Vehicle design method

Abstract

To provide a vehicle design method capable of designing a vehicle with improved traveling stability at the time of turning.SOLUTION: In a design method of a tricycle 200 (vehicle), determination is made on an inter-arm angle θ being an angle formed by a lower arm part viewed in a traveling direction and a steering arm part and an arm length ratio a / b being a ratio between a length a of the lower arm part viewed in the traveling direction and a length b of the steering arm part at the time of upright stand in which two front wheels are not inclined by a tilt mechanism such that a steering angle difference between the front wheels generated by the tilt mechanism causing the front wheels to be inclined is within 10°.SELECTED DRAWING: Figure 11

Description

[Technical Field]

[0001] The present invention relates to a method for designing a vehicle, and more particularly to a method for designing a vehicle having two front wheels that are inclined in the vehicle width direction relative to the vertical direction. [Background technology]

[0002] BACKGROUND ART Conventionally, vehicles having two front wheels that are inclined in the vehicle width direction with respect to the vertical direction are known (see, for example, Patent Document 1).

[0003] Patent Document 1 discloses a tricycle (vehicle) with two front wheels that tilt widthwise relative to the vertical. In Patent Document 1, the tricycle (vehicle) is equipped with a structure (tilt mechanism) in which a handlebar post to which a handle is connected and a pair of side posts that support the two front wheels so that they can be turned are rotatably connected. The structure (tilt mechanism) tilts the pair of side posts left and right in response to the left and right tilt of the handlebar post, making it possible to oscillate (tilt) the two front wheels. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-19281 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in conventional tricycles (vehicles) such as those described in Patent Document 1, tilting the two front wheels in the vehicle width direction relative to the vertical direction can cause differences in steering angles between the two front wheels. The difference in steering angle between the two front wheels can cause the operator to feel uncomfortable and reduce riding stability during cornering. For this reason, there is a need for a vehicle that improves riding stability during cornering by suppressing the operator's discomfort caused by the difference in steering angle between the two front wheels that occurs when the two front wheels are tilted in the vehicle width direction relative to the vertical direction, and ultimately a vehicle design method that can design a vehicle with improved riding stability during cornering.

[0006] The present invention has been made to solve the above-mentioned problems, and one object of the present invention is to provide a vehicle design method that makes it possible to design a vehicle with improved driving stability during cornering. [Means for solving the problem]

[0007] To achieve the above object, the present inventors conducted extensive research and found that the operator can turn without feeling any discomfort when the difference in steering angle between the two front wheels caused by tilting the front wheels with a tilt mechanism is within 10°. Furthermore, the present inventors found through experiments and simulations that the difference in steering angle between the two front wheels caused by tilting the front wheels with a tilt mechanism is correlated with the arm length ratio a / b, which is the ratio of the length a of the lower arm section to the length b of the steering arm section as viewed from the direction of travel, and the inter-arm angle θ, which is the angle between the lower arm section and the steering arm section as viewed from the direction of travel when the front wheels are upright and not tilted by the tilt mechanism, and that by adjusting the arm length ratio a / b and the inter-arm angle θ, the difference in steering angle between the two front wheels caused by tilting the front wheels with a tilt mechanism can be kept within 10°.

[0008] That is, a vehicle design method according to one aspect of the present invention is a method for designing a vehicle having two front wheels that rotate in the traveling direction of the vehicle, a tilt mechanism that tilts the front wheels in the vehicle width direction with respect to the vertical direction and includes lower arm parts connected to two suspension parts that are connected to each of the two front wheels, and a steering mechanism that changes the steering angle of the front wheels in response to steering of the vehicle and includes steering arm parts connected to the two suspension parts so as to be located below the lower arm parts or at the same height as the lower arm parts when viewed from the traveling direction, The present invention includes a steering angle difference calculation step of calculating the steering angle difference between the two front wheels caused by the tilting of the front wheels by the tilt mechanism based on the inter-arm angle θ, which is the angle between the lower arm and the steering arm as seen from the direction of travel when the front wheels are upright and not tilted by the mechanism, and the arm length ratio a / b, which is the ratio between the length a of the lower arm and the length b of the steering arm as seen from the direction of travel, and an arm placement determination step of determining the inter-arm angle θ and the arm length ratio a / b so that the steering angle difference calculated in the steering angle difference calculation step is within 10°. Here, the vehicle of the present invention is a broad concept that includes bicycles with two front wheels, saddle-type vehicles such as motorcycles and tricycles, kick scooters, and recumbent bicycles.

[0009] As described above, the vehicle design method according to this aspect determines the inter-arm angle θ, which is the angle between the lower arm and the steering arm as viewed from the direction of travel when the front wheels are not tilted by the tilt mechanism and the vehicle is upright, and the arm length ratio a / b, which is the ratio between the length a of the lower arm as viewed from the direction of travel and the length b of the steering arm, so that the difference in steering angle between the two front wheels (hereinafter referred to as the steering angle difference) caused by tilting the front wheels by the tilt mechanism is within 10°. This makes it possible to suppress the discomfort felt by the operator due to the difference in steering angle between the two front wheels caused by tilting the two front wheels in the vehicle width direction with respect to the vertical direction. As a result, it is possible to design a vehicle with improved driving stability when cornering.

[0010] In the vehicle design method according to the above aspect, the steering angle difference calculating step preferably includes a step of calculating a plurality of steering angle differences by performing at least one of changing the inter-arm angle θ within a first range and changing the arm length ratio a / b within a second range. With this configuration, a plurality of steering angle differences are calculated, which increases the likelihood of calculating a steering angle difference that is within 10° compared to a case where the steering angle difference is calculated without changing the inter-arm angle θ and the arm length ratio a / b. This makes it possible to easily determine the inter-arm angle θ and the arm length ratio a / b.

[0011] In this case, the second range is preferably a range near an arm length ratio a / b=1. With this configuration, the arm length ratio a / b is changed within the second range, which is a range near an arm length ratio a / b=1 in which the steering angle difference is likely to be within 10°, so that the time required to calculate the steering angle difference that is within 10° can be reduced. As a result, the design can be carried out efficiently. Note that the arm length ratio near a / b=1 is a broad concept that includes not only a / b=1 but also values ​​close to a / b=1.

[0012] In the vehicle design method for calculating the plurality of steering angle differences by at least one of varying the inter-arm angle θ within a first range and varying the arm length ratio a / b within a second range, the steering angle difference calculating step preferably includes a step of calculating the plurality of steering angle differences by varying the arm length ratio a / b within a second range with the inter-arm angle θ fixed at a predetermined value, and, if the calculated plurality of steering angle differences are not within 10 degrees, changing the inter-arm angle θ from the predetermined value within the first range until a steering angle difference within 10 degrees is calculated. With this configuration, the steering angle difference within 10 degrees can be calculated more reliably than when both the inter-arm angle θ and the arm length ratio a / b are set randomly each time the steering angle difference is calculated.

[0013] In the vehicle design method for calculating the plurality of steering angle differences by at least one of changing the inter-arm angle θ within a first range and changing the arm length ratio a / b within a second range, the steering angle difference calculating step preferably includes a step of calculating the plurality of steering angle differences by at least one of changing the inter-arm angle θ by a first change amount within a first range and changing the arm length ratio a / b by a second change amount within a second range. With this configuration, the steering angle differences can be calculated over a wider range compared to a case where the change amounts of the inter-arm angle θ and the arm length ratio a / b are not constant, making it possible to easily determine the inter-arm angle θ and the arm length ratio a / b.

