Rear wheel suspension device for two wheeled vehicle and method of setting rear wheel suspension

Abstract

To provide a new rear wheel suspension device for a motorcycle or the like capable of further concentrating mass while adopting a twin shock structure having shock absorbers on the right and left sides of a vehicle body.SOLUTION: A shock absorber S is provided on each of the left and right sides of the vehicle body, the shock absorber S being bridged between the vehicle body frame 1 and the swing arm 2 capable of pivotally supporting the rear wheel 5, upper and lower ends of a head pipe 1h of the vehicle body frame 1 are denoted by d and c, respectively, a pivot shaft center of the swing arm 2 and the vehicle body frame 1 is denoted by A, a coupling shaft center of the shock absorber S and the swing arm 2 is denoted by Z, in the rear wheel suspension device for the motorcycle or the like, a shock absorber ray ZY passes through a line segment Ad excluding a pivot shaft center A, a line segment Ac excluding the pivot shaft center A, or a part before a longitudinal position of an outputting shaft center b in the line segment Ad, or a part before the longitudinal position of the outputting shaft center b in the line segment Ac in a side view.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a rear wheel suspension system suitable mainly for motorcycles, and more particularly to a rear wheel suspension system for motorcycles and the like that employs a twin shock structure having shock absorbers on both the left and right sides of the vehicle body, and a rear wheel suspension setting method. [Background technology]

[0002] In rear wheel suspension systems for motorcycles and the like, a structure with a shock absorber (rear shock absorber) on each side of the vehicle body is called a twin shock absorber (hereinafter referred to as "TS"), also known as a two-suspension system. As disclosed in Patent Document 1, a conventional TS has a shock absorber installed in an upright position across the connecting and integrated section between the seat rail extending rearward from the lateral frame member and the side rail extending rearward and upward from the lower part of the lateral frame member, and the rear part of the swing arm. Patent Document 2 also discloses a rear wheel suspension system similar to that of Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 62-46397 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-19230 Summary of the Invention [Problem to be solved by the invention]

[0004] The TS rear wheel suspension systems shown in Patent Documents 1 and 2 have a relatively heavy shock absorber located rearward from the center of the vehicle body. This results in poor front-to-rear weight balance. Because the engine, a heavy component, is located in the center of the vehicle body, the center of gravity of the vehicle is often located near the engine, such as near the rear of the engine above it. Therefore, having heavy shock absorbers located on either side of the vehicle far behind the center of gravity is disadvantageous in terms of mass centralization.

[0005] An object of the present invention is to provide a rear wheel suspension for a motorcycle or the like that allows for better mass centralization while adopting a TS with shock absorbers on both the left and right sides of the vehicle body through ingenious shock absorber arrangement and structure. [Means for solving the problem]

[0006] [1] The present invention is a rear wheel suspension device for a motorcycle or the like, A shock absorber is provided on each of the left and right sides of the vehicle body, the shock absorber being installed across a swing arm capable of supporting a rear wheel and the vehicle body frame, Let the upper and lower ends of the head pipe center of the body frame be d and c respectively, the pivot axis between the swing arm and the body frame be A, the connecting axis between the shock absorber and the swing arm be Z, the connecting axis between the shock absorber and the body frame be Y, and the output axis of the engine be b. When viewed from the side, the shock absorber half line ZY passes through the line segment Ad excluding the pivot axis A, or the line segment Ac excluding the pivot axis A, or the part of the line segment Ad before the fore-and-aft position of the output axis b, or the part of the line segment Ac before the fore-and-aft position of the output axis b.

[0007] If the shock absorber half line ZY is configured to pass through the above-mentioned line segment Ad excluding the pivot axis A, or the line segment Ac excluding the pivot axis A, or the portion of the line segment Ad before the fore-and-aft position of the output shaft center b, or the portion of the line segment Ac before the fore-and-aft position of the output shaft center b, the shock absorber will be arranged in a forward-lying position, tilted significantly forward, above the swing arm. In other words, the shock absorber, which has conventionally been arranged in an upright position at the rear of the vehicle body, can now be arranged in a forward-lying position. For inventions other than [1], please refer to the claims, etc. [Effects of the Invention]

[0008] According to the present invention, the shock absorber, which has conventionally been placed in an upright position at the rear of the vehicle body, can be placed in a laid-down position and moved forward, so that the shock absorber, which is a heavy component, can be placed closer to the center of the front and rear of the vehicle body, and a rear wheel suspension device for a motorcycle or the like can be provided which achieves better mass centralization while adopting a TS structure in which shock absorbers are provided on both the left and right sides of the vehicle body. [Brief explanation of the drawings]

[0009] [Figure 1] (A) is a schematic left side view of a motorcycle, and (B) is an enlarged view of the main part of the rear wheel suspension system. [Figure 2] 1A and 1B show a first rear wheel suspension system, in which (A) is a left side view and (B) are diagrams of the left front and rear suspension supports. [Figure 3] 1A and 1B are a right side view and a right front and rear view, respectively, of a first rear wheel suspension system; [Figure 4] (A) is a right side view of the second rear wheel suspension system, and (B) is an enlarged side view of the main part on the left side. [Figure 5] (A) and (B) are schematic diagrams showing various shock absorber arrangements. [Figure 6] A diagram showing the relationship between the shock absorber body connection point and pivot axis center distance and the relative unsprung mass [Figure 7] Showing the original and new mounting structures, (A) E suspension bolt, (B) axle bolt [Figure 8] The original and new mounting structures are shown. (A) Left rear suspension body, (B) Right rear suspension body DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the rear wheel suspension device and rear wheel suspension setting method for a motorcycle or the like according to the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the illustrated examples. Appropriate modifications may be made within the scope of the spirit described above and below, and all such modifications are within the technical scope of the present invention. The dimensions, shapes, and proportions of the various parts in the drawings may not be exact replicas. A half-line is a line extending infinitely from one point in one direction. For example, half-line ZY means a line extending infinitely from point Z to point Y. Note that "before the front-rear position" refers to the portion forward of the front-rear position, including the front-rear position. This invention is applicable to three-wheeled vehicles with two front wheels and one rear wheel, and three-wheeled or four-wheeled vehicles with rear wheels on either side of a swing arm. These three-wheeled vehicles, three-wheeled and four-wheeled vehicles, and motorcycles are collectively referred to as motorcycles, etc.

[0011] 1(A) and 1(B) show a schematic right side view and a left side view of a main portion of a motorcycle, which is an example of a two-wheeled vehicle. The motorcycle includes a body frame 1, a swing arm 2, an engine 3 with a transmission case 3M, a front wheel 4, a rear wheel 5, a front fork (front wheel suspension) 6, a fuel tank 7, a seat 8, etc. The front end of the swing arm 2, which supports the rear wheel 5, is pivotally supported on the body frame 1 about a left-right pivot axis A so as to be able to swing up and down. The transmission case 3M has a crank axis a, a counter axis (not shown) of a built-in transmission mechanism (not shown), and an output axis b of a drive gear 9 around which a chain (a collective term for a chain, belt, etc., is an endless rotating belt) 10 for driving the rear wheel 5 is wound. The engine 3 can be of a lying-down type, an upright type, a forward-leaning type, a V-type, a two- or four-stroke cycle, or other types. Reference numeral 17 denotes a left rear suspension supported at the rear of the swing arm 2. The body frame 1 preferably has a head pipe 1H, a main pipe 1A, a main horizontal pipe 1B, a down pipe 1C, a vertical pipe 1D, a seat pipe 1E, and a rear pipe 1F. The motorcycle shown in Figure 1 can be used to modify an existing vehicle or as a new design. Figure 1(B) shows the mounting structure of the right shock absorber S temporarily mounted on the left side. The symbol p in Figure 1(A) indicates the reference position (hip point) when the rider is seated on the seat 7.

