JP2012167651A - Balancer shaft support structure for motorcycle engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a balancer shaft support structure for a motorcycle engine, wherein the structure allows high-accuracy assembly of a balancer shaft in a crank case and can prevent generation of vibration or abnormal sound.SOLUTION: The balancer shaft support structure for a motorcycle engine includes: a crank case 31 having an upper crank case 38 and a lower crank case 39; a crankshaft 42 having a rotational axis located on a division plane 53 between the upper crank case 38 and the lower crank case 39; a first balance shaft 48 having a rotational axis parallel to the rotational axis of the crankshaft 42 and spaced from the division plane 53; a bearing 78 journaling the balance shaft; and a splittable bearing holding part 79 holding the bearing 78.

Description

  The present invention relates to a balancer shaft support structure for a motorcycle engine.

  2. Description of the Related Art There is known a two-axis balancer shaft support structure for a motorcycle engine that includes a pair of balancer shafts having a rotation axis located in parallel with the rotation axis of the crankshaft.

  In addition, the conventional balancer shaft support structure for a motorcycle engine has a structure in which the pair of balancer shafts are arranged in front of and behind the crankshaft or above and below the crankshaft in order to prevent the engine from becoming large. The balancer shafts are arranged at the same time, and a line passing through the rotation axis of both balancer shafts is positioned in front of the rotation axis of the crankshaft (see, for example, Patent Document 1).

JP-A-2-113145

  By the way, since a crankcase receives the high load by the reciprocating motion of a piston, high rotation accuracy is required.

  Therefore, a conventional engine includes a crankcase that can be divided into two parts, an upper half and a lower half, and a crankshaft that has a rotation axis located on a division plane of the upper half and the lower half. Prepare. The conventional engine can be assembled with high dimensional accuracy by supporting the crankshaft between the upper half and the lower half so that the rotation accuracy of the crankshaft is improved.

  On the other hand, in the conventional balancer shaft support structure for a motorcycle engine, the balancer shaft is arranged at the front lower side and the rear upper side of the crankshaft, and a line passing through the rotation axis of both balancer shafts is arranged from the rotation axis of the crankshaft. In addition, it is located on the front side, avoiding the enlargement of the engine. In this case, the rotation axis of the balancer shaft is positioned away from the split surface of the crankcase (the split surface of the upper half and the lower half), and the bearing of the balancer shaft is separated from the split surface of the crankcase. Located apart.

  Therefore, a conventional balancer shaft support structure for a motorcycle engine includes a support shaft that is inserted into the crankcase through an opening in the side wall of the crankcase, a bearing that is arranged in advance in the crankcase together with the balancer shaft, and an outer diameter of the bearing. And a balancer shaft having a hole through which the support shaft passes along with the inner diameter of the bearing while being held. In the conventional balancer shaft support structure for a motorcycle engine, first, a balancer shaft having a bearing fitted in advance in a hole is disposed in the crankcase, and then the support shaft is inserted into the crankcase from the opening of the crankcase side wall. The balancer shaft is rotatably supported by being inserted and passed through the inner diameter of the bearing and the hole of the balancer shaft and fixed to the crankcase.

  However, the conventional balancer shaft support structure for a motorcycle engine requires that a clearance be provided between the support shaft and the bearing because the support shaft needs to be passed through the bearing when the balancer shaft is assembled to the crankcase. From the viewpoint of assembly accuracy, it is difficult to keep the rotation accuracy of the balancer shaft high. In addition, the conventional balancer shaft support structure for a motorcycle engine may further reduce the rotation accuracy of the balancer shaft if the gap between the support shaft and the bearing is widened due to uneven temperature distribution of the support shaft and the bearing. is there. Conventional balancer shaft support structures for motorcycle engines may generate vibration and noise due to a decrease in rotational accuracy of these balancer shafts.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a balancer shaft support structure for a motorcycle engine that can assemble a balancer shaft to a crankcase with high accuracy and prevent vibration and noise.