[0014] In this case, preferably, the first change amount is 0.1° and the second change amount is 0.01. In this way, even when the first change amount is 0.1° and the second change amount is 0.01, it is possible to design a vehicle with improved running stability during cornering.

[0015] The vehicle design method for calculating the plurality of steering angle differences by at least one of varying the inter-arm angle θ within a first range and varying the arm length ratio a / b within a second range preferably further includes a turning radius calculation step of calculating a plurality of turning radii for the vehicle by at least one of varying the inter-arm angle θ within the first range and varying the arm length ratio a / b within the second range, and the arm placement determination step includes a step of determining the inter-arm angle θ and the arm length ratio a / b so that the steering angle difference calculated in the steering angle difference calculation step is within 10° and the turning radius calculated in the turning radius calculation step is the smallest among the plurality of turning radii calculated based on the same inter-arm angle θ. This configuration not only improves driving stability during cornering but also enables the design of a vehicle with a relatively small turning radius, i.e., a vehicle with tight turning radius. As a result, a vehicle with higher usability (user convenience) can be designed.

[0016] In this case, preferably, the turning radius calculation step includes a step of calculating a plurality of turning radii of the vehicle by varying the arm length ratio a / b within a second range with the inter-arm angle θ fixed to a predetermined value, and the steering angle difference calculation step includes a step of calculating a plurality of the steering angle differences by varying the arm length ratio a / b within the second range with the inter-arm angle θ fixed to a predetermined value, and if, among the plurality of calculated steering angle differences, a minimum turning steering angle difference calculated based on the same arm length ratio a / b as the smallest turning radius among the plurality of turning radii calculated based on the same inter-arm angle θ in the turning radius calculation step is not within 10°, changing the inter-arm angle θ within a first range from the predetermined value until a minimum turning steering angle difference within 10° is calculated. With this configuration, it is possible to reliably calculate a minimum turning steering angle difference of 10° or less, compared to when both the inter-arm angle θ and the arm length ratio a / b are set randomly each time the steering angle difference and turning radius are calculated.

[0017] In a vehicle design method in which the turning radius calculation step and the calculation of the minimum turning steering angle difference are repeated by changing the inter-arm angle θ within a first range from a predetermined value until the minimum turning steering angle difference within 10° is calculated, preferably the first range is a range in which the inter-arm angle θ is |θ|≦10°, and the second range is a range in the vicinity of the arm length ratio a / b=1. With this configuration, the steering angle difference can be calculated in the range of the inter-arm angle θ |θ|≦10°, in which the steering angle difference is likely to be within 10°, and in the range in the vicinity of the arm length ratio a / b=1, thereby reducing the time required to calculate the minimum turning steering angle difference within 10°. [Effects of the Invention]

[0018] As described above, the vehicle design method of the present invention makes it possible to design a vehicle that improves running stability during cornering. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a schematic diagram showing the overall configuration of a tricycle according to one embodiment. [Figure 2] FIG. 1 is a side view of a tricycle according to one embodiment. [Figure 3] FIG. 1 is a front view of a suspension system for a tricycle according to one embodiment. [Figure 4] FIG. 1 is a rear view of a suspension system for a tricycle according to an embodiment. [Figure 5] FIG. 1 is a front view of a suspension system for a tricycle according to one embodiment, with the two front wheels not tilted in the vehicle width direction relative to the vertical direction. [Figure 6] FIG. 7 is a cross-sectional view of the joint portion taken along line VII-VII in FIG. 5. [Figure 7] 8 is a cross-sectional view of the joint portion taken along line VIII-VIII in FIG. 5. [Figure 8] 1 is a front view of a suspension device for a tricycle according to one embodiment, with the two front wheels tilted in the vehicle width direction relative to the vertical direction. FIG. [Figure 9] FIG. 10 is a top view illustrating the difference in steering angle between the two front wheels of a tricycle in one embodiment when the two front wheels are tilted in the vehicle width direction with respect to the vertical direction. [Figure 10] FIG. 1 is a top view of a suspension system for a tricycle according to one embodiment, in a state in which the two front wheels are not tilted in the vehicle width direction relative to the vertical direction. [Figure 11] 1 is a flowchart illustrating a method for designing a vehicle according to one embodiment. [Figure 12] 1 is a diagram illustrating an arm length ratio a / b, an inter-arm angle θ, and various parameters used in vehicle design according to one embodiment. FIG. [Figure 13] 10 is a graph illustrating the relationship between the arm length ratio a / b and the steering angle difference when the front wheels are tilted at an angle of 25° when the inter-arm angle θ=0° according to one embodiment. [Figure 14] 10 is a graph illustrating the relationship between the arm length ratio a / b and the turning radius of the vehicle when the inter-arm angle θ=0° according to one embodiment. [Figure 15]10 is a graph illustrating the range of the inter-arm angle θ and the arm length ratio a / b in which the steering angle difference is within 10° when the front wheels are tilted at 25° according to one embodiment. [Figure 16] 10 is a graph illustrating the difference in the range of the inter-arm angle θ and the arm length ratio a / b in which the steering angle difference is within 10° when the front wheels are tilted at 25° in one embodiment, depending on the inclination angle of the front wheels. DETAILED DESCRIPTION OF THE INVENTION

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings.

[0021] (Tricycle configuration) The configuration of a tricycle 200 according to this embodiment will be described with reference to Figures 1 and 2. In the following description, the direction along the width of the tricycle 200 is referred to as the X direction, the direction along the direction of travel of the tricycle 200 is referred to as the Y direction, and the direction perpendicular to the X and Y directions and along the height of the tricycle 200 is referred to as the Z direction. One side of the X direction will be referred to as the X2 direction, and the other side will be referred to as the X1 direction. In the Y direction, the direction in which the tricycle 200 moves forward will be referred to as the Y2 direction, and the direction in which the tricycle 200 moves backward will be referred to as the Y1 direction. In the Z direction, the direction in which the height increases will be referred to as the Z1 direction, and the direction in which the height decreases will be referred to as the Z2 direction. The tricycle 200 is an example of a "vehicle" as defined in the claims.

[0022] As shown in Figures 1 and 2, tricycle 200 includes two front wheels 201, a handlebar 202, a frame 203, a saddle 204, a rear wheel 205, a suspension system 100, a handlebar-side pulley 9, and a wire 8. Tricycle 200 is configured so that it can travel in the forward direction (Y2 direction) on the surface on which the two front wheels 201 and rear wheels 205 are placed by rotating in the forward direction (Y2 direction) of the two front wheels 201 and rear wheels 205. Tricycle 200 is a straddle-type vehicle configured so that an operator (not shown) can straddle saddle 204 while holding handlebars 202.

[0023] (Suspension system configuration) Next, the configuration of the suspension system 100 according to this embodiment will be described with reference to FIGS.

[0024] As shown in Figures 3 to 5, the suspension device 100 includes a knuckle arm 1, an upper arm 2, a lower arm 3, a suspension bracket 4, a damper 5, a tie rod 6, and a pivoting unit 7. The upper arm 2 and the lower arm 3 are provided to extend in the width direction (X direction) of the tricycle 200. Furthermore, the knuckle arm 1, the upper arm 2, the lower arm 3, the suspension bracket 4, the damper 5, the tie rod 6, and the pivoting unit 7 are line-symmetrical with respect to a center line C2 (see Figure 5) that divides the tricycle 200 into one side and the other side in the vehicle width direction when viewed from the direction of travel of the tricycle 200 (Y2 direction). Furthermore, the knuckle arm 1, the upper arm 2, the lower arm 3, and the tie rod 6 are provided in pairs so that they each have a symmetrical structure on one side (X2 side) and the other side (X1 side) in the vehicle width direction of the tricycle 200. Therefore, unless otherwise specified, the following description of the suspension device 100 will focus on one side (X2 side) in the vehicle width direction of the tricycle 200. The knuckle arm 1 is an example of a "suspension portion" in the claims. The lower arm 3 is an example of a "lower arm portion" in the claims. The tie rod 6 is an example of a "steering arm portion" in the claims.

