakened region (26) is formed in each of the side sections (24) and in the front (20) and / or the rear (22) wall section.

7. Fork stem (10) according to one of the preceding claims, wherein the at least one weakened region (26) is formed or shaped by removing material in the wall of the fork stem (10). 8 Fork shaft (10) according to claim 7, wherein the material removal is formed as a pocket with a triangular cross-section.

9. Fork stem (10) according to one of claims 6 to 8, wherein the weakened region (26) formed in the front (20) and / or rear wall section (22) comprises a complete removal of material.

10. Fork stem (10) according to claim 9, wherein the complete material removal is formed as an elliptical opening (28) whose main axis extends along the longitudinal axis (L).

11. Fork stem (10) according to one of claims 6 to 10, wherein the lateral weakened regions (26) are longer than the weakened regions (26) in the front (20) and / or rear wall section (22).

12. Fork stem (10) according to one of claims 7 to 11, wherein the material removal is formed on the outside of the fork stem (10), and wherein the material removal is introduced in particular mechanically.

13. Telescopic fork comprising a fork stem (10) according to one of the preceding claims.

14. Motor cycle, in particular a motorcycle, comprising a telescopic fork according to claim 13.

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