JP5302837B2 - Shift drum and internal combustion engine - Google Patents

Description

  The present invention relates to a shift drum used for an internal combustion engine such as a motorcycle and an internal combustion engine including the shift drum.

  2. Description of the Related Art Conventionally, a shift drum in which a lead groove is formed in a cylindrical outer peripheral wall and a supported portion that is rotatably supported by a transmission case is formed at an axial end portion is known (see, for example, Patent Document 1). ).

Japanese Utility Model Publication No. 62-54350

  By the way, the shift drum is usually integrally formed by hollow casting using a core, but in this case, since the core is used, it is difficult to reduce the manufacturing cost.

  Accordingly, the present invention provides a shift drum that can be formed into a hollow body without using a core, thereby reducing manufacturing cost, and an internal combustion engine that uses the shift drum to improve shift feeling at a predetermined shift position. I will provide a.

As a means for solving the above problems, the invention described in claim 1 is characterized in that a lead groove (for example, the lead groove 35 of the embodiment) is formed in a cylindrical outer peripheral wall (for example, the outer peripheral wall 32 of the embodiment) and an axial end portion is formed. Includes a shift drum (for example, the shift drums 30, 30 ′ of the embodiment) in which a supported portion (for example, the shaft support portion 34 of the embodiment) is rotatably supported by the transmission case (for example, the crankcase 2 of the embodiment). A shift drum that switches a gear position of a transmission (for example, the transmission 4 of the embodiment) by moving a shift fork (for example, the shift fork 31 of the embodiment) along the lead groove with the rotation of the shift drum. The lead groove is formed in a range that is substantially half the circumference of the outer peripheral wall and exceeds a half circumference, and in the range where the lead groove of the outer peripheral wall is not formed, the shift drum An opening (for example, the opening 36 of the embodiment) for extracting the inner mold for forming the inner space of the outer peripheral wall is formed, and the inner peripheral side of both ends in the circumferential direction of the portion where the lead groove is formed in the outer peripheral wall is thinned. A portion (for example, a lightening portion 32c of the embodiment) is provided .
According to a second aspect of the present invention, the shift drum is formed by casting using an outer mold that forms the outer peripheral side and an inner mold that forms the inner peripheral side, and the inner mold is extracted from the opening. It is characterized by.
According to a third aspect of the present invention, the shift drum is formed by forging using an outer mold that forms the outer peripheral side and an inner mold that forms the inner peripheral side, and the inner mold is extracted from the opening. It is characterized by.
The invention described in claim 4 is characterized in that a weight portion (for example, the weight portion 37 of the embodiment) is provided in the lead groove forming portion (for example, the lead groove forming portion 32a of the embodiment) of the shift drum.
According to a fifth aspect of the present invention, the lead groove has a shift position (for example, in the embodiment) with an interval of about 60 degrees in the axial center angle of the shift drum in the order of first speed, second speed, third speed, and fourth speed. Shift positions p1 to p4) and a neutral position (for example, neutral position pn in the embodiment) is defined between the first and second gear positions (for example, the first and second gear positions p1 and p2 in the embodiment). The shift drum is between the first and fourth speed positions (for example, the first and fourth speed positions p1, p4 of the embodiment) and the second speed and third speed positions (for example, the second and third speed positions of the embodiment). p2 and p3) are characterized in that the opening is formed at a portion facing in the radial direction.
According to a sixth aspect of the present invention, there is provided an internal combustion engine (for example, the engine 1 according to the embodiment) including the shift drum according to any one of the first to fifth aspects. A shift drum drive mechanism (for example, the shift drum drive mechanism 52A of the embodiment) is configured by the change arm 52) and a rotation mechanism (for example, the rotation mechanism 53A of the embodiment) that rotates the shift drum according to the movement of the shift arm. A shift fork (for example, the shift fork 31 of the embodiment) is engaged with a lead groove (for example, the lead groove 35 of the embodiment) at a substantially vertical upper end of the shift drum.
According to the seventh aspect of the present invention, the axial center (for example, the axis C1 of the embodiment) of the crankshaft (for example, the crankshaft 9 of the embodiment) and the transmission (for example, the transmission 4 of the embodiment) are viewed in the axial direction of the internal combustion engine. ) Counter shaft (for example, the counter shaft 6 of the embodiment) and the main shaft (for example, the embodiment of the embodiment) above a straight line (for example, the straight line t of the embodiment) connecting the axis center (for example, the axis C4 of the embodiment). The shaft center of the main shaft 5) (for example, the axis line C3 of the embodiment) is disposed, and the shaft center of the shift drum (for example, the axis line C5 of the embodiment) is disposed below the straight line and engaged with the shift drum. The shifter (for example, the slide gear 7a of the embodiment) on the main shaft and the counter shaft is moved through a shift fork.
According to an eighth aspect of the present invention, the shift drum includes at least first to fourth gears, and at least a part of the opening is located below the shaft center of the shift drum in each gear. And it is characterized by facing downward rather than the horizontal direction .