[0025] As shown in FIG. 5, the knuckle arm 1 includes a ball joint shaft 11 and a ball joint shaft 12. The upper arm 2 includes a ball joint bearing 21. The lower arm 3 includes a ball joint bearing 31. The ball joint shaft 11 is made up of a shaft portion 11a and a spherical portion 11b. The shaft portion 11a is fixed to the end of the knuckle arm 1 on the upper side (Z1 side), and the spherical portion 11b is connected to be fitted inside the ball joint bearing 21. The ball joint shaft 12 is made up of a shaft portion 12a and a spherical portion 12b. The shaft portion 12a is fixed to the end of the knuckle arm 1 on the lower side (Z2 side), and the spherical portion 12b is connected to be fitted inside the ball joint bearing 31.

[0026] As shown in Figure 6, ball joint bearing 21 has an opening 22 through which shaft 11a passes. Opening 22 extends in the width direction (X direction) of tricycle 200 and is provided to restrict swinging of ball joint shaft 11 in directions other than the width direction (X direction) of tricycle 200. In other words, ball joint shaft 11 is configured to swing only in the width direction (X direction) of tricycle 200 along opening 22.

[0027] As shown in Figure 7, the ball joint bearing 31 has an opening 32 through which the shaft 12a passes. The opening 32 extends in the width direction (X direction) of the tricycle 200 and is provided to restrict the ball joint shaft 12 from swinging in any direction other than the width direction (X direction) of the tricycle 200. In other words, the ball joint shaft 12 is configured to swing only in the width direction (X direction) of the tricycle 200 along the opening 32.

[0028] As shown in Figures 3 and 5, the suspension bracket 4 comprises an upper connection portion 41, a main bracket 42, a lower connection portion 43, and a frame connection portion 44. The upper connection portion 41 includes an upper connection shaft 41a extending in the direction of travel (Y direction) of the tricycle 200. The lower connection portion 43 includes a pair of lower connection shafts 43a extending in the direction of travel (Y direction) of the tricycle 200. The pair of lower connection shafts 43a have a symmetrical structure on one side (X2 side) and the other side (X1 side) in the vehicle width direction of the tricycle 200. The upper connection portion 41 is provided on the upper side (Z1 side) of the main bracket 42, and the lower connection portion 43 is provided on the lower side (Z2 side) of the main bracket 42. The main bracket 42 is connected to the frame 203 via the frame connection portion 44.

[0029] Of the pair of upper arms 2, the end of the upper arm 2 on one side (X2 side) in the vehicle width direction of the tricycle 200, on the other side (X1 side) in the vehicle width direction of the tricycle 200, is connected to the upper connecting shaft 41a so that they can rotate relatively around the axis C4 of the upper connecting shaft 41a. Here, the end of the upper arm 2 on the other side (X1 side) in the vehicle width direction of the tricycle 200 functions as a bush. Of the pair of lower arms 3, the end of the lower arm 3 on one side (X2 side) in the vehicle width direction of the tricycle 200, on the other side (X1 side) in the vehicle width direction of the tricycle 200, is connected to the lower connecting shaft 43a so that they can rotate relatively around the axis C5 of the lower connecting shaft 43a. Here, the end of the lower arm 3 on the other side (X1 side) in the vehicle width direction of the tricycle 200 functions as a bush. In FIG. 3, for convenience of illustration, only the other side (X1 side) of the lower connecting shaft 43a in the vehicle width direction of the tricycle 200 is visible.

[0030] The knuckle arm 1, upper arm 2, lower arm 3, and suspension bracket 4 connected as described above are configured with a link mechanism so that, as shown in Figure 8, the two front wheels 201 are tilted in the width direction (X direction) of the tricycle 200 with respect to the vertical direction (Z direction) of the frame 203 in accordance with the tilt of the tricycle 200 in the width direction (X direction) with respect to the vertical direction (Z direction). Hereinafter, the tilt angle of the two front wheels 201 is defined as the angle formed by the two front wheels 201 that are not tilted as shown in Figure 5 and the two front wheels 201 that are tilted as shown in Figure 8. The knuckle arm 1, upper arm 2, lower arm 3, and suspension bracket 4 connected as described above are an example of a "tilt mechanism" in the claims.

[0031] 9, when the two front wheels 201 are tilted in the width direction (X direction) of the tricycle 200 with respect to the vertical direction (Z direction), the steering angles α and β of the two front wheels 201 are the angles formed by axis D, which is the direction in which the two front wheels 201 face when the two front wheels 201 are not tilted in the width direction (X direction) of the tricycle 200 with respect to the vertical direction (Z direction), and axis S1 and S2, which are the direction in which the two front wheels 201 face when the two front wheels 201 are tilted in the width direction (X direction) of the tricycle 200 with respect to the vertical direction (Z direction). In this embodiment, the steering angle difference between the two front wheels 201 when the two front wheels 201 are tilted in the width direction (X direction) of the tricycle 200 with respect to the vertical direction (Z direction), is taken to be |α-β|.

[0032] As shown in Figures 3, 5, and 8, the damper 5 includes a damper arm 51. The damper arm 51 includes an upper damper shaft 51a on its upper side (Z1 side) that extends in the direction of travel (Y direction) of the tricycle 200. The end of the damper 5 on one side (X2 side) in the vehicle width direction of the tricycle 200 and the upper damper shaft 51a are connected so as to be relatively rotatable around axis C6 of the upper damper shaft 51a. Furthermore, the end of the damper arm 51 on its lower side (Z2 side) and the lower connecting shaft 43a are connected so as to be relatively rotatable around axis C5 of the lower connecting shaft 43a. As shown in FIG. 8, the damper 5 is configured to absorb vibrations and shocks caused by road surface conditions when the two front wheels 201 are tilted in the width direction (X direction) of the tricycle 200 relative to the vertical direction (Z direction), thereby attenuating the vibrations and shocks transmitted to the operator (not shown).

[0033] As shown in Figures 4 and 10, the rotating unit 7 includes a front wheel pulley 71 and a rotating bracket 72. The front wheel pulley 71 is configured to rotate about an axis C1 that is perpendicular to the direction of travel (Y direction) of the tricycle 200 and the width direction (X direction) of the tricycle 200. The front wheel pulley 71 is also configured so that a wire 8 is fitted into the front wheel pulley 71. The wire 8 is configured so that tension is applied in response to steering of the tricycle 200. The rotating bracket 72 is located below the front wheel pulley 71 (Z2 side), and is configured to rotate about the axis C1 as the front wheel pulley 71 rotates. Of the pair of tie rods 6, the end of the tie rod 6 on one side (X2 side) in the vehicle width direction of the tricycle 200 in the vehicle width direction of the tricycle 200 is connected to the lower side (Z2 side) of the knuckle arm 1 at a connection point 61, for example, by a ball joint. Also, of the pair of tie rods 6, the end of the tie rod 6 on one side (X2 side) in the vehicle width direction of the tricycle 20 ... tie rod 6 on the other side (X1 side) in the vehicle width direction of the tricycle 200 in the vehicle width direction of the tricycle 200 in the vehicle width direction of the tricycle 200 in the vehicle width direction of the tie rod 6, for example, is connected to the pivot bracket 72 at a connection point 62, for example, by a ball joint.

