JP2012207715A - Transmission - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transmission having a spline shaft capable of relieving a stress concentration applied to a spline groove by a quantity more than before.SOLUTION: The transmission 1 has a main shaft 12 having a gear 41 fitted to the spline groove 20 and a counter shaft 13 having a gear 43 fitted to the spline groove 20, and is constituted so as to be capable of changing the rotational ratio of the power transmission to the counter shaft 13 from the main shaft 12 by changing the meshing of the mutual gears. At least one groove end 20a in the axial direction in the spline groove 20 is constituted as a curved surface of shallowing the groove depth H toward the groove tail end side in a central part 21 in the axial direction of a groove bottom surface 20b of the spline groove 20, and the groove end 20a is also constituted so as to become gradually large toward the groove tail end side in curvature in the groove cross-sectional direction of both side parts 20e in the groove width direction of the groove bottom surface 20b.

Description

  The present invention relates to a transmission, and more particularly to a transmission provided with a dog clutch.

  Conventionally, in a multi-stage transmission having a plurality of transmission gear pairs, a transmission gear or sleeve that is slidably provided on the main shaft and the counter shaft is moved by moving on both shafts. There is. A configuration is known in which the speed change operation is performed smoothly by driving a shift fork that slides in parallel with the main shaft and the countershaft (see, for example, Patent Document 1).

  Patent Document 1 discloses a transmission including a transmission having a plurality of gear pairs between a main shaft and a counter shaft, and a clutch disposed on the main shaft. And in order to select one gear pair which transmits rotational drive force among several gear pairs, the slidable gear attached so that sliding was possible in the axial direction, and it was attached non-slidable in the axial direction A dog clutch is provided between the non-slidable gear.

JP 2008-248914 A

  In the connection between the main shaft and the transmission gear and the connection between the counter shaft and the transmission gear described above, both shafts are configured as spline shafts and are performed by spline fitting. In this type of spline fitting, for example, as shown in Patent Document 1 (FIG. 1 of Patent Document 1), for the purpose of relaxing stress concentration in the shaft, the end of the spline groove is a shaft. A structure having a tapered shape as viewed from the longitudinal section direction is employed.

  In this structure, for example, as shown in FIG. 16, the spline groove 120 provided in the spline shaft 112 has a groove end portion 120a that is made shallower toward the groove end side (left side in FIG. 16). The tapered surface 121b is used.

  This structure of the groove end portion 120a can provide a certain effect, but particularly in a spline shaft of a transmission using a dog clutch, there is a sudden change in power transmission force and a large stress concentration is likely to occur in the spline groove. Therefore, there has been a strong demand for a transmission structure that can alleviate the stress applied to the spline groove and further reduce the load on the spline shaft.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a transmission including a spline shaft that can more effectively relieve stress applied to the spline groove than ever before.

In order to achieve the above object, an invention according to claim 1 includes a main shaft including a gear fitted to a spline groove, and a countershaft including a gear fitted to the spline groove, In a transmission configured to be able to change the rotation ratio of power transmission from the main shaft to the counter shaft by changing the meshing between the gears,
At least one groove end portion in the axial direction of the spline groove is configured as a curved surface that is recessed in the shaft center direction where the groove depth becomes shallower as the axial center portion of the groove bottom surface of the spline groove moves toward the groove end side, Further, the groove end portion is configured such that the curvature in the groove cross-sectional direction of both side portions in the groove width direction of the groove bottom surface is gradually increased toward the groove end side.

  The invention according to claim 2 is characterized in that, in addition to the configuration according to claim 1, the end portion of the groove is formed into a curved line that bulges outward from the groove in plan view.

  According to a third aspect of the present invention, in addition to the configuration according to the first or second aspect, the groove end is configured such that the axial length of the curved groove bottom surface is at least four times the maximum groove depth. Features.