According to the first aspect of the present invention, the hollow cylindrical shift drum can be integrally formed without using a core, and the manufacturing cost of the shift drum can be reduced. Further, by providing an opening for die cutting in a range where the lead groove of the shift drum is not formed, the shift drum can be reduced in weight. Further, when the shift drum is rotated so that the lead groove side (non-opening side) of the shift drum is moved downward, the rotation of the shift drum is promoted by the weight imbalance between the lead groove forming portion and the opening forming portion of the shift drum. It is possible to improve the shift feeling at the predetermined shift position.
According to the second aspect of the present invention, the manufacturing process of the shift drum can be simplified, and the supported portion can be integrally formed.
According to the invention described in claim 3, the manufacturing process of the shift drum can be simplified, and the supported portion can be formed integrally.
According to the fourth aspect of the present invention, it is possible to further improve the shift feeling at a predetermined shift position by promoting the weight imbalance between the lead groove forming portion and the opening forming portion of the shift drum.
According to the fifth aspect of the present invention, the portion of the shift drum that opposes the second and third gear positions in the radial direction is relatively light, while the remaining portion of the shift drum that does not form an opening is relatively heavy. Therefore, when this part is moved downward, the shift operation becomes light and the shift feeling is improved. That is, the shift feeling at the predetermined shift position can be improved.
According to the sixth and seventh aspects of the invention, in addition to the function and effect of the first aspect, the shift drum can be easily arranged in the vicinity of the main shaft and the counter shaft, and the shift fork is downsized to provide a shift feeling. Further improvement can be achieved.
According to the eighth aspect of the present invention, oil does not remain in the shift drum, and the return of oil can be improved.

It is a right view of the engine in the Example of this invention. It is an expanded sectional view in alignment with the axis of each axis of the engine. FIG. 3 is a developed cross-sectional view along an axis around a change mechanism of the engine transmission. It is a right view of the said change mechanism. It is sectional drawing which follows the axis line of the shift drum of the said change mechanism. It is sectional drawing orthogonal to the axis line of the said shift drum. It is an expansion | deployment top view of the outer peripheral wall of the said shift drum. (A), (b) is explanatory drawing which shows the effect | action of the change mechanism using the said shift drum. (A), (b) is explanatory drawing which shows the effect | action of the modification of the change mechanism using the said shift drum. It is sectional drawing equivalent to FIG. 6 which shows the modification of the said shift drum.

  Embodiments of the present invention will be described below with reference to the drawings. In the following description, the directions such as front, rear, left and right are the same as those in the vehicle unless otherwise specified. In the figure, the arrow FR indicates the front of the vehicle, the arrow LH indicates the left side of the vehicle, and the arrow UP indicates the upper side of the vehicle.

  1 and 2 has a basic configuration in which a cylinder 3 is erected on a crankcase 2 thereof. The reciprocating motion of the piston 8 in the cylinder 3 is converted into the rotational motion of the crankshaft 9 in the crankcase 2. The crankcase 2 also serves as a transmission case (transmission case) that houses a transmission (transmission) 4. In the following description, it is assumed that the rotation center axis (crank axis) C1 of the crankshaft 9 is along the left-right direction (vehicle width direction).

  The cylinder 3 is configured such that a cylinder block 3a, a cylinder head 3b, and a head cover 3c are sequentially stacked from the crankcase 2 side. A carburetor or throttle body is connected to the rear side (intake side) of the cylinder head 3b, and an exhaust pipe is connected to the front side (exhaust side) of the cylinder head 3b (both not shown). The engine 1 is an air-cooled single cylinder engine, and a large number of air-cooling fins are formed around the cylinder block 3a and the cylinder head 3b. In the drawing, reference numeral C2 indicates an axis (cylinder axis) along the rising direction of the cylinder 3.

