JP4785132B2 - Front fork bracket of motorcycle - Google Patents

Description

  The present invention relates to a front fork bracket of a motorcycle that supports a front fork and is connected to a head pipe provided at a front end portion of a vehicle body frame.

As a front fork bracket of a motorcycle, there are a top bridge and a bottom bridge, each of which has a long arm shape in the left-right direction, a center boss in the center, and a pair of fork bosses provided at both left and right ends And a bridge portion for connecting them, the front fork is split and tightened through a fork hole formed in the fork boss, and is provided at the front end of the vehicle body frame via a steering shaft that passes through the center hole formed in the center boss. It is known that it is configured to be pivotably connected to a head pipe, and is formed integrally by casting with an aluminum alloy or the like so as to form a hollow portion within the thickness of the bridge portion (Patent Document) 1).
JP-A-9-309480

Such a front fork bracket needs to be lightweight and highly rigid, but the required rigidity and thickness differ depending on each part. The fork boss for cleaving the front fork is preferably as thick as possible in order to ensure a sufficiently large contact area with the front fork. In addition, there may be provided a handle support portion for supporting the handle on the bridge portion via the handle clamp. In this case, if the handle clamp is to be supported for vibration isolation, a sufficiently large volume vibration isolation rubber can be attached. Thus, it is preferable to make the handle support portion thick.
On the other hand, the center boss is a part that is connected to the top and bottom of the head pipe, and this part is preferably made thinner so that the steering shaft can be made as short as possible to make the vehicle height as low as possible.
In addition, when the bridge portion is thickened, it is necessary to provide a hollow portion in the wall thickness in order to reduce the weight. However, if the hollow portion is enlarged, a larger core is required. However, it is difficult to position and fix such a large core accurately in the mold, and it is difficult to control the wall thickness with high accuracy. . Therefore, it is also necessary to enable accurate positioning using as small a core as possible. The present application aims to realize such a request.

In order to solve the above problems, the invention of claim 1 relating to a front fork bracket of a motorcycle supports a pair of left and right front forks and rotates the head pipe provided at the front end portion of the vehicle body frame via a steering shaft. A front fork bracket supported movably,
A center boss formed with a center hole through which the steering shaft passes, a pair of fork bosses provided on both left and right ends across the center boss, each of which has a fork hole through which the front fork passes, and the center boss In the thing with the bridge part which connects the fork boss,
While providing a handle support portion between the center boss and fork boss of the bridge portion,
A hollow part is formed in the wall thickness in the range from the fork boss of the bridge part to the periphery of the handle support part ,
While making the vicinity of the center boss of the bridge part thinner than the other part of the bridge part, providing a recess with an open cross section,
Furthermore, the whole is integrally formed by casting, and the hollow portion communicates with the fork hole of the fork boss and the recess of the open cross section .

  The invention of claim 3 is characterized in that, in the above-mentioned claim 1, the fork boss connects the front fork passed through the fork hole by split tightening.

  According to a fourth aspect of the present invention, in the first aspect, the handle support portion supports the handle via a handle clamp for fixing the handle, and the handle clamp is coupled to the bridge portion via an elastic body. It is characterized by that.

  According to the first aspect of the present invention, the handle support portion is provided between the center boss and the fork boss of the bridge portion, and the hollow portion is formed in the thickness ranging from the fork boss of the bridge portion to the periphery of the handle support portion. Therefore, the thickness of the fork boss and the handle support portion can be sufficiently large while reducing the weight of the entire front fork bracket, and the front fork and the handle can be made suitable for support.

Further, since the vicinity of the center boss of the bridge portion is made thinner than the other portions, the height in the vertical direction when connected to the head pipe can be reduced to contribute to lowering the vehicle height, and the steering shaft can be shortened.
Furthermore, a hollow part can be reduced by providing the recessed part of an open cross section in the center boss vicinity part.
In addition, since the hollow portion communicates with the fork hole of the fork boss and the recessed portion of the open cross section, when the whole is integrally formed by casting, the core for forming the hollow portion can be made smaller, and the fork Since the fork hole of the boss and the recess of the open cross section can be formed integrally with the core for molding, the core for the hollow part in the mold can be accurately positioned and the thickness can be controlled with high accuracy. The thickness of the portion surrounding the hollow portion can be reduced as much as possible by reducing the thickness as much as possible.