[0012] As shown in Figure 1(A), the drive-side shock absorber S on the chain 10 side is, for example, mounted on the rear connector 32 (connector to the swing arm 2) of the left rear suspension body 17 and the front connector 23 to the body frame 1, and is positioned above or above the chain 10. As shown in Figure 1(B), the non-drive-side shock absorber S on the right side, where the chain 10 is not mounted, has, for example, a rear connector 32 that uses the cantilevered axle piece 2b attached to the rear end of the swing arm 2, and a front connector 23. It is preferable, but not limited to, that both of these left and right shock absorber half-lines ZY pass through the smallest line segment Ac-b. If the angle YAZ around the pivot axis A formed by the left and right front and rear connectors 23, 32 is the same, it is preferable, but not limited to, that the same shock absorber S can be used on both sides. The shock absorber S is preferably, but not limited to, a typical piston rod type with a fluid pressure damper and a coil spring. 49 is a rear sprocket.

[0013] As shown in Fig. 1, the rear wheel suspension K employs a TS structure in which shock absorbers S are provided on both the left and right sides of the vehicle body, spanning the swing arm 2 and the body frame 1. If the upper end of the head pipe center 1h of the body frame 1 is designated d and the lower end is designated c, the pivot axis between the swing arm 2 and the body frame 1 is designated A, the rear wheel axis of the swing arm 2 is designated C, the connecting axis between the shock absorber S and the swing arm 2 is designated Z, the connecting axis between the shock absorber S and the body frame 1 is designated Y, and the vertical line representing the fore-aft position of the output axis b is designated b, then a preferred configuration is one in which the shock absorber half line ZY passes through (passes through or crosses) the line segment Ad excluding the pivot axis A in a side view (see Fig. 5(A)). In side view, the shock absorber half line ZY may be configured to pass through line segment Ac excluding the pivot axis A (see FIG. 5(A)), or may be configured to pass through a portion of line segment Ad before the fore-and-aft position of the output shaft center b (see FIG. 5(B)), or may be configured to pass through a portion of line segment Ac before the fore-and-aft position of the output shaft center b (see FIG. 5(B)). In other words, the range of up-and-down positions that the shock absorber half line ZY can take, with the rear connecting axis Z as the fulcrum, is widest when it passes through line segment Ad excluding the pivot axis A (hereinafter referred to as line segment Ad-A), and gradually narrows in the order of line segment Ac excluding the pivot axis A (hereinafter referred to as line segment Ac-A), the portion of line segment Ad before the fore-and-aft position of the output shaft center b (hereinafter referred to as line segment Ad-b), and the portion of line segment Ac before the fore-and-aft position of the output shaft center b (hereinafter referred to as line segment Ac-b).

[0014] As shown in FIG. 5, the shock absorber half line ZY on the non-drive side (right side), indicated by a solid line, preferably passes through the line segments Ad-A and Ad-b and passes through the portions of the line segments Ad-A and Ad-b below the height of the lower end of the shaft center c (below line c), but this is not limited to this. The shock absorber half line ZY on the drive side (left side), indicated by a dashed-dot line, preferably passes through the line segments Ad-A and Ad-b as well as the line segments Ac-A and Ac-b, but this is not limited to this. The range of maximum and minimum angles that each of the left and right shock absorbers S can assume around the connecting shaft center Z with the swing arm 2 is shown by the two-dot dashed shock absorber half line ZY with respect to the line segment Ad-A shown in FIG. 5(A) as an example. For ease of understanding the drawing, the shock absorber half line ZY at the minimum angle (most reclined position) is drawn as a line (tangent) tangent to a circle of minimal diameter centered on the pivot shaft center A. The range of placement of the shock absorber S is widest when the shock absorber half line ZY passes through the line segment Ad-A, and narrowest when it passes through the line segment Ac-b, with the line segments Ad-b and Ac-A existing between the two.

[0015] In other words, in a configuration in which the shock absorber half line ZY passes through the line segment Ad-A, the shock absorber S will have its front-lowering orientation most downward when the shock absorber half line ZY passes through a point extremely close to the pivot axis A of the line segment Ad-A, and its front-higher orientation will be most upward when it passes through the upper end d of the axis (see Figure 5(A)).In a configuration in which the shock absorber half line ZY passes through the line segment Ad-b, the shock absorber S will have its front-lowering orientation most downward when the shock absorber half line ZY passes through the intersection t of the line segment Ad-A and the line b, and its front-higher orientation will be most upward when it passes through the upper end d of the axis (see Figure 5(B)).In a configuration in which the shock absorber half line ZY passes through the line segment Ac-A, the shock absorber S will have its front-lowering orientation most downward when the shock absorber half line ZY passes through a point extremely close to the pivot axis A of the line segment Ac-A, and its front-higher orientation will be most upward when it passes through the lower end c of the axis (see Figure 5(A)). In a configuration in which shock absorber half line ZY passes through line segment Ac-b, the shock absorber S will have its most forward-lower posture when shock absorber half line ZY passes through intersection point s between line segment Ac-A and line b, and its most forward-upward posture when it passes through the lower end of the axle c (see Figure 5(B)). Note that a configuration in which half line ZY passes through the intersection points of each of half lines Ad, td, Ac, and sc with a horizontal line passing through the overall height e of the vehicle body may be configured as the upper limit of the upward posture of the shock absorber S (see Figures 1, 2, and 4).

[0016] 2 and 3, the first rear wheel suspension K1 is an example in which the rear wheel suspension K is applied to an existing motorcycle, and has front suspension bodies 16 and 18 attached to the body frame 1, rear suspension bodies 17 and 19 attached to the swing arm 2, and left and right shock absorbers S installed across the front and rear suspension bodies. The engine 3 is a retractable type with a transmission case 3M, 11 is a footrest, 12 is a chain cover, 13 is a side cover that is detachable from the body frame 1, 14 is a body-side connection part of the existing shock absorber 15, 16 and 18 are left and right front suspension bodies, and 17 and 19 are left and right rear suspension bodies. It is preferable that one or more of the left and right front suspension bodies 16, 18 and the left and right rear suspension bodies 17, 19 are detachable, and it is even more preferable if all of them are detachable, since this allows for the optional interchange or selection of the new specification having the first rear wheel suspension device K1 and the original specification having the existing shock absorber 15 shown in phantom lines. The existing shock absorber 15 is installed across the shaft piece 2b at the rear end of the swing arm 2 and the vehicle body side connecting part 14. 47 is a muffler.

[0017] In the left-side first rear wheel suspension device K1 shown in Figure 2, the left front suspension body 16 is a component for connecting the drive-side shock absorber S on the left side of the vehicle body, where the chain 10 is disposed, to the vehicle frame 1. It is preferably detachably attached to the vehicle frame 1 by an E-suspension bolt 20 located on the top of the transmission case 3M and an axle bolt 21 having a pivot axis A. The left front suspension body 16 is conveniently constructed in two parts, with a left main body portion 16A and a left lower portion 16B screwed together. The left main body portion 16A has a front connecting portion 23 that supports the front end portion 22 of the shock absorber S, a front leg portion 24 having a front mounting hole 16a for the E-suspension bolt, a lower leg portion 25 having a pair of through holes (not shown) for fixing the left lower portion 16B, and a joining piece 26. The left lower portion 16B is preferably made of a plate material having a lower mounting hole 16b for the shaft bolt 21 and a pair of through holes (not shown) for mounting the left main body portion 16A.