  A cylinder bore 3d is formed in the cylinder block 3a along the cylinder axis C2, and a piston 8 is slidably fitted in the cylinder bore 3d. The piston 8 is connected to the crankpin 9a of the crankshaft 9 via the connecting rod 8a, and the reciprocating motion of the piston 8 is converted into the rotational motion of the left and right journals 9c of the crankshaft 9.

  The crankshaft 9 includes left and right crank webs 9b for supporting the crank pins 9a, left and right journals 9c projecting left and right outward from the left and right crank webs 9b, and left and right support shafts 9d extending further left and right outward from the left and right journals 9c. It has. A drive sprocket 12 for driving the camshaft 11 in the cylinder head 3b is provided coaxially on the base end side of the left support shaft 9d.

  The camshaft 11 is disposed in parallel with the crankshaft 9 in the cylinder head 3b, and left and right side portions thereof are rotatably supported by the cylinder head 3b. A driven sprocket 13 is coaxially provided at the left end of the camshaft 11, and the driven sprocket 13 and the drive sprocket 12 are linked via a cam chain 14. A cam chain chamber 15 for accommodating the cam chain 14 is provided in the left side portion of the cylinder 3. The cam chain chamber 15 is provided so as to straddle the cylinder head 3b, the cylinder block 3a, and the crankcase 2.

  When the crankshaft 9 is driven to rotate, the valve system (the camshaft 11 and the intake / exhaust valve (not shown)) of the cylinder head 3b is operated in conjunction with this to open and close the intake / exhaust port of the cylinder head 3b. In the figure, reference numerals 16 and 17 denote a kick arm and a starter motor for starting the engine, reference numeral 16a denotes a kick spindle to which the kick arm 16 is attached, and reference numeral C7 denotes a central axis of the cylindrical starter motor 17.

  The rotational power of the crankshaft 9 is driven by a drive sprocket disposed on the rear left side of the crankcase 2 via a multi-plate clutch 18 disposed on the right side in the crankcase 2 and a transmission 4 disposed on the rear side in the crankcase 2. 19 and is transmitted from the drive sprocket 19 to the drive wheel via a drive chain or the like.

  A primary drive gear 21 is coaxially provided on the right side of the crankshaft 9. The primary drive gear 21 meshes with a relatively large-diameter primary driven gear 22 provided coaxially on the right side of the main shaft 5 of the transmission 4. The main shaft 5 is parallel to the crankshaft 9, and a multi-plate clutch 18 that can be operated by the driver is coaxially provided at the right end portion thereof. A generator 23 is coaxially arranged at the left end of the crankshaft 9.

  In the figure, reference numerals 24 and 25 denote left and right case covers attached to the left and right sides of the crankcase 2, reference numeral 26 denotes a ball bearing for supporting the left and right journals 9c of the crankshaft 9, and reference numerals 27 and 28 denote main shafts 5 respectively. And ball bearings for supporting the left and right sides of the countershaft 6 are shown.

  Here, referring to FIG. 2, the crankcase 2 is divided into left and right case halves 2a and 2b with a mating surface (divided surface) S1 orthogonal to the left and right direction as a boundary. Each of the left and right case halves 2a and 2b is a cast aluminum product that is divided along the left and right directions. The mating surface S1 coincides with the left and right center plane of the engine 1 (and a vehicle equipped with the engine 1).

  The transmission 4 mainly includes a main shaft 5 and a counter shaft 6 parallel to the crankshaft 9 and a transmission gear group 7 supported across the shafts 5 and 6. The rotational power of the crankshaft 9 is appropriately decelerated from the main shaft 5 via an arbitrary gear pair of the transmission gear group 7 and transmitted to the countershaft 6, and is attached to the left end portion of the countershaft 6 outside the crankcase 2. It is transmitted to the drive wheel via the drive sprocket 19 and the like. In addition, the code | symbol C3, C4 in the figure shows the rotation center axis line of each shaft 5 and 6, respectively.

  The transmission gear group 7 is composed of gears corresponding to the number of shift stages respectively supported by the shafts 5 and 6. The transmission 4 is of a constant meshing type in which the corresponding gear pairs of the transmission gear group 7 are always meshed between the shafts 5 and 6. The gears supported by the shafts 5 and 6 are classified into free gears that can rotate with respect to the corresponding shafts and slide gears (shifters) that are spline-fitted to the corresponding shafts. One of these gears is provided with an axially convex dog, and the other is provided with an engaging recess for engaging the dog.