  According to a fourth aspect of the present invention, in addition to the configuration according to the first or second aspect, the groove end portion is a groove from the start-up start end of the groove end portion with respect to the cross-sectional area of the groove space traversing the deepest groove portion. In the region up to 60% of the total length of the groove end portion toward the end side, the cross-sectional area change rate of the cross-sectional area of the groove space is shifted to the position of 1% of the total length of the groove end portion from the start end to the groove end side. On the other hand, it is configured to be 0.3% or less.

  According to the invention of claim 1, the central portion in the axial direction of the groove bottom surface of the spline groove is thus configured to have a curved surface that is recessed toward the center of the shaft as the groove depth becomes shallower toward the groove end side. In addition, the curved bottom surface of the both side portions gradually increases in curvature in the cross-sectional direction of the groove toward the axial end portion, thereby synergistically forming the spline groove at a specific portion at the groove end portion. Stress concentration is relaxed, stress distribution is effectively performed, and the maximum stress can be reduced.

  According to the second aspect of the present invention, since the shape of the final end portion of the spline groove is constituted by a curved line, the stress distribution can be effectively achieved by the gentle shape of the groove end portion.

  According to the third aspect of the present invention, the axial length of the curved groove bottom surface of the groove end of the spline groove is configured to be at least four times the maximum groove depth, so that stress distribution can be effectively achieved. it can.

  According to the invention of claim 4, the rate of change of the cross-sectional area of the groove space formed at the groove end portion of the spline groove is 60% of the total length of the groove end portion from the start-up end of the groove end toward the groove end side. In the region up to this point, the stress distribution can be effectively achieved by being configured to be 0.3% or less with respect to the position movement of 1% of the total length of the groove end portion from the start end to the groove end side.

It is principal part sectional drawing of 1st Embodiment of the transmission which concerns on this invention. It is a fragmentary perspective view of the principal part (M part) of the main shaft shown in FIG. FIG. 3 is a partially enlarged view of FIG. 2. It is a top view which shows the groove edge part of the spline groove | channel shown in FIG. Sectional drawing of the part along the XX line of FIG. It is sectional drawing of the part along the AA line in the spline groove | channel shown in FIG. 4, BB line, CC line, DD line, and EE line. It is explanatory drawing shown in figure so that each cross section ((AA line)-(DD line)) shown in FIG. 6 might be piled up. It is a stress distribution figure at the time of the power transmission of the spline shaft shown in FIG. It is explanatory drawing shown in figure so that each cross section of the part along the AA line, BB line, CC line, and DD line in the conventional spline shaft shown in FIG. It is a stress distribution figure at the time of the power transmission of the conventional spline shaft shown in FIG. It is a top view which shows the groove edge part of the spline groove | channel in 2nd Embodiment. It is explanatory drawing shown in figure so that each sectional drawing of the part along the AA line, BB line, CC line, DD line, and EE line in FIG. 11 might overlap. It is a stress distribution figure at the time of the power transmission of the spline shaft of 2nd Embodiment shown in FIG. It is a graph which shows the cross-sectional area change rate of the groove space in the groove edge part of a spline groove. It is a perspective view of the conventional spline shaft. It is sectional drawing of the part along the XX line in FIG.

(First embodiment)
The first embodiment will be described below with reference to FIGS.
FIG. 1 is a cross-sectional view of a main part of a constantly meshing transmission according to this embodiment applied to a motorcycle. FIG. 2 is a perspective view of a main part (M portion in FIG. 1) of the main shaft 12. 3 is a partially enlarged view of FIG. 2, FIG. 4 is a plan view showing a groove end portion of the spline groove, and FIG. 5 is a cross-sectional view of the portion along the line XX of FIGS. 6 is a cross-sectional view of a portion along line AA, BB, CC, DD, and EE in FIG. 4, and FIG. 7 is a cross-sectional view of FIG. It is the figure shown to match | combine. 8 is a stress distribution diagram during power transmission of the spline shaft shown in FIG. 2, and FIG. 9 is an AA line, BB line, CC line, DD in the conventional spline shaft shown in FIG. FIG. 10 is a diagram illustrating stress distribution at the time of power transmission of the conventional spline shaft shown in FIG. 15.

