WO2024089992A1

WO2024089992A1 - Front fork

Info

Publication number: WO2024089992A1
Application number: PCT/JP2023/030415
Authority: WO
Inventors: 修宮崎; 渓須崎
Original assignee: カヤバモーターサイクルサスペンション株式会社
Priority date: 2022-10-24
Filing date: 2023-08-24
Publication date: 2024-05-02
Also published as: JP7431923B1

Abstract

A front fork (F) comprises: a fork main body (1) including a vehicle body-side tube (2), an axle-side tube (3), and an axle bracket (4) including a bottomed cylindrical cylinder (4a) attached to an outer periphery of a lower end of the axle-side tube; a damper cartridge (D); a collar (30) including a seal ring (30e) which is annular and which is in close contact with the axle-side tube (3), the collar (30) being sandwiched between the axle-side tube (3) and the axle bracket (4) and accommodated in the tube (4a); and a coupling bolt (40) which has a head portion (40a) that is inserted into a bolt insertion hole (4c) of the axle bracket (4) and a screw shaft (40b) that is inserted through an inner periphery of the collar (30) and that is screwed to a lower cap (13) fixed to a lower end of the damper cartridge (D), the coupling bolt (40) coupling the lower cap (13) to the collar (30).

Description

Front fork

The present invention relates to a front fork.

Traditionally, front forks have been used in suspension devices mounted between the body and front wheel of saddle-type vehicles, for example, to house a damper cartridge that generates a damping force when extended or retracted, thereby suppressing vibrations in the vehicle.

More specifically, the front fork includes a fork body having, for example, a vehicle body tube, an axle side tube that is movable in the axial direction relative to the vehicle body side tube, and an axle bracket that has a bottomed cylindrical portion that fits onto the outer periphery of the lower end of the axle side tube to close the lower end of the axle side tube and hold the axle of the front wheel, and a damper cartridge that is housed in the fork body.

The damper cartridge also includes a cylinder, a piston rod inserted into the cylinder so as to be movable in the axial direction, a piston connected to the piston rod and inserted into the cylinder so as to be movable in the axial direction, dividing the interior of the cylinder into an extension side chamber and a compression side chamber, and a bottom member that closes the lower end of the cylinder and has a screw hole that opens from the lower end.

The damper cartridge configured in this manner is housed within the fork body, as disclosed in JP2016-070313A, for example, and one end of the piston rod is connected to the vehicle body tube via the head cap, and a connecting bolt that penetrates the bottom of the cylindrical part of the axle bracket is screwed into the threaded hole of the bottom member, so that the damper cartridge is interposed between the vehicle body tube and the axle tube.

Therefore, when the front fork expands and contracts due to vibrations input to the front wheel while the saddle-type vehicle is traveling, the damper cartridge built into the fork body also expands and contracts, generating a damping force, suppressing vibrations of the front wheel and vehicle body and improving the ride comfort of the saddle-type vehicle.

JP2016-070313A

In conventional front forks, the axle bracket that closes the lower end of the axle tube also functions as part of a pressure vessel for storing liquid inside the fork body, and the inner circumference of the cylindrical part of the axle bracket that fits onto the outer circumference of the axle tube is provided with an annular groove that houses a seal ring that fits tightly against the outer circumference of the axle tube.

In addition, a threaded portion is provided on the opening end side of the cylindrical portion of the axle bracket, closer to the annular groove for accommodating the seal ring. The axle bracket configured in this manner is manufactured by first obtaining a roughly shaped casting by casting, and then performing a cutting process on the casting.

The inner circumference of the cylindrical part of the axle bracket is machined to form the threaded part and the annular groove, but if cutting chips generated by the machining are left behind in the annular groove, the chips can become contaminants in the hydraulic oil inside the front fork and can adversely affect the operation of the damping valve, etc. For this reason, when manufacturing conventional front forks, workers are forced to carry out the extremely tedious task of using a mirror or the like to check whether any cutting chips have been left behind in the annular groove at the deepest part of the cylindrical part of the axle bracket.

In addition, with conventional front forks, the axle bracket is a casting and also constitutes part of the pressure vessel, and any blown holes in the axle bracket will cause hydraulic oil to leak. This means that all manufactured axle brackets must be X-ray inspected for blown holes that could lead to hydraulic oil leaks, which increases manufacturing costs.

Furthermore, in order to provide an annular groove for accommodating a seal ring on the inner circumference of the cylindrical part of the axle bracket, it is necessary to increase the thickness of the cylindrical part accordingly, which increases the outer diameter of the cylindrical part and creates the problem of an increased weight for the front fork.

The present invention aims to provide a front fork that can reduce the workload of manufacturing workers and reduce manufacturing costs and weight.