  The gear change of the transmission 4 (sliding of the slide gear) is performed by a gear change mechanism 50 arranged below the gear.

  Referring also to FIG. 3, the gear change mechanism 50 has a plurality of (two in this embodiment) leads formed on the outer periphery thereof by the rotation of a hollow cylindrical shift drum 30 parallel to the shafts 5 and 6. A plurality of (two in this embodiment) shift forks 31 are appropriately operated according to the pattern of the groove (cam groove) 35 to switch the gear pair used for power transmission between the shafts 5 and 6 in the transmission gear group 7. A change spindle 51 parallel to the shift drum 30 is disposed obliquely below and rearward of the shift drum 30, and a shift fork shaft 31 b parallel to the change spindle 51 is disposed above the shift drum 30. In the drawing, reference numerals C5 and C5 'denote central axes along the axial direction of the shift drum 30 and the shift fork shaft 31b, respectively. Reference numeral 7a in the figure indicates the slide gear (shifter) supported by the main shaft 5, for example.

FIG. 4 is a front view of the gear change mechanism 50 (a side view seen from the right side of the engine 1 in a vehicle-mounted state, an arrow view along the axes C5 and C5 ′ (an axial arrow view)).
Referring to FIGS. 3 and 4, the gear change mechanism 50 is rotated integrally with a change spindle 51 and a shift drum 30 that are rotatably supported by the left and right case halves 2 a and 2 b and is welded to the change spindle 51. The change arm 52, the shifter plate 53 held by the change arm 52, the star plate 54 fixed to the right end surface of the shift drum 30, and the stopper roller assembly 55 are mainly used.

  The change spindle 51, the shift drum 30, and the shift fork shafts 31b are arranged in parallel with the crankshaft 9, the main shaft 5, and the counter shaft 6, respectively.

  Here, referring to FIG. 1, the axial line C <b> 3 of the main shaft 5 from the substantially horizontal straight line t connecting the axial line C <b> 1 of the crankshaft 9 and the axial line C <b> 4 of the countershaft 6 in the axial direction view of the shafts 5 and 6. Is also located on the upper side and closer to the countershaft 6. Further, the axis C5 of the shift drum 30 is disposed below the straight line t and closer to the counter shaft 6.

  Referring to FIGS. 1, 3, and 5, the shift drum 30 has lead grooves 35 formed on the outer surface of a cylindrical outer peripheral wall 32, and is rotatable to the left and right case halves 2a and 2b at both ends in the axial direction. The shaft support part 34 supported by is formed. When viewed in the axial direction of the shift drum 30, the axis C <b> 5 is disposed so as to be farther from the straight line t than the axis C <b> 3 of the main shaft 5. A shift fork shaft 31 b that supports the shift fork 31 is located immediately above the shift drum 30. The axis C5 'of the shift fork shaft 31b is disposed so as to be substantially symmetric with respect to the axis C3 of the main shaft 5 and the straight line t.

  3 and 4, the change arm 52 is fixed to one end of the change spindle 51 and extends in two directions with an included angle of about 60 degrees.

  The shifter plate 53 has two long holes 53a and 53b, and feed protrusions 53c and 53d are formed on the back surface of the shifter plate 53, respectively.

  The shifter plate 53 is held on the change arm 52 by guide pins 58 and 59. The guide pins 58 and 59 are gently inserted into the long holes 53 a and 53 b of the shifter plate 53 and are caulked to the change arm 52.

  The guide pin 58 is provided with a biasing spring 60 for the shifter plate 53 having two legs, and the two legs press the feed protrusions 53c and 53d, so that the shifter plate 53 is changed to the change spindle. It is urged to the 51 side.

  The star-shaped plate 54 has a plurality of outer peripheral protrusions 54a on its outer periphery, and has outer peripheral recesses 54b between the outer peripheral protrusions 54a. A plurality of feed pins 54c are press-fitted and protruded from the flat portion of the star plate 54 on the change arm 52 side.

  The star-shaped plate 54 is fixed to the end of the shift drum 30 by mounting bolts 61. The center position of the star plate 54 coincides with the center position of the shift drum 30 (the axis C5).

  On the reference line Y that forms an angle of about 60 degrees with respect to the reference line X that connects the center position of the change spindle 51 and the center position of the shift drum 30, a restriction bolt 56 that stands up from the right case half 2b is provided. .