  First, in FIG. 1, the constantly meshing transmission 1 has a main shaft 12 and a countershaft 13 that have axes parallel to each other and are rotatably supported by a crankcase 11. A plurality of shift stages provided between the shaft 12 and the counter shaft 13, for example, first to fifth speed gear trains G 1, G 2, G 3, G 4, G 5 are provided.

  At one end of the main shaft 12, a crankshaft (not shown) of the engine which is a power source and a starting clutch 14 for switching power connection / disconnection between the main shaft 12 are mounted. The starting clutch 14 is connected to the crankshaft. A clutch outer 17 to which power is transmitted via the primary speed reducer 15 and the torque damper 16, a clutch inner 18 disposed in the center of the clutch outer 17 and coupled to the main shaft 12 so as not to rotate relative thereto, A plurality of drive friction plates 19, which are spline-fitted to the outer peripheral wall of the outer 17 so as to be axially slidable, and the drive friction plates 19 are alternately stacked and slidable in the axial direction on the outer periphery of the clutch inner 18. So as to receive a plurality of driven friction plates 70 that are splined to each other and the innermost drive friction plate 19 Then, the pressure receiving plate 71 provided integrally with the inner end of the clutch inner 18, the pressure plate 22 capable of pressing the outermost drive friction plate 19, and the pressure plate 22 are urged toward the pressure receiving plate 71 side. A clutch spring 23.

  Thus, when the driving friction plates 19 and the driven friction plates 70 are sandwiched between the pressure plate 22 and the pressure receiving plate 71 by the urging force of the clutch spring 23, the starting clutch 14 is connected between the clutch outer 17 and the clutch inner 18. The clutch is engaged by frictional connection.

  In addition, a release member 25 having a release bearing 24 interposed between the clutch inner 18 and a pressure plate 22 is disposed at the center of the clutch inner 18. The release member 25 is inserted into the main shaft 12 so as to be movable in the axial direction. The push rods 26 are connected. Thus, when the push rod 26 is pushed by operating a clutch lever (not shown), the pressurizing plate 22 is retracted against the spring force of the clutch spring 23, whereby each drive friction plate 19. The driven friction plates 70 are in a free state, and the starting clutch 14 is in a clutch-off state in which the clutch outer 17 and the clutch inner 18 are not connected.

  A part of the countershaft 13 protrudes from the crankcase 11 on the side opposite to the starting clutch 14, and a drive sprocket 27 is fixed to the protruding end of the countershaft 13 from the crankcase 11. Thus, a chain (not shown) for transmitting rotational power to a rear wheel (not shown) is wound around the drive sprocket 27.

  By the way, the first speed gear train G1 is supported by the first speed drive gear 31 formed integrally with the main shaft 12 and the counter shaft 13 so as to be relatively rotatable with a constant axial position, and at the first speed. The second-speed gear train G2 includes a first-speed driven gear 32 that meshes with the driving gear 31. The second-speed gear train G2 is mounted on the main shaft 12 at a constant axial position so as not to be relatively rotatable. 33 and a second-speed driven gear 34 that is supported on the countershaft 13 so as to be relatively rotatable while keeping the axial position constant, and is engaged with the second-speed drive gear 33, and a third-speed gear train G3. Is supported by the third speed drive gear 35, which is unable to rotate relative to the main shaft 12, and the counter shaft 13 so as to be capable of relative rotation with a constant axial position. The fourth-speed gear train G4 is composed of a meshed third-speed driven gear 36. The fourth-speed gear train G4 is supported on the main shaft 12 so as to be relatively rotatable with a constant axial position, and a countershaft. 13 and a fourth-speed driven gear 38 that is engaged with the fourth-speed drive gear 37 and cannot be rotated relative to the fourth-speed drive gear 37. The fifth-speed gear train G5 has a constant axial position on the main shaft 12. A fifth-speed drive gear 39 that is supported so as to be relatively rotatable, and a fifth-speed driven gear 40 that is mounted on the countershaft 13 so as not to be capable of relative rotation and meshes with the fifth-speed drive gear 39.