  In order to solve the above problems, a balancer shaft support structure for a motorcycle engine according to the present invention includes a crankcase having a first case half and a second case half, the first case half, and the second case half. A crankshaft having a rotation axis positioned on a split surface with the case half, a balancer shaft having a rotation axis parallel to the rotation axis of the crankshaft and spaced from the split surface, and the balancer shaft And a bearing holder that holds the bearing and can be divided.

  ADVANTAGE OF THE INVENTION According to this invention, the balancer shaft support structure of the engine for motorcycles which can assemble | balance a balancer shaft to a crankcase with high precision and can prevent generation | occurrence | production of a vibration and abnormal noise can be provided.

1 is a left side view showing a motorcycle to which a balancer shaft support structure for a motorcycle engine according to an embodiment of the present invention is applied. 1 is a right side view showing an engine to which a balancer shaft support structure for a motorcycle engine according to an embodiment of the present invention is applied. Sectional drawing which shows the engine which applies the balancer shaft support structure of the motorcycle engine which concerns on embodiment of this invention in the III-III line of FIG. 1 is a right side view showing an engine to which a balancer shaft support structure for a motorcycle engine according to an embodiment of the present invention is applied. 1 is a right side view showing an engine to which a balancer shaft support structure for a motorcycle engine according to an embodiment of the present invention is applied. 1 is a perspective view showing a clutch chamber of an engine to which a balancer shaft support structure for a motorcycle engine according to an embodiment of the present invention is applied. 1 is a perspective view showing an engine to which a balancer shaft support structure for a motorcycle engine according to an embodiment of the present invention is applied. 1 is a perspective view showing an engine to which a balancer shaft support structure for a motorcycle engine according to an embodiment of the present invention is applied.

  An embodiment of a balancer shaft support structure for a motorcycle engine according to the present invention will be described with reference to the drawings.

  FIG. 1 is a left side view showing a motorcycle to which a balancer shaft support structure for a motorcycle engine according to an embodiment of the present invention is applied.

  In the present embodiment, front and rear, top and bottom, and left and right expressions are based on the rider who rides the motorcycle 1.

  As shown in FIG. 1, a motorcycle 1 to which a balancer shaft support structure for a motorcycle engine according to the present embodiment is applied includes a body frame 2, a front wheel 5 positioned in front of the body frame 2, and a body frame 2. A steering mechanism 6 that is positioned forward and rotatably supports the front wheel 5, a rear wheel 7 that is positioned rearward of the body frame 2, and a rear wheel 7 that extends rearward of the body frame 2 and rotatably supports the rear wheel 7. A swing arm 8 and an engine 10 as an internal combustion engine located in the lower center of the vehicle body are provided.

  The vehicle body frame 2 is, for example, a twin tube type, and a pair of left and right main frames 12 that extend in a pair in the left-right direction immediately after the head pipe 11 positioned at the front upper end and extend downward and obliquely downward in parallel to each other. A pair of left and right center frames 13 connected to the rear end portion of the main frame 12 and extending substantially upward and downward, and a pair of left and right seat rails 15 extending rearward from the rear upper end portion of the center frame 13 are provided.

  The main frame 12 also serves as a tank rail, supports the fuel tank 16 positioned above the main frame 12, and suspends the engine 10 below the fuel tank 16. The seat rail 15 supports a rider seat 17 located in the upper front half and a pillion seat 18 located in the upper rear half. The main frame 12 is provided with a pivot shaft 19 that is supported at a substantially central lower portion of the left and right center frames 13 and pivotally supports the swing arm 8 so as to be swingable in the vertical direction.

  The steering mechanism 6 includes a pair of left and right front forks 21 that include a suspension mechanism (not shown) and rotatably support the front wheels 5, and a handle bar 22. The rider steers the front wheel 5 left and right by the handle bar 22.

  The engine 10 is connected to an exhaust pipe 25 that extends rearward of the vehicle body and exhausts the exhaust gas of the engine 10. The rear end of the exhaust pipe 25 is connected to the exhaust muffler 26.

  The rear wheel 7 includes a driven sprocket 27.

  The motorcycle 1 includes a drive chain 28 that is wound around a driven sprocket 27 and transmits a driving force from the engine 10.