  According to the invention of claim 3, since the thickness of the fork boss can be secured sufficiently large, a large contact area can be obtained even in a split tightening structure in which the front fork passed through the fork hole is connected by split tightening. Can reliably support the front fork.

  According to the fourth aspect of the present invention, since the handle support portion has a sufficiently large thickness, when the handle clamp is supported in an anti-vibration manner via the elastic body, the volume of the elastic body can be sufficiently increased. And a greater vibration isolation effect can be obtained.

  An embodiment will be described below with reference to the drawings. FIG. 1 is a side view of an off-road motorcycle to which this embodiment is applied. The motorcycle body frame 1 includes a head pipe 2, a main frame 3, a center frame 4, a down frame 5 and a lower frame 6, which are connected in a loop shape, and an engine 7 is supported inside thereof. Yes. The main frame 3, the center frame 4 and the lower frame 6 are provided as a pair on the left and right, respectively, and the head pipe 2 and the down frame 5 are provided along the center of the vehicle body.

  The main frame 3 extends obliquely downward in a straight line above the engine 7 and is connected to the upper end portion of the center frame 4 extending in the vertical direction behind the engine 7. The down frame 5 extends obliquely downward in front of the engine 7 and is connected to the front end of the lower frame 6 at the lower end thereof. The lower frame 6 is bent from the lower front side of the engine 7 to the lower side of the engine 7 and extends rearward in a substantially linear shape, and is connected to the lower end of the center frame 4 at the rear end.

  An upper portion of the front fork 10 is supported on the head pipe 2 via a top bridge 8 and a bottom bridge 9. The top bridge 8 and the bottom bridge 9 correspond to front fork brackets, and the top bridge 8 is the subject of the present invention. A front wheel 11 supported by the lower end of the front fork 10 is steered by a handle 12. The front end portion of the rear arm 14 is swingably supported on the center frame 4 by a pivot shaft 13. A rear wheel 15 is supported at the rear end of the rear arm 14 and is chain driven by the engine 7.

Reference numeral 16 is a rear suspension cushion unit, and 17 is an exhaust pipe, which is bent from the front of the cylinder and extends rearward to muffler at the rear of the vehicle body (not shown).
Connect to. Reference numeral 18 denotes a fuel tank located above the upright cylinder of the engine 7, and 19 denotes a seat located behind the fuel tank 18.

  FIG. 2 is a side view showing the periphery of the head pipe. In the top bridge 8, the upper portion of the front fork 10 is split and fixed at the clamp portion 20 with bolts 21. A handle clamp 22 is supported on the top bridge 8 via a vibration isolating rubber (details will be described later), and the handle 12 is fixed thereto. Reference numeral 23 denotes a fastening cap, and 24 denotes a fastening bolt.

  The top bridge 8 and the bottom bridge 9 are connected by a steering shaft 25 that penetrates the head pipe 2 up and down. The top bridge 8, the bottom bridge 9, and the front fork 10 are integrated by a steering shaft 25 that is rotatably supported with respect to the head pipe 2, and the handle 12 is rotated to rotate around the steering shaft 25. Move and steer the front wheels 11.

  A known steering damper 26 has an upper end connected to the head pipe 2 and a lower end connected to the bottom bridge 9 to buffer a shock when a disturbance is input from the front wheel 11 to the steering shaft 25. A front fender 27 is supported by the bottom bridge 9.

  FIG. 3 is a front view around the head pipe. The handle clamp 22 has a bolt 30 integrally extending downward from its lower end, passes through the mounting hole 31 of the top bridge 8, and is fixed by a nut 32 on the lower surface of the top bridge 8. At this time, the handle clamp 22 is vibration-proof attached to the top bridge 8 via the vibration-proof rubber 33.

  Prior to the mounting of the handle clamp 22, a substantially frustoconical anti-vibration rubber 33 is fitted into the mounting hole 31 from above and below in the opposite direction so that the narrow tops are in contact with each other. The handle clamp 22 is attached to the top bridge 8 via the anti-vibration rubber 33 by passing the bolt 30 through a through hole formed in the center of the vibration rubber 33.