  The first shifter 41 is allowed to slide in the axial direction on the main shaft 12 between the fourth-speed drive gear 37 and the fifth-speed drive gear 39 that have a constant axial position with respect to the main shaft 12. The third speed drive gear 35 is integrally formed on the outer periphery of the first shifter 41. Further, the second shifter 42 can be slid in the axial direction on the counter shaft 13 between the first speed driven gear 32 and the third speed driven gear 36 whose axial position relative to the counter shaft 13 is constant. The fifth speed driven gear 40 is integrally formed on the outer periphery of the second shifter 42. Further, the third shifter 43 is allowed to slide in the axial direction on the counter shaft 13 between the second speed driven gear 34 and the third speed driven gear 36 whose axial position with respect to the counter shaft 13 is constant. The fourth speed driven gear 38 is integrally formed on the outer periphery of the third shifter 43.

  The constantly meshing transmission 1 in the present embodiment includes first to fifth dog clutches C1 to C5 for selectively establishing first to fifth gear trains G1 to G5.

  The first dog clutch C1 can move close to and away from the fifth speed drive gear 39 and the fifth speed drive gear 39, which are the first rotating body with a constant axial position, and can drive away from the fifth speed drive gear 39. It is provided between the first shifter 41 as the second rotating body disposed coaxially with the gear 39.

  The second dog clutch C2 is capable of moving close to and away from the fourth speed drive gear 37 and the fourth speed drive gear 37 as a first rotating body having a constant axial position, and the fourth speed drive. It is provided between the first shifter 41 as a second rotating body disposed coaxially with the gear 37.

  The third dog clutch C3 can be moved close to and away from the first speed driven gear 32, which is a first rotating body having a constant axial position, and the first speed driven gear 32. It is provided between a second shifter 42 as a second rotating body disposed coaxially with the gear 32.

  The fourth dog clutch C4 can be moved closer to and away from the fourth speed driven gear 38 and the third speed driven gear 36 as a first rotating body with a constant axial position. It is provided between the second shifter 42 serving as a second rotating body disposed coaxially with the gear 36.

  The fifth dog clutch C5 can move closer to and away from the second speed driven gear 34 and the second speed driven gear 34 as the first rotating body with a constant axial position. It is provided between a third shifter 43 as a second rotating body that is coaxially disposed opposite to the gear 34.

  An annular recess 38a is formed in the fourth speed driven gear 38, an annular recess 59 is formed in the fifth speed driven gear 40, and an annular recess 46 is formed in the first shifter 41. The gear is moved in the axial direction on the spline groove by this shift fork, and the dog clutch is appropriately engaged to make a shift change.

  As described above, the gears attached to the main shaft 12 and the counter shaft 13 are fitted into the spline grooves 20 formed on the outer circumferences of both shafts, and the meshing of the gears is appropriately changed by this fitting. Thus, the rotation ratio of power transmission from the main shaft 12 to the counter shaft 13 is changed. In particular, the stress applied to the main shaft 12 and the countershaft 13 at the time of a shift change increases. Therefore, stress concentration occurs on the spline groove 20.

  Hereinafter, a structure for avoiding stress concentration on the spline groove 20 will be described in detail with reference to FIGS.

As shown in FIGS. 2 and 3, the spline groove 20 in the transmission 1 of the present embodiment has a groove end portion 20 a at one end in the axial direction of the spline groove 20 in the axial direction and the axial circumferential direction (direction indicated by arrow S). It has a curved structure.
As shown in FIGS. 3 and 5, the curve in the axial direction, which is the first structure in this curved structure, makes the groove depth shallower as the axially central portion 21 of the groove bottom surface 20b moves toward the groove end side. Such a large curvature radius r2 is configured. That is, in this structure, the center of curvature of the radius of curvature r2 is such that the groove bottom surface 20b constituting the spline groove 20 gradually decreases the groove depth H toward the groove end side (H1, H2...). The configuration is set appropriately.