  Furthermore, the motorcycle 1 includes a streamlined cowling 29 that covers the front portion of the vehicle body. The cowling 29 reduces air resistance during traveling and protects the rider from traveling wind pressure.

  Next, the engine 10 to which the balancer shaft support structure for a motorcycle engine is applied will be described in detail.

  FIG. 2 is a right side view showing an engine to which a balancer shaft support structure for a motorcycle engine according to an embodiment of the present invention is applied.

  As shown in FIG. 2, an engine 10 to which the balancer shaft support structure for a motorcycle engine according to the present embodiment is applied is a four-cycle multi-cylinder engine, for example, a four-cycle in-line four-cylinder engine. A block 32, a cylinder head 33, a head cover 35, an oil pan 36, and a clutch mechanism 37 are provided.

  The crankcase 31 can be divided into two vertically, and includes an upper crankcase 38 as a first case half and a lower crankcase 39 as a second case half.

  The cylinder block 32 is located at the upper part of the upper crankcase 38 and is inclined slightly forward from the upright position. The cylinder block 32 has a cylinder bore (not shown) that houses a piston (not shown) so as to be slidable in a substantially vertical direction.

  The cylinder head 33 closes the upper part of the cylinder bore and partitions a combustion chamber (not shown) between the cylinder head 33 and the piston. The piston reciprocates by the combustion of the air-fuel mixture that occurs periodically in the combustion chamber.

  The oil pan 36 is assembled to the lower part of the lower crankcase 39.

  The clutch mechanism 37 is a dry clutch. The clutch cover 41 is assembled to the side wall of the crankcase 31 and partially covers the clutch mechanism 37.

  3 is a cross-sectional view showing an engine to which the balancer shaft support structure for a motorcycle engine according to an embodiment of the present invention is applied, taken along line III-III in FIG.

  As shown in FIGS. 2 and 3, the engine 10 includes a crankshaft 42, an input shaft 45 and an output shaft 46 of the speed change mechanism 43, a first balancer shaft 48, a second balancer shaft 49, and an auxiliary machine connection. A generator shaft 51 as a shaft and a pump driving shaft 52 are provided.

  The central axes of the crankshaft 42, the input shaft 45, the output shaft 46, the first balancer shaft 48, the second balancer shaft 49, the generator shaft 51 and the pump drive shaft 52 are positioned in parallel to each other so that the width direction of the engine 10 Extend to.

  The crankshaft 42, the input shaft 45, and the second balancer shaft 49 have rotation axes that are located on the dividing surface 53 between the upper crankcase 38 and the lower crankcase 39. In other words, the split surface 53 of the crankcase 31 is located on a plane including the respective rotation axes of the crankshaft 42, the input shaft 45, and the second balancer shaft 49.

  The crankshaft 42 is in a crank chamber 54 in which the upper crankcase 38 and the lower crankcase 39 cooperate to partition. The crankshaft 42 has a rotation axis located below the cylinder block 32, more specifically in the vicinity of a position where an extension line of the cylinder center line and the dividing surface 53 intersect. The crankcase 31 includes a journal bearing 55 that has a bearing half 55a of the upper crankcase 38 and a bearing half (not shown) of the lower crankcase 39 and rotatably supports the crankshaft 42.

  The crankshaft 42 is connected to the piston via a connecting rod 56, and converts the reciprocating motion of the piston into a rotational motion. The crankshaft 42 includes a rotation-integrated primary drive gear 58 that transmits a rotational force to the input shaft 45.

  The input shaft 45 is located behind the crankshaft 42 and is connected to the clutch mechanism 37. The input shaft 45 rotatably supports a primary driven gear 59 that meshes with the primary drive gear 58. The input shaft 45 includes a plurality of stages of mission drive gears 61.

  The clutch mechanism 37 is located in a clutch chamber 81 where the upper crankcase 38 and the lower crankcase 39 cooperate and partition. The clutch mechanism 37 includes a primary driven gear 59. The clutch mechanism 37 rotates and unifies or rotates the primary driven gear 59 with respect to the input shaft 45 by the intermittent connection, and transmits or blocks the rotational force between the crankshaft 42 and the input shaft 45.