  In the mutual position state, any of the plurality of feed pins 54c of the star-shaped plate 54 is located between the pair of feed protrusions 53c and 53d of the shifter plate 53.

  A return spring 57 for the change arm 52 is attached to the outer periphery of the change spindle 51. Two leg portions extending from the return spring 57 sandwich the spring receiving portion 52 d at the end of the change arm 52 and the restriction bolt 56.

  When the change arm 52 rotates as the change spindle 51 rotates, the leg portion of the return spring 57 is expanded by the spring receiving portion 52d of the change arm 52 and the restriction bolt 56, and the change arm 52 rotates to a predetermined angle. Move. Thereafter, when the force for rotating the change arm 52 disappears, the change arm 52 returns to the reference position by the resilient force of the return spring 57.

  One end of the stopper roller assembly 55 is swingably supported by a support shaft 63 formed in the crankcase, and a stopper roller 55b is provided at the other end via an arm 55a.

Stopper roller 55b is mounted on the support shaft 63, and is biased by a biasing spring 64 of the stopper roller 55b, which is interposed between the crank case 2 and the arm 55a to the shift drum 30 side, the star plate 54 The outer peripheral recess 54b is elastically fitted.

  Then, when the change spindle 51 is rotated in either the forward or reverse direction by the operation of a change pedal (not shown) by the occupant, the change arm 52 is integrally rotated along with this, and the shifter plate is correspondingly rotated. One of the pair of feed projections 53c, 53d of 53 is engaged with one of the feed pins 54c of the star plate 54 to rotate the star plate 54, and the shift drum 30 to which the star plate 54 is fixed is moved. Rotate. That is, a rotation mechanism 53A for rotating the shift drum 30 in conjunction with the movement of the change arm 52 is configured mainly with the shifter plate 53 and the star plate 54, and the rotation mechanism 53A and the change arm 52 are mainly used. A shift drum drive mechanism 52A is configured.

  When the force for rotating the change spindle 51 becomes zero, the change arm 52 is returned to the reference position by the elastic force of the return spring 57 and the cams 53e and 53f formed on the feed protrusions 53c and 53d of the shifter plate 53 are restored. When one of the feed pins 54c of the star plate 54 abuts on one side, the shifter plate 53 moves away from the change spindle 51 against the biasing force of the biasing spring 60, and the feed projections 53c, 53d One rides over one of the feed pins 54c. Thereby, the star-shaped plate 54 rotates about 60 degrees in one step. The position before and after the rotation of the star plate 54 is stably held when the stopper roller 55b is fitted into one of the outer peripheral recesses 54b of the star plate 54 by the biasing force of the biasing spring 64.

  Referring to FIG. 3, the left and right sides of the change spindle 51 protrude outward from the left and right case halves 2a and 2b. A change pedal (not shown) is directly or indirectly connected to the left end portion of the change spindle 51, and the base end portion of the change arm 52 is welded and fixed to the right end portion of the change spindle 51. The front end side of the change arm 52 is engaged with the left end portion of the shift drum 30 via the shifter plate 53 and the star plate 54 (the rotation mechanism 53A).

  Then, when the change spindle 51 and the change arm 52 perform one reciprocating motion forward and backward by a predetermined angle, the shift drum 30 rotates by a predetermined angle (about 60 degrees) in one direction via the rotation mechanism 53A. As the shift fork 31 moves in the axial direction along the lead groove 35 of the shift drum 30, the gear position of the transmission 4 is changed to an arbitrary gear position.

  Referring also to FIG. 1, each shift fork 31 is disposed between the shift drum 30 and the main shaft 5 or the counter shaft 6, and these pass through the single shift fork shaft 31 b so as to be movable in the axial direction. Supported. Both ends of the shift fork shaft 31b are pivotally supported by the left and right case halves 2a and 2b.

  6 and 7 together, each lead groove 35 of the shift drum 30 extends in the circumferential direction while displacing in the direction along the axis C5. In this example, five shift positions p1 to p4 and pn obtained by adding neutral to the fourth gear) are defined.