  The vibration isolating rubber 33 is a vibration isolating member designed to make it difficult to transmit to the handle 12 by insulating and absorbing vibration on the vehicle body side. The anti-vibration rubber 33 is made of a suitable rubber material and has a sufficiently large volume so that a sufficient anti-vibration effect can be obtained. However, it is not always necessary to use an anti-vibration rubber, and any elastic body that provides an anti-vibration effect can be used instead of rubber.

  A semicircular groove that opens upward is formed on the upper surface of the handle clamp 22 (see FIG. 2), and a horizontal portion that is a portion near the vehicle body center C of the handle 12 is placed in the semicircular groove. A fastening cap 23 formed with a semicircular groove (same as above) opened downward is covered, and the handle 12 is fixed by fastening to a nut portion formed on the handle clamp 22 from above with a fastening bolt 24. To do. The handle clamp 22 is provided on the top bridge 8 at a symmetrical position with respect to the vehicle body center C.

  The steering shaft 25 is arranged vertically on the vehicle body center C, the lower end thereof is press-fitted and fixed to the bottom bridge 9, the upper end provided with the male screw 34 passes through the steering shaft hole 35 of the top bridge 8, and the nut 36 from above. To the top bridge 8. The steering shaft 25 penetrates through the head pipe 2 and is rotatably supported by bearings (not shown) at upper and lower ends thereof. The steering damper 26 is provided along the vehicle body center C, and the upper and lower sides are connected via a joint.

  Hereinafter, the detailed structure of the top bridge 8 will be described. FIG. 4 is a plan view of the top bridge 8. The top bridge 8 has an arm shape extending left and right, a center boss 40 having a center hole 35 is provided on the vehicle body center C, and a fork having a fork hole 37 through which an upper portion of the front fork 10 passes is provided at both left and right ends. A boss 41 is provided.

  A slit 42 is provided in the front part of the fork boss 41 to open the fork hole 37, and a clamp part 20 and a nut part 43 are provided across the slit 42. The clamp part 20 is provided with a through hole 20a, the nut part 43 is provided with a nut hole 43a, and the bolt 21 passed through the through hole 20a of the clamp part 20 is fastened to the nut hole 43a.

  Before the bolt 21 is fastened, the fork hole 37 has a diameter larger than the outer diameter of the upper end portion that is the support portion of the front fork 10. When the upper end of the front fork 10 is passed through the fork hole 37 and the bolts 21 are fastened to narrow the gap between the slits 42, the fork hole 37 is reduced in diameter and the upper end of the front fork 10 is tightened with the fork boss 41. It comes to tighten.

  At the time of this tightening, the fork boss 41 portion has a sufficient thickness as will be described later, so that a sufficiently large contact area between the tightened portion which is the upper end portion of the front fork 10 and the fork boss 41 can be secured. . This cleaving structure is provided on the left and right fork bosses 41, respectively.

  A handle mounting boss 44 having a mounting hole 31 is provided at a position symmetrical between the center boss 40 and the left and right fork bosses 41. The handle mounting boss 44 is a handle support portion, and its position is close to the fork boss 41. Further, the centers of the fork boss 41, the handle mounting boss 44, and the center boss 40 retreat backward in this order, and the center boss 40 is in the rearmost position. Shape.

  A portion connecting the fork boss 41, the handle mounting boss 44 and the center boss 40 forms a bridge portion 45. The bridge portion 45 is a main body portion of the top bridge 8 and forms a substantial arm-like portion of the top bridge 8 except for boss portions such as the center boss 40, the fork boss 41 and the handle mounting boss 44.

  FIG. 5 is a bottom view of the top bridge 8. An open recess 46 is formed in the center of the bridge portion 45 and in front of the center boss 40. The open recess 46 has a substantially trapezoidal shape across the vehicle body center C. A long edge corresponding to the lower side of the trapezoid is curved to protrude rearward along the central front edge of the bridge portion 45, and a short edge corresponding to the upper side forms an arc shape protruding forward along the center boss 40. Edge portions corresponding to the left and right sides are inclined forward and outward.