In order to solve the above-mentioned problems, the front fork of the present invention includes a fork body that can expand and contract and has a vehicle body tube, an axle side tube that can move in the axial direction relative to the vehicle body tube, and an axle bracket that has a cylindrical, bottomed portion attached to the outer periphery of the lower end of the axle side tube; a cylinder, a piston rod that is inserted into the cylinder so as to be movable in the axial direction and one end of which is connected to the vehicle body tube; a piston that is connected to the piston rod and inserted into the cylinder so as to be movable in the axial direction, dividing the inside of the cylinder into an expansion side chamber and a compression side chamber; a lower cap that is fixed to the lower end of the cylinder and closes the lower end of the cylinder and has a damper cartridge that is housed in the fork body; a collar that is annular and has a seal ring that is in close contact with the axle side tube and is sandwiched between the axle side tube and the axle bracket and housed in the cylindrical portion; and a connecting bolt that has a head that is inserted into a bolt insertion hole that penetrates the bottom of the cylindrical portion of the axle bracket, and a screw shaft that is inserted into the inner periphery of the collar and is screwed to the lower cap, connecting the lower cap to the collar.

In a front fork configured in this way, the axle bracket is designed so that it does not come into contact with the liquid inside the front fork, so there is no need to provide an annular groove on the inner circumference of the cylindrical part of the axle bracket. This not only makes it very easy to check whether any chips generated during the cutting process have been left behind, but also allows the thickness of the cylindrical part to be made thinner, thereby reducing the outer diameter of the cylindrical part.

FIG. 1 is a cross-sectional view of a front fork according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view of a portion of a front fork according to an embodiment of the present invention. FIG. 3 is a partially enlarged cross-sectional view of a front fork according to a first modified example of the embodiment of the present invention.

The present invention will be described based on the embodiment shown in the figures. As shown in Figure 1, in one embodiment, a front fork F is interposed between the body and the front wheel of a saddle-type vehicle such as a motorcycle or trike (not shown) and functions as part of the suspension system.

Below, each component that constitutes the front fork F will be described in detail. As shown in Figures 1 and 2, the front fork F is composed of a fork body 1, a damper cartridge D, a collar 30, and a connecting bolt 40.

The fork body 1 comprises an outer tube 2 as a vehicle body side tube, an inner tube 3 as an axle side tube that can move in the axial direction relative to the outer tube 2, and an axle bracket 4 having a bottomed cylindrical portion 4a attached to the outer periphery of the lower end of the inner tube 3, and is expandable and contractable by the relative axial movement of the inner tube 3 relative to the outer tube 2.

The inner tube 3 is inserted into the outer tube 2, and is provided with an annular bush 3a on the outer periphery of the upper end that slides against the inner periphery of the outer tube 2, as well as a threaded portion 3b on the outer periphery of the lower end.

The outer tube 2 has a head cap 5 attached to its upper open end, and is equipped with an annular bush 2a, seal ring 2b, and dust seal 2c on the inner circumference of its lower end, which are in sliding contact with the outer circumference of the inner tube 3. The upper open end of the outer tube 2 is closed by the head cap 5. When the inner tube 3 is inserted into the outer tube 2, the bush 2a slides against the outer circumference of the inner tube 3, and the bush 3a slides against the inner circumference of the outer tube 2, allowing the inner tube 3 to move axially relative to the outer tube 2 without any axial wobble in the radial direction.

In addition, the seal ring 2b prevents liquid inside the fork body 1 from leaking out between the outer tube 2 and the inner tube 3, and the dust seal 2c prevents dust and water from entering the fork body 1 from outside the fork body 1 through the gap between the outer tube 2 and the inner tube 3.

The axle bracket 4 has a bottomed cylindrical tube portion 4a, a C-shaped gripping portion 4b that is provided below the bottom of the tube portion 4a and grips an axle that rotatably holds the front wheel of a saddle-type vehicle (not shown), and a bolt insertion hole 4c that penetrates the bottom of the tube portion 4a and leads to the inner circumference of the gripping portion 4b. A screw portion 4d is provided on the bottom side of the inner circumference of the tube portion 4a, into which a screw portion 3b provided on the outer circumference of the lower end of the inner tube 3 is screwed. Although not shown, the axle bracket 4 has a bracket that holds the brake caliper of the front wheel and a fender support arm that supports a fender that covers the upper part of the front wheel on the side of the tube portion 4a. The axle bracket 4 is attached to the inner tube 3 by screwing the tube portion 4a to the outer circumference of the lower end of the inner tube 3, but it may be attached to the inner tube 3 by other connection methods such as welding other than screw connection.