[0018] The front connecting portion 23 is, for example, a cylindrical boss that penetrates the left main body portion 16A and is integrated by welding or the like. The front end portion 22 is preferably connected by a bolt to a shaft support (e.g., a rubber bushing or a spherical bearing) 23A that is press-fitted into the cylindrical boss 23. The combining piece 26 extending rearward above the front connecting portion 23 is suitable for connecting and integrating the left and right front suspension bodies 16, 18 and preferably has a connecting hole 16c through which a connecting bolt (described below) 45 passes. The left front suspension body 16, which is integrated by the left main body portion 16A and the left lower portion 16B with bolts and nuts 28, is preferably attached to the vehicle frame 1 using an E-suspension bolt 20 and an axle bolt 21. Although not shown, the swing arm 2 has left and right arm bodies extending fore and aft and a connecting member that connects the left and right arm bodies at a position slightly rearward from the front end of the swing arm 2. The swing arm 2 is configured to have a generally H-shape that is biased forward when viewed in the vertical direction.

[0019] As shown in Figure 2, the left rear suspension body 17 preferably comprises a left rear main body 17A made of, for example, steel plate, a tubular boss 31 into which the axle piece constituting the swing arm side connecting part 2b is fitted, a rear connecting part 32 that supports the rear end part 30 of the shock absorber S, and a reinforcing member 33. The left rear suspension body 17 is preferably attached to the swing arm 2 by fastening the tubular boss 31 with a nut to the axle piece 2b that connects the existing shock absorber 15 of the swing arm 2, and by screwing the front end part of the left rear main body 17A with a front bolt 29 that attaches the front part of the chain cover 12 to the upper protrusion 2e of the swing arm 2 (see Figure 8(A)). The left rear main body 17A preferably has a recess 17c or a hole 17d to avoid interference with the bolts 34, 34 that attach the mounting piece 12B at the rear of the chain cover 12 to the nut part of the mounting piece 2a. The rear connecting portion 32 is, for example, made of an upwardly open U-shaped steel plate, and in addition to the main through-hole 32a for the rear end portion 30 mounting bolt, it is preferable to provide a sub-through-hole 32b for adjusting the vehicle height.

[0020] The right-side first rear wheel suspension K1 will now be described. As shown in FIG. 3, the right front suspension 18 is essentially the same in structure as the left front suspension 16. Functionally identical components are designated by corresponding reference numerals, and their descriptions will generally be omitted. As also shown in FIG. 3(B), the right front suspension 18 preferably has a two-piece structure in which a right main body 18A and a right lower part 18B are integrally connected. The right main body 18A preferably has a front connecting part 23, a front leg 24 having a cylindrical nut 18a that threads onto the male thread at the tip of the E suspension bolt 20, a lower leg 25, a joining piece 26 having a connecting hole 18c, and a clutch receiver 35. The right lower part 18B preferably has a pair of through holes (not shown) for screwing to the right main body 18A and a lower mounting hole 18b for receiving the axle bolt 21, and can be made common with the left lower part 16B. As described above, the connecting piece 26 is preferably connected to the connecting piece 26 of the left front suspension body 1 by bolts.

[0021] As shown in Figure 3(B), the clutch receiver 35 is a receiving member for the outer tip end (not shown) of the clutch cable 46, and is preferably a C-shaped metal piece when viewed in the axial direction to allow the inner cable (not shown) to be inserted and removed, but may be cylindrical or have other shapes. The clutch receiver 35 is preferably present in the case of an engine 3 in which a clutch passive arm (not shown) is located at the rear end on the right side of the transmission case 3M, but may not be present in the case of an engine 3 in which the clutch passive arm is located at a position other than the rear end, such as the front end. When the front leg 24 is formed in a bent shape with the rear side leaning more to the right than the front side, it is preferable to weld the clutch receiver 35 to the inner corner of the bent portion of the front side so as to contribute to improving the strength and rigidity of the bent portion.

[0022] As shown in Figure 3, the right rear suspension body 19 has a right rear main body 19A, an auxiliary arm 19B, and a connecting portion 19C that fixes the two halves 19A, 19B relative to each other. The right rear main body 19A preferably has a rear connecting portion 32 that has a pair of main and auxiliary through-holes 32a, 32b and is U-shaped with an upwardly open angle when viewed in the front-to-rear direction, a tubular boss portion 31 with a through-hole 19a, and a pair of front and rear connecting holes (not shown) for connecting the auxiliary arm 19B. The auxiliary arm 19B preferably has a through-hole 19b that passes through a cantilever shaft 2d that protrudes inward from the swing arm 2 to support a torque bar 48 for the rear brake, and a pair of front and rear connecting holes (not shown) for connecting the right rear main body 19A. The right rear suspension body 19A and the auxiliary arm 19B can be integrally connected by the bolt and nut 19d and the spacer 19c that are passed through the respective connecting holes. The right rear suspension body 19 is preferably attached to the swing arm 2 by fastening a nut 59 to the male thread portion 58 at the tip of the shaft piece 2b of the tubular boss portion 31 that is passed through the through-hole 19a, and by preventing the auxiliary arm 19B from rotating with the cantilever shaft 2d (preferably by adding a screw).

[0023] In the first rear wheel suspension K1, the shock absorber half line ZY passes through one of four line segments Ad-A, Ad-b, Ac-A, and Ac-b, similar to the rear wheel suspension K shown in FIG. 1 (see FIG. 5), and the explanation has been given by illustrating it in FIGS. 2 and 3. In the example shown in FIGS. 2 and 3, the shock absorber half line ZY on the drive side (left side) where the chain 10 is present passes through all four line segments, while the shock absorber half line ZY on the non-drive side (right side) where the chain 10 is not present passes through at least line segments Ad-A and Ad-b, but this is not limited to this. Either the left or right shock absorber half line may pass through one of the four line segments. Note that the upper limit of the four line segments may be defined as equivalent to the height of the connecting axis f of the vehicle-side connecting portion 14 of the existing shock absorber 15.

[0024] 2 and 3, it has been found that, if the value of the included angle α between the line segments YA and ZA is set to an angle condition (α≧β) that is equal to or greater than the value of the included angle β between the line segments AY and ZY (α≧β), the compression amount of the shock absorber S per unit swing angle of the swing arm 2 when the swing arm 2 swings upward relative to the body frame 1 changes linearly or progressively, which is preferable. In other words, if the shock absorber S is positioned so that the included angle α≧the included angle β (α≧β) while the shock absorber half line ZY passes through at least one of the four line segments Ad-A, Ad-b, Ac-A, and Ac-b, the first rear wheel suspension K1 will have the effect of improving suspension performance, and will also have a linear or progressive characteristic, resulting in smooth cushioning without a feeling of weakness, or excellent cushioning that provides good support as the stroke increases. When linearity and progressivity are not very important, the angle α between the line segments YA and ZA may be smaller than the angle β between the line segments AY and ZY (α<β). Furthermore, the angles α and β are preferably defined in the unequipped state, but may also be defined in the dry state or 1G state.

[0025] In the first rear wheel suspension device K1, the positions and orientations of the shock absorbers S, S may be different between the drive side and the non-drive side, for example, in a side view, such that "the orientation of the left shock absorber S relative to the swing arm 2 is downward-facing or parallel to the swing arm 2, and the orientation of the right shock absorber S relative to the swing arm 2 is upward-facing (the left line segment ZY is downward-facing or parallel to the line segment CA, and the right line segment ZY is upward-facing relative to the line segment CA)." This is preferable because it allows the drive side shock absorber S to be located above or on the upper side of the chain 10 or chain cover 12, suppressing the shock absorber S from protruding laterally (to the left), while allowing the shock absorber half line ZY to pass through one of the four line segments (line segment Ad-A, line segment Ad-b, line segment Ac-A, line segment Ac-b). In other words, it is preferable for the orientation of the drive side shock absorber S relative to the swing arm 2 to be downward-facing than the orientation of the non-drive side shock absorber S relative to the swing arm 2. 2 and 3, if the damper portion 38 of the shock absorber S is positioned to the side of the rear fender 36 so that the coil spring 37 with the largest diameter does not overlap the rear fender 36 in a side view, the amount of lateral protrusion of the shock absorber S can be further reduced, which is preferable. If the left and right shock absorbers S have the same amount of expansion and contraction, it is preferable to determine the positional relationship between the front and rear connecting portions 23, 32 on the left and right so that the amount of expansion and contraction of each shock absorber S per unit swing angle of the swing arm 2 is the same. In the first embodiment, the left and right shock absorbers S, S are positioned such that they are shifted from each other by an angle θ with respect to the pivot axis A.

