JPS62177339A - Shift drum structure of speed change gear - Google Patents

Abstract

PURPOSE:To eliminate the problem of double shift feeling for attaining a smooth speed change operation by making the inclination of inclined groove wall forming a shift operation region in the case where the engagement of a dog beings at the time of shift-up greater than that at the time of shift-down. CONSTITUTION:On one end of a pedal shaft 1 a speed change pedal, and on the other end of it a shift lever 2 are fixed respectively, and a shift drum 3 on the surface of which three cam grooves 4a, 4b, and 4c are formed is rotatably supported on the shaft 1. Further, shift forks 5a, 5b, and 5c are engaged with the cam grooves 4a, 4b, and 4c so that selective shifting can be carried out. Referring to the development of the cam grooves of this shift drum 3, the inclination alpha between the tangential line of groove wall 16 at the time of shift-up and the circumferential direction of drum is made greater than the inclination beta of groove wall 17 at the time of shift-down, or alpha>beta. Accordingly, the resistance in the case where the engagement of a dog begins at the time of shift-up can be reduced, enabling the elimination of the problem of double shift feeling for attaining a smooth speed change operation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a shift drum structure in a constant mesh transmission.

[Prior art]

For transmissions used in motorcycles, there is a so-called selection method in which the transmission gears are disengaged or engaged with each other, as in transmissions for automobiles, etc., for reasons such as not increasing the width of the vehicle. Sliding types are not used, but so-called constant-mesh types, in which the gears are always in mesh and the gears are shifted within a range that does not become disengaged, are often used.

In this constant-mesh type transmission, the speed change gear is made to be able to slide freely on the shaft via a spline and has a dog on the side. The gearshift gear has an engagement hole provided therein, and when the gear is changed, the former is shifted so that the dog meshes with the engagement hole of the latter. However, with this transmission, when upshifting, the dog of the transmission gear rarely engages directly with the engagement hole of the other transmission gear.
First, it comes into contact with the side of the other party's gear and receives strong resistance.
Then, it engages with the engagement hole while sliding. As a result, smooth upshifting operations are hindered, and the so-called ``two-stage feeling'' is not welcomed.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a shift drum structure that eliminates the problem of two-stage feeling in a constant-mesh transmission as described above and enables smooth gear shifting operations.

[Structure of the invention]

To achieve the above object, the present invention provides a constant mesh transmission in which a gear having a dog on the side surface is shifted via a shift fork engaged with a cam groove of a shift drum. Among the grooves, the angle of inclination of the inclined groove wall with respect to the drum circumferential direction that forms the shift operation area at the beginning of dog engagement during upshifting is made larger than the inclination angle of the inclined groove wall that forms the shift operation area during downshifting. It is characterized by this.

〔Example〕

Hereinafter, the present invention will be explained with reference to embodiments shown in the drawings.

4 and 5 show the main parts of the constant mesh transmission. Reference numeral 1 denotes a pedal shaft to which a speed change pedal (not shown) is fixed at one end, and a shift lever 2 is fixed to the other end. Reference numeral 3 denotes a rotatably supported shift drum, and three cam grooves 4a, 4b, and 4c are formed along the circumferential direction on the surface of the shift drum. Shift forks 5a, 5b, and 5c are respectively engaged with the cam grooves 4a, 4b, and 4c via pins 6.degree. 6.6, and when the shift drum 3 rotates due to this engagement, the shift forks 5a.

5b and 5c are selectively shifted.

The ends of these shift forks 5a, 5b, and 5c each engage with an engaging portion 21a of a speed change gear 21 having a dog 22 as illustrated in FIG. The dog 22 is shifted along the spline 26, and the dog 22 is inserted into the engagement hole 24 of the transmission gear 23 of the other party.
Make sure that they mesh with each other.