The collar 30 is annular and includes a fitting portion 30a that fits into the inner circumference of the lower end of the inner tube 3, an annular flange portion 30b that protrudes radially from the outer circumference of the lower end of the fitting portion 30a, an annular recess 30c provided on the inner circumference of the lower end of the fitting portion 30a, an annular groove 30d formed circumferentially on the outer circumference of the fitting portion 30a, and a seal ring 30e that is fitted into the annular groove 30d.

The outer diameter of the fitting portion 30a is set to a diameter that allows it to fit into the inner circumference of the inner tube 3, and the fitting portion 30a is allowed to fit into the lower end of the inner tube 3. When the fitting portion 30a is fitted into the inner tube 3, the seal ring 30e in the annular groove 30d is compressed radially by the inner surface of the inner tube 3 and elastically deforms, coming into close contact with the inner surface of the inner tube 3 and the bottom of the annular groove 30d, tightly sealing between the collar 30 and the inner tube 3.

The outer diameter of the flange portion 30b of the collar 30 is larger than the inner diameter of the inner tube 3 and is designed to fit into the inner circumference of the tubular portion 4a of the axle bracket 4. When the collar 30 is inserted into the tubular portion 4a of the axle bracket 4, the lower end of the collar 30 abuts against the bottom of the tubular portion 4a and the inner circumference of the collar 30 communicates with the bolt insertion hole 4c of the axle bracket 4.

The connecting bolt 40 has a head 40a that can be inserted into the bolt insertion hole 4c but is not allowed to pass through the inner circumference of the collar 30, and a screw shaft 40b extending from the head 40a. The head 40a has a hexagonal hole 40c that opens from the lower end of the head 40a in FIG. 2 and allows a tool to be fitted, so that the connecting bolt 40 can be rotated using a tool. An annular gasket 41 is attached to the outer periphery of the base end of the screw shaft 40b. When the connecting bolt 40 is inserted into the bolt insertion hole 4c from the inner periphery side of the gripping portion 4b of the axle bracket 4, the tip of the screw shaft 40b of the connecting bolt 40 can be protruded upward from the collar 30 through the inner circumference of the collar 30. The outer diameter of the head 40a is slightly smaller than the outer diameter of the annular recess 30c formed on the inner circumference of the lower end of the collar 30. The outer diameter of the packing 41 is smaller than the outer diameter of the annular recess 30c, and the axial length of the packing 41 is shorter than the depth (axial length) of the annular recess 30c.

As described above, when the collar 30 is inserted into the tubular portion 4a and the collar 30 is in contact with the bottom of the tubular portion 4a, the lower end of the inner tube 3 is inserted into the tubular portion 4a and the screw portion 3b is screwed into the screw portion 4d. Eventually, the lower end surface of the inner tube 3 comes into contact with the upper end surface of the flange portion 30b of the collar 30, and the flange portion 30b is clamped between the inner tube 3 and the axle bracket 4. The inner tube 3 and the axle bracket 4 clamp the flange portion 30b of the collar 30 by applying a load in the axial direction, and the load applied to the flange portion 30b can be adjusted by adjusting the tightening torque of the inner tube 3 relative to the axle bracket 4. Therefore, the collar 30 can be firmly fixed to the inner tube 3 and the axle bracket 4 by applying an appropriate load to the flange portion 30b.

The damper cartridge D is housed in the fork body 1. The damper cartridge D includes a cylinder 10, a piston rod 11 inserted axially into the cylinder 10 and connected at one end to an outer tube 2 as a vehicle body side tube via a head cap 5, a piston 12 connected to the piston rod 11 and inserted axially into the cylinder 10 to divide the cylinder 10 into an extension side chamber R1 and a compression side chamber R2, a lower cap 13 fixed to the lower end of the cylinder 10, closing the lower end of the cylinder 10 and having a screw hole 13e opening from the lower end, and a base valve 14 held by the lower cap 13 to divide the cylinder 10 into a compression side chamber R2 and a chamber r below the compression side chamber R2. The extension side chamber R1 and the compression side chamber R2 are filled with a liquid such as hydraulic oil, and a reservoir R for storing the liquid is formed between the damper cartridge D and the fork body 1.

As shown in FIG. 1, the cylinder 10 is cylindrical and has a screw portion 10a on the inner circumference of the lower end, and a through hole 10b that is provided above the screw portion 10a and connects the inside and outside of the cylinder 10. The through hole 10b opens below the liquid level O of the liquid filled in the reservoir R.

Also, an annular rod guide 15 through which the piston rod 11 is slidably inserted is attached to the open upper end of the cylinder 10. The rod guide 15 is annular and has a guide portion 15a that is in sliding contact with the outer periphery of the piston rod 11 that is screwed into the inner periphery of the upper end of the cylinder 10 and inserted into the inner periphery, and a cylindrical case portion 15b that protrudes upward from the upper end of the guide portion 15a. The upper end of the case portion 15b is always below the liquid level O of the liquid in the reservoir R, and the case portion 15b is always filled with liquid.