[0026] As shown in Figures 2(B) and 7(B), it is preferable to connect the rear ends of the connecting pieces 26 of the left and right front suspension bodies 16, 18 relative to each other by inserting connecting bolts 45 through the left and right connecting holes 16c and a cylindrical spacer 44 sandwiched between them, and then connecting the rear ends of the connecting pieces 26 relative to each other with bolts and nuts. It is also preferable to provide a detent 26s for the bolt head 45a of the connecting bolt 45 on the connecting piece 26 of the left front suspension body 16. Alternatively, one connecting piece 26 may be clamped (secured) by the bolt head 45a and one nut, and the other connecting piece 26 may be clamped (secured) by the connecting bolt 45 and two nuts, and the left and right connecting pieces 26 may be fixed relative to each other with three connecting bolts 45 and nuts without using the spacer 44. Connecting the connecting pieces 26 to each other has the advantage of improving the mounting strength and rigidity of the front suspension bodies 16, 18, particularly increasing lateral rigidity.

[0027] To attach or detach the left and right front suspension bodies 16, 18, it is necessary to temporarily remove both the E suspension bolt 20 and the axle bolt 21, which may cause some disadvantages. That is, if the engine 3 is bolted to the body frame 1 at two locations, a rear bolt (not shown) at the lower rear end and the E suspension bolt 20 at the upper middle part of the front and rear, removing the E suspension bolt 20 may cause the engine 3 to swing forward about the rear bolt, and removing the axle bolt 21 may cause the swing arm 2 to detach from the body frame 1 and fall, resulting in an unstable, unsupported state. Therefore, it is predicted that it will be difficult to perform the above-mentioned specification change work and various maintenance work while taking measures to prevent both the forward swing of the engine 3 and the unsupported state of the swing arm 2.

[0028] Therefore, by giving the front suspension bodies 16, 18 a two-piece structure, the main body parts 16A, 18A, which are attached and detached with the E suspension bolts 20, and the lower parts 16B, 18B, which are attached and detached with the axle bolts 21, can be attached and detached separately, which allows measures to be taken separately to prevent the engine 3 from swinging forward and to deal with the removal of the swing arm 2, making it easier to attach and detach the front suspension bodies 16, 18 to and from the body frame 1 and to perform maintenance work. Each of the left and right lower leg parts 25 has a generally crank-shaped structure in which the lower end, which has a pair of through-holes (not shown), protrudes laterally outward from the upper end where the front connecting part 23 is located, and therefore has a thick plate thickness (e.g., 5 to 9 mm) to ensure strength and rigidity, whereas the left and right lower parts 16B, 18B are simple and small parts such as flat plates and can be made of thin plate material (e.g., 2 to less than 5 mm). In other words, the two-piece structure of the front suspension bodies 16, 18 allows the main bodies 16A, 18A to be thick and curved, simplifying the left and right lower bodies 16B, 18B, resulting in the advantages of a simplified structure and improved workability in attachment and detachment. The two-piece structure of the front suspension bodies 16, 18 also has the following advantages. The left and right lower bodies 16B, 18B attached to both ends of the axle bolt 21 are relatively small parts and can be restored to the original specifications while still attached. Therefore, when switching between the new and original specifications, it is sufficient to simply replace the left and right main bodies 16A, 18A of the front suspension bodies 16, 18, and there is no need to attach or detach the axle bolt 21, i.e., there is no need to attach or detach the swing arm 2, reducing the burden of the specification changeover work.

[0029] [Method of Applying the First Rear Wheel Suspension Device K1] A method of applying the rear wheel suspension device K to an existing motorcycle, such as a used vehicle, will be described using the first rear wheel suspension device K1. As shown in FIGS. 2 and 3, the application method involves retrofitting or converting an original specification vehicle with an existing shock absorber 15 to a new specification vehicle with the first rear wheel suspension device K1 including the shock absorber S in a recumbent position or a similar position. It includes a removal step k1, a vehicle body side application step k2, a swing arm side application step k3, and a shock absorber installation step k4. It is preferable to design the first rear wheel suspension device K1 so that all four front and rear suspension bodies 16-19 are detachable with bolts or the like, allowing for arbitrary switching between the new specification and the original specification. This application method can also be implemented for the second rear wheel suspension device K2, which will be described later.

[0030] The removal process k1 is a process of removing the left and right existing shock absorbers 15 from the body frame 1 and the swing arm 2. The vehicle body side application process k2 is a process of attaching the left and right front suspension bodies 16, 18, which have been prepared in advance, to the body frame 1, and preferably includes a process of attaching the left and right main body parts 16A, 18A using E-suspension bolts 20, a process of attaching the left and right lower parts 16B, 18B using shaft bolts 21, and a process of fixing the left main body part 16A and the left lower part 16B relative to each other by screwing or the like, and may also include a process of fixing the left and right combining pieces 26, 26 relative to each other. The swing arm side application process k3 is a process of attaching the left and right rear suspension bodies 17, 19, which have been prepared in advance, to the swing arm 2. The rear suspension bodies 17, 19 share the same process of fitting the tubular boss portion 31 onto the axle piece 2b and fastening with a nut, but the left rear suspension body 17 includes a process of fastening the front end of the rear main body 17A together with the front bolt 29 for attaching the chain cover 12 using the front hole 17a, and the right rear suspension body 19 includes a process of supporting the front portion of the auxiliary arm 19B on the cantilever axle 2d. Shock absorber installation process k4 is a process of installing and connecting the shock absorber S to the front connecting portions 23 of the left and right front suspension bodies 16, 18 attached to the body frame 1 and the rear connecting portions 32 of the left and right rear suspension bodies 17, 19 attached to the swing arm 2. If the original E suspension bolt 20, axle bolt 21, and other bolts are insufficient in length due to the retrofitting of each suspension body 16-19, it is preferable to use various bolts (not shown and not labeled) that are longer to compensate for the shortfall.

[0031] The following describes examples of the original and new specifications of the first rear wheel suspension device K1, focusing on the differences in their mounting structures. As shown in Fig. 7(A), the original specification has a structure in which the E suspension bolt 20 and a long hexagonal nut 20a fasten the upper mounting stay 3s of the transmission case 3M and the left and right support wall portions 1a, 1b of the body frame 1 that are provided so as to sandwich it. On the right side of the long hexagonal nut 20a (the side opposite to the E suspension bolt), a muffler - The support stay 47a of 47 is fixed with a bolt 61. In the new specification, the front leg 24 of the left front suspension body 16 is attached to the outside of the left support wall portion 1a, and the nut portion 18a at the front end of the front leg 24 of the right front suspension body 18 is replaced with a long hexagonal nut 20a. In the new specification, the E suspension bolt 20 can be turned to engage and disengage with the nut portion 18a. If the E suspension bolt 20 of the original specification is too short for the new specification, a different, longer bolt may be used. It is preferable to provide washers w, as needed, on various parts, such as the outside of the front leg 24. It is convenient for the right front suspension body 18 to have a reinforcing member 24a on the back side (left side) of the front leg 24 (see the right side of Figure 3(B)). Although not shown, it is preferable for the front leg 24 of the left front suspension body 16 to have a reinforcing member 24a.