[0034] The knuckle arm 1, tie rod 6, and rotating part 7, connected as described above, form a link mechanism that changes the steering angle of the two front wheels 201 using a wire 8 that is tensioned in response to steering of the tricycle 200. Specifically, as shown in FIG. 2, the wire 8 is fitted into the front-wheel-side pulley 71 and also into the handle-side pulley 9. The handle-side pulley 9 is located below the handle 202 (Z2 side) and in the direction in which the tricycle 200 of the suspension system 100 moves backward (Y1 direction). The handle-side pulley 9 is located below the frame 203 (Z2 side) and is configured to rotate about an axis C3 that is perpendicular to the direction of travel of the tricycle 200 (Y direction) and the width direction of the tricycle 200 (X direction). The handle-side pulley 9 is configured to rotate about the axis C3 when an operator (not shown) operates (steers) the handle 202. The handle-side pulley 9 rotates about the axis C3, thereby applying tension to the wire 8. The tensioned wire 8 then rotates the front-wheel-side pulley 71 (rotating unit 7) about the axis C1, and the rotated rotating unit 7 pushes and pulls the tie rod 6, thereby changing the steering angle of the two front wheels 201. The link mechanism formed by the knuckle arms 1, tie rods 6, and rotating unit 7 connected as described above is a so-called parallel steering mechanism in which the steering angles of the two front wheels 201 are approximately the same when turning. Note that the knuckle arms 1, tie rods 6, and rotating unit 7 connected as described above are an example of a "steering mechanism" in the claims.

[0035] (How to design a tricycle) Next, a design method for the tricycle 200 according to this embodiment will be described with reference to FIGS. 11 to 16. The flowchart shown in FIG. 11 is implemented, for example, by a tricycle 200 designer using a computer equipped with a processor such as a CPU (Central Processing Unit) that executes a predetermined program based on input operations. The data shown in FIGS. 13 to 16 was obtained through simulations using the computer, but the inventors have confirmed that similar data can be obtained through experiments using an actual vehicle. In the following, when the coordinates of an end are used, if the end is a ball joint or a combination of a bush and an axle, this refers to the coordinates of the center of the ball or bush as viewed from the direction of travel (Y2 direction) of the tricycle 200. In this embodiment, the diameter of the ball or bush of all joints consisting of a ball joint or a combination of a bush and an axle is 50 mm.

[0036] As shown in FIG. 11, in step S1, the designer sets the coordinates of the inner end and outer end of the lower arm 3. Specifically, as shown in FIG. 12, the designer sets the coordinates (x3a, z3a) of the end 3a of the lower arm 3 on the inner side (X1 side) in the vehicle width direction of the tricycle 200, and the coordinates (x3b, z3b) of the end 3b of the lower arm 3 on the outer side (X2 side) in the vehicle width direction of the tricycle 200. The coordinates represent the amount of positional deviation along the X and Z directions, based on the coordinates (0, 0) of reference point CC, which is the intersection of the center line C2 and the axle line LH connecting the axles of the two front wheels 201. Note that when there is a deviation in the X direction, a deviation in the X2 direction is expressed as a positive value, and a deviation in the X1 direction is expressed as a negative value. Furthermore, when there is a deviation in the Z direction, a deviation in the Z2 direction is expressed as a positive value, and a deviation in the Z1 direction is expressed as a negative value.

[0037] 12, x3a, which is the coordinate (x3a, z3a) of end 3a of lower arm 3 on the inner side (X1 side) in the vehicle width direction of tricycle 200, must be offset from center line C2 toward the outer side (X2 side) in the vehicle width direction of tricycle 200 by at least the radius of the bushing of which end 3a is the center. Furthermore, z3a is calculated using axle height HH, which is the distance between a ground line LG connecting the ground contact points of the two front wheels 201 and the axle line LH; ground clearance GC, which is the distance between ground line LG and end 6a of tie rod 6 on the inner side (X1 side) in the vehicle width direction of tricycle 200; and distance d between end 3a of lower arm 3 on the inner side (X1 side) in the vehicle width direction of tricycle 200 and end 6a of tie rod 6 on the inner side (X1 side) in the vehicle width direction of tricycle 200, as follows: z3a = HH - GC - d. In this embodiment, the axle height HH is set to 203 mm, the ground clearance GC is set to 100 mm, and the distance d is set to 0 mm. As described above, in this embodiment, the coordinates of the end 3a are set to (25 mm, 103 mm).

[0038] The coordinate x3b (x3b, z3b) of the end 3b of the lower arm 3 on the outer side (X2 side) in the vehicle width direction of the tricycle 200 is calculated as x3b=WW / 2-WH-WN using the vehicle body width WW, which is the distance between the outer sides of the two front wheels 201, the front wheel width WH, which is the width of the front wheels 201, and the distance WN between the inner side of the front wheels 201 and the end 3b. In this embodiment, the vehicle body width WW=600 mm, the front wheel width WH=35 mm, and the distance WN=75 mm. As a result, in this embodiment, x3b=190 mm. Note that with x3b=190 mm and x3a=25 mm, in this embodiment, the length a along the extension direction of the lower arm 3 is x3b-x3a=165 mm. Note that the length a along the extension direction of the lower arm 3 is an example of the "length a of the lower arm portion" in the claims.

[0039] Furthermore, in this embodiment, the lower arm 3 is disposed so as to be perpendicular to the vertical direction (Z direction), so the coordinate z3b (x3b, z3b) of the end 3b of the lower arm 3 on the outer side (X2 side) in the vehicle width direction of the tricycle 200 is equal to the coordinate z3a. As a result, in this embodiment, the coordinates of end 3b are set to (190 mm, 103 mm). At this point, the processing of step S1 ends.

[0040] Returning to FIG. 11, in step S2, the designer sets the coordinates of the inner end of the tie rod 6. Specifically, as shown in FIG. 12, the designer sets the coordinates (x6a, z6a) of the end 6a of the tie rod 6 on the inner side (X1 side) in the vehicle width direction of the tricycle 200. In this embodiment, the end 6a and the end 3a are arranged along the vertical direction (Z direction), so the coordinate x6a is equal to the coordinate x3a of the end 3a of the lower arm 3 on the inner side (X1 side) in the vehicle width direction of the tricycle 200 (x3a, z3a). Furthermore, as shown in FIG. 12, the coordinate z6a is calculated as z6a = z3a + d. Here, in this embodiment, since d = 0 as described above, z6a = z3a. As a result, in this embodiment, the coordinates of the end 6a are set to (25 mm, 103 mm).

[0041] Returning to Figure 11, in step S3, the designer sets an initial value for the inter-arm angle θ. As shown in Figure 12, the inter-arm angle θ is the angle formed between an axis LL along the extension direction of the lower arm 3 and an axis LT along the extension direction of the tie rod 6 when viewed from the direction of travel of the tricycle 200 (direction Y2) with the two front wheels 201 in an upright position without tilting. In this embodiment, for example, the initial value of the inter-arm angle θ is set to θ = 0°.

[0042] Returning to FIG. 11, in step S4, the designer sets an initial value for the arm length ratio a / b. Step S4 is initiated when step S3 is completed or when step S10, described below, is completed with a negative result. As shown in FIG. 12, the arm length ratio a / b is the ratio between the length a along the extension direction of the lower arm 3 and the length b along the extension direction of the tie rod 6, when viewed from the direction of travel of the tricycle 200 (direction Y2). In this embodiment, for example, the initial value of the arm length ratio a / b is set to a / b = 0.75. The length b along the extension direction of the tie rod 6 is an example of the "length b of the steering arm portion" in the claims.