  In addition, the curve in the axial circumferential direction which is the second structure in the curved structure is such that the groove end portion 20a has both side portions 20e in the groove width direction of the groove bottom surface 20b (arrow S direction in FIGS. 3, 4 and 5). The curvature of 20e is configured to gradually increase toward the groove end side (in the direction of arrow G in the figure). Therefore, as shown in FIG. 4, the both side portions 20e and 20e are moved from the cut-off start end SP (starting position of the groove end portion 20a) to the groove end side (leftward), which is the position where the groove depth starts to become shallow. The width (width in the direction of arrow S in the figure) gradually increases to the middle, and the width narrows from the position MP where the flat portions of the side wall surfaces 20c and 20c disappear to the groove end side. Yes.

In the drawing, both side portions 20e and 20e in the groove width direction are formed between the side wall surfaces 20c and 20c and the groove bottom surface 20b along the axial radial direction in the cross section of the curved bottom surface, except for the groove end portion 20a. Although shown as intersecting corner portions, in the groove end portion 20a in the present embodiment, most of the portion is configured as a curved surface with a width (W1, W2, W3, W4...) Varying, and the end contour line 20f. This portion is configured as a continuous curved line.
In FIG. 4, both side portions 20e and 20e are shown as imaginary lines K and K as lines indicating substantially central valley portions. Further, in FIG. 4, the side portions 20e and 20e are separated from each other on the groove end side (the portion of the end contour line 20f) of the groove end portion 20a, but are actually configured to overlap.

In the present embodiment, the configuration in which the curvatures of both side portions 20e and 20e gradually increase toward the groove end side (in the direction of arrow G in the figure) is a configuration other than the groove end portion 20a as shown in FIG. Compared with the AA line cross section, the cross section of the portion along the BB line, the CC line, the DD line, and the EE line in the order of sequentially approaching the groove end side (in the direction of arrow G in the figure). In the shape, the radius of curvature is configured to gradually increase from the radius of curvature R1 to R4.
That is, FIG. 7 shows that the cross sections from AA to EE in FIG. 6 are overlapped, but as shown in FIG. 7, the groove end portion 20a is also directed toward the groove end side. Thus, the side wall surfaces 20c and 20c become smaller and the curvatures of both side portions 20e and 20e become larger and the grooves become shallower together.

In this way, in addition to the configuration in which the axial center portion 21 of the groove bottom surface 20b of the spline groove 20 is curved, the curvature in the groove cross-sectional direction of both side portions 20e, 20e is gradually increased toward the groove end side. As a result of the synergistic structure, the stress concentration on the specific portion of the groove end portion 20a of the spline groove 20 is relaxed, the stress distribution is effectively performed, and the maximum stress can be further reduced.
For example, in this embodiment, FIG. 8 shows a schematic diagram of a stress distribution obtained by analyzing the stress distribution of the groove end portion 20a when a driving force is applied to the first shifter 41.
The difference can be made clearer by comparing the stress distribution diagram shown in FIG. 8 with FIG. 10 which is a schematic diagram of a conventional stress distribution diagram as a comparative example.

Prior to comparison, first, a comparative example shown in FIGS. 9 and 10 will be described.
9, as in FIG. 7, the shape of the cross section along the AA, BB, CC, and DD lines of the groove end portion 120 a shown in FIG. 15 is overlapped. It is shown as follows. As shown in FIG. 9, in the conventional groove end portion 120a, the angles of both side portions 120e and 120e, which are portions where the side wall surfaces 120c and 120c intersect with the groove bottom surface 120b, are constant without changing in any cross section. It is. Further, the width of the groove bottom surface 120b is also constant.

  The stress distribution at the groove end 120a of the spline shaft 112 shown in FIGS. 9 and 15 is, as shown in FIG. 10, the region P1 showing the maximum value is the shaft rotation direction (Y direction) and the gear is the upper side in the figure Is formed on the side wall surface 120c. Then, the region P2, the region P3, the region P4, and the region P5, which are regions of higher stress than the other portions along the groove bending lines 125 and 126 of the groove end portion 120a, are narrow within the region P1. It extends in a dense state.