[0032] As shown in FIG. 7(B), bearings (e.g., rubber bushings) 51 are fitted (e.g., press-fit) to the left and right front end portions 2A of the swing arm 2, and a support tube 1c, which straddles the left and right support walls 1a and 1b at the lower end of the frame, is disposed between the inner tubes 51a of the bearings 51. Regarding the axle bolts 21, the original specification has a structure in which the left inner tube 51a, support tube 1c, and right inner tube 51a are fastened and fixed with the axle bolts 21 and nuts 21n that pass through these three. In the new specification, a left lower portion 16B and a right lower portion 18B are added to the outside of each of the left and right inner tubes 51a, and these five components, 16B, 51a, 1c, 51a, and 18B, are fastened and fixed with the axle bolts 21 and nuts 21n. In the new specification, it is preferable to provide washers w as appropriate. In either specification, the shaft bolt 21 can be inserted in either the left or right direction, and if the length of the shaft bolt 21 of the original specification is insufficient for the new specification, a different longer bolt can be used. The thickness of the left and right lower parts 16B, 18B is an example, and they may be thicker or thinner than shown in the figure.

[0033] The mounting structure of the left rear mounting body 17 will now be described. Regarding the front side, as shown on the right side of FIG. 8(A), in the original specification, the supported portion 12A at the front of the chain cover 12 is screwed with a front bolt 29 to the outside of the upper protrusion 2e (the nut portion of the upper protrusion 2e) erected at the front of the swing arm 2. In the new specification, the front end of the left rear body 17A is positioned outside the supported portion 12A, and is screwed together with the chain cover 12 to the upper protrusion 2e with the front bolt 29. If the length of the front bolt 29 is insufficient in the new specification, a different, longer bolt may be used. Regarding the rear side, as shown on the left side of FIG. 8(A), in the original specification, the rear end 30 of the existing shock absorber 15 is fitted onto the shaft piece 2b protruding laterally outward from the mounting piece 2a at the rear of the swing arm 2, and is attached by tightening a nut 59 via a washer w to the female thread portion 58 at the tip of the shaft piece 2b. An axle shaft 50 that supports the rear wheel is attached to the mounting piece 2a along with a chain adjuster 60. In the new specifications, instead of the rear end portion 30, the tubular boss portion 31 (of the main hole 17b) of the left main body portion 17A is fitted onto the axle piece 2b.

[0034] The mounting structure of the right rear erection body 19 will now be described. Regarding the front side, as shown on the right side of the paper in Figure 8(B), in the original specification, the front end of the torque bar 48 and a coil spring 52 are fitted onto a cantilever shaft 2d that protrudes inward (leftward) from the midpoint between the front and rear of the swing arm 2, and is prevented from coming off by a nut 53. In the new specification, an auxiliary arm 19B is added between the torque bar 48 and the nut 53. The cantilever shaft 2d has a shaft portion 54 and a tip male screw 55 with a smaller diameter than the shaft portion 54, and it is convenient if the through hole 19b is formed as a stepped hole having a large hole portion 56 that fits onto the shaft portion 54 and a small hole portion 57 that is smaller in diameter than the large hole portion 56 and fits onto the tip male screw 55. In other words, a preferred configuration is that, with the large hole portion 56 fitted onto the end of the shaft portion 54 by tightening the nut 53, the surrounding area of ​​the small hole portion 57 is sandwiched between the stepped annular surface (not shown) at the tip of the shaft portion 54 and the nut 53. While the rear side is not shown, in the original specifications, the rear end portion 30 of the existing shock absorber 15 is fitted onto the shaft piece 2b and fastened with a nut 59 via a washer w, just like on the left side (see the left side of Figure 8(A)). The outer 50n of the chain adjuster 60 is a nut. However, in the new specifications, a preferred configuration is that, instead of the rear end portion 30, the tubular boss portion 31 (through hole 19a) of the right rear main body 19A is fitted onto the shaft piece 2b, as shown on the left side of Figure 8(B).

[0035] The first rear wheel suspension device K1 may be defined as follows: [Definition 1] to [Definition 4]. [Definition 1] (a) On each of the left and right sides of the vehicle body, a shock absorber S in a reclined or lying position closer to a lying position than an upright position is mounted on a swing arm 2 pivotally supported on the body frame 1 so as to be able to swing up and down, and the body frame 1; (b) a front suspension body 16, 18 is provided which has a front connecting portion 23 to which a front end portion 22 of the shock absorber S is connected and which is attached to the body frame 1; (c) the front suspension body 16, 18 is composed of a main body portion 16A, 18A equipped with the front connecting portion 23 and a lower portion 16B, 18B attached to the body frame 1 using an axle bolt 21 for pivotally supporting the swing arm 2 to the body frame 1, which are detachably connected together as a single unit; (d) a rear wheel suspension device for a motorcycle, etc. [Definition 2] Having the above (a), (e) a front suspension body 16, 18 having a front connecting portion 23 to which the front end portion 22 of the shock absorber S is connected and attached to the body frame 1 and / or a rear suspension body 17, 19 having a rear connecting portion 32 to which the rear end portion 30 of the shock absorber S is connected and attached to the swing arm 2 is provided, (f) when the pivot axis of the swing arm 2 and the body frame 1 is A, the connecting axis of the shock absorber S on the swing arm 2 side is Z, and the connecting axis of the shock absorber S on the body frame 1 side is Y, the value of the included angle α between the line segment YA and the line segment ZA is equal to or greater than the value of the included angle β between the line segment AY and the line segment ZY (α≧β) (d). [Definition 3] (g) When the front suspension bodies 16, 18 are provided, the front suspension bodies 16, 18 are attached to the body frame 1 using an axle bolt 21 for pivotally supporting the swing arm 2 to the body frame 1 so that the swing arm 2 can swing up and down and / or an E suspension bolt 20 for supporting the engine 3 to the body frame 1, Definition 2. [Definition 4] (h) Any of Definitions 1 to 3, wherein the line segment ZY of the drive side shock absorber S, which is the side on which the endless rotating belt 10 for driving the rear wheel 5 is arranged, is forward and downward from the line segment ZY of the non-drive side shock absorber S, which is the side on which the endless rotating belt 10 is not arranged. [Definition 5] (i) If the rear wheel axis of the swing arm 2 is C, the line segment ZY of the drive side shock absorber S is downward in front of or parallel to the line segment CA, and the line segment ZY of the non-drive side shock absorber S is upward in front of or parallel to the line segment ZY of the drive side shock absorber S, Definition 4.

[0036] [Embodiment 2] Figure 4 shows the main components of a motorcycle equipped with a second rear wheel suspension system K2. This motorcycle is an example of applying a rear wheel suspension system K to an existing on-off type motorcycle that uses a TS. It shows a state in which the original specification, which was equipped with an existing shock absorber 15 in an upright position and tilted forward, has been modified to a new specification with shock absorbers S on both sides in a reclined or lying position. The body frame 1 includes a head pipe 1H, a main pipe 1A, diagonal main cross pipes 41 extending from above the engine 3 to the left and right and rearward and downward, a rear pipe 42 extending rearward and upward from their lower parts, and left and right pivot units 43 that integrate the main cross pipes 41 and rear pipe 42 at their lower parts and have a pivot axis A. The engine 3 has an upright engine unit 3E that is tilted slightly forward.