[0043] Returning to FIG. 11, in step S5, the designer calculates the coordinate of the outer end of the tie rod 6. Step S5 is initiated when step S4 is completed or when step S8, described below, is completed with a "No" result. Specifically, as shown in FIG. 12, the coordinate (x6b, z6b) of the end 6b of the tie rod 6 on the outer side (X2 side) in the vehicle width direction of the tricycle 200 is calculated. The coordinate x6b is calculated using the length b of the tie rod 6 along the direction of extension and the coordinate x6a, using the equation x6b = b × cos(θ) + x6a. Here, in this embodiment, when the arm length ratio a / b = 0.75, the calculation is that b = length a along the direction of extension of the lower arm 3 / (arm length ratio a / b) = 165 mm / 0.75 = 220 mm. From the above, in this embodiment, when the inter-arm angle θ=0°, the coordinate x6b is calculated as x6b=220 mm×cos(0°)+25 mm=245 mm.

[0044] Furthermore, coordinate z6b is calculated using the length b of the tie rod 6 along its extension and coordinate z6a according to the equation z6b = z6a + b × sin(θ). Here, as shown in FIG. 12, when end 6b of the tie rod 6 is located above end 6a of the tricycle 200 (Z1 direction) relative to end 6a when viewed from the direction of travel of the tricycle 200 (Y2 direction), the inter-arm angle θ is a negative value (θ < 0°). When end 6b of the tie rod 6 is located below end 6a of the tricycle 200 (Z2 direction) relative to end 6a when viewed from the direction of travel of the tricycle 200 (Y2 direction), the inter-arm angle θ is a positive value (θ ≧ 0°). In this embodiment, when inter-arm angle θ = 0°, coordinate z6b is calculated as z6b = y6a + b × sin(θ) = 103 mm + 220 mm × sin(0°) = 103 mm. From the above, the coordinates of the end 6b are calculated to be (245 mm, 103 mm).

[0045] Returning to Figure 11, in step S6, the designer calculates the steering angle difference when the tilt angle of the front wheels caused by the tilt mechanism is 25°. Note that step S6 is started after step S5 is completed. Specifically, the designer calculates the steering angle difference when the two front wheels 201 are tilted 25° in the vehicle width direction (X direction) of the tricycle 200 with respect to the vertical direction (Z direction) (when the tilt angle of the front wheels 201 is 25°) by simulating using the computer described above, using the data set and calculated in steps S1 to S5 as conditions.

[0046] Next, in step S7, the designer calculates the turning radius. The turning radius is the smallest radius of the path of the front wheel when tricycle 200 turns. Step S7 is started after step S5 is completed. Specifically, the designer calculates the turning radius of tricycle 200 through the computer-based simulation described above, using the data set and calculated in steps S1 to S5 as conditions.

[0047] Next, in step S8, the designer determines whether the arm length ratio a / b is 1.15. Note that step S8 is started after both steps S6 and S7 are completed. If the answer is Yes in step S8, proceed to step S9. If the answer is No in step S8, the arm length ratio at that time is set to a / b + 0.01 = new a / b, and return to step S5. Then, steps S5 to S7 are repeated until step S8 answers Yes (a / b = 1.15). When step S8 answers Yes, the calculated data (black circles) and an approximation line of the calculated data shown in FIG. 13 have been obtained. The approximation line can be obtained, for example, using a linear approximation method. When the answer is Yes in step S8, the calculated data (black circles) and an approximation curve of the calculated data shown in FIG. 14 have been obtained. The approximation curve can be obtained, for example, using a third-order polynomial approximation method.

[0048] As described above, in this embodiment, the designer calculates a plurality of steering angle differences by fixing the inter-arm angle θ to a predetermined value and varying the arm length ratio a / b within the range of 0.75 to 1.15, which is a range close to 1. Also, as described above, the designer calculates a plurality of turning radii by fixing the inter-arm angle θ to a predetermined value and varying the arm length ratio a / b within the range of 0.75 to 1.15, which is a range close to 1.

[0049] Next, in step S9, the designer specifies the minimum turning radius. The minimum turning radius is the smallest of the multiple turning radii repeatedly calculated in step S7 for the same inter-arm angle θ. Specifically, as shown in FIG. 14, the arm length ratio a / b is calculated when the turning radius of the approximation curve of the calculated data is smallest. In this embodiment, the arm length ratio a / b when the minimum turning radius is obtained is calculated to be a / b = 0.95.

[0050] Returning to FIG. 11 , in step S10, the designer determines whether the steering angle difference at a / b, which is the minimum turning radius, is within 10°. If the answer is No in step S10, the inter-arm angle θ is set to the current inter-arm angle θ - (or +) 0.1° = new θ within the range of -10°≦θ≦10°, and the process returns to step S4. Note that if θ≧0°, the change in the steering angle of the two front wheels 201 caused by the two front wheels 201 being tilted by 25° includes a relatively large change in the direction opposite to the tilt direction (turning direction) of the two front wheels 201. Therefore, in this embodiment, step S4 is started by first setting the inter-arm angle θ -0.1° = new θ. When θ = -10°, θ is returned to 0°, and the inter-arm angle θ + 0.1° = new θ, and step S4 is started again. Steps S4 to S9 are then repeated until the answer is Yes in step S10. If the answer is Yes in step S10, the process proceeds to step S11. In this embodiment, as shown in Fig. 13, the steering angle difference at a tilt angle of 25° when a / b = 0.95, which is the minimum turning radius, is 2.1°, so the answer to step S10 is Yes. Note that the steering angle difference of 2.1° is an example of the "minimum turning steering angle difference" in the claims.

[0051] Returning to FIG. 11, in step S11, the designer determines the inter-arm angle θ and the arm length ratio a / b. Specifically, the values ​​determined in step S10 are the inter-arm angle θ and the arm length ratio a / b when the steering angle difference at a tilt angle of 25° is within 10°. In this embodiment, the inter-arm angle θ is determined to be 0°, and the arm length ratio a / b is determined to be 0.95. Completion of step S11 marks the end of the processing of the design method for tricycle 200.

[0052] (Relationship between the front wheel tilt angle and the range in which the front wheel steering angle difference is within 10°) Next, with reference to Fig. 13, Fig. 15, and Fig. 16, the relationship between the inclination angle of the two front wheels 201 and the range in which the difference in steering angle between the two front wheels 201 is within 10° will be described. The relationship between the arm length ratio a / b and the difference in steering angle between the two front wheels 201 when the inter-arm angle θ is 0° and the difference in steering angle between the two front wheels 201 when they are inclined by 25° is represented by the solid line (an approximation line of the acquired data) shown in Fig. 13. Note that the dashed-dotted line shown in Fig. 13 indicates the line in which the difference in steering angle between the two front wheels 201 when they are inclined by 25° is 10°. In other words, within a range r4 in which the arm length ratio a / b is 0.725≦a / b≦1.15, the difference in steering angle between the two front wheels 201 when they are inclined by 25° is within 10°.