  The generator shaft 51 is positioned obliquely in front of the input shaft 45. The generator shaft 51 includes a rotation-integrated generator-driven gear 62 that meshes with the primary driven gear 59, and a rotation-integrated balancer drive gear 63 that transmits a rotational force to the first balancer shaft 48. The generator shaft 51 is connected to a generator 65 as an auxiliary machine. The generator shaft 51 drives the generator 65 to drive power generation. In addition to the generator 65, the generator shaft 51 can be connected to, for example, a starter motor (not shown) for starting the stopped engine 10 as an auxiliary machine.

  The first balancer shaft 48 has a rotation axis that is separated from the split surface 53 of the crankcase 31 and is located on the cylinder side of the input shaft 45 of the speed change mechanism 43. The rotation axis of the first balancer shaft 48 is located more biased toward the crankshaft 42 than the plane including the rotation axis of the input shaft 45 and the rotation axis of the generator shaft 51. The first balancer shaft 48 is located between the crankshaft 42 and the input shaft 45 and is located between the input shaft 45 and the generator shaft 51. The first balancer shaft 48 includes a rotation-integrated first balancer driven gear 67 that meshes with the balancer drive gear 63.

  That is, the rotational force of the crankshaft 42 is transmitted to the first balancer shaft 48 via the speed change mechanism 43. More specifically, the rotational force of the crankshaft 42 passes through the primary drive gear 58, the primary driven gear 59, the generator driven gear 62, the generator shaft 51, the balancer drive gear 63, and the first balancer driven gear 67 in order. It is transmitted to the balancer shaft 48.

  The generator driven gear 62 is a gear having the same specifications (the same diameter and the same number of teeth) as the primary drive gear 58, and rotates the generator shaft 51 in the same direction and in the same direction as the crankshaft 42. On the other hand, the first balancer driven gear 67 is a gear having the same specifications (the same diameter and the same number of teeth) as the balancer drive gear 63, and the first balancer shaft 48 rotates in the opposite direction to the generator shaft 51 at the same rotational speed. To drive. As a result, the first balancer shaft 48 is rotationally driven at the same rotational speed as the crankshaft 42 and in the opposite direction.

  On the other hand, the second balancer shaft 49 is positioned in front of the crankshaft 42 and faces the input shaft 45 of the speed change mechanism 43 with the crankshaft 42 interposed therebetween. The crankcase 31 includes a journal bearing 71 that has a bearing half 71a of the upper crankcase 38 and a bearing half (not shown) of the lower crankcase 39 and rotatably supports the crankshaft 42. Similarly, the second balancer shaft 49 is rotatably supported.

  Further, the second balancer shaft 49 includes a rotation-integrated second balancer driven gear 72 that meshes with the primary drive gear 58. The second balancer driven gear 72 is a gear having the same specifications (same diameter and number of teeth) as the primary drive gear 58, and drives the second balancer shaft 49 to rotate in the same rotational speed as the crankshaft 42 and in the opposite direction. .

  The pump drive shaft 52 is positioned in front of the second balancer shaft 49 and faces the first balancer shaft 48 with the crankshaft 42 interposed therebetween. The pump drive shaft 52 includes a pump driven gear (not shown) that meshes with the second balancer driven gear 72. The pump driving shaft 52 drives an oil pump (not shown) to draw up engine oil from the oil pan 36 and supply it to each part of the engine 10.

  By the way, the engine 10 is an unequally spaced explosion engine having different explosion timing intervals between a plurality of (four in the present embodiment) cylinders, and generates torque fluctuations in the crankshaft 42. In this rhythm, the rear wheel 7 grips the road surface and obtains traction more than the equidistant explosion engine. However, in the unequal interval explosion engine, the primary vibration of the engine 10 increases due to the rotational inertia of the crank weight 42a of the crankshaft 42 in addition to the inertial force accompanying the reciprocating motion of the piston. Therefore, the engine 10 includes a first balancer shaft 48 and a second balancer shaft 49 as vibration suppression mechanisms that cancel the rotational inertia of the crankshaft in order to suppress primary vibration of the engine 10. The first balancer shaft 48 and the second balancer shaft 49 rotate in the opposite direction at the same rotational speed as that of the crankshaft 42, thereby canceling the inertial force generated in the piston and the crank weight 42a, thereby generating the primary vibration of the engine 10. Suppress.