  Note that the size of the stress distribution region is region P1> region P2> region P3> region P4> region P5> region P6> region P7> region P8> region 9P> region P10. Further, the shape of the groove end portion 20a in plan view is linear in outline, and the intersection points 130 and 131 where the corner portions intersect form a boundary point of the stress region, and in particular, the intersection points on the groove bending lines 125 and 126 side. Distribution boundary lines are gathered with 130 and 130 as boundary points.

On the other hand, in the present embodiment, in the stress distribution diagram shown in FIG. 8, the region that spreads around the region P1 that is the maximum stress region is larger than the shape of each distribution region in FIG. Is wide across the entire width of the groove, and the boundary is also a gently curved boundary. Further, in this embodiment, not only the conventional groove bending lines 125 and 126 but also the entire groove bottom surface 20b is formed of a gently curved surface, so that stress is effectively dispersed. I understand.
Further, in the numerical value of the maximum stress generated in the maximum region P1, in the case of the structure of the present embodiment under the same conditions as in the comparative example, it was possible to reduce by 26% compared to the comparative example.

  Further, in the present embodiment, the groove end portion 20a is formed in a curved line whose end contour line 20f swells outside the groove in plan view. Since the shape of the final end portion of the spline groove 20 is constituted by a curved line, the gentle distribution of the groove end portion 20a (the shape having few bent portions) can effectively achieve stress distribution.

  Further, in the present embodiment, the groove end portion 20a is configured such that the length L (see FIG. 5) of the curved groove bottom surface 20b in the axial direction is sufficiently longer than the maximum groove depth H. It has been found that when the length L is configured to be four times or more the maximum depth H, a good effect can be obtained in the stress dispersion effect.

(Second Embodiment)
Hereinafter, a second embodiment of the present invention will be described with reference to FIGS.
In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.
11 is a plan view showing the groove end 20a of the spline groove 20, and FIG. 12 is taken along the lines AA, BB, CC, DD, and EE in FIG. It is explanatory drawing shown so that the sectional drawing of a part might overlap. FIG. 13 shows the stress distribution near the groove end 20a of the spline groove 20 under the same conditions as in the first embodiment.

  Also in the present embodiment, the central portion 21 in the axial direction of the groove bottom surface 20b has the same configuration as that in the first embodiment, and the curve end portion 20a is curved in the axial circumferential direction in the curved structure as in the first embodiment. Is configured such that the curvatures of both side portions 20e, 20e in the groove width direction (arrow S direction in FIG. 11) of the groove bottom surface 20b gradually increase toward the groove end side (arrow G direction in the figure).

  The configuration different from the first embodiment in the present embodiment is that the groove bottom portion 20a has a configuration in which the groove bottom surface 20b and both side portions 20e and 20e in the groove width direction are clearly separated. As shown in FIG. 12, in the present embodiment, flat portions 21b, 21c, 21d, and 21e of the groove bottom surface 20b are also provided in the groove end portion 20a, and the groove bottom surface 20b has its width ( W6> W7> W8> W9) is configured to gradually decrease.

  As shown in FIG. 12, this configuration is the same as that of the first embodiment in that the curvature of both side portions 20e, 20e gradually increases toward the groove end side (in the direction of arrow G in FIG. 11). The flat portion of the groove bottom surface 20b remains up to the end contour line 20f. That is, the groove end portion 20a is formed in a curved line whose end outline 20f swells outside the groove in plan view, but has a slight straight portion 21f in the central portion 21 in the axial direction. However, the entire end contour line 20f of the spline groove 20 is configured by a curved line, so that the stress distribution can be effectively achieved by the gentle shape of the groove end portion 20a (the shape having few bent portions). .

Also in the stress distribution diagram shown in FIG. 13, compared with the conventional stress distribution diagram shown in FIG. 10, the conventional groove bending lines 125 and 126 are not formed, and the groove bottom surface 20b is composed of a gentle curved surface as a whole. Therefore, the area P1 which is the maximum stress area is centered on the area P1 and is wider than the shape of each distribution area in FIG. 10, and the entire outline is composed of a gentle curve with few acute angles. Distribution. Therefore, it can be seen that the stress is effectively dispersed.
Also, the numerical value of the maximum stress generated in the region P1 can be reduced by 21% in the case of the structure of the present embodiment under the same conditions as in the conventional case.