One end of the piston rod 11, which is the upper end in FIG. 1, is connected to the head cap 5 by a screw connection, and the other end, which is the lower end in FIG. 1, is inserted into the cylinder 10 through the rod guide 15. A lock piece 16 is provided on the outer periphery of the middle part of the piston rod 11, which is annular and forms a restrictive gap between the outer periphery and the case part 15b when the piston rod 11 enters the case part 15b of the rod guide 15, providing resistance to the flow of liquid passing from inside the case part 15b to the outside of the case part 15b.

The lock piece 16 and case portion 15b form a hydraulic cushion, and when the piston rod 11 moves downward relative to the cylinder 10 in FIG. 1 and reaches the vicinity of the stroke end, the lock piece 16 enters the case portion 15b, increasing the pressure within the case portion 15b and suppressing the downward movement of the piston rod 11 relative to the cylinder 10.

The piston 12 is provided with an extension side damping passage 12a and a compression side passage 12b that communicate between the extension side chamber R1 and the compression side chamber R2, an extension side damping valve 12c that is provided in the extension side damping passage 12a and provides resistance to the flow of liquid from the extension side chamber R1 to the compression side chamber R2, and a compression side check valve 12d that is provided in the compression side passage 12b and allows only the flow of liquid from the compression side chamber R2 to the extension side chamber R1 with almost no resistance. The extension side damping passage 12a is set by the extension side damping valve 12c as a one-way passage that allows only the flow of liquid from the extension side chamber R1 to the compression side chamber R2, and the compression side passage 12b is set by the compression side check valve 12d as a one-way passage that allows only the flow of liquid from the compression side chamber R2 to the extension side chamber R1.

The lower cap 13 is fixed to the inner circumference of the lower end of the cylinder 10. Specifically, as shown in FIG. 2, the lower cap 13 is provided with a disk-shaped lid portion 13a that is inserted into the inner circumference of the lower end of the cylinder 10 and has a screw portion 13b on its outer circumference that screws into the screw portion 10a of the cylinder 10 to close the lower end of the cylinder 10, a shaft portion 13c that protrudes from the lid portion 13a toward the top in FIG. 2 into the cylinder 10, a screw portion 13d provided on the outer circumference of the upper end that is the tip of the shaft portion 13c, and a screw hole 13e that opens from the axial center of the lower end of the lid portion 13a in FIG. 2 and extends in the axial direction. Although not shown, a number of grooves that allow the insertion of a tool used when screwing the lower cap 13 to the screw portion 10a of the cylinder 10 are provided at intervals on the outer circumference of the lower end of the lid portion 13a. The shaft portion 13c is tapered from the middle to the tip, and has a step portion 13c1 in the middle. In the front fork F of this embodiment, the lower cap 13 is screwed to the cylinder 10 and fixed to the lower end of the cylinder 10, but other than screwing, the lower cap 13 may be fixed by crimping the outer periphery of the cylinder 10, or it may be fixed to the cylinder 10 by other connecting methods such as welding.

A base valve 14 is provided on the outer periphery of the tip side of the shaft portion 13c of the lower cap 13. The base valve 14 is annular and includes a partition body 17 attached to the outer periphery of the lower cap 13, a compression side damping valve 18 stacked on the lower end of the partition body 17, and an extension side check valve 19 stacked on the upper end of the partition body 17.

The partition wall 17 fits into the cylinder 10 at a position above the through hole 10b in FIG. 2, dividing the cylinder 10 into a compression side chamber R2 and a chamber r that is connected to the reservoir R, and is provided with a compression side damping passage 17a and a suction passage 17b that connect the compression side chamber R2 to the reservoir R.

The compression side damping valve 18 is a stacked leaf valve formed by stacking annular leaf valves below the partition body 17, and its inner periphery is fixed to the shaft portion 13c, allowing the outer periphery to flex, and opens and closes the outlet end at the lower end of the compression side damping passage 17a. In addition, the compression side damping valve 18 flexes its outer periphery to open the compression side damping passage 17a in response to the flow of liquid from the compression side chamber R2 to the reservoir R, and also provides resistance to the flow of liquid passing through the compression side damping passage 17a. In this way, the compression side damping passage 17a is set by the compression side damping valve 18 as a one-way passage that only allows the flow of liquid from the compression side chamber R2 to the reservoir R.