  The first balancer shaft 48 includes a first balancer weight 73 having a through hole 73a, and a first balancer support shaft 75 that penetrates the through hole 73a and is integrally rotated with the first balancer weight 73. On the other hand, the second balancer shaft 49 includes a second balancer weight 76 having a through hole 76a, and a second balancer support shaft 77 that penetrates the through hole 76a and is integrally rotated with the second balancer weight 76.

  The crankcase 31 is pivotally supported by the journal bearing 71 (that is, the bearing half 71a of the upper crankcase 38 and the bearing half of the lower crankcase 39) so as to sandwich the second balancer shaft 49 therebetween. The rotational accuracy of the balancer shaft 49 is increased.

  On the other hand, since the first balancer shaft 48 has a rotation axis that is separated from the split surface 53 of the crankcase 31, it is difficult to sandwich the first balancer shaft 48 between the upper crankcase 38 and the lower crankcase 39 like the second balancer shaft 49.

  Therefore, the balancer shaft support structure for a motorcycle engine according to the present embodiment includes a bearing 78 that supports the first balancer shaft 48 and a bearing holding portion 79 that holds the bearing 78 and can be divided.

  Next, the bearing 78 and the bearing holding portion 79 will be described in detail.

  4 and 5 are right side views showing an engine to which the balancer shaft support structure for a motorcycle engine according to the embodiment of the present invention is applied.

  FIG. 6 is a perspective view showing a clutch chamber of an engine to which the balancer shaft support structure for a motorcycle engine according to the embodiment of the present invention is applied.

  As shown in FIG. 4, when the clutch cover 41 is removed from the crankcase 31, the engine 10 exposes the clutch mechanism 37 toward the right side of the engine 10. The clutch mechanism 37 covers the bearing 78 when viewed in the rotational axis direction of the first balancer shaft 48.

  Next, as shown in FIGS. 5 and 6, when the engine 10 integrally removes the primary drive gear 58 and the clutch mechanism 37 from the input shaft 45, the engine 10 moves the first balancer shaft 48 toward the right side of the engine 10. The bearing 78 and the bearing holding portion 79 that support the shaft and the speed change mechanism 43 are exposed. In FIG. 6, the bearing 78 is not shown.

  The bearing holding portion 79 is a second bearing integrated with the first bearing holding half portion 79 a located adjacent to the mission cover 85 located in the mission chamber 82 and the crankcase 31 (more specifically, the upper crankcase 38). A holding half 79b, and a fastening member 95 that couples the first bearing holding half 79a and the second bearing holding half 79b are provided. Note that the second bearing holding half 79b may also be removable from the crankcase 31.

  FIG. 7 is a perspective view showing an engine to which a balancer shaft support structure for a motorcycle engine according to an embodiment of the present invention is applied.

  As shown in FIG. 7, the speed change mechanism 43 of the engine 10 is a unit type speed change mechanism that can be integrally inserted into and removed from the inside and outside of the transmission chamber 82 that the upper crankcase 38 and the lower crankcase 39 cooperate to partition. The speed change mechanism 43 includes an input shaft 45 and an output shaft 46 whose rotation axis directions are parallel to each other, a mission cover 85 as a shaft support member that supports the input shaft 45 and the output shaft 46, and a shift mechanism 86. .

  The output shaft 46 is located below the input shaft 45. The output shaft 46 includes a plurality of stages of mission driven gears 88 that mesh with the mission drive gear 61 of the input shaft 45, and a drive sprocket 89. The drive sprocket 89 is located at the left shaft end portion of the output shaft 46 that protrudes outward from the left side of the crankcase 31. The drive sprocket 89 transmits the driving force of the engine 10 to the driven sprocket 27 via the drive chain 28 and drives the rear wheel 7. That is, the rotational force of the crankshaft 42 (driving force of the engine 10) generated by the engine 10 is transmitted to the input shaft 45 through the primary drive gear 58, the primary driven gear 59 and the clutch mechanism 37, and is transmitted to the mission drive gear 61 and the mission driven. The rotation speed and torque are adjusted by the gear 88 and transmitted to the output shaft 46. Thereafter, the driving force of the engine 10 is transmitted to the rear wheel 7 through the drive sprocket 89, the drive chain 28, and the driven sprocket 27 in order.