[0053] As shown in Fig. 15, when the two front wheels 201 are tilted 25° at θ = -10°, -5°, -2.5°, 0°, 2.5°, 5°, and 10°, the ranges of a / b (first range r1, second range r2, third range r3, fourth range r4, fifth range r5, sixth range r6, and seventh range r7) within which the steering angle difference is within 10° are different from one another. Specifically, the first range r1 is 0.72≦a / b≦1.08. The second range r2 is 0.73≦a / b≦1.15. The third range r3 is 0.73≦a / b≦1.16. The fourth range r4 is 0.725≦a / b≦1.15. The fifth range r5 is 0.72≦a / b≦1.12. The sixth range r6 is 0.71≦a / b≦1.08, and the seventh range r7 is 0.75≦a / b≦0.98.

[0054] That is, within region R between line R1 connecting the minimum values ​​of the first range r1, second range r2, third range r3, fourth range r4, fifth range r5, sixth range r6, and seventh range r7, and line R2 connecting the maximum values ​​of the first range r1, second range r2, third range r3, fourth range r4, fifth range r5, sixth range r6, and seventh range r7, the difference in steering angle between the two front wheels 201 when they are tilted by 25° is within 10°. Lines R1 and R2 are represented by dashed lines in FIG. 15. Region R is the hatched region in FIG. 15.

[0055] 16, the smaller the inclination angle of the two front wheels 201, the larger the range of the arm length ratio a / b within which the difference in steering angle between the two front wheels 201 is within 10°. Specifically, the area between line R3 connecting the minimum values ​​of the range of the arm length ratio a / b within which the difference in steering angle between the two front wheels 201 is within 10° when the inclination angle of the two front wheels 201 is 20°, and line R4 connecting the maximum values ​​of the range of the arm length ratio a / b within which the difference in steering angle between the two front wheels 201 is within 10° when the inclination angle of the two front wheels 201 is 20°, is larger than area R. Furthermore, the area between line R5 connecting the minimum value of the range of arm length ratio a / b where the difference in steering angle between each of the two front wheels 201 is within 10° when the inclination angle of the two front wheels 201 is 15° and line R6 connecting the maximum value of the range of arm length ratio a / b where the difference in steering angle between each of the two front wheels 201 is within 10° when the inclination angle of the two front wheels 201 is 15° is larger than the area when the inclination angle is 20°. Furthermore, the area between line R7 connecting the minimum value of the range of arm length ratio a / b where the difference in steering angle between each of the two front wheels 201 is within 10° when the inclination angle of the two front wheels 201 is 10° and line R8 connecting the maximum value of the range of arm length ratio a / b where the difference in steering angle between each of the two front wheels 201 is within 10° when the inclination angle of the two front wheels 201 is 10° is larger than the area when the inclination angle is 15°.

[0056] Specifically, in the region between line R3 and line R4, when the inter-arm angle θ=−10°, 0.54≦a / b≦1.18; when the inter-arm angle θ=−5°, 0.53≦a / b≦1.23; when the inter-arm angle θ=−2.5°, 0.52≦a / b≦1.24; when the inter-arm angle θ=0°, 0.52≦a / b≦1.22; when the inter-arm angle θ=2.5°, 0.51≦a / b≦1.19; when the inter-arm angle θ=5°, 0.53≦a / b≦1.15; and when the inter-arm angle θ=10°, 0.63≦a / b≦1.05.

[0057] Specifically, in the region between line R5 and line R6, when the inter-arm angle θ=−10°, 0.05≦a / b≦1.32; when the inter-arm angle θ=−5°, 0.15≦a / b≦1.4; when the inter-arm angle θ=−2.5°, 0.2≦a / b≦1.39; when the inter-arm angle θ=0°, 0.28≦a / b≦1.39; when the inter-arm angle θ=2.5°, 0.37≦a / b≦1.35; when the inter-arm angle θ=5°, 0.43≦a / b≦1.29; and when the inter-arm angle θ=10°, 0.56≦a / b≦1.16.

[0058] Specifically, in the region between line R7 and line R8, when the inter-arm angle θ=−10°, 0.05≦a / b≦1.56; when the inter-arm angle θ=−5°, 0.06≦a / b≦1.69; when the inter-arm angle θ=−2.5°, 0.13≦a / b≦1.72; when the inter-arm angle θ=0°, 0.19≦a / b≦1.69; when the inter-arm angle θ=2.5°, 0.27≦a / b≦1.63; when the inter-arm angle θ=5°, 0.35≦a / b≦1.56; and when the inter-arm angle θ=10°, 0.49≦a / b≦1.42.

[0059] 11, if the inter-arm angle θ and the arm length ratio a / b are determined so that the steering angle difference is within 10° when the inclination angle of the two front wheels 201 is 25°, the steering angle difference will be within 10° at least when the inclination angle of the two front wheels 201 is 25° or less. Note that the turning radius has no correlation with the inclination angle of the two front wheels 201.

[0060] The simulation conditions not mentioned above are as follows: When viewed from the direction of travel of the tricycle 200 (Y2 direction), the tie rod 6 is disposed below the lower arm 3 (Z2 side) or at the same height. As shown in FIG. 10, the distance e along the direction of travel (Y direction) of the tricycle 200 between the ball joint shaft 12 and the connection point 62 between the end of the tie rod 6 on the other side (X1 side) in the vehicle width direction of the tricycle 200 and the pivot bracket 72 is 194.9 mm. As shown in FIG. 10, the distance f along the direction of travel (Y direction) of the tricycle 200 between the ball joint shaft 12 and the connection point 61 between the end of the tie rod 6 on one side (X2 side) in the vehicle width direction of the tricycle 200 and the lower side (Z2 side) of the knuckle arm 1 is set to 123.2 mm.

[0061] (Effects of the embodiment) Next, the effects of the embodiment will be described.

[0062] In this embodiment, as described above, the inter-arm angle θ, which is the angle between the lower arm 3 and the tie rod 6 as viewed from the direction of travel when the two front wheels 201 are not tilted by the tilt mechanism and the vehicle is upright, and the arm length ratio a / b, which is the ratio between the length a of the lower arm 3 as viewed from the direction of travel and the length b of the tie rod 6, are determined so that the difference in steering angle between the two front wheels 201 caused by tilting the two front wheels 201 with the tilt mechanism is within 10°. This makes it possible to reduce the discomfort felt by the operator due to the difference in steering angle between the two front wheels 201 caused by tilting the two front wheels 201 in the vehicle width direction with respect to the vertical direction. As a result, it is possible to design a tricycle 200 with improved driving stability when turning.

[0063] Furthermore, in this embodiment, as described above, the steering angle difference calculation step includes a step of calculating a plurality of steering angle differences by performing at least one of changing the inter-arm angle θ within a first range of |θ|≦10° and changing the arm length ratio a / b within a second range of 0.75≦a / b≦1.15. This allows a plurality of steering angle differences to be calculated, which increases the likelihood of calculating a steering angle difference that is within 10° compared to a case where the steering angle difference is calculated without changing the inter-arm angle θ and the arm length ratio a / b. This makes it possible to easily determine the inter-arm angle θ and the arm length ratio a / b.

[0064] Furthermore, in this embodiment, as described above, the second range is a range near the arm length ratio a / b = 1. As a result, the arm length ratio a / b is changed within the second range, which is a range near the arm length ratio a / b = 1 in which the steering angle difference is likely to be within 10°, so it is possible to reduce the time required to calculate the steering angle difference that is within 10°. As a result, design can be carried out efficiently.