[0037] The second rear wheel suspension device K2 preferably includes, for example, left and right front suspension bodies 16, 18 attached to the body frame 1, a left rear suspension body 17 attached to the swing arm 2, and left and right shock absorbers S installed using these three suspension bodies 16-18. The left rear suspension body 17 is preferably detachably attached to the swing arm 2 by screwing at two locations, one to the axle piece 2b of the swing arm 2 and the other, but may also be fastened by welding or the like. As shown in FIG. 4(A), if the rear end portion 30 of the shock absorber S is directly supported on the axle piece 2b, the rear suspension body on the non-drive side (the right side, but can also be on the left side of the drive side) can be omitted, and this is also true for the first rear wheel suspension device K1. In the motorcycle of embodiment 2, parts having the same functions as those of embodiment 1 are designated by the same reference numerals, and their description will be omitted.

[0038] As shown in FIG. 4(A), the right front suspension body 18 has a front connecting portion 23, which is fixed by welding or the like across the main cross pipe 41 and the rear pipe 42 above the pivot portion 43, but may also be detachably attached by bolts or the like. The front connecting portion 23 is preferably a portion (e.g., a cylindrical boss) that connects the front end portion 22 of the shock absorber S using a support (not shown), such as an elastic bushing or a spherical bearing. For example, as shown in FIG. 4(A), it is preferable to bolt a support supported by a press fit or the like to the front connecting portion 23, and the front end portion 22, which extends forward across the rear pipe 42 and the pivot portion 43 and has an open U-shape when viewed from the up-down direction. The front end portion 22 may also be configured to be attached to the shock absorber S as a cantilever member that passes only through the outside or inside of the rear pipe 42. The shock absorber S is directly fitted to the existing axle piece 2b and connected to the swing arm 2, but a right rear suspension body (see right rear suspension body 19 in Figure 3) may also be used. The shock absorber S is preferably configured so that its front end (body frame side end) 22 extends in a state that bypasses the body frame 1 (or a member on the body frame side), such as the rear pipe 42, and is connected to the body frame 1. The bypass state can be configured in various ways, such as the "open U-shape" and "passing through the inside or outside" mentioned above.

[0039] As shown in Figure 4(B), the left front suspension body 16 has a front connecting portion 23, which is preferably detachably attached by bolts or the like while straddling the main cross pipe 41 and rear pipe 42 above the pivot portion 43. However, it may also be fixed to the main cross pipe 41 and rear pipe 42 by welding or the like. The structure and shape of the left front connecting portion 23 and the structure and shape of the front end portion 22 are the same as those of the right front suspension body 18, and therefore will not be described here. The left rear suspension body 17 has a main hole 17b through which the axle piece 2b passes, a front hole 17a through which a bolt 40 passes, and a rear connecting portion 32 that connects the rear end portion 30, and is preferably fixed to the swing arm 2 with screws at two locations: one (e.g., the rear) bolt 40 of two bolts 40 for attaching the side stand 39 and the axle piece 2b. That is, the left rear suspension body 17 is preferably detachably attached to the swing arm 2 by a mounting bolt 2c that is threaded into the axle piece 2b and a bolt 40. The rear connecting portion 32 is preferably made of a steel plate formed into an upwardly open U-shape, and is preferably structured so that the axle support 30A provided on the rear end portion 30 is sandwiched between them and bolted, but other structures are also acceptable.

[0040] The left rear suspension body 17 is preferably configured so that the rear end 30 is located laterally outboard of the chain 10 and the front end 22 is positioned diagonally closer to the center of the left and right sides than the rear end 30, thereby reducing the amount of lateral outward protrusion of the front part of the shock absorber S, or so that the shock absorber S is located above the chain 10 to reduce the amount of lateral protrusion of the entire shock absorber S, but this is not limited to these. If the shock absorber S has a cylindrical damper section 38 and a coil spring 37, it is preferable to position the coil spring 37 with the largest diameter inside the wheel rim (not shown) of the rear wheel 5 or the tire with the widest width (not shown) in a side view, thereby moving the shock absorber S more inward and reducing the amount of lateral protrusion. As with the right side, the shock absorber S may be directly connected to the axle piece 2b, eliminating the left rear suspension body 17. As shown in Fig. 4, the shock absorber half line ZY of the left driving side shock absorber S passes through all four line segments (line segment Ad-A, line segment Ad-b, line segment Ac-A, and line segment Ac-b), and the shock absorber half line ZY of the right non-driving side shock absorber S passes through line segments Ad-A and Ad-b, but this is not limited to this. The configuration in which the shock absorber half line ZY passes through any of the four line segments is the same as in the case of the rear wheel suspension K shown in Fig. 1, and is illustrated in Fig. 4, but further verbal explanation here will be omitted.

[0041] [Method of Applying the Second Rear Wheel Suspension Device K2] A method of applying the rear wheel suspension device K to an existing motorcycle, such as a used vehicle, will be described below, taking the second rear wheel suspension device K2 as an example. As shown in FIG. 4, the application method involves retrofitting or converting an original specification vehicle equipped with an existing shock absorber 15 to a new specification vehicle equipped with a second rear wheel suspension device K2 having a shock absorber S in a recumbent position or a similar position. The application method includes a removal step k1, a vehicle body side application step k2, a swing arm side application step k3, and a shock absorber installation step k4. Each step is essentially the same as in the case of the first rear wheel suspension device K1. To ensure sufficient strength and compactness, the front suspension bodies 16, 18 may be fixed to the vehicle body frame 1 by welding or the like. However, a structure in which the suspension bodies 16-19 are detachably attached with screws, allowing for arbitrary specification changes between the new and original suspension bodies, is preferable.

[0042] The second rear wheel suspension device K2 may be defined as follows: [Definition 11] to [Definition 15]. [Definition 11] A rear wheel suspension device for on-off or off-road type motorcycles, etc., having the above (a) and (e). [Definition 12] (Ju) The body frame 1 has a main cross pipe 41 extending rearward and downward from above the engine 3, a pivot portion 43 which has a pivot axis A between the swing arm 2 and the body frame 1 and is integrated with the lower portion of the main cross pipe 41, and a rear pipe 42 which is connected to the lower portion of the main cross pipe 41 or to the pivot portion 43 and extends rearward and upward, (Ku) the front suspension bodies 16, 18 are attached so as to straddle the main cross pipe 41 and the rear pipe 42 or so as to straddle the main cross pipe 41 and the pivot portion 43. Definition 11. [Definition 13] (l) The front end 22 of the shock absorber S has a forward-opening U-shaped member 22 that straddles the rear pipe 42 and the pivot portion 43 when viewed in the vertical direction, or an outer member that passes laterally outside the rear pipe 42 and the pivot portion 43, or an inner member that passes laterally inside the rear pipe 42 and the pivot portion 43, Definition 12. [Definition 14] (W) When the connecting axis between the shock absorber S and the swing arm 2 is Z and the connecting axis between the shock absorber S and the body frame 1 is Y, the value of the included angle α between the line segments YA and ZA is greater than or equal to the value of the included angle β between the line segments AY and ZY (α≧β), any of Definitions 11 to 13. [Definition 15] (F) Any of Definitions 11 to 14, wherein the rear suspension 17, 19 is detachably attached to the swing arm 2 using the axle shaft 50 that supports the rear wheel 5 on the swing arm 2 and the shaft piece 2b. [Definition 16] (Y) Any of Definitions 11 to 15, wherein the shock absorber S has a detour-shaped portion u that avoids interference with structures. [Supplement to Definition 16] The detour-shaped portion u of the shock absorber S is a portion shaped to avoid interference with a structure (a collective term for the body frame 1, swing arm, or attachments attached thereto, etc.), and is, for example, a U-shaped front end portion 22 that straddles the rear pipe 42, etc., so as not to interfere with it (see Figure 4). As another example, the front end portion 22 or the intermediate portion between the front and rear of the shock absorber S may be eccentrically shaped so as to pass inside or outside the structure. Although not shown, when retrofitting a shock absorber to an existing vehicle, if the planned installation space for the shock absorber overlaps with a part of the body frame in a side view, it is also possible to add an eccentrically shaped extension member to the shock absorber that passes inside or outside of that part (such as the rear pipe 42) in order to avoid that part and establish a new connecting axis Y.