On the other hand, the extension side check valve 19 is provided with an annular valve body 19a that can be seated on and off the upper end of the partition body 17 to open and close the suction passage 17b, a valve stopper 19b having a flange facing the side of the valve body 19a opposite the partition body, and a spring 19c that is interposed between the valve body 19a and the valve stopper 19b and biases the valve body 19a toward the partition body 17. The extension side check valve 19 compresses the spring 19c against the flow of liquid from the reservoir R toward the compression side chamber R2, separating the valve body 19a from the partition body 17 and opening the suction passage 17b. The extension side check valve 19 is designed to provide almost no resistance to the flow of liquid passing through the suction passage 17b. In this way, the suction passage 17b is set by the extension side check valve 19 as a one-way passage that allows only the flow of liquid from the reservoir R toward the compression side chamber R2.

The compression side damping valve 18, partition wall 17, and extension side check valve 19 that make up the base valve 14 are attached to the outer periphery of the small diameter portion at the tip side of the shaft portion 13c of the lower cap 13, and then are held in the lower cap 13 by being clamped between the nut 20 attached to the threaded portion 13d at the tip of the shaft portion 13c and the step portion 13c1.

The lower cap 13 with the base valve 14 attached is inserted into the inner circumference of the bottom end of the cylinder 10 and is fixed to the cylinder 10 by screwing the screw portion 10a to the screw portion 13b on the outer circumference of the lid portion 13a. A gap is formed between the lid portion 13a and the base valve 14 by providing a step portion 13c1, and when the lower cap 13 is attached to the cylinder 10, the gap forms a chamber r that is connected to the through hole 10b.

The damper cartridge D thus constructed is obtained by assembling the various components that make up the damper cartridge D, and then inserted from the lower cap 13 side into the inner tube 3 with the collar 30 attached to the inner tube 3 and axle bracket 4 as described above. Then, while the lower end of the lower cap 13 is abutted against the upper end of the collar 30 fixed inside the axle bracket 4, the connecting bolt 40 is inserted into the bolt insertion hole 4c and the inner circumference of the collar 30, and the connecting bolt 40 is rotated to screw the screw shaft 40b into the screw hole 13e of the lower cap 13. When the screw shaft 40b of the connecting bolt 40 is screwed into the screw hole 13e of the lower cap 13, the head 40a of the connecting bolt 40 and the lid portion 13a of the lower cap 13 clamp the collar 30, and the collar 30 and the damper cartridge D are connected.

The collar 30 is sandwiched between the inner tube 3 (the axle side tube) and the axle bracket 4 and is fixed to the inner tube 3 and the axle bracket 4, so that the cylinder 10 and the inner tube 3 in the damper cartridge D are connected by screwing the connecting bolt 40 to the lower cap 13. When the lower cap 13, which closes the lower end of the cylinder 10 of the damper cartridge D, is fixed to the collar 30 with the connecting bolt 40, the damper cartridge D is connected to the inner tube 3, and then when the upper end of the piston rod 11 of the damper cartridge D is connected to the outer tube 2 via the head cap 5, the damper cartridge D is housed in the fork body 1 and is interposed between the outer tube 2 (the vehicle side tube) and the inner tube 3 (the axle side tube), and can expand and contract together with the fork body 1.

When the connecting bolt 40 is screwed to the lower cap 13 in this manner, the packing 41 attached to the outer periphery of the screw shaft 40b is accommodated in the annular recess 30c formed on the inner periphery of the lower end of the lower cap 13, and is sandwiched under load between the head 40a of the connecting bolt 40 and the surface of the annular recess 30c of the collar 30 that faces the head 40a in the axial direction, so that the packing 41 tightly seals the space between the connecting bolt 40 and the collar 30. In the front fork F of this embodiment, the inner periphery of the lower end of the collar 30 is provided with an annular recess 30c that accommodates the annular packing 41 fitted to the outer periphery of the screw shaft 40b of the connecting bolt 40, so that even if the packing 41 is compressed and deformed between the head 40a and the bottom of the annular recess 30c, it deforms while remaining contained within the annular recess 30c. Therefore, even if the connecting bolt 40 is screwed into the lower cap 13, the packing 41 does not protrude outward from the annular recess 30c.

Here, if the collar 30 does not have an annular recess 30c for accommodating the packing 41, there is nothing to prevent the packing 41 from expanding in outer diameter, and the packing 41 may be crushed between the head 40a and the lower end surface of the collar 30 by the screwing of the connecting bolt 40 into the lower cap 13, expanding the outer diameter of the packing 41 and entering the chamfered portion 4e formed on the inner edge of the end of the tubular portion 4a of the bolt insertion hole 4c of the axle bracket 4. In such a situation, even if the connecting bolt 40 is loosened and removed from the lower cap 13, since the packing 41 enters between the collar 30 and the chamfered portion 4e of the axle bracket 4, it may be difficult to pull the packing 41 out of the front fork F through the bolt insertion hole 4c, and the packing 41 may not be able to be replaced. Therefore, if the collar 30 has an annular recess 30c for accommodating the packing 41, not only can the packing 41 provide an appropriate sealing performance, but the packing 41 can also be easily replaced during maintenance of the front fork F.