[0065] Furthermore, in this embodiment, as described above, the steering angle difference calculation step includes a step of calculating the plurality of steering angle differences by changing the arm length ratio a / b within a second range of 0.75≦a / b≦1.15 while fixing the inter-arm angle θ to a predetermined value of θ=0°, and, if the calculated plurality of steering angle differences are not within 10°, repeatedly calculating the steering angle difference by changing the inter-arm angle θ from the predetermined value of θ=0° within a first range of |θ|≦10° until a steering angle difference within 10° is calculated. This makes it possible to reliably calculate the steering angle difference within 10° compared to a case in which both the inter-arm angle θ and the arm length ratio a / b are set randomly each time the steering angle difference is calculated.

[0066] Furthermore, in this embodiment, as described above, the steering angle difference calculation step includes a step of calculating a plurality of steering angle differences by performing at least one of changing the inter-arm angle θ by a first change amount within a first range of |θ|≦10° and changing the arm length ratio a / b by a second change amount within a second range of 0.75≦a / b≦1.15. This makes it possible to calculate the steering angle difference over a wider range compared to a case where the change amounts of the inter-arm angle θ and the arm length ratio a / b are not constant, making it possible to easily determine the inter-arm angle θ and the arm length ratio a / b.

[0067] Furthermore, in this embodiment, as described above, the first change amount is 0.1° and the second change amount is 0.01. This makes it possible to design a vehicle with improved running stability during cornering even when the first change amount is 0.1° and the second change amount is 0.01.

[0068] Furthermore, this embodiment further includes a turning radius calculation step of calculating multiple turning radii for the vehicle by at least one of varying the inter-arm angle θ within a first range of |θ|≦10° and varying the arm length ratio a / b within a second range of 0.75≦a / b≦1.15, as described above. The arm placement determination step includes a step of determining the inter-arm angle θ and the arm length ratio a / b so that the steering angle difference calculated in the steering angle difference calculation step is within 10° and the turning radius calculated in the turning radius calculation step is the smallest among multiple turning radii calculated based on the same inter-arm angle θ. This not only improves driving stability during turning, but also enables the design of a vehicle with a relatively small turning radius, i.e., a tight turning radius. As a result, a vehicle with improved usability (user convenience) can be designed.

[0069] Furthermore, in this embodiment, as described above, the turning radius calculation step includes a step of calculating a plurality of turning radii of the vehicle by changing the arm length ratio a / b within the second range of 0.75≦a / b≦1.15 while the inter-arm angle θ is fixed to a predetermined value of θ=0°, and the steering angle difference calculation step calculates a plurality of the steering angle differences by changing the arm length ratio a / b within the second range of 0.75≦a / b≦1.15 while the inter-arm angle θ is fixed to a predetermined value of θ=0°. and a step of repeating the turning radius calculation step and the calculation of the minimum turning steering angle difference by changing the inter-arm angle θ from a predetermined value of θ=0° within a first range of |θ|≦10° until a minimum turning steering angle difference within 10° is calculated, if, among the plurality of calculated steering angle differences, the minimum turning steering angle difference calculated based on the same arm length ratio a / b as the smallest turning radius among the plurality of turning radii calculated based on the same inter-arm angle θ in the turning radius calculation step is not within 10°. This makes it possible to reliably calculate a minimum turning steering angle difference within 10° compared to a case in which both the inter-arm angle θ and the arm length ratio a / b are set randomly each time the steering angle difference and turning radius are calculated.

[0070] Furthermore, in this embodiment, as described above, the first range is a range in which the inter-arm angle θ is |θ|≦10°, and the second range is a range in the vicinity of the arm length ratio a / b = 1. This makes it possible to calculate the steering angle difference in the range in which the inter-arm angle θ is |θ|≦10°, where the steering angle difference is likely to be within 10°, and in the range in the vicinity of the arm length ratio a / b = 1, thereby reducing the time required to calculate the minimum turning steering angle difference that is within 10°.

[0071] [Variations] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims rather than the above description of the embodiments, and further includes all modifications (variations) within the meaning and scope of the claims.

[0072] For example, while the above embodiment shows an example in which the vehicle is a tricycle 200, the present invention is not limited to this. For example, the vehicle may be a bicycle with two front wheels, a saddle-type vehicle such as a motorcycle or tricycle, a kick scooter, or a recumbent bicycle.

[0073] In the above embodiment, an example was shown in which the designer determined the inter-arm angle θ and the arm length ratio a / b based on data acquired by simulation, but the present invention is not limited to this. For example, the designer may determine the inter-arm angle θ and the arm length ratio a / b based on data acquired by experiments using an actual machine. Also, for example, the designer may determine the inter-arm angle θ and the arm length ratio a / b based on data acquired by a method other than simulation.

[0074] Furthermore, in the above embodiment, steps S1 to S11 in the design method for tricycle 200 are performed by a designer, but the present invention is not limited to this. For example, steps S5 to S11 may be performed automatically by a computer that has a processor such as a CPU (Central Processing Unit) and executes a predetermined program based on input operations, based on values ​​preset by the designer in steps S1 to S4.

[0075] Furthermore, in the above embodiment, an example was shown in which the arm length ratio a / b was varied within the range of 0.75≦a / b≦1.15 in the design method for tricycle 200, but the present invention is not limited to this. For example, the arm length ratio a / b could be varied within a narrower range such as 0.9≦a / b≦1.1, or within a wider range such as 0.5≦a / b≦1.5.

[0076] Furthermore, in the above embodiment, an example was shown in which the inter-arm angle θ was varied within the range of -10°≦θ≦10° in the design method for tricycle 200, but the present invention is not limited to this. For example, the inter-arm angle θ could be varied within a narrower range, such as -5°≦θ≦5°, or within a wider range, such as -15°≦θ≦15°.

[0077] Furthermore, in the above embodiment, an example was shown in which steps S5 to S7 were repeated while changing the arm length ratio a / b until a / b = 1.15 in the method for designing tricycle 200, but the present invention is not limited to this. For example, the inter-arm angle θ and arm length ratio a / b may be determined when the calculated steering angle difference when the two front wheels 201 are tilted by 25° falls within 10°. In this case, it is also possible to determine the inter-arm angle θ and arm length ratio a / b without ever changing the arm length ratio a / b.

[0078] Furthermore, in the above embodiment, an example was shown in which the arm length ratio a / b was varied within a range close to a / b=1 in the design method for tricycle 200, but the present invention is not limited to this. For example, the arm length ratio a / b may be varied within a range that does not include a / b=1.

[0079] Furthermore, in the above embodiment, an example was shown in which the inter-arm angle θ was fixed at an initial value and the arm-length ratio a / b was changed in the design method for tricycle 200, but the present invention is not limited to this. For example, the inter-arm angle θ may be changed while the arm-length ratio a / b is fixed at an initial value.

[0080] Furthermore, in the above embodiment, an example was shown in which the arm length ratio a / b was changed in increments of 0.01 in the design method for tricycle 200, but the present invention is not limited to this. For example, the arm length ratio a / b may be changed in increments of a value other than 0.01. Furthermore, for example, the value by which the arm length ratio a / b is changed does not have to be the same each time.

[0081] Furthermore, in the above embodiment, an example was shown in which the inter-arm angle θ was changed in increments of 0.1° in the design method for tricycle 200, but the present invention is not limited to this. For example, the inter-arm angle θ may be changed in increments of a value other than 0.1°. Furthermore, for example, the amount by which the inter-arm angle θ is changed does not have to be the same each time.

[0082] Furthermore, in the above embodiment, an example was shown in which the inter-arm angle θ was changed in increments of -0.1° and then +0.1° in the design method for tricycle 200, but the present invention is not limited to this. For example, the inter-arm angle θ could be changed in increments of +0.1° and then -0.1°.