  At the upper end of the shift drum 30, each lead groove 35 is engaged with a shift pin 31 a protruding downward from a base portion through which the shift fork shaft 31 b of the shift fork 31 is inserted. When the shift drum 30 rotates in this state, the shift pin 31a moves between the shift positions along the lead groove 35, and the shift fork 31 is displaced in the direction along the axis C5 '. The front end of the shift fork 31 is bifurcated, and the front end engages with the slide gear 7 a of the transmission gear group 7. As a result, the slide gear 7a also moves in the axial direction as the shift fork 31 moves in the axial direction, and the gear position of the transmission gear group 7 of the transmission 4 is changed to change the gear position.

  Here, referring to FIGS. 5 to 7, an opening 36 for opening the internal space of the shift drum 30 to the outside is formed on one side of the outer peripheral wall 32 of the shift drum 30. The outer peripheral wall 32 of the shift drum 30 forms the lead groove 35 in a substantially half-circumferential range and the opening 36 in the remaining substantially half-circumferential range. In the state where the transmission 4 is in each gear position from the first speed to the fourth speed, the opening 36 is shifted when at least a part thereof is located below the axis C5 of the shift drum 30 and directed downward from the horizontal direction. This prevents the engine oil from remaining in the drum 30. Hereinafter, the lead groove forming portion in the outer peripheral wall 32 is denoted by reference numeral 32a, and the opening forming portion is denoted by reference numeral 32b.

  Further, here, the shift drum 30 is formed into a cylindrical shape by casting (or forging) using an inner mold (core mold) that forms the inner peripheral side (internal space) and an outer mold (cavity mold) that forms the outer peripheral side. The outer peripheral wall 32, the right and left side wall portions 33 that close both ends of the outer peripheral wall 32, and the left and right shaft support portions 34 that protrude from the left and right side wall portions 33 to the left and right sides are integrally formed. The manufacture is completed by machining only the left and right shaft support portions 34. The inner mold enters and exits the inside and outside of the shift drum 30 through the opening 36. At this time, the inner mold passes through the central portion of the opening 36 along the radial direction of the shift drum 30. (See FIG. 6).

  Referring to FIG. 6, the lead groove 35 of the outer peripheral wall 32 is formed beyond the half circumference of the outer peripheral wall 32 for the convenience of forming the end portion in a bag shape. For this reason, the lead groove forming portion 32 a is provided in a range exceeding a half circumference of the outer peripheral wall 32, and the opening forming portion 32 b is provided in a range less than a half circumference of the outer peripheral wall 32. In order to prevent the width in the circumferential direction of the opening 36 from being narrowed and affecting the die cutting of the inner mold, the cutout portions 32c are provided on the inner peripheral side of both end portions in the circumferential direction of the lead groove forming portion 32a. Thereby, the total width h1 of the opening 36 is not made narrower than the total width (diameter) h2 of the inner peripheral surface of the outer peripheral wall 32 (lead groove forming portion 32a).

  The lead groove 35 defines the shift positions p1 to p4 with an interval of about 60 degrees at an angle centered on the axis C5 of the shift drum 30 in the order of first speed, second speed, third speed, and fourth speed. A neutral position pn is defined between the first and second speed positions p1 and p2. That is, the number of shift stages of the transmission 4 is four. The opening 36 is formed in a range between the first speed (low) and fourth speed (top) positions p1 and p4 and opposed to the second speed and third speed positions p2 and p3 in the radial direction. .

  Here, the opening forming portion 32b in the shift drum 30 is relatively light, while the lead groove forming portion 32a in the shift drum 30 relatively increases the weight. Due to such a weight imbalance in the circumferential direction (rotation direction) of the shift drum 30, the shift operation is lightened when the lead groove forming portion 32 a is moved downward. In addition, the code | symbol g in a figure shows the gravity center position of the outer peripheral wall 32 (lead groove formation part 32a).

  Specifically, as shown in FIG. 8, in this embodiment, the shift fork 31 is engaged with the shift drum 30 from above, so that the engagement position is changed from the neutral position pn or the second speed position p2 to the first speed position p1. 8 (when switching from neutral or second speed to first speed, see FIG. 8A), and when changing from the third speed position p3 to the fourth speed position p4 (when switching from third speed to fourth speed, FIG. (See (b)), since the center of gravity position g moves downward, the shift operation is lightened and the shift feeling is improved.

Depending on the position where the shift fork 31 engages with the shift drum 30, the shift operation at different shift positions becomes light.
Specifically, for example, as shown in FIG. 9, when the shift fork 31 is engaged with the lower end portion of the shift drum 30 from below, the engagement position is changed from the first speed position p1 to the neutral position pn or the second speed. When changing to the position p2 (when switching from the first speed to the neutral or second speed, see FIG. 9A) and when changing from the fourth speed position p4 to the third speed position p3 (when switching from the fourth speed to the third speed, The shift operation becomes lighter as shown in FIG.