[0043] [Rear Wheel Suspension Setting Method] The rear wheel suspension setting method N, which is also a design method for applying the rear wheel suspension K to an existing motorcycle or the like, will be described using the second rear wheel suspension K2, but it can also be applied to the first rear wheel suspension K1, etc. As shown in Figure 4, the rear wheel suspension setting method N is a method N for retrofitting an original specification vehicle having an existing shock absorber 15 (shown by phantom lines in Figure 4) in an upright position, tilted slightly forward, to a new specification vehicle having a second rear wheel suspension K2 including a shock absorber S in a forward-leaning or reclining position close to a lying position. The aforementioned application methods are retrofitting methods (modification methods) for assembling or attaching each suspension body 16-19 to an actual vehicle, whereas the setting method N is a design method (manufacturing method) for determining how to provide (construct) each suspension body 16-19.

[0044] It is preferable that the rear wheel suspension setting method N has a step (first step) of measuring the positions of the lower end c of the axis and the upper end d of the axis, and a step (second step) of determining each of the connecting axes Z and Y so that, in a side view, the shock absorber half line ZY passes through the line segment Ad excluding the pivot axis A, or the line segment Ac excluding the pivot axis A, or the part of the line segment Ad before the fore-and-aft position of the output axis b, or the part of the line segment Ac before the fore-and-aft position of the output axis b, where A is the pivot axis between the swing arm 2 and the body frame 1, C is the rear wheel axis of the swing arm 2, Z is the connecting axis between the shock absorber S and the swing arm 2, Y is the connecting axis between the shock absorber S and the body frame 1, and b is the output axis of the engine 3.

[0045] [First step tk] In a typical motorcycle, the head pipe 1H is located in front of the fuel tank and exposed, so the first step tk can be performed to determine the positions of the lower end c and upper end d of the shaft center, i.e., the front-to-back distance and the up-to-down distance from the pivot axis A. If the head pipe 1H is covered in whole or in part by various fittings such as a front cover, the first step tk can be performed by removing the fittings to expose the head pipe 1H. Note that instead of the line segment Ad, a configuration can be adopted in which the shock absorber half line ZY passes through a half line Ad whose upper limit is a point on the half line Ad equivalent to the height of the handlepost center or a point equivalent to the height of the hip point p.

[0046] [Second step jk] By measuring the position of the lower end of the shaft center c and / or the shaft center d (if the position is known without measurement, the first step tk can be omitted), the line segments Ad-A and Ac-A can be determined from the pivot axis A between the swing arm 2 and the body frame 1 and the rear wheel axis C of the swing arm 2. Furthermore, the line segments Ad-b and Ac-b can be determined from the fore-and-aft position (position in a side view) of the output shaft center b. From these four line segments (line segment Ad-A, line segment Ad-b, line segment Ac-A, line segment Ac-b), the second step jk, which is a shock absorber positioning step, can be performed to determine the connecting axes Y and Z of the shock absorber S with the body frame 1 and the swing arm 2.

[0047] It is preferable to use a connecting means (such as shaft piece 2b) between the swing arm 2 and the existing shock absorber 15 to set the swing arm side connecting axis Z of the shock absorber S (see FIG. 4(A)). However, if this is not the case, a member having the swing arm side connecting axis Z (see rear suspension body 17 in FIG. 4(B)) may be provided by bolting, welding, etc. If there is no means for attaching the shock absorber S at the target location of the body frame side connecting axis Y, it is also preferable to provide a member (see front suspension bodies 16, 18 in FIG. 4) having the body frame side connecting axis Y by bolting, welding, etc. In this way, according to the rear wheel suspension setting method N of the present invention, the rear wheel suspension device K of the present invention can be applied to existing TS vehicles and existing mono-suspension vehicles.

[0048] Examples of configurations in which shock absorber S is installed between body frame 1 and swing arm 2 using rear wheel suspension setting method N include configurations using front suspension bodies 16, 17 and rear suspension bodies 18, 19 shown in Figures 2 to 4. Shock absorber S may include, but is not limited to, a shock absorber having a forward-facing, open-U-shaped front end portion 22 as shown in Figure 4, or an eccentric front end portion 22 that is integral with or separate from the rear pipe 42 and passes only through the outside or inside of the rear pipe 42. Furthermore, if the value of the included angle α between line segments YA and ZA is not set to be equal to or greater than the value of the included angle β between line segments AY and ZY (α≧β), for example, in Figure 4(B), the body frame-side connecting axis Y may be located behind the rear pipe 42.

[0049] [Actions, Effects, etc.] Compared to the conventional TS structure, the rear wheel suspension system K can move the shock absorber S forward or forward and downward, which not only promotes mass centralization, but also improves the suspension performance itself. The moment of inertia J around a certain fulcrum is proportional to the mass M and proportional to the square of the radius R (J=MR 2 ), so when this is applied to the rear wheel suspension K, a certain fulcrum corresponds to the pivot axis A, mass M corresponds to the load that shock absorber S acts on the body frame 1, and radius R corresponds to the shortest distance between the shock absorber half line ZY and the pivot axis A. For example, when considering the moment of inertia around the pivot axis A of the vehicle body when the rear wheel rides over a convex part while driving, the load M (reaction force of shock absorber S) and radius R increase or decrease depending on the connection position and posture (forward tilt) of shock absorber S with respect to the swing arm 2 and body frame 1. In other words, as the forward tilt angle of shock absorber S increases, the load M increases and the radius R decreases, so the ratio of load M to the square of the radius R 2 We found that the moment of inertia J, which is the product of J and R, increases and decreases in accordance with the size of the radius R (see Figure 6).

[0050] Figure 6 shows the relationship line r between the radius R, which is the shortest distance between the half line ZY and the pivot axis A, and the relative unsprung mass m of the rear wheel 5, when the horizontal axis is the radius R and the vertical axis is the relative unsprung mass m of the rear wheel 5. The relationship line r may be nonlinear, progressive, or inversely progressive in addition to linear. The mass M, which is the reaction force of the shock absorber S, increases or decreases in sync with the increase or decrease in the radius R, and the moment of inertia J (J = MR 2) increases or decreases in proportion to the square of the radius R, so the relative unsprung mass m, which corresponds to the moment of inertia J, increases or decreases in sync with the increase or decrease in radius R, and the relationship line r shows a linear upward slope to the right. Now, strictly speaking, if the position of the shock absorber S changes, the position of the vehicle's center of gravity (not shown) also changes, but the relationship line r in Figure 6 does not take into account the center of gravity position or its fluctuations. As the forward tilt angle of the shock absorber S around the axle piece 2b increases (assuming the forward tilt angle of the shock absorber S is larger in the position shown in Figure 1(A) than in the position shown in Figure 1(B)), the vehicle's center of gravity also moves slightly forward and downward, so Figure 6 also shows a correction line rh that takes into account the difference in the vehicle's center of gravity due to the position and orientation of the shock absorber S. R1 is the distance when the shock absorber half line ZY passes through a point that does not include the pivot axis A but is closest to A. R2 is the distance when the shock absorber half line ZY passes through the intersection point s [see Figure 5(B)]. R3 is the distance when the shock absorber half line ZY passes through the intersection point t (see Figure 5(B)). R4 is the distance when the shock absorber half line ZY passes through the lower end c of the shaft center. R5 is the distance when the shock absorber half line ZY passes through the upper end d of the shaft center. Figure 6 shows the relative relationship between the relation line r and the correction line rh, and the shapes of each line are examples and do not necessarily represent absolute shapes.