  A hollow portion 47 is formed in the thickness of a portion of the bridge portion 45 surrounded by the center boss 40, the fork boss 41, the handle mounting boss 44 and the open recess 46. The hollow portion 47 is long in the front-rear direction, and is provided in a bilaterally symmetric manner so as to incline outward and forward. The rear part enters between the center boss 40 and the handle mounting boss 44, and the front part extends forward from the handle mounting boss 44 and enters between the fork boss 41 and the open recess 46, near the front edge of the bridge part 45. Has reached.

  6 is a cross-sectional view taken along line 6-6 of FIG. The bridge portion 45 has a substantially flat upper surface, while the lower surface changes so that the vertical width (thickness) becomes narrower toward the center, and the central portion in the vicinity of the center boss 40 is the thinnest. . The hollow portion 47 is formed within the thickness of the bridge portion 45, the inner side reaches the vicinity of the center boss 40, the outer side reaches the fork boss 41, and is opened into the fork hole 37 at the communication portion 48 that is a through hole. ing. This open position is on the vehicle body center side of the fork boss 41 and is displaced by approximately 90 ° from the slit 42 provided at the front (see FIG. 5).

  FIG. 7 is a right side view, and the clamp portion 20 is a flat portion that is formed vertically to the front edge portion of the bridge portion 45, and a through hole 20 a is provided vertically therethrough. From the upper surface of the bridge portion 45, the upper end of the handle mounting boss 44 protrudes slightly (d1) upward, and a central rear end portion 49 that forms the center boss 40 protrudes rearward from the rear portion of the bridge portion 45.

  Here, the dimension between the upper surface and the lower surface of the bridge portion 45 is a reference thickness T0, and the thickness of the central rear end portion 49 is T1. The lower surface of the central rear end portion 49 is located above the lower surface of the bridge portion 45 in a step shape by a dimension d2, and is the thinnest portion. The dimension between the upper end of the handle mounting boss 44 and the lower surface of the bridge portion 45 is T2. This T2 indicates the thickness of the thickest part.

  8 is a cross-sectional view taken along line 8-8 of FIG. The open recess 46 is formed in front of the center boss 40 and has a downward open cross section. The thickness t1 at the bottom 50 of the open recess 46 is such that the necessary rigidity can be obtained. This part is the part where the required rigidity is the smallest, and sufficient rigidity can be obtained even with such an open cross section. A through hole 51 is formed in the bottom 50.

  9 is a cross-sectional view taken along line 9-9 of FIG. The mounting hole 31 has a shape in which the middle portion in the vertical direction is narrowest and the diameter increases toward the upper and lower openings. The mounting hole 31 is similar to a shape in which the narrow tops of the two truncated cones face each other and are arranged vertically, and has a constricted shape in the middle in the vertical direction. In the partition 52 formed in the middle, A through hole 53 is formed. The through hole 53 has a diameter sufficient to allow the bolt 30 to pass through while communicating with the upper and lower portions.

  The hollow portion 47 is formed in front of the mounting hole 31 and is closed at this cross section. The thickness t2 of the upper wall surrounding the hollow portion 47 and the thickness t3 of the lower wall are relatively small. A small boss 54 is formed on the upper front edge of the bridge portion 45, and a nut hole 55 is provided here.

  Of the bridge portion 45, the thickness of the portion where the hollow portion 47 is formed is T3, and the lower surface side is positioned slightly above the reference thickness T0 by the dimension d3. Further, the maximum thickness T2 is further reduced by d1.

  10 is a cross-sectional view taken along line 10-10 of FIG. As shown in this figure, the handle mounting boss 44 and the fork boss 41 are partially continuous, and the fork hole 37 and the mounting hole 31 are not in communication. The hollow portion 47 is located between the handle mounting boss 44 and the center boss 40 in this cross section, and is independent of the mounting hole 31 and the center hole 35 without being communicated with each other.

  As is apparent from the figure, the thickness T0 of the fork boss 41 and the thickness T2 of the handle mounting boss 44 are almost the maximum thickness, respectively. On the other hand, the portion in the vicinity of the center boss 40 is the thinnest portion T1, and the thickness gradually decreases from the maximum thickness T2 of the handle mounting boss 44 toward the center boss 40 having the minimum thickness T1.