  The shift mechanism 86 includes a shift cam 91 having a rotation axis parallel to the output shaft 46, a shift fork shaft 92 having a center line parallel to the shift cam 91, and the shift cam 91 moving in the direction of the center line of the shift fork shaft 92. A shift fork 93 that rotates and integrates any of the driven gears 88 with the output shaft 46.

  On the other hand, when the transmission mechanism 43 is taken out from the transmission chamber 82, the bearing holding portion 79 is in a state in which the first bearing holding half 79a and the second bearing holding half 79b can be divided.

  FIG. 8 is a perspective view showing an engine to which a balancer shaft support structure for a motorcycle engine according to an embodiment of the present invention is applied.

  As shown in FIG. 8, when the bearing holding portion 79 of the balancer shaft support structure for a motorcycle engine releases the fastening of the fastening member 95 and removes the first bearing holding half 79a from the second bearing holding half 79b. The space in which the speed change mechanism 43 is located communicates with the bearing holding hole 79c that holds the bearing 78. In this state, the first balancer shaft 48 can be easily placed or taken out inside and outside the mission chamber 82 through the space in which the speed change mechanism 43 is located (broken line arrow in FIG. 8).

  The bearing holding portion 79 according to the present embodiment holds the bearing 78 so as to sandwich the bearing 78 by coupling the first bearing holding half 79a and the second bearing holding half 79b. The bearing 78 can be firmly held without a slight gap therebetween. As a result, the balancer shaft support structure for a motorcycle engine according to the present embodiment can increase the dimensional accuracy related to the holding of the bearing 78 and increase the rotational accuracy of the first balancer shaft 48.

  The balancer shaft support structure for a motorcycle engine according to the present embodiment configured as described above is configured to hold the bearing 78 supporting the first balancer shaft 48 so as to be sandwiched by the severable bearing holding portion 79. No extra clearance required by the balancer shaft support structure of a conventional motorcycle engine is required, and the assembly accuracy of the first balancer shaft 48 is increased, which in turn increases the rotation accuracy to prevent vibration and noise. it can.

  Here, the balancer shaft support structure of the conventional motorcycle engine is separated from the split surface of the crankcase, so that the balancer shaft together with the crankshaft is required even though a sufficient clearance is required for assembly of the balancer shaft. Place in the crankcase. Such a conventional balancer shaft support structure for a motorcycle engine has a large heat input to the balancer shaft, the support shaft and the bearing, and the gap is widened due to the difference in thermal expansion, and the rotation accuracy of the balancer shaft is further reduced. And there is a risk of generating abnormal noise.

  Therefore, in the balancer shaft support structure for a motorcycle engine according to the present embodiment, the first balancer shaft 48 is disposed on the mission chamber 82 side, which is different from the crank chamber 54, and the rotational force is transmitted via the speed change mechanism 43. As a result, the heat transmitted from the crank chamber 54 or the crankshaft 42 is suppressed, and thus the decrease in the rotation accuracy of the first balancer shaft 48 due to the heat effect is suppressed, and as a result, the rotation accuracy is increased to prevent the generation of vibration and noise. it can.

  In addition, the balancer shaft support structure for a motorcycle engine according to the present embodiment cools the clutch mechanism 37, which is a dry clutch, by introducing outside air into the clutch chamber 81. The bearing 78 is concealed by the clutch mechanism 37 so that mud sand does not adhere, and the bearing 78 can be protected from losing its function. The balancer shaft support structure for a motorcycle engine according to the present embodiment stores engine oil at the bottom of the clutch chamber 81 so as to immerse a part of the outer periphery of the primary driven gear 59 when a wet clutch is applied. . The primary driven gear 59 scoops up the engine oil in the clutch chamber 81 with the rotation of the input shaft 45, scatters the engine oil in the clutch chamber 81, and can properly lubricate the bearing 78.