A star-shaped segment 7 is attached to the side of the shift drum 3.
is welded, and the shift drum 3 is further welded to the segment 7.
A plurality of pins 8, ..., 8 are centered around the rotation axis of
are protruded at equal intervals. On the other hand, at the end of the shift lever 2, a bifurcated engagement pawl 9.9 is attached to the spring 1.
It is elastically supported through 0. This engaging claw 9 is
When the shift lever 2 swings in the upshift direction U or downshift direction by operating a speed change pedal (not shown), the pin 8 is hooked, thereby rotating the shift drum 3.

A stopper 14 is provided near the segment 7, and includes a swingable lever 11, a roll 12 attached to the tip thereof, and a spring 13. The stopper 14 is always urged toward the segment 7 by the elastic force of the spring 13, and engages the roll 12 at the tip with the concave portion between the leaf-shaped convex portion 7a and Ta of the segment 7, thereby holding the shift drum 3 at a predetermined position. The gear is kept stationary at the gear shift position.

FIG. 5 shows a case where the roll 12 is stopped at a neutral (neutral) position, and the roll 12 has a plurality of leaf-shaped convex portions 7a forming segments 7, . It is in a state of engagement with a recess provided at the tip of only one of a. At a shift position other than neutral, the leaf-like protrusions 7a and T adjacent to each other
The roll 12 is adapted to engage with the recessed portion between a.

FIG. 1 shows cam grooves 4a and 4 provided in the shift drum 3.
b, 4c are developed views. Of the three cam grooves, the cam groove 4a sets the 2nd speed position ■ by an inclined groove in the shift operation area indicated by A, and the 4th gear position ■ is set by the cam groove 4b by an inclined groove in the shift operation area indicated by B. and 5th speed position V are respectively set, and the cam groove 4C sets a 3rd speed position ■ by an inclined groove in the shift operation range indicated by C. The shift drum 3 having such a cam groove rotates in the direction of arrow U when shifting up, and rotates in the direction of arrow U when shifting down.

When shifting up to the second gear position ■, the shift drum 3 rotates in the direction of arrow U as shown in Figs. guided by an inclined groove. In particular, when the dog of a speed change gear starts to mesh with the engagement hole of the other speed change gear, it is guided by a groove wall 16 formed to bulge outward from the parallel groove wall of the inclined groove as shown by the chain line. . On the other hand, when the dog starts to pull out when downshifting from the second gear position (2), the pin 6 is guided by the groove wall 17 on the opposite side from the groove wall 16.

In such a shift operation range, the angle of inclination between the tangent of the groove wall 16 and the circumferential direction of the drum is α, and the groove wall 1 facing the opposite side is
If the angle of inclination between the tangent line of 7 and the circumferential direction of the drum is β, then the relationship between the two is α>β.In this relationship, the center of the pin 6 is aligned with the cam groove 4a. The locus drawn in the figure will look like a U when shifting amplifier, and like d when shifting down.

The configuration described above is the other 3rd speed position III and 4th speed position ■.

The same applies to each shift position such as the 5th speed position v, and the shift amplifier and the pin of the shift fork in downshifting behave in the same manner. (See Figures 2 and 3) During shift amplifier operation, when the dog of the transmission gear starts to mesh with the engagement hole of the other transmission gear, the
As shown in the figure, while the transmission gear 21 with the dog 22 is rotationally driven by the transmission shaft 25 via the spline 26, the dog 22 is brought into contact with the side surface 23a of the other transmission gear 23 along the spline 26. Then, it is fitted into the engagement hole 24 while sliding the side surface 23a. For this reason, if the pressing force when the dog 22 comes into contact with the side surface 23a of the speed change gear 23 is large, it will receive strong resistance, resulting in a so-called "two-stage human feeling".