[0083] Furthermore, in the above embodiment, an example was shown in which the inter-arm angle θ and the arm length ratio a / b were determined in the design method for tricycle 200 so that the steering angle difference when the two front wheels 201 are tilted by 25° is 10° or less when the arm length ratio a / b is at the minimum turning radius. However, the present invention is not limited to this. For example, the inter-arm angle θ and the arm length ratio a / b may be determined so that the steering angle difference when the two front wheels 201 are tilted by 25° is 10° or less, without calculating the turning radius. Note that, if the turning radius is not calculated, the inter-arm angle θ and the arm length ratio a / b may be determined so that the steering angle difference when the two front wheels 201 are tilted by 25° is 10° or less, and the slope of the approximate straight line or approximate curve of the calculated steering angle difference when the two front wheels 201 are tilted by 25°, as shown in FIG. 13, is at the boundary where it changes from negative to positive or from positive to negative. In addition, for example, the inter-arm angle θ and the arm length ratio a / b may be determined so that the minimum turning radius is equal to or less than a predetermined value such as 2.5 m, and the steering angle difference when the two front wheels 201 are tilted by 25° is equal to or less than 10°.

[0084] Furthermore, in the above embodiment, an example was shown in which the initial value of the inter-arm angle θ was set to θ = 0° in the design method for tricycle 200, but the present invention is not limited to this. For example, the initial value of the inter-arm angle θ may be set to a value other than θ = 0°.

[0085] Furthermore, in the above embodiment, an example was shown in which the initial value of the arm length ratio a / b was set to a / b = 0.75 in the design method for tricycle 200, but the present invention is not limited to this. For example, the initial value of the arm length ratio a / b may be set to a value other than a / b = 0.75.

[0086] Furthermore, in the above embodiment, an example was shown in which the inter-arm angle θ and the arm length ratio a / b were determined when the answer to step S10 in the design method for tricycle 200 was Yes, but the present invention is not limited to this. For example, multiple combinations of inter-arm angle θ and arm length ratio a / b that result in Yes in step S10 may be calculated within the inter-arm angle θ range of -10°≦θ≦10°, and the inter-arm angle θ and arm length ratio a / b may be determined so that the steering angle difference when the two front wheels 201 are tilted by 25° is minimized among them. Alternatively, multiple combinations of inter-arm angle θ and arm length ratio a / b that result in Yes in step S10 within the inter-arm angle θ range of -10°≦θ≦10° may be calculated, and the inter-arm angle θ and arm length ratio a / b may be determined so that the minimum turning radius is equal to or less than a predetermined value, such as 2.5 m, and the steering angle difference when the two front wheels 201 are tilted by 25° is minimized among them.

[0087] In the above embodiment, the designer determines in step S10 of the design method for tricycle 200 whether the steering angle difference when leaning 25° at a / b, which results in the minimum turning radius, is within 10°. However, the present invention is not limited to this. For example, in step S10, the designer may determine whether the steering angle difference when leaning 25° at a / b, which results in the minimum turning radius, is within 5°. Alternatively, in step S10, the designer may determine whether the steering angle difference when leaning 25° at a / b, which results in the minimum turning radius, is within 2°. Here, the smaller the steering angle difference when leaning 25° at a / b, which results in the minimum turning radius, the less discomfort the operator will feel, which is effective in improving the running stability of tricycle 200 when turning. [Explanation of symbols]

[0088] 1 Knuckle arm (suspension part) 3 Lower arm (lower arm part) 6 Tie rod (steering arm) 200 Tricycle (Vehicle) 201 front wheel a) Length along the direction in which the lower arm 3 extends (length a of the lower arm portion) b Length along the direction in which the tie rod 6 extends (length b of the steering arm part) a / b arm length ratio θ angle between arms α, β Rudder angle

Claims

1. A method for designing a vehicle comprising: a tilt mechanism having two front wheels that rotate in the traveling direction of the vehicle, tilting the front wheels in the vehicle width direction of the vehicle with respect to the vertical direction, and including a lower arm portion connected to two suspension portions that are connected to each of the two front wheels; and a steering mechanism that changes the steering angle of the front wheels in response to steering of the vehicle, and including a steering arm portion connected to the two suspension portions so as to be positioned below the lower arm portion or at the same height as the lower arm portion when viewed from the traveling direction, a steering angle difference calculation step of calculating a steering angle difference between the two front wheels caused by tilting the front wheels by the tilt mechanism, based on an inter-arm angle θ that is an angle formed between the lower arm portion and the steering arm portion as seen from the direction of travel when the front wheels are upright and not tilted by the tilt mechanism, and an arm length ratio a / b that is a ratio between a length a of the lower arm portion as seen from the direction of travel and a length b of the steering arm portion; an arm arrangement determination step of determining the inter-arm angle θ and the arm length ratio a / b so that the steering angle difference calculated in the steering angle difference calculation step is within 10°.

2. 2. The vehicle design method according to claim 1, wherein the steering angle difference calculation step includes a step of calculating the plurality of steering angle differences by performing at least one of changing the inter-arm angle θ within a first range and changing the arm length ratio a / b within a second range.

3. The vehicle design method according to claim 2 , wherein the second range is a range in the vicinity of the arm length ratio a / b=1.

4. 3. The vehicle design method according to claim 2, wherein the steering angle difference calculating step includes a step of calculating a plurality of the steering angle differences by changing the arm length ratio a / b within the second range with the inter-arm angle θ fixed to a predetermined value, and, if the calculated plurality of steering angle differences are not within 10 degrees, repeatedly calculating the steering angle difference by changing the inter-arm angle θ from the predetermined value within the first range until a steering angle difference within 10 degrees is calculated.

5. 3. The vehicle design method according to claim 2, wherein the steering angle difference calculation step includes a step of calculating the plurality of steering angle differences by performing at least one of changing the inter-arm angle θ by a first change amount within the first range and changing the arm length ratio a / b by a second change amount within the second range.

6. the first change amount is 0.1°, The vehicle design method according to claim 5 , wherein the second change amount is 0.

01.

7. a turning radius calculation step of calculating a plurality of turning radii of the vehicle by at least one of changing the inter-arm angle θ within the first range and changing the arm length ratio a / b within the second range, 3. The vehicle design method according to claim 2, wherein the arm arrangement determining step includes a step of determining the inter-arm angle θ and the arm length ratio a / b so that the steering angle difference calculated in the steering angle difference calculating step is within 10° and the turning radius calculated in the turning radius calculating step is the smallest among a plurality of turning radii calculated based on the same inter-arm angle θ.

8. the turning radius calculation step includes a step of calculating a plurality of turning radii of the vehicle by changing the arm length ratio a / b within the second range while the inter-arm angle θ is fixed to a predetermined value, 8. The vehicle design method according to claim 7, wherein the steering angle difference calculating step calculates a plurality of the steering angle differences by changing the arm length ratio a / b within the second range with the inter-arm angle θ fixed to the predetermined value, and when a minimum turning steering angle difference calculated based on the arm length ratio a / b identical to the turning radius that is smallest among the plurality of turning radii calculated based on the same inter-arm angle θ in the turning radius calculating step is not within 10 degrees, the turning radius calculating step and the calculation of the minimum turning steering angle difference are repeated by changing the inter-arm angle θ from the predetermined value within the first range until a minimum turning steering angle difference that is within 10 degrees is calculated.

9. the first range is a range in which the inter-arm angle θ is |θ|≦10°, 9. The vehicle design method according to claim 8, wherein the second range is a range in the vicinity of the arm length ratio a / b=1.

Images