  11 is a cross-sectional view taken along line 11-11 of FIG. As is apparent from this figure, the open recess 46 communicates with each other through a hollow portion 47 and a passage 56. The hollow portion 47 is opened to the fork hole 37 and the communication portion 48. The left and right hollow portions 47 are provided so as to be obliquely outwardly opened forward, and the front portion of each hollow portion 47 is located between the fork hole 37 and the open recess 46 and communicates with these via a communication portion 48 and a passage 56. The rear part is located between the mounting hole 31 and the center hole 35, and the rear end part extends rearward from the line connecting the centers of these holes.

  The range in which the hollow portion 47 is formed includes a range from the fork boss 41 to the periphery of the handle mounting boss 44. Specifically, as clearly shown in FIG. 5, there is a portion where the fork boss 41 and the handle mounting boss 44 are continuous, and the portion is inserted into the vicinity of the continuous portion. In other words, a part of the hollow portion 47 is formed so as to reach the fork boss 41 beyond the formation position of the handle mounting boss 44 in the left-right direction of the top bridge 8 in FIG.

  The top bridge 8 is formed by casting using an appropriate light alloy material such as an aluminum alloy. At this time, the hollow portion 47, the open recess 46, the mounting hole 31, the center hole 35, the fork hole 37, and the like are formed of a core. Although not shown, the core that forms the hollow portion 47 is continuously integrated with the core that forms the fork hole 37 and the open recess 46, and the formation portion of the communication portion 48 and the passage 56. Since the cores forming the fork hole 37 and the open recess 46 are respectively positioned on the mold surface of the casting mold, the cores forming the hollow part 47 are positioned in the mold via these cores. .

  Next, the operation of this embodiment will be described. When the upper portion of the front fork 10 is passed through the fork hole 37 of the top bridge 8 and the clamp portion 20 is tightened with the bolt 21, the front fork 10 is split and fixed to the top bridge 8. Similarly, the bottom bridge 9 is also tightened at a lower part than the top bridge 8 of the front fork 10. Further, when the steering shaft 25 extending upward from the bottom bridge 9 is passed through the head pipe 2 and the upper end portion is passed through the center hole 35 of the top bridge 8 and fastened with the nut 36, the top bridge 8 and the bottom bridge 9 are interposed. Thus, the front fork 10 and the bottom bridge 9 are rotatably connected to the vehicle body side.

  When the handle 12 is rotated in this state, the top bridge 8 and the bottom bridge 9 are rotatably supported on the head pipe 2 by the steering shaft 25, so that the front fork 10 rotates integrally and the front wheel 11. Steering. Further, the impact load from the road surface is transmitted from the front wheels 11 and the front forks 10 to the top bridge 8 and the bottom bridge 9, and the turning load by the driver is transmitted to the top bridge 8 from the handle mounting boss which is a handle support portion. The weight of the vehicle body is transmitted to the top bridge 8 and the bottom bridge 9 via the steering shaft 25. At this time, the top bridge 8 has sufficient rigidity while realizing weight reduction by the formation of the open recess 46 and the hollow portion 47, and therefore can sufficiently withstand these loads.

  In addition, by providing the hollow portion 47 within the thickness of the bridge portion 45 in the range from the fork boss 41 to the periphery of the handle mounting boss 44, the fork boss 41 and the handle mounting boss 44 have a thickness of T0. In addition, since the thickness is almost the maximum so as to be the thickness T2, it can be made suitable for supporting the front fork 10 and the handle 12. In the fork boss 41, a sufficient contact area with respect to the front fork 10 can be ensured, and a reliable split tightening is possible.

  In the handle mounting boss 44, by setting the maximum thickness T2, the mounting hole 31 can be enlarged, and a sufficiently large volume of the vibration isolating rubber 33 can be accommodated therein. Vibration support is possible. In addition, by providing a hollow portion 47 having a closed cross section instead of an open cross section at a portion where the highest rigidity is required, the section modulus can be increased and the required rigidity can be ensured.

  Also, since the portion near the center boss 40 of the bridge portion 45 has a thickness T1 and is the thinnest than the other portions, the height in the vertical direction at the mounting portion when connected to the head pipe 2 is lowered to lower the vehicle height. And the steering shaft 25 can be shortened.