However, according to the shift drum 3 described above, when the dog 22 of the speed change gear 21 starts to mesh with the engagement hole 24 of the speed change gear 23, the shift forks 5a, 5b are moved by the groove wall 16 having a large inclination angle α with respect to the drum circumferential direction. , 5c
pin 6 is shifted. Therefore, the groove wall 16
The magnitude of the component force in the drum axis direction of the driving force applied to the pin 6 in the normal direction from the conventional parallel groove (No. 2.3
This can be made smaller than the groove wall having the same inclination as the inclination angle β shown by the chain line in the figure. Furthermore, the speed of movement in the direction of the drum axis at this time can also be made slower than in the case of conventional parallel grooves. Therefore, the pressing force exerted by the dog 22 on the side surface 23a is smaller than that of the conventional parallel grooves, thereby reducing resistance and providing a two-stage impression.

Further, as shown in FIGS. 8A, B, and C, when the segment 7 rotates together with the shift drum 3 during shift amplifier, the roll 12 of the stopper 14 climbs over the leaf-like convex part 7a and reaches the adjacent concave part (shift position). When moving to the segment 7, the elastic force of the spring 13 provides a large resistance to the segment 7 in the process of riding over the lobe-shaped convex portion 7a, but when moving beyond the apex to the adjacent concave portion, the spring 13 provides a large resistance to the segment 7 (therefore, the shift Since it acts in a direction that promotes the rotation of the drum 3), there is no resistance. However, at the time when resistance is applied from the stopper 14 in this way,
Since the shift drum 3 acts to reduce the pressing force against the side surface 23a of the dog 22, the rotational operation of the shift drum 3, which is subject to resistance as described above, can be lightened and the upshift operation can be made smoother.

On the other hand, in a downshift operation, when the dog 22 of the speed change gear 21 comes out of the engagement hole 24 of the speed change gear 23,
The cam groove is formed by groove walls 17 whose inclination angle is β smaller than α. Therefore, contrary to the above-mentioned shift amplifier, a large component force acts in the direction of the drum axis, and the dog 22 can be easily removed.

〔Effect of the invention〕

As described above, the present invention provides a constant mesh transmission in which a gear having a dog on the side surface is shifted via a shift fork engaged with a cam groove of the shift drum. Among these, the angle of inclination of the inclined groove wall with respect to the drum circumferential direction that forms the shift operation area at the beginning of dog engagement during upshifting is greater than the inclination angle of the inclined groove wall that forms the shift operation area during downshifting. It is. With this configuration, the resistance at the start of dog engagement during upshifting is reduced, thereby eliminating the problem of two-gear feeling and enabling smooth gear shifting operations.

Also, when downshifting, it is easy to get out of the dog position.

[Brief explanation of drawings]

FIG. 1 is a developed view of a shift drum according to an embodiment of the present invention;
Figure 2 is an enlarged view of parts A and 0 in Figure 1, Figure 3 is an enlarged view of part B in Figure 1, and Figure 4 shows the main parts of a constant mesh transmission equipped with the same shift drum. 5 is a side view of the main parts of the same transmission, FIG. 6 is a side view showing an example of the transmission gear part in partial section, and FIG. 7 is a side view of the dog part of the transmission gear part. Explanatory diagram showing the state of engagement with the engagement hole, FIG. 8A,
B and C are explanatory diagrams showing the action of the segment on the side of the shift drum and the stopper. 3--Shift drum, 4a, 4b, 4c--Cam groove, 5a, 5b, 5c...-Shift fork, 16
．． 17--Groove wall, 21.23...-Speed gear, 22
-・-Dog, 24-・Engagement hole, A, B, C・-
Shift operation area consisting of slanted grooves.

Claims (1)

[Claims] In a constant-mesh type transmission in which a gear having a dog on its side is shifted via a shift fork engaged with a cam groove of a shift drum, the dog in the cam groove of the shift drum during upshifting is Shifting of a transmission characterized in that the angle of inclination of the inclined groove wall with respect to the circumferential direction of the drum that forms the shift operation area at the beginning of engagement is larger than the inclination angle of the inclined groove wall that forms the shift operation area at the time of downshifting. drum structure.