Next, the operation of the front fork F configured as above will be explained. First, when the front fork F extends, the outer tube 2 and the inner tube 3 move away from each other in the axial direction, so that the piston rod 11 moves upward relative to the cylinder 10 and the damper cartridge D also extends. When the damper cartridge D extends, the piston 12 moves upward in FIG. 1 within the cylinder 10, contracting the expansion side chamber R1 and expanding the compression side chamber R2. Then, the liquid passes through the expansion side damping passage 12a and the expansion side damping valve 12c and moves from the expansion side chamber R1 to the compression side chamber R2. The expansion side damping valve 12c provides resistance to the flow of liquid passing through the expansion side damping passage 12a, so the pressure in the expansion side chamber R1 increases.

On the other hand, as the piston rod 11 retreats from the cylinder 10, the expanding compression side chamber R2 lacks liquid by the volume of the piston rod 11 retreating from the cylinder 10. However, this shortage of liquid is supplied from the reservoir R to the compression side chamber R2 via the suction passage 17b as the extension side check valve 19 opens. Therefore, the pressure in the compression side chamber R2 becomes approximately equal to the pressure in the reservoir R.

In this way, when the front fork F extends, the pressure in the extension side chamber R1 rises and becomes higher than the pressure in the compression side chamber R2, acting on the piston 12, and the damper cartridge D generates an extension side damping force that impedes the extension of the front fork F.

Next, when the front fork F contracts, the outer tube 2 and the inner tube 3 approach each other in the axial direction, so that the piston rod 11 moves downward relative to the cylinder 10 and the damper cartridge D also contracts. When the damper cartridge D contracts, the piston 12 moves downward in FIG. 1 within the cylinder 10, contracting the compression side chamber R2 and expanding the extension side chamber R1. Then, the liquid passes through the compression side passage 12b and the compression side check valve 12d of the piston 12 and moves from the compression side chamber R2 to the extension side chamber R1. Also, because the piston rod 11 penetrates into the cylinder 10, the liquid in the cylinder 10 becomes excessive by the volume of the piston rod 11 penetrating into the cylinder 10, and this excess liquid pushes open the compression side damping valve 18 and moves from the compression side chamber R2 to the reservoir R through the compression side damping passage 17a. The compression side check valve 12d provides almost no resistance to the flow of liquid, making the pressure in the expansion side chamber R1 and the pressure in the compression side chamber R2 approximately equal, while the compression side damping valve 18 provides resistance to the flow of liquid passing through the compression side damping passage 17a, causing the pressure in the cylinder 10 to rise.

In this way, when the front fork F contracts, the pressure in the expansion side chamber R1 and the pressure in the compression side chamber R2 rise approximately equally, and the pressure in the expansion side chamber R1 acts on the upper surface of the piston 12, and the pressure in the compression side chamber R2 acts on the lower surface of the piston 12. However, because the piston 12 is connected to the piston rod 11, the pressure-receiving area of the lower surface of the piston 12 is larger than the pressure-receiving area of the upper surface, so the damper cartridge D generates a compression side damping force that prevents the front fork F from contracting.

As described above, the front fork F of this embodiment comprises an extendable fork body 1 having an outer tube (vehicle body side tube) 2, an inner tube (axle side tube) 3 that is movable in the axial direction relative to the outer tube (vehicle body side tube) 2, and an axle bracket 4 having a bottomed cylindrical portion 4a attached to the outer periphery of the lower end of the inner tube (axle side tube) 3, a cylinder 10, a piston rod 11 that is inserted into the cylinder 10 so as to be movable in the axial direction and has one end connected to the outer tube (vehicle body side tube) 2, and a piston rod 11 that is connected to the piston rod 11 and inserted into the cylinder 10 so as to be movable in the axial direction, dividing the cylinder 10 into an extension side chamber R1 and a compression side chamber R2. The damper cartridge D has a piston 12 and a lower cap 13 fixed to the bottom end of the cylinder 10 and closed off the bottom end of the cylinder 10, and is housed in the fork body 1; a collar 30 that is annular and has a seal ring 30e that is in close contact with the inner tube (axle side tube) 3 and is sandwiched between the inner tube (axle side tube) 3 and the axle bracket 4 and housed in the tubular portion 4a; and a connecting bolt 40 that has a head 40a that is inserted into a bolt insertion hole 4c that penetrates the bottom of the tubular portion 4a of the axle bracket 4 and a screw shaft 40b that is inserted into the inner circumference of the collar 30 and is screwed to the lower cap 13, and connects the lower cap 13 to the collar 30.