  Further, since an open recess 46 having a downward open cross section is provided in a portion in the vicinity of the front of the center boss 40 where relatively low rigidity is not required, the hollow portion 47 can be made small and light and highly rigid as much as possible. The top bridge 8 can be formed. Moreover, since the core which forms the hollow part 47 can be made small by making the hollow part 47 small, casting can be made easy.

  In addition, since the hollow portion 47 is communicated with the fork hole 37 and the open concave portion 46 through the communication portion 48 and the passage 56, when the core forming the hollow portion 47 is a sand mold, the hollow portion 47 can be quickly released from the fork hole 37 and the open concave portion 46. Since it can be discharged, workability is also improved.

  Further, the core for forming the hollow portion 47 can be connected and integrated with the core for the fork hole 37 and the open recess 46 at the portion where the communication portion 48 and the passage 56 are formed. Since the cores forming the fork holes 37 and the open recesses 46 can be positioned by being brought into contact with the inner surface of the casting mold, the cores of the hollow portions 47 are connected to the cores of the fork holes 37 and the open recesses 46. Can be accurately positioned in the mold.

  For this reason, the thicknesses t2 and t3 (FIG. 9) of the wall portions surrounding the hollow portion 47 can be managed with high accuracy, and the dimensional accuracy of the thickness can be increased. Therefore, these thicknesses t2 and t3 Can be made as thin as possible, and the thickness is not increased unnecessarily.

The present invention is not limited to the above-described embodiments, and various modifications and applications are possible within the principle of the invention. For example, as long as the position of the hollow portion 47 includes a range from the fork boss 41 to the periphery of the handle mounting boss 44, the range covered by other portions has a relatively high degree of freedom. Instead of the open recess 46, the hollow portion 47 may extend to the center. Further, it may be divided into a plurality of narrower portions, for example, a portion surrounded by the fork boss 41, the handle mounting boss 44 and the rear edge of the bridge portion 45, and the like.

Side view of a motorcycle to which this embodiment is applied Side view showing around the head pipe Front view around the head pipe Top bridge top view Bottom view of top bridge 6-6 sectional view of FIG. Right side view of top bridge Sectional view taken along line 8-8 in FIG. Sectional view along line 9-9 in FIG. Sectional view taken along line 10-10 in FIG. 11-11 sectional view of FIG.

Explanation of symbols

1: body frame, 2: head pipe, 8: top bridge, 9: bottom bridge, 10: front fork, 11: front wheel, 12: handle, 22: handle clamp, 25: steering shaft, 31: mounting hole, 35: Center hole, 37: Fork hole, 40: Center boss, 41: Fork boss, 44: Handle mounting boss, 45: Bridge part, 46: Opening recess, 47: Hollow part

Claims (3)

A front fork bracket of a motorcycle that supports a pair of left and right front forks and is rotatably supported via a steering shaft to a head pipe provided at a front end portion of a vehicle body frame,
A pair of center bosses (40) formed with a center hole (35) for passing the steering shaft and fork holes (37) provided on both left and right ends with the center boss interposed therebetween, each for passing a front fork. Fork boss (41) and a bridge portion (45) for connecting the center boss and the fork boss,
Setting handle support (44) between said center boss and fork boss of the bridge portion (45) (41),
A hollow portion (47) is formed in a thickness ranging from the fork boss (41 ) of the bridge portion (45) to the periphery of the handle support portion (44) ,
While making the vicinity of the center boss (40) of the bridge portion (45) thinner than other portions of the bridge portion (45), a recess (46) with an open cross section is provided,
Further, the whole is integrally formed by casting, and the hollow portion (47) communicates with the fork hole (37) of the fork boss (41) and the recess (46) of the open cross section. Front fork bracket for motorcycles. The front fork bracket of a motorcycle according to claim 1, wherein the fork boss (41) connects the front fork (10) passed through the fork hole (37) by split fastening. The handle support (44), to support the handle (12) via a handle clamp (22) for fixing the handle, an elastic body the handle clamp (22) to said bridge portion (45) (33 front fork bracket motorcycle according to claim 1) characterized by being connected via a.

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