Examples 1 and 2 tested based on the above-described embodiment of the present invention will be described below with reference to FIG. In addition, as a comparative example, it is the data implemented about the conventional groove edge part 120a shown in FIG.
In the graph shown in FIG. 14, an example of a change in the groove cross-sectional area (the area obtained by cutting the groove space along the cross-direction of the main shaft) of the groove end 20 a of the present embodiment and the conventional groove end 120 a is shown. It is shown.

Then, looking at this implementation result, as shown in FIG. 14, the change in the cross-sectional area of the comparative example has a sudden area change in the range indicated by Q in the figure.
On the other hand, in the first and second embodiments, the groove end portion 20a is shallower than the groove end portion 20a with respect to the transverse area of the groove space (groove space corresponding to the AA cross section) that crosses the deepest groove portion. The fact that the cross-sectional change is stable in the region of up to 60% of the total length from the beginning side (left side of the graph) to the groove end side (right side of the graph) has yielded knowledge that provides favorable results. Compared to the fact that stress concentration is easily caused by such a sudden area change, the change in the cross-sectional area of the present embodiment is a gentle curve, and stress concentration hardly occurs.
Further, the groove end portion 20a is in a region up to 60% of the total length of the groove end portion 20a from the start end of the groove end portion 20a toward the groove end side with respect to the cross-sectional area of the groove space crossing the deepest portion of the groove. The cross-sectional area change rate of the cross-sectional area of the groove space is 0.3% or less with respect to the position movement of 1% of the total length of the groove end portion 20a from the start end to the groove end side in FIG. As shown, it was possible to obtain knowledge that stress distribution can be effectively performed.

  As described above, the first and second embodiments applied to the main shaft in the constantly meshing transmission having the dog clutch have been described. However, the present invention is applicable to the counter shaft 13 as well, for example, a twin clutch type. It may be a transmission, another saddle-type vehicle, or a four-wheeled vehicle, and can be widely applied to a power transmission mechanism having a spline shaft that is a subject of the present invention.

DESCRIPTION OF SYMBOLS 1 Transmission 12 Main shaft 13 Countershaft 20 Spline groove 20a Groove end part 20b Groove bottom face 20c Side wall surface 21 Axis direction center part H Groove depth L Groove end length

Claims (4)

A main shaft (12) having a gear fitted in the spline groove (20); and a counter shaft (13) having a gear fitted in the spline groove (20), wherein the gears mesh with each other. In the transmission (1) configured to be able to change the rotation ratio of power transmission from the main shaft (12) to the countershaft (13) by changing
The at least one groove end portion (20a) in the axial direction of the spline groove (20) has a groove depth as the axial center portion (21) of the groove bottom surface (20b) of the spline groove (20) moves toward the groove end side. The groove end portion (20a) has a groove crossing of both side portions (20e, 20e) in the groove width direction of the groove bottom surface (20b). A transmission (1) characterized in that a curvature in a surface direction is gradually increased toward a groove end side.   The transmission (1) according to claim 1, wherein the groove end portion (20a) is formed in a curved line whose end contour line (20f) bulges outward in the plan view.   The groove end portion (20a) is configured such that the axial length (L) of the curved groove bottom surface (20b) is at least four times the maximum groove depth (H). Transmission (1) according to   The groove end portion (20a) is formed with respect to the cross-sectional area of the groove space traversing the deepest portion of the groove from the start end (SP) of the groove end portion (20a) toward the groove end side of the groove end portion (20a). In the region up to 60% of the total length, the cross-sectional area change rate of the cross-sectional area of the groove space is 0 with respect to the position movement of 1% of the total length of the groove end portion (20a) from the start end (SP) to the groove end side. 3. Transmission (1) according to claim 1 or 2, characterized in that it is configured to be 3% or less.

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