  Furthermore, the balancer shaft support structure for a motorcycle engine according to the present embodiment has a generator shaft 51 that transmits the rotational force of the crankshaft 42 to the first balancer shaft 48, between the rotation axis lines of the first balancer shaft 48 and the input shaft 45. The distance is reduced, contributing to the downsizing of the engine 10. In the case of a conventional engine, an additional gear (so-called idle gear) is generally arranged between a rotary shaft that drives an auxiliary machine and an input shaft of a transmission mechanism to transmit the rotational force between the mutual shafts. The balancer shaft support structure for a motorcycle engine according to the present embodiment increases the rotational force of the crankshaft 42 via the generator shaft 51 when the number of parts increases due to the additional gears and the engine increases in size. By transmitting to the balancer shaft 48, the number of parts of the power transmission path can be reduced and the engine 10 can be reduced in size.

  Furthermore, the balancer shaft support structure for a motorcycle engine according to the present embodiment has a crankshaft 42 that has a rotational axis of the first balancer shaft 48 that is more than a plane that includes the rotational axis of the input shaft 45 and the rotational axis of the generator shaft 51. By being biased to the side, the center of gravity of the engine 10 can be brought close to the vicinity of the crankshaft 42. Here, an engine whose center of gravity is far away from the crankshaft because the input shaft of the speed change mechanism, balancer shaft, generator shaft, etc. are linearly arranged is a production machine (especially a robot arm) for suspending the engine on the body frame. There is a risk that an excessive moment load acts on the engine holding jig attached to the tip of the production machine or the like to cause a failure of the production machine. In addition, such an engine requires a special special jig that can be held from multiple directions in consideration of the position of the center of gravity for safety reasons, and increases the manufacturing cost. Accordingly, the balancer shaft support structure for a motorcycle engine according to the present embodiment prevents the production machine from being broken by making the center of gravity of the engine 10 approximately close to the crankshaft 42, and no special special jig is required. Thus, an increase in extra manufacturing cost can be prevented.

  In addition, the balancer shaft support structure for a motorcycle engine according to the present embodiment has a rotation axis located on the split surface 53 of the crankcase 31 and a second balancer shaft 49 facing the input shaft 45 with the crankshaft 42 interposed therebetween. The crankshaft 42 and the input shaft 45 are based on the crankshaft 42 by the pump drive shaft 52 facing the first balancer shaft 48 across the crankshaft 42 and the first balancer shaft 48 located on the cylinder side of the input shaft 45. The output shaft 46, the first balancer shaft 48, the second balancer shaft 49, the generator shaft 51, and the pump drive shaft 52 can be arranged without being biased forward, backward, upward and downward, so that the position of the center of gravity of the engine 10 is approximately the crankshaft. Approaching 42 Rukoto can.

  Further, the balancer shaft support structure for a motorcycle engine according to the present embodiment includes a unit-type transmission mechanism 43 that can be integrally inserted and removed, and a space in which the transmission mechanism 43 is located when the first bearing holding half 79a is removed. And a bearing holding hole 79c for holding the bearing 78, it is possible to secure a work space required for the attachment and detachment of the first balancer shaft 48, and at the time of the work, an extremely large volume compared to the first balancer shaft 48. The first balancer shaft 48 can be easily attached and detached without coming into contact with the crankcase 31 by way of the space in which the transmission mechanism 43 is located. In addition, the balancer shaft support structure for a motorcycle engine according to the present embodiment allows the first balancer shaft 48 to be attached / detached by providing a work space required for the attachment / detachment of the first balancer shaft 48 in the space where the transmission mechanism 43 is located. The extra space required is not required, and as a result, the engine 10 can be reduced in size.

  Therefore, according to the balancer shaft support structure for a motorcycle engine according to the present embodiment, the balancer shafts 48 and 49 can be assembled to the crankcase 31 with high accuracy, and the occurrence of vibration and noise can be prevented.