  Then, as in the shift drum 30 ′ shown in FIG. 10, in order to promote the above-described operation, the portion (the center of gravity position g of the center of gravity position g) over the second and third speed positions p2 and p3 on the inner peripheral side of the lead groove forming portion 32a. For example, a configuration in which a weight portion 37 formed by thickening the outer peripheral wall 32 with respect to another portion may be provided on the periphery).

  As described above, the shift drum 30 in the above embodiment has the lead groove 35 formed in the cylindrical outer peripheral wall 32 and is rotatably supported by the transmission case (crankcase 2) at the end in the axial direction. The shaft support 34 is formed, and the shift fork 31 is moved along the lead groove 35 along with the rotation of the shift drum 30 to switch the gear position of the transmission 4. An opening 36 for removing an inner mold for forming an internal space of the shift drum 30 is formed in a range where the outer peripheral wall 32 is formed in a substantially half-circumferential range and the lead groove 35 of the outer peripheral wall 32 is not formed. Is.

  According to this configuration, the hollow cylindrical shift drum 30 can be integrally formed without using a core, and the manufacturing cost of the shift drum 30 can be reduced. Further, the shift drum 30 can be reduced in weight by providing the opening 36 for punching in a range where the lead groove 35 of the shift drum 30 is not formed. Further, when the shift drum 30 is rotated so that the lead groove 35 side (non-opening side) of the shift drum 30 is moved downward, the weight imbalance between the lead groove forming portion 32a and the opening forming portion 32b of the shift drum 30 is caused. The rotation of the shift drum 30 can be promoted, and the shift feeling at a predetermined shift position can be improved.

  Further, the shift drum 30 is formed by casting or forging using an outer mold that forms the outer peripheral side and an inner mold that forms the inner peripheral side, and the inner mold is extracted from the opening 36 so that the shift drum 30 is shifted. The manufacturing process of the drum 30 can be simplified, and the shaft support portion 34 can be integrally formed.

  Further, the shift drum 30 is further provided with a weight portion 37 in the lead groove forming portion 32a, thereby promoting weight imbalance between the lead groove forming portion 32a and the opening forming portion 32b and shifting at a predetermined shift position. Feeling can be further improved.

  In the shift drum 30, the lead grooves 35 are arranged at shift positions p1 to p4 at intervals of about 60 degrees in the axial center angle of the shift drum 30 in the order of first speed, second speed, third speed, and fourth speed. And a neutral position pn is defined between the first-speed and second-speed positions p1, p2, and the second-speed and third-speed positions between the first-speed and fourth-speed positions p1, p4 in the shift drum 30 Since the opening 36 is formed in a portion facing the p2 and p3 in the radial direction, the portion facing the second and third speed positions p2 and p3 in the shift drum 30 in the radial direction is relatively light, while the shift is performed. Since the remaining portion of the drum 30 where the opening 36 is not formed becomes relatively heavy, the shift operation becomes lighter and the shift feeling is improved when the portion is moved downward. That is, the shift feeling at the predetermined shift position can be improved.

  Here, the engine 1 including the shift drum 30 includes a shift drum driving mechanism 52A including a change arm 52 operated by a passenger and a rotation mechanism 53A that rotates the shift drum 30 according to the movement of the change arm 52. The shift fork 31 engages with the lead groove 35 at the substantially vertical upper end of the shift drum 30, and the shaft center (axis C 1) of the crankshaft 9 and the countershaft of the transmission 4 as viewed in the axial direction of the engine 1. The axis center (axis C3) of the main shaft 5 of the transmission 4 is arranged above the straight line t connecting the axis center 6 (axis C4), and the axis center (axis line) of the shift drum 30 is below the straight line t. C5) is arranged and the main shaft 5 and the shaft 5 are connected via a shift fork 31 engaged with the shift drum 30. Shifter on the counter shaft 6 (slide gears 7a) is for moving.

  According to this configuration, in addition to the effects of the shift drum 30 described above, the shift drum 30 can be easily disposed in the vicinity of the main shaft 5 and the counter shaft 6, and the shift fork 31 can be downsized to further improve the shift feeling. be able to.