In the front fork F configured in this manner, the cylinder 10 is fixed to the axle bracket 4 by a connecting bolt 40 that is inserted through the collar 30 sandwiched between the inner tube (axle side tube) 3 and the axle bracket 4 and screwed into the lower cap 13 that closes the lower end of the cylinder 10. In this manner, in the front fork F of this embodiment, the collar 30 is provided with a seal ring 30e that is in close contact with the inner tube (axle side tube) 3, sealing the space between the inner tube (axle side tube) 3 and the collar 30, and the lower cap 13 in the damper cartridge D is connected to the collar 30 by the connecting bolt 40, so that the axle bracket 4 does not come into contact with the liquid stored in the front fork F. In other words, in the front fork F of this embodiment, the components that directly block the lower end of the inner tube (axle side tube) are the collar 30, the lower cap 13 that is fixed to the collar 30, and the connecting bolt 40. The tubular portion 4a of the axle bracket 4 plays a role in holding the collar 30 together with the inner tube (axle side tube), but is not a component that directly blocks the lower end of the inner tube (axle side tube).

As described above, according to the front fork F of this embodiment, the axle bracket 4 is designed not to come into contact with the liquid inside the front fork F, so there is no need to cut an annular groove for installing a seal ring on the inner circumference of the tubular portion 4a of the axle bracket 4.

Therefore, according to the front fork F of this embodiment, since it is not necessary to provide an annular groove on the inner circumference of the tubular portion 4a of the axle bracket 4, it is very easy to check whether any chips generated during cutting have been left behind, reducing the workload of the workers manufacturing the front fork F. Also, according to the front fork F of this embodiment, since it is not necessary to provide an annular groove on the inner circumference of the tubular portion 4a of the axle bracket 4, it is possible to reduce the thickness of the tubular portion 4a of the axle bracket 4 and reduce the outer diameter of the tubular portion 4a, thereby reducing the weight of the front fork F.

In addition, the front fork F of this embodiment is designed so that the axle bracket 4 does not come into contact with the liquid inside the front fork F, so even if the axle bracket 4 is made of a casting, there is no need to X-ray inspect it for blowholes, which reduces manufacturing costs.

As described above, the front fork F of this embodiment can reduce the workload of the manufacturing workers, as well as reduce manufacturing costs and weight. Furthermore, with the front fork F of this embodiment, by loosening and removing the connecting bolt 40 from the lower cap 13, the damper cartridge D and the collar 30 can be separated and the damper cartridge D can be easily removed from the axle bracket 4 and the inner tube (axle side tube) 3, making maintenance easier. Note that, in the front fork F of this embodiment, the vehicle body side tube is the outer tube and the axle side tube is the inner tube, but the fork body 1 may be configured so that the vehicle body side tube is inserted axially movable into the axle side tube.

In the front fork F of this embodiment, the axle bracket 4 has a screw portion 4d that is screwed to the outer periphery of the lower end of the inner tube (axle side tube) 2 on the inner periphery of the tubular portion 4a, and the collar 30 has an annular fitting portion 30a that is fitted to the inner periphery of the lower end of the inner tube (axle side tube) 3, a flange portion 30b that is provided on the outer periphery of the lower end of the fitting portion 30a and is sandwiched between the inner tube (axle side tube) 3 and the bottom of the tubular portion 4a of the axle bracket 4, and a seal ring 30e that is accommodated in an annular groove 30d provided in the fitting portion 30a and is in close contact with the inner periphery of the inner tube (axle side tube) 3. With the front fork F configured in this way, the collar 30 can be easily fixed to the inner tube (axle side tube) 3 and the axle bracket 4 simply by accommodating the collar 30 in the tubular portion 4a and screwing the tubular portion 4a to the lower end of the inner tube (axle side tube) 3.

In addition, in the front fork F of this embodiment, a reservoir R is formed in the space between the fork body 1 and the damper cartridge D, and is provided with a base valve 14 that is held by the lower cap 13 and fits into the cylinder 10 to divide the inside of the cylinder 10 into a compression side chamber R2 and a chamber r that communicates with the reservoir R. With the front fork F configured in this manner, the base valve 14 is held in the lower cap 13 that is used to connect the cylinder 10 to the collar 30, so no other parts are required to install the base valve 14 in the cylinder 10, and the number of parts can be reduced.

Furthermore, the front fork F of this embodiment is provided with an annular packing 41 that fits onto the outer periphery of the screw shaft 40b of the connecting bolt 40, and the collar 30 is provided with an annular recess 30c that houses the packing 41 on the inner periphery of the lower end. With the front fork F configured in this manner, even if the packing 41 is sandwiched between the head 40a and the collar 30 and compressed and deformed, the packing 41 does not protrude from within the annular recess 30c, so not only is the packing 41 able to provide appropriate sealing performance, but the packing 41 can also be easily replaced during maintenance of the front fork F.