[0051] From Figure 6, it can be seen that the correction line rh, which takes into account fluctuations in the vehicle's center of gravity, exceeds the relationship line r, which does not take the vehicle's center of gravity into account, when the radius R is greater than a certain point (value), and falls below that point when the radius R is equal to or less than that point. This "certain point" is around R4 to R5 in Figure 6, which was found to correspond (or approximately correspond) to the distance when the shock absorber half line ZY passes through the lower end c of the axle center and the upper end d of the axle center. It was found that the "certain point" corresponds to R4 to R5 depending on the model of motorcycle, etc. Figure 6 shows an example where the "certain point" corresponds to R5, and the range below R5 corresponds to the line segment Ad-A. It was found that the correction line rh shows a significant decrease from the relationship line r when it corresponds (or approximately corresponds) to R2 to R4. Therefore, we found that the range of radius R between R1 and R5 (R1≦R≦R5) corresponds to (or approximately corresponds to) the line segment Ad-A, and that the range of radius R between R2 and R4 (R2≦R≦R4) (corresponding to line segment Ac-b) is even more preferable. Line segment Ad-b corresponds to (or approximately corresponds to) the range of radius R between R3 and R5, and line segment Ac-A corresponds to (or approximately corresponds to) the range of radius R between R1 and R4. Radius R may also be between R2 and R5. In other words, we found that in rear wheel suspension K, in addition to mass centralization, a radius R of R5 or less further promotes the reduction of relative unsprung mass m. Depending on the model, R5 falls within the range between R4 and R5. In the case of R4, the "range where the reduction is significant" corresponds to R3 to R2 or between the midpoint between R4 and R3 and R2.

[0052] As described above, with the rear wheel suspension device and rear wheel suspension setting method for motorcycles and the like according to the present invention, the shock absorber, which was conventionally located relatively high and rearward of the vehicle body, can be positioned forward or forward and lower, thereby achieving better mass centralization while adopting a TS structure with shock absorbers on both the left and right sides of the vehicle body.In addition, the relative unsprung mass can be made lighter (= the relative sprung mass can be made heavier), improving rear wheel suspension performance.

[0053] While it is generally recognized by those skilled in the art that "TS suspension cannot compete with mono-suspension in terms of suspension performance," there was a sense of doubt as to whether this was really the case. In other words, there was doubt that "TS suspension could achieve performance equal to or better than mono-suspension." Therefore, through diligent research, we identified the positional relationship between the pivot axis A and the upper end d and lower end c of the head pipe center 1h, the positional relationship with the shock absorber S, the posture (orientation), and the discrepancy between the calculated value (relation line r) and the actual value (correction line rh) of the relative unsprung mass. We then identified the orientation range of the shock absorber half line ZY that more efficiently reduces the relative unsprung mass. This turned these doubts into certainty, and led to the invention of the present invention, which quantitatively describes the four lines.

[0054] [Alternative Embodiment] When the shock absorber S is a commercially available, general-purpose product, a process may be employed in which an extension member that extends the overall length is attached to one or both ends, or a rear wheel suspension device K may be employed using an extended shock absorber S with the extension member attached to one or both ends. The rear end (or extended rear end) 30 of the shock absorber S may be connected to the axle piece 2b of the swing arm 2, eliminating the rear suspension bodies 17, 19. The present invention is also applicable to a unicycle with multiple front wheels and a single rear wheel, a sidecar (a motorcycle with a sidecar), and the like. The output shaft center b, which defines the line b used in the line segments Ad-b and Ac-b, may be replaced with the crank shaft center a, the counter shaft center (not marked), the center of gravity of the vehicle (not shown), or the centroid of a triangle formed by the pivot shaft center A, the crank shaft center a, and the center of gravity of the vehicle. When at least a portion of the shock absorber S (e.g., the rear end) is located to the left or right of the rear wheel 5 in a side view, the phrase "on each of the left and right sides of the vehicle body" in the claims may be replaced with "on each of the left and right rear wheels." Three-wheeled and four-wheeled vehicles with a two-rear-wheel structure, with rear wheels on each side of the swing arm, are also within the scope of this invention. The line segments Ad-A and Ac-A may be replaced with half-lines Ad-A and Ac-A extending to the height of the handlebar post center hp attached to the upper bracket or the overall height e (see Figure 1). It is also advantageous to configure the half-line ZY to pass through a line segment connecting the lower end c of the axle center to the intersection point t or a line segment connecting the upper end d of the axle center to the intersection point s. A configuration in which the front suspensions 16 and 18 are attached using the vehicle-side connecting portion 14 of the existing shock absorber 15 (e.g., using the E-suspension bolt 20 or the axle bolt 21 in combination) is also preferred. [Explanation of symbols]

[0055] 1: body frame, 1h: head pipe center, 2: swing arm, 5: rear wheel, 16, 18: front suspension body, A: pivot axis, C: rear wheel axis, S: shock absorber, Y: connecting axis between shock absorber and body frame, Z: connecting axis between shock absorber and swing arm, b: output axis, c: lower end of head pipe center (lower end of axis), d: upper end of head pipe center (upper end of axis), α: angle between line segments YA and ZA, β: angle between line segments AY and ZY

Claims

1. A shock absorber is provided on each of the left and right sides of the vehicle body, the shock absorber being installed across a swing arm capable of supporting a rear wheel and the vehicle body frame, Let d and c be the upper and lower ends of the head pipe center of the body frame, A be the pivot axis between the swing arm and the body frame, Z be the connecting axis between the shock absorber and the swing arm, Y be the connecting axis between the shock absorber and the body frame, and b be the output axis of the engine. A rear wheel suspension device for a motorcycle or the like, in which, in a side view, a shock absorber half line ZY passes through a line segment Ad excluding the pivot axis A, or a line segment Ac excluding the pivot axis A, or a portion of the line segment Ad before the fore-and-aft position of the output shaft center b, or a portion of the line segment Ac before the fore-and-aft position of the output shaft center b.

2. 2. The rear wheel suspension for a motorcycle or the like according to claim 1, wherein the angle α between the line segments YA and ZA is equal to or greater than the angle β between the line segments AY and ZY (α≧β).

3. 3. The rear wheel suspension for a motorcycle or the like according to claim 1, wherein a connecting axis Y between the shock absorber and the body frame is provided in a front suspension body that is retrofitted to the body frame.

4. A rear wheel suspension setting method applied to a motorcycle or the like in which shock absorbers are installed on each of the left and right sides of a vehicle body, the shock absorbers being installed between a swing arm capable of supporting a rear wheel and a vehicle body frame, comprising: Let d and c be the upper and lower ends of the head pipe center of the body frame, A be the pivot axis between the swing arm and the body frame, Z be the connecting axis between the shock absorber and the swing arm, Y be the connecting axis between the shock absorber and the body frame, and b be the output axis of the engine. A rear wheel suspension setting method in which the connecting axes Z, Y are determined so that, in a side view, the shock absorber half line ZY passes through the line segment Ad excluding the pivot axis A, or the line segment Ac excluding the pivot axis A, or the portion of the line segment Ad before the fore-and-aft position of the output axis b, or the portion of the line segment Ac before the fore-and-aft position of the output axis b.

5. 5. A rear wheel suspension setting method according to claim 4, wherein the connecting axis Y between the shock absorber and the swing arm is set at a connecting portion of the swing arm to an existing shock absorber or at a rear suspension body attached to the swing arm using said connecting portion.

6. 6. A rear wheel suspension setting method according to claim 4 or 5, wherein the shock absorber half line ZY is set so that the angle α between the line segments YA and ZA is equal to or greater than the angle β between the line segments AY and ZY (α≧β).

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