Note that the present invention is not limited to the above-described embodiment, and for example, the shift drum having the above-described structure may be used for a transmission (engine) having a gear number other than four. The engine to be applied may be an internal combustion engine of various types, such as a parallel or V-type multi-cylinder engine, and a vertical engine with a crankshaft along the front-rear direction.
And the structure in the said Example is an example of this invention, and it cannot be overemphasized that a various change is possible in the range which does not deviate from the summary of the said invention.

1 engine (internal combustion engine)
2 Crankcase (transmission case)
4 Transmission (transmission)
5 Main shaft 6 Counter shaft 7a Slide gear (shifter)
9 Crankshaft (Crankshaft)
C1, C3, C4, C5 Axis t straight line 30, 30 ' shift drum 31 shift fork 32 outer peripheral wall 32a lead groove forming part 34 shaft support part (supported part)
35 Lead groove 36 Opening 37 Weight part p1 First speed position (shift position)
p2 2nd gear position (shift position)
p3 Third gear position (shift position)
p4 4th gear position (shift position)
pn Neutral position (shift position)
52 Change arm (shift arm)
52A Shift drum drive mechanism 53A Rotation mechanism

Claims (8)

A shift drum (30, 30 ′) in which a lead groove (35) is formed in a cylindrical outer peripheral wall (32) and a supported portion is rotatably supported in the transmission case (2) at an axial end. ) And
The shift drum (30, 30 ′) that switches the gear position of the transmission (4) by moving the shift fork (31) along the lead groove (35) as the shift drum (30, 30 ′) rotates. In
The lead groove (35) is formed in a range that is substantially half the circumference of the outer peripheral wall (32) and more than half of the circumference. 30 ') is formed with an opening (36) for removing the inner mold for forming the internal space ,
The shift drum according to claim 1, wherein a thinned portion (32 c) is provided on an inner peripheral side of both ends in a circumferential direction of a portion where the lead groove (35) is formed in the outer peripheral wall (32) .   The shift drum (30, 30 ′) is formed by casting using an outer mold that forms the outer peripheral side and an inner mold that forms the inner peripheral side, and the inner mold is extracted from the opening (36). The shift drum according to claim 1.   The shift drum (30, 30 ′) is formed by forging using an outer mold that forms the outer peripheral side and an inner mold that forms the inner peripheral side, and the inner mold is extracted from the opening (36). The shift drum according to claim 1.   The shift drum according to any one of claims 1 to 3, wherein a weight portion (37) is provided in the lead groove forming portion (32a) of the shift drum (30, 30 ').   The lead groove (35) has a shift position (p1 to p4) at an interval of about 60 degrees in the axial center angle of the shift drum (30, 30 ′) in the order of 1st speed, 2nd speed, 3rd speed, and 4th speed. And a neutral position (pn) is defined between the first speed and second speed positions (p1, p2), and the shift drum (30, 30 ') has the first speed and fourth speed positions (p1, p2). 5. The opening according to claim 1, wherein the opening (36) is formed at a position between the second speed and the third speed positions (p 2, p 3) in the radial direction between p 4). The described shift drum. In an internal combustion engine (1) comprising a shift drum (30, 30 ') according to any one of claims 1 to 5,
A shift drum drive mechanism (52A) is composed of a shift arm (52) operated by a passenger and a rotation mechanism (53A) that rotates the shift drum (30, 30 ') in accordance with the movement of the shift arm (52). An internal combustion engine in which a shift fork (31) is engaged with a lead groove (35) at a substantially vertical upper end of the shift drum (30, 30 ').   A straight line (t) connecting the shaft center (C1) of the crankshaft (9) and the shaft center (C4) of the counter shaft (6) of the transmission (4) as viewed in the axial direction of the internal combustion engine (1). The shaft center (C3) of the main shaft (5) of the transmission (4) is disposed above, and the shaft center (C5) of the shift drum (30, 30 ′) is disposed below the straight line (t). The shifter (7a) on the main shaft (5) and the counter shaft (6) is moved via a shift fork (31) engaged with the shift drum (30, 30 '). 6. The internal combustion engine according to 6. The shift drum (30, 30 ′) includes at least first to fourth gears, and the opening (36) is at least partially a shaft of the shift drum (30, 30 ′) in each gear. The internal combustion engine according to claim 6 or 7, wherein the internal combustion engine is located below the center (C5) and directed downward from the horizontal direction .

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