DESCRIPTION OF SYMBOLS 1 Motorcycle 2 Body frame 5 Front wheel 6 Steering mechanism 7 Rear wheel 8 Swing arm 10 Engine 11 Head pipe 12 Main frame 13 Center frame 15 Seat rail 16 Fuel tank 17 Rider seat 18 Pillion seat 19 Pivot shaft 21 Front fork 22 Handlebar 25 Exhaust pipe 26 Exhaust muffler 27 Driven sprocket 28 Drive chain 29 Cowling 31 Crank case 32 Cylinder block 33 Cylinder head 35 Head cover 36 Oil pan 37 Clutch mechanism 38 Upper crank case 39 Lower crank case 41 Clutch cover 42 Crank shaft 42a Crank weight 43 Transmission mechanism 45 Input shaft 46 Output shaft 48 First balancer shaft 49 Second balancer shaft 51 Rator shaft 52 Pump drive shaft 53 Dividing surface 54 Crank chamber 55 Journal bearing 55a Bearing half 56 Connecting rod 58 Primary drive gear 59 Primary driven gear 61 Mission drive gear 62 Generator driven gear 63 Balancer drive gear 65 Generator 67 First balancer driven gear 71 Journal bearing 71a Bearing half 72 Second balancer driven gear 73 First balancer weight 73a Through hole 75 First balancer support shaft 76 Second balancer weight 76a Through hole 77 Second balancer support shaft 78 Bearing 79 Bearing holding portion 79a First Bearing holding half 79b Second bearing holding half 79c Bearing holding hole 81 Clutch chamber 82 Mission chamber 85 Mission cover 86 Shift mechanism 88 Mission driven gear 89 Drive Sprocket 91 cam 92 shift fork shaft 93 shift fork 95 fastened member

Claims (7)

A crankcase having a first case half and a second case half;
A crankshaft having a rotation axis located on a split surface between the first case half and the second case half;
A balancer shaft having a rotation axis parallel to the rotation axis of the crankshaft and spaced from the split surface;
A bearing for supporting the balancer shaft;
A balancer shaft support structure for a motorcycle engine, comprising: a bearing holding portion that holds the bearing and can be divided. A transmission mechanism that transmits the rotational force of the crankshaft located in a transmission chamber that the first case half and the second case half cooperate to partition;
The balancer shaft support structure for a motorcycle engine according to claim 1, wherein the rotational force of the crankshaft is transmitted to the balancer shaft via the speed change mechanism. The first case half and the second case half are located in a clutch chamber that cooperates to partition and transmit or block the rotational force between the crankshaft and the speed change mechanism, and the rotation axis direction of the balancer shaft The balancer shaft support structure for a motorcycle engine according to claim 2, further comprising a clutch mechanism that covers the bearing when viewed. The balancer shaft support structure for a motorcycle engine according to any one of claims 1 to 3, further comprising an auxiliary machine connecting shaft that transmits a rotational force of the crankshaft to the balancer shaft. The rotation axis of the balancer shaft is positioned to be biased toward the crankshaft with respect to a plane including a rotation axis of the input shaft of the speed change mechanism and a rotation axis of the auxiliary machine connecting shaft. 4. A balancer shaft support structure for a motorcycle engine according to 4. A second balancer shaft having a rotation axis located on a split surface between the first case half and the second case half and facing the input shaft of the speed change mechanism across the crankshaft;
A pump drive shaft facing the balancer shaft across the crankshaft,
The balancer shaft support structure for a motorcycle engine according to claim 2, wherein the balancer shaft is positioned on a cylinder side of the input shaft of the transmission mechanism. The transmission mechanism is a unit-type transmission mechanism that can be integrally inserted into and removed from the transmission chamber, and includes an input shaft and an output shaft whose rotation axis directions are parallel to each other, and a shaft that supports the input shaft and the output shaft. A support member,
The bearing holding portion includes a bearing holding half located adjacent to the bearing member located in the transmission chamber, and the bearing holding the bearing and the space where the transmission mechanism is located when the bearing holding half is removed. The balancer shaft support structure for a motorcycle engine according to claim 2, wherein the holding hole communicates with the holding hole.

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