3, the lower cap 13 may have a tapered surface 13f on the outer periphery of the lower end that narrows toward the lower end, and the collar 30 may have a recess 30f on the inner periphery of the upper end that fits into the tapered surface 13f of the lower cap 13 to align the lower cap 13. In the front fork F1 configured in this manner, when the tapered surface 13f of the lower cap 13 is abutted against the recess 30f of the collar 30 during the work of fixing the damper cartridge D to the collar 30 fixed to the axle bracket 4 with the connecting bolt 40, the tapered surface 13f of the lower end of the lower cap 13 slides on the tapered inclined surface 30f1 of the recess 30f, and the lower cap 13 is automatically aligned with respect to the collar 30 so that the axis of the screw hole 13e and the axis of the collar 30 coincide with each other. Therefore, when the screw shaft 40b of the connecting bolt 40 is passed through the inner circumference of the collar 30 from below, the tip of the screw shaft 40b faces the opening of the screw hole 13e in the axial direction, so that the connecting bolt 40 can be easily assembled to the lower cap 13. Furthermore, the collar 30 is provided with the recess 30f, so that the collar 30 can be made lighter. As described above, the tapered surface 13f is provided on the outer circumference of the lower end of the lower cap 13, and the collar 30 is provided with the recess 30f having the tapered inclined surface 30f1 that fits with the tapered surface 13f. However, the outer circumference of the lower end of the lower cap 13 may be provided with a curved surface, and the collar 30 may be provided with a recess having a curved surface that fits with the curved surface. In addition, in the front fork F1 of the first modified example, the collar 30 is provided with the recess 30f, so that the stroke length of the front fork F1 can be long, and the overall length of the front fork F1 can be shortened, and the design freedom of the front fork F1 is improved.

The above describes in detail the preferred embodiment of the present invention, but modifications, variations and changes are possible without departing from the scope of the claims.

This application claims priority to Patent Application No. 2022-169880, filed with the Japan Patent Office on October 24, 2022, the entire contents of which are incorporated herein by reference.

1: Fork body, 2: Outer tube (tube on vehicle body side), 3: Inner tube (tube on vehicle body side), 4: Axle bracket, 4a: Cylindrical part, 10: Cylinder, 11: Piston rod, 12: Piston, 13: Lower cap, 13g: Tapered surface, 14: Base valve, 30: Collar, 30a: Fitting part, 30b: Flange part, 30c: Annular recess, 30e: Seal ring, 30f: Recess, 40: Connecting bolt, 40a: Head, 40b: Screw shaft, 41: Gasket, D: Damper cartridge, F, F1: Front fork, R: Reservoir, R1: Expansion side chamber, R2: Compression side chamber

Claims

A front fork,
a fork body having a vehicle body tube, an axle side tube that is movable in an axial direction relative to the vehicle body side tube, and an axle bracket having a bottomed cylindrical portion attached to an outer periphery of a lower end of the axle side tube, the fork body being extendable and contractible;
a damper cartridge that is housed in the fork body and includes: a cylinder; a piston rod that is inserted into the cylinder so as to be axially movable and has one end connected to the vehicle body tube; a piston that is connected to the piston rod and inserted into the cylinder so as to be axially movable, dividing the interior of the cylinder into an expansion-side chamber and a compression-side chamber; and a lower cap that is fixed to a lower end of the cylinder and closes the lower end of the cylinder;
a collar having an annular seal ring that is in close contact with the axle-side tube, the collar being sandwiched between the axle-side tube and the axle bracket and accommodated within the cylindrical portion;
a connecting bolt having a head that is inserted into a bolt insertion hole that penetrates the bottom of the tubular portion of the axle bracket and a screw shaft that is inserted into the inner circumference of the collar and screw-connected to the lower cap, connecting the lower cap to the collar.
2. The front fork according to claim 1,
The lower cap has a tapered or curved surface on the outer periphery of the lower end, the diameter of which decreases toward the lower end side.
The collar has a recess on an inner periphery at an upper end thereof for fitting into the tapered surface or the curved surface to align the lower cap.
2. The front fork according to claim 1,
a ring-shaped packing fitted onto an outer periphery of the screw shaft of the connecting bolt;
The collar has an annular recess on the inner periphery of a lower end thereof for accommodating the packing.
2. The front fork according to claim 1,
A reservoir is formed in a space between the fork body and the damper cartridge,
a front fork comprising: a base valve held by the lower cap and fitted within the cylinder to divide the inside of the cylinder into the compression side chamber and a chamber communicating with the reservoir.